# Enhancing the Photocatalytic Activity of Immobilized TiO2 Using Laser-Micropatterned Surfaces
## 4 Conclusions  
The sol-gel process was employed to create thin TiO\({}_{2}\) films in the anatase phase, which were spin-cast onto laser-microstructured silicon substrates, resulting in the formation of improved photocatalytic surfaces. To evaluate the photocatalytic efficacy of these surfaces, the degradation of atrazine in aqueous solution (environmentally relevant low concentration) under UV irradiation was measured. The TiO\({}_{2}\) films were thoroughly characterized using XRD, SEM-EDX, UV-Vis spectroscopy and Raman spectroscopy. They exhibited significantly enhanced photocatalytic activity when cast on laser-microstructured silicon. The photocatalytic activity of these materials was observed to undergo significant enhancement on laser-microstructured silicon (average \(k_{\rm obs}\) 24.1 \(\times\) 10\({}^{-3}\) min\({}^{-1}\)) in contrast to flat silicon (average \(k_{\rm obs}\) 4.9 \(\times\) 10\({}^{-3}\) min\({}^{-1}\)). This enhancement brought their performance close to that of sol-gel TiO\({}_{2}\) fortified with Degussa P25, utilized as a reference material (\(k_{\rm obs}\) 32.7 \(\times\) 10\({}^{-3}\) min\({}^{-1}\)). Unlike pure TiO\({}_{2}\) films, the composite TiO\({}_{2}\) + Degussa films did not demonstrate enhanced photocatalytic activity when cast on microstrucured silicon substrates. SEM-EDX analysis showed this is due to the lack of conformal coating of the microstructured substrate by these films. The high sensitivity of the photocatalytic measuring device allowed us to discern between different substrate micromorphologies, revealing more efficient photocatalytic activity for TiO\({}_{2}\) films on silicon microcones, compared with silicon microripples. During the photocatalytic process, several TPs of atrazine, namely 2-chloro-4-(isopropylamino)-6-amino-s-triazine (CIAT), 2-chloro-4-amino-6-(ethylamino)-s-triazine (CAET), and 2-chloro-4.6-diamino-s-triazine (CAAT), were identified with LC-MS/MS. The stability of the photocatalytic surfaces was studied through multiple usage cycles, revealing that their activity remained consistent. SEM microscopy on these surfaces after photocatalysis experiments demonstrated that their morphology remains unchanged. The photocatalytic activity of TiO\({}_{2}\) films on laser-microstructured silicon was also evaluated for two other pollutants, i.e., 2,4,6-trichlorophenol and bisphenol-a (a frequent water pollutant and an endocrine disruptor, respectively), showing equally promising results with atrazine, demonstrating the wide application potential of these surfaces. These results, in combination with the immobilized state of the photocatalyst, leading to the elimination of expensive and time-consuming filtration post-processes, constitute an attractive photocatalytic system for efficient and affordable water treatment. The following supporting information can be downloaded at: [[https://www.mdpi.com/article/10.3390/app14073033/s1](https://www.mdpi.com/article/10.3390/app14073033/s1)]([https://www.mdpi.com/article/10.3390/app14073033/s1](https://www.mdpi.com/article/10.3390/app14073033/s1)). Conceptualization, T.M.T., C.C., G.M., A.H. and M.K. ; Data Curation, T.G., S.-K.Z., T.M.T., P.K., G.M., A.H. and M.K. ; Formal Analysis, T.G., S.-K.Z. and T.M.T. ; Methodology, T.G., S.-K.Z., T.M.T., S.V.S., G.M., A.H. and M.K. ; Project Administration, T.M.T., C.C., A.H. and M.K. ; Resources, T.M.T., C.C. and G.M. ; Supervision, T.M.T., G.M., A.H. and M.K. ; Visualization, T.G. and S.-K.Z. ; Writing--Original Draft, T.G., S.-K.Z., T.M.T., C.C., E.B., G.M., A.H. and M.K. ; Writing--Review and Editing, C.C., E.B., A.H. and M.K. All authors have read and agreed to the published version of the manuscript.