Preparation Of Multifunctional Mesoporous Material For Heavy Metal From Removal From Aqueous Solution

Heavy metal as one of the important pollutants in water becomes a severepublic health concern because of its persistent nature and negative effect on theenvironment. They are difficultto remove from aqueous waste streams with tracequantities using conventional methods such aschemical precipitation. The process ofsorption/ion exchange appears to be one of the few alternatives available for suchsituations. To explore the availability of different kinds of adsorbents associated withconvenient procedures for obtaining high efficiency has been a hot topic recently.This paper discussed the hazardous effect of heavy metal ions in aqueoussolution and the development of treatment technologies for heavy metal removal.Based on the viewpoints of speciation of heavy metals in waters, the distribution ofdifferent species of heavy metals and the binding mechanism with adsorbents wereinvestigated. To develop new efficient solid adsorbents by chemical modification,four different kinds of solid extractants were prepared including SA-SBA-15, S-SBA-15,EDTA-SBA-15and RBHS-SBA-15. Then these new adsorbents were characterized withFTIR, TEM and XRD. Furthermore, adsorption experiments in a batch method werecarried out to examine the adsorption performance for some heavy metal ions. Manymodels such as kinetic, thermodynamic, equilibrium models were used to fit theexperiment data to understand the adsorption mechanisms. This thesis contains thefollowing five sections:1. Salicylidene Schiff base-functionalized SBA-15mesoporous silica is prepared,characterized and used as an adsorbent for heavy metal ion, Cu （II）. By two modifiedmethods（post-grafting and co-condesnsation）, the organic-inorganic hybridmesoporous materials have been synthesized by tetraethoxysilane （TEOS） with3-aminopropyltrimethoxy-silane （APTES） and salicylaldehyde in sequence. Thefunctionalized mesoporous materials are characterized by means of XRD, FT-IR, TEMand N2adsorption-desorption analysis. The result indicates that, after sequentchemical modifications of aminopropyl and schiff base, the primary hexagonallyordered mesoporous structure of SBA-15is not affected, exhibits the excellent adsorption capacity. The removal rate of Cu²⁺ in aqueous media is high and theadsorbent can be regenerated by EDTA treatments without changing its properties.Meanwhile，Cu-SBA-15antibacterial agent was shown to be an effective bactericideagainst Bacillus coli and Staphylococcus aureus，indicating that it has goodantibacterial effect．2.8-hydroxyquinoline Schiff base-functionalized SBA-15mesoporous silica wasprepared and S-SBA-15was found to be a better adsorbent for selective removal ofCu²⁺ from polluted water. The maximum adsorption capacity of Cu²⁺（46.45mg g-1）onto S-SBA-15was obtained at pH5.5. From kinetic studies, it was found that theadsorption of Cu²⁺ was fast and it reached equilibrium around approximately30min.Langmuir models fitted the experimental data well. The kinetics of adsorption usingS-SBA-15was explained by the second-order kinetic model and theintraparticlediffusion model. Although the presence of other ions such as Zn²⁺, Co²⁺ werefound to have effect on Pb（II） adsorption, S-SBA-15show a good selective removal ofPb（II）from multi-metal ions solution. Meanwhile，Cu-S-SBA-15antibacterial agentwas shown to be an effective bactericide against Bacillus coli and Staphylococcusaureus even with the minimal inhibitory concentration （MIC） of40μg mL^-1，indicating that it has good antibacterial effect．3. An organic-inorganic hybrid mesoporous silica material was synthesized bytwo-step post-grafting method of SBA-15with3-aminopropyltrimethoxy-silane（APTES） and thionyl dichloride （SOCl2） activated ethylenediaminetetraacetic acid（EDTA） in sequence and measured by means of Fourier transform infraredspectroscopy （FT-IR）, X-ray diffraction （XRD）, elemental analysis （EA）, transmissionelectron microscopy （TEM）, nitrogen （N2） adsorption-desorption analysis and backtitration. The material was found having the beneficial properties of mesoporoussilica SBA-15and EDTA. Adsorption potential of the material for Pb（II） removal fromaqueous solution was investigated by varying experimental conditions such as pH,contact time and initial metal concentration. The removal efficiency of Pb²⁺ was highunder the studied experimental conditions. The adsorption equilibrium could bereached within20minutes and the kinetic data were fitted well by pseudo-second-order and intraparticle diffusion model. The adsorbent exhibited afavorable performance and its maximum adsorption capacity calculated by Langmuirmodel was273.2mg g?1. Recycling experiments showed the adsorbent could beregenerated by acid treatment without altering its properties. The chemical states ofthe elements involved in the adsorption were analyzed by X-ray photoelectronspectroscopy （XPS）. The results demonstrated that the adsorption mechanism of thematerial involved Na Pb ion-exchange and carboxyl group dominated surfacecomplexation.4. A novel,‘‘all-in-one’’, multifunctional microsphere with a fluorescentmesoporous silica （Rhodamine B coordinate receptor inside） has been successfullyfabricated using a sol–gel method and small molecular （CTAB） surfactants asstructure-directing agents. At the same time, they were examined for environmentalprotection applications to detect, adsorb and remove Hg²⁺ in aqueous solution. Theprepared mesoporous materials were fluorescent and mesoporous. Thesemultifuctional microspheres showed excellent fluorescence sensitivity and selectivitytowards Hg²⁺ over other metal ions (Na+, Mg²⁺, Mn²⁺, Co²⁺,Ni²⁺, Zn²⁺, Cd²⁺, Ag+,Pb²⁺ and Cu²⁺). Upon the addition of Hg²⁺, an overall emission change of16-foldwas observed, and the detection limit of Hg²⁺ was as low as1ppb. The adsorptionprocess of Hg²⁺ on the RBHS-SBA-15was well described by the Langmuir equation.The equilibrium can be established within30minutes and the adsorption capacitywas34.2mg g-1. These results suggest that these ‘‘all-in-one’’ multifunctionalmesoporous scilica are potentially useful materials for simultaneously rapidlydetecting and recovering dangerous pollutants in aqueous solution.Chemical modified SBA-15developed in this paper have great potential for theadvanced treatment of wastewater containing heavy metals.