Hydroxyl radicals (·OH) have been considered as one of the most important active species for many photocatalytic processes. However, the formation mechanism of free ·OH radicals is not well understood. Herein, we present our experimental evidence that the surface Brönsted acid/base sites play a vital role in the photocatalytic formation of these free ·OH radicals. In situ diffuse reflectance infrared Fourier transform (DRIFT) spectra show that the surface hydroxyl groups (Brönsted acid/base sites) on TiO₂ is responsible for the high formation of free ·OH radicals. Due to the lack of exposure of Brönsted acid/base sites, BiOCl is unfavorable for the formation of free ·OH radicals. Inspired by these findings, we further constructed Brönsted acid/base sites by grafting phosphate ions onto the BiOCl surface, which greatly enhanced the formation of free ·OH radicals. This work highlights the importance of surface Brönsted acid/base sites for the design of photocatalysts.

羟基（·OH）被认为是许多光催化过程中最重要的活性物质之一。但是，关于游离·OH自由基的形成机理尚不十分清楚。本文中，我们提供了实验证据，表明布朗斯台德酸/碱表面在这些游离·OH自由基的光催化形成中起着至关重要的作用。原位漫反射红外傅立叶变换（DRIFT）光谱显示TiO ₂的表面羟基（布朗斯台德酸/碱位）导致自由基·OH自由基的高形成。由于缺乏布朗斯台德酸/碱的暴露，BiOCl不利于游离·OH自由基的形成。受这些发现启发，我们通过将磷酸根离子接枝到BiOCl表面上进一步构建了布朗斯台德酸/碱位，这大大增强了游离·OH自由基的形成。这项工作强调了布朗斯台德酸/碱表面对光催化剂设计的重要性。