Adsorption Of Phthalic Acid Esters And Neonicotinoid Insecticides By Pristine And Functionalized Carbon Nanotubes

As a large agricultural country,China has a large population and a large demand for food,which has led to a huge amount of plastic film and pesticide use.Phthalate esters（PAEs）,as the most common plasticizers,are easily separated from plastics and enter to the environment.Neonicotinoid pesticides（NNIs）,as a kind of emerging neuropesticides,are widely used in the treatment of pests in crops and other fields.But they are easy to remain in the environment.Adsorption is widely used in the removal of organic pollutants in the water environment.But the current adsorption researches focus on the single-compound systems,and there are few studies about multi-compounds systems.Therefore,it is of great significance to explore the adsorption research under the multi-compounds coexisting system.Carbon nanotubes（CNTs）are considered to be excellent adsorbents for organic pollutants in the environment due to their huge specific surface area and strong hydrophobicity,but they poorly disperse in water.The introduction of active groups on the surface of CNTs can improve their surface properties and improve their dispersibility.In this study,CNTs were selected as adsorbents to explore the adsorption properties of diethyl phthalate（DEP）and phthalic acid（PA）on CNTs;CNTs were further modified by carboxylation to explore the influence of synthesis conditions on the modification,and they were used as adsorbents to explore NNIs sorption.The specific research content and relative results of this paper are as follows:（1）With PA and DEP as target pollutants,and CNTs as adsorbents,through single and double solute adsorption experiments under different p H conditions,combined with energy distribution theory,the competition and substitution adsorption of DEP on CNTs by PA were analyzed.The results showed that at the same p H,the adsorption of DEP on CNTs was stronger than that of PA.For DEP,the change of the dispersion of CNTs caused by the p H variation was the decisive factor affecting its adsorption.For PA,the p H of the solution affected the surface charge of CNTs and the dissociation degree of PA,both affecting the sorption process.In the dual solute system,PA had competition and substitution effects on the adsorption of DEP on CNTs.Under different p H conditions,the degree of PA’s competition and substitution of DEP on CNTs was related to the dispersion stability of CNTs and the degree of dissociation of PA.Analysis based on energy distribution showed that although the addition of PA lead to a significant decrease in the number of available high-energy adsorption sites for DEP on CNTs,the number of available low-energy adsorption sites increased.（2）Carboxylation modification of CNTs was carried out by the microwave method,and the best synthesis conditions were determined by their adsorption results for Imi.The results showed that under the conditions of 3 mol·L^-1 nitric acid as oxidant,microwave power of 500 W,reaction temperature of 60℃,and reaction time of 60 min,the adsorption of CNTs-COOH for Imi was the highest.CNTs-COOH was used to adsorb 5 kinds of NNIs（acetamiprid,Ace;clothianidin,Clo;imidacloprid,Imi;thiamethoxam,Thim;nitenpyram,Nit）in water.Its effect was better than that of pristine CNTs,due to the carboxylated carbon tube had a larger surface area,a richer pore structure and better dispersibility.The effects of CNTs-COOH dosage,initial p H value,temperature,and anion concentration on its adsorption for NNIs were investigated.The results showed that the adsorption rate was positively correlated with the dosage of CNTs-COOH.The initial p H has little effect on the removal rate of Ace,Clo,Imi,and Thim,while Nit has a decreasing trend with the increase of p H due to the electrostatic repulsion.The change of the concentration of Cl^-and SO₄^2-has little effect on the NNIs adsorption on CNTs-COOH,but HCO₃^-inhibits the adsorption of Nit.（3）Five kinds of NNIs were selected as target pollutants and CNTs-COOH was chosen as the adsorbent.The adsorption characteristics of the 5 kinds of NNIs on CNTs-COOH in the dual solute system were analyzed by adsorption isotherm and site energy distribution theory.In the dual-solute system,except for Imi and Clo which inhibit the adsorption of Ace on CNTs-COOH,other NNIs had a certain promotion effect on each other,and Nit and Thim promote the other three NNIs more significantly.In the dual-solute system,when the coexisting NNIs had a large difference in hydrophilicity,the promotion effect between each other was more obvious.The adsorption of substances with similar hydrophilicity on CNTs-COOH was competitive under certain conditions.The NNIs adsorbed on the surface of CNTs-COOH can interact with NNIs in water to increase the adsorption capacity.But when the increased adsorption due to the interaction between NNIs was less than the adsorption reduction due to the competition between them,it exhibited an inhibitory effect.