Nanomaterials Innovation

This special issue “Nanomaterials Innovation” gathers 26 articles, derived from the keynote presentations at the 1st 2018 International Conference of Novel Function Materials (ICNFM2018). The workshop was held from 16th to 18th September, 2018 in Anshan (China), as the 70th anniversary of the University of Science and Technology Liaoning (USTL), which has made outstanding contributions to novel functional materials. The ICNFM2018 was meant to provide a platform of academic communication and promote the development of subjects related to innovative materials. More than 500 global scientists participated in the events of the ICNFM2018. Nanomaterials have attracted increasing attention in the past decades. The interest in nanoscale materials stems from the fact that new properties are acquired at this length scale, and in addition, these properties may be changed with the size and shape. Consistent with traditional materials, the development of innovative nanomaterials also follows the route from fundamental exploration to practical applications. In general, nanomaterials innovation mainly focuses on the following aspects. Material innovation. New nanomaterials are continuously discovered or prepared. In the past decades, several intrinsic nanomaterials have been reported, such as 0-dimensional (quantum dots), 1-dimensional (nanotubes, nanowires), and 2-dimensional (graphene). These materials with unique structures have expanded the field of material science. With the development of elaborate synthesis approaches, some traditional materials such as metal, metal oxides and ceramics, have been also prepared in nanoscale structures, showing distinct properties such as surface plasmon resonance. In this special issue, Du et al. introduced germanene and functionalized germanene. Inspired by carbon-based graphene, germanene is a new family of single-atom-thick 2-dimensional (2D) germanium-based materials with graphene-like atomic arrangement.1 Resulting from a chemically active surface and easily tuned electronic states, germanene provides a large bandgap and easily tailored electronic properties, even superior to carbon-based materials. In addition to single-component materials, nano-composite integrates the advantages of multiple functional materials, exhibiting even more diversified designs. Shen et al. introduced artificial photosynthesis with metal nanoparticle decorated carbon nitride. The close-contacted semiconductors and metals may change the interfacial energy, thus promoting catalytic activity. However, material innovation may be the most challenging and fundamental research in nanomaterial innovation. Characterization innovation. Some characterization methods have been developed to demonstrate the special properties of nanomaterials, such as high-resolution scanning electron microscopy, transmission microscopy and scanning transmission microscopy. Recently, more advanced approaches have been reported to better demonstrate certain properties of nanomaterials. “Nanoimpact” is such an approach to observe performance in single-particle scale. It is a novel electrochemistry method and the characteristics of single particles were examined with stochastic collision of particles at microelectrode.2 The performance in single-particle scale would assist the mechanism exploration and property discovery of nanomaterials. In general, characterization innovation may provide tools for exploring fascinating properties of existing or innovative nanomaterials. Property innovation. Nanomaterials are characterized with various approaches to explore their properties. Because of the nanoscale structure, the materials also show some new properties distinguished from micromolecular or macromolecular materials. Aggregation-induced emission has been derived from the nanoaggregates of molecules with conjugated structure.3 The aggregation-induced emitters can also be well designed and tailored. Biomacromolecule-functionalized emitters are compatible with several biomedical applications. Carbon dots have been another class of luminescent materials that benefit from nanoscale size. Carbon dots are well compatible with matrices such as porous materials, layered materials and amorphous silica.4 The resultant composites show special luminescent properties, including room temperature phosphorescence and thermally activated delayed fluorescence. As the biomimetic products of biological ion channels, nanochannels/nanopores are promising materials in response to analyses or external stimuli and regulating the transport of ions/molecules.5 Xia summarized the biomolecule-functionalized solid-state ion nanochannels/nanopores, including its features on recognition and signal amplification. The modification of nucleic acids, proteins and small biomolecules specifically enhanced these features of nanochannels/nanopores.5 Several interesting properties of nanomaterials have been reported by researchers worldwide. As an interdisciplinary research field, nanotechnology has also played roles in traditional electrical engineering.6 However, more potential properties of innovative nanomaterials would be explored with innovative characterization approaches. Application innovation. The performance of nanomaterials in various applications can be evaluated according to their properties. With the research foundations in the past decades, most promising nanomaterials were extensively applied in various fields, with great achievements. The applications of most nanomaterials focus on biology, catalysis, energy conversion and storage. For applications in biology, nanomaterials have been extensively applied in biosensing, bioimaging and theranostics. Some nanomaterials show good optical properties compared to traditional dyes, such as quantum dots, carbon dots and AIEgens. As signaling molecules, these nanomaterials can be good candidates for diagnosis, bioimaging and therapy after they are integrated with targeted or recognizable components. For instance, lanthanide-doped nanoparticles could be signaling molecules, since the unique electronic configuration and ladder-like energy states of lanthanides endow the nanoparticles with desirable optical properties, such as long luminescence lifetimes, large Stokes/anti-Stokes shifts, and sharp emission bands. After the functionalization of target molecules, the lanthanide-doped nanoparticles are deeply applied in high-sensitivity biosensing and bioimaging.7 Carbon dots are commonly applied as both imaging agents and/or drug carriers, enabling this material a promising multi-functional theranostic system.8 Furthermore, after being prepared in nanostructures, traditional phototherapy agents show enhanced performance against cancer. Such nano-photosensitizers provide better efficacy when they are applied in photodynamic therapy and photothermal therapy.9 Zhang and Xu summarized the applications of nanoparticle-based drug delivery systems in cancer immunotherapy. The size, shape, surface charge, and elasticity of nano-delivery systems influence the efficacy of immuno-therapeutics, through affecting the transport and biodistribution behaviors.10 Due to the bio-compatibility of nanomaterials, their biological applications have achieved good results. However, in vivo biological applications of nanomaterials would face the challenge of biosafety. For application in catalysis, nanomaterials have been known for their large specific surface area and rich functional sites. However, other fantastic electrical and chemical properties are still being revealed. In this issue, Duan and co-workers have introduced metal–organic architectures based asymmetric catalysis. Metal–organic architectures including metal–organic cages and metal–organic frameworks with chiral confined cavities/pores can be applied as asymmetric catalysts with high enantioselectivity.11 Further, the integration of metal nanoparticles into metal–organic frameworks offers even more structure and property diversity, which exhibit characteristics of two components.12 Nanomaterials have found the vast majority of applications in energy conversion and storage. Sustainable energy applications have been a research hotspot since the exhaust of foil fuel. Meanwhile, nanomaterials have played various roles in energy conversion and storage devices, such as dye-sensitized solar cells, perovskite solar cells, photocatalysts, electrocatalysts, fuel cells, storage batteries, supercapacitors, hydrogen storage systems and nanogenerators. Siliceous materials are natural candidates of electric components. However, in recent years, nonsiliceous materials also show promising properties, with even more structure and component diversity, with the representative materials of titanic oxide, niobium oxides13 and carbon nitride.14 General applications of the above materials in energy conversion and storage have been reviewed in this special issue. The attractive properties of nanomaterials enable potential applications based on energy storage devices. Energy storage technology has benefited from the large surface area, short transport path, and excellent buffering ability of nanostructures such as multi-shell and hollow structures.15 Batteries may be the most important devices in energy storage, such as Li-ion/Na-ion batteries, supercapacitors, and Li–S batteries. The Li-ion battery has dominated the market for portable electronics and electric vehicles. Due to concerns on the cost and resource availability of lithium, Na-ion16, 17 and Mg-ion batteries18 are regarded as ideal alternatives for their similar electrochemistry to the Li-ion battery and the crust abundance of metal resources. Since the rapid development of nanotechnology and accumulated experience in Li-ion batteries, the previous challenges such as slow diffusion kinetics of Na-ion16, 17 and Mg-ion batteries are being resolved. Recently, high-power cathode and anode materials for Na-ion batteries have been explored. With innovative materials such as layered transition metal oxides, the Na ions could be reversibly intercalated.17 Several design strategies of Na-ion batteries have attracted more and more interest. Guo has reviewed unique Na-ion full-cells, including interface issues, major challenges, and recent progresses.19 For Mg-ion batteries, extensive studies have been reported to explore the cathode materials and optimal structure for overcoming the problems of high charge density, strong polarization effect, and very slow insertion/extraction speed of Mg ions.18 Other elaborately designed nanogenerators have also been introduced for energy conversion. Thermal energy harvesting from the ambient environment is an ideal way to realize self-powered operation of electronics, which can be realized with thermoelectric nanogenerators. Nanotechnology has affected both material optimization and structural designs in thermoelectric nanogenerators.20 Nanogenerators show promising applications in artificial intelligence, self-powered sensing systems, wearable electronics, artificial neuromorphic system and other fields in the future.21 In these future applications, structural design and material selection have been the key factors. Innovative nanomaterials with superior electrical and chemical properties would be good foundations. Materials innovation, characterization innovation and property innovation promote the prosperous application innovations. Good performance has been achieved in most of these applications, which support its further investigation. Richard Phillips Feynman has even stated, “There's plenty of room at the bottom!”, which opened a new century of nanotechnology. With the efforts of thousands of researchers in this field, nowadays we also believe, “There's plenty of room in the future of nanomaterials!” Yongfei Wang received his B.S. from China University of Mining and Technology in 2005, and his M.S. and Ph.D. in Chemical Engineering from the University of Science and Technology Liaoning (USTL) in 2008 and 2018, respectively. He is currently working as a lecturer in USTL. His current research interests include functional materials and catalysts for electrochemical energy technologies. Shulei Chou is a Principal Research Fellow in ISEM at the University of Wollongong (UOW). He obtained his bachelor's (1999) and master's degrees (2004) from Nankai University, China. His research focuses on energy storage materials for battery applications, especially on novel composite materials, new binders, and new electrolytes for Li-ion and Na-ion batteries. Zhiqiang Zhang received his B.S. from Nankai University in 1985, and his M.S. from the University of Science and Technology Liaoning (USTL) in 1990, and Ph.D. from Dalian University of Technology in 2009. He is currently working as a Professor in USTL. His current research interests include catalytic reactions such as the organometallic catalytic reaction and the photoelectric catalytic reaction.