Study On Adsorption Properties Of Ampholytic Surfactant Activated Clay Minerals For Tetracycline And Cadmium

With the rapid development of industry and the improvement of human’s living and medicine standards,antibiotics and heavy metal pollution have become the environmental issues that threaten human survival.Particularly,antibiotics-heavy metals combined contamination,which is seriously harmful to the ecological environmrnt and human health has been a challenge to the environmental remediation.Natural clay minerals have been widely used as adsorbent for environmental pollution treatment because of the superior properties of hign specific surface area,physicochemical stability,abundant reserves in our country and low cost.However,the adsorption capacity of natural clay minerals for both heavy metals and organics is limited.It is suggested that approptiatee modification of natural clay minerals to prepare highly effective adsorbents should not only be a new approach for the exploitation and utilization of clay minerals,but also provide a new direction for the treatment of antibiotics-heavy metals combined pollution.Based on an overview of the physicochemical properties,modification methods and the application of montmorillonite and vermiculite,the dissertation includes the main following contents:1.Ampholytic surfactant activated montmorillonite（BS-Mt）was synthesized with dodecyl dimethyl betaine（BS-12）as the organic modifier.The structural and physicochemical properties of BS-Mt and Mt were obtained by XRD,FTIR,SEM/EDS,BET,TG-DSC,XPS and Zeta potential analysis.The results showed that:（1）After modified by BS-12,the layered structure of montmorillonite was subjected to a slight structural collapse and decreased ordering.BS-Mt retained an intact basic crystal structure of pristine montmorillonite with more negative surface charges,which could provide more adsorption sites for the target reactants;（2）The adsorption capacity of tetracycline on BS-Mt was highly improved comparing to Mt.Additionally,the presence of Cd²⁺ could promote the adsorption of tetracycline,and the adsorption equilibrium was achieved within 60 min.The adsorption process of tetracycline on BS-Mt and Mt presented a good fitness with the pseudo-second-order model and Freundlich adsorption isotherm.The adsorption process was exothermic,feasible and spontaneous.（3）The adsorption capacity of Cd²⁺ on BS-Mt was stronger than Mt and the presence of tetracycline could also promote Cd²⁺ adsorption,and the adsorption equilibrium was achieved after about 60 min.The adsorption process followed the pseudo-first-order model and Langmuir adsorption isotherm,and belonged to a spontaneous and exothermic reaction.（4）The adsorption mechanisms of tetracycline on Mt and BS-Mt mainly involved electrostatic attraction and channel interception.（5）The removal of Cd²⁺ on Mt was mainly ascribed toion exchange,electrostatic interaction and channel interception,Besides the above reaction mechanism,chelation was also involvedin the Cd²⁺ adsorption mechanism on BS-Mt.（6）Themutual promoting adsorption of tetracycline and Cd²⁺ was attributed to the coexistence of tetracycline and Cd²⁺that could form TC-Cd composite,which had higher affinity to adsorbent than tetracycline or Cd²⁺.Meanwhile,the bridging effect between tetracycline and Cd²⁺ could promote the adsorption processof each other.2.Amphoteric surfactant activated vermiculite（BS-VER）was prepared with dodecyl dimethyl betaine（BS-12）as the organic modifier.The microstructural and physicochemical properties of VER and BS-VER were analyzed by XRD,FTIR,SEM/EDS,TG-DSC,XPS and Zeta potential analysis.The adsorption performance of tetracycline and Cd²⁺onVER and BS-VER were studied by batch adsorption experiments.The results showed that:（1）After modified by BS-12,the diffraction peak intensity of vermiculite decreased and the layered structure was slightly destroyed.The thermal stability of vermiculite increased with more negative surface charges in pH 5¹0.（2）The adsorption amount of tetracycline on BS-VER was higher than that on VER.The coexistence of Cd²⁺ could promote the adsorption of tetracycline.The adsorption process was spontaneous and exothermic.The adsorption equilibrium was achieved within 60 min,and the pseudo-second-order model and Freundlich adsorption isotherm could well describe the adsorption process of tetracycline.（3）The adsorption amount of Cd²⁺ of BS-VER were larger than Mt and the presence of tetracycline could also promote Cd²⁺ adsorption.The adsorption process belonged to spontaneous and exothermic reaction.After about 60 min,the adsorption equilibrium could be achieved and the adsorption process showed a good fitness to the pseudo-second-order model and Freundlich adsorption isotherm.（4）The removal mechanism of tetracycline by VER and BS-VER was mainly ascribed to channel interception and electrostatic adsorption.The enhancement of tetracycline adsorption on BS-VER was due to hydrophobic carbon chain of BS-12 that had a good affinity to tetracycline.（5）The removal of Cd²⁺ by VER and BS-VER was mainly attributed to ion exchange,charge adsorption and channel interception,while chelation was also involved in the adsorption mechanism of Cd²⁺ for BS-VER.