Insight into the Hydrogen Bond-Assisted Base-Catalytic Hydrolysis of Chloramphenicol on ZnO under Limited Moisture Conditions

Engineered ZnO nanoparticles (nano-ZnO), extensively utilized in agriculture, have accumulated in soil, potentially causing substantial environmental impacts. Metal oxide-mediated hydrolysis of contaminants under limited surface moisture conditions has attracted increasing attention due to its similarity to the natural soil environment. While the nonaqueous catalytic hydrolysis mechanisms differ significantly among varying metal oxides, this warrants further investigation to gain a new understanding of these processes. In this study, the nano-ZnO, exposed to atmospheric humidity conditions, exhibited strong surface basicity (pH > 9.0). It performed extremely strong catalytic hydrolysis activity on chloramphenicol (CAP) antibiotic, achieving a half-life of 3.3 h at the optimal surface moisture content (∼2.9 wt %), which is 7-347 times faster than previously reported acid-catalytic processes by other minerals. A novel nonaqueous catalytic hydrolysis mechanism is proposed, namely, the hydrogen-bond-assisted base catalysis by synergistic effects of surface lattice oxygen and ≡Zn-OH. Hydrogen-bonding significantly reduced the hydrolysis activation energy of base-catalysis. The drought nano-ZnO also demonstrated superior catalytic hydrolytic activities to other contaminants and showed effectiveness in actual soil, suggesting its unignorable environmental implications. This study highlights the superior catalytic hydrolysis activity of the engineered nano-ZnO released into field soil and adds new understanding about the nonaqueous catalytic hydrolysis mechanisms and processes in natural soil.