The Perforamnce And Mechanism Of Pollutants Removal By Water Treatment Materials Prepared From Rice Straw

In the need for the massive amount of waste biomass resources to be converted and reused,as well as the urgent threat from the refractory organic pollutants in the aqueous environment that endanger both human health and the eco-system,this paper has suggested a novel modification treatment for rice straw,based on the sufficient carbon components and heterogeneous structure of the biomass.From the proposed treatment,two environmental materials（nano-zero valent biochar catalyst and lignin-based flocculant）have been successfully developed.Furthermore,an iron-nitrogen biochar catalyst has been synthesized by one-step pyrolysis with flocculation-produced floc as raw materials.The three materials mentioned above have shown great application potential in the degradation of pharmaceutical organic pollutants and decolorization of anionic dyes.The research is of great significance to the comprehensive utilization of waste biomass and the remedation of water environment.The main contents and results are as follows:A new treatment method that FeCl₃coupled PEG400 was proposed to treat or modify the rice straw（RS）.The improvement of physical structure of the RS can be seen after the treatment.More ferric oxides were loaded on the improved straw surface due to the enhanced hydrolysis of FeCl₃ by PEG400.The results indicated that the Featom content on the treated RS surface was 19-times higher than that of untreated RS.Moreover,the chemical structure of treated RS remains intact.XRD and SEM confirm the treated RS was successfully synthesized to nZVI-BC by one-step pyrolysis.nZVI-BC not only has good magnetism,but also achevies the embedment of nZVI into the graphite layer,which improves the stability of the nZVI.In addition,nZVI-BC has a large specific surface area（386.51 m²/g）and abundant pore volume（0.232 cm³/g）,resulting in the microporous area and volume account for 73.85%and 49.59%,respectively.The introduction of nZVI makes nZVI-BC a defect structure.The catalytic ability of nZVI-BC was evaluated by the degradation efficiency of acetaminophen（ACT）in the advanced oxidation system of persulfate（PDS）.The results show that with 0.5 g/L of nZVI-BC,ACT concentration of 10 mg/L and PDS of 1.8 mmol/L,ACT could be removed 100%within 20 min in the PDS/nZVI-BC system,and the degradation constant was 0.3748 min^-1.Through the iron ion leaching concentration（0.036 mg/L）and ACT degradation efficiency（more than 90%）under the fifith recycling ultilization of nZVI-BC confirms the good stability and recyclability of nZVI-BC.The radical quenching experiment and EPR detection demonstrats that four reactive oxygen substances(·OH,SO₄^·-,·O₂^-and ¹O₂)can be generated in the reaction system,and·O₂^-plays a major role in the degradation of the pollutants.Based on the structure changes of nZVI-BC during the whole process,the multi-pores,defect,hybrid carbon,C–O,C=O,Fe（0）and Fe（II）participated in the activation reaction of PDS.During the degradation process,13 degradation products of ACT have been tested and the mineralization rate of ACT was 61.7%.It was found that the liquid product produced by FeCl₃coupled PEG400treatment of RS have the decolorization function for anionic dyes and could be regraded as a lignin-based flocculant.The tyndall effect and morphology analysis show that the liquid is a colloidal system,it can form spherical lignin nanoparticles（LNP）by self-assembly.FTIR and XPS results indicate that LNP have typical oxygen containing functional groups of lignin（-OH,C-C,C-O and C=O）.The decolorization efficiency of nine anionic dyes was used to evaluate the flocculation capacity of the lignin-based flocculant.Without adjusting the p H,the decolorization efficiencies of nine dyes are different,Congo red（CR）shows the best（99.84%）when the lignin-based flocculant of0.5%（m L/m L）was added.Compared with the CR removal by FeCl₃ alone at the same concentration,the LNP formed in the lignin-based flocculant promotes the formation of suspended solids in the reaction system,which is beneficial to the collision and sedimentation of flocs.This reaction system has a higher removal capacity for turbidity（2.9 NTU）and suspended solids（2.9 mg/L）.The reaction system between lignin-based flocculant and dye is not affected by inorganic salt ions.The floc produced from the flocculation reaction between lignin-based flocculant and CR is large and dense.The change of solution charge before and after reaction and the chemical valence of iron element indicate that Fe³⁺plays the role of charge neutralization in the flocculation reaction system.The C=O/O-C-O and C-O functional groups on the surface of lignin nanoparticles decreased,while the C-N content on the surface of flocs increased,indicating that chemical reaction occurred in the flocculation reaction system.The reduction of hydrophili c groups and theπ-πinteraction between the aromatic ring structure of dye and lignin nanoparticles enhance the hydrophobicity of particles,leading to the continuous increase of flocs and rapid sedimentation.A magnetic iron-nitrogen biochar catalyst（Fe-N@MFC）with two stable conformations of Fe₃C and Fe₄N catalytic sites was synthesized using flocs with iron,nitrogen and lignin as raw materials.Iron particles are wrapped in the graphite layer to protect them from oxidation.The magnetic strength of Fe-N@MFC is high（17.9 emu/g）,which makes it easy to realize solid-liquid separation.The catalytic ability of Fe-N@MFC is evaluated by the TC degradation efficiency in the Fe-N@MFC/PDS system.Under the Fe-N@MFC of 0.5 g/L,TC concentration of 5 mg/L and P DS of 1.8 mmol/L,the degradation efficiency of TC was the highest（90.5 0%）,and the degradation constant was 0.3304 min^-1.The radical quenching experiment,EPR and electrochemical analysis show that free radical,non free radical and electro transfer coexist in the system,and·OH and SO₄^·-play a major role in the TC degradation.The structural changes of Fe-N@MFC before and after reaction indicate that Fe₃C and Fe₄N in Fe-N@MFC were involved in the reaction.DFT calculation confirms that the presence of Fe₃C and Fe₄N enhanced the adsorption and dissociation for PDS onto the Fe-N@MFC,promoted the electron transfer between the material and PDS,which favor to the redox reaction between Fe（0）,Fe（II）and PDS,leaching to producing reactive subatances for degrading TC via free radical reaction.Fe-N@MFC can be recycled for many times and the iron ion leaching concentration is low（0.15mg/L）,which indicates Fe-N@MFC has a good application potential.