Research On The Removal Performance And Mechanisms Of Novel Artificial Carbon-based Materials For Pb（Ⅱ）and Cd（Ⅱ）in Water

In recent years,with the expansion of urbanization and the rapid development of industrialization,a large number of heavy metal pollutants have been released into the environment,seriously harming to the health of animals,plants,and humans.China,as a large food producing country,the environmental problems and resource utilization caused by the disposal of agricultural wastes have always been the focus of attention of scholars.Based on the resource utilization of typical agricultural wastes,the manuscript introduced new artificial carbon-based materials derived from agricultural wastes to remove heavy metal ions in polluted water(Cd²⁺and Pb²⁺were taken as examples)and combined advanced characterization techniques such as SEM,XRD,XPS,FTIR,etc.to analyze the structure and properties of artificial carbon-based materials,and then analyzed removal mechanisms for the heavy metal,which provided new ideas for enriching the types of artificial carbon-based materials and further industrial applications.The main research contents and results are as follows:（1）Artificial humic acid（A-HA）was utilized to modify nano-zero-valent iron（nZVI）particles to prepare artificial humic acid-nano zero-valent iron composite（AHA-nZVI）for Pb²⁺removal.Due to its small size and high reactivity,nZVI is often used as a heavy metal ion adsorbent.However,the removal performance of nZVI is poor and its application range is limited towing to the properties,e.g.,it is extremely easy to be oxidized and agglomerated,etc.In this experiment,A-HA prepared by hydrothermal humification（HTH）technology was used as a dispersant,and AHA-nZVI composite materials were prepared through the bonding between the rich oxygen-containing functional groups（-OH and-COOH,etc.）of A-HA and nZVI.And the characterization results of SEM,XRD and XPS showed that the combination of A-HA and nZVI can reduce the degree of agglomeration and oxidation of nZVI,so that nZVI has good dispersibility and oxidation resistance.The results of adsorption kinetics and isothermal adsorption experiments showed that the prepared AHA-nZVI composite had a higher removal efficiency（>99.2%）for Pb²⁺than nZVI（50.83%）.Moreover,the process of removing Pb²⁺was more closely related to the pseudo-second-order kinetic model,indicating that the process of removing Pb²⁺by AHA-nZVI composites is mainly chemical adsorption.In addition,the correlation（R²）of Langmuir isothermal model was higher than Freundlich isothermal model,indicating that the adsorption process of AHA-nZVI composite for Pb²⁺may be dominated by monolayer adsorption,and the maximum adsorption capacity of AHA-nZVI composite for Pb²⁺was 649.0 mg/g.AHA-nZVI may have multiple mechanisms for Pb²⁺removal,including reduction reaction between Pb²⁺and AHA-nZVI samples,functional groups bonding,and mineral co-precipitation.（2）We have successfully prepared porous magnetic biochar（Fe₃O₄-γFe₂O₃@PBC）using corn stalks（CS）and waste iron（WI）as precursors.The physicochemical properties of Fe₃O₄-γFe₂O₃@PBC composite material were analyzed through characterization.The BET data showed that Fe₃O₄-γFe₂O₃@PBC had a high specific surface area（906.9 m²/g）.The SEM image showed that the iron oxides were uniformly dispersed on the porous biochar framework.The comprehensive effects of different ratios of iron ions on the magnetic recovery rate and Pb²⁺adsorption capacity of the magnetic biochar were investigated.The results showed that the adsorption performance of the composites prepared when the iron ions were introduced at 0.04-0.06 mol/L had the best comprehensive performance.In order to further improve the properties of Fe₃O₄-γFe₂O₃@PBC composites,A-HA（rich in oxygen-containing functional groups,phenol-OH,-COOH,etc.）extracted from waste biomass was used as the activator to prepare AHA/Fe₃O₄-γFe₂O₃@PBC composites by using the bonding reaction between A-HA and iron oxide.FTIR and XPS results showed that AHA/Fe₃O₄-γFe₂O₃@PBC composite has rich functional groups,and through the dispersity test found that AHA/Fe₃O₄-γFe₂O₃@PBC composite has good dispersity and stability,which proved that A-HA can effectively improve the physical and chemical properties of the composite.Adsorption kinetics and isothermal adsorption experiments showed that the removal process of Pb²⁺by AHA/Fe₃O₄-γFe₂O₃@PBC composite was correlated with the pseudo-second-order kinetic model and Langmuir isothermal model,and the Langmuir fitted maximum adsorption capacity was 99.82 mg/g.In addition,the adsorption capacity of the composite was still 79.04 mg/g after 5 cycles,showing good cyclability.AHA/Fe₃O₄-γFe₂O₃@PBC has multiple removal mechanisms for Pb²⁺including reduction reaction,functional group bonding,and mineral coprecipitation.（3）In this experiment,a novel concept of colloidal-like magnetic biochar（Col-L-MBC）was prepared by using porous biochar prepared from corn straw as the skeleton in one step and directly used for the remediation of heavy metal polluted water.Through SEM,XRD,XPS and Zeta characterization technology analysis of the physical and chemical properties of Col-L-MBC showed that the introduction of A-HA provided abundant functional groups on the surface of the magnetic biochar,which was conducive to the uniform dispersion of magnetic iron oxide particles on the porous biochar framework,and provides abundant active sites for heavy metal removal.In addition,the introduction of A-HA decreased the surface potential of magnetic biochar（when p H=7,the Zeta potential value was reduced from-7.70 mV to-17.33 mV）,and improved the dispersion of magnetic biochar particles in water.Adsorption kinetics experiments showed that the adsorption capacity of Col-L-MBC composite material for Cd²⁺（169.68 mg/g）was much higher than that of AHA-MBC material（the solid form of Col-L-MBC）（70.61 mg/g）,and the adsorption process of Cd²⁺can be better fitted with the quasi-second-order kinetic model.In the experiment,Col-L-MBC’s multiple removal mechanisms for Cd²⁺were studied,including Cd-πinteraction,functional group bonding,ion exchange,and precipitation,which made a great contribution to the rapid removal of Cd²⁺.