Enhanced Solar Photocatalytic Degradation of Phenol with Coupled Graphene-Based Titanium Dioxide and Zinc Oxide

Abstract

In this study, graphene-based titanium dioxide and zinc oxide composites (TiO 2 -G, ZnO-G) were synthesized using a hydrothermal process. Materials were characterized using X-ray diffraction, X-ray photoelectron spectroscopy, Raman spectroscopy, UV−vis spectroscopy, scanning electron microscopy, and transmission electron microscopy. Photocatalytic activity of the composite materials under simulated solar light was studied using phenol as a model compound. A ca. 30% improvement on the degradation performance by the TiO 2 -G composite (and ZnO-G) was observed when reaction rate constants were compared with TiO 2 (and ZnO) only. This demonstrates the positive effect of graphene on suppressing charge recombination and extending the light absorption range. Further improvement on the photocatalytic degradation rate of phenol was obtained by coupling the two composites, ZnO-G and TiO 2 -G. This is attributed to more efficient charge separation and longer lifetime of the charge carriers, which eventually enhances the photocatalytic activity. The optimum stoichiometric amount of each component was obtained experimentally. Systematic parametric studies were also performed to study the effect of catalyst loading, initial phenol concentration, solution pH, and solar light intensity. Complete solar degradation of 40 ppm phenol was achieved within 60 min while using the coupled ZnO-G/TiO 2 -G photocatalysts at the optimum conditions.

Degradation of Phenolic Compounds Through UV and Visible- Light-Driven Photocatalysis: Technical and Economic Aspects

“…Sengupta et al [48] used a Taylor vortex reactor (TVR) for the degradation of phenol under UV light. Chowdhury et al [7] used slurry photoreactor with dye-sensitized photocatalyst, and Malekshoar et al [5] used slurry photoreactor with graphene-based photocatalyst for phenol degradation under solar light. Studies by other researchers reported degradation of phenols with (i) TiO 2 -coatedfiber-optic cable reactor [16], (ii) tubular photoreactor [49], (iii) continuous flow photoreactor [50], and (iv) solar photoreactor (CPC modules and flat reactor) [51].…”

“…When semiconductor photocatalyst is illuminated with light energy greater than the band gap of the photocatalyst, charge carriers (i.e., electron-hole pair) are produced which ultimately generate hydroxyl radicals (HO • ) in the system. Recently, photocatalytic degradation of phenol and phenolic compounds in wastewater has been extensively studied by several research groups [4][5][6][7][8][9][10][11][12][13]. Titanium dioxide (TiO 2 ) photocatalyst is frequently used in the degradation of phenols under ultraviolet light [14][15][16].…”

Synthesis of graphene–transition metal oxide hybrid nanoparticles and their application in various fields

“…If the lifetime is long enough, the electrons form a system which can be utilised as highly sensitive light detectors or sensors [251–252]. Due to this synergetic effect via interfacial charge transfer and inhibition of recombination of excited electrons, this hybrid has wide spread applications in waste water purification by the photocatalytic degradation of dye molecules like MB [253–259], rhodamine B [260], and for the degradation of phenol [261]. This hybrid also has potential for the fabrication of biogas sensors and electrochemical sensors.…”

Dye-Sensitized Photocatalytic Water Splitting and Sacrificial Hydrogen Generation: Current Status and Future Prospects

“…The higher apparent quantum efficiency of 18.5% was obtained over RB sensitized graphene sheets with dispersed Pt nanoparticles under visible light irradiation of 550 nm [86]. Graphene is known as a promising material in designing hybrids for photocatalysis [77,88]. Besides improving electron transfer and charge separation, dispersible graphene sheets provide great interfaces for highly dispersing nanoparticles, enhancing hydrogen generation compared to GO and MWCNT.…”