Enhanced sulfate radical generation through bimetallic Ni–Cu catalysts synthesized in a fluidized bed for rapid RB5 degradation

Abstract The treatment of dye-containing wastewater remains a significant environmental challenge, as persistent azo dyes such as Reactive Black 5 (RB5) are resistant to conventional oxidation and biological processes. In this study, we propose a Fe-free advanced oxidation strategy based on sodium persulfate activation using Ni–Cu bimetallic catalysts synthesized via fluidized-bed homogeneous crystallization (FBHC), with a systematic comparison to catalysts prepared by conventional jar-test precipitation (JAR). The novelty of this work lies in coupling FBHC synthesis with persulfate activation to produce highly reactive, amorphous Ni–Cu catalysts capable of rapid pollutant degradation under near-neutral conditions, thereby overcoming the sludge generation and pH limitations associated with traditional Fenton systems. Using 100 mg L −1 RB5 as a model contaminant, the FBHC-derived catalyst achieved > 90% decolorization within 10 min and 70.7% TOC removal within 5 min, significantly outperforming the JAR-derived material. Kinetic analysis indicated that the degradation followed the Langmuir–Hinshelwood model, suggesting a surface-controlled reaction pathway. Radical scavenging and EPR analyses identified SO 4 · − and 1 O 2 as the dominant reactive species, with minor contributions from ·OH and negligible involvement of O 2 · − . Overall, this study demonstrates that (i) FBHC is an effective method for fabricating highly reactive bimetallic catalysts and (ii) the Ni–Cu/persulfate system represents a rapid, Fe-free oxidation process operable under mild pH conditions, offering a promising strategy for efficient and scalable textile wastewater treatment.