Nanomolecularly-induced Effects at Titania/Organo-Diphosphonate Interfaces for Stable Hybrid Multilayers with Emergent Properties

Nanoscale hybrid inorganic-organic multilayers are attractive for accessing emergent phenomena and properties through superposition of nanomolecularly-induced interface effects for diverse applications. Here, we demonstrate the effects of interfacial molecular nanolayers (MNLs) of organo-diphosphonates on the growth and stability of titania nanolayers during the synthesis of titania/MNL multilayers by sequential atomic layer deposition and single-cycle molecular layer deposition. Interfacial organo-diphosphonate MNLs result in ∼20-40% slower growth of amorphous titania nanolayers and inhibit anatase nanocrystal formation from them when compared to amorphous titania grown without MNLs. Both these effects are more pronounced in multilayers with aliphatic backbone-MNLs and likely related to impurity incorporation and incomplete reduction of the titania precursor indicated by our spectroscopic analyses. In contrast, both MNLs result in two-fold higher titania nanolayer roughness, suggesting that roughening is primarily due to MNL bonding chemistry. Such MNL-induced effects on inorganic nanolayer growth rate, roughening, and stability are germane to realizing high-interface-fraction hybrid nanolaminate multilayers.

Nonaqueous Chemistry of Group 4 Oxo Clusters and Colloidal Metal Oxide Nanocrystals

We review the nonaqueous precursor chemistry of the group 4 metals to gain insight into the formation of their oxo clusters and colloidal oxide nanocrystals. We first describe the properties and structures of titanium, zirconium, and hafnium oxides. Second, we introduce the different precursors that are used in the synthesis of oxo clusters and oxide nanocrystals. We review the structures of group 4 metal halides and alkoxides and their reactivity toward alcohols, carboxylic acids, etc. Third, we discuss fully condensed and atomically precise metal oxo clusters that could serve as nanocrystal models. By comparing the reaction conditions and reagents, we provide insight into the relationship between the cluster structure and the nature of the carboxylate capping ligands. We also briefly discuss the use of oxo clusters. Finally, we review the nonaqueous synthesis of group 4 oxide nanocrystals, including both surfactant-free and surfactant-assisted syntheses. We focus on their precursor chemistry and surface chemistry. By putting these results together, we connect the dots and obtain more insight into the fascinating chemistry of the group 4 metals. At the same time, we also identify gaps in our knowledge and thus areas for future research.

Quasi-homogenous photocatalysis of quantum-sized Fe-doped TiO2 in optically transparent aqueous dispersions

In this study, the preparation of anatase TiO2 nanocrystals via a facile non-aqueous sol-gel route and their characterization are reported. The 3-4 nm particles are readily dispersable in aqueous media and show excellent photoreactivity in terms of rhodamine B degradation. The catalytic performance can be further increased considerably by doping with iron and UV-light irradiation as a pre-treatment. The effect of surface ligands (blocked adsorption sites, surface defects etc.) on the photoreactivity was thoroughly probed using thermogravimetric analysis combined with mass spectrometry. Photoelectrochemical characterization of thin-film electrodes made from the same TiO2 nanocrystals showed the opposite trend to the catalytic experiments, that is, a strong decrease in photocurrent and quantum efficiency upon doping due to introduction of shallow defect states.

Ultrasound-assisted synthesis of unzipped multiwalled carbon nanotubes/titanium dioxide nanocomposite as a promising next-generation energy storage material

Carbon-based systems have been discussed as prospective alternatives for conventional metal-based catalysts over the past decade. These studies were motivated by the abundance, low cost, lightweight and diversity of structural allotropes of carbon. We reported here the synthesis of a new type of unzipped multiwalled carbon nanotubes/titanium dioxide (UzMWCNT/TiO₂) nanocomposite by the two-stage procedure. By the modified Hummers method, multiwalled carbon nanotubes (MWCNTs) were converted to oxidized multi-walled carbon nanotubes (O-MWCNT). Then, through a facile ultrasound-assisted route prepared UzMWCNT/TiO₂ nanocomposite. For this, the oxidized multiwalled carbon nanotubes are treated with TiCl₄ under an ultrasonic probe for 3 h to generate UzMWCNT/TiO₂ and then explored its environmental friendliness and energy applications as a supercapacitor. This novel UzMWCNT/TiO₂ nanocomposite was characterized using XRD, TGA, FT-IR, Raman, TEM and EDX analysis. The electrochemical performance can be evaluated by using cyclic voltammetry (CV) and galvanostatic charging-discharging (GCD) study. Finally, the electrodes prepared using UzMWCNT/TiO₂ nanocomposite have been analyzed through electrochemical impedance spectroscopy (EIS) to probe the charge transfer characteristics and the results are consistent with other electrochemical measurements.

Nanoparticle processing: Understanding and controlling aggregation

Nanoparticles (NPs) are commonly defined as particles with size <100 nm and are currently of considerable technological and academic interest, since they are often the starting materials for nanotechnology. Novel properties develop as a bulk material is reduced to nanodimensions and is reflected in new chemistry, physics and biology. With reduction in size, a greater function of the atoms is at the surface, and promote different interaction with its environment, as compared to the bulk material. In addition, the reduction in size alters the electronic structure of the material, resulting in novel quantum effects. Size also influences mobility, primarily controlled by Brownian motion for NPs, and relevant in biological and environmental processes. However, the small size also leads to high surface energy, and NPs tend to aggregate, thereby lowering the surface energy. In all applications, the uncontrolled aggregation of NPs can have negative effects and needs to be avoided. There are however examples of controlled aggregation of NPs which give rise to novel effects. This review article is focused on the NP features that influences aggregation. Common strategies for synthesis of NPs from the gas and liquid phases are discussed with emphasis on aggregation during and after synthesis. The theory involving Van der Waals attractive force and electrical repulsive force as the controlling features of the stability of NPs is discussed, followed by examples of how repulsive and attractive forces can be manipulated experimentally to control NP aggregation. In some applications, NPs prepared by liquid methods need to be isolated for further applications. The process of solvent removal introduces new forces such as capillary forces that promote aggregation, in many cases, irreversibly. Strategies for controlling aggregation upon drying are discussed. There are also many methods for redispersing aggregated NPs, which involve mechanical forces, as well as manipulating capillary forces and surface characteristics. We conclude this review with a discussion of aggregation relevant real-world applications of NPs. This review should be relevant for scientists and technologists interested in NPs, since emphasis has been on the practical aspects of NP-based technology, and especially, strategies relevant to controlling NP aggregation.

Detrimental Effect and Neutralization of in Situ Produced Water on Zirconia Nanoparticles Obtained by a Nonaqueous Sol-Gel Method

In this work, the phase purity and size of zirconia nanocrystals samples were studied in terms of zirconium concentration, added water content, and subsequent use of a post solvothermal treatment. The progressive tetragonal-to-monoclinic transformation of zirconia sample was observed to be strongly related to the water content of the alcoholic medium. But more surprisingly, it has been shown that even under initially anhydrous conditions and for particle size below 5 nm, the phase purity of the samples was deteriorated by a side-reaction of alcohol dehydration catalyzed by the surface of the nanoparticles (NPs). Since the phase transformation is essentially driven by the water content of the reaction mixture, we have shown that it was possible to recover an excellent phase purity without the help of any usual dopants by adding a strong alkaline desiccating agent. Provided that a sufficient sodium to zirconium ratio was ensured, the formation of the monoclinic phase was not observed whatever the zirconium precursor concentration. The effectiveness of this cure was related to the ability of sodium metal to generate reactive alkoxide able to neutralize water and to catalyze an alternative sol-gel mechanism leading to the formation of the t-ZrO₂ NPs.

Nonaqueous Sol-Gel Synthesis of Anatase Nanoparticles and Their Electrophoretic Deposition in Porous Alumina

Titanium dioxide (TiO₂) nanoparticles were synthesized by nonaqueous sol-gel route using titanium tetrachloride and benzyl alcohol as the solvent. The obtained 4 nm-sized anatase nanocrystals were readily dispersible in various polar solvents allowing for simple preparation of colloidal dispersions in water, isopropyl alcohol, dimethyl sulfoxide, and ethanol. Results showed that dispersed nanoparticles have acidic properties and exhibit positive zeta-potential which is suitable for their deposition by cathodic electrophoresis. Aluminum substrates were anodized in phosphoric acid in order to produce porous anodic oxide layers with pores ranging from 160 to 320 nm. The resulting nanopores were then filled with TiO₂ nanoparticles by electrophoretic deposition. The influence of the solvent, the electric field, and the morphological characteristics of the alumina layer (i.e., barrier layer and porosity) were studied.

Experimental and numerical insights into the formation of zirconia nanoparticles: a population balance model for the nonaqueous synthesis

The nonaqueous synthesis of zirconia nanoparticles was investigated and modeled by a comprehensive population balance equation framework that simulates the entire particle formation process to predict final nanoparticle properties as well as their evolvement during the synthesis.

Matching the organic and inorganic counterparts during nucleation and growth of copper-based nanoparticles – in situ spectroscopic studies

Closing the loop: initially, the reactivity of benzyl alcohol determines the nucleation of Cu nanoparticles, but as soon as they start to form they begin to catalyze the condensation of benzyl alcohol to dibenzylether.

Fabrication of porous carbon/TiO₂ composites through polymerization-induced phase separation and use as an anode for Na-ion batteries

Polymerization-induced phase separation of nanoparticle-filled solution is demonstrated as a simple approach to control the structure of porous composites. These composites are subsequently demonstrated as the active component for sodium ion battery anode. To synthesize the composites, we dissolved/dispersed titanium oxide (anatase) nanoparticles (for sodium insertion) and poly(hydroxybutyl methacrylate) (PHBMA, porogen) in furfuryl alcohol (carbon precursor) containing a photoacid generator (PAG). UV exposure converts the PAG to a strong acid that catalyzes the furfuryl alcohol polymerization. This polymerization simultaneously decreases the miscibility of the PHBMA and reduces the mobility in the mixture to kinetically trap the phase separation. Carbonization of this polymer composite yields a porous nanocomposite. This nanocomposite exhibits nearly 3-fold greater gravimetric capacity in Na-ion batteries than the same titanium oxide nanoparticles that have been coated with carbon. This improved performance is attributed to the morphology as the carbon content in the composite is five times that of the coated nanoparticles. The porous composite materials exhibit stable cyclic performance. Moreover, the battery performance using materials from this polymerization-induced phase separation method is reproducible (capacity within 10% batch-to-batch). This simple fabrication methodology may be extendable to other systems and provides a facile route to generate reproducible hierarchical porous morphology that can be beneficial in energy storage applications.

Mechanistic aspects of molecular formation and crystallization of zinc oxide nanoparticles in benzyl alcohol

Zinc oxide nanostructures are known to exist in a great variety of morphologies. However, the underlying mechanisms leading to these architectures are far from being fully understood. Here, we present a time dependent study of the generation of zinc oxide nanorods, which arrange into bundles with a fan- or bouquet-like structure, using the benzyl alcohol route. The structural evolution of the nanoparticles was monitored by electron microscopy techniques, whereas the progress of the chemical reaction was followed by quantification of the organic by-products using gas chromatography. With this study we give a detailed insight into the formation of the zinc oxide structures, which involves a complex pathway based on many in parallel occurring processes such as crystallization of primary particles, their oriented attachment and surface reconstruction inside the nanoparticulate agglomerates. However, in spite of such an intricate growth behavior, the ZnO nanostructures are surprisingly uniform in size and shape.

Interplay between size and crystal structure of molybdenum dioxide nanoparticles--synthesis, growth mechanism, and electrochemical performance

A detailed study is presented on the formation of MoO(2) nanoparticles from the dissolution of the precursor to the final rodlike product, with a focus on the exploration of the inorganic reaction occurring ahead of the nucleation step, and interplay between size and crystal structure of MoO(2). In situ X-ray absorption spectroscopy experiments show that the crystallization and the growth process of MoO(2) nanorods is initiated by rapid reduction of the MoO(2) Cl(2) precursor in benzyl alcohol and acetophenone. This reaction triggers the nucleation of 2 nm MoO(2) particles with spherical shape and hexagonal crystal structure. The transformation from spheres into rods emerges as a complex process driven by oriented attachment. High-resolution transmission electron microscopy and X-ray diffraction results provide evidence that the 2 nm particles first aggregate into 5-20 nm-large oriented assemblies. The increase in particle size induces the phase transition from hexagonal to the less symmetrical monoclinic crystal structure, and finally the transformation into rods. Is it shown that electrodes for lithium-ion batteries based on MoO(2) nanorods have a long-term cycling life. The specific discharge capacity even after 200 cycles at a discharge rate of 1 C is about 300 Ah kg(-1) .

Toxicological Issues of Nanoparticles Employed in Photocatalysis

A huge amount of different nanomaterials is nowadays on the market used for various specific applications. Some nanomaterials such as TiO

Hence these materials are used for many applications, e.g., for self-cleaning and antibacterial coatings on different surfaces and for the purification of wastewater where the cleaning can be induced by simple exposure to sunlight. Because of the frequent use of these nanoparticles it is important to investigate the life cycles of these nanostructured materials as well as their environmental impact and their toxicity to animals and humans.

This review first gives a short overview about nanotechnology and nanotechnological products as well as about photocatalysis and semiconductors used in this field. We then discuss the need for a new technology named nanotoxicology and the problems occurring when investigating the toxic potential of nanomaterials as well as the life cycle of nanomaterials. Furthermore, we focus on the environmental impact of TiO