Efficiently photothermal conversion in a MnOx-based monolithic photothermocatalyst for gaseous formaldehyde elimination

The practical utility of ternary nickel-cobalt-manganese oxide-supported platinum catalysts for room-temperature oxidative removal of formaldehyde from the air

Formaldehyde (FA), a carcinogenic oxygenated volatile organic compound, is present ubiquitously in indoor air. As such, it is generally regarded as a critical target for air quality management. The oxidative removal of FA under dark and room-temperature (RT) conditions is of practical significance. A series of ternary nickel-cobalt-manganese oxide-supported platinum catalysts (Pt/NiCoMnO4) have been synthesized for FA oxidative removal at RT in the dark. Their RT conversion values for 50 ppm FA (XFA) at 5,964 h-1 gas hourly space velocity (GHSV) decrease in the following order: 1 wt% Pt/NiCoMnO4 (100 %) > 0.5 wt% Pt/NiCoMnO4 (25 %) > 0.05 wt% Pt/NiCoMnO4 (14 %) > NiCoMnO4 (6 %). The catalytic performance of 1 wt% Pt/NiCoMnO4 has been examined further under the control of various process variables (e.g., catalyst mass, flow rate, relative humidity, FA concentration, time on stream, and molecular oxygen content). The catalytic oxidation of FA at low temperatures (e.g., RT and 60 °C) is accounted for by Langmuir-Hinshelwood mechanism (single-site competitive-adsorption), while Mars van Krevelen kinetics is prevalent at higher temperatures. In situ diffuse-reflectance infrared Fourier-transform spectroscopy reveals that FA oxidation proceeds through a series of reaction intermediates such as DOM, HCOO-, and CO32-. Based on the density functional theory simulations, the unique electronic structures of the nearest surface atoms (platinum and nickel) are suggested to be responsible for the superior catalytic activity of Pt/NiCoMnO4.

Regulation of friction pair to promote conversion of mechanical energy to chemical energy on Bi2WO6 and realization of enhanced tribocatalytic activity to degrade different pollutants

Recently, friction-induced tribocatalysis has received tremendous attention through converting mechanical energy to chemical energy. However, its efficiency is much lower than those of photocatalysis and piezocatalysis, and its environmental application is limited in dye degradation. Herein, we developed a facile approach to improve the tribocatalytic activity of Bi2WO6 via adding trace polymer powders to form friction pairs with Bi2WO6. Among various polymers, PTFE was demonstrated to be the best counterpart of Bi2WO6. Subsequently, the PTFE dosage, stirring rate, magnetic bar size and number, and stirring mode were further optimized. The PTFE-promoted Bi2WO6 tribocatalysis was verified to possess excellent performance not only for removing different dyes, but also for degrading chlorophenols that are typical persistent organic pollutants. Multiple uses of the recycled catalysts indicated its good stability and prominent tribocatalytic durability. EPR measurements suggested the generation of hydroxyl radical and superoxide radical, which were determined to be continuously generated within 12 h at the rates of 0.88 μM h-1 and 85 μM h-1, respectively. Subsequently, a possible mechanism was proposed to explain the enhanced performance of the PTFE-promoted Bi2WO6 tribocatalysis. Finally, on basis of the detected intermediates, the degradation pathways of Rhodamine B and 2,4-Dichlorophenol during tribocatalysis were suggested.

Selective production of singlet oxygen for harmful cyanobacteria inactivation and cyanotoxins degradation: Efficiency and mechanisms

Knowledge about the impact of singlet oxygen (¹O₂) on the characteristics and inactivation of harmful cyanobacterial organic matter is limited. In this study, the feasibility of using an improved single-iron doped graphite-like phase carbon nitride catalyst (FeCN) to activate peroxymonosulfate (PMS) catalytic production of ¹O₂ to inactivate four harmful cyanobacteria was investigated. The inactivation efficiencies at 30 min were 92.77%, 66.84%, 91.06%, and 93.45% for Microcystis aeruginosa (M. aeruginosa), Nodularia harveyana, Oscillatoria sp., and Nostoc sp., respectively. This was associated with adjusting experimental parameters, such as the FeCN and PMS doses and initial pH, to obtain the maximum ¹O₂ yield. The quenching experiment results and electron paramagnetic resonance spectra showed that ¹O₂ generated via the non-radical pathway might play a dominant role in inactivating harmful cyanobacteria and degrading harmful algal toxins (Microcystin-LR and Nodularin). In addition, the FeCN-PMS system not only effectively destroyed the integrity of harmful cyanobacterial cells but also effectively degraded cyanobacterial toxins, thereby preventing severe secondary contamination by cell rupture. A possible removal mechanism was proposed. This reveals the potential of ¹O₂ to simultaneously inactivate harmful cyanobacteria and degrade harmful cyanobacterial toxins.

Unveiling the Mechanism of Frictional Catalysis in Water by Bi12TiO20: A Charge Transfer and Contaminant Decomposition Path Study

Tribocatalysis, as a new approach in environmental purification, has drawn increasing attention in the past few years. In this work, we successfully convert mechanical energy to chemical energy by Bi₁₂TiO₂₀, which was synthesized by a hydrothermal method. Under magnetic stirring, electrons transfer from the surface of Bi₁₂TiO₂₀ to the polytetrafluoroethylene-sealed magnetic bar due to their friction. Moreover, the holes that remain on Bi₁₂TiO₂₀ provide oxidation properties in the process for organic matter degradation. According to a series of tests, it is noticed that the shape of the stirring bar and the material of the reaction vessel have a remarkable influence on the removal efficiency of contaminants. Simultaneously, multiple tests reveal the high stability of Bi₁₂TiO₂₀. A great potential for Bi₁₂TiO₂₀ to control water pollutants under dark conditions during collection of ambient mechanical energy was clearly demonstrated in this study.

A Three-Dimensional Melamine Sponge Modified with MnOx Mixed Graphitic Carbon Nitride for Photothermal Catalysis of Formaldehyde

Much attention has been paid to developing effective visible light catalytic technologies for VOC oxidation without requiring extra energy. In this paper, a series of sponge-based catalysts with rich three-dimensional porosity are synthesized by combining MnOx and graphitic carbon nitride (GCN) with commercial melamine sponges (MS) coated with polydopamine (PDA), demonstrating excellent photothermal catalytic performance for formaldehyde (HCHO). The three-dimensional porous framework of MS can provide a good surface for material modification and a reliable interface for gas-solid interaction. The grown layer of PDA framework not only increases the near-infrared wavelength absorption for improving the light-to-heat conversion of catalysts, but also brings excellent adhesion for the subsequent addition of MnO_X and GCN. The efficient formaldehyde oxidation is attributed to the sufficient oxygen vacancies generated by co-loaded MnO_X and GCN, which is conducive to the activation of more O²⁻ in the oxidation process. As the surface temperature of catalyst rapidly increases to its maximum value at ca. 115 °C under visible light irradiation, the HCHO concentration drops from 160 ppm to 46 ppm within 20 min. The reaction mechanism is certified as a classical Mars-van Krevelen mechanism based on the photo-induced thermal catalysis process.

Copper Incorporated Molybdenum Trioxide Nanosheet Realizing High-Efficient Performance for Hydrogen Production

The development of highly active non-precious metal electrocatalysts is crucial for advancing the practical application of hydrogen evolution reaction (HER). Doping engineering is one of the important strategies to optimize the electrocatalytic activity of electrocatalysts. Herein, we put forward a simple strategy to optimize the catalytic activity of MoO3 material by incorporating the Cu atoms into the interlayer (denoted as Cu-MoO3). The prepared Cu-MoO3 nanosheet has a larger surface area, higher conductivity, and strong electron interactions, which contributes to optimal reaction kinetics of the HER process. As a result, the Cu-MoO3 nanosheet only needs a small overpotential of 106 mV to reach the geometric current density of 10 mA cm−2. In addition, it also delivers a low Tafel slope of 83 mV dec−1, as well as high stability and Faraday efficiency. Notably, when using the Cu-MoO3 as a cathode to construct the water electrolyzer, it only needs 1.55 V to reach the 10 mA cm−2, indicating its promising application in hydrogen generation. This work provides a novel type of design strategy for a highly active electrocatalyst for an energy conversion system.

Heterostructure engineering of iridium species on nickel/molybdenum nitride for highly-efficient anion exchange membrane water electrolyzer

Developing highly active electrocatalysts is a pivotal issue for anion-exchange membrane water electrolyzers (AEMWE). However, realizing the continuous hydrogen generation at a large current density remains challenging. Herein, a novel kind of hybrid electrode is successfully developed by introducing trace iridium (Ir) species onto a hierarchical Ni/Mo₅N₆ heterostructure on Ni foam (Ir-Ni/Mo₅N₆/NF). The synergistic advantages of high conductivity, abundant active sites, and strong electronic interaction endow superior reaction kinetics, presenting a highly-active bifunctional electrocatalyst. Remarkably, the Ir-Ni/Mo₅N₆/NF exhibit extremely low overpotentials of 52 mV and 250 mV at 100 mA cm^-2 for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). By exploiting the Ir-Ni/Mo₅N₆ as both anode/cathode, the constructed AEMWE device delivers superior performance. The current density reaches 2.1 A cm^-2 at a voltage of 2.0 V and 250 mA cm^-2 at 1.8 V in alkaline/neutral media. This work put forward a facile and effective strategy to synthesize advanced bifunctional electrocatalysts for water electrolysis.

Covalent Modification of Iron Phthalocyanine into Skeleton of Graphitic Carbon Nitride and Its Visible-Light-Driven Photocatalytic Reduction of Nitroaromatic Compounds

It is of great urgency to eliminate nitroaromatic compounds (NACs) in wastewater due to their high residue and toxicity. Photocatalysis reduction is considered to be an efficient technology for converting NACs to their corresponding aromatic amines. In this work, a visible-light-driven hybrid photocatalyst was synthesized by covalently doping Fe phthalocyanine (FePc) into graphitic carbon nitride skeleton. Compared to the pristine gCN, the optimized gCN-FePc-1 photocatalyst showed enhanced absorption in visible light region, which promoted photogenerated charge transfer and separation. Using p-nitrophenol (p-NP) as the model pollutant, the CN-FePc-1 effectively reduced it to p-aminophenol (p-AP), with the photocatalytic reaction rate being 18 and 3 times higher, respectively, than those of the pristine gCN and the mechanically mixed photocatalyst of gCN/FePc. Moreover, excellent photocatalytic universality for other NACs, high stability, and good reusability also were confirmed. Based on the band structure of the gCN-FePc-1 photocatalyst, a plausible mechanism was proposed to illustrate the photocatalytic reduction process of p-NP to p-AP. This study demonstrates that the covalent modification of FePc into gCN skeleton is an effective strategy to modulate the electronic structure, and the hybrid gCN-FePc is a potential visible-light-driven photocatalyst that potentially can be used for eliminating NAC contamination in wastewater.

Selective Ru Adsorption on SnO2/CeO2 Mixed Oxides for Efficient Destruction of Multicomponent Volatile Organic Compounds: From Laboratory to Practical Possibility

Ru-based catalysts have been extensively employed for the catalytic destruction of chlorinated volatile organic compounds (VOCs), but their versatility for other routine VOCs' destruction has been less explored. Herein, we show that Ru-decorated SnO₂/CeO₂ mixed oxides can sustain H₂O and HCl poisonings and are endowed with extraordinary versatility for a wide range of VOCs' destruction. Selective adsorption of Ru on the cassiterite SnO₂ and CeO₂ nanorods through a Coulomb force can rationally tune the oxidation and dechlorination centers on decorated catalysts, where the epitaxial growth of RuO_x on top of SnO₂ is endowed with excellent dechlorination ability and that on CeO₂ is functional as an oxidation center; the latter could also activate H₂O to provide sufficient H protons for HCl formation. Our developed Ru/SnO₂/CeO₂ catalyst can steadily destruct mono-chlorobenzene, ortho-dichlorobenzene, trichloroethylene, dichloromethane, epichlorohydrin, N-hexane, ethyl acetate, toluene, and their mixtures at an optimum temperature of 300 °C, and its monolithic form is also functional at this temperature with few dioxins being detected in the off-gas. Our results imply that the Ru-decorated SnO₂/CeO₂ catalyst can meet the demands of regenerative catalytic oxidation for the treatment of a wide range of VOCs from industrial exhausts.

Efficient Photothermal Elimination of Formaldehyde under Visible Light at Room Temperature by a MnOx-Modified Multi-Porous Carbon Sphere

Volatile organic compounds (VOCs) exert a serious impact on the environment and human health. The development of new technologies for the elimination of VOCs, especially those from non-industrial emission sources, such as indoor air pollution and other low-concentration VOCs exhaust gases, is essential for improving environmental quality and human health. In this study, a monolithic photothermocatalyst was prepared by stabilizing manganese oxide on multi-porous carbon spheres to facilitate the elimination of formaldehyde (HCHO). This catalyst exhibited excellent photothermal synergistic performance. Therefore, by harvesting only visible light, the catalyst could spontaneously heat up its surface to achieve a thermal catalytic oxidation state suitable for eliminating HCHO. We found that the surface temperature of the catalyst could reach to up 93.8 °C under visible light, achieving an 87.5% HCHO removal efficiency when the initial concentration of HCHO was 160 ppm. The microporous structure on the surface of the carbon spheres not only increased the specific surface area and loading capacity of manganese oxide but also increased their photothermal efficiency, allowing them to reach a temperature high enough for MnO_x to overcome the activation energy required for HCHO oxidation. The relevant catalyst characteristics were analyzed using XRD, measurement of BET surface area, scanning electron microscopy, HR-TEM, XPS, and DRS. Results obtained from a cyclic performance test indicated high stability and potential application of the MnO_x-modified multi-porous carbon sphere.

Electrochemical detection of Sudan red series azo dyes: Bibliometrics based analysis

Sudan red azo dyes are banned from food because of their carcinogenic properties. It is necessary to establish a method for the detection of Sudan azo dyes in food. Among them, electrochemical sensing technology has become a very potential analytical method for food detection because of its fast, sensitive and low price. In this paper, we analyze the electrochemical detection of Sudan red azo dyes by bibliometric method. A total of 161 articles were analyzed from 2007 to 2021. The geographical and institutional distribution of these papers is used to understand the form of collaboration on this topic. Keyword analysis in these papers is used to understand the different directions in which the topic is studied at different stages. The results show that the topic reached its peak in 2015. The development of novel materials with excellent electrochemical activity has promoted the research on this topic. As detection limits continue to be lowered and sensors continue to be optimized, this topic currently does not continue to attract much attention.