Enhanced CO2 photocatalytic conversion into CH3OH over visible‐light‐driven Pt nanoparticle-decorated mesoporous ZnO–ZnS S-scheme heterostructures

In the present contribution, the design and fabrication of Pt nanoparticle-decorated mesoporous ZnO–ZnS heterostructures were described and used effectively for photocatalytic CO₂ conversion to yield CH₃OH. TEM images of the mesoporous Pt/ZnS–ZnO heterostructure demonstrated spherical ZnO NPs ~20 nm, and Pt NPs ~3 nm were well dispersed on the porous ZnS–ZnO heterostructure. The formation of CH₃OH over the Pt/ZnS–ZnO heterostructure was 78, 39 and 20 times larger than that bare ZnS, ZnO NPs and ZnS–ZnO, respectively. The optimal Pt/ZnO–ZnS heterostructure exhibited a high CH₃OH formation rate of 81.1 μmolg^-1h^-1, which is about 44, 22 and 20 times larger than that of bare ZnS (1.86 μmolg^-1h^-1), ZnO (3.72 μmolg^-1h^-1), and ZnO–ZnS (4.15 μmolg^-1h^-1), respectively. The significantly enhanced reduction of CO₂ was imputed to the synergistic effects of the ZnO–ZnS heterostructure and the incorporation of Pt NPs. The synthesized photocatalyst provides a new transfer route through which carriers can migrate to the outer surface as well as pore channels of the mesoporous ZnO–ZnS, therefore significantly minimizing the transfer distance for carriers, inhibiting photoinduced electron-hole recombination, and diminishing the mobility resistance, as determined using photoluminescence, photocurrent response, and electrochemical impedance spectra measurements.     

Z-scheme g-C3N4 nanosheet photocatalyst decorated with mesoporous CdS for the photoreduction of carbon dioxide

Herein, novel mesoporous CdS nanoparticle (NP)-incorporated porous g-C₃N₄ nanosheets with large surface areas and varying CdS NP percentages were constructed for the first time. The synergistic effect of mesoporous CdS NPs and porous g-C₃N₄ nanosheets indicated effective charge carrier separation and promoted CO₂ photoreduction to form CH₃OH upon illumination. The highest yield of CH₃OH over 3% CdS-g-C₃N₄ heterostructures was determined to be approximately 1735 μmol g^?1, which was 3.8- and 5.50 times greater than those of mesoporous CdS NPs and pristine g-C₃N₄ nanosheets, respectively. In addition, the mesoporous 3%CdS-g-C₃N₄ heterostructure showed an outstandingly enhanced CO₂ photoreduction rate of 192.7 μmol g^?1 h^?1, which was estimated to be ~4.1 and 5.9- times better than CdS (47.1 μmol g^?1 h^?1) and pristine g-C₃N₄ (32.6 μmol g^?1 h^?1), respectively. The photoreduction performance was retained at approximately 94.7% after five cycles of illumination for 45 h. The remarkable synthesized mesoporous CdS-g-C₃N₄ heterostructure played an essential role, with its narrow bandgap and high surface area enabling improved photoinduced carrier separation and a widened range of light absorption. A plausible mechanism for CO₂ photoreduction by the mesoporous CdS-g-C₃N₄ heterostructure was proposed and verified by photoelectrochemical and photoluminescence measurements.     

Mesoporous Ag2O/ZrO2 heterostructures as efficient photocatalyst for acceleration photocatalytic oxidative desulfurization of thiophene

The production of fuels with a low sulfur content has been paid significant attention in the manufacturing of petroleum refining due to the progressively severe environmental legislations obliged by governments worldwide. In this paper, for the first time, two dimensional mesoporous Ag₂O/ZrO₂ heterostructures were synthesized by a facile approach for thiophene photocatalytic oxidative desulfurization under visible-light exposure at room temperature. The Ag₂O/ZrO₂ heterostructures significantly enhanced the photocatalytic desulfurization of thiophene obeyed the pseudo-first-order model compared to pristine ZrO₂ NPs. In particular, 1.5%Ag₂O/ZrO₂ photocatalyst exhibited better photocatalytic performance and the correspondent rate constant of 0.0235 min^?1, which was promoted 5.35 times than that of pristine ZrO₂ NPs (0.0044 min^?1). The desulfurization rate of thiophene over 1.5% Ag₂O/ZrO₂ heterostructure was enhanced 3.7 times larger than that of pristine ZrO₂ NPs. The thiophene was photocatalytically oxidized to CO₂ and SO₃. The photocatalytic performance of Ag₂O/ZrO₂ could be enhanced because of its synergetic effects, the intense visible-light harvest, rapid mobility of the thiophene to the active sites, a lower light scattering effect, and a large ^?OH radical contents formed. Moreover, the Ag₂O/ZrO₂ heterostructures revealed excellent stability toward the photocatalytic oxidative desulfurization of thiophene. A possible charge separation mechanism over mesoporous Ag₂O/ZrO₂ heterostructures was proposed.     

Tuning product selectivity of CO2 hydrogenation by OH groups on Pt/γ-AlOOH and Pt/γ-Al2O3 catalysts

Herein, we explore how OH groups on Pt/γ-AlOOH and Pt/γ-Al₂O₃ catalysts affect CO₂ hydrogenation with H₂ at temperatures from 250°C to 400°C. OH groups are abundant on γ-AlOOH, but rare at Pt-(γ-AlOOH) interface which is the most favorable site for CO₂ conversion on Pt/γ-AlOOH. This makes CO₂ hydrogenation on Pt/γ-AlOOH form CO weakly bonding to γ-AlOOH, which prefers to desorption from Pt/γ-AlOOH rather than further conversion, thus enhancing CO production on Pt/γ-AlOOH. Different from Pt/γ-AlOOH, OH groups are abundant at Pt-(γ-Al₂O₃) interface which is the most favorable site for CO₂ conversion on Pt/γ-Al₂O₃. This promotes CO₂ hydrogenation on Pt/γ-Al₂O₃ to form CO strongly bonding to Pt, which prefers to further hydrogenation to CH₄, and thereby increases CH₄ selectivity on Pt/γ-Al₂O₃. Therefore, the OH groups at metal-support interface are crucial factor influencing product distribution, and must be considered seriously when fabricating catalysts.     

Core–shell structured Cu@m-SiO2 and Cu/ZnO@m-SiO2 catalysts for methanol synthesis from CO2 hydrogenation

The core–shell catalysts with Cu and Cu/ZnO nanoparticles coated by mesoporous silica shells are prepared for CO₂ hydrogenation to methanol. With the confined effect of silica shell, the size of Cu nanoparticles is only about 5.0 nm, which results in high activity for CO₂ conversion. The CH₃OH selectivity is enhanced significantly with the introduction of ZnO. The core–shell structured catalysts endow the Cu nanoparticles trapped inside with excellent anti-aggregation and no deactivation is observed with time-on-stream. Therefore, the core–shell Cu/ZnO@m-SiO₂ catalyst exhibits the maximum CH₃OH yield with high stability.     

Visible light photocatalytic H2-production activity of epitaxial Cu2ZnSnS4/ZnS heterojunction

Novel visible light driven photocatalyst Cu₂ZnSnS₄/ZnS composites were prepared by two-step hydrothermal method. The two semiconductors in the composites are lattice-matched and form close contact between them. With 0.1% Cu₂ZnSnS₄ grew on ZnS surface, the composite exhibits a high and stable visible light photocatalytic H₂ generation of 432 μmolg^− 1 h^− 1. This excellent visible light activity could be attributed to the enhancement of visible light absorption by surfacial modification of ZnS with CZTS and the photoinduced interfacial charge transfer from the valence band of ZnS to Cu₂ZnSnS₄ in the close contact interface.     

Enhanced visible light response of heterostructured Cr2O3 incorporated two-dimensional mesoporous TiO2 framework for H2 evolution

Mesoporous TiO₂ frameworks incorporated with diverse percentages of Cr₂O₃ nanoparticles (NPs) were achieved through the one-step sol-gel approach for photocatalytic H₂ evolution under visible-light exposure. The obtained isotherms could be classified as type IV, indicating mesopore 2D-hexagonal symmetry. The H₂ evolution rate over mesoporous Cr₂O₃/TiO₂ photocatalyst was observably promoted employing glycerol as a sacrificial agent, providing a comparatively high H₂ yield of 14300 μmolg^?1. The highest photocatalytic efficiency was achieved with an optimal 4% Cr₂O₃/TiO₂ photocatalyst, and the evolution rate was enhanced 1430-fold compared to pristine TiO₂. The eminent photocatalytic performance of mesoporous Cr₂O₃/TiO₂ was ascribable to different key factors such as the narrow bandgap, wide visible light photoresponse, Cr₂O₃ as photosensitizer, synergistic effect and high surface area. The recycle tests for five times over synthesized photocatalyst revealed excellent durability and stability without loss in H₂ evolution. The photocatalytic mechanisms for H₂ evolution over Cr₂O₃/TiO₂ photocatalyst were proposed according to the photocurrent transient and photoluminescence measurements and photocatalytic H₂ evolution results.     

Generation of mesoporous n-p-n (ZnO–CuO–CeO2) heterojunction for highly efficient photodegradation of micro-organic pollutants

In this research, a mesoporous rod-shaped ZnO/CuO/CeO₂ n-p-n heterojunction has been designed via a two-step co-precipitation technique for photocatalytic applications. Characterization by powder X-ray diffraction (PXRD), fourier transform infrared spectroscopy (FTIR), UV–Vis, and Scanning Electron Microscopy (SEM) techniques confirmed the formation of mesoporous rod-shaped ZnO/CuO/CeO₂ n-p-n heterojunction having preferred interface developing between the ZnO, CuO, and CeO₂ phases, thus extended the light-absorption window up to 800 nm. Under sunlight, the ability of a mesoporous ZnO/CuO/CeO₂ n-p-n heterojunction to act as a photocatalyst was tested with methyl orange (MO) and crystal violet (CV) as target molecules. We found the degradation efficiencies of CV and MO dyes on mesoporous ZnO/CuO/CeO₂ to be 96% and 88%, respectively, after 90 min of sunlight irradiation. The estimated rate constants (k, min^?1) for deterioration of CV and MO under sunlight over ZnO/CuO/CeO₂ composite were 0.039 and 0.022 min^?1, respectively. We endorsed the greater photo-response, the well-aligned band-structure, and practical usage of the photo-induced carriers of the mesoporous photocatalyst to be the leading causes for the outstanding photocatalytic properties of ZnO/CuO/CeO₂ n-p-n heterojunction. The ultimate oxidizing species that destroyed dyes were O₂￣ and ·OH over ZnO/CuO/CeO₂ photocatalyst under sunlight illumination. Besides, the recycling tests confirmed the high photostability of the ZnO/CuO/CeO₂ photocatalyst. Hopefully, the mesoporous rod-shaped architecture of the n-p-n heterojunction with anticipated interface manufacturing will assist the photocatalyst strategy with better photocatalytic action under sunlight irradiation.     

Fabrication of mesoporous Cr2O3 with highly distributed α-Fe2O3 and Pt nanoparticles for ultrafast H2 evolution rate

In the present contribution, p-n type heterojunction α-Fe₂O₃/Cr₂O₃ S-scheme system photocatalyst has been fabricated utilizing a sol-gel approach with assisted nonionic surfactant for a highly effective H₂ evolution rate under visible illumination. Pt NPs have been reduced by photodeposition during the photocatalytic reaction to collect Pt@α-Fe2O3/Cr2O3 finally. XRD analysis of Fe₂O₃/Cr₂O₃ nanocomposites verified the construction of Fe₂O₃ and Cr₂O₃ with rhombohedral phases. TEM images of Cr₂O₃ NPs were almost spherical and uniform in shape and size (20 ± 5 nm), and very small Fe₂O₃ NPs (3-5 nm) were distributed on the mesoporous Cr₂O₃ networks. The obtained α-Fe₂O₃/Cr₂O₃ photocatalyst exhibited noteworthy photocatalytic H₂ evolution with high efficiency and stability for 45 h. Interestingly, the photocatalytic H₂ evolution rate gradually boosted with the extent of Fe₂O₃ percentage up to 15% and its rate of 2215.4 μmol g^-1h^-1, which was fostered 7.25 folds larger than that of Cr₂O₃ NPs (305.7 μmol g^-1h^-1). The enhancement H₂ evolution rate of Fe₂O₃/Cr₂O₃ photocatalyst in comparison with bare Cr₂O₃ NPs was ascribed to facilitate the separation of photocarriers and existing considerable reactive sites. In addition, constructing n-type Fe₂O₃ and p-type Cr₂O₃ with close contact is essential in improving the H₂ evolution rate. The possible photocatalytic mechanism over Fe₂O₃/Cr₂O₃ nanocomposite was addressed based on electrochemical measurements. The construction of the S-scheme system of Fe₂O₃/Cr₂O₃ nanocomposite could be suggested to improve the separation of photocarriers through optimal transfer channels owing to the formation of synergistic characteristics. Our results provide avenues for constructing stable photocatalysts with high efficiency for H₂ evolution through visible exposure.     

Direct Biomass Fuel Cell (BMFC) with Anode/Catalyst Comprising a Nanocomposite of a Mesoporous n-Semiconductor Film and a Metal Thin Layer: A New Concept of Catalyst Design

Abstract  

We designed an efficient direct biomass fuel cell (BMFC) anode and prepared a nanocomposite [base electrode/mesoporous n-semiconductor (SC) thin film/metal thin layer]. A Pt thin layer was photodeposited onto a mesoporous 20-μm thick TiO₂ thin film having a roughness factor of 2000, which was coated on an F-doped tin oxide/glass base electrode (FTO). This anode/catalyst nanocomposite was efficient at decomposing aqueous solutions of glucose and other biomass-related compounds in combination with an O₂-reducing cathode the other side of which was exposed to ambient air. The nanocomposite exhibited sharp optimum conditions at the atomic ratio of Pt/Ti = 0.33 in the BMFC, generating high electrical power of 2 mW cm⁻² without any light irradiation or bias potential when using a 1 M glucose aqueous solution. This output power is 20 times as large as that generated by a mesoporous TiO₂ film anode under UV-light (18 mW cm⁻²) irradiation. At this ratio, the coated Pt specifically exhibited metallic luster, and its average Pt thickness on the mesoporous TiO₂ nanostructure was calculated to be 0.40 nm. The high BMFC activity was interpreted by the simultaneous Schottky-junction/Ohmic contact nature of the nanocomposite. Other biomass compounds such as sucrose, ethanol and polysaccharides were also effective as direct fuels for the BMFC. Immediately after soaking this composite anode without a cathode in a glucose aqueous solution, continuous evolution of H₂ bubbles was observed from the anode surface. The electrical power generation and H₂ production are easily changed by connecting and disconnecting a cathode, respectively. Based on a simple design and calculation, the present system with glucose fuel has the potential to construct a module stack of 2 kW m⁻³. Simultaneous material/energy circulation by using the BMFC with biomass and its waste fuel is proposed for application in future social systems.     

Electrochemical promotion of the CO2 hydrogenation reaction using thin Rh, Pt and Cu films in a monolithic reactor at atmospheric pressure

A monolithic electropromoted reactor (MEPR) with up to 22 thin Rh/YSZ/Pt or Cu/TiO₂/YSZ/Au plate cells was used to investigate the hydrogenation of CO₂ at atmospheric pressure and temperatures 220–380 °C. The Rh/YSZ/Pt cells lead to CO and CH₄ formation and the open-circuit selectivity to CH₄ is less than 5%. Both positive and negative applied potentials enhance significantly the total hydrogenation rate but the selectivity to CH₄ remains below 12%. The Cu/TiO₂/YSZ/Au cells produce CO, CH₄ and C₂H₄ with selectivities to CH₄ and C₂H₄ up to 80% and 2%. Both positive and negative applied potential significantly enhance the hydrogenation rate and the selectivity to C₂H₄. It was found that the addition of small (0.5 kPa) amounts of CH₃OH in the feed has a pronounced promotional effect on the reaction rate and selectivity of the Cu/TiO₂/YSZ/Au cells. The selective reduction of CO₂ to CH₄ starts at 220 °C (vs 320 °C in absence of CH₃OH) with near 100% CH₄ selectivity at open-circuit and under polarization conditions at temperatures 220–380 °C. The results show the possibility of direct CO₂ conversion to useful products in a MEPR via electrochemical promotion at atmospheric pressure.     

Mesoporous BiVO4/2D-g-C3N4 heterostructures for superior visible light-driven photocatalytic reduction of Hg(II) ions

In this contribution, a Z-scheme mesoporous BiVO₄/g-C₃N₄ nanocomposite heterojunction with a considerable surface area and high crystallinity was synthesized by a simple soft and hard template-assisted approach. This material demonstrates superior visible light-driven photocatalysis for the photoreduction of Hg(II) ions. TEM and XRD results show that the mesoporous BiVO₄ NPs, with a monoclinic phase and an ellipsoid-like shape, are highly dispersed onto the porous 2D surfaces of g-C₃N₄ nanosheets with a particle size of 5–10 nm. The obtained BiVO₄/g-C₃N₄ nanocomposites with a p-n heterojunction show significantly enhanced Hg(II) photoreduction efficiency compared to the mesoporous BiVO₄ NPs and pristine g-C₃N₄. Among all synthesized photocatalysts, the 1.2% BiVO₄/g-C₃N₄ nanocomposite indicated the highest photoreduction of Hg(II) performance, reaching ~ 100% within 60 min; this result is 3.9 and 4.5 –fold larger than that of the BiVO₄ NPs and pristine g-C₃N₄. The Hg(II) photoreduction rates highly increase to 208.90, 314.95, 411.23 and 418.68 μmol g⁻¹min⁻¹ for the mesoporous 0.4, 0.8, 1.2 and 1.6% BiVO₄/g-C₃N₄ nanocomposites, respectively. The reduction rate of the mesoporous 1.2% BiVO₄/g-C₃N₄ nanocomposite demonstrated a 5.2 and 3.8 times larger increase than that of the pristine g-C₃N₄ nanosheets and pure BiVO₄ NPs. The superior Hg(II) photoreduction efficiency was ascribed to decreased carrier recombination and the improved utilization of visible light by constructing BiVO₄/g-C₃N₄ nanocomposites with a p-n junction. Transient photocurrent measurement and photoluminescence spectra were employed to confirm the possible Hg(II) photoreduction mechanism over these BiVO₄/g-C₃N₄ photocatalysts. This research provides an accessible route for the nanoengineered design of mesoporous BiVO₄/g-C₃N₄ heterostructures that demonstrated unique photocatalytic performance.     

Photoreduction of Carbondioxide on Surface Functionalized Nanoporous Catalysts

Nanoporous photocatalysts have been designed to exhibit unique photocatalytic activities through framework substitution of titanium species or surface immobilization of rhenium complex onto mesoporous silica. This article summarizes recent work on the synthesis, characterization and photocatalytic activities of the designed porous photocatalysts performed by the present authors. Various spectroscopic investigations revealed that the photo-excited states of these catalysts play a vital role in the photocatalytic reactions and their photocatalytic reactivities are strongly dependent on structures of active sites, which are confined and immobilized in the restricted framework structure of the mesoporous silica. Highly dispersed titanium oxide species incorporated in the framework of mesoporous silica exhibited high and unique photocatalytic reactivity for the reduction of CO₂ with H₂O to produce CH₄ and CH₃OH under UV irradiation, its reactivity being much higher than bulk TiO₂. The cationic rhenium(I) complex was encapsulated into a mesoporous AlMCM-41 material by ion-exchange method, yielding a visible light photocatalyst to be active for photocatalytic reduction of CO₂.     

Ultraviolet‐ray treatment of polysulfone membranes on the O2/N2 and CO2/CH4 separation performance

UV irradiation on polysulfone (PSF) membranes was studied to improve their gas‐separation properties. Membranes with 19–25% PSF contents were prepared by the phase‐inversion method, and the membrane surface was modified with UV rays with a wavelength of 312 nm and a power of 360 µw/cm². Measurements of gas permeation were conducted with pure carbon dioxide (CO₂), methane (CH₄), oxygen (O₂), and nitrogen (N₂) gases under 3–8 bar pressure at 25°C. Fourier transform infrared spectrometry revealed that the polar functional groups of hydroxyl and carbonyl were introduced by UV irradiation. The water contact angle of the treated membrane was reduced from 70–75° to 10–12° after 12 h of UV exposure. Scanning electron microscopy observation showed that the dense skin layer increased as the polymer concentration increased. After UV treatment, the permeation of O₂ decreased from 0.4–3.4 to 0.2–2.3 m³ m^?2 h^?1 bar^?1, whereas that of N₂, CO₂, and CH₄ increased for all of the pressures used from 0.1–1.7 m³ m^?2 h^?1 bar^?1 to about 0.1–3.4 m³ m^?2 h^?1 bar^?1; this depended on the applied pressure and the PSF content. As a result, the selectivity ratio of O₂/N₂ decreased from 1.9–7.8 to 0.6–1.5, whereas that of CO₂/CH₄ increased from 0.9–2.6 to 1.1–6.1. Moreover, the O₂/N₂ and CO₂/CH₄ of the untreated and the treated membranes decreased with increasing pressure and increased with increasing polymer concentration. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42074.     

Synthesis of Highly Active Nano-Sized Pt/CeO<Subscript>2</Subscript> Catalyst via a Cerium Hydroxy Carbonate Precursor for Water Gas Shift Reaction

Abstract  

A novel precipitation/digestion route has been developed to synthesize crystalline cerium hydroxy carbonate (CHC: Ce(OH)CO₃) by using an equimolar quantity of cerium nitrate (Ce(NO₃)₃·6H₂O) and mixed precipitants (KOH + K₂CO₃) at room temperature. Nano-sized CeO₂ supports could be prepared by the pre-calcination of CHC at 400 °C for 4 h. A highly active water gas shift (WGS) catalyst, 1 wt.% Pt/CeO₂ catalyst showed almost equilibrium CO conversion with 100% CO₂ selectivity at 320 °C even at the gas hourly space velocity (GHSV) of 45,625 h⁻¹.     

Size and Shape Dependence on Pt Nanoparticles for the Methylcyclopentane/Hydrogen Ring Opening/Ring Enlargement Reaction

Abstract  

Monodisperse Pt nanoparticles (NPs) with well-controlled sizes in the range between 1.5 and 10.8 nm, and shapes of octahedron, cube, truncated octahedron and spheres (~6 nm) were synthesized employing the polyol reduction strategy with polyvinylpyrrolidone (PVP) as the capping agent. We characterized the as-synthesized Pt nanoparticles using transmission electron microscopy (TEM), high resolution TEM, sum frequency generation vibrational spectroscopy (SFGVS) using ethylene/H₂ reaction as the surface probe, and the catalytic ethylene/H₂ reaction by means of measuring surface concentration of Pt. The nanoparticles were supported in mesoporous silica (SBA-15 or MCF-17), and their catalytic reactivity was evaluated for the methylcyclopentane (MCP)/H₂ ring opening/ring enlargement reaction using 10 torr MCP and 50 torr H₂ at temperatures between 160 and 300 °C. We found a strong correlation between the particle shape and the catalytic activity and product distribution for the MCP/H₂ reaction on Pt. At temperatures below 240 °C, 6.3 nm Pt octahedra yielded hexane, 6.2 nm Pt truncated octahedra and 5.2 nm Pt spheres produced 2-methylpentane. In contrast, 6.8 nm Pt cubes led to the formation of cracking products (i.e. C₁–C₅) under similar conditions. We also detected a weak size dependence of the catalytic activity and selectivity for the MCP/H₂ reaction on Pt. 1.5 nm Pt particles produced 2-methylpentane for the whole temperature range studied and the larger Pt NPs produced mainly benzene at temperatures above 240 °C.     

Development of mesoporous Bi2WO6/g-C3N4 heterojunctions via soft- and hard-template-assisted procedures for accelerated and reinforced photocatalytic reduction of mercuric cations under vis light irradiation

In this study, mesoporous Bi₂WO₆/g-C₃N₄ heterojunctions were developed using soft and hard templates [triblock copolymer surfactant (F127) and mesoporous silica (MCM-41), respectively]. The performance of the developed heterojunctions was assessed through the photocatalytic reduction of mercuric cations under Vis light illumination, with HCOOH being adopted to provide sacrificial holes agent. Surface measurements demonstrated that the fabricated specimens acquired large specific surface areas when compared with the neat ingredient. Furthermore, a transmission electron microscopy (TEM) analysis of the developed heterojunctions showed the homogeneous distribution of the spherical Bi₂WO₆ nanoparticles (NPs) on the surface of g-C₃N₄ nanosheets. Meanwhile, an accelerated rate (700 μ·mol·g^?1·h^?1) of photocatalytic mercuric cation reduction with improved efficiency (approximately 100%), compared with those of the pure ingredients [rate of 55 μ·mol·g^?1·h^?1 and efficiency of 13% for g-C₃N₄ nanosheets; rate of 95 μ·mol·g^?1·h^?1 and efficiency of 20% for mesoporous Bi₂WO₆ NPs], was accomplished via testing of the Bi₂WO₆/g-C₃N₄ heterojunction comprising 4 wt% Bi₂WO₆ after 40 min of illumination. Evidently, the efficiency of the photocatalytic reduction of mercuric cations endorsing the Bi₂WO₆/g-C₃N₄ heterojunction comprising 4 wt% Bi₂WO₆ NPs is 7.7 and 5 times more when compared with those of the neat g-C₃N₄ nanosheets and mesoporous Bi₂WO₆ NPs, respectively. The improved performance of the fabricated heterojunctions in the photocatalytic reduction of mercuric cations could be ascribed to i) fast diffusion of the mercuric cations through the mesoporous texture to the active ensembles, ii) greater specific surface area, iii) limited bandgap magnitude, iv) homogenous dispersion of the Bi₂WO₆ NPs on the surface of the nanosheets, and v) finite particle dimension of the mesoporous Bi₂WO₆ NPs. The durability and stability of the Bi₂WO₆/g-C₃N₄ heterojunctions were confirmed via their recyclability, which was maintained for up to five runs without pronounced activity loss.     

Catalytic synthesis of methanethiol from methanol and carbon disulfide over KW/Al2O3 catalysts

A series of KW/γ-Al₂O₃ catalysts with varying K/W mole ratio were prepared for the synthesis of methanethiol from carbon disulfide and methanol, and characterized by N₂ adsorption–desorption, XRD and NH₃/CO₂-TPD techniques. Experimental results showed that the acidic and basic property of the catalyst plays a key role on the catalytic performance. It is shown that the conversion of CH₃OH is chiefly related to the acid sites, while the base sites of catalysts are favorable for the selectivity toward CH₃SH and hydrocarbons, but the strong base sites will restrain the selectivity toward CH₃SH. When the K/W mole ratio is K/W = 2/1 and the reaction temperature is at 603 K, the conversion of CH₃OH and the selectivity toward CH₃SH are 98.3 and 56.2%, respectively.     

Oxygen hyper stoichiometric trimetallic titanium doped magnesium ferrite: Structural and photocatalytic studies

Oxygen hyper stoichiometric titanium doped magnesium ferrite, Mg_1-xTi_xFe₂O_4+δ (x = 0–1.0) nanoparticles (NPs) were synthesized using sol-gel method. XRD analysis revealed a decrease in the lattice parameter from 8.9 to 8.3 Å and confirmed the incorporation of Ti⁴⁺, a smaller ionic radius dopant. Presence of M-O vibrational bands at tetrahedral and octahedral sites were authenticated by FT-IR analysis. The observed reduction in saturation magnetization values from 23.3 emug^?1 to 18.3 emug^?1 was ascribed to the doping of non-magnetic Ti⁴⁺ ions in MgFe₂O₄ NPs. BET studies corroborated the mesoporous nature of the NPs and doped ferrite NPs displayed larger surface area (53.0–73.0 m²g^-1) as compared to pristine ferrite NPs (32.8–39.0 m²g^-1). Optical studies displayed red shift in the absorption edge of the Ti⁴⁺ doped MgFe₂O₄ NPs in contrast to pristine NPs. Oxygen hyper stoichiometry in the doped ferrite NPs was determined experimentally. Photoluminescence emission spectra exhibited reduction in the emission intensity in case of Ti⁴⁺ doped NPs which supported their higher light capturing potential. Among synthesized doped ferrite NPs Mg_0.5Ti_0.5Fe₂O_4.5 NPs exhibited maximum (98%) photodegradation capacity for rhodamine B. The ^?O₂^? and ^?OH were the main reactive species in the photodegradation. The present studies have clearly shown the potential of tuning the composition of oxygen hyper stoichiometric ferrite Mg_0.5Ti_0.5Fe₂O_4.5 for the removal of toxic organic contaminants from water.     

Reduction of aqueous carbonate photocatalysed by treated semiconductors

Heterogeneous photocatalysed reduction of aqueous Na₂CO₃ solution (1 m) was achieved by using phthalocyanine-coated semiconductor powders (1–3% coating) as well as bare semiconductors. The suspensions were irradiated with 254 nm light from a low-pressure mercury lamp in a nitrogen atmosphere. The phthalocyanine dyes (Fe²⁺-Pc or Co²⁺-Pc) absorb > 80% of the 254 nm radiation and thus sensitize the semiconductor. The products of reduction (CH₃OH and HCHO) were determined spectrophotometrically. The CH₃OH yields obtained are much higher than the HCHO yields, due to a photocatalysed reduction of HCHO to CH₃OH. The CH₃OH yields from coated titania increased linearly with irradiation time over the period 6–18 h. However, the straight line does not pass through the origin, and it seems that a slowing-down occurs at times > 6 h. Titania coated with both dyes gave an optimum CH₃OH yield at 2% surface coating. At higher coating percentages, phthalocyanine screens the surface, thus reducing the light reaching the semiconductor. Changing the redox potential of the phthalocyanine dye by changing its central metal from Fe to Co affects the CH₃OH yields. The bare MoS₂ photocatalyst gave a much higher CH₃OH yield due to the characteristic behaviour of the semiconducting layer-type disulphide, distinguished from that of classical semiconducting materials. In the various semiconductors studied, it seems that there is no correlation between the position of the conduction band and the yield of CH₃OH. Such correlation was argued. Generally, a decrease in the yield of CH₃OH was observed as the band gap width of the semiconductor increased. The yields of the photoproduced CH₃OH generally increased with the percentage of light absorbed at 254 nm by the various semiconductors. Irradiation leads to the production of electrons in the conduction band of the semiconductor. It is likely that the photoproduced electrons reduce CO₃²- initially to HCOO- and then to HCHO and CH₃OH.