8‑Hydroxyquinoline Anchoring 3‑D Networking Silica Gel Utilizing Its HOMO as a Metal Trapping Center for Selective Sample Cleanup of Cu(II), Cr(III), and Co(II) and Chemical Speciation of Sorbed Species

8-Hydroxyquinoline has been chemically anchored on three-dimensional networking silica gel (SG) for selective sample cleanup of Co­(II), Cr­(III), and Cu­(II) amidst several other naturally occurring ions as matrix. The extractor, utilizing its frontier orbital makes a 1:1 “ion-pair complexation” with different aqua species of Co­(II), Cr­(III), and Cu­(II), identified as {Co2(OH)­(H2O)4}3+, {Cr3(OH)4(H2O)10}5+, and {Cu2(OH)2(H2O)3}2+, through first-order sorption kinetics. The chemically stable (4 M HNO3) reusable material (820 cycles) attains an appreciable breakthrough capacity (BTC) of 557, 835, and 552 μmol·g–1, respectively, for Co­(II), Cr­(III), and Cu­(II). The process is endothermic and spontaneous and becomes more ordered upon an eventual consequence of sorption. After sorption, exploiting the differences in the stripping behavior, the analytes were sequentially resolved and retrieved with selective eluents (Co­(II): 0.01 M HNO3, Cr­(III): 0.05 M H2SO4 and Cu­(II): 0.1 M HCl) of minimum volume (4 mL) to attain a high preconcentration factor (Co­(II): 184.0; Cr­(III): 184.1; Cu­(II): 183.2). The equation for computation of BTC has been developed as BTC = {amount of highest occupied molecular orbital (μmol·g–1)} × x (where x is the degree of polymerization of the analyte under investigation at its relevant sorption pH).