Coping with the gradually increasing worldwide environmental issues, it is highly desired to develop efficient, cheap and visible-light responsive nano-photocatalysts for CO2 conversion and pollutant degradation. Herein, we have successfully synthesized SnO2-coupled boron and phosphorus co-doped g-C3N4 (SO/B-P-CN) nanocomposites as efficient cocatalyst-free visible-light photocatalysts of low cost for both CO2 conversion and pollutant degradation. It is shown that the amount-optimized SO/B-P-CN nanocomposite exhibits enhanced visible-light activities for CO2 conversion to CH4 from CO2-containing water by similar to 9 times, and for phenol and acetaldehyde degradation by similar to 7 times, as compared to the bare CN nanosheets. Moreover, it is confirmed that a large amount of produced hydroxyl radicals on SO/B-P-CN is well responsible for the greatly-enhanced photocatalytic activities. Interestingly, the evaluated quantum efficiency (2.02%) of optimized SO/B-P-CN nanocomposite for photocatalytic CO2 conversion at lambda=420 nm is much higher than other reported result. Mainly based on the surface photovoltage responses and the photocurrent action spectra, it is suggested that the enhanced activity of SO/B-P-CN nanocomposite depends on the extended visible-light absorption from 460 to 550 nm after B-P co-doping, and the promoted charge separation via the dopant-induced surface states and the coupled SO nanoparticles. This work implies that the modified CN nanosheets as cheap nanocomposites display promising applications in the photocatalytic field of CO2 conversion to useful fuels and pollutant degradation for environmental remediation. (C) 2016 Elsevier B.V. All rights reserved.