Photochromic−activity relationship insights for boosting C(sp3)-H Bonds activation in the BiOBr1-xIx colloid ultrathin nanosheets

Converting volatile organic compounds like ethylbenzene through CH bond activation to high-value organic intermediates under milder, energy-efficient conditions offers a sustainable approach to chemical synthesis and environmental protection. However, the activation of C(sp³)-H bonds in ethylbenzene poses significant challenges due to their high bond strength and low polarity. Here, we developed iodine-doped photochromic BiOBr_1-xI_x ultrathin nanosheets as photocatalysts to enhance the photooxidation process under visible light. Iodine doping optimizes the energy band structure and enriches the generation of oxygen vacancies of BiOBr_1-xI_x nanosheets, endowing pronounced photochromic behavior upon 450 nm light irradiation. The photochromism induced colored state effectively reduces energy waste by suppressing the recombination of photogenerated carriers, thereby increasing solar energy utilization. As the photochromic property of BiOBr_1-xI_x nanosheets intensifies, the carriers’ separation efficiency improves and thus results in significantly enhanced photooxidation activity of the CH bonds, exhibiting a strong relationship between the photochromic and photocatalytic properties. The photochromic-related photocatalytic coupling and oxidation reactions of ethylbenzene were efficiently realized by BiOBr_0.98I_0.02 nanosheets catalytic performance approach 7 times compared to pristine BiOBr. Under 450 nm light irradiation for 15 h, the turnover number (TON) of ethylbenzene reaches 274,000 µmol·g⁻¹, with acetophenone selectivity consistently exceeding 99 %. The apparent quantum yield (AQY) at 450 nm is calculated to be 1.3 %. This work highlights a green and sustainable strategy to design new photocatalysts for CH bonds activation by manipulating the photochromism.