Preparation Of N-doped Biochar/Molybdate Composite And Its Removal Of Tetracycline From Water

Water environment security is a key issue that needs to be solved for sustainable development.In recent years,the harm of antibiotics to the ecological environment has continued to increase.Among them,tetracycline(TC)is widely used due to its broad antibacterial spectrum and low price,which poses potential risks to the environment,especially the water environment.Photocatalytic technology is a promising method for water treatment,but its practical application is still challenging due to factors such as high cost and low efficiency.Therefore,the development of high-efficiency and lowcost photocatalytic materials is the key to the application of photocatalytic technology.In this paper,urea was used as a nitrogen source to modify the agricultural and forestry residue poplar sawdust by N-doping to prepare N-doped biochar(NBC)with good adsorption performance for TC,which was then used for the composite of two molybdates to prepare novel NBC/PbMoO4 and novel NBC/BMO composites.The photocatalytic activity of typical pollutant TC(40 mg/L)in water was evaluated by degradation.The main results are as follows:(1)Urea was used as a green N dopant for N doping modification of poplar powder.When the mass ratio of poplar powder and urea was 1:4,the NBC obtained by calcining at 500℃ for 2 h in muffle furnace had the best adsorption performance for TC,which was 2.52 times of that of unmodified BC.(2)Poplar powder was added in the process of co-precipitation to synthesize PbMoO4 precursor by two-step synthesis method,and PbMoO4 was in-situ deposited on poplar powder.According to the optimized NBC preparation scheme,three different proportions of NBC/PbMoO4 composites were successfully prepared.The characterization results show that the NBC skeleton increases the specific surface area and charge transfer rate of the composites,and expands the visible light absorption range.When the ratio of NBC in the composite was 65%,it exhibits the best performance.The total removal rate of TC was 85%after dark adsorption for 30 min and illumination for 120 min,which was 3.53 times that of pristine PbMoO4 and 2.25 times that of BC/PbMoO4.The main active species of the reaction system is h+.Finally,the degradation mechanism of NBC/PbMoO4 was proposed.(3)Using solvothermal synthesis method,NBC was added during the synthesis of Bi2MoO6 precursor for modification,and the NBC/BMO composite was successfully prepared by optimizing the composite ratio of NBC.The introduction of NBC obviously induces changes in the physical and chemical properties of Bi2MoO6,enhanced light absorption properties and reduced band gap.When the ratio of NBC in the composite material is 20%,it shows the best performance.After dark adsorption for 30 min,the total removal rate of TC under light for 120 min is 86%,which is 2.32 times that of pristine Bi2MoO6 and 2.12 times that of BC/PbMoO4.After 5 cycles of recycling,the removal rate of composites remained at 72%.The main active species of the reaction system were ·O2-and h+.Finally,the degradation mechanism of NBC/PbMoO4 was proposed.