g-C3N4/CeO2/Bi2O3 Dual Type-II Heterojunction Photocatalysis Self-Cleaning Coatings: From Spectral Absorption Modulation to Engineering Application Characterization

To enhance the purification of exhaust gas, a g-C3N4/CeO2/Bi2O3 dual type-II heterojunction photocatalysis was designed and prepared to suppress the recombination of electron–hole pairs and improve light energy utilization. The dual type-II heterojunction structure effectively reduced the bandgap (Eg) from 2.5 eV to 2.04 eV, thereby extending the light absorption of photocatalysis into the visible region. Following the design of the heterojunction, a self-cleaning process was developed and applied to asphalt pavement rut plates to evaluate its efficiency in degrading vehicle exhaust under real-road conditions. The coating was systematically characterized in terms of exhaust degradation efficiency, hardness, adhesion, water resistance, freeze–thaw durability, and skid resistance. Under 60 min of natural light irradiation, the purification efficiencies for HC, CO, CO2, and NOx reached 22.60%, 19.27%, 14.83%, and 50.01%, respectively. After three-repetition tests, the efficiencies remained high at 21.75%, 19.04%, 14.66%, and 49.83%, demonstrating excellent photocatalytic stability. All other road-performance indicators met the relevant China national standards. The application of this self-cleaning coating in road infrastructure presents a viable strategy for environmental remediation in transportation systems.