Optical Spectroscopy of Surfaces, Interfaces, and Thin Films

Optimization of hematite nanoparticles from natural ore as novel imaging agents: A Green Chemistry approach

In this research, we propose an environmentally friendly method for producing hematite nanoparticles (H-NPs) from natural hematite ore, focusing on their application as efficient contrast agents in x-ray and computed tomography (CT) imaging for medical purposes. The process involves the reduction of iron oxide within the ore to attain the desired hematite phase, crucial for synthesizing H-NPs. To ensure sustainability, we adopted a Green Chemistry approach, utilizing a combination of carbon soot and limestone for the purification process, thereby achieving eco-conscious production. The produced H-NPs were thoroughly characterized using various analytical techniques, such as x-ray fluorescence (XRF), x-ray diffraction (XRD), Fourier transmission infrared spectroscopy (FT-IR), and FESEM-EDX (field emission scanning electron microscopy-energy-dispersive x-ray spectroscopy). XRD analysis confirmed the crystalline rhombohedral hexagonal lattice structure, while FT-IR spectra indicated the presence of characteristic Fe-O stretching modes in line with the expected molecular composition. FESEM-EDX imaging unveiled agglomerated particles, ranging in size from 54.6 to 149.9 nm for iron ore and 22 nm for H-NPs. These particles were primarily composed of iron (Fe) and oxygen (O). The magnetic properties of the H-NPs were investigated through vibrating sample magnetometer (VSM) studies, highlighting their distinct ferromagnetic behavior. Of particular significance, the H-NPs demonstrated exceptional performance as contrast agents in both x-ray and CT imaging. Even at minimal concentrations, they exhibited remarkable x-ray absorption capabilities. CT scans further validated their exceptional absorptive capacity. These findings emphasize the potential of H-NPs as valuable assets in medical imaging, serving as sustainable tools for enhanced diagnostic applications. The study showcases an eco-conscious approach to harnessing natural resources, paving the way for a greener and more effective utilization of H-NPs in the medical imaging landscape.

Covalently linked pyrene antennas for optically dense yet aggregation-resistant light-harvesting systems

In this study we present a novel energy transfer material inspired by natural light-harvesting antenna arrays, zinc(II) phthalocyanine-pyrene (ZnPcPy). The ZnPcPy system facilitates energy transfer from 16 covalently linked pyrene (Py) donor chromophores to the emissive central zinc(II) phthalocyanine (ZnPc) core. Nearly 98% energy transfer efficiency is determined from the changes in emission decay rates between free MePy to covalently linked Py, supported by comparisons of photoluminescence quantum yields using different excitation wavelengths. A comparative analysis of ZnPcPy and an equivalent mixture of ZnPc and MePy demonstrates the superior light-harvesting performance of the covalently linked system, with energy transfer rates 9705 times higher in the covalently bound system. This covalent strategy allows for very high loadings of absorbing Py chromophores to be achieved while also avoiding exciton quenching that would otherwise arise, with the same strategy widely applicable to other pairs of Főrster resonance energy transfer (FRET) chromophores.

Carbonaceous Material Modified MoO2 Nanospheres with Oxygen Vacancies for Enhanced Visible-Light Photocatalytic Oxidative Coupling of Benzylamine

Surface oxygen vacancy (OV) plays a pivotal role in the activation of molecular oxygen and separation of electrons and holes in photocatalysis. Herein, carbonaceous materials-modified MoO₂ nanospheres with abundant surface OVs (MoO₂/C-OV) were successfully synthesized via glucose hydrothermal processes. In situ introduction of carbonaceous materials triggered a reconstruction of the MoO₂ surface, which introduced abundant surface OVs on the MoO₂/C composites. The surface oxygen vacancies on the obtained MoO₂/C-OV were confirmed via electron spin resonance spectroscopy (ESR) and X-ray photoelectron spectroscopy (XPS). The surface OVs and carbonaceous materials boosted the activation of molecular oxygen to singlet oxygen (¹O₂) and superoxide anion radical (•O₂^-) in selectively photocatalytic oxidation of benzylamine to imine. The conversion of benzylamine was 10 times that of pristine MoO₂ nanospheres with a high selectivity under visible light irradiation at 1 atm air pressure. These results open an avenue to modify Mo-based materials for visible light-driven photocatalysis.

In Situ Confocal Raman Microscopy of Redox Polymer Films on Bulk Electrode Supports

A spectroelectrochemical cell is described that enables confocal Raman microscopy studies of electrode-supported films. The confocal probe volume (∼1 μm³) was treated as a fixed-volume reservoir for the observation of potential-induced changes in chemical composition at microscopic locations within an ∼20 μm thickness layer of a redox polymer cast onto a 3 mm diameter carbon disk electrode. Using a Raman system with high collection efficiency and wavelength reproducibility, spectral subtraction achieved excellent rejection of background interferences, opening opportunities for measuring within micrometer-scale thickness redox films on widely available, low-cost, and conventional carbon disk electrodes. The cell performance and spectral difference technique are demonstrated in experiments that detect transformations of redox-active molecules exchanged into electrode-supported ionomer membranes. The in situ measurements were sensitive to changes in the film oxidation state and swelling/deswelling of the polymer framework in response to the uptake and discharge of charge-compensating electrolyte ions. The studies lay a foundation for confocal Raman microscopy as a quantitative in situ probe of processes within electrode-immobilized redox polymers under development for a range of applications, including electrosynthesis, energy conversion, and chemical sensing.

Methodologies for Operando ATR-IR Spectroscopy of Magnesium Battery Electrolytes

We explore the suitability of operando attenuated total reflection infrared (ATR-IR) spectroscopy methodologies for the study of organoaluminate electrolytes for Mg battery applications. The "all-phenyl complex" in tetrahydrofuran (THF), with the molecular structure [Mg₂Cl₃·6THF]⁺[AlPh₄]^-, is used as an exemplar electrolyte to compare two different spectroelectrochemical cell configurations. In one case, a Pt gauze is used as a working electrode, while in the second case, a thin (∼10 nm) Pt film working electrode is deposited directly on the surface of the ATR crystal. Spectroscopic measurements indicate substantial differences in the ATR-IR response for the two configurations, reflecting the different spatial arrangements of the working electrode with respect to the ATR sampling volume. The relative merits and potential pitfalls associated with the two approaches are discussed.

Impedance Analysis of Electrochemical Systems

Interpretation of impedance spectroscopy data requires both a description of the chemistry and physics that govern the system and an assessment of the error structure of the measurement. The approach presented here includes use of graphical methods to guide model development, use of a measurement model analysis to assess the presence of stochastic and bias errors, and a systematic development of interpretation models in terms of the proposed reaction mechanism and physical description. Application to corrosion, batteries, and biological systems is discussed, and emerging trends in interpretation and implementation of impedance spectroscopy are presented.