Osmium Nanoparticles With Peroxidase-like Activity For Highly Efficient Degradation Of Phenolic Pollutants

Noble metal-based nanomaterials（such as gold,platinum,palladium,etc.）exhibit excellent performance as enzyme mimics,raising widespread concerns in the fields of simulated enzyme catalysis,biosensors,disease diagnosis and treatment,and pollutant degradation.The noble metal osmium has unique physical and chemical properties such as high density,strong acid resistance,and fast electron transfer rate.However,there are few studies on osmium-based nanozymes.In this paper,osmium-based nanoparticles have been synthesized,showing the peroxidases-like activity,and used for the fast and efficient degradation of phenolic pollutants.The main findings are as follows:（1）Osmium nanoparticles modified with sodium citrate and binary alloy nanoparticles with different ratios of iridium to osmium（Ir-Os）were prepared by a"one pot synthesis"method.The synthesized Os-citrate NPs were characterized by scanning electron microscope（SEM）,High Resolution Transmission Electron Microscope（HRTEM）,X-ray diffraction（XRD）,X-ray photoelectron spectroscopy（XPS）,and Ultraviolet and visible spectrophotometry（UV-Vis）techniques.It was found that Os-citrate NPs were nanocrystals with an average particle size of 2.1 nm,and there were（101）characteristic crystal faces.Among them,there are two valence states of Os,namely（0 and IV）,mainly consisting of 0valent Os and doped with a small amount of IV valent Os of Os O₂.The structural characteristics of Ir-Os-citate NPs were characterized by spherical aberration electron microscopy,and the atomic proportions of Ir and Os were characterized by Energy Dispersive Spectroscopy（EDS）.（2）It was found that Os-citrate NPs can oxidize peroxidase substrates3,3’,5,5’-Tetramethylbenzidine（TMB）and o-Phenylenediamine（OPD）in the presence of H₂O₂,with maximum absorption peaks at 652 nm and 422 nm,accompanied by color changes in the solution.Electron Spin-Resonance（ESR）characterization can observe significant hydroxyl radical（·OH）signals,indicating that Os-citrate NPs can promote the production of·OH from H₂O₂,thereby possessing peroxidase like catalytic activity.When TMB and H₂O₂were used as substrates,the steady-state kinetic parameters K_m,V_max,and K_catof Os-citrate NPs as peroxidases were determined.Higher K_catvalues and K_cat/K_mvalues indicate that Os-citrate NPs have higher catalytic performance.（3）The factors that regulate the production of·OH from H₂O₂catalyzed by Os-citrate NPs were investigated;It was found that the p H value of the reaction system and the doping of a small amount of Os O₂on the surface of the material had significant effects on their peroxidase like activity,which could be used to regulate the formation of·OH.（4）The catalytic degradation of phenolic pollutants by Os-citrate NPs and Ir-Os-citrate NPs and their degradation mechanisms were studied.Nanocatalysts were used for the degradation of 4-nitrophenol（4-NP）and bisphenol A（BPA）in the presence of Os-citrate NPs and H₂O₂,and the degradation kinetic characteristics were investigated.The results show that both 4-NP and BPA can be almost completely degraded within 15-30 minutes（>99.5%）.Using Os-citrate NPs for the degradation of six phenolic mixed pollutants（4-NP,2,4-DCP,2-NP,4-CP,2,5-DCP,and 2,6-DCP）,it was found that within 30 minutes,the degradation rate of 2-NP was 91%,while the degradation rate of the remaining five phenolic compounds was close to 100%.The degradation pathway of 4-NP catalyzed by Os-citrate NPs was inferred,and the intermediate products were identified and confirmed using chromatography mass spectrometry,confirming the inference of 4-NP degradation mechanism.（5）The differences in the degradation efficiency of BPA between Ir-Os-trate NPs alloys,pure Os-ctrate NPs,and pure Ir-ctrate NPs with different ratios of Iridium and Osmium（Os:Ir=0.5:9.5,1:9,2:8,and 3:7）were investigated.The results showed that the reaction system with Os:Ir=1:9 Ir-Os-trate NPs had the highest efficiency,with a degradation efficiency of99%of BPA within 15 minutes.The effects of catalyst dosage and H₂O₂concentration of Os:Ir=1:9 Ir-Os-citate NPs on the degradation efficiency of BPA were studied.The degradation pathway of BPA was inferred,and the mass spectrometry data of intermediate products verified the inference of the degradation reaction mechanism of BPA.To sum up,this dissertation has prepared osmium-based nanocatalytic materials with peroxide-like nanozyme catalytic activity.Combined with advanced oxidation technology,they have been applied to the efficient and rapid degradation of phenolic pollutants,which has methodological guidance and potential application prospects for the removal of refractory pollutants in the environment.