Nano-zirconia - Evaluation of its antioxidant and anticancer activity

Bioactivity of nanomaterials largely depends on its size, shape and crystalline nature. In this work, the smaller sized spherical shaped nano-zirconia (ZrO₂ NPs) (of ~9 to 11nm) was fabricated and studied its biological activity especially antioxidant and cytotoxicity against human colon carcinoma (HCT-116) and human lung carcinoma (A-549) cell lines. To have its real applications in biological aspects readily available Eucalyptus globulus (E. globulus) leaf extract was used as an effective capping and reducing agent for its synthesis. The prepared ZrO₂ NPs was characterized by using different sophisticated instrumentations such as UV-visible spectrophotometer, XRD, FTIR, TEM, SAED, EDX, DLS and fluorescence spectroscopy. Cellular mitochondrial activity i.e. cell viability was measured by MTT assay and anti-oxidant activity was determined by DPPH assay. The smaller sized ZrO₂ NPs showed strong antioxidant activity as well as cytotoxicity on human cancer cell lines. Comparative cytotoxic studies were conducted on human cancerous cell lines using different techniques. Results confirmed the efficient anti-cancer activities of the fabricated ZrO₂ NPs towards the tested cell lines as well as efficient anti-oxidant activity. This is the first study in which E. globulus leaf extract was used to synthesize smaller spherical shaped ZrO₂ NPs for improved bioactivity i.e. antioxidant and cytotoxicity.

Complex surface structure of (110) terminated strontium titanate nanododecahedra

The surface structure of (110) faceted strontium titanate nanoparticles synthesized via solvothermal method has been resolved using high-resolution electron microscopy (HREM). We demonstrate that the surface is a titania-rich structure containing tetrahedrally coordinated TiO₄ units similar to the family of (n × 1) reconstructions observed on (110) surfaces of bulk crystalline strontium titanate. When compared with prior results for (001) terminated strontium titanate single crystals made with traditional transmission electron microscopy (TEM) sample preparation techniques, the results demonstrate that many models for oxide nanoparticles need to be revisited. This work serves as a reminder that attention must be paid to the surface of nanoparticles. Even with a simple perovskite as the starting point the end result can be very complex. As more materials are synthesized on the nanoscale, this will become increasingly important to take into consideration.

Synergistic photocatalysis of Cr(VI) reduction and 4-Chlorophenol degradation over hydroxylated α-Fe2O3 under visible light irradiation

A series of Fe2O3 materials with hydroxyl are synthesized in different monohydric alcohol (C2-C5) solvents by solvothermal method and characterized by XRD, BET, XPS, TG and EA. The amount of hydroxyl is demonstrated to be emerged on the surface of the as-synthesized Fe2O3 particles and their contents are determined to be from 7.99 to 3.74 wt%. The Cr(VI) reduction experiments show that the hydroxyl content of Fe2O3 samples exacts great influence on the photocatalytic activity under visible light irradiation (λ>400 nm) and that the Fe2O3 sample synthesized in n-butyl alcohol exhibits the optimal photocatalytic activity. The synergistic photocatalysis for 4-Chlorophenol (4-CP) degradation and Cr(VI) reduction over above Fe2O3 sample is further investigated. The photocatalytic ratio of Cr(VI) reduction are enhanced from 24.8% to 70.2% while that of 4-CP oxidation are increased from 13.5% to 47.8% after 1 h visible light irradiation. The Fe2O3 sample keeps good degradation rates of mixed pollutants after 9 runs. The active oxygen intermediates O2(-)˙, ˙OH and H2O2 formed in the photoreaction process are discovered by ESR measurement and UV-vis test. The photocatalytic degradation mechanism is proposed accordingly.

Controlling the crystallisation of oxide materials by solvothermal chemistry: tuning composition, substitution and morphology of functional solids

Three aspects in the synthesis of oxides under solvothermal conditions are reviewed: materials discovery, substitutional chemistry and crystal habit control.

Solvothermal synthesis and controlled self-assembly of monodisperse titanium-based perovskite colloidal nanocrystals

The rational design of monodisperse ferroelectric nanocrystals with controlled size and shape and their organization into hierarchical structures has been a critical step for understanding the polar ordering in nanoscale ferroelectrics, as well as the design of nanocrystal-based functional materials which harness the properties of individual nanoparticles and the collective interactions between them. We report here on the synthesis and self-assembly of aggregate-free, single-crystalline titanium-based perovskite nanoparticles with controlled morphology and surface composition by using a simple, easily scalable and highly versatile colloidal route. Single-crystalline, non-aggregated BaTiO3 colloidal nanocrystals, used as a model system, have been prepared under solvothermal conditions at temperatures as low as 180 °C. The shape of the nanocrystals was tuned from spheroidal to cubic upon changing the polarity of the solvent, whereas their size was varied from 16 to 30 nm for spheres and 5 to 78 nm for cubes by changing the concentration of the precursors and the reaction time, respectively. The hydrophobic, oleic acid-passivated nanoparticles exhibit very good solubility in non-polar solvents and can be rendered dispersible in polar solvents by a simple process involving the oxidative cleavage of the double bond upon treating the nanopowders with the Lemieux-von Rudloff reagent. Lattice dynamic analysis indicated that regardless of their size, BaTiO3 nanocrystals present local disorder within the perovskite unit cell, associated with the existence of polar ordering. We also demonstrate for the first time that, in addition to being used for fabricating large area, crack-free, highly uniform films, BaTiO3 nanocubes can serve as building blocks for the design of 2D and 3D mesoscale structures, such as superlattices and superparticles. Interestingly, the type of superlattice structure (simple cubic or face centered cubic) appears to be determined by the type of solvent in which the nanocrystals were dispersed. This approach provides an excellent platform for the synthesis of other titanium-based perovskite colloidal nanocrystals with controlled chemical composition, surface structure and morphology and for their assembly into complex architectures, therefore opening the door for the design of novel mesoscale functional materials/nanocomposites with potential applications in energy conversion, data storage and the biomedical field.