Single Dispersion of Fe(H₂O)₂‐Based Polyoxometalate on Polymeric Carbon Nitride for Biomimetic CH₄ Photooxidation

Abstract Direct methane conversion to value‐added oxygenates under mild conditions with in‐depth mechanism investigation has attracted wide interest. Inspired by methane monooxygenase, the K₉Na₂Fe(H₂O)₂{[γ‐SiW₉O₃₄Fe(H₂O)]}₂·25H₂O polyoxometalate (Fe‐POM) with well‐defined Fe(H₂O)₂ sites is synthesized to clarify the key role of Fe species and their microenvironment toward CH₄ photooxidation. The Fe‐POM can efficiently drive the conversion of CH₄ to HCOOH with a yield of 1570.0 µmol g_POM⁻¹ and 95.8% selectivity at ambient conditions, much superior to that of [Fe(H₂O)SiW₁₁O₃₉]⁵⁻ with Fe(H₂O) active site, [Fe₂SiW₁₀O₃₈(OH)]₂¹⁴⁻ and [P₈W₄₈O₁₈₄Fe₁₆(OH)₂₈(H₂O)₄]²⁰⁻ with multinuclear Fe−OH−Fe active sites. Single‐dispersion of Fe‐POM on polymeric carbon nitride (PCN) is facilely achieved to provide single‐cluster functionalized PCN with well‐defined Fe(H₂O)₂ site, the HCOOH yield can be improved to 5981.3 µmol g_POM⁻¹. Systemic investigations demonstrate that the (WO)₄−Fe(H₂O)₂ can supply Fe═O active center for C−H activation via forming (WO)₄−Fe_a−O_t···CH₄ intermediate, similar to that for CH₄ oxidation in the monooxygenase. This work highlights a promising and facile strategy for single dispersion of ≈1–2 Å metal center with precise coordination microenvironment by uniformly anchoring nanoscale molecular clusters, which provides a well‐defined model for in‐depth mechanism research.