Size-dependent chemistry: properties of nanocrystals

Size Dependent Specific Heat Capacity of PbSe Nanocrystals

Specific heat capacity is one of the most fundamental thermodynamic properties of materials. In this work, we measured the specific heat capacity of PbSe nanocrystals with diameters ranging from 5 to 23 nm, and its value increases significantly from 0.2 to 0.6 J g-1 °C-1. We propose a mass assignment model to describe the specific heat capacity of nanocrystals, which divides it into four parts: electron, inner, surface, and ligand. By eliminating the contribution of ligand and electron specific heat capacity, the specific heat capacity of the inorganic core is linearly proportional to its surface-to-volume ratio, showing the size dependence. Based on this linear relationship, surface specific heat capacity accounts for 40-60% of the specific heat capacity of nanocrystals with size decreasing. It can be attributed to the uncoordinated surface atoms, which is evidenced by the appearance of extra surface phonons in Raman spectra and ab initio molecular dynamics (AIMD) simulations.

Size-Controlled Cu3VSe4 Nanocrystals as Cathode Material in Platinum-Free Dye-Sensitized Solar Cells

In this work, we report the first single-step, size-controlled synthesis of Cu3VSe4 cuboidal nanocrystals, with the longest dimension ranging from 9 to 36 nm, and their use in replacing the platinum counter electrode in dye-sensitized solar cells. Cu3VSe4, a ternary semiconductor from the class of sulvanites, is theoretically predicted to have good hole mobility, making it a promising candidate for charge transport in solar photovoltaic devices. The identity and crystalline purity of the Cu3VSe4 nanocrystals were validated by X-ray powder diffraction (XRD) and Raman spectroscopy. The particle size was determined from the XRD data using the Williamson-Hall equation and was found in agreement with the transmission electron microscopy imaging. Based on the electrochemical activity of the Cu3VSe4 nanocrystals, studied by cyclic voltammetry, the nanomaterials were further employed for fabricating counter electrodes (CEs) in Pt-free dye-sensitized solar cells. The counter electrodes were prepared from Cu3VSe4 nanocrystals as thin films, and the charge transfer kinetics were studied by electrochemical impedance spectroscopy. The work demonstrates that Cu3VSe4 counter electrodes successfully replace platinum in DSSCs. CEs fabricated with the Cu3VSe4 nanocrystals having an average particle size of 31.6 nm outperformed Pt, leading to DSSCs with the highest power conversion efficiency (5.93%) when compared with those fabricated with the Pt CE (5.85%).

Recent advances in iridium-based catalysts with different dimensions for the acidic oxygen evolution reaction

Proton exchange membrane (PEM) water electrolysis is considered a promising technology for green hydrogen production, and iridium (Ir)-based catalysts are the best materials for anodic oxygen evolution reactions (OER) owing to their high stability and anti-corrosion ability in a strong acid electrolyte. The properties of Ir-based nanocatalysts can be tuned by rational dimension engineering, which has received intensive attention recently for catalysis ability boosting. To achieve a comprehensive understanding of the structural and catalysis performance, herein, an overview of the recent progress was provided for Ir-based catalysts with different dimensions for the acidic OER. The promotional effect was first presented in terms of the nano-size effect, synergistic effect, and electronic effect based on the dimensional effect, then the latest progress of Ir-based catalysts classified into zero-dimensional (0D), one-dimensional (1D), two-dimensional (2D) and three-dimensional (3D) catalysts was introduced in detail; and the practical application of some typical examples in the real PEM water electrolyzers (PEMWE) was also presented. Finally, the problems and challenges faced by current dimensionally engineered Ir-based catalysts in acidic electrolytes were discussed. It is concluded that the increased surface area and catalytic active sites can be realized by dimensional engineering strategies, while the controllable synthesis of different dimensional structured catalysts is still a great challenge, and the correlation between structure and performance, especially for the structural evolution during the electrochemical operation process, should be probed in depth. Hopefully, this effort could help understand the progress of dimensional engineering of Ir-based catalysts in OER catalysis and contribute to the design and preparation of novel efficient Ir-based catalysts.

Road Map of Semiconductor Metal-Oxide-Based Sensors: A Review

Identifying disease biomarkers and detecting hazardous, explosive, flammable, and polluting gases and chemicals with extremely sensitive and selective sensor devices remains a challenging and time-consuming research challenge. Due to their exceptional characteristics, semiconducting metal oxides (SMOxs) have received a lot of attention in terms of the development of various types of sensors in recent years. The key performance indicators of SMOx-based sensors are their sensitivity, selectivity, recovery time, and steady response over time. SMOx-based sensors are discussed in this review based on their different properties. Surface properties of the functional material, such as its (nano)structure, morphology, and crystallinity, greatly influence sensor performance. A few examples of the complicated and poorly understood processes involved in SMOx sensing systems are adsorption and chemisorption, charge transfers, and oxygen migration. The future prospects of SMOx-based gas sensors, chemical sensors, and biological sensors are also discussed.

Aerosol-based functional nanocomposite coating process for large surface areas

The incorporation of nanometric-sized objects in conventional coatings can improve the properties of the matrix alone or give rise to new functionalities brought by the nanostructures. Current processes call on various shaping technologies that depend on the nature of the nano-inclusions and the matrix considered. Here, we present an integrated process based on the incorporation of nanoparticles using the aerosol route. It combines divergent nanoparticle jets with a uniform spatial profile and Physical Vapor Deposition (PVD). The chemical nature of the nanoparticles is then independent of that used for the matrix. First samples show that the morphology of nanocomposites is strongly dependent on the particle density in the films. Moreover, using several aerodynamic lens arrays combined with smart masking demonstrate the ability for coating on large surface area (40 cm²) substrates. These extended possibilities for developing new types of nanocomposites on any type of substrate and on large surface areas at low temperatures proves to be of strategic interest for various applications.

Nanomaterials for biogas augmentation towards renewable and sustainable energy production: A critical review

Nanotechnology is considered one of the most significant advancements in science and technology over the last few decades. However, the contemporary use of nanomaterials in bioenergy production is very deficient. This study evaluates the application of nanomaterials for biogas production from different kinds of waste. A state-of-the-art comprehensive review is carried out to elaborate on the deployment of different categories of nano-additives (metal oxides, zero-valent metals, various compounds, carbon-based nanomaterials, nano-composites, and nano-ash) in several kinds of biodegradable waste, including cattle manure, wastewater sludge, municipal solid waste, lake sediments, and sanitary landfills. This study discusses the pros and cons of nano-additives on biogas production from the anaerobic digestion process. Several all-inclusive tables are presented to appraise the literature on different nanomaterials used for biogas production from biomass. Future perspectives to increase biogas production via nano-additives are presented, and the conclusion is drawn on the productivity of biogas based on various nanomaterials. A qualitative review of relevant literature published in the last 50 years is conducted using the bibliometric technique for the first time in literature. About 14,000 research articles are included in this analysis, indexed on the Web of Science. The analysis revealed that the last decade (2010–20) was the golden era for biogas literature, as 84.4% of total publications were published in this timeline. Moreover, it was observed that nanomaterials had revolutionized the field of anaerobic digestion, methane production, and waste activated sludge; and are currently the central pivot of the research community. The toxicity of nanomaterials adversely affects anaerobic bacteria; therefore, using bioactive nanomaterials is emerging as the best alternative. Conducting optimization studies by varying substrate and nanomaterials’ size, concentration and shape is still a field. Furthermore, collecting and disposing nanomaterials at the end of the anaerobic process is a critical environmental challenge to technology implementation that needs to be addressed before the nanomaterials assisted anaerobic process could pave its path to the large-scale industrial sector.

Near-Infrared Polarimetric Image Sensors Based on Ordered Sulfur-Passivation GaSb Nanowire Arrays

The near-infrared polarimetric image sensor has a wide range of applications in the military and civilian fields, thus developing into a research hotspot in recent years. Because of their distinguishing 1D structure features, the ordered GaSb nanowire (NW) arrays possess potential applications for near-infrared polarization photodetection. In this work, single-crystalline GaSb NWs are synthesized through a sulfur-catalyzed chemical vapor deposition process. A sulfur-passivation thin layer is formed on the NW surface, which prevents the GaSb NW core from being oxidized. The photodetector based on sulfur-passivation GaSb (S-GaSb) NWs has a lower dark current and higher responsivity than that built with pure GaSb NWs. The photodetector exhibits a large responsivity of 9.39 × 10² A/W and an ultrahigh detectivity of 1.10 × 10¹¹ Jones for 1.55 μm incident light. Furthermore, the dichroic ratio of the device is measured to reach 2.65 for polarized 1.55 μm light. Through a COMSOL simulation, it is elucidated that the origin of the polarized photoresponse is the attenuation of a light electric field inside the NW when the angle of incident polarization light rotates. Moreover, a flexible polarimetric image sensor with 5 × 5 pixels is successfully constructed on the ordered S-GaSb NW arrays, and it exhibits a good imaging ability for incident near-infrared polarization light. These good photoresponse properties and polarized imaging abilities can empower ordered S-GaSb NW arrays with technological potentials in next-generation large-scale near-infrared polarimetric imaging sensors.

Application of a solid-phase microextraction-gas chromatography-mass spectrometry/metal oxide sensor system for detection of antibiotic susceptibility in urinary tract infection-causing Escherichia coli - A proof of principle study

PURPOSE

Antibiotic resistance is widespread throughout the world and represents a serious health concern. There is an urgent need for the development of novel tools for rapidly distinguishing antibiotic resistant bacteria from susceptible strains. Previous work has demonstrated that differences in antimicrobial susceptibility can be reflected in differences in the profile of volatile organic compounds (VOCs) produced by dissimilar strains. The aim of this study was to investigate the effect of the presence of cephalosporin antibiotics on the VOC profile of extended spectrum beta-lactamase (ESBL) and non-ESBL producing strains of Escherichia coli.

MATERIAL AND METHODS

In this study, VOCs from strains of Escherichia coli positive and negative for the most commonly encountered ESBL, CTX-M in the presence of cephalosporin antibiotics were assessed using solid-phase microextraction (SPME) coupled with a combined gas chromatography-mass spectrometry/metal oxide sensor (GC-MS/MOS) system.

RESULTS

Our proof-of-concept study allowed for distinguishing CTX-M positive and negative bacteria within 2 ​h after the addition of antibiotics. One MOS signal (RT: 22.6) showed a statistically significant three-way interaction (p ​= ​0.033) in addition to significant two-way interactions for culture and additive (p ​= ​0.046) plus time and additive (p ​= ​0.020). There were also significant effects observed for time (p ​= ​0.009), culture (p ​= ​0.030) and additive (p ​= ​0.028). No effects were observed in the MS data.

CONCLUSIONS

The results of our study showed the potential of VOC analysis using SPME combined with a GC-MS/MOS system for the early detection of CTX-M-producing, antibiotic-resistant E. coli, responsible for urinary tract infections (UTIs).

Two-Dimensional Polymers and Polymerizations

Synthetic chemists have developed robust methods to synthesize discrete molecules, linear and branched polymers, and disordered cross-linked networks. However, two-dimensional polymers (2DPs) prepared from designed monomers have been long missing from these capabilities, both as objects of chemical synthesis and in nature. Recently, new polymerization strategies and characterization methods have enabled the unambiguous realization of covalently linked macromolecular sheets. Here we review 2DPs and 2D polymerization methods. Three predominant 2D polymerization strategies have emerged to date, which produce 2DPs either as monolayers or multilayer assemblies. We discuss the fundamental understanding and scope of each of these approaches, including: the bond-forming reactions used, the synthetic diversity of 2DPs prepared, their multilayer stacking behaviors, nanoscale and mesoscale structures, and macroscale morphologies. Additionally, we describe the analytical tools currently available to characterize 2DPs in their various isolated forms. Finally, we review emergent 2DP properties and the potential applications of planar macromolecules. Throughout, we highlight achievements in 2D polymerization and identify opportunities for continued study.

Inorganic Nanomaterials with Intrinsic Singlet Oxygen Generation for Photodynamic Therapy

Inorganic nanomaterials with intrinsic singlet oxygen (1 O2 ) generation capacity, are emerged yet dynamically developing materials as nano-photosensitizers (NPSs) for photodynamic therapy (PDT). Compared to previously reported nanomaterials that have been used as either carriers to load organic PSs or energy donors to excite the attached organic PSs through a Foster resonance energy transfer process, these NPSs possess intrinsic 1 O2 generation capacity with extremely high 1 O2 quantum yield (e.g., 1.56, 1.3, 1.26, and 1.09) than any classical organic PS reported to date, and thus are facilitating to make a revolution in PDT. In this review, the recent advances in the development of various inorganic nanomaterials as NPSs, including metal-based (gold, silver, and tungsten), metal oxide-based (titanium dioxide, tungsten oxide, and bismuth oxyhalide), metal sulfide-based (copper and molybdenum sulfide), carbon-based (graphene, fullerene, and graphitic carbon nitride), phosphorus-based, and others (hybrids and MXenes-based NPSs) are summarized, with an emphasis on the design principle and 1 O2 generation mechanism, and the photodynamic therapeutic performance against different types of cancers. Finally, the current challenges and an outlook of future research are also discussed. This review may provide a comprehensive account capable of explaining recent progress as well as future research of this emerging paradigm.

The Critical Number of Gold Atoms for a Metallic State Nanocluster: Resolving a Decades-Long Question

Probing the transition from a metallic state to a molecular state in gold nanoparticles is fundamentally important for understanding the origin of surface plasmon resonance and the nature of the metallic bond. Atomically precise gold nanoclusters are desired for probing such a transition based upon a series of precise sizes with X-ray structures. While the definition of the metallic state in nanoclusters is simple, that is, when the HOMO-LUMO gap (E_g) becomes negligibly small (E_g < k_BT, where k_B is the Boltzmann constant and T the temperature), the experimental determination of ultrasmall E_g (e.g., of k_BT level) is difficult, and the thermal excitation of valence electrons apparently comes into play in ultrasmall E_g nanoclusters. Although a sharp transition from nonmetallic Au₂₄₆(SR)₈₀ to metallic Au₂₇₉(SR)₈₄ (SR: thiolate) has been observed, there is still uncertainty about the transition region. Here, we summarize several criteria on determining the metallic state versus the molecular (or nonmetallic) state in gold nanoclusters, including (1) E_g determined by optical and electrochemical methods, (2) steady-state absorption spectra, (3) cryogenic optical spectra, (4) transient absorption spectra, (5) excited-state lifetime and power dependence, and (6) coherent oscillations in ultrafast electron dynamics. We emphasize that multiple analyses should be performed and cross-checked in practice because no single criterion is definitive. We also review the photophysics of several gold nanoclusters with nascent surface plasmon resonance. These criteria are expected to deepen the understanding of the metallic to molecular state transition of gold and other metal nanoclusters and also promote the design of functional nanomaterials and their applications.

Dissolution magnitude and kinetics of ZnO nanoparticles mediated by water are dependent on O vacancy abundance: The environmental implications

Metal oxide nanoparticles (NPs) dissolution in water environment is an important issue with regard to their environmental behaviors. The metal ion dissolves from surface defective site, but the effect of defect abundance remains largely unknown. This study aims to reveal this effect using ZnO NPs and O vacancy as the model system. The abundance of O vacancy is modulated by using different precursors and changing calcination atmosphere and temperature. X-ray photoelectron spectroscopy characterization shows that surface O vacancy abundance is effectively modulated to be distributed in a wide range from 15.3% to 41.8%. The deviation of O/Zn mole-ratio from 1.00 is used to denote O vacancy abundance in the bulk crystal, and the deviation reaches up to 0.32. Experiments show that the kinetics and magnitude of ZnO NPs dissolution vary in H₂O, which are highly dependent on O vacancy abundance. In comparison, the specific surface area and aggregation state take minor roles. Particularly, Zn²⁺ dissolution rate in the first hour is more linearly correlated with surface O vacancy abundance than with specific surface area. Defects and their abundances should thus be co-considered with other physicochemical properties to fully understand the dissolution behaviors of metal oxide NPs in water environment. This study is of significance in comprehensively assessing and predicting the environmental risk of metal oxide NPs.

Lattice distortion of CaF2 nanocrystals for shortening their 19F longitude relaxation time

As a promising ¹⁹F MRI tracer, the relatively slow lattice-spin relaxation of CaF₂ nanocrystals leads to an unacceptable scanning time in MR imaging, hampering their application. We herein controlled the size and lattice distortion of CaF₂ nanocrystals and showed that the shortened interplanar spacing pronouncedly sped up the longitude relaxation.

The Action-Networks of Nanosilver: Bridging the Gap between Material and Biology

The emergence of nanosilver (silver in nanoscale shapes and their assemblies) benefits the landscape of modern healthcare; however, this brings about concerns over its safety issues associated with an ultrasmall size and high mobility. By reviewing previous reporting details about the synthesis and characterization of nanosilver and its biological responses, a gap between materials synthesis and their biomedical uses is characterized by the insufficient understanding of the interacting and interplaying nanoscale actions of silver. To improve reporting quality and advance clinical translations, it is suggested that researchers have a comprehensive recognition of the "Indications for use" before designing innovative nanosilver-based materials and an "Action-network" concept addressing the acting range and strength of those nanoscale actions is implemented. Although this discussion is specific to nanosilver, the idea of "Indications for use" centered design and synthesis is generally applicable to other biomedical nanomaterials.

Synergistic Effect of Biosynthesized Silver Nanoparticles and Natural Phenolic Compounds against Drug-Resistant Fish Pathogens and Their Cytotoxicity: An In Vitro Study

Fish pathogens causing disease outbreaks represent a major threat to aquaculture industry and food security. The aim of the presented study is to develop safe and effective bioactive agents against two bacterial isolates: Aeromonas hydrophila and Pseudomonas fluorescens. We employed a broth microdilution method to investigate the antibacterial effect of biosynthesized silver nanoparticles (AgNPs); rutin, a natural flavonoid extracted from Ruta graveneoles; and heliomycin, a secondary metabolite produced by marine actinomycetes AB5, as monotherapeutic agents. Moreover, AgNPs in combination with rutin (AgNP + R) and heliomycin (AgNPs + H) were examined for their synergistic effect. The cytotoxic effect of individual bioactive compounds and in combination with AgNPs was investigated on epithelioma papulosum cyprini (EPC) fish cell lines. Individual treatment of AgNPs, rutin, and heliomycin exhibited a dose-dependent antimicrobial activity against A. hydrophila and P. fluorescens. Rutin minimum inhibitory concentration (MIC) showed the lowest cytotoxicity when tested on EPC cell lines, while heliomycin MIC was highly cytotoxic. Combined subtherapeutic doses of AgNPs + R and AgNPs + H displayed additive and synergistic effects against A. hydrophila and P. fluorescens, respectively, with improved results and relative safety profile. The study findings demonstrate that a combination of AgNPs and natural bioactive compounds may represent novel therapeutics fighting fish pathogens potentially affecting the fish farming industry.

Size dependence of CdS nanoparticles on the precursor concentration and visible light driven photocatalytic degradation of methylene blue

The effect of precursor concentration on the size of the nanoparticles and their visible light driven photocatalytic degradation of methylene blue are demonstrated.

Epigenetic effects induced by silver nanoparticles in Caenorhabditis elegans after multigenerational exposure

Multigenerational effects of silver nanoparticles (Ag-NPs) on reproduction of the soil nematode Caenorhabditis elegans have been observed previously. However, mechanisms of this reproductive sensitivity are unknown. Here we examine whether epigenetic changes occur as a result of multigenerational exposure to Ag-NPs and whether such modifications can be inherited by unexposed generations. Changes at histone methylation markers, histone 3 lysine 4 dimethylation (H3K4me2) and histone 3 lysine 9 trimethylation (H3K9me3), known to affect reproduction, as well as changes in the expression of the genes encoding demethylases and methyltransferases associated with the selected markers, were investigated. We exposed C. elegans at EC30 to AgNO3, pristine Ag-NPs, and its environmentally transformed product, sulfidized Ag-NPs (sAg-NPs). Histone methylation levels at H3K4me2 increase in response to pristine Ag-NP exposure and did not recover after rescue from the exposure, suggesting transgenerational inheritance. Compared to pristine Ag-NPs, exposure to transformed sAg-NPs significantly decreased H3K4me2 and H3K9me3 levels. These changes in the histone methylation were also supported by expression of spr-5 and jmjd-2 (H3K4me2 and H3K9me3 demethylases, respectively) and set-30 (H3K4me2 methyltransferase). Our study demonstrates that multigenerational exposure to Ag-NPs induces epigenetic changes that are inherited by unexposed offspring. However, environmental transformations of Ag-NPs may also reduce toxicity via epigenetic mechanisms, such as changes at histone methylation.

A Review of Microwave Synthesis of Zinc Oxide Nanomaterials: Reactants, Process Parameters and Morphoslogies

Zinc oxide (ZnO) is a multifunctional material due to its exceptional physicochemical properties and broad usefulness. The special properties resulting from the reduction of the material size from the macro scale to the nano scale has made the application of ZnO nanomaterials (ZnO NMs) more popular in numerous consumer products. In recent years, particular attention has been drawn to the development of various methods of ZnO NMs synthesis, which above all meet the requirements of the green chemistry approach. The application of the microwave heating technology when obtaining ZnO NMs enables the development of new methods of syntheses, which are characterised by, among others, the possibility to control the properties, repeatability, reproducibility, short synthesis duration, low price, purity, and fulfilment of the eco-friendly approach criterion. The dynamic development of materials engineering is the reason why it is necessary to obtain ZnO NMs with strictly defined properties. The present review aims to discuss the state of the art regarding the microwave synthesis of undoped and doped ZnO NMs. The first part of the review presents the properties of ZnO and new applications of ZnO NMs. Subsequently, the properties of microwave heating are discussed and compared with conventional heating and areas of application are presented. The final part of the paper presents reactants, parameters of processes, and the morphology of products, with a division of the microwave synthesis of ZnO NMs into three primary groups, namely hydrothermal, solvothermal, and hybrid methods.

Noble Metals Based Bimetallic and Trimetallic Nanoparticles: Controlled Synthesis, Antimicrobial and Anticancer Applications

Noble bimetallic and trimetallic nanoparticles (NBT-NPs) have superior biomedical applications as compared to their monometallic counterparts. The performance of these nanomaterials depends on their composition, shape and size. Hence, the controlled-synthesis of these nanomaterials is a hot area of research. Till date, no review article in the literature accounts regarding the controlled-synthesis and biomedical applications related to morphology, optimum composition, biocompatibility and versatile chemistry of NBT-NPs. Taking this into contemplation, an effort was made to provide a clear insight into the morphology-controlled synthesis and size/shape-dependent anticancer and bactericidal applications of NBT-NPs. Chemical reduction method for the controlled-synthesis of NBT-NPs is reviewed critically. Furthermore, the potential role of various reaction parameters such as time, reducing agents, stabilizing/capping agents, nature/concentration of precursors, temperature and pH in the shape/size-controlled synthesis of these nanomaterials are discussed. In the second part of this article, anticancer and bactericidal applications of the NBT-NPs are reviewed and the influences of optimum composition, size, surface structure, versatile chemistry and synergism are studied. Finally, the current challenges in the controlled-synthesis and biomedical applications of these nanomaterials, and prospects to resolve related issues are discussed. HighlightsChemical reduction method for the synthesis of NBT-NPs is reviewed.The influences of parameters on the control synthesis of NBT-NPs are discussed.Antibacterial and anticancer applications and cytotoxicity of NBT-NPs are reviewed.Possible solutions for the key challenges are discussed.Outlooks about the synthesis and biomedical applications of NBT-NPs are discussed.

Massively Parallel Nanoparticle Synthesis in Anisotropic Nanoreactors

This work reports a massively parallel approach for synthesizing inorganic nanoparticles (Au, Ag, Se, and mixed oxides of Cu, Co, Ni, Ge, and Ta) based upon lithographically generated arrays of square pyramidal nanoholes, which serve as nanoreactors. Particle precursor-containing polymers are spin-coated onto the nanoreactors, which upon dewetting generate a morphology of isolated polymer droplets in each nanoreactor. This dewetting process yields a well-defined and precisely controlled volume of polymer and therefore particle precursor in each nanoreactor. Subsequent stepwise annealing (first at 150 °C and then at 500 °C) yields arrays of monodisperse, site-isolated particles with sub-5 nm position control. By varying the precursor loading of the polymer, particle size can be systematically controlled in the 7-30 nm range. This work not only introduces the concept of merging block copolymer inks with nanohole arrays in the synthesis of nanoparticles but also underscores the value of the nanoreactor shape in controlling resulting particle position.

"Ghost" Silica Nanoparticles of "Host"-Inherited Antibacterial Action

We fabricated surface-rough mesoporous silica nanoparticles ("ghost" SiO₂NPs) by using composite mesoporous copper oxide nanoparticles ("host" CuONPs) as templates, which allowed us to mimic their surface morphology. The "host" CuONPs used here as templates, however, had a very high antibacterial effect, with or without functionalization. To evaluate the surface roughness effect on the "ghost" SiO₂NPs antibacterial action, we functionalized them with (3-glycidyloxypropyl)trimethoxysilane (GLYMO) to permit additional covalent coupling of 4-hydroxyphenylboronic acid (4-HPBA). The diol groups on the bacterial membrane can form reversible covalent bonds with boronic acid (BA) groups on the "ghost" SiO₂NPs surface and bind to the bacteria, resulting in a very strong amplification of their antibacterial activity, which does not depend on electrostatic adhesion. The BA-functionalized "ghost" SiO₂NPs showed a very significant antibacterial effect as compared to smooth SiO₂NPs of the same surface coating and particle size. We attribute this to the "ghost" SiO₂NPs mesoporous surface morphology, which mimics to a certain extent those of the original mesoporous CuONPs used as templates for their preparation. We envisage that the "ghost" SiO₂NPs effectively acquire some of the antibacterial properties from the "host" CuONPs, with the same functionality, despite being completely free of copper. The antibacterial effect of the functionalized "ghost" SiO₂NPs/GLYMO/4-HPBA on Rhodococcus rhodochrous (R. rhodochrous) and Escherichia coli (E. coli) is much higher than that of the nonfunctionalized "ghost" SiO₂NPs or the "ghost" SiO₂NPs/GLYMO. The results indicate that the combination of rough surface morphology and strong adhesion of the particle surface to the bacteria can make even benign material such as silica act as a strong antimicrobial agent. Additionally, our BA-functionalized nanoparticles ("ghost" SiO₂NPs/GLYMO/4-HPBA) showed no detectable cytotoxic impact against human keratinocytes at particle concentrations, which are effective against bacteria.

High-Performance Transparent Ultraviolet Photodetectors Based on InGaZnO Superlattice Nanowire Arrays

Due to the efficient photocarrier separation and collection coming from their distinctive band structures, superlattice nanowires (NWs) have great potential as active materials for high-performance optoelectronic devices. In this work, InGaZnO NWs with superlattice structure and controllable stoichiometry are obtained by ambient-pressure chemical vapor deposition. Along the NW axial direction, perfect alternately stacking of InGaO(ZnO)₄⁺ blocks and InO₂^- layers is observed to form a periodic layered structure. Strikingly, when configured into individual NW photodetectors, the Ga concentration is found to significantly influence the amount of oxygen vacancies and oxygen molecules adsorbed on the NW surface, which dictate the photoconducting properties of the NW channels. Based on the optimized Ga concentration (i.e., In_1.8Ga_1.8Zn_2.4O₇), the individual NW device exhibits an excellent responsivity of 1.95 × 10⁵ A/W and external quantum efficiency of as high as 9.28 × 10⁷% together with a rise time of 0.93 s and a decay time of 0.2 s for the ultraviolet (UV) photodetection. Besides, the obtained NWs can be fabricated into large-scale parallel arrays on glass substrates as well to achieve fully transparent UV photodetectors, where the performance is on the same level or even better than many transparent photodetectors with high performance. All the results discussed above demonstrate the great potential of InGaZnO superlattice NWs for next-generation advanced optoelectronic devices.

High-temperature annealing of ZnO nanoparticles increases the dissolution magnitude and rate in water by altering O vacancy distribution

The effects and mechanism of high-temperature annealing, a frequently-used strategy to modulate the properties of nanoparticles (NPs), on the dissolution of zinc oxide (ZnO) NPs are investigated in this study. The results show that annealing increases the ZnO NPs dissolution magnitude via increasing O vacancy abundance on the surface and in the bulk crystal. The face-dependent distribution of O vacancy is revealed by characterizing ZnO single crystal, and the (000-1) face has a higher abundance than the (10-10) face. Particularly, O vacancy abundance in the bulk (000-1) is about 3 times higher than in the bulk (10-10). Annealing further strengthens the face-dependence of O vacancy distribution, therefore both raw and annealed (000-1) faces contribute dominantly to the dissolution of ZnO NPs. Typical topographies of the surface defect sites on the (000-1) face and their evolutions during dissolution are collected. Annealing promotes the formation of larger and deeper etching pits. Elevated solution temperature and annealing synergize to further accelerate ZnO dissolution. The dissolution behaviors of ZnO NPs with different annealing statuses, surface properties, and solution temperatures investigated in this study have potential implications to the evaluations of environmental fate and risk of metal oxide NPs.

Self-grafting copper oxide nanoparticles show a strong enhancement of their anti-algal and anti-yeast action

We have developed and tested copper oxide nanoparticles (CuONPs) grafted with (3-glycidyloxypropyl)trimethoxysilane (GLYMO) and coupled with 4-hydroxyphenylboronic acid (4-HPBA), which provides a very strong boost of their action as anti-algal and anti-yeast agents. The boronic acid terminal groups on the surface of the CuONPs/GLYMO/4-HPBA can form reversible covalent bonds with the diol groups of glycoproteins and carbohydrates expressed on the cell surface where they bind and accumulate, which is not based on electrostatic adhesion. Results showed that, the impact of the 4-HPBA grafted CuONPs on microalgae (C. reinhardtii) and yeast (S. cerevisiae) is several hundred percent higher than that of bare CuONPs and CuONPs/GLYMO at the same particle concentration. SEM and TEM imaging revealed that 4-HPBA-functionalized CuONPs nanoparticles can accumulate more on the cell walls than non-functionalized CuONPs. We found a marked increase of the 4-HPBA functionalized CuONPs action on these microorganisms at shorter incubation times compared with the bare CuONPs at the same conditions. We also showed that the anti-algal action of CuONPs/GLYMO/4-HPBA can be controlled by the concentration of glucose in the media and that the effect is reversible as glucose competes with the diol residues on the algal cell walls for the HPBA groups on the CuONPs. Our experiments with human cell lines incubated with CuONPs/GLYMO/4-HPBA indicated a lack of measurable loss of cell viability at particle concentrations which are effective as anti-algal agents. CuONPs/GLYMO/4-HPBA can be used to drastically reduce the overall CuO concentration in anti-algal and anti-yeast formulations while strongly increasing their efficiency.

Synthesis and Characterization of Te Nanotubes Decorated with Pt Nanoparticles for a Fuel Cell Anode/Cathode Working at a Neutral pH

In fuel-cell technology development, one of the most important objectives is to minimize the amount of Pt, the most employed material as an oxygen reduction and methanol oxidation electro-catalyst. In this paper, we report the synthesis and characterization of Te nanotubes (TeNTs) decorated with Pt nanoparticles, readily prepared from stirred aqueous solutions of PtCl2 containing a suspension of TeNTs, and ethanol acting as a reducing agent, avoiding the use of any hydrophobic surfactants such as capping stabilizing substance. The obtained TeNTs decorated with Pt nanoparticles (TeNTs/PtNPs) have been fully characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), selected area diffraction patterns (SAD), X-ray photoelectron spectroscopy (XPS), and cyclic voltammetry (CV). We demonstrated that the new material can be successfully employed in fuel cells, either as an anodic (for methanol oxidation reaction) or a cathodic (for oxygen reduction reaction) electrode, with high efficiency in terms of related mass activities and on-set improvement. Remarkably, the cell operates in aqueous electrolyte buffered at pH 7.0, thus, avoiding acidic or alkaline conditions that might lead to, for example, Pt dissolution (at low pH), and paving the way for the development of biocompatible devices and on-chip fuel cells.

Glycerol-mediated synthesis of nanoscale zerovalent iron and its application for the simultaneous reduction of nitrate and alachlor

NZVI has long been used for the remediation of different groundwater contaminants but their tendency to get oxidized easily has always been a barrier to their reductive ability. In this work, we have made an attempt to enhance the aerobic stability of the nanoparticles by synthesizing them in a medium consisting of a viscous solvent, glycerol, and water. The XRD analysis of the nanoparticles reveals that the particles prepared in the presence of glycerol have a very thin coating of iron oxides on the outer surface of the nanoparticles in comparison with those prepared in the aqueous medium. These nanoparticles were applied for the simultaneous reduction of two groundwater contaminants, nitrate ions, and alachlor, which is an herbicide. Stock solutions of these two contaminants were prepared and then they were mixed in varying amounts and were treated by different doses of the nanoparticle. The optimized dose of the nanoparticles obtained for almost 97% removal of both the contaminants is 2.05 g/L. The studies showed that increasing the concentration of either of the contaminants while the other one was kept fixed led to a decrease in the removal efficiency. The studies conducted to see the effect of pH variation showed that the best removal can be achieved when the pH is 3 or even less than it, showing that acidic pH leads to higher removal values. Such nanoparticles which can be prepared easily at low-cost and can simultaneously act upon different contaminants are highly desired.

Defects and their behaviors in mineral dissolution under water environment: A review

Mineral dissolution is a spontaneous process that takes indispensible role in the determination of water quality in a specific water body. Deep insights into defects as a result of characterization technique development have greatly improved our understanding of their significances and behaviors in the dissolution within the mineral-water interface. Based on the progresses from previous decades, this review attempts to re-elaborate the molecular-scale process of dissolution. Material flow within the mineral/water interface is updated, with emphasis on the function of defect sites. A brief introduction of defect properties is presented, including the microscopic appearances and typical physicochemical characteristics. Feasible strategies that have been adopted to increase the defect abundance are inferred, which maybe enlightening for hydrometallurgy. The merits and drawbacks of the techniques that could be employed for the qualitative and quantitative determination of defect presence are introduced, although relatively satisfactory performances are noted. With the aid of these techniques, it is concluded that screw dislocation is the main defect type responsible for surface topography evolution as a result of dissolution. Finally, this review identifies the current knowledge gaps and future research needs for comprehensively identifying the significance of defects in mineral dissolution.

The influence of support materials on the structural and electronic properties of gold nanoparticles – a DFT study

This study investigates the effect of commonly used support materials (MgO, C, CeO₂) on small gold particles using dispersion corrected density functional theory (DFT-D).

Electrochemiluminescence of gold nanoparticles and gold nanoparticle-labelled antibodies as co-reactants

Gold nanoparticles (AuNPs) and AuNP-labelled antibodies can participate in the electrochemiluminescence (ECL) reaction of tris(2,2'-bipyridyl) ruthenium(ii) (Ru(bpy)3 2+) as a co-reactant. The electrochemical and spectral characteristics of this new ECL system were confirmed by experiments, and its reaction mechanism was speculated to be different from that of typical ECL. The experimental results showed that the new ECL system exhibited higher ECL efficiency, and AuNP-labelled substances can be sensitively measured with the help of AuNPs. Based on the dual role of AuNPs as a co-reactant and marker, the AuNP-Ru(bpy)3 2+ ECL system will be a useful tool in biochemical analysis.

Evaluation of Paeonia emodi and its gold nanoparticles for cardioprotective and antihyperlipidemic potentials

Paeonia emodi Wall. ex Royle is an important member of family Paeoniaceae and folklorically used for constipation, hysteria, respiratory diseases, epilepsy and cardiac diseases like hypertension, palpitations, congestive heart failure and atherosclerosis. In the present study, ethyl acetate fraction of P. emodi (Pe.EA) was subjected to column chromatography to obtain sub- fractions. These sub-fractions were screened for their cardioprotective activity in isoproterenol hydrochloride (ISO) induced myocardial infarction (MI) in mice. The most active fraction Pe. EA 40 was used for its gold nanoparticles synthesis (Pe.EA 40-AuNPs). Pe.EA 40 and Pe.EA 40-AuNPs were investigated for their cardioprotective, antihyperlipidemic, DNA fragmentation assay and histopathological study. Pe.EA 40 (80 mg/kg body weight) significantly reduced the serum levels of Alanine Aminotransferase (ALT), Aspartate Aminotransferase (AST), Lactate Dehydrogenase (LDH), Creatine Phosphokinase (CPK) to 66.07 ± 1.54, 77.08 ± 1.79, 84.86 ± 1.34 and 265.34 ± 4.34 IU/L respectively as compared to ISO treated group. Pe.EA 40-AuNPs (40 mg/kg) reduced the levels of ALT, AST, CPK and LDH to 60.74 ± 2.79, 75.47 ± 1.67, 80.48 ± 2.64 and 247.54. ± 5.57 IU/L respectively. A significant reduction was observed in lipid profile, protection in DNA damage and restoration of histopathological changes as compared to ISO treated group. Based on the results, it can be suggested that preparation of Pe.EA 40-AuNPs enhances the therapeutic potential of plant extract for the treatment of atherosclerosis and MI.