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Nanostructured Alkaline‐Cation‐Containing δ‐MnO2 for Photocatalytic Water Oxidation

“…It is evident that the K‐edges of Mn for all the K‐containing δ‐MnO 2 samples overlap the K‐edge of bulk MnO 2 , indicating that the K‐δ‐MnO 2 samples have an average Mn oxidation state of 4+. Although it is expected that the insertion of alkaline cations into MnO 2 channels decreases the oxidation state of Mn due to the charge balance, the phenomenon observed in the K‐ containing δ‐MnO 2 samples could be explained as the formation of oxygen‐rich manganese oxide phases, which has also been reported in previous literature 46–48. For the proton version of nanostructured δ‐MnO 2 , the XANES curves (Figure 4b) closely match the data for their potassium‐version counterparts, suggesting that the proton‐exchange process did not affect the oxidation state of Mn in both nanostructures.…”

“…Further studies have been done to clarify the role of potassium in the photocatalytic oxygen‐evolution reaction. We synthesized Na‐containing δ‐MnO 2 nanosheets through a solution‐chemistry approach 47. The SEM image ( Figure a) shows that as‐prepared Na‐containing δ‐MnO 2 had a nanosheet morphology, similar to the K‐containing δ‐MnO 2 sample.…”

“…Synthesis of Na‐δ‐MnO 2‐ Nanosheets : In a typical synthesis of Na‐δ‐MnO 2 nanosheets (with Na), 100 mL of Mn(NO 3 ) 2 aqueous solution (containing 3 mmol of Mn) was slowly added into a mixture of 180 mL of NaOH aqueous solution (containing 6.88 g of NaOH) and 20 mL of 30% H 2 O 2 under stirring. After stirring at room temperature for 1 h, the resulting precipitate was centrifuged and washed with water, then dried at 60 °C 47…”

A Core–Corona Hierarchical Manganese Oxide and its Formation by an Aqueous Soft Chemistry Mechanism

“…In this context, porous manganese oxide materials are attracting great interest due to their applicability in domains such as ion‐exchange,5a catalysis,5b and energy storage in Li batteries and supercapacitors 5c,d. Indeed, layered birnessite‐like manganese oxides (LMO) are particularly relevant due to their lamellar structure, which contain layers of MnO 6 octahedra between which different species can be intercalated (see Figure S1 in the Supporting Information) 5a,b. However, the design of ordered LMO architectures remains a significant challenge6, 7 as their synthesis usually takes place in an aqueous medium by sol–gel or precipitation methods,6, 7 both of which result in fast and uncontrolled solid growth that hinders the synthesis of well‐ordered nanostructures.…”

Efficient Electrochemical Water Oxidation and Oxidative Degradation of Rhodamine B: A Comparative Study Using High‐Purity Birnessites Containing Li+, Na+ or K+ Ions

“…Alkali metal ions play critical roles in balancing charge, which are indispensable to the formation of birnessite. Birnessite containing only Na + in the layered structure has been prepared, with only a few studies on the fabrication of birnessite with Na + , K + and Li + ,, where high reaction and long reaction time were required for yieldig impure products. By tuning alkali metal ions of layered structure can reveal how ions in a layered material affect its water oxidation activities.…”