Totally found 1715 items.

  • [期刊] Z-Scheme 2D/2D alpha-Fe2O3/g-C3N4 heterojunction for photocatalytic oxidation of nitric oxide
    Heterojunctions have attracted considerable attention for efficiently utilizing solar energy and improving conversion efficiency during pollutant degradation. Herein, carbon nitride and hematite (alpha-Fe2O3) are used to prepare a Z-scheme 2D/2D alpha-Fe2O3/g-C3N4 heterojunction using an impregnation-hydrothermal method. The unique 2D/2D structure has a high interfacial area and widely-dispersed active sites. The energy band structure of the Z-scheme heterojunction leads to broad visible-light absorption and promotes charge transfer. Optimizing the content of the alpha-Fe2O3 precursor in composite leads to a maximum efficiency of 60.8% for the removal of 600 ppb of NO, which is approximately 1.78 times that of g-C3N4 (34.2%). The photocatalytic performance is greatly promoted because of the formation of the heterojunction and the strong interfacial action between g-C3N4 nanosheets and alpha-Fe2O3 nanoplates. Cycling experiments verify that the alpha-Fe2O3/g-C3N4 heterojunction has good stability and reusability. The alpha-Fe2O3/g-C3N4 heterojunction therefore has great potential in sustainable and efficient pollutant degradation.
  • [期刊] Self-assembly of highly-dispersed phosphotungstic acid clusters onto graphitic carbon nitride nanosheets as fascinating molecular-scale Z-scheme heterojunctions for photocatalytic solar-to-fuels conversion
    Rational assembly of small-sized photosensitizers onto 2D semiconductors can effectively promote the photo-catalytic activity of the formed 2D heterojunction photocatalyst due to the hetero-interfacial charge-transfer process. However, the achievement of the 2D semiconductor-based heterojunction photocatalyst with the exposures of both abundant light-harvesting and catalytic sites at the hetero-interface region is still a huge challenge. Herein, we synthesized phosphotungstic acid/graphitic carbon nitride (HPW/g-C3N4) heterojunction nanosheets (NSs) with the highly-dispersed distribution of ultra-small HPW clusters (1 similar to 2 nm) by using a facile self-assembly method based on the static adsorption-deposition process. The formed molecular-scale heterointerface between HPW clusters and g-C3N4 NSs resulted in the exposure of abundant active-sites on the highly -dispersed HPW/g-C3N4 hetero-interface. By combining the steady-state and transient photoluminescence spectra with the wavelength-controlled experiments, we demonstrated that the hetero-interfacial charge-transfer process occurring in the HPW/g-C3N4 heterojunction NSs obeyed the Z-scheme mechanism rather than the common "type-II" heterojunction mechanism. In this way, the lifetimes of photoinduced electrons on the conduction band of g-C3N4 could be prolonged for initiating the photocatalytic solar-to-fuels conversion. Upon interband excitations of both the two hetero-components in the HPW/g-C3N4 heterojunction NSs, the photocatalytic activities of H-2 generation and CO2 reduction could be enhanced by similar to 2.2 and similar to 6.7 times as compared to the pure g-C3N4 NSs, even though the HPW component was photocatalytic-inert for either H-2 generation or CO2 reduction upon UV-vis light irradiation.
  • [期刊] Probing the enhanced methanol electrooxidation mechanism on platinum-metal oxide catalyst
    Pt-metal oxide nanocomposites are classified as an alternative promising catalyst besides Pt-Ru nanoalloys for electrochemical methanol oxidation reaction (MOR), and yet the relevant enhancement mechanism for MOR remains largely elusive in terms of catalyst functions and reaction pathways. Herein, interface-rich Pt-SnO2 nanoflakes supported on reduced graphene oxide have been prepared and employed as a model catalyst for such a study. X-ray photoelectron spectroscopy and X-ray absorption spectroscopy measurements reveal significant electronic structure modification on Pt in contact with SnO2, concomitant with enhanced MOR. In-situ surface enhanced infrared absorption spectroscopy and on-line differential electrochemical mass spectrometry measurements indicate that the non-CO pathway is selectively enhanced on Pt-SnO2 compared to the CO pathway which prevails on Pt. DFT calculations reinforce that this electronic structure manipulation favors the non-CO reaction pathway on Pt-SnO2.
  • [期刊] Femtosecond time-resolved diffuse reflectance study on facet engineered charge-carrier dynamics in Ag3PO4 for antibiotics photodegradation
    The contamination of antibiotics micro-pollutants in water bodies causes increasing concerns currently. Semiconductor-based photocatalysis has been considered as an efficient method for the removal of contaminations from aquatic environment, while its catalytic performance always depends on facets in semiconductor. To deeply understand the relation between facet and catalytic process, herein we take the different morphologies of Ag3PO4 as the cases to investigate the charge-carrier dynamics in different facets of Ag3PO4 for the photodegradation of antibiotic ciprofloxacin (CIP), sulfamethoxazole (SMX), and tetracycline (TC). The degradation results show that Ag3PO4 tetrahedrons with dominated {111} facets exhibit 1.83 times higher CIP degradation rate than Ag3PO4 cubes with dominated {100} facets. Femtosecond time-resolved diffuse reflectance (fs-TDR) spectroscopy is used to give the detail charge-carrier dynamics in different facets of Ag3PO4 in accordance with the antibiotics pollutants degradation rate, which provides a more direct and visual proof.
  • [期刊] Carbon quantum dots implanted CdS nanosheets: Efficient visible-light-driven photocatalytic reduction of Cr(VI) under saline conditions
    Chromium(VI) (Cr(VI)), a toxic metal, is generally present together with ionic salts in industrial effluents. An efficient reduction of Cr(VI) to Cr(III) in saline water is an imperative issue but still a challenging task. Literature has rarely addressed reducing Cr(VI) effectively under saline conditions. Herein, carbon quantum dots (CQDs) were successfully implanted in the CdS nanosheets (CdS-NSs) to prepare nanocomposites (i.e., CCNs) for the first time to efficiently reduce Cr(VI) to Cr(III). The newly fabricated CCNs demonstrated superior performance to reduce Cr(VI) compared to pristine CdS-NSs and CQDs-deposited CdS nanosheets (i.e., CQD/CdS-NSs) in saline water. The nanostructures were examined by spectral and photoelectrochemical measurements as well as density functional theory (DFT) calculations. Results showed that CCNs facilitated the photo-electron transport and thus suppressed charge recombination via formation of micro-regional heterostructures. A lower band gap of CCNs relative to pristine CdS-NSs and CQD/CdS-NSs extended the light absorption spectrum. The optimal photocatalyst, denoted as CCNs-2, exhibited an efficiency of similar to 94% for photocatalytic Cr(VI) reduction within 10 min in water containing 1200 mg/L salts. The obtained rate constant of reduction of Cr(VI) was (2.62 +/- 0.04) x 10(-1) min(-1), approximately 4 and 3 times higher than that of pristine CdS-NSs and CQD/CdS-NSs, respectively. After 3 cycles, the CCNs-2 still showed an efficiency of similar to 78% aqueous Cr(VI) reduction within 10 min. Our results clearly presented that implantation relative to deposition of CQDs for CdS-NSs is a preferential strategy to enhance photocatalytic Cr(VI) reduction in saline water under visible light irradiation.
  • [期刊] Sustained, photocatalytic CO2 reduction to CH4 in a continuous flow reactor by earth-abundant materials: Reduced titania-Cu2O Z-scheme heterostructures
    Photocatalytic conversion of CO2 and water vapor to hydrocarbon fuels is a promising approach for storing solar energy while reducing greenhouse gas emissions. However, still certain issues including low product yields, limited photocatalyst stability and relatively high cost have hampered practical implementation of this technology. In the present work, a unique strategy is adopted to synthesize a stable, and inexpensive photocatalyst comprised of earth-abundant materials: a reduced titania-Cu2O Z-scheme heterostructure. Under illumination for 6 h, the optimized reduced titania-Cu2O photocatalyst enables 0.13 % photoreduction of highly diluted CO2 with water vapors to 462nmol g(-1) of CH4 while showing excellent stability over seven testing cycles (42 h). Our studies show the Z-scheme inhibits Cu2O photocorrosion, while its synergistic effects with reduced titania result in sustained CH4 formation in a continuous flow photoreactor. To the best of our knowledge stability exhibited by the reduced titania-Cu2O Z-scheme is the highest for any Cu-based photocatalyst.
  • [期刊] Rationally designed/assembled hybrid BiVO4-based photoanode for enhanced photoelectrochemical performance
    BiVO4, an attractive photoanode material, has been extensively researched in recent years. However, the photocurrent density of BiVO4-based photoanode is still much less than its theoretical value of 7.5 mA/cm(2) at 1.23 V-RHE. The performance of BiVO4 is generally considered to be hindered by its photocorrosion and sluggish kinetics of oxygen evolution reaction. Herein, a hybrid BiVO4-based photoanode is constructed by modifying nanoporous BiVO4 with a Fe-phenolic layer (FTA) and a case of molecular catalyst 1 ([CO4(H2O)(4)(HPMIDA)(2)(PMIDA)(2)](6-)). The FTA layer with abundant phenolic groups can protect BiVO4 from photocorrosion. With assembling catalyst 1 on FTA interlayer, an eye-catching photocurrent density of 5.5 mA/cm(2) is obtained at 1.23 V-RHE, which is much higher than that of bare BiVO4 (1.5 mA/cm(2)). The stability of 1/FTA/BiVO4 photoanode is investigated, maintaining 93% of the photocurrent density at 0.7 V-RHE after 3 h stability test. Systematic studies reveal that the excellent PEC activity comes from the protection of BiVO4 and the enhancement of surface reaction efficiency. These results support the concept of designing and assembling hybrid photoanode containing heterogeneous cocatalyst and molecular catalyst for efficient solar-fuel conversion.
  • [期刊] NiSe@NiOx core-shell nanowires as a non-precious electrocatalyst for upgrading 5-hydroxymethylfurfural into 2,5-furandicarboxylic acid
    A key challenge for the conversion of 5-hydroxymethylfurfural (HMF) into value-added 2,5-furandicarboxylic acid (FDCA) is improving the sluggish kinetics of selective oxidation alcohol groups. Electrocatalysis has been proved to be a green and efficient strategy for heterogeneous synthetic chemistry. Herein, we report an electrocatalyst of NiSe@NiOx core-shell nanowires for efficiently upgrading HMF into FDCA. The NiSe@NiOx features conductive NiSe nanowires as a core and active NiOx as a shell, showing a smaller Tafel slope of 23 mV dec(-1) accompanying with a near-quantitative yield of FDCA and 99% Faradaic efficiency (FE). X-ray photoelectron spectroscopy unveils the high valence of Ni species in the NiOx shell may be the active sites. Further integrated electrolyzer can produce FDCA and hydrogen simultaneously, showing a 100% FE even after six successive cycles, disclosing robust stability. All these results demonstrate NiSe@NiOx core-shell nanowires as a promising robust non-precious electrocatalyst for highly efficient biomass transformation.
  • [期刊] Low temperature catalytic conversion of oligomers derived from lignin in pubescens on Pd/NbOPO4
    Two-step conversion of pubescens to aromatic monomers and small molecular weight oligomers (mainly dimers and trimers) was studied. Lignin-derived oligomers (LDO) were obtained by formic acid assisted solvo-thermal conversion of pubescens in the H2O-ethanol system at 160 degrees C. In the second step, hydrogenolysis of LDO on Pd/NbOPO4 catalyst was carried out over the temperature range of 60-120 degrees C. Pd/NbOPO4 showed acceptable catalytic performance for efficient degradation of oligomers at low temperature. The NbOx species on the catalyst facilitated the breakage of C-O-C bonds to depolymerize the oligomers toward small molecules, while Pd species accelerated the selective hydrogenation of side chain and furans. The esterification of S (Syringol) unit phenols took place simultaneously with the depolymerization of LDO. The hydrogenated mixture at 100 degrees C and reaction time of 20 h had an average molecular weight of 908 g/mol, and the yield of aromatic monomers was 22.4 wt.% based on lignin contained.
  • [期刊] Global kinetic model of NO oxidation on Pd/gamma-Al2O3 catalyst including PdOx formation and reduction by CO and C3H6
    Pd is often used in diesel oxidation catalysts (DOC) together with Pt to ensure thermal stability and durability. Besides CO and hydrocarbon oxidation, NO oxidation is important for the function of subsequent converters in the exhaust line, such as SCR and DPF. Though Pt sites exhibit a significantly higher NO oxidation rate, Pd also provide some catalytic activity for this reaction and therefore affect the overall NO2 yield in DOC. Palladium oxides (PdOx) formation decreases the NO oxidation activity like PtOx.