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Although the post-doping approach as a typical and effective method has been widely employed to improve the gas sensing performance of nanostructured metal oxides, it easily breaks their porous nanostructures. Herein a facile partial cation-exchange strategy combined with thermal oxidation has been developed to prepare porous CuO-doped ZnO nanobelts. Using ZnSe$0.5N 2 H 4 nanobelts as the precursor template, Cu 2 Se-doped precursor nanobelts were obtained with Zn 2+ cations partially exchanged by Cu 2+ cations. After annealing in air, they are further oxidized into well-defined porous CuO-doped ZnO nanobelts. Through manipulating the amount of exchanged Cu 2+ cations, the CuOdoping concentration can be precisely tuned. Based on the assembly approach and in situ thermal oxidation, a uniform and stable sensing film consisting of porous CuO-doped nanobelts was fabricated.Compared with pristine porous ZnO nanobelts, the as-prepared porous CuO-doped nanobelts with ptype CuO|n-type ZnO heterojunctions exhibited better sensing performance toward volatile organic compounds (VOCs). Especially for 3 at% CuO-doped porous ZnO nanobelts, the relative responses toward 100 ppm of ethanol, acetone and formaldehyde were greatly enhanced more than two, four and ten times, respectively. Due to the porous structure, they also displayed a fast response/recovery time.Finally, this enhanced sensing mechanism was discussed for porous CuO-doped ZnO nanobelts.Scheme 1 The process of preparation of porous CuO-doped ZnO nanobelts: (1) Zn 2+ cations of ZnSe$0.5N 2 H 4 nanobelts as a precursor template partially exchanged by Cu 2+ , (2) the transformation from Cu 2 Se doped precursor nanobelts to porous CuO-doped ZnO nanobelts via thermal oxidation.This journal is

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