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Journal ArticleDOI: 10.1021/ACS.EST.1C00490

Improved Oxygen Activation over a Carbon/Co3O4 Nanocomposite for Efficient Catalytic Oxidation of Formaldehyde at Room Temperature.

Rong Li1, Rong Li2, Yu Huang2, Yu Huang1  +6 more
04 Mar 2021-Environmental Science & Technology (American Chemical Society)-Vol. 55, Iss: 6, pp 4054-4063
Abstract: Oxygen activation is a key step in the catalytic oxidation of formaldehyde (HCHO) at room temperature. In this study, we synthesized a carbon/Co3O4 nanocomposite (C-Co3O4) as a solution to the insufficient capability of pristine Co3O4 (P-Co3O4) to activate oxygen for the first time. Oxygen activation was improved via carbon preventing the agglomeration of Co3O4 nanoparticles, resulting in small particles (approximately 7.7 nm) and more exposed active sites (oxygen vacancies and Co3+). The removal efficiency of C-Co3O4 for 1 ppm of HCHO remained above 90%, whereas P-Co3O4 was rapidly deactivated. In static tests, the CO2 selectivity of C-Co3O4 was close to 100%, far exceeding that of P-Co3O4 (42%). Various microscopic analyses indicated the formation and interaction of a composite structure between the C and Co3O4 interface. The carbon composite caused a disorder on the surface lattice of Co3O4, constructing more oxygen vacancies than P-Co3O4. Consequently, the surface reducibility of C-Co3O4 was improved, as was its ability to continuously activate oxygen and H2O into reactive oxygen species (ROS). We speculate that accelerated production of ROS helped rapidly degrade intermediates such as dioxymethylene, formate, and carbonate into CO2. In contrast, carbonate accumulation on P-Co3O4 surfaces containing less ROS may have caused P-Co3O4 inactivation. Compared with noble nanoparticles, this study provides a transition metal-based nanocomposite for HCHO oxidation with high efficiency, high selectivity, and low cost, which is meaningful for indoor air purification.

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Topics: Oxygen (57%), Catalytic oxidation (56%), Nanocomposite (51%) ... read more

5 results found

Journal ArticleDOI: 10.1016/J.APCATB.2021.120786
Abstract: Hormuz Red Soil (HRS), as a naturally hematite-containing mineral was used to enhance the catalytic ozonation process (COP) of Acetaminophen (ACT) elimination. The surface properties and particle size of HRS mainly composed of ɑ-Fe2O3 were modified via calcination (C-HRS) demonstrating notable catalytic activity. The catalytic activity of C-HRS was evaluated for the ozonation of ACT under various conditions. Complete degradation of 50 mg L−1 ACT was obtained within 10 min at natural conditions with 1.0 g L−1 of C-HRS which was > 10 times faster than single ozonation process (SOP). The C-HRS accelerated the decomposition of ozone to hydroxyl radical on the catalyst’s surface. Moreover, the C-HRS efficiently catalyzed the peroxone reaction for the degradation and mineralization of ACT. The C-HRS exhibited high stability and reusability in consecutive catalytic cycles. This work offers a new, effective, and low-cost catalyst for accelerating of ozone decomposition that can be used in oxidation of pollutants.

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Topics: Catalysis (52%)

1 Citations

Journal ArticleDOI: 10.1016/J.JHAZMAT.2021.127593
Dandan Zhu1, Dandan Zhu2, Meijuan Chen1, Yu Huang2  +8 moreInstitutions (4)
Abstract: Formaldehyde is a typical indoor air pollutant that has posed severely adverse effects on human health. Herein, a novel FeCo alloy nanoparticle-embedded nitrogen-doped carbon (FeCo@NC) was synthesized with the aim of tailoring the transition-metal d-band structure toward an improved formaldehyde oxidation activity for the first time. A unique core@shell metal–organic frameworks (MOFs) architecture with a Fe-based Prussian blue analogue core and Co-containing zeolite imidazole framework shell was firstly fabricated. Then, Fe and Co ion alloying was readily achieved owing to the inherent MOF porosity and interionic nonequilibrium diffusion occurring during pyrolysis. High-angle annular dark-field scanning transmission electron microscopy and X-ray absorption fine structure spectra confirm that small FeCo alloys in situ form in FeCo@NC, which exhibits a higher formaldehyde removal efficiency (93%) than the monometallic Fe-based catalyst and a remarkable CO2 selectivity (85%) at room temperature. Density functional theory calculations indicate the number of electrons transferred from the metal core to the outer carbon layer is altered by alloying Fe and Co. More importantly, a downshift in the d-band center relative to the Fermi level occurs from − 0.93 to − 1.04 eV after introducing Co, which could alleviate the adsorption of reaction intermediates and greatly improve the catalytic performance.

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Topics: Prussian blue (51%), Carbon (51%)

Journal ArticleDOI: 10.1016/J.CEJ.2021.132636
Mabrouk Abidi1, Mabrouk Abidi2, A. Hajjaji, Abdelkrim Bouzaza2  +7 moreInstitutions (3)
Abstract: Indoor air pollution is a complex problem that involves a wide range and diversity of pollutants that threaten human health. In this context, significant efforts must be made to improve the quality of indoor air. It is therefore important to start controlling the sources of indoor pollution. However, where eliminating or minimizing sources of emissions is not technically feasible, technologies to reduce them should be used. The present work deals with the photocatalytic depollution of hospitals indoor air, using a continuous photocatalytic process. In order to get closer to real conditions, two model pollutants representing the indoor air of hospitals were chosen as targets; chloroform (CHCl3) and glutaraldehyde (C5H8O2). The photocatalytic oxidation of VOCs alone and their mixture (binary mixing system) has been studied on a pilot scale. Indeed, the experiments were carried out in a continuous planar reactor using a new technology based on the TiO2/optical fiber photocatalyst. The effects of experimental conditions such as air flow rate (4–12 m3.h−1), VOCs inlet concentration (4–40 mg.m−3) and humidity levels (5–90%) were pointed out. The photocatalytic effect of the OF-TiO2 composite was found to be improved under UV irradiation as compared to TiO2. The presence of water molecules in small amounts (less than RH = 30%) can promote the degradation process due to the formation of •OH radicals. Biomolecular Langmuir-Hinshelwood model including mass transfer step has been developed to represent the process behavior. Reusability test show that the optical fiber -based photocatalysts presented good photocatalytic activities towards CHCl3/C5H8O2 removal.

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Topics: Indoor air quality (56%)

Open accessJournal ArticleDOI: 10.1016/J.MTENER.2021.100911
Chao Huang1, Ping Qin2, Yang Luo1, Qingdong Ruan1  +6 moreInstitutions (3)
Abstract: Water splitting which encompasses the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is a promising approach for large-scale and sustainable production of hydrogen (H2) and oxygen (O2). However, the water splitting kinetics is slow and noble metal catalysts such as Pt, RuO2/IrO2 are typically required to improve water splitting efficiency. Therefore, non-noble metals such as Co-based catalysts with a lower cost, natural abundance, catalytic performance comparable to that of noble metal catalysts, and good structural stability are highly desirable as substitutes for the expensive and environmentally scarce noble metals in energy applications. In this review, recent progress pertaining to the advance and development of different types of Co-based catalysts is reviewed. In addition, the fundamental mechanisms of water electrolysis and ways to improve the HER/OER activity are discussed. Finally, the present challenge and prospective for the future development of water splitting electrocatalysts are discussed.

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Topics: Water splitting (59%), Noble metal (51%)

Open accessJournal ArticleDOI: 10.1016/J.APSUSC.2021.151823
Tingting Pan1, Hua Deng1, Shunyu Kang1, Hong He1Institutions (1)
Abstract: Manganese dioxide (MnO2) has been widely used in environmental catalysis. The precipitation method is commonly used for preparing MnO2 in industrial applications, but always leads to unsatisfactory removal efficiency due to the intense precipitation rates of the metal precursors. Herein, a simple strategy was designed to control the precipitation rate. On the basis of 2MnO4- (aq) + 2NH4+ (aq) = N2 (g) + 2MnO2 (s) + 4H2O (l), the precipitation rate was well regulated by the release of NH4+ in solution. Different precipitants with various release rates of NH4+ (i.e. urea, ammonium carbonate, and sodium bicarbonate) were investigated. The lower precipitate rate obtained by urea is favorable for the formation of nanoparticle-like MnO2 with larger surface area and stronger catalytic activity than the nanorods and bulk MnO2 obtained with ammonium carbonate and sodium bicarbonate, respectively. The precipitate rate could be further optimized by changing the amount of urea to obtain the optimal MnO2 catalysts, which were efficiently applied in the complete catalytic oxidation of VOC, mineralizing 100% of 1000 ppm of ethyl acetate into CO2 at 200 °C under a high GHSV of 78,000 h-1. Various characterization methods combined to reveal that the morphology, surface Mn4+ /Mn3+ ratio, surface oxygen species and low-temperature reducibility determined the excellent catalytic performance. This work provides a new strategy for tuning MnO2 and enhancing VOC elimination via improved precipitation methods.

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Topics: Precipitation (chemistry) (53%), Catalytic oxidation (53%), Ammonium carbonate (53%) ... read more

56 results found

Journal ArticleDOI: 10.1016/J.SNB.2013.11.005
Hyo Joong Kim1, Jong Heun Lee1Institutions (1)
Abstract: High-performance gas sensors prepared using p-type oxide semiconductors such as NiO, CuO, Cr2O3, Co3O4, and Mn3O4 were reviewed. The ionized adsorption of oxygen on p-type oxide semiconductors leads to the formation of hole-accumulation layers (HALs), and conduction occurs mainly along the near-surface HAL. Thus, the chemoresistive variations of undoped p-type oxide semiconductors are lower than those induced at the electron-depletion layers of n-type oxide semiconductors. However, highly sensitive and selective p-type oxide-semiconductor-based gas sensors can be designed either by controlling the carrier concentration through aliovalent doping or by promoting the sensing reaction of a specific gas through doping/loading the sensor material with oxide or noble metal catalysts. The junction between p- and n-type oxide semiconductors fabricated with different contact configurations can provide new strategies for designing gas sensors. p-Type oxide semiconductors with distinctive surface reactivity and oxygen adsorption are also advantageous for enhancing gas selectivity, decreasing the humidity dependence of sensor signals to negligible levels, and improving recovery speed. Accordingly, p-type oxide semiconductors are excellent materials not only for fabricating highly sensitive and selective gas sensors but also valuable additives that provide new functionality in gas sensors, which will enable the development of high-performance gas sensors.

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Topics: Oxide (59%), Doping (51%)

1,242 Citations

Journal ArticleDOI: 10.1002/ANIE.201600687
Lei Xu1, Qianqian Jiang1, Zhaohui Xiao1, Xingyue Li1  +3 moreInstitutions (2)
18 Apr 2016-Angewandte Chemie
Abstract: Co3O4, which is of mixed valences Co2+ and Co3+, has been extensively investigated as an efficient electrocatalyst for the oxygen evolution reaction (OER). The proper control of Co2+/Co3+ ratio in Co3O4 could lead to modifications on its electronic and thus catalytic properties. Herein, we designed an efficient Co3O4-based OER electrocatalyst by a plasma-engraving strategy, which not only produced higher surface area, but also generated oxygen vacancies on Co3O4 surface with more Co2+ formed. The increased surface area ensures the Co3O4 has more sites for OER, and generated oxygen vacancies on Co3O4 surface improve the electronic conductivity and create more active defects for OER. Compared to pristine Co3O4, the engraved Co3O4 exhibits a much higher current density and a lower onset potential. The specific activity of the plasma-engraved Co3O4 nanosheets (0.055 mA cm−2BET at 1.6 V) is 10 times higher than that of pristine Co3O4, which is contributed by the surface oxygen vacancies.

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Topics: Oxygen evolution (55%), Electrocatalyst (54%), Oxygen (50%)

1,220 Citations

Journal ArticleDOI: 10.1021/JA3012676
Abstract: The increasing need for new materials capable of solar fuel generation is central in the development of a green energy economy. In this contribution, we demonstrate that black TiO2 nanoparticles obtained through a one-step reduction/crystallization process exhibit a bandgap of only 1.85 eV, which matches well with visible light absorption. The electronic structure of black TiO2 nanoparticles is determined by the unique crystalline and defective core/disordered shell morphology. We introduce new insights that will be useful for the design of nanostructured photocatalysts for energy applications.

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Topics: Solar fuel (51%)

1,199 Citations

Open accessJournal ArticleDOI: 10.1002/ADMA.201606793
Linzhou Zhuang1, Lei Ge1, Yisu Yang1, Mengran Li1  +3 moreInstitutions (2)
01 May 2017-Advanced Materials
Abstract: Electrochemical water splitting is a promising method for storing light/electrical energy in the form of H2 fuel; however, it is limited by the sluggish anodic oxygen evolution reaction (OER). To improve the accessibility of H2 production, it is necessary to develop an efficient OER catalyst with large surface area, abundant active sites, and good stability, through a low-cost fabrication route. Herein, a facile solution reduction method using NaBH4 as a reductant is developed to prepare iron-cobalt oxide nanosheets (FexCoy-ONSs) with a large specific surface area (up to 261.1 m2 g−1), ultrathin thickness (1.2 nm), and, importantly, abundant oxygen vacancies. The mass activity of Fe1Co1-ONS measured at an overpotential of 350 mV reaches up to 54.9 A g−1, while its Tafel slope is 36.8 mV dec−1; both of which are superior to those of commercial RuO2, crystalline Fe1Co1-ONP, and most reported OER catalysts. The excellent OER catalytic activity of Fe1Co1-ONS can be attributed to its specific structure, e.g., ultrathin nanosheets that could facilitate mass diffusion/transport of OH− ions and provide more active sites for OER catalysis, and oxygen vacancies that could improve electronic conductivity and facilitate adsorption of H2O onto nearby Co3+ sites.

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Topics: Oxygen evolution (55%), Water splitting (53%), Overpotential (53%) ... read more

754 Citations

Journal ArticleDOI: 10.1002/AENM.201400696
Yongcheng Wang1, Tong Zhou1, Kun Jiang1, Peimei Da1  +6 moreInstitutions (1)
Abstract: While electrochemical water splitting is one of the most promising methods to store light/electrical energy in chemical bonds, a key challenge remains in the realization of an efficient oxygen evolution reaction catalyst with large surface area, good electrical conductivity, high catalytic properties, and low fabrication cost. Here, a facile solution reduction method is demonstrated for mesoporous Co3O4 nanowires treated with NaBH4. The high-surface-area mesopore feature leads to efficient surface reduction in solution at room temperature, which allows for retention of the nanowire morphology and 1D charge transport behavior, while at the same time substantially increasing the oxygen vacancies on the nanowire surface. Compared to pristine Co3O4 nanowires, the reduced Co3O4 nanowires exhibit a much larger current of 13.1 mA cm-2 at 1.65 V vs reversible hydrogen electrode (RHE) and a much lower onset potential of 1.52 V vs RHE. Electrochemical supercapacitors based on the reduced Co3O4 nanowires also show a much improved capacitance of 978 F g-1 and reduced charge transfer resistance. Density-functional theory calculations reveal that the existence of oxygen vacancies leads to the formation of new gap states in which the electrons previously associated with the Co-O bonds tend to be delocalized, resulting in the much higher electrical conductivity and electrocatalytic activity.

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Topics: Nanowire (56%), Water splitting (54%), Reversible hydrogen electrode (54%) ... read more

642 Citations