Nanoheterojunction Arrays Research Articles

Development of stable S-scheme 2D–2D g-C3N4/CdS nanoheterojunction arrays for enhanced visible light photomineralisation of nitrophenol priority water pollutants

The investigation focused on creating and studying a new 2D–2D S-scheme CdS/g-C3N4 heterojunction photocatalyst. Various techniques examined its structure, composition, and optical properties. This included XRD, XPS, EDS, SEM, TEM, HRTEM, DRS, and PL. The heterojunction showed a reduced charge recombination rate and more excellent stability, helping to lessen photocorrosion. This was due to photogenerated holes moving more quickly out of the CdS valence band. The interface between g-C3N4 and CdS favored a synergistic charge transfer. A suitable flat band potential measurement supported enhanced reactive oxygen species (ROS) generation in degrading 4-nitrophenol and 2-nitrophenol. This resulted in remarkable degradation efficiency of up to 99% and mineralization of up to 79%. The findings highlighted the practical design of the new 2D–2D S-scheme CdS/g-C3N4 heterojunction photocatalyst and its potential application in various energy and environmental settings, such as pollutant removal, hydrogen production, and CO2 conversion.

Enhanced photoelectrochemical activity of α-Fe2O3/TiO2 nanoheterojunction by controlling hydrodynamic conditions

Interfacial heterostructuring has appeared to be an efficient strategy to address the efficiency and applicability of the photocatalysts in solar energy conversion. Herein, we developed one-dimensional (1D) α-Fe2O3/TiO2 nanoheterojunction arrays for enhanced photoelectrochemical (PEC) activity. α-Fe2O3 nanotubes were firstly prepared via anodization under controlled hydrodynamic conditions to increase the efficiency. 1D α-Fe2O3/TiO2 nanoheterojunction arrays were then prepared through a hydrothermal treatment and a subsequent annealing process. A controlled anodization by modulating the hydrodynamic conditions, added a fine coating of TiO2 overlayer, to finally give an optimized composition and geometry for improved light absorption and spatial charge separation efficiency. Consequently, the optimized α-Fe2O3 generated a photocurrent of 0.07 mA cm−2 (3.5 times higher than that of pristine α-Fe2O3), and the as-obtained α-Fe2O3/TiO2 nanoheterojunction exhibited a photocurrent intensity of 0.12 mA cm−2 (about 6 times higher than that of pristine α-Fe2O3). A long-term stability can also be ensured. The well-controlled architectures provides a guideline for synthesis of advanced nanomaterials.

Synthesis of a high-quality Al-doped CdS/Si nanoheterojunction array and characterization of its electrical and electroluminescence properties

A high-quality nanoheterojunction composed of p-type Si nanoporous pillar array (Si-NPA) and n-type CdS:Al was successfully constructed by growing Al-doped CdS film on a silicon nanoporous pillar array via a simple chemical bath deposition method. The fabricated CdS:Al/Si-NPA nanoheterojunction exhibits a pronounced rectification behavior at a low turn-on voltage of ~ 0.5 V, a relatively high rectification ratio of 217 at ± 1.5 V, and good ideality factors of 0.85 in the low-voltage region and 2.45 in a high-voltage region. The electroluminescence spectra of a nanolight-emitting diode based on the nanoheterojunction are dominated by an intense band-edge emission located at ~ 520 nm under a small forward voltage and free from defect emissions. The intensity increased rapidly with the forward voltage. The emission mechanism and CIE chromaticity coordinates of the electroluminescence spectra were also discussed. The obtained CdS:Al/Si-NPA nanoheterojunction could be used for important applications in nanoscale optoelectronic devices.

Synthesis of Al-doped CdS/Si nanoheterojunction arrays and their electrical and electroluminescence properties

The Al-doped CdS/Si nanoheterostructures were prepared by growing Al-doped CdS films on silicon nanoporous pillar array (Si-NPA) through chemical bath deposition (CBD). Their structure, electrical, and electroluminescence properties were investigated as a function of [Al]/[Cd]. At low [Al]/[Cd], Al ions tend to enter the lattice substitutionally, decreasing the lattice constants, micro-strain along (0 0 2) plane, and resistivity, and enhancing average crystallite size and carrier mobility. However, this behavior is reversed at high [Al]/[Cd], because Al ions tend to enter the lattice interstitially. The electroluminescence (EL) properties were most affected by Al doping. As Al concentration increases, the EL intensity initially increased rapidly to a maximum with [Al]/[Cd] and then decreased with further increased [Al]/[Cd]. The maximum of EL intensity was observed in sample S-0.07. Its EL intensity is 320 times that of S-0 and its applied voltages are very low. It could be observed by the naked eyes even at 3 V. These results indicated that Al-doped CdS/Si-NPA might be a great potential in constructing optoelectronic nanodevices. The measured results show the incorporation of suitable amount of Al would improve significantly the performances of CdS/Si-NPA heterojunctions, increasing the uniformity of CdS thin film, decreasing the resistivity, enhancing carrier mobility, improving obviously the rectification behavior, and increasing greatly the EL emission intensity. These results indicated that Al-doped CdS/Si-NPA might be a great potential in constructing optoelectronic nanodevices.

CdCl2-assisting heat-treatment: Enhanced photoelectrocatalytic hydrogen generation and stability of CdS/ZnO nanoheterojunction arrays

Hydrogen generation efficiency and stability of the photoelectrocatalytic (PEC) water splitting relate closely to the crystallinity and the interface structure of the photoanodes. Here we demonstrated a feasible strategy for improving the cystallinity and interface quality of the ZnO/CdS nanoheterojunction arrays (NHAs) via CdCl2-assisting post-treatment. CdCl2 treatment was found to promote the recrystallization and densification of the CdS shell layer, the formation of the ZnxCd1-xS intermediate layer between ZnO and CdS, and the creation of an intermediate band (IB) in the forbidden band of CdS due to the high-density ClS states. Meanwhile, the annealing temperature was also lowered from 550 °C to 430 °C with the assistance of CdCl2 treatment. These improvements facilitate the seperation and transport of the photogenerated carriers and extends the light absorption range, resulting in extremely enhanced photocatalytic current and stability. Consequently, the photocatalytic currency reaches to 22 mA cm−2 under the 100 mW cm−2 illumination with the xenon lamp (λ > 420 nm), which is nearly two times larger than that annealed solely at 550 °C but without CdCl2 treatment. The photocatalytic current remains 92% of the initial value after 20-h photocatalytic test.

Structural modulation of CdS/ZnO nanoheterojunction arrays for full solar water splitting and their related degradation mechanisms

Higher PEC performance for full water splitting was realized for a CoPi–CdS/ZnO NHA via structural modulation, and degradation in the performance was elucidated.

Fabrication and optically pumped lasing of plasmonic nanolaser with regular ZnO/GaN nanoheterojunction array

We present the design and fabrication of a novel regularly arrayed plasmonic nanolasers. This main microstructure of the device is composed of a hexagonal array of n-ZnO/p-GaN nanoheterojunctions fabricated using the micro-fabrication method. Furthermore, the optically pumped lasing in the device is demonstrated. The spectroscopy characterization results of the device show that the surface plasmon excited around the NWs surface can be used to stimulate and strongly compress the optical modes in the NW cavity. This electromagnetic confinement effect is employed to optimize the beam quality and increase the light intensity compared to the laser fabricated with the bare NWs array. The impact of the array arrangement on the coherent combining efficiency of the arrayed nanolasers has been numerically studied. The results show that the arrayed hexagonal nanolasers could improve the combining efficiency compared to the nanolaser with the randomly positioned array. Qualitatively, these calculated results agree well with the experimental results of the laser beam spot mapping. This demonstrates the scope for using such architectures to improve the combination efficiency of the arrayed nanolasers.

Fabrication of the glass microlens arrays and the collimating property on nanolaser

The influence of the glass microlens array on the collection efficiency and beam collimating with the ZnO/GaN nanoheterojunction nanolaser is investigated. Ultraviolet random lasing behavior from the ZnO/GaN nanoheterojunction array has been demonstrated with both optical and electrical pumping. The refractive microlens arrays are designed and fabricated on the glass slide using the microfabrication procedures and integrated on the nanolaser. We show that, for the nanolaser with divergent output beams, the introduction of glass microlens arrays reduces the beam divergence and increases transmission. The detected optical power is enhanced by more than 1.8 times for the nanolaser integrated with glass microlens arrays. The drastic increase in the optical collection efficiency is resulted from the laser beam collimating.

Optically pumped lasing and electroluminescence in ZnO/GaN nano-heterojunction array devices

The preparation of a highly ordered ZnO/GaN nano-heterojunction array is introduced. Combining the merits of nanolaser and plasmonic Fabry–Perot nanolaser, we designed and fabricated an ultraviolet nanolaser with Ag-dielectric hybrid film-coated n-ZnO nanowires (NWs) array on p-GaN substrate. Ultraviolet random lasing behavior from the ZnO/GaN nano-heterojunction array has been demonstrated with both optical and electrical pumping, where the surface plasmon enhancement effect in the lasing process is discussed. The numerical simulation results show the surface plasmon at the Ag/SiO2/ZnO interface may be excited and strongly compress the wave-guided modes, which were found to optimize the lasing spectrum and increase the light intensity compared to the bare NWs array. With the electric pumping of the device, the electroluminescence parameters are characterized and the underlying mechanism is also discussed.

Towards Perfectly Ordered Novel ZnO/Si Nano-Heterojunction Arrays

The fabrication of a highly ordered novel ZnO/Si nano-heterojuntion array is introduced. ZnO seed layer is first deposited on the Si (P<111>) surface. The nucleation sites are then defined by patterning the surface through focused ion beam (FIB) system. The ZnO nanorods are grown on the nucleation sites through hydrothermal process. The whole fabrication process is simple, facile and offers direct control of the space, length and aspect ratio of the array. It is found that ZnO/Si nanojunctions show an improved interface when subjected to heat treatment. The recrystallization of ZnO and the tensile lattice strain of Si developed during the heating process contribute the enhancement of their photoresponses to white light. The photoluminescence (PL) measurement result of nano-heterojunction arrays with different parameters is discussed.

Piezo-phototronic Effect Enhanced Visible/UV Photodetector of a Carbon-Fiber/ZnO-CdS Double-Shell Microwire

A branched ZnO-CdS double-shell NW array on the surface of a carbon fiber (CF/ZnO-CdS) was successfully synthesized via a facile two-step hydrothermal method. Based on a single CF/ZnO-CdS wire on a polymer substrate, a flexible photodetector was fabricated, which exhibited ultrahigh photon responsivity under illuminations of blue light (1.11 × 10(5) A/W, 8.99 × 10(-8) W/cm(2), 480 nm), green light (3.83 × 10(4) A/W, 4.48 × 10(-8) W/cm(2), 548 nm), and UV light (1.94 × 10(5) A/W, 1.59 × 10(-8) W/cm(2), 372 nm), respectively. The responsivity of this broadband photon sensor was enhanced further by as much as 60% when the device was subjected to a -0.38% compressive strain. This is because the strain induced a piezopotential in ZnO, which tunes the barrier height at the ZnO-CdS heterojunction interface, leading to an optimized optoelectronic performance. This work demonstrates a promising application of piezo-phototronic effect in nanoheterojunction array based photon detectors.

Photovoltaic effect of CdS/Si nanoheterojunction array

Nanostructured materials have attracted much attention for enhancing the performance of solar cells due to their unique advantage of high light absorption. In this regard, here we propose a CdS/Si nanoheterojunction array, called CdS/Si-NPA, for harvesting the energy of sunlight. CdS/Si-NPA was obtained by depositing a continuous film of CdS onto silicon nanoporous pillar array (Si-NPA) via a chemical bath deposition (CBD) method and the average reflectance of CdS/Si-NPA was less than 7% in the wavelength range of 200–1000 nm. Under 1 sun air mass (AM) 1.5 G illumination, CdS/Si-NPA exhibits an obvious photovoltaic effect. These results indicate that CdS/Si-NPA has a strong broadband optical antireflection and might be a promising candidate for the assembly of high efficiency solar cells.

Sono‐ and Photochemical Routes for the Formation of Highly Dispersed Gold Nanoclusters in Mesoporous Titania Films

AbstractA sono‐ and photochemical approach has been developed to incorporate highly dispersed gold nanoclusters into mesoporous TiO2 films. The first step involves the sonication of a TiO2 film immersed in a gold chloride solution. This effectively removes the air trapped in the porous film matrix and drives the gold chloride into the pore channels, leading to a homogeneous adsorption of ionic Au in the TiO2 mesoporous matrix. The second step takes advantage of the photocatalytic property of TiO2 to reduce the adsorbed Au ions to Au0. As the gold nanoclusters thus produced are stabilized by the TiO2 mesonetwork, no organic capping molecules are required. Highly dispersed Au/TiO2 nanoheterojunction arrays can be obtained using this interesting approach.