WO3 Nanoparticles for Photocatalytic Degradation of Dyes

Oxide nanomaterials are used to develop advanced photovoltaic materials, photocatalysts, and smart devices. Among metal oxides, tungsten oxide (WO3) is an n-type semiconductor with a small bandgap of 2.6 eV and unique thermal, optical, physical, chemical, and electrical properties. These properties have led to many applications in chemical and selective catalysis, sensors, fuel cells, color change, and pollutant adsorption. WO3 is considered a suitable candidate for the photodegradation of organic pollutants in the visible light region.

In order to control the morphology of WO3 and increase the photocatalytic degradation of organic dyes, a new method to synthesize WO3 nanoparticles by acid citric-assisted precipitation has been proposed. The photocatalytic activity of the samples obtained was determined in the degradation reaction of the organic dyes rhodamine B (rhB), indigo carmine (IC), methyl orange (MO) and Congo red (CR) under UV and UV–vis irradiation. Thus, WO3 nanoparticles have been synthesized by precipitation in presence of citric acid at different temperatures for photocatalytic degradation of dyes. The synthesis process of WO3 particles is as below:

First, 0.00179 moles of ammonium paratungstate hydrate (H42N10O42W12·xH2O) was dissolved in 50 mL of nitric acid solution (30%, v/v, HNO3) and stirred continuously at 70 °C. Then, under continuous stirring and constant temperature, 0.00269 moles of citric acid (C6H8O7) were added to the solution until a light yellow viscous substance was formed. Place the material in a porcelain capsule and heat it at 70 °C until the water has completely evaporated. This step produces a solid material, which will be later identified as a precursor.Heat the as-prepared samples at 500, 600, and 700°C at a rate of 10 °C min-¹ ( Marked as C500, C600, and C700) .Finally, the synthesized sample is supplemented by transmission electron microscopy (TEM), Bruno-Emmett-Taylor surface area (BET) and diffuse reflectance spectroscopy (DRS).

In summary, WO3 nanoparticles with monoclinic structures have been synthesized by precipitation in the presence of citric acid at different temperatures for photocatalytic degradation of dyes. All samples used as photocatalysts showed better photocatalytic activity than commercial WO3 in the degradation reaction of rhB, IC, MO, and CR in an aqueous solution. Under UV-visible light irradiation, sample C700 showed higher photocatalytic efficiency for dye degradation than C600 and C500. Through UV and UV-vis radiation experiments, it can be concluded that the decomposition of the dye is achieved through a combination of two processes: the photosensitization of the dye under visible light irradiation and the true heterogeneous photocatalysis. TOC analysis confirmed the potential of WO3 nanoparticles for the mineralization of organic dyes, especially for the almost complete mineralization of rhB and IC.

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