Recent Developments of Nanocomposite Adsorbents for Removal of Heavy Metals from Water: A Review

Abstract

Recently, there has been an increase in interest in nanotechnology to improve water quality due to its large surface area and high efficiency. This review aimed to study the recently developed nanocomposite adsorbents for removing heavy metals from water. The majority of the nanocomposites achieved maximum adsorption capacity with a moderate pH (5-9), a minimum adsorbent dosage (0.1-2 g/L), and 20-60 min for achieving equilibrium and could be used for 4-6 cycles, suggesting economic feasibility. The study showed that the physisorption occurred at a low mean free energy of surface adsorption and, in contrast, chemisorption occurred at a higher value, and most of the adsorption processes followed the pseudo-2nd-order kinetics reaction. A thermodynamic study of the adsorbents illustrated the spontaneous nature and increase of randomness during the adsorption process. A comparative analysis of the nanocomposites revealed the selectivity of iron oxide nanocomposites towards the removal of Pb(II) ions; polythiophene-modified chitosan/magnetite nanocomposites could remove 100% of Hg(II) ions. The nanocomposite adsorbents face challenges in large-scale production, regeneration, and economic suitability. The study provides valuable insights for future research on the green synthesis of nanocomposite adsorbents for heavy metal removal processes.