Unusual morphology transformation and basicity of magnesium oxide controlled by ageing conditions and its carbon dioxide adsorption

•Morphologies of MgO were controlled with different ageing times and temperatures.•Microsphere-shaped MgO was formed even at 25 °C despite its reported instability.•Ageing at 60 °C furnished abundant strong basic sites on MgO.•Strongly adsorbed OH− groups were observed when the aging temperature was 80 °C.•Ageing at 80 °C was the most effective for maximizing the CO2 capture performance.