Stable self-assembly AgI/UiO-66(NH2) heterojunction as efficient visible-light responsive photocatalyst for tetracycline degradation and mechanism insight

UiO-66(NH2) is a fascinating visible-light responsive amino functionalized zirconium-MOF. However, its photocatalytic performance is less satisfactory because of the disappointing separation rate of electron-hole pairs and the poor solar energy utilization ability. In this research, an unique AgI/UiO-66(NH2) heterojunction was constructed via a facile ion exchange precipitation method to reinforce the photocatalytic performance of UiO-66(NH2). The photocatalytic performance was evaluated by degrading tetracycline (TC) under visible light. The optimal TC removal rate was obtained by AgI(30% wt)/UiO-66(NH2) which was 3.8-fold of UiO-66(NH2) and 2.1-fold of AgI. TOC removal rate of AgI(30% wt)/UiO-66(NH2) reached 65.6% after 40 min irradiation which was better than pure UiO-66(NH2) (16.2%) and AgI (22.4%). The detailed intermediates and pathway of TC degradation were also illustrated. According to the results of characterization, it was determined that Ag nanoparticles (small amount) were occurred in the initial stage of photocatalytic process, which resulted in the transformation from AgI/UiO-66(NH2) type II heterojunction to AgI/Ag/UiO-66(NH2) Z-scheme heterojunction. Benefiting from the novel heterojunction and the Surface Plasmon Resonance (SPR) Ag, the redox capacity of photogenerated electron-hole pairs was enhanced and the photocorrosion of AgI was significantly suppressed, resulting in the excellent photocatalytic performance of AgI/UiO-66(NH2) composites. Moreover, the SPR Ag also resulted in the expansion of light absorption range. Besides, considerable active sites and depressed recombination of electron-hole pairs also exerted vital influence on enhancing photocatalytic activity. This work illustrates the great application potential of AgI/UiO-66(NH2) heterostructure photocatalyst in water remediation and provides a new insight in optimizing UiO-66(NH2).