Steering ^•OH-triggered radicalization of surface phosphate functionality and its protonated analogues to accelerate mineralization of aqueous organic wastes

Herein, iron oxide served as a host to support mono-dentate H_3-XPO₄^X- guests (H_3-XPO₄^X-_SUP; X = 1–3), whose relative compositions were varied by calcining a synthetic intermediate at 250–450 °C. This could produce H₂PO₄^-_SUP-rich P250, HPO₄^2-_SUP-rich P350, and PO₄^3-_SUP-rich P450 catalysts, all of which were subjected to characterizations, DFT calculations, and kinetic assessments of bisphenol A (BPA) mineralization runs for justifying six compelling findings specified below. The catalysts could proceed with the overall ^•OH → H_3-XPO₄^•(X-1)-_SUP route consisting of heterolytic H₂O₂ dissection and ^•OH → H_3-XPO₄^•(X-1)-_SUP cycles, where the former was enabled by Lewis acidic (LA) sites to generate ^•OH, whereas the latter was enabled using ^•OH as a radicalizer of H_3-XPO₄^X-_SUP functionalities to exothermically generate H_3-XPO₄^•(X-1)-_SUP analogues. Of significance, the overall ^•OH → H_3-XPO₄^•(X-1)-_SUP route energetically hinged on endothermic ^•OH desorption from LA sites. H₂PO₄^-_SUP was most adequate to reduce LA strength, desorbed ^•OH in the easiest manner, thereby rendering P250 to display the smallest energy barrier (E_BARRIER) among P250-P450. Of additional significance, PO₄^3-_SUP bore the largest number of P⁺-O^- bonds available to ^•OH → H_3-XPO₄^•(X-1)-_SUP cycle, elevated collision frequency of ^•OH ↔ H_3-XPO₄^X-_SUP or H_3-XPO₄^•(X-1)-_SUP ↔ pollutant in the most efficient fashion, thus making P450 exhibit the largest pre-factors (k_{APP, 0}) among P250-P450. In addition, E_BARRIER outweighed k_{APP, 0} in dictating BPA mineralization efficiencies for P250-P450, among which P250 with the largest H₂PO₄^-_SUP composition revealed the greatest BPA mineralization rate, while sustaining BPA mineralization multiple times via electron transfer pathway. Moreover, H_3-XPO₄^•(X-1)-_SUP outperformed conventional ^•OH and SO₄^•-_SUP/NO₃^•_SUP analogues in mineralizing real wastewaters.