Efficient removal of polystyrene microplastics from seawater using a chitosan-activated carbon nanocomposite: Preparation of the adsorbent and optimisation of removal methods

Abstract

The article discusses the modification of chitosan with activated carbon to form a chitosan-activated carbon nanocomposite (CS-AC) and its use in removing polystyrene (PS) from seawater. The composite was found to be stable in both acidic and basic media. FTIR spectra of the composite indicated the presence of O-H, N − H, C-O, and C O groups capable in binding to PS. The SEM micrograph revealed a rough, irregular, and perforated structure with pores on the composite, which facilitated adsorption. The XRD results indicated that the composite is more amorphous (2θ 20–30), compared to semi crystalline chitosan (2θ 19.9). An approximate 77.4% adsorption efficiency was achieved at an initial PS concentration of 50 mg/L at pH 6 in seawater. The correlation coefficient (R 2 ) from the isotherm plots revealed that the Langmuir model (R 2 = 0.9994) was most ideal for the experimental data. The correlation coefficients (R 2 = 0.9921) in intraparticle diffusion indicated multi-stage diffusion but not solely the rate-limiting due to boundary layer effects, while the Boyd’s model (R 2 = 0.992) further suggest that intraparticle pore diffusion occur in the process. The pseudo second order (R 2 = 0.9920) conform best to experimental data than pseudo first-order (R 2 = 0.9883) and Elovich (R 2 = 0.9453) pointing chemical adsorption as key step. The spent composite was most effectively regenerated using chloroform, achieving an 83.98% desorption capacity after five cycles. • The removal of polystyrene using chitosan-activated carbon composites is presented. • The chitosan-activated carbon composite was able to eliminate 99% of polystyrene. • The composite can be regenerated and reused for more than five cycles. • The adsorbent has been successfully applied to real samples.