The conversion of carbon dioxide (CO2) into high-value-added chemicals by photocatalysis is recognized as a potential method to ease the greenhouse effect and the global energy crisis simultaneously. ...Herein, boron-doped graphitic carbon nitride (g-C3N4) was combined with few-layer Ti3C2 MXene (FLTC) by electrostatic self-assembly. The composite exhibited superior performance to bare g-C3N4 and B-doped g-C3N4 (BCN). The optimized 12FLTC/BCN produced 3.2- and 8.9-times higher CO and CH4 yields, respectively, than bare g-C3N4 under visible light. Moreover, 12FLTC/BCN showed excellent stability during the cycling experiment. Several characterizations (photoluminescence, time-resolved photoluminescence, and i–t curves) were carried out to demonstrate the synergy of boron dopants and the addition of FLTC. Besides, 12FLTC/BCN showed enhanced separation of photoinduced carriers and accelerated charge transport, leading to better photocatalytic activity. We believe that this work will encourage more research on MXene-based photocatalysts for different photocatalysis processes including photocatalytic CO2 reduction.
In this article, the underlying effect of phosphoric acid etching and additional water vapor on chlorine desorption behavior over a model catalyst La3Mn2O7 was explored. Acid treatment led to the ...formation of LaPO4 and enhanced the mobility of lattice oxygen of La3Mn2O7 evidenced by a range of characterization (i.e., X-ray diffraction, temperature-programmed analyses, NH3–IR, etc.). The former introduced thermally stable Brönsted acidic sites that enhanced dichloromethane (DCM) hydrolysis while the latter facilitated desorption of accumulated chlorine at elevated temperatures. The acid-modified catalyst displayed a superior catalytic activity in DCM oxidation compared to the untreated sample, which was ascribed to the abundance of proton donors and Mn(IV) species. The addition of water vapor to the reaction favored the formation and desorption of HCl and avoided surface chlorination at low temperatures. This resulted in a further reduction in reaction temperature under humid conditions (T 90 of 380 °C for the modified catalyst). These results provide an in-depth interpretation of chlorine desorption behavior for DCM oxidation, which should aid the future design of industrial catalysts for the durable catalytic combustion of chlorinated organics.
Industrial combustion of chloroaromatics is likely to generate unintentional biphenyls (PCBs), polychlorinated dibenzo-p-dioxins (PCDDs), and polychlorinated dibenzofurans (PCDFs). This process ...involves a surface-mediated reaction and can be accelerated in the presence of a catalyst. In the past decade, the effect of surface nature of applied catalysts on the conversion of chloroaromatics to PCBs/PCDD/PCDF has been well explored. However, studies on how the flue gas interferent components affect such a conversion process remain insufficient. In this article, a critical flue gas interferent component, alkali potassium, was investigated to reveal its effect on the chloroaromatics oxidation at a typical solid acid–base catalyst, Mn x Ce1–x O2/HZSM-5. The loading of alkali potassium was found to improve the Lewis acidity of the catalyst (by increasing the amounts of surface Mn4+ after calcination), which thus promoted the CO2 selectivity for catalytic chlorobenzene (CB) oxidation. The KOH with a high hydrophilicity has favored the adsorption/activation of H2O molecules that provided sufficient hydroxyl groups and possibly induced a hydrolysis process to promote the formation of HCl. The K ion also served as a potential sink for chorine ions immobilization (via forming KCl). Both of these inhibited the formation of phenyl polychloride byproducts, thereby blocking the conversion of CB to chlorophenol and then PCDDs/PCDFs, and potentially ensuring a durable operation and less secondary pollution for the catalytic chloroaromatics combustion in industry.
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•Bi-metal-decorated amorphous bismuth oxide photocatalysts were fabricated.•The Bi metal could activate the amorphous bismuth oxide via the SPR effect.•The photocatalytic performance ...can be well tuned via content of Bi metal.•Bi metal/amorphous bismuth oxide displayed enhanced photocatalytic activity.•The photocatalysis mechanism was revealed with ESR and in situ DRIFT.
Amorphous semiconductors are seldom exploited as effective photocatalysts, as they are restricted by abundant bulk defects as carrier recombination centers. To activate amorphous bismuth oxide for efficient visible-light photocatalytic performance, a novel and facile strategy was developed. Plasmonic Bimetal-decorated amorphous bismuth oxide (Bi–BiO) was prepared by partial reduction with NaBH4. The content of Bi metal and the photocatalytic activity of the catalysts can be modulated by controlling the concentration of NaBH4 solution. Various techniques were employed to explore the structural features, optical properties, and active species during photocatalysis. The as-synthesized Bi–BiO catalysts were applied in photocatalytic removal of NO in air under and exhibited highly enhanced visible light photocatalytic activity. The significantly increased photocatalytic capability can be attributed to the combined effects of the enhanced visible light absorption and the improved separation efficiency of the charge carriers attributed to the surface plasmon resonance conferred by Bi metal. The advanced Bi–BiO catalysts also exhibited high photochemical and structural stability under repeated irradiation. Moreover, in situ DRIFT was carried out to reveal the time-dependent evolution of reaction intermediates during photocatalytic NO oxidation. A molecular-level photocatalysis mechanism was first proposed for Bi–BiO based on ESR and in situ DRIFT. This work could provide a new perspective in utilizing non-noble-metal Bi as a key activation factor to trigger the photocatalytic ability of amorphous semiconductors.
The bismuth element synthesized by a facile chemical solution method exhibited an admirable and stable photocatalytic activity towards the removal of NO under 280 nm light irradiation due to the ...surface plasmon resonance mediated direct photocatalysis, and most strikingly, showed a catalytic "memory" capability following illumination.
Graphitic carbon nitride (g-C3N4) is an intriguing metal-free photocatalyst for pollution control. This research represents an efficient visible light photocatalytic removal of gaseous NO at 600 ppb ...level with porous g-C3N4 nanostructures synthesized by pyrolysis of thiourea. TG-DSC was employed to simulate the pyrolysis of thiourea, and the mechanistic formation process of g-C3N4 was revealed. The crystallinity, morphology, surface area, pore structures, band structure, and photocatalytic activity of g-C3N4 can be engineered by variation of pyrolysis temperature and time. A layer-by-layer coupled with layer-splitting process was proposed for the gradual reduction of layer thickness and size of g-C3N4 obtained at elevated temperature and prolonged time. The visible light photocatalytic activity of g-C3N4 nanosheets toward NO purification was significantly enhanced due to the enhanced crystallinity, nanosheet structure, large surface areas and pore volume and enlarged band gap as the pyrolysis temperature was increased and the pyrolysis time was prolonged. The optimized g-C3N4 nanosheets (CN-600 °C and CN-240 min) exhibited higher photocatalytic activity of 32.7% and 32.3% than C-doped TiO2 (21.8%) and BiOI (14.9%), which are also highly stable and can be used repeatedly without obvious deactivation under repeated irradiation, demonstrating their great potential for practical applications.
The ring-opening process is the rate-determining step for photocatalytic decomposition of aromatic volatile organic compounds (VOCs). However, the ring-opening pathway has not been fully revealed, ...which enables efficient photocatalytic VOC degradation. Taking the photocatalytic toluene degradation as a typical case, the ring-opening pathway and regulation strategy were systematically investigated and proposed with an aim to regulate the rate-determining step and accelerate the reaction rates. Herein, BiOCl with tailored facets was designed as a model photocatalyst to clarify the mechanism of photocatalytic toluene degradation. Theoretical calculations and
in situ
DRIFTS technology were closely combined to dynamically predict and monitor the photocatalytic toluene degradation reactions. It is revealed that the lowest energy barrier was precisely located at the ring-opening of benzoic acid which was generated from toluene oxidation. This result implied that the benzyl must be fully oxidized to benzoic acid to elevate the ring-opening reaction rates. Moreover, the alternative charge arrangement on the {010} facet of BiOCl facilitated the benzyl oxidation and selectivity for benzoic acid ring-opening reactions, subsequently resulting in remarkably enhanced photocatalytic efficiency, exceeding that of the {001} facet by 100% towards toluene decomposition. This work demonstrates that probing and tailoring the ring-opening pathway are vital to increase the overall toluene decomposition efficiency and could provide new insights into the understanding of the photocatalytic reactions in VOC degradation.
Mesoporous C-doped TiO2 nanomaterials with an anatase phase are prepared by a one-pot green synthetic approach using sucrose as a carbon-doping source for the first time. A facile post-thermal ...treatment is employed to enhance visible light photocatalytic activity of the as-prepared photocatalyst. The enhancement effect of post-thermal treatment between 100 and 300 °C is proved by the photodegradation of gas-phase toluene, and the optimum temperature is 200 °C. Physicochemical properties of the samples are characterized in detail by X-ray diffraction, Raman spectroscopy, N2 adsorption–desorption isotherms, transmission electron microscopy, Fourier transform-infrared spectroscopy, X-ray photoelectron spectroscopy, UV–vis diffuse reflectance spectroscopy, and photoluminescence. The results indicate that the promotive effect of the post-thermal treatment can be attributed to the changes of the catalysts’ surface and optical properties. The results also show that the recombination of electron–hole pairs is effectively inhibited after thermal treatment due to the reduction of surface defects. The facile post-thermal treatment provides a new route for potential industrial applications of C-doped TiO2 nanomaterials prepared by a green approach owing to its low cost and easy scale-up.
We report the synthesis of core/shell face-centered tetragonal (fct)-FePd/Pd nanoparticles (NPs) via reductive annealing of core/shell Pd/Fe3O4 NPs followed by temperature-controlled Fe etching in ...acetic acid. Among three different kinds of core/shell FePd/Pd NPs studied (FePd core at ∼8 nm and Pd shell at 0.27, 0.65, or 0.81 nm), the fct-FePd/Pd-0.65 NPs are the most efficient catalyst for the oxygen reduction reaction (ORR) in 0.1 M HClO4 with Pt-like activity and durability. This enhanced ORR catalysis arises from the desired Pd lattice compression in the 0.65 nm Pd shell induced by the fct-FePd core. Our study offers a general approach to enhance Pd catalysis in acid for ORR.
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