Mechanisms Underlying the Selective Separation of Cerium from Lanthanum Using Functionalized Mesoporous Silica Sorbents

With the rising transition to carbon negative energy due to the issues of global warming and geopolitical policies, there is a rapid increase in utilization of energy critical metals.These critical metals are crucial for several modern applications.On the other hand, the natural resources of these metals are depleting, and the conventional supply chain of these metals produces multiple environmental hazards.Therefore, an alternative eco-friendly way to recover this critical metal from waste is of utmost importance for the near future economy.In this light the adsorption of those metals on innovative functionalized porous adsorbents is proved to be very promising.In this research, an organic ligand was designed and fabricated to functionalize mesoporous silica particles to tune its adsorption capacity.The functionalized silica particles showed remarkable selective adsorption for cerium from a binary solution of lanthanum and cerium.The in-depth characterization of the synthesized mesoporous adsorbent was conducted through various characterization techniques such as XPS, TGA, BET, and SEM to investigate the stability, topology and functional groups of the material and the mechanism of adsorption bond formation.The adsorption isotherm disclosed that it is monolayer adsorption process following Jain and Snoeyink modified extended Langmuir model and adsorption kinetics analysis revels the second order adsorption process.the maximum adsorption capacity for cerium at site-1 were 120.38 µmol/g and for site-2 52.81 µmol/g.While the maximum adsorption capacity for lanthanum at site-1 is revealed to be 120.38 µmol/g and at site-2 is 29.24 µmol/g.Furthermore, the bonds formed due to adsorption of metals were examined using XPS analysis.The adsorbent has two sites to adsorb the metals.Additionally, the experimental observations were further validated by Density Functional Theory (DFT) in aqueous medium using Gaussian software.This molecular simulation was conducted using 6-311G++(2d,2p)/B3LYP basis set for the functionalized adsorbent and SDD/B3LYP for the critical metals.The molecular simulation disclosed the active adsorption sites, length of adsorption bonds and angles and the adsorption energies.DFT simulation says the adsorbent has stable adsorption affinity for La and Ce, moreover two adsorption sites were detected on the functionalized adsorbent.