Adsorption of dissolved organic matter on clay minerals as assessed by infra-red,CPMAS 13C NMR spectroscopy and low field T1 NMR relaxometry

Dissolved organic matter (DOM) is a very important environmental constituent due to its role in controllingfactors for soil formation, mineral weathering and pollutant transport in the environment. Predictionof DOM physical–chemical properties is achieved by studying its chemical structure and spatial conformation.In the present study, dissolved organic matter extracted from compost obtained from the organicfraction of urban wastes (DOM-P) has been analysed by FT-IR, CPMAS 13C NMR spectroscopy and 1H T1NMR relaxometry with fast field cycling (FFC) setup. While the first two spectroscopic techniquesrevealed the chemical changes of dissolved organic matter after adsorption either on kaolinite (DOMK)or montmorillonite (DOM-S), the latter permitted the evaluation of the conformational variations asassessed by longitudinal relaxation time (T1) distribution at the fixed magnetic field of 500 mT. Alterationsof T1 distributions from DOM-P to DOM-K and DOM-S were attributed to a decreasing molecularcomplexity following DOM-P adsorption on the clay minerals. This study applied for the first time solidstate 1H T1 NMR relaxometry to dissolved organic matter from compost obtained from the organic fractionof urban wastes and revealed that this technique is very promising for studying environmentally relevantnatural organic systems.