Colloidal Approaches to Zinc Oxide Nanocrystals

Abstract

Zinc oxide is an extensively studied semiconductor with a wide band gap in the near-UV. Its many interesting properties have found use in optics, electronics, catalysis, sensing, as well as biomedicine and microbiology. In the nanoscale regime the functional properties of ZnO can be precisely tuned by manipulating its size, shape, chemical composition (doping), and surface states. In this review, we focus on the colloidal synthesis of ZnO nanocrystals (NCs) and provide a critical analysis of the synthetic methods currently available for preparing ZnO colloids. First, we outline key thermodynamic considerations for the nucleation and growth of colloidal nanoparticles, including an analysis of different reaction methodologies and of the role of dopant ions on nanoparticle formation. We then comprehensively review and discuss the literature on ZnO NC systems, including reactions in polar solvents that traditionally occur at low temperatures upon addition of a base, and high temperature reactions in organic, nonpolar solvents. A specific section is dedicated to doped NCs, highlighting both synthetic aspects and structure−property relationships. The versatility of these methods to achieve morphological and compositional control in ZnO is explicated. We then showcase some of the key applications of ZnO NCs, both as suspended colloids and as deposited coatings on supporting substrates. Finally, a critical analysis of the current state of the art for ZnO colloidal NCs is presented along with existing challenges and future directions for the field.

Synthesis and Antimicrobial Applications of ZnO Nanostructures: A Review

“…For the interested reader, there are several reports on the synthesis-dependent applications of ZnO nanostructures. 25,107,108 Considering the role of ZnO NSs, it is not possible to include all of the applications in a single work. However, we wanted to provide a general overview about the wide variety of technological fields where nanostructured ZnO is used by collecting some published reviews about its application in Table 2.…”

“…Table reports a demonstrative comparison between the above-mentioned synthesis approaches and the respective features of ZnO NSs, proving their tunability according to the final applications. For the interested reader, there are several reports on the synthesis-dependent applications of ZnO nanostructures. ,, …”

Back to the Basics: Probing the Role of Surfaces in the Experimentally Observed Morphological Evolution of ZnO

“…This plethora of complex morphologies appears because ZnO crystals exhibit exposed surfaces with low surface energy values and with both polar and non-polar natures. This behavior causes relative rates of crystal surface growth to be modulated by temperature, reaction time, and the presence of a surfactant, a capping agent, counterions, or a solvent in the synthesis process [ 23 , 26 , 27 , 28 , 29 ].…”

All-Solution-Processed Perovskite Light-Emitting Diodes Based on a Thiol-Modified ZnO Electron-Transporting Layer

“…ZnO nanoparticles (NPs) have been widely used to fabricate an electron transport layer (ETL) in all-solution-processed quantum dot light-emitting diodes, because of their high electron mobility, low work function, excellent optical transparency, and environmentally friendly nature, resulting in excellent performance. − However, ZnO NPs used in all-solution-processed LEDs are commonly dispersed in polar solvents such as ethanol, isopropanol, butanol, etc., which can cause destruction of the perovskite film. , As a result, the fabrication of ZnO films atop the perovskite emissive layers would cause severe exciton quenching. These problems can be alleviated by regulating the perovskite compositions and using metal dopants and orthogonal dispersants of ZnO NPs. − Additionally, the unsuitable energy levels between ZnO NPs and perovskite can cause electron transfer from perovskite to ZnO, which also causes photoluminescence (PL) quenching .…”