| Chitosan, a kind of new bioadsorbent, has been prepared to different adsorbents used in the actual wastewater treatment, for its higher adsorption capacity and selectivity for heavy metal ions. However, chitosan’s application is limited because it is not good at degrading organic pollutants in wastewater. Using nano-TiO2to degrade organic pollutants in water is a new water treatment technology. In this work, based on the molecular imprinting technology, the complex adsorbents by cross-linking chitosan and TiO2was prepared, which can selectively adsorb heavy metal ions as well as degrade organisms. The complex technology of the molecular imprinting technology with photocatalytic reaction brings novel ways to the treatment of industrial and living sewage.1Preparation of Chitosan/TiO2adsorbentUniform complex adsorbents was prepared with molecular imprinting technology by using Ni2+as imprinting template, chitosan and TiO2as primary raw materials.. This novel adsorbent can not only degrade organic compound but also adsorb the heavy metal ions. The optimum quality ratio of Chitosan to TiO2was5:2(w/w)Epichlorohydrin was selected as the cross-linking agent, and the optimum dosage was0.2ml/gchitosan.0.02M NaOH was selected as the solidifying agent, and the solidifying time was8-10h.The optimum dosage of Ni2+during imprinting process was8mg Ni2+/gChitosan.2Study of the adsorption performances of chitosan/TiO2adsorbentThe degradation of Methyl Orange (MO) would be improved under acidity circumstances (pH=4-5), and at the same time it would be deduced under alkalescent circumstances (pH=8-10). With the increase of Ni2+concentration, the adsorption capacity for Ni2+increased, and little influences were observed on the degradation of MO. For the purpose of a practical implementation, it is essential to evaluate the stability and reuse of the adsorbent. The adsorption-desorption cycle was repeated10times with the same adsorbent. After10batches, the adsorption capacity for Ni2+could reach85%of the first batch, and the degradation ratio of MO could reach90%.3disposal of Cu2+/MO systemThe effect of Cu2+on the removal of Methyl Orange was studied. When the concentration of Cu was lower (20mg/L), the removal of Methyl Orange would reach90%. But if the concentration of Cu2+was higher than50mg/L, the removal of Methyl Orange would improved firstly, but later the removal ratio would reduced. During the disposal of Cu2+/MO system, the-NH2group and-OH group in chitosan participated the adsorption for Cu2+, however the characteristic peak C6-OH and C3-OH didn’t change.4disposal of Ag+/MO systemWith the increase of MO concentration, the adsorption capacity for Ag+reduced slightly. At lower Ag+concentration, MO could be removed effectively. With the increase of Ag+, the color of reaction system changed from yellow to black due to the form of nano-sized Ag-grains (50-100nm). As can be analyzed from FI-IR spectrum, the-NH2groups and-OH groups in chitosan participated the adsorption for Ag+.5effects of pre-adsorption of metal ions on the removal of MOIf Ag+was pre-adsorbed on the chitosan/TiO2adsorbent, the degradation ratio and degradation rate increased remarkably. The removal ratio of MO could reach90%after2h which was close to the pure TiO2. With the pre-adsorption capacity for Ni2+, the degradation ratio and degradation rate increased too. The same results were obtained for Fe3+and Pb2+. When Cu load capacity was higher (Qcu=69mg/g), the binding energy of the Cu2p peak with the characteristic shake-up feature at a binding energy of942eV are indicative of Cu2+species. Meanwhile, when Cu load capacity was lower (Qcu=6.68mg/g,), the binding energy of the Cu3P peak with the characteristic shake-up feature at a binding energy of939eV are indicative of Cu1+species. Two obverse peaks of379.4eV and373.2eV are quite close to the binding energy of Ag+and Ag0. The generation of Ag0would be the result of deoxidization reaction from Ag+to Ag0, and Ag0may act as the photoactive species favoring the electron transfer to the surface and avoiding the electron-hole recombination. The pre-adsorption for Ag+and Ni2+showed stimulative improvement on the removal of Amaranth and Sunset Yellow. |
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