JOYA, M. R.

MALAFATTI, J.

PARIS, E. C.

PARRA, C. A.

RABA, A. M. P.

English

Repository Open Access to Scientific Information from Embrapa

       629?SÍNTESE, CARACTERIZAÇÃO E AVALIAÇÃO DA DEGRADAÇÃO ORGÂNICA DE POLUENTES DE MATERIAIS HETEROESTRUTURADOS À BASE DE CuWO4  A. M. Raba P.1,2,*, J. Malafatti3,4, C. A. Parra1, M. R. Joya5, E. C. Paris4  1 Universidad Pedagógica y Tecnológica de Colombia, Carretera Central del Norte, 150001, Tunja, Boyacá, Colombia 2 Universidad Francisco de Paula Santander, Avenida Gran Colombia, 12E-96, 540003, Cúcuta, Norte de Santander, Colombia 3 Universidade Federal de São Carlos UFSCar, Rod. Washington Luiz, 13565-905, São Carlos, SP 4 Embrapa Instrumentação, Rua 15 de Novembro, 1452, 13560-970, São Carlos, SP 5 Universidad Nacional de Colombia, Ciudadela Universitaria, 111321, Bogotá, Cundinamarca * Autor correspondente, e-mail: angelamercedesrp@ufps.edu.co.  Resumo: O CuWO4 foi sintetizado pelo método hidrotérmico com o objetivo de estudar a possível formação do sistema heteroestruturado CuWO4/CuO. A análise do padrão de DRX dos materiais obtidos revela a formação de CuWO4 como fase principal e Cu2WO4 como fase minoritária. Uma modificação no pH antes do processo hidrotérmico leva à formação de óxido de tungstênio não estequiométrico. Através da comparação com outra heteroestrutura CuWO4/CuO obtida anteriormente, esperamos verificar as propriedades fotocatalíticas dos materiais obtidos neste trabalho.  Palavras-chave: CuWO4, Hidrotérmica, Caracterização, Heteroestrutura, Fotocatálise.  SYNTHESIS, CHARACTERIZATION AND EVALUATION OF POLLUTANTS ORGANIC DEGRADATION OF HETEROSTRUCTURED MATERIALS BASED ON CuWO4  Abstract: CuWO4 was synthesized by hydrothermal method with the purpose to study the formation possible of CuWO4/CuO heterostructured system. XRD pattern analysis of materials obtained reveals the formation of CuWO4 like a principal phase and Cu2WO4 like minority phase. A modification on the pH before hydrothermal process leads to the formation of non-stoichiometric tungsten oxide. Through the comparison with another CuWO4/CuO heterostructure previously obtained, we hope to check the photocatalytic properties of the obtained materials in this work.     Keywords: CuWO4, Hydrothermal, Characterization, Heterostructure, Photocatalysis.  1. Introduction  Cooper tungstate (CuWO4) is a ternary oxide semiconductor that crystallize in a triclinic structure at room temperature. CuWO4 has two molecular formula units per unit cell (Z =2) at high and low-pressure (SOUZA et al., 2017). This oxide has considerable attention due to interesting technological properties such as ionic conductivity (MATHEW et al., 1992) and photoluminescence (SCHMITT et al., 2011). In particular, its electronic properties enable it to photocatalytic degradation of organic dyes (MONTINI et al., 2010) (CHEN et al., 2015) (DUTTA et al., 2015) and visible and solar-assisted water splitting (GAILLARD et al., 2013), among other environmental applications of semiconductors. With respect to the preparation, different synthesis methods have been used to obtain CuWO4 such as co-precipitation (GARCÍA et al., 2012) (CHEN et al., 2014), sol-gel (DAMIÁN et al., 2003), hydrothermal (MA et al., 2014) and sonochemistry (SOUZA et al., 2017) (DUTTA et al., 2015) method. Heterostructure is a material with distinct crystalline phase in one particle and sharing at least one surface in a coherent manner. The charge migration between interconnected phases occurs and because the Fermi levels may be equals at the semiconductor’s interface, the charge separation        630?in the phases will occur when the system is stimulated (ALVES de CASTRO et al., 2015). Coupling CuWO4 with other semiconductors has shown better performance photocatalytic of oxide due to that this configuration results an effective way to reduce the charge recombination (CHEN et al., 2014) (CHEN et al., 2015). Type-I (CuWO4/WO3∙0.33H2O, CuWO4/WO3) and type-II (CuWO4/Cu2O, CuWO4/Cu2O/CuO, CuWO4/CuO) heterojunction were obtained as function of pH (KANNAN et al., 2017). These nanocomposites exhibited the enhanced visible light absorption and the band gap (1.7 eV) of CuWO4 is smaller than the early reported value (2.1-2.3 eV). As to photocatalytic degradation, the CuWO4/Cu2O/CuO and CuWO4/WO3∙0.33H2O were showed 1.66 fold times higher and nearly equal apparent rate constant respectively than that of CuWO4. The surface modification of CuWO4 with 1.8 wt% of CuO can increase the activity by approximately 9 times under UV light and by 5 times under visible light, for phenol degradation in aerated aqueous suspension (CHEN et al., 2014). In this work also was demonstrated through a (photo) electrochemical method, the processes of the electron transfer from CuO to CuWO4 and the hole transfer from CuWO4 to CuO, so that the efficiency of charge separation is improved, and organic degradation is accelerated. These previous works have reported that CuWO4/CuO system improves the response photocatalytic both of CuWO4 because the recombination of the photogenerated charge carriers can be reduced which is a process desirable to optimize the photocatalytic performance under light solar. Thus, in this work we report the hydrothermal synthesis of CuWO4 with the purpose to study the formation possible of CuWO4/CuO heterostructured system. The solids obtained will be characterized with XRD, DRS, SEM, EDS, IR and Raman spectroscopy. Their photocatalytic response for organic degradation in water will be measured under UV light.  2. Materials and Methods CuWO4-(1) was prepared by using a hydrothermal method modifying the process reported in Chen (2014). 2.416 g of cooper (II) nitrate 3-hydrate (Cu(NO3)2∙3H2O) were dissolved in 200 mL of distilled water and the solution pH was adjusted to 5.0 with NaOH aqueous solution dropwise, followed by heating to 60°C. 3.2985 g of sodium tungstate dihydrate (Na2WO4∙2H2O) were dissolved in 50 mL of distilled water and right away added to solution of cooper. Immediately after the solution was heated to 90°C during 1 h. After cooling until room temperature aqueous NaOH and aqueous HNO3 was added drop by drop until pH was adjusted to 5.0. The precipitated was transferred into a stainless autoclave, and heated at 180°C for 24 h. After the reactor cooled down the particles were collected by centrifuge, washed with water, rinsed with ethanol and dried at 60°C for 18 h. Finally, the sample was sintered in air at 500°C for 2 h. For obtaining CuWO4/CuO heterostructures, an appropriate amount of a solution containing CuWO4 and Cu complex will be prepared. In order to prepare Cu complex, a specific amount of cooper (II) Nitrate 3-hydrate will be dissolved in distilled water. PEG400 will be poured in the cooper aqueous solution and after that PEG400 is uniformly dispersed, NaOH pellets will be put into the above solution. After 30 min stirring, a solution containing CuWO4 and an appropriate amount of Cu complex will be prepared in order to study three different molar ratios of CuWO4/CuO, 0:1, 1:1, 2:1. Subsequently, the suspension obtained will be transferred to an autoclave, at 80°C for 12 h. After cooling to room temperature, the formed precipitates will be washed with water and dried in air at 60°C for 24 h.  The determination of the present phases was realized by X-ray Diffraction (XRD) through Shimadzu XRD 6000; CuKα radiation with λ = 1,5488 Å was used. The 2θ angle range was 10-80°, with a step of 1.0°/min. Additionally, it is hoped to characterize the samples obtained through Diffuse Reflectance Spectroscopy (DRS), Scanning Electronic Microcopy (SEM), Energy Dispersive Spectroscopy (EDS), Infrared (IR) and Raman spectroscopy. Experiments of pollutants organic degradation in water under visible light will be carried out.          631?3. Results and Discussion XRD pattern of the CuWO4-(1) bulk material is shown in Figure 1. This pattern show the characteristic peaks of CuWO4 phase (JCPDF No. 01-070-1732) and other minority peak indexed too, associated to Cu2WO4 phase. It is hoped to obtain the CuWO4 phase with the purpose to study the formation possible of CuWO4/CuO heterostructured system.   Figure 1. XRD of CuWO4-(1) sample. Peak corresponding to other phase had been indicated.  Since the synthesis process we identified that if the solution was not heated to 90°C WO3 phase will be formed. Similarly, to bring the pH at 6, after cooling until room temperature, promotes the formation of non-stoichiometric tungsten oxide. We hope compare the properties of CuWO4/CuO heterostructured system with the properties of CuWO4/CuO heterostructure obtained through a simple sol-gel method, since ammonium paratungstate and annealing at 300°C. XRD pattern of this heterostructure allowed identify the CuO and CuWO4 crystalline phases. IR analysis showed the vibrational bands of the CuO and CuWO4 phases. In FE-SEM images, well-defined polyhedral (CuWO4) coverage with agglomerates of nanoparticles (CuO) are distinguished, indicating the heterostructure was obtained (Figure 2). Two indirect gap values were obtained: 1.35 eV for CuO and 2.11 eV for CuWO4. All these results show that CuWO4/CuO heterostructure was obtained and their properties make it a promising candidate for testing of photocatalytic degradation, which was confirmed by a single Rhodamine-B degradation experiment.   Figure 2. FE-SEM image CuO/CuWO4 heterostructure.  4. Conclusions XRD pattern of the CuWO4-(1) bulk material showed the characteristic peaks of CuWO4 phase and one minority peak associated to Cu2WO4 phase. CuWO4/CuO heterostructure was obtained through a simple sol-gel method like a sample comparison. This material is the base of this        632?study, because will allow us to compare the structural, morphological and optical properties of the CuWO4/CuO heterostructured system with the properties of that heterostructure obtained previously.   Acknowledgment We acknowledge the financial support from COLCIENCIAS (757 - 2016), Universidad Francisco de Paula Santander and EMBRAPA Instrumentação. We acknowledge the scientific contributions from GFM of Universidad Pedagógica y Tecnológica de Colombia, GIMAPOL of Universidad Francisco de Paula Santander, Universidad Nacional de Colombia and EMBRAPA Instrumentação.  References ALVES de CASTRO, I.; ARIANE de OLIVEIRA, J.; PARIS, E. C.; GIRALDI, T. G.; RIBEIRO, C. Production of heterostructured TiO2/WO3 nanoparticulated photocatalysts through a simple one pot method. Ceramics International, v. 41, p. 3502-3510, 2015. CHEN, H.; LENG, W.; XU, Y. Enhanced visible-light photoactivity of CuWO4 through a surface-deposited CuO. The Journal of Physical Chemistry C, v. 118, p. 9982-9989, 2014. CHEN, H.; XU.; Y. Photocatalytic organic degradation over W-rich and Cu-rich CuWO4 under UV and visible light. RSC Advances, v. 5, p. 8108-8113, 2015. DAMIÁN, M. A.; RODRIGUEZ, Y.; SOLISA, J. L.; ESTRADA, W. Characterization and butanol/etanol sensing properties of mixed tungsten oxide and cooper tungstate films obtained by srpay-sol-gel. Thin Solid Films, v. 444, p. 104-110, 2003. DUTTA, D. P.; RATHORE, A.; BALLAL, A.; TYAGI, A. K. Selective sorption and subsequent photocatalytic degradation of cationic dyes by sonochemically synthesized nano CuWO4 and Cu3Mo2O9. RSC Advances, v. 5, p. 94866-94878, 2015. GAILLARD, N.; CHANG, Y.; ANGELIS, A. De; HIGGINS, S.; BRAUN. A. A nanocomposite photoelectrode made of 2.2 eV band gap cooper tungstate (CuWO4) and multi-wall carbon nanotubes for solar-assisted water splitting. International Journal of Hydrogen Energy, v. 38, p. 3166-3176, 2013. GARCÍA-PÉREZ, U. M.; MARTÍNEZ de la CRUZ, A.; PERAL, J. Transition metal tungstates synthesized by co-precipitation method: Basic photocatalytic properties. Electrochimica Acta, v. 81, p. 227-232, 2012. KANNAN, S.; MOHANRAJ, K. Preparation of bifunctional CuWO4-based heterostructure nanocomposites for noble-metal-free photocatalysts. Chemistry Select, v. 2, p. 4484-4498, 2017. MA, D.; XIE, J.; LI, J.; LIU, S.; WANG, F.; ZHANG, H.; WANG, W.; WANG, A.; SUN, H. Synthesis and hydrogen reduction of nano-sized cooper tungstate powders produced by a hydrothermal method. International Journal of Refractory Metals and Hard Materials, v. 46, p. 152-158, 2014. MATHEW, T.; BATRA, N. M.; ARORA, S. K. Electrical conduction in CuWO4 crystals. 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Síntese, caracterização e avaliação da degradação orgânica de poluentes de materiais heteroestruturados à base de CuWO4.

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Síntese, caracterização e avaliação da degradação orgânica de poluentes de materiais heteroestruturados à base de CuWO4.

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