Constructing of novel phosphonate-based MOF/P-TiO2 Heterojunction Photocatalysts: enhanced photocatalytic performance and mechanistic insight
Development of high-efficiency photocatalysts for photocatalysis research has been a hotspot in recent years. Herein, the phosphate-based MOF/P-TiO2 hybrid composites (MOFx/P-TiO2) were first synthesized by phosphonate-based MOF [Cd(H2L)]n (H4L = 2,5-dimethylbenzene-1,4-diylbis(methylene) diphosphonic acid) and phosphated mesoporous TiO2 beads (P-TiO2) using a versatile step-by-step self-assembly strategy for the environment remediation. Results showed that the Cd-MOF loading content in the MOFx/P-TiO2 displays important influence on the pollutants degradation, and the hybrid materials could significantly enhance photocatalytic activity for the photo-oxidative degradation of RhB (97.6% in 25 min over MOF1.5/P-TiO2) and reduction of Cr(VI) (96.1% in 60 min over MOF0.5/P-TiO2) in comparison with the single-component Cd-MOF or P-TiO2. The enhancement of photocatalytic activity of MOFx/P-TiO2 could be mainly attributed to (i) strong light absorption capacity, and (ii) effective photogenerated charge separation and transfer through the coupled heterojunction interfaces of P-TiO2 and Cd-MOF. What's more, the results verified that matched band structure of P-TiO2 and Cd-MOF could induce a superfast Z-scheme interfacial charge transfer path. Therefore, a reasonable Z-scheme charge transfer mechanism was proposed based on the active species trapping experiments and ESR. More importantly, MOF0.5/P-TiO2 and MOF1.0/P-TiO2 possess good stability and reusability after recycling 5 times due to the high chemical stability of the Cd-MOF, P-TiO2 and heterojunctions. The present work provides a promising approach to construct the direct Z-scheme porous heterojunctions for elimination of environmental pollutants.