Joyashish Debgupta

Homogeneous Photochemical Water Oxidation by Biuret-Modified Fe-TAML: Evidence of FeV(O) Intermediate

Water splitting, leading to hydrogen and oxygen in a process that mimics natural photosynthesis, is extremely important for devising a sustainable solar energy conversion system. Development of earth-abundant, transition metal-based catalysts that mimic the oxygen-evolving complex of photosystem II, which is involved in oxidation of water to O2 during natural photosynthesis, represents a major challenge. Further, understanding the exact mechanism, including elucidation of the role of active metal-oxo intermediates during water oxidation (WO), is critical to the development of more efficient catalysts. Herein, we report Fe(III) complexes of biuret-modified tetra-amidomacrocyclic ligands (Fe-TAML; 1a and 1b) that catalyze fast, homogeneous, photochemical WO to give O2, with moderate efficiency (maximum TON = 220, TOF = 0.76 s(-1)). Previous studies on photochemical WO using iron complexes resulted in demetalation of the iron complexes with concomitant formation of iron oxide nanoparticles (NPs) that were responsible for WO. Herein, we show for the first time that a high valent Fe(V)(O) intermediate species is photochemically generated as the active intermediate for the oxidation of water to O2. To the best of our knowledge, this represents the first example of a molecular iron complex catalyzing photochemical WO through a Fe(V)(O) intermediate.

Co3O4 Nanorods—Efficient Non-noble Metal Electrocatalyst for Oxygen Evolution at Neutral pH

Hydrogen, as a universal fuel, is expected to play an important role in the sustainable development of energy generation, utilization and storage. In addition, it possesses higher energy density in comparison to other common fuels such as petrol, diesel and LPG. Presently, 95 % of the demand for hydrogen is fulfilled from fossil fuels, mainly through the steam reforming process [1], which emits CO2 as a by-product. Photoelectrochemical water splitting is one of the most attractive ways of utilizing the most important renewable energy source, sunlight, for the production of hydrogen without any carbon footprint [2]. Multijunction photoelectrochemical cells (PEC) have, therefore, been used to achieve a better solar to hydrogen efficiency in alkaline conditions. However, water splitting is thermodynamically an uphill reaction, requiring 237 kJ of energy to split 1 mol of water [3]. The mechanism of water splitting involves many steps associated with hydrogen and oxygen evolution at the cathode and anode, respectively. Among these, oxygen evolution reaction (OER), with its sluggish kinetics, is considered as a bottleneck for oxygen formation, since two water molecules have to come closer in order to form a bond between two oxygen atoms [4]. This is supported by the fact that the rate for oxygen evolution is six orders slower when compared to that for hydrogen evolution [4, 5] over polycrystalline platinum, and hence, more efficient catalysts are needed to improve the overall rate of water splitting to make this route of H2 generation commercially viable. At present, precious metal oxides such as RuO2 and IrO2 [6, 7] are some of the best known catalysts for oxygen evolution in water electrolyzers. However, apart from their high cost, both Ir and Ru sources are sparse on earth’s crust, thereby limiting their practical use, especially, on a large commercial scale. Among these, IrO2 is a better catalyst 2 because RuO2 gets converted into RuO4 during the process of oxygen evolution and hence loses its catalytic activity with time [8]. Doping of iridium in RuO2 has been shown to improve its stability, and the catalyst was found to be more active than IrO2 [9]. Fluorine doping has been shown to improve the catalytic activity of IrO2 for oxygen evolution due to the decrease in the energy of the rate determining step by the p,dhybridization of Ir 5d and F 2p states [10, 11]. Recent research work has been focused on developing nonprecious metal oxides for the oxygen evolution to reduce the capital cost of hydrogen production [12]. In particular, nanostructures of earth-abundant transition metal oxides are shown to have promising catalytic activities for oxygen evolution compared to the precious metal oxides such as RuO2 and IrO2. NiO, Ni(OH)2 and MnO2 nanostructures have shown remarkably low overpotential (~300–320 mV) for oxygen evolution in alkaline medium [13–15]. Spinel oxides such as NiCo2O4, ZnCo2O4 and CoFe2O4 are shown to have better stability and catalytic activity towards oxygen evolution [16–18]. The perovskite oxide Ba0.5Sr0.5Co0.8Fe0.2O3–δ exhibits higher catalytic activity than IrO2, and the enhanced activity has been correlated to the occupancy at the eg state of Co [19]. Most of the currently used catalysts work in alkaline conditions (pH>7) with higher overpotential associated with the oxygen evolution and also at higher temperatures, which corrode the electrode as well as the experimental setup. A * Pattayil A. Joy pa.joy@ncl.res.in

Carbon nanotube-modified sodium dodecyl sulfate-polyacrylamide gel electrophoresis for molecular weight determination of proteins.

The effect of incorporating carbon nanotubes (CNTs) in the gel matrix on the electrophoretic mobility of proteins based on their molecular weight differences was investigated using sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). More specifically, a reduction in standard deviation in the molecular weight calibration plots by 55% in the case of multiwalled carbon nanotubes (MWCNTs) and by 34% in the case of single-walled carbon nanotubes (SWCNTs) compared with that of pristine polyacrylamide gels was achieved after incorporating an insignificant amount of functionalized CNTs into the gel matrix. A mechanism based on a more uniform pore size distribution in CNT modified polyacrylamide gel matrix is proposed. Furthermore, the impact of SWCNTs and MWCNTs on the mobility of proteins in different molecular weight regimes at a given acrylamide concentration offers a tunable gel matrix in terms of the selection of molecular weight ranges of proteins. The robustness and excellent reproducibility of the CNT-PAGE protocol are expected to have a significant impact on the molecular weight determination of newly isolated proteins.

Photophysical and photoconductivity properties of thiol-functionalized graphene–CdSe QD composites

Graphene–semiconductor QD hybrid nanostructure materials have recently emerged as a new class of functional materials because of their potential applications in solar energy conversion, optoelectronic devices, sensing etc. Here, oleic acid-capped CdSe QDs are attached to –PhSH functionalized graphene by ligand exchange via bonding with the –SH group. The shifting of the G-band and D-band due to structural changes for the attachment of QD with graphene has been evaluated by using Raman spectroscopy. Steady state photoluminescence (PL) and time resolved fluorescence measurements have been employed to understand the electronic interactions between graphene and CdSe QDs. A time resolved fluorescence spectroscopic study has been used to understand the fluorescence dynamics of the photoexcitated CdSe QDs in the presence of graphene. It is evident that the electron transfer occurs from photoexcited QDs to graphene and the electron transfer rate is found to be 12.8 × 108 s−1 for 3.8 nm CdSe QDs. Photoconductivity properties of the graphene–QD device under illumination have been examined and it is to be noted that 2–3 fold increase in the photocurrent is found in this composite device in presence of 1.5 AM solar simulated light. The enhancement of the photocurrent in this hybrid device is found to be suitable for potential applications in optoelectronic and solar cell systems.

Facile Green Synthesis of BCN Nanosheets as High-Performance Electrode Material for Electrochemical Energy Storage.

Two-dimensional hexagonal boron carbon nitride (BCN) nanosheets (NSs) were synthesized by new approach in which a mixture of glucose and an adduct of boric acid (H3 BO3 ) and urea (NH2 CONH2 ) is heated at 900 °C. The method is green, scalable and gives a high yield of BCN NSs with average size of about 1 μm and thickness of about 13 nm. Structural characterization of the as-synthesized material was carried out by several techniques, and its energy-storage properties were evaluated electrochemically. The material showed excellent capacitive behaviour with a specific capacitance as high as 244 F g(-1) at a current density of 1 A g(-1) . The material retains up to 96 % of its initial capacity after 3000 cycles at a current density of 5 A g(-1) .

C@SiNW/TiO2 Core-Shell Nanoarrays with Sandwiched Carbon Passivation Layer as High Efficiency Photoelectrode for Water Splitting

One-dimensional heterostructure nanoarrays are efficiently promising as high performance electrodes for photo electrochemical (PEC) water splitting applications, wherein it is highly desirable for the electrode to have a broad light absorption, efficient charge separation and redox properties as well as defect free surface with high area suitable for fast interfacial charge transfer. We present highly active and unique photoelectrode for solar H2 production, consisting of silicon nanowires (SiNWs)/TiO2 core-shell structures. SiNWs are passivated to reduce defect sites and protected against oxidation in air or water by forming very thin carbon layer sandwiched between SiNW and TiO2 surfaces. This carbon layer decreases recombination rates and also enhances the interfacial charge transfer between the silicon and TiO2. A systematic investigation of the role of SiNW length and TiO2 thickness on photocurrent reveals enhanced photocurrent density up to 5.97 mA/cm2 at 1.0 V vs.NHE by using C@SiNW/TiO2 nanoarrays with photo electrochemical efficiency of 1.17%.

Thiolated graphene – a new platform for anchoring CdSe quantum dots for hybrid heterostructures

Effective organization of small CdSe quantum dots on graphene sheets has been achieved by a simple solution exchange with thiol terminated graphene prepared by diazonium salt chemistry. This generic methodology of CdSe QD attachment to any graphene surface has remarkable implications in designing hybrid heterostructures.

Comparative study of dG affinity vs. DNA methylation modulating properties of side chain derivatives of procainamide: insight into its DNA hypomethylating effect

Procainamide derivatives have been synthesized to investigate the role of side chains in modulating the DNA methylation level in cancer cells and gain insight into its mechanism of action. The synthesized derivatives comprised of flexible (dimethyl), constrained (pyrrolidine, piperidine, morpholine) and planar aromatic (pyridine, phenyl) side chain motifs. The affinity of procainamide and its derivatives towards the deoxyguanosine (dG) base in neutral form has been assessed by performing Differential Pulse Voltammetry (DPV) under physiological conditions. Further, molecular docking with hemimethylated CpG rich DNA acquired from an active mDNMT-1-DNA (PDB ID-4DA4) crystal structure, reveals their preferential non-covalent interaction with dG nucleobase in the intercalation cavity of the minor groove. Differential affinity of the derivatives to dG base in neutral and bound forms (DNA) is correlated with their DNA methylation modulating properties at sub-lethal concentrations. Among all the derivatives, a compound with an aromatic phenyl side chain (1) has shown a highest binding affinity for dG nucleobase in neutral form as well as for partially denatured CpG rich DNA which is attributed to the formation of π⋯π stacking interaction in addition to N–H⋯O hydrogen bonding with the pyrimidine ring of dG base. It also shows the highest cytotoxicity and global hypomethylation at a sub-lethal level in the MCF-7 cancer cell line compared to other derivatives and procainamide. A docking study has also illustrated the plausible structural basis of DNA methylation modulating a property of procainamide. Strong association of procainamide with dG bases of partially denatured CpG rich DNA via H-bonding and other non-covalent interactions may alter the active topology of DNA required by the DNA-binding regulatory proteins (e.g. DNMT-1) which is validated by a DNMT-1 inhibition assay. This systematic investigation leads to a new potent alternative to procainamide being found and gives a plausible insight into the DNA hypomethylating effect of procainamide.