Effects of shell thickness on Ag-Cu 2 O core-shell nanoparticles with bumpy structures for enhancing photocatalytic activity and stability

Light Absorption Analysis and Optimization of Ag@TiO2 Core-Shell Nanospheroid and Nanorod

For photothermal therapy of cancer, it is necessary to find Ag @TiO2 core-shell nanoparticles that can freely tune the resonance wavelength within the near-infrared biological window. In this paper, the finite element method and the size-dependent refractive index of metal nanoparticles were used to theoretically investigate the effects of the core material, core length, core aspect ratio, shell thickness, refractive index of the surrounding medium, and the particle orientation on the light absorption properties of Ag@TiO2 core-shell nanospheroid and nanorod. The calculations show that the position and intensity of the light absorption resonance peaks can be freely tuned within the first and second biological windows by changing the above-mentioned parameters. Two laser wavelengths commonly used in photothermal therapy, 808 nm (first biological window) and 1064 nm (second biological window), were selected to optimize the core length and aspect ratio of Ag@TiO2 core-shell nanospheroid and nanorod. It was found that the optimized Ag@TiO2 core-shell nanospheroid has a stronger light absorption capacity at the laser wavelengths of 808 nm and 1064 nm. The optimized Ag@TiO2 core-shell nanoparticles can be used as ideal therapeutic agents in photothermal therapy.

Nanocomposites of Cu2O with plasmonic metals (Au, Ag): design, synthesis, and photocatalytic applications

Metal-semiconductor nanocomposites have been utilized in a multitude of applications in a wide array of fields, prompting substantial interest from different scientific sectors. Of particular interest are semiconductors paired with plasmonic metals due to the unique optical properties that arise from the individual interactions of these materials with light and the intercomponent movement of charge carriers in their heterostructure. This review focuses on the pairing of Cu2O semiconductor with strongly plasmonic metals, particularly Au and Ag. The design and synthesis of Au-Cu2O and Ag-Cu2O nanostructures, along with ternary nanostructures composed of the three components, are described, with in-depth discussion on the synthesis techniques and tunable parameters. The effects of compositing on the optical and electronic properties of the nanocomposites in the context of photocatalysis are discussed as well. Concluding remarks and potential areas for exploration are presented in the last section.

Plasmonic Hybrid Nanostructures in Photocatalysis: Structures, Mechanisms, and Applications

(Sun)Light is an abundantly available sustainable source of energy that has been used in catalyzing chemical reactions for several decades now. In particular, studies related to the interaction of light with plasmonic nanostructures have been receiving increased attention. These structures display the unique property of localized surface plasmon resonance, which converts light of a specific wavelength range into hot charge carriers, along with strong local electromagnetic fields, and/or heat, which may all enhance the reaction efficiency in their own way. These unique properties of plasmonic nanoparticles can be conveniently tuned by varying the metal type, size, shape, and dielectric environment, thus prompting a research focus on rationally designed plasmonic hybrid nanostructures. In this review, the term "hybrid" implies nanomaterials that consist of multiple plasmonic or non-plasmonic materials, forming complex configurations in the geometry and/or at the atomic level. We discuss the synthetic techniques and evolution of such hybrid plasmonic nanostructures giving rise to a wide variety of material and geometric configurations. Bimetallic alloys, which result in a new set of opto-physical parameters, are compared with core-shell configurations. For the latter, the use of metal, semiconductor, and polymer shells is reviewed. Also, more complex structures such as Janus and antenna reactor composites are discussed. This review further summarizes the studies exploiting plasmonic hybrids to elucidate the plasmonic-photocatalytic mechanism. Finally, we review the implementation of these plasmonic hybrids in different photocatalytic application domains such as H₂ generation, CO₂ reduction, water purification, air purification, and disinfection.

TiO2 Thickness-Dependent Charge Transfer in an Ordered Ag/TiO2/Ni Nanopillar Arrays Based on Surface-Enhanced Raman Scattering

In this study, an ordered Ag/TiO2/Ni nanopillar arrays hybrid substrate was designed, and the charge transfer (CT) process at the metal–semiconductor and substrate–molecule interface was investigated based on the surface-enhanced Raman scattering (SERS) spectra of 4-Aminothiophenol (PATP) absorbed on the composite system. The surface plasmon resonance (SPR) absorption of Ag changes due to the regulation of TiO2 thickness, which leads to different degrees of CT enhancement in the system. The CT degree of SERS spectra obtained at different excitation wavelengths was calculated to study the contribution of CT enhancement to SERS, and a TiO2thickness-dependent CT enhancement mechanism was proposed. Furthermore, Ag/TiO2/Ni nanopillar arrays possessed favorable detection ability and uniformity, which has potential as a SERS-active substrate.

Recent advances in Cu2O-based composites for photocatalysis: a review

Cu₂O-based composites for photocatalysis have been extensively explored owing to their promising application in solving environmental and energy problems. At present, the research on photocatalysis is focused on improving the photocatalytic performance of materials. It has been reported that adjusting the morphology and size of Cu₂O can effectively improve its photocatalytic property. However, photocorrosion is still an inevitable problem, which hinders the application of Cu₂O in photocatalysis. The strategies of constructing heterogeneous nanostructures and ion doping can significantly improve the light stability, light absorption capacity and separation efficiency of electron-hole pairs. Cu₂O-based composites exhibit superior performances in degrading organic matter, producing hydrogen, reducing CO₂ and sterilization. Therefore, the construction of multi-materials will be one of the future directions in their photocatalytic application. This review summarizes the recent strategies for enhancing the photocatalytic activity of Cu₂O by analyzing different Cu₂O-based photocatalysts, and the charge transfer pathway is further discussed in detail. Finally, several opportunities and challenges in the field of photocatalysis are illustrated.

Rapid fabrication of silver–cuprous oxide core–shell nanowires for visible light photocatalysts

This work reports a novel method that enables facile fabrication of Ag–Cu₂O core–shell nanowires (Ag@Cu₂O NWs) for visible light photocatalysts.

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.

Complementary behavior of doping and loading in Ag/C-ZnTa2O6 for efficient visible-light photocatalytic redox towards broad wastewater remediation

This work reports on the simple fabrication of a silver loaded and carbon doped zinc tantalate (Ag/C-ZnTa₂O₆) photocatalyst with visible light photocatalytic activity toward broad wastewater remediation, including high photo-reduction of Cr(vi) (98.4% in 210 min), excellent photo-oxidation of tetracycline hydrochloride (94.7% in 210 min), and superior photo-degradation of multiple dyes (>99.0% within 210 min). The optimal photocatalytic performance of Ag/C-ZnTa₂O₆ is mainly due to the excellent visible light absorption capacity and superior electron-hole separation efficiency, which is ascribed to the complementary behavior between carbon doping and silver loading. Particularly, the generation of defects due to C-doping is greatly inhibited by Ag-loading, and the SPR effect of Ag nanoparticles is enhanced due to the obstruction of Ag⁺ by C doping.

Charge Transfer-Mediated Blue Luminescence in Plasmonic Ag-Cu2O Quantum Nanoheterostructures

Metal-semiconductor hybrid nanoheterostructures have the possibility to exhibit new synergic properties other than the combination of properties from discrete components due to the interaction of metal and semiconductor components at the interfaces. Here, we have synthesized Ag-Cu₂O eyeball-shaped quantum nanoheterostructures with diameter ranging between 8 and 12 nm using a single-step low-cost solvothermal process. It is observed that the presence of a minimum 3% of Ag is required for the formation of Ag-Cu₂O quantum nanoheterostructures. The formation of nanoheterostructures has introduced new synergic properties like intense blue luminescence and surface-enhanced Raman scattering due to the interactions between Ag and Cu₂O atoms at the interfaces. The significant presence of charge transfer through the interfaces is identified from the peak shift of Raman modes. The increase in the electron density at the metal surface due to the charge transfer and the recombination of these electrons with sp- or d-band holes of Ag could be the effective mechanism of the observed blue luminescence. The blue luminescence of Ag-Cu₂O quantum nanoheterostructures together with its low band gap value (≈2.3 eV) is believed to have important applications in optoelectronic devices.

Enhanced photocatalytic activity of CO2 reduction to methanol through the use of a novel-structured CuCaAg2Se–graphene–TiO2 ternary nanocomposite

Effective charge transfer is a key factor in enhancing the catalytic activity of photocatalytic nanocomposite materials.

A Novel Au@Cu2O-Ag Ternary Nanocomposite with Highly Efficient Catalytic Performance: Towards Rapid Reduction of Methyl Orange Under Dark Condition

Au@Cu2O core-shell nanocomposites (NCs) were synthesized by reducing copper nitrate on Au colloids with hydrazine. The thickness of the Cu2O shells could be varied by adjusting the molar ratios of Au: Cu. The results showed that the thickness of Cu2O shells played a crucial role in the catalytic activity of Au@Cu2O NCs under dark condition. The Au@Cu2O-Ag ternary NCs were further prepared by a simple galvanic replacement reaction method. Moreover, the surface features were revealed by TEM, XRD, XPS, and UV-Vis techniques. Compared with Au@Cu2O NCs, the ternary Au@Cu2O-Ag NCs had an excellent catalytic performance. The degradation of methyl orange (MO) catalyzed by Au@Cu2O-Ag NCs was achieved within 4 min. The mechanism study proved that the synergistic effects of Au@Cu2O-Ag NCs and sodium borohydride facilitated the degradation of MO. Hence, the designed Au@Cu2O-Ag NCs with high catalytic efficiency and good stability are expected to be the ideal environmental nanocatalysts for the degradation of dye pollutants in wastewater.

Dynamic growth of rhombic dodecahedral Cu2O crystals controlled by reaction temperature and their size-dependent photocatalytic performance

Compared with low-index {100} or {111} planes of Cu₂O crystals, rhombic dodecahedra (RD) Cu₂O crystals exposing 12 {110} facets exhibit the most superior photodegradation of organic pollutants. Herein, a series of RD Cu₂O crystals with different sizes were successfully synthesized by precisely adjusting the reaction temperature ranging from 40 °C to 100 °C. The results revealed that truncated rhombic dodecahedra (TRD) Cu₂O crystals were fabricated when the temperatures was 40 °C. More importantly, on raising the temperature to above 40 °C, Cu₂O architectures dynamically evolved from TRD to RD. Meanwhile, the sizes gradually decreased with elevation of the temperature, while the RD morphology of Cu₂O crystals remained, demonstrating the importance of temperature for determining the morphology and size of Cu₂O crystals. In addition, we also carefully investigated the visible-light photodegradation performance of Cu₂O crystals for methyl orange (MO). RD Cu₂O crystals exhibited superior photocatalytic activity compared with TRD, and showed size-dependent photocatalytic activity for MO. The photocatalytic activity of RD Cu₂O crystals can be greatly improved by decreasing the size. In particular, RD-60 with the minimum size achieved the best photocatalytic properties compared to the other RD and TRD Cu₂O crystals, and still displayed high photocatalytic efficiency even after three cycles. Such results advance the understanding that temperature modulation serves as an effective means to fabricate RD Cu₂O crystals.

Compared with low-index {100} or {111} planes of Cu₂O crystals, rhombic dodecahedra (RD) Cu₂O crystals exposing 12 {110} facets exhibit the most superior photodegradation of organic pollutants.

Catalysis of Organic Pollutants Abatement Based on Pt-Decorated Ag@Cu2O Heterostructures

Pt-decorated Ag@Cu2O heterostructures were successfully synthesized using a simple and convenient method. The Pt nanoparticle density on the Ag@Cu2O can be controlled by changing the concentration of the Pt precursor. The synthesized Ag@Cu2O-Pt nanoparticles exhibited excellent catalytic performance, which was greatly affected by changes in the Ag@Cu2O-Pt structure. To optimize the material's properties, the synthesized Ag@Cu2O-Pt nanoparticles were used to catalyze toxic pollutants and methyl orange (MO), and nontoxic products were obtained by catalytic reduction. The Pt-decorated Ag@Cu2O nanoparticles showed excellent catalytic activity, which significantly decreased the pollutant concentration when the nanoparticles were used for catalytic reduction. The redistribution of charge transfer is the nanoparticles' main contribution to the catalytic degradation of an organic pollutant. This Pt-decorated Ag@Cu2O material has unique optical and structural characteristics that make it suitable for photocatalysis, local surface plasmon resonance, and peroxide catalysis.

Sustainable Recovery of CO2 by Using Visible-Light-Responsive Crystal Cuprous Oxide/Reduced Graphene Oxide

A simple solution-chemistry method has been investigated to prepare crystal cuprous oxide (Cu2O) incorporated with reduced graphene oxide (designated as Cu2O-rGO-x, where x represents the contents of rGO = 1%, 5% and 10%) in this work. These Cu2O-rGO-x composites combine the prospective advantages of rhombic dodecahedra Cu2O together with rGO nanosheets which have been studied as visible-light-sensitive catalysts for the photocatalytic production of methanol from CO2. Among the Cu2O-rGO-x photocatalysts, the methanol yield photocatalyzed by Cu2O-rGO-5% can be observed to be 355.26 μmol g−1cat, which is ca. 36 times higher than that of pristine Cu2O nanocrystal in the 20th hour under visible light irradiation. The improved activity may be attributed to the enhanced absorption ability of visible light, the superior separation of electron–hole pairs, well-dispersed Cu2O nanocrystals and the increased photostability of Cu2O, which are evidenced by employing UV-vis diffuse reflection spectroscopy, photoluminescence, scanning electron microscopy/transmission electron microscopy and X-ray photoelectron spectroscopy, respectively. This work demonstrates an easy and cost-effective route to prepare non-noble photocatalysts for efficient CO2 recovery in artificial photosynthesis.

In Situ Synthesis of Ag@Cu₂O-rGO Architecture for Strong Light-Matter Interactions

Emerging opportunities based on two-dimensional (2D) layered structures can utilize a variety of complex geometric architectures. Herein, we report the synthesis and properties of a 2D+0D unique ternary platform-core-shell nanostructure, termed Ag@Cu₂O-rGO, where the reduced graphene oxide (rGO) 2D acting as a platform is uniformly decorated by Ag@Cu₂O core-shell nanoparticles. Cu₂O nanoparticles occupy the defect positions on the surface of the rGO platform and restore the conjugation of the rGO structure, which contributes to the significant decrease of the I_D/I_G intensity ratio. The rGO platform can not only bridge the isolated nanoparticles together but also can quickly transfer the free electrons arising from the Ag core to the Cu₂O shell to improve the utilization efficiency of photogenerated electrons, as is verified by high efficient photocatalytic activity of Methyl Orange (MO). The multi-interface coupling of the Ag@Cu₂O-rGO platform-core-shell nanostructure leads to the decrease of the bandgap with an increase of the Cu₂O shell thickness, which broadens the absorption range of the visible light spectrum.