A new “solar” catalyst based on molybdenum sulfide for water purification was developed by NUST MISIS scientists together with colleagues from FEFU, Fudan University (China) and Tokai University (Japan). The new material has a high photocatalytic activity, which is several times higher than the activity of previously known materials of this class, and also has high stability of properties and can be reused. The research results are published in the Nanomaterials international scientific journal.
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Pollution of the aquatic environment by industrial emissions, as well as wastes from the chemical, pharmaceutical and cosmetic industries poses a real threat to all life on Earth and reducing the level of water pollution is already becoming a vital task. Therefore, scientists are faced with the task of minimizing the amount of harmful emissions, as well as developing effective methods for purifying water from these emissions.
Photocatalytic degradation by sunlight is a technology with minimal anthropogenic impact on the environment, as it uses only natural sunlight and a catalyst. Therefore, with the use of non-toxic photocatalysts scientists can create a “green technology” for processing harmful emissions, similar to natural photosynthesis. The idea is simple – if a photocatalyst is added to water, contaminated with an organic chemical compound, and shone with ultraviolet light or sunlight, then this compound will decompose into safe compounds, like water and carbon dioxide. Obviously, the catalysts themselves must not harm the environment and must be non-toxic, have a long service life, and also be produced using “green technology”. Considering all these aspects, it becomes clear that the development of photocatalysts, as well as methods for their production, is a serious scientific and technical challenge.
Molybdenum sulfide is one of the promising catalysts for the photodegradation of organic pollutants in water. “Its activity arises from unsaturated sulfur bonds and increases with the introduction of structural defects and/or oxygen substitutions. Therefore, we assumed that amorphous molybdenum may have many active centers and, accordingly, high catalytic activity,” explains Andrei Matveev, a researcher at the NUST MISIS Inorganic Nanomaterials Laboratory and one of the authors of the research.
An international research team from NUST MISIS, Fudan University (Shanghai, China), Far Eastern Federal University and Tokai University (Japan) has developed a new method for the synthesis of nanohybrids from amorphous molybdenum oxysulfide (a-MoSxOy) and boron oxynitride (h-BNxOy) and studied their activity in the process of photodegradation of an organic compound (methylene blue) as a model organic pollutant.
“We have developed a new method for the synthesis of nanohybrids a-MoSxOy/h-BNxOy as a result of a chemical reaction between MoCl5, H2S and h-BNxOy in dimethylformamide. The main difference between this method and the traditional methods for the molybdenum disulfide synthesis is that the synthesis proceeds not through the reduction of MoO3 clusters, but as a result of the exchange reaction between MoCl5 and H2S, while the replacement of sulfur with oxygen occurs due to the reaction with boron oxynitride, which was chosen as a carrier catalyst. This leads to the formation of Mo-Sx-Oy clusters with a large number of unsaturated chemical sulfur bonds, which determines the high photocatalytic activity of this material. The use of a liquid medium for synthesis ensures uniform deposition of MoSxOy, and a relatively low synthesis temperature ensures its amorphous state,” adds Andrey Matveev.
Laboratory experiments have shown that nanohybrids are stable and remain highly active for a long time. The developers emphasize that the new material is more than 10 times more effective than many similar materials of the same class (containing no precious metals). Both components of nanohybrids are non-toxic and chemically stable.