NMR FOR ENVIRONMENTAL SCIENCES: SELECTED APPLICATIONS

Climate change and sustainable land use are among the most pressing environmental problems that modern society is facing, and to which other important issues, such as renewable energy and waste management, are directly related. These problems mainly involve environmental matrices, such as air particulate, soil, ocean sediments, and water dissolved matter, and, in order to be able to face them, a deep understanding of the chemistry and the key processes that take place in such matrices is required. Given the complexity of these systems, where different components (organic matter, sand, clay, minerals, roots, microbes, etc.) and different phases (solid, soft and liquid) coexist, NMR is often the only tool that can provide information on the molecular-level framework that underlies the problem. Furthermore, thanks to the combined application of solution and solid state techniques and the use of different types of pulse sequences, NMR allows environmental samples in a relatively unaltered state to be studied. This is extremely important since the structure, morphology and physical arrangement of the investigated material in part determines its environmental reactivity. Selected examples of the application of NMR in two different fields of environmental sciences, taken from the experience of the Magnetic Resonance Laboratory (MarsLab) at ICCOM-CNR, will be shown. The first one concerns the application of 13C solid state NMR for the investigation of soil quality in relation to land management practices. Organic carbon is one of the indicators of soil quality and NMR gives a detailed indication of the speciation and reactivity of carbon in soils. The former is fundamental to evaluate the degree of humification and to assess the effects of agricultural practices or other anthropic activities on soils; the latter is of great relevance since transformations of soil organic matter directly influence the production of greenhouse gases, with consequences on climate. The second example is the application of solid state NMR techniques to investigate the structure of biochars obtained from the carbonization of biomass through different types of thermochemical processes. Biochar is gaining much interest because it has a higher energy content than the biomass it is obtained from, and because, if used in soils, it contributes to reduce greenhouse gas emissions thanks to its long-term stability. Furthermore, biochar can be efficiently used for soil amendment thanks to its porosity, which can be studied by means of 1H NMR relaxometry, a technique that also gives insight into the interaction of biochar with water.