| At present,China's heavy metal pollution in water is very serious,and it has caused serious harm to human life,health and living environment.The state has established strict standards for the discharge of heavy metal wastewater.Adsorption method has the advantages of being able to efficiently treat low-concentration heavy metal wastewater,high-quality effluent water,economy and abundant resources.The research and application of magnetic core-shell nanocomposite adsorbent materials have been the focus of attention in recent years.In this paper,a thiol-modified magnetic core-shell nanocomposite adsorbent(Fe3O4@SiO2-SH)with excellent adsorption properties for heavy metal cations was prepared,and its adsorption properties and mechanism were investigated.The main results are as follows:(1)The 3-mercaptopropyltrimethoxysilane(3-TMMPS)was selected as a modification reagent,the optimum conditions for the modification of thiol group were as follows:toluene was the reaction solvent,3-TMMPS ratio was 10:1,temperature was 110? and reflux time was 48h.The static adsorption experiments of Fe3O4@SiO2-SH on Cd2+ show that the increase of initial pH value is beneficial to the adsorption of Cd2+,and the optimal pH is 6.5.The increase of reaction temperature can promote the adsorption reaction.When the temperature is 298K,308K and 318K,the saturated adsorption amount is 61.92mg/g,68.02mg/g and 71.92mg/g,respectively.The effect of interfering ions on the adsorption of Cd2+ was Mg2+>SO42->Ca2++>NO3-.Na+,K+,Cl-had almost no effect.The adsorbent was reused five times for regeneration,and the removal rate of low concentration Cd2+ could still reach 100%.The adsorption of Cd2+ is a spontaneous,endothermic and entropy increasing process.(2)Adsorption experiments of Cd2+,Pb2+,Cu2+ and Ni2+ in a single solution system showed that the adsorption of four heavy metal ions conformed to the Langmuir and pseudo-second-order kinetic model,what's more,the adsorption process is controlled by two stages:out diffusion and inward diffusion.In a single system,the equilibrium adsorption capacity was Pb2+>Cd2+>Cu2+>Ni2+,and was 74.00mg/g,61.92mg/g,42.08mg/g and 26.97mg/g,respectively;moreover,the adsorption rate was Cd2+?Pb2+>Cu2+>Ni2+.In the mixed system of Cd2+-Pb2+-Cue+-Ni2+,the adsorption capacity and adsorption selectivity were both Cu2+>Pb2+>Cd2+>Ni2+.When the initial concentration was 10mg/L,the equilibrium adsorption capacities of Cu2+and Pb2+were 82.93mg/g and 70.55mg/g,respectively;the adsorption capacities of Cd2+ and Ni2+ were all in accordance with the "single system>Cd2+-Ni2+ coexisting system>Cd2+-Pb2+-Cu2+-Ni2+mixed system".Pb2+and Cu2+ both had an adsorption competition for Cd2+ and Ni2+;the amount of Pb2+adsorbed was "Cd2+-Pb2+-Cu2+-Ni2+ mixed system>single Pb2+ system>Pb2+-Cu2+coexisting system",Cd2+,Ni2+ promotes adsorption of Pb2+ and is greater than the competition effect of Cu2+;the adsorption capacity of Cu2+ is "Cd2+-Pb2+-Cu2+-Ni2+mixed system>Pd2+-Cu2+ coexisting system>Cu2+ single system",the presence of Pb2+,Cd2+,Ni2+ has different degrees of adsorption promoting effects on Cu2+.(3)Characterization test results show that the thiol-modified magnetic sorbent Fe3O4@SiO2-SH were successfully prepared.Cd2+,Pb2+,Cu2+and Ni2+ can all be removed by chelating coordination with-SH and-OH.Cd2+ is mainly bound to-SH,and a small part is bound to-OH;Cu2+ and Pb2+ not only preferentially occupy-SH adsorption sites,the binding ability to-OH is also strong.The combination of heavy metal ions and the surface groups of the adsorbent may promote the deformation or fracture of its skeleton,generate debris molecules,expose more hydroxyl groups,and improve the adsorption of boundary acid ions(Pb2+,Cu2+)... |
PDF Full Text Request