| As an excellent adsorbent for heavy metal ions,attributing to the high loading capacity,high stability of carbon skeletons and rich surface functional groups,biochar derived from agricultural and domestic wastes have attracted extensive attention in wastewater treatments.However,the stabilization of heavy metals adsorbed in the spent biochar remains a challenge,because environmental changes will rise the risk of secondary pollution under inadequate post-treatment.Hyperaccumulators are widely used in the remediation of soil contaminated by heavy metals,but the dispose of biomass generated from phytoremediation has restricted its future application,especially if the heavy metals containing in hyperaccumulators cannot be properly disposed and utilized,it will spell more serious secondary pollution.Biomass has been used as the source of carbon-based materials and combined with heavy metals to prepare biochar composites which could serve as high-efficiency catalysts for advanced oxidation processes to degrade organic pollutants in water.Notably,the research of carbon-based metal single-atom catalysts is remarkable and puts on the top agenda,since its high activity and stability of the isolated metal atoms has profound implication for environmental remediation.Therefore,it is of great practical significance for the common biomass wastes to study their stability mechanism combined with heavy metals and their potential application in the field of environmental remediation.Base on this problem,rice straw and coffee grounds,kinds of common biomass and domestic wastes,were used as raw materials,cobalt(Co)and nickel(Ni)as exogenous model heavy metals,to study the adsorption and stabilization mechanism of rice straw and coffee grounds biochar with different pyrolysis treatments for cobalt and nickel.Additionally,biochar loaded with Co and Ni can serve as activators for advanced oxidant processes(AOPs)to activate peroxymonosulfate(PMS)to degrade organic pollutants(diethyl phthalate and trichlorobiphenyl).The manganese(Mn)hyperaccumulator plant(Pokeweed Americana)was selected as the raw material to study the stabilization mechanism between biochar obtained via different pyrolysis conditions and the endogenous metallic manganese,and it was used as a photocatalyst to degrade rhodamine B(RhB).The main contents were summarized as follows:(1)The adsorption capacities of rice straw grounds biochar(RSBC)pyrolyzed at different temperatures(500℃,700℃ and 900℃)for Co(Ⅱ)and Ni(Ⅱ)were detected and the Co(Ⅱ)and Ni(Ⅱ)adsorbed on biochar were successfully immobilized via a two-step solution-phase strategy.The adsorption capacities of RSBC for Co(Ⅱ)and Ni(II)were 39.92 mg g-1 and 32.12 mg g-1 when the pyrolysis temperature increased to 700℃.The mechanism research has proved that Co(Ⅱ)and Ni(Ⅱ)formed a stable hydrotalcite-like structure on the surface of biochar after stabilization treatment.The solid waste toxicity leaching experiment proved that leching rate of Co(Ⅱ)and Ni(Ⅱ)decreased from 60%to 0.005%after the stabilization treatment,reaching the requirement of national solid waste leaching standard(GB 5058.3-2007).Moreover,the biochar composite material after stabilization treatment has the potential for resource utilization to activate the PMS to degrade RhB and DEP.The catalytic experiments suggested that RhB was completely removed and 90%of DEP could be degraded in a short time,yet the dissolution of heavy metal ions could be ignored.Electron paramagnetic resonance(EPR)technique and quenching studies were employed to identify the reactive oxygen species in the processes of DEP degradation.The results indicated that·OH,SO4·-and 1O2 were the main reactive oxygen species accounting for DEP degradation.GC-MS was conducted to identify the dominant intermediates for DEP degradation.(2)To enhance the safe and efficient utilization of biochar with heavy-metal loaded,the mechanism of existence and stabilization of cobalt in coffee grounds biochar were systematically studied via pyrolyzing coffee grounds with cobalt adsorbed at different temperatures(300℃,500℃,700℃,and 900℃).The results showed that the amount of cobalt loading could reach 8.12 mg g-1 and the leaching rate was just 0.42%washed by 1 M H2SO4 when the pyrolysis temperature was 500℃.Cobalt dispersed with a well-defined single atomic site in the carbon skeletons and coordinated with the nitrogen and sulfur atoms,forming the active site of Co-N3S,which was confirmed by HAADF-STEM,XAFS and DFT calculation.This biochar composite material exhibited extraordinary activity for PMS activation and was capable to degrade a series of organic pollutants with more than 90%degradation rate,such as PCB28,DEP,and BPA,yet the dissolution of Co could be ignored.Electron paramagnetic resonance(EPR)technique and quenching studies were applied to identify the reactive oxygen species for PCB28 degradation.The results indicated that·OH,SO4·-were the dominant free radicals accounting for organic pollutants degradation.GC-MS was conducted to identify the dominant intermediates for PCB28 degradation.(3)Based on the successful preparation of carbon-based single-atom catalyst(SAC)with the addition of exogenous heavy metal ions,the preparation method of SAC with endogenous heavy metals was further studied.A carbon-based Mn single-atom catalyst was successfully prepared from Mn hyperaccumulator plant-Pokeweed Americana via adjusting the pyrolysis and heating condition.Mn dispersed with a well-defined single atomic site in the carbon skeletons,which was proved by a series of characterizing methods including HAADF-STEM,in-situ XAFS,and DFT calculation.The high photocatalytic activity of the prepared biochar composite can completely degrade RhB within 10 minutes and remained its photocatalytic performance after 6 times recycling experiments.In the photocatalytic process,Mn served as the reactive center to degrade the target organic pollutant and its valence state existed a cycle between divalent and trivalent when it captured electrons from organic pollutants. |
PDF Full Text Request