A novel bio-mimetic approach for the fabrication of Bi2O3 nanoflakes from rambutan (Nephelium lappaceum L.) peel extract and their photocatalytic activity

This paper describes a highly efficient and robust solar photocatalytic treatment for the degradation of methyl orange dye over bio-synthesized Bi₂O₃ nanoflakes. Bio-mimetic way is adapted to synthesis Bi₂O₃ nanoflakes from the plant source of rambutan (Nephelium lappaceum L.) fruit peel extract. The bio-synthesized nanoflakes were characterized using X-ray diffraction studies, ultra-violet-visible diffuse reflectance spectra, field emission scanning electron microscope, high resolution transmittance electron microscope, energy dispersive X-ray spectroscopy, BET Surface area, ultra-violet-visible spectrophotometer and FT-IR spectroscopy. The photocatalytic activity of Bi₂O₃ nanoflakes were investigated using methyl orange dye under direct sunlight illumination in open atmosphere. The result shows that Bi₂O₃ nanoflakes were effectively degrading the dye to about 94.66% at 10 h of exposure time. The decreases in chemical oxygen demand values from 88.8 mg/l to 16.2 mg/l, shows the mineralization of methyl orange dye along with color removal.     

Synergistic effect of Pt or Pd and perovskite oxide for water gas shift reaction

The water gas shift (WGS) reaction over Pt and Pd catalysts supported on various perovskite oxides has been investigated at 573 K without catalyst pretreatment. The Pt and Pd catalysts on LaCoO₃ support showed high catalytic activity. Interaction between Pt or Pd and the support is considered to promote the WGS reaction: Pt/LaCoO₃ had high initial activity but deactivated immediately; Pd/LaCoO₃ was less active than Pt/LaCoO₃, but had superior stability. Catalysts were characterized using XRD, STEM, XPS, and H₂-temperature programmed reduction (TPR). Results of this study showed that reduction of the support decreased the CO conversion on Pt/LaCoO₃. On the other hand, Pd/LaCoO₃ showed stable activity for the WGS reaction. Therefore, Pd was added to Pt/LaCoO₃ for stabilizing the catalyst activity, and 0.5 wt.% Pd/1 wt.% Pt/LaCoO₃ catalyst showed higher activity and stability.     

In situ hydrothermally synthesized mesoporous LaCoO3/SBA-15 catalysts: High activity for the complete oxidation of toluene and ethyl acetate

Mesoporous yLaCoO₃/SBA-15 (y = 10–50 wt%) catalysts were prepared and characterized for the combustion of toluene and ethyl acetate (EA). The results show that well-ordered mesoporous LaCoO₃/SBA-15 catalysts of high surface areas (338–567 m²/g) could be fabricated by a facile in situ method of hydrothermal treatment. The particles of perovskite-type LaCoO₃ were highly dispersed on the walls of pore channels. The ordered mesoporous structure and high dispersion of LaCoO₃ are beneficial to the adsorption and activation of toluene and EA molecules. We found that in terms of specific activity, the in situ fabricated 35LaCoO₃/SBA-15 and 40LaCoO₃/SBA-15 is, respectively, superior to 35LaCoO₃/SBA-15_imp (generated by incipient wetness impregnation method) and bulk LaCoO₃ (prepared by sol–gel method) in catalytic performance. Based on the above results, we conclude that the excellent performance can be attributed to the good dispersion of highly reducible LaCoO₃ species in yLaCoO₃/SBA-15.     

Simple fabrication of thermally stable apertured N-doped TiO2 microtubes as a highly efficient photocatalyst under visible light irradiation

Apertured N-doped TiO₂ microtubes have been fabricated by simple hydrolysis of titania tetrachloride using ammonia without any external templates. The morphology and microstucture characteristics of apertured N-doped TiO₂ microtubes were characterized by means of the specific surface area (BET), transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), Fourier transformed infrared (FT-IR), UV–visible diffuse reflectance spectra (DRS) and X-ray powder diffraction (XRD). The unique morphology of microtubes and mesoporous microstructure were maintained after a heat treatment at 723 K for 3 h, exhibiting significantly thermal stability. The catalysts exhibited high ultraviolet and visible light photocatalytic activity in degrading phenol and methyl orange.     

Sol–gel preparation of titania multilayer membrane for photocatalytic applications

The main goal of the present study is to prepare a titania membrane with high permeability and photocatalytic activity for environmental applications. In this investigation a mesoporous titania multilayer membrane on alumina substrate is successfully fabricated via the sol–gel processing method. The prepared titania polymeric sol for the membrane top layer has an average particle size of 11.7 nm with a narrow distribution. The resulting TiO₂ multilayer membrane exhibits homogeneity with no cracks or pinholes, small pore size (4 nm), large specific surface area (83 m²/g), and small crystallite size (10.3 nm).The permeability and photocatalytic properties of the titania membrane were measured. The photoactivity of the titania membrane was examined to be 41.9% after 9 h UV irradiation based on methyl orange degradation. This measurement indicates high photocatalytic activity per unit mass of the catalyst. Through multilayer coating procedure, the photocatalytic activity of the membrane improved by 60% without sacrificing the membrane permeation. The prepared TiO₂ photocatalytic membrane has a great potential in developing high efficient water treatment and reuse systems due to its multifunctional capability such as decomposition of organic pollutants and physical separation of contaminants.     

Catalytic removal of diesel soot particulates over K and Mg substituted La1 − xKxCo1 − yMgyO3 perovskite oxides

K and Mg substituted perovskite catalysts La_1 − xK_xCo_1 − yMg_yO₃ (x = 0–0.4, y = 0–0.2) for soot combustion were prepared by citric acid complexation and characterized by XRD, FT-IR, SEM, TEM, EDS, H₂-TPR, XPS and TG. Soot combustion was remarkably accelerated when K was introduced into LaCoO₃. Then Mg was doped into the K substituted LaCoO₃, soot combustion was further improved for the restrained growth of Co₃O₄ phase. K/Mg substitutions were responsible for enhancing activity of catalysts by improving reducibility as suggested by H₂-TPR studies. Among all the catalysts, La_0.6K_0.4Co_0.9Mg_0.1O₃ exhibited the highest activity.     

Photocatalytic degradation of bisphenol A by Ag3PO4 under visible light

Ag₃PO₄ catalysts exhibited excellent photocatalytic performance in the degradation and the mineralization of bisphenol A, displaying considerably higher photocatalytic activity than N–TiO₂ under visible light (λ > 420 nm). The trapping effects of different scavengers and spectrophotometric results proved that the oxidation of bisphenol A mainly occurred at photogenerated holes on the Ag₃PO₄ surface, along with a two-electron reduction of dissolved oxygen to H₂O₂.     

Facile one-pot synthesis of porous Ln2Ti2O7 (Ln = Nd,Gd, Er) with photocatalytic degradation performance for methyl orange

Porous nanocrystalline Ln₂Ti₂O₇ (Ln = Nd, Gd, Er) was prepared by a facile self-propagating combustion method using metal nitrates (Ln(NO₃)₃ (Ln = Nd, Gd, Er), TiO(NO₃)₂) and glycine. The photocatalytic activity of Ln₂Ti₂O₇ (Ln = Nd, Gd, Er) was evaluated by the photocatalytic degradation of methyl orange (MO). The results showed that the photocatalytic activity of Ln₂Ti₂O₇ (Ln = Gd, Er) with cubic pyrochlore structure was higher than that of Nd₂Ti₂O₇ with monoclinic perovskite structure and Gd₂Ti₂O₇ showed the best photocatalytic activity. The different photocatalytic activities observed for Ln₂Ti₂O₇ (Ln = Nd, Gd, Er) could be related to its different crystal structures and Ln 4f shells.     

Catalytic performance of NO oxidation over LaMeO3 (Me = Mn,Fe, Co) perovskite prepared by the sol–gel method

The catalytic performance of LaMeO₃ (Me = Mn, Fe, Co) perovskite prepared by a sol–gel method was studied. These catalysts were characterized by X-ray diffraction (XRD), N₂ adsorption (BET), H₂ temperature programmed reduction (TPR), NO temperature programmed desorption (TPD) and CO–O₂ pulse. LaCoO₃ exhibited the best activity than that of LaFeO₃ and LaMnO₃ even after hydrothermal ageing. The activity sequence is in accordance with the reducibility of the samples. The activated oxygen species and adsorbed NO play key roles in the NO oxidation reaction.     

Synthesis of MoS2/g-C3N4 as a solar light-responsive photocatalyst for organic degradation

A novel molybdenum disulfide (MoS₂) and graphitic carbon nitride (g-C₃N₄) composite photocatalyst was synthesized using a low temperature hydrothermal method. MoS₂ nanoparticles formed on g-C₃N₄ nanosheets greatly enhanced the photocatalytic activity of g-C₃N₄. The photocatalyst was tested for the degradation of methyl orange (MO) under simulated solar light. Composite 3.0 wt.% MoS₂/g-C₃N₄ showed the highest photocatalytic activity for MO decomposition. MoS₂ nanoparticles can increase the interfacial charge transfer and thus prevent the recombination of photo-generated electron–hole pairs. The novel MoS₂/g-C₃N₄ composite is therefore shown as a promising catalyst for photocatalytic degradation of organic pollutants using solar energy.     

Solar-light-induced photocatalytic decomposition of two azo dyes on new TiO2 photocatalyst containing nitrogen

The photocatalytic decolourisation of two azo dyes—Reactive Red 198 and Direct Green 99—in an aqueous solution by the artificial visible light radiation was investigated. The industrial metatitanic acid (H₂TiO₃) obtained directly from the sulphate technology installation was N-doped and used as photocatalyst. H₂TiO₃ was calcinated at different temperatures, ranging from 300 to 500 °C, for 4 or 20 h, respectively, in an ammonia atmosphere. The UV–vis/DR spectra of the modified catalysts exhibited an additional maximum in the vis region (λ ≈ 476.8 nm, E_G = 2.60 eV for catalysts calcinated for 4 h and λ ≈ 479.5 nm, E_G = 2.59 eV for catalysts calcinated for 20 h, which may be due to the presence of nitrogen in TiO₂ particles. The chemical structure of the modified photocatalysts was investigated using FTIR/DRS spectroscopy and the presence of nitrogen was confirmed. A photocatalytic activity of the investigated catalysts was determined on the basis of a decomposition rate of azo dyes. The decomposition of Reactive Red 99 increased with increasing the calcination temperature of photocatalysts, whereas the activity of the prepared photocatalysts towards Direct Green 198 degradation was as follows: 300–20 h < 400–20 h < 500–20 h < 300–4h < 400–4 h < 500–4 h. Both, the calcination time and temperature had no influence on the amount of nitrogen-doped into TiO₂ structure. The inversely proportional linear dependence between the decomposition rates of azo dyes and the intensity of the band attributed to the hydroxyl groups for both dissociated water and molecularly adsorbed water was observed. With increasing temperature of calcinations, the amount of the hydroxyl groups decreased, whereas the decomposition of azo dyes increased.     

Preparation of Cu2O/exfoliated graphite composites with high visible light photocatalytic performance and stability

Cu₂O/exfoliated graphite composites (Cu₂O/EG (1 wt%), Cu₂O/EG (4 wt%), Cu₂O/EG (7 wt%), Cu₂O/EG (10 wt%), and Cu₂O/EG (15 wt%)) were prepared by the precipitation method. The photocatalytic activity of the material was evaluated using the decolorization of methyl orange (MO) solution as model reaction. Results showed that Cu₂O deposited on the worm-like flakes of EG in the form of nanocrystals. The EG provided a three-dimensional environment for photocatalytic reaction and endowed a high adsorption capacity for the sample. Under optimal conditions, the decolorization efficiencies of MO for 60 min reached 96.7%. Recycling of the catalyst showed Cu₂O/EG composites (10 wt%) to possess high photocatalytic efficiency even when repeatedly used for five times.     

Novel visible light-induced g-C3N4–Sb2S3/Sb4O5Cl2 composite photocatalysts for efficient degradation of methyl orange

A series of g-C₃N₄–Sb₂S₃/Sb₄O₅Cl₂ (SCL-CX) composite photocatalysts were successfully prepared via a hydrothermal method. The as-prepared materials were characterized by TM3000, powder X-ray diffraction (XRD), X-ray Photoelectron Spectroscopy (XPS) and UV–vis diffuse reflectance spectra (UV–vis DRS). The obtained photocatalyst showed higher photocatalytic activity than pure g-C₃N₄, Sb₄O₅Cl₂ and Sb₂S₃/Sb₄O₅Cl₂ (SCL). The optimum photocatalytic of the composite with the mass of 170 mg g-C₃N₄ and a degradation efficiency up to 95% for methyl orange (MO) under visible light was achieved within 60 min. The enhanced photocatalytic performance could be attributed to the stronger absorption in the visible region and the more efficient electron–hole separation.     

Carbon nanotubes-templated assembly of LaCoO3 nanowires at low temperatures and its excellent catalytic properties for CO oxidation

This work reports the mild synthesis of LaCoO₃ catalyst with the interesting nanowire morphology in the presence of both carbon nanotubes (CNTs) and citrate. In comparison, LaCoO₃ nanoparticles were prepared by conventional citrate method. The samples were characterized by TEM (Transmission electron microscopy), XRD (X-ray diffraction), N₂ adsorption isotherm and CO-TPD (Temperature-programming desorption), etc. The results showed that the morphology of LaCoO₃ catalyst was controlled effectively by the CNTs template; and that the adding of citrate not only controlled effectively the stoichiometric ratio of La to Co, but also reduced the crystallizing temperature of LaCoO₃ crystal greatly. Moreover, after calcined at 750 °C for 48 h, LaCoO₃ nanowires exhibited higher thermal stability and catalytic activity for CO oxidation, compared with the nanoparticles.     

Development of [60] fullerene supported on silica catalysts for the photo-oxidation of alkenes

Simple or successive incipient wetness impregnation followed by heating at 180 °C is proved an efficient preparation method for dispersing effectively onto the silica surface various amounts of C₆₀ in the range 1–4% (w/w). BET, XRD, DRS, TGA, microelectrophoresis and photoluminescence have been used to characterize the photocatalysts prepared. A high dispersion was obtained for the quite stable supported C₆₀ phase, comprised mainly from relatively small or medium size C₆₀ clusters/aggregates. The photocatalytic activity was assessed in the singlet oxygen oxidation of alkenes by examining the photo-oxygenation of 2-methyl-2-heptene as a probe reaction. The catalytic tests were carried out at 0–5 °C in CH₃CN, under oxygen atmosphere and using a 300 W xenon lamp as the light source. The heterogeneous catalysts obtained were proved to be active in the photocatalytic oxidation of olefins via a ¹O₂ ene reaction. The catalysts exhibited significant conversion, turnover number and turnover frequency values, substantially higher than those achieved over the unsupported C₆₀. The conversion increases with the amount of the supported C₆₀ up to a value equal to 3% (w/w) and then it decreases whereas turnover number and turnover frequency decreases monotonically as the amount of the supported C₆₀ increases. The easy separation of these solid catalysts from the reaction mixture, the high activity and stability as well as the retained activity in subsequent catalytic cycles, make these supported catalysts suitable for a small-scale synthesis of fine chemicals.     

Low temperature catalytic oxidation of nitric oxide over the Mn–CoOx catalyst modified by nonthermal plasma

Nonthermal plasma (NTP) treatment was investigated to modify the Mn–CoO_x catalyst for the low-temperature oxidation of nitric oxide. The catalysts were characterized by XRD, BET, TGA and XPS techniques. The results showed that the activity of NTP-treated catalysts improved significantly, and that NTP treatment has the advantage of changing the structural and morphological properties (higher surface areas and pore volume) and varying the relative surface concentration and oxidation states of surface species over catalysts. High surface areas and pore volume, high concentration of chemisorbed oxygen, Mn^4 + and Co^2 +, and the efficient synergetic catalytic effect between Co and Mn ions were thought to be the main reasons for the high activity of NTP-treated catalysts.     

Catalytic decomposition of biomass tars with iron oxide catalysts

Catalytic gasification of wood (Cedar) biomass was carried out using a specially designed flow-type double beds micro reactor in a two step process: temperature programmed non-catalytic steam gasification of biomass was performed in the first (top) bed at 200–850 °C followed by catalytic decomposition gasification of volatile matters (including tars) in the second (bottom) bed at a constant temperature, mainly 600 °C. Iron oxide catalysts, which transformed to Fe₃O₄ after use possessed catalytic activity in biomass tar decomposition. Above 90% of the volatile matters was gasified by the use of iron oxide catalyst (prepared from FeCl₃ and NH_3aq) at SV of 4.5 × 10³ h^?1. Tar was decomposed over the iron oxide catalysts followed by water gas shift reaction. Surface area of the iron oxide seemed to be an important factor for the catalytic tar decomposition. The activity of the iron oxide catalysts for tar decomposition seemed stable with cyclic use but the activity of the catalysts for the water gas shift reaction decreased with repeated use.     

Non-congruence of high-temperature mechanical and structural behaviors of LaCoO3 based perovskites

This paper presents the mechanical behavior of LaCoO₃ and La_0.8Ca_0.2CoO₃ ceramics under four-point bending in which the two cobaltites are subjected to a low stress of ∼8 MPa at temperatures ranging from room temperature to 1000 °C. Unexpected stiffening is observed in pure LaCoO₃ in the 700–900 °C temperature range, leading to a significant increase in the measured Young’s modulus, whereas La_0.8Ca_0.2CoO₃ exhibits softening from 100 °C to 1000 °C, as expected for most materials upon heating. Neutron diffraction, X-ray diffraction and micro-Raman spectroscopy are used to study the crystal structure of the two materials in the RT–1000 °C temperature range. Despite a detailed study, there is no conclusive evidence to explain the stiffening behavior observed in pure LaCoO₃ as opposed to the softening behavior in La_0.8Ca_0.2CoO₃ at high temperatures (above 500 °C).     

Enhancement of MTBE photocatalytic degradation by modification of TiO2 with gold nanoparticles

The photocatalytic degradation of methyl tert-butyl ether by gold-modified TiO₂ has been studied by a combination of high resolution electron microscopy, X-ray photoelectron spectroscopy and reactor measurements. The optimum gold loading corresponded to a mean Au particle size of ⩽ 3 nm at which point the gold may no longer be metallic. Such catalysts exhibited a threefold rate enhancement compared to unmodified TiO₂, possibly due to injection of photo-excited electrons from semiconducting Au into the TiO₂ conduction band. Since the presence of dissolved oxygen was crucially important to good performance, it is possible that an additional factor was lowering of the local work function, thus promoting electron transfer to dioxygen molecules adsorbed at the Au/TiO₂ interface.     

A unique nanoporous graphene-ZnxCd1−xS hybrid nanocomposite for enhanced photocatalytic degradation of water pollutants

In this work, a novel in-situ solvothermal reduction route has been made to immobilize nanoporous Zn_xCd_1−xS aggregates on graphene nanoribbons by using PVP as a stabilizer and thiourea as a sulphur source. The nanoporous ZnxCd_1−xS aggregates with diameters of 20–30 nm assembled from Zn_xCd_1−xS nanocrystals (3–5 nm) are homogeneously anchored on graphene nanoribbons and the unique structure of graphene-Zn_xCd_1−xS nanocomposites has contributed to large specific surface area (102.1 m²g^-1). Despite the analogous size and configuration, the nanoporous graphene-Zn_xCd_1−xS hybrid nanocomposites exhibited composition-dependent photocatalytic performances for the degradation of methyl orange (MO) under visible light. In particular, graphene-Zn_0.5Cd_0.5S was capable of nearly completely degrading MO in 150 min. The excellent photocatalytic activity was proposed to arise from the synergy effect between nanoporous Zn_xCd_1−xS aggregates and graphene, the suitable band gap, intimate interfacial contact, and unique nanoporous structure. Moreover, the work provides a simple strategy to prepare various nanoporous graphene-semiconductor nanocomposites.