Milan K. Barman

Solid-phase extraction, separation and preconcentration of titanium(IV) with SSG-V10 from some other toxic cations: a molecular interpretation supported by DFT

The present work reports the separation and preconcentration of titanium(IV) with functionalized silica gel (SSG-V10). A density functional theory (DFT) calculation has been performed to analyze the structure of both the extractor and the titanium(IV)-extractor complex to rationalize the sorption pathway. The systematic studies on the solid phase extraction of titanium(IV) ensured its quantitative sorption at solution pH: 5.0–6.0, influent volume: 1000 mL, analyte concentration: 23.95–35.92 μg mL−1, flow rate: 2.5 mL min−1, temperature: 27 °C, time of equilibration: 1.5 minutes and stress of foreign ions concentration (Cl−, SO42−, ClO4− and NO3−): 200 μg mL−1. The extractor, i.e., SSG-V10 (29 567.465 eV; η = 3.671 eV), has a high BET surface area (149.46 m2 g−1), a good value of exchange capacity (2.54 meq. of H+ g−1 of dry SSG-V10), break-through capacity (Q0 = 37.4–40.7 μg mg−1) and column efficiency (N: 108) with respect to titanium(IV). The +ve ΔH (0.048 kJ mol−1), ΔS (5 J K−1 mol−1) and −ve ΔG (−1.1488 kJ mol−1) indicate that the sorption process was endothermic, entropy-gaining and spontaneous in nature. The DFT calculations reveal that the guest, [(OH)(H2O)Ti(-μO)2(OH)(H2O)]+2 (15 531.185 eV; η = 3.39 eV), is stabilized as a syn isomer. This syn isomer was then placed at the exchange site and a second DFT calculation was performed. It was found that the hydrogen bonded anti complex gets stabilized by 0.286 eV over the syn isomer as the extracted species. The loading of titanium(IV) has been confirmed by EDX. The sorbed titanium(IV) was eluted as a distinct and detectable color with 1 M HCl containing H2O2. The preconcentration factor has been optimized at 60.8 ± 0.5. Titanium(IV) amid congeners and other metal ions, associated with it in ores and alloy samples, have been separated from synthetic mixtures. Moreover, the method was found effective for alloy samples.

Extraction chromatographic method of preconcentration, estimation and concomitant separation of vanadium (IV) with silica gel-versatic 10 composite.

A selective method has been developed for the extraction chromatographic separation of V(IV) with SSG-V-10 composite. V(IV) was quantitatively extracted at pH 5.0-6.0, and its loading has been confirmed by EDAX. XRD studies indicate that the SSG network does not get influenced by impregnation with V-10 or by the sorption of V(IV) on the surface of SSG-V-10 composite. The binding between SSG and V-10 is a hydrophobic interaction only, and it takes place at the surface of the hydrophobic SSG. TGA-DTA analysis indicates its thermal stability up to 45°C. The exchange capacity (1.65 meq of H(+) g(-1)), break-through capacity (34.5 mg g(-1)) and column efficiency (360) of the extractor have been rationalized by Brunauer-Emmett-Teller analysis (SA = 149.46 m(2) g(-1) and PV = 0.2001 mL g(-1) at a relative pressure of 0.9-1.0). The sorption process was endothermic (ΔH = 12.63 kJ mol(-1)), entropy gaining (ΔS = 0.271 kJ mol(-1) K(-1)) and spontaneous (ΔG = -68.241 kJ mol(-1)) in nature. Preconcentration factor has been optimized at 182.3 ± 0.2. Formation constants (Kf) of the metal centers [Zn(II) (0.6 × 10(3)), Cd(II) (0.9 × 10(4)), Pb(II) (0.6 × 10(5)), Cu(II) (0.2 × 10(5)), Al(III) (6.2 × 10(5)), Ga(III) (4.2 × 10(5)), Hg(II) (2.2 × 10(6)), Bi(III) (6.2 × 10(6)), Tl(III) (8.9 × 10(6)), Zr(IV) (6.8 × 10(9)), Fe(III) (0.9 × 10(9)) and V(IV) (0.8 × 10(6))] have been determined. The desorption constants Kdesorption (1.9 × 10(-2)) and [Formula: see text] have been determined. Rf values and selectivity factors for diverse metal ions have been determined. V(IV) has been separated from the synthetic and real samples containing its congeners. A plausible mechanism for the extraction of V(IV) has been suggested.

Combined cation-exchange and solid phase extraction for the selective separation and preconcentration of zinc, copper, cadmium, mercury and cobalt among others using azo-dye functionalized resin

A facile synthesis of an ion exchange material (FSG-PAN) has been achieved by functionalizing silica gel with an azo-dye. Its composition and structure are well assessed by systematic analysis. Extractor possesses high BET surface area (617.794m(2)g(-1)), exchange capacity and break-through capacity (BTC) (Q0 Zn(II): 225; Cd(II): 918; Hg(II): 384, Cu(II): 269 and Co(II): 388μMg(-1)). The sorption process was endothermic (+ΔH), entropy-gaining (+ΔS) and spontaneous (-ΔG) in nature. Preconcentration factor has been optimized at 172(Zn(II)); 157.2(Cd(II)); 193.6(Hg(II)); 176(Cu(II)); 172.4(Co(II)). Density functional theory calculation has been performed to analyze the sorption pathway. BTC (μMg(-1)) of FSG-PAN was found to be the product of its frontier orbitals and state of sorbed metal ion species, x (at x=1, mononuclear and x>1, a polynuclear species; i.e., BTC=[amount of HOMO]×x). FSG-PAN is used for the selective separation and preconcentration of Zn(II), Cd(II), Hg(II), Cu(II),Co(II) from large volume sample (800mL) of low concentration (0.017-0.40mML(-1)) in presence of foreign ions (50-300mML(-1)) at optimum conditions (pH: 7.0±1.5, flow rate: 2.5mLmin(-1), temperature: 27°C, equilibration-time: 5min). The method was found to be effective for real samples also.

EBT anchored SiO2 3-D microarray: a simultaneous entrapper of two different metal centers at high and low oxidation states using its highest occupied and lowest unoccupied molecular orbital, respectively

A quick and facile synthesis of a mesoporous (pore diameter = 46.2–47.1 nm) material (FSG-EBT) through the immobilization of azo dye (EBT) on functionalized silica gel (FSG) has been achieved. FSG-EBT simultaneously binds two different metal centers, Zr(IV) and Tl(I) at their high and low oxidation states, respectively. Highest occupied molecular orbital (HOMO) of the extractor binds Zr(IV) with a breakthrough capacity (BTC) of 490 μmol g−1 and its lowest unoccupied molecular orbital (LUMO) extracts Tl(I) (BTC = 120 μmol g−1). The LUMO has thus enhances the BTC of the resin as a whole. This binding mode sequence differs from earlier existing mode of binding where extractors bind metals using HOMO and LUMO operative on the same metal centre only. HOMO/LUMO value (μmol g−1) reiterates itself as a definite quantum mechanical descriptor of BTC, and BTC is a definite descriptor of the state of metal (monomer/polymer) sorbed. The synthesis needs no stringent reaction condition such as refluxing. Its corresponding nanomaterial has been well assessed (composition: [Si(OSi)3(OH)·xH2O]n[–Si(CH3)2–NH–C6H4–NN–EBT]4; structure: tetrahedral) and is reiterated by density functional theory (DFT) calculation. Along with its good extractor qualities [high pore volume, PV = 0.3747 cm3 g−1; surface area, SA = 330.97 m2 g−1; BTC (Q0 = 476.7 μmol g−1); column efficiency, CE = 296 and preconcentration factor, PF = 120.20 ± 0.04; reusability > 1000 cycles; and faster rate of sorption–desorption], FSG-EBT possesses well demarcated spatial placement of HOMO–LUMO with a substantial band gap (η = 7.1471 eV). This makes charge recombination by mixing difficult and thus shows its potential applicability as a good donor–acceptor organic electronic device.

Chromatographic method for pre-concentration and separation of Zn(II) with microalgae and density functional optimization of the extracted species

A novel wild strain of microalgae, Phormidium luridum containing Gloeothece rupestris and Chlorococcum infusionum (99:0.08:0.02), was studied for its ability to remove and retrieve Zn(II) from aqueous solutions in the presence of some commonly occurring ions (Na+, K+, Cl−, SO42−, ClO4−, NO3−) in their natural contamination concentration range (50–300 mg L−1). The algae, which were previously collected from the river basin (Ajay), were grown on naturally occurring gravels in a glass column of nutrient enriched raw water media. Systematic studies of the sorption of Zn(II) (0.02 mg mL−1) over a pH range of 4.5–7.5 identified a maximum removal extent of 104 μM g−1 at neutral pH, mainly by adsorption at the surface layer. Zn(II) was retrieved by selective elution with 5 × 10−3 M HNO3 solution. Initially, [Zn(H2O)(OH)]+ (η[Zn(OH)(H2O)]+ = 1.25 eV) is adsorbed at the surface of the algae, which is built up of polysaccharides (η[glucose] = 6.34 eV), before moving inside by the formation of a more stable complex with Phycocyanobilin2, which has similar hardness (η[Phycocyanobilin] = 2.37 eV). The complex is stabilized by −52195.48 eV mol−1 through the formation of two strong intramolecular hydrogen bonds (–OH⋯O = 163.54 pm; HOH⋯O = 129.71 pm). Density functional theory optimization corroborates a stable [Zn(H2O)(OH)]+–Phycocyanobilin2 tetrahedral complex.

Solid phase extraction, separation and preconcentration of rare elements thorium(IV), uranium(VI), zirconium(IV), cerium(IV) and chromium(III) amid several other foreign ions with eriochrome black T anchored to 3-D networking silica gel

The present work reports the systematic studies on extraction, separation and preconcentration of Th(IV), U(VI), Zr(IV), Ce(IV) and Cr(III) amid several other foreign ions using EBT anchored {SiO2}n3-D microarray. The effect of various sorption parameters, such as pH, concentration, temperature, sample volume, flow-rate and co-existing foreign ions were investigated. Quantitative sorption was ensured at solution pH: 6.0-6.5 for Th(IV), Ce(IV), Cr(III) and pH: 2.75-3.0 for Zr(IV), U(VI) couple. Analysis on extracted species and extraction sites reveals that [Th4(μ(2)-OH)8(H2O)4](8+), [Ce6(μ(2)-OH)12(H2O)5](12+), [Cr3(μ(2)-OH)4(H2O)](5+), [(UO2)3(μ(2)-OH)5(H2O)3](+) and [Zr4(μ(2)-OH)8(H2O)0.5](8+) for the respective metal ions gets extracted at HOMO of the extractor. HOMO-{metal ion species} was found to be 1:1 complexation. Sorption was endothermic, entropy-gaining, instantaneous and spontaneous in nature. A density functional theory (DFT) calculation has been performed to analyze the 3-D structure and electronic distribution of the synthesized extractor.

Facile Synthesis of a Luminescent Material, PAN@{SiO2}n, Having a Simultaneous Binding Capacity of High and Low Oxidation States: HOMO and LUMO, Quantum-mechanical Descriptor of Break-through Capacity

A time-cost effective, chemically stable mesoporous resin (FSG-PAN), simultaneous binder of two different metal centers (both high (Cd(II)) and low (Tl(I)) oxidation states), has been synthesized by immobilizing azo-dye (1-(2-pyridylazo)-2-napthol: PAN) on functionalized silica gel (FSG). Its corresponding synthesized nano material possesses good luminescent properties, and has been utilized in fluoride sensing at trace levels (1.8 × 10(-6) - 7.2 × 10(-6) M). The composition ({Si[OSi]p=4[H2O]x=0.81}12[-Si(CH3)2-NH-C6H4-N=N-PAN]4.·51H2O) and structure (tetrahedral) have been well assessed. Under the optimum extraction conditions, the soft extractor (ηFSG-PAN = 1.31 eV), FSG-PAN quantitatively extracts the soft metal centers Cd(II), followed by Tl(I) at its respective HOMO and LUMO by soft-soft interactions. The extractor possesses a high Brunauer-Emmett-Teller (BET) surface area (SABET) (374 m(2) g(-1)), high preconcentration factor (PF, 192), selective pore size and two kinds of break-through capacity (BTCHOMO, 945 μmol g(-1); BTCLUMO, 120 μmol g(-1)). BTC is spelled out as a function of the electron density over the ligand binding site as analyzed from a DFT calculation.

In vivo detection of fluoride at trace levels and its removal from raw water at neutral pH utilizing a cyanobacterium pigment as a luminescent probe

A selective method has been developed for trace level (0.01 mg L−1) fluoride detection in HEPES buffer in the presence of interfering ions (such as Cl−, I−, Br−, SO42−, ClO4−, and CH3COO−) using a cyanobacterium as a luminescent probe. It is able to detect trace levels well below the PHS recommended levels for drinking water (0.7–1.2 ppm), which places this probe among the most sensitive fluoride sensors reported to date. The cellular pigment, phycocyanobilin 2, of living algae plays an anchoring role to sense fluoride at trace levels via instantaneous fluorescence. Algal biomass was used for the removal of fluoride from raw water at neutral pH. The maximum uptake capacity (BTC: 6.76 mg g−1 and Q0: 6.08 mg g−1) and preconcentration factor (PF: 64.2) were found to be appreciably high. Interference caused by the presence of several co-existing ions is also discussed. The proposed method has been applied to real samples, such as pond water, well water and ground water, with good analytical reliability: removal of fluoride up to 92.3% ± 1.3%, with a relative standard deviation of 2–3%, and re-usability of 70–90 cycles.

Detection and selective sample clean-up of beryllium(II) through {extractor-HOMO}(:){Be3O(OH)2}2+ ‘ion pair complexation’ amidst aluminum(III) and uranium(VI) by employing a fluorescent resin: the resin's HOMO amount is a quantitative descriptor of BTC

FSG–PAN, an effective extractor, has been synthesized by chemically immobilizing PAN (1-{2-prydylazo}-2-naphthol) on silica-gel using an efficient silane-coupling-reagent, dimethyldichlorosilane. The corresponding luminescent nanomaterial has been utilized for the selective detection of Be(II) (LOD ≥ 0.75 × 10−6 mol L−1) amidst natural contaminants. The extractor selectively sorbed beryllium and aluminum (both as aqua-tri-nuclear-species, {Be3O(OH)2}2+ and {Al3(OH)3(H2O)2}6+), and uranium (as a bi-nuclear-aqua-species, {(UO2)2(OH)2(H2O)7}2+) at its highest occupied molecular orbital (HOMO) through HOMO : metal-ion-species 1 : 1 ion-pair formation. The binding stability of this interaction (0.012 eV mol−1/0.28 kcal mol−1) lies well below the classical bond energy (104 kcal mol−1) of any kind of chemical bond. The HOMO (μmol g−1) is thus an important quantitative part of the breakthrough capacity (BTC) and is expressed as BTC = {amount of HOMO (μmol g−1) × x}, where HOMO = 218 μmol g−1 and x = degree of polymerization; here, x = 3 for Be(II)/Al(III) and 2 for U(VI). Along with its excellently high BTC and enrichment factor (PF) (BTCBe(II): 645, BTCAl(III): 640, BTCU(VI): 428 μmol g−1; PFBe(II): 93.6, PFAl(III): 90.5, PFU(VI): 91.6), the appreciable durability (reusability ≥1000 cycles) and remarkable chemical inertness (BTC4M HNO3/H2SO4/HCl ≥ 95% at 4 mol L−1 acid-treatment) of the material signify its stability. By exploiting sorption-desorption selectivity, Be(II) has been sequentially separated (recovery ≥94.5 ± 2.5%) from several real and ‘synthetic multicomponent’ samples comprising its congeners.

n-Capric acid-anchored silanized silica gel: its application to sample clean-up of Th(IV) sorbed as a dinuclear species in quantified H-bonded dimeric metal-trapping cores

The selective separation, preconcentration and recovery of Th(IV) from aqueous solutions were investigated using reusable (>800 cycles @ 95% recovery) silanized silica gel impregnated with n-capric acid (nCA) (SSG–nCA) via batch column adsorption methods. SSG–nCA is a porous material (pore volume: 2.21 mL g−1) with a large Brunauer–Emmett–Teller (BET) surface area (1820 m2 g−1). Dimethyldichlorosilane (DMDCS) binds unit cells of the SG skeleton (i.e., {Si(OSi)4·xH2O}θ=2.4) via an {SiO2}n=12–O–Si(Me)2–O–{SiO2}n=12 3-D network to produce SSG by an intra-particle silanization reaction. In SSG–nCA, long hydrophobic hydrocarbon chains of nCA, which are anchored to the hydrophobic surface of SSG, generate 121 μmol g−1 H-bonded dimeric metal-trapping cores (HBDMTC), which are oriented towards the hydrophilic mobile phase. It exhibited significant sorption of Th(IV) (breakthrough capacity (BTC): 235 ± 15 μmol g−1; minimum sorption equilibrium time: >12 minutes; high recovery: >95% from a large sample volume of 1000 mL; and a high preconcentration factor (PF): 192). The dimeric aquo-{Th2(OH)2(H2O)2}6+ sorbed species that was identified anchored with an appreciable binding energy (−38.37 eV per mole) at the optimum pH of 5.0 ± 0.4. Together with the existing standard methodology, density functional theory (DFT)-based computations were performed for the characterization of both the extractant and the extracted species. The sorption process was endothermic (+ΔH), entropy-increasing (+ΔS) and spontaneous (−ΔG) in nature. It was found to be effective in the presence of 0.125–0.150 mmol mL−1 Na/K salts of coexisting ions. The sequential separation of Zr(IV), U(VI), Ce(IV), and Th(IV) was achieved by exploiting the differences in the pH used for extraction (Zr(IV) at a pH of 2.5 and U(VI), Ce(IV), and Th(IV) at a pH of 5.0 ± 0.4), followed by their selective elution from the respective extracted portion (Zr(IV): 4 M HNO3, U(VI): 0.6 M CH3COOH, Ce(IV): 1 M CH3COOH, and Th(IV): 0.5 M HNO3).