Efficient selective methylene blue adsorption by polyurethane/montmorillonite-based antifouling electrospun composite membranes

A robust antifouling membrane with pollutant-removing capacity is in high demand for industrial wastewater treatment. Here, we report a new multifunctional polyurethane/montmorillonite-oxidized multi-walled carbon nanotube (PU/MMT) nanofibrous composite membrane, beneficial for both water filtration and selective methylene blue adsorption. It was observed that oxidized multi-walled carbon nanotube (o-MWCNT) imparted high flexibility with a high percentage elongation (318%-405%) to the composites, whereas montmorillonite (Mt) improved the hydrophilicity, antifouling property, and dye adsorption capacity of the fibrous PU membrane. The sample with 20 wt% Mt (PU/20-MMT) showed a minimum water contact angle of 57 degrees. It showed a high water flux, oil rejection, and flux recovery ratio compared to the pristine electrospun PU membrane. The Hermia fouling mechanism suggested that electrospun PU obeyed an intermediate blocking model, whereas PU/20-MMT was best fitted with a cake formation model. During adsorption, the cationic dye methylene blue (MB) was selectively adsorbed on the sample from a methyl orange/methylene blue (MO/MB) mixture. It showed a maximum adsorption capacity (q(m)) of 112.35 mg/g. The anionic dye methyl orange, on the other hand, remained unadsorbed. The adsorption kinetics and the adsorption isotherm were pseudo-second-order kinetics and the Langmuir adsorption isotherm, respectively. The developed, robust electrospun composite membrane opens a new avenue for the selective adsorption of MB from dye mixtures and contaminated water.