Utilizing alkaline solid waste for low-carbon photocatalytic composite material via in-situ growth of bismuth oxyhalides

As a typical industrial solid waste, red mud exhibits low utilization rates and poses serious ecological threats due to its high alkalinity. Meanwhile, tetracycline pollutions in water are difficult to degrade naturally, presenting numerous challenges to conventional water treatment methods. This study utilized red mud and granulated blast furnace slag as raw materials to prepare geopolymer microspheres (RGGMs) through suspension polymerization. BiOX (X = Cl, Br, I)-RGGMs were synthesized via in-situ growth, with BiOX nanoparticles uniformly dispersed on the RGGMs surface. BiOI-RGGMs, with the narrowest bandgap, achieved a 79.70% removal rate for 50 ppm tetracycline within 180 min, demonstrating excellent degradation performance. Additionally, BiOI-RGGMs maintain high stability, exhibiting only a 7.77% efficiency loss after five cycles. •O₂^- and h⁺ dominated the partial mineralization of tetracycline through three pathways due to their high reactivity, ultimately transforming it into CO₂ and H₂O. The CO₂ emissions from electricity consumption during in-situ growth of BiOX on RGGMs accounted for only 11.59%, confirming the low-carbon characteristics of this process. This study proposes a low-carbon in-situ synthesis strategy that realizes high-value utilization of alkaline solid waste while efficiently treating tetracycline pollution in water.