Controlled growth of ultrasmall Cu2O clusters on TiO2nanoparticles by atmospheric-pressure atomic layer deposition for enhanced photocatalytic activity

This work presents a gas-phase approach for the synthesis of Cu₂O/TiO₂powder-based photocatalysts using atomic layer deposition (ALD). The process is carried out in a fluidized bed reactor working at atmospheric pressure using (trimethylvinylsilyl)-hexafluoroacetulacetonate copper(I) as the Cu-precursor and H₂O vapor as the oxidizer. The saturating regime of the chemical reactions and the linear growth of ALD are achieved. In combination with the unsaturated regime, the ALD approach enables the deposition of ultrasmall Cu₂O clusters with average diameters in the range of 1.3-2.0 nm, narrow particle size distributions and tunable Cu₂O loadings on P25 TiO₂nanoparticles. The photocatalytic performance of Cu₂O/TiO₂photocatalysts is investigated by the degradation of organic dyes, including Rhodamine B (RhB), methyl orange, and methylene blue; the results demonstrate that the surface modification of TiO₂nanoparticles by Cu₂O nanoclusters significantly enhances the photocatalytic activity of TiO₂. This is attributed to the efficient charge transfer between Cu₂O and TiO₂that reduces the charge recombination. The photocatalytic reaction mechanism is further investigated for the degradation of RhB, revealing the dominating role of holes, which contribute to both direct hole oxidation and indirect oxidation (i.e. via the formation of hydroxyl radicals). Our approach provides a fast, scalable and efficient process to deposit ultrasmall Cu₂O clusters in a controllable fashion for surface engineering and modification.

Cu Nanocluster-Loaded TiO2 Nanosheets for Highly Efficient Generation of CO-Free Hydrogen by Selective Photocatalytic Dehydrogenation of Methanol to Formaldehyde

Safe storage and transportation of H₂ is a fundamental requirement for its wide applications in the future. Controllable release of high-purity H₂ from a stable storage medium such as CH₃OH before use offers an efficient way of achieving this purpose. In our case, Cu nanoclusters uniformly dispersed onto (001) surfaces of TiO₂ nanosheets (TiO₂/Cu) are selectively prepared by thermal treatment of HKUST-1 loaded TiO₂ nanosheets. One of the TiO₂/Cu composites, TiO₂/Cu_50, exhibits remarkably high activity toward the selective dehydrogenation of CH₃OH to HCHO with a H₂ evolution rate of 17.8 mmol h^-1 per gram of catalyst within a 16-h photocatalytic reaction (quantum efficiency at 365 nm: 16.4%). Theoretical calculations reveal that interactions of Cu nanoclusters with TiO₂ could affect their electronic structures, leading to higher adsorption energy of CH₃OH at Ti sites and a lower barrier for the dehydrogenation of CH₃OH by the synergistic effect of Cu nanoclusters and TiO₂, and lower Gibbs free energy for desorption HCHO and H₂ as well.

Charge Carrier Processes and Optical Properties in TiO2 and TiO2-Based Heterojunction Photocatalysts: A Review

Photocatalysis based technologies have a key role in addressing important challenges of the ecological transition, such as environment remediation and conversion of renewable energies. Photocatalysts can in fact be used in hydrogen (H₂) production (e.g., via water splitting or photo-reforming of organic substrates), CO₂ reduction, pollution mitigation and water or air remediation via oxidation (photodegradation) of pollutants. Titanium dioxide (TiO₂) is a “benchmark” photocatalyst, thanks to many favorable characteristics. We here review the basic knowledge on the charge carrier processes that define the optical and photophysical properties of intrinsic TiO₂. We describe the main characteristics and advantages of TiO₂ as photocatalyst, followed by a summary of historical facts about its application. Next, the dynamics of photogenerated electrons and holes is reviewed, including energy levels and trapping states, charge separation and charge recombination. A section on optical absorption and optical properties follows, including a discussion on TiO₂ photoluminescence and on the effect of molecular oxygen (O₂) on radiative recombination. We next summarize the elementary photocatalytic processes in aqueous solution, including the photogeneration of reactive oxygen species (ROS) and the hydrogen evolution reaction. We pinpoint the TiO₂ limitations and possible ways to overcome them by discussing some of the “hottest” research trends toward solar hydrogen production, which are classified in two categories: (1) approaches based on the use of engineered TiO₂ without any cocatalysts. Discussed topics are highly-reduced “black TiO₂”, grey and colored TiO₂, surface-engineered anatase nanocrystals; (2) strategies based on heterojunction photocatalysts, where TiO₂ is electronically coupled with a different material acting as cocatalyst or as sensitizer. Examples discussed include TiO₂ composites or heterostructures with metals (e.g., Pt-TiO₂, Au-TiO₂), with other metal oxides (e.g., Cu₂O, NiO, etc.), direct Z-scheme heterojunctions with g-C₃N₄ (graphitic carbon nitride) and dye-sensitized TiO₂.

Plasmonic quaternary heteronanostructures (HNSs) for improved solar light utilization, spatial charge separation, and stability in photocatalytic hydrogen production

Recently, the frenetic development of stable quaternary material with a wide range of solar energy absorption and separation of charge carrier has emerged as a favorable material for the solar-to-hydrogen conversion. In this work, quaternary CuS-AgVO₃/Ag-TNR heteronanostructures (HNSs) synthesized by an ultra-sonication method for stabilized solar light photocatalytic hydrogen production in glycerol-water mixture. Among the prepared photocatalysts, the 1 wt% CuS-AgVO₃/Ag-TNR HNS produced the highest H₂ activity (756 µmol/g), approximately 84 times greater than the TNR due to higher charge separation, excellent conductivity, plasmonic resonance effect, and electron-storing capacity. Interestingly, the accelerated charge transfer pathway through the Schottky junction between the AgVO₃ and Ag to the conduction band of the TNR and thereafter to the electron acceptor of CuS for the reduction of H⁺ ions to H₂. Additionally, a possible photocatalytic mechanism of CuS-AgVO₃/Ag-TNR HNS for improved H₂ production was proposed based on the results obtained by various characterization techniques. Therefore, present research work explores the new insights to design high-performance CuS-AgVO₃/Ag-TNR HNS material for the conversion of clean renewable H₂ energy for the futuristic transport applications.

Fabrication of a Cu2O-Au-TiO2 Heterostructure with Improved Photocatalytic Performance for the Abatement of Hazardous Toluene and α-Pinene Vapors

In the current research, a Cu2O-Au-TiO2 heterostructure was fabricated via a step-wise photodeposition route to determine its possible application in the photocatalytic oxidation of hazardous vapors. The results of electron microscopy and X-ray photoelectron spectroscopy confirm the successful fabrication of the Cu2O-Au-TiO2 heterostructure. Strong absorption in the visible region, along with a slight red-shift in the absorption edge, was observed in the UV–vis diffuse reflectance spectrum of Cu2O-Au-TiO2 composite, which implies that the composite can generate a greater number of photoexcited charges necessary for photocatalytic reaction. Toluene and α-pinene, as common gas contaminants in the indoor atmosphere, were employed to assess the photooxidation efficiency of the Cu2O-Au-TiO2 composite. Importantly, photocatalytic activity results indicate that the Cu2O-Au-TiO2 composite showed excellent photodegradation performance compared to pure TiO2 and Cu2O-TiO2 and Au-TiO2, where photocatalytic efficiency was approximately 92.9% and 99.9% for toluene and α-pinene, respectively, under standard daylight illumination. The increased light-harvesting capacity and boosted separation efficiency of electron-hole pairs were mainly accountable for improved degradation performance of the Cu2O-Au-TiO2 composite. In addition, the degradation efficiencies for toluene and α-pinene by the Cu2O-Au-TiO2 composite were also examined under three different light sources: 0.32 W white, blue and violet LEDs. The findings of this work suggested a great promise of effective photooxidation of gas pollutants by the Cu2O-Au-TiO2 composite.

Enhanced Photocatalytic and Antimicrobial Performance of Cuprous Oxide/Titania: The Effect of Titania Matrix

A simple, low-cost method was applied to prepare hybrid photocatalysts of copper (I) oxide/titania. Five different TiO₂ powders were used to perform the study of the effect of titania matrix on the photocatalytic and antimicrobial properties of prepared nanocomposites. The photocatalytic efficiency of such a dual heterojunction system was tested in three reaction systems: ultraviolet-visible (UV-Vis)-induced methanol dehydrogenation and oxidation of acetic acid, and 2-propanol oxidation under visible light irradiation. In all the reaction systems considered, the crucial enhancement of photocatalytic activity in relation to corresponding bare titania was observed. The reaction mechanism for a specific reaction and the influence of titania matrix were discussed. Furthermore, antimicrobial (bactericidal and fungicidal) properties of Cu₂O/TiO₂ materials were analyzed. The antimicrobial activity was found under UV, visible and solar irradiation, and even for dark conditions. The origin of antimicrobial properties with emphasis on the role of titania matrix was also discussed.

Photoreduction route for Cu2O/TiO2 nanotubes junction for enhanced photocatalytic activity

Here, we synthesized copper(i) oxide and titanium dioxide nanotubes (TNTs) heterojunctions (HJs) by a photoreduction method using a low-power UV lamp without involving any additional steps, such as chemical reduction, surfactant, or protection agents. Transmission electron microscopy, X-ray diffraction, Raman scattering, X-ray photoelectron spectroscopy, diffuse reflectance spectra, and photoluminescence spectroscopy were carried out to verify the formation of a HJ between the Cu₂O nanoparticles (Cu₂O NPs) and TNTs. The efficiency and the rate of methylene blue photo-degradation over the Cu₂O/TNTs HJ were found to be nearly double and triple compared to the isolated TNTs. The enhanced efficiency is attributed to the narrow band gap and defect states caused by the oxygen vacancies in the vicinity of HJs. Moreover, the type II band alignment of Cu₂O NPs and TNTs naturally separates the photo-generated carriers and constrains the recombination process owing to the internal electric field across the Cu₂O/TNTs interface.

Good photocatalytic performance is demonstrated by Cu₂O NPs directly loaded onto hydrothermally synthesized TiO₂ NTs via photoreduction method conducted with a lower power UV lamp at room temp. This is due to narrowing bandgap and forming an internal electric field.

Ag/AgFeO2: An Outstanding Magnetically Responsive Photocatalyst for HeLa Cell Eradication

A superfast, room-temperature, one-step carrier-solvent-assisted interfacial reaction process was developed to prepare Ag/AgFeO2 composite nanocrystals (NCs) of less than 10 nm in size within a 1 min reaction time. These composite NCs were with a direct energy band gap of 2.0 eV and were paramagnetic, making them suitable for optical activation and magnetic manipulation. These composite NCs, applied as a photocatalyst for the treatment of HeLa cells, achieved a significant reduction of 74% in cell viability within 30 min. These Ag/AgFeO2 composite NCs proved to be a promising magnetically guidable photocatalyst for cancer cell treatment.

One-pot synthesis of manganese porphyrin covalently functionalized graphene oxide for enhanced photocatalytic hydrogen evolution

In this paper, graphene oxide (GO) sheets covalently functionalized with (5,10,15,20-tetraphenyl) porphinato manganese(III) (MnTPP) has been successfully synthesized and tested as a photocatalyst for hydrogen evolution from water under UV-vis light irradiation. The obtained sample was systematically characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), UV-vis, Fourier transform infrared (FTIR), and Raman spectroscopy. The results show that the MnTPP moiety has been successfully grafted on the graphene oxide surface to form MnTPP modified GO (GO-MnTPP). The fluorescence quenching and photocurrent enhancement of GO-MnTPP confirm that the rapid electrons transfer from photoexcited the MnTPP moiety to the GO sheets. The platinized GO-MnTPP exhibits enhanced photocatalytic activity for water reduction to produce hydrogen. Moreover, with the assistance of polyvinyl pyrrolidone (PVP), the photocatalytic activity is further improved because of aggregation prevention of the GO-MnTPP nanocomposite. This study provides a facile method to build porphyrin-graphene-based photocatalysts for solar energy conversion.

Titania supported MOF-199 derived Cu–Cu2O nanoparticles: highly efficient non-noble metal photocatalysts for hydrogen production from alcohol–water mixtures

Water splitting over Cu–Cu₂O/TiO₂ photocatalysts.

Hybrid nanostructures of TiO2 nanorod array/Cu2O with a CH3NH3PbI3 interlayer for enhanced photocatalytic activity and photoelectrochemical performance

A novel composite photocatalyst constructed from TiO₂ NRAs, CH₃NH₃PbI₃ and Cu₂O exhibits highly efficient visible light photocatalysis activity.

Recent advances in hybrid Cu2O-based heterogeneous nanostructures

Hybrid Cu2O-based heterogeneous nanostructures possess novel synergistic properties that arise from the integrated interaction between the disparate components, thereby showing promising potential for various important applications including solar cells, carbon monoxide oxidation, photocatalysts, field emission, sensors, templates and so on. With the rapid progress in nanomaterials science and nanotechnology, hybrid Cu2O-based heterogeneous nanostructures with well-controlled compositions, shapes and sizes have been rationally designed and synthesized. This review attempts to summarize the important advances in the development of different types of hybrid Cu2O-based heterogeneous nanostructures, such as hybrid Cu2O-metal nanostructures, hybrid Cu2O-metal oxide nanostructures and hybrid Cu2O-carbon nanostructures. The correlations between the improved performances and interfacial structures of the hybrid Cu2O-based heterogeneous nanostructures are discussed based on some important and representative examples. Several key scientific issues and perspective research directions in this field are also given.

Improved propane photooxidation activities upon nano Cu2O/TiO2 heterojunction semiconductors at room temperature

The Cu₂O/TiO₂ nano composites with a direct Z scheme charge transfer mode show both significantly improved propane photooxidation activity and increased stability of Cu₂O.

Facile synthesis of highly efficient one-dimensional plasmonic photocatalysts through Ag@Cu₂O core-shell heteronanowires

A novel class of one-dimensional (1D) plasmonic Ag@Cu2O core-shell heteronanowires have been synthesized at room temperature for photocatalysis application. The morphology, size, crystal structure and composition of the products were investigated by XRD, SEM, TEM, XPS, and UV-vis instruments. It was found the reaction time and the amount of Ag nanowires play crucial roles in the formation of well-defined 1D Ag@Cu2O core-shell heteronanowires. The resultant 1D Ag@Cu2O NWs exhibit much higher photocatalytic activity toward degradation of organic contaminants than Ag@Cu2O core-shell nanoparticles or pure Cu2O nanospheres under solar light irradiation. The drastic enhancement in photocatalytic activity could be attributed to the surface plasmon resonance and the electron sink effect of the Ag NW cores, and the unique 1D core-shell nanostructure.