Preparation Of Electrospun Micro/Nano-Materials For Adsorption Of Heavy Metals From Aqueous Solution

Heavy metal contaminations in water systems are one of the serious environmentalproblems throughout the world. Most of heavy metal ions are highly toxic, even at very lowconcentrations. These metal ions are non-degradable and can accumulate in living organisms,causing several disorders and diseases. Therefore, the removal of heavy metal ions fromaqueous solutions is very important to protect the environment and public health.Recently, micro/nano-materials are of great interest to be developed as efficientadsorbents for heavy metal ions in water. A large number of advanced techniques have beendeveloped to fabricate micro/nano-materials with well-controlled morphology and chemicalcomposition. Among these techniques, electrospraying and electrospinning seem to be thesimplest and most versatile techniques capable of generating micro/nano-materials, andhave attracted a great deal of attention in recent years.Micro/nano-materials produced by electrospraying and electrospinning methods haveinteresting properties, such as high specific surface area, porous surface structure, highchemical strength, good mechanical properties, and favorable morphology for recoveryand recycling. So electrospun micro/nano-materials could be used as effective adsorptivematerials.In this thesis, a series of micro/nano-materials with different structures and functionshave been prepared by combining the electrospraying and electrospinning techniques withthe subsequent process of heat treatment, acidic-dissolution, and chemical modification. Then,these electrospun micro/nano-materials are used for adsorption of heavy metals such ascopper, arsenic from aqueous solution. Detailed research results are listed as follows: 1. Anatase mesoporous titanium nanofibers （m-TiO₂NFs） have been synthesizedfrom calcination of the as-spun TiO₂/Polyvinyl pyrrolidone （PVP）/Pluronic123（P123）composite nanofibers at450oC in air for3h. An investigation of Cu（II） adsorption ontom-TiO₂NFs has been demonstrated. The pH effect, adsorption kinetics, and adsorption isothermsare examined in batch experiments. Experimental data were analyzed using pseudo-firstorder and pseudo-second order kinetic models. It was found that adsorption kinetics were thebest fitting by a pseudo-second order kinetic model. The optimum pH for Cu（II）adsorption was found to be6.0. The adsorption equilibrium data were analyzed by theLangmuir, Freundlich, Temkin, and Dubinin-Radushkevich isotherm models, whichrevealed that the Freundlich isotherm is the best-fit isotherm for the adsorption of Cu（II）.Compared to the TiO₂NFs （regular anatase titanium nanofibers） in the same experimentalconditions to elucidate the role of the mesoporous structure of m-TiO₂NFs, experimentalresults showed that the m-TiO₂NFs had a better adsorption capacity for Cu（II） ions. Thisstudy may lead to a simple and effective method for fabricating porous materials andm-TiO₂NFs can be a very promising material for removing Cu（II） ions from aqueoussolution.2. TiO₂nanofibers （NFs） with different phases such as amorphous, anatase, mixedanatase rutile, and rutile have been prepared by combining the electrospinning techniquewith the subsequent process of heat treatment or acidic-dissolution method. The obtainedTiO₂nanofibers are characterized by a Fourier transform infrared spectrometer （FT-IR）,X-ray photoelectron spectroscopy （XPS）, X-ray diffraction （XRD）, scanning electronmicroscopy （SEM）, transmission electron microscopy （TEM）, and N2adsorption desorptionisotherm measurements. Phase-structure effects of the electrospun TiO₂NFs on As（III）adsorption behaviors have been investigated. The results showed a significant effect ofthe phase structures of TiO₂NFs on As（III） adsorption rates and capacities. AmorphousTiO₂NFs have the highest As（III） adsorption rate and capacity in the investigated samples,which can be attributed to higher surface area and porous volume. This research providesa simple and low-cost method for phase-controlled fabrication of TiO₂NFs and applicationfor the effective removal of arsenic from aqueous solution.3. Poly（acrylo-amidino ethylene amine）（PAEA） nanofiber membranes have beensynthesized by combining the electrospinning technique and subsequent chemicalmodification. The membranes were used to remove As（V） from aqueous solution. Theadsorption followed pseudo second-order kinetic models well and Langmuir isotherm model could be well-described the experimental equilibrium data. The PAEA nanofibersare effective for As（V） adsorption at pH3. The maximum Langmuir adsorption capacityof the PAEA nanofibers with As（V） is76.92±1.03mg.g^-1, which is much higher thanthat of the PAEA microfibers (27.62±0.50mg.g^-1) in the same experimental conditions.The adsorption rate of the PAEA nanofibers is faster than that of PAEA microfibers due toits higher specifc surface area. The PAEAnanofibers can be used as an effective adsorbentfor the removal of As（V） in aqueous solution due to high adsorption capacity and shortadsorption time to achieve equilibrium.4. Porous chitosan（CS）/magnetite（Fe₃O₄）/ferric hydroxide（Fe（OH）₃） microsphere asnovel and low-cost adsorbents for the removal of As（III） have been synthesized via theelectrospraying technology by a simple process of two steps. The adsorption kinetics andequilibrium isotherms were investigated in batch experiments. The Langmuir, Freundlichisotherm, and pseudo-second order kinetic models agree well with the experimental data.The adsorption of As（III） onto the CS/Fe₃O₄/Fe（OH）₃microspheres occurred rapidly andreached adsorption equilibrium after about45min. The maximum adsorption capacity of theCS/Fe₃O₄/Fe（OH）₃microspheres, calculated by the Langmuir isotherm model, was8.47±0.18mg.g^-1, which is higher than that of the CS/Fe₃O₄/Fe（OH）₃prepared by theconventional method (4.72±0.04mg.g^-1). The results showed that the CS/Fe₃O₄/Fe（OH）₃microspheres had a high adsorption capacity for As（III） and a high separation efficiencydue to their microporous structure and superparamagnetic characteristics. The compositematerials, therefore, are significant for water purification.