Lisa D. Pfefferle

Quantum dots (QDs) and single-walled carbon nanotubes (SWNTs) have electronic and photonic properties ideally suited for applications to solar cells, catalysts, sensors, and light-emitting diodes. Many of those applications require efficient energy transfer interfacing different semiconductor nanomaterials. In this study, we develop covalently bonded interfaces to optimize charge transfer from the photoexcited QD to the carbon nanotube acceptor exploiting interfacial strong electronic coupling. Ultrafast transient absorption spectroscopy of CdSe QDs reveals considerably shorter lifetimes of electronic excited states when the QDs are covalently bonded to mildly oxidized SWNTs with surface-anchoring carboxylic acid groups. We define a set of spectroscopic fingerprints to characterize strong coupling. These include suppression of photoluminescence (PL), broadened UV-vis spectra, and transient absorption time scales faster than the picosecond timescale. Thus, the QD-SWNT assemblies were characterized by UV-visible spectroscopy, transmission electron microscopy (TEM), X-ray absorption fine structure (EXAFS), transient absorption, and photoluminescence (PL) experiments. Calculations of fully atomistic models relaxed at the density functional theory (DFT) level of theory provide a rigorous interpretation of the experiments as directly compared to the simulated Cd-edge EXAFS spectra and quantum dynamics simulations of interfacial electron transfer (IET). Charge-separated states exhibit ultrafast electron transfer from the CdSe QDs to the SWNTs due to the strong electronic coupling with negligible energy barriers for charge transport between components in the QD-SWNT nanocomposites. The experimental and theoretical calculation results consistently indicate that strong interfacial coupling fundamentally modifies the electronic structure and charge-transfer dynamics, demonstrating that the QD-SWNT assemblies cannot be regarded as a simple combination but instead a hybrid system with distinct properties.

Longer wavelengths of light contain less energy but comprise more of the solar spectrum, making them important to incorporate into any process aiming for high efficiency. Here, we developed a novel redox-mediated synthetic mechanism to construct a heterojunction with strongly coupled interfaces. Specifically, an α-Fe 2 O 3 /Cu 2 O/CuO nanosheet composite was synthesized, forming an S-scheme α-Fe 2 O 3 /Cu 2 O electronic interface, a burgeoning class of materials designed to upconvert longer wavelengths of light and utilize solar energy more effectively. Through a series of experiments including X-ray photoelectron spectroscopy (XPS), ultraviolet–visible (UV–Vis) diffuse reflectance spectroscopy (UV–Vis-DRS), electrochemical impedance spectroscopy (EIS), and photocatalytic measurements, we were able to fully confirm the electronic structure of the α-Fe 2 O 3 /Cu 2 O interfacial heterojunction. These characterizations demonstrate the S-scheme flow of electrons, which is further supported by COMSOL numerical simulations. The successful formation of the S-scheme heterojunction is made possible through the direct Fe–O–Cu covalent bonding at the interface. These bonds provide ultrafast interfacial charge transfer pathways on picosecond time scales followed by long-lived charge-separated states, as quantified by our transient optical experiments. The proposed redox-mediated synthetic strategy provides a valuable guideline for constructing effective solid heterojunctions with strongly coupled interfaces, which are desirable for various applications in catalysis, energy storage, electronics, photovoltaics, and beyond.

The transition from fossil fuels to sustainable fuels offers a unique opportunity to select new fuel compositions that will not only reduce net carbon dioxide emissions , but also improve combustor performance and reduce emissions of other pollutants. A particularly valuable goal is finding fuels that reduce soot emissions. These emissions cause significant global warming , especially from aviation since soot particles are the nucleation site of contrails . Furthermore, soot contributes to ambient fine particulates , which are responsible for millions of deaths worldwide each year. Fortunately, soot formation rates depend sensitively on the molecular structure of the fuel, so fuel composition provides a strong lever for reducing emissions. Sooting tendencies measured in laboratory-scale flames provide a scientific basis for selecting fuels that will maximize this benefit. Recent work has developed new techniques that expand the range of compounds that can be tested by reducing the required sample volume and increasing the dynamic range. This has many benefits, but it is particularly essential for the development of structure-property relationships using machine learning algorithms : the accuracy and predictive ability of these relationships depends strongly on the number of compounds in the training set and the coverage of structural features. This paper reviews: (1) these new techniques; (2) trends in sooting tendency versus molecular structure; (3) structure-property relationships for sooting tendency; and (4) interpretation of the observed trends based on first-principle chemical kinetic and molecular dynamic simulations.

Quantitative sooting tendencies were measured for 10 lactones with a wide range of molecular structures. Lactones have potential as low-soot, sugar-derived alternative fuels.

Pyruvate-derived dialkoxyalkanoates (DAOAs) were synthesized in good yield using a mild protocol. Combustion performance and physical properties of DAOAs compare favorably to other low-carbon diesel fuels.

In this study, a facile method has been developed to synthesize a novel type of porous magnetic molecularly imprinted polymers (Fe3O4-MER-MMIPs) for the selective adsorption and removal of meropenem. The Fe3O4-MER-MMIPs, with abundant functional groups and sufficient magnetism for easy separation, are prepared in aqueous solutions. The porous carriers reduce the overall mass of the MMIPs, greatly improving their adsorption capacity per unit mass and optimizing the overall value of the adsorbents. The green preparation conditions, adsorption performance, and physical and chemical properties of Fe3O4-MER-MMIPs have been carefully studied. The developed submicron materials exhibit a homogeneous morphology, satisfactory superparamagnetism (60 emu g-1), large adsorption capacity (11.49 mg g-1), quick adsorption kinetics (40 min), and good practical implementation in human serum and environmental water. Finally, the protocol developed in this work delivers a green and feasible method for synthesizing highly efficient adsorbents for the specific adsorption and removal of other antibiotics as well.

Transition metal-substituted MCM-41 framework structures with a high degree of structural order and a narrow pore diameter distribution were reproducibly synthesized by a hydrothermal method using a surfactant and an anti-foaming agent. The pore size and the mesoporous volume depend linearly on the surfactant chain length. The transition metals, such as cobalt, are incorporated substitutionally and highly dispersed in the silica framework. Single wall carbon nanotubes with a narrow diameter distribution that correlates with the pore diameter of the catalytic framework structure were prepared by a Boudouard reaction. Nanostructures with a specified diameter or cross-sectional area can therefore be predictably prepared by selecting a suitable pore size of the framework structure.

The synthesis of green and multifeatured montmorillonite-supported Fe 3 O 4 -Cu 2+ hybrid adsorbents creates a roadmap for developing adsorbents for a high-abundance proteins.

2D nanoscale confined systems exhibit behavior that is markedly different from that observed at the macroscale. Confinement can be tuned by controlling the interlayer spacing between confining layers using organic dithiol linkers. Adjusting spacing and selective intercalation have important impacts for catalysis, superconductivity, spin engineering, sodium ion batteries, 2D magnets, optoelectronics, and many other applications. In this study, we report how reaction conditions and organic linkers can be used to create variable, reproducible spacings between graphene oxide to provide confinement systems. We determined the conditions under which the spacing can be variably adjusted by the type of linker used, the concentration of the linker, and the reaction conditions. Employing dithiol linkers of different lengths, such as three (TPDT) and four (QPDT) aromatic rings, we can adjust the spacing between graphene oxide layers under varied reaction conditions. Here, we show that by varying dithiol linker length and using different reaction conditions, we can reproducibly control the spacing between graphene oxide layers from 0.37 nm to over 0.50 nm.