Research On Preparation And Adsorption Mechanism Of Functional Organo-Clays Towards Organic Pollutants

In recent years,water pollution has gradually attracted attention.The improvement of adsorbent performance has become a research hotspot in wastewater treatment.Therefore,designing universally efficient organic adsorbents and clarifying the adsorption mechanism are the key issues.This thesis simulates specific organic pollutants in wastewater,as well as designs and synthesizes organic modifiers based on the molecular level and adsorption performance evaluation of organoclays.The comprehensive evaluation of organic adsorbents is improved by preparation of series organo-clays.In addition,the adsorption mechanism and structure-adsorptivity relationship are deeply studied by combining adsorption experiments and theoretical calculations.The main research conclusions of the thesis are as follows:(1)A multi-hydroxyl containing gemini surfactant(1,3-bis(dodecyldimethylammonium)-2,2-dimethylolpropane dibromide,BHDHMP)is designed and used to prepare organo-vermiculite(BDHMP-Vt).The adsorption of BDHMP-Vt for the removal high concentration cationic dyes methylene blue(MB)and crystal violet(CV)is investigated.Through the comprehensive evaluation of the structure and adsorption performance,it is found that BDHMP are mainly arranged in the interlayer of BDHMP-Vt.The arrangement of BDHMP is paraffin bilayer through electrostatic interaction,and the modifier availability of BDHMP is 71.03%.The maximum adsorption capacity of BDHMP-Vt for MB/CV is about 320/670 mg/g,and the adsorption process conforms to the pseudo-second-order kinetic model.The adsorption of MB conforms to the Langmuir monolayer adsorption isotherm,which is endothermic in nature.Freundlich multilayer isotherm is more suitable for describing CV adsorption,which is exothermic.In binary-component dye system,the maximum adsorption capacity of BDHMP-Vt for MB is 475 mg/g,and the maximum adsorption capacity for CV is 685 mg/g.There is a competitive effect in the adsorption process of CV and MB.(2)For the drugs of mefenamic acid(MEA)and ibuprofen(IBP),a rigid head group(quinoline)surfactant(1,3-hexadecylquinolin-6-yl-bromo urea,DHQU)is designed,and used to prepare organo-vermiculite(DHQU-Vt).Through the comprehensive evaluation of the structure and adsorption performance of DHQU-Vt,it is found that DHQU is physically adsorbed on the surface of DHQU-Vt.The modifier availability of DHQU is 84.18%.The adsorption capacity of DHQU-Vt for MEA/IBP is 127/148 mg/g.The adsorption process is in accordance with pseudo-second-order kinetics and Freundlich isotherm models.IBP has obvious diffusion and π-π stacking during the adsorption.In the MEA adsorption process,the partition process plays a major role.In addition,π-π and NH-π interactions can further enhance the adsorption capacity of DHQU-Vt for MEA and IBP.Three regeneration cycles of DHQU-Vt are achieved by washing with 0.1 mol/L HCl solution.(3)For the dyes malachite green(MG),crystal violet(CV)and bromophenol blue(BPB),hexadecyltrimethylammonium bromide(HDTAB)and hexadecyltrimethoxysilane(HDTMS)are selected to modify silica nanosheets(Si NSs)and silica particles(Si NPs).A series of organic adsorbents(organo-SASs)are prepared.Through a comprehensive evaluation of the structure and adsorption properties of organo-SASs,HDTAB is mainly adsorbed on the surface of SASs through ion exchange and electrostatic attraction.In case of HDTMS,a new covalent bond is formed between HDTMS and SASs.HDTAB-Si NPs,HDTMS-Si NSs and HDTAB-Si NPs have the highest adsorption capacities for MG(424.80 mg/g),CV(409.18 mg/g)and BPB(261.60 mg/g).The adsorption processes are in accordance with pseudo-second-order kinetics and Freundlich isotherm models.MG and CV are more likely to interact with the original active sites of SASs.Their adsorption on organo-SASs relies on the partition process and π-π stacking.The adsorption of anionic dye BPB mainly depends on the porosity and hydrophobicity of organo-SASs.The adsorption process is less affected by the morphology of the adsorbent,slightly more affected by the dye steric hindrance and intermolecular interaction,and most affected by the dye charge.The order of affecting the adsorption capacity is: adsorbate charge > functionalization mode >adsorbate steric hindrance > additional interaction.(4)For the cationic dye Congo red(CR),a series of amide gemini surfactants(1,3-bis(lauramidopropyldimethylammonium chloride)n-butane(LDAB),1,3-bis(lauramidopropyl dimethyl ammonium chloride)p-dimethylphenyl(LDAPP),1,3-bis(lauramidopropyl dimethyl ammonium chloride)m-dimethyl ammonium ylphenyl(LDAMP)and 1,3-bis(lauramidopropyl dimethyl ammonium chloride)4,4’-dimethylbiphenyl(LDABP))are synthesized.Organo-vermiculites(LDAB-Vt,LDAPPVt,LDAMP-Vt and LDABP-Vt)is prepared.Through the comprehensive evaluation of the structure and adsorption performance,the surfactant is mainly inserted between the vermiculite layers through physical action.The values of modifier availability are 75.00%,70.63%,62.10% and 50.59%,respectively.The maximum adsorption capacity of LDAB-Vt,LDAPP-Vt,LDAMP-Vt and LDABP-Vt reach 1214,1375,1449 and 713mg/g,respectively.The introduction of amide into the alkyl chain of the surfactant and benzene ring into the spacer can significantly enhance the adsorption of organo-Vts.The adsorption processes follow the pseudo-second-order kinetic model and the Freundlich isotherm.The cyclic regeneration of organo-Vts is achieved by washing with ethanol for at least three cycles.