Zinc oxide can be called a multifunctional material thanks to its unique physical and chemical properties. The first part of this paper presents the most important methods of preparation of ZnO divided into metallurgical and chemical methods. The mechanochemical process, controlled precipitation, sol-gel method, solvothermal and hydrothermal method, method using emulsion and microemulsion enviroment and other methods of obtaining zinc oxide were classified as chemical methods. In the next part of this review, the modification methods of ZnO were characterized. The modification with organic (carboxylic acid, silanes) and inroganic (metal oxides) compounds, and polymer matrices were mainly described. Finally, we present possible applications in various branches of industry: rubber, pharmaceutical, cosmetics, textile, electronic and electrotechnology, photocatalysis were introduced. This review provides useful information for specialist dealings with zinc oxide.

Zinc Oxide-From Synthesis to Application: A Review.

High concentrations of defects are introduced into nanoscale ZnO through non-equilibrium processes and resultant blue emissions are comprehensively analyzed, focusing on defect origins and broad controls. Some ZnO nanoparticles exhibit very strong blue emissions, the intensity of which first increase and then decrease with annealing. These visible emissions exhibit strong and interesting excitation dependences: 1) the optimal excitation energy for blue emissions is near the bandgap energy, but the effective excitation can obviously be lower, even 420 nm (2.95 eV < Eg = 3.26 eV); in contrast, green emissions can be excited only by energies larger than the bandgap energy; and, 2) there are several fixed emitting wavelengths at 415, 440, 455 and 488 nm in the blue wave band, which exhibit considerable stability in different excitation and annealing conditions. Mechanisms for blue emissions from ZnO are proposed with interstitial-zinc-related defect levels as initial states. EPR spectra reveal the predominance of interstitial zinc in as-prepared samples, and the evolutions of coexisting interstitial zinc and oxygen vacancies with annealing. Furthermore, good controllability of visible emissions is achieved, including the co-emission of blue and green emissions and peak adjustment from blue to yellow.

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Blue Luminescence of ZnO Nanoparticles Based on Non‐Equilibrium Processes: Defect Origins and Emission Controls

Lithium-sulfur (Li-S) batteries have attracted tremendous interest because of their high theoretical energy density and cost effectiveness. The target of Li-S battery research is to produce batteries with a high useful energy density that at least outperforms state-of-the-art lithium-ion batteries. However, due to an intrinsic gap between fundamental research and practical applications, the outstanding electrochemical results obtained in most Li-S battery studies indeed correspond to low useful energy densities and are not really suitable for practical requirements. The Li-S battery is a complex device and its useful energy density is determined by a number of design parameters, most of which are often ignored, leading to the failure to meet commercial requirements. The purpose of this review is to discuss how to pave the way for reliable Li-S batteries. First, the current research status of Li-S batteries is briefly reviewed based on statistical information obtained from literature. This includes an analysis of how the various parameters influence the useful energy density and a summary of existing problems in the current Li-S battery research. Possible solutions and some concerns regarding the construction of reliable Li-S batteries are comprehensively discussed. Finally, insights are offered on the future directions and prospects in Li-S battery field.

More Reliable Lithium-Sulfur Batteries: Status, Solutions and Prospects.

Driven by functionality and purity demand for applications of inorganic nanoparticle colloids in optics, biology, and energy, their surface chemistry has become a topic of intensive research interest. Consequently, ligand-free colloids are ideal reference materials for evaluating the effects of surface adsorbates from the initial state for application-oriented nanointegration purposes. After two decades of development, laser synthesis and processing of colloids (LSPC) has emerged as a convenient and scalable technique for the synthesis of ligand-free nanomaterials in sealed environments. In addition to the high-purity surface of LSPC-generated nanoparticles, other strengths of LSPC include its high throughput, convenience for preparing alloys or series of doped nanomaterials, and its continuous operation mode, suitable for downstream processing. Unscreened surface charge of LSPC-synthesized colloids is the key to achieving colloidal stability and high affinity to biomolecules as well as support materials,...

Laser Synthesis and Processing of Colloids: Fundamentals and Applications

Laser ablation of solid targets in the liquid medium can be realized to fabricate nanostructures with various compositions (metals, alloys, oxides, carbides, hydroxides, etc.) and morphologies (nanoparticles, nanocubes, nanorods, nanocomposites, etc.). At the same time, the post laser irradiation of suspended nanomaterials can be applied to further modify their size, shape, and composition. Such fabrication and modification of nanomaterials in liquid based on laser irradiation has become a rapidly growing field. Compared to other, typically chemical, methods, laser ablation/irradiation in liquid (LAL) is a simple and “green” technique that normally operates in water or organic liquids under ambient conditions. Recently, the LAL has been elaborately developed to prepare a series of nanomaterials with special morphologies, microstructures and phases, and to achieve one-step formation of various functionalized nanostructures in the pursuit of novel properties and applications in optics, display, detection, and biological fields. The formation mechanisms and synthetic strategies based on LAL are systematically analyzed and the reported nanostructures derived from the unique characteristics of LAL are highlighted along with a review of their applications and future challenges.

Nanomaterials via Laser Ablation/Irradiation in Liquid: A Review

ZnO nanostructures for optoelectronics: Material properties and device applications

ZnO is a material which is of great interest for a variety of applications due to its unique properties and the availability of a variety of growth methods resulting in a number of different morphologies and a wide range of material properties of synthesized nanostructures. In this review, we will discuss recent advances in important and/or controversial issues concerning ZnO properties and its applications. We will also discuss areas where further improvements are needed, and in particular discuss the issues related to the environmental stability of ZnO and its implications on reproducibility of measurements and the toxicity of ZnO nanomaterials.

ZnO nanostructures: growth, properties and applications

The utilization of porous carbon frameworks as hosts for sulfur loading is an important theme in current Li-S battery research. Unfortunately, the high loading of insulating sulfur often leads to low specific capacities, poor rate properties, and rapid capacity loss. To address this challenge, a facile templating route to fabricate a novel host material, hierarchical porous carbon rods constructed by vertically oriented porous graphene-like nanosheets (HPCR) is presented. With a high specific surface area, ultralarge pore volume, hierarchical porous structures, and ideal ion transfer pathways, HPCR is a promising candidate for high sulfur loading. When used as the active material for a sulfur cathode, the HPCR-S composite with 78.9 wt% sulfur exhibits excellent rate performance (646 mAh g−1sulfur at 5 C) and cycling stability (700 mAh g−1sulfur after 300 cycles at 1 C). Even with a sulfur content of 88.8 wt%, the HPCR-S composite, without any additional protective polymer coating, still delivers a good rate performance (545 mAh g−1sulfur at 3 C) and cycling stability (632 mAh g−1sulfur after 200 cycles at 1 C). More importantly, the high sulfur loading (88.8 wt%) ensures that the HPCR-S composite has a high energy density (880 mAh cm−3cathode after 200 cycles at 1 C).

High Sulfur Loading in Hierarchical Porous Carbon Rods Constructed by Vertically Oriented Porous Graphene‐Like Nanosheets for Li‐S Batteries

Cathodoluminescence spectroscopy is used to address the ultraviolet (UV) luminescence of a single pencil-like ZnO nanowire whose diameter gradually reduces from bottom to top in the range of 700-50 nm. It is found that the UV emission energy evidently shifts to the high energy with the ZnO nanowire's diameter decreasing and the blue-shift of 90 meV is observed when the nanowire diameter reduces to 50 from 700 nm. The physical mechanism of the UV blue-shift of the ZnO nanowire is attributed to the Burstein-Moss effect under the high carrier concentration.

Physical mechanism of blue-shift of UV luminescence of a single pencil-like ZnO nanowire.

We have investigated the effect of ZnO nanoparticle properties on the dye-sensitized solar cell performance. Nanoparticles with different sizes and optical properties were considered. We found that there is a complex relationship between native defects, dye adsorption, charge transport and solar cell performance. The presence of a high concentration of nonradiative defects was found to be detrimental to photovoltaic performance, whereas for radiative defects, samples displaying orange-red defect emission exhibited better performance compared to samples with green defect emission (when the samples had similar emission intensities). Detailed discussion of the nanoparticle properties and their relationship with dye adsorption, electron injection, electron lifetime, electron transport time, and solar cell performance is given.

Xinyi Chen

Papers

ZnO nanostructures for optoelectronics: Material properties and device applications

ZnO nanostructures: growth, properties and applications

High Sulfur Loading in Hierarchical Porous Carbon Rods Constructed by Vertically Oriented Porous Graphene‐Like Nanosheets for Li‐S Batteries

Physical mechanism of blue-shift of UV luminescence of a single pencil-like ZnO nanowire.

Effect of ZnO nanoparticle properties on dye-sensitized solar cell performance.