Sulfone based conjugated porous organic polymer-immobilized electrospun nanofibers for continuous-flow photoreduction of hexavalent chromium

Material synthesis under continuous flow offers a route for large scale production while offering the possibility of engineering the properties. Here we report the continuous flow synthesis of sulfone based conjugated porous organic polymer (SCPOP) with enhanced physicochemical and photophysical properties. SCPOP was further immobilized on electro-spun nanofibers of polyacrylonitrile (PAN) for ensuring better processibility, flexibility and portability. This SCPOP@PAN nanocomposite membrane was used as an outstanding visible light active photocatalyst for the reduction of toxic Cr(VI) in both batch and continuous flow processes without using any hole scavenger. We could achieve almost complete (96.38 %) photoreduction of 500 ppm Cr(VI) in continuous flow process using SCPOP@PAN within just 45 min whereas the same extent of photoreduction required 210 min in a batch process. This enhanced photocatalytic activity of the SCPOP@PAN over the SCPOP is due to the prevention of agglomeration of the SCPOP particles due to the immobilization as well the efficient photon and mass transfer. Additionally, the continuous flow reaction offers the possibility of onstream regeneration of the catalyst and recycling without any significant loss in the activity. This is indeed the first report on the photocatalytic reduction of Cr(VI) in batch and continuous flow using SCPOP@PAN nanocomposite membrane as a photocatalyst. Hexavalent chromium (Cr(VI)) is a persistent and carcinogenic contaminant frequently detected in industrial wastewater, posing significant risks to environmental and human health. In this work, we introduce a sulfone-based conjugated porous organic polymer immobilized on electrospun PAN nanofibers (SCPOP@PAN) as a highly effective photocatalyst for Cr(VI) reduction under visible light. When integrated into a continuous-flow system, the membrane facilitates rapid and scalable treatment without chemical reducing agents, achieving markedly improved performance compared to traditional batch methods. The material also demonstrates strong stability and reusability, highlighting its potential for long-term, real-world use. Overall, this study showcases a metal-free, non-toxic, and straightforwardly synthesized porous polymer combined with a portable membrane configuration and process intensification, providing a green and efficient strategy for mitigating hazardous metal pollution in water. Looking ahead, full automation from synthesis to application may be challenged by the continuous-flow incorporation of SCPOP onto PAN nanofibers; however, this limitation could be addressed through droplet-flow processing, which represents a promising future direction for this technology. • First report on the continuous flow photocatalytic Cr(VI) reduction using electrospun SCPOP@PAN nanocomposite as a visible light active photocatalyst. • Highly efficient and fast photocatalytic reduction of Cr(VI) under visible light irradiation. • Enhanced photocatalytic reduction efficiency due to excellent photon and mass transfer in continuous flow. • Onstream catalyst regeneration and recyclability. • Facile processibility and portability of the experimental setup making it suitable for industrial applications.