Platinum–nitrogen-codoped TiO₂ (Pt–N–TiO₂) was prepared by a conventional sol–gel process via the addition of different acid catalysts: nitric acid (HNO₃), acetic acid (HAc) and both (HNO₃–HAc). The Pt–N–TiO₂ samples were then characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy and UV–visible diffuse reflectance analysis. The samples successfully exhibited visible-light-induced photocatalysis for the degradation of dichloroacetate (DCA) and 4-chlorophenol (4-CP). The HAc/450 sample (following the notation “added acid catalyst/calcination temperature”) exhibited the highest visible activity for DCA degradation. This finding can be explained by the much stronger visible absorption of the calcined samples than the uncalcined samples and the slightly larger surface area of HAc/450 compared to other calcined TiO₂ samples. However, the performance of 4-CP degradation was proportional to the Pt–N–TiO₂ sample surface area regardless of visible absorption, which could be ascribed to the fact that 4-CP degradation can occur through a surface-complex-mediated pathway under visible irradiation.