Presence Of Sacrificial Electron Donor Research Articles

Charge separation control in organic photosensitizers for photocatalytic water splitting without sacrificial electron donors

Photocatalytic hydrogen evolution reaction (photoHER) is one of the most promising approaches towards production of “green” hydrogen. Currently, the state-of-the-art photoHER systems require the use of sacrificial electron donors (SED), because of inefficient charge separation in photosensitizers and thermodynamically challenging water oxidation by the same catalyst. Here, we present a molecular design approach for all-organic photosensitizers with effective intramolecular charge separation, microsecond lifetime of excited states, controllable direction of electron transfer, and ability to oxidize water for recovery of the photocatalytic system to its initial state. Such photosensitizers comprise weakly conjugated strong electron donor and acceptor what enables charge transfer during the light absorption. The excitation energy is stored in long-living triplet states, whose lifetime can be monitored by the thermally activated delayed fluorescence. Additionally, application of heavy-atom effect helps not only to increase the population of triplet state but also to increase its stability and lifetime. When such photosensitizers are attached to the platinized TiO2, efficient photoHER catalysts are obtained which produce H2 under irradiation with sunlight. In the presence of SED, the highest turnover number after 24 h (TON24h) of such systems exceed 3500, whilst in pure water without any SED, TON24h reaches 2000. Our best system performs photocatalytic SED-free water-splitting for 48 h keeping 100 % of its activity and constant turnover frequency of 26 h−1. The described here investigations reveal that water splitting can be performed by a simple three component system “photosensitizer|TiO2|Pt” under specific control of 1) the charge separation and its direction, 2) intersystem crossing rate and triplet state lifetime, and 3) favorable water oxidation thermodynamics within a photosensitizer together with 4) appropriate alignment of energy levels to the catalyst.

Development of Aldehyde Functionalized Iridium(III) Complexes Photosensitizers with Strong Visible-Light Absorption for Photocatalytic Hydrogen Generation from Water

Four iridium(III) dyes functionalized with aldehyde functional group in the cyclometalating (C^N) ligands, bearing either diethyl [2,2′-bipyridine]-4,4′-dicarboxylate or tetraethyl [2,2′-bipyridine]-4,4′-diylbis(phosphonate) anchoring groups, coded as Ir1–Ir4, are synthesized and explored as photosensitizers. The synthetic route is described and all of the complexes are characterized with respect to their electrochemical and photophysical properties. Density functional theory (DFT) calculation was used to gain insight into the factors responsible for the photocatalytic properties of Ir1–Ir4 as effective photosensitizers for photocatalytic hydrogen generation. Relative to common iridium(III) dyes, such as [Ir(ppy)2(dcbpy)]+ (ppy = 2-phenylpyridine), the absorption spectra of our dyes are broader, which is attributed to the extended π-conjugation in their C^N ligands. All of the new iridium(III) dyes were used as photosensitizers for visible-light driven hydrogen production by attaching to platinized TiO2 nanoparticles (Pt–TiO2) in the presence of sacrificial electron donor (SED) of ascorbic acid (AA) in a purely aqueous solution. A H2 turnover number (TON) up to 5809 was demonstrated for 280 h irradiation. Complexes with tetraethyl [2,2′-bipyridine]-4,4′-diylbis(phosphonate) anchoring groups were found to outperform those with classical diethyl [2,2′-bipyridine]-4,4′-dicarboxylate, which may be one of the important steps in developing high-efficiency iridium(III) photosensitizers in water splitting hydrogen generation.

A covalent organic framework inspired by C3N4 for photosynthesis of hydrogen peroxide with high quantum efficiency

Carbon nitride (C3N4) has been the main research focus for photocatalytic H2O2 synthesis that may enable the on-site and on-demand H2O2 production under mild conditions. Its potential is unfortunately shadowed by the narrow light absorption and fast charge recombination. Building on the understanding of the inherent merits and pitfalls of C3N4, we here propose to assemble active heptazine motifs with functional linkers in ordered molecular frameworks for highly efficient photocatalytic H2O2 production. Herein, a heptazine-based covalent organic framework is synthesized via the Schiff-base reaction. It has enhanced light absorption and charge separation. When irradiated with visible light in the presence of sacrificial electron donors, the sample exhibits an excellent H2O2 production rate of 11986 μmol h–1 g–1 and an apparent quantum efficiency up to 38% at 420 nm, outperforming most organic or inorganic competitors in our best knowledge. Impressively, the catalyst can also endure long time operation that affords the linear H2O2 accumulation to a practically usable concentration.

Photochemical charge accumulation in a heteroleptic copper(i)-anthraquinone molecular dyad via proton-coupled electron transfer.

Developing efficient photocatalysts that perform multi electron redox reactions is critical to achieving solar energy conversion. One can reach this goal by developing systems which mimic natural photosynthesis and exploit strategies such as proton-coupled electron transfer (PCET) to achieve photochemical charge accumulation. We report herein a heteroleptic Cu(i)bis(phenanthroline) complex, Cu-AnQ, featuring a fused phenazine-anthraquinone moiety that photochemically accumulates two electrons in the anthraquinone unit via PCET. Full spectroscopic and electrochemical analyses allowed us to identify the reduced species and revealed that up to three electrons can be accumulated in the phenazine-anthraquinone ring system under electrochemical conditions. Continuous photolysis of Cu-AnQ in the presence of sacrificial electron donor produced doubly reduced monoprotonated photoproduct confirmed unambiguously by X-ray crystallography. Formation of this photoproduct indicates that a PCET process occurred during illumination and two electrons were accumulated in the system. The role of the heteroleptic Cu(i)bis(phenanthroline) moiety participating in the photochemical charge accumulation as a light absorber was evidenced by comparing the photolysis of Cu-AnQ and the free AnQ ligand with less reductive triethylamine as a sacrificial electron donor, in which photogenerated doubly reduced species was observed with Cu-AnQ, but not with the free ligand. The thermodynamic properties of Cu-AnQ were examined by DFT which mapped the probable reaction pathway for photochemical charge accumulation and the capacity for solar energy stored in the process. This study presents a unique system built on earth-abundant transition metal complex to store electrons, and tune the storage of solar energy by the degree of protonation of the electron acceptor.

Development of new thiocyanate-free Ruthenium(II) dyes bearing isoquinoline chromophores for hydrogen production via water splitting

Four thiocyanate-free ruthenium(II) dyes, [RuII(4, 4-dicarboxylic acid-2,2-bipyridine)2(L1 or L2)](PF6)] and [RuII(tetraethyl[2,2′-bipyridine]-4,4′-diylbis(phosphonate))2(L1 or L2)](PF6)] with different anchoring groups, coded as Ru1–Ru4, were synthesized and characterized by NMR spectroscopy and mass spectrometry, and their electrochemical and photophysical properties were investigated. Density functional theory (DFT) calculation was used to gain insight into the factors responsible for photocatalytic properties of Ru1–Ru4 as effective photosensitizers. Relative to common ruthenium dyes, such as [Ru(bpy)3]2+ and N719, the absorption spectra of our dyes with triphenylamine moiety are broader with enhanced molar absorptivities (ε), especially, in the region between 400 nm and 650 nm. This is attributed to the extended π-conjugation system by inserting electron-donating triphenylamine to isoquinoline through thiophene moiety in their cyclometalating (C∧N) ligands, in which strong intramolecular charge transfer (ICT) ability was induced. All the new ruthenium(II) complexes were used as photosensitizers for visible-light driven hydrogen production reactions by attaching to platinized TiO2 nanoparticles (Pt–TiO2) in the presence of sacrificial electron donor (SED) ascorbic acid (AA) in purely aqueous solution. A H2 turnover number (TON) up to 14232 was demonstrated after 236 h irradiation. Complexes with tetraethyl[2,2′-bipyridine]-4,4′-diylbis(phosphonate) anchoring groups were found to be outperform to those with classical 4, 4-dicarboxylic acid-2,2-bipyridine, which may be one of the crucial steps in designing superior ruthenium(II) photosensitizers for hydrogen generation from water.

Smart protection of surfaces during day-night by a novel composite self-cleaning coating with catalytic memory

For the first time this work reports a new idea to develop a round-the-clock self-cleaning coating which was successfully applied to preserve cultural heritage and modern artifacts under sunlight illumination and at night. To fabricate this structure, namely, H2:TiO2/WO3@Pt, soft templating and hydrogen treatment approaches were selected to enhance the performance of TiO2/WO3 photocatalyst, together with the addition of Pt plasmonic nanoparticles. The coating can be photochemically charged in the presence of sacrificial electron donors and keep its stability, benefiting from the remained electrons stock for over 10 h to clean the surface from aggressive pollution also at night, in absence of light. This transparent heterostructure with high surface area, proper interfacial contacts in TiO2/WO3@Pt system, and extended visible light absorption resulting from the synergistic interactions of the composite system (TiO2, WO3, and Pt) presents an efficient self-cleaning performance. The smart coated surface could clean the substrate benefiting from 70% pollutants photodegradation after irradiation followed by dark storage (2 and 6 h, individually), and superhydrophilic properties were maintained for hours in the dark, thanks to oxygen vacancies resulted from hydrogen treatment.

Porous Graphitic Carbons Containing Nitrogen by Structuration of Chitosan with Pluronic P123.

Using Pluronic P123 as a structure-directing agent and chitosan as a carbon precursor, different porous carbons with remarkable morphologies such as orthohedra or spheres with diametrically opposite holes are obtained. These particles of micrometric size are constituted by the stacking of thin sheets (60 nm) that become increasingly bent in the opposite sense, concave in the upper and convex in the bottom hemispheres, as the chitosan proportion increases. TEM images, after dispersion of the particles by sonication, show that besides micrometric graphene sheets, the material is constituted by nanometric onion-like carbons. The morphology and structure of these porous carbons can be explained based on the ability of Pluronic P123 to undergo self-assembly in aqueous solution due to its amphoteric nature and the filmogenic properties of chitosan to coat Pluronic P123 nanoobjects undergoing structuration and becoming transformed into nitrogen-doped graphitic carbons. XPS analysis reveals the presence of nitrogen in their composition. These porous carbons exhibit a significant CO2 adsorption capacity of above 3 mmol g–1 under 100 kPa at 273 K attributable to their large specific surface area, ultraporosity, and the presence of basic N sites. In addition, the presence of dopant elements in the graphitic carbons opening the gap is responsible for the photocatalytic activity for H2 generation in the presence of sacrificial electron donors, reaching a H2 production of 63 μmol g–1 in 24 h.

Photoinduced Charge Accumulation and Prolonged Multielectron Storage for the Separation of Light and Dark Reaction.

The utilization of solar energy is restricted by the intermittent nature of solar influx. We present novel noble-metal free complexes that can be photochemically charged in the presence of sacrificial electron donors and remain stable in its charged form for over 14 h. This allows the doubly reduced Cu(I) 4H-imidazolate complex to be stored after photochemical charging and used as a reagent in dark reactions, such as the reduction of methyl viologen or oxygen. Combined UV-vis/EPR spectroelectrochemistry indicates that a two-electron reduction is induced by introducing sacrificial electron donors that facilitate proton-coupled electron transfer. Repeated photochemical reduction and chemical oxidation reveals that the complex retained a charging capacity of 72% after four cycles. We demonstrate a chemical system that can decouple photochemical processes from the day-night cycle, which has been a barrier to realizing utilization of solar energy in photochemical processes on a global scale.

Alkene-Linked Covalent Organic Frameworks Boosting Photocatalytic Hydrogen Evolution by Efficient Charge Separation and Transfer in the Presence of Sacrificial Electron Donors.

Covalent organic frameworks (COFs) are potential photocatalysts for artificial photosynthesis but they are much less explored for photocatalytic hydrogen evolution (PHE). COFs, while intriguing due to crystallinity, tunability, and porosity, tend to have low apparent quantum efficiency (AQE) and little is explored on atomistic structure–performance correlation. Here, adopting triphenylbenzene knots and phenyl linkers as a proof of concept, three structurally related COFs with different linkages are constructed to achieve a tunable COF platform and probe the effect of the linkage chemistry on PHE. Cyano‐substituted alkene‐linked COF (COF–alkene) yields a stable 2330 µmol h−1 g−1 PHE rate, much superior to imine‐ and imide‐linked counterparts (<40 µmol h−1 g−1) under visible light irradiation. Impressively, COF–alkene achieves an AQE of 6.7% at 420 nm. Combined femtosecond transient absorption spectroscopy and theoretical calculation disclose the critical role of cyano‐substituted alkene linkages toward high efficiency of charge separation and transfer in the presence of sacrificial electron donors—the decisive key to the superior PHE performance. Such alkene linkages can also be extended to design a series of high‐performance polymeric photocatalysts, highlighting a general design idea for efficient PHE.

Photochemical regeneration of flavoenzymes – An Old Yellow Enzyme case-study

Direct, NAD(P)H-independent regeneration of Old Yellow Enzymes represents an interesting approach for simplified reaction schemes for the stereoselective reduction of conjugated C=C-double bonds. Simply by illuminating the reaction mixtures with blue light in the presence of sacrificial electron donors enables to circumvent the costly and unstable nicotinamide cofactors and a corresponding regeneration system.In the present study, we characterise the parameters determining the efficiency of this approach and outline the current limitations. Particularly, the photolability of the flavin photocatalyst and the (flavin-containing) biocatalyst represent the major limitation en route to preparative application.

Decolorization of textile dyes by TiO2 -based photocatalyst using polyol as electron donor

Decolorization of textile dyes including 2,6-dichlorophenolindophenol (DCIP), congo red (CR) and methyl orange (MO) by using TiO2-based photocatalyst in the presence of polyols such as glycerol and ethylene glycol was investigated. Polyols were used as sacrificial electron donors (SEDs). The results showed that the polyols improved the rate and yield of a light-induced decolorization of dyes in comparison with a photocatalytic reaction without polyols. A possible reaction mechanism of dye decolorization by the photocatalyst in the presence of electron donors was proposed. TiO2 photocatalyst absorbed light to generate electrons (e-) and holes (h+). The electrons and holes were prevented from recombining by the presence of SEDs. The free electrons and holes then involved in decolorization processes through reduction or oxidation reactions. The effects of TiO2 catalyst amounts, irradiation time and polyol concentrations on dye decolorization were investigated. The decolorization efficiency significantly increased with the increasing irradiation time, SED concentrations and certain amounts of TiO2.

Rational Design of MOF/COF Hybrid Materials for Photocatalytic H2 Evolution in the Presence of Sacrificial Electron Donors

AbstractCrystalline and porous covalent organic frameworks (COFs) and metal‐organic frameworks (MOFs) materials have attracted enormous attention in the field of photocatalytic H2 evolution due to their long‐range order structures, large surface areas, outstanding visible light absorbance, and tunable band gaps. In this work, we successfully integrated two‐dimensional (2D) COF with stable MOF. By covalently anchoring NH2‐UiO‐66 onto the surface of TpPa‐1‐COF, a new type of MOF/COF hybrid materials with high surface area, porous framework, and high crystallinity was synthesized. The resulting hierarchical porous hybrid materials show efficient photocatalytic H2 evolution under visible light irradiation. Especially, NH2‐UiO‐66/TpPa‐1‐COF (4:6) exhibits the maximum photocatalytic H2 evolution rate of 23.41 mmol g−1 h−1 (with the TOF of 402.36 h−1), which is approximately 20 times higher than that of the parent TpPa‐1‐COF and the best performance photocatalyst for H2 evolution among various MOF‐ and COF‐based photocatalysts.

Rational Design of MOF/COF Hybrid Materials for Photocatalytic H2 Evolution in the Presence of Sacrificial Electron Donors.

Crystalline and porous covalent organic frameworks (COFs) and metal-organic frameworks (MOFs) materials have attracted enormous attention in the field of photocatalytic H2 evolution due to their long-range order structures, large surface areas, outstanding visible light absorbance, and tunable band gaps. In this work, we successfully integrated two-dimensional (2D) COF with stable MOF. By covalently anchoring NH2 -UiO-66 onto the surface of TpPa-1-COF, a new type of MOF/COF hybrid materials with high surface area, porous framework, and high crystallinity was synthesized. The resulting hierarchical porous hybrid materials show efficient photocatalytic H2 evolution under visible light irradiation. Especially, NH2 -UiO-66/TpPa-1-COF (4:6) exhibits the maximum photocatalytic H2 evolution rate of 23.41 mmol g-1 h-1 (with the TOF of 402.36 h-1 ), which is approximately 20 times higher than that of the parent TpPa-1-COF and the best performance photocatalyst for H2 evolution among various MOF- and COF-based photocatalysts.

Defect States Control Effective Band Gap and Photochemistry of Graphene Quantum Dots.

Graphene quantum dots (GQDs) have emerged as a new group of quantum-confined semiconductors in recent years, with possible applications as light absorbers, luminescent labels, electrocatalysts, and photoelectrodes for photoelectrochemical water splitting. However, their semiconductor characteristics, such as the effective band gap, majority carrier type, and photochemistry, are obscured by defects in this material. Herein, we use surface photovoltage spectroscopy (SPS) in combination with photoelectrochemical measurements to determine the parameters that are essential to the use of GQDs as next-generation semiconductor devices and photocatalysts. Our results show that ordered GQDs (1-6 nm) behave as p-type semiconductors, based on the positive photovoltage in the SPS measurements on Al, Au, and fluorine-doped tin oxide substrates, and generate mobile charge carriers under excitation of defect states at 1.80 eV and under band gap excitation at 2.62 eV. Chemical reduction with hydrazine removes some defects and increases the effective band gap to 2.92 eV. SPS measurements in the presence of sacrificial electron donor and acceptors show that photochemical charge carriers can be extracted and promote redox reactions. A reduced GQDs photocathode supports an unprecedented photocurrent of 50 μA cm-2 using K3Fe(CN)6 as sacrificial electron acceptor. Additionally, while pristine GQDs do not photoreduce protons under visible light, hydrazine-treated GQDs generate H2 from aqueous methanol under visible and UV light (0.04% quantum efficiency at 375 nm) without added co-catalysts. These findings are relevant to the use of GQDs in photochemical and photovoltaic energy-conversion systems.

(Invited) Efficient Hot Electron Transfer By Plasmon Induced Interfacial Charge Transfer Transitio

Surface plasmon resonance in metal nanostructures has been widely used to enhance the efficiency of semiconductors and/or molecular chromophore based solar energy conversion devices by increasing absorption or energy transfer rates through the enhanced local field strength. In more recent years, it has been shown that excitation of plasmons in metal nanostructures can also lead to the injection of hot electrons into semiconductors and enhanced photochemistry. This novel mechanism suggests that plasmonic nanostructures can potentially function as a new class of widely tunable and robust light harvesting materials for solar energy conversion. More importantly, it provide a novel approach to access highly energetic and reactive states of metals that is difficult to utilize with thermal chemistry. However, plasmon-induced hot electron injections from metal to semiconductor or molecules are still inefficient because of the competing ultrafast hot electron relaxation processes within the metallic domain. In this talk, I will discuss a recent study on the key factors that limit the efficiency of plasmon induced hot electron transfer in colloidal quantum-confined semiconductor-gold nanorod heterostructures. These heterostructures provide a well-defined and systematically tunable model system for studying the mechanism of hot electron transfer. In CdSe NRs with Au tips, the distinct plasmon band of the Au nanoparticles was completely damped due to strong interaction with the CdSe domain. Using transient absorption spectroscopy, we show that optical excitation of plasmons in the Au tip leads to efficient hot electron injection into the semiconductor nanorod. In the presence of sacrificial electron donors, this plasmon induced hot electron transfer process can be utilized to drive photoreduction reactions under continuous illumination. We propose that the strong metal/semiconductor coupling in CdSe/Au hetersostructures leads to a new pathway for this surprising efficient hot electron transfer. In this plasmon induced interfacial charge transfer transition (PICTT) the a plasmon decay by direct excitation of an electron from the metal to semiconductor, bypassing the competition with hot electron transfer in metal. Ongoing studies are examining the generality of this mechanism and exploring possible approaches for improving its efficiency through controlling the size and shape of the plasmonic and excitonic domains. Reference [1]. Kaifeng Wu, Jinquan Chen, James R. McBride, Tianquan Lian, “Efficient hot-electron transfer by a plasmon-induced interfacial charge-transfer transition”, Science (2015), 349 (6248): 632. DOI: 10.1126/science.aac5443 [2]. Kaifeng Wu, William E. Rodríguez-Córdoba, Ye Yang, and Tianquan Lian, “Plasmon-Induced Hot Electron Transfer from the Au Tip to CdS Rod in CdS-Au Nanoheterostructures”, Nano Lett. (2013), 13(11), 5255-5263. DOI: 10.1021/nl402730m

(Invited) Light-Driven H2 Generation Using 1D and 2D Multicomponent Semiconductor/Catalyst Nanoheterostructures

Quantum confined semiconductor nanocrystals have been widely investigated as light harvesting and charge separation components in photovoltaic and photocatalytic devices. The efficiency of these semiconductor nanocrystal-based devices depends on many processes, including light harvesting, carrier relaxation, charge separation and charge recombination. The competition between these processes determines the overall solar energy conversion (solar to electricity or fuel) efficiency. Compared with single component quantum dots (QDs), semiconductor nanoheterostructures, combining two or more materials, offer additional opportunities to control their charge separation properties by tailoring their compositions and dimensions through relative alignment of conduction and valence bands. Further integration of catalysts (heterogeneous or homogeneous) to these materials form multifunctional nanoheterostructures. Using Pt tipped CdSe/CdS dot-in-rod nanorods(NRs) and CdS nanoplatelets as model systems for 1D and 2D hetersotrtuctures, we are examining the mechanism of long-lived charge separation and H2 generation in the presence of sacrificial electron donor. The rates of carrier transport, interfacial charge (electron and hole) transfer, and charge recombination can be directly monitored by transient absorption and time-resolved fluorescence spectroscopy. In this talk, we will discuss how the rates of these elementary carrier transfer and transport processes depend on the dimension (size and length), morphology and band alignment in these materials, affect the overall H2 generation efficiency and can be optimized through rational material design.

Milling effect on the photo-activated properties of $$\hbox {TiO}_{2}$$ TiO 2 nanoparticles: electronic and structural investigations

Commercial PC105 titanium dioxide nanoparticles were studied under mechanical milling process. The effect of milling time and speed on the structural and electronic properties of $$\hbox {TiO}_{2}$$ powder was then investigated using X-ray powder diffraction (XRD), dynamic light scattering (DLS), transmission electronic microscopy (TEM), electron paramagnetic resonance (EPR) and UV–visible spectroscopy. The related photo-catalytic properties of the milled nanoparticles were probed following the degradation rate of methylene orange (MO) under UV-light irradiation and through EPR spin-scavenging approach. Comparison with pristine powder shows that milled nanoparticles are significantly less reactive upon illumination, despite decreased radius and hence, higher specific area. Such low yield of reactive species is attributed to the apparition of the amorphous $$\hbox {TiO}_{2}$$ and brookite phase upon milling, as well as increased charge carrier recombination as pointed out by the presence of sacrificial electron donor.

Solar pilot plant scale hydrogen generation by irradiation of Cu/TiO2 composites in presence of sacrificial electron donors

A Cu/TiO2 photocatalyst has been synthesised by reducing a Cu precursor with NaBH4 onto the surface of a sulphate pretreated TiO2 obtained by a sol-gel procedure. The catalyst, that shows a clearly defined anatase phase with high crystallinity and relatively high surface area, and contains Cu2O and CuO deposits on its surface, has been used to produce hydrogen in a solar driven pilot plant scale photocatalytic reactor. Different electron donor aqueous solutions (methanol, glycerol, and a real municipal wastewater treatment plant influent) have been tested showing similar or even higher energy efficiency than those obtained using more expensive noble metal based photocatalytic systems. The glycerol solutions have provided the best reactive environments for hydrogen generation.

Indirect photocatalytic reduction of arsenate to arsenite in aqueous solution with TiO 2 in the presence of hole scavengers

Abstract The indirect photocatalytic reduction of arsenate to arsenite in aqueous solution with titanium dioxide (TiO 2 ) was investigated with various hole scavengers such as methanol, ethanol, 2-propanol, formaldehyde, acetone, formic acid and acetic acid. Although the direct photocatalytic reduction of arsenate to arsenite with TiO 2 was impossible, an indirect reduction of As(V) was possible in the presence of sacrificial electron donors to form strongly reductive radicals. The addition of ethanol was very effective for indirect photocatalytic reduction of As(V) in aqueous solution with TiO 2 photocatalyst. The indirect photocatalytic reduction rate of As(V) may be related with both the reaction rate constants of reaction of hydroxyl radicals with hole scavenger and the reactivities for the radicals M which are produced by the reaction of OH with hole scavenger.

Development of Various Metal Sulfide Photocatalysts Consisting of d0, d5, and d10 Metal Ions for Sacrificial H2 Evolution under Visible Light Irradiation

We have developed metal sulfide photocatalysts with various crystal structures and constituent metal cations with d0, d5, and d10 electron configurations. Cu3VS4, Cu3NbS4, and Cu3TaS4 with a sulvanite structure, ZnGaxIn2−xS4 (x = 0–0.6), and MnGaInS4 with layered structures, BaLaCuS3 with a one-dimensionally anisotropic structure along the b-axis, and a (ZnS)0.9-(CuCl)0.1 solid solution with a zinc blende structure have arisen as new photocatalysts for H2 evolution in the presence of sacrificial electron donors under visible light irradiation.