Co₄(PW₉O₃₄)₂ Polyoxmetalate Cluster Intercalated in Layered Double Hydroxides as Catalyst for the Oxidation of <i>p</i>-Arsanilic Acid and Subsequent Immobilization of Arsenic-Containing Byproducts

The ecological risk associated with the hidden release of inorganic arsenic from p-arsanilic acid (p-ASA) due to microbial activities and sunlight irradiation underscores the urgent need for an effective p-ASA control strategy. Herein, polyoxometalate cluster intercalated layered double hydroxides (LDH-CoPW) were synthesized to activate peroxymonosulfate (PMS) for the rapid degradation of p-ASA while simultaneously immobilizing inorganic arsenic. CoPW was loaded into the nanolayer of LDH through a simple ion exchange method, LDH-CoPW with a confined structure possessed independent adsorption and catalytic sites, and the confined CoPW acted as the activator for PMS activation while the LDH layer was responsible for the adsorption of inorganic arsenic. Noninterfering operation of the active sites endowed LDH-CoPW with distinguished performance. Satisfactory removal of p-ASA and TOC by the LDH-CoPW/PMS system was attributed to the long-acting oxidation capacity of Co(IV)═O. By calculating the second-order reaction rate constants of Co(IV)═O with probes for the first time, we determined the striking contribution of Co(IV)═O to the p-ASA degradation via the probe-based kinetic model and revealed the underlying mechanism of PMS activation. This work lies in providing a catalyst synthesis strategy that mitigates the antagonism between active sites and elucidating the activation mechanism of PMS by LDH-CoPW synthesized using this strategy.