Photocatalytic nitrate reduction by a non-metal catalyst h-BN: Performance and mechanism

It is highly desirable but challenging to control nitrate contamination using photocatalytic reduction technology over non-mental catalysts. Herein, hexagonal boron nitride (h-BN), a typical non-metal catalyst, was employed to photocatalytic denitration in water with formic acid (FA) as a hole scavenger. Compared with a mental catalyst TiO2 and a non-mental catalyst g-C3N4, h-BN obtained a more effective reduction performance with nitrate conversion of 97.16% and N2 selectivity of 95.42%. After three cyclic use, it still presented excellent reduction activity and structure stability. In the h-BN system, the initial pH had a significant effect on the nitrate reduction performance because it determined the surface charge property of the catalyst or the dispersibility in water, and the presence of anions slightly decreased the nitrate conversion process since the competitive adsorption of NO3– or NO2–. Photocatalytic denitration over h-BN was well according with the Extended-Langmuir-Hinshelwood model. By comparing the average stoichiometric ratio of consumed FA and removed NO3– (i.e. experiment value) with the theoretical value, it was determined that there were additional electrons involved in the reduction reaction in addition to CO2•- radicals, which was also supported by the quenching experiments. Moreover, CO2•- radicals were mainly responsible for the conversion of NO2– to N2. Exposed B atoms on the h-BN edges behaved as the adsorption sites of nitrogen oxide anions. This study provides a proof-of-concept demonstration of non-mental photocatalyst h-BN for more effective management of nitrate contamination.