Insights into bridging hydroxyl groups to enhance the efficient-generation of hydroxyl radicals for microplastic decomposition

Developing efficient microplastics (MPs) treatment technologies is a key approach to addressing the challenge of MPs pollution. Hydroxyl radical (•OH) is a crucial active species in the MPs photodegradation. Herein, we propose the strategy of constructing bridging-hydroxyl groups (-OH B ) on the surface of BiOCl photocatalyst containing oxygen vacancies to boost the production of •OH and efficiently decompose MPs. Our findings revealed that the OH B15 /BOC-OV system attained the highest steady-state concentration of •OH, exhibiting the best degradation effects on polystyrene-MPs (PS-MPs). The weight-loss rate was approximately twice that of other systems and could increase to 80 % in 48 h. Meanwhile, the changes of the physicochemical properties of PS-MPs under •OH attack, including its micro-structure and functional groups, molecular-weight, and molecular chain structure, was thoroughly explored. Theoretical calculations results demonstrated that -OH B extended the O-H bond length of H 2 O through directly bonding H atoms in H 2 O, lowering the energy-barrier of bond-breakage and promoting the formation of •OH. Additionally, the results of gas chromatography-mass spectrometry and acute toxicity studies indicated that the primary products of PS-MPs were predominantly non-toxic cycloalkane and branched alkanes. Above all, -OH B served as a “bridge” mediating the electron transfer from MPs to the photocatalyst surface, leaving MPs in an electron-poor state and increasing the probability of •OH targeted attack. This work not only offers advanced technology to address MPs pollution but also elucidates the evolution of MPs' physicochemical properties under • OH attacks, thereby furnishing data support for assessing the ecological risks associated with MPs treatment processes.