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• The flower-like TiO 2 microspheres were synthesized by a tunable tetrabutyl titanate-assisted hydrothermal method. • The as-made gas sensors showed high sensitivity and selectivity to NH 3 at the room temperature. • The underlying mechanism for the high selectivity to NH 3 was discussed using DFT calculations. TiO 2 is proved to be a promising material in the detection of various hazardous gases at the high temperature. However, gas adsorption-diffusion capacity at the room temperature is limited by their insufficient specific surface area and surface active sites. Herein, we report a strategy to synthesis of flower-like TiO 2 microspheres assembled by nanosheets and characterize the selective adsorption of NH 3 by using density functional theory (DFT). The as fabricated flower-like TiO 2 microspheres show an outstanding gas sensitivities (∼122 to 50 ppm NH 3) and high selectivity for NH 3 detection at room temperature. The higher adsorption energy and smaller adsorption distance of NH 3 on TiO 2 (001) indicate the much stronger interaction NH 3 -TiO 2 system. The present studies provide useful gas sensing materials with fine morphologies for the development of high-performance room temperature NH 3 sensors. [ABSTRACT FROM AUTHOR]