A Facile Strategy for the Preparation of N-Doped TiO2 with Oxygen Vacancy via the Annealing Treatment with Urea.

Although titanium dioxide (TiO2) has a wide range of potential applications, the photocatalytic performance of TiO2 is limited by both its limited photoresponse range and fast recombination of the photogenerated charge carriers. In this work, the preparation of nitrogen (N)-doped TiO2 accompanied by the introduction of oxygen vacancy (Vo) has been achieved via a facile annealing treatment with urea as the N source. During the annealing treatment, the presence of urea not only realizes the N-doping of TiO2 but also creates Vo in N-doped TiO2 (N-TiO2), which is also suitable for commercial TiO2 (P25). Unexpectedly, the annealing treatment-induced decrease in the specific surface area of N-TiO2 is inhibited by the N-doping and, thus, more active sites are maintained. Therefore, both the N-doping and formation of Vo as well as the increased active sites contribute to the excellent photocatalytic performance of N-TiO2 under visible light irradiation. Our work offers a facile strategy for the preparation of N-TiO2 with Vo via the annealing treatment with urea.

Facile Vacuum Annealing-Induced Modification of TiO2 with an Enhanced Photocatalytic Performance.

In this work, the photocatalytic performance enhancement of hydrothermally prepared TiO2 was achieved by facile vacuum annealing treatment. Calcination of TiO2 powder in air (CA-TiO2) maintained its white color, while gray powder was obtained when the annealing was performed under vacuum (CV-TiO2). Fourier transform infrared, total organic carbon, X-ray photoelectron spectroscopy, and electron paramagnetic resonance analyses proved that vacuum annealing transformed ethanol adsorbed on the surface of TiO2 into carbon-related species accompanied by the formation of surface oxygen vacancies (Vo). The residual carbon-related species on the surface of CV-TiO2 favored its adsorption of organic dyes. Compared with TiO2 and CA-TiO2, CV-TiO2 exhibited an improved charge carrier separation with surface Vo as trapping sites for electrons. Vacuum annealing-induced improvement of crystallinity, enhancement of adsorption capacity, and formation of surface Vo contributed to the excellent photocatalytic activity of CV-TiO2, which was superior to that of commercial TiO2 (P25, Degussa). Obviously, vacuum annealing-triggered decomposition of ethanol played an important role in the modification of TiO2. In the presence of ethanol, vacuum annealing was also suitable for the introduction of Vo into P25. Therefore, the current work offers an easy approach for the modification of TiO2 to enhance its photocatalytic performance by facile vacuum annealing in the presence of ethanol.

An Efficient Uranium Adsorption Magnetic Platform Based on Amidoxime-Functionalized Flower-like Fe3O4@TiO2 Core-Shell Microspheres.

Efficient removal of uranium (U) from aqueous solutions is crucial for ecological safety. Functionalized magnetic nanoparticles provide a promising strategy for radionuclide recovery and separation. However, designing and synthesizing magnetic adsorbents with high sorption capacity and selectivity, accompanied by excellent stability and reusability, remain a challenge. In this work, novel amidoxime-functionalized flower-like magnetic Fe3O4@TiO2 core-shell microspheres are designed and synthesized to efficiently remove U(VI) from aqueous solutions and actual seawater. The magnetic Fe3O4 core facilitates easy separation by an external magnetic field, and flower-like TiO2 nanosheets provide abundant specific surface areas and functionalization sites. The grafted amidoxime (AO) groups could function as a claw for catching uranium. The maximum adsorption capacity on U(VI) of the designed nanospheres reaches 313.6 mg·g-1 at pH 6.0, and the adsorption efficiency is maintained at 97% after 10 cycles. In addition, the excellent selectivity of the magnetic recyclable AO-functioning Fe3O4@TiO2 microspheres endows the potential of uranium extraction from seawater. The designed material provides an effective and applicable diagram for radioactive element elimination and enrichment.

Plasmonic photocatalysis applied to solar fuels.

The induction of chemical processes by plasmonic systems is a rapidly growing field with potentially many strategic applications. One of them is the transformation of solar energy into chemical fuel by the association of plasmonic metal nanoparticles (M NPs) and a semi-conductor (SC). When the localized surface plasmon resonance (LSPR) and the SC absorption do not match, one limitation of these systems is the efficiency of hot electron transfer from M NPs to SC through the Schottky barrier formed at the M NP/SC interfaces. Here we show that high surface area 1 wt% Au/TiO2-UV100, prepared by adsorption of a NaBH4-protected 3 nm gold sol, readily catalyzes the photoreduction of carbon dioxide with water into methane under both solar and visible-only irradiation with a CH4vs. H2 selectivity of 63%. Tuning Au NP size and titania surface area, in particular via thermal treatments, highlights the key role of the metal dispersion and of the accessible Au-TiO2 perimeter interface on the direct SC-based solar process. The impact of Au NP density in turn provides evidence for the dual role of gold as co-catalyst and recombination sites for charge carriers. It is shown that the plasmon-induced process contributes up to 20% of the solar activity. The plasmon-based contribution is enhanced by a large Au NP size and a high degree of crystallinity of the SC support. By minimizing surface hydroxylation while retaining a relatively high surface area of 120 m2 g-1, pre-calcining TiO2-UV100 at 450 °C leads to an optimum monometallic system in terms of activity and selectivity under both solar and visible irradiation. A state-of-the-art methane selectivity of 100% is achieved in the hot electron process.

Plasmonic core-shell nanostructure as an optical photoactive nanolens for enhanced light harvesting and hydrogen production.

Hydrogen production using plasmonic photocatalyst has attracted increasing attention since it improves light harvesting and photoefficiency. Herein, we have designed a plasmonic photocatalyst in a core-shell nanostructure that enabled an improvement of light harvesting and photocatalytic production of hydrogen using a very low amount of gold nanoparticles. The core-shell nanostructure was found to mimic the focusing of light observed for the lens-like epidermal cells. Thus, the core-shell nanostructure acts as a convex nanolens to reinforce the electromagnetic field at the nanostructure surface. The electric field was also found to be enhanced, which improves the energy absorbed for gold particles located in the core-shell nanostructure. Thus, by adjusting the diameter of the core-shell nanostructure, an optimal intensity for the localized surface plasmon resonance of gold was obtained. Tuning the size of the core-shell nanostructure enabled to improve the absorption at the reactive surface, thus increasing the photocatalytic hydrogen production efficiency by 5-fold.

Electron-induced growth mechanism of conducting polymers: a coupled experimental and computational investigation.

Pulse radiolysis was used to study the mechanism of HO(•)-induced polymerization of poly(3,4-ethylenedioxythiophene), PEDOT, in aqueous solution. A step-by-step mechanism has been found which involves a recurrent oxidation process by HO(•) hydroxyl radicals produced by water radiolysis. Furthermore, the cation radical, EDOT(•)(+), has been proposed as the promoter of the first step of polymerization. The determination of rate constants values and the attribution of transient and stable species were confirmed by molecular simulations and spectrokinetic analysis. Moreover, applying a series of electron pulses enabled in situ PEDOT polymerization. These polymers, which were characterized in solution or after deposition, form globular self-assembled structures with interesting conducting properties. Such a synthesis initiated for the first time by an electron accelerator gives us a glimpse of future promising industrial applications in the field of conducting polymers synthesis.

Radiolytic method as a novel approach for the synthesis of nanostructured conducting polypyrrole.

In this study, a novel and extremely facile method for the synthesis of conducting polypyrrole (PPy) was achieved in aqueous solution. This radiolytic method is totally free of template and environmentally friendly compared with traditional chemical methods. According to ultraviolet-visible (UV-vis) spectroscopy and Fourier transform infrared (FTIR) spectroscopy analysis, pyrrole (Py) monomers were polymerized into PPy thanks to their oxidation by HO(•) radicals produced by the radiolysis of water when exposed to γ irradiation. The morphology of PPy was characterized by cryo-transmission electron microscopy (cryo-TEM) in aqueous solution and by scanning electron microscopy (SEM) after deposition. In an original way, high-resolution atomic force microscopy, coupled with infrared nanospectroscopy, was used to probe the local chemical composition of PPy nanostructures. The results demonstrated that spherical and chaplet-like PPy nanostructures were formed by γ-radiolysis. Thermogravimetric analysis (TGA) and electronic conductivity measurements showed that radiosynthesized PPy had good thermal stability and an electrical conductivity higher than that of chemically synthesized PPy.

Towards understanding the color change of 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide during gamma irradiation: an experimental and theoretical study.

The application of room-temperature ionic liquids (RTILs) in nuclear spent fuel recycling requires a comprehensive knowledge of radiation effects on RTILs. Although preliminary studies indicate a relatively high radiation stability of RTILs, little attention is paid to the color change of RTILs, an obvious phenomenon of RTILs during irradiation. In this paper, we have investigated radiation-induced darkening and decoloration of 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([BMIm][NTf2]), an ionic liquid representing the most popular class of RTILs, by means of UV-Vis analysis and time-dependent density functional theory calculations. Based on the experimental and computational results, it is proposed that the color change of [BMIm][NTf2] upon irradiation originates from the formation of double bonds in the aliphatic chains of pristine organic cations (or radiolytic products of RTILs) and various associated species containing these "double-bond products". This work sheds light on the understanding of the radiation-induced color change of RTILs.

Identification of radiolytic products of [C4mim][NTf2] and their effects on the Sr2+ extraction.

The trace water-soluble radiolytic products of neat 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([C(4)mim][NTf(2)]) were identified by analysing water-washed samples of γ-ray irradiated ionic liquids. CF(3)SO(2)OH, CF(3)SOOH, CF(3)SO(2)NH(2), HF and H(2)SO(3) were confirmed as main radiolytic products of [C(4)mim][NTf(2)], and the total radiation chemical yields of the water-soluble radiolytic products (0.35 µmol J(-1)) and that of hydrogen ions (0.46 ± 0.02 µmol J(-1)) were determined by using ion chromatography and neutralization titration, respectively. It was found that the water-soluble radiolytic products of [C(4)mim][NTf(2)] greatly reduced the extraction efficiency of Sr(2+) from water to irradiated [C(4)mim][NTf(2)], while the water-insoluble radiolytic products of [C(4)mim][NTf(2)] had a slight influence on the Sr(2+) extraction.