Active Site Engineering and Theoretical Aspects of "Superhydrophilic" Nanostructure Array Enabling Efficient Overall Water Electrolysis.

The rational design of noble metal-free electrocatalysts holds great promise for cost-effective green hydrogen generation through water electrolysis. In this context, here, the development of a superhydrophilic bifunctional electrocatalyst that facilitates both oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) in alkaline conditions is demonstrated. This is achieved through the in situ growth of hierarchical NiMoO4 @CoMoO4 ·xH2 O nanostructure on nickel foam (NF) via a two-step hydrothermal synthesis method. NiMoO4 @CoMoO4 ·xH2 O/NF facilitates OER and HER at the overpotentials of 180 and 220 mV, respectively, at the current density of 10 mA cm-2 . The NiMoO4 @CoMoO4 ·xH2 O/NF ǁ NiMoO4 @CoMoO4 ·xH2 O/NF cell can be operated at a potential of 1.60 V compared to 1.63 V displayed by the system based on the Pt/C@NFǁRuO2 @NF standard electrode pair configuration at 10 mA cm-2 for overall water splitting. The density functional theory calculations for the OER process elucidate that the lowest ΔG of NiMoO4 @CoMoO4 compared to both Ni and NiMoO4 is due to the presence of Co in the OER catalytic site and its synergistic interaction with NiMoO4 . The preparative strategy and mechanistic understanding make the windows open for the large-scale production of the robust and less expensive electrode material for the overall water electrolysis.

Co-Ni Layered Double Hydroxide for the Electrocatalytic Oxidation of Organic Molecules: An Approach to Lowering the Overall Cell Voltage for the Water Splitting Process.

Electrocatalytic oxidation of simple organic molecules offers a promising strategy to combat the sluggish kinetics of the water oxidation reaction (WOR). The low potential requirement, inhibition of the crossover of gases, and formation of value-added products at the anode are benefits of the electrocatalytic oxidation of organic molecules. Herein, we developed cobalt-nickel-based layered double hydroxide (LDH) as a robust material for the electrocatalytic oxidation of alcohols and urea at the anode, replacing the WOR. A facile synthesis protocol to form LDHs with different ratios of Co and Ni is adapted. It demonstrates that the reactants could be efficiently oxidized to concomitant chemical products at the anode. The half-cell study shows an onset potential of 1.30 V for benzyl alcohol oxidation reaction (BAOR), 1.36 V for glycerol oxidation reaction (GOR), 1.33 V for ethanol oxidation reaction (EOR), and 1.32 V for urea oxidation reaction (UOR) compared with 1.53 V for WOR. Notably, the hybrid electrolyzer in a full-cell configuration significantly reduces the overall cell voltage at a 20 mA cm-2 current density by ∼15% while coupling with the BAOR, EOR, and GOR and ∼12% with the UOR as the anodic half-cell reaction. Furthermore, the efficiency of hydrogen generation remains unhampered with the types of oxidation reactions (alcohols and urea) occurring at the anode. This work demonstrates the prospects of lowering the overall cell voltage in the case of a water electrolyzer by integrating the hydrogen evolution reaction with suitable organic molecule oxidation.

Red fluorescent ultra-small gold nanoclusters functionalized with signal molecules to probe specificity in quorum sensing receptors in gram-negative bacteria.

Ultra-small (size < 2 nm) gold nanoclusters (AuNCs) are used as fluorescent probes which have excellent applications in bioimaging and sensing due to their emission in visible and NIR spectral region. Here, this property is exploited for understanding the quorum sensing phenomenon in bacteria which is regulated by signal molecules which are specific to various species. AuNCs are then functionalized with the signal molecules, Acyl Homoserine Lactones (AHL) of varying carbon chain length, C-6, C-8, and C-12 without 3rd C modification, to sense different strains of gram-negative bacteria i.e., Escherichia coli, Cronobacter sakazakii and Pseudomonas aeruginosa. In the concentration employed, selectivity to a limited extent is observed between the three Gram-negative bacteria tested. E. coli showed emission with all the AHL conjugates and P. aeruginosa did not interact with any of the three conjugates, whereas C. sakazakii showed specificity to C-8AHL. This is probably due to selectivity for cognate AHL molecules of appropriate concentrations.

Efficient Electrochemical Oxygen Reduction to Hydrogen Peroxide by Transition Metal-Doped Silicate Sr0.7Na0.3SiO3-δ.

Electrochemical oxygen reduction in a selective two-electron pathway is an efficient method for onsite production of H2O2. State of the art noble metal-based catalysts will be prohibitive for widespread applications, and hence earth-abundant oxide-based systems are most desired. Here we report transition metal (Mn, Fe, Ni, Cu)-doped silicates, Sr0.7Na0.3SiO3-δ, as potential electrocatalysts for oxygen reduction to H2O2 in alkaline conditions. These novel compounds are isostructural with the parent Sr0.7Na0.3SiO3-δ and crystallize in monoclinic structure with corner-shared SiO4 groups forming cyclic trimers. The presence of Na stabilizes O vacancies created on doping, and the transition metal ions provide catalytically active sites. Electrochemical parameters estimated from Tafel and Koutechy-Levich plots suggest a two-electron transfer mechanism, indicating peroxide formation. This is confirmed by the rotating ring disc electrode method, and peroxide selectivity and Faradaic efficiency are calculated to be in the range of 65-82% and 50-68%, respectively, in a potential window 0.3 to 0.6 V (vs RHE). Of all the dopants, Ni imparts the maximum selectivity and efficiency as well as highest rate of formation of H2O2 at 1.65 µmol s-1.

Role of B site ions in bifunctional oxygen electrocatalysis: a structure-property correlation study on doped Ca2Fe2O5 brownmillerites.

The role of B site doping with transition metals in brownmillerites, a perovskite related family of compounds, in bifunctional oxygen electrocatalysis, viz., simultaneous reduction and evolution reactions, is analysed. Ca2Fe1.9M0.1O5 (M = Mn, Co, Ni, and Cu) is synthesised and structurally characterised by powder XRD and Rietveld refinement. Valence states of the surface B site ions are identified by X-ray photoelectron spectroscopy. Bifunctional oxygen electrochemistry is studied with the RDE and RRDE techniques and correlated with the structural and electronic parameters like oxygen non-stoichiometry and B site catalytic activity. Since the widely accepted electronic descriptors like eg filling may not be sufficient for explaining the bifunctional activity, B site electron donating capability as well as the extent of oxygen vacancies enhancing O2 adsorption is also considered. Such structural parameters are also found to influence both the ORR and OER and based on this, Ni doping is proposed as advantageous for the bifunctional activity.

Hierarchical Nanoflower Arrays of Co9 S8 -Ni3 S2 on Nickel Foam: A Highly Efficient Binder-Free Electrocatalyst for Overall Water Splitting.

Hydrogen production is vital for meeting future energy demands and managing environmental sustainability. Electrolysis of water is considered as the suitable method for H2 generation in a carbon-free pathway. Herein, the synthesis of highly efficient Co9 S8 -Ni3 S2 based hierarchical nanoflower arrays on nickel foam (NF) is explored through the one-pot hydrothermal method (Co9 S8 -Ni3 S2 /NF) for overall water splitting applications. The nanoflower arrays are self-supported on the NF without any binder, possessing the required porosity and structural characteristics. The obtained Co9 S8 -Ni3 S2 /NF displays high hydrogen evolution reaction (HER), as well as oxygen evolution reaction (OER), activities in 1 m KOH solution. The overpotentials exhibited by this system at 25 mA cm-2 are nearly 277 and 102 mV for HER and OER, respectively, in 1 m KOH solution. Subsequently, the overall water splitting was performed in 1 m KOH solution by employing Co9 S8 -Ni3 S2 /NF as both the anode and cathode, where the system required only 1.49, 1.60, and 1.69 V to deliver the current densities of 10, 25, and 50 mA cm-2 , respectively. Comparison of the activity of Co9 S8 -Ni3 S2 /NF with the state-of-the-art Pt/C and RuO2 coated on NF displays an enhanced performance for Co9 S8 -Ni3 S2 /NF both in the half-cell as well as in the full cell, emphasizing the significance of the present work. The post analysis of the material after water electrolysis confirms that the surface Co(OH)2 formed during the course of the reaction serves as the favorable active sites. Overall, the activity modulation achieved in the present case is attributed to the presence of the open-pore morphology of the as formed nanoflowers of Co9 S8 -Ni3 S2 on NF and the simultaneous presence of the surface Co(OH)2 along with the highly conducting Co9 S8 -Ni3 S2 core, which facilitates the adsorption of the reactants and subsequently its conversion into the gaseous products during water electrolysis.

Bifunctional Oxygen Reduction and Evolution Activity in Brownmillerites Ca2Fe(1-x)Co x O5.

State-of-the-art catalysts for oxygen reduction and evolution reactions (ORR and OER), which form the basis of advanced fuel cell applications, are based on noble metals such as Pt and Ir. However, high cost and scarcity of noble metals have led to an increased demand of earth-abundant metal oxide catalysts, especially for bifunctional activity in ORR and OER. The fact that Pt and Ir or C, the cost-effective alternatives suggested, do not display satisfactory bifunctional activity has also helped in turning the interest to metal oxides which are stable under both ORR and OER conditions. Brownmillerite A2B2O5 type oxides are promising as bifunctional oxygen electrocatalysts because of intrinsic structural features, viz., oxygen vacancy and catalytic activity of the B-site transition metal. In this study, Co-doped Ca2Fe2O5 compounds are synthesized by the solid state method and structurally analyzed by Rietveld refinement of powder X-ray diffraction data. The compound Ca2Fe2O5, crystallizing in the Pcmn space group has alternative FeO4 tetrahedral and FeO6 octahedral layers. Its Co-doped analogue, Ca2Fe1.75Co0.25O5, also crystallizes in the same space group with both tetrahedral and octahedral Fe positions substituted with Co. However, Ca2FeCoO5 in the Pbcm space group shows interlayer ordering with Co-rich octahedra connected to Fe-rich tetrahedra and vice versa. Oxygen bifunctional activities of these catalysts are monitored by rotating disc electrode and rotating ring disc electrode techniques in alkaline media. A close analysis of the ORR and OER was conducted through comparison of various parameters such as onset potential, current density, halfwave potential, and other kinetic parameters, which suggests that the presence of Co in the B site aids in achieving better bifunctional activity and bulk conductivity. In addition, Co(II)/Co(III) redox systems and their comparative concentrations also play a decisive role in enhancing the activity.

A squaraine-linked metalloporphyrin two-dimensional polymer photocatalyst for hydrogen and oxygen evolution reactions.

Efficient water splitting photocatalysts are an energetically demanding and cost-effective method for generating renewable energy. Significant research has been reported to advance this approach. However, the use of organic photocatalysts and the presence of residual catalysts trapped in the porous frameworks present major concerns about the efficiency of this strategy. Herein, we report the photocatalytic evolution of H2 and O2 by a multi-hydroxyl group-decorated metalloporphyrin-based two-dimensional catalyst developed via metal catalyst-free synthetic route. Though metalloporphyrins have long been used for catalytic functions, a heterogeneous photocatalyst delivering both H2 and O2 has not yet been realized. This polymer catalyst design enables the photocatalytic diatomic O2 release, a bottleneck in water splitting, in a facile way. Photocatalytic release of H2 as well as O2 occurs with long-term durability of 20 cycles in 300 days with negligible decrease in efficiency, thus demonstrating the excellent performance of this new catalyst.

Cobalt-Doped Ba2In2O5 Brownmillerites: An Efficient Electrocatalyst for Oxygen Reduction in Alkaline Medium.

A series of compounds with cobalt doping in the indium site of Ba2In2O5 brownmillerites exhibited excellent oxygen reduction activity under alkaline conditions. Doping (25%) retains the brownmillerite structure with disorder in the O3 site in the two-dimensional alternate layer along the ab plane. Further substitution of cobalt in the indium site leads to the loss of a brownmillerite structure, and the compound attains a perovskite structure. Cobalt-doped samples exhibited far better oxygen reduction reaction (ORR) activity when compared to the parent Ba2In2O5 brownmillerite. Among the series of compounds, BaIn0.25Co0.75O3-δ with the highest Co doping and oxygen vacancies randomly distributed in the lattice exhibited the best ORR activity. BaIn0.25Co0.75O3-δ showed a 40 mV positive shift in the onset potential with better limiting current density and a nearly four-electron-transfer reduction pathway when compared to the parent Ba2In2O5 brownmillerite.

Nitrogen Doping in Oxygen-Deficient Ca2Fe2O5: A Strategy for Efficient Oxygen Reduction Oxide Catalysts.

Oxygen reduction reaction (ORR) is increasingly being studied in oxide systems due to advantages ranging from cost effectiveness to desirable kinetics. Oxygen-deficient oxides like brownmillerites are known to enhance ORR activity by providing oxygen adsorption sites. In parallel, nitrogen and iron doping in carbon materials, and consequent presence of catalytically active complex species like C-Fe-N, is also suggested to be good strategies for designing ORR-active catalysts. A combination of these features in N-doped Fe containing brownmillerite can be envisaged to present synergistic effects to improve the activity. This is conceptualized in this report through enhanced activity of N-doped Ca2Fe2O5 brownmillerite when compared to its oxide parents. N doping is demonstrated by neutron diffraction, UV-vis spectroscopy, X-ray photoelectron spectroscopy, and X-ray absorption spectroscopy. Electrical conductivity is also found to be enhanced by N doping, which influences the activity. Electrochemical characterization by cyclic voltammetry, rotating disc electrode, and rotating ring disk electrode (RRDE) indicates an improved oxygen reduction activity in N-doped brownmillerite, with a 10 mV positive shift in the onset potential. RRDE measurements show that the compound exhibits 4-electron reduction pathways with lower H2O2 production in the N-doped system; also, the N-doped sample exhibited better stability. The observations will enable better design of ORR catalysts that are stable and cost-effective.

Acute myeloid leukemia presenting as galactorrhea.

Acute myeloid leukemia (AML) presents with symptoms related to pancytopenia (weakness, infections, bleeding diathesis) and organ infiltration with leukemic cells. Galactorrhea is an uncommon manifestation of AML. We report a case of AML presenting with galactorrhea.

Understanding the electron transfer process in ZnO-naphthol azobenzoic acid composites from photophysical characterisation.

Semiconductor nanoparticles surface modified with organic molecules capable of visible light absorption and effectively transferring the electrons to the catalytic sites have the potential to be good photocatalysts. ZnO nanoparticles of size ∼3 nm are grafted with two azonaphthols, one conjugated and the other non-conjugated. The photophysical properties of modified ZnO indicate an effective electron transfer from the conjugated azonaphthol to ZnO but not in the case of the non-conjugated molecule. It is also observed from lifetime studies that the conjugated molecule stabilises the defect sites on ZnO nanoparticles. It is possible that excited electrons from the conjugated molecule are transferred to specific defect sites in ZnO. This apparently does not occur in the non-conjugated molecule, bringing to focus the importance of the photophysical characteristics of organic modifiers in designing visible light active photocatalysts.

Synthesis and structural characterization of AMV2O8 (A = K, Rb, Tl, Cs; M = Nb, Ta) vanadates: a structural comparison of A(+)M(5+)V2O8 vanadates and A(+)M(5+)P2O8 phosphates.

Eight new quaternary vanadates of niobium and tantalum, AMV2O8 (A = K, Rb, Tl, Cs; M = Nb, Ta), have been prepared by solid state reactions and structurally characterized by single crystal and powder X-ray diffraction (XRD) techniques. The two cesium compounds, unlike the known CsSbV2O8 with a layered yavapaiite structure, have a new three-dimensional structure and the other six compounds possess the known KSbV2O8 structure type. The three types of [(MV2O8)(-)]∞ anionic frameworks of twelve A(+)M(5+)V2O8 (A = K, Rb, Tl, Cs; M = Nb, Ta, Sb) vanadates could be conceived to be built by different connectivity patterns of M2V4O18 ribbons, which contain MO6 octahedra and VO4 tetrahedra. A structural comparison of these twelve vanadates and the nineteen A(+)M(5+)P2O8 phosphates has been made. The spectroscopic studies of these eight new quaternary vanadates are presented.

Effect of B site coordination environment in the ORR activity in disordered brownmillerites Ba2In2-xCexO5+δ.

Ba2In2O5 brownmillerites in which the In site is progressively doped with Ce exhibit excellent oxygen reduction activity under alkaline conditions. Ce doping leads to structural changes advantageous for the reaction. Twenty-five percent doping retains the ordered structure of brownmillerite with alternate layers of tetrahedra and octahedra, whereas further increase in Ce concentration creates disorder. Structures with disordered oxygen atoms/vacancies are found to be better oxygen reduction reaction catalysts probably aided by isotropic ionic conduction, and Ba2In0.5Ce1.5O5+δ is the most active. This enhanced activity is correlated to the more symmetric Ce site coordination environment in this compound. Stoichiometric perovskite BaCeO3 with the highest concentration of Ce shows very poor activity emphasizing the importance of oxygen vacancies, which facilitate O2 adsorption, in tandem with catalytic sites in oxygen reduction reactions.

Nanostructured donor-acceptor self assembly with improved photoconductivity.

Nanostructured supramolecular donor-acceptor assemblies were formed when an unsymmetrical N-substituted pyridine functionalized perylenebisimide (UPBI-Py) was complexed with oligo(p-phenylenevinylene) (OPVM-OH) complementarily functionalized with hydroxyl unit and polymerizable methacrylamide unit at the two termini. The resulting supramolecular complex [UPBI-Py (OPVM-OH)]1.0 upon polymerization by irradiation in the presence of photoinitiator formed well-defined supramolecular polymeric nanostructures. Self-assembly studies using fluorescence emission from thin film samples showed that subtle structural changes occurred on the OPV donor moiety following polymerization. The 1:1 supramolecular complex showed red-shifted aggregate emission from both OPV (∼500 nm) and PBI (∼640 nm) units, whereas the OPV aggregate emission was replaced by intense monomeric emission (∼430 nm) upon polymerizing the methacrylamide units on the OPVM-OH. The bulk structure was studied using wide-angle X-ray diffraction (WXRD). Complex formation resulted in distinct changes in the cell parameters of OPVM-OH. In contrast, a physical mixture of 1 mol each of OPVM-OH and UPBI-Py prepared by mixing the powdered solid samples together showed only a combination of reflections from both parent molecules. Thin film morphology of the 1:1 molecular complex as well as the supramolecular polymer complex showed uniform lamellar structures in the domain range <10 nm. The donor-acceptor supramolecular complex [UPBI-Py (OPVM-OH)]1.0 exhibited space charge limited current (SCLC) with a bulk mobility estimate of an order of magnitude higher accompanied by a higher photoconductivity yield compared to the pristine UPBI-Py. This is a very versatile method to obtain spatially defined organization of n and p-type semiconductor materials based on suitably functionalized donor and acceptor molecules resulting in improved photocurrent response using self-assembly.

Nitrogen-doped graphene interpenetrated 3D Ni-nanocages: efficient and stable water-to-dioxygen electrocatalysts.

Herein, we report the synthesis of a nitrogen-doped graphene (NGr) interpenetrated 3D Ni-nanocage (Ni-NGr) electrocatalyst by a simple water-in-oil (w/o) emulsion technique for oxidation of water to dioxygen. Correlation of adsorption of NGr and subsequent interpenetration through the specific surface plane of nickel particles as well as the concomitant interaction of N and C with Ni in the nano-regime has been investigated. Apart from the benefits of the synergistic interactions between Ni, N, and C, the overall integrity of the structure and its intra-molecular connectivity within the framework help in achieving better oxygen evolution characteristics at a significantly reduced overpotential. The engineered Ni-NGr nanocage displays a substantially low overpotential of ∼290 mV at a practical current density of 20 mA cm(-2) in 0.1 M KOH. In comparison, NGr and Ni-particles as separate entities give overpotentials of ∼570 and ∼370 mV under similar conditions. Moreover, the long term stability of Ni-NGr was investigated by anodic potential cycling for 500 cycles and an 8.5% increment in the overpotential at 20 mA cm(-2) was observed. Additionally, a chronoamperometric test was performed for 15 h at 20 mA cm(-2), which highlights the better sustainability of Ni-NGr under the actual operating conditions. Finally, the quantitative estimation of evolved oxygen was monitored by gas chromatography and was found to be 70 mmol h(-1) g(-1) of oxygen, which is constant in the second cycle as well.

Photocatalytic H2 evolution from water-methanol system by anisotropic InFeO3(ZnO)(m) oxides without cocatalyst in visible light.

InFeO3(ZnO)m series of oxides are found to give unprecedented H2 evolution from water-methanol mixtures without using any cocatalysts. This family of compounds has an anisotropically layered structure in which Zn/FeOn polyhedra are sandwiched between InO6 octahedral layers. Local structure characterization by X-ray absorption spectroscopy reveals that Zn coordination changes from pentacoordinated to tetrahedral geometry across the series, whereas Fe geometry remains trigonal bipyramidal in all the compounds. This peculiar structure is conducive for a spatial separation of photogenerated charges reducing recombination losses. Band gap energies calculated from absorption spectra indicate potential visible light activity, and this may be due to the orbital mixing of Fe 3d and O 2p as revealed by pre-edge features of X-ray absorption spectra. Band positions are also advantageously placed for a visible light H2 generation and is indeed found to be the case in methanol-assisted water splitting with standardized hydrogen evolution of ∼19.5 mmol g(-1) h(-1) for all the catalysts.

Investigations into variations in local cationic environment in layered oxide series InGaO3(ZnO)m (m = 1-4).

Layered oxides of the series InGaO3(ZnO)m (m = 1-4) are interesting due to their structural anisotropy. Here, we report a comprehensive study of their structural details, focusing on the local cationic environment in bulk powder samples by MASNMR and EXAFS, which is hitherto not attempted. It is found that the Ga geometry varies gradually from pure pentacoordinated to a mixture of penta and tetracoordinated with increasing amounts of tetracoordination as we move across the series, contrary to previous reports suggesting exclusively trigonal bipyramidal coordination in all the compounds. A similar observation is also made in the case of Zn and structural evolution involving the dissolution of Ga in a ZnO4 tetrahedral network in a sandwich layer can be discerned, as the insulating ZnO layer size increases.

Selective imaging of quorum sensing receptors in bacteria using fluorescent Au nanocluster probes surface functionalized with signal molecules.

Fluorescent ultrasmall gold clusters decorated with bacterial quorum sensing signal molecules, acyl homoserine lactone, are synthesized. These fluorescent probes are found to have emission in the near-infrared spectral region advantageous for bioimaging. Imaging studies using different strains of bacteria with and without acyl homoserine lactone receptors with the aid of confocal microscopy have shown that the probe interacts preferentially with cells possessing these receptors. This indicates that, with appropriate surface functionalization, the Au clusters can be used for receptor specific detection with enhanced selectivity.

Motion of aromatic hydrocarbons in the microporous aluminum methylphosphonates AlMePO-alpha and AlMePO-beta.

(2)H wide-line NMR has been used, in conjunction with molecular dynamics simulations where appropriate, to follow the reorientation of the monoaromatic compounds benzene, toluene, and p-xylene within the one-dimensional channels of the alpha- and beta-polymorphs of aluminum methylphosphonate, Al(2)(CH(3)PO(3))(3). Variable-temperature, static, (2)H NMR spectra of adsorbed d(6)-benzene, d(3)-, d(5)-, and d(8)-toluenes, and d(3),d(3)-p-xylene were matched by line shape simulation. The motion of p-xylene in both polymorphs is approximated by the long axis of the molecule describing a cone within the channels, the half-angle of which is greater for the slightly wider channels in AlMePO-beta (27-30 degrees cf. 18-19 degrees). The (2)H NMR of d(3)-toluene is simulated using a similar model, whereas the signal from aromatic deuterons in d(5)- and d(8)-toluenes is simulated by a ring undergoing 2pi/3 flips around the para axis. The reorientation of benzene shows the largest differences between the two pore structures. In AlMePO-beta it tumbles with little restriction, although at low temperatures the spectral details are better matched by allowing the molecule to spend a greater proportion of its time closer to the wall. In AlMePO-alpha the much broader line shape arises from constrained motion within the strongly triangular channels. Molecular dynamics simulations of benzene in the two structures confirm the differences. They support a model for benzene in AlMePO-alpha where its motion is restricted to rotations about its 6-fold axis and 2pi/3 jumps between symmetry-related sites in the pores, so that the plane of the aromatic ring remains approximately parallel to the c-axis.