National Nanotechnology Center

Copper oxide-derived Cu catalysts are known to exhibit enhanced energetic efficiencies and selectivities towards the reduction of carbon dioxide to commercially vital C2 products such as ethylene (C2H4). However, the cause of this selectivity is not fully understood. In this work, we elucidated a fundamental reason underlying the selectivity of CO2 reduction toward C2 products by studying its reactivity on Cu(100), Cu(111), and Cu(110) single-crystal surfaces. A combination of cyclic and linear sweep voltammetries, chronoamperometry, online gas chromatography, 1H nuclear magnetic resonance spectroscopy, and density functional theory (DFT) calculations was employed for this end. A wide range of electrochemical potentials from −0.28 to −1.25 V versus the reversible hydrogen electrode was investigated. Aqueous 0.1 M KHCO3 was used as the electrolyte. We report here two general trends on Cu2O-derived Cu and Cu single-crystal surfaces: (i) the onset potential for the formation of C2H4 always starts 300–400 mV more negative than the onset potential for CO evolution, and (ii) C2H4 was formed only after a significant amount of CO gas was produced. Among the single-crystal surfaces investigated, Cu(100) required the lowest overpotential to reduce CO2 to C2H4. These observations were rationalized using DFT simulations. Of the three single-crystal surfaces modeled, the dimerization of two CO* molecules on Cu(100) exhibited the lowest energy barrier, and this barrier can be further lowered with higher CO* coverages. The application of our observed experimental trends to other previously reported Cu-based systems strongly suggests that a high surface coverage of CO* is central for the selective formation of C2H4.

Continuing improvement in the pharmacological and therapeutic properties of drugs is driving the revolution in novel drug delivery systems. In fact, a wide spectrum of therapeutic nanocarriers has been extensively investigated to address this emerging need. Accordingly, this article will review recent developments in the use of nanoparticles as drug delivery systems to treat a wide variety of diseases. Finally, we will introduce challenges and future nanotechnology strategies to overcome limitations in this field.

This tutorial review will introduce and explore the fundamental aspects of nanopore (bio)sensing, fabrication, modification, and the emerging technologies and applications that both intrigue and inspire those working in and around the field. Although nanopores can be classified into two categories, solid-state and biological, they are essentially two sides of the same coin. For instance, both garner popularity due to their ability to confine analytes of interest to a nanoscale volume. Due to the vast diversity of nanopore platforms and applications, no single review can cover the entire landscape of published work in the field. Therefore, in this article focus will be placed on recent advancements and developments taking place in the field of solid-state nanopores. It should be stated that the intention of this tutorial review is not to cite all articles relating to solid-state nanopores, but rather to highlight recent, select developments that will hopefully benefit the new and seasoned scientist alike. Initially we begin with the fundamentals of solid-state nanopore sensing. Then the spotlight is shone on the sophisticated fabrication methods that have their origins in the semiconductor industry. One inherent advantage of solid-state nanopores is in the ease of functionalizing the surface with a range of molecules carrying functional groups. Therefore, an entire section is devoted to highlighting various chemical and bio-molecular modifications and explores how these permit the development of novel sensors with specific targets and functions. The review is completed with a discussion on novel detection strategies using nanopores. Although the most popular mode of nanopore sensing is based upon what has come to be known as ionic-current blockade sensing, there is a vast, growing literature based around exploring alternative detection techniques to further expand on the versatility of the sensors. Such techniques include optical, electronic, and force based methods. It is perhaps fair to say that these new frontiers have caused further excitement within the sensing community.

Rising world population is expected to increase the demand for nitrogen fertilizers to improve crop yield and ensure food security. With existing challenges on low nutrient use efficiency (NUE) of urea and its environmental concerns, controlled release fertilizers (CRFs) have become a potential solution by formulating them to synchronize nutrient release according to the requirement of plants. However, the most significant challenge that persists is the "tailing" effect, which reduces the economic benefits in terms of maximum fertilizer utilization. High materials cost is also a significant obstacle restraining the widespread application of CRF in agriculture. The first part of this review covers issues related to the application of conventional fertilizer and CRFs in general. In the subsequent sections, different raw materials utilized to form CRFs, focusing on inorganic and organic materials and synthetic and natural polymers alongside their physical and chemical preparation methods, are compared. Important factors affecting rate of release, mechanism of release and mathematical modelling approaches to predict nutrient release are also discussed. This review aims to provide a better overview of the developments regarding CRFs in the past ten years, and trends are identified and analyzed to provide an insight for future works in the field of agriculture.

Abstract An approach to transforming amorphous organic networks into crystalline covalent organic frameworks (COFs) with retention of the colloidal nanosize and uniform morphology is presented. Specifically, Fe 3 O 4 nanoclusters are encapsulated by a disordering polyimine network via the Schiff‐base reaction. The formed imine bonds could be reconstructed under thermodynamic control to reform the polyimine networks into imine‐linked COFs in situ. Such a core–shell microsphere exhibits the uniform size and spherical shape, controllable COF shell thickness, accessible surface modification, and improved solution dispersibility as well as maintenance of high surface area, periodic micropores, and superior magnetic responsiveness. Additionally, the photothermal conversion effect is demonstrated for the first time on the nanoCOF layers upon exposure to near infrared light, providing convincing evidence for potential use in phototherapy.

Mats of PVA nanofibres were successfully prepared by the electrospinning process and were developed as carriers of drugs for a transdermal drug delivery system. Four types of non-steroidal anti-inflammatory drug with varying water solubility property, i.e. sodium salicylate (freely soluble in water), diclofenac sodium (sparingly soluble in water), naproxen (NAP), and indomethacin (IND) (both insoluble in water), were selected as model drugs. The morphological appearance of the drug-loaded electrospun PVA mats depended on the nature of the model drugs. The 1H-nuclear magnetic resonance results confirmed that the electrospinning process did not affect the chemical integrity of the drugs. Thermal properties of the drug-loaded electrospun PVA mats were analysed by differential scanning calorimetry and thermogravimetric analysis. The molecular weight of the model drugs played a major role on both the rate and the total amount of drugs released from the as-prepared drug-loaded electrospun PVA mats, with the rate and the total amount of the drugs released decreasing with increasing molecular weight of the drugs. Lastly, the drug-loaded electrospun PVA mats exhibited much better release characteristics of the model drugs than drug-loaded as-cast films.

Exploring active and low-cost transition metal oxides (TMOs) based catalysts for volatile organic compounds (VOCs) abatement is vital for air pollution control technologies. Since 18 oxygen atoms are required for the complete mineralization of a toluene molecule, the participation of a large amount of active oxygen is a key requirement for the catalytic oxidation of toluene. Here, toluene degradation was improved by weakening the Co–O bond strength on the surface of cobalt oxide, so as to increase the amount of active oxygen species, while maintaining the high stability of the catalyst for toluene combustion. The bond strength of Co–O and the amount of surface active O2 was regulated by tuning the pyrolysis temperature. The catalyst’s redox ability and surface oxygen species activity are improved due to the weakening of the Co–O bond strength. It has been demonstrated that active oxygen plays a crucial role in boosting toluene combustion by engineering Co–O strength in cobalt oxide catalysts. This work provides a new understanding of the exploration and development of high-performance TMO catalysts for VOCs abatement.

Silver nanoparticles have been used in numerous commercial products, including textiles, to prevent bacterial growth. Meanwhile, there is increasing concern that exposure to these nanoparticles may cause potential adverse effects on humans as well as the environment. This study determined the quantity of silver released from commercially claimed nanosilver and laboratory-prepared silver coated fabrics into various formulations of artificial sweat, each made according to AATCC, ISO and EN standards. For each fabric sample, the initial amount of silver and the antibacterial properties against the model Gram-positive (S. aureus) and Gram-negative (E. coli) bacteria on each fabric was investigated. The results showed that silver was not detected in some commercial fabrics. Furthermore, antibacterial properties of the fabrics varied, ranging from 0% to greater than 99%. After incubation of the fabrics in artificial sweat, silver was released from the different fabrics to varying extents, ranging from 0 mg/kg to about 322 mg/kg of fabric weight. The quantity of silver released from the different fabrics was likely to be dependent on the amount of silver coating, the fabric quality and the artificial sweat formulations including its pH. This study is the unprecedented report on the release of silver nanoparticles from antibacterial fabrics into artificial sweat. This information might be useful to evaluate the potential human risk associated with the use of textiles containing silver nanoparticles.

Systematic evaluation of the accuracy of exchange-correlation functionals is essential to guide scientists in their choice of an optimal method for a given problem when using density functional theory. In this work, accuracy of one Generalized Gradient Approximation (GGA) functional, three meta-GGA functionals, one Nonseparable Gradient Approximation (NGA) functional, one meta-NGA, and three hybrid GGA functionals was evaluated for calculations of the closest interatomic distances, cohesive energies, and bulk moduli of all 3d, 4d, and 5d bulk transition metals that have face centered cubic (fcc), hexagonal closed packed (hcp), or body centered cubic (bcc) structures (a total of 27 cases). Our results show that including the extra elements of kinetic energy density and Hartree-Fock exchange energy density into gradient approximation density functionals does not usually improve them. Nevertheless, the accuracies of the Tao-Perdew-Staroverov-Scuseria (TPSS) and M06-L meta-GGAs and the MN12-L meta-NGA approach the accuracy of the Perdew-Burke-Ernzerhof (PBE) GGA, so usage of these functionals may be advisable for systems containing both solid-state transition metals and molecular species. The N12 NGA functional is also shown to be almost as accurate as PBE for bulk transition metals, and thus it could be a good choice for studies of catalysis given its proven good performance for molecular species.

Gold nanoparticles (AuNPs) have been extensively used as nanomaterials for theranostic applications due to their multifunctional characteristics in therapeutics, imaging, and surface modification. In this study, the unique functionalities of exosome-derived membranes were combined with synthetic AuNPs for targeted delivery to brain cells. Here, we report the surface modification of AuNPs with brain-targeted exosomes derived from genetically engineered mammalian cells by using the mechanical method or extrusion to create these novel nanomaterials. The unique targeting properties of the AuNPs after fabrication with the brain-targeted exosomes was demonstrated by their binding to brain cells under laminar flow conditions as well as their enhanced transport across the blood brain barrier. In a further demonstration of their ability to target brain cells, in vivo bioluminescence imaging revealed that targeted-exosome coated AuNPs accumulated in the mouse brain after intravenous injection. The surface modification of synthetic AuNPs with the brain-targeted exosome demonstrated in this work represents a highly novel and effective strategy to provide efficient brain targeting and shows promise for the future in using modified AuNPs to penetrate the brain.

The performance of various commonly used density functionals is established by comparing calculated values of atomic structure data, cohesive energies, and bulk moduli of all transition metals to available experimental data. The functionals explored are the Ceperley-Alder (CA), Vosko-Wilk-Nussair (VWN) implementation of the Local Density Approximation (LDA); the Perdew-Wang (PW91) and Perdew-Burke-Ernzerhof (PBE) forms of the Generalized Gradient Approximation (GGA), and the RPBE and PBEsol modifications of PBE, aimed at better describing adsorption energies and bulk solid lattice properties, respectively. The present systematic study shows that PW91 and PBE consistently provide the smallest differences between the calculated and experimental values. Additional calculations of the (111) surface energy of several face centered cubic (fcc) transition metals reveal that LDA produces the most accurate results, while all other functionals significantly underestimate the experimental values. RPBE severely underestimates surface energy, which may be the origin for the reduced surface chemical activity and the better performance of RPBE describing adsorption energies.

The facet-dependent catalytic performance of Fe2O3/CeO2 catalysts for the selective catalytic reduction of NO with NH3 (NH3–SCR) has been investigated using combined experimental and density functional theory (DFT) methods. The structure and surface characteristics of the synthesized samples were characterized by XRD, XPS, TEM, ICP–AES, N2 sorption isotherms, Raman spectra, photoluminescence spectra, H2–TPR, NH3–TPD and NO + O2–TPD. It is found that the CeO2 nanorods and Fe2O3/CeO2 nanorods predominately exposed {110} and {100} facets rather than the stable {111} facets on CeO2 nanopolyhedra and Fe2O3/CeO2 nanopolyhedra. The influence of the micromorphologies and surface properties of CeO2 supports on the NO conversion and N2 selectivity has been compared. The Fe2O3/CeO2 nanorods achieve higher catalytic activity than the Fe2O3/CeO2 nanopolyhedra for NH3–SCR of NO. The synergetic effect between CeO2 supports and Fe2O3 species has been demonstrated. The insight into molecular facet dependence by the DFT method clearly showed that the Fe2O3/CeO2 {110} catalyst is more reactive to NO and NH3 gases than the Fe2O3/CeO2 {111} and naked CeO2 {110}, which agree well with the experimental results. As a result, the outstanding catalytic performance of Fe2O3/CeO2 nanorods is attributed to the adsorbed surface oxygen, oxygen defects and atomic concentration of Fe which are associated with their exposed {110} and {100} facets of nanorods.

The working potential of symmetric supercapacitors is not so wide because one type of material used for the supercapacitor electrodes prefers either positive or negative charge to both charges. To address this problem, a novel asymmetrical supercapacitor (ASC) of battery-type MnCo2O4 nanofibers (NFs)//N-doped reduced graphene oxide aerogel (N-rGOAE) was fabricated in this work. The MnCo2O4 NFs at the positive electrode store the negative charges, i.e., solvated OH–, while the N-rGOAE at the negative electrode stores the positive charges, i.e., solvated K+. An as-fabricated aqueous-based MnCo2O4//N-rGOAE ASC device can provide a wide operating potential of 1.8 V and high energy density and power density at 54 W h kg–1 and 9851 W kg–1, respectively, with 85.2% capacity retention over 3000 cycles. To understand the charge storage reaction mechanism of the MnCo2O4, the synchrotron-based X-ray absorption spectroscopy (XAS) technique was also used to determine the oxidation states of Co and Mn at the MnCo2O4 electrode after being electrochemically tested. The oxidation number of Co is oxidized from +2.76 to +2.85 after charging and reduced back to +2.75 after discharging. On the other hand, the oxidation state of Mn is reduced from +3.62 to +3.44 after charging and oxidized to +3.58 after discharging. Understanding in the oxidation states of Co and Mn at the MnCo2O4 electrode here leads to the awareness of the uncertain charge storage mechanism of the spinel-type oxide materials. High-performance ASC here in this work may be practically used in high-power applications.

Recent advances in the fabrication of silicene devices have raised exciting prospects for practical applications such as gas sensing. We investigated the gas detection performance of silicene nanosensors for four different gases (NO, NO2, NH3, and CO) in terms of sensitivity and selectivity, employing density functional theory and nonequilibrium Green’s function method. The structural configurations, adsorption sites, binding energies and charge transfer of all studied gas molecules on silicene nanosensors are systematically discussed in this work. Our results indicate that pristine silicene exhibits strong sensitivity for NO and NO2, while it appears incapable of sensing CO and NH3. In an attempt to overcome sensitivity limitations due to weak van der Waals interaction of those latter gas molecules on the device, we doped pristine silicene with either B or N atoms, leading to enhanced binding energy as well as charge transfer, and subsequently a significant improvement of sensitivity. A distinction between the four studied gases based on the silicene devices appears possible, and thus these promise to be next-generation nanosensors for highly sensitive and selective gas detection.

The efficient electroreduction of CO2 has received significant attention as it is one of the crucial means to develop a closed-loop anthropogenic carbon cycle. Here, we describe the mechanistic workings of an electrochemically deposited CuSx catalyst that can reduce CO2 to formate with a Faradaic efficiency (FEHCOO–) of 75% and geometric current density (jHCOO–) of −9.0 mA/cm2 at −0.9 V versus the reversible hydrogen electrode. At this potential, the formation of other CO2 reduction products such as hydrocarbons and CO was notably suppressed (total FE < 4%). The formate intermediate (HCOO*) was identified by operando Raman spectroscopy with isotopic labeling. A combination of electrochemical and materials characterization techniques revealed that the high selectivity toward formate production can be attributed to the effect of S dopants on the Cu catalyst, rather than surface morphology. Density functional theory calculations showed that the presence of sulfur weakens the HCOO* and *COOH adsorption energies, such that the formation of *COOH toward CO is suppressed, while the formation of HCOO* toward formate is favored.

Abstract Porous single crystals are promising candidates for solar fuel production owing to their long range charge diffusion length, structural coherence, and sufficient reactive sites. Here, a simple template‐free method of growing a selectively branched, 2D anatase TiO 2 porous single crystalline nanostructure (PSN) on fluorine‐doped tin oxide substrate is demonstrated. An innovative ion exchange–induced pore‐forming process is designed to successfully create high porosity in the single‐crystalline nanostructure with retention of excellent charge mobility and no detriment to crystal structure. PSN TiO 2 film delivers a photocurrent of 1.02 mA cm −2 at a very low potential of 0.4 V versus reversible hydrogen electrode (RHE) for photo‐electrochemical water splitting, closing to the theoretical value of TiO 2 (1.12 mA cm −2 ). Moreover, the current–potential curve featuring a small potential window from 0.1 to 0.4 V versus RHE under one‐sun illumination has a near‐ideal shape predicted by the Gartner Model, revealing that the charge separation and surface reaction on the PSN TiO 2 photoanode are very efficient. The photo‐electrochemical water splitting performance of the films indicates that the ion exchange–assisted synthesis strategy is effective in creating large surface area and single‐crystalline porous photoelectrodes for efficient solar energy conversion.

Janus or anisotropic colloidal particles comprising of at least two components of different chemistry, functionality, and/or polarity have attracted attentions in a wide range of applications, e.g., in optics, magnetics, plasmonics, colloidal chemistry, and biomedicine. The interesting features of Janus colloidal particles are attributed to their tunable and controllable asymmetric structure, which allows controlling their physicochemical properties, down to the nanoscale. Moreover, their synergistic potential for multiplexing, multilevel targeting, and combination therapies make them particularly attractive for biomedical applications. However, the synthesis of Janus colloidal particles must be well-adapted to get particles with precise control of their various structural/physical/chemical properties. Nowadays, the advance in new fabrication processes is a strong need for fabricating compact composite particles with spatially separated functionalities, uniform size, tunable composition, and effective response to stimuli. In this review article, we summarized the most recent representative works on Janus colloidal particles including the various fabrication methods, important properties, and their potential applications, particularly in the biomedical field.

The acquired capability of tumor cells to migrate and invade neighboring tissues is associated with high metastatic potential and advanced stage of cancers. Recently, signaling molecules such as reactive oxygen species (ROS) and caveolin-1 (Cav-1) have been implicated in the aggressive behavior of cancer cells. However, the roles of specific ROS in cancer cell migration and Cav-1 regulation are unclear. We demonstrate here that Cav-1 plays an important role in the migration and invasion of human lung carcinoma H460 cells and that these effects are differentially regulated by cellular ROS. Using various known inhibitors and donors of ROS, we found that different ROS have different effects on Cav-1 expression and cell migration and invasion. Superoxide anion and hydrogen peroxide down-regulated Cav-1 expression and inhibited cell migration and invasion, whereas hydroxyl radical up-regulated the Cav-1 expression and promoted cell migration and invasion. The down-regulating effect of superoxide anion and hydrogen peroxide on Cav-1 is mediated through a transcription-independent mechanism that involves protein degradation via the ubiquitin-proteasome pathway. These results indicate the essential role of different ROS in cancer cell motility and through Cav-1 expression, which may provide a key mechanism controlling tumor progression and metastasis. The up-regulation of Cav-1 and cell motility by hydroxyl free radical suggests an important role of this ROS as a positive regulator of tumor progression. The acquired capability of tumor cells to migrate and invade neighboring tissues is associated with high metastatic potential and advanced stage of cancers. Recently, signaling molecules such as reactive oxygen species (ROS) and caveolin-1 (Cav-1) have been implicated in the aggressive behavior of cancer cells. However, the roles of specific ROS in cancer cell migration and Cav-1 regulation are unclear. We demonstrate here that Cav-1 plays an important role in the migration and invasion of human lung carcinoma H460 cells and that these effects are differentially regulated by cellular ROS. Using various known inhibitors and donors of ROS, we found that different ROS have different effects on Cav-1 expression and cell migration and invasion. Superoxide anion and hydrogen peroxide down-regulated Cav-1 expression and inhibited cell migration and invasion, whereas hydroxyl radical up-regulated the Cav-1 expression and promoted cell migration and invasion. The down-regulating effect of superoxide anion and hydrogen peroxide on Cav-1 is mediated through a transcription-independent mechanism that involves protein degradation via the ubiquitin-proteasome pathway. These results indicate the essential role of different ROS in cancer cell motility and through Cav-1 expression, which may provide a key mechanism controlling tumor progression and metastasis. The up-regulation of Cav-1 and cell motility by hydroxyl free radical suggests an important role of this ROS as a positive regulator of tumor progression.

Supported Au25 clusters were prepared through the calcination of Au25(SC12H25)18 on hierarchically porous carbon nanosheets under vacuum at temperatures in the range of 400–500 °C for 2–4 h. TEM and EXAFS analyses revealed that the thiolate coverage on Au25 gradually decreased with increasing calcination temperature and period and became negligibly small when the calcination temperature exceeded 500 °C. The catalysis of these Au25 clusters was studied for the aerobic oxidation of benzyl alcohol. Interestingly, the selectivity for benzaldehyde formation was remarkably improved with the increase in the amount of residual thiolates on Au25, while the activity was reduced. This observation is attributed to the dual roles of the thiolates: the reduction of the oxidation ability of Au25 by electron withdrawal and the inhibition of the esterification reaction on the cluster surface by site isolation.

A novel wearable electronic nose for armpit odor analysis is proposed by using a low-cost chemical sensor array integrated in a ZigBee wireless communication system. We report the development of a carbon nanotubes (CNTs)/polymer sensor array based on inkjet printing technology. With this technique both composite-like layer and actual composite film of CNTs/polymer were prepared as sensing layers for the chemical sensor array. The sensor array can response to a variety of complex odors and is installed in a prototype of wearable e-nose for monitoring the axillary odor released from human body. The wearable e-nose allows the classification of different armpit odors and the amount of the volatiles released as a function of level of skin hygiene upon different activities.