Preparation Of Modified Chitosan Nanomaterials And Their Application In Water Treatment

Water pollution has been becoming a more and more serious problem with industrialization and urbanization since recent decades. Wastewater containing lead, cadmium, mercury, chromium, copper, nickel and other heavy metal ions, is one of the most serious water pollution. It is mainly originated from some industrial production, such as mining, machinery, manufacturing, chemical engineering, electrical, instrumentation, construction, defense, etc. In water or soil, heavy metals are non-biodegradable by microorganism and can only transform in various chemical forms and are enriched or dispersed. They can cause serious irreversible harm to human health and the environment. Therefore, the treatment of heavy metals from wastewater is very critical. At present, the treatments for heavy metals of wastewater mainly include chemical, physical and biological method. Compared with others, adsorption seems to be easy operation and inexpensiveness. Therefore, to develop novel adsorbent materials with the characteristic of economics and high efficient has become a hot subject.In this paper, three kinds of modified chitosan nanomaterials were prepared by the graft polymerization of chitosan with functional olefins and then proper crosslinking. Their morphologies and structures were characterized. The adsorption of heavy metal ions on these materials was studied by a series of experiments. The major results were given as follows:1. Selective adsorption of lead on grafted and crosslinked chitosan nanoparticles prepared by using Pb²⁺ as template. Poly（acrylic acid） grafted and glutaraldehyde-crosslinked chitosan nano adsorbent（PAACS） was synthesized by using Pb²⁺ as a template ion. The structure and morphology of PAACS were characterized by FT-IR, XRD, SEM and elemental analyses. The adsorption of PAACS for different heavy metal ions was compared and the effects of various variables for adsorption of Pb²⁺ were systematically studied. The results indicated that the PAACS was the aggregates of nanoparticles with the diameter of about 50–200 nm and had selectivity for Pb²⁺ adsorption. The adsorption for Pb²⁺ showed a maximum adsorption capacity of 734.3 mg g-1 at pH 5.0 and 303 K, which was higher than in a study previously reported on ion-imprinted adsorbents. The adsorption followed the pseudo-second-order kinetics and Langmuir isotherm models. The adsorption was spontaneous and changed from chemical process into physical process when the temperature exceeded 303 K. The adsorbent could be recycled with EDTA. Therefore, PAACS would be useful as a selective and high uptake nano adsorbent in the removal of Pb²⁺ from effluents.2. Adsorption of Hg（II） in aqueous solutions on a novel poly（maleic acid）-modified cross-linked chitosan nanomaterial. A novel chitosan nano composite（PMACS） was prepared by grafting poly（maleic acid） onto chitosan and then crosslinking with glutaraldehyde. The structure and morphology of this composite were characterized by FT-IR, XRD, SEM and TGA. The adsorption of PMACS for different heavy metal ions was compared and the effects of various variables for adsorption of Hg²⁺ were systematically studied. The experimental results indicated that the PMACS was the aggregates of nanoparticles with the average diameter of about 496 nm and had selectivity for Hg²⁺ adsorption. The adsorption for Hg²⁺ at 303 K showed a maximum adsorption capacity of 1044 mg g-1 at pH 6.0, which approached the maximal value of reported other adsorbents. The kinetic studies indicated that the adsorption followed the pseudo-second-order kinetics model and was mainly governed by chemical process. Adsorption isotherm conformed to the Langmuir model. The thermodynamic researches meant that the adsorption was a spontaneous process. The uptake increased as temperature rise. The adsorbent could be recycled with EDTA. Hence, this composite would be used as a selective and high uptake adsorbent in the removal of Hg（II） from wastewaters.3. Synthesis and characterization of poly（itaconic acid）-grafted cross-linked chitosan nanomaterials with high uptake for sorption of Hg（II） and Pb（II）. Using itaconic acid and chitosan as raw materials, a novel chitosan composite（PIACS） was successfully prepared by grafting poly（itaconic acid） onto chitosan and then crosslinking with glutaraldehyde under proper controls. The morphology and structure of PIACS were characterized by FT-IR, XRD, SEM and TGA. The adsorption of Hg²⁺ and Pb²⁺ on PIACS was studied by a series of adsorption experiments. Results showed that the maximum adsorption capacities of Hg²⁺ and Pb²⁺ at 303 K were 870.1 mg g-1 at pH 6.0 and 1320 mg g-1 at pH 5, respectively. The adsorption for both Hg²⁺ and Pb²⁺ conformed to the pseudo-second-order kinetics and Langmuir isotherm models. According to thermodynamic researches, the adsorption of Pb²⁺ on PIACS was an exothermic and spontaneous chemical process while the uptake of Hg²⁺ changed little when the temperature increased from 293 K to 333 K. Regenerative experiments showed that the adsorbent could be reused after desorption with EDTA.The above-mentioned grafted and crosslinked-chitosan nanoadsorbents have high capacity and good properties for the adsorption of Pb²⁺ and Hg²⁺. Thus, they have impressing application prospect in the treatment of relative heavy metal ions from wastewaters.