Preparation Of Carbon-Based Single-Atom Catalysts And Its Catalytic Performance Of Organic Pollutants In Water

With the rapid advancement of industrialization and urbanization,the amount of energy required by human beings is increasing day by day.Energy shortage and environmental degradation are two major challenges facing mankind.Catalysts have been widely used in environmental protection,reducing energy consumption and energy production.The research on catalysts has gradually extended from the nano level（>5 nm）to the level of metal clusters（>1 nm）and single atoms（0.1-0.2 nm）.However,the catalysts will show different catalytic behavior with the decrease of size.In this paper,single-atom catalysts（SACs）were selected as catalysts for Fenton-like reaction.Compared with most traditional heterogeneous catalysts,SACs have great metal utilization,excellent catalytic activity and structural stability,and have shown great potential and advantages in the field of heterogeneous catalysis.However,SACs also have shortcomings.For example,metal single-atoms have higher surface energy than related metal nanoparticles and clusters,and metal single-atoms are easy to agglomerate under reaction conditions,which will affect the subsequent reaction.Therefore,it is necessary to reasonably design the preparation method of SACs to reduce the agglomeration of metal single atoms.One of the effective ways to reduce agglomeration is to combine single-atoms with appropriate supports.In this paper,biocarbon-based materials are selected as the support,and nitrogen is used to regulate the coordination of single-atoms.The successful synthesis and micro and macro properties of SACs were analyzed by a series of characterization methods.The optimal metal coordination structure and catalytic performance of the prepared SACs were simulated and analyzed by density functional theory（DFT）.The prepared monatomic catalyst was applied to the degradation of organic pollutants in water by activated peroxymonosulfate（PMS）.The removal effect of the prepared SACs on organic pollutants was measured,and the mechanism of organic pollutants removal by the SACs were analyzed combined with the experimental and characterization results.The following results and conclusions were reached:1.Preparation,DFT analysis and catalyst optimization of biocarbon based single atom catalysts.Ni and Co SACs supported on lignin biochar were prepared by pyrolysis.The micro and macro characteristics of the prepared catalysts were analyzed by a series of characterization methods,which proved the atomic dispersion of the catalysts and the successful anchoring of metal single-atoms on the catalyst.The optimal coordination structure of metal single atom in the prepared catalyst is analyzed by DFT,which is a three-fold coordination configuration.According to the optimal metal single-atom coordination configuration,the performance of SACs activated PMS is analyzed through simulation calculation.It is concluded that the performance of Co-N-C catalyst is better than that of Ni-N-C catalyst.Finally,the simulation results are verified by several groups of experiments.2.Study on degradation performance and mechanism of chloroquine phosphate by biocarbon based Co single atom catalyst.Co SACs（SA-Co-N-C（30））with lignin biochar as carrier were prepared by pyrolysis.In view of the outbreak of COVID-19 and the possible water pollution problems,the degradation performance and mechanism of the prepared catalysts activated PMS to chloroquine phosphate（CQP）were studied.The results show that SA Co-N-C（30）catalyst has superior PMS activation effect and can efficiently catalyze the degradation of CQP in water.Under the same experimental conditions,the reaction rate constant(k_obs)of CQP degradation in SA Co-N-C（30）/PMS system was 0.12345 min^-1,which was 2.0,1.3,1.7,8.1,17.6 and 44.7 times higher than that in SA Co-N-C（15）/PMS,Co-N-C（45）/PMS,NP-Co-N-C（30）-5/PMS,Co-N-C（30）-0/PMS,N-C/PMS and Co₂O₃/PMS systems,respectively.Quenching experiment,electron paramagnetic resonance（EPR）and electrochemical characterization showed that the efficient degradation of CQP was mainly realized by non-radical pathway,in which non-radical electron-transfer was dominant.The metal masking experiment shows that the rich Co-N₃ sites of SA Co-N-C（30）catalyst are the key to the effective activation of PMS and the efficient degradation of chloroquine phosphate.3.Research and pilot test on treatment of organic wastewater with biomass carbon based co monatomic catalyst.By adding different concentrations and types of anions to simulated wastewater,the degradation effect of SA Co-N-C（30）/PMS system on CQP under different coexisting anions was studied.The performance of SA Co-N-C（30）catalyst was studied by configuring simulated wastewater solution with different water sources（such as lake water and tap water）.The experimental results show that SA Co-N-C（30）/PMS system still maintains high catalytic degradation performance for CQP in the presence of coexisting anions or in simulated wastewater prepared from different water sources.In addition,the selectivity of SA Co-N-C（30）/PMS system was explored by adding different organic pollutants to the system.The experimental results show that SA Co-N-C（30）/PMS system has good degradation performance for organic pollutants containing electron donating groups（such as hydroxyl）,but poor degradation performance for organic pollutants containing nitro（electron absorbing groups）.Finally,two small-scale experimental models are designed and dynamic simulation experiments are carried out to further prove the superior performance of the prepared catalyst.