- Email: [email protected]
RuO2–IrO2 anodes by using polyvinyl alcohol as the solvent
Journal Pre-proof Novel eco-friendly method to prepare Ti/RuO2–IrO2 anodes by using polyvinyl alcohol as the solvent
Charlys Wilton dos Anjos Bezerra, Géssica de Oliveira Santiago Santos, Marilia Moura de Salles Pupo, Maria de Andrade Gomes, Ronaldo Santos da Silva, Katlin Ivon Barrios Eguiluz, Giancarlo Richard Salazar-Banda PII:
S1572-6657(20)30005-9
DOI:
https://doi.org/10.1016/j.jelechem.2020.113822
Reference:
JEAC 113822
To appear in:
Journal of Electroanalytical Chemistry
Received date:
1 November 2019
Revised date:
13 December 2019
Accepted date:
3 January 2020
Please cite this article as: C.W. dos Anjos Bezerra, G. de Oliveira Santiago Santos, M.M. de Salles Pupo, et al., Novel eco-friendly method to prepare Ti/RuO2–IrO2 anodes by using polyvinyl alcohol as the solvent, Journal of Electroanalytical Chemistry(2020), https://doi.org/10.1016/j.jelechem.2020.113822
This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
© 2020 Published by Elsevier.
Journal Pre-proof
Novel eco-friendly method to prepare Ti/RuO2–IrO2 anodes by using polyvinyl alcohol as the solvent
Charlys Wilton dos Anjos Bezerraa, Géssica de Oliveira Santiago Santosa,b, Marilia Moura de
of
Salles Pupoa,b, Maria de Andrade Gomesd, Ronaldo Santos da Silvac, Katlin Ivon Barrios
Laboratório de Eletroquímica e Nanotecnologia – LEN, Instituto de Tecnologia e Pesquisa,
Aracaju, SE, Brazil
Programa de Pós-graduação em Engenharia de Processos, Universidade Tiradentes, Avenida
na
b
lP
a
re
-p
ro
Eguiluza,b, Giancarlo Richard Salazar-Bandaa,b,*
Jo ur
Murilo Dantas, 300, Aracaju, SE, Brazil
c Grupo de Nanomateriais Funcionais, Departamento de Física, Universidade Federal de Sergipe, Campus Universitário, CEP: 49100-000, São Cristovão, SE, Brazil d
Laboratório de Preparação e Caracterização de Materiais, Departamento de Física,
Universidade Federal de Sergipe, 49000-100, São Cristóvão-SE, Brazil
*Corresponding author: [email protected] (Giancarlo Richard Salazar-Banda)
Journal Pre-proof 1 Abstract Electrochemical oxidation processes are promising solutions for wastewater treatment due to their high efficiency, effortless control, and versatility. Mixed metal oxides anodes are particularly attractive due to their low cost and specific catalytic properties. Here, we report the synthesis of a new Ti/RuO2-IrO2 anode fabricated through an innovative eco-friendly methodology using polyvinyl alcohol (PVA) as the solvent. Comparative anodes were also prepared by the conventional method of polymeric precursors. For both methods, anodes were
of
calcined at 300, 400, and 500 °C. X-ray diffraction data confirmed the formation of RuO2 and
ro
IrO2 in the rutile-type structure for all conditions. Moreover, compared to conventional
-p
polymeric precursor method, PVA-made anode obtained at 300 °C presented increased
re
voltammetric charge (210%), besides reduced charge-transfer resistance (1.8-fold lower). Electrochemical degradation of the RB-21 dye showed that the PVA-made Ti/RuO2-IrO2
lP
anode has the highest degradation efficiency, and its kinetic rate constant is until 2 times
na
greater than the conventional anode. Besides, due to rougher and more compact surfaces, the better adhesion of the film observed for the PVA-made anodes, the accelerated service
Jo ur
lifetime of the anode was prolonged 4.3-fold.
Keywords: PVA, MMOs anodes, ruthenium dioxide, iridium dioxide, electrocatalysis
Journal Pre-proof 2 1. Introduction Among anthropogenic and industrial activities, dye-containing effluent discharge from textile industries is of severe environmental concern due to its adverse effects on the aquatic environment. It is because these compounds limit light penetration inhibiting the photosynthesis of aqueous flora and also due to its low biodegradability and potential toxicity effect on aquatic life [1–3]. In this context, the electrochemical oxidation process stands out as a practical approach for treating these toxic or bio-refractory organic pollutants due to its high
of
efficiency, effortless control, versatility, and environmental compatibility [4,5]. Although
ro
organic wastes can, in general, be oxidised at numerous electrode materials, the
-p
electrochemical efficacy depends on the kind, and, on the structure of the anode materials [6–
re
10].
In that sense, the use of mixed metal oxides (MMO) anodes is especially attractive due
lP
to their low cost, ease of preparation, and their variety of electrochemical applications
na
primarily because their electrocatalytic properties may be significantly modulated by changing the composition or preparation conditions of these anodes [11,12]. Among different
Jo ur
candidates, RuO2–IrO2 anodes are considered quite promising anode materials due to their outstanding mechanical stability, long service life, and reasonable electrocatalytic activity [9,13,14]. In these systems, the presence of IrO2 improves the stability of RuO2 [15,16]. Coster et al. studied the electrochemical oxidation of 4-chlorophenol in the presence of chlorides by the use of a Ti/RuO2-IrO2 anode. After 120 min of treatment, the contaminant is rapidly degraded, and even total mineralization could be obtained after prolonged oxidation[17]. Similar results have been reported for the electrochemical oxidation of methylene blue using Ti/RuO2-IrO2 anode, where the complete color elimination with 73 % of chemical oxygen demand elimination was achieved within 90 min of electrolysis[18].
Journal Pre-proof 3 Given its importance in the electrochemical system, it is critical to developing novel and sustainable methods capable of producing anodes with superior electrochemical activity for oxidation of pollutants, also having a long service lifetime at a low production cost. Herein, we propose polyvinyl alcohol (PVA)-assisted thermal decomposition method as an attractive alternative route to prepare Ti/RuO2–IrO2 anodes, in which a water-based PVA solution is used as both solvent and polymerising agent of precursor metal salts. The use of PVA as a modifier to improve the properties of PbO2 electrodes was
of
reported by Li et al. [19]. In addition, PVA has already been used for the synthesis of efficient
ro
luminescent nanoparticles [20,21]. However, at present, studies employing PVA as a solvent
-p
to prepare the precursor solution for MMO anodes preparation have never been reported. PVA
re
is a water-soluble environmentally friendly synthetic polymer, with the chemical formula [CH2CH(OH)]n, with a hydroxyl group for each PVA monomer. When added to the salt
lP
solution, the OH– groups of the polymer chains can solvate the metal ions in the solution,
na
forming metal hydroxides. At the same time, the surfactant property of the polymer network of PVA promotes the steric stabilisation of the nuclei and prevents the approximation between
Jo ur
them, leading to the formation of structures in nanometric dimensions [22,23]. Moreover, advantages of PVA method are: (i) the low degree of toxicity, even being used as a component of biodegradable composite polymers, since it is non-toxic to organisms [24], (ii) methodological simplicity and (iii) possibility of using of water as the solvent for the precursor salts. Therefore, we present, for the first time, PVA adopted as a solvent to prepare Ti/RuO2–IrO2 anodes by thermal decomposition and the effect of three different calcination temperatures (300, 400, and 500 °C) was investigated. In order to investigate the actual efficiency and advantages of this new proposed methodology, Ti/RuO2-IrO2 anodes prepared by conventional Pechini’s method were used for comparison throughout the study. X-ray
Journal Pre-proof 4 diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray (EDX) spectroscopy, linear sweep voltammetry (LSV), cyclic voltammetry (CV) accelerated service lifetime, and electrochemical impedance spectroscopy (EIS) measurements were carried out to characterise the physical and electrochemical properties of the MMO anodes. Furthermore, Reactive Blue 21 (RB21) textile dye was employed as the target organic molecule for electrochemical oxidation to evaluate the electrocatalytic activity of the developed MMO
of
anodes.
ro
2. Experimental
-p
2.1 Electrode synthesis
re
Titanium plates (1 cm × 1 cm × 0.5 mm) were used as metallic support, and a prior cleaning
lP
pre-treatment was carried out as previously reported [25,26]. The metal salts of ruthenium chloride (III) hydrate (RuCl3 × H2O, 99.99%) and iridium chloride hydrate (IrCl3 × H2O,
na
99.0%) from Sigma-Aldrich® were used without further purification. Polyvinyl alcohol (PVA) (99%), or anhydrous citric acid (CA) (99.5 %), from Vetec®, dissolved in ethylene glycol
Jo ur
(EG) (99.8%) from Sigma-Aldrich® were used as solvents. Besides, ultrapure water (18.18 mΩ, by Gehaka MS 2000 system) was used to prepare all solutions. Firstly, a stock solution of PVA 10 wt.% was prepared by dissolving the PVA powder in ultrapure water at 80 °C under continuous stirring until complete dissolution. Ruthenium chloride and iridium chloride in a molar ratio Ru/Ir = 0.5/0.5 were dissolved in 1 mL of ultrapure water, followed by the gradual addition of 3 mL of the PVA 10 wt% stock solution. The PVA-based precursor solution is kept under stirring until a homogeneous solution is obtained. Similarly, the precursor solutions prepared following Pechini’s method [27] were obtained employing a solution of CA in EG as a solvent in the ratio CA:EG = 3:10, stirring,
Journal Pre-proof 5 and heating the solution up to 90 °C for complete dissolution. The molar ratio of RuCl3– IrCl3/CA/EG was maintained at 1:3:10 (with the molar ratio Ru/Ir = 0.5/0.5). Finally, the obtained precursor solutions were brushed over the titanium plates and afterwards heated up to 130 °C being kept for 30 min, then up to 250 °C being kept for 10 min and finally calcinated at 300, 400 or 500 °C for 5 min. This procedure is repeated, for both methods, until a mass loading of 1.2 mg cm–2 is achieved. Finally, when this condition is achieved, the anodes are submitted to a final calcination process at 300, 400, or 500 °C for 60
ro
of
min.
-p
2.2 Physical characterisation
re
The XRD patterns of the obtained anodes were recorded in a diffractometer (RIGAKU RINT 2000 / PC), with Cu radiation Kα (wavelength = 1.5406 Å), in a scan-interval 2θ between 20°
lP
and 80°, in continuous scan mode with steps of 0.02°. Phase identification was performed
na
using the Joint Committee on Powder Diffraction Standards (JCPDS) database by using the X’pert High Score Plus software version 2.2.2. The surface morphology and the composition
Jo ur
of the coating were analysed by SEM in a JEOL model JMC 5700 microscope equipped with an X-ray detector for EDX spectroscopy.
2.3 Electrochemical characterisation The electrochemical measurements, CV, LSV, morphology factor (φ), accelerated service lifetime tests, and EIS were performed in a one-compartment three-electrode cell by using a potentiostat/galvanostat (PGSTAT302N METROHM AUTOLAB) equipped with Nova 2.0 Metrohm Autolab Software. The reference and the counter electrodes were an Ag/AgCl (3.0 mol L–1 KCl) and a 2 cm2 platinum counter electrodes, respectively. The working electrode consisted of the Ti/RuO2–IrO2 synthesised.
Journal Pre-proof 6 Cyclic voltammetry experiments were performed at 50 mV s–1 in 0.5 mol L–1 H2SO4 solution, between the potential limits from 0.2 V to 1.2 V. The total voltammetric charges (q*), which can be considered as a relative measure to electrochemically active surface areas, were calculated by integrating the area of the cyclic voltammograms [28]. According to the methodology proposed by Da Silva et al. [29], continuous voltammetric curves were recorded at several scan rates (10–300 mV s–1) in a 0.5 mol L–1 H2SO4 medium, in order to determine the morphology factor of each anode prepared. The EIS measurements were performed in a
of
0.5 mol L–1 H2SO4 medium covering a frequency range of 0.01 Hz–10 kHz using an AC sine
ro
signal amplitude of 5 mV with a logarithmic distribution of 10 frequencies per decade. The
-p
potential applied for each electrode was 1.12 V, which corresponds to the oxygen evolution
re
reaction (OER) onset potential at each anode studied (according to data obtained with LSV in the same electrolyte). EIS data were treated using the Zview 2.0 software.
lP
The accelerated service lifetime tests were carried out in 1.0 mol L–1 H2SO4 solution
na
by applying 1 A cm–2 in order to evaluate the electrochemical stability of metal oxides under extreme electrolysis conditions. The operational electrocatalytic conditions of the electrode
Jo ur
were considered viable until the potential response of the anode was over 10 V.
2.4 Electrochemical oxidation of RB21 The electrochemical oxidations of the Reactive Blue dye (RB21) were carried out in 100 mL of a solution containing 50 mg L–1 of the dye in 0.1 mol L–1 Na2SO4. The experiments were also carried out in sodium sulphate solutions with the previous concentration containing 0.005, 0.010, and 0.020 mol L–1 NaCl to evaluate the effect of chloride ions in the electrolyte. The colour removal was evaluated as a time function, and representative samples were collected at 0, 5, 15, 30, 60, 90, 120 min, and analysed on a UV-vis spectrophotometer Hach
Journal Pre-proof 7 DR-500. Colour removal (CR) was calculated based on absorbance at 622 nm, according to equation (1):
CR = [(Abs0 – Abst/Abs0) × 100]
(1)
where Abs0 and Abst are, respectively, the absorbance of the solution before and at a given
of
time of electrolysis.
ro
3. Results and discussion
-p
3.1 SEM-EDX and XRD analyses
re
Figure 1 displays the SEM images of the Ti/RuO2–IrO2 anodes, synthesised by the PVA and Pechini methods, in different temperatures. Note the presence of cracks on the anode surfaces,
lP
which are attributed to the mechanical stress resulted from the plasticity of the coating and the
na
difference of the thermal expansion coefficients between the substrate and the film. This ―cracked-mud‖ appearance has been commonly reported for coatings deposited by using
Jo ur
thermal decomposition [30–32]. Additionally, for both methods, as the temperature increases, the surface becomes smoother. This fact is commonly associated with grain growth (swelling effect) and agglomeration of the particles at high temperatures [33,34]. Although similar cracked-mud structures were obtained, the PVA anodes presented surfaces with a minimised number of deeper cracks when compared to Pechini ones. In the aqueous solution containing RuCl3 and IrCl3, it is believed that ruthenium and iridium ions, driven by electrostatic force, are complexed with OH– ligands, forming Ru(OH)3 and Ir(OH)3 distributed regularly on the PVA chains [20]. Then, the hydroxides are transformed into oxides and grow homogeneously during the thermal treatment.
Journal Pre-proof 8 EDX analyses were performed for all synthesised anodes to confirm the chemical composition of the coatings. Table 1 shows the results obtained by EDX and the theoretical Ru and Ir concentrations in the films. Notably, the expected and the observed values have a good agreement, indicating that Ru and Ir elements were successfully combined in the desired proportions regardless of the calcination temperature and preparation method. Also, in order to assess the ruthenium and iridium distribution on the film surface, either in grains or in cracks, EDX elemental mapping (Figure 2) confirms the sample composition and
of
homogenous elements distribution.
ro
The XRD patterns of the prepared anodes at different temperatures are shown in
-p
Figure 3. In both cases, PVA (Fig. 3a) and Pechini (Fig. 3b) anodes, the peaks were indexed
re
according to RuO2 (JCPDS-40-1290) and IrO2 (JCPDS-15-0870) tetragonal rutile structure, for all calcination temperatures.
lP
In agreement with the Hume–Rothery theory since ionic radii of Ru4+ (0.076 nm) and
na
Ir4+ (0.077 nm) are very similar as well as RuO2 and IrO2 present the same crystalline rutilelike structure [35,36], it is expected the formation of a stable solid solution between RuO2 and
Jo ur
IrO2 compounds. However, due to the low intensity, highly broad, and angular proximity of the diffraction peaks, these analyses from XRD patterns are impaired and complementary techniques are needed.
Moreover, the intensity of the peaks related to RuO2 and IrO2 for PVA-made films are relatively lower than those observed for the electrodes prepared by the Pechini method, when also compared with Ti peaks. This result suggests a better-coated anode surface when synthesised by the PVA method. Additionally, the crystallite sizes were estimated by the Scherrer equation using the full width at half-maximum (FWHM) of the (110) peak. In general, the average crystallite size decreased when PVA was employed in the synthesis process. The average crystallite sizes for PVA-made films obtained at 300, 400, and 500 were
Journal Pre-proof 9 3.8 nm, 4.2, and 4.3, as for Pechini were 7.5 nm, 8.6 nm, and 12.5 nm. The lower degree of the crystallinity combined with the decrease in the mean crystallite size contributes to the enhancement of active surface area [42]. Similar results were reported by Li et al. [29], after PbO2 modification with PVA. They found smoother films and reduction of the grain size estimated by Scherrer equation, which explained longer service lifetime. These features influence the efficiency of anodes since larger grains reduces the electroactive area available
of
for the catalytic reactions [37].
ro
3.2 Electrochemical characterisation
-p
Fig. 4 shows the voltammetric profiles obtained for the PVA-made (Fig. 4a) and Pechini-
re
made (Fig. 4b) anodes calcinated at 300, 400, and 500 °C. The recorded CVs were integrated into the whole potential range (that is between the onsets of HER and OER) to gain a
lP
complete and more clear macroscopic insight in the surface features of the prepared materials.
na
The voltammetric charge obtained is used as a relative measure of the electrochemically
prepared anodes.
Jo ur
active area of the MMO anodes. Table 2 shows the voltammetric charge values found for all
The higher the calcination temperature, the lower the electrochemically active area of the anodes. It is because the increase of the calcination temperature leads to grain growth, thus reducing the surface area, as discussed previously. However, when comparing both methods, the PVA-made anodes stands out with higher values of voltammetric charge. Amongst the studied temperatures, the PVA-made anode prepared at 300 °C presented the highest voltammetric charge value of 256.1 mC cm–2, which is 210 % higher than the correspondent anode prepared by the Pechini method.
Journal 10 Pre-proof The morphology factor can be considered as a measure of the contribution of the internal sites of the electrodes to the total differential capacitance and is determined as the ratio in Equation (2) [29,38].
φm = C i / Ct
(2)
Where Cd,i and Cd represents, respectively, the inner and total differential pseudocapacitance
of
of the film. The value of φm can vary between 0 and 1, where values close to 0 indicate that
ro
the contribution of the inner sites is small or negligible, and values near 1 indicate that the
-p
electrode has a large internal area [29,38].
re
Morphology factor values were then determined for the anodes prepared at 300 °C, according to the methodology described by Da Silva et al. [29]. Thus, cyclic voltammograms
lP
were recorded for a narrow potential interval (ΔE = 0.55–0.65 V vs Ag/AgCl) where only
na
double layer charging occurs, which allows the determination of the capacitive current density (jc). As reported by Da Silva et al. [29] the potential range used to determining jc should be
Jo ur
localised as close as possible to the anodic switching potential, on the last 20 % of the capacitive potential range in order to obtain meaningful results (i.e., 0.63 V vs Ag/AgCl ). The voltammograms covering the potential interval of 0.2–1.2 V vs Ag/AgCl and in a capacitive potential interval as a function of the potential scan rate for the anodes obtained by both methods calcined at 300 °C are shown in Figure S1. As a result, Fig. 5 shows the dependence of the capacitive voltammetric current density, jc, on ν., of the anodes calcined at 300 °C obtained by both methods. Two linear segments are located in the low and high scan rates, indicating the existence of two distinct surface regions described as typical behaviour exhibited by highly roughness films [29]. Both anodes display morphology factor near to 1, which indicates that regardless of the preparation
Journal 11 Pre-proof method, Ti/RuO2–IrO2 anodes presented a high contribution of the internal sites of the coating. The values of the total (Ct) and external (Ce) differential capacitance, were obtained from the angular coefficients observed in the low and high scan rates, respectively. The total (Ct), external (Ce), internal (Ci = Ct – Ce) differential capacitance values and the morphology factor (φm) are presented in Table 3. EIS measurements for the anodes were carried out at the potential of 1.23 V vs Ag/AgCl corresponding to the OER onset potential at each studied anode. The choice of the
of
potential was based on the LSV data (Figure S2). Fig. 6 show the Nyquist plots of the PVA
ro
and Pechini anodes calcinated at 300 °C. Both impedance spectra exhibited well-developed
-p
semicircles typically related to the charge-transfer process for the OER [39,40]. The Nyquist
re
plots obtained were fitted with a characteristic equivalent circuit for a simple redox reaction characterised by one capacitive loop, represented by RΩ(RctQdl) combination (inset on Fig. 6).
lP
RΩ, Rct, and Qdl correspond, respectively, to solution resistance, charge-transfer resistance, and
na
the double-layer capacitance. The constant phase element (CPE) is often used to replace Qdl, considering electrode roughness and heterogeneity. The proposed equivalent circuit fitted well
fitting.
Jo ur
all impedance data displaying a quality factor χ2 < 5 × 10–4, which indicates a high quality of
The values of RΩ, Rct, and Qdl obtained by the fitting procedure are listed in Table 4. For both anodes, RΩ, values were estimated between 1.21 to 1.31 Ω which is attributed to cell resistance, including the connections, the electrolyte, and the resistance of the film. An Rct value of the 3.1 Ω was found for the PVA-made anode, which is almost 2-fold lower than the value obtained for the Pechini anode (5.55 Ω). This result indicates that the reaction occurs more efficiently at the surface of the PVA-made anode, which is supported by CV data that shows an increase in the voltammetric charge, related to the higher presence of active sites at the surface of the anode.
Journal 12 Pre-proof Electrochemical stability tests were carried out, focusing on the understanding of the overall electrode response to highly aggressive medium. Thus, the also known accelerated service lifetime tests, which have the advantage of providing a quick answer on a laboratory scale, since the study of the real service life needs very long experiments. Figure S3 shows the potential variations against time during the accelerated service lifetime tests in an acid medium (1.0 mol L–1 H2SO4) at high current density (e.g. 1 A cm–2) for the anodes calcined at 300 °C. Results show that the PVA-made anode has service time 4.3-fold higher than the
of
Pechini anode. The reason for the longer accelerated service life can be attributed to
ro
minimised presence of broad and deep cracks in the PVA-made anodes, as previously seen in
-p
SEM image (Fig. 1a). As a result, the presence of deeper cracks on Pechini anodes surfaces
re
facilitates the electrolytic solution penetration through these cracks and increases the pressure
na
deactivation [41–43].
lP
inside the anode caused by the internal O2 evolution, which is the main factor for fast anode
3.3 Electrolysis of Reactive Blue 21 dye
Jo ur
The PVA- and Pechini-made anodes calcined at 300 °C were used to investigate their electrocatalytic activity in the electrochemical oxidation of 50 mg L–1 Reactive Blue 21 aqueous dye solution, by applying 25 mA cm–2 in 0.1 mol L–1 Na2SO4 solution and with the use of different NaCl concentrations. Figure 7 displays the effect of chloride concentration (0.005–0.02 mol L–1) on colour removal as a function of the time for the PVA (Fig. 7a) and Pechini (Fig. 7b) anodes. The use of 0.005 mol L–1 NaCl promotes a slight improvement on colour removal percentages, i.e., from 51.02 to 56.85 % for PVA-made anodes prepared and from 50.01 to 54.28 % for Pechini. On the other hand, electrolysis carried out with the addition of 0.01 mol L–1 NaCl shows a more significant improved treatment, reaching 100 % of colour removal after 120 min of electrolysis. Further increasing the NaCl concentration to
Journal 13 Pre-proof 0.02 mol L–1 led to the best result in colour removal percentage, since 100 % of the colour was removed in only 30 min for the PVA-made anode and in 60 min for Pechini anode. Then, for both methods, the optimal chloride concentration responsible for the fastest colour removal is 0.02 mol L–1. The colour removal improvement observed for the higher chloride concentrations has been explained by the conversion of chlorides to chlorine, hypochlorous acid, and hypochlorite species in solution, which promotes a synergic action of indirect oxidation together with direct oxidation on the anode surface, as previously reported
of
[3,12,19,44]. The fastest electrochemical degradation of RB21 dye for the PVA-made anode
-p
and generating more ●OH and chlorine radicals.
ro
could be related to its larger surface area, providing more active site centres on the coating
re
The kinetic order with respect to RB-21 colour removal was evaluated in the presence of different electrolyte concentrations that, as mentioned before, affects oxidation efficiency
lP
due to different amounts of oxidants generated during electrolysis, such as sulphates and
na
chlorine species. The exponential profile of the curves obtained for RB-21 colour removal in
8).
Jo ur
the first period of reaction could be fitted reasonably well to pseudo-first-order kinetic (Figure
The obtained kapparent values (Table 5) show that the addition of NaCl (from 0.005 to 0.02 mol L–1) the higher the colour removal rate. Considering the anode performance, the faster kinetic rate was observed for the PVA-made anode (0.0174 min–1 in 0.02 mol L–1 NaCl addition) being 2-times greater than observed for Pechini-made anode (0.0085 min–1). These results point out that PVA method may increase the kinetic rate constant more importantly in chloride media.
4. Conclusions
Journal 14 Pre-proof This study reported, for the first time, the synthesis of Ti/RuO2–IrO2 anodes prepared by using a PVA-assisted thermal decomposition method. The use of PVA as the solvent of the precursor salts led to a better-coated anode surface with the minimised presence of crack and fissures. Moreover, the use of PVA increases the voltammetric charge values for all the investigated temperatures. Amongst the studied calcination temperatures, the lowest one (300 °C) was the most suitable, presenting an increase of 210% in the total voltammetric charge and service lifetime 4.3 times longer than the anodes synthesised in different temperatures.
of
Furthermore, the use of PVA reduced the charge-transfer resistance of the anodes compared to
ro
the Pechini anodes. Also, the Ti/RuO2–IrO2 PVA anodes prepared at 300 °C presented higher
-p
electrocatalytic activity being capable of reducing 100 % of the colour of the model organic
re
compound BR21 dye in 30 min, while 60 min was required for Pechini anode. Finally, the PVA-assisted method stands out as a clean, eco-friendly, and promising
lP
alternative route to improve the characteristics of MMO anodes and to optimise their
na
synthesis. This method can produce electrodes with improved physical and electrochemical properties compared to the electrode obtained by the conventional Pechini method. Besides,
Jo ur
the low toxicity of PVA and the use of water to compose the solvent mixture are favourable particularities of the developed method.
Acknowledgements
The authors thank the Brazilian National Counsel of Technological and Scientific Development-CNPq (grants: 305438/2018-2, 304419/2015-0 and 310282/2013-6), to the Coordination for the Improvement of Higher Education Personnel – CAPES (grants: 88882.365552/2018-01 and 88881.187890/2018-01) and to Sergipe State Research and Technological Innovation Foundation (FAPITEC/SE) for the scholarships and financial support for this work.
Journal 15 Pre-proof
References [1]
L. Jiancheng, Y. Jie, L. Weishan, H. Qiming, X. Hongkang, Electrochemical degradation of Reactive Brilliant Red K-2BP on Ti/RuTiIrSnMn oxide anode in a batch cell, J. Electrochem. Sci. Eng. 2 (2012) 171–183. doi:10.5599/jese.2012.0022.
[2]
S. Raghu, C.A. Basha, Dye destruction and simultaneous generation of sodium hydroxide using a divided electrochemical reactor, Ind. Eng. Chem. Res. 47 (2008)
J.M. Aquino, M. a. Rodrigo, R.C. Rocha-Filho, C. Sáez, P. Cañizares, Influence of the
ro
[3]
of
5277–5283. doi:10.1021/ie070675b.
-p
supporting electrolyte on the electrolyses of dyes with conductive-diamond anodes,
[4]
re
Chem. Eng. J. 184 (2012) 221–227. doi:10.1016/j.cej.2012.01.044. I. Sirés, E. Brillas, M.A. Oturan, M.A. Rodrigo, M. Panizza, Electrochemical advanced
lP
oxidation processes : today and tomorrow . A review, Environ. Sci. Pollut. Res. 21
[5]
na
(2014) 8336–8367. doi:10.1007/s11356-014-2783-1. C.A. Martínez-Huitle, M.A. Rodrigo, I. Sirés, O. Scialdone, Single and Coupled
Jo ur
Electrochemical Processes and Reactors for the Abatement of Organic Water Pollutants: A Critical Review, Chem. Rev. 115 (2015). doi:10.1021/acs.chemrev.5b00361. [6]
W. Wu, Z.-H. Huang, T.-T. Lim, Recent development of mixed metal oxide anodes for electrochemical oxidation of organic pollutants in water, Appl. Catal. A Gen. 480 (2014) 58–78. doi:10.1016/j.apcata.2014.04.035.
[7]
F. Moradi, C. Dehghanian, Addition of IrO2 to RuO2 +TiO2 coated anodes and its effect on electrochemical performance of anodes in acid media, Prog. Nat. Sci. Mater. Int. 24 (2014) 134–141. doi:10.1016/j.pnsc.2014.03.008.
[8]
T. Audichon, E. Mayousse, S. Morisset, C. Morais, C. Comminges, T.W. Napporn,
Journal 16 Pre-proof K.B. Kokoh, Electroactivity of RuO2 e IrO2 mixed nanocatalysts toward the oxygen evolution reaction in a water electrolyzer supplied by a solar profile, Int. J. Hydrogen Energy. 9 (2014) 16785–16796. doi:10.1016/j.ijhydene.2014.07.170. [9]
T. Audichon, B. Guenot, S. Baranton, M. Cretin, C. Lamy, C. Coutanceau, Preparation and characterization of supported RuxIr(1-x)O2 nano-oxides using a modified polyol synthesis assisted by microwave activation for energy storage applications, Appl. Catal. B Environ. 200 (2017) 493–502. doi:10.1016/j.apcatb.2016.07.048.
of
[10] A. Kapałka, G. Fóti, C. Comninellis, The importance of electrode material in
ro
environmental electrochemistry. Formation and reactivity of free hydroxyl radicals on
re
doi:10.1016/j.electacta.2008.06.045.
-p
boron-doped diamond electrodes, Electrochim. Acta. 54 (2009) 2018–2023.
[11] A.N.S. Rao, V.T. Venkatarangaiah, Metal oxide-coated anodes in wastewater
lP
treatment, Environ. Sci. Pollut. Res. 21 (2014) 3197–3217. doi:10.1007/s11356-013-
na
2313-6.
[12] F.C. Moreira, R.A.R. Boaventura, E. Brillas, V.J.P. Vilar, Electrochemical advanced
Jo ur
oxidation processes: A review on their application to synthetic and real wastewaters, Appl. Catal. B Environ. 202 (2017) 217–261. doi:10.1016/j.apcatb.2016.08.037. [13] F.I. Mattos-Costa, P. de Lima-Neto, S.A.. Machado, L.A. Avaca, Characterisation of surfaces modified by sol-gel derived RuxIr1−xO2 coatings for oxygen evolution in acid medium, Electrochim. Acta. 44 (1998) 1515–1523. doi:10.1016/S00134686(98)00275-8. [14] T. Le Luu, J. Kim, J. Yoon, Physicochemical properties of RuO2 and IrO2 electrodes affecting chlorine evolutions, J. Ind. Eng. Chem. 21 (2015) 400–404. doi:10.1016/j.jiec.2014.02.052. [15] M.E.G. Lyons, S. Floquet, Mechanism of oxygen reactions at porous oxide electrodes.
Journal 17 Pre-proof Part 2—Oxygen evolution at RuO2, IrO2 and IrxRu1−xO2 electrodes in aqueous acid and alkaline solution, Phys. Chem. Chem. Phys. 13 (2011) 5314. doi:10.1039/c0cp02875d. [16] M.J.R. Santos, M.C. Medeiros, T.M.B.F. Oliveira, C.C.O. Morais, S.E. Mazzetto, C.A. Martínez-Huitle, S.S.L. Castro, Electrooxidation of cardanol on mixed metal oxide (RuO2-TiO2 and IrO2-RuO2-TiO2) coated titanium anodes: insights into recalcitrant phenolic compounds, Electrochim. Acta. 212 (2016) 95–101. doi:10.1016/j.electacta.2016.06.145.
of
[17] J. De Coster, W. Vanherck, L. Appels, R. Dewil, Selective electrochemical degradation
ro
of 4-chlorophenol at a Ti/RuO2-IrO2 anode in chloride rich wastewater, J. Environ.
-p
Manage. 190 (2017) 61–71. doi:10.1016/j.jenvman.2016.11.049.
re
[18] A. Baddouh, B. El Ibrahimi, M.M. Rguitti, E. Mohamed, S. Hussain, L. Bazzi, Electrochemical removal of methylene bleu dye in aqueous solution using Ti/RuO2–
lP
IrO2 and SnO2 electrodes, Sep. Sci. Technol. 6395 (2019) 1–10.
na
doi:10.1080/01496395.2019.1608244.
[19] X. Li, H. Xu, W. Yan, Preparation and characterization of PbO2 electrodes modified
Jo ur
with polyvinyl alcohol (PVA), RSC Adv. 6 (2016) 82024–82032. doi:10.1039/C6RA17230J.
[20] M. De Andrade Gomes, M.E. Giroldo Valerio, J.F. Queiruga Rey, Z.S. Macedo, Comparative study of structural and optical properties of ZnO nanostructures prepared by three different aqueous solution methods, Mater. Chem. Phys. 142 (2013) 325–332. doi:10.1016/j.matchemphys.2013.07.024. [21] G.A. Sobral, M.A. Gomes, Z.S. MacEdo, M.A.R.C. Alencar, S.M.V. Novais, Synthesis and characterization of multicolour fluorescent nanoparticles for latent fingerprint detection, Bull. Mater. Sci. 39 (2016) 1565–1568. doi:10.1007/s12034-016-1303-y. [22] W.S. Ã, Y. Fang, J. Fan, Y. He, J. Min, Y. Qian, Novel synthesis method of ZnO
Journal 18 Pre-proof nanorods by ion complex transformed PVA-assisted nucleation, 299 (2007) 272–276. doi:10.1016/j.jcrysgro.2006.10.240. [23] F. Meshkani, M. Rezaei, Effect of process parameters on the synthesis of nanocrystalline magnesium oxide with high surface area and plate-like shape by surfactant assisted precipitation method, Powder Technol. 199 (2010) 144–148. doi:10.1016/j.powtec.2009.12.014. [24] X. Hu, R. Mamoto, Y. Shimomura, K. Kimbara, F. Kawai, Cell surface structure
of
enhancing uptake of polyvinyl alcohol (PVA) is induced by PVA in the PVA-utilizing
ro
Sphingopyxis sp. strain 113P3, Arch. Microbiol. 188 (2007) 235–241.
-p
doi:10.1007/s00203-007-0239-4.
re
[25] L.M. Da Silva, G.O.S. Santos, M.M.D.S. Pupo, K.I.B. Eguiluz, G.R. Salazar-Banda, Influence of heating rate on the physical and electrochemical properties of mixed metal
lP
oxides anodes synthesized by thermal decomposition method applying an ionic liquid,
na
J. Electroanal. Chem. 813 (2018) 127–133. doi:10.1016/j.jelechem.2018.02.026. [26] T.É.S. Santos, R.S. Silva, C.T. Meneses, C.A. Martínez-Huitle, K.I.B. Eguiluz, G.R.
Jo ur
Salazar-Banda, Unexpected Enhancement of Electrocatalytic Nature of Ti/(RuO2)x(Sb2O5)y Anodes Prepared by the Ionic Liquid-Thermal Decomposition Method, Ind. Eng. Chem. Res. 55 (2016) 3182–3187. doi:10.1021/acs.iecr.5b04690. [27] M.P. Pechini, N. Adams, Method of preparing lead and alkaline earth titanates and niobates and coating method using the same to form a capacitor, United states Pat. Off. (1967) 01–07. [28] R. Berenguer, J.M. Sieben, C. Quijada, E. Morallón, Pt- and Ru-Doped SnO2−Sb Anodes with High Stability in Alkaline Medium Rau l, Appl. Mater. Interfaces. 6 (2014) 22778–22789. [29] L.M. Da Silva, L.A. De Faria, J.F.C. Boodts, Determination of the morphology factor
Journal 19 Pre-proof of oxide layers, Electrochim. Acta. 47 (2001) 395–403. doi:10.1016/S00134686(01)00738-1. [30] F. Moradi, C. Dehghanian, Influence of heat treatment temperature on the electrochemical properties and corrosion behavior of RuO2-TiO2 coating in acidic chloride solution, Prot. Met. Phys. Chem. Surfaces. 49 (2013) 699–704. doi:10.1134/S2070205113060245. [31] T.É.S. Santos, R.S. Silva, C. Carlesi Jara, K.I.B. Eguiluz, G.R. Salazar-Banda, The
of
influence of the synthesis method of Ti/RuO2 electrodes on their stability and catalytic
ro
activity for electrochemical oxidation of the pesticide carbaryl, Mater. Chem. Phys. 148
-p
(2014) 39–47. doi:10.1016/j.matchemphys.2014.07.007.
re
[32] C. Comninellis, G.P. Vercesi, Characterization of dsa-type oxygen evolving electrodes.
6031(91)80257-J.
lP
Choice of a coating, Thermochim. Acta. 176 (1991) 31–47. doi:10.1016/0040-
na
[33] Y. Hou, J. Hu, L. Liu, J. Zhang, C. Cao, Effect of calcination temperature on electrocatalytic activities of Ti/IrO2 electrodes in methanol aqueous solutions, 51
Jo ur
(2006) 6258–6267. doi:10.1016/j.electacta.2006.04.008. [34] A.J. Terezo, E.C. Pereira, Preparation and characterization of Ti/RuO2-Nb2O5 electrodes obtained by polymeric precursor method, Electrochim. Acta. 44 (1999) 4507–4513. doi:10.1016/S0013-4686(99)00182-6. [35] T. Audichon, E. Mayousse, S. Morisset, C. Morais, C. Comminges, T.W. Napporn, K.B. Kokoh, Electroactivity of RuO2-IrO2 mixed nanocatalysts toward the oxygen evolution reaction in a water electrolyzer supplied by a solar profile, Int. J. Hydrogen Energy. 39 (2014) 16785–16796. doi:10.1016/j.ijhydene.2014.07.170. [36] G.O.S. Santos, L.R.A. Silva, Y.G.S. Alves, R.S. Silva, K.I.B. Eguiluz, G.R. Salazarbanda, Enhanced stability and electrocatalytic properties of Ti / RuxIr1-xO2 anodes
Journal 20 Pre-proof produced by a new laser process, Chem. Eng. J. 355 (2019) 439–447. doi:10.1016/j.cej.2018.08.145. [37] D.T. Araújo, M. de A. Gomes, R.S. Silva, C.C. de Almeida, C.A. Martínez-Huitle, K.I.B. Eguiluz, G.R. Salazar-Banda, Ternary dimensionally stable anodes composed of RuO2 and IrO2 with CeO2, SnO2,or Sb2O3 for efficient naphthalene and benzene electrochemical removal, J. Appl. Electrochem. 47 (2017) 547–561. doi:10.1007/s10800-017-1057-2.
of
[38] G.R.P. Malpass, R.S. Neves, A.J. Motheo, A comparative study of commercial and
ro
laboratory-made Ti/Ru0.3Ti0.7O2 DSA® electrodes: ―In situ‖ and ―ex situ‖ surface
re
doi:10.1016/j.electacta.2006.06.032.
-p
characterisation and organic oxidation activity, Electrochim. Acta. 52 (2006) 936–944.
[39] Z. Ye, H. Meng, D. Sun, Electrochemical impedance spectroscopic ( EIS )
lP
investigation of the oxygen evolution reaction mechanism of Ti/IrO2 + MnO2
na
electrodes in 0 . 5 m H 2 SO 4 solution, J. Electroanal. Chem. 621 (2008) 49–54. doi:10.1016/j.jelechem.2008.04.009.
Jo ur
[40] T. Audichon, S. Morisset, T.W. Napporn, K.B. Kokoh, C. Comminges, C. Morais, Effect of Adding CeO2 to RuO2-IrO2 Mixed Nanocatalysts: Activity towards the Oxygen Evolution Reaction and Stability in Acidic Media, ChemElectroChem. 2 (2015) 1128–1137. doi:10.1002/celc.201500072. [41] D. Shao, X. Li, H. Xu, W. Yan, An improved stable Ti/Sb–SnO2 electrode with high performance in electrochemical oxidation processes, RSC Adv. 4 (2014) 21230. doi:10.1039/c4ra01990c. [42] Y. Xin, L. Xu, J. Wang, The Deactivation Mechanism of RuO2-IrO2-SnO2/Ti Anodes Under Alternative Current Electrolysis Condition, (2015) 1762–1765. [43] S.M. Hoseinieh, F. Ashrafizadeh, Influence of electrolyte composition on deactivation
Journal 21 Pre-proof mechanism of a Ti/Ru0.25Ir0.25Ti0.5O2 electrode, Ionics (Kiel). 19 (2013) 113–125. doi:10.1007/s11581-012-0737-5. [44] F. Zaviska, P. Drogui, J.F. Blais, G. Mercier, In situ active chlorine generation for the treatment of dye-containing effluents, J. Appl. Electrochem. 39 (2009) 2397–2408.
re
-p
ro
of
doi:10.1007/s10800-009-9927-x.
Jo ur
na
lP
Figures
lP
re
-p
ro
of
Journal 22 Pre-proof
na
Figure 1: Scanning electron micrographs of the Ti/RuO2–IrO2 anodes obtained by PVA (a,c, e) and Pechini (b,d,f) methods calcined at 300, 400 and 500 °C with magnification of 500×,
Jo ur
and inset by 2000×.
ro
of
Journal 23 Pre-proof
Figure 2. Scanning electron micrographs, elemental mapping, and EDX analysis of the
Jo ur
na
lP
re
-p
Ti/RuO2–IrO2 anodes calcined at 300 °C obtained by PVA (a) Pechini (b) method.
Journal 24 Pre-proof
Ti Ti
PVA Ti
Ti
500°C
400°C
300°C
RuO2 Pattern
of
Intensity / normalized
a)
IrO2
20
30
ro
Pattern
40
50
60
70
b) Ti
lP
Ti
na
400°C
300°C
Pechini
Jo ur
Intensity / normalized
500°C
re
Ti Ti
-p
2/ degrees
RuO2
Pattern
IrO2
Pattern
20
30
40
50
60
70
2/ degrees Figure 3: X-ray diffraction patterns of Ti/RuO2–IrO2 anodes calcined at different temperatures. (a) PVA anodes and (b) Pechini anodes.
Journal 25 Pre-proof
j / mA cm
-2
12 10 8
300 °C 400 °C 500 °C
PVA
6 4 2 0 -2
0.2
0.4
ro
of
-4 -6 -8 0.6
0.8
1.0
1.2
1.0
1.2
na
6 4
Pechini
lP
300 °C 400 °C 500 °C
2 0 -2
Jo ur
j / mA cm
-2
12 10 8
re
-p
E / V vs. Ag/AgCl
-4 -6 -8
0.2
0.4
0.6
0.8
E / V vs. Ag/AgCl Figure 4: Cyclic voltammograms recorded at 50 mV s–1 in 0.5 mol L–1 H2SO4 of the Ti/RuO2–IrO2 anodes obtained by PVA (a) and Pechini (b) methods calcined at 300, 400 and 500 °C.
Journal 26 Pre-proof
14
a)
PVA
j / mA cm
-2
12 10
Co
8 6 4
re
10
lP
8 6 4 2
Ct
Jo ur
0
Co
na
j / mA cm
-2
12
ro
b) Pechini
-p
0 14
of
Ct
2
0
50
100 150 200 250 300 350 -1 / mV s
Figure 5: Dependence of the capacitive voltammetric current density, jc, on ν for the Ti/RuO2–IrO2 anodes calcined at 300 °C.
Journal 27 Pre-proof
Pechini PVA Fitting
6 5
Rct R
-Z'' /
4
CPE
3
of
2
ro
1 0 1
2
3 Z' /
4
5
6
re
-p
0
Figure 6: Nyquist plots of Ti/RuO2–IrO2 PVA (□) and Pechini (○) anodes calcined at 300 °C,
lP
recorded at 1.12 V versus Ag/AgCl at the OER onset potential in 0.5 mol L–1 H2SO4 solution
Jo ur
na
at 25 °C. Scatters: experimental data. Lines: fitting results.
Journal 28 Pre-proof
a)
100 PVA
60
40 [NaCl] -1 0 mol L -1 0.005 mol L -1 0.010 mol L -1 0.020 mol L
of
20
0 0
20
40
60
ro
Colour removal / %
80
80
100
120
b) 100
re
-p
t / min
lP
Pechini
na
60
40
20
Jo ur
Colour removal / %
80
[NaCl] -1 0 mol L -1 0.005 mol L -1 0.010 mol L -1 0.020 mol L
0 0
20
40
60
80
100
120
t / min Figure 7: Percentage of colour removal as a function of the electrolysis time of the RB21 dye, carried out in different electrolytes concentrations, employing the Ti/RuO2–IrO2 PVA (A) and
Journal 29 Pre-proof Pechini (B) anodes calcined at 300 °C, with an applied current density of 25 mA cm2. The lines are guide for eyes.
a)
0 -1
ln (C/C0)
-2 -3
PVA
-4
of
NaCl concentration -1 0 mol L -1 0.005 mol L -1 0.010 mol L -1 0.020 mol L
ro
-5
b)
20
40
80
100
120
lP
0 -1
na
-2 -3
Pechini
Jo ur
ln (C/C0)
60 t / min
re
0
-p
-6
-4
NaCl concentration -1 0 mol L -1 0.005 mol L -1 0.010 mol L -1 0.020 mol L
-5 -6
0
20
40
60 t / min
80
100
120
Figure 8: Pseudo-first-order kinetic model fitted to the colour removal of RB-21 dye in different electrolyte concentrations.
Journal 30 Pre-proof
Table 1. EDX determination of the metals in the Ti/RuO2–IrO2 films prepared using PVA and Pechini methods at different calcination temperatures. Ru / MTα Precursor Oxide film solution (%) (%) 50.0 0.55 ± 0.08
Ir / MTα Precursor Oxide film solution (%) (%) 50.0 0.45 ± 0.08
PVA
400
50.0
0.55 ± 0.06
50.0
0.45 ± 0.06
PVA
500
50.0
0.53 ± 0.04
50.0
0.47 ± 0.04
Pechini
300
50.0
0.40 ± 0.11
50.0
0.60 ± 0.11
Pechini
400
50.0
0.45 ± 0.24
50.0
0.55 ± 0.24
Pechini
500
50.0
50.0
0.44 ± 0.05
-p
ro
of
PVA
Calcination temperature (°C) 300
0.56 ± 0.05
re
Method
Jo ur
na
lP
Total metal content, MT = Ru + Ir
Journal 31 Pre-proof Table 2. Voltammetric charge behaviour for the Ti/RuO2–IrO2 anodes, obtained in the potential limits from 0.2 V to 1.2 V versus Ag/AgCl.
121.9
400
30.3
500
38.3
300
256.1
400
167.3
500
138.8
re
-p
ro
of
300
lP
PVA
Voltammetric Charge (mC cm–²)
na
Pechini
Temperature (°C)
Jo ur
Method
Journal 32 Pre-proof Table 3. Dependence of the total (Ct), external (Co) and internal (Ci) differential capacitances and morphology factor (φm) on the synthesis method used. Anodes were calcined at 300 °C. Method
Ct (mF cm–2)
Cd,o (mF cm–2)
Cd,i (mF cm–2)
φm (Cd,i /Cd)
69.0
18.0
51.0
0.74
PVA
107.3
19.0
88.3
0.82
Jo ur
na
lP
re
-p
ro
of
Pechini
Journal 33 Pre-proof Table 4. Summary of fitted EIS data for the Ti/RuO2–IrO2 anodes, recorded at 1.23 V versus Ag/AgCl. E vs Ag/ AgCl (V)
RΩ (Ω)
Rct (Ω)
Qdl (F)
ndl
Pechini
1.23
1.21
5.55
0.14
0.88
PVA
1.23
1.31
3.10
0.30
0.90
Jo ur
na
lP
re
-p
ro
of
Method
Journal 34 Pre-proof
Table 5. Effect of electrolyte concentration and of the synthesis method on the kinetic constants for colour removal of RB-21 dye. Method
0 mol L-1
0.005 mol L-1
0.010 mol L-1
0.002 mol L-1
R2
k min-1
R2
k min-1
R2
k min-1
R2
Pechini
0.006
0.977
0.007
0.986
0.024
0.969
0.085
0.994
PVA
0.006
0.978
0.007
0.981
0.034
0.174
0.967
Jo ur
na
lP
re
-p
ro
of
k min-1
0.966
Journal 35 Pre-proof CRediT author statement
Charlys W. A. Bezerra: Acquisition, analysis, and interpretation of the data, Methodology, Investigation.
Géssica de O. S. Santos: Acquisition, analysis, and interpretation of the data, Methodology, Investigation, Writing - Original Draft, Review & Editing.
Marilia M. S. Pupo: Acquisition, analysis, and interpretation of the data, validation, investigation,
of
Review & Editing.
ro
Maria A. Gomes: Acquisition, analysis, and interpretation of the data, validation, investigation,
-p
Review & Editing.
re
Ronaldo S. da Silva: Acquisition, Resources, Formal analysis, Writing - Review & Editing.
lP
Katlin I. B. Eguiluz: Project administration, Supervision, Funding acquisition, conceptualization and
na
planning of the work and Writing - Review & Editing
Giancarlo R. Salazar-Banda: Project administration, Supervision, Funding acquisition,
Jo ur
conceptualization and planning of the work and Writing - Review & Editing
Journal 36 Pre-proof Declaration of interests
☒ The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Jo ur
na
lP
re
-p
ro
of
☐The authors declare the following financial interests/personal relationships which may be considered as potential competing interests:
Journal 37 Pre-proof Graphical abstract
Highlights
The green method developed employing PVA as solvent improves RuO2-IrO2 anode lifetime The most suitable calcination temperature was proven to be 300 °C
Charge-transfer resistance is 1.8-fold lower than the anodes made by Pechini method
Anode made using PVA is the most efficient towards reactive blue 21 dye oxidation
Jo ur
na
lP
re
-p
ro
of
Charlys Wilton dos Anjos Bezerra, Géssica de Oliveira Santiago Santos, Marilia Moura de Salles Pupo, Maria de Andrade Gomes, Ronaldo Santos da Silva, Katlin Ivon Barrios Eguiluz, Giancarlo Richard Salazar-Banda PII:
S1572-6657(20)30005-9
DOI:
https://doi.org/10.1016/j.jelechem.2020.113822
Reference:
JEAC 113822
To appear in:
Journal of Electroanalytical Chemistry
Received date:
1 November 2019
Revised date:
13 December 2019
Accepted date:
3 January 2020
Please cite this article as: C.W. dos Anjos Bezerra, G. de Oliveira Santiago Santos, M.M. de Salles Pupo, et al., Novel eco-friendly method to prepare Ti/RuO2–IrO2 anodes by using polyvinyl alcohol as the solvent, Journal of Electroanalytical Chemistry(2020), https://doi.org/10.1016/j.jelechem.2020.113822
This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
© 2020 Published by Elsevier.
Journal Pre-proof
Novel eco-friendly method to prepare Ti/RuO2–IrO2 anodes by using polyvinyl alcohol as the solvent
Charlys Wilton dos Anjos Bezerraa, Géssica de Oliveira Santiago Santosa,b, Marilia Moura de
of
Salles Pupoa,b, Maria de Andrade Gomesd, Ronaldo Santos da Silvac, Katlin Ivon Barrios
Laboratório de Eletroquímica e Nanotecnologia – LEN, Instituto de Tecnologia e Pesquisa,
Aracaju, SE, Brazil
Programa de Pós-graduação em Engenharia de Processos, Universidade Tiradentes, Avenida
na
b
lP
a
re
-p
ro
Eguiluza,b, Giancarlo Richard Salazar-Bandaa,b,*
Jo ur
Murilo Dantas, 300, Aracaju, SE, Brazil
c Grupo de Nanomateriais Funcionais, Departamento de Física, Universidade Federal de Sergipe, Campus Universitário, CEP: 49100-000, São Cristovão, SE, Brazil d
Laboratório de Preparação e Caracterização de Materiais, Departamento de Física,
Universidade Federal de Sergipe, 49000-100, São Cristóvão-SE, Brazil
*Corresponding author: [email protected] (Giancarlo Richard Salazar-Banda)
Journal Pre-proof 1 Abstract Electrochemical oxidation processes are promising solutions for wastewater treatment due to their high efficiency, effortless control, and versatility. Mixed metal oxides anodes are particularly attractive due to their low cost and specific catalytic properties. Here, we report the synthesis of a new Ti/RuO2-IrO2 anode fabricated through an innovative eco-friendly methodology using polyvinyl alcohol (PVA) as the solvent. Comparative anodes were also prepared by the conventional method of polymeric precursors. For both methods, anodes were
of
calcined at 300, 400, and 500 °C. X-ray diffraction data confirmed the formation of RuO2 and
ro
IrO2 in the rutile-type structure for all conditions. Moreover, compared to conventional
-p
polymeric precursor method, PVA-made anode obtained at 300 °C presented increased
re
voltammetric charge (210%), besides reduced charge-transfer resistance (1.8-fold lower). Electrochemical degradation of the RB-21 dye showed that the PVA-made Ti/RuO2-IrO2
lP
anode has the highest degradation efficiency, and its kinetic rate constant is until 2 times
na
greater than the conventional anode. Besides, due to rougher and more compact surfaces, the better adhesion of the film observed for the PVA-made anodes, the accelerated service
Jo ur
lifetime of the anode was prolonged 4.3-fold.
Keywords: PVA, MMOs anodes, ruthenium dioxide, iridium dioxide, electrocatalysis
Journal Pre-proof 2 1. Introduction Among anthropogenic and industrial activities, dye-containing effluent discharge from textile industries is of severe environmental concern due to its adverse effects on the aquatic environment. It is because these compounds limit light penetration inhibiting the photosynthesis of aqueous flora and also due to its low biodegradability and potential toxicity effect on aquatic life [1–3]. In this context, the electrochemical oxidation process stands out as a practical approach for treating these toxic or bio-refractory organic pollutants due to its high
of
efficiency, effortless control, versatility, and environmental compatibility [4,5]. Although
ro
organic wastes can, in general, be oxidised at numerous electrode materials, the
-p
electrochemical efficacy depends on the kind, and, on the structure of the anode materials [6–
re
10].
In that sense, the use of mixed metal oxides (MMO) anodes is especially attractive due
lP
to their low cost, ease of preparation, and their variety of electrochemical applications
na
primarily because their electrocatalytic properties may be significantly modulated by changing the composition or preparation conditions of these anodes [11,12]. Among different
Jo ur
candidates, RuO2–IrO2 anodes are considered quite promising anode materials due to their outstanding mechanical stability, long service life, and reasonable electrocatalytic activity [9,13,14]. In these systems, the presence of IrO2 improves the stability of RuO2 [15,16]. Coster et al. studied the electrochemical oxidation of 4-chlorophenol in the presence of chlorides by the use of a Ti/RuO2-IrO2 anode. After 120 min of treatment, the contaminant is rapidly degraded, and even total mineralization could be obtained after prolonged oxidation[17]. Similar results have been reported for the electrochemical oxidation of methylene blue using Ti/RuO2-IrO2 anode, where the complete color elimination with 73 % of chemical oxygen demand elimination was achieved within 90 min of electrolysis[18].
Journal Pre-proof 3 Given its importance in the electrochemical system, it is critical to developing novel and sustainable methods capable of producing anodes with superior electrochemical activity for oxidation of pollutants, also having a long service lifetime at a low production cost. Herein, we propose polyvinyl alcohol (PVA)-assisted thermal decomposition method as an attractive alternative route to prepare Ti/RuO2–IrO2 anodes, in which a water-based PVA solution is used as both solvent and polymerising agent of precursor metal salts. The use of PVA as a modifier to improve the properties of PbO2 electrodes was
of
reported by Li et al. [19]. In addition, PVA has already been used for the synthesis of efficient
ro
luminescent nanoparticles [20,21]. However, at present, studies employing PVA as a solvent
-p
to prepare the precursor solution for MMO anodes preparation have never been reported. PVA
re
is a water-soluble environmentally friendly synthetic polymer, with the chemical formula [CH2CH(OH)]n, with a hydroxyl group for each PVA monomer. When added to the salt
lP
solution, the OH– groups of the polymer chains can solvate the metal ions in the solution,
na
forming metal hydroxides. At the same time, the surfactant property of the polymer network of PVA promotes the steric stabilisation of the nuclei and prevents the approximation between
Jo ur
them, leading to the formation of structures in nanometric dimensions [22,23]. Moreover, advantages of PVA method are: (i) the low degree of toxicity, even being used as a component of biodegradable composite polymers, since it is non-toxic to organisms [24], (ii) methodological simplicity and (iii) possibility of using of water as the solvent for the precursor salts. Therefore, we present, for the first time, PVA adopted as a solvent to prepare Ti/RuO2–IrO2 anodes by thermal decomposition and the effect of three different calcination temperatures (300, 400, and 500 °C) was investigated. In order to investigate the actual efficiency and advantages of this new proposed methodology, Ti/RuO2-IrO2 anodes prepared by conventional Pechini’s method were used for comparison throughout the study. X-ray
Journal Pre-proof 4 diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray (EDX) spectroscopy, linear sweep voltammetry (LSV), cyclic voltammetry (CV) accelerated service lifetime, and electrochemical impedance spectroscopy (EIS) measurements were carried out to characterise the physical and electrochemical properties of the MMO anodes. Furthermore, Reactive Blue 21 (RB21) textile dye was employed as the target organic molecule for electrochemical oxidation to evaluate the electrocatalytic activity of the developed MMO
of
anodes.
ro
2. Experimental
-p
2.1 Electrode synthesis
re
Titanium plates (1 cm × 1 cm × 0.5 mm) were used as metallic support, and a prior cleaning
lP
pre-treatment was carried out as previously reported [25,26]. The metal salts of ruthenium chloride (III) hydrate (RuCl3 × H2O, 99.99%) and iridium chloride hydrate (IrCl3 × H2O,
na
99.0%) from Sigma-Aldrich® were used without further purification. Polyvinyl alcohol (PVA) (99%), or anhydrous citric acid (CA) (99.5 %), from Vetec®, dissolved in ethylene glycol
Jo ur
(EG) (99.8%) from Sigma-Aldrich® were used as solvents. Besides, ultrapure water (18.18 mΩ, by Gehaka MS 2000 system) was used to prepare all solutions. Firstly, a stock solution of PVA 10 wt.% was prepared by dissolving the PVA powder in ultrapure water at 80 °C under continuous stirring until complete dissolution. Ruthenium chloride and iridium chloride in a molar ratio Ru/Ir = 0.5/0.5 were dissolved in 1 mL of ultrapure water, followed by the gradual addition of 3 mL of the PVA 10 wt% stock solution. The PVA-based precursor solution is kept under stirring until a homogeneous solution is obtained. Similarly, the precursor solutions prepared following Pechini’s method [27] were obtained employing a solution of CA in EG as a solvent in the ratio CA:EG = 3:10, stirring,
Journal Pre-proof 5 and heating the solution up to 90 °C for complete dissolution. The molar ratio of RuCl3– IrCl3/CA/EG was maintained at 1:3:10 (with the molar ratio Ru/Ir = 0.5/0.5). Finally, the obtained precursor solutions were brushed over the titanium plates and afterwards heated up to 130 °C being kept for 30 min, then up to 250 °C being kept for 10 min and finally calcinated at 300, 400 or 500 °C for 5 min. This procedure is repeated, for both methods, until a mass loading of 1.2 mg cm–2 is achieved. Finally, when this condition is achieved, the anodes are submitted to a final calcination process at 300, 400, or 500 °C for 60
ro
of
min.
-p
2.2 Physical characterisation
re
The XRD patterns of the obtained anodes were recorded in a diffractometer (RIGAKU RINT 2000 / PC), with Cu radiation Kα (wavelength = 1.5406 Å), in a scan-interval 2θ between 20°
lP
and 80°, in continuous scan mode with steps of 0.02°. Phase identification was performed
na
using the Joint Committee on Powder Diffraction Standards (JCPDS) database by using the X’pert High Score Plus software version 2.2.2. The surface morphology and the composition
Jo ur
of the coating were analysed by SEM in a JEOL model JMC 5700 microscope equipped with an X-ray detector for EDX spectroscopy.
2.3 Electrochemical characterisation The electrochemical measurements, CV, LSV, morphology factor (φ), accelerated service lifetime tests, and EIS were performed in a one-compartment three-electrode cell by using a potentiostat/galvanostat (PGSTAT302N METROHM AUTOLAB) equipped with Nova 2.0 Metrohm Autolab Software. The reference and the counter electrodes were an Ag/AgCl (3.0 mol L–1 KCl) and a 2 cm2 platinum counter electrodes, respectively. The working electrode consisted of the Ti/RuO2–IrO2 synthesised.
Journal Pre-proof 6 Cyclic voltammetry experiments were performed at 50 mV s–1 in 0.5 mol L–1 H2SO4 solution, between the potential limits from 0.2 V to 1.2 V. The total voltammetric charges (q*), which can be considered as a relative measure to electrochemically active surface areas, were calculated by integrating the area of the cyclic voltammograms [28]. According to the methodology proposed by Da Silva et al. [29], continuous voltammetric curves were recorded at several scan rates (10–300 mV s–1) in a 0.5 mol L–1 H2SO4 medium, in order to determine the morphology factor of each anode prepared. The EIS measurements were performed in a
of
0.5 mol L–1 H2SO4 medium covering a frequency range of 0.01 Hz–10 kHz using an AC sine
ro
signal amplitude of 5 mV with a logarithmic distribution of 10 frequencies per decade. The
-p
potential applied for each electrode was 1.12 V, which corresponds to the oxygen evolution
re
reaction (OER) onset potential at each anode studied (according to data obtained with LSV in the same electrolyte). EIS data were treated using the Zview 2.0 software.
lP
The accelerated service lifetime tests were carried out in 1.0 mol L–1 H2SO4 solution
na
by applying 1 A cm–2 in order to evaluate the electrochemical stability of metal oxides under extreme electrolysis conditions. The operational electrocatalytic conditions of the electrode
Jo ur
were considered viable until the potential response of the anode was over 10 V.
2.4 Electrochemical oxidation of RB21 The electrochemical oxidations of the Reactive Blue dye (RB21) were carried out in 100 mL of a solution containing 50 mg L–1 of the dye in 0.1 mol L–1 Na2SO4. The experiments were also carried out in sodium sulphate solutions with the previous concentration containing 0.005, 0.010, and 0.020 mol L–1 NaCl to evaluate the effect of chloride ions in the electrolyte. The colour removal was evaluated as a time function, and representative samples were collected at 0, 5, 15, 30, 60, 90, 120 min, and analysed on a UV-vis spectrophotometer Hach
Journal Pre-proof 7 DR-500. Colour removal (CR) was calculated based on absorbance at 622 nm, according to equation (1):
CR = [(Abs0 – Abst/Abs0) × 100]
(1)
where Abs0 and Abst are, respectively, the absorbance of the solution before and at a given
of
time of electrolysis.
ro
3. Results and discussion
-p
3.1 SEM-EDX and XRD analyses
re
Figure 1 displays the SEM images of the Ti/RuO2–IrO2 anodes, synthesised by the PVA and Pechini methods, in different temperatures. Note the presence of cracks on the anode surfaces,
lP
which are attributed to the mechanical stress resulted from the plasticity of the coating and the
na
difference of the thermal expansion coefficients between the substrate and the film. This ―cracked-mud‖ appearance has been commonly reported for coatings deposited by using
Jo ur
thermal decomposition [30–32]. Additionally, for both methods, as the temperature increases, the surface becomes smoother. This fact is commonly associated with grain growth (swelling effect) and agglomeration of the particles at high temperatures [33,34]. Although similar cracked-mud structures were obtained, the PVA anodes presented surfaces with a minimised number of deeper cracks when compared to Pechini ones. In the aqueous solution containing RuCl3 and IrCl3, it is believed that ruthenium and iridium ions, driven by electrostatic force, are complexed with OH– ligands, forming Ru(OH)3 and Ir(OH)3 distributed regularly on the PVA chains [20]. Then, the hydroxides are transformed into oxides and grow homogeneously during the thermal treatment.
Journal Pre-proof 8 EDX analyses were performed for all synthesised anodes to confirm the chemical composition of the coatings. Table 1 shows the results obtained by EDX and the theoretical Ru and Ir concentrations in the films. Notably, the expected and the observed values have a good agreement, indicating that Ru and Ir elements were successfully combined in the desired proportions regardless of the calcination temperature and preparation method. Also, in order to assess the ruthenium and iridium distribution on the film surface, either in grains or in cracks, EDX elemental mapping (Figure 2) confirms the sample composition and
of
homogenous elements distribution.
ro
The XRD patterns of the prepared anodes at different temperatures are shown in
-p
Figure 3. In both cases, PVA (Fig. 3a) and Pechini (Fig. 3b) anodes, the peaks were indexed
re
according to RuO2 (JCPDS-40-1290) and IrO2 (JCPDS-15-0870) tetragonal rutile structure, for all calcination temperatures.
lP
In agreement with the Hume–Rothery theory since ionic radii of Ru4+ (0.076 nm) and
na
Ir4+ (0.077 nm) are very similar as well as RuO2 and IrO2 present the same crystalline rutilelike structure [35,36], it is expected the formation of a stable solid solution between RuO2 and
Jo ur
IrO2 compounds. However, due to the low intensity, highly broad, and angular proximity of the diffraction peaks, these analyses from XRD patterns are impaired and complementary techniques are needed.
Moreover, the intensity of the peaks related to RuO2 and IrO2 for PVA-made films are relatively lower than those observed for the electrodes prepared by the Pechini method, when also compared with Ti peaks. This result suggests a better-coated anode surface when synthesised by the PVA method. Additionally, the crystallite sizes were estimated by the Scherrer equation using the full width at half-maximum (FWHM) of the (110) peak. In general, the average crystallite size decreased when PVA was employed in the synthesis process. The average crystallite sizes for PVA-made films obtained at 300, 400, and 500 were
Journal Pre-proof 9 3.8 nm, 4.2, and 4.3, as for Pechini were 7.5 nm, 8.6 nm, and 12.5 nm. The lower degree of the crystallinity combined with the decrease in the mean crystallite size contributes to the enhancement of active surface area [42]. Similar results were reported by Li et al. [29], after PbO2 modification with PVA. They found smoother films and reduction of the grain size estimated by Scherrer equation, which explained longer service lifetime. These features influence the efficiency of anodes since larger grains reduces the electroactive area available
of
for the catalytic reactions [37].
ro
3.2 Electrochemical characterisation
-p
Fig. 4 shows the voltammetric profiles obtained for the PVA-made (Fig. 4a) and Pechini-
re
made (Fig. 4b) anodes calcinated at 300, 400, and 500 °C. The recorded CVs were integrated into the whole potential range (that is between the onsets of HER and OER) to gain a
lP
complete and more clear macroscopic insight in the surface features of the prepared materials.
na
The voltammetric charge obtained is used as a relative measure of the electrochemically
prepared anodes.
Jo ur
active area of the MMO anodes. Table 2 shows the voltammetric charge values found for all
The higher the calcination temperature, the lower the electrochemically active area of the anodes. It is because the increase of the calcination temperature leads to grain growth, thus reducing the surface area, as discussed previously. However, when comparing both methods, the PVA-made anodes stands out with higher values of voltammetric charge. Amongst the studied temperatures, the PVA-made anode prepared at 300 °C presented the highest voltammetric charge value of 256.1 mC cm–2, which is 210 % higher than the correspondent anode prepared by the Pechini method.
Journal 10 Pre-proof The morphology factor can be considered as a measure of the contribution of the internal sites of the electrodes to the total differential capacitance and is determined as the ratio in Equation (2) [29,38].
φm = C i / Ct
(2)
Where Cd,i and Cd represents, respectively, the inner and total differential pseudocapacitance
of
of the film. The value of φm can vary between 0 and 1, where values close to 0 indicate that
ro
the contribution of the inner sites is small or negligible, and values near 1 indicate that the
-p
electrode has a large internal area [29,38].
re
Morphology factor values were then determined for the anodes prepared at 300 °C, according to the methodology described by Da Silva et al. [29]. Thus, cyclic voltammograms
lP
were recorded for a narrow potential interval (ΔE = 0.55–0.65 V vs Ag/AgCl) where only
na
double layer charging occurs, which allows the determination of the capacitive current density (jc). As reported by Da Silva et al. [29] the potential range used to determining jc should be
Jo ur
localised as close as possible to the anodic switching potential, on the last 20 % of the capacitive potential range in order to obtain meaningful results (i.e., 0.63 V vs Ag/AgCl ). The voltammograms covering the potential interval of 0.2–1.2 V vs Ag/AgCl and in a capacitive potential interval as a function of the potential scan rate for the anodes obtained by both methods calcined at 300 °C are shown in Figure S1. As a result, Fig. 5 shows the dependence of the capacitive voltammetric current density, jc, on ν., of the anodes calcined at 300 °C obtained by both methods. Two linear segments are located in the low and high scan rates, indicating the existence of two distinct surface regions described as typical behaviour exhibited by highly roughness films [29]. Both anodes display morphology factor near to 1, which indicates that regardless of the preparation
Journal 11 Pre-proof method, Ti/RuO2–IrO2 anodes presented a high contribution of the internal sites of the coating. The values of the total (Ct) and external (Ce) differential capacitance, were obtained from the angular coefficients observed in the low and high scan rates, respectively. The total (Ct), external (Ce), internal (Ci = Ct – Ce) differential capacitance values and the morphology factor (φm) are presented in Table 3. EIS measurements for the anodes were carried out at the potential of 1.23 V vs Ag/AgCl corresponding to the OER onset potential at each studied anode. The choice of the
of
potential was based on the LSV data (Figure S2). Fig. 6 show the Nyquist plots of the PVA
ro
and Pechini anodes calcinated at 300 °C. Both impedance spectra exhibited well-developed
-p
semicircles typically related to the charge-transfer process for the OER [39,40]. The Nyquist
re
plots obtained were fitted with a characteristic equivalent circuit for a simple redox reaction characterised by one capacitive loop, represented by RΩ(RctQdl) combination (inset on Fig. 6).
lP
RΩ, Rct, and Qdl correspond, respectively, to solution resistance, charge-transfer resistance, and
na
the double-layer capacitance. The constant phase element (CPE) is often used to replace Qdl, considering electrode roughness and heterogeneity. The proposed equivalent circuit fitted well
fitting.
Jo ur
all impedance data displaying a quality factor χ2 < 5 × 10–4, which indicates a high quality of
The values of RΩ, Rct, and Qdl obtained by the fitting procedure are listed in Table 4. For both anodes, RΩ, values were estimated between 1.21 to 1.31 Ω which is attributed to cell resistance, including the connections, the electrolyte, and the resistance of the film. An Rct value of the 3.1 Ω was found for the PVA-made anode, which is almost 2-fold lower than the value obtained for the Pechini anode (5.55 Ω). This result indicates that the reaction occurs more efficiently at the surface of the PVA-made anode, which is supported by CV data that shows an increase in the voltammetric charge, related to the higher presence of active sites at the surface of the anode.
Journal 12 Pre-proof Electrochemical stability tests were carried out, focusing on the understanding of the overall electrode response to highly aggressive medium. Thus, the also known accelerated service lifetime tests, which have the advantage of providing a quick answer on a laboratory scale, since the study of the real service life needs very long experiments. Figure S3 shows the potential variations against time during the accelerated service lifetime tests in an acid medium (1.0 mol L–1 H2SO4) at high current density (e.g. 1 A cm–2) for the anodes calcined at 300 °C. Results show that the PVA-made anode has service time 4.3-fold higher than the
of
Pechini anode. The reason for the longer accelerated service life can be attributed to
ro
minimised presence of broad and deep cracks in the PVA-made anodes, as previously seen in
-p
SEM image (Fig. 1a). As a result, the presence of deeper cracks on Pechini anodes surfaces
re
facilitates the electrolytic solution penetration through these cracks and increases the pressure
na
deactivation [41–43].
lP
inside the anode caused by the internal O2 evolution, which is the main factor for fast anode
3.3 Electrolysis of Reactive Blue 21 dye
Jo ur
The PVA- and Pechini-made anodes calcined at 300 °C were used to investigate their electrocatalytic activity in the electrochemical oxidation of 50 mg L–1 Reactive Blue 21 aqueous dye solution, by applying 25 mA cm–2 in 0.1 mol L–1 Na2SO4 solution and with the use of different NaCl concentrations. Figure 7 displays the effect of chloride concentration (0.005–0.02 mol L–1) on colour removal as a function of the time for the PVA (Fig. 7a) and Pechini (Fig. 7b) anodes. The use of 0.005 mol L–1 NaCl promotes a slight improvement on colour removal percentages, i.e., from 51.02 to 56.85 % for PVA-made anodes prepared and from 50.01 to 54.28 % for Pechini. On the other hand, electrolysis carried out with the addition of 0.01 mol L–1 NaCl shows a more significant improved treatment, reaching 100 % of colour removal after 120 min of electrolysis. Further increasing the NaCl concentration to
Journal 13 Pre-proof 0.02 mol L–1 led to the best result in colour removal percentage, since 100 % of the colour was removed in only 30 min for the PVA-made anode and in 60 min for Pechini anode. Then, for both methods, the optimal chloride concentration responsible for the fastest colour removal is 0.02 mol L–1. The colour removal improvement observed for the higher chloride concentrations has been explained by the conversion of chlorides to chlorine, hypochlorous acid, and hypochlorite species in solution, which promotes a synergic action of indirect oxidation together with direct oxidation on the anode surface, as previously reported
of
[3,12,19,44]. The fastest electrochemical degradation of RB21 dye for the PVA-made anode
-p
and generating more ●OH and chlorine radicals.
ro
could be related to its larger surface area, providing more active site centres on the coating
re
The kinetic order with respect to RB-21 colour removal was evaluated in the presence of different electrolyte concentrations that, as mentioned before, affects oxidation efficiency
lP
due to different amounts of oxidants generated during electrolysis, such as sulphates and
na
chlorine species. The exponential profile of the curves obtained for RB-21 colour removal in
8).
Jo ur
the first period of reaction could be fitted reasonably well to pseudo-first-order kinetic (Figure
The obtained kapparent values (Table 5) show that the addition of NaCl (from 0.005 to 0.02 mol L–1) the higher the colour removal rate. Considering the anode performance, the faster kinetic rate was observed for the PVA-made anode (0.0174 min–1 in 0.02 mol L–1 NaCl addition) being 2-times greater than observed for Pechini-made anode (0.0085 min–1). These results point out that PVA method may increase the kinetic rate constant more importantly in chloride media.
4. Conclusions
Journal 14 Pre-proof This study reported, for the first time, the synthesis of Ti/RuO2–IrO2 anodes prepared by using a PVA-assisted thermal decomposition method. The use of PVA as the solvent of the precursor salts led to a better-coated anode surface with the minimised presence of crack and fissures. Moreover, the use of PVA increases the voltammetric charge values for all the investigated temperatures. Amongst the studied calcination temperatures, the lowest one (300 °C) was the most suitable, presenting an increase of 210% in the total voltammetric charge and service lifetime 4.3 times longer than the anodes synthesised in different temperatures.
of
Furthermore, the use of PVA reduced the charge-transfer resistance of the anodes compared to
ro
the Pechini anodes. Also, the Ti/RuO2–IrO2 PVA anodes prepared at 300 °C presented higher
-p
electrocatalytic activity being capable of reducing 100 % of the colour of the model organic
re
compound BR21 dye in 30 min, while 60 min was required for Pechini anode. Finally, the PVA-assisted method stands out as a clean, eco-friendly, and promising
lP
alternative route to improve the characteristics of MMO anodes and to optimise their
na
synthesis. This method can produce electrodes with improved physical and electrochemical properties compared to the electrode obtained by the conventional Pechini method. Besides,
Jo ur
the low toxicity of PVA and the use of water to compose the solvent mixture are favourable particularities of the developed method.
Acknowledgements
The authors thank the Brazilian National Counsel of Technological and Scientific Development-CNPq (grants: 305438/2018-2, 304419/2015-0 and 310282/2013-6), to the Coordination for the Improvement of Higher Education Personnel – CAPES (grants: 88882.365552/2018-01 and 88881.187890/2018-01) and to Sergipe State Research and Technological Innovation Foundation (FAPITEC/SE) for the scholarships and financial support for this work.
Journal 15 Pre-proof
References [1]
L. Jiancheng, Y. Jie, L. Weishan, H. Qiming, X. Hongkang, Electrochemical degradation of Reactive Brilliant Red K-2BP on Ti/RuTiIrSnMn oxide anode in a batch cell, J. Electrochem. Sci. Eng. 2 (2012) 171–183. doi:10.5599/jese.2012.0022.
[2]
S. Raghu, C.A. Basha, Dye destruction and simultaneous generation of sodium hydroxide using a divided electrochemical reactor, Ind. Eng. Chem. Res. 47 (2008)
J.M. Aquino, M. a. Rodrigo, R.C. Rocha-Filho, C. Sáez, P. Cañizares, Influence of the
ro
[3]
of
5277–5283. doi:10.1021/ie070675b.
-p
supporting electrolyte on the electrolyses of dyes with conductive-diamond anodes,
[4]
re
Chem. Eng. J. 184 (2012) 221–227. doi:10.1016/j.cej.2012.01.044. I. Sirés, E. Brillas, M.A. Oturan, M.A. Rodrigo, M. Panizza, Electrochemical advanced
lP
oxidation processes : today and tomorrow . A review, Environ. Sci. Pollut. Res. 21
[5]
na
(2014) 8336–8367. doi:10.1007/s11356-014-2783-1. C.A. Martínez-Huitle, M.A. Rodrigo, I. Sirés, O. Scialdone, Single and Coupled
Jo ur
Electrochemical Processes and Reactors for the Abatement of Organic Water Pollutants: A Critical Review, Chem. Rev. 115 (2015). doi:10.1021/acs.chemrev.5b00361. [6]
W. Wu, Z.-H. Huang, T.-T. Lim, Recent development of mixed metal oxide anodes for electrochemical oxidation of organic pollutants in water, Appl. Catal. A Gen. 480 (2014) 58–78. doi:10.1016/j.apcata.2014.04.035.
[7]
F. Moradi, C. Dehghanian, Addition of IrO2 to RuO2 +TiO2 coated anodes and its effect on electrochemical performance of anodes in acid media, Prog. Nat. Sci. Mater. Int. 24 (2014) 134–141. doi:10.1016/j.pnsc.2014.03.008.
[8]
T. Audichon, E. Mayousse, S. Morisset, C. Morais, C. Comminges, T.W. Napporn,
Journal 16 Pre-proof K.B. Kokoh, Electroactivity of RuO2 e IrO2 mixed nanocatalysts toward the oxygen evolution reaction in a water electrolyzer supplied by a solar profile, Int. J. Hydrogen Energy. 9 (2014) 16785–16796. doi:10.1016/j.ijhydene.2014.07.170. [9]
T. Audichon, B. Guenot, S. Baranton, M. Cretin, C. Lamy, C. Coutanceau, Preparation and characterization of supported RuxIr(1-x)O2 nano-oxides using a modified polyol synthesis assisted by microwave activation for energy storage applications, Appl. Catal. B Environ. 200 (2017) 493–502. doi:10.1016/j.apcatb.2016.07.048.
of
[10] A. Kapałka, G. Fóti, C. Comninellis, The importance of electrode material in
ro
environmental electrochemistry. Formation and reactivity of free hydroxyl radicals on
re
doi:10.1016/j.electacta.2008.06.045.
-p
boron-doped diamond electrodes, Electrochim. Acta. 54 (2009) 2018–2023.
[11] A.N.S. Rao, V.T. Venkatarangaiah, Metal oxide-coated anodes in wastewater
lP
treatment, Environ. Sci. Pollut. Res. 21 (2014) 3197–3217. doi:10.1007/s11356-013-
na
2313-6.
[12] F.C. Moreira, R.A.R. Boaventura, E. Brillas, V.J.P. Vilar, Electrochemical advanced
Jo ur
oxidation processes: A review on their application to synthetic and real wastewaters, Appl. Catal. B Environ. 202 (2017) 217–261. doi:10.1016/j.apcatb.2016.08.037. [13] F.I. Mattos-Costa, P. de Lima-Neto, S.A.. Machado, L.A. Avaca, Characterisation of surfaces modified by sol-gel derived RuxIr1−xO2 coatings for oxygen evolution in acid medium, Electrochim. Acta. 44 (1998) 1515–1523. doi:10.1016/S00134686(98)00275-8. [14] T. Le Luu, J. Kim, J. Yoon, Physicochemical properties of RuO2 and IrO2 electrodes affecting chlorine evolutions, J. Ind. Eng. Chem. 21 (2015) 400–404. doi:10.1016/j.jiec.2014.02.052. [15] M.E.G. Lyons, S. Floquet, Mechanism of oxygen reactions at porous oxide electrodes.
Journal 17 Pre-proof Part 2—Oxygen evolution at RuO2, IrO2 and IrxRu1−xO2 electrodes in aqueous acid and alkaline solution, Phys. Chem. Chem. Phys. 13 (2011) 5314. doi:10.1039/c0cp02875d. [16] M.J.R. Santos, M.C. Medeiros, T.M.B.F. Oliveira, C.C.O. Morais, S.E. Mazzetto, C.A. Martínez-Huitle, S.S.L. Castro, Electrooxidation of cardanol on mixed metal oxide (RuO2-TiO2 and IrO2-RuO2-TiO2) coated titanium anodes: insights into recalcitrant phenolic compounds, Electrochim. Acta. 212 (2016) 95–101. doi:10.1016/j.electacta.2016.06.145.
of
[17] J. De Coster, W. Vanherck, L. Appels, R. Dewil, Selective electrochemical degradation
ro
of 4-chlorophenol at a Ti/RuO2-IrO2 anode in chloride rich wastewater, J. Environ.
-p
Manage. 190 (2017) 61–71. doi:10.1016/j.jenvman.2016.11.049.
re
[18] A. Baddouh, B. El Ibrahimi, M.M. Rguitti, E. Mohamed, S. Hussain, L. Bazzi, Electrochemical removal of methylene bleu dye in aqueous solution using Ti/RuO2–
lP
IrO2 and SnO2 electrodes, Sep. Sci. Technol. 6395 (2019) 1–10.
na
doi:10.1080/01496395.2019.1608244.
[19] X. Li, H. Xu, W. Yan, Preparation and characterization of PbO2 electrodes modified
Jo ur
with polyvinyl alcohol (PVA), RSC Adv. 6 (2016) 82024–82032. doi:10.1039/C6RA17230J.
[20] M. De Andrade Gomes, M.E. Giroldo Valerio, J.F. Queiruga Rey, Z.S. Macedo, Comparative study of structural and optical properties of ZnO nanostructures prepared by three different aqueous solution methods, Mater. Chem. Phys. 142 (2013) 325–332. doi:10.1016/j.matchemphys.2013.07.024. [21] G.A. Sobral, M.A. Gomes, Z.S. MacEdo, M.A.R.C. Alencar, S.M.V. Novais, Synthesis and characterization of multicolour fluorescent nanoparticles for latent fingerprint detection, Bull. Mater. Sci. 39 (2016) 1565–1568. doi:10.1007/s12034-016-1303-y. [22] W.S. Ã, Y. Fang, J. Fan, Y. He, J. Min, Y. Qian, Novel synthesis method of ZnO
Journal 18 Pre-proof nanorods by ion complex transformed PVA-assisted nucleation, 299 (2007) 272–276. doi:10.1016/j.jcrysgro.2006.10.240. [23] F. Meshkani, M. Rezaei, Effect of process parameters on the synthesis of nanocrystalline magnesium oxide with high surface area and plate-like shape by surfactant assisted precipitation method, Powder Technol. 199 (2010) 144–148. doi:10.1016/j.powtec.2009.12.014. [24] X. Hu, R. Mamoto, Y. Shimomura, K. Kimbara, F. Kawai, Cell surface structure
of
enhancing uptake of polyvinyl alcohol (PVA) is induced by PVA in the PVA-utilizing
ro
Sphingopyxis sp. strain 113P3, Arch. Microbiol. 188 (2007) 235–241.
-p
doi:10.1007/s00203-007-0239-4.
re
[25] L.M. Da Silva, G.O.S. Santos, M.M.D.S. Pupo, K.I.B. Eguiluz, G.R. Salazar-Banda, Influence of heating rate on the physical and electrochemical properties of mixed metal
lP
oxides anodes synthesized by thermal decomposition method applying an ionic liquid,
na
J. Electroanal. Chem. 813 (2018) 127–133. doi:10.1016/j.jelechem.2018.02.026. [26] T.É.S. Santos, R.S. Silva, C.T. Meneses, C.A. Martínez-Huitle, K.I.B. Eguiluz, G.R.
Jo ur
Salazar-Banda, Unexpected Enhancement of Electrocatalytic Nature of Ti/(RuO2)x(Sb2O5)y Anodes Prepared by the Ionic Liquid-Thermal Decomposition Method, Ind. Eng. Chem. Res. 55 (2016) 3182–3187. doi:10.1021/acs.iecr.5b04690. [27] M.P. Pechini, N. Adams, Method of preparing lead and alkaline earth titanates and niobates and coating method using the same to form a capacitor, United states Pat. Off. (1967) 01–07. [28] R. Berenguer, J.M. Sieben, C. Quijada, E. Morallón, Pt- and Ru-Doped SnO2−Sb Anodes with High Stability in Alkaline Medium Rau l, Appl. Mater. Interfaces. 6 (2014) 22778–22789. [29] L.M. Da Silva, L.A. De Faria, J.F.C. Boodts, Determination of the morphology factor
Journal 19 Pre-proof of oxide layers, Electrochim. Acta. 47 (2001) 395–403. doi:10.1016/S00134686(01)00738-1. [30] F. Moradi, C. Dehghanian, Influence of heat treatment temperature on the electrochemical properties and corrosion behavior of RuO2-TiO2 coating in acidic chloride solution, Prot. Met. Phys. Chem. Surfaces. 49 (2013) 699–704. doi:10.1134/S2070205113060245. [31] T.É.S. Santos, R.S. Silva, C. Carlesi Jara, K.I.B. Eguiluz, G.R. Salazar-Banda, The
of
influence of the synthesis method of Ti/RuO2 electrodes on their stability and catalytic
ro
activity for electrochemical oxidation of the pesticide carbaryl, Mater. Chem. Phys. 148
-p
(2014) 39–47. doi:10.1016/j.matchemphys.2014.07.007.
re
[32] C. Comninellis, G.P. Vercesi, Characterization of dsa-type oxygen evolving electrodes.
6031(91)80257-J.
lP
Choice of a coating, Thermochim. Acta. 176 (1991) 31–47. doi:10.1016/0040-
na
[33] Y. Hou, J. Hu, L. Liu, J. Zhang, C. Cao, Effect of calcination temperature on electrocatalytic activities of Ti/IrO2 electrodes in methanol aqueous solutions, 51
Jo ur
(2006) 6258–6267. doi:10.1016/j.electacta.2006.04.008. [34] A.J. Terezo, E.C. Pereira, Preparation and characterization of Ti/RuO2-Nb2O5 electrodes obtained by polymeric precursor method, Electrochim. Acta. 44 (1999) 4507–4513. doi:10.1016/S0013-4686(99)00182-6. [35] T. Audichon, E. Mayousse, S. Morisset, C. Morais, C. Comminges, T.W. Napporn, K.B. Kokoh, Electroactivity of RuO2-IrO2 mixed nanocatalysts toward the oxygen evolution reaction in a water electrolyzer supplied by a solar profile, Int. J. Hydrogen Energy. 39 (2014) 16785–16796. doi:10.1016/j.ijhydene.2014.07.170. [36] G.O.S. Santos, L.R.A. Silva, Y.G.S. Alves, R.S. Silva, K.I.B. Eguiluz, G.R. Salazarbanda, Enhanced stability and electrocatalytic properties of Ti / RuxIr1-xO2 anodes
Journal 20 Pre-proof produced by a new laser process, Chem. Eng. J. 355 (2019) 439–447. doi:10.1016/j.cej.2018.08.145. [37] D.T. Araújo, M. de A. Gomes, R.S. Silva, C.C. de Almeida, C.A. Martínez-Huitle, K.I.B. Eguiluz, G.R. Salazar-Banda, Ternary dimensionally stable anodes composed of RuO2 and IrO2 with CeO2, SnO2,or Sb2O3 for efficient naphthalene and benzene electrochemical removal, J. Appl. Electrochem. 47 (2017) 547–561. doi:10.1007/s10800-017-1057-2.
of
[38] G.R.P. Malpass, R.S. Neves, A.J. Motheo, A comparative study of commercial and
ro
laboratory-made Ti/Ru0.3Ti0.7O2 DSA® electrodes: ―In situ‖ and ―ex situ‖ surface
re
doi:10.1016/j.electacta.2006.06.032.
-p
characterisation and organic oxidation activity, Electrochim. Acta. 52 (2006) 936–944.
[39] Z. Ye, H. Meng, D. Sun, Electrochemical impedance spectroscopic ( EIS )
lP
investigation of the oxygen evolution reaction mechanism of Ti/IrO2 + MnO2
na
electrodes in 0 . 5 m H 2 SO 4 solution, J. Electroanal. Chem. 621 (2008) 49–54. doi:10.1016/j.jelechem.2008.04.009.
Jo ur
[40] T. Audichon, S. Morisset, T.W. Napporn, K.B. Kokoh, C. Comminges, C. Morais, Effect of Adding CeO2 to RuO2-IrO2 Mixed Nanocatalysts: Activity towards the Oxygen Evolution Reaction and Stability in Acidic Media, ChemElectroChem. 2 (2015) 1128–1137. doi:10.1002/celc.201500072. [41] D. Shao, X. Li, H. Xu, W. Yan, An improved stable Ti/Sb–SnO2 electrode with high performance in electrochemical oxidation processes, RSC Adv. 4 (2014) 21230. doi:10.1039/c4ra01990c. [42] Y. Xin, L. Xu, J. Wang, The Deactivation Mechanism of RuO2-IrO2-SnO2/Ti Anodes Under Alternative Current Electrolysis Condition, (2015) 1762–1765. [43] S.M. Hoseinieh, F. Ashrafizadeh, Influence of electrolyte composition on deactivation
Journal 21 Pre-proof mechanism of a Ti/Ru0.25Ir0.25Ti0.5O2 electrode, Ionics (Kiel). 19 (2013) 113–125. doi:10.1007/s11581-012-0737-5. [44] F. Zaviska, P. Drogui, J.F. Blais, G. Mercier, In situ active chlorine generation for the treatment of dye-containing effluents, J. Appl. Electrochem. 39 (2009) 2397–2408.
re
-p
ro
of
doi:10.1007/s10800-009-9927-x.
Jo ur
na
lP
Figures
lP
re
-p
ro
of
Journal 22 Pre-proof
na
Figure 1: Scanning electron micrographs of the Ti/RuO2–IrO2 anodes obtained by PVA (a,c, e) and Pechini (b,d,f) methods calcined at 300, 400 and 500 °C with magnification of 500×,
Jo ur
and inset by 2000×.
ro
of
Journal 23 Pre-proof
Figure 2. Scanning electron micrographs, elemental mapping, and EDX analysis of the
Jo ur
na
lP
re
-p
Ti/RuO2–IrO2 anodes calcined at 300 °C obtained by PVA (a) Pechini (b) method.
Journal 24 Pre-proof
Ti Ti
PVA Ti
Ti
500°C
400°C
300°C
RuO2 Pattern
of
Intensity / normalized
a)
IrO2
20
30
ro
Pattern
40
50
60
70
b) Ti
lP
Ti
na
400°C
300°C
Pechini
Jo ur
Intensity / normalized
500°C
re
Ti Ti
-p
2/ degrees
RuO2
Pattern
IrO2
Pattern
20
30
40
50
60
70
2/ degrees Figure 3: X-ray diffraction patterns of Ti/RuO2–IrO2 anodes calcined at different temperatures. (a) PVA anodes and (b) Pechini anodes.
Journal 25 Pre-proof
j / mA cm
-2
12 10 8
300 °C 400 °C 500 °C
PVA
6 4 2 0 -2
0.2
0.4
ro
of
-4 -6 -8 0.6
0.8
1.0
1.2
1.0
1.2
na
6 4
Pechini
lP
300 °C 400 °C 500 °C
2 0 -2
Jo ur
j / mA cm
-2
12 10 8
re
-p
E / V vs. Ag/AgCl
-4 -6 -8
0.2
0.4
0.6
0.8
E / V vs. Ag/AgCl Figure 4: Cyclic voltammograms recorded at 50 mV s–1 in 0.5 mol L–1 H2SO4 of the Ti/RuO2–IrO2 anodes obtained by PVA (a) and Pechini (b) methods calcined at 300, 400 and 500 °C.
Journal 26 Pre-proof
14
a)
PVA
j / mA cm
-2
12 10
Co
8 6 4
re
10
lP
8 6 4 2
Ct
Jo ur
0
Co
na
j / mA cm
-2
12
ro
b) Pechini
-p
0 14
of
Ct
2
0
50
100 150 200 250 300 350 -1 / mV s
Figure 5: Dependence of the capacitive voltammetric current density, jc, on ν for the Ti/RuO2–IrO2 anodes calcined at 300 °C.
Journal 27 Pre-proof
Pechini PVA Fitting
6 5
Rct R
-Z'' /
4
CPE
3
of
2
ro
1 0 1
2
3 Z' /
4
5
6
re
-p
0
Figure 6: Nyquist plots of Ti/RuO2–IrO2 PVA (□) and Pechini (○) anodes calcined at 300 °C,
lP
recorded at 1.12 V versus Ag/AgCl at the OER onset potential in 0.5 mol L–1 H2SO4 solution
Jo ur
na
at 25 °C. Scatters: experimental data. Lines: fitting results.
Journal 28 Pre-proof
a)
100 PVA
60
40 [NaCl] -1 0 mol L -1 0.005 mol L -1 0.010 mol L -1 0.020 mol L
of
20
0 0
20
40
60
ro
Colour removal / %
80
80
100
120
b) 100
re
-p
t / min
lP
Pechini
na
60
40
20
Jo ur
Colour removal / %
80
[NaCl] -1 0 mol L -1 0.005 mol L -1 0.010 mol L -1 0.020 mol L
0 0
20
40
60
80
100
120
t / min Figure 7: Percentage of colour removal as a function of the electrolysis time of the RB21 dye, carried out in different electrolytes concentrations, employing the Ti/RuO2–IrO2 PVA (A) and
Journal 29 Pre-proof Pechini (B) anodes calcined at 300 °C, with an applied current density of 25 mA cm2. The lines are guide for eyes.
a)
0 -1
ln (C/C0)
-2 -3
PVA
-4
of
NaCl concentration -1 0 mol L -1 0.005 mol L -1 0.010 mol L -1 0.020 mol L
ro
-5
b)
20
40
80
100
120
lP
0 -1
na
-2 -3
Pechini
Jo ur
ln (C/C0)
60 t / min
re
0
-p
-6
-4
NaCl concentration -1 0 mol L -1 0.005 mol L -1 0.010 mol L -1 0.020 mol L
-5 -6
0
20
40
60 t / min
80
100
120
Figure 8: Pseudo-first-order kinetic model fitted to the colour removal of RB-21 dye in different electrolyte concentrations.
Journal 30 Pre-proof
Table 1. EDX determination of the metals in the Ti/RuO2–IrO2 films prepared using PVA and Pechini methods at different calcination temperatures. Ru / MTα Precursor Oxide film solution (%) (%) 50.0 0.55 ± 0.08
Ir / MTα Precursor Oxide film solution (%) (%) 50.0 0.45 ± 0.08
PVA
400
50.0
0.55 ± 0.06
50.0
0.45 ± 0.06
PVA
500
50.0
0.53 ± 0.04
50.0
0.47 ± 0.04
Pechini
300
50.0
0.40 ± 0.11
50.0
0.60 ± 0.11
Pechini
400
50.0
0.45 ± 0.24
50.0
0.55 ± 0.24
Pechini
500
50.0
50.0
0.44 ± 0.05
-p
ro
of
PVA
Calcination temperature (°C) 300
0.56 ± 0.05
re
Method
Jo ur
na
lP
Total metal content, MT = Ru + Ir
Journal 31 Pre-proof Table 2. Voltammetric charge behaviour for the Ti/RuO2–IrO2 anodes, obtained in the potential limits from 0.2 V to 1.2 V versus Ag/AgCl.
121.9
400
30.3
500
38.3
300
256.1
400
167.3
500
138.8
re
-p
ro
of
300
lP
PVA
Voltammetric Charge (mC cm–²)
na
Pechini
Temperature (°C)
Jo ur
Method
Journal 32 Pre-proof Table 3. Dependence of the total (Ct), external (Co) and internal (Ci) differential capacitances and morphology factor (φm) on the synthesis method used. Anodes were calcined at 300 °C. Method
Ct (mF cm–2)
Cd,o (mF cm–2)
Cd,i (mF cm–2)
φm (Cd,i /Cd)
69.0
18.0
51.0
0.74
PVA
107.3
19.0
88.3
0.82
Jo ur
na
lP
re
-p
ro
of
Pechini
Journal 33 Pre-proof Table 4. Summary of fitted EIS data for the Ti/RuO2–IrO2 anodes, recorded at 1.23 V versus Ag/AgCl. E vs Ag/ AgCl (V)
RΩ (Ω)
Rct (Ω)
Qdl (F)
ndl
Pechini
1.23
1.21
5.55
0.14
0.88
PVA
1.23
1.31
3.10
0.30
0.90
Jo ur
na
lP
re
-p
ro
of
Method
Journal 34 Pre-proof
Table 5. Effect of electrolyte concentration and of the synthesis method on the kinetic constants for colour removal of RB-21 dye. Method
0 mol L-1
0.005 mol L-1
0.010 mol L-1
0.002 mol L-1
R2
k min-1
R2
k min-1
R2
k min-1
R2
Pechini
0.006
0.977
0.007
0.986
0.024
0.969
0.085
0.994
PVA
0.006
0.978
0.007
0.981
0.034
0.174
0.967
Jo ur
na
lP
re
-p
ro
of
k min-1
0.966
Journal 35 Pre-proof CRediT author statement
Charlys W. A. Bezerra: Acquisition, analysis, and interpretation of the data, Methodology, Investigation.
Géssica de O. S. Santos: Acquisition, analysis, and interpretation of the data, Methodology, Investigation, Writing - Original Draft, Review & Editing.
Marilia M. S. Pupo: Acquisition, analysis, and interpretation of the data, validation, investigation,
of
Review & Editing.
ro
Maria A. Gomes: Acquisition, analysis, and interpretation of the data, validation, investigation,
-p
Review & Editing.
re
Ronaldo S. da Silva: Acquisition, Resources, Formal analysis, Writing - Review & Editing.
lP
Katlin I. B. Eguiluz: Project administration, Supervision, Funding acquisition, conceptualization and
na
planning of the work and Writing - Review & Editing
Giancarlo R. Salazar-Banda: Project administration, Supervision, Funding acquisition,
Jo ur
conceptualization and planning of the work and Writing - Review & Editing
Journal 36 Pre-proof Declaration of interests
☒ The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Jo ur
na
lP
re
-p
ro
of
☐The authors declare the following financial interests/personal relationships which may be considered as potential competing interests:
Journal 37 Pre-proof Graphical abstract
Highlights
The green method developed employing PVA as solvent improves RuO2-IrO2 anode lifetime The most suitable calcination temperature was proven to be 300 °C
Charge-transfer resistance is 1.8-fold lower than the anodes made by Pechini method
Anode made using PVA is the most efficient towards reactive blue 21 dye oxidation
Jo ur
na
lP
re
-p
ro
of