Graphite carbon nitride nanosheets decorated with ZIF-8 nanoparticles: Effects of the preparation method and their special hybrid structures on the photocatalytic performance

A highly efficient ZIF-8/g-C₃N₄ photocatalyst was prepared by a facile ultrasonic in-situ method. The structure-property relationship of ZIF-8/g-C₃N₄ composite was analysed by various characterization techniques. The comprehensive study illustrated that ZIF-8 served as an adsorbent to capture the substrates in the contaminated solution and increased the contact possibilities of the active species and substrates. The formation of ZIF-8/g-C₃N₄ hybrids helped to significantly enhance visible light absorption and facilitate charge transfer and separation of the photogenerated electron-hole pairs, eventually improving the photocatalytic efficiency. Meanwhile, compared with ZIF-8/g-C₃N₄ composites obtained by incipient wetness impregnation method, ultrasonic in-situ synthesis contributed to hindering the aggregation of g-C₃N₄ nanosheets and simultaneously promoting ZIF-8 well dispersed on the surface of g-C₃N₄ nanosheets. The synergistic effect of preparation method and special hybrid structure was studied in-depth and could significantly enhanced photocatalytic activity and stability for the degradation of organic pollutants (such as tetracycline, rhodamine B and methyl orange) under visible light irradiation. The reaction rate constant K values of optimal ratio sample for degradation of TC, RhB and MO were 0.039 min⁻¹, 0.034 min⁻¹ and 0.012 min⁻¹, respectively 1.69, 3.96 and 4.10 times as big as that of pure g-C₃N₄. Meanwhile, the photoresponse current of optimal ratio sample was 3.3 μA/cm², around 4.73 times as big as that of the pure g-C₃N₄. A reasonable photocatalytic mechanism was proposed by the photoelectrochemical experiments and the controlled experiments using radical scavengers.