Gaseous 2-propanol Research Articles

LaO1.5 surface modification of titanium-substituted hydroxyapatite photocatalyst and effects on 2-propanol photocatalytic decomposition mechanisms

After using impregnation to prepare LaO1.5 cluster modified titanium-substituted hydroxyapatites (Ti-HAps), photocatalytic decomposition activity on gaseous 2-propanol (IPA) under UV illumination was increased by three times through LaO1.5 modification while preserving its high adsorption capability for organic compounds. First-principles molecular dynamics simulations and electronic structure investigations revealed that photo-excited electron transfer from Ti to La does not occur in LaO1.5-modified Ti-HAp. Rather, the results implied that its photocatalytic activity increase is related to gaseous IPA and O2 adsorption properties. The IPA dissociative adsorption at Ca sites was observed in LaO1.5-modified Ti-HAp. The obtained electronic structure suggests that the adsorbed IPA molecule can be oxidized easily and directly. Moreover, O2 molecule adsorption and desorption were observed, which implies charge recombination suppression and that O2●- radical can be involved in IPA decomposition. Results demonstrate that control of the adsorption properties of target molecules by cluster modification can enhance photocatalytic decomposition activity.

Experimental and theoretical investigation of WOx modification effects on the photocatalytic activity of titanium-substituted hydroxyapatite

Titanium-substituted hydroxyapatite (Ti-HAp) is a potential photocatalyst with high adsorption capability for organic compounds. As described herein, the surface of Ti-HAp was modified by WOx. Photocatalytic decomposition activity on gaseous 2-propanol was increased by seven times by the modification. Little difference was obtained in the crystalline phase, specific surface area, and the light absorption edge between before and after the modification. However, photoluminescence emission intensity by UV irradiation was decreased by the modification. Results show that UV irradiation changed the valence number ratio of W cations under N2 atmosphere. Furthermore, first-principles simulations of molecular dynamics and electronic structure suggest that carrier separation is promoted by WOx clusters acting as a co-catalyst and suggest that those photoexcited electrons can be consumed by atmospheric oxygen. These experimental and theoretical investigations have demonstrated clearly that the photoexcited electrons can transfer from a Ti-hybridized band in Ti-HAp to WOx, thereby promoting charge separation.

Effects of MoOx modification on photocatalytic activity of hydroxyapatite and Ti-doped hydroxyapatite

Titanium-doped hydroxyapatite (Ti-HAp, (Ca10-2x, Tix, □x) (PO4)6(OH)2, □: defect in Ca site) and hydroxyapatite (HAp, Ca10(PO4)6(OH)2) powders were modified with an ethanol solution of molybdenyl acetylacetonate (MoO2(C5H8O2)2) using chemisorption calcination cycle (CCC) technique, which provides metal oxide clusters. Their photocatalytic activity under UV illumination was evaluated by the decomposition of gaseous 2-propanol. The photocatalytic activity of the Mo-modified Ti-HAp samples increased concomitantly with increasing Mo concentration up to 0.72% against P. The highest photocatalytic activity of Mo-modified Ti-HAp was about 13 times higher than that of Ti-HAp. The signal appearance of Mo(V) in electron spin resonance spectra and the decrease of photoluminescence intensity suggest electron transfer from the Ti-hybridized band to the MoOx cluster, which suppresses recombination of the photoinduced electron and hole pairs. The photocatalytic activity of Mo-modified HAp samples was attributed to HOMO–LUMO excitation of MoOx cluster.

Adsorption and Photocatalytic Decomposition of Gaseous 2-Propanol Using TiO2-Coated Porous Glass Fiber Cloth

Combinations of TiO2 photocatalysts and various adsorbents have been extensively investigated for eliminating volatile organic compounds (VOCs) at low concentrations. Herein, TiO2 and porous glass cloth composites were prepared by acid leaching and subsequent TiO2 dip-coating of the electrically applied glass (E-glass) cloth, and its adsorption and photocatalytic ability were investigated. Acid leaching increased the specific surface area of the E-glass cloth from 1 to 430 m2/g while maintaining sufficient mechanical strength for supporting TiO2. Further, the specific surface area remained large (290 m2/g) after TiO2 coating. In the photocatalytic decomposition of gaseous 2-propanol, the TiO2-coated porous glass cloth exhibited higher adsorption and photocatalytic decomposition ability than those exhibited by the TiO2-coated, non-porous glass cloth. The porous composite limited desorption of acetone, which is a decomposition intermediate of 2-propanol, until 2-propanol was completely decomposed to CO2. The CO2 generation rate was affected by the temperature condition (15 or 35 °C) and the water content (2 or 18 mg/L); the latter also influenced 2-propanol adsorption in photocatalytic decomposition. Both the conditions may change the diffusion and adsorption behavior of 2-propanol in the porous composite. As demonstrated by its high adsorption and photocatalytic ability, the composite (TiO2 and porous glass cloth) effectively eliminates VOCs, while decreasing the emission of harmful intermediates.

Preparation and photocatalytic activity of Mo-modified Ti-doped HAp

Titanium-doped hydroxyapatite (Ti-HAp, (Ca10-2x, Tix, □x) (PO4)6(OH)2, □: defect in Ca site) powders were modified with a CaMoO4 aqueous solution. Then their photocatalytic activity under UV illumination was evaluated by the decomposition of gaseous 2-propanol. The crystal structure, morphology, light absorption, and specific surface area were almost unchanged by the modification, but small clusters were deposited onto the Ti-HAp surface. The photocatalytic activity of the Mo-modified samples increased concomitantly with increasing Mo concentration until 0.5% against Ti. The highest photocatalytic activity of Mo-modified Ti-HAp was about nine times higher than that of Ti-HAp. Computer modeling revealed that the contribution of MoO42− doping into the Ti-HAp structure plays no important role in the activity increase. A Mo(V) signal appeared by UV illumination in electron spin resonance spectra of Mo-modified Ti-HAp. The Mo modification decreased the photoluminescence intensity. These results suggest that photoinduced electrons can transfer from the Ti-hybridized band to the cluster, thereby improving the carrier separation efficiency and engendering higher photocatalytic activity.

High-yield and low-cost method to synthesize large-area porous g-C3N4 nanosheets with improved photocatalytic activity for gaseous nitric oxide and 2-propanol photodegradation

A high-yield and low-cost method was developed for preparing graphitic carbon nitride (g-C3N4) with high photocatalytic activity. A trace amount of glyoxal-treated melamine was used as the precursor for g-C3N4. Glyoxal played a remarkable role in the thermal condensation of g-C3N4 as it improved the yield, inhibited the grain growth, and increased the specific surface area (up to 119 m2 g−1). The yield of g-C3N4 obtained with this method was 10 times higher than that in the traditional method. SEM, TEM, and EPR results showed that the prepared photocatalysts have a porous nanosheet structure with nitrogen vacancy defects. The photocatalytic activity of the obtained g-C3N4 was estimated by using it for the photodegradation of gaseous nitric oxide (NO) and isopropyl alcohol (IPA) under visible light (λ > 420 nm). The photocatalytic activity of the porous g-C3N4 nanosheets was well improved as compared with that of bulk g-C3N4. The addition of trace amounts of glyoxal improved the photocatalytic activity remarkably, so this method could open up a new channel for the development of low-cost, high-activity g-C3N4 photocatalysts for green chemistry.

Controlling Photocatalytic Activity and Size Selectivity of TiO2 Encapsulated in Hollow Silica Spheres by Tuning Silica Shell Structures Using Sacrificial Biomolecules

Yolk-shell nanostructured photocatalyst which consists of inner core photocatalytic particles and outer silica shell exhibits high photocatalytic efficiency and molecular size selectivity due to the molecular sieving property of the outer shell. Creation of extended porosity in the shell endows it with improved adsorption properties and size selectivity toward targeted reactants. In this study, yolk-shell nanostructured photocatalyst consisting of TiO2 NPs core and porous silica shell with controllable pore size was fabricated through a facile single-step dual-templating approach utilizing oil-in-water (O/W) microemulsions and amphiphilic protein molecules. Addition of optimum amount of protein (ovalbumin) as a sacrificial template together with O/W microemulsion during the synthesis led to the expansion of average pore size from 2.0 to 3.6 nm, while retaining TiO2-encapsulated yolk-shell nanostructures. Photocatalytic degradation tests using gaseous 2-propanol and huge proteins as model substrates clearly revealed that the obtained material (TiO2@HSS_pro) showed superior photocatalytic performances with both improved photocatalytic efficiency and molecular size selectivity due to the increased surface area and expanded pore diameter.

Preparation of visible light photocatalyst by interface reaction between tungsten-molybdenum oxide and copper clusters

A tungsten-molybdenum solid solution oxide ((Mo,W)O3) powder was prepared using hydrothermal processing. The crystal structure of the obtained powder was orthorhombic WO3 type with 0.22M H2O per unit chemical formula weight. This powder was dehydrated and transformed into monoclinic WO3 type structure by heat treatment at 500°C in air. When uncalcined powder was modified with Cu by impregnation with a CuCl2 solution and subsequent firing at 500°C in air, photocatalytic decomposition activity against gaseous 2-propanol (IPA) was achieved under visible light illumination. Results suggest that Cu(W1−xMox)O4 was formed on the (Mo,W)O3 powder surface by the Hedvall effect during its phase transition, and that the Z-scheme became feasible between (Mo,W)O3 and Cu(W1−xMox)O4.

E-beam evaporated TiO2 and Cu-TiO2 on glass: Performance in the discoloration of methylene blue and 2-propanol oxidation

TiO2 and Cu-TiO2 thin films were deposited by e-beam evaporation and then annealed at 350 and 500°C. Their structure, surface morphology and optical properties were studied by X-ray diffraction, scanning electron microscopy, cross-sectional TEM, UV–vis, FT-IR spectroscopy and X-ray absorption spectroscopy. A single-phase source material was used for the first time in the deposition process, thus avoiding preferential evaporation of Cu with respect to TiO2, and resulting in an even concentration of Cu in the doped films. The photocatalytic activity was evaluated by degradation of pre-adsorbed methylene blue (MB) in dry conditions and gaseous 2-propanol in oxygen atmosphere under visible and simulated solar light, respectively. Results suggested that high surface hydroxylation of the as-deposited films is an important factor for MB oxidation occurring through a dye-sensitized mechanism activated by visible light absorption. Conversely, the rate of photodegradation of 2-propanol is enhanced in annealed samples due to the greater crystallinity and less electron-hole recombination, with the TiO2 annealed at 500°C being the most efficient photocatalyst. However, Cu-doped samples resulted the most active samples during the degradation of MB under visible radiation. Finally, the performance at increasing thickness (250, 500, 1000, up to 2000nm) was tested for the most reactive films revealing a marked rise in photocatalytic activity up to 1000nm.

Synthesis of CeO2 nanocrystalline powders using DC non-transferred thermal plasma at atmospheric pressure

Nanocrystalline CeO2 powders were synthesized by using a DC non-transferred thermal plasma system at atmospheric pressure. Ce(NO3)3·6H2O powders were employed as a raw material and a cerium nitrate solution was used as a precursor. The liquid precursor was injected into a cylindrical reactor through two different directions: the vertical and the horizontal direction. The difference of the properties of CeO2 nanocrystalline powders according to the directions of injection were investigated by using XRD, TEM and an UV/VIS/NIR spectrometer. For the horizontal case, the cylindrical reactor acted as a cyclone providing greater tangential velocities. The higher tangential velocities increased the centrifugal forces of as-synthesized powders causing the thicker deposition layer of powders at the upper part of the reactor. The thicker deposition layer of powders was considered as the reason of the less heat treatment of powders prepared. This was confirmed by the relatively lower intensities of XRD peaks. In addition, CeO2 nanocrystalline powders were tested as a photocatalyst using the gaseous 2-propanol decomposition. For the test, the photocatalytic activity was defined and evaluated. It appears that CeO2 nanocrystalline powders are more suitable for the treatment of the dyes in the wastewater than the removal of the volatile organic compound (2-propanol).

In situ photoacoustic FTIR studies on photocatalytic oxidation of 2-propanol over titanium(IV) oxide

Adsorption and photocatalytic reaction of 2-propanol over titanium(IV) oxide (TiO2) were studied by Fourier transform infrared spectroscopy (FTIR) using a photoacoustic (PA) technique. At first, the validity of the FTIR system using a home-made PA cell was confirmed by comparison with conventional transmission FTIR. The spectrum of TiO2 with 2-propanol showed different propoxy peaks from those of gaseous 2-propanol as a result of chemisorption on TiO2. Finally, in situ FTIR observation of the photocatalytic oxidation of 2-propanol was carried out. Under ultraviolet irradiation, PA spectra changed due to complete oxidation of 2-propanol through acetone as an intermediate.

Enhanced photocatalytic degradation of 2-propanol over macroporous GaN/ZnO solid solution prepared by a novel sol-gel method

Macroporous GaN/ZnO solid solution photocatalyst is synthesized through a novel sol-gel method under mild conditions. The performance of as-synthesized solid solution photocatalyst is evaluated for decomposition of gaseous 2-propanol (IPA). It is found that due to enhancement in both the adsorption to gaseous IPA and the absorbance to visible light, the porous GaN/ZnO solid solution exhibits a good photocatalytic performance for IPA decomposition. Moreover, the mechanism for photocatalytic degradation IPA over porous GaN/ZnO solid solution is also investigated in comparison with those for the two end materials ZnO and GaN. The trapping effects with different scavengers prove that both the photoexcited electrons and holes affect the IPA photodegradation process, simultaneously.

Comparison of photocatalytic activity and surface friction force variation on Ti-doped hydroxyapatite and anatase under UV illumination

Abstract Photocatalytic activity and surface friction variation were evaluated on Ti-doped hydroxyapatite (Ti-HAp) and anatase-type TiO 2 powders under UV illumination. Although the adsorption capability of Ti-HAp against gaseous 2-propanol (IPA) in the dark was greater than that of anatase, photocatalytic decomposition activity and water adsorption capability of Ti-HAp under UV illumination were inferior to those of anatase. Experiments using powder/epoxy composites revealed that Ti-HAp does not exhibit photocatalytic wettability conversion to a hydrophilic state, which was confirmed on anatase. The surface friction force variation of anatase under UV illumination was similar to previously reported trend for rutile ceramics. That of Ti-HAp exhibited a different trend against anatase, suggesting that its surface was originally more hydrophobic than anatase or cantilever.

Fe2WO6/TiO2, an efficient visible-light photocatalyst driven by hole-transport mechanism

Fe2WO6 nanocrystal with an average size of ~300nm was prepared by solid-state reaction between Fe2O3 and WO3 at 950°C. The coupled structure of Fe2WO6/TiO2 was then fabricated by covering the Fe2WO6 surface with polycrystalline TiO2 by sol–gel process. Under visible-light irradiation, the Fe2WO6/TiO2 exhibits remarkable photocatalytic activity in decomposing gaseous 2-propanol and aqueous salicylic acid which is comparable to that of typical nitrogen-doped TiO2. It is deduced that its high catalytic activity originates from the hole-transfer from Fe2WO6 to TiO2. Evidences for the hole-transport were provided by monitoring the hole-scavenging reactions, employing iodide (I−) and 1,4-terephthalic acid (TA), respectively.

Novel coupled structures of FeWO4/TiO2 and FeWO4/TiO2/CdS designed for highly efficient visible-light photocatalysis.

A quadrilateral disk-shaped FeWO4 nanocrystal (NC) with an average size of ∼35 nm was prepared via hydrothermal reaction. The obtained dark brown FeWO4 NC with a bandgap (Eg) of 1.98 eV was then coupled with TiO2 to form FeWO4/TiO2 composites. The valence band (VB) of FeWO4 (+2.8 eV vs NHE) was more positive than that of TiO2 (+2.7 eV); thus this system could be classified as a Type-B heterojunction. Under visible-light irradiation, 5/95 FeWO4/TiO2 (by wt %) exhibited remarkable photocatalytic activity: the amount of CO2 evolved from gaseous 2-propanol (IP) and the decomposition rate of aqueous salicylic acid (SA) were, respectively, 1.7 and 2.5 times greater than those of typical nitrogen-doped TiO2 (N-TiO2). This unique catalytic property was deduced to arise from the intersemiconductor hole transfer between the VBs of FeWO4 and TiO2. Herein, several experimental evidence were also provided to confirm the hole-transfer mechanism. To further enhance the catalytic efficiency, double-heterojunctioned FeWO4/TiO2/CdS composites were prepared by loading CdS quantum dots (QDs) onto the FeWO4/TiO2 surface. Surprisingly, the catalytic activity for evolving CO2 from IP was 2.6 times greater than that of bare FeWO4/TiO2 and 4.4 times greater than that of N-TiO2, suggesting that both holes and electrons were essential species in decomposing organic compounds.

Platinum loaded NaNbO3-xNx with nanostep surface nanostructures toward enhanced visible-light photocatalytic activity

Pt loaded NaNbO3-xNx (Pt-NNON), a visible-light-sensitive photocatalyst, was synthesized by an in situ photodeposition method from H2PtCl6·6H2O onto NaNbO3-xNx (NNON) sample. Pt-NNON exhibited a much higher photocatalytic activity for gaseous 2-propanol (IPA) degradation under visible-light irradiation in contrast to NNON. The apparent quantum efficiency (AQE) of Pt-NNON sample for IPA photodegradation achieved up to 8.6% at the wavelength of 419nm. The notably enhanced photocatalytic performance was attributed to the promoted charge separation and transfer capability in the Pt-NNON system. This work suggests that surface nanosteps possibly play an important role as an electron transfer at high way, which facilitates to the charge carrier collection onto Pt rich zones and thus suppresses recombination between photogenerated electrons and holes. This method can thus be considered as an excellent strategy to enhance photocatalytic activity of organic decomposition in addition to the commonly applied noble metal doping method.

Comparative study of photoinduced wettability conversion between [PW12O40]3−/brookite and [SiW12O40]4−/brookite hybrid films

Two tungsten-based Keggin-type heteropolyacids (PW12: ([PW12O40]3−) and SiW12: ([SiW12O40]4−)) were hybridized with brookite-type TiO2. Then photocatalytic decomposition activity, photoinduced hydrophilicity, and sustainability of the hydrophilicity in the dark were evaluated using gaseous 2-propanol (IPA) decomposition and sessile drop method. The obtained films were transparent in the visible wavelength range. Both hybrid films exhibited higher photocatalytic decomposition activity and had higher photoinduced hydrophilicizing rates than pure brookite films under UV illumination. The PW12/TiO2 film exhibited better photocatalytic performance than the SiW12/TiO2 film did. Atmosphere dependence, XPS analysis, and electrochemical experiments indicated the cause of these two films' different levels of sustainability of hydrophilicity to be differences in their electron storage capability. Results show that the electron scavenger capability and reoxidation efficiency of the heteropolyacid are key factors affecting the overall performance of wettability conversion of this hybrid film system before and after UV illumination.

Preparation of WO3/TiO2/In2O3 composite structures and their enhanced photocatalytic activity under visible light irradiation

A novel visible light (λ ≥ 420 nm) active WO3/TiO2/In2O3 composite photocatalyst was prepared by a two-step process. At first, TiO2/In2O3 was synthesized utilizing maleic acid as an organic linker. Afterwards, WO3/TiO2/In2O3 composite heterojunction structure was prepared by the incipient wetness method. The composite was characterized by SEM mapping, high-resolution TEM, BET, UV–Vis diffuse reflectance spectroscopy, XPS and surface acidity measurement. The photocatalytic activity of the composite was evaluated through the decomposition of organic pollutants in gas and aqueous phases. The WO3/TiO2/In2O3 composite demonstrated greatly improved photocatalytic efficiency in compare with TiO2/In2O3 composite and Degussa P25 for the degradation of gaseous 2-propanol and evolution of CO2 and, 1,4-terephthalic acid in aqueous phase under visible light (λ ≥ 420 nm) irradiation. The concentration of WO3 in the composite was optimized to 3.5 mol% WO3/TiO2/In2O3. Based upon these observations, the mechanistic role of WO3 in enhancing the photocatalytic activity of WO3/TiO2/In2O3 has been suggested.

Enhanced photocatalytic activity of Bi2O3 under visible light irradiation by Cu(II) clusters modification

Using a facile hydrothermal method, pure α-Bi2O3 samples with rod-like structure were synthesized. Amorphous Cu(II) clusters were loaded on the as-obtained α-Bi2O3 samples by an impregnation method. The prepared samples were characterized by X-ray diffraction, scanning electron and transmission microscopy, X-ray photoelectron spectroscopy, and UV–visible diffuse reflectance spectroscopy. The photocatalytic activities were evaluated from gaseous 2-propanol decomposition under visible light irradiation. It is found that crystal structure and the morphologies were not changed by the Cu(II) clusters modification. Pure Bi2O3 sample showed a limited photocatalytic activity due to its low conduction band edge. After Cu(II) clusters modification, the photocatalytic activity was significantly improved. The Cu(II) clusters play a critical role in the charge separation and efficient oxygen reduction, which explains the enhanced photocatalytic activity.

Enhanced visible-light photocatalytic properties of Fe3+-grafted N-doped TiO2 nanoporous spheres

Monodispersed 250nm-sized TiO2 sphere (TiO2 SP) with large internal surface area was successfully employed in fabricating the Fe3+-grafted nitrogen-doped TiO2 (Fe3+/N-TiO2), exhibiting ultra-high visible-light photocatalytic efficiency. In evolving CO2 from the gaseous 2-propanol (IP) and acetaldehyde, the prepared Fe3+/N-TiO2 SP demonstrated twice of catalytic activity, comparing with the nanoparticle (NP)-based Fe3+/N-TiO2. Consequently, the optimized Fe3+/N-TiO2 SP exhibited 5.0–7.3 times higher efficiency than the bare N-TiO2 NP. The instability of photocatalytic activity is a well-known drawback of the Fe3+/N-TiO2 system, caused by the inherent weakness of Fe3+ ions from the chemical attacks. Herein, however, it was found that SP system with large internal surface is remarkably advantageous for protecting the grafted Fe3+ ions. With mixing of 20wt% silica binder, which is regarded to be a typical dosage for application, photocatalytic efficiency of the Fe3+/N-TiO2 SP was decreased by only 21–25%, whereas that of the NP-based sample was reduced by 73–80%.