Bandgap modulation of polyimide photocatalyst for optimum H2 production activity under visible light irradiation

► Polyimide photocatalysts with different degree of polymerization are prepared. ► The polymerization degree greatly depends on thermal condensation temperature. ► The bandgap decreases with increasing polymerization degree. ► Polyimide with moderate bandgap shows the highest photocatalytic activity. ► The bandgap engineering method is expected to prepare other efficient polymer photocatalysts.