Waterborne pathogenic viruses, with an ultra-small particle size of tens of nanometers, a high risk of causing disease, and strong persistence in natural environment and water treatment processes, pose a serious threat to human health. Here, a new class of metal-free heterojunction photocatalysts was developed by integrating oxygen-doped graphitic carbon nitride microspheres (O-g-C3N4) with hydrothermal carbonation carbon (HTCC) via a facile low-temperature solvothermal-hydrothermal approach for the inactivation of human adenovirus type 2 (HAdV-2). The sample of O-g-C3N4 /HTCC-2 with a uniform coverage of HTCC, strong visible light absorption, and a narrow band gap exhibited the higher virucidal activity against highly resistant HAdV-2 under visible light irradiation, compared to HTCC, bulk g-C3N4, and O-g-C3N4. A titer of 10(5) MPN/mL viruses was completely inactivated within 120 min of photocatalysis, and viral inactivation efficiency was enhanced with the increase of water temperature from 4 to 37 degrees C, the decrease of pH from 8 to 5, or the presence of salinity (NaCl) and hardness (Ca2+). Furthermore, the effectiveness for HAdV-2 inactivation in real drinking water and excellent photocatalyst stability of O-g-C3N4/HTCC-2 highlighted its promising potential for water disinfection in practice. The mechanism of enhanced virucidal performance of O-g-C3N4/HTCC was revealed, and it was because of enhanced charge separation by the formation of heterojunction in the photocatalyst. Besides, Z-scheme heterojunction was proposed to enable the production of (OH)-O-center dot as a strong antiviral agent in photocatalysis, in contrast to Type II heterojunction. Interestingly, (OH)-O-center dot rather than O-center dot(2)- dominated HAdV-2 inactivation, and it led to the rupture, distortion, and hole formation of viral capsid. In addition to the excellent photocatalytic performance of O-g-C3N4/HTCC for HAdV-2 inactivation, the photocatalyst exhibited negligible toxicity to a human cell line, suggesting the material is safe for water purification. Our study not only highlights the promising future of an emerging metal-free visible-light-responsive heterostructure of O-g-C3N4/HTCC for viral disinfection and an effective, sustainable, and safe water purification process, but also sheds light on the key photocatalyst properties and mechanisms that improve photocatalytic performance.