Microwave-assisted synthesis of porous heterojunction ZnO/ZnMn2O4 microrods for efficient degradation of organic pollutants

Abstract

The ZnO/ZnMn 2 O 4 heterojunction photocatalysts are synthesized through microwave-assisted hydrothermal route, and show high photocatalytic activity towards methylene blue and methyl orange under UV light irradiation. • Microwave-assisted hydrothermal method is used to obtain porous heterojunction ZZMO. • The active species in the photocatalytic system are the O 2 − and h + by trapping experiments. • The enhanced catalytic activities of ZZMO result from the formation of n-p junction. • A maximum degradation of MB is estimated as ∼100% for optimized ZZMO within 60 min. • Photocatalytic degradation mechanism of hetero ZZMO towards organic dyes is proposed. Photocatalytic activity of a semiconductor with low band gap has been greatly suppressed due to the high recombination rate of photogenerated charge carriers. The most economic and efficient remedy is to construct a heterojunction to enhance the transfer/separation of interfacial charge carriers. Inspired by this, the rod-like ZnO/ZnMn 2 O 4 composite heterojunction photocatalysts are synthesized via a facile template-free microwave-assisted hydrothermal route. The photocatalytic activities of the as-prepared samples are evaluated by the photocatalytic degradation of methylene blue and methyl orange under UV light irradiation. The optimized ZnO/ZnMn 2 O 4 demonstrates enhanced photocatalytic efficiencies towards degradation of methylene blue and methyl orange, which are about 4.3 and 3.0 times higher than those of pure ZnO, respectively. Furthermore, the composite could still maintain good photocatalytic activity for photocatalytic methylene blue even after four recycles. The active species in the photocatalytic system are·O 2 − and h + , which can be confirmed by the trapping experiments. The enhanced photocatalytic activity of ZnO/ZnMn 2 O 4 composite may result from the formation of n-p junction, which supports the generation of·O 2 − and h + . More significantly, the intrinsic photocatalytic degradation mechanism of ZnO/ZnMn 2 O 4 composite towards organic dyes is tentatively proposed.