Ujjwal Pal

Co-MOF as a sacrificial template: manifesting a new Co3O4/TiO2 system with a p–n heterojunction for photocatalytic hydrogen evolution

The present work reports a novel method for preparing an elusive Co3O4/TiO2 p–n heterojunction using Co-based metal organic frameworks (Co-MOFs) as a TiO2-absorbent cum sacrificial template for nanocomposite formation. Four new Co-MOFs based on a bispyrazole ligand and different carboxylic acids, with a wide variety of dimensionality, porosity and surface characteristics, were exploited for this purpose. We detail here the synthesis of cobalt MOFs using the hydro(solvo)thermal method and structural characterization by single crystal X-ray diffraction (XRD). We have also successfully demonstrated our strategy of using MOFs for fabricating superior p–n diode-type Co3O4/TiO2 hetero-nanocomposites for photocatalytic hydrogen production. The characterization results suggested that the nanocomposites consisted of highly crystalline desired anatase TiO2 nanoparticles and spinel Co3O4-like species. The nanocomposite with 2 wt% Co loading exhibited the maximum photoactivity with a hydrogen evolution rate of ∼7 mmol g−1 h−1 under UV-vis light irradiation. The above results indicate that the present preparative strategy is an amenable route for the synthesis of desirable synergistic photocatalysts combining a remarkable reactivity relevant to solar energy conversion.

A simple carbazole based sensitizer attached to a Nafion-coated-TiO2 photocatalyst: the impact of controlling parameters towards visible light driven H2 production

Here we report a new composite material consisting of a simple and cost effective carbazole based photosensitizer attached onto a Nafion/Pt/TiO2 (NPT) hybrid as a high-performance photocatalyst for H2 evolution under visible light. The engineered composite of dye with NPT is shown to render improvement in its photocatalytic activity. We have spectroscopically observed that the spacer free simple carbazole based dye was perfectly attached onto TiO2 surfaces, which also remained unaffected in alkaline medium. The development of the photocatalyst was confirmed by different morphological characterization procedures. Under optimum conditions (pH 10, 1.0 × 10−4 mol/10 mg AM dye, 0.5 wt% Pt), the maximal apparent quantum yield (AQY%) of D1@PT and D1@NPT for hydrogen evolution increases up to 16.5% and 19.16% under ∼2-sun-intensity of visible light irradiation with triethanolamine (TEOA) as a sacrificial agent. The combined effects of several factors may contribute to the remarkably enhanced photocatalytic activity for the D1@NPT sample including dye concentration, pH and catalyst amount variation, and the spacer effect of the sensitizers (with and without oligothiophene moieties).

Modulated Binary–Ternary Dual Semiconductor Heterostructures

A generic modular synthetic strategy for the fabrication of a series of binary-ternary group II-VI and group I-III-VI coupled semiconductor nano-heterostructures is reported. Using Ag2 Se nanocrystals first as a catalyst and then as sacrificial seeds, four dual semiconductor heterostructures were designed with similar shapes: CdSe-AgInSe2 , CdSe-AgGaSe2 , ZnSe-AgInSe2 , and ZnSe-AgGaSe2 . Among these, dispersive type-II heterostructures are further explored for photocatalytic hydrogen evolution from water and these are observed to be superior catalysts than the binary or ternary semi-conductors. Details of the chemistry of this modular synthesis have been studied and the photophysical processes involved in catalysis are investigated.

Kinetics and mechanism for oxidation of [RuIII(edta)(H2O)]− with peroxydisulfate in aqueous medium

The kinetics of oxidation of [RuIII(edta)(H2O)]− (edta4− = ethylenediaminetetraacetate) with peroxydisulfate ( ) was studied spectrophotometrically as a function of [ ] at pH 6.0. Oxidation was found to be first order in both ruthenium complex and concentrations. The effect of alkali cations (K+, Na+, and Li+) is attributed to triple-ion formation through an alkali cation bridging between two negatively charged reactants, facilitating the electron-transfer process. Kinetic data and activation parameters are indicative of an outer-sphere electron-transfer process. A detailed mechanism in agreement with the rate and activation parameters is presented, and the results are discussed in reference to data reported for the [RuIII(edta)(H2O)]−/XO (XO = H2O2, t-BuOOH, and KHSO5) systems.