Surface Engineering of Nanostructured ZnO Surfaces

Abstract

are oriented in one direction and their assembly and stacking produces the wurtzite hexagonal symmetry. The noncentrosymmetric and anisotropic crystalline structure of wurtzite-like ZnO generates very interesting properties such as piezo-and pyro-electricity: the application of an external stimulus, like mechanical stress or temperature, deforms the tetrahedron structure. This deformation results in a separation between the positive and negative centers of charge, inducing the formation of a dipole moment. [7,8] The polar surface and anisotropic structure of ZnO can be usefully exploited to form different kinds of micro and nanostructures from 0D to 3D, [5] including, but not limited to nanowires, [9][10][11][12] nanotubes, [13,14] nanobelts, [15][16][17][18][19] nanorings, [20] flower-like morphologies, [21][22][23][24][25] multipods, [26,27] tetrapods, [28][29][30] sponge-like structures [31][32][33][34] and so on [29,[35][36][37][38][39] (Figure 1). Therefore, several research efforts have been invested in studying various preparation procedures for ZnO micro and nano-materials. Wet chemical approaches, like sol-gel, hydrothermal growths, electrodeposition and template-assisted routes, [40,41] as well as vapor-phase methods, for example chemical vapour deposition (CVD), physical vapour deposition (PVD) including sputtering and evaporation approaches, [42][43][44] and epitaxial growth methods [45] are among the most used ones. The great advantages of the wet chemical approaches are the high synthesis versatility, low temperature employed and low costs. [9] From the other side, dry methods take advantage of the high quality and excellent control over the level of crystallinity of the synthesized ZnO structures, as well as the absence of contamination and high purity of the final material. [46] The combination of different properties with the ease and high versatile synthesis of ZnO material in different micro and nanostructures offers a huge possibility of potential applications.For example, ZnO is already used as an efficient catalyst in the selective oxidation of involving oxygenates (i.e., alcohols, aldehydes, and carboxylic acids) and in methanol synthesis catalysts. It is also largely applied as protective, anti-corrosion layer in galvanized steel products, [49][50][51] as well as in paints and sunscreens as an UV absorber. Its biocompatibility makes this material suitable, in the form of microparticles, for paste formulations in cosmetic applications.The combination of the piezoelectric with the semiconducting properties of ZnO is found to result into new exciting physical properties, [52][53][54] and it has recently opened the research field to energy harvesting application. ZnO nanomaterials can be thus used as nanogenerators, able to convert the mechanical deformation from the surrounding environment into electrical Zinc Oxide (ZnO) nanostructures represent promising substrate materials for numerous applications, ranging from new generation solar cells, to bio-and chemical sensors. This interest is due ...

ZnO Nanostructures for Tissue Engineering Applications

“…From left to right and from top to bottom: Quantum dot; Nanotubes; Nanowires; Nanobelts; Nanoring; Nanocombs; Tetrapod; Nanoflowers; Hollow spheres; Sponge-like film; Nanosphere; Nanoplates. Adapted with permission from reference [ 65 ]. Copyright (2017) John Wiley & Sons, Inc.…”

Computational Approaches to Photoelectrode Design through Molecular Functionalization for Enhanced Photoelectrochemical Water Splitting

“…Refs. provide comprehensive overviews of experimental efforts to enhance photoelectrode stability using this approach. However, the computational study of photoelectrode stability has traditionally been challenging even for non‐functionalized surfaces because the presence of the aqueous electrolyte needs to be taken into account.…”

“…Extending this approach to functionalized surfaces can shed light on design strategies for choosing functional group termination, steric size, and electrolyte pH value . First‐principles MD might also better explain the relatively wide‐ranging experimental observations of water interactions with functionalized semiconductor surfaces such as the instability of TiO 2 /silane interfaces or the superior stability of alkyne‐based monolayers . However, despite the potential of the approach, an important challenge for the computational community is to develop a framework for obtaining widely applicable design principles or heuristics to avoid having to perform expensive first‐principles MD simulations for every functionalized photoelectrode system.…”

Solution‐Processed Molybdenum Oxide with Hydroxyl Radical‐Induced Oxygen Vacancy as an Efficient and Stable Interfacial Layer for Organic Solar Cells

“…[10][11][12] The demand for a highly efficient and stable IL, acting as an electrode modifier and charge-transporting layer, led to the development of various types of ILs including conducting polymers, self-assembled monolayers, conjugated polyelectrolytes, and metal oxides. [13][14][15][16][17][18][19] To date, a large number of studies for cathode ILs have been undertaken, whereas relatively few studies were reported for anode ILs, which simultaneously serve as good efficiency enhancers and stabilizers. A commonly used anode IL, poly(3,4-ethylene dioxythiophene):poly(styrene sulfonate) (PEDOT:PSS), has desirable optical and electrical properties but shows limitation in terms of device stability, due to its well-known hygroscopic and acidic nature.…”