Efficient Dye Degradation Catalyzed by Manganese Oxide Nanoparticles and the Role of Cation Valence

Abstract

The ménage of 20–35 nm manganese oxide (Mn−O) nanoparticles (NPs) namely MnO, α‐Mn2O3, Mn3O4 and δ‐MnO2 have been employed as highly recyclable heterogeneous Fenton catalysts for organic dye degradation in wastewater treatment. Mn3O4 was found to be superior to MnO, α‐Mn2O3 and δ‐MnO2 in the descending order under similar reaction conditions. The availability of active sites proportionate with the specific surface area could not interpret the relative performance since the specific surface area of MnO, α‐Mn2O3, Mn3O4 and δ‐MnO2 NPs were 71(±4), 16(±5), 63(±2) and 165(±5) m2/g, respectively. In fact, the presence of unpaired eg electrons in both Mn2+ and Mn3+ ions in Mn−O was found to be crucial for effective electron transfer to H2O2 for the generation of intermediate radicals.The best MB degradation activity of 99.3(±2)% was observed with 100 mg/L 15–20 nm Mn3O4 particles and 0.25 mol/L H2O2 at 80°C within 60 min. The mechanism of the degradation process follows first‐order kinetics and is dependent on the generation of •OH radicals at the initial stage and 1O2 radicals after 30 min.

Manganese Trioxide with Various Morphologies: Applications in Catalytic Dye Degradation

“…Similar shift of absorption maxima was also observed by Mikac et al . It also appears that the nature of the absorption peak in case of MB changes with the type of catalyst and pH condition . There is also report of adsorptive removal accompanied by oxidative degradation of MB and the nature of UV‐vis absorption is different from what is observed by us .…”

“…No further shift in the absorption maxima is observed at the later stage of degradation and the dye degraded at the same absorption peak. However, when the MB degradation was mediated by H 2 O 2 in the presence of different manganese oxide nanoparticles, radical species mediated mechanism is followed and the primary absorption peak of MB remained intact …”

Effective Dye Degradation by Graphene Oxide Supported Manganese Oxide

“…Manganese dioxide (MnO 2 ) is a promising material because of it is low cost, it presents high stability, and it has environmental compatibility as well as abundant availability [14]. Nano-manganese dioxide have been studied as adsorbents [15,16] and oxidants/degradants [17][18][19][20] for a great variety of organic pollutants and dyes due to its octahedral crystal structure (MnO 6 ) and its high redox potential [21]. MnO 2 is usually synthesized at nanoscale in order for more reaction sites to be obtained [22,23], presenting difficulties in separation from aquatic solutions.…”

A facile soft template method to synthesize hollow carbon and MnOx composite particles for effective methylene blue degradation

“…As H 2 O 2 is added, the peak intensity of the MB solution decreases sharply in the rst 10 min, and then continuously drops to nearly 0 at 50 min, indicating the gradual degradation of MB. 33,41 The degree of MB degradation is calculated by the absorbance of the MB at 664 nm. As can be seen in Fig.…”

“…The superior catalytic activity of the HC-Mn-0.7 is attributed to the relatively high content, small size, well dispersion, and low valence states of the MnO x . 18,41 In addition, the large surface area of the hollow structure can provide faster mass exchange, which is favourable for the catalytic reaction. Compared to those of the manganese oxides-based catalysts (Table S1 †), the results are more remarkable, even though the Mn loading in our case is relatively low.…”