Hot injection-induced synthesis of ZnCdS-rGO/MoS2 heterostructures for efficient hydrogen production and CO2 photoreduction.

A highly efficient hybrid ZnCdS-rGO/MoS2 heterostructure is successfully synthesized through a hot injection method and control loading of rGO/MoS2. The synergism provides an unprecedently high H2-generation rate of 193.4 mmol H2 g-1 h-1 from water under full arc solar radiation and MeOH production (5.26 mmol g-1 h-1, AQY of 14.6% at λ = 420 ± 20 nm) from CO2 reduction.

Ruthenium(iii)-bis(phenolato)bipyridine/TiO2 hybrids: unprecedented photocatalytic hydrogen evolution.

In this work, two new bis-(hydroxyphenyl)bipyridine based ruthenium complexes with 4-picoline (coded as MCS-B4M) and isonicotinic acid (coded as MCS-B5M), which act as ancillary ligands, have been synthesized and employed for the first time as photosensitizers in photocatalytic hydrogen evolution studies. The photocatalyst MCS-B5M/TiO2-Pt showed an impressive hydrogen generation rate of up to 4.2 mmol h-1 and turnover number (TON) of 84 959 after 5 h. The better performance of B5TP over B4TP was due to the higher excited state lifetime of MCS-B5M (∼2.6 ns) than that of MCS-B4M (∼1.4 ns). This leads to a higher probability of electron transfer to the TiO2/Pt composite in the case of the former and a stronger coupling of MCS-B5M excited states with the conduction band of the TiO2/Pt composite by the -COOH linkers of the isonicotinic acid moiety, resulting in better photosensitization as observed in the UV-Vis (DRS mode) absorbance study. The comparative study of the two dyes clearly shows the manifestations of their respective ancillary ligands having contrasting electronic properties. This work gives a new class of ruthenium photosensitizers as efficient light harvesting photocatalysts.

Fabrication of mixed phase TiO2 heterojunction nanorods and their enhanced photoactivities.

Substantial efforts have been made in recent times in solving the major limiting factors affecting the efficiency of a photocatalyst. The fabrication of efficient junction architectures is one of the viable approaches to resolve this setback. We have developed a facile and systematic approach for the synthesis of anatase TiO2 () nanoparticles and 1-D anatase and rutile TiO2 () heterojunction nanorods to enhance the interfacial contact area by adjusting the titanium(iv) butoxide (TBOT) to titanium chloride (TiCl4) volume ratio. Their narrower band gap, increasing surface area and anatase phase composition engineered by adjusting the relative concentrations of titanium butoxide (TBOT) and titanium chloride (TiCl4) (TBOT/TiCl4, 1 : 0, 1 : 0.25, 1 : 1 and 1 : 4 v/v for , , and respectively) are also addressed. The materials showed impressive photocatalytic activity for H2 evolution from water/methanol and the photodegradation of organic pollutants like rhodamine B (RhB) and methylene blue (MB) dyes. showed superior activity (16.4 mmol g(-1) h(-1)) with an apparent quantum efficiency (AQE) of 7.7% together with its long-term stability. This is attributed to the synergistic effect observed in the mixed phase nanorod heterojunction photocatalyst. Methyl viologen (MV(2+)) has been used as a probe to elucidate the photocatalytic activities and highlight the heterojunction driven separation of photo-excited charge carriers for enhanced hydrogen production.

Dithiafulvalene functionalized diketopyrrolopyrrole based sensitizers for efficient hydrogen production.

We have designed and synthesized two new diketopyrrolopyrrole (DPP) based organic sensitizers (DPPCA and DPPCN) with the dithiafulvalene (DTF) unit as donor and cyanoacrylic acid/malononitrile as acceptor moieties. These dyes showed excellent efficiency of photocatalytic hydrogen production over a Pt-TiO2 composite via solar-induced water splitting. The sensitizers showed broad absorptions over the wide visible regime (500-800 nm). In DPPCN, the malononitrile moiety led to strong intra-molecular charge transfer, as evidenced by red shifted (∼24 nm) absorption maxima with highly enhanced molar absorptivity (108 190 M(-1) cm(-1)). The electrochemical characterization of as-prepared sensitizers confirmed the feasible electron injection from the dye to the TiO2 conduction band (CB) which has been further validated by theoretical studies. In this study, the rate of the photocatalytic activity was found to be dependent on the acceptor part of the dye molecule as DPPCN sensitized Pt-TiO2 (DNPT) exhibited remarkable (1208 µmol) hydrogen evolution yield in comparison to DPPCA sensitized Pt-TiO2 (DAPT) (840 µmol). The rigid DPP core made the sensitizers significantly photo-stable as affirmed by their high hydrogen production efficiency over 80 h of prolonged irradiation. As predicted from density functional theory (DFT) calculations, ground state geometry of the dyes was almost planar, facilitating continuous conjugation throughout the molecule. Time-dependent DFT (TD-DFT) calculations were also carried out to make clear the understanding of charge transfer transition of the dye molecules.