It is highly desired to produce more O-.(2)- by regulating photogenerated electrons for efficiently degrading organic pollutants with recyclable feature. In this work, g-C3N4/active carbon fiber (ACF) photocatalysts with high activities for degrading 2,4-dichlorophenol (2,4-DCP) and bisphenol A (BPA) have been successfully fabricated via an in-situ thermal polycondensation method, attributed to the enhanced charge separation and promoted reactant adsorption from ACF. Moreover, the photocatalytic activities of optimized g-C3N4/ACF photocatalyst could be improved by introducing the carbon layer between them, especially for the nickel regulated one. It is attributed to the promoted charge transfer and separation by improving the interface contacts between g-C3N4 and ACF, and the function of introduced Ni species to O-2 activation, mainly based on the fluorescence spectra related to the formed hydroxyl radical amounts, and the electrochemical oxygen reduction. Furthermore, the photocatalytic activities could be further improved by modifying phosphoric acid to promote the capture of photogenerated electrons by the increased adsorbed oxygen based on the O-2 temperature-programmed desorption curves. Interestingly, it is shown that the optimal photocatalyst exhibits 10-time higher photocatalytic activities for 2,4-DCP degradation compared to bare g-C3N4. It is demonstrated through the radical-trapping experiments that O-.(2)- is the dominant active species to induce the degradation of 2,4-DCP, along with a suggested decomposition pathway according to the detected main intermediates. This further verifies this point that the photocatalytic activities for degrading organic pollutants could be efficiently improved by mediating electrons. As for the ACF-supported photocatalysts, a specific device has been designed to efficiently purify polluted water with convenient and continuous features. This work opens up a feasible route to develop a high-efficiency photocatalytic technology for recyclable degradation of environmental contaminants.