Facet-Controlled Synthesis of Mn₃O₄ Nanorods for Photothermal Synergistic Catalytic Oxidation of Carcinogenic Airborne Formaldehyde

Abstract

Crystal facet engineering, the selective exposure of reactive crystal facets, has emerged as an important technique for the design of efficient catalysts. However, in the facet-controlled synthesis of nanocrystals by either traditional top-down or bottom-up routes, the selection of capping agents is crucial and challenging. Herein, a phase transition strategy that does not require the assistance of capping/etching agents was developed to achieve the selective exposure of {103}, {101}, and {112} facets in Mn 3 O 4 . Facet-dependent activity in the photothermal decomposition of the carcinogen formaldehyde was investigated. The resulting Mn 3 O 4 with exposed {103} facets showed the best photothermal catalytic activity, achieving the complete mineralization of formaldehyde at ambient temperature. The synergistic mechanism of the photothermal catalysis of Mn 3 O 4 was discovered to be a thermal-assisted photocatalytic process rather than solar-light-driven thermal catalysis. In addition, the photothermal synergistic decomposition process of HCHO was also revealed. The photothermal decomposition of HCHO undergoes the processes of HCHO → DOM (dioxymethylene) → formates → carbonates → CO 2 . The findings proposed in this work not only broaden the study of crystal facet engineering but also provide suggestions for the purification of volatile organic compounds (VOCs) in indoor air.

Probing the Annealing-Induced Phase Evolution of Nanostructured Manganese Oxide Thin Films by X-Ray Diffraction

“…Similarly, Nilsen et al described the growth by a significantly different technique such as ALD of thin Mn 3 O 4 films from Mn­(thd) 3 precursors, underlining the transition from a randomly oriented to a more (103)-oriented film when the deposition temperature was increased from 283 to 331 °C. It is worth noting that the preferential exposure of {103} crystal planes plays an important role in the enhancement of the functional properties of Mn 3 O 4 nanostructures, as recently discussed for the photothermal catalytic oxidation of formaldehyde by Mn 3 O 4 nanorods or for the combustion of benzene via Au/Mn 3 O 4 nanocomposites …”

Precursor- and waste-free synthesis of spark-ablated nanoparticles with enhanced photocatalytic activity and stability towards airborne organic pollutant degradation

“…Furthermore, this thermal energy contributes to enhancing lattice oxygen activity, generating additional surface-active oxygen, while the remaining oxygen vacancies are replenished by the surrounding O 2 molecules. 11,68 The coexistence of various manganese oxides, such as Mn 2 O 3 , Mn 3 O 4 , and MnO 2 , has been reported to be beneficial for improved visible-light-driven organic degradation due to their stronger visible light absorption, more active sites, and enhanced charge separation performance. 10,69 In such heterojunction nanostructures, the efficient spatial separation and prolonged lifetime of photo-induced carriers ( e.g.…”

“…7,8,10 Given the complexity of the driving mechanism that further exacerbated by the multitude of manganese oxide variations, the investigation of the primary driving mechanism in most cases poses a substantial challenge yet holds profound significance. 11 It is believed that the oxidation activity is based on either light-driven thermal catalysis or the synergy of photochemical and thermochemical effects involving both photogenerated electron–hole pairs and the activation of surface lattice oxygen due to the temperature elevation. 6,12,13…”

Manganese oxide-based catalysts for the sustainable synthesis of value-added chemicals through oxidation processes: a critical review and perspectives for the future

“…Many efforts have been made to study facet engineering of MnO x catalysts (Table 1). He et al 61 developed a novel phase transition strategy to enable the facet-controlled synthesis of Mn 3 O 4 with predominantly exposed (103), (101), and (112) facets (Fig. 5).…”