Self-Assembly of Novel Mesoporous Manganese Oxide Nanostructures and Their Application in Oxidative Decomposition of Formaldehyde

Abstract

Monodisperse manganese oxide honeycomb and hollow nanospheres have been prepared facilely at room temperature by varying the molar ratio of KMnO 4 and oleic acid. These new nanomaterials were characterized by XRD, SEM, EDS, TEM, and BET measurements. They had robust nanostructures and were stable even after ultrasonic treatment (40 kHz, 120 W) for 30 min. A plausible mechanism of the formation of manganese oxide nanostructures was proposed. The manganese oxide nanomaterials showed high catalytic activities for oxidative decomposition of formaldehyde at low temperatures. Complete conversion of formaldehyde to CO 2 and H 2 O could be achieved, and harmful byproducts were not detected in effluent gases. The catalytic activity of manganese oxide hollow nanospheres was much higher than that of honeycomb nanospheres, although the surface area of the latter was nearly 2 times as high as that of the former. The mechanism of such morphologydependent catalytic activity was discussed in detail. The catalytic activities of the obtained manganese oxide nanospheres were also significantly higher than those of previously reported manganese oxide octahedral molecular sieve (OMS-2) nanorods, MnO x powders, and alumina-supported manganese-palladium oxide catalysts. Potential applications and future research efforts were proposed.

Hollow, Branched and Multifunctional Nanoparticles: Synthesis, Properties and Applications

“…Chen et al have also attributed the enhanced catalytic activity for oxygen reduction of porous Pt nanospheres to both large surface area and high density of defects at the shell surface. 79 An interesting result was reported by Chen et al 74 They found that K x MnO 2 hollow nanospheres demonstrate much higher catalytic activity for oxidative decomposition of formaldehyde than honeycomb nanospheres although the surface area of the latter is nearly two times as high as that of the former. The authors believe it is mainly because that the hollow K x MnO 2 nanospheres could adsorb and retain formaldehyde for a longer period of time than the honeycomb K x MnO 2 nanospheres and eventually enhance the oxidation of formaldehyde.…”

“…Other different yet related approaches have also been employed to synthesize hollow nanoparticles such as hydrothermal, 72,73 emulsion, 74,75 and micelle 76 methods.…”

“…6,31,58,73,74,79,80 Pores present on the shell allow efficient mass-transfer of species into the cavity and thus their access to both the inner and outer surface of the hollow nanoparticles. Liang and co-workers reported that the catalytic activity of Pt hollow nanospheres in the room temperature oxidation of methanol is twice that of the solid Pt nanoparticles (Fig.…”

“…Several types of reactions including crosscouplings, oxidations and hydrogenations have been conducted using hollow nanosphere or nanocage based catalysts. 6,31,34,58,73,74,79,80,[90][91][92][93] Suzuki reaction couples arylboronic acids and aryl halides to form biaryls, which Pd nanoparticles have been most commonly used to catalyze. Table 1 summarizes the yield of Suzuki reactions of various aryliodides (or arylbromides) and phenylboronic acid when hollow Pd spheres are used as a catalyst.…”

“…The oxidative decomposition of formaldehyde to CO 2 ,am a j o r indoor air pollutant, has been conducted at relatively low temperatures by using highly active hollow K x MnO 2 nanospheres. 74 The conversion of formaldehyde reaches 61.8% at 60 • C and 100% at 80 • C. Pt and Co-Pt hollow nanoparticles have been used as catalysts for methanol oxidation and demonstrated greatly enhanced activity, important for the anode electrocatalysis of the direct methanol fuel cells. 80,90 As another example, photocatalytic degradation of organics has been carried out using NiO, Fe 2 O 3 , Pt-ZnO and Au-ZnO hollow nanoparticles.…”