Photodeposition of CdSe using Se-TiO2 suspensions as photocatalysts

Photocatalytic inactivation of Escherischia coli under UV light irradiation using large surface area anatase TiO2 quantum dots

In this study, high specific surface areas (SSAs) of anatase titanium dioxide (TiO2) quantum dots (QDs) were successfully synthesized through a novel one-step microwave-hydrothermal method in rapid synthesis time (20 min) without further heat treatment. XRD analysis and HR-TEM images showed that the as-prepared TiO2 QDs of approximately 2 nm size have high crystallinity with anatase phase. Optical properties showed that the energy band gap (E g) of as-prepared TiO2 QDs was 3.60 eV, which is higher than the standard TiO2 band gap, which might be due to the quantum size effect. Raman studies showed shifting and broadening of the peaks of TiO2 QDs due to the reduction of the crystallite size. The obtained Brunauer-Emmett-Teller specific surface area (381 m2 g-1) of TiO2 QDs is greater than the surface area (181 m2 g-1) of commercial TiO2 nanoparticles. The photocatalytic activities of TiO2 QDs were conducted by the inactivation of Escherischia coli under ultraviolet light irradiation and compared with commercially available anatase TiO2 nanoparticles. The photocatalytic inactivation ability of E. coli was estimated to be 91% at 60 µg ml-1 for TiO2 QDs, which is superior to the commercial TiO2 nanoparticles. Hence, the present study provides new insight into the rapid synthesis of TiO2 QDs without any annealing treatment to increase the absorbance of ultraviolet light for superior photocatalytic inactivation ability of E. coli.

Recyclable Magnetic Titania Nanocomposite from Ilmenite with Enhanced Photocatalytic Activity

Using ilmenite as a raw material, iron was converted into Fe₃O₄ magnetic fluid, which further was combined with titanium filtrate by a solvothermal method. Finally Fe₃O₄/TiO₂ nanocomposites with the uniform size of 100-200 nm were prepared. This approach uses rich, inexpensive ilmenite as a titanium and iron source, which effectively reduces the production cost. The crystal structure, chemical properties and morphologies of the products were characterized by SEM, TEM, XRD, FTIR, BET, UV-Vis, XPS and VSM. The novel photocatalyst composed of face-centered cubic Fe₃O₄ and body-centered tetragonal anatase-TiO₂ exhibits a spherical shape with porous structures, superparamagnetic behavior and strong absorption in the visible light range. Using the degradation reaction of Rhodamine B (RhB) to evaluate the photocatalytic performance, the results suggest that Fe₃O₄/TiO₂ nanocomposites exhibit excellent photocatalytic activities and stability under visible light and solar light. Moreover, the magnetic titania nanocomposites displayed good magnetic response and were recoverable over several cycles. Based on the trapping experiments, the main active species in the photocatalytic reaction were confirmed and the possible photocatalytic mechanism of RhB with magnetic titania was proposed. The enhanced photocatalytic activity and stability, combined with excellent magnetic recoverability, make the prepared nanocomposite a potential candidate in wastewater purification.

Visible-Light Active and Magnetically Recyclable Nanocomposites for the Degradation of Organic Dye

Recyclable visible-light photocatalyst Fe₃O₄@TiO₂ with core-shell structure was prepared by a simple synthetic strategy using solvothermal crystallization of titanium precursor on preformed Fe₃O₄ nanopartiles. The photo-degradation reaction of neutral red aqueous solution was tested to evaluate the visible-light photocatalytic activity of the as prepared Fe₃O₄@TiO₂ nanoparticles, which show excellent photocatalytic activity compared with commercial P25 catalyst. Moreover, the Fe₃O₄@TiO₂ nanocomposites can be easily separated from the reaction mixture, and maintain favorable photocatalytic activity after five cycles. The high visible light absorption of the Fe₃O₄@TiO₂ nanocomposites may originate from the absence of electronic heterojunction, excellently dispersity and the high specific surface area of the as-synthesized Fe₃O₄@TiO₂ samples.

Photodeposition of Ag2S quantum dots and application to photoelectrochemical cells for hydrogen production under simulated sunlight

UV light irradiation of TiO(2) (λ > 320 nm) in a mixed solution of AgNO(3) and S(8) has led to the formation of Ag(2)S quantum dots (QDs) on TiO(2), while Ag nanoparticles (NPs) are photodeposited without S(8). Photoelectrochemical measurements indicated that the Ag(2)S photodeposition proceeds via the preferential reduction of Ag(+) ions to Ag(0), followed by the chemical reaction with S(8). The application of this in situ photodeposition technique to mesoporous (mp) TiO(2) nanocrystalline films coated on fluorine-doped SnO(2) (FTO) electrodes enables formation of Ag(2)S QDs (Ag(2)S/mp-TiO(2)/FTO). Ag(2)S/mp-TiO(2)/FTO has the interband transition absorption in the whole visible region, while in the spectrum of Ag/mp-TiO(2)/FTO, a localized surface plasmon resonance absorption of Ag NPs is present centered at 490 nm. Ag(2)S QD-sensitized photoelectrochemical cells using the Ag(2)S/mp-TiO(2)/FTO and Ag/mp-TiO(2)/FTO photoanodes were fabricated. Under illumination of one sun, the Ag(2)S photoanode cell yielded H(2) at a rate of 0.8 mL·h(-1) with a total conversion efficiency of 0.29%, whereas the Ag/mp-TiO(2)/FTO photoanode is inactive.

Photodeposition of metal sulfide quantum dots on titanium(IV) dioxide and the applications to solar energy conversion

Heteronanojunction systems consisting of narrow gap semiconductors represented by metal sulfides and TiO(2) are highly expected as visible-light-active photocatalysts and the key materials for various photoelectrochemical devices. The common central issue is increasing efficiency of the light-induced interfacial electron transfer from the metal sulfide quantum dots (QDs) to TiO(2). We have newly developed simple and versatile low-temperature photodeposition techniques for directly coupling metal sulfide QDs and TiO(2) by taking advantage of its photocatalysis and the photoinduced surface superhydrophilicity. This critical review summarizes the recent developments in the photodeposition techniques and their unique characteristics. Subsequently to the Introduction, a theoretical view of the interfacial electron transfer is presented to obtain the guidelines for the design of the heteronanojunction systems. Then, the itemized description is given for the photodepositions of several kinds of metal sulfides on TiO(2) followed by the summary of the features of the photodeposition technique. Finally, the applications of the resulting heteronanojunction systems to the photocatalysts and QD-sensitized solar cells are described, and the excellent performances are discussed by relating with the features of the photodeposition technique (87 references).

Microwave-Assisted Synthesis of Titania Nanocubes, Nanospheres and Nanorods for Photocatalytic Dye Degradation

TiO(2) nanostructures with fascinating morphologies like cubes, spheres, and rods were synthesized by a simple microwave irradiation technique. Tuning of different morphologies was achieved by changing the pH and the nature of the medium or the precipitating agent. As-synthesized titania nanostructures were characterized by X-ray diffraction (XRD), UV-visible spectroscopy, infrared spectroscopy (IR), BET surface area, photoluminescence (PL), scanning electron microscopy (SEM) and transmission electron microscopy (TEM), and atomic force microscopy (AFM) techniques. Photocatalytic dye degradation studies were conducted using methylene blue under ultraviolet light irradiation. Dye degradation ability for nanocubes was found to be superior to the spheres and the rods and can be attributed to the observed high surface area of nanocubes. As-synthesized titania nanostructures have shown higher photocatalytic activity than the commercial photocatalyst Degussa P25 TiO(2).