Co₃O₄ Nanosheets Preferentially Growing (220) Facet with a Large Amount of Surface Chemisorbed Oxygen for Efficient Oxidation of Elemental Mercury from Flue Gas

Abstract

Oxygen vacancies can capture and activate gaseous oxygen, forming surface chemisorbed oxygen, which plays an important role in the Hg 0 oxidation process. Fine control of oxygen vacancies is necessary and a major challenge in this field. A novel method for facet control combined with morphology control was used to synthesize Co 3 O 4 nanosheets preferentially growing (220) facet to give more oxygen vacancies. X-ray photoelectron spectroscopy (XPS) results show that the (220) facet has a higher Co 3+ /Co 2+ ratio, leading to more oxygen vacancies via the Co 3+ reduction process. Density functional theory (DFT) calculations confirm that the (220) facet has a lower oxygen vacancy formation energy. Furthermore, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) results suggest that Co 3 O 4 nanosheets yield more defects during the synthesis process. These results are the reasons for the greater number of oxygen vacancies in Co 3 O 4 nanosheets, which is confirmed by electron energy loss spectroscopy (EELS), Raman spectroscopy, and photoluminescence (PL) spectroscopy. Therefore, Co 3 O 4 nanosheets show excellent Hg 0 removal efficiency over a wide temperature range of 100−350 °C at a high gas hourly space velocity (GHSV) of 180 000 h −1 . Additionally, the catalytic efficiency of Co 3 O 4 nanosheets is still greater than 83%, even after 80 h of testing, and it recovers to its original level after 2 h of in situ thermal treatment at 500 °C.

In Situ Aluminothermic Reduction Induced by Mechanochemical Activation Enhances the Ability of the Spent LiCoO2 Cathode to Activate Peroxymonosulfate

“…Compared with that of the pristine sample, the A 1g peaks of 500-6h and 500-6h-N showed different degrees of a red shift, and the half-width value was significantly wider. This phenomenon was due to the presence of more oxygen vacancies and metal cation vacancies in 500-6h and 500-6h-N than in the pristine sample. , …”

“…This phenomenon was due to the presence of more oxygen vacancies and metal cation vacancies in 500-6h and 500-6h-N than in the pristine sample. 40,50 Electrochemical Analysis. The electron transport capacity of different catalysts also greatly affects the catalytic performance.…”

Rational Design of Cobaltate MCo2O4−δ Hierarchical Nanomicrostructures with Bunch of Oxygen Vacancies toward Highly Efficient Photocatalytic Fixing of Carbon Dioxide

“…Figure b,c and Figure S4 illustrated the O 1s and Cu 2p, Zn 2p, Ni 2p high-resolution XPS spectra of CuCo 2 O 4−δ DSHoMs, ZnCo 2 O 4−δ CSHoMs, and NiCo 2 O 4−δ SMs, respectively. The O 1s XPS spectrum can be fitted into three peaks at 529.1, 530.8–531.2, and 532.6–532.8 which could be assigned to the lattice oxygen, O 2– ions in the oxygen-deficient regions (oxygen vacancies, O V ), and the hydroxy of surface-adsorbed water molecules, respectively . The concentration of oxygen vacancies could be indirectly reflected by the intensity of the binding energy peak around 531 eV in the O 1s spectra for cobalt-based HNMs, and the corresponding rates of oxygen vacancies and lattice oxygen (O v /O l ) for pure CuCo 2 O 4 DSHoMs, ZnCo 2 O 4 CSHoMs, and NiCo 2 O 4 SMs were calculated to be 0.90, 0.59, and 0.67, respectively (Figure c).…”

“…Figure 2b,c 8 which could be assigned to the lattice oxygen, O 2− ions in the oxygen-deficient regions (oxygen vacancies, O V ), and the hydroxy of surface-adsorbed water molecules, respectively. 16 The concentration of oxygen vacancies could be indirectly reflected by the intensity of the binding energy peak around 531 eV in the O 1s spectra for cobalt-based HNMs, and the corresponding rates of oxygen vacancies and lattice oxygen (O v /O l ) for pure CuCo 2 O 4 DSHoMs, ZnCo 2 O 4 CSHoMs, and NiCo 2 O 4 SMs were calculated to be 0.90, 0.59, and 0.67, respectively (Figure 2c). The more oxygen vacancies in CuCo 2 O 4−δ DSHoMs could provide more electrons into the conduction band and then promote CO 2 adsorption which enhanced the reaction between catalysts and CO 2 molecules.…”

“…As is well-known, cobalt-based ternary transition metal oxides with a spinel structure, MCo 2 O 4−δ (M = Zn, Ni, Mn, and Cu) nanoarchitectures, have shown great opportunities in energy conversion applications which have been applied in batteries, , supercapacitors, , water oxidation reactions, and catalysis. − To date, a number of cobaltate spinel structures have been applied for CO 2 photocatalytic fixing reaction (CO 2 PFR) and presented great CO 2 photoreduction capability. For example, Chen et al prepared ultrathin two-dimensional (2D) porous Co 3 O 4 catalysts (Co 3 O 4 -NS) by air calcining of the ultrathin metal–organic framework (MOFs) nanosheet templates to validly reduce CO 2 under visible light irradiation .…”