Preparation Of Chitosan-based Adsorbents And Adsorption Removal Of Antibiotics From Water

After raising growing concern over the use of antibiotics,water pollution resulting from such abuse has become a significant issue.Adsorption has been established as an efficient method for removing antibiotic pollutants from water,and designing effective adsorbents is crucial to achieve antibiotic pollutant removal.In this study,chitosan-based carbon microspheres and chitosan beads with high adsorption capacity were designed and synthesized using natural biomass chitosan as a substrate.Moreover,we investigated the effects of metal doping and ionic liquid functionalization in enhancing adsorption performance to elucidate the mechanisms underlying adsorption reactions.The main contents are summarized as follows:（1）Cu and Al bimetallically doped chitosan-based low molecular weight carbon microspheres（Cu/Al@NC-x,x=1,2,3）were synthesized by a one-step hydrothermal method.The effect of chitosan molecular weight on the adsorption capacity of Cu/Al@NC-x was investigated,and the results showed that Cu/Al@NC-2 had the best adsorption performance,and its maximum adsorption capacities of oxytetracycline（OTC）and tetracycline（TC）were up to 1727.65 and 981.95 mg g^-1（25℃）,respectively.The excellent adsorption performance was mainly attributed to the hydroxyl and amino groups on the Cu/Al@NC-2 surface and the synergistic action of Cu and Al bimetallic adsorption sites.The adsorption of Cu/Al@NC-2 on OTC was in accordance with the pseudo-second-order kinetics and Langmuir isotherm model,and the adsorption process is a spontaneous endothermic reaction.After five cycles,Cu/Al@NC-2 was still able to maintain 92.25%of the OTC removal rate.The adsorption mechanism of Cu/Al@NC-2 for OTC was proposed based on the effect of p H solution and coexisting ions on adsorption properties.（2）In order to enhance the adsorption capacity of Cu/Al@NC-2,2-methylimidazole（Me）was introduced by utilizing oil bath impregnation to modify Cu/Al@NC-2,forming Me-Cu/Al@NCx carbon material.The impact of Cu/Al@NC-2 addition on the adsorption capacity of Me-Cu/Al@NC_x was examined,and the results indicated that Me-Cu/Al₅₀ exhibited the most outstanding adsorption performance.It showed the maximum adsorption capacity for TC and OTC increased up to 1616.49and 2137.92 mg g^-1,respectively,which was 64.62%and 36.73%increase compared to the Cu/Al@NC-2.The loading modification of Me has enhanced theπ-πinteraction between the adsorbent and tetracycline.The adsorption of Me-Cu/Al@NC₅₀ on TC fitted well with the pseudo-second-order kinetics and the Langmuir isotherm model.The adsorption process appeared to be an endothermic reaction,driven spontaneously.With the reutilization of the adsorbent for five cycles,Me-Cu/Al@NC₅₀ still retained approximately 95%removal rate for TC.The mechanism of TC adsorption in Me-Cu/Al@NC₅₀ was explored using the adsorption performance results examined under the impact of p H and coexisting ions.（3）In response to the difficulty in recycling powder adsorbents,and the improved adsorption performance of loading modification,polyvinyl alcohol（PVA）-fixed chitosan beads（Cu-ZIF/CP_xB）with 3D porous structures were synthesized by coupling room-temperature impregnation with cold-drying through gelation.Based on the"waste-to-treasure"design concept,PVA-fixed chitosan beads（CP_xB）were first formed by hydrogen bonding between PVA and chitosan,and then copper-doped CP_xB（Cu/CP_xB）was obtained after absorbing and recycling Cu（II）.Subsequently,Cu-ZIF/CP_xB was synthesized through the coordination of 2-methylimidazole and copper to form a zeolitic imidazolate framework（Cu-ZIF）composite with CP_xB..The effect of PVA mass fraction on the adsorption capacity of Cu-ZIF/CP_xB showed that the Cu-ZIF/CP₄B had the best adsorption performance,and its maximum adsorption capacity for chlortetracycline hydrochloride（CTC）was 574.50 mg g^-1.The adsorption process was in accordance with the pseudo-second-order kinetics and Langmuir isotherm model,and the adsorption process was a spontaneous endothermic reaction.The mechanism of Cu-ZIF/CP₄B adsorption on CTC was proposed based on the results of adsorption performance evaluation under the influence of p H and coexisting ions,and the industrial application prospect of the prepared 3D monolithic Cu-ZIF/CP₄B adsorbent was evaluated by column adsorption experiments.