Researchers at the University of Johannesburg have created a highly efficient material powered by sunlight. It has the potential to clean dirty water or create hydrogen fuel in future, while using very little energy from conventional sources.
The three-layer photosensitive material has an unusual ability to perform two key types of chemical processes, namely oxidation and reduction. This means it can be used in many different ways, says the study’s lead author, Professor Langelihle (Nsika) Dlamini.
In particular, it can break down organic pollutants in air and water, turning toxic substances into harmless ones without the need for harsh or dangerous chemicals, he adds.
The study is part of an ongoing collaboration between the UJ Faculties of Science and Engineering, says Prof Dlamini. He leads the Photocatalytic Nanomaterials Research Group (PNRG) within the UJ Department of Chemical Sciences, in the Faculty of Science.
PNRG works with two research groups within the UJ Faculties of Science, and Engineering and the Built Environment.
The team includes Associate Professor Bonginkosi Thango of Electrical and Electronic Engineering Technology at UJ, Dr Thulane Paepae of Mathematics and Applied Mathematics at UJ, Associate Professor Nkosinathi Gule, at the Department of Electrical and Electronic Engineering of the University of Stellenbosch, and UJ PhD candidate Mr Majahekupheleni Malati.
In the study, the researchers designed, manufactured and tested a new, promising photosensitive material. To build it, they designed a custom combination of materials, called a nanocomposite, using two special electrical mechanisms.
The mechanisms are the S-Scheme and Schottky Junction, pathways that force electricity to move in the right direction, so it is not wasted. The resulting material is much better at capturing light and driving chemical reactions, says Prof Dlamini.
In addition, the researchers created a completely new component for the three-layer photosensitive material. It is called Ti1.33N, and belongs to an emerging family of super-thin, 2D materials called MXenes, which are only a few atoms thick.
After the researchers built the three-layer material, they compared its energy efficiency with the three components alone and with a two-layer material using only two of the components.
They found that the three-layer material can capture and use much more solar energy than the individual components, as measured by charge-carrier density.
The three-layer material has 20 times more electrical conductivity than one of the components (BiVO4) on its own and 10 times more than another component (GdIn2Se3). This means that the three-layer material can hold 10 to 20 times more electrical energy and move it with 10 times less effort than the three materials by themselves.
Photosensitive materials for water purification and hydrogen manufacturing are an emerging field. Currently, it is slow because the electrical charge created in the photosensitive material tends to be lost almost instantly (a problem called recombination) before it can do any useful work. Also, earlier photosensitive materials only use UV light, which is just a tiny part of the sun’s energy.
The three-layer material in this study is designed to tackle these challenges. Its structure ‘holds’ onto energy from light for much longer, potentially to clean water or make hydrogen at an industrial scale, among many other possible uses.
In component BiVO4, the energy only lasted for about 3.33 milliseconds. In the new three-layer material, it stayed active for 44.86 milliseconds, which is over 13 times longer. In some tests of the three-layer material, the energy stayed active for nearly a full minute (59.5 seconds), compared to just 7 or 9 seconds in the individual materials.
In particular, the MXene that the researchers custom-built as the third component, acts like a metal conductor to provide a very low electrical resistance. [para-49] This new material has 9.3 times less resistance than component BiVO4 and 14 times less than component GdIn2Se3.
With the MXene added, the three-layer material effectively acts like a highway for electrical charges, allowing much more efficient movement for energy, says Dlamini.
Following this study, the researchers are working on the design of a light-driven reactor using the material to purify water at laboratory scale.
Harnessing the sun’s energy alone to purify water in rivers and dams from dangerous chemicals, medical drugs, wastewater and sewage inflows is some way off. However, the three-layer photosensitive material (photocatalyst) produced in the study is a promising step towards cleaner, more economical drinking water from polluted dams, rivers and aquifers in future.
Research articles:
2026 Fabrication of a multijunction nitride-based Ti1.33N@BiVO4/GdIn2Se3 MXene heterostructure with enhanced optoelectronic and photoelectrochemical properties
2025 Nb4N3TX MXene decorated Bi2WO6/NbSe2 S-scheme heterojunction with improved optoelectronic and photoelectrochemical properties: Experimental and In-silico studies
2024 Interfacial engineering of a multijunctional In2O3/WO3@Ti4N3Tx S-scheme photocatalyst with enhanced photoelectrochemical properties.
2023 An insight into a novel calixarene-sensitized Calix@Nb2CTx/g-C3N4 MXene-based photocatalytic heterostructure: Fabrication, physicochemical, optoelectronic, and photoelectrochemical properties
2022 MXene mediated layered 2D-2D-3D g-C3N4@Ti3C2T@WO3 multijunctional heterostructure with enhanced photoelectrochemical and photocatalytic properties
2022 Facile fabrication of a metal-free 2D–2D Nb2CTx@g-C3N4 MXene-based Schottky-heterojunction with the potential application in photocatalytic processes
