Study of possibility to produce hydrogen in process of photocatalytic degradation of organic water pollutants using Fe-containing composites

The photocatalytic decomposition of water for hydrogen production is considered as one of the most important approaches to solving the world's energy crisis. Given the economic and environmental factors, water pollutants or components belonging to the waste water of various industries are preferable as "consumable" organic reagents. Organic compounds act as electron donors, they are gradually oxidized to CO2, absorbing the photogenerated holes and/or oxygen thus increasing the rate of hydrogen production. Iron-containing catalysts are attractive not only from the economic point of view, they are environmentally friendly and are of interest to create a variety of catalytic systems (Fenton, Fenton-Raff, ferrioxalic system, etc.) by combining heterogeneous and homogeneous catalyses. Thus, Fe-containing composition of silicon nitride and boron nitride, and iron-modified peat and zeolites we previously studied showed high catalytic activity in the processes of degradation of some organic pollutants: oxalic acid, formaldehyde and phenol compounds - just as sources of iron for the combined catalysis. In the present study, we investigated Fe-containing composites for simultaneous photochemical generation of hydrogen. The objectives of the study were: selection of reagents most promising for the generation of hydrogen and estimation of hydrogen production rate by gas chromatography depending on the concentration of pollutants, weight of the catalyst, the phase composition of the catalyst, its surface area. H -production rates (mL/h) and the performance of the investigated composites for hydrogen evolution (mkmol/hg) under UV irradiation of aqueous solutions of formic and oxalic acids, hydrazine, phenolic compounds were estimated. It is shown that there is principal possibility of using natural sorbents: peat and zeolites modified with iron for hydrogen production, however, the efficiency of this process is not high and requires further optimization. In the case of synthetic boron nitride and silicon nitride with the phase of iron hydrogen evolution is more efficient. The optimal conditions (mass of sample composites, concentration of organic chemicals and auxiliary chemicals - hydrogen peroxide or sodium ethylenediaminetetraacetate) were estimated. It has been found that production of hydrogen is the most effective in the aqueous solutions of formic acid and hydrazine with boron nitride.

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