The Regulation Of Micro-environments In Polyacrylonitrile Fiber And Its Catalytic And Adsorption Applications

With the rapid development of the industrial production,the traditional chemical industry has brought a great burden to the environment,and the introduction of“green chemistry”has affected the direction of chemical research.Due to the reusability and better performance of heterogeneously supported materials,its application conforms to environmentally friendly,green and pollution-free requirements.Moreover,the support materials play a decisive role in the field of industrial catalysis and environmental pollution treatment.In this work,polyacrylonitrile fiber was selected as the carrier material,and the quaternary ammonium base was immobilized on the polyacrylonitrile fiber to study the catalytic activity of this functionalized material on the C-C formation reaction such as Henry reaction,Knoevenagel reaction and Michael addition reaction.In another work,quaternary ammonium salts was immobilized on polyacrylonitrile fiber and their adsorption capacities for azo dyes in sewage was studied.Due to the special microenvironment of polyacrylonitrile fiber,we have designed different hydrophilic and hydrophobic microenvironment systems to assist the catalytic reaction and the adsorption of pollutants.A series of quaternary ammonium base functionalized polyacrylonitrile fibers as superbase catalysts for C-C bond forming reactions were prepared.The hydrophobic/hydrophilic surface microenvironment of the quaternary ammonium base functionalized polyacrylonitrile fiber catalyst was adjusted using alkyls with different chain lengths and benzyl groups.After screening the optimal catalyst,it was found that quaternary ammonium base functionalized fiber catalyst with alkyl chain of 8 carbon atoms had the most satisfactory catalytic performance for the Henry reaction,Knoevenagel condensation and Michael addition reaction.Combined with the enrichment test of different fiber catalysts for substrates,the hydrophobic quaternary ammonium base fiber catalyst has excellent catalytic effect because it allows more substrate to accumulate at the catalytic site of the fiber catalyst and release the product more easily,so that the reaction can be carried out smoothly.The fiber catalyst has high catalytic activity in an aqueous solvent,and has the characteristics of low catalyst dosage,mild conditions,high efficiency and wide substrate adaptability.In addition,the quaternary ammonium base functionalized fiber catalyst is very suitable for a continuous flow process,achieving a yield of more than 86%after 160 hours.Moreover,the fiber can be easily recovered and recycled more than 10 times in a continuous flow system.In addition,a novel adsorbent with cationic adsorption site and hydrophobic microenvironment was designed and prepared by immobilizing quaternary ammonium salts onto polyacrylonitrile fiber and introducing a series of different alkyl chains.These quaternary ammonium salts functionalized fibers with different hydrophobicity were studied to adsorb anionic azo dyes such as methyl orange(MO),alizarin yellow R(AYR)and methyl red(MR).And PAN_QAS-12F with twelve carbon alkyl chain has best adsorption effect for methyl orange(Q_e=1.82 mmol·g^-1).After researching kinetic model and isotherm model,the adsorption process of quaternary ammonium salts functionalized fiber is fitted second-order kinetics and Langmuir model.Based on that,a possible adsorption mechanism was presented,which is that the chemical adsorption plays a dominated role in quaternary ammonium salts functionalized fiber adsorption process and accompanied by the synergetic effects of effective hydrophobic interaction and weak hydrogen bond.The desorption of quaternary ammonium salts functionalized fiber rapidly occurs in HCl solution at pH=1 and the desorption rate can achieve over 99%.Moreover,the quaternary ammonium salts functionalized fiber was used for ten times and still keep removal rate over 99%.