Preparation Of Cellulose Adsorbent Materials And Study On Their Adsorption Performance Towards Hexavalent Chromium And P-arsanilic Acid

Heavy metal pollution in water is a serious threat to the global ecological environment and human health,and the treatment of it is one of the important issues in the current sustainable development of the national economy and society in China.Cellulose is a natural polymer with abundant reserves in nature,which has the advantages of non-toxic,environmentally friendly,cheap,and renewable.The development of cellulose adsorption materials for the treatment of heavy metal pollutants in water bodies is of great importance for maintaining ecological balance and achieving sustainable national economy.Although many researchers have studied the modification of cellulose and its adsorption performance towards heavy metal contaminants,the modified cellulose materials still remain some problems to be solved,such as low grafting yield of the functional group,low adsorption selectivity and affinity.In addition,the removal of emerging pollutants by cellulose materials is still in infant.In this paper,a variety of methods are used to modify cellulose to prepare cellulose materials with high grafting rate,high adsorption selectivity and adsorption affinity.The adsorption properties and mechanisms of these modified cellulose materials toward hexavalent chromium?Cr?VI??and the emerging pollutant,para-aminoarsinic acid?p-ASA?were also explored.The main research contents and results are as follows:A homogeneous cross-linking method was proposed to increase the loading of functional groups on the cellulose surface,and polyvinylimidazole modified cellulose composite?MCC-PVIM?was fabricated through this method.The characterization results showed that the homogeneous cross-linking method increased the loading amount of imidazole functional groups on the cellulose surface,and the MCC-PVIM exhibited a three-dimensional grid structure.The adsorption experiment results revealed that MCC-PVIM exhibited good adsorption performance toward Cr?VI?:the adsorption equilibrium time was 3 hours,and the maximum adsorption capacity of MCC-PVIM was 134.1 mg/g at p H 3.0,which was 13 times higher than that of the unmodified cellulose.The adsorption process was spontaneous and endothermic,and followed the pseudo-second order kinetic model and Langmuir adsorption isotherm model.Spectral analysis and density functional theory?DFT?calculations revealed that multiple functional groups on the surface of MCC-PVIM synergistically promoted the adsorption of Cr?VI?through hydrogen bonding,electrostatic attraction,and dispersion effect.In addition,the ion exchange and redox reactions were also involved in the adsorption process.Based on the Donnan membrane effect,it's proposed that the strong interaction between counter anions and Cr?VI?could effectively enhance selective adsorption of Cr?VI?.In combination of the method of homogeneous cross-linking and ion exchange,Mo S₄^2-was supported on polyvinylimidazole functionalized cellulose to prepare N/S functionalized cellulose porous material?MPS?,and studied its selective adsorption performance and mechanism on Cr?VI?.Adsorption experiments showed that in a high concentration coexisting ion environment,the adsorption partition coefficient of Cr?VI?on MPS was as high as 1.01×10⁷ m L/g,indicating that MPS has excellent adsorption selectivity for Cr?VI?.The positively charged imidazolium salt functional group on the MPS surface promoted the pre-concentration of Cr?VI?on its surface through the Donnan membrane effect,and Mo S₄^2-underwent redox and coordination with Cr?VI?,which synergistically enhanced the adsorption selectivity.In addition,the removal efficiency of Cr?VI?on MPS was above 95%in a wide p H range?from 1.0 to 8.0?,and the maximum adsorption capacity was as high as379.78 mg/g at p H 3.0,indicating that MPS has great application potential for treating industrial Cr?VI?wastewater.The idea of using imidazole-functionalized cellulose material for p-ASA adsorption was proposed to broaden the application of cellulose in the field of emerging pollutant adsorption.Adsorption experiment showed that the nitrogen-containing cellulose porous material?MP?has high adsorption capacity?216.9 mg/g?and rapid adsorption efficiency(3.21×10^-3g·mg^-1·min-¹)toward p-ASA.The process conformed to Frendlich isothermal model and pseudo-second order kinetic model.The influence of environmental factors on the adsorption performance of p-ASA,spectrum analysis and DFT calculations showed that hydrogen bonding was the main force in the adsorption process,and the imine group on the imidazole ring was the preferred adsorption site for p-ASA.It was proposed that the introduction of iron oxide nanoparticles in cellulose composite materials could effectively enhanced the adsorption affinity of cellulose for p-ASA.Iron oxide-based cellulose composites?Mn Fe-MP and HFO-MP?were prepared by homogeneous cross-linking and in-situ precipitation,and their adsorption properties for p-ASA were explored.Mn Fe-MP and HFO-MP showed enhanced adsorption performance for p-ASA,their maximum adsorption capacity and single point adsorption K_d0.03 values were 351.5 mg/g and468.8 mg/g,14.05 g/L and 46.83 g/L,respectively.The adsorption process of p-ASA by composite materials was spontaneous and exothermic,and conformed to pseudo-second order kinetic model and Langmuir adsorption isotherm model.The theoretical adsorption model and spectroscopic analysis showed that coordination and hydrogen bonding synergistically enhanced the adsorption of p-ASA on the composite materials.In HFO-MP,HFO formed both inner-and outer-sphere complexes with p-ASA through coordination and hydrogen bonding.Mn Fe₂O₄ in Mn Fe-MP mainly formed inner-sphere complexes with p-ASA through coordination.The modified cellulose adsorbents prepared in this paper have the application potential for the removal of heavy metal anions and organic pollutants,and can provide a reference for the design of cellulose adsorbent materials and their application in wastewater treatment.