With excellent physical/chemical stability and feasible synthesis, g-C3N4 has attracted much attention in the field of photocatalysis. However, its weak photoactivity limits its practical applications. Herein, by easily planting hydrophobic alkyl groups onto g-C3N4, the hydrophilicity of g-C3N4 can be well regulated and its specific surface area be enlarged simultaneously. Such a modification ensures enhanced CO2 capture and increased active sites. In addition, the introduction of alkyl groups endows g-C3N4 with abundant charge density and efficient separation of photoinduced excitons. All these advantages synergistically contribute to the enhanced photocatalytic CO2 reduction performance over the optimized catalyst (DCN90), and the total CO2 conversion is 7.4-fold that of pristine g-C3N4 (CN).