Heterojunction synergies in titania-supported gold photocatalysts: implications for solar hydrogen production

Hierarchical TiO2 Nanoflower Photocatalysts with Remarkable Activity for Aqueous Methylene Blue Photo-Oxidation

This study systematically evaluates the performance of a series of TiO₂ nanoflower (TNF) photocatalysts for aqueous methylene blue photo-oxidation under UV irradiation. TNF nanoflowers were synthesized from Ti(IV) butoxide by a hydrothermal method and then calcined at different temperatures (T = 400-800 °C) for specific periods of time (t = 1-5 h). By varying the calcination conditions, TNF-T-t photocatalysts with diverse physicochemical properties and anatase/rutile ratios were obtained. Many of the TNF-T-1 photocatalysts demonstrated remarkable activity for aqueous methylene blue photo-oxidation at pH 6 under UV excitation (365 nm), with activities following the order TNF-700-1 > TNF-600-1 > TNF-500-1 > TNF-400-1 ∼ P25 TiO₂ ≫ TNF-800-1. The activity of the TNF-700-1 photocatalyst (99% anatase, 1% rutile) was 2.3 times that of P25 TiO₂ at pH 6 and 14.4 times that of P25 TiO₂ at pH 4. Prolonged calcination of the TNFs at 700 °C proved detrimental to dye degradation performance due to excessive rutile formation, which reduced the photocatalyst surface area and suppressed OH^• generation. The outstanding activities of TNF-700-1 and TNF-600-1 are attributed to their hierarchical nanoflower morphology which benefitted UV absorption, a near-ideal anatase crystallite size for efficient charge separation, and their unusually low isoelectric point (IEP = 4.3-4.5).

Polydimethylsiloxane Sponge-Supported Nanometer Gold: Highly Efficient Recyclable Catalyst for Cross-Dehydrogenative Coupling in Water

Polydimethylsiloxane (PDMS, a stable hydrophobic polymer material) sponge-supported nanometer-sized gold can be used as a highly efficient recyclable catalyst for cross-dehydrogenative coupling of tertiary amines with various nucleophiles in water. This PDMS sponge nanometer gold catalyst can provide much better activity than the free nanometer gold in water. The reaction can be scaled up by using an easy-to-build continuous flow reactor. These results indicate the potential application of porous hydrophobic PDMS sponge material as a promising support for highly efficient recyclable catalysts in water.

New insights into the surface plasmon resonance (SPR) driven photocatalytic H2 production of Au–TiO2

The Surface Plasmon Resonance (SPR) driven photocatalytic H₂ production upon visible light illumination (≥500 nm) was investigated on gold-loaded TiO₂ (Au–TiO₂). It has been clearly shown that the Au-SPR can directly lead to photocatalytic H₂ evolution under illumination (≥500 nm). However, there are still some open issues about the underlying mechanism for the SPR-driven photocatalytic H₂ production, especially the explanation of the resonance energy transfer (RET) theory and the direct electron transfer (DET) theory. In this contribution, by means of the EPR and laser flash photolysis spectroscopy, we clearly showed the signals for different species formed by trapped electrons and holes in TiO₂ upon visible light illumination (≥500 nm). However, the energy of the Au-SPR is insufficient to overcome the bandgap of TiO₂. The signals of the trapped electrons and holes originate from two distinct processes, rather than the simple electron–hole pair excitation. Results obtained by Laser Flash Photolysis spectroscopy evidenced that, due to the Au-SPR effect, Au NPs can inject electrons to the conduction band of TiO₂ and the Au-SPR can also initiate e⁻/h⁺ pair generation (interfacial charge transfer process) upon visible light illumination (≥500 nm). Moreover, the Density Functional Theory (DFT) calculation provided direct evidence that, due to the Au-SPR, new impurity energy levels occurred, thus further theoretically elaborating the proposed mechanisms.

The Surface Plasmon Resonance (SPR) driven photocatalytic H₂ production upon visible light illumination (≥500 nm) was investigated on gold-loaded TiO₂ (Au–TiO₂).

A novel and highly efficient earth-abundant Cu3P with TiO2 "P-N" heterojunction nanophotocatalyst for hydrogen evolution from water

Semiconductor-based photocatalytic hydrogen (H₂) evolution from water is of great importance for solar-to-chemical conversion processes to boost and promote the future hydrogen economy. Here, for the first time, we demonstrate that p-Cu₃P coupled with n-TiO₂ forms a novel hybrid structure which accelerates electron-hole pair separation and transfer for improved photocatalytic H₂-evolution activity. The rate of H₂ evolution of the optimized Cu₃P/TiO₂ (7940 μmol h^-1 g^-1) is 11 times higher than that of bare TiO₂, with an apparent quantum efficiency (AQE) of 4.6%. This work may provide more insight into the synthesis of novel phosphide-based hybrid materials with high photocatalytic H₂-evolution activity and sufficient stability for solar-to-chemical conversion and utilization.

Fabrication of 3 D Mesoporous Black TiO2 /MoS2 /TiO2 Nanosheets for Visible-Light-Driven Photocatalysis

A novel 3 D mesoporous black TiO2 (MBT)/MoS2 /MBT sandwich-like nanosheet was successfully fabricated using a facile mechanochemical process combined with an in situ solid-state chemical reduction approach, followed by mild calcination (350 °C) under an argon atmosphere. The MBT/MoS2 /MBT exhibits a 3 D sandwich-like nanosheet structure and heterojunctions are formed at the interfaces between MoS2 and black TiO2 . The significantly narrowed band gap of MBT/MoS2 /MBT is attributed to the introduction of MoS2 and the formed Ti(3+) species in the frameworks. The visible-light photocatalytic degradation rate of methyl orange and the hydrogen production rate are as high as 89.86 % and 0.56 mmol h(-1)  g(-1) , respectively. The introduction of MoS2 and Ti(3+) in the frameworks favors the visible-light absorption and the separation of photogenerated charges, and the 3 D sandwich-like heterojunction structure facilitates the transfer of photogenerated charges.

Photodegradation of estrogenic endocrine disrupting steroidal hormones in aqueous systems: Progress and future challenges

This article reviews different photodegradation technologies used for the removal of four endocrine disrupting chemicals (EDCs): estrone (E1), 17β-estradiol (E2), estriol (E3) and 17α-ethinylestradiol (EE2). The degradation efficiency is greater under UV than visible light; and increases with light intensity up to when mass transfer becomes the rate limiting step. Substantial rates are observed in the environmentally relevant range of pH7-8, though higher rates are obtained for pH above the pKa (~10.4) of the EDCs. The effects of dissolved organic matter (DOM) on EDC photodegradation are complex with both positive and negative impacts being reported. TiO2 remains the best catalyst due to its superior activity, chemical and photo stability, cheap commercial availability, capacity to function at ambient conditions and low toxicity. The optimum TiO2 loading is 0.05-1gl(-1), while higher loadings have negative impact on EDC removal. The suspended catalysts prove to be more efficient in photocatalysis compared to the immobilised catalysts, while the latter are considered more suitable for commercial scale applications. Photodegradation mostly follows 1st or pseudo 1st order kinetics. Photodegradation typically eradicates or moderates estrogenic activity, though some intermediates are found to exhibit higher estrogenicity than the parent EDCs; the persistence of estrogenic activity is mainly attributed to the presence of the phenolic moiety in intermediates.