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

Abstract

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).

Controlled Primary Amine-Enriched SG-Bonded Papain Surface: Synthesis, Characterization, and Extraction of Protonated Dichromate

“…After extraction, we completely stripped out the Cr 2 O 7 2– for three reasons: to recover the extracted species in its purest form, obtain the recovered analyte in its concentration enrichment state, and get the extractor thoroughly cleaned for its reusability. The Cr 2 O 7 2– at 2 N CH 3 COOH was quantitatively extracted at the extractor’s primary −NH 2 groups; , it saturates the extractor with a BTC of 480 μmol g –1 Papain@{SiO 2 }(Section ). Because of the slowest dimerization reaction observed nearly at pH 7 with a lifetime of a few minutes, the equilibrium 2CrO 4 2– ⇄ Cr 2 O 7 2– + H 2 O shifted almost entirely toward CrO 4 2– at left .…”

“…As a result, after immobilization, all of the protein groups of the native enzyme keep their status quo on the functionalized SG surface. Immobilized papain, on its protein folded surface, contains a wide variety of free protein groups, viz., 64 primary −NH 2 , 7 secondary NH, 16 COOH, 19 phenolic −OH, 1 −SH, and 1 −S–S– groups of different hard–soft characters; among them, the primary amine groups act as ligating sites for the hexavalent Cr 2 O 7 2– species. , In the process of selective sample cleanup of Cr 2 O 7 2– , two significant steps operate consecutively: the Cr 2 O 7 2– gathered on the extractor by its selective extraction at its optimized sorption condition from a large sample of low concentration, and subsequently, it is stripped off with the help of a selective eluent of least possible volume (mL) at which the recovered Cr 2 O 7 2– belongs in “concentration enriched purified form.” We carried out the studies with the help of column chromatography, as stated below. We have determined the Cr 2 O 7 2– concentration spectrophotometrically (Figure ) employing the absorbance (nm) versus concentration (mmol L –1 ) linear regression ( y = 0.4470 x + 0.02; Figure b; eq ); the absorbance(s) was recorded for a series standard of 0.25–4.0 mmol L –1 (Figure a). y = 0.4470 x + 0.02 .25em ( normalS normalD : 0.04 ; R : 0.9988 ) …”

“…Immobilized papain, on its protein folded surface, contains a wide variety of free protein groups, viz., 64 primary −NH 2 , 7 secondary �NH, 16 COOH, 19 phenolic −OH, 1 −SH, and 1 −S−S− groups of different hard−soft characters; among them, the primary amine groups act as ligating sites for the hexavalent Cr 2 O 7 2− species. 31,42 In the process of selective sample cleanup of Cr 2 O 7 2− , two significant steps operate consecutively: the Cr 2 O 7 2− gathered on the extractor by its selective extraction at its optimized sorption condition from a large sample of low concentration, and subsequently, it is stripped off with the help of a selective eluent of least possible volume (mL) at which the recovered Cr 2 O 7 2− belongs in "concentration enriched purified form." We carried out the studies with the help of column chromatography, as stated below.…”

“…Nowadays, the SPE is much more applicable ,− over the tedious and time-consuming solvent extraction processes; it requires a competent solid phase, usually built with efficient adsorbate-selective chelating ligands, interacting with anions selectively . Chromium in hexavalent chromate anion combination CrO 4 2– /HCrO 4 – /Cr 2 O 7 2– has a great affinity toward the well-known primary amine containing sites. , Thus, among the other common adsorbents, viz., biochar, activated carbon, cellulose, clays, and silica-based materials, , a lot of researchers were attracted to the biopolymer chitosan, built with primary amine groups as ligating sites to capture chromate ions from aqueous solutions effectively (Xiao et al 2021; Yang et al.…”