Cu 2 O rhombic dodecahedra, octahedra, and cubes were densely modified with conjugated 4-ethynylaniline (4-EA) for facet-dependent photocatalytic activity examination. Infrared spectroscopy affirms bonding of the acetylenic group of 4-EA onto the surface copper atoms. The photocatalytically inactive Cu 2 O cubes showed surprisingly high activity toward methyl orange photodegradation after 4-EA modification, while the already active Cu 2 O rhombic dodecahedra and octahedra exhibited a photocatalytic activity enhancement. Electron, hole, and radical scavenger experiments prove that the photocatalytic charge transport processes have occurred in the functionalized Cu 2 O cubes. Electrochemical impedance spectroscopy also indicates reduced charge transfer resistance of the functionalized Cu 2 O crystals. A band diagram constructed from UV−vis spectral and Mott−Schottky measurements reveals significant band energy shifts in all Cu 2 O samples after decorating with 4-EA. From density functional theory (DFT) calculations, a new band has emerged slightly above the valence band maximum within the band gap of Cu 2 O, which has been found to originate from 4-EA through banddecomposed charge density analysis. The increased charge density localized on the 4-EA molecule and the smallest electron transition energy to reach the 4-EA-generated band are factors making {100}-bound Cu 2 O cubes photocatalytically active. Proper molecular decoration represents a powerful approach to improving the photocatalytic efficiency of semiconductors.

Hydrothermally grown one-dimensional ZnO nanowire (1D ZnO NW) and a newly synthesized metal-free, D-π-A type, carbazole dye (SK1) sensitizer-based photovoltaic device with a power conversion efficiency (PCE) of more than 5% have been demonstrated by employing the cobalt tris(2,2'-bipyridyl) redox shuttle. A short-circuit current density (Jsc) of ∼12.0 mA/cm(2), an open-circuit voltage (Voc) of ∼719 mV, and a fill factor (FF) of ∼65% have been afforded by the 1D ZnO NW-based dye-sensitized solar cell (DSSC) incorporating [Co(bpy)3](3+/2+) complex as the one-electron redox mediator. In contrast, the identical DSSC with traditional I3(-)/I(-) electrolyte has shown a Jsc ≈ 12.2 mA/cm(2), a Voc ≈ 629 mV, and a FF ≈ 62%, yielding a PCE of ∼4.7%. The persuasive role of the inherent superior electron transport property of 1D ZnO NWs in enhancing the device efficiency is evidenced from the impoverished performance of the DSSCs with photoanodes fabricated using ZnO nanoparticles (NPs). The DSSCs having ZnO NP-based photoanodes have achieved the PCEs of ∼3.6% and ∼3.2% using cobalt- and iodine-based redox electrolytes, respectively. The electronic interactions between the SK1 sensitizer and ZnO (NWs and NPs) to induce the photogenerated charge transfer from SK1 to the conduction band (CB) of ZnO are evidenced from the significant quenching of photoluminescence and exciton lifetime decay of SK1, when it is anchored onto the ZnO architectures. The energetics of the SK1 dye molecule are estimated by combining the spectroscopic and electrochemical techniques. The electronic distributions of SK1 dye molecule in its HOMO and LUMO energy levels are interpreted using density functional theory (DFT)-based calculations. The electron donor-π linker-acceptor (D-π-A) configuration of SK1 dye provides an intramolecular charge transfer within the molecule, prompting the electron migration from the carbazole donor to cyanoacrylic acceptor moiety via the oligo-phenylenevinylene linker group. The D-π-A-mediated electron movement witnesses the favorable photoexcited electron transfer from the LUMO of SK1 dye to the CB of ZnO through the carboxyl anchoring group.

Previously, Cu2O cubes have been shown to remain photocatalytically inert toward methyl orange degradation even after surface decoration with ZnO, ZnS, CdS, and Ag3PO4 nanostructures. Surprisingly, when Ag2S nanoparticles are lightly deposited on Cu2O cubes as seen through scanning electron microscopy (SEM) images, the heterostructures become highly photocatalytically active. X-ray diffraction (XRD) patterns show mainly Cu2O diffraction peaks due to lightly deposited Ag2S, but Ag2S peaks can emerge with increased Ag2S deposition. X-ray photoelectron spectroscopy (XPS) analysis also supports Ag2S formation on Cu2O crystals. The Ag2S-deposited Cu2O octahedra and rhombic dodecahedra show the expected activity enhancement. Electron paramagnetic resonance (EPR) measurements, as well as electron, hole, and radical scavenger tests, all confirmed the emergence of photocatalytic activity from the Ag2S–Cu2O cubes. Photoluminescence lifetimes are shortened after Ag2S deposition. Electrochemical impedance measurements revealed a large decrease in charge transfer resistance for Cu2O cubes after the Ag2S deposition. Unexpectedly, the separately synthesized Ag2S particles are also photocatalytically inactive. No specific lattice planes of Ag2S are formed directly over the {100} face of Cu2O. Diffuse reflectance and ultraviolet photoelectron spectral data were used to construct band diagrams of different Cu2O crystals and Ag2S nanoparticles. A Z-scheme charge transfer mechanism may be involved at the heterojunction interface to promote charge carrier separation. However, to explain the sudden appearance of photocatalytic activity from the Ag2S-deposited Cu2O cubes, a large change in the {100} surface band bending after Ag2S deposition should be used. This work illustrates that an unusual photocatalytic outcome is possible to semiconductor heterojunctions, where two photocatalytically inert components can become highly active when joined together.

Since the exciting discovery that binding of 4-ethynylaniline on the inert Cu2O cubes makes the functionalized cubes highly photocatalytically active toward methyl orange (MO) degradation, binding of 2-ethynyl-6-methoxynaphthalene (2E-6MN) molecules...

Rational design of hierarchical nanocomposites is a promising approach for efficient energy harvesting and conversion. A noble-metal-free ternary hierarchical composite, Cd0.5Zn0.5S-g-C3N4-MoS2, has been developed. Materials were chosen based on their relative band-edge alignments and they were studied as a composite for photocatalytic properties. The photocatalytic activity was evaluated by measuring the rate of photodriven H2 evolution with concomitant degradation of organic pollutants, such as Rhodamine B. Optimization of the loading of g-C3N4 and MoS2 onto Cd0.5Zn0.5S results in an enhanced yield of hydrogen evolution by ∼120% (Cd0.5Zn0.5S-g-C3N4) and ∼197% (Cd0.5Zn0.5S-g-C3N4-MoS2) compared to bare Cd0.5Zn0.5S. The ternary hybrid, Cd0.5Zn0.5S-g-C3N4-MoS2 resulted in an apparent quantum yield (AQY) of 38% at 420 nm. The significant improvement in photocatalytic performance in the composite can be attributed to enhanced interfacial charge transfer of electrons from g-C3N4 to Cd0.5Zn0.5S and MoS2. We surmise that the close proximity of the energies of conduction band edge for each component in the ternary composite promotes better charge separation.

To the best of our knowledge this is the first report in which ruthenium doped polycrystalline lanthanum manganite, LaMnRuO (x = 0.0-0.4), having high efficacy for oxygen production from water without the use of any sacrificial reagent or co-catalyst and as an efficient photocatalyst for dye degradation is reported. Ruthenium doping alters the crystal structure of the parent LaMnO (LMO) due to the induced chemical pressure of the larger Ru ion, which facilitates a bond angle of 180° in the Mn-O-Mn plane resulting in the easy extraction of a photo-generated charge carrier population leading to enhanced photocatalytic activity. Rietveld refinements reveal that the parent compound LMO crystallizes in the rhombohedral phase, while upon an increase in the doping concentration of ruthenium, the phase of the compounds changes from the rhombohedral to the cubic phase. The percentage contribution of each phase has been estimated using the sixth-order polynomial and pseudo-Voigt function. Typically, all the compositions, LaMnRuO (x = 0.0-0.4), were prepared by a conventional solid state route and studied for their photocatalytic activity. The synthesized compounds were investigated by powder X-ray diffraction (PXRD), UV-visible diffuse reflectance spectroscopy (DRS), Fourier transform infrared spectroscopy (FTIR), field emission scanning electron microscopy (FESEM), energy-dispersive X-ray spectroscopy (EDX) and X-ray photoelectron spectroscopy (XPS) analysis. The structure-property correlation of the compound is presented based on Rietveld refinement combined with the experimental data. The as-prepared compounds show efficient photocatalytic oxygen gas production from water without the use of any co-catalyst or sacrificial reagents. Among the five compositions, LaMnRuO shows the highest O production efficiency (4.73 mmol g h) with an apparent quantum yield (AQY) of 7.43%. These ruthenium doped compositions also exhibit superior dye degradation properties, studied by taking the industrial dye methyl orange (MO) as the model compound.

Overlayer passivation minimizes surface defects and arrests the back transfer of electrons for an enhanced charge extraction. Surface passivation of ZnFe2O4 using alumina yields enhanced charge carrier density from 8.43 × 1020 cm-3 to 18.83 × 1020 cm-3 giving a record efficiency in this class of compounds.

One of the major limiting factorsf or efficient photoelectrochemical water oxidation is the fast recombination kinetics of photogenerated charge carriers. Herein,w ep ropose am odel system that utilizes ZnIn 2 S 4 and hierarchical VS 2 microflowersf or efficient charge separation through aZscheme pathway,w ithoutt he need for an electron mediator. An impressive 18-fold increase in photocurrent was observed for ZnIn 2 S 4 -VS 2 compared to ZnIn 2 S 4 alone. The charge-transfer dynamics in the composite were found to follow aZ -scheme pathway,w hich resulted in decreased charger ecombination and greater accumulation of the surface charge. Furthermore, slow kinetics of the surfacer eaction in the ZnIn 2 S 4 -VS 2 composite correlated to an increased surface-charge capacitance. This feature of the composite materialf acilitated partial storage of the photogenerated chargec arriers (e À /h + + )u nder illumination andd ark-current conditions, thus storing and utilizing solar energy more efficiently.