| A large amount of wastewater,especially one containing heavy metal ions(HMIs),has been produced in modern industrial processing,which cause serious pollution to ecological environment.As an environment-friendly neutralizer,magnesium hydroxide has become an important hot topic in the frontier field of science because of its good performance in removing HMIs.However,although HMIs can be deposited when applying Mg(OH)2 to purify water system,the complete separation is difficultly achieved from the water and the secondary pollution is always accompanied.In this thesis,a variety of magnesium hydroxide-based(derived)composite materials have been designed and prepared,which not only achieve high removal rate,but also provide potential solutions to effectively separate HMI deposits from wastewater.The novelties are addressed as follows:Binary composite cellulose-magnesium hydroxide precursor has been prepared via a facile hydrothermal method.The calcinations have successful access to a novel biochar fibril-magnesium oxide(labeled as BCF@Mg O)composite,in anticipation of being a promising wastewater treatment agent.It is shown that the cellulose fibril is transformed into BCF in a high graphitization degree through calcining,and it is covered by a cubic Mg O flakes of about 200 nm in size.The multiple crevice(pore)structures on Mg O flakes endow the composite with a large specific surface area(201.4m~2·g-1).BCF@Mg O has distinguished removal performance of HMIs,for example the maximum removal amount qmax towards Cd2+and Pb2+reaching 2035.4 and 3410.1mg·g-1,respectively.In conjunction with the density functional theory calculations,the interfacial interaction between metal salt precipitate and BCF is revealed to be dative and/or hydrogen bonds;and cadmium and lead precipitates are captured under the inner-and outer-sphere immobilization mechanisms,respectively,which eventually accomplish the complete separation of HMI pollutants from water and avoid the secondary pollution simultaneously.Ternary composite cellulose/zinc oxide/magnesium hydroxide(marked as Cel/Zn O/Mg(OH)2)has been prepared by adding zinc acetate in the synthetic route.The characterizations show that granular Zn O and lamellar Mg(OH)2 are evenly distributed on Cel.Upon starting from the electrostatic driving force,hydrogen and Mg/Zn-Ocdative bonds(Oc denotes the oxygen of cellulose)are formed between the interface of cellulose and Zn O/Mg(OH)2.The composite bears better HMI removal and antibacterial activities.The Mg(OH)2 component offers the composite outstanding performance in removing HMIs,and the qmax of Cd2+,Cu2+and Pb2+reaches 693.2,764.6 and 1407.6mg·g-1 respectively.The existence of the Zn O component improves the antibacterial property of the composite,indicated by the inhibition zones for S.aureus and E.coli of3.75 and 2.45 mm,respectively.Another ternary composite water treatment agent,cellulose nanofiber/ferroferric oxide/magnesium hydroxide(labeled as CNF/Fe3O4/Mg(OH)2),with the desired magnetic property,has been prepared via a hydrothermal method by adding the ferric chloride.Morphological analyses exhibit that the composite has a layered structure in general,in which Mg(OH)2 is dispersed in the networks formed by CNF and Fe3O4.The qmax of CNF/Fe3O4/Mg(OH)2 for Cd2+is 382.7 mg·g-1,and 99%removal rate is still maintained even after 15-cycle operations.In the removal reaction process,the Mg(OH)2 component in composite deposits HMI,CNF immobilizes the formed HMI salt precipitate by hydrogen bonding,and the magnetization of Fe3O4 helps to quickly separate HMI pollutants from water without bringing the secondary pollution.In brief,a series of binary and ternary composites,supported(derived)by renewable cellulose,have successfully synthesized,which are found to have various advantages of their precursors at one time.The simple synthesis method,low cost,high removal performance of HMIs and elimination of the secondary pollution allow our newly-prepared composite materials to have favorable application in future. |
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