Application of BiOX Photocatalyst to Activate Peroxydisulfate Ion-Investigation of a Combined Process for the Removal of Organic Pollutants from Water

The persulfate-based advanced oxidation processes employing heterogeneous photocatalysts to generate sulfate radicals (SO4 center dot-) from peroxydisulfate ion (PDS, S2O82-) have been extensively investigated to remove organic pollutants. In this work, BiOX (X = Cl, Br, and I) photocatalysts were investigated to activate PDS and enhance the transformation rate of various organic substances under UV (398 nm) and Vis (400-700 nm) radiation. For BiOCl and BiOBr, in addition to excitability, the light-induced oxygen vacancies are decisive in the activity. Although without organic substances, the BiOI efficiency highly exceeds that of BiOBr and BiOCl for PDS activation (for BiOI, 15-20%, while for BiOBr and BiOCl, only 3-4% of the PDS transformed); each BiOX catalyst showed enhanced activity for 1,4-hydroquinone (HQ) transformation due to the semiquinone radical-initiated PDS activation. For sulfamethoxypyridazine (SMP), the transformation is driven by direct charge transfer, and the effect of PDS was less manifested. BiOI proved efficient for transforming various organic substances even under Vis radiation. The efficiency was enhanced by PDS addition (HQ is wholly transformed within 20 min, and SMP conversion increased from 40% to 90%) without damaging the catalyst; its activity did change over three consecutive cycles. Results related to the well-adsorbed trimethoprim (TRIM) and application of biologically treated domestic wastewater as a matrix highlighted the limiting factors of the method and visible light active photocatalyst, BiOI.

Automated summary

Persulfate-based advanced oxidation processes using BiOX photocatalysts have been investigated for the removal of organic pollutants under UV and visible light radiation. BiOI showed higher efficiency in PDS activation compared to BiOBr and BiOCl, and all BiOX catalysts exhibited enhanced activity for 1,4-hydroquinone transformation. The transformation of sulfamethoxypyridazine was driven by direct charge transfer, with a less pronounced effect of PDS. BiOI demonstrated efficient degradation of various organic substances under visible light radiation, and its efficiency was further enhanced by PDS addition.