Temperature-responsive polymer-tethered Zr-porphyrin MOFs encapsulated carbon dot nanohybrids with boosted visible-light photodegradation for organic contaminants in water

Zirconium-based porphyrin metal–organic frameworks (MOFs) have attracted extensive attention in the photocatalysis because of their considerable specific surface area, powerful visible light efficiency and semiconductor properties. However, the rapid charge recombination and self-aggregation limit their applications. Here, porphyrin-based Zr-MOF (PCN-222) nanohybrids (CDs@PCN-222@PNIPAM) as an efficient hydrophilic photocatalyst were fabricated by encapsulating various carbon dots (CDs) into PCN-222 nanopores with surface wettability modification by catechol-terminated thermo-responsive PNIPAM having various chain lengths. Due to the electron collecting effect of the nitrogen-doped CDs (N-CDs) and their synergistic effect with PCN-222, the photocatalytic performance of the prepared nano-hybrid photocatalyst were significantly improved. Furthermore, the introduction of hydrophilic polymer with moderate molecular weight effectively enhanced the transfer efficiency of photo-generated charges and the surface wettability of photocatalyst, and improved the water dispersibility of catalyst so that effectively promotes the enrichment and catalytic conversion of water-soluble target pollutants around the active site of the photocatalyst. The removal efficiency of RhB and tetracycline (TC) under visible light irradiation reached almost 100 % and 90.93 % in just 20 min, respectively. In addition, polymer-functionalized Zr-MOF-based nanohybrids revealed an interesting temperature-response switching behavior for the photocatalysis. The study on the catalytic mechanism and degradation pathways of TC showed that the h+ plays a major role in the degradation process, and other reactive species are also involved in the further mineralization of pollutants. This work provides a new insight for the functional modification of MOFs and the design of high efficiency photocatalyst.