polyaniline nanocomposites in degradation of dyes

Accepted Manuscript Preparation, characterization and investigation of sonophotocatalytic activity of thulium titanate/polyaniline nanocomposites in degradation of dyes Ali Sobhani-Nasab, Mohsen Behpour, Mehdi Rahimi-Nasrabadi, Farhad Ahmadi, Saeid Pourmasoud, Farideh Sedighi PII: DOI: Reference:

S1350-4177(18)30245-1 https://doi.org/10.1016/j.ultsonch.2018.08.021 ULTSON 4285

To appear in:

Ultrasonics Sonochemistry

Received Date: Revised Date: Accepted Date:

14 February 2018 4 August 2018 17 August 2018

Please cite this article as: A. Sobhani-Nasab, M. Behpour, M. Rahimi-Nasrabadi, F. Ahmadi, S. Pourmasoud, F. Sedighi, Preparation, characterization and investigation of sonophotocatalytic activity of thulium titanate/ polyaniline nanocomposites in degradation of dyes, Ultrasonics Sonochemistry (2018), doi: https://doi.org/10.1016/ j.ultsonch.2018.08.021

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Preparation, characterization and investigation of sonophotocatalytic activity of thulium titanate/polyaniline nanocomposites in degradation of dyes Ali Sobhani-Nasab1*, Mohsen Behpour1, Mehdi Rahimi-Nasrabadi2,3*, Farhad Ahmadi4, Saeid Pourmasoud5, Farideh Sedighi1 1

Institute of Nano Science and Nano Technology, University of Kashan, P. O. Box 8731751167, Kashan, I. R. Iran

2

Chemical Injuries Research Center, Baqiyatallah University of Medical Sciences, Tehran, Iran 3

Department of Chemistry, Faculty of Pharmacy, Baqiyatallah University of Medical Sciences, Tehran, Iran

4

Department of Medicinal Chemistry, School of Pharmacy-International Campus, Iran University of Medical Sciences, Tehran, Iran 5

Department of Physics, University of Kashan, Kashan, Iran

*Corresponding author: Tel: +98 9137290874, Fax: +98 9137290874. E-mail address: [email protected] (Ali Sobhani-Nasab) E-mail address: [email protected] ( Mehdi Rahimi-Nasrabadi)

Abstract Thulium

titanate/polyaniline

nanocomposites

were

synthesized

to

observe

the

sonophotocatalytic degradation of dyes (widely used as a model pollutant) under ultrasonic irradiation and visible light. Based on our results, the synthesis process can improve sol-gel assisted sonochemical method in the presence of ultrasound and starch. To prepare pure thulium titanate nanostructures, the presence of starch and sonication treatment were

concurrently obligatory. Therefore, sol-gel assisted sonochemical method can be used as a successful process for synthesis of thulium titanate nanostructures. According to the BET results, in the presence of ultrasound and starch surface area increased from 9.5305 m2/g to 40.28 m2/g. For verification of photacatalytic behavior of nanoparticles, several factors were studied. The nanocomposites/ultrasonic system showed greater photocatalytic activity for the degradation of Rh B rather than separately treatment of nanocomposites under visible light.

Keywords: Thulium titanate/polyaniline; Nanocomposites; Sonochemical method; Visible light; Starch; Sonophotocatalytic 1. Introduction During the past decade, an interest in the lanthanide titanate oxides (Ln2Ti2O7) which crystallize in pyrochlore structure have been expressed. This is due to their intriguing properties in photocatalysts, radiation absorbing, solid electrolytes materials, ferroelectric device component, host materials for actinide immobilization, solid oxide fuel cells, magnetic (for compounds of Dy and Ho) and anti-ferromagnetic materials (in the case of Er and Gd compounds) [1-13]. According it is well known that environmental pollution due to the rapid industrial expansion and human population growth is one of the most important challenges facing all living beings worldwide [14-16]. Therefore, the photocatalytic behavior of lanthanide titanate has been considered [17-19] Recently, scientists have devoted much effort to synthesize lanthanide titanate oxides compounds. They, up to now, have been prepared by traditional high temperature solid state method, which needs calcinations of oxides at a temperature higher than 1000 °C with frequent grindings, one-step hydrothermal technique, sol-gel approach with organic ligands, i.e. citric acid or stearic acid, high energy ball milling, pulsed laser deposition, and polymerized complex method [20-27]. However, some of these procedures have been faced

problems such as the requirement of complicated equipment and time consuming caused by multiple steps and formation of undesirable phase. In this study, thulium titanate nanostructures and thulium titanate/polyaniline nanocomposites were synthesized through sonochemical procedure, which can be considered as a new technique for preparation of this product. For achieving the final products with the high homogeneity and smallest size, different parameters such as time and power of sonocation, type of capping agent, and the molar ratio of Ti+4 to Tm+3 as experimental parameters were changed. For the first time, we used of a green capping agent such as glucose, lactose and starch for the preparation of thulium

titanate

nanostructures.

Photocatalytic

performance

of

the

thulium

titanate/polyaniline nanocomposites in various conditions. The ability for the degradation of the organic contaminants including rhodamine B (Rh B), eosin Y (EY), and phenol red (Ph R) (as a model contaminants) were examined by photocatalysis experiments. The effects of various factors including type of pollutant, grain size of thulium titanate nanostructures and thulium titanate/polyaniline nanocomposites, ultrasonic wave, and type of light on photocatalytic behavior of products were evaluated. Then, we confirmed the enhancement of sonophotocatalytic activity in the thulium titanate/polyaniline nanocomposites/ultrasonic system. Afterwards, thulium titanate/polyaniline nanocomposites were characterized through Fourier transforms infrared spectroscopy (FT-IR), X-ray diffraction (XRD), UV–visible absorption, Brunauer–Emmett–Teller (BET), X-ray energy dispersive spectroscopy (EDS), and vibrating sample magnetometer (VSM). 2. Experimental 2.1. Materials and Characterizations Materials used in the this study were (Tm(NO3)3.6H2O, Merck, 99.9%), (Tetraethyl orthotitanate, Merck, 99.9%), and (glucose, lactose and starch, Merck, 99.9%),. All chemicals were used without further purification. Moreover, de-ionized water and ethanol were utilized

as solvent. The formation has been done with the aid of ultrasonic generator (MPI Ultrasonics; Switzerland). The XRD of products was recorded by Philips and X-ray diffractometer through Ni-filtered Cu K_radiation. The EDX analysis with 20kV accelerated voltage was done. FT Infrared (FT-IR) spectra were gained as potassium bromide pellets in the range of 400-4000 cm-1 with a Nicolet-Impact 400D spectrophotometer. The SEM images were taken by the LEO instrument model 1455VP. Prior to taking images, the samples were coated by a very thin layer of Pt (using a BAL-TEC SCD 005 sputter coater) to make the sample surface conductor, to prohibit charge accumulation, and to get a better contrast. The magnetic properties of the samples were detected at room temperature using a vibrating sample magnetometer (VSM, Meghnatis Kavir Kashan Co., Kashan, Iran). Transmission electron microscope (TEM) images of the as-obtained zinc chromite nanostructures were taken on a JEM-2100 with an accelerating voltage of 200 kV. The N2 adsorption/desorption analysis (BET) was performed at -196 °C using an automated gas adsorption analyzer (Tristar 3000, Micromeritics). Pore size distribution was calculated by using desorption branch of the isotherm by the Barrett, Joyner and Halenda (BJH) method. Magnetic properties were measured using a vibrating sample magnetometer 60 (VSM, Meghnatis Kavir Kashan Co. Kashan, Iran).

The UV–vis diffuse reflectance spectrum of the as-produced nanostructures was obtained on a UV–vis spectrophotometer (Shimadzu, UV-2550, Japan). 2.2. Synthesis of Thulium Titanate Nanoparticles We used Tm(NO3)3.6H2O, tetraethyl orthotitanate, and various capping agents as starting materials. For finding optimum condition, different experiments were carried out. Therefore, various parameters such as the molar ratio of Ti+4 to Tm+3, the type of capping agent (glucose, lactose and starch), power and time of sonication were changed [28]. The details of experiments have been presented in Table 1.

Firstly, 0.2 g of Tm(NO3)3.6H2O was dissolved in 50 ml of distilled water, and then aqueous solutions including 0.5 g of capping agent was added to it. Afterwards, based on the molar ratio of Ti+4 to Tm+3 that was given in table 1, the stoichiometric amount of tetraethyl orthotitanate (Ti+4) was added to the solution gained in former step under ultrasonic irradiation (frequency of 35 kHz) with various parameters (for example: 1.2 g of tetraethyl orthotitanate was used in sample 1). The resulted solution was vigorously stirred at 60 °C for 30 min. The reaction was completed without regulation of pH solution. The obtained cream precipitate was collected and dried at 100 °C. Finally, the dried powder was calcined at 900 °C for 2 h. 2.3 Synthesis of Thulium Titanate/Polyaniline Nanocomposites Thulium titanate/polyaniline nanocomposites were prepared by an in situ polymerization in aqueous solution with ultrasonic waves. 1 ml of aniline was dissolved in 40 ml 0.1 M HCl solution and thulium titanate nanoparticles was dispersed in aniline solution with ultrasonic waves (15 min, 160 W). Then 40 mL of 3 M K2S2O8 and NaOH solution were slowly added to the solution, under ultrasonic waves (160 W) for 10 min. After 12 h, the polymerization was achieved and the suspension was in dark green. The thulium titanate/polyaniline nanocomposites was obtained by filtering and washing the suspension with 0.1 M HCl and deionized water, and was dried under vacuum at 70 °C for 18 h. In order to evaporate the solvent, the product was casted on a piece of glass plate and left it, for 2 h (Scheme 2). 2.4. Photocatalytic Measurement: The photocatalytic activities of as-synthesized thulium titanate nanoparticles, were investigated through destruction of 100 ml aqueous rhodamine B (Rh B) under visible light. Moreover, we investigated the effects of ultrasonic irradiation with powers 320w and frequency of 35 kHz employed on the destruction of Rh B solution. Afterwards, for transportation of the suspension, a self-designed glass reactor was picked. The photocatalytic

behavior of nanoparticles reaction was evaluated using dye solution. Moreover, the destruction reaction was performed in a photocatalytic reactor. The photocatalytic destruction was performed with 10 ppm of dye solution including 0.1 g of thulium titanate nanostructures. The mixture was aerated for 30 min to achieve adsorption equilibrium. Next, the mixture was perfectly positioned to the photoreactor in which the vessel was 25 cm away from visible source of 400 W Osram lamp. In addition, the quartz vessel and light source were placed inside a black box equipped with a fan to prevent light leakage. The aliquots of the mixture were taken at periodic intervals. Then, they were centrifuged and analyzed with the UV-Vis spectrometer, during irradiation. The Rh B destruction value, in terms of percentage, was evaluated as the following, (1) In which Ct and C0 are the gained absorbance value of the dye solution at t and 0 min by a UV–vis spectrometer, respectively. 3. Results and Discussions 3.1. XRD Patterns XRD analysis is one of the most important procedures for identification of materials. In this study, three molar ratios of Ti+4 to Tm+3 were verified to obtain the high-purity product. In Fig. 1 (a-c) the XRD patterns of samples nos. 1-3 has been shown, respectively. By considering the thulium titanate formula, the molar ratio of Ti+4 to Tm+3 was adjusted (1:4) for sample 1. According to Fig. 1a, in addition to the peaks associated with thulium titanate (JCPDS = 23-0590; cubic structure), the diffraction lines of Tm2O3 phase with JCPDS = 653174 which refers to cubic structure have been demonstrated in this pattern. The existence of Tm2O3 as impurity in sample 1 confirmed the decrease in the molar ratio of Ti+4 to Tm+3 for sample 2. The XRD pattern of sample 2 indicates two phases of Tm2O3 (JCPDS = 65-3174) as impurity and thulium titanate (JCPDS = 23-0590; cubic structure) as the main product. As

shown in these patterns, any decrease in molar ratio can increases the diffraction line intensities of thulium titanate phase. Therefore, it was reduced to (1:1) in sample 3. According to Fig. 1c, a product with high purity and good crystallinity was resulted in ratio = 1. All of diffraction lines in this pattern were in good agreement with the pattern of Thulium titanate with JCPDS = 23-0590 and space group of Fd-3m (a = b = c = 10.0550). Consequently, this ratio was optimized in (1:1), and fixed for other experiments. The crystal structure of thulium titanate is cubic, and the crystallite diameter (Dc) of products was computed by the Scherrer formula [29]: (2) In which K is the so-called shape factor, which usually takes a value of about 0.9, β is the breadth of the noticed diffraction line at its half intensity maximum, and λ is the wavelength of X-ray source applied in XRD.

To investigate the effects of sonication and capping agent on purity of product, XRD patterns of samples nos. 12, 13 and 14 are presented in Fig. 2a, b and c, respectively. According to these patterns, the phases of Tm2O3 (JCPDS = 65-3174 with cubic structure) and TiO2 in sample 13 and 14 (JCPDS = 48-1278 with monoclinic structure) as impurities in addition to the main product were detected. The XRD pattern of sample no. 12 which was synthesized shows that thulium titanate with cubic structure (JCPDS = 23-0590) as the main in present sonication. Therefore, the sample was synthesized in existence of starch as capping agent. The molar ratio of Ti+4 to Tm+3 (1:1), sonication time for 15 min and the power of ultrasound waves of 240 W were considered as the desired sample (sample no. 12). In Fig. 2d the structure of thulium titanate/polyaniline nanocomposites has been illustrated using XRD pattern. This pattern shows amorphous structure of these compounds. 3.2 SEM and TEM Images

In the current work, we changed different parameters to produce the smallest particles with high homogeneity. The impacts of the altered parameters on the particle size and morphology of final products were inspected through the SEM technique. Based on the literature [30], on can conclude that capping agents have major role to determine the size and morphology of nanopaticles. Various capping agents such as starch, lactose, and glucose were used in this study. Also, their effects on the shape and size of samples nos 3, 4, and 5 were investigated in Fig. 3a-c, respectively. According to Fig. 3c the synthesized nanoparticles in the presence of glucose as a capping agent led to agglomerated nanoparticles. Changing capping agent into lactose, resulted in irregular nanoparticles. According to Fig. 3a using starch as a capping agent led to smaller and uniform nanoparticles. Therefore, it was considered as the desired capping agent and was fixed in the other experiments. For the synthesis of thulium titanate nanostructures, different ultrasonic powers with 160 W, and 240 W were employed. It was confirmed that the any increase in the value of ultrasonic power could result in increase in collapse of the bubble. This can lead to higher temperature and pressure, and consequently, increase the impact of ultrasonic chemical reaction [31]. The SEM images of thulium titanate samples prepared with various ultrasonic powers have been shown in Fig 3d-e. Moreover, it was showed that an increase in ultrasonic power could result in smaller particle size (Fig. 3e). The effects of time on the morphology of products, were investigated by changes in the sonication time. The experiments were performed in three various times: 10min and 15 min. In Fig. 4 the SEM images of these samples have been shown. The increase in sonication time from 10 min to 15 min, can reduce the aggregation and size of particles throughout the energy added into reaction system, This can disintegrate the collected particles. Based on the reported experiments, during sonication treatment, initial nanoparticles can be dissolved and grown into large crystals. The dissolution and crystal

growth are parallel procedures [32]. Therefore, the optimum sonication time was found to be 15 min with the power of 240 W in this paper. The impacts of reaction temperature in sonochemical method on the morphology and shape of thulium titanate samples have been illustrated in Fig. 4. To do so, reactions were performed at three various temperatures. It was observed that increase in temperature from 25 °C to 40 °C (Fig. 4a) and then to 50 °C (Fig. 4b), can improve the agglomeration and size of the nanoparticles. We synthesized our final products with and without ultrasonic reaction to understand how ultrasound waves can affect morphology of thulium titanate nanostructures. In the former effort, the large and agglomerated nanostructures were prepared (Fig. 5a), whereas in the later one, the sphere-like and separated were obtained (Fig. 5b). The TEM analysis of as-synthesized thulium titanate nanostructures (sample no. 12) with the average particle size of 30-50 nm have been depicted in Fig. 6. 3.3. Sonication Mechanism Acoustic cavitation is composed of three different stages. These are including formation, growth, and collapse of bubble in a liquid, when it is exposed to radiation of ultrasonic waves. Bubbles collapse throughout cavitation, and make a temperature approximately up to 5000 K and high pressure (500 atm). Moreover, instability of high temperature and highpressure field make a good condition for anisotropic growth of nanocrystals. The physical and chemical process can occur thanks to extreme conditions by cavitation bubble collapse. The spherical symmetry of bubble and microjets forms can be finally disordered by bubble collapse near a solid surface. These physical processes can make ultrasonic irradiation as an appropriate and useful means for mixing of liquids and erosion of solid surface. The distribution of particle size, particle morphologies, and surface compositions can change, once the velocity of interparticle collisions reach hundreds of meters per second. As a result, particle fragmentation can be observed. Ultimately, collusions of interparticles cause to

happen a significant change in the composition reactivity and surface morphology [34-37]. Because ultrasound method is a straightforward and flexible synthetic procedure, one can suggest the preparation of nanosized particles without high pressure, high temperature, and prolonged reaction time. An experiment was performed without considering sonochemical process to investigate the mechanism and the impact of sonication (sample no. 13). In Fig. 2, the XRD pattern of this sample has been illustrated. As one can conclude, the diffraction lines of this pattern are in good agreement with two phases Tm2O3 (JCPDS = 65-3174 with cubic structure) and TiO2 (JCPDS = 48-1278 with monoclinic structure), as impurity and thulium titanate with cubic structure (JCPDS = 23-0590) as the main product. As one can expect, the products of the sol-gel reaction are hydroxides, which are produced by the reaction between starch and metal salt. The spherical-like structures inclusive of the fine particles in present starch together irregular structures in absent starch have been presented in this image (Fig. 5). The structures of this sample (sample no. 14) was compared to the sample no. 13, which had been prepared in the same condition .Furthermore, the impacts of starch as the optimum capping agent (based on the Fig. 5) on purity of products were examined through performing another experiment without starch. The XRD pattern of this sample has been illustrated in Fig. 2a. As depicted the diffraction lines of this pattern are in conformity with two phases Tm2O3 (JCPDS = 65-3174) and thulium titanate (JCPDS = 23-0590). Therefore, it should be noticed that the presence of starch in sonochemical reaction to prepare products with high purity, and small particle size is obligatory (Scheme 1). Based on the literature [36], radicals generated in sononalysis of water molecules can participate in the reaction with metallic cations and produce metal oxide nanoparticles [42]. The associated procedures have been shown as follows:

(3)

(4) (5) (6) (7) (8)

starch (9) (10) (11) (12) (13) (14) (15) (16) (17) (18) (19) (20) In which symbol )))) applies for ultrasound waves. The reactions cited above, were based on the reported in the literature [44]. The impacts of radicals made in sonolysis of water on metallic cations could be prevented by starch as a polyol, which applied as a capping agent and reductant. That is to say, in the presence starch, the reactions were performed by sol-gel method under sonochemical method. Therefore, metal hydroxides can reacts with alcoholic group in order to construct alkooxide precursors. Then, two products can be formed

M(OH)3M (based on olation reaction) (Ti(OH)3Tm) or M-O-M (based on oxolation reaction) (Ti-O-Tm) throughout condensation process which occurs after hydrolysis reactions. So, one can explain the mechanisem given as follows by formation of Thulium titanate as the main product though sonochemical process and in the presence of starch [45]: (21) (22) (23) (24) (25) We can confirm the formation of thulium titanate as the main product by sonochemical method based on the above mechanism. To do so, XRD patterns of sample synthesized by sonochemical process and prior to putting in furnace and calcinations were given. As depicted in Fig. 2a the product prepared by sonochemical rout after calcinations was thulium titanate with hexagonal structure which was in a good agreement with JCPDS = 17-0660. Therefore, the formation of M-O-M (Ti-O-Tm) through the oxolation reaction during condensation process and based on the written mechanism was proved. 3.4. EDX and FT-IR Patterns The EDS analysis was used to determine the chemical compositions of the product (sample no. 12). Fig. 7 shows that the synthesized product is composed of Tm, Ti, C, and O peaks. Thus, they can be attributed to thulium titanate/polyaniline nanocomposites and confirm the purity of synthesized products. The FT-IR spectrum of the thulium titanate nanostructures before and after calcination reports in Fig. 8 a and b to explore chemical interactions and bonding structures . In both spectra, the absorption from 3000 cm-1 to 3600 cm-1 can be assigned to the stretching vibration of the hydrogen bonded OH groups of the adsorbed water [46]. Fig 8a shows as-

made sample before calcination.The presence of some compounds such as starch and nitrate salt in sample can be seen from the FT-IR spectra. This spectrum shows an absorption at 1041 cm−1 which was related to C-O bond stretching mode. There are two strong peaks at 1383 cm−1 and 1599 cm−1 that was attributed to N=O bond stretching. As can be seen from the spectra, the stretching frequency of C-H bond was appeared at 2952 cm−1. Fig 8a shows additional peaks in thulium titanate spectrum, which clearly confirms the presence of starch over the thulium titanate nanostructures. Therefore, the FT-IR spectrum of thulium titanate nanostructures in the molar ratio of Ti+4 to Tm+3 1:1 at 900 °C was recorded in the range of 400cm-1-4000 cm-1 (Fig. 8b). Furthermore, the strong absorptions bonds at 662.10 cm-1 are attributed to the stretching of Ti-O bond and bending bond of O-Ti-O, respectively. Moreover, the bond at 449 cm-1 can be assigned to the absorption band of Tm-O, which confirms the formation of thulium titanate nanostructures [47]. 3.5. VSM and UV-Vis Techniques The magnetic behaviour of thulium titanate/polyaniline nanocomposites have been verified through VSM technique as illustrated in Fig. 9 sample no. 10. The VSM data showed that thulium

titanate/polyaniline

nanocomposites

have

paramagnetic

properties.

The

magnetization product is approximately 0.016 emu/g at room temperature. The optical absorption property of a semiconductor is associated with electronic structure. This can be considered as a crucial factor for specification of photocatalytic property. The UV-Vis diffuse reflectance spectra of thulium titanate nanostructures and thulium titanate/polyaniline nanocomposites have been represented in Fig. 10a. The optical band gaps of samples can be computed though the Tauc’s formula [29]: (26)

Where α is absorption coefficient, hν is the photon energy, α0 and h are the constants, Eg is the optical band gap of the material, and n depends on the type of electronic transition and can take a value between 1/2 and 3. Obviously, the optical band gap for thulium titanate nanostructures is 2.97 eV and the band gap for sample thulium titanate/polyaniline nanocomposites is 2.73 eV. Our findings showed that the red shift in the thulium titanate/polyaniline nanocomposites can increase photicatalytic properties in visible light. When thulium titanate nanoparticles are dispersed in the PANI matrix, a significant change is measured in the absorption spectrum. The red shift of the absorption transition to higher wavelength may be due to the successful interaction of metal nanoparticles with the polymer chain. The characteristic features of absorption spectrum indicate that thulium titanate/polyaniline nanocomposites nanocomposite is in the conducting state [48]. 3.6. Photocatalytic Application 3.6.1 Evaluation of Photocatalytic Activity of the Thulium Titanate Nanostructures Nowadays, a great deal of research has focused on the nanocomposites [49, 50]. A photocatalytic test as blank has been presented in Fig. 11. We carried out this blank test without catalyst powder to study the stability of Rh B under visible light. The efficiency of blank test was approximately 6% and demonstrated a comparatively good stability. The influence of the type of capping agent of time and power on photocatalytic behavior of the thulium titanate nanostructures at the temperature 900 °C, have been represented in Fig. 11. The type of capping agent and powers were picked up to be 80 W, 160 W and 240 W, and time was including 5 min, 10 min and 15 min, 5 min interval. In the presence of optimum reaction conditions, which were the power of 240 W and the time of 15 min with capping agent starch, destruction percentage was about 96% at 180 min. The photo destruction activity of thulium titanate nanostructures in different pH values was verified. According to the Fig.12 a, maximum destruction was obtained in pH=7 (sample no.

12). The impacts of various rhodamine B (Rh B), eosin Y (EY), and phenol red (Ph R), contaminants on photocatalytic behavior of thulium titanate nanostructures (samples no. 12), have been displayed in Fig. 12b. The percentage of destruction efficiency for EY and Ph R are 86% and 100% respectively. 3.6.2 Assessment of Ultrasonication Effect on the Photodestruction of Thulium Titanate Nanostructures In Fig. 12, we have shown the role of the ultrasonic radiation in the photocatalytic behavior of thulium titanate nanostructures. Making use of as-synthezied thulium titanate nanostructures, (samples nos. 12, 13) as photocatalyst, destruction of Rh B pollutant under visible light has been compared. Our findings showed that, thulium titanate nanostructures prepared with the power of 240 W for 15 min (sample No. 12) operate as the most effective photocatalyst. According to photocatalytic calculations, the Rh B pollutant destruction was nearly 100% with ultrasonic waves and 61% in the absence of ultrasonic radiation. This substantial difference can be described in the process of photocatalytic destruction. The anionic contaminant adsorption on thulium titanate nanostructures is smaller than the quantity of adsorption of cationic contaminant on it. The electron density of oxygen atoms on the surface of thulium titanate nanostructures, is substantial which can be related to negative charge of thulium titanate nanostructures which adsorb the cationic contaminants (Rh B) with positive charge. The suggested procedure of photocatalytic destruction of Rh B can be as following: (27) (28) (29) (30) [46]

These results confirmed the significant capability of the as-produced thulium titanate nanostructures (sample no. 12) to be used as an appropriate, novel, and advantageous type of photocatalyst under UV light for eradication of cationic contaminants. Interestingly, to the best of our knowledge, this is first report on the survey of photocatalytic properties of thulium titanate nanostructures. Moreover, it was confirmed that, different factors such as, grain size, ultrasonic waves, dosage, kind of pollutant and light for fabrication of thulium titanate nanostructures have an influence on photocatalytic activity of final products. The findings showed that the as-sythesized thulium titanate nanoparticles exhibit considerable potential to be exercised as an useful, original, and appropriate kind of photocatalyst under UV light in order to erase the cationic contaminant. Respecting to the production of thulium titanate nanostructures, one can simply realize the, convenience, simplicity, and novelty of the approach mentioned above [51-56]. 3.6.3 Assessment of Sonophotocatalytic Activity of Thulium Titanate/Polyaniline Nanocomposites During the ultrasonic process, dyes may be degraded in three type reaction regions [57]: i) the gaseous zone by a strong pyrolysis process at a high temperature up to ∼5000 K and high pressure up to ∼1000 atm; ii) according to the Eqs. (27)-(29), the gas-liquid interfacial zone by the attack of reactive radicals at supercritical condition and moderate pyrolysis at temperature up to 2000 K; and iii) the bulk liquid zone by the oxidation by reactive radicals. The destruction rate of dyes in the presence of wave led production more

and

and

was increases using ultrasonic

, As a result of further destruction [58]: (31) (32) (33) [58]

To investigate the effects of ultrasonic waves on the destruction of dye, three tests were done as shown in Fig. 13a. Firstly, the Rh B solution was exposed to light and ultrasonic waves in the absence of catalysts. In this stage, destruction rate was 13 percent for 100 min. Then Rh B solution was exposed to ultrasonic waves and catalysts in the absence of light, and destruction rate was 18 percent for 100 min. Next, dye solution was exposed to light without ultrasonic waves, in the presence of catalysts with light, which showed destruction rate up to 78 % and in the presence of catalysts without light, which showed destruction rate up to 4% for 100 min. Finally, in the last test, nanocomposites with ultrasonic waves were subjected to light and consequently, destruction rate was 99 percent for 100 min 3.6.4 Evaluation of recyclability Thulium Titanate/Polyaniline Nanocomposites In addition, repeated destruction reactions have been conducted in order to achieve the stability of the as-fabricated thulium titanate nanostructures. As shown in Fig. 13 b, the asprepared thulium titanate nanostructures (sample no. 12) did not demonstrate any substantial loss of activity after five consecutive reaction cycles, which indicate the high stability of catalyst. The destruction efficiency was decreased to 90 % after five cycles. The results of photocatalysis survey clearly disclosed that as-synthesized thulium titanate nanostructures may be employed as useful and effective photocatalyst under visible light 3.7. BET Analysis Fig. 14 (a,b) and (c,d) show the adsorption/desorption isotherm and BJH plot of as-made thulium titanate without ultrasound (sample No. 13) and with ultrasound (sample No. 12) to evaluate their pore volume and surface area. Fig. 14 b reveals broad pore size distribution with maximum around pores of 90 nm diameter. The total pore volume and average pore diameter for this sample were measured to be 0.08207 cm3/g and 92.26 nm, respectively. Moreover, the BET analysis was found to be 9.5305 m2/g specific surface areas which could be classified as non-porous. The surface of the prepared thulium titanate in the presence of

ultrasound and starch increased, whereas its size decreased, as shown in Fig. 14 (c,d). Based on the IUPAC classifications, the N2 adsorption/desorption isotherm belongs with H1-type hysteresis loops, that is the substantial features for ordered mesophorous materials. The pore of size distribution for thulium titanate has been depicted in Fig. 14d which demonstrates broad pore size distribution with maximum around pores of 12 nm diameter. The total pore volume and mean pore diameter for this sample was computed approximately 0.1 cm3/g and 9.23 nm, respectively, and the BET analysis was found to be 40.35 m2/g specific surface areas. Hence, one can conclude that the use of capping agent in the synthesis of nanoparticles can lead to decreased size and increased surface area of nanoparticles. Conclusions Current work presents the synthesis of thulium titanate nanostructures by sonochemical method. This compound was characterized by various techniques such as DRS, TEM, BET, IR, FESEM, XRD, and VSM. Moreover, starch, glucose, and lactose were employed as capping agents. The impacts of some parameters such as time of sonication, irradiation power, molar ratio of Tm3+ to Ti+4, type of capping agents, and temperature were examined. Based one our results, it seemed that the experiment was performed by sol-gel assisted sonochemical method in the presence of starch as a polyol capping agent. By considering the mechanism mentioned earlier, the formation of alkoxide as precursor and M-O-M (based on oxolation reaction) (Ti-O-Tm) in the presence of starch and ultrasound waves can lead to preparation of pure thulium titanate nanostructures, without thermal treatment process. Nevertheless, thermal treatment procedure increased particle size and crystallinity of final products. Furthermore, in the absence of starch and ultrasonic waves, the metal oxides acts as the impurity. Therefore, the major role of starch and ultrasound was proved. Our findings exhibited that the optimum condition for synthesis of the small particles with the best size

distribution is 240 W and 15 min with the molar ratio of Ti+4 to Tm+3 in the presence of starch.

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Figure captions Fig. 1 XRD pattern of thulium titanate nanostructures obtained with the power of 240 W for 15 min and the different molar ratio of Ti+4 to Tm+3 (a) (1:4), (b) (1:2), (c) (1:1), and (d) thulium titanate/polyaniline nanocomposites Fig. 2 XRD pattern of thulium titanate nanostructures (a) Without of capping agent, (b) Without of ultrasonic wave and (c) With ultrasonic wave and capping agent Fig. 3 SEM images of thulium titanate nanostructures obtained with various capping agent of (a) Starch, (b) Lactose, and (c) Glucose and various sonication power of (a) 160 min, and (b) 240 min Fig. 4 SEM images of thulium titanate nanostructures obtained at various sonication time of (a) 10 min, and (b) 15 min and various sonication reaction temperature of (a) 40 min, and (b) 50 min Fig. 5 SEM images of thulium titanate nanostructures with starch (a) With ultrasonic wave and b) Without of ultrasonic wave Fig. 6 TEM images of thulium titanate nanostructures obtained with the power of 240 W for 15 min (Sample No. 12) Fig. 7 EDS pattern of thulium titanate/polyaniline nanocomposites obtained with the power of 240 W for 15 min (Sample No. 12) Fig. 8 FT-IR spectra of (a) thulium titanate nanostructures at room temperature, and (b) thulium titanate nanostructures after calcined at 800 ◦C (Sample No. 12) Fig. 9 (sample No. 12).

Fig. 10 UV–vis diffuse reflectance spectrum (a) of the asprepared thulium titanate nanostructures and NPs/PANI and (b) Tauc plot pattern thulium titanate nanostructures and NPs/PANI (sample No. 12 and 15) Fig. 11The photocatalytic behavior thulium titanate nanostructures photocatalytic Rh B destruction (samples No. 2-9) Fig. 12 The photocatalytic behavior of (a) Shows the effect of solution pH on photocatalytic activity of the thulium titanate nanostructures (sample No. 12) b) thulium titanate nanostructures (sample No. 12) on destruction of various contaminants and (c) for the preparation of thulium titanate nanostructures with ultrasonic wave and without of ultrasonic radiation. Fig. 13 (a) The sonophotocatalytic behavior NPs/PANI and (b) Effect of the reuse of the NPs/PANI on the destruction efficiency of Rh B (sample No. 12) Fig. 14 BET pattern of thulium titanate obtained (a,b) without ultrasound and (c,d) with ultrasound Scheme 1 Schematic depiction for the preparation of thulium titanate nanostructures (a) with ultrasonic wave and (b) Without of ultrasonic radiation. Scheme 2 Schematic diagram of preparation the nanocomposites (thulium titanate/polyaniline nanocomposites) Table 1 The preparation conditions of the thulium titanate nanostructures and thulium titanate/polyaniline nanocomposites. Table 2 The comparison of the properties of nanoparticles in the presence and absence of ultrasonic waves.

0.15

Magnetization(emu/g)

0.10

0.05

0.00 -0.05

-0.10

-0.15 -10000 -8000

-6000 -4000

-2000

0

2000

Applied Field(Oe)

4000

6000

8000

10000

1) For the first time, thulium titanate and thulium titanate/polyaniline nanocomposites were synthesized by sonochemical method. 2) According to the BET results, in the presence of ultrasound and starch surface area increased from 8.9288 m2/g to 110.35 m2/g. 3) The results showed that the smallest particles were obtained with maximum time and power of sonication. 4) Photocatalytic efficiency of NPs and nanocomposites were compared for degradation of dye 5) The nanocomposites/US system showed greater photocatalytic activity for the degradation of Rh B than separately treatment of nanocomposites and US under visible light. 6) Nanocomposites were characterized by FESEM, TEM, VSM, XRD, DRS, BET and FT IR.