## 3 Results
### Intermediate Products and Degradation Mechanism  
The intermediate products of DCF (10 mg/L) in aqueous solution under EB irradiation and EB irradiation after nanobubbling in a flow system were analyzed using LC-MS (Table 2). As an example, Figure 12 represents the chromatogram of a DCF solution after EB irradiation and nanobubbling in a flow system, recorded at 280 nm. DCF and its radiolytic by-products gave strong mass spectrometric signals under positive ionization conditions; thus, the measurements were performed mainly in this mode, where DCF generated a peak at \(m/z\) 296 ([DCF + H]\({}^{+}\)). In comparison with the non-irradiated solution, the peak area of DCF indicated a considerable decrease after both treatments, meaning that degradation of the compound was taking place and corroborated the results presented in Figure 2 with a decomposition of 99% at 0.5 kGy. At the same time, other peaks appeared, and they could be attributed to decomposition products of DCF (Figure 12). For the solutions treated by EB radiation and EB irradiation after nanobubbling in flow system, five peaks were positively identified, with two similar products (P1 and P5, and P3, P4 and P*) (Table 2). P3, P4 and P* ([C\({}_{14}\)H\({}_{11}\)C\({}_{2}\)NO\({}_{3}\) + H]\({}^{+}\) at \(m/z\) 312) were the products formed from the addition reaction of \({}^{\bullet}\)OH radicals to the aromatic ring of DCF, followed by H atom abstraction from H-C bonds. The specificity of electrophilic aromatic substitution is normally governed by the nature of the substituent. In this context, the amino group is a strong donating group and acts as the ortho-para director, which makes it possible for a hydroxyl radical to be added at two positions of the aromatic ring [39], as can be seen for Nano + EB (Table 2, P3 and P4). These products were also observed in previous studies [18; 20; 39]. P# ([C\({}_{5}\)H\({}_{9}\)O\({}_{2}\)N + H]\({}^{+}\) at \(m/z\) 152), P5 ([C\({}_{9}\)H\({}_{11}\)N + H]\({}^{+}\) at \(m/z\) 134) and P' ([C\({}_{7}\)H\({}_{7}\)N + H]\({}^{+}\) at \(m/z\) 106) could be related to C-N bond cleavage, maintaining a nitrogen-containing group on the aromatic moiety [22; 39]. P' ([C\({}_{6}\)H\({}_{4}\)ClN + H]\({}^{+}\) at \(m/z\) 126) was not previously detected as a DCF by-product but can be described as a declonization product of DCF. P2 ([C\({}_{14}\)H\({}_{10}\)C\({}_{12}\) + H]\({}^{+}\) at \(m/z\) 260) and P5 ([C\({}_{14}\)H\({}_{9}\)Cl\({}_{2}\)NO\({}_{2}\) + H]\({}^{+}\) at \(m/z\) 294) were only observed as degradation products of DCF when using EB irradiation after nanobubbling  
Figure 11: Chemical oxygen demand (COD) of DCF aqueous solutions under electron-beam radiation (EB) and EB with nanobubbling (Nano + EB) pretreatment processes in batch and flow systems ([DCF]\({}_{0}\) = 125 mg/L). in the flow system. P2 seemed to result from the dechlorination-cyclization of DCF [39], as was also reported by [PERSON] et al. [10] using UV-activated peroxymonosulfate. P5 could be generated by the possible cyclization of P3/P4 with the loss of H\({}_{2}\)O, as described by [PERSON] et al. [16] for the degradation of DCF under a photo-Fenton treatment. Taking into consideration the previous results and the identification of radiolytic by-products of DCF, its degradation mechanism under EB irradiation after the nanobubbling process was proposed (Figure 13).