Photocatalytic disinfection over a high performance metal-free photocatalyst under visible light irradiation was studied. An atomic single layer g-C3N4 (SL g-C3N4) with the thickness of 0.5 nm was fabricated by a two-step approach including thermal etching of bulk g-C3N4 into g-C3N4 nanosheets (g-C3N4 NS) and followed by an ultrasonic exfoliation of g-C3N4 NS. The performance of photocatalytic disinfection was investigated by inactivation of Escherichia coli. Under the visible light irradiation, 2 x 10 cfu mL(-1) of E. coli could be killed completely over the SL g-C3N4 within 4h, whereas only about 3 log and 5 log of E. coil could be killed on bulk g-C3N4 and g-C3N4 NS under the same condition, respectively. Especially, the direct destruction of the E. coli cell wall was observed by TEM. The enhancement of photocatalytic efficiency of SL g-C3N4 was attributed to the low charge transfer resistance and efficient charge separation which were confirmed by electrochemical impedance spectroscopy and photo-current measurements. Owing to the excellent performance of SL g-C3N4, a visible light response and environmental friendly photocatalyst for disinfection was achieved. (C) 2014 Elsevier B.V. All rights reserved.