| Chromium(Cr)is a common heavy metal with a wide range of industrial uses.A large amount of Cr-containing wastewaters are yielded from various industrial processes,such as mining,metal smelting,electroplating,and chemical production.Cr(VI)in water is difficult to be degraded,and difficult to be handled due to its great toxicity.It thus poses a significant threat to the natural environment and human society.The traditional treatment methods mainly include physical adsorption and chemical precipitation.The physical adsorption method has the advantages of low cost,low pollution,high adsorption amount,and thus is being widely used.Activated carbon appears to be an excellent choice for adsorbent materials,in terms of its wide range of raw materials with high availability and low cost.Activated carbon is often used to treat Cr(Ⅵ)wastewater,but the adsorption capacity is generally low.The treatment performance of activated carbon for Cr(Ⅵ)-containing wastewater is far from excellent.The modification of activated carbon can enhance the electrostatic attraction and ion exchange capacity of metal ions,and thus increase the adsorption amount.It has been reported that the modification of activated carbon by humic acid can introduce a large number of oxygen-containing functional groups and thus improve the chemical adsorption capacity of activated carbon.The metal ion(e.g.,Fe,Mn)modification can form metal oxides on the surface of activated carbon or combine with the functional groups to enhance the adsorption capacity of activated carbon for heavy metals.However,the studies on the adsorption of Cr(Ⅵ)in water by modified activated carbon about manganese fulvate,the combination of humic acid kind substances and metal ion.have not been reported.In this study,typha orientalis presl activated carbon(TAC)was firstly modified in-situ respectively with fulvic acid(FA),manganese fulvate(FA-Mn)and iron fulvate(FA-Fe)at different doping ratios.The adsorption performances of Cr(Ⅵ)in water with the activated carbons modified under different conditions were investigated.The TAC modified by manganese fulvate(TAC-FA-Mn)exhibiting the best adsorption performances and the unmodified TAC were selected for the following experiments.The physicochemical properties of TAC and TAC-FA-Mn were characterized to analyze the effects of manganese fulvate modification on the surface morphology,specific surface area,pore size distribution and surface functional groups of TAC.Static adsorption experiments were carried out to analyze the thermodynamic and kinetic data of Cr(VI)adsorbed by TAC and TAC-FA-Mn,and the effect of solution pH on Cr(VI)adsorption.The main conclusions drawn from this research are listed as below:(1)Activated carbon was modified with FA,FA-Mn or FA-Fe,and the doping ratio,which is equal to mass ratio,was set from 1%to 5%.By comparison,the adsorption ability fo Cr(VI)by TAC-FA-Mn was the best,which was used as the adsorbent for subsequent experiments.(2)The surface physical properties of activated carbon were characterized by scanning electron microscopy(SEM),specific surface area and pore size analysis(BET).The results showed that the surface of activated carbon appeared to be fragmented due to the doping with manganese fulvate.Besides,it was found that the area and volume of micro-pores increased by 41.9%and 44.3%,respectively;the area and volume of meso-pores decreased by 20.5%and 21.6%,respectively;and the total pore volume decreased by 5.3%and 3.6%,respectively.The modification of manganese fulvate increased the microporous ratio of activated carbon,and contributed to the enhanced adsorption capacity of small molecular pollutants.(3)The surface chemistry of activated carbon was characterized by infrared spectroscopy(FTIR),X-ray photoelectron spectroscopy(XPS)and titration experiments.The results showed that the content of functional groups,such as carboxvl group,lactone group and phenolic hydroxvl group on the surface of modified carbon increased.The total amount of acidic functional groups increased from 2.269 mmol/g to 2.912 mmol/g;the ratio of C=O on modified carbon surface increased from 21.74%to 45.39%;the C-O ratio decreased from 46.49%to 31.20%;and the C-OH ratio decreased from 18.62%to 8.91%.(4)The effects of initial adsorption concentration and adsorption time on the activated carbon adsorption of Cr(VI)were investigated by static adsorption experiments.The results showed that when the initial concentration of Cr(VI)was 60 mg/L and the temperature was 298 K,the maximum adsorption capacity of modified activated carbon was 23.396 mg/g,13%higher than the maximum adsorption capacity of the unmodified activated carbon,i.e.,20.656 mg/g.This is mainly attributed to the increase of micro-pores and the introduction of more acidic oxygen-containing functional groups.The Frenudlich model can commendably fit the Cr(VI)isotherm adsorption curve of both the modified and unmodified activated carbon.The adsorption process can be better fitted with a pseudo-second-order kinetic model.The adsorption process was dominated by chemical adsorption,in which multi-molecular layer adsorption existed.(5)The effect of solution pH on the adsorption of Cr(Ⅵ)by modified and unmodified activated carbon was investigated.The results showed that with the increase of pH,the adsorption capacity of activated carbon for Cr(Ⅵ)decreased,and the adsorption capacity of TAC-FA-Mn was stronger than that of TAC.This is probably due to the fact that when the pH of the solution is high,the functional groups on the surface of activated carbon are dissociated,and correspondingly the surface of activated carbon is deprotonated,resulted in the decreased electrostatic attraction capacity of Cr(Ⅵ)in the form of acid anions.In addition,as the concentration of OH-in the solution increases,more OH-participates in the competition of the adsorption sites on activated carbon surface,resulting in the decrease of the adsorption of Cr(Ⅵ). 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