MnO₂ Framework for Instantaneous Mineralization of Carcinogenic Airborne Formaldehyde at Room Temperature

Abstract

Formaldehyde (HCHO) causes increasing concerns, because of its ubiquitous presence in the indoor environment and its irritating and carcinogenic nature, with regard to humans. The fast abatement of HCHO is of significant practical interest at room temperature. In this paper, we fabricate a three-dimensional manganese dioxide framework (3D-MnO2), which has interconnected network structures, low mass density (∼7.3 mg cm–3), and high absorption capacity for organic liquids. In particular, the 3D-MnO2 showed excellent activity and stability for HCHO oxidation at room temperature, achieving 45% of 100 ppm of HCHO mineralized into CO2 under high gas hourly space velocity (GHSV = 180 L gcat –1 h–1). The excellent performance of 3D-MnO2 catalysts in decomposing HCHO can be ascribed to their quick reversibility and high water content for replenishing the consumed surface hydroxyl groups during HCHO decomposition, and fully exposed active reaction sites. It is valuable to know that inexpensive metal oxides such as MnO2 can transform ppm-level HCHO into harmless CO2 in a timeframe as brief as a subsecond at room temperature.

Progress of Catalytic Oxidation of Formaldehyde over Manganese Oxides

“…Catalytic oxidation of formaldehyde over manganese oxide is a heterogeneous catalytic reaction. Therefore, the morphology, and microstructure (pore structure and surface defects) of the catalysts have an important impact on the catalytic performance . Hierarchically porous (eg: meso‐/macro‐porous) structures favor the diffusion process of reactants and products, and the special morphology structure benefits the adsorption of reactant molecules.…”

“…Three‐dimensional (3D) network structure has been attracting much attention in the fields of catalysts and catalyst supports because it can fully expose the active sites and facilitate the diffusion of reactants and products. For example, Rong et al . fabricated a three‐dimensional MnO 2 network structure with MnO 2 nanosheets as the wall and MnO 2 nanowires as the framework through a freeze‐drying method (see Figure ).…”

“…In general, abundant surface adsorbed active oxygen species favor the higher catalytic activity. The surface active oxygen species are often detected by X‐ray photoelectron spectroscopy (XPS), time‐of‐flight secondary ion mass spectrometry (ToF‐SIMS) and infrared spectrometry (IR), HCHO‐TPD and so on …”

“…Among them, δ‐MnO 2 exhibited the best catalytic performance at low temperature (see Figure ), one of reasons was that δ‐MnO 2 had the highest active surface lattice oxygen content at low temperature (verified by XPS, lattice oxygen test and HCHO‐TPD). The surface adsorbed oxygen species (surface hydroxyl and/or adsorbed water) were also found to play an important role in the oxidation of HCHO at room temperature over 3D‐MnO 2 fabricated by freeze‐drying aqueous solutions of MnO 2 nanosheets and nanowires . The 3D‐MnO 2 sample has higher surface hydroxyl and/or adsorbed water content than MnO 2 nanosheets and MnO 2 nanowires, partially resulting in the higher HCHO catalytic activity (45% of HCHO (100 ppm) over 3D‐MnO 2 at room temperature and GHSV=180 L/g cat h).…”

Production of Useful Composite Particleboard From Waste Orange Peel

“…Formaldehyde-based resins, such as urea formaldehyde and phenol formaldehyde, are often used for producing particleboards and their VOCs are known as carcinogenic. [28][29][30][31] Therefore, formaldehyde emissions from wood materials have become a topic of great research interest. For example, Kim et al tried to determine the formaldehyde and VOC emissions from wood-based composites, such as medium density fiberboard (MDF) and particleboard (PB), by the desiccator and perforator methods.…”