Recent progress in barium zirconate proton conductors for electrochemical hydrogen device applications: A review

Electrochemical hydrogen devices like fuel cells are widely investigated as promising technologies to mitigate the rising environmental challenges and enhance the renewable energy economy. In these devices, proton-conducting oxides (PCOs) are applied as electrolyte materials to transport protons. Excellent physical stability and higher proton transport number are two essential properties of electrolyte materials. Doped BaZrO₃ (BZO) is a solid ion-conducting perovskite material with high chemical stability and good proton-conducting properties at an intermediate temperature range of 400–650 °C. Therefore, BZO is an attractive material among the exciting proton-conducting oxides as electrolyte material. To enhance the proton transport properties and improve the material fabrication process of BZO, techniques such as the use of dopants, sintering aid, synthesis methods are crucial. The present review work highlights the applications of BZO as electrolyte material in electrochemical hydrogen devices such as hydrogen isotopes separation systems, hydrogen sensors, hydrogen pumps, and protonic ceramic fuel cells (PCFCs) or solid oxide fuel cells (SOFCs). The central section of this review summarizes the recent research investigations of these applications and provides a comprehensive insight into the various synthesis process, doping, sintering aid, operating environments, and operating condition's impact on the composition, morphology, and performance of BZO electrolyte materials. Based on the reviewed literature, remarks on current challenges and prospects are provided. The presented information on in-depth analysis of the physical properties of barium zirconate electrolyte's along with output performance will guide aspirants in conducting research further on this field.     

A sandwich structure assisted by defect engineering for higher thermoelectric performance in ZnO-based films

Gallium (Ga) doping together with low dimensionality has been a promising approach to improve thermoelectric performance of zinc oxide (ZnO) materials, due to the increase of carrier concentration and suppression of phonon transport. So far, the highest power factor of Ga-doped ZnO (GZO) thin films has reached 280 μW m⁻¹ K⁻², which is still limited for practical applications. In this work, we have simultaneously optimized the electrical conductivity and Seebeck coefficient of GZO thin films using the combination of oxygen defects and sandwich structure (GZO-ZnO-GZO). Benefiting from energy filtering effect at the interface between GZO and ZnO layers and high oxygen vacancy concentration, the density of states (DOS) effective mass has been increased together with a relatively high carrier concentration. As a result, an improved power factor value of 434 μW m⁻¹ K⁻² at 623 K has been achieved, which is comparable to the best values reported for ZnO-based films. This method of combining defect engineering and sandwich structure design shows great potential in enhancing the thermoelectric performance of ZnO-based thin films or other oxide materials.     

ZnO基光电极的构筑及其光电催化水分解性能研究进展

光电催化水分解制取氢气是最理想的制氢技术之一。光电极材料作为光电催化水分解反应系统最核心的部分,决定着太阳能到化学能的转换效率。氧化锌（ZnO）半导体因具有较低的超电势、高的电子迁移速率和价格低廉等优点,引起了广泛关注。然而,ZnO半导体的禁带较宽、电子-空穴易于复合和表面水氧化反应动力学缓慢,阻碍了其高效利用太阳能和实现理论效率。本文从ZnO的微纳结构和表界面修饰两个方面出发,综述了近年来ZnO基光电极的构筑策略及其光电催化性能的研究进展。首先阐述了ZnO的微观形貌和缺陷对光电性质的影响。然后总结了元素掺杂、量子点敏化、贵金属沉积、异质结构造和共催化剂沉积等策略对ZnO基半导体的表界面的构筑及对光电催化性能的影响。最后对未来高效ZnO基半导体光电极研究方向进行了展望,具体包括5个方面：ZnO表面改性;在原子水平构筑复合半导体催化剂的相界面;用廉价双金属或多金属纳米颗粒取代纯贵金属Au、Ag和Pt纳米颗粒;构建高效的电催化剂助剂;在ZnO半导体和助剂界面引入空穴储存层或电子堵塞层。     

The use of bioelectrochemical systems in environmental remediation of xenobiotics: a review

Remediation of anthropogenic pollutants in our environment has become an imperative of the 21st century in order to sustain human activity and all life on the planet. With the current limitations of the existing technologies for this purpose, the need for innovative bioremediation technologies has become vitally important. Hitherto, electrochemically active microorganisms have only been a scientific curiosity and a platform for sustainable power production from waste material. However, recent research utilizing these electrochemically active microorganisms in bioelectrochemical systems (BES) has revealed their promising potential for bioremediation applications. The primary research focus of BES applications up-to now has been to optimize and increase their power output. The possibility of utilizing these systems for bioremediation applications has been a new facet of this field of work. This review provides a comprehensive outlook on the utilization of BES based technologies for remediation of xenobiotic environmental pollutants. © 2018 Society of Chemical Industry     

Developments in photocatalytic antibacterial activity of nano TiO<Subscript>2</Subscript>: A review

TiO₂, which is one of the most explored materials, has emerged as an excellent photocatalyst material for environmental and energy fields, including air and water purification, self-cleaning surfaces, antibacterial and water splitting. This review summarizes recent research developments of TiO₂-based photocatalyst used for photocatalytic antibacterial applications. Several strategies to enhance the efficiency of TiO₂ photocatalyst are discussed, including doping with metal ions, noble metals, non-metals, and coupling with other materials. The mechanism of photocatalytic antibacterial activity in the presence of nano-sized TiO₂ is also discussed. The modified TiO₂ photocatalyst significantly inhibits the growth of bacterial cells in response to visible light illumination. TiO₂ photocatalysis appears to be promising as a route of advanced oxidation process for environmental remediation.     

Zinc ferrite based gas sensors: A review

Flammable, explosive and toxic gases, such as hydrogen, hydrogen sulfide and volatile organic compounds vapor, are major threats to the ecological environment safety and human health. Among the available technologies, gas sensing is a vital component, and has been widely studied in literature for early detection and warning. As a metal oxide semiconductor, zinc ferrite (ZnFe₂O₄) represents a kind of promising gas sensing material with a spinel structure, which also shows a fine gas sensing performance to reducing gases. Due to its great potentials and widespread applications, this article is intended to provide a review on the latest development in zinc ferrite based gas sensors. We first discuss the general gas sensing mechanism of ZnFe₂O₄ sensor. This is followed by a review of the recent progress about zinc ferrite based gas sensors from several aspects: different micro-morphology, element doping and heterostructure materials. In the end, we propose that combining ZnFe₂O₄ which provides unique microstructure (such as the multi-layer porous shells hollow structure), with the semiconductors such as graphene, which provide excellent physical properties. It is expected that the mentioned composites contribute to improving selectivity, long-term stability, and other sensing performance of sensors at room or low temperature.     

Nano-confined ammonia borane for chemical hydrogen storage

There is a great demand for a sufficient and sustainable energy supply. Hence, the search for applicable hydrogen storage materials is extremely important owing to the diversified merits of hydrogen energy. In this regard, ammonia borane (NH₃BH₃, AB) containing 19.6 wt-% hydrogen has been considered as a promising material for hydrogen storage applications to realize the “hydrogen economy”, but with limits from slow kinetics of hydrogen release and by-product of trace gases such as ammonia and borazine. In this review, we introduce the recent research on AB, regarding to the nanoconfinement effect on improving the kinetics at a relatively low temperature and the prevention/reduction of undesirable gas formation.     

金属-有机框架材料在石化环保领域的应用

石油化工是我国的支柱产业，也是环境污染的主要来源。近年来，随着国家环保形势的日益严峻和相应环保法规的陆续出台，高效处理石化行业所涉及的各类污染问题已成为重中之重。作为一种新型的纳米多孔材料，金属-有机框架（MOF）在石化环保领域展现出了广阔的应用前景。该材料可作为高性能吸附剂、分离膜以及催化材料去除或降解石化行业中的典型污染物。本文系统梳理了MOF材料及其相关工艺在石化环保领域的潜在应用，重点介绍了近年来国内外取得的突破性进展，并在此基础上深入分析了该材料的应用现状、存在问题及未来的研发方向。总体而言，MOF材料具有比传统多孔材料更优异的结构特征和应用性能；展望未来，其能够作为吸附剂、分离膜或是催化材料在石化环保领域得到更大规模的推广与应用。     

铋系半导体光催化剂研究进展

铋系半导体材料具有特殊的层状结构以及合适的带隙,具有良好的可见光响应能力以及稳定的光化学特性,作为一类新型的环境友好型光催化剂在环境修复与解决能源危机等领域受到广泛关注,已成为近年来的研究热点。然而,铋系半导体光催化剂距离实际大规模应用仍存在一些亟需解决的问题,如光生载流子复合率高、对可见光谱的响应范围有限、光催化活性较差、还原能力较弱等。本文首先介绍了铋系半导体材料的典型特征、制备方法与反应机理,在此基础上着重阐述了铋系半导体光催化在形貌调控、构建异质结、离子掺杂、碳质材料掺杂、贵金属沉积、染料敏化等改性手段的研究进展以及在降解水体污染物、杀菌消毒、空气净化、制氢、还原CO2、有机合成等领域的应用成果。最后对铋系半导体光催化剂的未来前景做出展望,指出其未来的研究方向应致力于从多手段耦合改性、拓展其应用领域以及深入探究反应机理等方面开展。     

Greener synthesis and medical applications of metal oxide nanoparticles

Over the past decade, the subject of “greener chemistry" and chemical processes has been emphasized. The “greener chemistry” improves environmental efficiency in reducing the consumption of resources and energy and achieving a stable economic development of the environment. Nanotechnology is investigating nanoscale materials that have applications in the area of biotechnology and nanomedicine alongside several other significant applications such as cosmetics, drug delivery, and biosensors. The different shapes and sizes of nanoparticles can be synthesized with physical, chemical, or biological methods. The tendency to produce nanomaterials, especially metal oxides, and use them, is increasing because of their exciting properties in the nanoscale. However, metal oxide nanoparticles produced by chemical methods have significant concerns due to hazardous and toxic chemicals and their environmental damage. The production of metal oxide nanoparticles using the principles of greener chemistry has found a special place in research. Increased awareness of greener chemistry and biological processes has necessitated using environmentally friendly methods for the production of non-toxic nanomaterials. Plants and polymeric materials as renewable and inexpensive sources have received particular attention to prepare nano biomaterials. The use of plants to synthesize metal oxide nanoparticles because of the non-use toxic pollutants is one of the environmentally friendly methods, and that's why this type of synthesis is called greener synthesis. In this review, we exhibit a total sight of greener synthesis methods for producing metal oxide nanoparticles and their medical applications.     

球磨改性生物炭在环境修复中的应用进展

利用球磨机械力化学技术制备的改性生物炭具有成本低、产能高、绿色无溶剂等优点,近年来受到研究人员的广泛关注.球磨改性增加生物炭表面官能团、扩大其比表面积以及提高吸附容量,使球磨改性生物炭对环境污染物具有优异的去除性能,在环境修复领域应用前景广阔.介绍了球磨改性生物炭的制备与理化性质,总结了球磨改性生物炭在环境修复中对污染物质去除的最新进展,同时明确其对各类污染物的去除机制.在此基础上,探讨球磨改性生物炭在环境修复中目前存在的问题与限制因素,从明确技术和经济可行性、扩展材料应用范围以及厘清潜在生态环境风险等方面提出未来研究方向.     

Recent progress in zinc oxide nanomaterials and nanocomposites: From synthesis to applications

The global market of ZnO grows at an annual rate of 4.03%. ZnO has been used in a wide array of applications owing to its unique chemical, physical, and biological properties. In general, the properties of ZnO, such as band gap, crystallite size, and morphology, depend on the synthesis method and parameters employed. In this review, recent progress in the research on ZnO is presented. This review focuses on the latest advancements in pristine ZnO, doped ZnO, ZnO-based nanocomposites with other metal oxides, carbon-based materials, and spinels. The effect of the synthesis method and conditions on the properties of ZnO is discussed. In particular, recent studies on ZnO prepared through precipitation method, green synthesis, green combustion method, hydrothermal method, microwave-assisted hydrothermal, and sol–gel synthesis are reviewed. The effect of dopants and metal oxides on ZnO characteristics is also laid out. This review aims to provide the readers with a thorough understanding of structure–property relationships achieved by varying the synthesis parameters of ZnO, which will be beneficial for the fabrication of high-performance ZnO-based materials for photocatalytic, biological, gas sensing, and flexible electronic applications.     

Current developments in nanostructurally engineered metal oxide for removal of contaminants in water

Clean water is one of the vital resources of every living being residing on this earth. However, rapid industrialization, growing human population, urbanization, global warming, extensive agricultural practices, and climatic change have deprived them of access to clean water. These factors convert clean water into wastewater by polluting water and making it poisonous due to heavy metals. 3.575 million deaths are observed from diseases caused by waste or polluted water every year, according to the World Health Organization report. Hence, wastewater treatment has become every country's primary concern. Although several conventional methods are available for wastewater treatment, their utilization has been restrained due to the high maintenance cost of equipment, the large surface area for installation, and a large amount of energy. Nanotechnology offers a lot of potential for improving the efficiency of water purification and disinfection. Nanomaterials can remove inorganic and organic pollutants, biological pollutants (fungi, bacteria, and microbes), and heavy metal ions from wastewater. Metal oxide nanoparticles (NPs) are the most diverse class of materials due to their unique properties such as good adsorption capacity, large surface area, improved catalysis, and enhanced reactivity. Hence, metal oxide NPs have applications in wastewater treatment. A comprehensive overview of the numerous metal oxide NPs in wastewater treatment has been presented in this review. Here, in detail, we have discussed zinc oxide, titanium oxide, silver oxide, tungsten oxide, iron oxide, and copper oxide NPs and their application in wastewater treatment.     

木质素基碳材料催化剂的制备及应用研究进展

木质素具有三维网状苯环结构、来源丰富、含碳量高、官能团丰富可控等特点,是一种理想的碳材料前体。通过化学改性和微结构调控制备具有特殊功能的木质素基碳材料,其在能源催化转化、电化学储能和环境修复等领域应用广泛。本文介绍了木质素基碳材料催化剂的国内外最新研究进展,总结了木质素基碳材料催化剂的制备方法,重点综述了木质素基碳材料催化剂在氧化反应、氢解反应、酯化反应、水解反应、脱水反应、费托合成等热催化反应、电解水析氢和锌空气电池氧还原等电催化反应、有机污染物降解等光催化反应的研究进展,但如何构筑高效、稳定、廉价、可规模生产的木质素基碳材料催化剂仍然是一个具有挑战性的课题。文章总结：今后研究中应加强对木质素的基础化学结构和微结构调控、活性组分与木质素碳材料载体间的相互作用、木质素基碳材料催化剂在催化反应中的作用机理等的研究,更好地发挥其低成本、三维结构易成型和微结构可调控等优势,拓展木质素生物质资源的高值化利用领域。     

Recent progress on metal core@semiconductor shell nanocomposites as a promising type of photocatalyst

The creation of core-shell nanocomposites (CSNs) has attracted considerable attention and developed into an increasingly important research area at the frontier of advanced materials chemistry. CSNs, which are nanoscaled assemblies with a chemical composition that is different on the surface compared to the core region, have found versatile applications in many fields, such as electrooptics, quantum dots, microscopy labels, drug delivery, chemical sensors, nanoreactors and catalysis. This review is primarily focused on the applications of metal core@semiconductor shell nanocomposites in heterogeneous photocatalysis, including photocatalytic nonselective processes for environmental remediation, selective organic transformations to fine chemicals and water splitting to clean hydrogen energy. It is hoped that this minireview can inspire multidisciplinary research interest in the precisely morphology-controlled synthesis of a variety of metal core@semiconductor shell nanoassemblies and their wide applications in the realm of heterogeneous photocatalysis.     

Synthesis of ZnO rod arrays on aluminum recyclable paper and effect of the rod size on power density of eco-friendly nanogenerators

In this work, we demonstrated a novel and effective approach on the use of low-cost electrodes, an eco-friendly substrate and zinc oxide (ZnO) micro or nanorods (MRs or NRs, respectively) for building triboelectric devices (TENGs). The reported strategy focuses on using low-cost materials and fabrication processes. For the first time and without any pre-treatment, an aluminum recyclable paper from the milk carton (named ARP) was used as a substrate and TENG bottom electrode. A systematic study on the growing of ZnO structures on ARP by chemical bath deposition has been carried out. We found that the ZnO rods size, and resistivity of the TENG upper electrode considerably influence the power density of the device. Such sustainable, low-priced ZnO-based TENGs can produce up to 1.6μW/cm² output power density when operated at 50?Hz. The fabrication of an eco-friendly nanogenerator demonstrates the possibility of manufacturing low-cost, flexible, and large-area energy harvesting devices for future applications.     

Perspectives and challenges of hydrogen storage in solid-state hydrides

Hydrogen has been widely considered as a clean energy carrier that bridges the energy producers and energy consumers in an efficient and safe way for a sustainable society. Hydrogen can be stored in a gas, liquid and solid states and each method has its unique advantage. Though compressed hydrogen and liquefied hydrogen are mature technologies for industrial applications, appropriate measures are necessary to deal with the issues at high pressure up to around 100 MPa and low temperature at around 20 K. Distinct from those technologies, storing hydrogen in solid-state hydrides can realize a more compact and much safer approach that does not require high hydrogen pressure and cryogenic temperature. In this review, we will provide an overview of the major material groups that are capable of absorbing and desorbing hydrogen reversibly. The main features on hydrogen storage properties of each material group are summarized, together with the discussion of the key issues and the guidance of materials design, aiming at providing insights for new material development as well as industrial applications.     

Construction of CuS/ZnO Z-scheme heterojunction as highly efficient piezocatalyst for degradation of organic pollutant and promoting N2 fixation properties

Piezocatalytic technology has great potential in addressing water-system pollution and countering energy crises issues. Herein, high-performance CuS/ZnO Z-scheme heterojunction piezocatalyst was prepared by environmentally friendly solid-state chemistry approach and explored piezocatalytic performances toward degradation of organic methylene blue (MB) dye pollutant and nitrogen (N₂) fixation activity under ultrasonic vibration. The CuS/ZnO piezocatalyst presents outstanding property in MB degradation process with high efficiency (94.7% in 40 min), high rate constant (0.06804 min⁻¹) and good recyclability stability in comparison with the numerous ZnO-based piezocatalysts. In addition, this catalyst also exhibits superior piezocatalytic activity with a production rate of nitrogen fixation rate of 77.5 μmol L⁻¹ g_cat⁻¹ h⁻¹ in the reduction of N₂ to ammonia process, which is approximately 4-folds higher than that of pristine ZnO. Such improvement was mainly attributed to the facilitating charge carriers separation via rational construction of Z-scheme heterojunction as well as enhanced redox capacity. A novel piezocatalytic Z-scheme heterojunction mechanism of CuS/ZnO has been proposed and elucidated. This work suggests that designing highly efficient CuS/ZnO piezocatalyst will be a promising candidate material for prospects application in coping with the environmental remediation pollutants and energy crisis problems.     

Microbial electrolysis cell as an emerging versatile technology: a review on its potential application,advance and challenge

Microbial electrolysis cells (MECs) have been studied in a wide range of potential applications such as recalcitrant pollutants removal, chemicals synthesis, resources recovery and biosensors. However, MEC technology is still in its infancy and poses serious challenges for practical large-scale applications. To understand the diversified applications of MEC, this review aims to explore MEC applications in the following contexts: an overview of MEC for energy generation and recycling such as hydrogen, methane, formic acid and hydrogen peroxide; contaminant removal, specifically complex organic pollutants and inorganic pollutants; as a sensor; as well as resource recovery. New concepts of MEC technology; configuration optimization; electron transfer pathways in biocathodes, and coupling with other technologies for value-added applications such as MEC-anaerobic digestion, MEC-MFC, MEC-MDC and bio-E-Fenton system are discussed. Finally, challenges and outlooks are suggested. The review aims to assist researchers and engineers to understand the latest trends in MEC technologies and applications. © 2018 Society of Chemical Industry     

Polymer - phyllosilicate nanocomposites for high-temperature structural application

ABSTRACT

The increasing demand for more weight efficient material systems has called upon for the development of polymer composites for various applications where special properties are anticipated like thermo-physical resistance, bio-compatibility, anti-bacterial, electromagnetic characteristics etc. In recent years, polymeric materials have been explored with wide range of additives to optimize the overall performance of the final composite product. In this review, the authors have tried to comprehend the effect of such modification especially by layered silicates on the mechanical properties and design compatibility of the material.