Study On Preparation And Adsorption Degradation Properties Of Castor Straw Activated Carbon And Its Composites

China is a large country of agricultural cultivation,of which castor plant area of about 3 million mu.Planting castor will produce a large number of stems,straw and other agricultural leftovers.If castor straw is burned,it will not only waste resources,but also lead to environmental pollution.Since castor straw contains lignin and cellulose,these components provide the possibility for the preparation of biomass-based activated carbon.The preparation of activated carbon with castor straw as raw material can not only realize the effective use of agricultural leftovers,but also make growers increase agricultural added value and increase income.Therefore,in this paper,castor straw was selected as the raw material to study the preparation process of castor straw activated carbon and its adsorption performance to heavy metal ions,and the photocatalytic degradation performance of modified castor straw activated carbon to organic matter.The main work is concentrated on the following aspects:(1)Castor straw was used as raw material,and KOH,ZnCl2 and H3PO4 were used as chemical activators to control the activator concentration,material to liquid ratio,activation temperature and activation time and other variables.Single factor and orthogonal experiment were used to prepare castor straw activated carbon(CSAC).The preparation conditions of three activators were studied by using iodine(I2)and methylene blue(MB)as adsorbents.The results of orthogonal experiments showed that the best preparation process of adsorbing I2 with KOH as activator was material-liquid ratio 1:2,KOH concentration 40%,activation temperature 700℃,activation time 1.0h.The adsorption values of I2 and MB were 927.35mg/g and 129.05mg/g,respectively.With KOH as the activator,the best preparation process for adsorption of MB by CSAC was material-liquid ratio of 1:2.5,KOH concentration of 40%,activation temperature of 800℃,activation time of 2.0h.The adsorption values of I2 and MB were 794.65mg/g and 234.17mg/g,respectively.With ZnCl2 as the activator,the best preparation process of I2 adsorption by CSAC was 1:4,ZnCl2 concentration 30%,activation temperature 800℃,activation time 2.5h.The adsorption values of I2 and MB were 1182.00mg/g and 285.28mg/g,respectively.With ZnCl2 as the activator,the best preparation process for adsorption of MB was material to liquid ratio 1:4,ZnCl2 concentration of 40%,activation temperature of 800℃,activation time of 2.5h.The adsorption values of I2 and MB were 1056.50mg/g and 386.92mg/g,respectively.Using H3PO4 as the activator,the best preparation process for the adsorption of I2 and MB on CSAC was as follows:the ratio of material to liquid was 1:3,the concentration of H3PO4 was 50%,the activation temperature was 800℃,and the activation time was 2.0h.The CSAC prepared under this condition had the best comprehensive performance,and the adsorption values of I2 and MB were 1221.27mg/g and 305.82mg/g respectively,which reached the national level one activated carbon standard.The specific surface area(BET),X-ray diffraction(XRD),Fourier infrared spectroscopy(FTIR),scanning electron microscopy(SEM)and other characterization methods were used to prove that CSAC is mainly composed of amorphous carbon and graphite particles,the specific surface area reached 453.75m2/g above,the surface has hydroxyl active functional groups.(2)The adsorption of heavy metal ions Zn(Ⅱ),Mn(Ⅱ)and Pb(Ⅱ)was studied with CSAC prepared by H3PO4 activation method.The influence of four factors on the adsorption performance of CSAC was investigated by single factor experiment,namely the initial concentration,pH value,adsorption temperature and adsorption time of heavy metal ion solution,and three optimal adsorption conditions were obtained respectively.At the same time,the order of saturated adsorption was determined as Zn(Ⅱ)(78.662mg/g)>Pb(Ⅱ)(67.358mg/g)>Mn(Ⅱ)(17.804mg/g).The adsorption kinetics were in accordance with the quasi-second-order kinetic equation,and the correlation coefficient R2 was greater than 0.9200.The adsorption isotherms were all fitted by the Langmuir isotherm model,and the correlation coefficient R2 was greater than 0.9600.The adsorption process is dominated by single layer chemisorption.(3)TiO2/CSAC composite photocatalyst was prepared with CSAC as the carrier,and the TiO2/CSAC composite photocatalyst was characterized by XRD,FTIR,SEM/EDS.The results showed that anatase crystalline TiO2 nanoparticles were successfully loaded on the surface of CSAC.Using TiO2/CSAC as photocatalyst,the effects of light conditions,catalyst dosage,load,calcination time,calcination temperature and solution concentration on catalytic performance were studied.Under the optimal preparation conditions,the adsorption degradation rate(ADR)of 200mL and 3.06×10-4 M methyl orange by 0.1 g TiO2/CSAC under ultraviolet light was 97.6%.For 100mL,4.25×10-4M phenol,the ADR was 87.7%under ultraviolet light.(4)Ag-TiO2/CSAC composite photocatalyst was prepared by photodeposition method.XRD,FTIR,SEM/EDS were used to characterize the composite photocatalyst.The results showed that Ag nanoparticles were deposited on TiO2/CSAC successfully.Photocatalytic degradation experiments showed that Ag-TiO2/CSAC with load of 3%had good photodegradability.0.1 g Ag-TiO2/CSAC for 100mL and 4.25×10-4M phenol,the ADR was 98.4%under ultraviolet light and 85.4%under visible light.Compared with TiO2/CSAC,the ADR of Ag-TiO2/CSAC composite photocatalyst increased by more than 10%.Ag nanoparticles can effectively reduce electron-hole recombination and improve the photocatalytic performance of the catalyst.