Simultaneous production of hydrogen and chlorine through overall brine splitting with a particulate photocatalyst.

Sunlight-driven photocatalytic water splitting shows promise for green H2 production. In an attempt to achieve seawater splitting, we constructed a new stoichiometric brine splitting system that produces H2 along with Cl2 instead of O2. Cl2-a more potent high-value-added oxidant than O2-was obtained with 100% selectivity over 10 h by adjusting the solution pH to acidic using a UV-light-driven Pt-loaded TiO2 photocatalyst. Our new photosynthesis system can permit economically feasible solar chemical production.

Insights into the carbonate effect on water oxidation over metal oxide photocatalysts/photoanodes.

Photocatalytic/photoelectrochemical water splitting using metal oxide semiconductors is a promising technology for direct and simple solar-energy conversion. The addition of carbonate salts to an aqueous reaction solution has been known to promote stoichiometric O2 evolution and H2O2 production via H2O oxidation. To elucidate the effect of carbonates, density functional theory calculations are performed to study the photoinduced H2O and H2CO3 oxidation mechanisms on TiO2 and BiVO4. The oxidation reactions proceeded via peroxide intermediates, such as H2O2 for H2O, H2C2O6 for H2CO3, and H2CO4 for the coexistence of H2O and H2CO3 molecules. Regardless of the reactant and metal oxide, the free energy changes in the four proton-coupled electron-transfer (PCET) steps of the oxidation mechanism indicate that the first PCET requires the highest energy input and is the rate-limiting step. All PCET steps of the H2O oxidation, except the second one, are more endergonic than those of the H2CO3 oxidation. The H2O reactant requires a larger energy barrier at the highest energy profile, as well as at the final state, than the H2CO3 reactant. The computational results verify that the adsorbed H2CO3 molecule is easily photo-oxidized compared with the adsorbed H2O molecule, facilitating the formation of the peroxide intermediate and improving O2 evolution and H2O2 production.

A slight bluish-white fluorescence from E,E-2,6-bis(4-cyanostyryl)pyridine pristine crystals.

Among various light emission phenomena, multicolour light emission, such as white light emission, is an interesting phenomenon. Bis-styrylbenzene derivatives show unique and excellent emission behaviours. In this study, three types of bis-styrene derivatives, with thiophene, pyridine, and benzene rings at the central position, were synthesised, and their photophysical properties were studied in detail. Among them, pristine crystals of E,E-2,6-bis(4-cyanostyryl)pyridine (Py4CN) showed a slight bluish-white emission because the Py4CN pristine crystals were mixtures of two separate crystals emitting blue and yellow-green fluorescence.

A comparative computational study on the interactions of N719 and N749 dyes with iodine in dye-sensitized solar cells.

The intermolecular interactions of the two most basic Ru(II) complex dyes for dye-sensitized solar cells (DSSCs), N719 and N749, with the iodine species are investigated using density functional theory (DFT). In addition to interactions with a single I2 molecule, multiple I2 interactions and simultaneous interactions of I2 and I(-) occur. N719 with two isothiocyanato (NCS) ligands interacts with two I2 molecules via the two terminal S atoms in the ground singlet electronic state, whereas N749 with three NCS ligands forms three S···I-I bonds. Irrespective of the NCS position and the number of I2 molecules, N749 has a stronger interaction with I2 than N719. Conversely, the interaction of I(-) with oxidized N749 via the terminal S atom of the NCS ligand is weaker than that with oxidized N719. However, simultaneous interactions of oxidized N749 with two I2 molecules promote the I(-) interaction, and the I(-) interaction with N749 becomes stronger than that with N719 bonded to both an I2 and I(-). The computational results of multiple interactions between the dye and iodine species suggest that the difference in DSSC performance between N719 and N749 dyes is explained by recombination related to the I2 interaction and regeneration of the oxidized dye by I(-).

Intermolecular interactions between a Ru complex and organic dyes in cosensitized solar cells: a computational study.

Intermolecular interactions in cyclometalated Ru complex dye (FT89) dimers, carbazole organic dye (MK-45 and MK-111) dimers, FT89-MK-45 complexes, and FT89-MK-111 complexes were investigated using density functional theory (DFT) and time-dependent DFT (TD-DFT) to elucidate the improvement mechanism of dye-sensitized solar cell (DSSC) performance due to cosensitization with FT89 and MK dyes. All of the dimers and complexes form intermolecular cyclic hydrogen bonds via the carboxyl groups. The FT89 dimer and complexes with the TiO2Na model system promote intermolecular interactions with I2via the NCS ligand of the FT89 monomer. The computational results verify that MK-111 behaves not only as a sensitizer but also inhibits FT89 aggregation by effectively serving as a coadsorbent similar to deoxycholic acid (DCA) in the dye solution, suppressing recombination of the injected electrons in TiO2 with I2, improving DSSC performance.

Combinatorial search for iron/titanium-based ternary oxides with a visible-light response.

A combinatorial approach has been carried out to systematically investigate visible-light responsiveness of Fe-Ti-M (M: various metal elements) oxides for photoelectrochemical water splitting. Among the 25 elements tested, strontium was the most effective. A ternary metal oxide with the composition Fe(86.1)Ti(9.6)Sr(4.3)O(x) has been identified as a new lead structure for a visible-light responsive, n-type semiconductor. We have conducted various kinds of characterization of the Fe-Ti-Sr oxide semiconductor and discussed the reason why Sr in the Fe-Ti oxide gave the highest photocurrent.

TiO2 band shift by nitrogen-containing heterocycles in dye-sensitized solar cells: a periodic density functional theory study.

A density functional theory (DFT) method (periodic DMol3) with full geometry optimization was used to study the adsorption of nitrogen-containing heterocycles such as pyrazole, imidazole, 1,2,4-triazole, pyridine, pyrimidine, pyrazine, and 4-t-butylpyridine (TBP) on TiO2 anatase (101), (100), and (001) surfaces. All structures displayed a negative shift in the TiO2 Fermi level upon adsorption of N-containing heterocycles. Additionally, the heterocycles were examined as an additive in an I-/I3- redox electrolyte solution of dye-sensitized TiO2 solar cell. The DFT results indicated that the negative shift of TiO2 Fermi level was due to the adsorbate dipole moment component normal to the TiO2 surface plane, and corresponded to the enhanced open-circuit photovoltage (Voc) and the reduced short-circuit photocurrent density (Jsc) in a dye-sensitized solar cell.

Theoretical study of quinolines-I(2) intermolecular interaction and implications on dye-sensitized solar cell performance.

The monomer and intermolecular charge-transfer complexes of 13 different quinoline derivatives with diiodine were studied using ab initio molecular orbital (MO) and density functional theory (DFT) methods. Calculations revealed that the sigma* orbital of iodine interacts with the nitrogen lone pair in the quinoline ring. The open-circuit photovoltage (V(oc)) values of an Ru(II) complex dye-sensitized nanocrystalline TiO(2) solar cell with an I(-)/I(3) (-) redox electrolyte in acetonitrile using quinoline additives were compared to the computational calculations on the intermolecular interaction between quinolines and I(2). The optimized geometries, frequency analyses, Mulliken population analyses, natural bond orbital (NBO) analyses, and interaction energies indicate that the V(oc) value of the solar cell is higher when quinoline complexes more favorably interact with I(2). Therefore, the interaction between the quinoline additives and iodine redox electrolyte is an important factor for controlling dye-sensitized solar cell performance.