Synthesis of a Bi2O2CO3/ZnFe2O4 heterojunction with enhanced photocatalytic activity for visible light irradiation-induced NO removal

Although bismuth subcarbonate (Bi2O2CO3), a member of the Aurivillius-phase oxide family, is a promising photocatalyst for the removal of gaseous NO at parts-per-billion level, the large band gap of this material restricts its applications to the UV light region. The above problem can be mitigated by heterojunction fabrication, which not only broadens the light absorbance range, but also inhibits the recombination of photogenerated charge carriers. Herein, we implement this strategy to fabricate a novel Bi2O2CO3/ZnFe2O4 photocatalyst for NO removal under visible light irradiation and authenticate the formation of the above p-n heterojunction using an array of analytical techniques. Notably, the above composite showed activity superior to those of its individual constituents, and the underlying mechanisms of this activity enhancement were probed by density functional theory calculations and photocurrent measurements. Elevated electron/hole separation efficiency caused by the presence of an internal electric field at the Bi2O2CO3/ZnFe2O4 interface was identified as the main reason of the increased photocatalytic activity, with the main active species were determined as center dot O-2(-) and center dot OH by electron spin resonance spectroscopy. Finally, cytotoxicity testing proved the good biocompatibility of Bi2O2CO3/ZnFe2O4. Thus, this work presents deep insights into the preparation and use of a green p-n heterojunction catalyst in various applications

Biocompatible FeOOH-Carbon quantum dots nanocomposites for gaseousNOx removal under visible light: Improved charge separation and Highselectivity

Development of biocompatible photocatalysts with improved charge separation and high selectivity is essential for effective removal of air pollutants. Iron-containing catalysts have attracted extensive attention due to their low-toxicity and high natural abundance. Here, carbon quantum dots (CQDs) modified FeOOH nanocomposites fabricated using a facile hydrothermal route showed enhanced NO removal efficiency (22%) compared to pure FeOOH. Moreover, generation of toxic NO2&nbsp;intermediates was significantly inhibited using the nanocomposites, demonstrating high selectivity for final nitrate formation. Photo-electrochemical results showed that both charge separation and transfer efficiency were significantly improved by CQDs addition, and the lifetime of photo-generated carriers was increased eventually. Density functional theory calculations further elucidated that the suppressed recombination of photo-induced electron-hole pairs was due to enhanced electron migration from the FeOOH to CQDs. A NO degradation mechanism was proposed based on detection of the reactive oxygen species using electron paramagnetic spectroscopy. In addition, the nanocomposite showed good biocompatibility and low cytotoxity, ensuring minimal environmental impact for potential application in large-scale.</span

Photocatalytic NO removal on BiOI surface: The change from nonselective oxidation to selective oxidation

Numerous publications have investigated nitric oxide (NO) removal through semiconductor photocatalytic technology. However, few reports are available on the products and mechanisms of the photocatalytic NO removal process. In this study, BiOI hollow microspheres are synthesized for the photocatalytic removal of NO under the visible light irradiation. Results show that NO removal product and NO removal mechanism could interfere with each other. NO removal process could be changed from nonselective oxidation to selective oxidation as the irradiation time increases. Meanwhile, the product of NO removal could be changed from nitrate (NO3-) to nitrogen dioxide (NO2). These interesting changes were attributed to the generated NO3-, which was produced from the reactions between NO and (OH)-O-center dot. The generated NO3- could inhibit (OH)-O-center dot generation, thus leading to a change in the NO removal products and NO removal mechanism. This study can improve our understanding of NO removal on the photocatalyst surface and serve as a guide in using photocatalysts for NO removal. (C) 2015 Elsevier B.V. All rights reserved.</p

Mechanism of NO Photocatalytic Oxidationon g-C3N4 Was Changed by Pd-QDs Modification

Quantum dot (QD) sensitization can increase the light absorption and electronic transmission of photocatalysts. However, limited studies have been conducted on the photocatalytic activity of photocatalysts after modification by noble metal QDs. In this study, we developed a simple method for fabricating Pd-QD-modified g-C3N4. Results showed that the modification of Pd-QDs can improve the NO photocatalytic oxidation activity of g-C3N4. Moreover, Pd-QD modification changed the NO oxidation mechanism from the synergistic action of h+ and O2− to the single action of ·OH. We found that the main reason for the mechanism change was that Pd-QD modification changed the molecular oxygen activation pathway from single-electron reduction to two-electron reduction. This study can not only develop a novel strategy for modifying Pd-QDs on the surface of photocatalysts, but also provides insight into the relationship between Pd-QD modification and the NO photocatalytic oxidation activity of semiconductor photocatalysts

Enhanced visible-light photo-oxidation of nitric oxide using bismuth-coupled graphitic carbon nitride composite heterostructures

Pure bismuth (Bi) metal-modified graphitic carbon nitride (g-C3N4) composites (Bi-CN) with a pomegranate-like structure were prepared by an in situ method. The Bi-CN composites were used as photocatalysts for the oxidation of nitric oxide (NO) under visible-light irradiation. The inclusion of pure Bi metal in the g-C3N4 layers markedly improved the light absorption of the Bi-CN composites from the ultraviolet to the near-infrared region because of the typical surface plasmon resonance of Bi metal. The separation and transfer of photogenerated charge carriers were greatly accelerated by the presence of built-in Mott-Schottky effects at the interface between Bi metal and g-C3N4. As a result, the Bi-CN composite photocatalysts exhibited considerably enhanced efficiency in the photocatalytic removal of NO compared with that of Bi metal or g-C3N4 alone. The pomegranate-like structure of the Bi-CN composites and an explanation for their improved photocatalytic activity were proposed. This work not only provides a design for highly efficient g-C3N4-based photocatalysts through modification with Bi metal, but also offers new insights into the mechanistic understanding of g-C3N4-based photocatalysis.(C) 2016, Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by Elsevier B.V. All rights reserved

Photocatalytic reactive oxygen species generation activity of TiO2 improved by the modification of persistent free radicals

Environmentally persistent free radicals (EPFRs) may help mineral dust to produce more reactive oxygen species (ROS). However, the mechanism of this effect is not yet clear. Therefore, in this study, anatase modified with EPFRs was synthesized via a simple two-step method. The presence of EPFRs was confirmed using a series of characterization techniques, including electron paramagnetic resonance and nuclear magnetic resonance. Herein, we found that EPFRs can improve OH generation via the oxidation reaction between photogenerated holes (h(+)) and OH- (or H2O). This result was due to two reasons. The first is that the EPFRs construct a built-in electric field, which helps the migration of h(+) from the bulk to the surface of anatase and then to EPFRs. The other reason is that EPFRs help anatase adsorb more H2O molecules, which are then oxidized to OH by h(+). This study will help to understand the photochemical production mechanism of ROS on the surface of mineral dust

Template-free synthesis of ternary sulfides submicrospheres as visible light photocatalysts by ultrasonic spray pyrolysis

CdIn(2)s(4), ZnIn2S4 and AgIn5S8 were prepared by ultrasonic spray pyrolysis method without using templates which demonstrated a general route for the synthesis of ternary sulfides submicrospheres

Active Complexes on Engineered Crystal Facets of MnOx-CeO2 and Scale-Up Demonstration on an Air Cleaner for Indoor Formaldehyde Removal

Crystal facet-dominated surfaces determine the formation of surface-active complexes, and engineering specific facets is desirable for improving the catalytic activity of routine transition-metal oxides that often deactivate at low temperatures. Herein, MnOx-CeO2 was synthetically administered to tailor the exposure of three major facets, and their distinct surface-active complexes concerning the formation and quantitative effects of oxygen vacancies, catalytically active zones, and active-site behaviors were unraveled. Compared with two other low-index facets {110} and {001}, MnOx-CeO2 with exposed {111} facet showed higher activity for formaldehyde oxidation and CO2 selectivity. However, the {110} facet did not increase activity despite generating additional oxygen vacancies. Oxygen vacancies were highly stable on the {111} facet, and its bulk lattice oxygen at high migration rates could replenish the consumption of surface lattice oxygen, which was associated with activity and stability. High catalytically active regions were exposed at the {111}-dominated surfaces, wherein the predominated Lewis acid-base properties facilitated oxygen mobility and activation. The mineralization pathways of formaldehyde were examined by a combination of in situ X-ray photoemission spectroscopy and diffuse reflectance infrared Fourier transform spectrometry. The MnOx-CeO2-111 catalysts were subsequently scaled up to work as filter substrates in a household air cleaner. In in-field pilot tests, 8 h of exposure to an average concentration of formaldehyde after start-up of the air cleaner attained the Excellent Class of Indoor Air Quality Objectives in Hong Kong