Synthesis of nitrogen-doped carbon nanotubes-FePO4 composite from phosphate residue and its application as effective Fenton-like catalyst for dye degradation

Abstract

Phosphate residue is regarded as a hazardous waste, which could potentially create significant environmental and health problems if it is not properly treated and disposed of. In this study, nitrogen-doped carbon nanotubes-FePO₄ (NCNTs-FePO₄) composite was successfully synthesized from phosphate residue, and its application as an effective catalyst was explored. Firstly, an effective method was developed to recover FePO₄ from phosphate residue, achieving an impressive FePO₄ mass recovery rate of 98.14%. Then, the NCNTs-FePO₄ catalyst was synthesized from the recovered FePO₄ by two main reactions, including surface modification and chemical vapor deposition. Finally, the synthesized NCNTs-FePO₄ was applied to photo-degrade 15 mg/L Rhodamine B (RhB) in a Fenton-like system. The results showed that 98.9% of RhB could be degraded in 60 min, closely following the pseudo-first-order kinetics model. It was found that even after six consecutive cycles, NCNTs-FePO₄ still retained a high catalytic capacity (>50%). Moreover, •OH radicals participating in the RhB degradation process were evidenced using quenching experiments and electron paramagnetic resonance analysis, and a rational mechanism was proposed. It was demonstrated that the materials synthesized from hazardous phosphate residue can be used as an effective catalyst for dye removal.

Keywords: Fenton-like; Hydroxyl radical; Nitrogen-doped carbon nanotubes-FePO(4); Phosphate residue.