Photocatalytic Aging Of Microplastics And Its Interaction With Methyl Orange

In recent years,microplastics have been recognized as an emerging pollutant and have attracted much attention worldwide,not only attributed to its physical hazards,but mainly to the fact that it can interact with other pollutants.Microplastics and non-adsorbed pollutants can be easily ingested by Marine animals and accumulate in their bodies,causing further impacts on the surrounding ecosystems.Microplastics will undergo different degrees of aging processes after entering the environment,such as mechanical wear,photoaging and chemical aging,which more or less change the adsorption capacity of microplastics to pollutants.Among them,photocatalytic aging can significantly improve the degradation rate of microplastics by generating hydroxyl free radicals（·OH）and superoxide free radicals（·O₂^-）,which has caused widespread concern.In this paper,PVC microplastics with excellent physicochemical properties and widely used were subjected to UV light aging experiments,combined Ti O₂/O₃/UV aging experiments and combinedα-Fe OOH/O₃/UV aging experiments by coexisting with photocatalysts titanium dioxide（Ti O₂）,goethite（α-Fe OOH）,bismuth tungstate（Bi₂WO₆）and bismuth oxybromide（Bi OBr）under laboratory conditions.Scanning electron microscopy,Fourier transform infrared spectroscopy,X-ray diffraction,Zeta potential and other techniques were used to characterize the microplastics before and after aging.Combined with adsorption kinetics and adsorption isotherm model,the adsorption characteristics of methyl orange（MO）of microplastics before and after aging were studied,and the change characteristics and formation causes of PVC adsorption capacity under different aging processes were discussed.This study provides a theoretical basis for the migration and transformation of microplastics carrying organic pollutants in the environment,and provides data support for the toxicological analysis of microplastics in the water environment.Key findings were as follows:（1）During the co-aging process of PVC and photocatalyst,the four photocatalysts had a certain increase in the aging rate of PVC,and the weight loss rate from large to small was PVC-T₂（2.07%）>PVC-G₂（1.92%）>PVC-Bb₂（1.62%）>PVC-Bt₂（1.53%）,in which the weight loss rate coexisting with titanium dioxide was 1.43 times that of pure UV photoaging（1.4%）.At the same time,all kinds of photocatalytic aging promoted the appearance of cracks and gullies on the surface of PVC,accompanied by the generation of new oxygen-containing functional groups.The results of adsorption kinetics and adsorption isotherms showed that the adsorption kinetic data of MO on the aged microplastics were well fitted by the second-order kinetic model.The adsorption equilibrium was reached after 48 hours,and the adsorption capacity increased after aging.The Freundlich model can well fit the adsorption isotherm data,and the adsorption process is mainly controlled by electrostatic and partition interactions.（2）The mechanism of PVC in the combined aging process of Ti O₂/O₃/UV was explored.With the progress of aging,the surface fragmentation of PVC particles deepened,the particle size decreased significantly,and two additional absorption bands appeared at 1742cm^-1（C=O）and 3445cm^-1（O-H）.At the same time,the Zeta potential value also changed from-31.68 to-3.80 with the increase of aging time,which reduced the electrostatic repulsion between them.From the adsorption kinetics and adsorption isotherms of MO on PVC,the original PVC was better in accordance with the first-order kinetic equation,while the combined aging microplastics could be well fitted by the second-order kinetics,and the R² value was up to 0.98.The difference between the experimental and predicted adsorption amount was small.Throμgh the simulation of adsorption isotherms,Freundlich isotherms can better fit the adsorption of methyl orange on microplastic PVC,indicating that the interaction between methyl orange and microplastic PVC is a multi-layer adsorption on a non-uniform surface,which is affected by chemical and physical adsorption processes at the same time.The adsorption mechanism is mainly based on partition and electrostatic interaction.（3）After the combined aging ofα-Fe OOH/O₃/UV,more cracks and concavity appeared on the surface of microplastics.Fourier transform infrared spectroscopy（FTIR）showed that the number of oxygen-containing functional groups on the surface of microplastics increased significantly after aging,and the carbonyl index（CI）increased with aging time.X-ray diffraction（XRD）showed that the crystallinity of the aged microplastics showed a decreasing trend.The results of adsorption kinetics and adsorption isotherms of MO on PVC showed that the adsorption kinetics data of MO on microplastics could be well fitted by the quasi-second-order adsorption kinetic model,and the Freundlich adsorption isotherm model had a better fit than Langmuir adsorption isotherm model and Henry adsorption isotherm model.The results of adsorption experiments show that the aged microplastics have stronger adsorption capacity than the virgin microplastics,but the effect is not significant enoμgh due to the insufficient aging time.According to the adsorption data and characterization results,the adsorption of MO on microplastics is mainly chemistry adsorption,and electrostatic force interaction and functional group complexation also play a role in the adsorption process.Figure[36]Table[15]Reference[148]...