Animes Kumar Golder

Removal of Cr(VI) from Aqueous Solution: Electrocoagulation vs Chemical Coagulation

Abstract Hydrolyzed products of Al(III) have affinity below pHzpc for oppositely charged mono and bi‐nuclear species of hexavalent chromium. This study investigates the comparative performance of electrocoagulation (EC) and chemical coagulation (CC) for the removal of Cr(VI) from aqueous solution. The highest removal of Cr(VI) achieved with EC was about 42% with 4.36 mA/cm2 current density. Cathodic adsorption of chromium boosted up Cr(VI) removal during EC. Simultaneous electro‐ and chemical‐dissolution lead to high current efficiency of about 178%. Both the pH and the coagulant dosage have a significant impact on Cr(VI) removal in the pH ranges from 4.9 to 7.0. CC with alum and aluminum sulfate (AS) removed about 11% and 12% of Cr(VI). Co‐adsorption of divalent SO4 2− ions with Cr(VI) is responsible for the lower removal observed with chemical coagulants. About 0.061 and 0.099 mole of SO4 2− was adsorbed per mole Al in the precipitate in the pH range 4.9 to 7.0 with AS and alum. A higher coagulant dosage increases the removal of Cr(VI) but adversely affects the removal efficiency (Cr(VI) removed per unit of Al dosing). Cell current density (CD) has shown little effect on Cr(VI) removal and the pH elevation at the same charge density. Higher initial Cr(VI) concentration improves the removal efficiency as the species of Cr(VI) is acidic in solution and decreases the pH elevation rate.

Ciprofloxacin degradation from aqueous solution by Fenton oxidation: reaction kinetics and degradation mechanisms

Pharmaceutical wastewater from a large number of manufacturing units is extremely contaminated by ciprofloxacin (CIP), an antibiotic drug. In this work, aqueous CIP solution was treated by Fenton oxidation (FO). The effects of typical process parameters on drug mineralization have been reported. The optimal Fe2+/H2O2 molar ratio of 0.125 and pH of 3.5 were determined with 15 mg L−1 initial CIP at 25 °C temperature. Maximum CIP, COD and TOC removal of 74.4, 47.1 and 37.9% were obtained under the optimal conditions. The mean oxidation number of carbon determined in terms of COD and TOC values was in accordance with that from the oxidation number of individual carbon atom. The concentration of hydroxyl radicals was measured using the N,N-dimethyl phenyl hydrazine method using dimethyl sulphoxide as a probe. Thirteen fragments appeared in the mass spectra and the proposed mechanism explored the routes of daughter ion formation. The cleavage of the piperazine ring was more effective in CIP oxidation due to high nucleophilic character of lone pair of electrons present on the nitrogen atom. A simple 2nd order kinetic model was proposed for the oxidation of CIP and degradation products (DPs) with respect to OH˙ concentration. The rate constants of 3.13 × 103, 4.89 × 103 M−1 s−1 were estimated for CIP and DPs. The initial concentration of OH˙ was found to be 11.67 μM.

Reduction of Cr(VI) into Cr(III) by Spirulina dead biomass in aqueous solution: kinetic studies.

Microalga species are potential scavengers of heavy metals. The active functional groups of a number of biomaterials are capable to detoxify Cr(VI) to Cr(III). A 2nd order kinetic model was developed in terms of concentration of protonated acidic groups of Spirulina sp. biomass for the reduction of Cr(VI) into Cr(III). Cr(VI) reduction reaction grounded on the concentration of functional groups was validated over a broad range of pH, temperature and anionic strength. Lower pH favoured Cr(VI) reduction reaction and the experimental results well fitted to the kinetic model. The overall rate constant, kt, decreased logarithmically from 22.7 to 2.8 mM⁻¹ s⁻¹ with rise of pH from 0.5 to 6.0. Whereas, k(t) increased nearly by 23% with elevation temperature from 25 to 45 °C. Higher concentration (>0.235 mM) of background anions (Cl⁻, SO₄²⁻ and NO₃⁻) was resulted in decreases in k(t) values. The rate constant expression developed can be employed to quantify Cr(VI) reduction into Cr(III) using Spirulina biomass.

Decomposition of drug mixture in Fenton and photo-Fenton processes: Comparison to singly treatment, evolution of inorganic ions and toxicity assay

The degradation of three pharmaceutical compounds i.e. chloramphenicol (CHPL), ciprofloxacin (CIP) and dipyrone (DIPY) singly and from equimolar (CCD) mixture has been investigated in Fenton and photo-Fenton processes. Drug mineralization was slightly less when present singly than their mixture. The degradation efficiency was likely hindered due to formation of common ions like Cl(-), F(-), NH4(+) and NO3(-). Addition of the same ions i.e. Cl(-) and F(-) in drug solution released upon cleavage of CHPL and CIP in CCD mixture suppressed the decomposition efficiency remarkably in both the oxidation processes. The major intermediates appeared in the mass spectra in combination of ion chromatograph were used to validate the routes of CCD decomposition and evolution inorganic ions. Furthermore, the bacterial toxicity assay was investigated using Escherichia coli (E. coli). The average reduction in cell death was about 38% in CCD system compared to 52%, 42% and 47% for CHPL, CIP and DIPY, respectively.

pH dependent size control, formation mechanism and antimicrobial functionality of bio-inspired AgNPs

Sechium edule is rich in ascorbic acid which was extracted from aqueous media for the synthesis of AgNPs. This work reports the effects of pH on the kinetics and mechanisms of AgNPs formation using this extract leading to different particle sizes, morphology, spectral response, and antimicrobial functionality. Thermodynamically facile Ag2O reduction at a higher pH (≥9) resulted in spherical particles of smaller sizes; however, the particles were laden with a trace of Ag2O at pH 12.5. A broad and bimodal distribution of AgNPs of different shapes and sizes were originated at a lower pH (3 ≤ pH ≤ 5) from Ag+ and Ag2O reductions where ascorbic acid mostly exists as dehydro-ascorbic acid. A single surface plasmon resonance peak at 425 nm exhibited a blue shift with the decrease in AgNPs size and increase in sphericity in the abundance of OH− ions. The silver–ascorbate layer induced particles destabilization along with the formation of ascorbate free radical (g-factor: 2.0052 to 2.0056) which was also responsible for the inhibition of B. subtilis and E. coli.

Bio-mediated silver nanoparticle synthesis: mechanism and microbial inactivation

ABSTRACT Even though plenty of literature is available on the biosynthesis of metal nanoparticles, there are serious lacunae on the mechanisms of their formation. In the present study, the mechanism of formation of mono-crystalline silver nanoparticles using a fruit extract of the ornamental tree Thevetia peruviana is emphasized, i.e. how the pH of the reaction mixture affected reaction kinetics and size of the nanoparticles. The facilitation of formation of Ag2O at higher pH resulted in a faster rate of particle formation. The diameter of the bare particles at neutral pH determined by field emission scanning electron microscopy and the hydrodynamic diameter determined by dynamic light scattering were 53 and 104 nm, respectively. The silver nanoparticles exhibited good inactivation of Escherichia coli due to participation of free radicals as evidenced by electron spin resonance spectroscopy.

Synthesis of a functionalized fibrous adsorbent of high uptake capacity: a study on Pb(II) uptake and simple acidic site model development

The breakdown of the lignin barrier by acid treatment could expose cellulosic functional groups on the surface of biomaterials. In this study, a new functionalized fibrous adsorbent (FFA) was prepared using arecanut (Areca catechu) husk in sulfuric acid media. The synthesized FFA was characterized using proximate & ultimate analyses, thermogravimetric analysis (TGA), Brunauer–Emmett–Teller (BET) surface area, scanning electron microscopy (SEM), energy dispersive X-ray (EDX) and Fourier transform infrared (FTIR) spectroscopy. A simple dual-site proton adsorption (DSPA) model was developed and applied for equilibrium Pb(II) uptake on the basis of mass balance. The quantity of proton absorbed onto FFA, obtained from potentiometric titrations, was used to determine the acid dissociation constants (pKa) and the concentration of functional groups. The model fitted parameters showed a great agreement to the experimental results. The FTIR spectra and also the pKa values of 3.21 and 1.62, respectively, confirmed the presence of surface carboxylic and sulfonic groups. FFA exhibited significant Pb(II) uptake and the Pb(II) ions predominantly attached to the carboxylic group even though the concentration was about 25% lower than the sulfonic group. FFA with a dose of 1 g L−1 showed around 98.3% Pb(II) removal at pH 5 from an initial concentration of 32 mg L−1 (0.157 mM). It could be used for 12 cycles with the exhaustion capacity of 194.94 mg g−1 of FFA which was about 3.4 times higher than the commercial activated carbon.

Colour diminution and COD reduction in treatment of coloured effluent by Electrocoagulation

This work experimentally investigates the colour and Chemical Oxygen Demand (COD) removal of effluents containing: Trypan Blue (TB); Orange G (OG) dye using the two most common electrode materials – Mild Steel (MS) and Aluminium (Al). Effects of the time of electrotreatment, solution pH, electrode material, current density and initial dye concentration on decolourisation and COD reduction are reported. MS electrodes show better colour removal efficiency event at lower cell current efficiency compared with Al electrodes and are able to achieve up to 90–98% removal in less than 60 min. Removal efficiency is higher in the case of TB compared with OG irrespective of electrode material due to higher electrostatic attraction between TB molecules and metal hydroxide sludge. Higher current density enhances colour removal even though pH elevation (approaching close to zero point charge) rate is higher. COD reduction is found to be about 10-20% lower than colour diminution measured spectrophotometrically suggesting different mechanisms of dye removal involved during EC.

Synthesis and characterization of carboxylic cation exchange bio-resin for heavy metal remediation

A new carboxylic bio-resin was synthesized from raw arecanut husk through mercerization and ethylenediaminetetraacetic dianhydride (EDTAD) carboxylation. The synthesized bio-resin was characterized using thermogravimetric analysis, field emission scanning electron microscopy, proximate & ultimate analyses, mass percent gain/loss, potentiometric titrations, and Fourier transform infrared spectroscopy. Mercerization extracted lignin from the vesicles on the husk and EDTAD was ridged in to, through an acylation reaction in dimethylformamide media. The reaction induced carboxylic groups as high as 0.735mM/g and a cation exchange capacity of 2.01meq/g functionalized mercerized husk (FMH). Potentiometric titration data were fitted to a newly developed single-site proton adsorption model (PAM) that gave pKa of 3.29 and carboxylic groups concentration of 0.741mM/g. FMH showed 99% efficiency in Pb(II) removal from synthetic wastewater (initial concentration 0.157mM), for which the Pb(II) binding constant was 1.73×103L/mol as estimated from modified PAM. The exhaustion capacity was estimated to be 18.7mg/g of FMH. Desorption efficiency of Pb(II) from exhausted FMH was found to be about 97% with 0.1N HCl. The FMH simultaneously removed lead and cadmium below detection limit from a real lead acid battery wastewater along with the removal of Fe, Mg, Ni, and Co.

Ag-doping on ZnO support mediated by bio-analytes rich in ascorbic acid for photocatalytic degradation of dipyrone drug

The analytes such as ascorbic acid (AA) present in Sechium edule were extracted (294 mg AA kg-1 fruit) in an aqueous media for its potential application for Ag-doping onto wurtzite ZnO. The bandgap of ZnO was decreased to 2.85 eV at the optimal Ag-loading of 1.18% (w/w) against 3.13 eV for the control catalyst without using the analytes and, the commercial AA only could reduce the bandgap to 2.91 eV. The saturation photo-electrochemical current density (46.68 mA cm-2) at Eanode ≥ 0.31 V vs. Ag/AgCl was almost double than pristine ZnO under visible light illumination (λmean = 525 nm, 18 K lux) and, the current density was insignificant in the dark. The doped catalyst exhibited the maximum 79.5% degradation (71% COD removal) of an anti-analgesic drug, dipyrone (100 μg L-1 dipyrone, catalyst 100 mg L-1) resulted from the formation of O2•- radical (g-factor of 2.002-2.008) and paramagnetic oxygen vacancies (g-factor of 2.020) and, no effect of dye-sensitization was noted. The highest quantum yield was found to be 34.7%. The catalyst loss was 6% after the fourth cycle and the dipyrone degradation was reduced to 70.8%.