Physical Processing Controls the Structure, Mesoporosity, and Suspension-Phase Functionality of Nanostructured MnO_x...

Physical processing can modify the structural, textural, and dispersion characteristics of nanostructured oxide materials, thereby altering their functional state under suspension conditions. Here, poorly crystalline, sol-gel-derived porous MnO_x materials were used to establish how post-synthetic physical processing affects the relationship between nanoscale structure, accessible mesoporosity, powder-to-suspension transfer, and chromogenic response in 3,3',5,5'-tetramethylbenzidine (TMB) oxidation. Two compositionally distinct processing series were examined: an ultrasonic processing/recovery route for Sr- and Fe-containing MnO_x and vibratory milling followed by identical ultrasonic dispersion for Sr-free Fe-containing MnO_x. The recovered SrFeMn-US-S solid showed higher N₂-accessible surface area and pore volume, stronger hydration signatures, and a larger low-temperature H₂ temperature-programmed reduction (H₂-TPR) contribution than SrFeMn-S. In contrast, vibratory milling of FeMn-S preserved the bulk Fe/Mn ratio but decreased S_BET from 305.9 to 127.1 m² g^-1, V_tot from 0.533 to 0.215 cm³ g^-1, total H₂ uptake from 0.38 to 0.34 mmol g^-1, and the Mn concentration in the operationally defined stable suspension fraction from 50.5 to 17.3 mg L^-1. At an identical assay concentration of 500 ng Mn mL^-1, milled FeMn-S5 also exhibited a lower time-summed ΣA₆₅₂ response than FeMn-S. Thus, milling affected both the efficiency of powder-to-suspension transfer and the Mn-normalized functional response of the dispersed material. The contrasting outcomes show that the functional state of nanostructured, powder-derived MnO_x is route-dependent and cannot be predicted from a single solid-state descriptor.