Preparation Of Modified Carbon Materials And Its Application In The Sorption Of Heavy Metal Ions

Carbonaceous materials,such as activated carbon,graphene,carbon nanotubes and fullerene,are the materials which are almost made up carbon atoms.They are widely applied as adsorbents due to their unique structures and special properties.For example,activated carbon is called as an all-round adsorbent because it has huge surface area and complicated pore structure.Graphene can also be used as an adsorbent for its high specific surface area and abundant active groups on the surface.As adsorbents for heavy metal ions,however,they have some shortages.Activated carbon has low recyled adsorption capacity.And the poor hydrophilicity and easy agglomeration in water restrict the regeneration of graphene as an adsorbent.Hence,functional modifications of carbonaceous materials must be carried out to acquire economic,environment friendly,high efficient and renewable applied adsorbents.In this paper,three new modified carbonaceous materials have been prepared.The structures and morphologies of these adsorbents were characterized by FTIR,XRD,SEM,TEM,TG,BET and nanoparticle size analyzer.Various factors,such as pH value,adsorption time,initial concentration,temperature and the amount of the adsorbents for the adsorption of heavy metal ions have been studied.The main results are given as follows:1.Preparation of ear-like poly?acrylic acid?-activated carbon nanocomposite adsorbent and its application in the adsorption of Cd?II?.The poly?acrylic acid?-activated carbon nanocomposite adsorbent?PAA-AC?was prepared by using K2S2O4 as initiator and N,N'-methylenebisacrylamide as cross-linking agent under nitrogen atmosphere.The results obtained by SEM,TEM and nanoparticle size analyzer indicated that PAA-AC is a novel ear-like nanosheet material with the thickness of about 40 nm and the diameter of about 300 nm.The adsorption assays showed that the introduction of carboxyl groups into activated carbon evidently increased its uptake for Cd?II?.At pH 6.0 and 303 K,the capacity of PAA-AC for Cd?II?could reach to 473.2 mg·g^-1in 15 min.The adsorption process fitted well with the pseudo-second-order kinetic model and Langmuir isotherm model,indicating that the adsorption was a chemical process.Thermodynamic study revealed that the adsorption was a spontaneous endothermic process.While PAA-AC was used in the treatment of industrial electroplating wastewater,98.5% of Cd²⁺ was removed.2.Preparation of activated carbon/ silicon dioxide/ chitosan-poly?acrylic acid?composite and its application in the adsorption of Hg?II?.Using activated carbon as matrix,activated carbon/ silicon dioxide/ chitosan-poly?acrylic acid?composite?AC/SiO₂/CS-PAA?was prepared by conjugating SiO₂ with chitosan,then graft polymerization with crylic acid.The structure and morphology of this composite was characterized.The composite was used to adsorb heavy metal ions.The experimental results indicated that it had selectivity for the adsorption of Hg²⁺,and the capacity could reach to 401.2 mg·g^-1at pH 6.0 and 303 K in 60 min.The adsorption followed the pseudo-second-order kinetic and Langmuir isotherm models,indicating that the adsorption was a chemical process.The thermodynamic study showed that the adsorption was spontaneous,but the capacity changed little when the temperature increased.The adsorbent could be recycled by EDTA,and the adsorption capacity could keep 73.53% of the first after five adsorption-desorption cycles.3.The preparation of ethanediamine/ chitosan/ oxidized graphene composite and its application in the adsorption of Hg?II?.Graphene oxide?GO?with the higher degree of oxidation was prepared by the microwave method.Using GO as matrix and glutaraldehyde as crosslinker,ethanediamine/ chitosan/ oxidized graphene composite?GO-ED-CS?was prepared by reacting with ethylenediamine,and cross-linking with chitosan?CS?.The structure and morphology of this material was characterized and its adsorption for Hg²⁺ was studied.The adsorption results indicated that the adsorption could reach equilibrium in 60 min,and the maximum adsorption capacity was 769.2 mg·g-1.The adsorption of Hg²⁺ on this material was a spontaneous and exothermic chemical process.Moreover,the adsorbent could be recycled by EDTA,and the uptake could maintain above 70.37% of the first after five regeneration cycles.