Preparation Of Biochar/Geopolymer Composite Membrane And Its Removal Of Tetracycline From Water

With the intensification of industrialization in modern society,the problem of water pollution is becoming more and more serious.Antibiotic residues in the water will destroy the ecological balance,cause microbial resistance,resulting in the enrichment of drug-resistant bacteria.Fenton process is one of the common methods to treat tetracycline wastewater,but the traditional Fenton process mainly uses Fe²⁺as catalyst,which will inevitably lead to the secondary pollution of iron salt.New non-metallic catalyst biochar has attracted more and more attention,but there are still some shortcomings,such as low efficiency and difficult recovery of powder.Using geopolymer inorganic membrane（GM）as carrier,biochar/geopolymer composite membrane（BC/GM）and nitrogen doped biochar/geopolymer composite membrane（NC/GM）were prepared by a new method of in-situ synchronous carbonation and self-activation.Using tetracycline（TC）as simulated pollutant,the effects of different process parameters on the structure,surface physicochemical properties and catalytic performance of the composite membrane were studied,and the effects of different factors on the catalytic reaction kinetics in the degradation process were also studied.The results are as follows:（1）Preparation and properties of geopolymer carrier（GM）:Geopolymer inorganic membrane carrier（GM）was prepared with modified sodium silicate as alkali activator,metakaolin and slag as raw materials,Sodium dodecyl sulfate as surfactant and H₂O₂ as foaming agent.After calcined at 600℃for 2 h in nitrogen atmosphere,GM still has higher pore volume(0.135 cm³·g^-1),water flux（6420.55 L/m²·h）and alkalinity,which can be used as the carrier and activator of biochar at the same time.Under the conditions of 0.15 g GM,100m L TC solution,p H=5,50 mg·L^-1 initial concentration and 1.0 m L H₂O₂,the removal rate of TC was 48.31%after 11 h reaction at room temperature.（2）Preparation and properties of biochar/geopolymer composite membrane（BC/GM）:Using alkali lignin as carbon source and geopolymer inorganic membrane as carrier,biochar/geopolymer composite membrane catalyst was prepared by in-situ synchronous carbonization and self-activation.The BC/GM prepared under the conditions of alkali lignin solution dosage of 0.2 m L,sodium silicate modulus of 1.2 and calcination temperature of 600℃has excellent effect on the removal of TC due to its layered porous structure and rich functional groups.When BC/GM dosage is 0.15 g,VH₂O₂=1.0 m L,the volume of TC solution is 100 m L,p H=5.0,C₀=50 mg·L^-1,BC/GM can degrade almost 100%of TC after 6 h at 60℃.The kinetic fitting of this process shows that it is more in line with the second-order kinetic model.In addition,BC/GM has good stability and reusability in Fenton like reaction.In the process of BC/GM catalyzing the degradation of TC by H₂O₂,the C=O functional group is the main catalytic active site,and the hydroxyl radical（·OH）is the main active component.（3）Preparation and properties of nitrogen doped biochar/geopolymer composite membrane（NC/GM）:Nitrogen doped biochar/geopolymer composite membrane was prepared by one-step in-situ doping synchronous carbonization activation method with geopolymer inorganic membrane as carrier and urea as nitrogen source.When the mass ratio of urea to alkali lignin is 2:1 and the calcination temperature is 600℃,the NC/GM has the best removal effect on TC.When the addition of NC/GM is 0.15 g,VH₂O₂=0.2 m L,the volume of TC solution is 100 m L,p H=5.0,C₀=50 mg·L^-1,NC/GM can degrade almost 100%of TC after 5 h reaction at 60℃,which is more in line with the first-order kinetic model.NC/GM also has good reusability and continuous processing ability.In the process of NC/GM catalyzing H₂O₂ to degrade TC,the nitrogen-containing functional groups in NC/GM are the main catalytic active sites,in which pyridine nitrogen（N-6）and graphite nitrogen（N-Q）play an important role in the catalytic activity of nitrogen doped carbon materials.The intermediate products in the degradation process of TC are mainly degraded into small molecules through ring opening reaction,isomerization,demethylation,deamination and dehydration.