Graphitic carbon nitride(g-C3N4) with high photocatalytic activity toward degradation of 4-nitrophenol under visible light irradiation was prepared by HCl etching followed by ammonia neutralization.The structure,morphology,surface area,and photocatalytic properties of the prepared samples were studied.After treatment,the size of the g-C3N4 decreased from several micrometers to several hundred nanometers,and the specific area of the g-C3N4 increased from 11.5 m2/g to 115 m2/g.Meanwhile,the photocatalytic activity of g-C3N4 was significantly improved after treatment toward degradation of 4-nitrophenol under visible light irradiation.The degradation rate constant of the small particle g-C3N4is5.7 times of that of bulk g-C3N4,which makes it a promising visible light photocatalyst for future applications for water treatment and environmental remediation. Graphitic carbon nitride (g-C3N4) with high photocatalytic activity toward degradation of 4-nitrophenol under visible light irradiation was prepared by HCl etching followed by ammonia neutralization. Structure, morphology, surface area, and photocatalytic properties of the prepared samples were studied. After treatment, the size of the g-C3N4 decreased from several micrometers to several hundred nanometers, and the specific area of ​​the g-C3N4 increased from 11.5 m2 / g to 115 m2 / g.Meanwhile, the photocatalytic activity of g-C3N4 was significantly improved after treatment toward degradation of 4-nitrophenol under visible light irradiation. The degradation rate constant of the small particle g-C3N4is 5.7 times of that of bulk g-C3N4, which makes it a promising visible light photocatalyst for future applications for water treatment and environmental remediation.