Preparation Of Indole-based Organic Aerogel And Study On Its Dye Adsorption Performance

Environmental problems caused by human factors have become a hot focuses that attract global concern,dye pollutants from wastewater is the most crucial problem.Commercial dyes are widely used in many industries such as textile and printing and dye pollution is mainly caused by industrial effluents.Once discharged into natural water bodies directly,dyes have serious harmful impacts on human life and the environment.Thus it is an important and challenging task to eliminate dyes effectively in industrial effluents before they are discharged into the environment.Various methods have been used for removing dyes from industrial wastewater,among which adsorption has been widely adopted because of its low cost,easy operation,simple design,and insensitivity to substrates.The development of low-cost,efficient,selective as well as recyclable adsorbents is an urgent problem to be solved.Among various adsorbents developed in recent years,aerogel as a kind of excellent adsorbents have attracted widespread interest as a result of its advantages such as low density,porosity,and high specific surface area.At present,however,complicated synthesis process such as supercritical drying and pyrolysis at high-temperature which are high cost and time-consuming are still necessary during the synthesis process of some aerogels.In this work,cheap indole-based monomers are used,and indole based hydrogel were obtained by one-step polymerization method,and then the corresponding organic aerogel were prepared by ambient drying which is low cost and easy operation.Enlightened by the synthesis mechanism of resorcinol-formaldehyde(RF)aerogel,we use hydroxyl functionalized indole which react with formaldehyde by nucleophilic addition to yield a series of novel indole-based organic aerogel.Subsequently,the morphology of theaerogelwasobservedbyscanningelectronmicroscopy(SEM).The4-hydroxyindole-formaldehyde(4-HIF)aerogel with typical network structure and5-hydroxyindole-3-acetic acid-formaldehyde(5-HIF)aerogel with irregularly shaped stratified structure were selected as model porous polymers to characterized.Brunauer-Emmett-Teller(BET)analysis was performed and the specific surface areas was calculated to be 130 m~2/g and 102 m~2/g,the average pore diameter was 46 nm and 7.1 nm respectively.Fourier transform infrared(FT-IR)spectra and solid-state cross-polarization magic-angle-spinning(CP/MAS)NMR spectrum were also recorded,confirmed that the reaction mechanism is the nucleophilic addition followed by polymerization-condensation reaction then crosslink to produce a gel.Subsequently,the NaOH-modified aerogels were used for the adsorption of cationic dyes.Methylene blue and crystal violet were selected as model compounds to investigate the adsorption kinetics,adsorption isotherm,adsorption thermodynamics.Besides,competitive experiments with anionic dyes shown that the aerogels can remove cationic dyes selectively.Furthermore,synergistic effects of cation-?induced electrostatic interaction,electrostatic interaction and?-?stacking interaction explained the efficient adsorption of modified aerogels towards cationic dyes.In addition,the aerogel can be desorbed under the mild conditions,the saturated dye-loaded aerogel were easily regenerated by washing with ethanol and 0.1 M HCl and retaining high adsorption capacity after recycling five times.