Simultaneous removal of fluoride and nitrate from photovoltaic wastewater utilizing a bifunctional polymer-based nanocomposite encapsulating Ce-Fe bimetal oxyhydroxides

The widespread use of HF and HNO3 in photovoltaic (PV) cell manufacturing results in the generation of substantial wastewater containing fluoride and nitrate, posing a serious threat to ecological safety and human health. In this study, a novel bifunctional nanocomposite adsorbent CFBOs@TPM, exhibiting a specific affinity for both fluoride and nitrate, was developed for their concurrent removal from PV wastewater. A triethylamine functionalized polystyrene microsphere (TPM) of nanoporous and crosslinked structure was synthesized as the host of CFBOs@TPM, with Ce-Fe bimetal oxyhydroxides (CFBOs) nanoparticles of sufficient hydroxyl groups impregnated inside the pores of TPM as the active species. Comparative studies with other analogous adsorbents highlighted the superior selectivity and efficacy of CFBOs@TPM for fluoride and nitrate retention, with minimal interference from coexisting anions. Fixed-bed adsorption tests on pre-treated PV wastewater demonstrated that CFBOs@TPM could effectively reduce fluoride from 2.93 to < 1.5 mg F/L over -250 bed volume (BV), and nitrate from 34.8 to < 10 mg N/L over -220 BV. Remarkably, the spent CFBOs@TPM could be efficiently regenerated using a NaOH-NaCl mixed reagent, allowing for cyclic utilization with sustained efficiency. Such exceptional performance of CFBOs@TPM arises from its dual-function structure, that is, the functionalized triethylamine groups on TPM enhance preferential nitrate adsorption via selective electrostatic attraction, while the encapsulated CFBOs nanoparticles within TPM facilitate specific fluoride uptake through hydroxyl ligand exchange and inner-sphere complexation. This study represents a significant advancement in the development of multifunctional adsorbents for simultaneous removal of coexisting contaminants from wastewater, providing valuable insights for future environmental remediation strategies.