Ce/W-MIL-88B(Fe) photo-Fenton material achieving synchronous arsenate uptake and nitrite resourcing: unexpected role of arsenate in boosting photo-Fenton activity

Abstract

Here, a novel MOF-based photo-Fenton material (Ce/W-MIL-88B(Fe)) was fabricated, which achieved synchronous arsenate (As(V)) uptake and nitrite (NO₂⁻) resourcing. The NO₂⁻ oxidation efficiency reaches 97% with a very low molar ratio of PMS/NO₂⁻ (1 : 3); meanwhile the As(V) adsorption capacity is 181 mg g⁻¹. Ce-doping not only enhances the photocatalytic activity of W-MIL-88B(Fe) but also alters its crystal microstructure and forms numerous surface defects, favoring active site exposure and PMS activation. ESR and radical quenching tests reveal that the contribution sequence of various ROS to NO₂⁻ oxidation is e⁻ > h⁺ > SO_4^·− ≥ ¹O₂ > HO· > O_2^·−. Amazingly, As(V) embedded on Ce/W-MIL-88B(Fe) greatly improves its photo-Fenton activity: the NO₂⁻ oxidation rate (0.0935 min⁻¹) increases by 0.8 times compared with Ce/W-MIL-88B(Fe) alone (0.0505 min⁻¹). Mechanism analyses demonstrate that the formed new ‘Fe–O–As’ and ‘Ce–O–As’ sites via hydroxyl bridging lower the band gap energy, inhibit the h⁺–e⁻ recombination and increase the oxygen vacancies (OVs). This study offers new insights into the development of photo-Fenton technology for harmless recovery of wet oxidation flue gas purification wastewater.