A versatile synthetic method based on solvothermal technique has been developed for the fabrication of TiO(2) nanocrystals with different shapes such as rhombic, truncated rhombic, spherical, dog-bone, truncated and elongated rhombic, and bar. The central features of our approach are the use of water vapor as hydrolysis agent to accelerate the reaction and the use of both oleic acid and oleylamine as two distinct capping surfactants which have different binding strengths to control the growth of the TiO(2) nanoparticles. We also show that the presence of an appropriate amount of water vapor along with the desired oleic acid/oleylamine molar ratio plays a crucial role in controlling size and shape of TiO(2) nanocrystals.

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.

Monodisperse samaria nanospheres and nanorods have been synthesized from commercial bulk Sm2O3 powders and various capping long-chain alkyl acids (e.g., oleic acid, myristic acid, decanoic acid). The synthesized materials were characterized by X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy (XPS), Fourier transform IR, thermogravimetric analysis, and N2 adsorption/desorption isotherms was employed to characterize these materials. The results revealed that the synthesis of nanorods consists of two steps of growth: (i) the nanoparticles were formed at relatively low temperature (120−140 °C) by Ostwald ripening and (ii) were followed by oriented attachment of these nanoparticles at higher temperature (160−200 °C) to produce the nanorods (average size of 7 nm × 160 nm). Furthermore, the width of nanorods can be controlled by the length of capping alkyl chain agents; on the basis of the experimental results, it seems that a longer alkyl chain agent leads to thinner nanorods; however, the length of nanorods remains unchanged. For the whole process, the possible Ostwald ripening and oriented attachment mechanisms were also discussed. The XPS results for the calcined nanorods sample shows the presence of two oxidation states, Sm3+/Sm2+ (it is found to be 40% Sm2+), and three components by deconvolution of O 1s peak indicating the defected structure. The surface chemical composition is found to be Sm2O3−x (x = 1.8). We believe that this synthetic method is simple, highly reproducible, inexpensive, and applicable for large-scale production.

Simultaneous integration of light emission and iridescence into a semiconducting photonic material is attractive for the design of new optical devices.Here, a straightforward, one-pot approach for liquid crystal self-assembly of semiconductor quantum dots into cellulose nanocrystal-templated silica is developed. Through a careful balance of the intermolecular interactions between a lyotropic tetraalkoxysilane/cellulose nanocrystal dispersion and water-soluble polyacrylic acid/mercaptopropionic acid-stabilized CdS quantum dots, CdS/silica/nanocellulose composites that retain both chiral nematic order of the cellulose nanocrystals and emission of the quantum dots are successfully co-assembled. Subsequent removal of the cellulose template and organic stabilizers in the composites by controlled calcination generates new freestanding iridescent, luminescent chiral nematic mesoporous silica-encapsulated CdS fi lms. The pores of these materials are accessible to analytes and, consequently, the CdS quantum dots undergo strong luminescence quenching when exposed to TNT solutions or vapor.

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Silver orthophosphate nanocrystals with controlled particle size have been synthesized using a simple, reproducible and easily scaled up route based on the reaction between silver ions, oleylamine and phosphoric acid. The obtained nanocrystals are highly uniform in size and exhibit high visible light activity for the photodecomposition of organic compounds.

The introduction of polymers into a chiral nematic cellulose nanocrystal (CNC) matrix allows for the tuning of optical and mechanical properties, enabling the development of responsive photonic materials. In this study, we explored the incorporation of hydroxypropyl cellulose (HPC) into a CNC film prepared by slow evaporation. In the composite CNC/HPC thin films, the CNCs adopt a chiral nematic structure, which can selectively reflect certain wavelengths of light to yield a colored film. The color could be tuned across the visible spectrum by changing the concentration or molecular weight of the HPC. Importantly, the composite films were more flexible than pure CNC films with up to a ten-fold increase in elasticity and a decrease in stiffness and tensile strength of up to six times and four times, respectively. Surface modification of the films with methacrylate groups increased the hydrophobicity of the films, and therefore, the water stability of these materials was also improved.

Different two-phase approaches have been developed for the synthesis of two classes of monodisperse colloidal metal oxide nanocrystals (NCs): rare earth oxide NCs and transition metal oxide NCs. These routes were simple and inexpensive, using metal salts instead of organometallic compounds, with mild reaction conditions, easily controlled size and shape, and multigram-scale products. The obtained products were characterized by transmission electron microscopy (TEM), selected area electron diffraction (SAED), X-ray diffraction (XRD), X-ray photoelectron spectra (XPS), Fourier transform infrared absorption spectroscopy (FTIR), and nitrogen adsorption−desorption isotherms (BET). The possible mechanisms for the formation and growth of nanocrystals were discussed. Accordingly, tert-butylamine (nucleophile agent) and ethanol (reduced agent) are the key factors for the formation of rare earth oxide NCs and transition metal oxide NCs, respectively. Different sizes and shapes of monodisperse nanoparticles such as spherical, cubic, peanut, rod, and hexagonal NCs were obtained, depending on the nature of metal precursors. Furthermore, the effect of monomeric precursor concentration, type of precursors, and reaction time on the size and shape of the products was also studied. The SAED patterns of the obtained NC samples show a set of sharp spots that are characteristic of single crystalline structures indexed accordingly with the structures determined by the XRD spectra. The XPS results revealed the presence of two oxidation states of cerium, samarium, manganese, and cobalt on the nanocrystal surface, whereas it seems only one oxidation state is present on the surface for Y, Cr, La, Gd, and Er oxide nanocrystals. A large O 1s XPS peak attributed to two oxygen components for these Ce, Sm, Mn, and Co oxide NC samples refer to the defected structure. Our approaches may be also applicable to synthesize other uniform metal oxide NCs as well as doped metal oxide NCs and multicomponent NCs.