The capabilities of temperature-monitored IR spectroscopy for studying the organic matter and mineral composition of humic substances (HS) were tested. Temperature dependences of the mid-IR spectra of humic substances heated in the air in the range 25–215 °C (298–488 K, with a step of 2.5 °C)—for three commercially available samples isolated from brown coal (leonardite)—were performed. The characteristic bands were identified, and their changes in band maxima positions and intensities were compared. From the viewpoint of interpretation of HS components, the spectra were divided into regions of quartz lattice region (800–260 cm⁻¹), quartz overtone region (1270–800 cm⁻¹), humic substance organic matter region (1780–1270 cm⁻¹), quartz combination region (2800–1780 cm⁻¹), CH-speciation region (3100–2800 cm⁻¹), and hydrogen-speciation region (4000–3100 cm⁻¹) thus selected to contain the dominating type of bands. For the first time, a reversible change in the frequencies of the band maxima in IR spectra upon heating was observed, which can be interpreted as forming structures with a particular order in the studied humic substances in the dry state. For a single sample, both the band-shift scale and the functional dependence of the various bands on temperature differ significantly. The approach differentiates crystalline quartz bands, amorphous silica, and HSOM/surface groups experiencing a different temperature behavior of the band maxima and their intensities. Band-maximum temperature dependence can be considered more stable to changes in experimental conditions than band maxima at a single temperature, thus providing a more detailed HS structure analysis without HS decomposition or destruction.

中文翻译：

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褐煤腐殖质红外光谱的温度依赖性

测试了温度监测红外光谱在研究腐殖质 (HS) 有机质和矿物成分方面的能力。在 25–215 °C（298–488 K，步长为 2.5 °C）范围内在空气中加热的腐殖质的中红外光谱的温度依赖性——对于从褐煤（风化褐煤）中分离的三个市售样品——进行了。识别特征带，并比较它们在带最大值位置和强度方面的变化。从HS成分的解释来看，光谱分为石英晶格区（800-260 cm ^-1）、石英泛音区（1270-800 cm ^-1）、腐殖质有机质区（1780-1270 cm ^-1）⁻¹)、石英组合区 (2800–1780 cm ^-1 )、CH 形态区 (3100–2800 cm ^-1 ) 和氢形态区 (4000–3100 cm ^-1) 因此选择包含主导类型的波段。首次观察到加热后红外光谱中频带最大值的频率发生可逆变化，这可以解释为所研究的腐殖质在干燥状态下形成具有特定顺序的结构。对于单个样品，带移尺度和各种带对温度的函数依赖性都有显着差异。该方法区分了结晶石英带、无定形二氧化硅和 HSOM/表面组，它们经历了带最大值及其强度的不同温度行为。可以认为带最大温度依赖性比单一温度下的带最大值对实验条件的变化更稳定，从而提供更详细的 HS 结构分析，而不会 HS 分解或破坏。