Preparation Of Chitosan/Poly(Vinyl Alcohol)Based Nanocomposites And Its Application In Wastewater Treatment

Chitosan(CTS),also known as deacetylated chitin,can be obtained by deacetylating chitin(CT),which is widely existed in nature.The large amounts of functional groups(-OH and-NH2)on the surface of chitosan endow them to adsorb heavy metal ions,dyes and other pollutants from wastewater.However,chitosan is unstable in acidic solution and difficult to be separated from solution after adsorption,which limits its application in the field of wastewater treatment.In this paper,the PVA/CTS based composite adsorbents were prepared by instantaneous gelation,continuously gelation,freeze-drying and casting gelation methods,using polyvinyl alcohol(PVA)reinforced chitosan hybrids(PVA/CTS)as the matrix material and nanochitin(n-CT)or montmorillonite(MMT)as the main adsorbent.The morphology,chemical structure and magnetic properties of the prepared nanocomposites were studied by various characterization methods.In addition,the adsorption performance of the prepared nanocomposites on main pollutants in sewage was studied and the selection principles of adsorbents under different conditions were also summarized.The main research works and results of the dissertation can be summarized into the following five aspects:1)The PVA/CTS composite matrix materials were prepared by instantaneous gelation method.The composites were characterized by SEM,FTIR and BET technologies.The results showed that the prepared PVA/CTS matrix material had a three-dimensional network structure and was a kind of porous material w-ith micro-nano pore structure.The material contains a large number of hydroxyl groups,amino groups and other active functional groups,which was considered an ideal carrier material for wastewater treatment.2)The chitosan hydrogel beads nano-composites(FPCC)which contained nano-chitin(n-CT)and nylon 6 magnetic particles(FP)were prepared via in situ instantaneous gelation method.The morphology and structural characteristics of hydrogel beads nanocomposites were analyzed by SEM-EDS,TEM,VSM,FTIR and XRD technologies.At the same time,the Cu(?)adsorption performance by hydrogel beads nanocomposites was studied to find out the best adsorption conditions,and the adsorption mechanism was also discussed.The results showed that FP magnetic particles and n-CT nanoparticles were well distributed in the FPCC hydrogel beads nanocomposites.The maximum adsorption capacity of FPCC hydrogel beads nanocomposites on Cu(?)was 100.9 mg/g,and the adsorption equilibrium time was 10 min.Complexation adsorption,nano-enhanced adsorption and micro-sized medium adsorption are the main adsorption mechanisms of FPCC hydrogel beads nanocomposites for Cu(?)adsorption.3)FPCC microfiber nanocomposites were prepared by continuous injection gelation method.The advantages and disadvantages of the microfiber nanocomposites and hydrogel beads nanocomposites were evaluated in terms of production speed,effective quality,effective magnetic response distance and adsorption efficiency.The results showed that the maximum Ni(?)ion removal percentage was 99,7%.The obtained FPCC microfibers had shown significant advantages in production,separation,and adsorption when compared to the hydrogel beads prepared by the traditional method(instantaneous gelation method).Besides,intermolecular chelation adsorption is considered as the main reason for FPCC microfiber nanocomposites' high Ni(?)removal percentage.More attractively,the hybridized microfibers could be easily separated from the aqueous solution through a magnetic separation method after Ni(?)adsorption.4)The PVA/CTS/MMT aerogel nanocomposites were prepared by freeze-drying method.The adsorption performance of heavy metal ions Pb(?)and cationic dye methylene blue(MeB)on PVA/CTS/MMT aerogel nanocomposites was studied.The results indicated that the maximum removal percentage of PVA/CTS/MMT aerogel nanocomposites on MeB and Pb(?)was 99.9%and 97.3%,respectively.The adsorption efficiency of Pb(?)was increased with the addition of adsorbent and adsorption time,but the initial concentration of Pb(?)had little effect on the adsorption efficiency of Pb(?).Furthermore,the comprehensive adsorption performance of the PVA/CTS/MMT aerogel nanocomposites was better than that of PVA/CTS/n-CT hydrogel beads nanocomposites and PVA/CTS/n-CT microfiber nanocomposites.5)The PVA/CTS/MMT membrane nanocomposites were prepared by gelation-casting method.The surface morphology and mechanical properties of the PVA/CTS/MMT membrane nanocomposites were studied,and the adsorption performance of heavy metal ions(Cu(?),Zn(?),Ag(?)),antibiotics(tetracycline,TC),cationic dyes(malachite green,MG,neutral red,NR)and anionic dyes(methyl blue,MB)were also investigated.Besides,the adsorption mechanism of PVA/CTS/MMT membrane nanocomposites for heavy metal ions,antibiotics and dyes was studied.The results indicated that the breaking strength and elongation at break of the prepared PVA/CTS/MMT membrane nanocomposites increased about 37.9%and 40.2%,respectively.The maximum adsorption capacity of PVA/CTS/MMT membrane nanocomposites toward malachite green(MG),neutral red(NR),methyl blue(MB),tetracycline(TC),Cu(?),Zn(?)and Ag(?)were 738.0,408.4,2569.3,275.0,377.8,650.0,and 567.0 mg/g,respectively.Complexation interaction,electrostatic interaction,hydrogen bond interaction,cation exchange interaction and bridging interaction were considered as the main adsorption mechanisms.The PVA/CTS/MMT membrane nanocomposites that adsorbed Ag(?)and TC exhibited a good antibacterial property to S.aureus and E.coli.Furthermore,PVA/CTS/MMT membrane nanocomposites can be stable in PBS solution but degradable in PBS+lysozyme solution.