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Nitrogen-doped titanium dioxide (N/TiO2) nanophotocatalysts were successfully synthesized in the presence of environmentally benign nitrogen dopant source,guanidinium chloride,by the sol-gel method.The effect of calcination temperature (300-600 ℃) on their physicochemical properties was investigated by means XRD,XPS,FESEM,HRTEM,Raman spectroscopy,UV-vis DRS,PL and BET.Moreover,their photocatalytic activities were evaluated against rhodamine B (RhB) degradation under direct sun light.Results showed that the crystal phase of spheroidal N/TiO2 nanoparticles was changed from anatase (300 ℃) to rutile (600 ℃) via an intermediate anatase/rutile (A/R) mixed phase (400-500 ℃),and the RhB photodegradation performance was increased with the decrease of the calcination temperature.Notably,N/TiO2 prepared at 400 ℃demonstrated the best degradation performance (99％) after 5 h irradiation.The enhanced performance with high photostability was mainly attributed to its higher surface area and pore volume,stronger light absorption,and lower recombination rate.Such nanomaterials have practical applications for environmental remediation.