## 1 Introduction  
Since the first reports on the photoelectrolytic water splitting of titanium dioxide (TiO\({}_{2}\)) by [PERSON] and [PERSON] in 1972, photocatalysis has been recognized as an effective technique for the degradation of water contaminants over the past decades [1, 2]. Among the semiconductors for photocatalysis, TiO\({}_{2}\)-based nanomaterials are most widely used because of their high efficiency, low cost, mechanical robustness, chemical stability, and non-corrosive property [3, 4]. However, the wide-band-gap energy (3.2 eV) that is only photoactive under ultraviolet (UV) light (\(\lambda<\) 366 nm) and the relatively high recombination rate of electron-hole pairs restrict the photocatalytic activity of TiO\({}_{2}\)[5].  
Visible-light-response photocatalysts provide a popular way to solve environmental problems by directly harvesting energy from sunlight [6]. In this regard, much effort has been made to extend the photo-response region of TiO\({}_{2}\) to visible light and to increase its photocatalytic efficiency under UV and visible-light irradiation by surface modification, such as metal loading, impurity doping, inorganic adsorbates, polymer coating, dye sensitization, and charge-transfer complexation [7].  
Among the surface modification methods for oxide-based semiconductors, conducting polymers have attracted much attention owing to their high conductivity and stability, simple synthesis, and excellent environmental compatibility [8]. With an extended \(\pi\)-conjugated electron system, the conducting polymer acts as a stable photosensitizer to sensitize TiO\({}_{2}\) by the absorption of a wide spectrum of UV and visible-light (190-800 nm) irradiation [5]. TiO\({}_{2}\) modified with conducting polymers, such as polyaniline (PANI), polypyrrole, and polythiophene, has demonstrated excellent photocatalytic activity for the degradation of contaminants under visible-light irradiation [5; 9; 10].  
Especially, PANI has been widely used as a conducting polymer in semiconductor modification because of its high stability, low cost, and easy polymerization [11]. In addition, it has also been regarded as a promising material to overcome the inherent drawbacks of TiO\({}_{2}\) by facilitating charge (electron-hole) transport due to its well-matched energy level. TiO\({}_{2}\) is a typical n-type semiconductor, whereas PANI is generally considered a p-type semiconductor [5]. Thus, their strategic combination provides excellent stability and conductivity, as well as enhanced photocatalytic performance. There are several reports on the manufacture, properties, and applications of PANI/TiO\({}_{2}\) composite for photocatalytic degradation of water contaminants [5; 12; 13].  
Here, we demonstrate the enhanced photocatalytic efficiency of PANI/TiO\({}_{2}\) composite under visible-light irradiation for degradation of water contaminants (methylene blue (MB), bisphenol A (BPA), and bacteriophage MS2). The PANI/TiO\({}_{2}\) composites were prepared using different PANI to TiO\({}_{2}\) weight ratios, and their performance was evaluated by photocatalytic dye degradation experiments. The properties of the prepared samples were analyzed. The applicability and reusability of PANI/TiO\({}_{2}\) composites were also evaluated.