Modification Of Clay Mineral And Their Adsorption/Degradation Performance On Cd/Pb And BPA

With the increasingly severe environmental pollution,a variety of contaminants including organics and inorganics have been released into the environment.The type of environmental pollution gradually changes from single pollution to multiple type pollutions.Bisphenol A?BPA?,as one of the most widely used industrial materials in the world,has been detected in the surrounding environment.Besides,it can co-exist with various heavy metals(e.g.,Cd²⁺and Pb²⁺)and their interactions pose a serious threat to the ecological environment and human health.Therefore,the remediation of compound pollutions should be given the high priority.Because of high specific surface area,stable physical and chemical properties,environmental friendliness and low cost,clay minerals have been widely used in the environmental remediation.For removal purpose,clay minerals modified with some functional groups could prospectively remove heavy metals and BPA from aqueous solution simultaneously.In our study,the modification of clay minerals consists of two parts.On the one hand,organo-functionalized montmorillonites?OMts?with amphoteric surfactants give them the ability to remove Cd²⁺/Pb²⁺and BPA in a step.On the other hand,layered double hydroxide?LDH?loaded with manganese dioxide can improve its ability to degrade bisphenol A and adsorb heavy metal.The main findings are as follows:?1?Organo-functionalized montmorillonites?OMts?were prepared by two different carbon chain lengths ampholytic surfactant of tetradecyl dimethyl betaine?BS-14?and octadecyl dimethyl betaine?BS-18?.The results of power XRD and FTIR showed that the head and tail part of BS-14 molecules could enter into the interlayer of Mt,while the tail part of BS-18 may enter into the interlayer of Mt by parallel or slightly sloping way,or pseudotrilayer arrangements.The structure of Mt was not damaged after BS-14 and BS-18modification,but its surface morphology changed because of the loaded surfactants from SEM results.Besides,the specific surface area of OMts decreased,while the hydrophobicity and thermostability improved after modification.?2?The obtained OMts were used as adsorbents for removal of Cd²⁺/Pb²⁺and BPA in single,sequential and binary systems.The adsorption ability of Cd²⁺/Pb²⁺onto OMts had no obvious change in single and binary systems,while the maximum adsorption capacity of Cd²⁺/Pb²⁺showed a slightly decline after functionalization.OMts showed strong affinity to BPA compared with Mt,and adsorption capacity of BPA was improved substantially in the presence of Cd²⁺/Pb²⁺.Besides,the prepared OMts had a good selectivity for the adsorption of Cd²⁺/Pb²⁺and BPA in sequential systems.The above results revealed that Cd²⁺/Pb²⁺adsorption on OMts were owing to surface adsorption,cation exchange and electrostatic attraction and chelate action,while high selectivity and affinity of BPA onto OMts was due to their hydrophobic effect.?3?LDH was loaded with different amount of MnO₂,and the characterization results of the composite materials showed that the optimal MnO₂ loading content was 0.01.LDH plays an important role in template and reinforcement for the production of high-oxidation MnO₂.The composite material of MnO₂-LDH showed high oxidation and mineralization for BPA and an effective adsorption for Pb²⁺.Besides,Pb²⁺adsorption and BPA oxidation had good synergistic reaction in binary systems.Moreover,their adsorption and oxidation performance on MnO₂-LDH are less dependent on pH value and ambient temperature.The above results reflected that the mechanism for BPA degradation was resulted from oxidation of MnO₂ under acid condition.Pb²⁺adsorption was mainly attributed to electrostatic effect,ion exchange effect and surface complexation.From the above conclusions,the organo-clay materials showed high adsorption capacity for heavy metal and BPA.MnO₂ loaded LDH composite material revealed good adsorption ability for heavy metal and degradation of BPA as well.These studies could provide some experimental foundation and theoretical basis for the removal of combined pollutions.