The reuse of nano-TiO2 under different concentration of CO32– using coagulation process and its photocatalytic ability in treatment of methyl orange

•Al-based coagulants can effectively separate nano-TiO2.•Flocs formed by different coagulants can degrade methyl orange.•AT2 achieved high degradation efficiency under UV irradiation.•It proposes a new perspective on recycling coagulated flocs for sewage treatment.