Preparation Of Biomass-based Carbon Foam And Treatment Of Polycyclic Aromatic Hydrocarbons And Cadmium Pollution In The Environment

Polycyclic aromatic hydrocarbons（PAHs）and heavy metal cadmium（Cd）are two common classes of pollutants in soil,which are carcinogenic and highly toxic,having non-negligible potential risks to ecosystems and human health.At present,the research on the remediation of single organic matter or heavy metal contaminated soil has been relatively mature.However,due to the large difference in physicochemical properties between organic pollutants and heavy metals as well as the complicated mechanism of action,there are relatively few studies on the treatment of composite pollutants,and the mechanism of soil remediation is not clears.Therefore,it is of great significance to develop a green,economical and efficient remediation technology for the soil composite pollution.In this paper,functional carbon foams were prepared using agricultural and forestry waste pine cones as precursors by doping heteroatoms and loading nanoparticles,and realized the efficient treatment of heavy metal Cd and the polycyclic aromatic hydrocarbon pollutants such as fluoranthene and naphthalene in water and soil.The effects of the morphology and structure of materials and different reaction conditions on the adsorption and degradation of pollutants were discussed,and the reaction mechanisms of the materials adsorbing heavy metals and activating PMS to degrade organic pollutants were elucidated.Furthermore,the impacts of the remediation system on environmental quality and ecological functions were studied.The main contents include the following two parts:（1）Iron nanoparticles supported on nitrogen-doped carbon foam（Fe@CF-N）was prepared by in-situ impregnation and unique calcination process using agricultural and forestry waste pine cones as the main precursor,and used for activating peroxymonosulfate（PMS）to degrade fluoranthene（FLT）in water and soil.The Fe@CF-N material was characterized by SEM,TEM,EDS-mapping,BET,XRD,XPS analytical techniques,and the adsorption and catalytic performance of the material was studied by the degradation experiments of fluoranthene in water and soil.The results showed that Fe@CF-N had a three-dimensional network structure with a specific surface area of 294.0 m~2·g^-1,and exhibited the excellent catalytic performance,which could effectively activate PMS to degrade FLT.At the reaction time of 180 minutes,the maximum removal rates of fluoranthene in water and soil by Fe@CF-N/PMS system were81.83%and 78.12%,respectively.After four cycles,the removal rate of FLT in water by Fe@CF-N still reached 55%.Radical quenching results showed that sulfate radical(SO₄^-.),hydroxyl radicals（·OH）and singlet oxygen（~1O₂）were the major reactive oxygen species（ROS）in degradation reaction.A series of low molecular weight intermediates were generated during the FLT degradation progress,such as C₆H₆O₃ and C₃H₈O₂.The effects of Fe@CF-N/PMS system on soil environmental quality and phytotoxicity were studied with peas as the experimental object,and the results showed that the seed germination rate,stem length and root length of peas in the remediated soil by the Fe@CF-N/PMS system were not significantly different from those in the uncontaminated soil.This study provides a cost-effective remediation method for the treatment of PAH pollutants in water and soil.（2）The core-shell structural nitrogen-doped carbon foam loaded with nano zero-valent iron（n ZVI@NCF）was synthesized through Mannich reaction and high-temperature carbon reduction using pine cones as the major precursor,which was applied to simultaneously remediate the composite pollutants of Cd（II）and naphthalene（NAP）in water and soil.The results exhibited that the adsorption capacity of n ZVI@NCF for Cd（II）in water and soil were13.9 mg·g^-1 and 1.97 mg·g^-1,respectively under the optimal conditions,and the rates of adsorptionconformed to the pseudo-second-order kinetic model.The degradation rates of NAP in water(10 mg·L^-1)by n ZVI@NCF reached almost 100%as well as it could reach 59.12%in soil(10 mg·kg^-1).Moreover,in the Cd（II）-NAP composite pollution,it was proved that the presence of NAP could compete with Cd（II）for the active sites on the surface of the material to inhibit the adsorption of Cd（II）,while the co-existence of Cd（II）could improve the degradation of NAP by the n ZVI@NCF/PMS system due to the n ZVI-Cd bimetallic effect and the pro-oxidant effect of Cd（II）promoting the generation of ROS.The free radical quenching experiment revealed that the generated·O₂^-was the main substance that mediated the redox of n ZVI/Fe²⁺/Fe³⁺to oxidative NAP during the degradation process.Furthermore,the results of the phytotoxicity test demonstrated that the n ZVI@NCF/PMS system could effectively remediate the soil co-contaminated with Cd（II）and NAP as well as improve the soil environment quality.This research will provide new materials and potential technologies for the efficient treatment of heavy metal-organic matter composite pollution in the environment.