Study On Preparation And Catalytic Capacity Of Sludge-based Catalyst Supported With TiO₂-NPs

The increasing production of waste sludge from sewage treatment plants,as well as the related pollution caused by sludge,has been obtained more and more attention.Sludge-based catalyst is one of the important alternatives for recycling waste sludge.In this study,The waste sludge from wastewater treatment plant was selected as the main raw materials,with the ZnCl₂ and TiO₂-NPs as the activator and supplementary photocatalytic materials,respectively,by using the sol gel-chemical activation processes.The characteristics of the sludge-based catalysts were characterized by means of BET,SEM,FT-IR,and XRD.Based on,the catalytic performance and mechanism of the prepared sludge-based catalyst were investigated by using Cefradine as the target pollutant.The main conclusions of this study are as follows:（1）Based on the orthogonal experiment analysis,it can be concluded that the optimal experimental conditions for preparing the sludge-based catalysts loaded with TiO₂-NPs（SAC-TiO₂）were as follows:the mass ratio of TiO₂-NPs and sludge of 1:40,ZnCl₂ concentration of4.5 mol/L,solid-liquid ratio of 1:3,pyrolytic temperature of 550°C,and the pyrolysis time of45 min.（2）The effects of various influencing factors on the catalytic performance of SAC-TiO₂were studied by using the orthogonal experimental analysis.And the decreasing influencing order was concentration of ZnCl₂>mass ratio of TiO₂ and sludge>pyrolytic temperature>pyrolytic time>solid-liquid ratio.（3）Based on the characterization and analysis of the sludge-based catalysts,the BET of SAC-TiO₂ and SAC/TiO₂ was 381.042 and 365.958 m²/g,respectively.The average pore size of the two kinds of sludge-based catalysts was less than 2 nm,indicating that they were mainly microporous and mesoporous.It can be concluded from the SEM and FT-IR analysis that the sludge-based catalyst prepared by one-step was granular,porous and has many functional groups.The XRD analysis showed that TiO₂ was mainly in anatase form and of high activity.（4）The photo-catalytic degradation experiments of cefradine were conducted by using SAC-TiO₂,SAC/TiO₂,GAC-TiO₂,TiO₂-NPs and a blank control group to investigate the catalytic performances.The results showed that the removal rate of cefradine was 20%,48.96%,98.79%,79.80%,and no more than 10%in the group treated by GAC-TiO₂,TiO₂-NPs,SAC-TiO₂,SAC/TiO₂,and a blank control group,respectively.SAC-TiO₂ exhibited a higher degradation rate of 19%than that of SAC/TiO₂,suggested that sludge-based catalyst prepared by one-step has a higher photolysis capacity.（5）The degradation of cefradine by SAC-TiO₂ was optimized by batch assays in this study.The optimum condition for degradation of cefradine by SAC-TiO₂ was determined as initial concentration of 20 mg/L,and SAC-TiO₂ of 1.5 g/L,and the pH of 7.55.Additionally,the degradation rate of cefradine would be affected by the NH₄⁺and PO₄^-ions,and the presence of PO₄^-could improve the degradation rate of cefradine.（6）Adsorption isotherm and kinetic analysis were investigated for SAC-TiO₂,SAC/TiO₂,and GAC-TiO₂.The results showed that the degradation of cefradine were fitted well to the Langmuir adsorption isotherm and pesudo-second-order kinetic model.These results also indicated that the degradation of cefradine by sludge-based catalyst is consistent with physical adsorption and chemical adsorption.（7）The photo-catalytic mechanism for SAC-TiO₂ might mainly be attributed to that the electron（e^-）on TiO₂-NPs will move to SAC with the C as a conductor,reduce its hole recombination rate in the internal and surface of TiO₂-NPs,and increase photo-catalytic activity.In addition,the degradation pathway of cefradine by SAC-TiO₂ was assumed by analysis the degradation products of cefradine by mass spectrometr.In conclusion,using waste sludge as the main raw materials to prepare catalyst can effectively recycle waste sludge,and can also make adsorption and photocatalytic create synergies,providing an effective composite photo-catalytic material for degradation of organic pollutants.