The strong interaction and confinement effect of Ag@NH2-MIL-88B for improving the conversion and durability of photocatalytic Cr(VI) reduction in the presence of a hole scavenger.

Selectively regulating active factors in photocatalytic reactions by designing materials is one of the very important factors. Herein, we prepared spindle-like core-shell Ag@NH2-MIL-88B composites (Ag@NM-88) by a two-step hydrothermal method. The as-prepared Ag@NM-88 displayed superior photocatalytic activity for Cr(VI) reduction under LED light, compared with the activities of pure NH2-MIL-88B (NM-88) and Ag/NM-88 (Ag was deposited on NH2-MIL-88B). The core-shell structure Ag@NM-88 was not only beneficial to the absorption of light but also beneficial to the separation of photogenerated e- and h+. More importantly, it was further confirmed by active radical capture experiments and nitroblue tetrazolium (NBT) conversion experiments that the design of the core-shell structure could effectively prevent photogenerated e- from combing with O2 to form •O2-, so that photogenerated e- directly reduced Cr(VI), thereby improving the reaction rate. In addition, it could still maintain good stability after 5 cycles, indicating that the construction of a core-shell structure is also conducive to improving stability. This work provides a strategy for selectively regulating the active components of photocatalysts, and provides new insights into the relationship between interfacial charge transfer and molecular oxygen activation in photocatalytic reduction Cr(VI) systems.