Selective Electrosynthesis of High-Concentration MnIV═O in Oxidant-Free Systems for Sustainable Water Remediation.

High-valent metal-oxo (HVMO) exhibit selective oxidation properties, but their selective synthesis and high-concentration aggregation remain challenging in oxidant-free systems. This work employs sinusoidal alternating current (AC) to efficiently synthesize MnIV═O with water as an oxygen source. The positive half-cycle continuously transforms H2O adsorbed on ≡MnII site into high-concentration HVMO through a multi-step electron transfer and deprotonation process (≡MnII-OH2→≡MnII-OH→≡MnIII-OH→≡MnIV═O). The negative half-cycle reduces the inactive MnIII generated during the consumption of MnIV═O back to the initial MnII state and simultaneously alleviates proton accumulation. This AC strategy achieves stable cycling of the Mn oxidation state and effectively suppresses the overoxidation of ≡MnIII-OH to ≡MnIV-OOH, thereby realizing the efficient preparation of HVMO with 99.3% selectivity and a steady-state concentration of 2.8 × 10-6 mM. Employing the selective removal of bisphenol A (BPA) as a model, MnIV═O can selectively oxidize target pollutants in the presence of interferents, achieving removal rates approaching 99% within 1 h. Stable operation in a continuous flow reactor scaled up by 40 times for over 100 h highlights the application potential of this strategy. This work reveals a novel green strategy to generate HVMO without rectification or additional oxidants for water purification.