Enhanced Hydrolysis of p-Nitrophenyl Phosphate by Iron (Hydr)oxide Nanoparticles: Roles of Exposed Facets

Abstract

Iron (hydr)­oxide nanoparticles are one of the most abundant classes of naturally occurring nanoparticles and are widely used engineered nanomaterials. In the environment these nanoparticles may significantly affect contaminant fate. Using two goethite materials with different contents of exposed {021} facet and two hematite materials with predominantly exposed {001} and {100} facets, respectively, we show that exposed facets, one of the most intrinsic properties of nanocrystals, significantly affect the efficiency of iron (hydr)­oxide nanoparticles in catalyzing acid-promoted hydrolysis of 4-nitrophenyl phosphate (pNPP, selected as a model organophosphorus pollutant). Attenuated total reflectance Fourier-transform infrared spectroscopy analysis and density functional theory calculations indicate that the pNPP hydrolysis reaction on the iron (hydr)­oxide surface involves the inner-sphere complexation between the phosphonate moiety of pNPP and the surface ferric iron (Fe­(III)), through ligand exchange with primarily the singly coordinated surface hydroxyl groups of iron (hydr)­oxides. Both the abundance and affinity of these adsorption sites are facet-dependent. Exposed facets also determine the reaction kinetics of surface-bound pNPP mainly by regulating the Lewis acidity of the surface Fe­(III) atoms. These findings underline the important roles of facets in determining the reactivity of naturally occurring metal-based nanoparticles toward environmental contaminants and may shed light on the development of nanomaterial-based remediation strategies.

Toward Informed Design of Nanomaterials: A Mechanistic Analysis of Structure–Property–Function Relationships for Faceted Nanoscale Metal Oxides

“…76 The higher density of singly coordinated hydroxyl groups on the {100} surface of hematite was also shown to be responsible for the greater sorption capacity (per surface area) of humic substances compared with the {001} facet, 235 with analogous conclusions for enhanced sorption and subsequent hydrolysis of 4-nitrophenyl phosphate on the {100} vs. {001} facet of nanohematite. 238 In addition to relative differences in sorption capacities, recent research has demonstrated that different facets of nanoscale hematite also promote different complexation geometries for both inorganic and organic contaminants. For example, Huang et al showed that chromate bound via a monodentate, mononuclear complex on the {001} facet, but on the {110} facet bound as a bidentate, binuclear complex, and was removed with much greater efficiency.…”

“…For example, Catalano et al have reported the preference of arsenate (As­(VI)) and selenite (Se­(IV)) to bind to singly and triply coordinated oxygen functional groups because of favorable sterics, kinetics, and acidities. , Noerpel et al used resonant anomalous X-ray reflectivity (RAXR) to determine the surface coverages of Pb 2+ sorbed on various hematite facets and similarly showed that the {012} and {110} facets (with higher densities of singly and triply coordinated hydroxyl groups than {001}) had a higher surface coverage of Pb 2+ per surface area . The higher density of singly coordinated hydroxyl groups on the {100} surface of hematite was also shown to be responsible for the greater sorption capacity (per surface area) of humic substances compared with the {001} facet, with analogous conclusions for enhanced sorption and subsequent hydrolysis of 4-nitrophenyl phosphate on the {100} vs. {001} facet of nanohematite …”

Fulvic Acid-Mediated Interfacial Reactions on Exposed Hematite Facets during Dissimilatory Iron Reduction

“…The results of previous studies showed that the exposed facets affect the adsorption of proteins and heavy metals, − the decomposition of organic pollutants on metal oxides, , and the mobility and fate of OM components. , The combination between Fe oxides and OM is mainly driven by surface complexation between carboxyl groups in OM and surface Fe atoms. During the adsorption process, OM molecules with a high oxidation state and high aromaticity preferentially form ligand-exchange complexes with hydroxyl functional groups on the hematite surface, and OM components with low molecular weight exhibit a strong facet-dependent selective fractionation .…”

“…The results of previous studies showed that the exposed facets affect the adsorption of proteins 27 and heavy metals, 28−30 the decomposition of organic pollutants on metal oxides, 31,32 and the mobility and fate of OM components. 22,23 The combination between Fe oxides and OM is mainly driven by surface complexation between carboxyl groups in OM and surface Fe atoms.…”

Metastable Facet-Controlled Cu2WS4 Single Crystals with Enhanced Adsorption Activity for Gaseous Elemental Mercury

“…There has been extensive research on crystal facet engineering and the role of special facets in affecting the fate of environmental contaminants, − like TiO 2 and FeWO 4 materials. It was reported that anatase (TiO 2 ) crystals with highly exposed active {001} facets had the enhanced ability of photocatalytic performance .…”