###### Abstract
[28] have reported about electrospun ZnO/TiO\({}_{2}\) composites nanofibers (NFs) endowed with enhanced photocatalytic activity with respect to both single-metal oxide NFs. [PERSON] et al. [31] have synthesized coaxial ZnO/TiO\({}_{2}\) core/shell NFs needing less energy to be activated and showing better photocatalytic activity for the degradation of MB than ZnO, TiO\({}_{2}\) or blending ZnO-TiO\({}_{2}\) NFs. [PERSON] et al. [26] have prepared composite Ti/Zn-based NFs, containing ZnO, TiO\({}_{2}\), Ti\({}_{2}\)O\({}_{3}\), and ZnTiO\({}_{3}\) oxides, with improved photocatalytic performance compared to TiO\({}_{2}\). Upon irradiation with photons having sufficient energy, electrons (\(e^{-}\)) on the surface of the photocatalyst are excited to the conduction band (CB) and holes (\(h^{+}\)) are generated in the valence band (VB). The \(e^{-}\)-\(h^{+}\) pairs can either recombine and produce thermal energy or react with adsorbed water, oxygen, and organic species via oxidation and reduction reactions [21; 23; 32; 33; 34]. As sketched in Figure S1, the trapping of \(e^{-}\) by oxygen molecules gives rise to superoxide radicals (O\({}_{2}\)*); the reaction of \(h^{+}\) with the chemisorbed water molecules leads to the formation of hydroxyl groups (OH\({}^{-}\)) or hydroxyl radicals (OH\({}^{\bullet}\)) and maintains electrical neutrality within the catalyst [23; 32]. The dye degradation and complete oxidation in non-toxic organic products can occur through (\(i\)) direct and (\(ii\)) indirect oxidation via the reaction with \(h^{+}\) and OH\({}^{\bullet}\) radicals, respectively [32; 33; 35]. Lattice defects (such as vacancies and/or interstitials) that introduce trap states in the band gap [36] strongly affect the recombination rate of the photogenerated \(e^{-}\)-\(h^{+}\) pairs and, hence, the catalyst activity toward the dye molecule degradation [20; 21]. Introducing \(e^{-}\)-capture centers, through doping [34] or surface engineering [20; 21], to reduce the probability of the \(e^{-}\)-\(h^{+}\) recombination, has been shown to be a viable strategy to enhance the photocatalytic efficiency of ZnO. Moreover, morphology and specific surface area have a great influence [20]. Electrospinning (ES) is a simple and cost-effective technique widely utilized for the growth of high aspect-ratio and surface-area (organic, inorganic, and hybrid) nanostructures with different morphologies [37; 38; 39] used in a great variety of applications ranging from energy conversion and storage, to biomedicine, gas sensing, and water remediation [37; 40; 41; 42; 43]. ES scalability and the availability of commercial machineries capable of producing fibrous sheets of up to 300-600 m\({}^{2}\) in size make it a suitable technique for the production of NF catalysts on an industrial scale. This work deals with binary (Ti or Zn) or ternary (Ti and Zn) oxide NFs and the comparative evaluation of their photocatalytic activity towards the degradation of MB in an aqueous solution. In order to produce porous NFs and generate capture centers located at the boundaries between the oxide grains constituting them, calcination and subsequent cooling were operated at fast rates. The critical features of the produced NFs were investigated to find out if the conclusions previously drawn on the key role of defects in the design of ZnO photocatalyst have more general validity. The optimal loads of the best performing NFs were determined to maximize the efficiency of the photocatalytic process, which is a fundamental recipe for its industrial use. Moreover, the photocatalyst reusability was investigated.