Preparation Of Iron-loaded Graphene Oxide/Chitosan And Its Adsorption Of Arsenic And Chromium In Water

Arsenic and chromium are the two elements which have highly toxic.With the development of human society and economy,resulting the arsenic and chromium in excess of the standards,which seriously endangers human health.Therefore,the adsorption materials for efficient removal of arsenic and chromium are widely concerned.Based on the principle of self-assembly,graphene oxide（GO）and chitosan（CS）were mixed,while FeCl3·6H2O and FeCl2·4H2O were used as modifiers respectly,to prepareα-Fe O（OH）coated graphite oxide/chitosan（Fe@GOCS）and iron-loaded graphene oxide/chitosan（Fe-GOCS）spherical materials.Combined with the static adsorption,kinetics experiment,thermodynamics experiment and characterization,the adsorption mechanism of As（Ⅲ）in aqueous solution by Fe@GOCS and the adsorption mechanism of Cr（Ⅵ）by Fe-GOCS were investigated,which the main conclusions were as follows.（1）The characterization results of Fe@GOCS showed that the iron existed in the composites main in form ofα-Fe O（OH）,and the adsorption capacity of As（Ⅲ）increased with the increase of the amount of iron.While the iron main existed on Fe-GOCS composites in form ofα-Fe2O3,and the adsorption capacity of Cr（Ⅵ）increased with the increase of the mass concentration of the solution,after the concentration exceeded 0.25 mol/L,the adsorption capacity decreased.（2）The Zeta zero potential of Fe@GOCS and Fe-GOCS composites were about8.2 and 7.5 respectly,and the adsorption capacity of As（Ⅲ）and Cr（Ⅵ）increased with the decrease of pH.According to the coexisting ions research,PO₄^3-and Fe³⁺had a great influence on As（Ⅲ）adsorption,While the SO₄^2-had a certain extent on Cr（Ⅵ）adsorption.（3）The experimental results of adsorption kinetics showed that the adsorption reaction of As（Ⅲ）by Fe@GOCS followed the pseudo second-order kinetic equation.While the solution of pH value was 3.0,the tempeture was 318.15 K,and the dosage of adsorbent was 1.0 g/L,the maximum adsorption capacity could reach 289.4 mg/g.After five times of adsorption-desorption cycle,the adsorption capacity did not decrease,but increased.For Fe-GOCS,the adsorption reaction of Cr（VI）by Fe-GOCS was followed the pseudo first-order kinetic equation in the first 10 hours,after 10hours later,the adsorption process followed the pseudo second-order kinetic equation.While the solution temperature was 318.15 K,pH value was 2.0 and the dosage was0.9 g/L,the maximum adsorption capacity about Cr（VI）can reach 141.5 mg/g.However,after five times of adsorption-desorption cycle,the adsorption capacity decreased slightly.（4）The thermodynamics study showed that the adsorption process of As（Ⅲ）on Fe@GOCS and the adsorption process of Cr（VI）on Fe-GOCS were spontaneous reactions of endothermic with entropy increased,and higher the temperature,greater the adsorption capacity.Langmuir,Freundlich and sips isotherm adsorption models can describe the adsorption behavior of As（Ⅲ）,while the thermodynamics study showed that Langmuir and Sips model can better describe the adsorption behavior of Cr（VI）.（5）XPS studies showed that the arsenic adsorbed on Fe@GOCS was As（Ⅲ）,while combined with the results of material characterization and adsorption experiments,it was considered that ion exchanges and surface complexation were the main mechanisms of As（Ⅲ）removal by Fe@GOCS.For Fe-GOCS,the main groups of Cr（VI）adsorption were—NH2,Fe—OH and—OH,and the adsorption mechanisms mainly included redox reactions,electrostatic binding and ion exchanges.