Studies On Removal Of Heavy Metals And Antibiotics By Pyridine-functionalized Chitosan Adsorbents

Heavy metals and antibiotics are widely found in various wastewaters,causing serious pollution in surface water and groundwater.Antibiotics pollutants always have abundant functional groups,which can coordinate with heavy metal ions and form complex contaminants.Thus physical and chemical properties of the pollutants will be changed.Due to various forms of complex contaminants,it is difficult to remove them completely.On the one hand,the complexes are various,which will increase the difficulty of the pollution treatment greatly;on the other hand,the higher toxicology of complex contaminants will pose a threat to environmental safety and human health.At present,there is no specific method for the treatment of such pollutants,while traditional pollutant treatments and their combination technologies,such as precipitation,oxidation,mineralization,etc.,have such defects as high cost,complicated process and serious secondary pollution.Therefore,it is urgent to develop a integrated and resource-based treating technology for such pollutants.Adsorption can be operated easily with low cost and no secondary pollution.Now,some novel adsorbents can remove heavy metals or antibiotics separately,and realize co-adsorption of heavy metals and antibiotics within a certain range,but few are reported.Bio-adsorbents have a large number of functional groups,which guaranteed they are convenient for subsequent modification;while they are easy to obtain with low cost.These make bio-adsorbent a research hotspot and an optimal adsorbent for controlling complex pollutants.Currently,the interaction between adsorbent and pollutants is lack of systematic knowledge.Thus theoretical guidance for practical application and technical evaluation cannot be provided.In this research,heavy metals and antibiotics used in the production and domestic life are selected as models of pollutants,including Cu,Zn,Cd,ciprofloxacin,sulfamethoxazole,and tetracycline.A series of bio-adsorption materials were designed and prepared.Their adsorption characteristics and mechanism are investigated.Their integration and resource recovery technology are discussed subsequently.The results are as following.(1)In this research,amino modified chitosan adsorbent(CN)and pyridine modified adsorbent(CNP)were prepared independently.The nitrogen contents of resins were 8.91%and 12.77%for CN and CNP respectively.With grafting polyethyleneimine(PEI),great amount of amino groups were introduced,and increased active adsorption sites.With the introduction of pyridine groups,nitrogen content was raised further.For both CN and CNP,amino groups are the strong coordination groups,and pyridine groups in CNP are the auxiliary coordination groups.It was found that while CN and CNP had good adsorption effect on heavy metals.They also had synergistic effect on heavy metals and antibiotic substances,so that co-adsorption of heavy metals and antibiotics is accessible.(2)While adsorbing HMIs,within the scope of the pH=1?5,CN and CNP achieved maximum adsorption quantities at pH=5,while the adsorption of CNP was obviously higher than that of CN.Adsorption isotherm of CNP fitted the Langmuir model better and kinetic curves fitted the secondary dynamics equation better,with the maximum adsorption quantities of copper,zinc and cadmium for 1.92 mmol/g,1.43 mmol/g and 1.02 mmol/g respectively,and can maintain good adsorption of heavy metal ions at low pH range(1?2),showed strong resistance to acid.In ternary system,CNP showed good copper-specificity,because of the stronger combination between adsorbents and Cu(II),rather than Zn(II)and Cd(II).Salts in the solution also showed influence on the adsorption quantities,and Na~+and Cl~-ions,the most common type in natural waters,promoted the adsorption quantity the strongest,with a promoting rate of 45%?50%.With the help of FTIR and XPS,it was found that the amino and pyridine groups play a significent role in the adsorption of heavy metals.(3)While adsorbing antibiotics,ciprofloxacin(CIP)and tetracycline(TC)were difficult to be adsorbed,while sulfamethoxazole(SMZ)could be adsorbed easily,the theoretical maximum adsorption capacity could reach 1.99 mmol/g.At the same time,through the analysis of the kinetics and thermodynamics,it could be found the adsorption process can be affected by the pH of solution,which means the adsorption is related to the forming of H-bridge.(4)While adsorbing complex pollutants,there is complex interaction between heavy metals and antibiotics.Utilizing mass spectrometry and UV-Vis spectrum,we found the combination forms included two antibiotics with a single metal core(2L+M),monogamous single metal core(L+M)and bridging double metal core(L+2M).Usually the compounds'concentrations are relatively low.In the co-adsorption process,the adsorption of heavy metals decreased slightly,but the adsorption amount of antibiotics increased.In the adsorption process,it showed synergistic effect and competitive effect between antibiotics and heavy metals.At low concentrations,it showed the synergistic effect,metal ions provided the bridging sites for antibiotics,and antibiotics also acted as the bridging sites to improve the adsorption capacity of metal ions.At high concentrations,antibiotics competed with metal ions for adsorption sites,resulting in a decrease in the adsorption capacity of both.In brief,CN and CNP have good capacity for heavy metals and antibiotics,especially for their complex pollutants.It has a broad application prospect for integrated remover and resource recovery of such pollutants.