Synthesis And Application Of Novel Carbon Nanomaterials Based Molecularly Imprinted Polymers For Adsorption Of Environmental Pollutants

Molecularly imprinted polymers(MIPs) have been widely used in sensors, separation, solid-phase extraction and catalysis because of their predetermination, specific recognition and practicability. Nowdays, the environmental pollution is one of the most serious issues in the world, which strongly affects the sustainable development of human society. Molecular imprinting technology provides a new route for the detection and separation of environmental pollutants. In the present dissertation, we focused on designing and fabricating efficient MIPs on various carbon nanomaterials for selective adsorption of environmental contaminants in organic phase and aqueous solution. The structure and adsorption performances of the synthesized MIPs were investigated systematically. Following is the brief introduction.(1) Molecularly imprinted polymers on carbon microspheres for selective adsorption of dibenzothiopheneMolecularly imprinted polymers for selective adsorption of dibenzothiophene(DBT/MIPs) were synthesized on carbon microspheres using DBT as templates, ethylene glycol dimethacrylate(EGDMA) as crosslinker and 2-acrylamido-2-methylpropanesulfonic acid(AMPS) as functional monomer via reversible addition-fragmentation chain transfer polymerization(RAFT). The adsorption performances of DBT/MIPs were tested by dynamic adsorption. The adsorption capacity of DBT/MIPs towards DBT is 2.16 mg/g, which was much higher than that of DBT/NIPs(0.49 mg/g). In specific adsorption, DBT/MIPs showed specific adsorption towards DBT and the adsorption capacity is 1.1 mg/g, higher than that of BT(0.25 mg/g); while DBT/NIPs did not show selective recognition towards the two different molecules.(2) Preparation and evaluation of surface molecularly imprinted polymerson carbon microspheres for selective adsorption of bisphenol A from aqueous solutionWater-compatible molecularly imprinted polymers(MIPs) for adsorbing bisphenol A(BPA) in aqueous solutions were synthesized using two different water-soluble monomers AMPS and 4-vinyl pyridine(4-VP) via surface RAFT polymerization. From the test of contact angle, two kinds of MIPs showed excellent hydrophilicity, however, the adsorption capacity of MIPs prepared with AMPS(AMPS/MIPs) towards BPA in aqueous solution ishigher than that of MIPs prepared with 4-VP(4-VP/MIPs). The adsorption capacity of AMPS/MIPs in water is 5.38 mg/g at 293 K, and adsorption equilibrium time is 120 min, while the adsorption of AMPS/NIPs is 3.54 mg/g. The kinetics and isotherm data of AMPS/MIPs can be well described by the pseudo-second-order kinetic model and the Langmuir isotherm, respectively. In addition, the thermodynamic studies indicate that the adsorption process is a spontaneous exothermic process, whereas the acid(pH<3) and alkaline(pH>8) p H range and higher temperature of the solution are unfavorable. In the regeneration tests, after fifthadsorption-desorption cycle, the adsorption capacity of AMPS/MIPs is 5.03 mg/g and the adsorption efficiency loses only 6.5% compared with the initial adsorption. The experimental results obtained in this work show that the water-soluble AMPS is a promising monomer for preparing water-compatible MIPs for BPA adsorption in aqueous phase.(3) Efficient adsorptive removal of dibenzothiophene by graphene oxide-based surface molecularly imprinted polymersGraphene oxide(GO) was chosen as support of MIPs because of its high surface area and rich functional group. Molecularly imprinted polymers on GO nanosheets(MIPs/GO) for desulfurization were synthesized using DBT as template, methacrylic acid(MAA) as monomer and EGDMA as cross-linker. The adsorption results show that the prepared MIPs/GO exhibit excellent adsorption capacity(up to 181.9 mg /gat 298 K) while the adsorption capacity of GO and NIPs/GO is 97 mg/g and 106.3 mg/g, respectively. Because of the unique 2D platform of GO, the equilibrium time is about 35 min for all samples. The kinetics and isotherm data can be well described by the pseudo-first-order kinetic model and the Freundlich isotherm, respectively. Competitive adsorption experiments demonstrate that MIPs/GO show higher affinity towards target molecule DBT than toward structural analogue BT.(4) Water-compatible surface molecularly imprinted polymerswith synergy of bi-functional monomers for enhanced selective adsorption of bisphenol A from aqueous solutionWater-compatible molecularly imprinted polymers(AMPS-St/MIPs) with bimonomer template interactions were synthesized via the synergy of bi-functional monomers of water-soluble AMPS and styrene(St) for selective adsorption of BPA from aqueous media using porous graphene oxide(PGO)material as support. PGO was selected as support because of its high surface area and easy separation from the solution. The water-soluble AMPS not only formshydrogen bonds with the template, but also enhancs the hydrophilic property of the MIPs, which reduced the nonspecific adsorption on MIPs. Besides, between St and the templates, π-π interactions are formed which can not be disturbed by water molecules. The adsorption results show that adsorption capacity of MIPs is greatly enhanced byboththe high surface area of PGO and the synergy of AMPS and St.A series of MIPs with different ratio of the two functional monomers were prepared and the adsorption ability of each sample was determined. The MIPs prepared with molar ratio(AMPS:St) of 2.5:2.5 exhibit the highest adsorption capacity(up to 85.7 mg/g at 293 K) towards BPA in aqueous media. The adsorption equilibrium time of all the MIPs is 60 min, much shorter than that of BPA/MIPs based on CMSs, which can be attributed to the macroporous structure of PGO.The kinetics and isotherm data can be wellfitted with the pseudo-second-order kinetic model and the Freundlich isotherm, respectively. The thermodynamic studies indicate that the adsorption process is a spontaneous exothermic process.Competitive adsorption experiments and the adsorption experiments in real water samples demonstrate that the synthesized MIPs display excellent selectivity towards BPA against other structural analogue molecules such as tetrabromobisphenol A and 4-tert-butylphenol. Through 5 adsorption-desorption cycles, the regenerated MIPs exhibit a good recoverability with a slight loss of 7.7%(the adsorption capacity is 78.43 mg/g) of initial adsorption capacity. This work provides aversatile approach for fabrication of high performance MIPs for application in aqueous phase.