Tuning Thermal Catalytic Enhancement in Doped MnO₂–Au Nano-Heterojunctions

Abstract

Sodium (Na)- and potassium (K)-doped δ-MnO2, which presented different band gaps, were synthesized by a hydrothermal method. Then, uniform Au nanoparticles (NPs) were deposited on MnO2 to form metal–semiconductor nano-heterojunctions (MnO2–Au). By comparing their temperature-dependent thermal catalytic performances, p-aminothiophenol to p,p′-dimercaptoazobenzene conversion was used as proof-of-concept transformations. MnO2–Au hybrid materials demonstrated better thermal catalytic performances relative to individual Au NPs. Meanwhile, K-doped MnO2–Au, with a MnO2 support displaying a narrower bandgap, displayed superior catalytic activities relative to Na-doped MnO2–Au. To get the same catalytic performance by individual Au NPs, it can be ∼50 K less by Na-doped MnO2–Au and ∼100 K less by K-doped MnO2–Au. The enhancement is mainly attributed to the thermally excited electrons in MnO2, which were transferred to Au NPs. The additional electrons in Au NPs increase the electron density and thus contribute to the improvement of thermal catalysis. Our findings show that the establishment of a nano-heterojunction formed by metal NPs on a semiconductor support has a significant impact on thermal catalysis, where a narrower band gap can facilitate thermally excited carriers and thus bring about better catalytic performances. Thus, the results presented here shed light on the design of a nano-heterojunction catalyst to approach reactions with superior performance under moderate conditions.

Enhanced Spontaneous Antibacterial Activity of δ-MnO2 by Alkali Metals Doping

“…The band gap for the Mg-doped MnO 2 nanoflowers was calculated as 1.13 eV from the UV-VIS spectrum shown in Supplementary Figure S3A. The narrower bandgap observed here relative to the previously reported (Sakai et al, 2005;John et al, 2016) might be attributed to the doping of Mg 2+ ions between layers of MnO 2 (Luo et al, 2000;Wang et al, 2017;Hu et al, 2019;Zhu et al, 2019), which will be discussed later.…”

“…We regarded I Mn and I K as the Mn and K intensities from one Mn and K atom, respectively. The total intensities of Mn 2p 3/2 and K 2p 3/2 can be expressed by following expression (Hu et al, 2019;Zhu et al, 2019):…”

MnO2‐Based Materials for Environmental Applications

“…j) Reproduced with permission. [ 305 ] Copyright 2019, American Chemistry Society. k) Schematic illustration of the fabrication route of MnO 2 /PANI.…”

“…uniformly loaded Au on the surface of MnO 2 nanoflowers and obtained Au/MnO 2 metal–semiconductor nano‐heterojunctions (Figure 17j). [ 305,306 ] They found that Au/MnO 2 heterojunctions showed better thermal catalytic performances compared to individual Au NPs. This can be ascribed to the transfer of thermally excited electrons from MnO 2 to Au NPs, which increases the electron density, thus helping to improve the thermal catalytic performance.…”

In-Situ Growth of Au on KTaO3 Sub-Micron Cubes via Wet Chemical Approach for Enhanced Photodegradation of p-Nitrophenol

“…While potassium tantalates exhibit excellent stability in photocatalysis, their absorption locates at Ultra-violet (UV) range and limits the employment of visible light. In order to make use of solar energy with higher efficiency, various methods are explored to modify potassium tantalates, such as cations doping [11,12] and construction of hetero-structure [13,14]. For instance, porphyrin was used as mixing dyes to sensitize potassium tantalates for photo-splitting water to H 2 or O 2 [8].…”