Co-Adsorption Behavior And Mechanism Of TiO₂ NPs And Tetracycline/Cadmium Onto Different Characterization Surfaces

Nanoparticles?NPs?in the environment are gradually becoming an emerging pollutant.In the actual environment,water-soluble pollutants,nanoparticles,and environmental surface coexist and form a new pollution form.The interaction between NPs,pollutants,and solid surface in the environment is of great significance for predicting and evaluating the behavioral characteristics and biological effectiveness of NPs and pollutants in the environment.This study investigated the co-adsorption and the interaction among nano-titanium dioxide particles?TiO₂ NPs?,tetracycline?TC?,and cadmium(Cd²⁺)on the solid surface with different characteristics?zeolite,coconut shell carbon and magnetized kaolin?.Systematically explored the interaction mechanism among NPs-organic/heavy metal pollutants-environmental medium by comparing the surface characteristics of environmental medium before and after adsorption in the single and composite systems.The purposes of the research are to provide a theoretical basis for an in-depth understanding of the adsorption behavior and interaction of NPs and organic/inorganic pollutants on solid surface in the coexistence environment and to evaluate the behavior characteristics and biological effectiveness of NPs and pollutants in the coexistence environment.The main results are as follows:?1?On the negatively charged clay minerals?zeolite,Zeo?surface,the co-adsorption behaviors between organic/inorganic pollutants(TC/Cd²⁺)and TiO₂ NPs in the composite system were mutual antagonism,that is,the mobility of the pollutants and TiO₂ NPs were increased in the coexistence systems.The Sips model could describe the the adsorption of Cd²⁺and TiO₂ NPs on Zeo in the single and composite systems.Compared with the single Cd and single TiO₂ NPs system,the theoretical maximum adsorption capacity?Qm S?of Cd²⁺and TiO₂ NPs in the Cd+TiO₂NPs composite system was reduced by 8.75%and 23.33%,respectively.The antagonism between Cd²⁺and TiO₂ NPs in the Cd+TiO₂ NPs composite system was more obvious in the acidic environment at low temperature.The characterization results confirmed that the antagonism between TiO₂ NPs and Cd²⁺was caused by the competing for adsorption sites?-OH and the Si-O/Al-O bond broken by hydrolysis at the edge of the Zeo structure?.In addition,the filling and blockage of the pore by Cd²⁺and TiO₂ NPs also led to a decrease in the adsorption of Cd²⁺and TiO₂ NPs in the composite system.The TiO₂ NPs adsorbed on Zeo in the composite system will provide some new electrostatic attraction sites?-OH?for Cd²⁺.The Cd²⁺and TiO₂ NPs in the composite system combine by electrostatic attraction to form a Cd-TiO₂ NPs complex,so the Cd²⁺adsorption affinity in the composite system increases.For the TC+TiO₂ NPs composite system,the Sips model fitting results show that,compared with the single TC and single TiO₂ NPs system,the Qm S of TC and TiO₂ NPs in the TC+TiO₂ NPs composite system was reduced by 45.37%and 46.67%,respectively.The mutual antagonism of TC and TiO₂ NPs on Zeo was stronger in the neutral environment at high temperatures.In the TC+TiO₂ NPs composite system,TC and TiO₂ NPs also compete for adsorption sites?-OH?on Zeo.In addition,organic macromolecules TC and TiO₂ NPs have a stronger blocking and filling effect on the Zeo surface pore structure,and TC's encapsulation effect on Zeo has further reduced the adsorbable sites on Zeo,the above reasons caused the antagonism between TC and TiO₂ NPs to be stronger than Cd²⁺and TiO₂ NPs.In the composite system,TC and TiO₂ NPs were combined by hydrogen bonding.This interaction leads to a decrease in the aggregate size of TiO₂ NPs in the composite system,which also leads to a decrease in the number of TiO₂ NPs adsorbed on the Zeo.?2?On the surface of the negatively charged porous environmental medium?coconut shell carbon,CBC?,the TiO₂ NPs appearing in the composite system have an antagonistic effect on the adsorption of TC and Cd²⁺.The Cd²⁺in the Cd+TiO₂ NPs composite system showed an antagonistic effect on the adsorption of TiO₂ NPs,but the TC in the TC+TiO₂NPs composite system promoting the adsorption of TiO₂ NPs.In the Cd²⁺+TiO₂ NPs composite system,the Q_{m S} of Cd²⁺and TiO₂ NPs obtained by the Sips model was reduced by 2.05%and 54.46%,respectively.The antagonism between TiO₂ NPs and Cd²⁺was due to the fact that TiO₂ NPs and Cd²⁺will compete for adsorption sites?-OH and-COOH?on the surface and pores of CBC,resulting in a decrease in the adsorption of Cd²⁺and TiO₂ NPs.In addition,the size of TiO₂ NPs agglomerates in the Cd+TiO₂ NPs composite system increases,which makes it difficult to diffuse into the pore structure of CBC,so the adsorption of TiO₂ NPs in the Cd²⁺+TiO₂ NPs composite system decreases.In the TC+TiO₂ NPs composite system,the Qm S of TC decreased by 57.99%,and the Qm S of TiO₂ NPs increased by 12.12%.The TiO₂ NPs in the composite system will not only compete for hydrogen bonding sites on CBC but also inhibit the?-?/n-?bond interaction between CBC and TC,causing the two main adsorption ways of TC to be inhibited.The blockage of TiO₂ NPs on the pore structure of CBC also affects the pore filling of TC.The promoting of TC on the TiO₂ NPs adsorption is divided into two aspects.On the one hand,TC promotes the adsorption of TiO₂ NPs on the surface of CBC through bridging;on the other hand,the TC in the composite system caused the size of the TiO₂ NPs aggregates to decrease and enhanced the TiO₂ NPs adsorption in the CBC pores,resulting in the TiO₂ NPs adsorption on the CBC was increased in the composite system.?3?On the positively charged clay minerals?magnetized kaolin,MK?surface,the TiO₂NPs in the Cd+TiO₂ NPs composite system promote the adsorption of Cd²⁺on MK,and Cd²⁺showed an antagonistic effect on the adsorption of TiO₂ NPs on MK.The co-adsorption behavior of TiO₂ NPs and TC on MK in the TC+TiO₂ NPs composite system was shown as cooperative adsorption.In the Cd+TiO₂ NPs composite system,the Cd²⁺adsorption increased by 31.56%,averagely,and the total TiO₂ NPs adsorption and the steady-state adsorption TiO₂ NPs decreased by 19.57%and 17.71%,respectively.Although TiO₂ NPs inhibited the pore-filling effect of Cd²⁺and occupied part of the-OH adsorption sites on MK,the adsorbed TiO₂ NPs on the surface of MK provided additional electrostatic attraction sites for Cd²⁺,causing the adsorption of Cd²⁺to be larger than the single Cd system.For the TiO₂ NPs in the Cd+TiO₂ NPs composite system,Cd²⁺occupies part of the-OH adsorption sites and inhibits the hydrogen bonding between TiO₂ NPs and Fe-O,resulting in both the total adsorption and steady-state adsorption TiO₂ NPs decreased in the composite system.Compared with the single Cd system,the Cd²⁺desorption in the Cd+TiO₂ NPs composite system was increased by 122.73%.This was due to the weakening of the electrostatic attraction between TiO₂ NPs and MK which caused by the Cd²⁺adsorbed on the TiO₂ NPs surface in the composite system.As a result,Cd²⁺adsorbed on TiO₂ NPs was easier to desorb together with TiO₂ NPs.In the TC+TiO₂ NPs composite system,the TC adsorption increased by 2.02%,averagely.On the one hand,the adsorbed TiO₂ NPs increase the number of-OH and negative charges on the MK surface.On the other hand,the adsorbed TiO₂ NPs on the MK surface also inhibits the?-?or n-?bond interaction of TC on the surface of MK.The inhibitory of TiO₂ NPs on TC adsorption was greater than the promotion,this result leads to a smaller increasing of TC adsorption in the TC+TiO₂ NPs composite system.In the composite system,the TiO₂ NPs adsorption increased by 57.59%,averagely,while the steady-state adsorption TiO₂ NPs on the MK surface was decreased by 29.07%,averagely.The desorption of TC was increased by 45.26%.The coexisting TC in the composite system weakens the stability of the TiO₂ NPs which adsorbed on the MK,which makes TC and TiO₂ NPs easier to desorb from the MK surface.?4?The charge properties of the environmental medium were the main factors that determine the co-adsorption behavior?antagonistic or synergistic?of Cd²⁺and TiO₂ NPs.For negatively charged solid surface?Zeo and CBC?,porosity determines the strength of the mutual antagonism between Cd²⁺and TiO₂ NPs on negatively charged surfaces.The porosity,functional group,and the charge properties determine the co-adsorption behavior of TC and TiO₂ NPs on the environmental medium in the TC+TiO₂ NPs composite system.On solid surface with the same electrical properties,such as CBC and Zeo,the porosity and functional group types of the environmental medium determine the co-adsorption behavior of TC and TiO₂ NPs on the environmental medium in the TC+TiO₂ NPs composite system.