Preparation And Mechanism Study Of Water Purification Materials Based On Chitosan And Graphitic Carbon Nitride

With the rapid development of industrialization and the improvement of living standards,people become much concerned about the increasingly serious problems of water pollution.In particular,some of the nonbiodegradable pollutants have brought great challenges to traditional water treatment technologies.Therefore,searching for efficient,economical and environmentally friendly technologies and water purification materials has attracted considerable attention in recent years.Using chitosan and graphitic carbon nitride,the present paper developed a series of new materials for water purification.Their ability to remove pollutants,the relative mechanisms and the tentative exploration for practical application using magnetic separation technology were investigated.The main conclusions of this work are shown as follow.(1)An Al and Fe bimetal modified chitosan hydrogel was prepared.Compared with monometallic products,this adsorbent exhibits a higher defluoridation capacity and is also more resistant to changes of pH in the solution and the effects of coexisting ions.The adsorption process is in line with the Langmuir adsorption model with a high maximum adsorption capacity of 31.16 mg/g.The main mechanism of adsorption is ligand exchange and ion exchange.Moreover,the adsorbent can be quickly regenerated by NaOH and HCl solutions.(2)A facile,green and low-cost co-precipitation method using chitosan-Fe hydrogel was developed to fabricate the magnetic powdered activated.Its removal of tetracycline hydrochloride from water is rapid and efficient.It possesses a good usability and stability to co-existing ions,organics and different pH values due to its dispersive interactions nature.In addition,this adsorbent is also suitable for the removal of other antibiotics and tetracycline with quite low concentrations.A fluidized-bed reactor with electromagnetic separation function is designed for the practical use of this magnetic adsorbent.The adsorption of pollutants,the separation from water and in-situ regeneration can be easily achieved in this reactor.(3)A Fe-doped graphitic carbon nitride/graphitized mesoporous carbon composite was prepared,which can be used as an efficient Fenton-like catalyst for the removal of contaminants in a wide pH range of 4-10.Under neutral pH conditions,99.2%of Acid Red 73 and 42.9%of TOC can be removed in 40 min.The degradation process is well agreed to the pseudo-first-order kinetics model.By correlating the constant of reaction rates and the Fe speciation contents,we deduced that Fe-N species are the most important active sites for the Fenton-like reaction.The addition of mesoporous graphitic carbon accelerates the Fe(Ⅲ)/Fe(Ⅱ)redox cycle by enhancing electron transfer,and thus greatly improves the catalytic ability of the catalyst.(4)A Cu+-graphitic carbon nitride complex with an efficient Fenton-like activity as well as stability was prepared.Under neutral pH conditions,99.2%removal of Rhodamine B(50 mg/L)could be attained in 1 h.During the preparation process,the Cu precursor is spontaneously reduced,and Cu+ is thereby firmly embedded in the fragmentary g-C3N4 sheet through the coordination with pyridine N.XAFS and other characteristic results illustrate the unique Cu-N2 structure in the composite.Due to its coordinatively unsaturated structure,the catalyst exhibits a high activity towards H2O2 activation.Besides,the valence and coordination of Cu has no obvious change even after the reaction,confirming the high stability of this cuprous structure.(5)Based on the consideration of cost and simplicity,a magnetic Fe-doped graphitic carbon nitride/graphite composite was prepared using the chitosan-Fe co-precipitation method.The study investigated the influence of different supporters on the morphology and active sites of the catalysts.Compared with activated carbon and SBA-15,the introduction of graphite can not only increase the number of Fe-N active sites,but also accelerate the electron transfer rate through the electron interaction with graphite,thereby improve the activity in the Fenton-like reactions.The catalyst shows a high efficiency for bisphenol A removal.More importantly,it exhibits a good reusability and stability,as well as a quick separation from water when using a magnet,indicating this material would be a promising Fenton-like catalyst in practical applications.