Polymeric carbon nitride (g-C3N4) exhibits only mediocre catalytic activity in photocatalytic environmental remediation and energy conversion because of its limited light absorption and sluggish charge transfer. Herein, we assembled novel, tubular carbon nitride (D-TCN450) with nitrogen defects/boron dopants via a self-supramolecular reaction and NaBH4 thermal reduction approach. Advanced characterization results suggested that introducing the nitrogen defects/boron dopants can effectively promote light trapping, charge separation, and valance-band downshift. Density functional theory and electron spin resonance results further proved that the fusion of cyano groups (nitrogen defects) into the framework of D-TCN450 can facilitate oxygen adsorption to form superoxide radicals. As a result, D-TCN450 exhibited dramatically improved photocatalytic hydrogen evolution and photodegradation of tetracycline hydrochloride at a 4- and 9-fold enhancement compared to pristine g-C3N4, respectively. This integrated engineering strategy might provide a unique paradigm for the rational design of novel photocatalysts for sustainable remediation and energy innovation.