| Adsorption method is often used for the advanced treatment of aqueous excessive heavy metals,azo dyes and their complexes due to its high efficiency and designability of materials.However,traditional adsorbents generally have shortcomings such as inconvenient recycling,low adsorption capacity,poor selective adsorption,needing secondary treatment,etc.Secondly,research objects are often focused on the mono-polluted water environment,while less research has been done on the coexistence of polluted systems,especially the effects and interaction of each other in the binary-polluted system,as well as the performance and removal mechanism of the formed heavy metal complexes(HMCs).Thirdly,due to the existence of adsorption equilibrium,adsorption method is often difficult to eliminate pollutants in water,especially trace organic pollutants and HMCs.Therefore,aiming at aqueous mono and binary polluted systems,the development of adsorbents with easy recovery,high adsorption capacity,strong selectivity,safety and economy has gradually become a new focus.In order to solve the above problems,this paper intends to design the molecular structure of adsorption materials from the following aspects:(1)magnetic performance of adsorption materials;(2)functionalization of active groups;(3)hyper-branching of adsorption site on the surface;(4)embedding of modified materials;(5)synergistic effect of adsorption and degradation,etc.Magnetic composite materials are an important new type of aqueous pollutants adsorbents because of their unique nano and magnetic properties and abundant active functional groups which enable them to integrate the above-mentioned excellent properties.Hence,in this paper,we focused on the preparation and characterization of magnetic composite materials modified by inorganic materials,organic small molecule materials,natural high molecule materials and the application performance,effect factors,adsorption models,interaction and mechanism of heavy metal ions,azo dyes and HCMs in water.The details are as follow:(1)A magnetic adsorption microsphere modified by Schiff-base(Fe3O4@SiO2-S2)was synthesized by grafting methyl acrylate,ethylenediamine and salicylaldehyde to the prepared magnetic hybrid material(Fe3O4@SiO2-NH2)successively,furthermore,its structure was characterized and the adsorption performance were studied.The results showed that Fe3O4@SiO2-S2 had magnetic intensity of about 46 emu/g and was a microsphere particle with core-shell structure.Fe3O4@SiO2-S2 had selective adsorption for Hg(Ⅱ)with a maximum adsorption capacity of 384.26 mg/g(1.18 mmol/g),which was superior to other adsorbents and the adsorption capacity remained about 81%after 5 cycles of adsorption-desorption.The results shown from Density Functional Theory(DFT)calculation that the N atoms of Schiff-base mainly contributed to the selective adsorption for Hg(Ⅱ),furthermore,the N atoms of tertiary amine,and the O atoms of hydroxy and carbonyl also contributed to the adsorption for heavy metal ions.(2)On the basis of Fe3O4@SiO2-S2,a Schiff-base modified hyper-branched magnetic composite microsphere(Fe3O4@SiO2-S4)was fabricated by a method of "grafting-branching-modification" and applied for selective adsorption for aqueous heavy metal ions with same property.Fe3O4@SiO2-S4 possessed excellent selective absorption for Hg(Ⅱ),Cd(Ⅱ)and Ag(I)in a mixed solution of heavy metal ions,and all achieved a maximum adsorption capacity more than 3.00 mmol/g and had good reproducibility.The adsorption of heavy metal ions by Fe3O4@SiO2-S4 mainly depended on the complexing of N and O atoms in the surface active groups of composite microsphere,and the selective adsorption for Hg(Ⅱ),Cd(Ⅱ)and Ag(I)was mainly from N atoms of imine groups.(3)Two sulfur-containing hyper-branched magnetic composite microsphere(MCP-S4 and MCP-S8)were prepared based on the research of Fe3O4@SiO2-S4 to verify the universality relationship between the construction characteristics of materials and adsorption properties,models and mechanisms.Both MCP-S4 and MCP-S8 had superparamagnetism and obvious core-shell structure with magnetic intensities of 22.10 and 22.26 emu/g,respectively.MCP-S4 and MCP-S8 also showed selective adsorption for Hg(Ⅱ)in aqueous solution with coexistence of other heavy metal ions,with maximum adsorption capacities of 1.95 and 3.13 mmol/g,respectively.The adsorption for Hg(Ⅱ)by MCP-S4 and MCP-S8 was also more consistent with pseudo-second-order and Langmuir models,and the adsorption was a spontaneous,entropy-increasing and endothermic process.Active groups(C-N,-CONH,C=S,-SH)could form stable chelates with Hg(Ⅱ),which was the main reason that MCP-S4 and MCP-S8 could adsorb heavy metal ions.Among them,sulfur-containing groups(-SH)in MCP-S4 and double sulfur-containing groups(C=S,-SH)in MCP-S8 played a dominant role in the selective adsorption for Hg(Ⅱ).(4)Based on the research of magnetic composite microspheres of aqueous heavy metal ions in the previous three chapters,a magnetic chitosan/polyethyleneimine embedded hydrophobic sodium alginate composite microsphere(MCPS)was fabricated to simultaneous adsorption aqueous heavy metals and azo dyes.In mono-polluted system,the optimal pH for Cr(Ⅵ),methyl orange(MO),Cu(Ⅱ)and methylene blue(MB)were 3,2,6 and 12 with the maximum adsorption capacities of 88.69,331.25,93.51 and 253.31 mg/g,respectively.In binary-polluted system,MCPS possessed simultaneous adsorption for Cr(Ⅵ)-MO and Cu(Ⅱ)-MB complex pollutants at their optimal pH.In addition,the removal of heavy metals were promoted with the addition of azo dyes but the removal of azo dyes were suppressed with the addition of heavy metals.The removal for Cr(Ⅵ)-MO and Cu(Ⅱ)-MB binary pollutants by MCPS mainly included electrostatic attraction,chelation,Van der Waals force,hydrogen bonding,reduction,pore diffusion,etc.(5)Heavy metals and organic pollutants are universally co-existing in water,except for dissociated pollutants,their complexes have also caused huge damage to environment and humans.Hence,two novel microcrystalline cellulose(MCC)modified hyper-branched chitosan aerogels(HCS/MCCs,M-HCS/MCCs)were fabricated to remove aqueous heavy metals,azo dyes and their complexes simultaneously.HCS/MCC-30 exhibited fast and efficient adsorption effect on dissociated pollutants(Cu(Ⅱ),Pb(Ⅱ),MO and CR),and the adsorption kinetics fitted better with pseudo-second-model reaching maximum adsorption capacities of 412.50,425.14,435.13,538.46 mg/g respectively in mono-molecular layer adsorption,and the adsorption was an endothermic,spontaneous and randomness-increasing process in mono-polluted system.M-HCS/MCCs showed a synergistic effect of adsorption-degradation on Cu(Ⅱ)-MO and Pb(Ⅱ)-CR binary-polluted systems.Furthermore,the evolution,configuration and free energy variation of the complexes in binary systems were figured out by DFT calculation.Both radical and non-radical pathways were discovered in the two process of self-catalysis of the complexes and activating-catalysis of magnetic particle for PS,and the organics were degraded to CO2 and H2O ultimately.Finally,the synergistic effect of complexation-adsorption-catalytic degradation,removal mechanism and models were revealed. |
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