Fabrication of Fe Nanoparticles of 1-nm Crystallite with Boosted Reactivity and Electron Efficiency

During the preparation of Fe nanoparticles (NPs) through aqueous reduction of Fe³⁺, it is discovered that the addition of sodium anthraquinone-2-sulfonate (AQS) results in the formation of ultrasmall Fe crystallites (down to 1.0 nm), which is the hitherto reported smallest Fe crystallite size. This crystallite-shrinking effect of AQS is rather unique and subtle, as its various structural analogs, including sodium benzenesulfonate, methanesulfonate, and anthraquinone-2-carboxylate, conversely increase the crystallite size of Fe NPs from 9.0 to 16.6-32.4 nm. The applied AQS/Fe molar ratio is crucial to the crystallite-shrinking effect, with 0.5% as a noticeable threshold and 1% as the optimal dosage, respectively. The AQS-induced ultrasmall crystallite size steers significant changes in a spectrum of key physicochemical properties of Fe NPs, including smaller particle size with narrower distribution, uniform morphology, suppressed electrochemical impedance, and lowered Tafel corrosion potential. More importantly, AQS modulation results in 18.6- and 4.7-fold increase in the reactivity and electron efficiency of Fe NPs toward nitrobenzene (NB), respectively. In addition, AQS advances the thorough conversion of NB by Fe NPs to the terminal reduction product aniline, thus minimizing the accumulation of intermediates. This study opens an avenue to fabricate Fe NPs of 1-nm crystallite with significantly promoted reactivity and selectivity.