Hydroxyl groups are the cornerstone species driving catalytic reactions on mineral nanoparticles of Earth’s crust, water, and atmosphere. Here we directly identify populations of these groups on ferrihydrite, a key yet misunderstood iron oxyhydroxide nanomineral in natural sciences. This is achieved by resolving an enigmatic set of vibrational spectroscopic signatures of reactive hydroxo groups and chemisorbed water molecules embedded in specific chemical environments. We assist these findings by exploring a vast array of configurations of computer-generated nanoparticles. We find that these groups are mainly disposed along rows at edges of sheets of iron octahedra. Molecular dynamics of nanoparticles as large as 10 nm show that the most reactive surface hydroxo groups are predominantly free, yet are hydrogen bond acceptors in an intricate network formed with less reactive groups. The resolved vibrational spectroscopic signatures open new possibilities for tracking catalytic reactions on ferrihydrite, directly from the unique viewpoint of its reactive hydroxyl groups.

羟基是驱动地壳、水和大气的矿物纳米粒子催化反应的基石。在这里，我们直接在水铁矿上识别这些群体的种群，水铁矿是自然科学中一种关键但被误解的羟基氧化铁纳米矿物。这是通过解析特定化学环境中反应性羟基和化学吸附水分子的一组神秘的振动光谱特征来实现的。我们通过探索大量计算机生成的纳米粒子的配置来协助这些发现。我们发现这些基团主要沿着铁八面体片边缘的行排列。大至 10 nm 的纳米颗粒的分子动力学表明，最具反应性的表面羟基主要是游离的，但在由反应性较低的基团形成的复杂网络中是氢键受体。解析的振动光谱特征为直接从反应性羟基的独特角度追踪水铁矿催化反应开辟了新的可能性。