Phthalimide based new photocatalysts featured with highly selective photodegradation of azo-dyes and good photocatalytic activity in both homogeneous and heterogeneous systems

[Display omitted] •Phthalimide (PI) preferentially photodegrades azo dye in mixture with non-azo dye.•PI shows good photocatalytic activity in homogeneous and heterogeneous systems.•Halogenation of PI tunes the photocatalytic performance.•PI with selective photodegradation of dye is promising in environment remediation. Selective degradation of the target pollutants allows delicate manipulation of the environmental remediation process via photocatalysis, and has attracted much attention in recent years. Herein, we report the preparation and photocatalytic behaviors of an organic semiconductor of phthalimide (PI). It is found that PI could effectively degrade the azo-dyes under UV irradiation in both heterogeneous and homogeneous reaction systems, which is rarely reported for the photodegradation of the dyes. In comparison, the halogenation of PI has an adverse effect on the photocatalytic activity of corresponding PI derivatives. Moreover, PI is used to photodegrade the mixtures of azo-dyes and non-azo dyes. It is found that PI achieves highly selective photodegradation of the azo-dyes in a heterogeneous reaction system, while its halogenated derivatives exhibit lower selectivity. By contrast, no preferential photodegradation is observed in the homogeneous methanol solution. It is proposed that the regular π-π stacking conjugated structure of the PI based molecules are responsible for the selective photodegradation behaviors. The work offers new approaches for the development of advanced organic molecule photocatalysts with desirable features including selective photodegradation and efficient degradation of dyes in both heterogeneous and homogeneous photocatalysis.