## 3 Results
### Characterization of the Materials
#### 3.1.4 X-ray Photoelectron Spectroscopy  
XPS measurements were carried out to study the superficial chemical composition of the samples. Figure 4a shows C 1s spectra for LAC and composite samples.  
Considering C 1s signal, Ti and LAC samples show three contributions at ca. 284.8, 286.5, and 288.5 eV. The main contribution is located at 284.8 eV and assigned to C-C bonds in graphitic carbon and also from the adventitious carbon contamination layer. The other two contributions are due to alcoholic (C-O-H) and carbonyl C=O groups, respectively [41]. Moreover, the LAC sample shows another small contribution at 289.1 eV associated to ester (O-C=O) and CO\({}_{3}\)\({}^{2-}\) groups.  
In the case of samples containing both titania and LAC, a new contribution at ca. 283.7 eV appeared. This new contribution is due to the presence of two phases with different conductivity, that is LAC and titania, and is also due to adventitious carbon.  
Figure 2: Scanning electron microscopy images for (**a**) raw Luffa, (**b**) LAC (**c**) TiLAC-7/3 and (**d**) TiLAC-9/1 (with high vacuum mode (pressure range 10\({}^{-2}\)–10\({}^{-4}\) Pa), imaging resolution of 1.0 nm for ‘a’ and ‘b’ and 0.8 for ‘c’ and ‘d’ at 10 kV, mode secondary electron image SE, integrated monochromator (UC) and beam deceleration mode. ETD detectors).  
Figure 4: Core level spectra for all samples of (**a**) C 1\({}_{s}\), (**b**) Ti 2\(p\), (**c**) O 1\(s\) and (**d**) P 2\(p\).  
Figure 3: X-ray diffractograms of (a) LAC, (b) Ti, (c) TiLAC-7/3 and (d) TiLAC-9/1.  
Ti 2\(p\) core-level spectra for all samples presented two contributions associated with the doublet Ti 2\(p_{1/2}\) y Ti 2\(p_{3/2}\), being the latter the most noticeable one at ca. 458.8 eV, which corroborates the presence of Ti\({}^{4+}\) octahedrally coordinated (see Figure 4b) [42].  
Concerning the O 1\(s\) core-level spectra (Figure 4c), differences between pure samples and composites become more evident. Table 2 includes the corresponding binding energy values. LAC signal presents a major contribution at 533.6 eV, which can be associated with organic C-O bonds in phenolic groups. In addition, a second contribution at lower binding energy, ca. 531.5 eV is present, attributable to carboxylate species. On the other hand, in the pure P25 sample, two signals are observed, one associated with oxygen in the lattice of TiO\({}_{2}\) (529.3 eV) and a second one at 532.1 eV, assigned to surface Ti-O-H groups. In the case of composites, signals associated to lattice oxygen in TiO\({}_{2}\) and LAC are present.  
Due to the low presence of phosphorus on the surface, P 2\(p\) spectra are quite noisy (Figure 4d). Nonetheless, a contribution located at 133.6 eV associated to pentavalent tetra-coordinated phosphorus (PO\({}_{4}\)), as in phosphate and/or polyphosphate compounds as C-O-PO\({}_{3}\), is noticeable, which suggests that P atom is bonded to four oxygen atoms by one double bond and three single bonds, indicating that the P atom in Luffa activated carbon (LAC) is mainly present on the carbon surface by bonding to O atoms resulting from the phosphoric acid (polyphosphate) remaining after the washing step [43; 44; 45].  
The atomic surface composition obtained from XPS spectra is displayed in Table 3. It can be seen that the atomic composition depends on the content of each material in the sample. A small content of phosphorus has been detected for TiLAC, which can be associated to some traces left behind during the preparation of the LAC activated carbon.