Fabrication Of Multi-dimensional Carbon-based Molecular Imprinting Materials And Their Selective Adsorption And Separation Properties Towards Phenol

Non-destructive and selective adsorption separation of phenol,one of the major organic pollutants of coking wastewater,is of great significance for the deep purification of coking wastewater and the resource utilization of phenol compound.Adsorption using porous carbon materials as adsorbents is one of the key technologies for phenolic wastewater purification.Since porous carbon materials possess advantages such as rich pore structure,large specific surface area,low density,and high chemical stability.However,conventional porous carbon adsorbents often fail to selectively identify specific molecules.In addition,a lot of porous carbon-based adsorbents exist in powder form,which makes them easy to agglomerate and difficult to be separated in application process,and further leads to uneven distributed adsorption sites,blocked mass transfer channels,low recovery rate,and secondary pollution.These problems seriously limit the practical application of porous carbon-based adsorbents in liquid phase.Therefore,the construction of a porous carbon-based adsorbent owns comprehensive outstanding ability in all aspects including efficient adsorption,selective recognition,and solid-liquid separation is essential for the selective and deep removal of phenol from coking wastewater.To address above issues,functional enhancement and macro-morphology readjustment are both adopted to combine molecular imprinting technology with magnetic response technology,membrane separation technology,and carbon aerogel technology separately.In this way,a series of multi-dimensional carbon-based molecular imprinting materials with high phenol selective adsorption capability and excellent solid-liquid separation performance are designed and constructed.In the process of research,the phenol adsorption capacity of carbon-based imprinting materials is improved through optimizing pore structure and increasing affinity of adsorption sites.Besides,the problems of agglomeration and solid-liquid separation inconvenience are solved through endowing magnetism to and rising the macro dimension of the carbon-based imprinted adsorbents.Hence,this work is very helpful to enhance the practical application potential of carbon-based molecularly imprinted adsorbent materials.The specific research contents and results are as follows:（1）For the selective adsorption of phenol,the molecular imprinting technology was adopted to prepare the imprinted polymer（4-VP/SMIP）by coating an imprinted layer on the surface of glucose-derived carbon nanosphere with 4-vinylpyridine（4-VP）as functional monomer.In this system,glucose-derived carbon nanosphere was used as imprinting matrix for it possesses abundant porous structure.In addition,the type and amount of functional monomer were optimized according to the structural and chemical properties of template molecule phenol for the purpose of imprinting sites precise construction.The results show that under the same adsorption conditions,the imprinted adsorption material 4-VP/SMIP that used 4-VP as functional monomer shows the best phenol adsorption performance.The average particle size of 4-VP/SMIP is about 132 nm and the thickness of imprinted layer is about 10 nm.The adsorption capacity of 4-VP/SMIP for phenol at 298 K is 85.7 mg g^-1 and the adsorption process follows pseudo-second-order model and Langmuir-Freundlich model.The results of NMR hydrogen spectra and adsorption model fitting show that the basic functional monomer 4-VP is more likely to form hydrogen bond andπ-πinteraction with acidic phenol,which reveals the reason for the high adsorption capacity of 4-VP/SMIP.The relative selection factors of 4-VP/SMIP towards hydroquinone（HQ）and p-tert-butylphenol（PTBP）are 2.94 and 6.71,respectively,which implies that 4-VP/SMIP owns excellent phenol selective adsorption ability.（2）To further improve the pore structure and adsorption activity of carbon-based imprinting adsorbent,which may help to enhance its phenol adsorption and solid-liquid separation efficiencies,ZIF-8 derived nitrogen-doped porous carbon-based phenol magnetic imprinting material（MIP@N-1000）was designed and constructed.Moreover,the effect of pore and imprinted structure on adsorption performance of MIP@N-1000 was investigated by adjusting the heat treatment conditions of carbon precursors and imprinting parameters.The results show that by adjusting the annealing temperature of imprinted substrate and the coating amount of imprinted polymer,the optimized specific surface area and pore volume of MIP@N-1000 reaches 1112 m² g^-1 and 2.01 cm³ g^-1,respectively,which facilitates the exposure of adsorption sites and mass transfer of phenol.Additionally,MIP@N-1000 is endowed with magnetic responsive ability by Fe3O4 nanoparticles loading through impregnating with iron and urea-containing solution and annealing.The obtained MIP@N-1000,with the saturation magnetic intensity of 5.4 emu g^-1,can be separated from a liquid solution easily by an applied magnetic field.On the surface of MIP@N-1000,the homogeneous distribution of pyridine nitrogen sites can form hydrogen bonds and acid-base interactions with phenol.Therefore,the phenol adsorption capacity of MIP@N-1000significantly increases to 995.2 mg g^-1,which is higher than that of imprinted adsorbent reported in literatures.The adsorption behavior of MIP@N-1000 is consistent with pseudo-second-order model and Langmuir-Freundlich model,and its relative selectivity factors towards HQ and PTBP are 3.90 and 3.78,respectively,showing excellent phenol selectivity.The preparation of MIP@N-1000 provides a theoretical basis for the design of efficient comprehensive carbon-based molecularly imprinted adsorbent.（3）To address the bottleneck of solid-liquid separation of carbon-based powder adsorbents,porous carbon nanosphere/polydopamine synergistic phenol imprinted composite membrane（m-MIM）was constructed for the selective adsorption and efficient separation of phenol by considering the enhancement of adsorbent macroscopic dimension.Polyethersulfone substrate membrane is modified by dopamine to provide a secondary adhesion platform for the uniform and stable double-sided loading of carbon nanospheres on the surface of substrate membrane.On the other hand,the abundant hydroxyl and amino groups on dopamine can enhance the hydrophilicity and imprinting activity of m-MIM,thus enhancing its selective adsorption performance towards phenol.The results show that the specific surface area of m-MIM composite increases to 2.72 times that of substrate membrane,and the water contact angle decreases from 46°（substrate membrane）to 29°.The significant increase of effective imprinting area and selective adsorption capacity is due to the improvement of structural stability and adsorption sites distribution of m-MIM through the combination of dopamine adhesion platform and carbon nanospheres that have high porosity and large specific surface area.The phenol adsorption capacity of m-MIM is 51.4 mg g^-1 at298 K.In addition,the selective permeation tests confirm the selective separation ability of m-MIM for Phenol.The selective permeation parametersβHQ/Phenol is 7.61 andβPTBP/phenol is6.12,which consists with the delayed permeation mechanism.The adsorption and molecular simulation results show that the selective adsorption of m-MIM towards phenol can be attributed to the specific stereoscopic configuration of imprinted cavities,the high affinity from functional monomer,and the promoting effect from dopamine modification.（4）To further enhance the adsorption capacity and separation efficiency of the carbon-based imprinted adsorbent,carbonized ZIF-8/chitosan biomass phenol imprinted hybrid carbon aerogel（MIP@CZIF-8/CS-CA）was constructed as a macro-block adsorbent for phenol adsorption.The results suggest that chitosan-derived carbon aerogel with open porous channels and large available surface area can be used as high adsorption activity scaffold to immobilize CZIF-8 to construct monolithic adsorbent.The porous structure of MIP@CZIF-8/CS-CA was optimized by regulating CZIF-8 loading amount on chitosan-derived carbon aerogel,and the superhydrophilicity and adsorption site amount were improved by nitrogen atom doping.Through such structure and property improvement,MIP@CZIF-8/CS-CA shows excellent phenol adsorption capacity of 246.6 mg g^-1,which is2.9 times that of pure chitosan-derived carbon aerogel.The adsorption behavior of MIP@CZIF-8/CS-CA consists with pseudo-second-order model and Langmuir-Freundlich model.Besides,the relative selectivity factors of MIP@CZIF-8/CS-CA towards HQ and PTBP are 3.17 and 2.39,respectively,which shows excellent phenol selectivity.The macro-monolithic structure of MIP@CZIF-8/CS-CA makes it easy to be separated and thus prevents secondary contamination to the liquid solution.Furthermore,the practical potential of MIP@CZIF-8/CS-CA has been proved by the realization of phenol-containing wastewater dynamic filtration during a series of fixed-bed column adsorption tests.