Porous Carbon/Geopolymer Supported With Iron And Copper Nanoparticles For Treatment Of Cr(Ⅵ) And Naphthalene Pollution In The Environment

Heavy metals（Cr）and polycyclic aromatic hydrocarbon（PAHs）are two common toxic pollutants in water.They are persistent,hidden,carcinogenic and highly bioaccumulative,expressing unpredictable effects on the ecological environment and human health.PAHs and Cr（Ⅵ）coexist in an aqueous environment for a long time,and their water solubility and bioavailability may change due to the influence of functional groups and surface charges,which will further aggravate the harm to human body.Compared with the treatment of single pollutant,the difficulty of synergistic treatment for composite pollutants is greatly increased.Therefore,it has great significance for developing an eco-friendly,low-cost and efficient Cr（Ⅵ）-PAHs composite pollution remediation technology for the protection of ecological environmental and the sustainable use of water resources.In this paper,the different porous carbon/geopolymer composite materials were prepared by doping heteroatoms and introducing metal active sites using metakaolin and lignin as the precursors,which realized the efficient treatment of Cr（Ⅵ）-PAHs in contaminated water.The effects of the morphology and structure of the material on the adsorption and degradation performance were investigated by multiple characterization methods,and the effects of experimental parameters such as catalyst dosage and initial p H value were explored as well as the adsorption and degradation conditions were optimized.The interaction mechanism between composite material,Cr（Ⅵ）and naphthalene（NAP）was further clarified by studying the reaction mechanism of Cr（Ⅵ）adsorption and NAP degradation.The main contents include the following two parts:（1）A low-cost and environment-friendly biochar/geopolymer composite loaded with Fe and Cu nanoparticles（Fe-Cu@BC-GM）was prepared by impregnation-calcination using lignin and kaolin as precursors.The Fe-Cu@BC-GM was characterized by SEM,FTIR and XRD,and the properties of the material were evaluated by degradation experiments in water and soil.These results suggested that Fe-Cu@BC-GM had interconnected porous morphology,rich functional groups and stable crystal structure,exhibiting excellent catalytic performance for the degradation of NAP by activated PMS.The maximum removal rate of NAP in water and soil by Fe-Cu@BC-GM/PMS system reached 98.35%and 67.98%within 120 min,respectively.The XPS measurement confirmed the presence of successive Fe（Ⅲ）/Fe（Ⅱ）and Cu（Ⅱ）/Cu（Ⅰ）redox pairs cycles on the surface of Fe-Cu@BC-GM,which made the continuous generation of Fe（Ⅱ）for activating PMS to produce SO₄^·-and·OH for the degradation of NAP.The experimental results of radical quenching showed that sulfate radical(SO₄^·-),singlet oxygen（¹O₂）,hydroxyl radical（·OH）and superoxide radical(O₂^·-)participated in the degradation of NAP as well as the NAP was degraded and transformed into low-toxic intermediates such as 1-propanol（C₃H₈O）.The effects of Fe-Cu@BC-GM/PMS system on plant toxicity were evaluated by bioassay of mung bean.It was proved that the seed germination rate,root and stem length of mung bean after soil remediation via Fe-Cu@BC-GM/PMS system were significantly improved compared with the polluted soil.This work has opened new prospect for the application of geopolymer in degradation of persistent organic pollutants（POPs）.（2）A novel,inexpensive and eco-friendly aminated lignin/geopolymer supported with Fe nanoparticles（Fe@N-L-GM）composite was successfully synthesized using kaolin and lignin as the major precursors.The prepared Fe@N-L-GM had larger specific surface area,rich oxygen-containing and nitrogen-containing functional groups,greater electron transfer ability and interconnective porous structure.The Fe@N-L-GM could be employed as the adsorbent of Cr（Ⅵ）and the activator of potassium peroxymonosulfate（PMS）for treatment of Cr（Ⅵ）and naphthalene（NAP）in wastewater.The adsorption and degradation results indicated that the maximum adsorption capacity of Cr（Ⅵ）could reach 65.83?mg·g^-1,whereas the maximum NAP degradation efficiency could reach 97.81%.The adsorbed Cr（Ⅵ）was mostly converted to the low toxic Cr（Ⅲ）through the reduction of electron donors such as Fe（Ⅱ）,amino and hydroxyl groups.The quenching experiment results confirmed that·OH might be the crucial ROSs in mediating NAP degradation.In the simultaneous removal experiment of Cr（Ⅵ）and NAP,the Cr（Ⅵ）removal rate was significantly improved in the presence of NAP,while phenol as the degradation intermediate of NAP might be the main substance for promoting the reduction of Cr（Ⅵ）.This work provided the theoretical foundation and a new type of material for the simultaneous removal of heavy metal and POPs.