Abstract
Photocatalytic materials and semiconductors of appropriate structural and morphological architectures as well as energy band gaps are materials needed for mitigating current environmental problems, as these materials have the ability to exploit the full spectrum of solar light in several applications. Thus, constructing a Z-scheme heterojunction is an ideal approach to overcoming the limitations of a single component or traditional heterogeneous catalysts for the competent removal of organic chemicals present in wastewater, to mention just one of the areas of application. A Z-scheme catalyst possesses many attributes, including enhanced light-harvesting capacity, strong redox ability and different oxidation and reduction positions. In the present work, a novel ternary Z-scheme photocatalyst, i.e., Bi2WO6/C-dots/TiO2, has been prepared by a facile chemical wet technique. The prepared solar light-driven Z-scheme composite was characterized by many analytical and spectroscopic practices, including powder X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), N2 adsorption–desorption isotherm, Fourier-transform infrared spectroscopy (FT-IR), photoluminescence (PL) and UV-vis diffuse reflectance spectroscopy (DRS). The photocatalytic activity of the Bi2WO6/C-dots/TiO2 composite was evaluated by studying the degradation of fluoroquinolone drug, levofloxacin under solar light irradiation. Almost complete (99%) decomposition of the levofloxacin drug was observed in 90 min of sunlight irradiation. The effect of catalyst loading, initial substrate concentration and pH of the reaction was also optimized. The photocatalytic activity of the prepared catalyst was also compared with that of bare Bi2WO6, TiO2 and TiO2/C-dots under optimized conditions. Scavenger radical trap studies and terephthalic acid (TPA) fluorescence technique were done to understand the role of the photo-induced active radical ions that witnessed the decomposition of levofloxacin. Based on these studies, the plausible degradation trail of levofloxacin was proposed and was further supported by LC-MS analysis.
Highlights
The occurrence of pharmaceuticals and personal care products (PPCPs) in environmental samples has been observed over the past few decades and these compounds are considered as contaminants of emerging concern, as they are biologically active even at low concentrations [1,2,3,4,5]
FESEM images explained that Bi2WO6 exhibited nanoflakes like morphology that aggregated to form nanosheets, while nanoparticles of TiO2/Carbon quantum dots (C-dots) were found to be assembled over the surface of nanoflakes
PL studies emphasized the optical properties of Bi2WO6/C-dots/TiO2, indicating the hindrance in the recombination of photo-induced charge transporters in Z-scheme catalyst over bare Bi2WO6, suggesting that Z-scheme catalyst could enhance the photocatalytic activity
Summary
The occurrence of pharmaceuticals and personal care products (PPCPs) in environmental samples has been observed over the past few decades and these compounds are considered as contaminants of emerging concern, as they are biologically active even at low concentrations [1,2,3,4,5]. A single photocatalyst cannot possess all the ideal characteristics; for example, wide absorption range and strong redox abilities are difficult to achieve simultaneously in a single photocatalyst [28] These properties can be achieved by designing appropriate photocatalytic systems. The redox capabilities of both photocatalysts are neglected as the oxidation and reduction processes occur on the semiconductors with the lower oxidation and reduction potentials, respectively Even if this heterogeneous photocatalytic system can hinder the recombination of photogenerated charge carriers, it cannot possess efficient charge separation and the strong redox ability simultaneously [29,30].
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