Disentangling the size-dependent redox reactivity of iron oxides using thermodynamic relationships

被引:10
作者
Chen, Gongde [1 ]
Thompson, Aaron [2 ]
Gorski, Christopher A. [1 ]
机构
[1] Penn State Univ, Dept Civil & Environm Engn, University Pk, PA 16801 USA
[2] Univ Georgia, Dept Crop & Soil Sci, Athens, GA 30602 USA
基金
美国国家科学基金会;
关键词
iron oxides; redox reactivity; nanoparticles; thermodynamics; reactive surface area; GOETHITE ALPHA-FEOOH; ORGANIC-MATTER; MAGNETITE STOICHIOMETRY; SURFACE-CHEMISTRY; PARTICLE-SIZE; FE-II; REDUCTION; NANOPARTICLES; FE(II); OXIDATION;
D O I
10.1073/pnas.2204673119
中图分类号
O [数理科学和化学]; P [天文学、地球科学]; Q [生物科学]; N [自然科学总论];
学科分类号
07 ; 0710 ; 09 ;
摘要
Nanoparticles often exhibit size-dependent redox reactivities, with smaller particles being more reactive in some cases, while less reactive in others. Predicting trends between redox reaction rates and particle sizes is often complicated because a particle's dimensions can simultaneously influence its aggregation state, reactive surface area, and thermodynamic properties. Here, we tested the hypothesis that interfacial redox reaction rates for nanoparticles with different sizes can be described with a single linear free-energy relation-ship (LFER) if size-dependent reactive surface areas and thermodynamic properties are properly considered. We tested this hypothesis using a well-known interfacial redox reaction: the reduction of nitrobenzene to aniline by iron-oxide-bound Fe2+. We measured the reduction potential (E-H) values of nano-particulate hematite suspensions containing aqueous Fe2+ using mediated potentiometry and characterized the size and aggregation states of hematite samples at circumneutral pH values. We used the measured E-H values to calculate surface energies and reactive surface areas using thermodynamic relationships. Nitrobenzene reduction rates were lower for smaller particles, despite their larger surface areas, due to their higher surface energies. When differences in surface areas and thermodynamic properties were considered, nitrobenzene reduction kinetics for all particle sizes was described with a LFER. Our results demonstrate that when Fe2+ serves as a reductant, an antagonistic effect exists, with smaller particles having larger reactive surface areas but also more positive reduction potentials. When Fe3+ serves as an oxidant, however, these two effects work in concert, which likely explains past discrepancies regarding how iron oxide particle sizes influence redox reaction rates.
引用
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页数:10
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