Tunable thickness of mesoporous ZnO-coated metal nanoparticles for enhanced visible-light driven photoelectrochemical water splitting

The insufficient utilization of sunlight of ZnO, due to its broad band gap, results in low efficiency for photocatalytic hydrogen production. In this work, plasmonic noble metal nanoparticles (NPs) with different shapes (spheres and rods) were combined with mesoporous ZnO forming core-shell nanostructure to enhance the photocatalytic efficiency of ZnO in visible-light region. The photoelectrochemical water splitting activities of the metal@ZnO core-shell nanocomposites (NCs) were investigated. The photocurrent response of metal@ZnO NCs was found higher than pure ZnO or the mixture of metal NPs and ZnO ascribed to the effective charge transfer mechanism. It was also found that the photocurrent of metal@ZnO NCs was related to the thickness of ZnO and there was optimized shell for each kind of metal cores. Moreover, the introduction of Ag shell can get a higher photoelectrocatalytic efficiency compared to pure Au NPs core due to lower Schottky barrier between Ag and ZnO and wider extinction range in the visible light of Au@Ag NPs.

Recent Advances in the Design and Photocatalytic Enhanced Performance of Gold Plasmonic Nanostructures Decorated with Non-Titania Based Semiconductor Hetero-Nanoarchitectures

Plasmonic photocatalysts combining metallic nanoparticles and semiconductors have been aimed as versatile alternatives to drive light-assisted catalytic chemical reactions beyond the ultraviolet (UV) regions, and overcome one of the major drawbacks of the most exploited photocatalysts (TiO2 or ZnO). The strong size and morphology dependence of metallic nanostructures to tune their visible to near-infrared (vis-NIR) light harvesting capabilities has been combined with the design of a wide variety of architectures for the semiconductor supports to promote the selective activity of specific crystallographic facets. The search for efficient heterojunctions has been subjected to numerous studies, especially those involving gold nanostructures and titania semiconductors. In the present review, we paid special attention to the most recent advances in the design of gold-semiconductor hetero-nanostructures including emerging metal oxides such as cerium oxide or copper oxide (CeO2 or Cu2O) or metal chalcogenides such as copper sulfide or cadmium sulfides (CuS or CdS). These alternative hybrid materials were thoroughly built in past years to target research fields of strong impact, such as solar energy conversion, water splitting, environmental chemistry, or nanomedicine. Herein, we evaluate the influence of tuning the morphologies of the plasmonic gold nanostructures or the semiconductor interacting structures, and how these variations in geometry, either individual or combined, have a significant influence on the final photocatalytic performance.

Multi-interfacial plasmon coupling in multigap (Au/AgAu)@CdS core-shell hybrids for efficient photocatalytic hydrogen generation

Plasmon coupling induced intense light absorption and near-field enhancement have vast potential for high-efficiency photocatalytic applications. Herein, (Au/AgAu)@CdS core-shell hybrids with strong multi-interfacial plasmon coupling were prepared through a convenient strategy for efficient photocatalytic hydrogen generation. Bimetallic Au/AgAu cores with an adjustable number of nanogaps (from one to four) were primarily synthesized by well-controlled multi-cycle galvanic replacement and overgrowth processes. Extinction tests and numerical simulations synergistically revealed that the multigap Au/AgAu hybrids possess a gap-dependent light absorption region and a local electric field owing to the multigap-induced multi-interfacial plasmon coupling. With these characteristics, hetero-photocatalysts prepared by further coating of CdS shells on multigap Au/AgAu cores exhibited a prominent gap-dependent photocatalytic hydrogen production activity from water splitting under light irradiation (λ > 420 nm). It is found that the hydrogen generation rates of multigap (Au/AgAu)@CdS have an exponential improvement compared with that of pure CdS as the number of nanogaps increases. In particular, four-gap (Au/AgAu)@CdS core-shell catalysts displayed the highest hydrogen generation rate, that is 96.1 and 47.2 times those of pure CdS and gapless Au@CdS core-shell hybrids. These improvements can be ascribed to the strong plasmon absorption and near-field enhancement induced by the multi-interfacial plasmon coupling, which can greatly improve the light-harvesting efficiency, offer more plasmonic energy, and boost the generation and separation of electron-hole pairs in the multigap catalysts.

Ultrasound-assisted synthesis of 3D flower-like zinc oxide decorated fMWCNTs for sensitive detection of toxic environmental pollutant 4-nitrophenol

Sonochemical synthesis of functionalized multi-walled carbon nanotubes (fMWCNTs) embellished 3D flower-like zinc oxide (ZnO) nanocomposite based novel electrochemical sensor for the detection of toxic environmental pollutant 4-nitrophenol (4-NP) is detailed in this paper. We have used laser-assisted synthesis technique in the development of 3D flower-like ZnO nanoparticles (NPs) and ultrasonication method was employed in preparation of ZnO NPs@fMWCNTs nanocomposite using a high-intensity ultrasonic bath DC200H with power of 200 W/cm² and 40 KHz frequency. The nanocomposite was meticulously fabricated on screen printed carbon electrode (SPCE) to carry out various electrochemical analysis. Different characterizations such as Raman spectroscopy, Fourier transform infrared (FT-IR) spectroscopy, UV visible spectroscopy (UV-Vis), X-ray diffraction (XRD), scanning electron microscopy (SEM), and high-resolution transmission electron microscopy (HRTEM) of the materials used in this work were taken. Cyclic voltammetry (CV) and differential pulse voltammetry (DPV) techniques are used in electrochemical investigations. We have observed well-defined oxidation and reduction peak currents representing electrochemical mechanism of 4-NP at very low potentials for ZnO NPs@fMWCNTs/SPCE. Furthermore, we were able to achieve efficient electrochemical determination of 4-NP using the developed sensor with a high sensitivity of 11.44 μA μM^-1 cm^-2 and very low detection limit (LOD) of 0.013 μM in a broad linear range of 0.06-100 μM. All the significant features of a good sensor including anti-interference, good stability, excellent repeatability, and reproducibility were exhibited by the sensor. Moreover, we have tested practical feasibility of sensor by carrying out real sample analysis on different water samples.

The Response of UV/Blue Light and Ozone Sensing Using Ag-TiO2 Planar Nanocomposite Thin Film

We successfully fabricated a planar nanocomposite film that uses a composite of silver nanoparticles and titanium dioxide film (Ag-TiO₂) for ultraviolet (UV) and blue light detection and application in ozone gas sensor. Ultraviolet-visible spectra revealed that silver nanoparticles have a strong surface plasmon resonance (SPR) effect. A strong redshift of the plasmonic peak when the silver nanoparticles covered the TiO₂ thin film was observed. The value of conductivity change for the Ag-TiO₂ composite is 4–8 times greater than that of TiO₂ film under UV and blue light irradiation. The Ag-TiO₂ nanocomposite film successfully sensed 100 ppb ozone. The gas response of the composite film increased by roughly six and four times under UV and blue light irradiation, respectively. We demonstrated that a Ag-TiO₂ composite gas sensor can be used with visible light (blue). The planar composite significantly enhances photo catalysis. The composite films have practical application potential for wearable devices.

Surface plasmon resonance enhanced direct Z-scheme TiO2/ZnTe/Au nanocorncob heterojunctions for efficient photocatalytic overall water splitting

Solar-driven photocatalytic overall water splitting is regarded as one of the ideal strategies to generate renewable hydrogen energy without the initiation of environmental issues. However, there are still a few remaining challenges to develop wide-light-absorption and stable photocatalysts for the simultaneous production of H2 and O2 in pure water without sacrificial reagents. Herein, we report the design and preparation of Z-scheme TiO2/ZnTe/Au nanocorncob heterojunctions by homogeneously decorating Au nanoparticles onto the surface of core-shell TiO2/ZnTe coaxial nanorods for highly efficient overall water splitting. With the appropriate band structure of TiO2/ZnTe heterojunctions and the surface plasmon resonance enhancement of Au nanoparticles, the well-designed TiO2/ZnTe/Au nanocorncob heterojunctions can synergistically make effective utilization of broad-range solar light illunimation and enhance the separation efficency of electron-hole pairs, as evidenced by UV-Vis absorption and time-resolved photoluminescence spectroscopy. Photoelectrochemical characterization confirms that the water-splitting reaction on TiO2/ZnTe/Au nanocorncobs is mainly carried out via a two-electron/two-electron transfer process with an intermediate product of H2O2. As a result, the TiO2/ZnTe/Au nanocorncob photocatalyst can generate H2 and O2 with a stoichiometric ratio of 2 : 1 under light irradiation without any sacrificial agents, exhibiting a high H2 production rate of 3344.0 μmol g-1 h-1 and a solar-to-hydrogen (STH) efficiency of 0.98%. Moreover, the TiO2/ZnTe/Au nanocorncob heterojunctions show high stability and well-preserved morphological integrity after long-term photocatalytic tests. This study provides a prototype route to produce clean hydrogen energy from only sunlight, pure water, and rationally-designed heterojunction photocatalysts.

High Tunability of Size Dependent Optical Properties of ZnO@M@Au (M = SiO2, In2O3, TiO2) Core/Spacer/Shell Nanostructure

This theoretical work presents a comparative study of high tunability size dependent optical properties of quantum dot/wire triple layered core shell nanostructure based on the quasi-static approximation of classical electrodynamics embedded in a fixed dielectrics function of host matrix. In this paper, local field enhancement factor (LFEF), refractive index and optical absorbance of nanocomposite are analyzed by varying core size, thickness of spacer and shell as well as dielectrics function of the spacer for the size of the nanocomposite with the range of 20 nm to 40 nm. For both quantum dot and quantum wire triple layered core shell nanostructure (CSNS), there are two resonances in visible and near/in infrared spectral region with high tunability. When the shell thickness increase and therefore increasing the gold content, the surface plasmon resonance (SPR) at the outer interface shifts to higher energy (blue-shifted) and at the inner interface weak peaks and shifted to lower energy (red-shifted). All of three optical properties, depend on core size, dielectrics and thickess of spacer, thickness of shell, shape of composite and filling factor. For the same thickness of spacer and shell of the two configurations, cylindrical triple layered CSNS less pronounced and shifted to infrared red (IR) spectral region which is recommendable for biological and photocatalysis application.      

Well-defined Pd anchoring on the surface of porous ZnO nanocomposites with excellent photocatalytic activity and good reusability for the removal of phenol from water

Well-defined Pd/ZnO nanocomposites prepared by modifying ZnO nanosheets with Pd nanoparticles exhibit excellent photocatalytic activity and good reusability for the removal of phenol from water.

Extremely rapid engineering of zinc oxide nanoaggregates with structure-dependent catalytic capability towards removal of ciprofloxacin antibiotic

ZnO nanoaggregates with structure-dependent catalytic capability of removal of ciprofloxacin antibiotics were engineered by an extremely rapid polyol-mediated synthesis approach.

Biomimetic synthesis of urchin-like CuO/ZnO nanocomposites with excellent photocatalytic activity

Highly photocatalytic urchin-like CuO/ZnO nanocomposites were synthesized using glutamine as a growth regulator by a hydrothermal process with subsequent calcination.

Visible light-enhanced thermal decomposition performance of ammonium perchlorate with a metal–organic framework-derived Ag-embedded porous ZnO nanocomposite

An Ag-embedded porous ZnO nanocomposite (Ag–ZnO NC) fabricated using an MOF exhibits high catalytic activity for the thermal decomposition of AP under the assistance of visible light.

Insights into the structure-induced catalysis dependence of simply engineered one-dimensional zinc oxide nanocrystals towards photocatalytic water purification

One-dimensional nanocrystalline semiconductors have been comprehensively studied because of their fascinating properties and practical applications in various fields.

Synergistically enhanced photocatalysis from plasmonics and a co-catalyst in Au@ZnO–Pd ternary core–shell nanostructures

Ternary core–shell nanostructures of Au@ZnO–Pd have been designed to achieve the synergetic utilization of a plasmonic effect and a co-catalyst for enhanced photocatalytic performance.

A dual-band photodetector based on ZnO nanowires decorated with Au nanoparticles synthesized on a glass substrate

ZnO nanowires (NWs) decorated with Au nanoparticles (NPs) of various grain sizes are fabricated into a dual-band photodetector on a glass substrate.