Mechanisms Of Aging Effects On The Adsorption Of Ciprofloxacin In Aqueous Humor By Typical Nanoparticles

Plastic is a man-made material that is widely used due to its low price,durability,light weight and ease of production.Most plastics are directly discharged into the water environment,causing serious environmental pollution.Not only that,the plastic that enters the water environment will be broken into microplastics and even Nanoplastics(NPs)by physicochemical and other effects.In addition,the use of consumer products is also an important source of NPs in nature,which has greatly increased the amount of NPs in the water environment and caused a series of pollution problems.Biochar(BC)is a carbon-rich,porous,pyrolytic carbonaceous material with important applications in energy,environment,and agriculture.Biochar applied to the environment will gradually undergo aging and weathering effects over time,resulting in the decomposition of lumpy biochar into nano-biochar(NBC).In addition,during the production and use of biochar,NBCs are usually released,and these NBC particles enter the water bodies through migration and diffusion,especially with the widespread use of biochar,leading to the accumulation of more NBCs in the water bodies,thus posing certain ecological risks.NBCs and NPs entering the environment will undergo weathering,UV radiation and biological aging under natural reactions,which will significantly change their surface morphology and physicochemical properties,thus leading to changes in the migration and adsorption behavior of these nanoparticles in the environment and causing ecological risks that cannot be ignored.Therefore,the enrichment and adsorption of pollutants by aging nanoparticles have become the focus of research on new pollutants in the aquatic environment,and it is particularly important to study their adsorption behavior and mechanism of action under aging.In this study,wheat straw nano-biochar(WSNB)was collected using a combination of ultrasonication,sedimentation and centrifugation,and polystyrene nanoplastic(PSNP),which is more widely used,was selected as the research object.Combining the results of surface morphology and microstructure analysis and characterization of the materials before and after aging,the effects of aging on the adsorption of antibiotics by WSNB and PSNP and the mechanisms were systematically investigated.In addition,ciprofloxacin(CIP),a typical antibiotic commonly found in water bodies,was selected as the target,and a photochemical reaction apparatus was used to simulate UV irradiation while controlling different p H,salinity and dose to determine the effects of environmental factors on the process.The above study contributes to a better understanding of the environmental behavior of nanoparticles coexisting with organic pollutants in water bodies.The main findings of this thesis are as follows.(1)A 360 W mercury lamp was used to continuously irradiate PSNP for 10 h(the treated plastic was noted as PSNP-UV)to simulate and accelerate the natural aging process of NPs,and to investigate the changes of physicochemical properties of NPs by UV aging and its effects on the adsorption behavior and mechanism of CIP.It was shown that PSNP showed obvious yellowing after UV irradiation,the surface became rough and disordered and introduced a large number of oxygen-containing functional groups,such as C=O,—C—O,O—C=O,etc.The particle size was slightly reduced,the carbonyl index increased from 0.56 to 1.15,the surface hydrophilicity increased and the surface negative charge was enhanced,and these changes of physicochemical properties affected the adsorption behavior of NPs on CIP.The adsorption processes of PSNP and PSNP-UV on CIP were consistent with the quasi-secondary kinetic model,indicating that the adsorption processes were mainly controlled by chemical interactions.The results of the adsorption kinetics experiments showed that the adsorption rate increased sharply at the initial stage and reached equilibrium after 24 h.The equilibrium adsorption capacity of PSNP-UV increased from 38.39 mg/g to 46.48 mg/g when the CIP concentration was 6 mg/L.The results of the isothermal adsorption experiments indicated that the whole adsorption process of PSNP and PSNP-UV on CIP was a chemisorption-driven multilayer adsorption process.PSNP-UV showed higher overall adsorption performance than PSNP,which may be related to the larger specific surface area,stronger hydrophilicity and the increase of oxygen-containing functional groups generated by aging.The analysis of Fourier infrared spectroscopy(FTIR)and X-ray photoelectron spectroscopy(XPS)results showed that no new covalent bonds were generated during the adsorption process,the role of hydrogen bonding andπ-πinteraction in the adsorption process was confirmed,and the new oxygen-containing functional groups on the surface of PSNP-UV played an important role in the adsorption process.Also,the solution p H and salinity had a large effect on the adsorption behavior,and the adsorption of both PSNP and PSNP-UV on CIP was maximum at the solution p H of 6.The adsorption increased gradually with the increase of Na~+strength of the coexisting ions in the solution,and the adsorption was inhibited when the Na~+strength was greater than 0.2 mol/L.The total adsorption of both PSNP and PSNP-UV on CIP increased with the gradient of adsorbent dose,but the adsorption capacity on unit NPs decreased subsequently.(2)The WSNB suspensions were prepared using repeated sonication and centrifugation.The adsorption kinetics of WSNB and WSNB-UV on CIP were in accordance with the quasi-secondary kinetic model(R~2>0.977),indicating that the adsorption process was mainly chemisorption.the isothermal adsorption mechanism of WSNB on CIP was more in accordance with the Langmuir model,indicating that the process was monomolecular layer adsorption.In contrast,the Temkin model could better fit the adsorption process of WSNB-UV on CIP(R~2>0.943),and the adsorption equilibrium constant k _T of WSNB-UV(0.60 L/mol)was larger than that of WSNB(0.39 L/mol),indicating that WSNB-UV had a stronger binding capacity for CIP.In addition,the increase in solution p H under acidic conditions was more favorable for the adsorption of CIP by WSNB,but when the p H transitioned to alkaline,the presence of CIP in the form of anions repelled each other with NBC,which also had a negative charge,thus inhibiting the adsorption and leading to a decrease in the adsorption amount,which proved the existence of electrostatic interactions.Dose-effect studies showed that WSNB-UV showed better removal of CIP than WSNB when the NBC dose was increased from 5 mg TOC/L to 25mg TOC/L.The adsorption mechanisms involved in CIP on WSNB and WSNB-UV include pore filling,electrostatic gravitational force and hydrogen bonding.