Department of Chemistry, Umeå University, Umeå SE-901 87, Sweden.
Phys Chem Chem Phys. 2023 Jul 5;25(26):17352-17359. doi: 10.1039/d3cp01209c.
Water films captured in the interlayer region of birnessite (MnO) nanosheets can play important roles in biogeochemical cycling, catalysis, energy storage, and even atmospheric water harvesting. Understanding the temperature-dependent loadings and properties of these interlayer films is crucial to comprehend birnessite reactivity when exposed to moist air and temperature gradients. Using vibrational spectroscopy we show that birnessite intercalates one water (1W) monolayer at up to ∼40 °C, but that loadings decrease by half at up to 85 °C. Our results also show that the vibrational properties of intercalated water are unaffected by temperature, implying that the hydrogen bonding network of water remains intact. Using molecular simulations, we found that the lowered water storage capacity at high temperatures cannot be explained by variations in hydrogen bond numbers or in the solvation environments of interlayer K ions initially present in the interlayer region. It can instead be explained by the compounded effects of larger evolved heat, as inferred from immersion energies, and by the larger temperature-driven mobility of water over that of K ions, which are electrostatically bound to birnessite basal oxygens. By shedding new light on the temperature-driven intercalation of water in a nanolayered mineral, this study can guide future efforts to understand the (geo)chemical reactivity of related materials in natural and technological settings.
水膜在锰矿纳米片中的夹层区域捕获，可以在生物地球化学循环、催化、储能甚至大气水收集等方面发挥重要作用。了解这些夹层膜的温度依赖性负载和性质对于理解暴露在潮湿空气和温度梯度下的锰矿的反应性至关重要。我们使用振动光谱表明，锰矿在高达约 40°C 的温度下可以嵌入一层水（1W）单层，但在高达 85°C 的温度下负载量减少一半。我们的结果还表明，嵌入水的振动特性不受温度影响，这意味着水的氢键网络保持完整。通过分子模拟，我们发现高温下水储存能力降低不能用氢键数量的变化或初始存在于夹层区域的层间 K 离子的溶剂化环境来解释。相反，这可以通过从浸出能量推断出的更大的演化热以及水相对于静电结合到锰矿基面氧的 K 离子的更大的温度驱动的迁移率的复合效应来解释。通过阐明纳米层状矿物中水分的温度驱动嵌入，本研究可以指导未来努力理解相关材料在自然和技术环境中的（地球）化学反应性。
