Study On The Regeneration Performance Of TiO₂/biochar Nanocomposite Adsorbents

Biochar has the characteristics of large specific surface area,porous structure and abundant surface functional groups.It also has the advantages of rich feedstocks,low cost,high adsorption capacity and less energy consumption in the producing process.Biochar adsorbents provide economic and environmental benefits to remove pollutants in water.After the adsorbent reaches saturated adsorption,it will lose its effectiveness and become useless.However,inappropriate disposal for spent biochar may cause the secondary pollution problems.The regeneration of spent biochar can not only eliminate the pollutants,but also restore the adsorption ability of biochar,which is of great significance for decreasing the cost of adsorbent.The emerging photocatalytic regeneration technology has the advantages of simple equipment,in situ degradation of pollutants and little damage to the carbon structure of biochar.However,problems such as low regeneration efficiency and light utilization of the photocatalytic regeneration need to be further improved.In this dissertation,for increasing the light utilization and facilitating the recovery of regenerated biochar,the photocatalytic regeneration of TiO₂/biochar adsorbents was studied in a solid phase method.The regeneration performance was evaluated to compare with the conventional thermal and solvent regeneration.The main research contents and conclusions could be summarized as follows:(1)Commercial TiO₂(P25)was selected as the photocatalytic active ingredient,in order to improve the problems of P25 powders easy to agglomerate,poor stability,and inadequate binding with biochar,P25 was surface-modified by phosphoric acid soaking and the followed heat treatment.The effects of heat treatment temperature on the surface state and photocatalytic performance of P25 were investigated.XRD,XPS,FT-IR,SEM,TEM,DRS and other analytical tests showed that the intermediate phases such as phosphorus titanium salt on the surface of P25 were formed by the soaking and sintering,and the composition of intermediate was related to the heat treatment temperature.Photocatalytic degradation of methylene blue(MB)showed that the optimized degradation of MB was achieved by the photocatalyst treated at 200?for 2 hours,and its photocatalytic efficiency was 1.57 times that of pure P25.The results demonstrated that phosphoric acid modification significantly improved the photocatalytic performance of P25 and their photocatalytic activity was closely related to the content of Ti(HPO₄)₂.(2)Jute fiber biochar(BC)was prepared via chemical activation method using jute fiber as raw material and phosphorus acid as activator.And the biochar-supported TiO₂composite adsorbent(P-P25/BC)was obtained by the method of phosphoric acid soaking and followed heat treatment.The samples were characterized by XRD,FT-IR,SEM and N₂ adsorption-desorption test.The adsorption of MB and Congo Red(CR)were systematically studied,including the effects of adsorbent dosage,initial concentration of adsorbate,and initial pH of the solution.The adsorption kinetics,thermodynamics and isotherms were simulated by corresponding models,and the saturated adsorption capacity,adsorption equilibrium constant,and basic thermodynamic constants were obtained.The results indicated that the adsorption of dyes by BC and P-P25/BC were mainly controlled by chemical action.Solvent desorption experiments showed that a suitable solvent can restore the adsorption capacity of the adsorbent to more than 80%.(3)The adsorption-saturated BC and P-P25/BC were subjected to solid-phase photocatalytic regeneration.Their re-adsorption performance was studied and compared with the thermal regeneration and solvent regeneration methods.The results showed that solid-phase photocatalytic regeneration can in-situ removal MB and CR in BC and P-P25/BC.The removal rate of CR in BC and P-P25/BC under visible light was as high as99.71%and 98.66%,respectively.However,the re-adsorption capacity of the adsorbent was reduced to 48.32%and 35.89%of the original adsorption capacity,which was significantly lower than the regeneration efficiency of thermal and solvent regeneration methods.