Volume 5, Issue 1 - Special issue: Emerging nanotechnology for environmental applications / Issue editors: Yanbiao Liu, Choon Nam Ong and Jianping Xie

This paper provides a comprehensive review of recent progress in the synthesis and performance of graphene and carbon-based nanomaterials as efficient adsorbents for oils and organic solvents. Several advantages of these adsorbents are emphasized, including adjustable three-dimensional networks, high surface area, high chemical/thermal stability, high flexibility and elasticity, and extremely high surface hydrophobicity/ oleophilicity. Technical challenges are discussed, and future research directions are proposed.

In recent decades, carbon aerogels (CAs) have attracted increasing attention. Compared with other carbon materials, CAs are available in macroscopic diverse morphologies with tunable hierarchical porosity and large specific surface area. The interconnected carbonaceous framework also endows CAs with excellent electrical properties. CA can be a promising material for various purposes through proper design and functionalization. In this article, we place an emphasis on CAs based on resorcinol-formaldehyde resin and graphene sheets. We review the state-of-the-art progress on the preparation of functionalized CAs, and the relationships between their advanced nanoarchitectures and performances in environmental remediation, including adsorption, capacitive deionization and catalysis, are discussed. The challenges in design and application of CAs are also proposed.

Electrochemically active carbon nanotube (CNT) filters have been developed as a highly efficient technology for water and wastewater treatment during the last few years. CNT filters have been widely used to adsorb chemical and biological contaminants due to their high stability, great flexibility, and large specific surface area. Electrochemically active CNT filters provide additional electrooxidation of the adsorbed contaminants and have been proven to be a highly effective treatment technology in a few recent lab-scale studies. The working principles, impacting factors, and some of the latest development of electrochemically active CNT filters are reviewed in this paper. The existing challenges and future perspectives are also discussed.

Over the last few decades, the excess exploitation of our planet and degradation of environment have gone up at an alarming rate. Environmental problems, especially air and water pollution, which takes a huge number of years to recover, have become the major concern affecting the progress of human society. The overwhelming threats have driven global research and innovation in the development of advanced technology and devices toward a cleaner environment. In this context, the generation of functional one-dimensional (1-D) nanomaterials has become an area of intense interest from both academia and industry due to their unique advantages for environmental applications. Electrospinning is recognized as the most powerful technique for producing 1-D composite nanofibers via facile incorporation of active ingredients in the solutions for electrospinning or by some posttreatment process. In this review, we give an overview on the latest research progress in the fabrication and utilization of functional polymer/ceramic/carbon nanofibers generated by electrospinning for air and water purification, as well as their applications as sensors for pollutant monitoring and control. We also present the perspectives and challenges of the current electrospinning technique for environmental applications.

Titanium dioxide nanotube arrays (TiO 2 NTAs) have attracted much interest due to their unique highly ordered array structure, outstanding properties, and potential applications in photo/photoelectrocatalytic degradation of pollutants, hydrogen production, supercapacitors, dye-sensitized solar cells, sensors, and biomedical devices. It has been fabricated via a facile electrochemical anodic oxidation of Ti substrate in fluoride-containing electrolytes. Combined with our previous work, we comprehensively review the recent progress of TiO 2 TNAs on the synthesis processes, forming mechanism, and modification used to improve the photoelectric properties. In addition, this article summarizes some of the recent advances on the photo/photoelectrocatalytic degradation of pollutants. Besides, other applications and the future development of TiO 2 TNAs are also briefly discussed and addressed.

The use of nanoscale materials for efficient solar light harvesting has attracted immense attention in the recent time in order to address the energy and environmental issues. Among them, semiconductor materials such as ZnO have been widely used in the field of photocatalysis and dye-sensitized solar cells (DSSC). However, due to limited visible-light activity and low photo-conversion efficiency, ZnO needs to be modified to design heterostructures with efficient charge separation. Several strategies have been made to modify the wide-bandgap semiconductors including narrow-bandgap semiconductor coupling, noble metal deposition, conducting polymer sensitization and organic dye sensitization. However, the activity of such heterogeneous systems critically depends on the charge dynamics across the involved nanostructured interface. The present review is an effort to unravel the ultrafast dynamical processes across the interface of heterostructures to enhance the solar light-harvesting efficiency. Here, we have discussed few of our selected results covering the different modification strategies of the ZnO nanostructures. The special emphasis has been given to the correlation between the ultrafast processes at the interface and their implications in the light-harvesting applications. The detailed spectroscopic investigations revealing electronic pathways for light harvesting will be helpful in designing future solar devices.

Photocatalysis has received much attention as it is considered one of the potential solutions for solar energy conversion and counteracting environmental degradation. In order to promote the research work of the field and meet the requirements of practical applications, it is necessary to develop high efficiency visible-light-driven photocatalysts, especially the red semiconductor photocatalysts. This review aims to sum up the progress recently made in this field, concentrating on the scientific and technological possibilities offered by three kinds of red semiconductor photocatalysts for water splitting, organic contaminant decomposition, and CO 2 photoreduction. The important progress is discussed and explained in detail, including the synthesis, characterization, and specific applications of red semiconductor photocatalysts. Finally, the review concludes by summarizing both findings and perspectives.

The strong growing interest in using catalytic oxidation to remove volatile organic compounds (VOCs), which seriously threaten the health of human being, is rooted in its desirable features such as relative energy savings, low cost, operation safety and environmental friendliness. Within the last decades, the development of manufacturing processes, characterization techniques and testing methods has led to the blossom of research in synthesis and application of various nanostructured materials, which creates great opportunities and also a tremendous challenge to apply these materials for highly efficient catalytic removal of VOCs. We herein will systematically introduce the latest research developments of nanostructured materials for the catalytic degradation of VOCs so as to provide the readers a coherent picture of the field, mainly focusing on noble metals and metal oxides, which are currently two primary types of VOC catalysts. This review will focus on synthesis, fabrication and processing of nanostructured noble metals and metal oxides as well as the fundamentals and technical approaches in catalytic removal of VOCs, providing technical strategies for effectively developing novel nanostructured catalysts with low cost, enhanced activity and high stability for pollutant removal from surrounding environments.