Preparation And In-situ Modification Of Activated Carbons From Typha Orientalis And Investigation On Its Adsorption Mechanisms Of Antibiotic And Heavy Metal Ion

Heavy metals and antibiotics are important sources of water pollution,seriously threatening drinking water safety and human health.The wastewater treatment technologies of heavy metals and antibiotics have become a hot topic for water pollution prevention and control.Activated carbon adsorption is an effective method for removing heavy metal wastewater and antibiotic from wastewater.However,the high cost of preparation from coal or wood and the low adsorption capacity limit the extensive application of activated carbon.It has been a hot issue in recent years to search for cheap and efficient precursor material to for the preparation of activated carbon.Typha orientalis is a kind of aquatic plants.Because of its adaptability to environmental conditions,rapid propagation,and can provide large biomass,it is often used as a core plant for the construction of constructed wetland wastewater treatment ecosystems.A large amount of T.orientalis straw wastes will be produced in autumn and winter each year,improper disposal of them will lead to huge waste of resources and form repeated pollution problems.T.orientalis is rich in lignocellulose and its vascular bundle structure is conducive to the preparation of high porosity activated carbon.Using T.orientalis straw to prepare activated carbon and apply it to sewage treatment can not only control water pollution,but also realize the utilization of plant straw waste and reduce the cost of activated carbon.Low-cost and efficient activated carbon was prepared from T.orientalis straw via phosphoric acid activation and in-situ modification methods,in order to achieve the resource utilization of the cattail straw waste and reduce the cost of activated carbon.The preparation parameters of phosphoric acid activation method by conventional heating method were optimized,in order to prepare high adsorption capacity Typha-based activated charcoal and applied to the adsorption of wastewater containing heavy metals and antibiotics.The Na2EDTA in-situ modification method and EDTAFeNa in-situ modification method were also proposed,the activated carbon was in-situ modified in preparation by combining the phosphoric acid activation and modification processes.The in-situ modification method could enhance the surface functional groups content and load the metal iron on activated carbon,while maintain the pore structure of activated carbon,thereby improved the adsorption capacity of Ni(II)and amoxicillin of modified activated carbon.In addition,the adsorption mechanisms of Chloramphenicol(CAP),Amoxicillin(AMX)and Ni(II)were investigate through physicochemical properties of Typha-based activated carbon in combined with adsorption experiments.This study has a good theoretical guiding significance for the resource utilization of T.orientalis straw and the application of Typha-based activated carbon to different types of wastewater treatment.The main conclusions of this research are as follows:(1)Low-cost and high-absorption capacity activated carbon was prepared from T.orientalis straw wastes via phosphoric acid activation by optimizing the preparation process parameters.The effects of the impregnation time,impregnation ratio(g H3PO4/g T.orientalis)and activation temperature on the pore structure and yield of Typha-based activated carbon were investigated by single-factor experiments.The specific surface area and total pore volume of the activated carbon increased first with the the increase of impregnation time and impregnation ratio,then decreased.When the activation temperature was gradually increased,the specific surface area of activated carbon showed a slight increase,while the total pore volume increased first and then decreased.Considering the pore structure,yield,and energy consumption during preparation,the optimum preparation parameters of Typha-based activated carbon were:impregnation ratio of 2.5,impregnation time of 12 h,and activation temperature of 450?.The physicochemical properties of the optimal activated carbon(AC)were characterized,the optimal activated carbon(AC)has the yield of 43%,SBET of 794.8 m2/g and Vtot of 1.266 cm3/g,the micropore volume(Vmic)accounts for 12.2%of Vtot.,reflecting a mostly mesoporous structure of AC.A large number of functional groups were found on the surface of AC,and the acidic functional group accounted for 67.62%.The CAP and Ni(II)were used as the representatives of antibiotics and heavy metals to investigate the adsorption capacity of AC.The maximum adsorption capacity of CAP and Ni(II)on AC was 137.0 mg/g and 15.8 mg/g,which is higher than that of many other reported adsorbents.The Typha-based activated carbon has a good adsorption capacity.(2)The adsorption mechanisms of CAP the optimal activated carbon(AC)was studied.The specific surface area,pore volume,and pore size distribution of AC before and after CAP adsorption were studied.The results showed that the pore volume of micropores and mesopores in AC after CAP adsorption were reduced at the same time.It was proved that pore-filling effect occurred in micropores,and combination of CAP and functional groups in mesopores occupied part of the pore volume.The microporous-mesoporous mixed structure of AC facilitated rapid adsorption of CAP on AC.The adsorption equilibrium time of CAP on AC was 6 h.The adsorption kinetic that was well described by a pseudo-second-order rate model implied a chemical controlling step,and the intraparticle diffusion model shows that the adsorption rate of CAP on AC was controlled by the intraparticle diffusion and surface adsorption.The adsorption isotherm was well fitted with the Freundlich isotherm model indicating a multi-layer adsorption.The CAP adsorption capacity of AC was not sensitive to the variation of pH value and ionic strength for the CAP molecules were adsorbed on AC mainly in neutral form in this research.The dominant CAP adsorption mechanisms on AC were ?-? electron-donor-acceptor(EDA)interaction,hydrophobic nteraction,hydrogen-bonding interaction in conjunction with weak physical adsorption.(3)Na2EDTA in-situ modification was used to improve the adsorption of Ni(II)on AC,and the adsorption mechanisms of Ni(II)were studied.Na2EDTA in-situ modification,simplified the conventional activated carbon modification process,Na2EDTA,as the modifying agent,modified activated carbon with doping 0-40 mmol Na2EDTA/10 g T.orientalis during phosphoric acid activation.The method simplied the modification process of activated carbon.Ni(II)adsorption capacitis of modified activated carbon increased by 10-80%compared with original carbon.The optimal dosage of Na2EDTA was 35 mmol Na2EDTA/lOg T.orientalis with the adsorption capacity of Ni(II)was 24.6 mg/g.The Na2EDTA in-situ modification method successfully maintained the pore structure of the activated carbon and simultaneously increased the content of oxygen and nitrogen containing functional groups.The higher adsorption capacity of modified activated carbon for Ni(II)was mainly due to its higher surface functional group content than the original carbon.The adsorption isotherm was well fitted with the Langmuir isotherm model indicating a monolayer adsorption.The adsorption equilibrium time of Ni(II)on AC was 12 h.The adsorption kinetic that was well described by a pseudo-second-order rate model implied a chemical controlling step.The adsorption capacity of Ni(II)on activated carbon was greatly affected by pH and ionic strength,high pH and low ionic strength were favorable for Ni(II)adsorption on activated carbon.XPS analysis showed that the surface functional groups of activated carbon were chemically bonded to Ni(II).The dominant adsorption mechanism of Ni(II)on activated carbon were:electrostatic attraction,ion exchange and internal surface complexation.(4)EDTAFeNa in-situ modification was used to improve the adsorption of AMX on activated carbon,and the adsorption mechanism of AMX was studied.EDTAFeNa,as the modifing agent,modified AC with doping 0-8 mmol EDTAFeNa/10 g T,orientalis during phosphoric acid activation.The AMX adsorption capacities of modified activated carbon increased by 30-104%.The optimal dose of EDTAFeNa was 2 mmol EDTAFeNa/10g T.orientalis with the adsorption capacity of AMX was 243.9 mg/g.The the content of functional groups were increased by 67%while Fe(III)was loaded on the surface of activated carbon.The porous structures of modified AC were similar with original carbon.The higher adsorption capacity of modified activated carbon for AMX was mainly due to its higher surface functional group content and iron loaded than the original carbon.The adsorption isotherm was well fitted with the Langmuir isotherm model indicating a monolayer adsorption.The adsorption equilibrium time of AMX on activated carbon was 500 min,and the adsorption kinetic was well described by pseudo-second-order rate model implying a chemical controlling step.The maximTum AMX adsorption capacities of activated carbon were obtained in the pH range of 3-6,and the AMX adsorption capacity of EDTAFeNa modified activated carbon was less affected by the variation of solution pH value.The dominant AMX adsorption mechanisms of activated carbon were electrostatic interaction,ion exchange,and surface complexation.