Preparation of Single-Crystalline AgIn₅S₈ Octahedrons with Exposed {111} Facets and Its Visible-Light-Responsive Photocatalytic H₂ Production Activity

Although AgIn₅S₈ as one kind of ternary chalcogenides has been extensively investigated due to its band-edge positions meeting the thermodynamic requirement for water photosplitting, very little attention has been focused on the crystallinity and facet effects of AgIn₅S₈ on its photocatalytic activity. Herein, a facile hydrothermal route was developed to fabricate regular single-crystalline AgIn₅S₈ octahedrons with only {111} facets exposed. Also, the effects of the hydrothermal reaction conditions on the composition, crystal phase, crystallinity, and morphology of the obtained Ag_<i>x</i>In_<i>y</i>S_{(<i>x</i>+3<i>y</i>/2)} products (hereafter denoted as AIS-<i>x</i>, where <i>x</i> represents the pH value of the reaction solution) were investigated, and it was found that the accurately released S^2– ions from the thermal decomposition of thioacetamide (TAA) is the central factor for the nucleation and growth of the AgIn₅S₈ octahedrons. The experimental results indicate that the resultant regular AgIn₅S₈ octahedrons (AIS-10.6) exhibit the best photocatalytic activity for H₂ production among those Ag_<i>x</i>In_<i>y</i>S_{(<i>x</i>+3<i>y</i>/2)} products, and the higher crystallinity and fewer defects of the AgIn₅S₈ octahedrons compared to the other Ag_<i>x</i>In_<i>y</i>S_{(<i>x</i>+3<i>y</i>/2)} products can retard the photogenerated charge recombination, while those indium atoms with higher density in the exposed {111} facets might be beneficial for the photocatalytic H₂ production reaction by acting as active sites to promote the charge separation and transfer processes. The results presented here provide new insights into the significance of crystallinity and exposed facets in the visible-light-responsive activity of AgIn₅S₈, thus paving new ways into the design and synthesis of high-performance, cost-effective AgIn₅S₈ photocatalysts for H₂ production

Controllable Fabrication of Regular Hexagon-Shaped SnS₂ Nanoplates and Their Enhanced Visible-Light-Driven H₂ Production Activity

SnS₂ nanoplate-like products were fabricated via a facile hydrothermal process of a mixed solution containing SnCl₄ and thiourea (SC­(NH₂)₂) without organic capping agent, and their composition, crystallinity, and morphology can be adjusted by varying the SC­(NH₂)₂/SnCl₄ molar ratio. In particular, regular hexagon-shaped SnS₂ nanoplates with an average size of ∼275 nm and thickness of ∼56 nm were attained when the SC­(NH₂)₂/(SnCl₄) molar ratio is 6:1. The obtained SnS₂ nanoplates exhibit layered structures with exposed {001} facets and a single-crystalline feature, and its growth mechanism was proposed according to the hydrothermal time-dependent experimental results. The regular hexagon-shaped SnS₂ nanoplates achieve high photocatalytic H₂ production activity of 356 μmol h^–1 under visible light (λ ≥ 420 nm) irradiation, much better than that of the irregular nanoplate-like products. The higher crystallinity and fewer defects of the regular hexagon-shaped SnS₂ nanoplates compared to the irregular ones can more efficiently retard the photogenerated charge recombination, while the S atoms with higher density in the exposed {001} facets might be beneficial for the formation of H bonds with H₂O molecules, which then cause good dispersity and photocatalytic activity for H₂ production of the SnS₂ nanoplates. These results demonstrate the potential application of SnS₂ nanoplates in the photocatalytic H₂ production field, and might provide guidance to the controllable syntheses of the family of MS₂ photocatalysts with a highly efficient H₂ production property

Controllable Preparation of Rutile TiO₂ Nanorod Array for Enhanced Photovoltaic Performance of Perovskite Solar Cells

A vertically oriented rutile TiO₂ nanorod (NR) array, as an efficient electron transport layer (ETL), has been used in the perovskite solar cells (PSCs), and its microstructure has a great impact on the corresponding photovoltaic conversion efficiency (PCE). Here we employ a facile control strategy to modulate the microstructures of rutile TiO₂ NR arrays hydrothermally grown on the fluorine tin oxide (FTO) glass from a water–HCl solution of titanium <i>n</i>-butoxide (TBOT). It was found that introducing commercial TiO₂ nanoparticles (P25, Degussa) into the hydrothermal reaction system can efficiently slow down the growth rate of rutile TiO₂ NRs, thus causing the controllable preparation of an NR array on the FTO substrate. The device fabricated with an optimized NR array derived from the hydrothermal reaction solution containing P25 exhibits an improvement of 26.5% in PCE compared with the device fabricated with the NR array from the hydrothermal solution without P25, which is mainly attributed to the reduced charge recombination and the enhanced fill factor stemming from the better contact at the NRs array/perovskite interface. This successful finding demonstrates that the introduction of TiO₂ nanoparticles into the hydrothermal reaction solution of TBOT slows down the growth rate and the electron recombination process of the rutile TiO₂ NRs array, and thus acts as a facile control strategy for improving the photovoltaic performance of the rutile TiO₂ NRs array film-based PSCs

Asymmetric Zinc Porphyrin Derivative-Sensitized Graphitic Carbon Nitride for Efficient Visible-Light-Driven H₂ Production

An asymmetric zinc porphyrin (ZnPy) derivative bearing one benzoic acid and three 3-pyridines as <i>meso</i>-position substituents (zinc-5-(4-carboxyphenyl)-10,15,20-tri­(3-pridyl)­porphyrin, ZnMT3PyP) was used to sensitize graphitic carbon nitride (g-C₃N₄) for visible-light-driven photocatalytic H₂ production. It was found that ZnMT3PyP exhibits more excellent photosensitization and stability on g-C₃N₄ than its counterpart bearing one benzoic acid and three phenyls (zinc-5-(4-carboxyphenyl)-10,15,20-triphenylporphrin, ZnMTPP) under visible light (λ > 420 nm) irradiation even though they have very similar physicochemical properties such as optical absorption capacities and energy band structures. Especially, ZnMT3PyP-Pt/g-C₃N₄ gives an apparent quantum yield (AQY) up to 25.1% at λ = 420 nm light illumination, greater than that (11.6%) of ZnMTPP-Pt/g-C₃N₄. The differences in photosensitization and stability between ZnMT3PyP and ZnMTPP are mainly due to the substitution of 3-pyridine for the phenyls in ZnMTPP, which leads to the electron transfers between ZnMT3PyP and g-C₃N₄ faster than that between ZnMTPP and g-C₃N₄. The present results provide a new insight applying porphyrin derivatives to the photocatalytic H₂ production and open up a new path for further improving the conversion efficiency of solar energy to hydrogen energy through molecular designing

Highly Asymmetric Phthalocyanine as a Sensitizer of Graphitic Carbon Nitride for Extremely Efficient Photocatalytic H₂ Production under Near-Infrared Light

Highly asymmetric zinc phthalocyanine derivative (Zn-<i>tri</i>-PcNc) with intense near-IR light (650–800 nm) absorption is utilized as a sensitizer to extend the spectral response region of graphitic carbon nitride (g-C₃N₄) from ∼450 nm to more than 800 nm. Ultraviolet–visible light (UV-vis) diffuse reflectance absorption spectra (DRS), photoluminescence (PL) spectra, time-resolved photoluminescence spectra (TRPS), and energy band structure analyses are adopted to investigate the photogenerated electron transfer process between Zn-<i>tri</i>-PcNc and g-C₃N₄ on both thermodynamics and dynamics aspects. After optimizing the photocatalytic condition and adding chenodeoxycholic acid (CDCA) as coadsorbent, Zn-<i>tri</i>-PcNc sensitized g-C₃N₄ photocatalyst shows a H₂ production efficiency of 125.2 μmol h^–1 under visible/near-IR-light (λ ≥ 500 nm) irradiation, corresponding to a turnover number (TON) of 5008 h^–1 with an extremely high apparent quantum yield (AQY) of 1.85% at 700 nm monochromatic light irradiation. The present work should be the rarely fundamental investigation on the utilization of near-IR light of solar radiation for the photocatalytic H₂ production from water splitting over a dye-sensitized semiconductor

Two Different Roles of Metallic Ag on Ag/AgX/BiOX (X = Cl, Br) Visible Light Photocatalysts: Surface Plasmon Resonance and Z-Scheme Bridge

Ag/AgX/BiOX (X = Cl, Br) three-component visible-light-driven (VLD) photocatalysts were synthesized by a low-temperature chemical bath method and characterized by X-ray diffraction patterns, X-ray photoelectron spectroscopy, field emission scanning electron microscopy, transmission electron microscopy, high-resolution transmission electron microscopy, and UV–vis diffuse reflectance spectra. The Ag/AgX/BiOX composites showed enhanced VLD photocatalytic activity for the degradation of rhodamine B, which was much higher than Ag/AgX and BiOX. The photocatalytic mechanisms were analyzed by active species trapping and superoxide radical quantification experiments. It revealed that metallic Ag played a different role for Ag/AgX/BiOX VLD photocatalysts, surface plasmon resonance for Ag/AgCl/BiOCl, and the Z-scheme bridge for Ag/AgBr/BiOBr

Attempt to Improve the Performance of Pyrrole-Containing Dyes in Dye Sensitized Solar Cells by Adjusting Isolation Groups

Four new pyrrole-based organic sensitizers with different isolation groups were conveniently synthesized and applied to dye sensitized solar cells (DSCs). The introduction of isolation group in the side chain could both suppress the formation of dye aggregates and electron recombination. Especially, when two pieces of D-π-A chromophore moieties shared one isolation group to construct the “H” type dye, the performance was further improved. Consequently, in the corresponding solar cell of <b>LI-57</b>, a short-circuit photocurrent density (<i>J</i>_sc) was tested to be 13.85 mA cm^–2, while 0.72 V for the open-circuit photovoltage (<i>V</i>_oc), 0.64 for the fill factor (FF), and 6.43% for the overall conversion efficiency (η), exceeding its analogue <b>LI-55</b> (5.94%) with the same isolation group. The results demonstrated that both the size (bulk and shape) and the linkage mode between the D-π-A chromophores and the isolation groups, could affect the performance of sensitizers in DSCs in a large degree, providing a new approach to optimize the chemical structure of dyes to achieve high conversion efficiencies

Organic Sensitizers Featuring 9,10-Diaryl-Substituted Anthracene Unit

A series of anthracene-based dyes were designed and employed in dye-sensitized solar cells in which different 9,10-diaryl-substituted anthracene groups acted as a π-bridge with 2,6-linkage mode. The <i>tert</i>-butylphenyl and hexyloxyphenyl groups in the 9 and 10 positions of the anthracene unit were almost perpendicular to the conjugated plane, which would be beneficial to suppressing the possible π–π stacking and retarding the charge recombination. Their photophysical properties and photovoltaic performance could be tuned by the modification of the substituted groups to the anthracene ring in some degree. Consequently, dye <b>LI-59</b>-based solar cells gave the best performance, with a <i>J</i>_sc (short circuit current) of 13.42 mA cm^–2, <i>V</i>_oc (open circuit voltage) of 722 mV, and FF (fill factor) of 0.66, corresponding to an overall conversion efficiency of 6.42% without the presence of CDCA