Tannin-based thin-film composite membranes integrated with nitrogen-doped graphene quantum dots for butanol dehydration through pervaporation

Abstract

A thin-film composite membrane was prepared through the interfacial polymerization of tannic acid (TA), a natural oligomer, and acyl chloride monomers – terephthaloyl chloride (TPC) or trimesoyl chloride (TMC). Thin-film nanocomposite (TFN) membranes were also prepared by loading a new class of carbon nanoparticles – nitrogen-doped graphene quantum dots (NGQDs). The composite membranes were characterized with ATR-FTIR, XPS, SEM and water contact angle. The TA-TMC membrane provided lower flux and better water permselectivity than those prepared with TA-TPC due to availability of more reactive acyl chloride. The concentrations of each reactant used, appropriate loading amount of NGQD and contact time between TA and acyl chloride monomers were all determined and investigated to separate 90/10 wt% n-butanol/water mixture at 25 °C. The TA-TMC was found to have higher surface hydrophilicity due to more hydroxyl groups present. The incorporation of 50 ppm NGQD during the interfacial polymerization enhanced the pervaporation performance by providing additional hydrophilicity and mass transfer resistance to larger permeating molecule. The TA0.075-TMC0.4-NGQD(50) membrane at 3-min contact time had a total flux of 1100 g m−2 h−1 and a water concentration in permeate of 97.1 wt% compared to TA0.075-TPC0.4-NGQD(50) membrane with 2196 g m−2 h−1 and 93.2 wt% in separating 90/10 wt% n-butanol/water mixture at 25 °C. The water permselectivity was also found to be more efficient for isobutanol/water mixtures due to the sterically hindered structure of the alcohol. Furthermore, the TA0.075-TMC0.4-NGQD(50) membrane was also tested to separate all butanol isomer/water mixtures at 25 °C showing better separation performance for sterically hindered or branched butanol isomer. The membrane fabricated herein shows the potential use of cheap and natural oligomer (TA) to produce thin-film composite membranes that provided enough barrier to separate butanol from water through pervaporation.