Guru C. Pradhan

Influence of the nature and concentration of precursor metal ions in the brucite layer of LDHs for phosphate adsorption – a review

Layered double hydroxides (LDHs) are an important class of layered materials consisting of hydroxides of some of the most common and abundant metals on Earth. In addition to compositional flexibility, these materials are good anion exchangers and are important sinks for environmental contaminants. In this article, we review the past achievements of LDHs concerning their synthesis, structural development, characterization, and especially the removal of phosphate from aqueous solution. Major factors such as the nature and concentration of LDH precursor metals, layer charge and interlayer anion charge, competitive anions, pH, temperature, etc. for phosphate removal are discussed. Additionally, the possible phosphate removal mechanisms by LDHs are also discussed to know the efficacy of the materials. The phosphate removal capacities of LDHs are compared with other materials for accessing the future prospects of LDHs. The possible improvement of LDHs in terms of stability, regeneration and reusability are also proposed for cost effective applications.

Thermal, electrical and tensile properties of synthesized magnetite/polyurethane nanocomposites using magnetite nanoparticles derived from waste iron ore tailing

The synthesis of magnetite nanoparticles (MNP) using waste iron tailing as one of the starting materials and its use in preparation of MNP/polyurethane (MNP/PU) nanocomposites with bio-based PU were described. A comparison of XRD patterns, FT-IR and UV–vis diffuse reflectance spectra of neat MNP, neat PU and MNP/PU nanocomposites indicated the incorporation of MNP in PU resin. The SEM and TEM micrographs showed nearly uniform dispersion of MNP in MNP/PU nanocomposites. Both thermal stability and electrical conductivity of MNP/PU nanocomposites were increased with increase of MNP loading while MNP addition significantly improved the tensile properties of PU. The magnetic measurements revealed a transition from superparamagnetic behaviour of neat MNP to ferromagnetic in MNP/PU at lower MNP content. The MNP/PU nanocomposites may be exploited further for electronic and optoelectronic applications.

Glyoxylate as a reducing agent for manganese(III) in salen scaffold: A kinetics and mechanistic study

AbstractThe kinetics of oxidation of glyoxylic acid (HGl) by MnIII(salen)(OH2)2+

Kinetics of aquation and base hydrolysis ofcis-(carboxylato) (ethylamine)bis(ethylenediamine)cobalt(III) ions

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Ligand substitution and electron transfer reactions of trans-(diaqua)(salen)manganese(III) with oxalate: an experimental and computational study†

((H2salen = N,N′- bis(salicylidene)ethane-1,2-diamine) is investigated at 30.0–45.0°C, 1.83 ≤ pH ≤ 6.10, I = 0.3 mol dm−3(NaClO4). The products are identified as formic acid, CO2 and MnII with the reaction stoichiometry, |Δ[MnIII]/Δ[HGl]| = 2. The overall reaction involves fast equilibrium pre-association of MnIII(salen)(OH2)2+

Medium effects on the reactions of coordination complexes: Base hydrolysisof(αβS)(p-hydroxybenzoato)(tetraethylenepentamine) cobalt(III) in iso-propanol–water, tert-butanol–water and dimethyl sulfoxide–water media

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Kinetics of acid- and iron(III)-catalysed aquation of cis-(salicylato)-(methyl/ethylamine)bis(ethylenediamine)cobalt(III)

with HGl and its conjugate base Gl− forming the corresponding inner sphere complexes (both HGl and Gl− being the monohydrate gem-diol forms) followed by the slow electron transfer steps. In addition, the second order electron transfer reactions involving the inner-sphere complexes and HGl/Gl− are also observed. The rate, equilibrium constants and activation parameters for various steps are presented. MnIII(salen)(OH2)(Gl) is virtually inert to intra molecular electron transfer while the process is facile for MnIII(salen)(OH2)(HGl)+ (105ket = 2.8 ± 0.3 s−1 at 35.0°C) reflecting the involvement of proton coupled electron transfer mechanism in the latter case. A computational study of the structure optimization of the complexes, trans-MnIII(salen)(OH2)2+

Kinetics and mechanism of complexation of iron(III) bycis-(salicylato)(methyl/ethylamine)bis(ethylenediamine)cobalt(III) ions

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Medium effect on the reactions of complexes: kinetics and mechanism of the base hydrolysis of cis-[(salicylato)(amine)bis(ethylenediamine)cobalt(III)] compounds in methanol-water

, trans-MnIII(salen)(OH2)(Gl), and trans- MnIII(salen)(OH2)(HGl)+ (all high spin MnIII(d4) systems), reveals strongest axial distortion for the (aqua)(Gl) complex ; HGl bound to MnIII centre by the C=O function of the carboxyl group in the (aqua)(HGl) complex facilitates the formation of a hydrogen bond between the proton of the carboxyl group and the coordinated phenoxide moiety ((O-H …O hydrogen bond distance 1.745 Å) and the gem-diols are not involved in H-bonding in either case. A rate comparison for the second order paths: MnIII(salen)(OH2)(HGl)/Gl)+/0+ HGl/Gl−→ products, shows that HGl for the (aqua)(HGl) complex is a better reducing agent than Gl− for the (aqua)(Gl) complex (kHG ∼ 5 kGl). The high values of activation enthalpy ( ΔH≠= 93–119 kJ mol−1) are indicative of substantial reorganization of the bonds as expected for inner-sphere ET process. Graphical AbstractMnIII(salen)(OH2)2+ is reduced by glyoxylic acid (HGl) and its conjugate base via inner sphere mechanism. DFT calculations reveal intra molecular hydrogen bonding in the inner sphere complex, MnIII(salen)(OH2)(HGl)+ which leads to the proton coupled electron transfer process. Reduction of MnIII(salen)(OH2)(HGl)+ by HGl follows outer sphere mechanism.

Base hydrolysis ofcis-(methyl/ethylamine)bis(ethylenediamine) (salicylato)cobalt(III) complexes

SummaryThe aquation ofcis-[Co(en)2(NH2Et)O2CR]2+ [R=H or Me] is strongly acid-catalysed and the rate and activation parameters for this process are reported. No significant rate difference is observed in the spontaneous aquation path for the complexes. The acetato complex undergoes acid catalysed aquation at a rate comparable to the of the corresponding formato complex, in contrast with the relative basicities of the coordinated formate and acetate. This result is interpreted in terms of relative solvation effects of the initial and transition states of both complexes.The base hydrolysis of both complexes obeys overall second order kinetics in the 0.05≤[OH−]T ≤0.35 mol dm−3 range (I=0.5 mol dm−3). The formato complex reacts five times faster than its acetato analogue under comparable conditions, which is fully consistent with the dissociative mode of activation of the amido conjugate base involving Co−O bond heterolysis. A substantially large positive value for the activation entropy supports SN1CB mechanism for base hydrolysis.