How to purify water from phenol, dyes and other pollutants created by humans? You can add some reagent to the water, but it might result in even more problematic pollution.
And this is where photocatalysts come to rescue. These are semiconductor materials that, under the influence of ultraviolet light (special radiation or simply the Sun), promote the decomposition of difficult-to-oxidize pollutants, thus ensuring water purification.
“Carbon nitride (a compound of carbon and nitrogen), a reliable and at the same time non-toxic photocatalyst, is well known. One of its allotropes is polytriazine imide, when the composition of the substance remains the same as in other compounds of nitrogen and carbon: three carbon atoms and four nitrogens, but in the crystal lattice they are arranged differently,” explains Head of the SUSU Department of Ecology and Chemical Engineering of the Institute of Natural Sciences and Mathematics Vyacheslav Avdin.
This substance, polytriazine imide, was the focus of study for SUSU scientists under the leadership of Doctor of Sciences (Chemistry) Vyacheslav Avdin. The article based on the results of their research has been recently published in the collection of the All-Russian Science-to-practice Conference of Modern Materials and Methods for Solving Environmental Problems of Post-industrial Agglomeration.
Polytriazine imide is a pale-yellow powder consisting of tiny particles, approximately 1.5 microns in size. It is a challenge to transport it in tons in this form, add it to water, and then filter it. That is why, the powder is added to silica gel (a colloid, sol of silicic acid), dried and formed into 1.5 mm granules. And now the photocatalyst is ready to be used.
How to test its photocatalytic activity? Scientists took methylene orange as a pollutant. This is an organic dye well known to chemists. By the way, it can be used, for example, to determine the acidity of the environment. If the environment is acidic (pH <7), the dye will turn red; if alkaline (pH> 7), it will turn yellow, and it will actually be orange only in a pH-neutral environment.
So, it is necessary to make the “orange” water transparent again. A series of experiments were conducted with different modifications of silica gel. When necessary, the solution was acidified by adjusting its pH.
Let us add that the research team faced the task of choosing the optimal proportion of both the photocatalyst and silica gel. An option was found experimentally: 200 milligrams of polytriazine imide in 35 ml of silica gel. It gives the best results; water comes out without dye. This composition also demonstrated the highest purification rate. At the same time, even the weakest of the compositions participating in the experiment showed a result of approximately 30% efficiency, which is also not bad.
This was the result at the time of publication of the scientific research. Now, as the scientists assure, they manage to achieve 100% water purification by this method, making it completely transparent.
Today, the use of photocatalysts is one of the frontiers where fundamental science and applications in demand by modern industry meet.
The work was conducted within the framework of the Priority 2030 program under the Science and Universities national project.