###### Abstract  
Synthetic dyes, dispersed in water, have harmful effects on human health and the environment. In this work, Ti and/or Zn oxide nanofibers (NFs) with engineered architecture and surface were produced via electrospinning followed by calcination. Calcination and subsequent cooling were operated at fast rates to generate porous NFs with capture centers to reduce the recombination rate of the photogenerated charges. After morphological and microstructural characterisation, the NFs were comparatively evaluated as photocatalysis for the removal of methylene blue from water under UV irradiation. The higher band gap and lower crystallinity were responsible for the lower photocatalytic activity of the ternary oxides (ZnTiO\({}_{3}\) and Zn\({}_{2}\)TiO\({}_{4}\)) towards the degradation of the dye. The optimal loads of the highly performing binary oxides were determined. By using 0.66 mg mL\({}^{-1}\) wurtzite ZnO for the discoloration of an aqueous solution with a dye concentration of 15 uM, a higher rate constant (7.94 \(\times\) 10\({}^{-2}\) min\({}^{-1}\)) than previously reported was obtained. The optimal load for anatase TiO\({}_{2}\) was lower (0.33 mg mL\({}^{-1}\)). The corresponding rate constant (1.12 \(\times\) 10\({}^{-1}\) min\({}^{-1}\)) exceeds the values reported for the commonly used P25-TiO\({}_{2}\) benchmark. The catalyst can be reused twice without any regeneration treatment, with 5.2% and 18.7% activity decrease after the second and third use, respectively. m 2021 11  
to the environment and constitutes a serious risk to human health [2; 3]. Dispersed in water, the dyes inhibit the transmission of light, which causes a reduction in the dissolved oxygen levels and rate of photosynthesis [4]; their ingestion has harmful effects such as gastrointestinal and urogenital diseases, irritation of the mucous membranes, dermatology, and alterations of the blood [5]. 3,7-Bis(dimethylamino)-phenothiazzin-5-ium chloride, better known as methylene blue (MB), is a broadly utilized dye in the textile industry [6]. Its use is also extended to the pharmaceutical, printing, cosmetics, leather, and food industries [7]. The presence of aromatic rings in its structure makes difficult its complete removal [8]. In the last decades, advanced oxidation processes, including both homogenous and heterogeneous catalysis, have been frequently employed to remove a wide range of inorganic and organic contaminants from water and wastewater [9; 10; 11]. Various semiconducting metal oxides have been successfully utilized as heterogeneous catalysts for the photodassisted degradation of dye pollutants [12; 13; 14; 15; 16; 17; 18; 19]. Among them, zinc oxide (ZnO) [20; 21; 22] and titanium dioxide (TiO\({}_{2}\)) [3; 23; 24] have received particular attention thanks to their non-toxicity, chemical stability, biocompatibility, and low-cost. Recently, the use of coupled ZnO-TiO\({}_{2}\) photocatalysts has been proposed for MB degradation under ultraviolet (UV) or visible (VIS) light irradiation [25; 26; 27; 28; 29; 30; 31]. [PERSON] et al. [30] have followed the hydrothermal route to prepare coupled ZnO-TiO\({}_{2}\) nanocomposites consisting of ZnO nanorods (NRs) decorated by TiO\({}_{2}\) nanoparticles (NPs). They show that, thanks to the favorable electron-transfer properties of the heterojunctions ZnO/TiO\({}_{2}\), the coupled ZnO-TiO\({}_{2}\) nanocomposites exhibit largely improved degradation performance with respect to both ZnO NRs and TiO\({}_{2}\) NPs. [PERSON] et al. [29] have produced ZnO-TiO\({}_{2}\) nanohybrids for sunlight-driven photodegradation of textile dyes and other pollutant molecules via the hydrothermal method. The superior photodegradation performance of the nanohybrids, consisting of ZnO nanoflakes functionalized with TiO\({}_{2}\) nanoparticles with one- (1D) or three-dimensional (3D) architecture depending on the Zn:Ti volume ratio, is attributed to the ZnO/TiO\({}_{2}\) synergy induced increased charge separation efficiency. [PERSON] et al.