## 3 Results and Discussion  
### Characterization of Volcanic Glass  
The elemental bulk composition of volcanic glass evaluated from X-ray Fluorescence Spectrometer (XRFS) analysis shows how this material is mainly composed and Si and Al, with small proportions of K, Fe, Ni, Ca, and Na. Previous research has pointed out that the viscosity of volcanic glass is directly related to the SiO\({}_{2}\) content [21]. Thus, volcanic glass with low SiO\({}_{2}\) content (\(<\)50%) is less viscous than glass with SiO\({}_{2}\) content above 65%. Considering the SiO\({}_{2}\) concentration shown in Table 1, the Cuban volcanic glass must display low fluency and high viscosity, probably due to slow cooling [21]. The textural parameters of volcanic glass were determined from N\({}_{2}\) adsorption-desorption at 77 K (Figure 1). According to the International Union of Pure and Applied Chemistry (IUPAC) classification, the adsorption isotherm can be adjusted to type II [41], which is typical of nonporous or macroporous materials. Nonetheless, the N\({}_{2}\) adsorbed at lower relative pressure indicates that this volcanic glass also displays slight microporosity. The hysteresis loop can be considered as type H3, which is given by nonrigid aggregates of platelike particles (e.g., certain clays), but also if the pore network consists of macropores that are not completely filled with pore condensate [41]. The specific surface area, estimated by the Brunauer-Emmett-Teller equation [39], determined a low specific surface area (51 m\({}^{2}\)/g), with a pore volume of 0.083 cm\({}^{3}\)/g. After Cu exchange, the specific surface area was lower (19 m\({}^{2}\)/g). Considering the low specific surface area and the macroporosity, the N\({}_{2}\) adsorbed must be attributed to the fillings between adjacent particles. According to the data of raw volcanic glass reported previously [20], XRD of volcanic glass hardly displays defined diffraction peaks. A broad band can be observed at 20 = 20-30\({}^{o}\) which is attributed to the amorphous structure of volcanic glass. In addition, the existence of a pseudo-amorphous phase of aluminosilicate and Ca\({}_{3}\)SiO\({}_{5}\) species, which shows higher crystallinity, is noteworthy. As indicated previously [20], the FTIR spectrum of volcanic glass displays a broad signal between 3000 and 3700 cm\({}^{-1}\), which corresponds to -OH groups. Thus, the band located at 3620 cm\({}^{-1}\) is assigned to structural OH-stretching, and those at 3420 cm\({}^{-1}\) and 1640 cm\({}^{-1}\) correspond to OH stretching and bending vibrational bands of adsorbed water [42]. After Cu incorporation, the broad signal remains, but the contribution located at 3620 cm\({}^{-1}\) decreases in intensity, indicating that Cu interacts with OH groups. On the low wavelength side, Si-O stretching bands are located at 1148 cm\({}^{-1}\), 991 cm\({}^{-1}\), and 804 cm\({}^{-1}\)[43; 44]. The band at 908 cm\({}^{-1}\) corresponds to the bending mode of Al-OH [43]. Raw volcanic glass also displays a weak shoulder band centered at \(\sim\)1425 cm\({}^{-1}\) and attributed to CO\({}_{3}\)\({}^{-2}\) species, which must interact with the Ca\({}^{2+}\) and Mg\({}^{2+}\) species [45], reported in Table 1.  
In order to evaluate the chemical composition of the surface of volcanic glass, X-ray Photoelectron Spectroscopy (XPS) analysis was performed for the raw material (Table 2). Similar to the elemental bulk composition (Table 1), Si and Al are the main elements in volcanic glass. In addition, the presence of other elements is noted, such as Mg and Ca, which can partially replace Al\({}^{3+}\) sites by other Mg\({}^{2+}\) ones, as well as carbonates and hydroxides, confirmed from the C 1s core level spectrum. The small