In a mixed solvent of water and ethanol, polystyrene/titanium dioxide (PSt/TiO2) composite particles of core-shell structure were prepared by hydrolysis of tetrabutyl titanate in the presence of cationic PSt particles or anionic PSt particles surface-treated using gamma-aminopropyl triethoxysilane. Hollow TiO2 particles were obtained through calcination of the PSt/TiO2 core-shell particles to burn off the PSt core or through dissolution of the core by tetrahydrofuran (THF). An alternative process constituted of preheating the PSt/TiO2 particles at 200[degree sign]C to allow partial crystallization followed by calcination or PSt dissolution by THF. The outcome TiO2 particles thus prepared were examined by TEM, and hollow TiO2 particles were observed. The crystalline phase structure and phase transformation were characterized, which revealed that preheating before the removal of the PSt core was useful to achieve the desired hollow TiO2 particles, and the calcination process was beneficial to the formation of anatase and rutile structures. The tests of TiO2 particles as catalyst in the photodegradation of Rhodamine B demonstrated that a much higher catalytic activity was observed with the TiO2 hollow particles prepared through calcination combined with preheating.
Tuning the photonic band gap (PBG) to the electronic band gap (EBG) of Au/TiO2 catalysts resulted in considerable enhancement of the photocatalytic water splitting to hydrogen under direct sunlight. Au/TiO2 (PBG-357 nm) photocatalyst exhibited superior photocatalytic performance under both UV and sunlight compared to the Au/TiO2 (PBG-585 nm) photocatalyst and both are higher than Au/TiO2 without the 3 dimensionally ordered macro-porous structure materials. The very high photocatalytic activity is attributed to suppression of a fraction of electron-hole recombination route due to the co-incidence of the PBG with the EBG of TiO2 These materials that maintain their activity with very small amount of sacrificial agents (down to 0.5 vol.% of ethanol) are poised to find direct applications because of their high activity, low cost of the process, simplicity and stability.
Flower-like AgCl microstructures with enhanced visible light-driven photocatalysis are synthesized by a facile one-pot hydrothermal process for the first time. The evolution process of AgCl from dendritic structures to flower-like octagonal microstructures is investigated quantitatively. Furthermore, the flower-like AgCl microstructures exhibit enhanced ability of visible light-assisted photocatalytic degradation of methyl orange. The enhanced photocatalytic activity of the flower-like AgCl microstructure is attributed to its three-dimensional hierarchical structure exposing with  facets. This work provides a fresh view into the insight of electrochemical process and the application area of visible light photocatalysts.
The prototypical photocatalyst TiO2 exists in different polymorphs, the most common forms are the anatase- and rutile-crystal structures. Generally, anatase is more active than rutile, but no consensus exists to explain this difference. Here we demonstrate that it is the bulk transport of excitons to the surface that contributes to the difference. Utilizing high -quality epitaxial TiO2 films of the two polymorphs we evaluate the photocatalytic activity as a function of TiO2-film thickness. For anatase the activity increases for films up to ~5 nm thick, while rutile films reach their maximum activity for ~2.5 nm films already. This shows that charge carriers excited deeper in the bulk contribute to surface reactions in anatase than in rutile. Furthermore, we measure surface orientation dependent activity on rutile single crystals. The pronounced orientation-dependent activity can also be correlated to anisotropic bulk charge carrier mobility, suggesting general importance of bulk charge diffusion for explaining photocatalytic anisotropies.
The engineering of acetylenic carbon-rich nanostructures has great potential in many applications, such as nanoelectronics, chemical sensors, energy storage, and conversion, etc. Here we show the synthesis of acetylenic carbon-rich nanofibers via copper-surface-mediated Glaser polycondensation of 1,3,5-triethynylbenzene on a variety of conducting (e.g., copper, graphite, fluorine-doped tin oxide, and titanium) and non-conducting (e.g., Kapton, glass, and silicon dioxide) substrates. The obtained nanofibers (with optical bandgap of 2.51 eV) exhibit photocatalytic activity in photoelectrochemical cells, yielding saturated cathodic photocurrent of ca. 10 µA cm-2(0.3-0 V vs. reversible hydrogen electrode). By incorporating thieno[3,2-b]thiophene units into the nanofibers, a redshift (ca. 100 nm) of light absorption edge and twofold of the photocurrent are achieved, rivalling those of state-of-the-art metal-free photocathodes (e.g., graphitic carbon nitride of 0.1-1 µA cm-2). This work highlights the promise of utilizing acetylenic carbon-rich materials as efficient and sustainable photocathodes for water reduction.
The generation of hydrogen from water using sunlight could potentially form the basis of a clean and renewable source of energy. Various water-splitting methods have been investigated previously, but the use of photocatalysts to split water into stoichiometric amounts of H2 and O2 (overall water splitting) without the use of external bias or sacrificial reagents is of particular interest because of its simplicity and potential low cost of operation. However, despite progress in the past decade, semiconductor water-splitting photocatalysts (such as (Ga1-xZnx)(N1-xOx)) do not exhibit good activity beyond 440 nm (refs 1,2,9) and water-splitting devices that can harvest visible light typically have a low solar-to-hydrogen efﬁciency of around 0.1%. Here we show that cobalt(II) oxide (CoO) nanoparticles can carry out overall water splitting with a solar-to-hydrogen efficiency of around 5%. The photocatalysts were synthesized from non-active CoO micropowders using two distinct methods (femtosecond laser ablation and mechanical ball milling), and the CoO nanoparticles that result can decompose pure water under visible-light irradiation without any co-catalysts or sacrificial reagents. Using electrochemical impedance spectroscopy, we show that the high photocatalytic activity of the nanoparticles arises from a significant shift in the position of the band edge of the material.
The combination of photocatalysis under visible light irradiation and sonolysis in the continuous system has been used to degrade an aqueous solution of phenol. ZnFe(2)O(4)/TiO(2)-GAC was employed as the photocatalysts which were obtained by sol-gel process and characterized by spectroscopic X-ray diffraction (XRD), scanning electron microscopy with energy dispersive X-ray microanalyses (SEM-EDX) and Brunauer-Emmett-Teller sorptometer (BET). It was observed that the rates of phenol degradation were affected by the initial pH value of phenol solution, salt addition, gas supplying and the recycling times of the recovered photocatalyst. The kinetic law for the phenol degradation can be apparently expressed as the first-order with respect to the concentration of phenol. Degradation of phenol solution in the continuous system, i.e., photocatalysis and sonolysis has synergistic effect in comparison with the photocatalytic reaction and sonolysis, respectively.
Nanostructured particles with a magnetic core and a photocatalytic shell are very interesting systems for their properties to be magnetically separable (and so reusable) in photocatalytic water depuration implant. Here, a robust, low time-consuming, easily scale up method to produce Fe(3)O(4)/SiO(2)/TiO(2) hierarchical nanostructures starting from commercial precursors (i.e. Fe(3)O(4), SiO(2)) by employing a colloidal approach (i.e. heterocoagulation) coupled with the spray-drying technique is presented. In particular, a self-assembled layer-by-layer methodology based on the coagulation of dissimilar colloidal particles was applied. First, a passive layer of silica (SiO(2), amorphous) was created on magnetite in order to avoid detrimental phenomena arising from the direct contact between magnetite and titania, then the deposition of titania onto silica-coated-magnetite was promoted. TiO(2), SiO(2) and Fe(3)O(4) nanosols were characterized in terms of zeta potential, optimized and a self-assembled layer-by-layer approach was followed in order to promote the heterocoagulation of silica onto magnetite surface and of titania onto silica coated magnetite. Once optimized the colloidal route, the mixture was then spray-dried to obtain a granulated powder with nano-scale reactivity, easier to handle and re-disperse in comparison to starting nanopowders with the same surface properties. The nanostructured particles have been characterized by different techniques such as SEM, TEM, XDR and their magnetic properties have been investigated. Moreover, preliminary photocatalytic texts have been performed.
Uniform bismuth oxide (Bi(2) O(3) ) and bismuth subcarbonate ((BiO)(2) CO(3) ) nanotubes were successfully synthesized by a facile solvothermal method without the need for any surfactants or templates. The synergistic effect of ethylene glycol (EG) and urea played a critical role in the formation of the tubular nanostructures. These Bi(2) O(3) and (BiO)(2) CO(3) nanotubes exhibited excellent Cr(VI) -removal capacity. Bi(2) O(3) nanotubes, with a maximum Cr(VI) -removal capacity of 79 mg g(-1) , possessed high removal ability in a wide range of pH values (3-11). Moreover, Bi(2) O(3) and (BiO)(2) CO(3) nanotubes also displayed highly efficient photocatalytic activity for the degradation of RhB under visible-light irradiation. This work not only demonstrates a new and facile route for the fabrication of Bi(2) O(3) and (BiO)(2) CO(3) nanotubes, but also provides new promising adsorbents for the removal of heavy-metal ions and potential photocatalysts for environmental remediation.
A new 1D core-shell strategy is demonstrated for a hydrogen-generation photo-electrochemical cell (PEC). This Si/iodine-doped poly(3,4-ethylenedioxythiophene) (PEDOT) 1D nanocable array shows an encouraging solar-to-chemical energy-conversion efficiency. Coating with iodine-doped PEDOT can effectively enhance the photocatalytic efficiency and stability of SiNW arrays. The PEC model proposed shows a potentially promising structure for H(2) production using solar energy.