Paper by Dr. Saeed M. Alhassan, Associate Professor of Chemical Engineering, and researchers Dr. Sunil P. Lonkar and Dr. Vishnu V. Pillai, announced as one of Scientific Report’s top 100 papers in Chemistry
A paper authored by Khalifa University researchers that explains a new method for developing high-efficient photocatalysts – materials that absorb sunlight to cause a chemical reaction – has been named one of 2019’s top 100 most important papers in the field of Chemistry in the renowned journal Scientific Reports.
The paper, titled “Facile and scalable production of heterostructured ZnS-ZnO/Graphene nano-photocatalysts for environmental remediation,” identified an affordable, scalable, and environmentally friendly way to synthesize nano-sized photocatalysts from zinc sulfide, zinc oxide, and graphene – a first in the research community.
“The aim of our project was to develop highly efficient photocatalysts through a scalable, solvent-free approach in an effort to promote sustainability while utilizing sulfur – a byproduct of oil extraction that the UAE and Middle East has in abundance, further creating value for one of the UAE’s core industries,” said Dr. Saeed Alhassan, Associate Professor of Chemical Engineering, who led the research team.
Photocatalysts are semiconductor materials that absorb different wavelengths of light energy and transfer that energy buildup to a reacting substance, resulting in a chemical reaction called photocatalysis. Two simultaneous reactions are required for photocatalysis to occur – in the first reaction, a reactant gains an electron – a reduction from photogenerated electrons – while in the second reaction, a reactant loses an electron – an oxidation from photogenerated holes – a process more commonly known as redox. When the electrons and holes are utilized, photocatalysis occurs.
The novel approach undertaken by KU’s research team is an environmentally-friendly alternative to traditional methods of fabricating photocatalysts. Typically, photocatalysts are developed through wet-chemical synthesis, co-precipitation, thermal/hydrothermal methods, and sulfurization. These common methods to synthesize photocatalysts use highly complex and costly processes that often include toxic agents, which in turn restricts their large-scale production and eco-friendly applications.
The KU process produces photocatalysts without using toxic solvents, via a ‘solvent-free’ approach, through a method that employs a solid-state mixing of the constituent materials.
“We used ball-milling and thermal annealing for a uniform distribution of the hybrid particles. This process yielded hybrid mixtures of varying compositions of zinc sulfide and zinc oxide combined with graphene, that we categorized and tested,” Dr. Alhassan explained.
Rather than dissolving the materials with a solvent, the team used a ball mill to ground the compounds into uniform particles in a process where ball bearings inside a cylinder rotate around an axis, filled partially with the materials to be ground – in this case, graphite oxide, zinc salt, and elemental sulfur.
“We further refined the different photocatalysts through thermal annealing to enhance the physical properties of the materials. The thermal treatment proved to be a crucial factor in enhancing the photocatalytic activity,” said Dr. Alhassan. “Hybridization of zinc sulfide and zinc oxide combined with graphene also promoted bandgap narrowing when compared to pristine zinc sulfide nanoparticles. The result was a non-toxic, efficient, and scalable photocatalyst.”
Photocatalysis plays a vital role in sustainable development and environmental cleanup as a means to break down toxic pollutants into simpler compounds that can be absorbed and recycled naturally. Photocatalysts also aids in the development of solar fuels – renewable sources of green energy – by enabling solar energy to produce fuels that can be stored and used even when the sun is not shining.
However, the prevailing methods and materials used to induce photocatalysis absorb light poorly and utilize electrons and holes inefficiently. These inefficiencies have demanded experimentation and fine-tuning to achieve ideal bandgaps – the energy it takes for a molecule to go from a non-conducting to a conducting state – that effectively utilize the absorbed light energy for redox reactions involving toxic pollutants and organic compounds.
Growing environmental concerns across the globe have identified the need for efficient and inexpensive photocatalysts. The work being conducted at Khalifa University directly addresses this concern and is an important contribution to the research and development of viable environmentally-friendly photocatalysts.
The team’s research is gaining significant attention from the scientific community, and the researchers have already filed a patent for the unique process, titled “Mechano-thermal preparation of zinc sulfide nanoparticles.”
Read the full paper here.
Zaman Khan
News and Features Writer
24 June 2019
