Tailoring (Bio)chemical Activity of Semiconducting Nanoparticles: Critical Role of Deposition and Aggregation

Abstract

The impact of deposition and aggregation on (bio)chemical properties of semiconducting nanoparticles (NPs) is perhaps among the least studied aspects of aquatic chemistry of solids. Employing a combination of in situ FTIR and ex situ X-ray photoelectron spectroscopy (XPS) and using the Mn(II) oxygenation on hematite (α-Fe(2)O(3)) and anatase (TiO(2)) NPs as a model catalytic reaction, we discovered that the catalytic and sorption performance of the semiconducting NPs in the dark can be manipulated by depositing them on different supports or mixing them with other NPs. We introduce the electrochemical concept of the catalytic redox activity to explain the findings and to predict the effects of (co)aggregation and deposition on the catalytic and corrosion properties of ferric (hydr)oxides. These results offer new possibilities for rationally tailoring the technological performance of semiconducting metal oxide NPs, provide a new framework for modeling their fate and transport in the environment and living organisms, and can be helpful in discriminating between weakly and strongly adsorbed species in spectra.

Rational Design of Interfacial Properties of Ferric (Hydr)oxide Nanoparticles by Adsorption of Fatty Acids from Aqueous Solutions

“…Generally speaking, − the surface density, binding geometry, and type as well as packing order of the adsorbate on metal (hydr)oxide NPs depend on the NP morphology, size, crystallinity, and synthetic history, as these properties in turn control the arrangement, structure, and affinity of the adsorption sites. An external way to tune the adsorption affinity and hence the adsorption characteristics is to electrically polarize NPs to manipulate their Fermi level energy and the surface charge . In the following, we discuss contributions of these characteristics to the adsorption of laurate on hematite NPs and FH.…”

“…We explain this effect by the dominance of chemisorbed fatty acid on H38 (Figure a) and the geometric incompatibility of the rhombohedral (104) facets of these NPs with self-assembly (Supporting Information). Fortunately, the morphological obstacle can be removed by negatively charging the NPs: The resulting upward shift of the Fermi level of the NPs decreases their capacity to accept electrons and thus decreases the surface population of the ISMM laurate. The increased spatial gap between remaining chemisorbed fatty acids is now filled by OS complexes which have more freedom to rearrange laterally and promote better packing and the formation of SAMs, in agreement with the general trend observed for alkanoate SAMs on extended alumina surfaces. − In the case of weak adsorption affinity (FH), although a larger fraction of OS complexes is formed, the low adsorption density precludes the surfactant ordering.…”

“…To verify if the morphology-driven geometrical incompatibility and the high propensity to chemisorb carboxylates are the main obstacles in the chain self-assembly, we studied the effect of negative polarization on the speciation and packing of the first monolayer of laurate on these NPs. As shown in our recent study, 22 the surface charge of the metal oxide NPs can be changed by depositing them on substrates with different work functions. Specifically, deposition on Ge renders negatively charge to hematite NPs.…”

“…Semiconducting (nano)particles can electrically be polarized by varying the redox potential of the suspensions, through contact with other (semi)conducting particles with different work functions (the so-called galvanic interactions) , or, as shown in our recent paper, upon aggregation or deposition on different substrates. Hence, being implemented by one of these approaches, electric polarization presents an important extrinsic control of the adsorption properties of NPs, which has escaped attention of previous researchers.…”

Nanoparticle Clusters: Assembly and Control Over Internal Order, Current Capabilities, and Future Potential

“…In addition, the electronic properties of the strongly interacting NPs, such as bandgap width or surface charging, can be better suited for the desired reaction than those isolated NPs. [124] Importantly, the close contact of NPs within a cluster promotes charge separation, owing to electron hopping between the particles (see Scheme 3b). [125] The geminate electron-hole recombination can thus be reduced, improving the photocatalytic efficiency.…”