Upendra A. Joshi

Microwave synthesis of single-crystalline perovskite BiFeO3 nanocubes for photoelectrode and photocatalytic applications

A simple microwave synthesis procedure has been developed for the single-crystalline perovskite nanocubes composed of bismuth ferrite (BiFeO3). Typical nanocubes had sizes ranging from 50to200nm. The single-crystalline nature of nanocubes was confirmed by high resolution transmission electron microscopy and selected area electron diffraction pattern. X-ray diffraction pattern showed the rhombohedral phase with R3c space group. The material showed photoinduced water oxidation activity in both photoelectrochemical and photocatalytic modes. It could become a useful material for photoelectrode and photocatalytic applications.

CuNb3O8: A p-Type Semiconducting Metal Oxide Photoelectrode.

A new p-type CuNb3O8 polycrystalline photoelectrode was investigated and was determined to have indirect and direct bandgap sizes of 1.26 and 1.47 eV, respectively. The p-type polycrystalline film could be prepared on fluorine-doped tin oxide glass and yielded a cathodic photocurrent under visible-light irradiation (λ > 420 nm) with incident photon-to-current efficiencies of up to ∼6-7% and concomitant hydrogen evolution. A Mott-Schottky analysis yielded a flat band potential of +0.35 V versus RHE (pH = 6.3) and a calculated p-type dopant concentration of ∼7.2 × 10(15) cm(-3). The conduction band energies are found to be negative enough for the reduction of water under visible light irradiation. A hole mobility of ∼145 cm(2)/V·s was obtained from J(I)-V(2) measurements using the Mott-Gurney relation, which is ∼50% higher than that typically found for p-type Cu2O. DFT-based electronic structure calculations were used to probe the atomic and structural origins of the band gap transitions and carrier mobility. Thus, a new p-type semiconductor is discovered for potential applications in solar energy conversion.

Band gap tuning of lead-substituted BaSnO3 for visible light photocatalysis

The Pb substitution effect was investigated experimentally and theoretically on the crystal structure of BaSnO3 and on the photo-oxidation activity of H2O. The chemically doped Pb in BaSnO3 induced a concentration-dependent redshift of the experimental band gap (BG). The BaPb0.8Sn0.2O3 system produced 32μmol∕h of O2 under λ⩾420nm photons, but no O2 for BaSnO3. The DFT calculations of BaPbxSn1−xO3 (x=0,0.5,1) by using generalized approximation, implying the BG alteration and the photocatalytic activity of BaPbxSn1−xO3, are due to the induced Pb 6s orbital in the BG of BaSnO3. Thus Pb modified the insulating nature of BaSnO3 to semiconducting and semimetallic.

Growth of single crystalline barium titanate nanowires from TiO2 seeds deposited on conducting glass.

A new synthetic method is reported for depositing BaTiO(3) nanowire film on conducting glass. First, a TiO(2) particle thin film is prepared by spray coating, and then transformed to single crystalline BaTiO(3) nanowires grown on the conducting glass by hydrothermal treatment using TiO(2) particles as seeds of nanowire growth. The BaTiO(3) nanowires are 50-100 nm in diameter and have a film thickness of 4 µm. The capacitance of the BaTiO(3) one-dimensional (1D) nanowire array film was found to be 4.5 times higher than that of the nanoparticle film by measuring the impedance. The piezoelectric property of an individual BaTiO(3) nanowire was also demonstrated by piezoforce microscopy.

Hydrothermal Synthesis, Characterization and Electrocatalytic Activity of La0.8Sr0.2MnO3 Nanocubes for Oxygen Reduction Reaction

The La0.8Sr0.2MnO3 nanocubes have been synthesized by simple precipitation followed by hydrothermal process. The as-obtained nanocubes were characterized by SEM, TEM, EDS, XRD and ICP-AA. The SEM and TEM images clearly showed cube type morphology of reaction product. The XRD pattern gave evidence for the phase purity and high crystallinity of the La0.8Sr0.2MnO3 nanocubes. The ICP-AA analysis along with EDS confirms the stoichiometry of the product. Electrochemical activity for oxygen reduction reaction was carried out in 1 M KOH. The oxygen reduction current measured by cyclic voltametry showed six times higher value for nanocubes than that of bulk catalysts of same composition.

Surfactant-free hydrothermal synthesis of lithium aluminate microbricks and nanorods from aluminium oxide nanoparticles.

Beta-LiAlO2 microbricks and rectangular nanorods have been successfully synthesized from Al2O3 nanoparticles by a simple hydrothermal process without any surfactant or template, by simply changing the Li/Al molar ratio.