Continuous flow synthesis of visible light-active conjugated porous polymer for pollutant degradation and plastic waste photoreforming

Abstract

Developing metal free, visible light active photocatalysts is a green and sustainable approach towards environmental remediation and energy generation. Here, we present a sulfone based conjugated porous organic polymer (CPOP) as a visible light active catalyst for the photocatalytic degradation of pollutants, and photoreformation of waste plastic into green hydrogen, and other value-added products. High temperature (120 °C) refluxing of 3, 3′ diamino diphenylsulfone (APS) and 1, 3, 5-Triformylphloroglucinol (TFP) for 10 h yielded APS-TFPBatch. When compared to the traditional batch approach, the continuous flow method allowed the synthesis of APS-TFPFlow in less time (3 h) and lower temperature (60–70 °C) because of efficient heat and mass transfer. The APS-TFPFlow CPOP had higher surface area, dispersibility, optical absorbance, charge separation, and transportation characteristics than APS-TFPBatch. Thus, APS-TFPFlow was found to be a better photocatalyst for the degradation of a model pollutant, methylene blue (MB) than APS-TFPBatch. Additionally, performing the photocatalytic degradation of MB in continuous flow led to further enhancement in the photocatalytic pollutant removal (96%) than in batch (74%). Moreover, the catalyst could be reactivated efficiently in the flow process for repeated usage.Additionally, photoreforming of polyethylene terephthalate (PET) waste bottles in presence of APS-TFPFlow under visible light irradiation resulted in the generation of high amount of green hydrogen (77 mmol/gcat/h) along with terephthalate, lactate and glycolate. Thus, the present study emphasises the advantages of using continuous flow method for the synthesis of CPOP as well as for performing photocatalytic reactions.