Efficacy of nanoclays as the potential adsorbent for dyes and metal removal from the wastewater: A review

The purpose of the present review work is to provide an overview of different types of nanoclays (NC), which are utilized for removing heavy metals and dyes from the wastewater. The review work broadly covers various synthesis methods of NC, with special context to the thermodynamic attributes. The NC is an effective adsorbent due to its high specific surface area (SSA > 800 m²/g), cation exchange capacity (CECs >120 cmol kg⁻¹). Besides SSA and CECs, various processes such as surface complexation, ion exchange, and surface precipitation are the governing phenomenon, which are also discussed in the present review work. From the present review work, it can be summarized that the NC demonstrates as a promising adsorbent for different types of dyes and heavy metal with little discrepancies with some of the reported studies. Based on the studies, for 1:1 clay type, Kaolinite performed better than Halloysite for metal removal, also the 2:1 clay exhibited better removal potential than the 1:1 clay type. Moreover, the thermodynamic study concludes that the removal process for both dyes and metal was spontaneous due to –ΔG (Gibbs free energy), indicating better removal efficiency. Further, it was observed that the in-situ method (ISM) yields the best exfoliation and dispersion effect for the synthesis of NC contrasted to other methods. For the laboratory-scale study, the solution-induced intercalation method (SIIM) was found to be feasible, whereas the melt processing method (MPM) for industrial purposes. Though studies are confirming the efficacy of NC as an effective adsorbent, yet the field scale application is still to be answered. Apart from that, the absolute dearth of literature related to NC’s mechanical and thermodynamic properties, desorption for waste repositories, economic analysis, and governing removal mechanism are the additional challenges for the scientific community.