Photocatalytic degradation of methyl orange dye by pristine titanium dioxide, zinc oxide, and graphene oxide nanostructures and their composites under visible light irradiation

Applied Nanoscience, Apr 2017

Discharge of azo dyes by textile and allied industries to the environment is a growing problem. Degradation of an azo dye, methyl orange (MO), was tested in simulated wastewater with different oxide nanomaterials acting as photocatalysts under visible light. Titanium dioxide (TiO2), zinc oxide (ZnO), and graphene oxide (GO) were synthesized, characterized, and applied for adsorptive and photocatalytic removal of the dye. Factors such as initial concentration of MO and size of nanoparticle photocatalyst were varied to determine the optimum conditions for dye removal. Finally, nanocomposites of the three materials (GO–TiO2–ZnO) were synthesized and tested for its photocatalytic performance. The composition of the individual oxide in the nanocomposite was then varied to achieve the best photocatalytic performance.

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Photocatalytic degradation of methyl orange dye by pristine titanium dioxide, zinc oxide, and graphene oxide nanostructures and their composites under visible light irradiation

Appl Nanosci Photocatalytic degradation of methyl orange dye by pristine titanium dioxide, zinc oxide, and graphene oxide nanostructures and their composites under visible light irradiation Ramesh Raliya 0 1 2 Caroline Avery 0 1 2 Sampa Chakrabarti 0 1 2 Pratim Biswas 0 1 2 0 & Pratim Biswas 1 Department of Chemical Engineering, University of Calcutta , Calcutta, West Bengal 700073 , India 2 Department of Energy, Environmental and Chemical Engineering , Washington University in St. Louis, St. Louis, MO 63130 , USA Discharge of azo dyes by textile and allied industries to the environment is a growing problem. Degradation of an azo dye, methyl orange (MO), was tested in simulated wastewater with different oxide nanomaterials acting as photocatalysts under visible light. Titanium dioxide (TiO2), zinc oxide (ZnO), and graphene oxide (GO) were synthesized, characterized, and applied for adsorptive and photocatalytic removal of the dye. Factors such as initial concentration of MO and size of nanoparticle photocatalyst were varied to determine the optimum conditions for dye removal. Finally, nanocomposites of the three materials (GO-TiO2-ZnO) were synthesized and tested for its photocatalytic performance. The composition of the individual oxide in the nanocomposite was then varied to achieve the best photocatalytic performance. Nanoparticles; Photocatalysis; ZnO; Graphene oxide - TiO2 Introduction Textile and dye-manufacturing industries are discharging toxic and non-biodegradable azo dyes, such as methyl orange, into the environment (Daneshvar et al. 2003) . Of the total world production of dyes, up to 20% is lost during industrial processing, causing environmental pollution and contributing to eutrophication that affects aquatic life (Konstantinou and Albanis 2004) . Current methods used to treat these effluents are mainly physicochemical, causing a disposal issue for the sludge residue. For example, chemical precipitation and separation of pollutants, electrocoagulation and elimination by adsorption do not destroy the contaminants: they only transfer them to solids which are primarily disposed of into landfills (Daneshvar et al. 2003) . Applying nanotechnology to dye degradation shows great potential, as nanoparticles can chemically react with the dyes to form non-toxic products that may require no removal (Biswas and Wu 2005) . Photocatalysis is a technique utilizing nanotechnology under thorough study now (Ahmad et al. 2015; Meng et al. 2014; Meng and Ugaz 2015) . The process of photocatalysis is powered by photons that match or exceed the band gap energy of a given semiconductor (Saleh and Gupta 2012) . An electron in its valence band (VB) is excited to the conduction band (CB), leaving a positive hole in the VB that forms a hydroxyl radical with the hydroxyl ion in water, which is then available for oxidation. Meanwhile, the excited electron reduces oxygen in the CB, which can also act as an oxidizing agent (Saleh and Gupta 2012) . However, the photogenerated electrons are unstable in the excited state, thus can easily recombine to their respective holes. This process dissipates the input light energy and results in low-efficiency photocatalysis. Therefore, the development of a more efficient photocatalyst is an important consideration (Saleh and Gupta 2012; Dai et al. 2014; Sakthivel et al. 2003; Ahmad et al. 2015) . Titanium dioxide has been extensively studied as a photocatalyst due to its physical and chemical stability, non-toxicity, low cost, and insolubility under various conditions (Saleh and Gupta 2012) . TiO2 is a semiconductor oxide with a high band gap energy of 3.2 eV, allowing pollutant degradation when exposed to high energy light. Similarly, zinc oxide also possesses wider band gap (3.37 eV) than TiO2, as well as higher electron mobility (Dai et al. 2014) . While both materials show great potential, they alone do not operate with high photocatalytic efficiency due to electron/hole pair recombination (Dai et al. 2014; Liu et al. 2016) . Strategies to improve the photocatalytic performance of these metal oxides have been widely tested over the past decade (Dai et al. 2014; Konstantinou and Albanis 2004; Saleh and Gupta 2012) . For example, altering the textural design, doping, and forming semiconductor composites have been examined. One particular focus of research is the utilization of graphene in combination with semiconductor photocatalysts to act as an electron-transfer medium to reduce recombination (Dai et al. 2014; Nguyen-Phan et al. 2011) . There are reports on the performance of nanocomposites of graphene oxide (GO) and TiO2; however, little work has been done with GO?ZnO, GO?TiO2 at different concentrations, composite ratios, and size. In the present study, photocatalytic degradation efficiencies of nanomaterials in pristine (TiO2, ZnO) and composite (ZnO?TiO2, GO?TiO2, GO?ZnO, GO?ZnO?TiO2) form were investigated for the degradation of methyl oran (...truncated)


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Ramesh Raliya, Caroline Avery, Sampa Chakrabarti, Pratim Biswas. Photocatalytic degradation of methyl orange dye by pristine titanium dioxide, zinc oxide, and graphene oxide nanostructures and their composites under visible light irradiation, Applied Nanoscience, 2017, pp. 253-259, Volume 7, Issue 5, DOI: 10.1007/s13204-017-0565-z