## 3 Results
### Methylene Blue Removal by Adsorption and Photocatalytic Degradation  
The prepared TiLAC composites have been tested in the methylene blue dye (MB) photodegradation under UV light irradiation in an aqueous solution. The MB removal from the solution is likely due to a combined adsorption and photodegradation process. Figure 7a shows the variation of C/C\({}_{0}\) versus time in the experiment that includes a previous step of 30 minutes in darkness. During this dark step, LAC sample showed a high adsorption capacity of MB, which was expected according to its developed porosity, while the pure titania sample, Ti, showed moderate adsorption, of ca. 10% of the MB initial concentration. However, the TiLAC composites showed much higher MB adsorption than pure Ti, 45% and 74% for TiLAC-9/1 and TiLAC-7/3, respectively, which are in agreement with the higher adsorption capacity of the activated carbon (see Table 1). Under UV-irradiation, the MB removal by the Ti sample reached 94% after 2 h. In contrast, using the TiLAC samples, the MB removal is faster and the total disappearance of the dye from solution occurs within a maximum of 40 min or 60 min, depending on the TiLAC sample (Figure 7a). It must be considered that, in this case, the dye removal is the result of a combination of adsorption and photodegradation processes. A high concentration of MB is assumed to occur in the interphase Ti-LAC for the composite materials through adsorption, in contrast to what happens on Ti's surface, the adsorbed MB can then be photo-oxidized, leading simultaneously to LAC regeneration. This enhancement of the dye removal is in accordance with the LAC content in each sample, as the removal is faster for sample TiLAC-7/3 compared to TiLAC-9/1 and pure titania Ti, respectively. These results are in good agreement with those reported in the literature for methylene blue photocatalytic degradation where similar results using a carbonaceous TiO\({}_{2}\) composite material were obtained [16; 46; 52]. The UV-vis diffuse reflectance analysis shows that the bandgap of the prepared composites is lower than that of titania, which is attributed to the narrowing effect of the addition of LAC, which means an extension of the absorption of TiO\({}_{2}\) to the visible light range [53]. Thus, the prepared _AdsCats_ could be photoactive in the visible light region. According to the results obtained when the UV lamp is switched on without the previous 30 minutes in darkness (Figure 7b), it is assumed that MB removal takes place by simultaneous adsorption and photocatalytic processes. The cationic dye is adsorbed from solution on the LAC porosity and then it reacts with the photoactive sites generated through the excitation of the irradiated titania's nanoparticles, resulting in the total dye elimination after 40 to 60 min UV-irradiation. There are no significant differences between the performance of the catalysts in the two tested scenarios. Thus, the second one, skipping  
Figure 6: (a) UV-visible diffuse reflectance spectra and (b) energy band-gap vs (aho)\({}^{1/2}\) of Ti; TiLAC-7/3 and TiLAC-9/1. the adsorption equilibrium step, is more efficient for direct MB removal from the point of view of saving time and energy. Figure 8 shows the experimental MB removal curves obtained for each composite and for its individual components (in the amount in which they are present in the composite) and the calculated MB removal by the composite considering the sum of the contribution of each component. These data suggest a synergetic effect between TiO\({}_{2}\) particles and LAC and, in this sense, the \"excess\" MB experimental removal with respect to the theoretical one would be related to photodegradation enhanced by the presence of LAC. These results are consistent with the constant rates obtained from the kinetics modeling (Table 4), showing that the photodegradation of methylene blue by all the studied composites follows the first-order kinetics.