CuOx‐TiO2Composites: Electronically Integrated Nanocomposites for Solar Hydrogen Generation

Exploring Defect-Engineered Metal-Organic Frameworks with 1,2,4-Triazolyl Isophthalate and Benzoate Linkers

Synthesis and characterization of DEMOFs (defect-engineered metal-organic frameworks) with coordinatively unsaturated sites (CUSs) for gas adsorption, catalysis, and separation are reported. We use the mixed-linker approach to introduce defects in Cu2-paddle wheel units of MOFs [Cu2(Me-trz-ia)2] by replacing up to 7% of the 3-methyl-triazolyl isophthalate linker (1L2-) with the "defective linker" 3-methyl-triazolyl m-benzoate (2L-), causing uncoordinated equatorial sites. PXRD of DEMOFs shows broadened reflections; IR and Raman analysis demonstrates only marginal changes as compared to the regular MOF (ReMOF, without a defective linker). The concentration of the integrated defective linker in DEMOFs is determined by 1H NMR and HPLC, while PXRD patterns reveal that DEMOFs maintain phase purity and crystallinity. Combined XPS (X-ray photoelectron spectroscopy) and cw EPR (continuous wave electron paramagnetic resonance) spectroscopy analyses provide insights into the local structure of defective sites and charge balance, suggesting the presence of two types of defects. Notably, an increase in CuI concentration is observed with incorporation of defective linkers, correlating with the elevated isosteric heat of adsorption (ΔHads). Overall, this approach offers valuable insights into the creation and evolution of CUSs within MOFs through the integration of defective linkers.

Research Progress of Co-Catalysts in Photocatalytic CO2 Reduction: A Review of Developments, Opportunities, and Directions

With the development of the global economy, large amounts of fossil fuels are being burned, causing a severe energy crisis and climate change. Photocatalytic CO2 reduction is a clean and environmentally friendly method to convert CO2 into hydrocarbon fuel, providing a feasible solution to the global energy crisis and climate problems. Photocatalytic CO2 reduction has three key steps: solar energy absorption, electron transfer, and CO2 catalytic reduction. The previous literature has obtained many significant results around the first two steps, while in the third step, there are few results due to the need to add a co-catalyst. In general, the co-catalysts have three essential roles: (1) promoting the separation of photoexcited electron–hole pairs, (2) inhibiting side reactions, and (3) improving the selectivity of target products. This paper summarizes different types of photocatalysts for photocatalytic CO2 reduction, the reaction mechanisms are illustrated, and the application prospects are prospected.

Oxygen Reduction Reaction in the Field of Water Environment for Application of Nanomaterials

Water pollution has caused the ecosystem to be in a state of imbalance for a long time. It has become a major global ecological and environmental problem today. Solving the potential hidden dangers of pollutants and avoiding unauthorized access to resources has become the necessary condition and important task to ensure the sustainable development of human society. To solve such problems, this review summarizes the research progress of nanomaterials in the field of water aimed at the treatment of water pollution and the development and utilization of new energy. The paper also tries to seek scientific solutions to environmental degradation and to create better living environmental conditions from previously published cutting edge research. The main content in this review article includes four parts: advanced oxidation, catalytic adsorption, hydrogen, and oxygen production. Among a host of other things, this paper also summarizes the various ways by which composite nanomaterials have been combined for enhancing catalytic efficiency, reducing energy consumption, recycling, and ability to expand their scope of application. Hence, this paper provides a clear roadmap on the status, success, problems, and the way forward for future studies.

Cu-Ag Bimetal Alloy Decorated SiO2@TiO2 Hybrid Photocatalyst for Enhanced H2 Evolution and Phenol Oxidation under Visible Light

With a broader objective to replace visible light driven Pt-based photoelectrochemical/catalytic hydrogen evolution, a series of cost-effective bimetallic nanoalloys of Cu-Ag have been deposited on core-shell nanostructured SiO₂@TiO₂ through a facile reduction route. The physicochemical properties, i.e. crystal structure, morphology, chemical environment, and optical properties of Cu-Ag bimetal alloy decorated SiO₂@TiO₂ hybrid photocatalyst, have been thoroughly investigated through X-ray diffraction, high resolution transmission electron microscopy, field emission scanning electron microscopy, X-ray photoelectron spectroscopy, UV-vis diffuse reflectance spectroscopy, and photoluminescence spectroscopy, respectively. TEM study confirms the coating of an ultrathin layer of TiO₂ shell on 100 nm sized SiO₂ core, and about 4.5 nm of Ag-Cu nanoalloys are uniformly distributed on the core-shell nanostructure. The higher light absorption throughout the visible range and better separation of charge carrier by Ag-Cu (1:3) deposited SiO₂@TiO₂ hybrid compared to other counterparts is confirmed from UV-vis, diffuse reflectance spectroscopy, photoluminescence, and electrochemical impedance studies. Eightfold higher photocurrent enhancements, threefold enhanced photocatalytic hydrogen generation, and twofold higher phenol oxidation activities of Ag-Cu (1:3) deposited SiO₂@TiO₂ hybrid compared to those of the monometallic plasmonic catalyst may be attributed to the synergetic effect of enriched light harvesting and surface plasmon induced hot electron transfer from the nanoalloy to the TiO₂ interface, resulting in efficient charge transfer.

Electronic Integration and Thin Film Aspects of Au-Pd/rGO/TiO2 for Improved Solar Hydrogen Generation

In the present work, we have synthesized noble bimetallic nanoparticles (Au-Pd NPs) on a carbon-based support and integrated with titania to obtain Au-Pd/C/TiO₂ and Au-Pd/rGO/TiO₂ nanocomposites using an ecofriendly hydrothermal method. Here, a 1:1 (w/w) Au-Pd bimetallic composition was dispersed on (a) high-surface-area (3000 m² g^-1) activated carbon (Au-Pd/C), prepared from a locally available plant source (in Assam, India), and (b) reduced graphene oxide (rGO) (Au-Pd/rGO); subsequently, they were integrated with TiO₂. The shift observed in Raman spectroscopy demonstrates the electronic integration of the bimetal with titania. The photocatalytic activity of the above materials for the hydrogen evolution reaction was studied under 1 sun conditions using methanol as a sacrificial agent in a powder form. The photocatalysts were also employed to prepare a thin film by the drop-casting method. Au-Pd/rGO/TiO₂ exhibits 43 times higher hydrogen (H₂) yield in the thin film form (21.50 mmol h^-1 g^-1) compared to the powder form (0.50 mmol h^-1 g^-1). On the other hand, Au-Pd/C/TiO₂ shows 13 times higher hydrogen (H₂) yield in the thin film form (6.42 mmol h^-1 g^-1) compared to the powder form (0.48 mmol h^-1 g^-1). While powder forms of both catalysts show comparable activity, the Au-Pd/rGO/TiO₂ thin film shows 3.4 times higher activity than that of Au-Pd/C/TiO₂. This can be ascribed to (a) an effective separation of photogenerated electron-hole pairs at the interface of Au-Pd/rGO/TiO₂ and (b) the better field effect due to plasmon resonance of the bimetal in the thin film form. The catalytic influence of the carbon-based support is highly pronounced due to synergistic binding interaction of bimetallic nanoparticles. Further, a large amount of hydrogen evolution in the film form with both catalysts (Au-Pd/C/TiO₂ and Au-Pd/rGO/TiO₂) reiterates that charge utilization should be better compared to that in powder catalysts.

Plasmonic Ag decorated CdMoO4 as an efficient photocatalyst for solar hydrogen production

The synthesis of Ag-nanoparticle-decorated CdMoO4 and its photocatalytic activity towards hydrogen generation under sunlight has been demonstrated. The CdMoO4 samples were synthesized by a simple hydrothermal approach in which Ag nanoparticles were in situ decorated on the surface of CdMoO4. A morphological study showed that 5 nm spherical Ag nanoparticles were homogeneously distributed on the surface of CdMoO4 particles. The UV/DRS spectra show that the band gap of CdMoO4 was narrowed by the incorporation of a small amount of Ag nanoparticles. The surface plasmonic effect of Ag shows broad absorption in the visible region. The enhanced photocatalytic hydrogen production activities of all the samples were evaluated by using methanol as a sacrificial reagent in water under natural sunlight conditions. The results suggest that the rate of photocatalytic hydrogen production using CdMoO4 can be significantly improved by loading 2% Ag nanoparticles: i.e. 2465 μmol h-1 g-1 for a 15 mg catalyst. The strong excitation of surface plasmon resonance (SPR) absorption by the Ag nanoparticles was found in the Ag-loaded samples. In this system, the role of Ag nanoparticles on the surface of CdMoO4 has been discussed. In particular, the SPR effect is responsible for higher hydrogen evolution under natural sunlight because of broad absorption in the visible region. The current study could provide new insights for designing metal/semiconductor interface systems to harvest solar light for solar fuel generation.

Highly Active Photocatalyst of Cu2O/TiO2 Octahedron for Hydrogen Generation

Heterojunction catalysts are attracting attention in the field of photocatalytic hydrogen generation for their effective light utilization and charge separation personalities. In this work, we report a simple and low-cost two-step solvothermal method for synthesizing Cu₂O/TiO₂ heterojunction catalysts with an octahedral morphology and a mean particle size of about 30 nm. It is found that the introduction of Cu₂O astonishingly enhances the photocatalytic performance of TiO₂. Under the condition of methanol acting as a sacrificial agent, the heterojunction with 0.19% Cu species shows an optimal hydrogen generation rate of 24.83 mmol g^-1 h^-1, which is nearly 3 orders of magnitude higher than that of the pristine TiO₂ catalyst.