Among metal oxide photocatalysts, zinc oxide (ZnO) has attracted extensive attention due to its advantages of low toxicity and relatively low cost of production. In this work, ZnO nanopowders doped with different metal ions (Li+, Mg2+, Al3+ and Ti4+) were synthesized by a sol-gel method. Multiple techniques such as X-ray diffraction (XRD), transmission electron microscope (TEM), X-ray photoelectron spectroscopy (XPS), UV-vis diffused reflectance spectra (UV-vis DRS), photoluminescence (PL) spectra and Brunauer-Emmett-Teller (BET) measurements were employed to study the structures, morphologies and physicochemical properties of the photocatalysts. The influence of metal ion doping on the photocatalytic activity of ZnO was assessed by inactivating a typical Gram-negative bacterium, Escherichia coli K-12 under visible-light irradiation. It was found that Al doping and Ti doping could promote the photocatalytic bacterial inactivation activity of ZnO, while Li doping and Mg doping hindered the bacterial inactivation activity of ZnO photocatalysts. Moreover, Al-doped ZnO exhibited the best visible-light-driven (VLD) photocatalytic activity among these samples, with 7-log of E. coli K-12 cells being completely inactivated within 4 h. The large percentage of absorbed oxygen, narrow band gap and extended visible light absorption were considered to contribute to the powerful VLD photocatalytic activity of Al-doped ZnO. (C) 2017 Elsevier B.V. All rights reserved.