Photocatalytic Water Reduction Research Articles

Prolonged electron lifetime in sulfur vacancy-rich ZnCdS nanocages by interstitial phosphorus doping for photocatalytic water reduction

Sulfur vacancy-rich ZnCdS nanocages with interstitial P dopant atoms were fabricated. The promoted Fermi level caused by interstitial P doping facilitates the S vacancy level to be an effective electron trapping center, thus enhancing the photocatalytic performance.

Nitrogen-doped LaZrTa3O11 as a visible light-active photocatalyst for water-reduction and -oxidation reactions

Nitrogen doping red-shifted the absorption edge of LaZrTa3O11 markedly and induced visible-light activity for photocatalytic water-reduction and -oxidation reactions.

Highly efficient hydrogen generation in water using 1D CdS nanorods integrated with 2D SnS2 nanosheets under solar light irradiation

The development of low-cost and noble-metal-free catalysts for the photoconversion of water into hydrogen (H2) is of great interest. Here, 2D tin(IV) sulfide (SnS2) ultrathin nanosheets as co‐catalysts are coupled with 1D cadmium sulfide (CdS) nanorods for the photosplitting of water into H2. The design of the catalyst can facilitate the passivation of the physiochemical properties of CdS and enhance H2 evolution activity. The prepared CdS/SnS2 composite catalyst increases the H2 generation activity and exhibits excellent and continuous long-term photostability. The H2 evolution rate of the optimized CdS/SnS2 composite is approximately 9-fold that of pristine CdS nanorods. The characterization results of the CdS/SnS2 composite reveal that the loading of SnS2 can enhance the synergistic effects of the photocatalyst due to the effective separation, large number of exposed catalytic sites, and highly dispersed nature of the layered SnS2. Several characterization outcomes of CdS/SnS2 are examined in detail (e.g., structural and surface elemental results of transmission electron microscopy, X-ray diffraction analysis, X-ray photoelectron spectroscopy). Further, the optoelectrical properties and charge-carrier excitations are investigated via ultraviolet diffuse reflectance spectroscopy, photoluminescence spectroscopy, and photoelectrochemical analysis. The proposed CdS/SnS2 composite is a promising low-cost, noble-metal-free, and high-efficiency catalyst for the photocatalytic water-reduction reaction.

Hydrogen producing water treatment through mesoporous TiO2 nanofibers with oriented nanocrystals

The development of well-defined TiO2 nanoarchitectures is a versatile strategy to achieve high-efficiency photocatalytic performance. In this study, mesoporous TiO2 nanofibers consisting of oriented nanocrystals were fabricated by a facile vapothermal-assisted topochemical transformation of preformed H-titanate nanobelts. The vapothermal temperature is crucial in tuning the microstructures and photocatalytic redox properties of the resulting mesoporous TiO2 nanofibers. The microstructures were characterized with XRD, TEM, XPS and nitrogen adsorption-desorption isotherms, etc. The photocatalytic activities were evaluated by photocatalytic oxidation of organic pollutant (Rhodamine B as an example) as well as photocatalytic reduction of water to generate hydrogen (H2). The nanofibers vapothermally treated at 150°C showed the highest photocatalytic activity in both oxidation and reduction reactions, 2 times higher than that of P25. The oriented alignment and suitable mesoporosity in the resulting nanofiber architecture were crucial for enhancing photocatalytic performances. The oriented alignment of anisotropic anatase nanocrystals shall facilitate faster vectorial charge transportation along the nanofibers architecture. And, the suitable mesoporosity and high surface area would also effectively enhance the mass exchange during photocatalytic reactions. We also demonstrate that efficient energy-recovering photocatalytic water treatments could be accomplished by a cascading oxic-anoxic process where the dye is degraded in the oxic phase and hydrogen is generated in the successive anoxic phase. This study showcases a novel and facile method to fabricate mesoporous TiO2 nanofibers with high photocatalytic activity for both clean energy production and environmental purification.

The photoluminescence properties and latent photocatalytic hydrogen evolution application of AlN:Eu3+

Eu3+-activated AlN phosphors with hexagonal wurtzite structures were successfully prepared by a low-cost, nontoxic and simple solid-state route at 880 °C which is lower than many other synthesis temperatures. The structure and phase formation, morphology, elements analysis, photoluminescence and photocatalysis properties are investigated in detail. All the phosphors present red emission due to 5D0→7F2 transition of Eu3+. The optimal doping concentration of Eu3+ in AlN matrix is 0.8% mole fraction, and the phosphors exhibit high color purity and high brightness. Meanwhile, AlN:xEu3+ phosphors exhibit excellent photocatalytic hydrogen evolution activity, and the maximum rate of H2 evolution from water splitting is 77 μmol h−1 g−1. These findings signify that bifunctional AlN:Eu3+ with photoluminescence and photocatalytic properties may be anticipated to apply in both white light-emitting diodes (WLEDs) and photocatalytic water reduction.

Supramolecular Anchoring of Octahedral Molybdenum Clusters onto Graphene and Their Synergies in Photocatalytic Water Reduction.

Dihydrogen (H2) production from sunlight should become one of the most important energy production means in the future. To reach this goal, low-cost and efficient photocatalysts still need to be discovered. Here we show that red near-IR luminescent metal cluster anions, once combined with pyrene-containing cations, are able to photocatalytically produce molecular hydrogen from water. The pyrene moieties act simultaneously as energy transmitters and as supramolecular linkers between the cluster anions and graphene. This association results in a hybrid material combining the emission abilities of pyrene and cluster moieties with the electronic conduction efficiency of graphene. Hydrogen evolution reaction (HER) studies show that this association induces a significant increase of H2 production compared to that produced separately by clusters or graphene. Considering the versatility of the strategy described to design this photocatalytic hybrid material, transition-metal clusters are promising candidates to develop new, environmentally friendly, and low-cost photocatalysts for HER.

Preparation of Zn0.5Cd0.5S@Ni-Glycerate composite for photocatalytic water reduction

Large specific surface is beneficial to improve the performance of catalyst in the application of water photolysis. In this work, we designed and successfully prepared the metal compound Ni-Glycerate with a large specific surface area, and combined it with Zn0.5Cd0.5S to form Zn0.5Cd0.5S@Ni-Glycerate core-shell structure nanocomposites. It was revealed that the introduction of nickel-glycerate can promote the separation of photoinduced charges and accelerate the photocatalytic water decomposition reaction. The optimized H2 production rate on Zn0.5Cd0.5S@Nickel-glycerate (3%) can reach 2800 μmol/h/0.1 g, about 6 times that of pure Zn0.5Cd0.5S. This work indicates that the sulfide-metal organic complex can play a synergistic role in the entire photocatalytic reaction.

Development of a bismuth-based metal-organic framework for photocatalytic hydrogen production

A novel 3D bismuth-organic framework (called Bi-TBAPy) single crystal was synthesized by employing 1,3,6,8-tetrakis(p-benzoic acid)pyrene (H 4 TBAPy) as an organic linker. The study demonstrates that the Bi-TBAPy not only possesses good chemical stability and suitable band edge positions for promising photocatalytic H 2 evolution, but it also exhibits a typical ligand-to-metal charge transfer for favorable charge separation. The photocatalytic H 2 evolution rates on the as-obtained Bi-TBAPy with different cocatalysts modified were examined with triethanolamine as the sacrificial reagent. Based on this, the hydrogen evolution rate of 140 μmol h −1 g −1 was obtained on the optimized sample with a loading of 2 wt % Pt as a cocatalyst. To the best of our knowledge, this is the first bismuth-based metal-organic framework (MOF) that functions as an effective photocatalyst for photocatalytic water reduction. Our study not only adds a new member to the family of photocatalyst materials, but also reveals the importance of cocatalyst modification in improving photocatalytic activity of MOFs. A new 3D bismuth-organic framework (Bi-TBAPy) with ligand-to-metal charge transfer (LMCT) process was synthesized to exhibit for the first time robust photocatalytic water reduction, demonstrating its promising future in solar energy conversion.

In situ decomposition-thermal polymerization method for the synthesis of Au nanoparticle–decorated g-C3N4 nanosheets with enhanced sunlight-driven photocatalytic activity

Plasmonic Au nanoparticle (NP)–decorated g-C3N4 nanosheets were synthesized by a direct in situ decomposition-thermal polymerization method with dicyandiamide and gold chloride trihydrate (HAuCl4·3H2O) as the precursors. Au NPs were closely anchored on the surface of g-C3N4 with high dispersion, and Au/g-C3N4 composites showed strong surface plasmon resonance in the visible light region. The photocurrent density of Au/g-C3N4 composite with 1 wt% Au (0.32 μA/cm2) was 6.3 times higher than that of pure g-C3N4 (0.05 μA/cm2) under simulated sunlight irradiation. The 1 wt% Au/g-C3N4 composite exhibited improved activity in the photodegradation of organic dyes under natural sunlight and enhanced photocatalytic water reduction performance under simulated sunlight illumination due to the uniform distribution of Au NPs and heterostructure at the interface of Au/g-C3N4. This work provided a new platform for the preparation of metal/g-C3N4 to replace traditional photoreduction or chemical reduction method.

Solar-Light Harvesting Bimetallic Ag/Au Decorated Graphene Plasmonic System with Efficient Photoelectrochemical Performance for the Enhanced Water Reduction Process

Nowadays, surface plasmon resonance (SPR) induced hot-electron transfer from noble metals to host materials has been a widely used concept in solar energy conversion. On the other hand, the development of graphene-based photocatalytic systems for photocatalytic water reduction has attracted tremendous interest. In the present article, we develop a novel efficient photocatalytic system for clean energy production, i.e., semiconductor-free, solar-light harvesting graphene sensitized Ag/Au-bimetallic plasmonic system, by cost-effective and eco-friendly one-pot in situ green reduction process. Here, graphene oxide (GO) reduced well under the reflux conditions approximately at 90 °C with vitamin C, and simultaneously the Ag and Au nanoparticles (NPs) deposited on the graphene sheet. The reduction of GO to graphene and deposition of an alloy of Ag and Au nanoparticles on graphene sheet have been analyzed by UV–vis and PXRD. These results revealed that bimetallic Ag/Au-graphene has all the characteristic peaks o...

Rational design of Z-scheme PtS-ZnIn2S4/WO3-MnO2 for overall photo-catalytic water splitting under visible light

ZnIn2S4/WO3 nanocomposites, with ZnIn2S4 nanosheets loaded on WO3 nanorods, were synthesized by self-assembly of hexagonal ZnIn2S4 in the presence of preformed WO3·H2O nanoplates. PtS and MnO2, the co-catalysts for H2 and O2 evolution, respectively, were selectively loaded on ZnIn2S4 and WO3 in the nanocomposites. The resultant PtS-ZnIn2S4/WO3-MnO2 nanocomposites show photocatalytic activity for overall water splitting to produce H2 and O2 under visible light. An optimum activity was achieved over 0.5%PtS-20%ZnIn2S4/WO3-3.0%MnO2, in which 5.94 μmol of H2 and 2.24 μmol O2 were evolved in 8 h. The apparent quantum yield (AQY) for H2 evolution was determined to be ca. 0.50% at 420 nm. The superior photocatalytic activity for overall water splitting over PtS-ZnIn2S4/WO3-MnO2 nanocomposites can be ascribed to an efficient coupling of photocatalytic water reduction over PtS-ZnIn2S4 and photocatalytic water oxidation over MnO2-WO3 via a Z-scheme charge transfer pathway. This study demonstrates a high potential of fabrication of the all-solid Z-scheme photocatalytic systems for overall water splitting.

Boosting the performance of visible light‐driven WO 3 /g‐C 3 N 4 anchored with BiVO 4 nanoparticles for photocatalytic hydrogen evolution

In this article, a ternary WO3/g-C3N4@ BiVO4 composites were prepared using eco-friendly hydrothermal method to produce efficient hydrogen energy through water in the presence of sacrificial agents. The prepared samples were characterized by scanning electron microscopy (SEM), scanning transmission electron microscopy (STEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), ultraviolet-visible (UV-vis), Brunauer-Emmett-Teller (BET) surface area, and photoluminescence spectroscopy (PL) emission spectroscopy. The experimental study envisages the formation of 2-D nanostructures and observed that such kinds of nanostructures could provide more active sites for photocatalytic reduction of water and their inherent reactive-species mechanism. The results showed the excellent photocatalytic performance (432 μmol h−1 g−1) for 1.5% BiVO4 nanoparticles in WO3/g-C3N4 composite when compared with pure WO3 and BiVO4. The optical properties and photocatalytic activity measurement confirmed that BiVO4 nanoparticles in WO3/g-C3N4 photocatalyst inhibited the recombination of photogenerated electron and holes and enhanced the reduction reactions for H2 production. The enhanced photocatalytic efficiency of the composite nanostructures may be attributed to wide absorption region of visible light, large surface area, and efficient separation of electrons/holes pairs owing to synergistic effects between BiVO4 and WO3/g-C3N4. The prepared samples would be a precise optimal photocatalyst to increase their suppliers for worldwide applications especially in energy harvesting.

Improved Electro- and Photocatalytic Water Reduction by Confined Cobalt Catalysts in Streptavidin

Incorporation of biotinylated aminopyridine cobalt complexes derived from the triazacyclononane scaffold into the streptavidin protein leads to formation of artificial metalloenzymes for water redu...

Dye activation of heterogeneous Copper(II)-Species for visible light driven hydrogen generation

Heterogeneous Cu catalysts are widely used in photocatalytic hydrogen generation. The typical working mode includes the transfer of photo-induced charges from a semiconductor to CuO which itself is reduced to Cu2O to initiate the catalytic cycle. In this contribution a photosensitizer (dye), excited by visible light absorption, was used to transfer an electron to the CuO which after reduction catalyzes the water reduction to hydrogen. Several copper(II)-catalysts on high surface silica were prepared by impregnation or precipitation and applied in photocatalytic water reduction. The best catalyst CuO(Cl0.1)/SiO2, synthesized via incipient wetness impregnation of CuCl2 in MCM-41 and a following precipitation with NaOH, achieved a 6 times higher activity (1702 mmol h−1 g−1) compared to a previously investigated copper system (280 mmol h−1 g−1 for CuI) under the same reaction conditions. All materials were fully characterized by XRD, TEM and N2 sorption and further by magnetic resonance and X-ray methods EPR, ASAXS and XAS. In situ measurements evidenced a reduction of the initial Cu(II)-species, which confirms the (proposed) photocatalytic mechanism.

Visible light driven photocatalytic H2 generation property of trigonal ZnIn2S4 prepared by high temperature solid state reaction

For the first time, we prepared the trigonal ZnIn2S4 (in the space group R-3m) by typical solid state reaction at 700 °C in an evacuated quartz tube. It has a high crystallinity indicated by sharp reflection peaks in X-ray diffraction pattern, and its suitable band structure ensure the visible light driven photocatalytic H2 generation in Na2S and Na2SO3 aqueous solution. The as-prepared ZnIn2S4 possesses a constant photocatalytic H2 generation rate of ∼32 μmol/g/h after 5 cycles, which could be significantly enhanced to 1582 μmol/g/h by co-loading 0.5 wt% Pt and 0.5 wt% Pd. By varying the incident beam intensity, the apparent quantum yield of photocatalytic water reduction was evaluated and optimized to 3.57(1)% at 405 nm.

Construction of two dimensional Sr2Ta2O7/S-doped g-C3N4 nanocomposites with Pt cocatalyst for enhanced visible light photocatalytic performance

Visible light-driven photocatalytic hydrogen production has been deemed a potential means to solve the increasingly serious energy shortage problem. Herein, two dimensional (2D) Sr2Ta2O7/S-doped g-C3N4 nanocomposites that applied in photocatalytic water reduction were fabricated through thermal condensation of thiourea with hydrothermal-prepared Sr2Ta2O7. The resulted Sr2Ta2O7/S-doped g-C3N4 nanocomposite exhibited enhanced hydrogen evolution rate (11.36 μmol g−1 h−1) under visible light irradiation, which is about 3.5 times higher than that of pure S-doped g-C3N4. In light of the UV–vis diffuse reflectance spectroscopy, Mott-Schottky curve and photoluminescence spectra, the enhanced photocatalytic performance could be mainly attributed to the conduction band difference between Sr2Ta2O7 and S-doped g-C3N4. In addition, transient photoluminescence spectra, electrochemical impedance spectra and photocurrent responses proved that the presence of Pt cocatalyst also plays an important role in facilitates the transport of photoexcited electron-hole pairs, subsequently promoting the photocatalytic performance.

Isoelectric point-controlled preferential photodeposition of platinum on Cu2O-TiO2 composite surfaces

Photodeposition emerges as a convenient method to synthesize metal particles on semiconductor supports. In this work, we study the photodeposition of Pt on Cu2O-TiO2 composite surfaces employing H2PtCl6 aqueous solution as the precursor and reveal a key role of isoelectric point of oxide surfaces on the Pt photodeposition process. Under the photodeposition conditions, Pt metal particles are facilely photodeposited on TiO2 support; on Cu2O-TiO2 composite supports, the Cu2O surface is positively charged and enriched with photo-excited holes while the TiO2 surface is negatively charged and enriched with photo-excited electrons. This lead to the preferential adsorption of PtCl62− anion precursor on the Cu2O surface of Cu2O-TiO2 composite and the dominant formation of Pt oxide particles on Cu2O surface but few Pt metal particles on TiO2 surface. Consequently, the activity of resulting Pt/Cu2O-TiO2 composite photocatalysts in photocatalytic water reduction decreases as the Cu2O content increases. These results deepen the understanding of photodeposition processes on oxide composite surfaces.

Enhanced light harvesting and electron-hole separation for efficient photocatalytic hydrogen evolution over Cu7S4-enwrapped Cu2O nanocubes

P-type Cu2O is an advantageous photocatalyst as the appropriate bandgap structure and low-cost. However, poor photocatalytic and instability of such promising material is still a great challenge. Here the core-shell Cu7S4-coated Cu2O nanocubes (Cu2O/Cu7S4 NCs) were successfully synthesized by solution method coupled with anion exchange, and were firstly employed to hydrogen evolution reaction (HER). The resultant integrated structure of Cu2O/Cu7S4 NCs exhibited apparent improved photocatalytic hydrogen evolution activity compared with Cu2O photocatalyst. Particularly, Cu2O/Cu7S4 NCs had a high hydrogen production rate of 1689.00 μmol g−1 h−1 under full spectra irradiation with additive of Na2SO3, which was higher than that of Cu2O NCs with a factor of 1.71 times. Excellent synergistic effect of Cu2O and Cu7S4 can be responsible for the improved hydrogen evolution properties, namely, the presence of Cu7S4 with localized surface plasma resonance (LSPR) can promote the photogenerated electrons transfer from the Cu2O surface, prolong the photogenerated holes lifetime, accelerate the separation of photogenerated electrons and holes, and ameliorate the photoelectric properties of semiconductors. The in situ formed multifunctional Cu7S4 layer offers a promising avenue to design photocathodes rationally for photocatalytic water reduction.

Highly efficient H2 production over NiCo2O4 decorated g-C3N4 by photocatalytic water reduction

Herein, ternary nickel cobalt oxide (NiCo2O4) was firstly employed to increase the photocatalytic water reduction ability of g-C3N4. 17.5 wt%-NiCo2O4/g-C3N4 shows excellent water splitting performance with a H2 production rate of 5480 μmol h−1 g−1, which is extremely better than that of Co3O4, NiO, Pt modified g-C3N4. The quantum efficiency of 17.5 wt%-NiCo2O4/g-C3N4 can reach 4.5% under 400 (±7.5) nm light irradiation. The greatly increased activity of 17.5 wt%-NiCo2O4/g-C3N4 can be attributed to the richer active sites and the superior electrical performance provided by co-existing nickel and cobalt ions with multivalent state. Moreover, the activity of composite almost shows no significant weaken even after 20 h irradiation. A Z-scheme route was put forwarded for H2 production over NiCo2O4/g-C3N4 instead of the traditional p-n junction based on our study.

Direct evidence for hydrated protons as the active species in artificial photocatalytic water reduction into hydrogen

Photocatalytic water reduction to hydrogen over oxide semiconductors is one of the most extensively investigated artificial photocatalytic reactions, but the nature of the active species has not yet been elucidated. Here, we successfully prepared Pt/rutile TiO2(110) surfaces with hydrated proton species via co-adsorption of hydrogen and water and observed the photocatalytic reduction of hydrated protons to H2 upon UV light illumination. These results provide experimental evidence to prove hydrated protons as the active species for photocatalytic water reduction to hydrogen and demonstrate the occurrence of photocatalytic reduction of hydrated protons to H2 within the H-bonding network on the catalyst surface instead of directly on the catalyst surface. The Pt-TiO2 interface is capable of dissociating water to form hydroxyl groups that facilitate the formation of H-bonding network on the catalyst surface to enhance the photocatalytic H2 production. Our results greatly advance fundamental understanding of artificial photocatalytic water reduction.