In this report, the synthesis, characterization and electrocatalytic oxidation of water by a mononuclear cobalt(
iii
) complex, Co
III
(dpaq)(Cl)Cl (
1
) featuring a redox-active pentadentate amidate ...ligand (H-dpaq = 2-bis(pyridin-2-ylmethyl)amino-
N
-quinolin-8-yl-acetamidate) is reported. Complex
1
has been found to be a stable and homogeneous water oxidation catalyst (WOC) in 0.1 M phosphate buffer (pH 8.0). A series of experiments (rinse test, SEM, EDX spectroscopy) confirm that this complex acts as a molecular electrocatalyst, and not a precursor of CoOx. The electrocatalytic water oxidation proceeds with high faradaic efficiency (81%) and fast rate (85 s
−1
). Analysis of the electrochemical reaction kinetics by
foot-of-the-wave
(FOWA) methodology reveals a high turnover frequency of 1.6 × 10
4
s
−1
which is comparable to the best performing Ru-based WOCs.
A cobalt complex bearing a redox-active monoanionic amidate ligand is shown to act as an efficient molecular electrocatalyst for water oxidation at a moderate overpotential (∼500 mV) in mildly alkaline medium.
A copper complex, Cu(dpaq)(ClO4) (1), of a monoanionic pentadentate amidate ligand (dpaq) has been isolated and characterized to study its efficacy toward electrocatalytic reduction of oxygen in ...neutral aqueous medium. The Cu(II) mononuclear complex, poised in a distorted trigonal bipyramidal structure, reduces oxygen at an onset potential of 0.50 V vs RHE. Kinetics study by hydrodynamic voltammetry and chronoamperometry suggests a stepwise mechanism for sequential reduction of O2 to H2O2 to H2O at a single-site Cu-catalyst. The foot-of-the-wave analysis records a turnover frequency of 5.65 × 102 s–1. At pH 7.0, complex 1 undergoes a quasi-reversible mixed metal–ligand-based reduction and triggers the reduction of dioxygen to water. Electrochemical studies in tandem with quantum chemical investigation, conducted at different redox states, portray the active participation of ligand in completing the process of proton-coupled electron transfer internally. The protonated carboxamido moiety acts as a proton relay, while the quinoline-based orbital supplies the necessary redox equivalent for the conversion of complex 1 to Cu(II)-hydroperoxo species. Thus, a suitable combination of redox non-innocence and proton shuttling functionality in the ligand makes it an effective electron–proton-transfer mediator and subsequently assists the process of oxygen reduction.
In a previous work, the dynamic compression behavior of Ti6Al4V with 0, 10 and 20% porosities, at the strain rate of 1 × 10−3, 1 × 103, 4 × 103 and 8 × 103/s, was experimentally characterized. The ...objective of this study is to use numerical simulations to gain insights on the observed material behavior and a general understanding of the dynamic responses of porous metals. The study indicates that the pore in general could serve as both a failure initiator and an inhibitor. The pore would lead to lower strength due to higher stress concentration as a result of the reduction of load bearing area and geometric discontinuity. On the other hand, the pore could also result in lower matrix stress at the onset of failure due to the reduced overall load bearing capacity. This lower stress and associated lower potential energy could lead to slower failure propagation and higher apparent ductility. The study also shows that the pore distribution and pore shape play significant role on the deformation and fracture behavior of porous material. For a fixed porosity, the more densely populated small pores could lead to faster failure propagation due to the enhancement of the failure propagation through void coalescence. However, the distribution does not seem to affect much the stress-stain response prior to the onset of failure. The effects of pore shape are similar to that porosity. Different pore shapes lead to different degrees of stress concentration and the apparent strengths. However, the higher stress concentration could also result in slower failure propagation due to the lower matrix stress and the associated potential energy at the onset of catastrophic failure. Besides pore density and morphology, matrix properties also played important roles on the response of porous metals. Although higher strength enhanced material's resistance to deformation, it could also lead to faster failure propagation once it was initiated due to the higher matrix stress. On the other hand, higher hardening rate could provide increasing resistance to failure propagation.
•Pores in general could serve as both a failure initiator and an inhibitor.•Pore results in lower strength due to reduced load bearing area and stress concentration.•Pore results in higher ductility due to slower failure propagation as a result of lower matrix stress.•Pore morphology and matrix properties play important roles on the deformation and fracture behavior of porous materials.
A Co(III)−hydroxo complex, CoIII(dpaq)OHClO4 (1‐OH) bearing a pentadentate ligand, H‐dpaq, (H‐dpaq=(2‐bis(pyridin‐2‐ylmethyl)amino‐N‐quinolin‐8‐yl‐acetamidate) catalyses water oxidation in mildly ...alkaline medium (pH 8.0) at a potential of 1.4 VNHE with an average Turn‐Over‐Frequency (TOFmax) of 2.8×104 s−1 and faradaic efficiency of 88 %. Post‐electrolysis characterization of the electrode rules out the formation of any heterogeneous electroactive species. Electrochemical results and theoretical calculations confirm the occurrence of both metal and ligand centered PCET processes during anodic scanning. The resulting formally Co(V)−oxo/oxyl intermediate undergoes water nucleophilic attack to install the O−O bond. The role of axial ligand in water oxidation by Co(III)−dpaq system has been examined by comparing the reactivity of the Co‐hydroxide complex (1‐OH) with that of its chloride‐ligated counterpart, CoIII(dpaq)ClCl (1‐Cl). The results confirm the ability of the Co‐dpaq complexes to bind water/or water derived ligands over chloride or non‐aqueous solvents. The interplay of ligand redox non‐innocence and σ‐donating ability of the N5‐carboxamido ligand helps to store oxidizing equivalents and triggers O−O bond formation.
A mononuclear cobalt(III) complex bearing a redox‐active pentadentate ligand acts as an efficient molecular water oxidation catalyst in a mildly alkaline solution. The presence of the σ‐donating amidate moiety and the redox non‐innocence nature of the ligand stabilize high oxidation states and trigger water oxidation.
The oxomanganese(IV) complex (dpaq)MnIV(O)+-M n+ (1-M n+ , M n+ = redox-inactive metal ion, H-dpaq = 2-bis(pyridin-2-ylmethyl)amino-N-quinolin-8-ylacetamide), generated in the reaction of the ...precursor hydroxomanganese(III) complex 1 with iodosylbenzene (PhIO) in the presence of redox-inactive metal triflates, has recently been reported. Herein the generation of the same oxomanganese(IV) species from 1 using various combinations of protic acids and oxidants at 293 K is reported. The reaction of 1 with triflic acid and the one-electron-oxidizing agent RuIII(bpy)33+ leads to the formation of the oxomanganese(IV) complex. The putative species has been identified as a mononuclear high-spin (S = 3/2) nonheme oxomanganese(IV) complex (1-O) on the basis of mass spectrometry, Raman spectroscopy, EPR spectroscopy, and DFT studies. The optical absorption spectrum is well reproduced by theoretical calculations on an S = 3/2 ground spin state of the complex. Isotope labeling studies confirm that the oxygen atom in the oxomanganese(IV) complex originates from the MnIII–OH precursor and not from water. A mechanistic investigation reveals an initial protonation step forming the MnIII–OH2 complex, which then undergoes one-electron oxidation and subsequent deprotonations to form the oxomanganese(IV) transient, avoiding the requirements of either oxo-transfer agents or redox-inactive metal ions. The MnIV–oxo complex cleaves the C–H bonds of xanthene (k 2 = 5.5 M–1 s–1), 9,10-DHA (k 2 = 3.9 M–1 s–1), 1,4-CHD (k 2 = 0.25 M–1 s–1), and fluorene (k 2 = 0.11 M–1 s–1) at 293 K. The electrophilic character of the nonheme MnIV–oxo complex is demonstrated by a large negative ρ value of 2.5 in the oxidation of para-substituted thioanisoles. The complex emerges as the “most reactive” among the existing MnIV/V–oxo complexes bearing anionic ligands.
This study evaluated the physicochemical properties of palm mid-fraction (PMF), refined bleached deodorized palm kernel oil (RBDPKO) and refined bleached deodorized palm stearin (RBDPS) as binary ...mixtures in terms of their fatty acid compositions (GC), triacylglycerols (HPLC), solid fat contents (p-NMR), melting behaviors (DSC) and polymorphisms (XRD) for cocoa butter (CB) alternative formulations. All the PMF/RBDPKO and RBDPS/RBDPKO blends showed mixtures of short/long-chain fatty acids with corresponding triacylglycerols. 10–70 % PMF in RBDPKO showed a eutectic effect between 20 and 30 °C. However, a monotectic effect was observed at 10–15 °C for 20–40 % PMF in RBDPKO and 40–80 % of RBDPS in RBDPKO. For PMF/RBDPS blends, a monotectic effect was observed at less than 30 °C. Broad endotherms at 20–38 °C were observed for 30–50 % RBDPS in RBDPKO which are closer to CB, with polymorphs of β′
1
> β′
2
≫ β
2
based on XRD analysis. 50–80 % PMF in RBDPS exhibited significantly higher contents of long-chain fatty acids with the exception of stearic and lower constituents of monounsaturated triacylglycerols compared to CB. Broad endotherms were observed at 20–38 °C for 50–80 % PMF in RBDPS which are closer to CB, with β′
1
≫ β′
2
> β
2
. Therefore, 20–40 % PMF in RBDPKO, 30–50 % RBDPS in RBDPKO and 50–80 % PMF in RBDPS could be used as CB substitutes because of their comparable physicochemical behaviors.
This paper reports the research findings of a laboratory-based study on the removal of Cr(VI) from solution using the biomass (both roots and stems) of the non-living
Eichhornia Crassipes as a ...biosorbent. The effect of physico-chemical parameters like pH, sorbent dose, contact time and initial concentrations were investigated. Although the Lagergren first order model was applicable to some of the data, the pseudo-second-order reaction model was applicable to all data. The Freundlich isotherm was found to represent the measured sorption data well. The Fourier transform infrared spectrometry showed that the hydroxyl group was the chromium-binding site within pH range (pH 1–5) where chromium does not precipitate. The results indicated that the biomass of
E. Crassipes is suitable for development of efficient biosorbent for the removal of chromium from wastewater of chemical and allied process industries.
► Deformation and fracture of laser processed dense and porous Ti6Al4V were studied. ► Both dense and porous materials exhibited appreciable rate sensitivity. ► Formation of the adiabatic shear band ...is the dominant failure mechanism. ► Failure strain depends on degree of porosity and imposed strain rate. ► Solidification texture had insignificant effects on the observed material behavior.
Deformation and fracture behavior of laser processed dense and porous Ti6Al4V alloy under uniaxial static and dynamic compression loadings were experimentally investigated in this study. Samples with 0%, 10% and 20% porosities were fabricated using a continuous wave Nd–YAG laser in a controlled environment. The dynamic tests were performed at the strain rates of 1×103, 4×103 and 8×103/s using the split Hopkinson pressure bar (SHPB) test system and the static tests were done at the strain rate of 1×10−3/s. In addition, SEM and EBSD analyses were also carried out to study the failure mechanisms and texture development due to solidification and deformation. Both deformation and fracture exhibited appreciable rate sensitivity. For the former, the material strength increased, and for the latter, the failure strains decreased with the increased strain rates. The 20% porous Ti6Al4V showed lower strength, but higher ductility compared to the 10% material, but the 10% porous material had both less strength and ductility than the dense (0% porosity) material and the ductility of 20% porous material was only comparable to that of the dense material, i.e., did not exhibit appreciable increase of ductility. The texture analysis indicated that all the samples had reasonably consistent textures due to solidification. Hence the texture effect is essentially negligible and the observed material behavior is mainly a manifestation of the induced porosity. Both the macroscopic experiments and the microstructure analysis suggest that the formation of adiabatic shear band (ASB) could likely be the major failure mechanism for Ti6Al4V and the pores likely be the sites for nucleating ASB and subsequent catastrophic failure. For initially dense Ti6Al4V, the failure and the corresponding failure strain seem to depend on the duration of the incubation period for developing a nucleation site.
Adsorption onto activated carbons is a potent method for the treatment of dye-bearing effluents because it offers various advantages. In this study, activated carbons, prepared by a new technique ...from low-cost rice husk by sulfuric acid and zinc chloride activation, were used as the adsorbent for the removal of crystal violet, a basic dye, from aqueous solutions. The effects of various experimental parameters, such as adsorbent dosage and size, initial dye concentration, pH, contact time, and temperature, were investigated in batch mode. The kinetic data were well fitted to the Lagergren, pseudo-second-order, and intraparticle diffusion models. It was found that intraparticle diffusion plays a significant role in the adsorption mechanism. The isothermal data could be well described by the Langmuir and Freundlich equations. The maximum uptakes of crystal violet by sulfuric acid activated (RHS) and zinc chloride activated (RHZ) rice husk carbon were found to be 64.875 and 61.575 mg/g of adsorbent, respectively. The results indicate that RHS and RHZ could be employed as low-cost alternatives to commercial activated carbon in wastewater treatment for the removal of basic dyes.
