Cu2O precipitation-assisted with ultrasound and microwave radiation for photocatalytic hydrogen production

Copper oxides are considered efficient photocatalysts for H₂ generation. In addition, due to their interesting properties such as surface plasmon resonance, they are applied in photo-induced reactions. In heterogeneous photocatalysis, CuO and Cu₂O are the main oxides based in copper that are used as catalysts in water splitting. In this work, Cu₂O is prepared by precipitation method assisted with ultrasound and microwave radiation at 80 °C. For the Cu₂O synthesis, the use of glucose is proposed as a reducing agent due to its abundance in nature, non-toxicity, and low cost. According to the results obtained, the highest glucose concentration and the suspension exposure to microwave irradiation promote the formation of Cu₂O particles with low and homogeneous particle size and a convenient position of their conduction and valence band to produce H₂. The highest H₂ generation using Cu₂O under the aforementioned experimental conditions is 78 μmol g_cat^?1. Additionally, the effect of adding glucose in the photocatalytic reaction is studied in order to provide more electrons to the reaction due to its effect as a hole scavenger, which inhibits the recombination of the electron and hole, promoting a higher H₂ production (400 μmol g_cat^?1).     

A transparent electrode with water-oxidizing activity

Hydrogen production by water splitting is a promising method to store energy. Water-oxidation reaction is a bottleneck in water-splitting systems. Herein, a mononuclear nickel(II) phosphine complex with 1,2-bis(dicyclohexylphosphino)ethane ligand, was synthesized and characterized by X-ray crystallography method. The water-oxidizing catalyst under the electrochemical condition was studied. The role of Ni compound for the water-oxidation reaction on the surface of fluorine-doped tin oxide as one of the true catalysts was investigated by the electrochemical methods and Scanning Electron Microscopy coupled with Energy Dispersive X-ray (SEM/EDX) Spectroscopy. The big ligand around the Ni ion causes a very small size of Ni-based particles on the surface of the electrode, which are the active catalysts for the water-oxidation reaction. Such small nanosized Ni-based compounds are transparent and have no effect on the transparency of the obtained fluorine-doped tin oxide. Thus, it is a promising method to synthesize a transparent fluorine-doped tin oxide with water-oxidizing activity.     

Influence of the reduction of graphene oxide (rGO) on the structure and photoactivity of CdS-rGO hybrid systems

Solvothermal and chemical reduction of graphene oxide with N₂H₄ or HI affect the surface composition, rupture and delamination degree of reduced graphene oxide (rGO). Higher reduction and stacking of rGO was achieved by chemical reduction with HI, while solvothermal reduction and, especially, the chemical reduction with N₂H₄ lead to higher delamination of rGO. The incorporation of the different rGO to CdS implies changes in the characteristics and photoactivity of the CdS-rGO hybrids. A promoter effect was observed in all CdS-rGO hybrids respect to the photoactivity of bare CdS, observing the better photoactivity on the hybrid in which the graphene oxide was reduced with HI (CdS-rGO/HI). The variations in the photoactivity of CdS-rGO hybrids are analyzed in terms of changes in the structure, surface and light absorption ability of CdS and also analyzing the contact of CdS with rGO. The greater concentration of small CdS nanostructures with strong quantum confinement is in the origin of the enhancement in photoactivity observed in the CdS-rGO/HI hybrid.     

Enhanced Z-scheme visible light photocatalytic hydrogen production over α-Bi2O3/CZS heterostructure

Depletion of fossil fuels and associated environmental issues has drawn attention of researchers to renewable energy resources and photocatalytic hydrogen production is considered to be safe and applicable method to meet future energy demand. Herein, we have used α-Bi₂O₃ nanorods for loading CZS (Cd_0.5Zn_0.5S) to form a heterostructure for photocatalytic H₂ production. The α-Bi₂O₃/CZS heterostructure was characterized through TEM, Elemental Mapping, XRD and XPS analysis. The α-Bi₂O₃/CZS heterostructure shows photocatalytic H₂ production rate of 254.1 μmol h^?1 with apparent quantum yield of 6.8% (λ = 420 nm). The enhanced photocatalytic performance was supported by transient photocurrent response curves and electrochemical impedance spectroscopy (EIS) results which suggest the efficient charge separation and electron mobility in α-Bi₂O₃/CZS heterostructure. The intimate contact formed between α-Bi₂O₃ nanorods and CZS nanoparticles responsible for the efficient flow of electrons following a Z-scheme pattern resulting in higher photocatalytic H₂ production. Moreover, the as-synthesized α-Bi₂O₃/CZS heterostructure shows negligible loss of activity after 4 consecutive recycling cycles. Our findings open new possibilities for the design of heterostructure based photocatalysts.     

Mesocrystalline Ta2O5 nanosheets supported PdPt nanoparticles for efficient photocatalytic hydrogen production

We successfully synthesized mesocrystalline Ta₂O₅ nanosheets supported bimetallic PdPt nanoparticles by the photo-reduction method. The as-prepared mesocrystalline Ta₂O₅ nanosheets in this work showed amazing visible-light absorption, mainly because of the formation of oxygen vacancy defects. And the as-prepared bimetallic PdPt/mesocrystalline Ta₂O₅ nanaosheets also showed highly enhanced UV–Vis light absorption and highly improved photocatalytic activity for hydrogen production in comparison to that of commercial Ta₂O₅, mesocrystalline Ta₂O₅ nanosheets, Pd/mesocrystalline Ta₂O₅ nanosheets and Pt/mesocrystalline Ta₂O₅ nanosheets. The highest photocatalytic hydrogen production rate of PdPt/mesocrystalline Ta₂O₅ nanaosheets was 21529.52 g^?1 h^?1, which was about 21.2 times of commercial Ta₂O₅, and the apparent quantum efficiency of PdPt/mesocrystalline Ta₂O₅ nanaosheets for hydrogen production was about 16.5% at 254 nm. The highly enhanced photocatalytic activity was mainly because of the significant roles of PdPt nanoparticles for accelerating the charge separation and transport upon illumination. The as-prepared PdPt/mesocrystalline Ta₂O₅ nanaosheets in this work could serve as an efficient photocatalyst for green energy production.     

MoS2 “inorganic fullerenes” combined with TiO2 in water-methanol suspensions: Highly active hydrogen production photo catalysts operating via transfer of accumulated electrons

Water-methanol suspensions of size-tuned hollow MoS₂ “inorganic fullerenes” (IF) combined with high surface area anatase TiO₂ efficiently promote photo catalytic hydrogen evolution reaction (PHER). Despite low amount of the MoS₂ slabs edges in the structure of closed-shell IF-MoS₂ particles and relatively poor dispersion of co-catalyst, the best composite catalysts were nearly 50% as active as Pt/TiO₂ benchmark and considerably more active than the reference MoS₂–TiO₂ catalysts containing highly dispersed MoS₂ slabs. Straightforward experimental evidence is given that hydrogen can be formed due to transfer of stored (accumulated) electrons from TiO₂ to the IF-MoS₂ particles in liquid suspension. Electrochemical flat band potential measurements support the possibility of electrons transfer from TiO₂ to IF-MoS₂.     

Hydrogen production from glucose degradation in water and wastewater treated by Ru-LaFeO3/Fe2O3 magnetic particles photocatalysis and heterogeneous photo-Fenton

An optimized Ru-doped LaFeO₃ photocatalyst was coupled with magnetic Fe₂O₃ particles and was tested in the photocatalytic hydrogen production from glucose degradation under visible light irradiation. The catalysts were successfully synthesized by solution combustion synthesis using citric acid as organic fuel. Complete glucose degradation and hydrogen production of 5460 μmol/L was obtained after 4 h of irradiation using composite containing 67 wt% of Ru-doped LaFeO₃. After seven cycles of reuse, the photocatalytic activity did not change, evidencing the high stability of the magnetic photocatalyst, which can be recovered from the photoreactor using an external magnetic force. The recyclable sample was finally tested in the treatment of real wastewater from cherries washing process, and a very high hydrogen production (12344 μmol/L) was achieved. Finally, the possibility to couple the photocatalytic process (used for the production of hydrogen) with a heterogeneous photo-Fenton process was investigated in order to mineralize the unconverted organics in the wastewater coming from the photoreactor.     

Design and preparation of CdS/H-3D-TiO2/Pt-wire photocatalysis system with enhanced visible-light driven H2 evolution

In recent years, tremendous efforts have been devoted to develop new photocatalyst with wide spectrum response for H₂ generation from water or aqueous solution. In this work, CdS nanoparticles (NPs) have been immobilized on hydrogenated three-dimensional (3D) branched TiO₂ nanorod arrays, resulting in a highly efficient photocatalyst, i.e, CdS/H-3D-TiO₂. In addition, electrochemical reduction of H⁺ ion is identified as a limiting step in the photocatalytic generation of H₂ at this catalyst, while here a Pt wired photocatalysis system (CdS/H-3D-TiO₂/Pt-wire) is designed to overcome this barrier. Without the application of potential bias, visible light photocatalytic hydrogen production rate of CdS/H-3D-TiO₂/Pt-wire is 18.42 μmol cm^?2 h^?1, which is 11.2 times that of CdS/H-3D-TiO₂ without Pt (1.64 μmol cm^?2 h^?1). The Pt wire acts as an electron super highway between the FTO substrate and H⁺ ions to evacuate the generated electrons to H⁺ ions and catalyze the reduction reaction and consequently generate H₂ gas. This work successfully offers a novel direction for dramatic improvement in H₂ generation efficiency in photocatalysis field.     

New insights in the performance and reuse of rGO/TiO2 composites for the photocatalytic hydrogen production

The viability of the photocatalytic hydrogen production is closely related to the performance and long term stability of the photocatalyst. In this work rGO/TiO₂ composites have been synthetized with graphene oxide (GO) ratios from 1% to 10% and experimentally assessed towards hydrogen generation from methanol solutions. The performance of the composite with 2% of rGO (2 GT) has been compared to bare TiO₂ working with 20% volume methanol solution. The hydrogen production initial rate showed similar values with both photocatalysts decreasing after about 24 h. Further analysis of the photocatalytic process at longer times showed the negative influence of hydrogen accumulation in the reaction system. Thus, an experimental procedure with argon purge was developed and the behavior of TiO₂ and 2 GT photocatalysts was compared. It is concluded that TiO₂ keeps its activity after 8 operation cycles while 2 GT performance reduces progressively. This can be attributed to the further reduction of GO and the increase of defects in its structure.