Strong visible photoluminescence emission of ZnO nanosheets and nanoflowers by a facile hydrothermal route

Highly C-oriented (002) plane ZnO nanowires synthesis

Nanowires are widely used for energy harvesting, sensors, and solar cells. We report a study on the role of buffer layer in the growth of zinc oxide (ZnO) nanowires (NWs) synthesised by a chemical bath deposition (CBD) method. To control the thickness of the buffer layer, multilayer coatings corresponding to one layer (100 nm thick), three layers (300 nm thick), and six layers (600 nm thick) of ZnO sol-gel thin-films were used. The evolution of the morphology and structure of ZnO NWs was characterized by scanning electron microscopy, X-ray diffraction, photoluminescence, and Raman spectroscopy. Highly C-oriented ZnO (002)-oriented NWs were obtained on both substrates, silicon and ITO, when the thickness of the buffer layer was increased. The role of ZnO sol-gel thin films used as a buffer layer for the growth of ZnO NWs with (002)-oriented grains also resulted in a significant change in surface morphology on both substrates. The successful deposition of ZnO NWs on a variety of substrates, as well as the promising results, open up a wide range of applications.

Influence of Ag Photodeposition Conditions over SERS Intensity of Ag/ZnO Microspheres for Nanomolar Detection of Methylene Blue

Surface enhanced Raman spectroscopy (SERS) is considered a versatile and multifunctional technique with the ability to detect molecules of different species at very low molar concentration. In this work, hierarchical ZnO microspheres (ZnO MSs) and Ag/ZnO MSs were fabricated and decorated by hydrothermal and photodeposition methods, respectively. For Ag deposition, precursor molar concentration (1.9 and 9.8 mM) and UV irradiation time (5, 15, and 30 min) were evaluated by SEM, TEM, X-ray diffraction and Raman spectroscopy. X-ray diffraction showed a peak at 37.9° corresponding to the (111) plane of Ag, whose intensity increases as precursor concentration and UV irradiation time increases. SEM images confirmed the formation of ZnO MSs (from 2.5 to 4.5 µm) building by radially aligned two-dimensional ZnO nanosheets with thicknesses below 30 nm. The Raman spectra of Ag/ZnO MSs exhibited a vibration mode at 486 cm⁻¹ which can be directly associated to Ag deposition on ZnO MSs surface. The performance of SERS substrate was evaluated using rhodamine 6G. The SERS substrate grown at 9.8 mM during 30 min showed the best SERS activity and the ability to detect methylene blue at 10⁻⁹ M.

High-Performance Piezo-Electrocatalytic Sensing of Ascorbic Acid with Nanostructured Wurtzite Zinc Oxide

Nanostructured piezoelectric semiconductors offer unprecedented opportunities for high-performance sensing in numerous catalytic processes of biomedical, pharmaceutical, and agricultural interests, leveraging piezocatalysis that enhances the catalytic efficiency with the strain-induced piezoelectric field. Here, a cost-efficient, high-performance piezo-electrocatalytic sensor for detecting l-ascorbic acid (AA), a critical chemical for many organisms, metabolic processes, and medical treatments, is designed and demonstrated. Zinc oxide (ZnO) nanorods and nanosheets are prepared to characterize and compare their efficacy for the piezo-electrocatalysis of AA. The electrocatalytic efficacy of AA is significantly boosted by the piezoelectric polarization induced in the nanostructured semiconducting ZnO catalysts. The charge transfer between the strained ZnO nanostructures and AA is elucidated to reveal the mechanism for the related piezo-electrocatalytic process. The low-temperature synthesis of high-quality ZnO nanostructures allows low-cost, scalable production, and integration directly into wearable electrocatalytic sensors whose performance can be boosted by otherwise wasted mechanical energy from the working environment, for example, human-generated mechanical signals.