Degradation of profenofos in an electrochemical flow reactor using boron-doped diamond anodes

Diamond & Related Materials 32 (2013) 54–60

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Degradation of profenofos in an electrochemical flow reactor using boron-doped diamond anodes G.S. Cordeiro a, R.S. Rocha b, R.B. Valim b, F.L. Migliorini a, M.R. Baldan a, M.R.V. Lanza b, N.G. Ferreira a,⁎ a b

Laboratório Associado de Sensores e Materiais, Instituto Nacional de Pesquisas Espaciais, 12245-010, São José dos Campos, SP, Brazil Instituto de Química de São Carlos, Universidade de São Paulo, 13560-970, São Carlos, SP, Brazil

a r t i c l e

i n f o

Article history: Received 22 August 2012 Received in revised form 9 November 2012 Accepted 24 November 2012 Available online 8 December 2012 Keywords: Profenofos Pesticides Electrochemical degradation Boron-doped diamond film

a b s t r a c t A study of the electrochemical degradation of profenofos in a flow reactor with electrodes comprising boron-doped diamond films deposited on titanium substrate (BDD/Ti) as anodes has been performed. The BDD films were produced at growth times of 7 and 24 h with similar B/C ratios corresponding to acceptor concentrations of around 10 20 atoms cm −3. The morphological and structural characteristics of the BDD/Ti electrodes were evaluated by scanning electron microscopy and Raman scattering spectroscopy. Degradation experiments were carried out with applied current densities in the range 10 to 200 mA cm −2 and flow rates of 50 and 300 L h−1. The rates of degradation of profenofos were evaluated by high performance liquid chromatography and variations in total organic carbon (TOC) were monitored during the electrochemical process in order to determine the level of mineralization of organic compounds present in the electrolyte. Under the best conditions (anode comprising a BDD film deposited on titanium for 7 h and reactor operating at a flow rate of 300 L h−1) more than 95% of the profenofos was degraded and approximately 87% of TOC was removed within 120 min of reaction time. © 2012 Elsevier B.V. All rights reserved.

1. Introduction Although pesticides are of benefit in increasing agricultural production, their use poses serious risks to the environment through contamination of surface and ground waters. The problem of contamination by pesticides has been exacerbated by the massive increase in consumption of these agents over the last decade. For example, Brazil spent US$ 988 million on pesticides in 1981, but this increased to US$ 2.2 billion in 1997 and reached US$ 4.495 billion in 2004 [1,2]. Even though Brazil is currently the largest consumer of pesticides in Latin America, no reliable data are available regarding pesticide-related poisoning or death in the country [3,4]. Organophosphate- and carbamate-based pesticides are employed most widely in agriculture by virtue of their highly efficient insecticidal activities. Such agents act by interfering with the nervous systems of insects, but they are also known to be toxic to fish, birds and mammals. Contamination of natural resources by these compounds is, therefore, of considerable concern because of the negative consequences to public health that may cause serious problems with respect to infrastructure and economic conditions, particularly in rural communities. Unfortunately, the lack of sensitive analytical techniques, coupled with the behaviour of the agents in the environment (i.e. a half-life in the soil of between 10 and 120 days and water-solubility above 0.5 mg L −1 for most pesticides [2–5]), have ⁎ Corresponding author. Tel.: +55 12 3208 6675; fax: +55 12 3208 6717. E-mail address: [email protected] (N.G. Ferreira). 0925-9635/$ – see front matter © 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.diamond.2012.11.008

made it difficult to determine the precise extent of pesticide contamination. However, a recent study conducted in a rural district in southeast Brazil revealed that up to 70% of the monitored area was contaminated with pesticides [4]. In Brazil, considerable quantities of pesticides are employed annually in protecting the potato crop [6]. The agents authorized by the Brazilian government for application to this crop comprise 14 active principles of the organophosphate class, including acephate, monocrotophos, dimethoate, triazophos, methamodophos, ethoprophos, chlorpyrifos, profenofos and methyl parathion [7]. In 2007, the total potato harvest in Brazil was around 3.2 million tons, some 82% of which was produced in the states of Minas Gerais, São Paulo and Paraná [7]. Studies relating to the removal of pesticide-contamination from surface and ground waters are, therefore, of paramount importance for these potatoproducing regions. Electrochemical processes offer viable alternatives to the more traditional methods employed in the treatment of effluent waters containing organic compounds. Electrochemical degradation uses the electron as the principal reagent, and the reactions occur between the compound and the electrode surface or by synergism of the degradation processes coupled with the oxidant species generated in situ [8]. In this manner, application of electrochemical technology avoids the necessity of modifying the effluent after processing. A number of studies have demonstrated that anodes composed of boron-doped diamond grown on titanium substrate (BDD/Ti) provide very favourable results for the degradation of organic compounds in aqueous medium because of their high capacity to oxidize organic

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Basel, Switzerland). An Instrutherm (São Paulo, Brazil) 5A/30 V power supply was employed in all experiments, and the equipment was thermostated at 20 °C. Electrolyte was sampled at 5 min intervals during the first 15 min, at 15 min intervals during the next 45 min, and at 30 min intervals during the final 60 min in each experiment. The ultraviolet-visible (UV–Vis; 250–600 nm) spectra of collected samples were measured using a Hitachi High-Technologies (Tokyo, Japan) model U-4100 spectrometer. The concentration of pesticide in the electrolyte was monitored by high performance liquid chromatography (HPLC) using a Perkin-Elmer (USA) Flexar model and a Phenomenex (Torrance, CA, USA) Luna C18 column (250 mm × 4.6 mm i.d.; 5 μm). Isocratic elution was with a mobile phase comprising water and acetonitrile (70:30) at a flow rate of 0.7 mL min −1, and detection was at 262 nm. Quantitative analysis of the pesticide was performed with the aid of a calibration curve constructed using profenofos analytical standard (Sigma-Aldrich, St. Louis, MO, USA; product PS 1024 Supelco). The variation in total organic carbon (TOC) in the samples of electrolyte was measured using a Shimadzu TOC-VCPN analyzer.

compounds and their low energy consumption [8–10]. However, in order to develop novel electrochemical systems for the decontamination of effluent waters contaminated with pesticides, it is necessary to combine the activity of diamond electrodes with the applicability of a flow reactor. The aims of the present study were, therefore, to investigate the electrochemical degradation of aqueous solution of commercial formulation of profenofos (Fig. 1A) with small content of cypermethrin (Fig. 1B) using BDD/Ti anodes produced with growth times of 7 and 24 h, and to test the electrode responses in an electrochemical flow reactor operating at different hydrodynamic conditions. 2. Experimental The BDD films were grown on Ti substrates using the hot filament chemical vapour deposition (HFCVD) technique. The degree of deposition of diamond on titanium is determined by the existence of strong stresses between the film and the substrate that arise from extrinsic and intrinsic factors. Typically, some form of pre-treatment of the substrate surface is necessary in order to decrease the stress and to increase the rate of nucleation [11,12]. Mechanical erosion is efficient in increasing the effective surface area and the roughness of the titanium substrate, thereby improving film adhesion. Appropriate pre-treatments involve air abrasion with glass beads or scratching the surface with an abrasive agent such as diamond paste. In the present study, titanium plates measuring 25 × 25× 0.5 mm were subjected to blasting process to clean the electrode surface. The BDD films were grown in a chamber reactor maintained at 650 °C and 50 Torr with a standard gas mixture comprising 99% hydrogen and 1% methane. Boron doping was effected by an additional flow of hydrogen that passed though a solution of boron trioxide dissolved in methanol with a B/C ratio that was appropriate for the level of doping required. The additional flow of hydrogen into the reactor was maintained at 40 standard cubic centimetres per minute (sccm) by a rotameter, and films were deposited over a period of 7 h (electrode E1) or of 24 h (electrode E2). The quality of the BDD film was assessed from the micro-Raman spectrum recorded in the range 250–3500 cm −1 using a Renishaw plc (Wotton-under-Edge, UK) Raman System 2000 microscope operated in the backscattering configuration. The acceptor concentration of the film was estimated from the Raman spectrum to be approximately 10 20 atoms cm −3 of boron. The top view morphology and thickness of the BDD film was evaluated from scanning electron microscope (SEM) images obtained using a JEOL (Tokyo, Japan) model JSM-5310 instrument. The degradation of profenofos was carried out in an electrochemical reactor (the construction of which has been described previously [13–19]) comprising two parallel polypropylene plates fitted with four BDD/Ti anodes (E1 or E2; total geometric area 16.6 cm 2) and four 316 L stainless steel cathodes (total geometric area 16.6 cm 2) (Fig. 2). The reactor was connected to a recirculation system (capacity 2.0 L) through which electrolytes could be supplied at flow rates of 50 L h −1 (laminar flow; Re 300) or 300 L h −1 (turbulent flow; Re 1900). Degradation reactions were performed at constant applied current densities (jappl) in the range 10 to 200 mA cm −2 for a total of 2 h with an aqueous electrolyte containing sulphuric acid (0.1 mol L −1), potassium sulphate (0.1 mol L −1) and 400 mg L −1 of profenofos, purchased commercially as Polytrin 400 (Syngenta,

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3. Results and discussion 3.1. Morphological and structural characterization of BDD/Ti electrodes SEM images (Fig. 3) representing the top view morphologies of the BDD films deposited during 7 and 24 h on E1 and E2 electrodes, respectively, revealed continuous and homogeneous films covering the entire substrates. Moreover, the films adhered strongly to the substrate and showed no signs of cracks or delaminations. This result is important because the growth of diamond films on titanium is challenging owing to the difference in coefficients of thermal expansion of diamond and titanium and to the formation of intermediate phases such as hydrides and titanium carbides [20]. The thickness of the film deposited on the E1 electrode was 1.0 μm, while that on E2 was around 5.0 μm. Moreover, the grain size of the E1 film was smaller than that of the E2 film. During the deposition of microcrystalline diamond, the first layers of grains are laid down very rapidly and exhibit crystallinity owing to the random nature of the polycrystalline and non-orientated film so-formed [21]. Rapid growth continues until the process of nuclear coalescence commences, at which stage a steady state is established with a decline in the competitiveness of crystal orientation and in the stresses generated by intrinsic surface accommodation. At this point, the grains exhibit columnar-type growth and size increase becomes dominant over other processes, thereby decreasing the intrinsic stress component [22]. Furthermore, a set of processes may occur over the duration of deposition, including the disappearance of some crystals by etching or decomposition [23]. Increased grain size is, therefore, a function of deposition time and is associated with the decrease in nucleation density that occurs at steady state conditions when columnar growth is dominant [21]. An earlier study of the HFCVD of diamond on silicon revealed that pyramidal grains were present in films of thickness ≥3 μm, and that columnar growth had already been established in films thicker than 10 μm. The Raman scattering spectra of the BDD films deposited on electrodes E1 and E2 (Fig. 4) presented a sharp peak at around 1332 cm −1 corresponding to the first-order phonon line in diamond.

B

Fig. 1. Molecular structure of (A) profenofos and (B) cypermethrin.

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Fig. 2. Schematic view of the electrochemical flow reactor.

The emergent band at 1220 cm −1 may be attributed to disorder in the diamond structure caused by the incorporation of boron [24–26]. At higher levels of doping, the intensity of the 1220 cm −1 band is increased significantly while that of the 1332 cm −1 peak is drastically reduced, an effect that has been assigned to the relaxation of the k = 0 selection rule of Raman scattering induced by the presence of very high concentrations of boron in the diamond lattice [25]. The less pronounced band at around 1580 cm −1 is attributed to the graphite phase and, as expected, is more evident in the diamond film grown for 7 h owing to the higher density of bound grains. The band at around 500 cm −1 is associated with the vibration of boron pairs in the diamond lattice. Since the sp 2 phase is found at the grain boundary, the larger grains of the E2 film presented a lower contribution to the sp 2 phase than the E1 film when equivalent areas of the electrodes were exposed to the Raman laser. 3.2. Electrochemical degradation of profenofos Polytrin 400, the commercial formulation employed in the degradation study, contained profenofos, cypermethrin and various other components that were not identified in the product documentation. Electrolyte samples collected during degradation experiments, performed with E1 and E2 under laminar and turbulent flow conditions and at current densities of 25 and 100 mA cm−2, were analyzed by UV–Vis spectroscopy. The representative spectra displayed in Fig. 5 (obtained with E1 and an electrolyte flow rate of 50 L h−1) show that an absorption band centred on 366 nm could be detected after 30 min of electrolysis, and that the intensity of the band increased as a function of reaction time at a constant current of 25 mA cm−2. Increases in the intensity of this band were more pronounced in the spectral set obtained when electrolysis was performed at a constant current of 100 mA cm−2. These results indicate that the electrolyte was modified in a time-dependent manner during electrolysis, possibly as a result of the degradation of the components of Polytrin 400 and the formation of by-products that were not originally present. However, because of the complexity of the pesticide formulation, it was not possible to confirm the degradation of profenofos by spectroscopic monitoring of the electrolytic reaction. HPLC chromatograms of the electrolyte containing Polytrin 400 (Fig. 6A) showed peaks at 2.9 min (peak E corresponding to the supporting electrolyte), 9.2 min (peak II corresponding to cypermethrin; identity confirmed by analysis of reference standard — data not shown) and 13.7 min (peak I corresponding to profenofos; identity confirmed by analysis of reference standard — Fig. 6A). Analysis of the HPLC chromatograms of electrolyte samples obtained during degradation experiments

Fig. 3. SEM images of the surfaces of BDD films deposited onto electrodes E1 and E2.

G.S. Cordeiro et al. / Diamond & Related Materials 32 (2013) 54–60 Profenofos Compound

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performed with E1 at flow rates of 50 and 300 L h−1 revealed that the areas of the profenofos (I) and cypermethrin (II) peaks decreased in comparison with that of the supporting electrolyte peak (E) in a time-dependent manner (Fig. 6B and C). This result at 50 and 300 L h−1 was expected and has already been described in the literature [9,10,13]. In order to complete the analysis, the electrochemical removal of profenofos as a function of time of electrolysis was monitored by HPLC in experiments performed with electrodes E1 and E2 operated at current densities in the range 10 to 200 mA cm −2 and at flow rates of 50 and 300 L h −1 (Fig. 7). With E1, no significant changes in the rate of removal of the analyte were observed with increased flow rate, but an increase in applied current density promoted an increase in the removal of profenofos, with maximum values of 96 and 96.5% being attained after 120 min of electrolysis at a jappl of 200 mA cm −2 with flow rates of 50 and 300 L h −1, respectively (Fig. 7A and B). In the case of E2, while the removal of profenofos increased as jappl increased under both flow rate conditions (Fig. 7C and D), the overall efficiency of the process was much lower than that obtained with E1. Thus, with E2 operating at a flow rate of 50 L h −1 and an applied current density of 10 mA cm −2, only 19%

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Fig. 6. Panel A: HPLC chromatograms of standard profenofos and of a commercial preparation (Polytrin 400) containing profenofos (peak I) and cypermethrin (peak II) in supporting electrolyte (E). Panels B and C: HPLC chromatograms of electrolyte samples obtained during profenofos degradation experiments performed in an electrochemical reactor using electrode E1 with an applied current density of 50 mA cm−2 at electrolyte flow rates of 50 L h−1 (panel B) and 300 L h−1 (panel C).

of the analyte was removed after 120 min of electrolysis, although a maximum removal of 95% was attained with a jappl of 200 mA cm−2. By contrast, the maximum removal of profenofos with E2 operating at a flow rate of 300 L h−1 was just 70% after 120 min of reaction. The difference in the capacity of the two electrodes to remove profenofos may be associated with the different grain sizes of the BDD films. The larger grain size of the diamond surface of E2 may have restricted the coupling of profenofos molecules at the active sites of the electrode, an effect that was not apparent with E1. Another consideration relates to the influence of electrolyte flow rate on the efficiency of E1 and E2 in degrading profenofos. According to Walsh [27], experiments performed at a flow rate 50 L h −1 (Re 300) were conducted under an internal laminar hydrodynamic regime in the reactor which, in comparison with the turbulent regime (flow rate 300 L h −1; Re 1900), promoted a longer residence time at the electrode surface, thus increasing the contact time of profenofos molecules with the electrode surface. The influence of the hydrodynamic regime on the efficiency of profenofos removal appeared to be greater with the BDD film comprising larger grains since the removal efficiency of E2 was higher at a flow rate of 50 L h−1 than at 300 L h−1. By contrast, the removal efficiency of E1 was apparently unaffected by flow rate. Although the results presented in Fig. 7 show a clear reduction in the concentration of profenofos following electrochemical degradation, this finding does not necessarily imply a diminution in organic load in the electrolyte samples. In order to verify a reduction in organic carbon, the variation in TOC was monitored as a function of applied current density with E1 and E2 operating at flow rates of 50 and 300 L h−1. The results (Fig. 8) revealed that the removal of TOC was more efficient with E1 in comparison with E2 at both flow rates and for all values of jappl in the range 25 to mA cm−2. The difference in TOC removal between the electrodes may be associated with the different grain sizes in the BBD/Ti surface, with the electrode with lower grain (greater area) showing higher TOC removal. The relation between characteristics of the anode and the catalytic activity for the removal of TOC is discussed in the literature, where Feng et al., associated the presence of more active sites with the grain size decrease on the electrode surface, thus achieving a higher TOC removal [28]. Although an increase in flow rate from 50 to 300 L h −1 did not give rise to significant changes in the removal of organic load by either electrode, in the case of E2 the removal of TOC was slightly greater in experiments performed at the higher flow rate. This effect

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Fig. 7. Variation in the concentration of profenofos (as determined by HPLC analysis) during degradation experiments performed in an electrochemical reactor using: electrode E1 and an electrolyte flow rate of 50 L h−1 (panel A); electrode E1 and an electrolyte flow rate of 300 L h−1 (panel B); electrode E2 and an electrolyte flow rate of 50 L h−1 (panel C); and electrode E2 and an electrolyte flow rate of 300 L h−1 (panel D). The applied current densities were: –□– 10 mA cm−2, –●– 25 mA cm−2, –▵– 50 mA cm−2, –▼– 75 mA cm−2, –⊲– 100 mA cm−2, –►– 150 mA cm−2, and –◊– 2000 mA cm−2.

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was possibly associated with the hydrodynamic regime, which was more turbulent at 300 L h −1 than that at 50 L h −1. The results presented in Fig. 8 also reveal that TOC removal improved as the current density applied to E1 increased up to a value of 100 mA cm −2, under which conditions 85 and 83% of organic load was removed in 120 min at flow rates of 50 and 300 L h −1, respectively. At higher values of jappl, however, the efficiency of TOC removal decreased. A somewhat different pattern was displayed by E2 whereby TOC removal was not significantly affected by changes in the applied current density. In this case, maximum TOC removal values of 45 and 34% were obtained at 50 mA cm −2 with flow rates of 50 and 300 L h −1, respectively. Fig. 9 displays the variations in the apparent rate constants (kap) for the removal of profenofos and in the energy consumed in removing organic load (calculated according to [13]) as functions of the applied current density and the flow rate. In the case of E1, the change in profenofos concentration with respect to time was exponential (Fig. 7A and B) such that the plot of ln(C/C0) versus time was linear (data not shown) indicating pseudo first-order kinetics [29]. With regard to E2, Fig. 7C and D display a linear tendency in the plot of profenofos concentration against time, indicating pseudo zero-order kinetics [17]. The difference in the kinetics of degradation of profenofos

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Fig. 9. Variations in the apparent rate constant (kap) for the removal of profenofos and in the energy consumed (CE) in removing organic load from the electrolyte as functions of applied current densities in the range 10 to 200 mA cm−2 using an electrochemical reactor with electrode E1 (panel A) or electrode E2 (panel B) operating at an electrolyte flow rate of 50 or 300 L h−1.

may be associated with the grain size in the BDD films whereby E1, with smaller diamond grains on its surface, presented a greatly increased active area resulting in a higher rate of organic degradation. Assuming first-order kinetics for experiments with E1 and zero-order kinetics for E2, values of kap were determined from the slope of the line ln(C/C0) versus time for E1 and of the line (C/C0) versus time for E2 [13,29,17]. The highest values of kap were obtained with E1 and attained approximately 15.9 × 10 −3 mg L −1 min −1 at an applied current density of 100 mA cm −2. Although increases in jappl were typically associated with a rise in the rate of removal of profenofos, augmentation of the applied current density above 100 mA cm −2 did not promote any significant improvement in kap, such that the value at 200 mA cm −2 was just 16.4 × 10 −3 mg L −1 min −1. With regard to the consumption of energy in experiments involving E1, the amount required per kg of TOC removed was inversely proportional to the applied current [13]. As shown in Fig. 8A, each increase in applied current density gave rise to a significant increase in energy consumption, which attained 180 and 2150 kWh per kg of TOC removed at jappl values of 100 and 200 mA cm −2, respectively. In the case of E2, increased applied current density promoted only small increases in kap for the removal of profenofos, with the highest values of 4.2 × 10 −3 and 5.1 × 10 −3 mg L −1 min −1 being attained with jappl values of 100 and 200 mA cm −2, respectively, at a flow

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rate of 300 L h −1. However, the energy consumed per kg of organic load removed increased significantly with increased jappl and attained levels of 645 and 1600 kWh per kg of TOC removed in experiments with applied currents of 100 and 200 mA cm −2, respectively, at a flow rate of 300 L h −1. 4. Conclusions The grain sizes and surface morphologies of BDD films deposited on titanium electrodes were strongly influenced by growth time, and these characteristics affected the response of the electrodes in the catalytic degradation of profenofos (Polytrin 400) using an electrochemical flow-by reactor. Electrode E1, with a smaller grain size, operating at a flow rate of 300 L h −1 was highly efficient in the degradation of profenofos and attained 96.5% removal of analyte after 120 min of electrolysis at 200 mA cm −2 giving an apparent rate constant of 15.9 × 10 −3 mg L −1 min −1. Electrode E2 operating under the same conditions removed just 70% of the profenofos present in the electrolyte. Regarding the reduction of organic load, E1 also showed better results than E2 providing TOC removal of 83% with the former and 45% with the latter. The present study has confirmed the importance of optimizing the growth parameters of doped diamond films employed as anodes in electrochemical reactors. The promising results reported here indicate that parameters relating to the surface structure of the electrode and the operating conditions of the electrochemical reactor must be systematically controlled in order to achieve the best configuration for the degradation of profenofos (Polytrin 400). Prime novelty statement The promising results to degrade electrochemically organophosphate and carbamate pesticides using BDD/Ti anodes. The influence of the BDD/Ti morphology in the hydrodynamics conditions of the electrochemical flow reactor to optimize the degradation process. The profenofos degradation using BDD/Ti films as anodes in the electrochemical reactor at a flow rate of 300 L·h −1 reached over 95% of efficiency with a TOC reduction of around 87%. Acknowledgements The authors gratefully acknowledge the following Brazilian funding authorities for financial support: Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP), Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) and Conselho Nacional de Desenvolvimento Cientíco e Tecnológico (CNPq). We wish to offer special thanks to M.L. Brison and W.B. Carvalho (LAS/INPE, Brazil) for providing essential experimental support. References [1] C.F.B. Coutinho, S.T. Tanimoto, A. Galli, G. Garbellini, M. Takayama, R.B. Amaral, L.H. Mazo, L.A. Avaca, S.A.S. Machado, Rev. Ecotoxicol. Meio Ambiente 15 (2005) 65–72. [2] J.J. Oliveira-Silva, S.R. Alves, A. Meyer, F. Perez, P.N. Sarcinelli, R.C.O.C. Mattos, J.C. Moreira, Rev. Saude Publica 35 (2001) 130–135. [3] H.F. Filizola, V.L. Ferracini, R.B. Abakerli, M.A.F. Gomes, Rev. Bras. Agrociência 11 (2005) 245–250. [4] M.M. Veiga, D.M. Silva, L.B.E. Veiga, M.V.C. Faria, Cad. Saude Publica 22 (2006) 2391–2399. [5] V.M.R. Santos, C.L. Donnici, J.B.N. Da Costa, J.M.R. Caixeiro, Quím. Nova 30 (2007) 159–170. [6] E.D. Caldas, R. Coelho, L.C.K.R. Souza, S.C. Silva, Bull. Environ. Contam. Toxicol. 62 (1999) 199–206. [7] Agência Nacional de Vigilância Sanitária, Programme of Analysis of Pesticide Residues in Food — Activity Report 2012, ANVISA, Brasília, 2011. [8] R.S. Freire, R. Pelegrini, L.T. Kubota, N. Duran, Quim. Nova 23 (2000) 504–511. [9] F.L. Migliorini, N.A. Braga, S.A. Alves, M.R.V. Lanza, M.R. Baldan, N.G. Ferreira, J. Hazard. Mater. 192 (2011) 1683–1689. [10] S.A. Alves, T.C.R. Ferreira, N.S. Sabatini, A.C.A. Trientini, F.L. Migliorini, M.R. Baldan, N.G. Ferreira, M.R.V. Lanza, Chemosphere 88 (2012) 155–160.

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