Dual microenvironment modulation via carbon dots incorporated into metal-organic frameworks for photocatalytic...

Based on interfacial interactions, heterostructure photocatalysts were rationally designed to achieve efficient separation of photogenerated charge carriers, which is essential for enhancing photocatalytic hydrogen evolution. Carbon dots (CDs) hold considerable promise in catalysis; however, their pronounced aggregation tendency and strong dependence on the surface environment pose critical challenges that impede further progress in this field. In this work, two types of carbon dots, namely carboxyl-functionalized (CA-CD) and amino-functionalized (CP-CD), were encapsulated into Ti-MOF-R (R means functional groups, where R = -H, -NH₂, -Br, -NO₂) to construct CDs@Ti-MOF-R heterostructure. The internal pores of Ti-MOF provide highly dispersed anchoring sites for CDs, serving as a primary microenvironment that alleviates the aggregation-induced decline in catalytic activity. The distinct electronic substituents introduced on the Ti-MOF linkers create a microenvironment around the CDs. This microenvironment modulates the interfacial electron transfer between Ti-MOF-R and CDs, leading to a differentiated catalytic activity in the order of -NH₂ > -Br > -H > -NO₂. Among them, the CA-CD@Ti-MOF-NH₂ achieved a hydrogen evolution rate of 950 μmol g^-1·h^-1, which is 20 and 307 times higher than those of CA-CD@Ti-MOF and Ti-MOF, respectively. The substituent groups of the MOF affect charge transfer at the MOF-CD interface. Notably, interfacial amide bonds (Ti-N‧‧‧H-O-C) are formed between the -COOH groups of CA-CD and the amino groups of Ti-MOF-NH₂, providing an efficient pathway for the separation and transport of photogenerated electron-hole pairs and thereby enhancing charge migration efficiency. By modulating the electronic microenvironment of Ti-MOF via diverse functional ligands, this work clarifies the intrinsic structure-activity relationship of CD@Ti-MOF hybrids and provides a feasible ligand engineering strategy to fabricate low-cost, high-efficiency photocatalysts for hydrogen evolution.