Effects Of Graphene Oxide And Its Derivatives On The Photolysis Of Imidacloprid

Neonicotinoids(NEOs)have become an ideal alternative to traditional insecticides and are widely used in agricultural production,urban horticulture and plant protection.Because of their small molecular weight and high water solubility,they can easily enter water environment through surface runoff and infiltration.It has been considered as an emerging pollutant and are ubiquitous in the detection of aquatic environment.In addition,graphene oxide(GO),as a typical carbonaceous nanomaterial,has been widely used in production and life,which inevitably leads to its environmental release.The abundant oxygen-containing functional groups on the surface of GO make it easy to disperse in water.Therefore,it has a great potential to coexist with NEOs in water,which may affect the environmental behavior and fate of NEOs.Specifically,GO entering the environmental media will undergo further transformation under specific conditions,causing changes in the physicochemical properties of the nanoparticle,which may lead to more complex interactions with coexisting contaminants.In this study,the potential transformation pathways of GO in the environment were investigated by treating GO with ozone(a commonly used disinfectant in wastewater treatment systems)and ultraviolet(UV)irradiation(wavelength>290 nm)respectively,and the differences between GO and its derivatives in terms of optics,functional groups,morphological structure,stability and aggregation properties were analyzed by various material characterization means.Imidacloprid(IMD),which has the highest market share of NEOs,was selected as the representative insecticide.The photochemical reaction and various research methods were used to reveal the influence of GO and its derivatives on the photolysis process and mechanism of IMD,and the photolysis pathway of IMD was clarified by high resolution mass spectrometry.The aquatic toxicity of photolysis products of IMD was analyzed using ECOSAR software.Finally,the influence of different environmental conditions on the photolysis reaction was discussed.The main conclusions are as follows:1.GO has the potential to undergo further transformation under environmentally relevant conditions,and the physicochemical properties of the derivatives produced are significantly different from those of the parent.Specifically,the light-treated GO(reduced graphene oxide,RGO)shows an increase in C/O ratio and light absorption intensity,obvious wrinkles and fragmentation on the morphology,loss of most of the O-functional groups on the surface,the increase on the defective structure,and the decrease in electronegativity and suspension stability.The ozone-treated GO(oxidized graphene oxide,OGO)is introduced more Ofunctional groups,which leads to the expansion of layer folds of original GO.It also exhibits reduced light absorption intensity and defect structure,as well as enhanced surface electrical susceptibility and hydrophilicity.2.The presence of GO and its derivatives significantly inhibits the photodegradation of IMD,and the inhibition degree is positively correlated with the C/O ratio of the material,following the order of RGO>GO>OGO.The mechanism mainly includes two aspects.On the one hand,the special sp2 π-conjugated structures contained in the above three graphenebased nanomaterials(GNs)give them strong light-shielding ability,thus competing with IMD molecules for limited photons and inhibiting the direct photolysis of coexisting IMD.On the other hand,the GNs can produce reactive oxygen species(ROS)under UV irradiation and thus promote the indirect photolysis of IMD.Between these two mechanisms,the former plays a dominant role.The presence of GO and OGO rich in O-functional groups alters the photolytic pathway of IMD and induces the production of more toxic intermediates.3.The influence of environmental conditions on the photolysis of IMD mediated by the GNs is largely determined by the direct photolysis process of IMD.The pH does not have significant effect on the photolysis of GNs-mediated IMD,and the mechanisms of coexisting ions on the photolysis of IMD mediated by the GNs include light-shielding effect,changes in suspension stability of the GNs,adsorption affinity and photosensitive effect.Additionally,the mechanism of influence varies for anions and cations.Anions affect the photodegradation of IMD mediated by the GNs mainly through light-shielding effect,while cations can also affect the photolysis process through their photosensitive effect and adsorption by the GNs.The above results show that GO and its derivatives can inhibit the photodegradation of IMD in aquatic environment and change the photolysis pathway of IMD,which may increase the product toxicity.It can be concluded that carbonaceous nanomaterials have significant effects on the environmental behavior and fate of coexisting NEOs in environmental media.Overall,the findings of this study provide a theoretical basis for elucidating the interfacial processes and interaction mechanisms between carbonaceous nanoparticles and NEOs,observing and assessing the environmental behaviors and risks of NEOs and offer references for scientific formulation of relevant environmental management policies.