X-ray photoelectron spectroscopy (XPS) is a non-destructive analytical technique in which x-rays bombard the surface of a material and the kinetic energy of the emitted electrons is measured. It is widely used to characterize the surfaces of various materials (inorganic compounds, organics, semiconductors, natural materials (lignocellulose) and synthetics (meso- and microporous ceramics). This technique analyzes the outer layer of materials (1 to 10 nm; 30 atomic layers) and allows the characterization of: 1) the chemical composition of material surfaces (element identification); 2) the relative abundance of these components on surfaces (semi-quantitative analysis) and; 3) the oxidation state of surface elements (precision depending on the quantity and complexity of the sample). All elements of the periodic table (Li to U) are detectable, with the exception of hydrogen and helium.