Research On Preparation And Adsorption Performance Of Nitrogen-containing Functional Organoclays Towards Heavy Metal Ions And Complicated Pollutants

The heavy metal ions are difficult to degrade and have caused serious harm to the production and life of people.Therefore,in recent years,various technologies for treating wastewater containing heavy metal ions are in the ascendant.Among them,clay-based adsorbent is one of the widely used materials.Vermiculite has attracted much attention in wastewater treatment because of its low cost,adjustable interlayer distance,and strong ion exchange capacity.Nevertheless,vermiculite has weak adsorption capacity,low selectivity for heavy metal ions,and inferior treatment of multi-component wastewater since it is contained fewer functional groups and unsatisfactory functionalization effect.As a result,the research on the efficient and selective removal of heavy metal ions by vermiculite-based adsorbents needs to be further developed.Consequently,in this dissertation,a series of functionalized organoclays are designed and prepared by means of adjusting the structure,number and type of nitrogen-containing functional groups in the modifier and the functionalization method.The single and simultaneous adsorption properties of different cationic(Hg(Ⅱ),Pb(Ⅱ),Ag(Ⅰ))and anionic(Cr(Ⅵ),MnO4-)heavy metal ions,organic pollutants on functionalized organoclays are investigated.In addition,through the analysis of different adsorption models,the characterization of spent adsorbents and theoretical calculations,the adsorption mechanism and the structure-effect relationship are clarified.The dissertation results not only deepens the understanding of different types of heavy metal ion adsorption systems,but also counted upon establishing a theoretical basis for the design and utilization of functionalized organoclays.The specific research results are as follows:(1)For cationic heavy metal ions,Hg(Ⅱ)and Pb(Ⅱ),the copoly(indole-aniline)-vermiculite(PIn-co-PANI-Vt)adsorbent containing assorted nitrogen-containing functional groups are constructed and prepared via in-situ polymerization.The results display that the PIn-co-PANI-Vt not only has good thermal stability and abundant indole and aniline functional groups,but also has high adsorption amounts for Hg(Ⅱ)and Pb(Ⅱ).In the single-component system,the maximum removal amounts of Hg(Ⅱ)and Pb(Ⅱ)onto PIn-co-PANI-Vt are 328 mg/g and 165 mg/g,respectively.The pseudo-second-order kinetic model could explain the chemisorption process of the Hg(Ⅱ)and Pb(Ⅱ)ions.The retention of Hg(Ⅱ)and Pb(Ⅱ)onto PIn-co-PANI-Vt are agree with the Freundlich and Langmuir isotherm models,respectively.The coordination and electrostatic interactions are the preponderant driving forces for retention of Hg(Ⅱ)and Pb(Ⅱ).The stronger coordination of PIn-co-PANI-Vt to Hg(Ⅱ)leads to the difference in adsorption capacities.In the co-adsorption system,there is antagonistic effect on the simultaneous adsorption of Hg(Ⅱ)and Pb(Ⅱ)on PIn-co-PANI-Vt.(2)In regard with the cationic noble metal ion Ag(Ⅰ),a series of organosilica nano sheets(organo-SiNSs)containing nitrogen and sulfur bifunctional groups(2-mercaptoimidazole(MI),2-mercaptobenzimidazole(MBT)and 1H-1,2,4-triazole-3Thiol(MTT))are constructed and prepared via silylation method.The experimental results indicate that a range of azole-based modifiers are mainly combined with the precursor SiNSs through covalent bonds,and further enhance the efficient and selective adsorption of Ag(Ⅰ)on organo-SiNSs.The maximum adsorption capacities of MI-SiNSs,MBI-SiNSs,and MTT-SiNSs for Ag(Ⅰ)ions are 70.30 mg/g,103.20 mg/g and 139.50 mg/g,respectively,within 10-30 min.The removal process is chemisorption,which is accord with the pseudo-second-order kinetic model and the Langmuir adsorption isotherm model.It is worth noting that MTT-SiNSs has a strong selectivity to Ag(Ⅰ),and the distribution coefficient value of Ag(Ⅰ)ions reaches 2331.26 mL/g.The main mechanism for Ag(Ⅰ)adsorption on organo-SiNSs is coordination.Moreover,the amino and sulfhydryl groups of MTT-SiNSs and MBI-SiNSs may have a synergistic effect on Ag(Ⅰ)capture.The differences in adsorption behavior and selectivity of the three organo-SiNSs are mainly interrelated to the form of function groups,charge density and steric hindrance of adsorbent.(3)In view of anionic heavy metal ions Cr(Ⅵ)and the phenolic pollutants,the organic vermiculite(BDIEP-Vt)containing imidazole ether is designed and prepared through ion exchange method.The test results demonstrate that the arrangement of BDIEP on Na-Vt is the coexistence of paraffin and monolayer with high modifier utilization rate of 85.16%.In single system,the results of standard batch adsorption experiment represent that BDIEP-Vt could adsorb the three contaminants(220.40 mg/g for TCS,74.60 mg/g for 4-CP,18.40 mg/g for Cr(Ⅵ))effectively as well as rapidly within 5-10 min.The adsorption process is in great pertinence with pseudo second-order model,and the equilibrium data are consisted with Freundlich model greatly for TCS and Cr(Ⅵ),while Langmuir model suites for 4-CP.In TCS-Cr(Ⅵ)/4-CP-Cr(Ⅵ)binary system,the trend variation of φ value indicates an antagonism effect is exerted by Cr(Ⅵ)ions on TCS/4-CP removal whereas Cr(Ⅵ)uptake is slightly affected.The impact sequence of Cr(Ⅵ)on the removal of TCS/4-CP follows as:TCS<4-CP.The adsorption mechanism of BDIEP-Vt on TCS/4-CP is dominated by hydrophobic interactions,π-π and π-π stacking interactions,while the removal of Cr(Ⅵ)is controlled by electrostatic interaction.The strength of the competition between Cr(Ⅵ)and TCS/4-CP may be bound up with the discrepancy of pollutants structures.(4)In case of the anionic heavy metal ion MnO4-and containing Congo red(CR)dye,a range of bifunctional vermiculite-based adsorbents named DDPA-Vt as well as DDPU-Vt,are constructed via gemini surfactants containing pyridine-amide/pyridine-urea groups as modifiers.The experimental results demonstrate that in the single-component system,the maximum adsorption capacities are up to 504/822 mg/g for CR and 279/371 mg/g for MnO4-onto DDPA-Vt/DDPU-Vt,respectively.Pseudo-second-order kinetic model as well as Freundlich isotherm model could depict the adsorption processes.The co-adsorption tests display that organo-Vts are still effective retention to CR and MnO4-,especially onto DDPU-Vt.The π-π,NH-π,hydrophobic and electrostatic interactions are the mechanism of CR adsorption,while electrostatic interaction and coordination are the driving forces for the adsorption of MnO4-.The diverse nitrogen-containing groups on the pyridine ring and the spacer have a synergistic effect on CR and MnO4-retention.The more preference of DDPU-Vt to pollutants is based on the spacer differences(urea group).