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ZnO nanorods were successfully deposited on Transparent Conductive Oxide (TCO) glass by electrochemical deposition, during which initial pulse potential proves important for the fast nucleation and even distribution of ZnO. CdS nanoparticles were coated outside the as-prepared ZnO nanorods by chemical-bath deposition forming ZnO/CdS nanoarrays. The nanoarrays were characterized by X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), ultraviolet-visible (UV-vis) spectroscopy, and photoelectrochemistry. The short-circuit current density (J(sc)) of some ZnO/CdS sample showed over 3.3 mA/cm(2) under solar-simulated illumination. The ZnO/CdS nanoarrays showed promising photocatalytic activity with respect to the degradation of Eriochrome Black T (EBT). The relatively high photoelectrochemical properties and photocatalytic performance under visible light irradiation can be ascribed to the enhanced visible light harvest from CdS and charge separation by the coupling of the semiconductors. The combination of electrodeposition and chemical-bath deposition can provide a simple and facile approach to the fabrication of one-dimensional nanocomposites. 

ZnO is a widely used semiconductor photocatalyst. However, the bandgap of ZnO is too large to utilise visible light or solar energy. Therefore, ZnO can couple with a narrow band gap semiconductor that is a visible-light-responsive photocatalyst. ZnO can help with charge seperation through attracting electrons or holes from the other semiconductor. In this work, ZnO nanorods were electrodeposited on FTO glass, and then coated with ultrathin layer of Fe₂O₃ via ALD.

SEM, TEM, XPS, Raman and UV-Vis spectroscopies were used to characterise the prepared samples. Raman shows that ALD-coated Fe₂O₃ is hematite (α-Fe₂O₃). The prepared ZnO/Fe₂O₃ shows photocatalytic activity of EBT degradation under visible light illumination. The synthetic strategy can also beextended to prepare other heterostructured photocatalysts.

Zinc oxide is a well-known metal oxide semiconductor with a wide direct band gap that offers a promising alternative to titanium oxide in photocatalytic applications. ZnO is studied here as quantum dots (QDs) in colloidal suspensions, where ultrasmall nanoparticles of ZnO show optical quantum confinement with a band gap opening for particles below 9 nm in diameter from the shift of the band edge energies. The optical properties of growing ZnO QDs are determined with Tauc analysis, and a system of QDs for the treatment and degradation of distributed threats is analyzed using an organic probe molecule, methylene blue, whose UV/vis spectrum is analyzed in some detail. The effect of optical properties of the QDs and the kinetics of dye degradation are quantified for low-dimensional ZnO materials in the range of 3-8 nm and show a substantial increase in photocatalytic activity compared to larger ZnO particles. This is attributed to a combined effect from the increased surface area as well as a quantum confinement effect that goes beyond the increased surface area. The results show a significantly higher photocatalytic activity for the QDs between 3 and 6 nm with a complete decolorization of the organic probe molecule, while QDs from 6 nm and upward in diameter show signs of competing reduction reactions. Our study shows that ultrasmall ZnO particles have a reactivity beyond that which is expected because of their increased surface area and also demonstrates size-dependent reaction pathways, which introduces the possibility for size-selective catalysis.

Thermal losses through vibrational coupling are critical bottlenecks limiting several materials classes from reaching their full potential. Altering the phonon–phonon and electron–phonon coupling by controlled suppression of vibrational degrees of freedom through low-dimensionality are promising but still largely unexplored approaches. Here we report a detailed study of the first- and second-order Raman processes as a function of size for low-dimensional ZnO. Wurtzite ZnO nanoparticles were synthesised into 3D frameworks of ZnO crystallites, with tailored crystallite diameters from 10 nm to 150 nm and characterised by electron microscopy, X-ray diffraction and non-resonant and resonant Raman spectroscopy.

We present a short derivation of how resonance Raman and the relation between the longitudinal optical (LO) phonons can be utilised to quantify the electron–phonon coupling, its merits, and limitations. Theoretical Raman response using density functional theory is corroborating the experimental data in assigning first- and second-order Raman modes. The Lyddane-Sachs-Teller equation was applied to the measured LO–TO split and revealed no change in the ratio between the static and high-frequency dielectric constant with changing ZnO dimension from 10 nm to 150 nm. The second-order Raman revealed a phonon–phonon coupling that generally increased with particle size and markedly so for differential modes. Resonance Raman showed the fundamental LO mode and the 2nd, 3rd, and 4th overtones. The intensity relation between the fundamental LO mode and its overtones enabled the extraction of the change in electron–phonon coupling via the Huang-Rhys parameter as a function of particle size, which showed an increase with particle size.