<p>This article presents the development of an efficient visible-light active Carbon-modified nanosized TiO₂ (C-TiO₂) photocatalyst for environmental remediation. The C-TiO₂ nanoparticles are synthesized by a facile single-step low-temperature (150–250 °C) hydrothermal (HT) route without additives. The absorption edge of nanosized TiO₂ is shifted into the visible region by incorporating carbon into the titania matrix solely from the titania precursor and solvent. X-ray diffraction (XRD) and Raman spectroscopy studies establish that the catalyst is the more photoactive anatase phase of titania. Raman spectroscopic analyses of the samples provide valuable insights into the structural details. The morphology of the materials is observed by Transmission and Scanning electron microscopy (TEM &amp; SEM). The presence and percentage of carbon incorporated into the titania matrix are confirmed and quantified by elemental analysis as ~ 1% irrespective of the synthesis conditions. The carbon impurity in the titania matrix resulted in a red shift in the optical band gap (430–455&#xa0;nm i.e. 2.9–2.7&#xa0;eV) for the synthesized samples estimated from the shift in the absorption edge in Ultraviolet diffuse reflectance spectroscopy (UV-DRS). Fourier Transform Infrared (FTIR)&#xa0;spectroscopy and X-ray Photoelectron Spectroscopy (XPS) established the presence of carbon in the form of carbonate. The specific surface area determined by the Brunauer–Emmett–Teller&#xa0;(BET) technique is in the range of 160–201 m²/g depending on the synthesis conditions. The photoactivity of the synthesized C-TiO₂ samples has been assessed by the photodegradation of the well-known wastewater pollutant azo-dye, Methyl Orange (MO) under artificial solar light exposure in the presence of oxygen at pH2. The conversion is monitored by UV–visible spectrophotometry. Complete photodegradation of the dye is confirmed by high-performance liquid chromatography (HPLC) and liquid chromatography–mass spectrometry (LC–MS) studies. The dependence of dye photodegradation rate on the catalyst size, specific surface area, carbon content etc. is investigated in detail. Varying the reaction parameters, the photocatalytic activity of the C-TiO₂ samples is optimized under artificial solar light exposure. Catalyst performance is evaluated from the concentration of MO versus time of photodegradation plots which shows extraordinarily high activity for all the synthesized C-TiO₂ photocatalyst samples compared to undoped TiO₂, commercial anatase TiO₂ and Degussa P25 taken as reference. Among all synthesized C-TiO₂, the catalyst synthesized at 175 ^°C for 0.5&#xa0;h showed the best activity. The dye degradation is observed significantly high (&gt; 95%) for the carbon-doped sample after 2&#xa0;h of reaction compared to the undoped sample (54%). In comparison only 40% conversion was observed even after 3&#xa0;h of reaction for the commercial sample and Degussa P25.</p> Graphical abstract <p></p>