Lignin Based Electrospun Nanomaterials as Adsorbents for Remediation of Harmful Environmental Pollutants: A Review

Abstract

Lignin is an amorphous natural polymer with multifunctional phenolic network accounting for approximately 15-30% of lignocellulosic biomass. Different functional groups like carboxyl, hydroxyl, phenolic and methoxy in lignin molecules may act as suitable interaction sites for the removal of pollutants. Lignin, as an abundant and renewable bioresource, can be used to create nanofibrous membranes via electrospinning technique. Such membranes with elevated specific surface area, uniform fiber diameter, and high porosity serve as highly remarkable and efficient adsorbents for the entrapment of detrimental pollutants like dyes, heavy metals, particulates, etc. For example, a low-cost electrospun nano-fibrous membrane (ENM) comprising of alkali lignin/polyvinyl alcohol (PVA) was developed for effective removal of Safranine T dye1. Similarly, palm fronds and banana bunch waste biomass derived lignin was successfully employed as an electrospun material for the removal of methylene blue dye. An alkali lignin/PVA ENM with 78% adsorption capability was developed for the adsorption of fluoxetine contaminant from its solution2. In another study, hydrophobic TiO2/lignin based carbon ENM demonstrated great performance in methylene blue elimination. Similarly, with an adsorption capacity of 588 mg/g, polyacrylonitrile/sago lignin carbon nanofibers acted as a suitable biosorbent for Pb(II) ions removal from its aqueous solution. Lignin nanofibers with 220 mg/g adsorption capacity have been prepared to capture radioiodine. Furthermore, an electrospun lignin-aloe vera air filter membrane with efficient particulate pollutant capture ability was synthesised. This review explores the up-to-date information on the development and usage of eco-friendly, sustainable and cost-effective lignin nano-adsorbents for the removal of various environmental contaminants.