Regular ArticleRoom-temperature synthesis of OMS-2 hybrids as highly efficient catalysts for pollutant degradation via peroxymonosulfate activation
Graphical abstract
Introduction
In recent years, sulfate radical (SO4−) based advanced oxidation processes have received widespread attention as one of the most efficient technologies to get rid of groundwater and wastewaters in both research and application areas [1]. Various methods such as thermolysis [4], photolysis [3], radiation [2], and catalytic activation [5], [6], [7], [8], [9] of persulfate (PS) or peroxymonosulfate (PMS), have been proposed to obtain SO4−. Due to superior physical-chemical properties, low toxicity, low cost and natural abundance, several manganese oxides have been developed as promising heterogeneous catalysts for activation of PMS [10], [11], [12], [13], [14]. For example, Wang et al. synthesized three one-dimensional α-MnO2 nanostructures (nanorods, nanotubes and nanowires) by a hydrothermal method at 120–140 °C, and observed the shape-dependent performance of the catalyst for phenol degradation in the presence of PMS [15]. Liu et al. prepared the highly porous manganese oxide spheres via a hydration-calcination process, and found the decrease of activity of the catalysts but increase of stability for phenol degradation with PMS with increasing of calcination temperature from 200 to 1000 °C [16]; and only the catalyst synthesized at 400 °C showed the best performance for the reaction. Yang et al. also found that the performance of MnOx/SBA-15 can be regulated by synthetic conditions, such as manganese weight ratio, calcination time and temperature (450–750 °C) [17], [11]. In spite of many methods reported for synthesizing manganese oxides materials for PMS activation, these routes are complex and usually need high temperatures and long reaction time. Moreover, the loading amount of PMS and catalyst was still high, leading to the increase of cost. Thus, how to synthesize high-efficient Mn-based materials for PMS activation with a simple proceed under low temperatures is still essential.
Among the various manganese oxides, OMS-2 (KMn8O16), a form of manganese dioxide constructed from edge-shared double [MnO6] octahedral chains with a tunnel size of 0.46 nm × 0.46 nm, has received great attention due to the porous structure, mixed-valence of Mn species, easy release and storage of lattice oxygen [18], [19]. For example, in our previous work, OMS-2 was found to be highly efficient for PMS activation [20], [21]. The synthesis of OMS-2 with high specific surface area, large pore volume and the controllable manganese valence has also been explored by various procedures such as reflux, hydrothermal and solid state chemical reactions. OMS-2 and transition metal doped OMS-2 can be successfully prepared by reflux and hydrothermal methods within 24 h under the temperatures of 70–180 °C [22], [23], [24]. With the assistance of microwave and ultrasonic waves, OMS-2 can be synthesized rapidly within minutes [25], [26]. However, until now there have been no reports about the synthesis of OMS-2 at room temperature with a simple proceed.
In this work, the promising manganese oxide catalyst, OMS-2 was fabricated by an easy approach at room temperature from KMnO4 and MnSO4 in the presence of carbon materials such as carbon nanotubes (CNTs). The electron transfer from carbon materials to the precursor, amorphous manganese oxide, is the key step to increase the ratio of low valent manganese species and to form OMS-2 phase. The characteristics of the oxides can be further regulated by synthesis conditions such as time, temperature and CNTs dosage. The synthesized hybrid catalysts exhibited excellent performance for PMS activation, compared with pure OMS-2, CNTs and other manganese oxides. Moreover, the catalysts presented a superior reusability during ten successive cycles. This study provides a simple method for the synthesis of OMS-2 catalysts at room temperature for wastewater remediation with high efficiency.
Section snippets
Chemicals
Multi-walled carbon nanotubes (CNTs) with diameters of 8–15 nm, lengths of about 50 μm and a purity of more than 95% were purchased from Nanjing Xianfeng Tech Co., Ltd. KMnO4, MnSO4, and HNO3 were purchased from Sinopharm Chemical Reagent Co.,Ltd. The oxidant potassium peroxymonosulfate (KHSO5, PMS), derived from the triple salt, Oxone (2KHSO5·KHSO4·K2SO4, containing 47% KHSO5), and 5,5-Dimethyl-1-pyrrolidine N-oxide (DMPO) were obtained from Aladdin Industrial Inc. Acid Orange 7 (AO7) was
Synthesis and characterization
The three catalysts, OCT, OMS-2, and MnOx were all prepared from the redox reaction between KMnO4 and MnSO4. When KMnO4 solution was well mixed with MnSO4 solution under acid conditions, an amorphous manganese oxide (AMO) phase will be formed [27]; but after ageing at the room temperature in the presence of CNTs, the AMO phase can be transformed to OMS-2. The formation of OMS-2 phase in OCT catalyst can be confirmed by XRD analysis with the results given in Fig. 1(A). It can be seen that the
Conclusions
In summary, the OCT hybrids have been successfully synthesized at room temperature from KMnO4, Mn2+ and CNTs. The redox reaction between MnOx and CNTs was the key step during the process. The synthesis conditions such as CNTs dosages, time and temperature also influenced the process significantly. The prepared OCT catalysts, with higher ratios of low valent manganese species, higher surface areas and more exposed active sites, exhibit superior catalytic performance for PMS activation to degrade
Acknowledgements
The authors gratefully acknowledge the financial support provided by Science and Technology Research Project of Hubei Provincial Department of Education (D20181706).
References (39)
- et al.
Chem. Eng. J.
(2017) - et al.
Chem. Eng. J.
(2013) - et al.
Water Res.
(2015) - et al.
Chem. Eng. J.
(2018) - et al.
Appl. Catal. B
(2018) - et al.
Chem. Eng. J.
(2016) - et al.
Chemosphere
(2018) - et al.
J. Colloid Interface Sci.
(2018) - et al.
Appl. Catal. B
(2016) - et al.
Appl. Catal. B
(2017)
Appl. Catal. B
Appl. Catal. B
Chemosphere
Chem. Eng. J.
Chem. Eng. J.
Appl. Catal. B
Appl. Catal. B
J. Hazard. Mater.
Appl. Catal. B
Cited by (27)
A review on mycelial pellets as biological carriers: Wastewater treatment and recovery for resource and energy
2022, Bioresource Technology