Abstract Magnetically functionalized biomaterials represent an exciting prospect in the development of stimuli‐responsive tissue engineering scaffolds. Magneto‐responsive properties are traditionally imparted to scaffold systems via integration of iron oxide‐based magnetic nanoparticles (MNPs), yet poor understanding of long‐term MNP toxicity presents a significant translational challenge. Given the demonstrated iron‐binding capacity of silk fibroin (SF), passive chelation of ferric iron ions is explored herein as an alternative, MNP‐free approach for magnetic functionalization of silk fibroin (SF)‐based biomaterials. SF microfibers treated with aqueous ferric chloride (FeCl 3 ) exhibit significantly increased iron content relative to the nascent protein. Coupled with the absence of detectable chlorine traces and inorganic iron oxide species, the ferric oxidation state of the iron detected within the FeCl 3 ‐treated microfibers suggests that iron is incorporated, without reduction, at innate oxygen‐containing ligands in SF. On exposure to an external magnetic field, these ferric iron‐chelated SF microfibers (Fe 3+ ‐mSF) display paramagnetic magnetization behaviors that facilitate field‐parallel alignment. Both magnetization and directional uniformity increase with iron exposure during FeCl 3 treatment, suggesting the observed magnetic response of Fe 3+ ‐mSF is derived from the chelated iron. This work is the first to investigate the magneto‐responsive properties and biocompatibility of ferric iron‐chelated SF, highlighting a novel, MNP‐free mechanism for synthesizing magnetically functionalizedscaffolds.
SnS 2 is a member of the van der Waals 2D layered materials family. Its moderate bandgap, environmental stability and high carrier mobility makes it attractive for solar energy conversion application. We explore how nanostructuring SnS 2 in the form of vertically-aligned nanoflakes to increase the surface area impacts the lifetime and microscopic conductivity of photoinjected carriers compared to the bulk SnS 2 . Increased surface area and the presence of edges is beneficial to the efficiency of SnS 2 photoanode performance but it comes at a cost of increased carrier trapping at surface and edge states.
We quantified the chemical species present at and reactivity of the (100) face of tetrahedral single-crystal methylammonium lead iodide, MAPbI3(100), and polycrystalline cesium tin bromide, CsSnBr3. For these ABX3 perovskites, experiments utilized the orthogonal reactivity of the A+-site cation, the B2+-site cation, and the X–-site halide anion. Ambient pressure exposure to BF3 solutions probed the reactivity of interfacial halides. Reactions with p-trifluoromethylanilinium chloride probed the exchange reactivity of the A+-site cation. A complex-forming ligand, 4,4′-bis(trifluoromethyl)-2,2′-bipyridine, probed for interfacial B2+-site cations. Fluorine features in X-ray photoelectron spectroscopy (XPS) quantified reaction outcomes for each solution-phase species. XPS revealed adsorption of BF3, indicating surface-available halide anions on both MAPbI3(100) and on CsSnBr3. Temperature-programmed desorption quantified a ∼200 kJ mol–1 desorption activation energy from MAPbI3(100) and a ∼215 kJ mol–1 desorption energy from CsSnBr3. Adsorption of the fluorinated anilinium cation included no concomitant adsorption of chlorine as revealed by the absence of Cl 2p features within the limits of XPS detection. We interpret the observation of the anilinium species as exchanging for interfacial methylammonium species on MAPbI3(100) surfaces and interfacial cesium on the polycrystalline CsSnBr3 surface. Within detection limits, the bipyridine ligand demonstrated no adsorption to MAPbI3(100), suggestive of a Pb2+ deficient surface, but adsorption to the polycrystalline CsSnBr3 that suggests surface-accessible Sn2+. The combination of results implies that methylammonium cations and iodide anions dominate tetragonal MAPbI3(100) surface that, respectively, enables cation exchange and Lewis adduct formation for surface derivatization. We discuss the present results in the context of interfacial stability, passivation, and reactivity for perovskite-based energy conversion.
This thesis explores the evaporation and Rayleigh discharge dynamics of highly charged micron-sized droplets and explores new methodologies for extracting ions for mass analysis from neutral droplets using strong electric fields in a technique termed field-induced droplet ionization.
A phase Doppler anemometer characterizes individual highly charged droplets moving through a uniform, mild electric field within an ion mobility cell according to size, velocity, and charge. Repeated reversals of the electric field allow multiple characterizations on selected droplets. This technique provides droplet histories that determine the solvent evaporation and Rayleigh discharge behavior. The ping-pong experiment characterizes volatile droplets of the hydrocarbon solvents n-heptane, n-octane, and p-xylene as well as two-component droplets of either 2-methoxyethanol, tert-butanol, or m-nitrobenzyl alcohol with methanol. On average, hydrocarbon droplets eject 18% of their net charge into progeny droplets with an undetectable loss in mass. Rayleigh discharge events in the polar, binary droplets release between 20 and 35% of the net charge with a correspondingly undetectable loss in mass.
In other experiments, strong electric fields elongate neutral droplets along the field axis. Field-induced droplet ionization (FIDI) occurs at sufficient field strengths as the droplets eject opposing jets of positively and negatively charged progeny droplets. Images of droplets from a vibrating orifice aerosol generator illustrate this phenomenon, and mass spectrometric sampling of the progeny droplets demonstrates that they are a viable source of desolvated gas-phase ions. Switched electric field experiments relate the timescale of droplet elongation and progeny droplet formation in FIDI to the timescale of oscillations of droplets in sub-critical field strengths. FIDI mass spectra are presented for several species, including tetraheptyl ammonium cation, deprotonated benzene tetracarboxylic acid, and multiply protonated cytochrome c.
Droplets may serve as reactors before being sampled by FIDI-MS. FIDI-MS probes the products of heterogeneous reactions between solution-phase oleic acid or a lysophosphatidic acid and gas-phase ozone.
A neutral droplet elongates along the axis of a strong electric field, ejecting opposing jets of positively and negatively charged progeny droplets. Images of droplets from a vibrating orifice aerosol generator illustrate this phenomenon, and mass spectrometric sampling of the progeny droplets demonstrates that they are a viable source of desolvated gas-phase ions. Field-induced droplet ionization (FIDI) mass spectra are presented for several species, including tetraheptylammonium cation, deprotonated benzene tetracarboxylic acid anion, and multiply protonated cytochrome c.
We have developed a simple strategy allowing molecular guests to be trapped within MOF-5 using carboxylic acids bearing sterically demanding substituents as capping reagents. We demonstrate that introducing triphenylacetic acid or diphenylacetic acid onto the surface of crystals of MOF-5 loaded with crystal violet (CV) prevents CV from escaping by blocking the openings of pores. In this study, MOF-5 was capped with four carboxylic acids and two 3° amines, and diffusion of CV out of capped MOFs was monitored using UV–vis spectroscopy to assess how variation in the steric demand of substituents affected retention of CV.
We investigate the impact of grain boundaries and interfaces on dynamics of photoexcited charge carriers in polycrystalline lead sulfide (PbS) films and at interfaces between polycrystalline PbS and ZnO by studying transient photoconductivity over sub-picoseconds to microseconds timescales using time-resolved terahertz spectroscopy and time-resolved microwave conductivity measurements. Narrow band gap bulk-like polycrystalline PbS with high absorption in the infrared paired with wide band gap metal oxide current collectors holds promise for infrared photodetectors and photovoltaics for converting infrared radiation to electricity. We find that grain boundaries in polycrystalline PbS suppress long-range conductivity and confine photoexcited carriers within individual crystallites. The mobility of photoexcited holes inside the ∼150 nm crystallites reaches 750 cm2/V s, and their lifetime exceeds hundreds of microseconds, while electrons get rapidly trapped at grain boundary states. The presence of PbS/ZnO interfaces dramatically reduces the lifetime of the photoexcited free holes in the PbS crystallites. Moreover, we detect no injection of free electrons from PbS to ZnO. Optimal transfer of photoexcited electrons, as is needed for optoelectronic devices with PbS/ZnO heterojunctions, may require engineering PbS/ZnO heterojunctions with buffer layers or organic ligands to passivate deleterious interface states.
The photoelectrochemical behavior of methyl-terminated p-type and n-type Si(111) surfaces was determined in contact with a series of one-electron, outer-sphere, redox couples that span >1 V in the Nernstian redox potential, E(A/A–), of the solution. The dependence of the current vs potential data, as well as of the open-circuit photovoltage, Voc, on E(A/A–) was compared to the behavior of H-terminated p-type and n-type Si(111) surfaces in contact with these same electrolytes. For a particular E(A/A–) value, CH3-terminated p-Si(111) electrodes showed lower Voc values than H-terminated p-Si(111) electrodes, whereas CH3-terminated n-Si(111) electrodes showed higher Voc values than H-terminated n-Si(111) electrodes. Under 100 mW cm–2 of ELH-simulated Air Mass 1.5 illumination, n-type H–Si(111) and CH3–Si(111) electrodes both demonstrated nonrectifying behavior with no photovoltage at very negative values of E(A/A–) and produced limiting Voc values of >0.5 V at very positive values of E(A/A–). Illuminated p-type H–Si(111) and CH3–Si(111) electrodes produced no photovoltage at positive values of E(A/A–) and produced limiting Voc values in excess of 0.5 V at very negative values of E(A/A–). In contact with CH3CN-octamethylferrocene+/0, differential capacitance vs potential experiments yielded a −0.40 V shift in flat-band potential for CH3-terminated n-Si(111) surfaces relative to H-terminated n-Si(111) surfaces. Similarly, in contact with CH3CN-1,1′-dicarbomethoxycobaltocene+/0, the differential capacitance vs potential data indicated a −0.25 V shift in the flat-band potential for CH3-terminated p-Si(111) electrodes relative to H-terminated p-Si(111) electrodes. The observed trends in Voc vs E(A/A–), and the trends in the differential capacitance vs potential data are consistent with a negative shift in the interfacial dipole as a result of methylation of the Si(111) surface. The negative dipole shift is consistent with a body of theoretical and experimental comparisons of the behavior of CH3–Si(111) surfaces vs H–Si(111) surfaces, including density functional theory of the sign and magnitude of the surface dipole, photoemission spectroscopy in ultrahigh vacuum, the electrical behavior of Hg/Si contacts, and the pH dependence of the current–potential behavior of Si electrodes in contact with aqueous electrolytes.
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