High Photocatalytic Stability Research Articles

A new chemical route to a hybrid nanostructure: room-temperature solid-state reaction synthesis of Ag@AgCl with efficient photocatalysis

The room-temperature solid-state chemical reaction technique has been used to synthesize the silver nanoparticle-loaded semiconductor silver@silver chloride for the first time. It has the advantages of convenient operation, lower cost, less pollution, and mass production. This simple technique created a wide array of nanosized silver particles which had a strong surface plasmon resonance effect in the visible region, and built up an excellent composite structure of silver@silver chloride hybrid which exhibited high photocatalytic activity and stability towards decomposition of organic methyl orange under visible-light illumination. Moreover, this work achieved the control of composition of the silver@silver chloride composite simply by adjusting the feed ratio of reactants. It offers an alternative method for synthesising metal@semiconductor composites.

Room-temperature synthesis of Zn0.80Cd0.20S solid solution with a high visible-light photocatalytic activity for hydrogen evolution

Visible light photocatalytic H(2) production from water splitting is of great significance for its potential applications in converting solar energy into chemical energy. In this study, a series of Zn(1-x)Cd(x)S solid solutions with a nanoporous structure were successfully synthesized via a facile template-free method at room temperature. The obtained solid solutions were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), ultraviolet-visible (UV-vis) diffuse reflectance spectroscopy, X-ray photoelectron spectroscopy (XPS), energy-dispersive X-ray spectroscopy (EDS) and N(2) adsorption-desorption analysis. The solid solutions show efficient photocatalytic activity for H(2) evolution from aqueous solutions containing sacrificial reagents S(2-) and SO(3)(2-) under visible-light irradiation without a Pt cocatalyst, and loading of the Pt cocatalyst further improves the visible-light photocatalytic activity. The optimal photocatalyst with x = 0.20 prepared at pH = 7.3 displays the highest activity for H(2) evolution. The bare and 0.25 wt% Pt loaded Zn(0.80)Cd(0.20)S nanoparticles exhibit a high H(2) evolution rate of 193 μmol h(-1) and 458 μmol h(-1) under visible-light irradiation (λ ≥ 420 nm), respectively. In addition, the bare and 0.25 wt% Pt loaded Zn(0.80)Cd(0.20)S catalysts show a high H(2) evolution rate of 252 and 640 μmol h(-1) under simulated solar light irradiation, respectively. Moreover, the Zn(0.80)Cd(0.20)S catalyst displays a high photocatalytic stability for H(2) evolution under long-term light irradiation. The incorporation of Cd in the solid solution leads to the visible light absorption, and the high content of Zn in the solid solution results in a relatively negative conduction band, a modulated band gap and a rather wide valence bandwidth, which are responsible for the excellent photocatalytic performance of H(2) production and for the high photostability.

Architecture of Cu 2O@TiO 2 core–shell heterojunction and photodegradation for 4-nitrophenol under simulated sunlight irradiation

A Cu 2O@TiO 2 core–shell heterojunction photocatalyst was prepared by an in situ hydrolysis and crystallization method. The as-prepared catalyst was characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), UV–vis diffuse reflectance spectroscopy and photoluminescence (PL) spectroscopy. Under simulated sunlight irradiation, it exhibited high photocatalytic activity and stability for 4-nitrophenol (4-NP) degradation. Compared with neat Cu 2O and Cu 2O/TiO 2(PM) prepared by physical mixing, the heightened photocatalytic activity of Cu 2O@TiO 2 was attributed to the improvement of charge separation since large close interface was formed between the two semiconductors. The in situ method may generally be applied to develop other core–shell heterojunction photocatalysts.

Facile Preparation of P-25 Films Dip-Coated Nickel Foam and High Photocatalytic Activity for the Degradation of Quinoline and Industrial Wastewater

A kind of P-25 TiO2 films coated nickel foam was synthesized by a facile dip-coating/calcination route, and used to fabricate a continuous-flow three-phase photocatalytic reactor. The morphology, crystal phase structure, surface composition and specific surface area of P-25 films coated nickel foam were investigated by field emission scanning electron microscope (FE-SEM), X-ray diffractometer (XRD), X-ray photoelectron spectroscopy (XPS) and nitrogen adsorption-desorption measurements, respectively. The results indicated that the coated/ calcined P-25 films had the porous surface structure fabricated by nano-sized titanium dioxide consisted of two crystal phases and incorporated with a NiO interlayer. The increase of P-25 contents enhanced the specific surface area; however, 20 percent of initial P-25 sol would result in visible large cracks because of too high P-25 content and consequently cause the peeling of films. The photocatalytic activities of nickel foam with different coating amounts of P-25 for the degradation of quinoline aqueous solutions were investigated with a continuous-flow three-phase photocatalytic reactor based on the P-25 films coated nickel foam. The results suggested that nickel foam coated with 10 percent of P-25 sol had an optimal photocatalytic activity for the degradation of quinoline aqueous solutions. The continuous-flow three-phase photocatalytic reactor fabricated with P-25 films coated nickel foam with an optimal P-25 coating amount shows high photocatalytic activity and stability for the degradation of quinoline aqueous solutions and industrial wastewater. The treated industrial wastewater meets the international discharge standard.

Reactive Ion Exchange Synthesis of Nano-ZnO and Its Photocatalytic Properties

Nano-crystalline ZnO particles were synthesized by a reactive ion exchange procedure using ZnSO4 and NaOH as precursors and a strong basic anion exchange resin as substrate. The precursors and ZnO samples were characterized by scanning electron microscopy, X-ray diffraction, and UV-Vis spectroscopy. The ZnO particles were club shape, and the synthesis process depended on the reactant concentration of ZnSO4 in the solution. The ZnO powders had high photocatalytic activity and stability for the gradation of methyl orange.

High-performance photocatalyst prepared from metallic titanium

TiO2 photocatalysts are attractive and promising materials due to their excellent properties such as high photocatalytic activity, stability and non-toxicity. Therefore, TiO2 photocatalyst has applied into various fields such as environmental purifications. The major forms of TiO2 photocatalysts are fine particles in order to obtain high surface areas. In order to fabricate commercial applications, the coating procedures using binder chemicals must be employed. However, the fine TiO2 particles slightly scattered at the surface, since most particles are buried in binder chemicals, leading to obtaining poor photocatalytic activity. TiO2 films can be easily formed on a metallic titanium substrate by anodization. However, the amorphous TiO2 films with no photocatalytic activities are usually obtained in conventional anodization. We have successfully obtained the high performance photocatalytic TiO2 films by using combined treatment of pre-nitridation and anodization. The photocatalytic TiO2 films show the high photocatalytic activities to decompose the various volatile organic compounds such as trichloroethylene, isopropyl alcohol, acetaldehyde, and so on.

Efficient and stable photocatalytic H 2 evolution from water splitting by (Cd 0.8Zn 0.2)S nanorods

Well-dispersed (Cd 0.8Zn 0.2)S single crystal nanorods were synthesized by a facile solvothermal route. The (Cd 0.8Zn 0.2)S nanorods exhibit wide visible light absorption up to 550 nm. The photocurrent of the (Cd 0.8Zn 0.2)S photoanode is three times higher that of pure CdS, and 1710 and 3020 μmol h −1 g −1 of H 2 was photocatalytically evolved from aqueous solutions containing SO 3 2 - and S 2− sacrificial reagents by the (Cd 0.8Zn 0.2)S nanorods without and with 3 wt% Pt co-catalyst under a simulated solar light irradiation, respectively. Furthermore, the (Cd 0.8Zn 0.2)S nanorods show a high photocatalytic stability for H 2 evolution under a long-term light irradiation.

Scratch test for immobilization of photocatalytic ZnO nanopowders synthesized by solution combustion method

Four kinds of organic binders and three kinds of inorganic binders were prepared. All of the binding materials are commercially available except zinc phosphate. The zinc phosphate was synthesized by the reaction of ZnO powders and phosphoric acid. All of these binders were used to immobilize the solution combustion method (SCM) ZnO powders on the glass substrates. Scratch test result showed that the zinc phosphate has the best overall adhesion properties such as high cohesive force with the ZnO powders and high adhesive force with the glass substrate. Furthermore, it showed the highest photocatalytic efficiency among organic and inorganic binders. Its photocatalytic efficiency reached to about 80% of the powder-type photocatalytic reaction. In general, organic binders have good adhesion properties but they could be decomposed by photocatalytic reaction. Inorganic binders, however, have poor adhesion properties but they are not decomposed by photocatalytic reaction. Contrary to general aspect, the zinc phosphate inorganic binder synthesized in this work showed good adhesion properties, high photocatalytic efficiency and good mechanical stability. This surprising result might be due to the chemical reaction between ZnO powders and the zinc phosphate binder.

High photocatalytic activity and stability for decomposition of gaseous acetaldehyde on TiO2/Al2O3 composite films coated on foam nickel substrates by sol-gel processes

A set of anatase titanium dioxide (TiO2) films coated on foam nickel that modified by Al2O3 films as transition layer (indicated as TiO2/Al2O3 films) were synthesized via sol-gel route. The bulk and surface properties of the TiO2/Al2O3 films were characterized by thermal gravimetric and differential scanning calorimetry (TG-DSC), X-ray diffraction (XRD), field-emission scanning electron microscope (FE-SEM), and BET. The photocatalytic activities of TiO2/Al2O3 films were investigated based on the degradation of gaseous acetaldehyde under ultraviolet (UV) irradiation. The foam nickel is a promising substrate material in practical applications because of its excellent hydrodynamic properties for gas passing. The TiO2/Al2O3 composite films showed much higher photocatalytic activity and stability for degradation of gaseous acetaldehyde than the onefold TiO2 films. The significant enhancement in photocatalytic activity and stability can be ascribed to the coating of Al2O3 transition layer, which concentrates the target substances around TiO2 particles and increases the specific surface area (SSA) of the substrate (the SSAs of bare foam nickel and Al2O3 modified foam nickel are 0.12 and 113.7 m2/g, respectively) to provide more sites for TiO2 loading.

Influence of Pretreatment of Titanium Substrate on Long-Term Stability of TiO2 Film

Abstract TiO2 films coated on titanium substrates pretreated using different methods were prepared and characterized by scanning electron microscopy, atomic force microscopy, X-ray diffraction, and electrochemical impedance spectroscopy. The results indicated that the TiO2 film coated on the substrate pretreated with oxalic acid (TiO2/Ti-OC) was tight, whereas the film coated on the substrate pre-treated with sodium carbonate solution (TiO2/Ti-SC) was loose. The catalytic activity of the TiO2/Ti-OC film for the degradation of ben-zamide remained up to 70% even after being dipped in deionized water for 280 d, whereas the TiO2/Ti-SC film lost its photoactivity after being dipped in water for 60 d. The deactivation of the catalyst was attributed to the flaking of the coated TiO2, which was caused by the continuous growth of the passive film between the substrate and the coated catalyst. Oxalic acid pretreatment could largely prevent the passive film from growing on the substrate and therefore greatly increased the stability of the catalyst during a long-term running. In a 35-d test of continuous decolorization of an aqueous reactive brilliant red X-3B solution, TiO2/Ti-SC exhibited very high photocatalytic activity and stability.

Vanadium-Containing Mesoporous Silica of High Photocatalytic Activity and Stability Even in Water

Vanadium-containing mesoporous silica molecular sieve (V proportional HMS) with tetrahedrally coordinated V-oxide species (VVO4) has been prepared by a modified surfactant-templating method, consisting of an addition of surfactant to a mixture of water, alcohol, and Si and V precursors followed by calcination. The V proportional HMS demonstrates high photocatalytic activity even in the presence of water, while other V proportional HMS's prepared by conventional templating methods and V/HMS prepared by an impregnation method show almost no activity owing to hydrolysis of the VVO4 species. ESR and photoluminescence measurements reveal that the modified templating method creates VVO4 species confined within a silica layer, while other methods create VVO4 species exposed on silica surface. The former VVO4 species are highly stabilized by the confinement within the silica, thus suppressing the hydrolysis. Another notable property of the confined VVO4 species is the higher photocatalytic activity even without water, despite their confined structure. This is explained by higher electrophilicity and longer lifetime of the excited-state VVO4 species (VIVO4*) derived from their distorted structure. The obtained findings suggest potential use of the modified surfactant-templating method for synthesis of stable and recyclable V-containing mesoporous silica with high photocatalytic activity.