A general procedure to synthesize highly crystalline metal oxide and mixed oxide nanocrystals in aqueous medium and photocatalytic activity of metal/oxide nanohybrids

Co/Ni-polyoxotungstate photocatalysts as precursor materials for electrocatalytic water oxidation

An open-core cobalt polyoxometalate (POM) [(A-α-SiW9O34)Co4(OH)3(CH3COO)3]8-Co(1) and its isostructural Co/Ni-analogue [(A-α-SiW9O34)Co1.5Ni2.5(OH)3(CH3COO)3]8-CoNi(2) were synthesized and investigated for their photocatalytic and electrocatalytic performance. Co(1) shows high photocatalytic O2 yields, which are competitive with leading POM water oxidation catalysts (WOCs). Furthermore, Co(1) and CoNi(2) were employed as well-defined precursors for heterogeneous WOCs. Annealing at various temperatures afforded amorphous and crystalline CoWO4- and Co1.5Ni2.5WO4-related nanoparticles. CoWO4-related particles formed at 300 °C showed substantial electrocatalytic improvements and were superior to reference materials obtained from co-precipitation/annealing routes. Interestingly, no synergistic interactions between cobalt and nickel centers were observed for the mixed-metal POM precursor and the resulting tungstate catalysts. This stands in sharp contrast to a wide range of studies on various heterogeneous catalyst types which were notably improved through Co/Ni substitution. The results clearly demonstrate that readily accessible POMs are promising precursors for the convenient and low-temperature synthesis of amorphous heterogeneous water oxidation catalysts with enhanced performance compared to conventional approaches. This paves the way to tailoring polyoxometalates as molecular precursors with tuneable transition metal cores for high performance heterogeneous electrocatalysts. Our results furthermore illustrate the key influence of the synthetic history on the performance of oxide catalysts and highlight the dependence of synergistic metal interactions on the structural environment.

Multiscale Metal Oxide Particles to Enhance Photocatalytic Antimicrobial Activity against Escherichia coli and M13 Bacteriophage under Dual Ultraviolet Irradiation

Antimicrobial activity of multiscale metal oxide (MO) particles against Escherichia coli (E. coli) and M13 bacteriophage (phage) was investigated under dual ultraviolet (UV) irradiation. Zinc oxide (ZnO), magnesium oxide (MgO), cuprous oxide (Cu₂O), and cupric oxide (CuO) were selected as photocatalytic antimicrobials in MO particles. Physicochemical properties including morphology, particle size/particle size distribution, atomic composition, crystallinity, and porosity were evaluated. Under UV-A and UV-C irradiation with differential UV-C intensities, the antimicrobial activity of MO particles was monitored in E. coli and phage. MO particles had nano-, micro- and nano- to microscale sizes with irregular shapes, composed of atoms as ratios of chemical formulae and presented crystallinity as pure materials. They had wide-range specific surface area levels of 0.40–46.34 m²/g. MO particles themselves showed antibacterial activity against E. coli, which was the highest among the ZnO particles. However, no viral inactivation by MO particles occurred in phage. Under dual UV irradiation, multiscale ZnO and CuO particles had superior antimicrobial activities against E. coli and phage, as mixtures of nano- and microparticles for enhanced photocatalytic antimicrobials. The results showed that the dual UV-multiscale MO particle hybrids exhibit enhanced antibiotic potentials. It can also be applied as a next-generation antibiotic tool in industrial and clinical fields.

Shape control of inorganic nanoparticles from solution

Inorganic materials with controllable shapes have been an intensely studied subject in nanoscience over the past decades. Control over novel and anisotropic shapes of inorganic nanomaterials differing from those of bulk materials leads to unique and tunable properties for widespread applications such as biomedicine, catalysis, fuels or solar cells and magnetic data storage. This review presents a comprehensive overview of shape-controlled inorganic nanomaterials via nucleation and growth theory and the control of experimental conditions (including supersaturation, temperature, surfactants and secondary nucleation), providing a brief account of the shape control of inorganic nanoparticles during wet-chemistry synthetic processes. Subsequently, typical mechanisms for shape-controlled inorganic nanoparticles and the general shape of the nanoparticles formed by each mechanism are also expounded. Furthermore, the differences between similar mechanisms for the shape control of inorganic nanoparticles are also clearly described. The authors envision that this review will provide valuable guidance on experimental conditions and process control for the synthesis of inorganic nanoparticles with tunable shapes in the solution state.

Electrodeposition of Prussian blue films on Ni3Si2O5(OH)4 hollow nanospheres and their enhanced electrochromic properties

Porous PB films were electrodeposited on Ni₃Si₂O₅(OH)₄ hollow nanospheres, resulting in enhanced electrochromic properties due to the coarse substrate.

Tailoring the assembly, interfaces, and porosity of nanostructures toward enhanced catalytic activity

The evolution of nanotechnology has inspired materials scientists to invent nanostructures with achievements in numerous practical applications, particularly in catalysis.

Oxide-based nanostructures for photocatalytic and electrocatalytic applications

The enormous efforts on the design of efficient oxide-based materials towards photocatalysis & electrocatalysis have been highlighted in this article with emphasis on their size, structure & morphology.

Role of synthesis variables on controlled nucleation and growth of hexagonal molybdenum oxide nanocrystals: investigation on thermal and optical properties

Solution based chemical precipitation route has been utilized for the controlled synthesis of novel and single phase 3Dhierarchical flower-like microspheres of hexagonal molybdenum oxide nanocrystals.

Enhanced photocatalytic performances of CeO2/TiO2 nanobelt heterostructures

CeO2 /TiO2 nanobelt heterostructures are synthesized via a cost-effective hydrothermal method. The as-prepared nanocomposites consist of CeO2 nanoparticles assembled on the rough surface of TiO2 nanobelts. In comparison with P25 TiO2 colloids, surface-coarsened TiO2 nanobelts, and CeO2 nanoparticles, the CeO2 /TiO2 nanobelt heterostructures exhibit a markedly enhanced photocatalytic activity in the degradation of organic pollutants such as methyl orange (MO) under either UV or visible light irradiation. The enhanced photocatalytic performance is attributed to a novel capture-photodegradation-release mechanism. During the photocatalytic process, MO molecules are captured by CeO2 nanoparticles, degraded by photogenerated free radicals, and then released to the solution. With its high degradation efficiency, broad active light wavelength, and good stability, the CeO2 /TiO2 nanobelt heterostructures represent a new effective photocatalyst that is low-cost, recyclable, and will have wide application in photodegradation of various organic pollutants. The new capture-photodegradation-release mechanism for improved photocatalysis properties is of importance in the rational design and synthesis of new photocatalysts.

From formation mechanisms to synthetic methods toward shape-controlled oxide nanoparticles

Metal oxide nanomaterials have been intensively pursued for modern science and nanotechnology. Control over the size and shape of the oxide nanoparticles enables tunability of their unique properties sought for many useful applications. This review presents a comprehensive overview of the recent advances in the shape-controlled synthesis of colloidal oxide nanoparticles. We introduce the size- and shape-dependent properties of the oxide nanoparticles along with their potential applications and subsequent descriptions of the kinetic regime concepts of the formation of the monodisperse nanocolloids. Variations of the experimental conditions including capping molecules, precursor monomer concentration, and reaction temperature/aging have been explored to control the shape of the oxide nanoparticles in wet-chemistry syntheses. The different capping molecule-assisted synthetic methods of the hydro-solvothermal route, the two-phase route, heating-up thermolysis, and reverse micelle are presented as a collection of clear examples of the regular oxide nanoparticles. We also discuss the advantages and obstacles of the synthetic methods that have proven to be controllable and reproducible. The author concludes this review with valuable portraits on working hypotheses for the shape-controlled oxide nanoparticle synthesis.

Single-step solvothermal synthesis of mesoporous Ag-TiO2-reduced graphene oxide ternary composites with enhanced photocatalytic activity

With growing interest in the photocatalytic performance of TiO2-graphene composite systems, the ternary phase of TiO2, graphene, and Ag is expected to exhibit improved photocatalytic characteristics because of the improved recombination rate of photogenerated charge carriers and potential contribution of the generation of localized surface plasmon resonance at Ag sites on a surface of the TiO2-graphene binary matrix. In this work, Ag-TiO2-reduced graphene oxide ternary nanocomposites were successfully synthesized by a simple solvothermal process. In a single-step synthetic procedure, the reduction of AgNO3 and graphene oxide and the hydrolysis of titanium tetraisopropoxide were spontaneously performed in a mixed solvent system of ethylene glycol, N,N-dimethylformamide and a stoichiometric amount of water without resorting to the use of typical reducing agents. The nanocomposites were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, along with different microscopic and spectroscopic techniques, enabling us to confirm the successful reduction of AgNO3 and graphite oxide to metallic Ag and reduced graphene oxide, respectively. Due to the highly facilitated electron transport of well distributed Ag nanoparticles, the synthesized ternary nanocomposite showed enhanced photocatalytic activity for degradation of rhodamine B dye under visible light irradiation.

Shape-controlled synthesis and catalytic application of ceria nanomaterials

Because of their excellent properties and extensive applications, ceria nanomaterials have attracted much attention in recent years. This perspective provides a comprehensive review of current research activities that focus on the shape-controlled synthesis methods of ceria nanostructures. We elaborate on the synthesis strategies in the following four sections: (i) oriented growth directed by the crystallographic structure of cerium-based materials; (ii) oriented growth directed by the use of an appropriate capping reagent; (iii) growth confined or dictated by various templates; (iv) other potential methods for generating CeO(2) nanomaterials. In this perspective, we also discuss the catalytic applications of ceria nanostructures. They are often used as active components or supports in many catalytic reactions and their catalytic activities show morphology dependence. We review the morphology dependence of their catalytic performances in carbon monoxide oxidation, water-gas shift, nitric oxide reduction, and reforming reactions. At the end of this review, we give a personal perspective on the probable challenges and developments of the controllable synthesis of CeO(2) nanomaterials and their catalytic applications.

Portraits of colloidal hybrid nanostructures: controlled synthesis and potential applications

Inorganic hybrid nanostructures containing two or more nanocomponents have been emerging in many areas of materials science in recent years. The particle-particle interactions in a hybrid particle system could significantly improve existing local electronic structure and induce tunable physiochemical responses. The current work reviews the diverse inorganic hybrid nanostructures formed by adhesion of the different single components via seed-mediated method. The hybrid nanomaterials have great potentials for real applications in many other fields. The nanohybrids have been used as efficient heterocatalysts for carbon monoxide conversion and photodegradation of organic contaminants. The enhanced catalytic activity of these hybrid nanocatalysts could be attributed the formation of oxygen vacancies and electron transfer across the structural junction in a hybrid system as a result of the interfacial particle-particle interactions. The synergistic combination of up-converting and semiconducting properties in an up-converting semiconducting hybrid particle results in appearance of sub-band-gap photoconductivity. This behavior has a great significance for the design of photovoltaic devices for effective solar energy conversion. The functionalization and subsequent bioconjugation of the hybrid nanostructures to afford the multifunctional nanomedical platforms for simultaneous diagnosis and therapy are reviewed. The conjugated multifunctional hybrid nanostructures exhibit high biocompatibility and highly selective binding with functional groups-fabricated alive organs through delivering them to the tumor sites. The clever combinations of multifunctional features and antibody conjugation within these vehicles make them to generally offer new opportunities for clinical diagnostics and therapeutics.