Construction of BiIn2 quantum dots-modified BiOBr heterojunctions and their visible light-driven photocatalytic performance and mechanism

Bismuth oxybromide (BiOBr), as a typical layered visible light-responsive photocatalyst, has received widespread attention in the field of environmental pollutant degradation due to its suitable energy band structure and built-in electric field between layers. However, pure BiOBr still has key scientific problems such as limited visible light absorption range, fast photogenerated electron-hole recombination rate, and insufficient surface active sites, which seriously restrict its practical application. In order to solve the above bottleneck, this study used the solvothermal method for the first time to form BiIn 2 QDs/BiOBr composites by in-situ nucleation in an ethylene glycol reducing environment. The existence and chemical state of BiIn 2 QDs were confirmed by TEM and XPS. UV-Vis DRS shows that the absorption edge of BiIn 2 QDs/BiOBr composite is red-shifted from 409   nm to 417   nm, and the absorption intensity is enhanced. The quenching and peak broadening of the PL spectrum indicate that radiative recombination is significantly reduced. The transient SPV test shows that the BiOBr carrier lifetime is 0.43 μs, while the BiIn 2 QDs/BiOBr composite has no obvious attenuation and the lifetime is greater than 800 μs, confirming that the separation efficiency of photogenerated carriers has been greatly improved. Steady-state SPV further observed a significantly enhanced photovoltage signal and a red shift of the photoelectric response spectrum. Liquid Chromatography-Mass Spectrometry (LC-MS) was used to study the degradation pathway of ciprofloxacin, showing that h + targets HOMO (piperazine N/aromatic ring, leading to pathway I), and •O 2 - targets LUMO (F/carboxylic acid, leading to pathway II). Density functional theory (DFT) calculations further constructed a periodic model of BiIn 2 quantum dots modified BiOBr to study charge transfer characteristics, carrier spatial distribution and local bonding environment changes. This study shows that the localized surface plasmon resonance (LSPR), induced oxygen vacancies (OVs) and enhanced built-in electric field of BiIn 2 QDs work synergistically with the BiOBr layered structure to overall improve the photocatalytic efficiency of BiIn 2 QDs/BiOBr composites. This work provides new design ideas and theoretical basis for the development of efficient and stable bismuth-based heterojunction photocatalysts.