Functionalized natural fibre composite filter for the removal of microplastics and heavy metal ions from water

Microplastics is an emerging pollutant that pollutes water and great threat to the environment. To remove microplastics and other pollutants from drinking water, a biodegradable multifunctional filter was developed from a natural resource (coir fibre and pith) to reduce microplastic pollution in the environment. Coir fibre and pith were alkali-treated with 5% sodium hydroxide to expose the surface morphology (pores and cellulose) and functionalized with chitosan using citric acid as a cross-linker. As per the experimental plan developed by the Box–Behnken method, chitosan (1%, 2% and 3%) was cross-linked with coir fibre and pith by citric acid (5%, 10% and 15%) at various curing temperatures (120 °C, 130 °C and 140 °C). Characterization by Fourier transform infrared spectroscopy and thermogravimetric analysis was performed to analyse the cross-linking nature. Regression and composite desirability analysis was conducted to find the best input parameters which are 1% chitosan, 10% citric acid concentration and 120 °C curing temperature. The filter was constructed from the functionalized fibre and pith with the parameters of variation in fibre and pith weight and fibre length and evaluated for removal of microplastics, heavy metal ions (Pb, Cd and Cr) and total organic content. Filtration efficiency was analysed by the Box-Behnken method, and based on composite desirability analysis, 5 g of fibre, 3 g of pith and 1 cm fibre length are the best parameter to achieve maximum efficiency. The removal efficiency of the filter for microplastics was 99%, total organic content 94% and heavy metal ions in the order of Pb(II) > Cr(VI) > Cd(II).