The emerging role of quantum computations in elucidating adsorption mechanism of heavy metal ions: a review

The process of removal of heavy metal ions from contaminated aqueous systems has been studied extensively in terms of mechanisms, influencing factors, thermodynamics and kinetics. However, due to the complex nature of the adsorption process, a thorough understanding related to the adsorption process is still missing. An insight into the adsorption parameters like adsorption energy, preferred adsorption sites, structural dynamics of adsorbents before and after the metal ion removal process, etc. is quite difficult to obtain from experimental studies. Under such conditions, quantum mechanical computations make an important complementary aid in understanding the adsorption process of metal ions effectively, accurately and thoroughly by experimental researchers. Here, in this review paper, we have discussed the importance of quantum computations in elucidating the removal of toxic metal ions and highlighted the mechanistic details of the adsorption process by considering some real-time adsorbents systems for metal ion uptake and recovery from aqueous systems. A comparative analysis is presented throughout to highlight the accuracy and perfection of theoretically supported experimental results in dealing with the heavy metal ion removal process. Finally, optimized geometries, interaction energies, preferable metal ion binding sites and possible mechanism of adsorption on various metal ion adsorbents with special reference to graphene oxide have been discussed in detail.