Renewable Energy Global Innovations features: Graphene oxide/WS2/Mg-doped ZnO nanocomposites for solar-light catalytic and anti-bacterial applications

Significance Statement

Semiconductor oxides find an array of applications in water purification for photocatalytic degradation of organic dyes. Zinc oxide is perhaps the most popular component for photocatalytic applications owing to its wide band gap, low cost, environmental friendliness, and large exciton binding energy leading to superior optical activity. This makes zinc oxide an important ingredient for photo catalyst for organic pollutants treatments.

However, high recombination rate of electron-hole pairs in semiconductors as well as insufficient solar spectrum absorption limit its photocatalytic reaction efficiency. Doping, constructing heterojunctions and catalyzer carrier are viewed as solutions to these problems, and are used mainly to enhance the photocatalytic activity of zinc oxide nanostructure. Doping the zinc oxide with a suitable element is an important approach for improving its sunlight absorption.

Catalyzer carrier is viewed as an effective approach for decreasing recombination rate of photo generated electron-hole pairs. Graphene is an important catalyst support, which has been deemed as the most promising building block to trap and transfer the photo-induced electrons because of its large surface area, high carrier capacity, and large electronic storage ability. Graphene can fix zinc oxide nanoparticles defects for conducting electron and function as a conducting network. It can as well prevent zinc oxide from aggregation and result in the improvement of the photocatalytic performance.

A group of researchers led by Professor Yuenhong Tsang at The Hong Kong Polytechnic University Shenzhen Research Institute demonstrated the scalable approach to fabricate large amount of tungsten disulfide Nano plates through the mechanical shear exfoliation approach. They adopted a versatile method to produce 3D reduced graphene oxide-tungsten disulfide nanosheet magnesium doped zinc oxide hybrid implementing a layer-by-layer assembly method. They achieved photocatalytic attributes enhancement adopting the 3D graphene tungsten disulfide hybrid. Their work is published in Solar Energy Materials & Solar Cells.

The authors used Rhodamine as a model dye in a bid to evaluate the photocatalytic activity of the specimens. The research team computed the degradation ratio as the quotient between original concentration and the residual concentration at varying time. After a complete degradation of the Rhodamine, the authors isolated the graphene nanocomposites and added them to a different solution with the same Rhodamine concentration. This was in a bid to analyze the photocatalytic stability of the resulting composites.

The authors observed the adsorption ability of the specimen before opening light in order to differentiate adsorption effect and photocatalytic ability of the samples for Rhodamine. They realized that the adsorption ratio of all samples for Rhodamine was less than 10% in the dark. When exposed to about 100W UV light irradiation, the group without a photo catalyst indicated about 20% photo degradation. However, a 60% photo degradation was recorded when reduced graphene oxide/magnesium doped zinc oxide composites samples were imported.

However, a 90% removed rate of reduced graphene oxide-tungsten disulfide nanosheet magnesium doped zinc oxide hybrid for Rhodamine was recorded after 5 min, and the Rhodeamine was completely removed after 10min.

Inhibition rings sizes against E, coli as well as S. aureus were 8.64mm and 6.07mm respectively for magnesium doped zinc oxide specimen.  However, when graphene was introduced, the rings sizes increased to 9.23mm and 10.21mm.

Tungsten disulfide nanosheet played a critical role in improving photocatalytic and antibacterial activity of the magnesium-doped zinc oxide composite. The outcomes of the study prove that the resulting 3-D tungsten doped zinc oxide composites could be good candidates for sunlight-driven photocatalytic, self-cleaning, environmental protecting, and photovoltaic applications.

About The Author

Dr. Yuen Hong Tsang has completed his undergraduate and PhD study in the School of Physics and Astronomy, The University of Manchester, UK in 2004. He came back to Hong Kong in 2009 and he is now Assistant Professor in Applied Physics Department, The Hong Kong Polytechnic University. He has published >100 SCI international peer reviewed journals with H-index >20 and total citation >1400.

His current research interests include development of novel materials, e.g. graphene, MoS₂, WS₂ etc. for laser photonics, photo-catalysis, solar energy conversion applications, e.g. photo-catalyst, solar heat absorber, saturable absorber, optical limiter, photo detection, fiber laser, Q-switched and mode locked lasers, etc. He has involved and successfully completed several research projects funded by some well-known international companies.

These projects include 1.  Laser range funder for military applications (funded by Thales.) 2. Imaging system for dental applications (funded by Colgate Palmolive) 3. Narrow linewidth tunable lasers (funded by Huawei) 4. Carbon based mode locking laser system (funded by Fianium Asian Ltd.)

Reference

Chuansheng Chen, Weiwei Yu, Tiangui Liu, Shiyi Cao, Yuenhong Tsang. Graphene oxide/WS2/Mg-doped ZnO nanocomposites for solar-light catalytic and anti-bacterial applications. Solar Energy Materials & Solar Cells, volume 160 (2017), pages 43–53.

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