Adsorption Behavior And Mechanism Of Hydrophilic Antibiotics By Microplastics In Water Environment

The composite pollution formed by the combination of Microplastics（MPs）and Hydrophilic pollutants（HOCs）in natural water environments has attracted widespread attention due to its potential toxicity to the human body.However,the current research on the adsorption of HOCs by MPs mainly focuses on the macroscopic adsorption behavior and adsorption mechanism,and lacks the research on the adsorption mechanism at the molecular level and the corresponding quantitative analysis.At the same time,studies have shown that heavy metals(such as Cu²⁺,Pb²⁺,etc.)produced by industrial pollution will coexist with antibiotics in some water bodies,and will change the environmental behavior of MPs after accumulating on MPs.In view of the fact that the current research on the action behavior and mechanism of microplastics adsorbing hydrophilic antibiotics in the water environment is still in the qualitative analysis of the apparent mechanism,this study aims to study the effect of typical MPs（Polystyrene,PS）on ciproza The adsorption behavior and mechanism of Ciprofloxacin（CIP）and Ofloxacin（OFL）were studied to explore the adsorption mechanism of original and aged PS on CIP and OFL,and to quantitatively analyze the contribution of different mechanisms to the adsorption process under different conditions.In addition,the influence and internal principle of heavy metals under different conditions on the adsorption of antibiotics by PS were further investigated.Below are key research findings:（1）The specific surface area of PS after aging treatment was significantly increased（original PS:0.162 m²/g;aged PS:0.627 m²/g）,oxygen-containing groups increased,and hydrophilicity was also significantly enhanced.The amount is higher than the original PS.The adsorption kinetics of pristine PS to antibiotics conformed to pseudo-first-order kinetics,while aged PS was more in line with pseudo-second-order kinetics.The Linear model can well describe the adsorption isotherms of pristine and aged PS to antibiotics,and the Kd values are as follows:aged PS-CIP（15.985）>aged PS-OFL（14.657）>pristine PS-CIP（14.234）>pristine PS-OFL（13.699）.PS has a strong p H dependence on the adsorption process of antibiotics.Coexisting ions such as Ca²⁺and Mg²⁺will inhibit the adsorption of antibiotics by PS.（2）Through X-ray photoelectron spectroscopy（XPS）and Fourier transform infrared spectroscopy（FTIR）studies,it was found that there are mainlyπ-πconjugation,hydrogen bond（HB）and electrostatic adsorption（EA）three mechanisms involved.The results of quantitative analysis of the adsorption mechanism showed that the contribution rate of the three adsorption mechanisms to the adsorption process varied with the change of p H,and the adsorption process could be divided into the following four stages:（1）When 3.0<p H<5.0,both PS and antibiotics carried With positive charge,EA is suppressed,and the contribution rate of HB to adsorption exceeds 60%;（2）When 5.0<p H<8.0,PS starts to carry negative charge,the contribution of EA increases to about 50-60%,and the contribution rate of HB decreases;（3）At 8.0<p H<10.0,both PS and antibiotics carry negative charges,the contribution of EA and HB to the total adsorption decreases to 30-40%and 25-40%,respectively,while theπ-πconjugation increases to 20-45%;（4）When 10.0<p H<12.0,the contribution rate of EA and HB to the adsorption is extremely low,and the contribution rate ofπ-πconjugation reaches 90-100%.Since CIP has a higher dissociation coefficient（PKa;CIP:PKa=6.09;OFL:PKa=5.77）than OFL,there are more CIP+/CIP±molecules in the solution under the same conditions,which can produce stronger EA with PS effect.In addition,there is an additional secondary amino group（-NH-）in the CIP molecule,which can form an additional negative charge-assisted hydrogen bond（CAHB）with COO-on the PS surface,enhancing the affinity of PS for CIP.Therefore,under the same conditions,the adsorption amount of original and aged PS to CIP is always slightly higher than that of OFL.（3）PS can adsorb Cu²⁺and Pb²⁺dissolved in water,and the adsorption capacity of aged PS is also significantly stronger than that of pristine PS.When PS adsorbed antibiotics and heavy metals at the same time,the competition between heavy metals and antibiotics inhibited the adsorption of antibiotics by PS,and heavy metal ions could also form complexes with antibiotics to produce steric hindrance to further inhibit the adsorption process.When PS first adsorbs heavy metals and then adsorbs antibiotics,low-concentration Cu²⁺（0-5 mg/L）forms PS-Cu-Antibiotic complexes through bridging to promote the adsorption of PS to antibiotics,while high-concentration Cu²⁺（5-10 mg/L L）A large number of PS-Cu-Antibiotic complexes formed under the conditions will instead produce steric hindrance to hinder the adsorption.However,Pb²⁺loaded on PS occupied the adsorption sites on the surface of microplastics and could not produce bridging effect,so Pb²⁺always inhibited the process of PS adsorption of antibiotics.As an emerging pollutant,MPs exist in the environment and can absorb and carry organic/inorganic pollutants in the water body to produce a compound pollution effect,thereby causing potential ecological environmental hazards and even threats to human health.Therefore,on the basis of studying the adsorption behavior and apparent adsorption mechanism of microplastics on antibiotics,this study deeply studied the adsorption mechanism at the molecular level and carried out a quantitative analysis of the adsorption mechanism.It is of great significance and provides a theoretical basis for clarifying the environmental chemical behavior of MPs.