Design and evaluation of Cu-modified ZnO microspheres as a high performance formaldehyde sensor based on density functional theory.

• Cu metal deposition on the ZnO can provide more surface oxygen free radicals. • Cu metal increase the binding energy of HCHO to Cu-modified ZnO. • Cu metal can effectively improve the performance of ZnO for HCHO detection. • Cu-modified ZnO displaying the excellent endurance to humidity. • Mechanism of Cu-modified ZnO gas sensor was studied by first-principles calculation. Based on Cu-modified ZnO (CZO), a highly sensitive gas sensor for formaldehyde (HCHO) detection at room temperature was prepared by the sol–gel method, and the sensing mechanism was studied by density functional theory. Calculations indicate that the binding energy of CZO to HCHO is higher than that of pure ZnO when Cu metal occupies the oxygen vacancy on the surface of ZnO, which is beneficial for CZO to capture more HCHO molecules. Moreover, Cu metal splits oxygen molecules in the air to form a large number of oxygen free radicals on the surface of CZO and react with HCHO molecules. The lowest band gap can be obtained when HCHO is adsorbed in CZO compared to other gases, which means CZO has better selectivity in the detection for HCHO. Experiments show that Cu metal can effectively improve the performance of ZnO for HCHO detection. CZO with 3 mol% Cu exhibits short response/recovery times (1.7 s/2.9 s) and the limit of detection (LOD) is 0.61 ppm at HCHO concentration of 1 ppm. Moreover, CZO displays the excellent endurance to humidity. Such a metal-modified ZnO offers great potential for the development of highly sensitive gas sensor for HCHO detection. [ABSTRACT FROM AUTHOR]