The photo is sourced from misis.ru
Effluents from oil refineries, wood chemistry and paint-and-varnish enterprises are most common sources of phenol. Phenol-containing compounds absorb the oxygen diluted in water, hence, their intrusion into rivers and lakes may cause damage to the environment. Effluents treatment to remove such compounds requires expensive chemical agents and follow-up disposal of the toxic waste generated as the result of such treatment process.
The scientists from the Science and Technology University within Moscow Institute of Steel and Alloys and Fudan University proposed to clean the polluted water by adding the hexagonal boron nitride (h-BN) into it. This is a powder with high chemical stability and big surface area. This powder performs as the photocatalytic filter oxidising the phenol-containing compounds to water and carbon dioxide when exposed to UV-light – the respective chemical reaction takes place at the interface between the surfaces of the photocatalyst and the water solution.
However, the deficiency of h-BN is a big width of the prohibited zone – the energy gap for the electron to cover to activate the photocatalysis process. The bigger this gap is, the higher is the need for using special radiating sources. The researchers succeeded in decreasing the energy gap by way of ball milling the powder, i.e., pulverising and plastic deformation.
“We found that due to creating a big number of defects on the boron nitride structure the energy gap decreases. This also results in increased light absorption and longer life of the excited electrons. When our material is exposed to the UV light, active hydroxyl radicals emerge in water oxidising phenol to carbon dioxide and water”, says Denis Leibo, the researcher from the R&D centre of non-organic materials within Moscow Institute of Steel and Alloys.
In future, the researchers propose to use heterostructure-based materials composed on the basis of defective boron nitride as photocatalyst allowing for photocatalytic oxidising not under the UV light exposure, but under the visible light.