Virgínia S. Souza

Synthesis and Characterisation of Fluorescent Carbon Nanodots Produced in Ionic Liquids by Laser Ablation

Carbon nanodots (C-dots) with an average size of 1.5 and 3.0 nm were produced by laser ablation in different imidazolium ionic liquids (ILs), namely, 1-n-butyl-3-methylimidazolium tetrafluoroborate (BMI.BF4 ), 1-n-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (BMI.NTf2 ) and 1-n-octyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (OMI.NTf2 ). The mean size of the nanoparticles is influenced by the imidazolium alkyl side chain but not by the nature of the anion. However, by varying the anion (BF4 vs. NTf2 ) it was possible to detect a significant modification of the fluorescence properties. The C-dots are much probably stabilised by an electrostatic layer of the IL and this interaction has played an important role with regard to the formation, stabilisation and photoluminescence properties of the nanodots. A tuneable broadband fluorescence emission from the colloidal suspension was observed under ultraviolet/visible excitation with fluorescence lifetimes fitted by a multi-exponential decay with average values around 7 ns.

Hydrogen generation and degradation of trypan blue using fern-like structured silver-doped TiO2 nanoparticles

TiO2:Ag nanoparticles have been successfully prepared at 120 °C in one day using an ionic liquid assisted hydrothermal method with methoxyethyl methyl imidazolium methanesulfonate as the ionic liquid. The obtained product was characterized using various techniques. The XRD pattern indicated the formation of TiO2:Ag nanoparticles, the average crystallite size was found to be 40 nm. XPS confirmed the formation of TiO2:Ag nanoparticles. The UV-Vis spectrum indicated a maximum absorbance at 362 nm which is red shifted compared to nano-sized TiO2. The surface morphology was analyzed using SEM, which shows a leaf-like structure for the TiO2:Ag nanoparticles. TEM images showed almost elliptically (rice pellet) shaped nanoparticles with an average particle size of about 60 nm. The EDS spectrum revealed the presence of Ti, O and Ag with atomic percentages of 42.6, 43.7 and 2.3%, respectively. The TiO2:Ag nanoparticles generate 2230 μmol H2 per 1 g of photocatalyst in 2.5 h via the water splitting reaction. They also show good photocatalytic activity in the degradation of trypan blue.

Hybrid tantalum oxide nanoparticles from the hydrolysis of imidazolium tantalate ionic liquids: efficient catalysts for hydrogen generation from ethanol/water solutions

The reaction of equimolar amounts of 1-n-butyl-3-methylimidazolium chloride (BMI·Cl) or 1-n-decyl-3-methylimidazolium chloride (DMI·Cl) with TaCl5 affords imidazolium tantalate ionic liquids (ILs) BMI·TaCl61 and DMI·TaCl62. The hydrolysis of ILs 1 and 2 yields hybrid-like tantalum oxide nanoparticles (NPs) with size distribution dependent on the nature of the IL used (3.8–22 nm from IL 1 and 1.5–6 nm from 2). A significant aggregation/agglomeration of the particles was observed after the removal of the IL content of the hybrid material by calcination, forming predominantly large particles (mainly bulk tantalum oxides). These new hybrid-like Ta2O5/IL NPs are highly active photocatalyst nanomaterials for hydrogen production by reforming of ethanol at ambient temperature. Hydrogen evolution rates up to 7.2 mmol H2 g−1 h−1 and high apparent quantum yields up to 17% were measured. The hybrid-like Ta2O5/IL NPs sputtered-decorated with ultra-small Pt NPs (1.0 ± 0.3 nm) as co-catalysts reached activities leading to even higher hydrogen production (9.2 H2 mmol g−1 h−1; apparent quantum yield of 22%). The calcined materials (with or without Pt NPs) showed much lower photocatalytic activity under the same reaction conditions (up to 2.8 mmol g−1 of H2). The remarkable activity of the hybrid-like Ta2O5/IL NPs may be related to the presence of the remaining IL that provides hydrophilic regions, facilitating the approach of polar molecules (water and alcohol) to the semiconductor active photocatalytic sites.

Superior activity of the CuS–TiO2/Pt hybrid nanostructure towards visible light induced hydrogen production

A CuS–TiO2 hybrid nanostructure has been synthesized and employed for photocatalytic hydrogen production under UV-Vis light using Na2S and Na2SO3 as the sacrificial agents. The remarkable hydrogen production recorded for the CuS–TiO2 heterostructure was 458 μmol h−1 g−1 and for CuS–TiO2/Pt was 746 μmol h−1 g−1. The corresponding apparent quantum yield values are 1.01% and 1.55%. The addition of Pt to the hybrid structure acts as a metallic sandwich between two semiconductors CuS and TiO2 which assist in charge separation.

Mesoporous Foam TiO2 Nanomaterials for Effective Hydrogen Production

Hydrolysis of TiCl4 in a diether-functionalized imidazolium ionic liquid (IL), namely 1-methyl-3-[2-(2-methoxy(ethoxy)ethyl]imidazolium methane sulfonate (M(MEE)I⋅CH3 SO3 ), results in a heterostructured organic/inorganic and sponge-like porous TiO2 material. The thermal treatment (300 °C) followed by calcination (500 °C) affords highly porous TiO2 . The characterization of the obtained samples (with and without IL, before and after calcination) by XRD, SEM, and TEM reveals TiO2 anatase crystalline phases and irregular-shaped particles with different porous structures. These hierarchical-structured mesoporous TiO2 nanomaterials were employed as efficient photocatalysts in the water-splitting process, yielding up to 1304 μmol g(-1) on hydrogen production.

Heterojunction CuO-TiO2 nanocomposite synthesis for significant photocatalytic hydrogen production

Effective and low-cost photocatalysts have been synthesized by a simple hydrothermal process. In this process, the two CuO and TiO2 bound one over the other and formed a heterojunction CuO-TiO2 nanocomposite. CuO serves as electron reservoir by receiving electrons from TiO2, which suppresses the recombination of e−/h+ and transfers the received electron to split water, which results in enhanced H2 production. Heterojunction CuO-TiO2 nanocomposite material recorded a maximum of 9284 μmolg−1 H2 production for 2.5 h. The recorded result is 15 times higher than bare TiO2 and 16 times higher than bare CuO. The synthesized materials were characterized and analyzed using various analytical techniques such as XRD, FTIR, UV–vis spectra and the morphology was studied using SEM, TEM, and HRTEM images.

Effect of the magnetic core of (MnFe)2O3@Ta2O5 nanoparticles on photocatalytic hydrogen production

The combination of the pre-formed magnetic (Mn0.983Fe0.017)2O3 particles with Ta2O5 prepared from ionic liquids affords (MnFe)2O3@Ta2O5 core–shell composites. The photocatalytic activities of these core–shell materials were evaluated for hydrogen production, for which they appeared to be superior catalysts to the individual (Mn0.983Fe0.017)2O3 and Ta2O5 components.

Frontispiece: Synthesis and Characterisation of Fluorescent Carbon Nanodots Produced in Ionic Liquids by Laser Ablation

Carbon Nanodots The fabrication of fluorescent C-dots by laser ablation from graphite powder dispersed in ionic liquids is described. The final luminescent solution illuminated by a violet laser is shown in inset. For more details, see the Full Paper by J. D. Scholten, J. Dupont, R. R. B. Correia et al. on page 138 ff.

Frontispiece: Mesoporous Foam TiO2 Nanomaterials for Effective Hydrogen Production

Photocatalysis The development of highly ordered porous materials has gained increased attention in scientific research. These multifunctional materials with controlled porosity can be applied to photocatalysis, photovoltaics, solar-energy conversion, sensors, textiles, paints, and cosmetics. In their Full Paper on page 17624 ff., J. Dupont, R. Thippeswamy, and co-workers describe a simple method for the preparation of large amounts of highly porous, novel, and spongy-type TiO2 materials, which were employed as efficient photocatalysts in the water-splitting process.