PANI (polyaniline)-g-C3N4-TiO2 composite was prepared and utilized in the photocatalyzed synthesis of alpha-chloro aryl ketones via a radical-triggered domino process under oxygen atmosphere. This semiconductor photocatalyst showed good photocatalytic performance and chemoselectivity under visible light irradiation. A variety of aryl diazonium salts and aryl alkynes survived the reaction conditions well to afford the corresponding products in moderate to good yields. Scale-up (10 mmol) synthesis was also achieved. The recycle studies showed that the semiconductor composite could be readily recovered and reused for eight consecutive runs with a slight decrease in the catalytic activity. Control experiments were also performed, and a plausible catalytic mode was proposed.