N-(2,3,4-Trifluoro­phen­yl)pyrrolidine-1-carboxamide

In the title compound, C11H11F3N2O, a urea derivative, the best plane through the pyrrole ring makes a dihedral angle of 9.69 (13)° with the benzene ring. The amino H atom is shielded, so that it is not involved in any hydrogen-bonding inter­actions

Defect redistribution along grain boundaries in SrTiO3_3 by externally applied electric fields

During thermal annealing at 1425 °C nominal electric field strengths of 50 V/mm and 150 V/mm were applied along the grain boundary planes of a near 45° (100) twist grain boundary in SrTiO$_3$. Electron microscopy characterization revealed interface expansions near the positive electrode around 0.8 nm for either field strength. While the interface width decreased to roughly 0.4 nm after annealing at 50 V/mm, the higher field strength caused decomposition of the boundary structure close to the negative electrode. Electron energy-loss and X-ray photoelectron spectroscopies demonstrated an increased degree of oxygen sublattice distortion at the negative electrode side, and enhanced concentrations of Ti$^{3+}$ and Ti$^{2+}$ compared to bulk for both single crystals and bicrystals annealed with an external electric field, respectively. Oxygen migration due to the applied electric field causes the observed alteration of grain boundary structures. At sufficiently high field strength the agglomeration of anion vacancies may lead to the decomposition of the grain boundary

Utilization of In-situ Electron Microscopy in Controlling of Oxidation and Reduction Behaviors in Nanoscale Metals and Ceramics

The redox behaviors of nanoscale metal and ceramic materials are affected by various parameters and are important in determining certain properties of the material. This dissertation reports the controlling of oxidation and reduction behaviors in some example metal and ceramic materials at the nanoscale by varying material dimensions, gaseous environments, surface energy densities and application of electric fields and currents. It was suggested in previous studies that iron oxide FeO is thermodynamically unstable under 1000 K with dimensions smaller than 100 nm. In this study, in-situ heating experiments to gradually reduce Fe2O3 nanoparticles under 50 nm and nanochains were conducted in a transmission electron microscope. Electron energy loss spectroscopy and selected area electron diffraction both confirmed previous predictions and also revealed the stabilization of FeO phase in nanochains above a critical length. It provides direct evidence that metal (Ⅱ) oxide with dimensions (particle size) below 100 nm can be stabilized by assembling particles in 1D nanochains. In the case of nickel nanoparticle oxidation, anisotropic growth of nickel oxide nanostructures was observed during in-situ heating of the particles at 800 °C under water vapor atmospheres in an environmental scanning electron microscope. The NiO stoichiometry was confirmed by both energy dispersive X-ray spectroscopy and selected area electron diffraction. Annealing of the nickel particles under different oxygen partial pressures prior to ESEM heating showed that anisotropic NiO growth only takes place at specific locations where local surface energy density is high enough. The results suggested that the oxide growth can be prevented by manipulation of the surface energy by annealing under low oxygen partial pressures. One directional growth of single crystalline nickel oxide nanostructures during nickel particle oxidation is also reported at 650 C and 4 ×10-4 Pa oxygen partial pressure in a transmission electron microscope. In-situ high resolution TEM revealed the layer-by-layer growth of nickel oxide at the Ni/NiO interface while the nickel particle was being consumed. Ledge movement and disconnection migration was observed at the interface that resembled a terrace-ledge-kink growth mechanism. The study demonstrates the applicability of TLK crystal growth mechanism at buried reactive heterophase interfaces. The role of electric current on one directional nickel nanostructure growth in an SEM is also reported in the study. A positive DC bias was applied to a tungsten carbide nanoindenter tip and electric current flow was established by contacting the tip to a nickel particle sitting on a nickel micropillar. Dielectric breakdown of the nickel oxide surface layer was observed prior to nanostructure growth. Nanostructure growth was achieved upon the retraction of the indenter tip. It was demonstrated by both theoretical calculations and finite element modeling that growth was caused by the combination of electromigration and Joule heating. For ceramic materials, the study reports electric field effects on the (100) twist grain boundary core structure of SrTiO3 bicrystals. Nominal field strengths of 50 V/mm and 150 V/mm were applied to the bicrystal in the direction that’s parallel to the grain boundary during high temperature annealing after the formation of the grain boundary. High angle angular dark field imaging displayed different grain boundary structure near the positive and negative electrode side. Electron energy loss spectroscopy and X-ray photoelectron spectroscopy both showed higher oxygen vacancy concentrations, i.e. more local reduction near the negative electrode side. The defect redistribution is caused by the migration of oxygen vacancies to the negative electrode side driven by the external electric field

Mechanistic Insight into Degradation of Cetirizine under UV/Chlorine Treatment: Experimental and Quantum Chemical Studies

UV/chlorine treatment is an efficient technology for removing organic pollutants in wastewater. Nevertheless, degradation of antihistamines in the UV/chlorine system, especially the underlying reaction mechanism, is not yet clear. In this study, the degradation of cetirizine (CTZ), a representative antihistamine, under UV/chlorine treatment was investigated. The results showed that CTZ could undergo fast degradation in the UV/chlorine system with an observed reaction rate constant (kobs) of (0.19 ± 0.01) min−1, which showed a first-increase and then-decrease trend with its initial concentration increased. The degradation of CTZ during the UV/chlorine treatment was attributed to direct UV irradiation (38.7%), HO• (35.3%), Cl• (7.3%), and ClO• (17.1%). The kobs of CTZ decreased with the increase in pH and the increase in concentrations of a representative dissolved organic matter, Suwannee River natural organic matter (SRNOM), due to their negative effects on the concentrations of reactive species generated in the UV/chlorine system. The detailed reaction pathways of HO•, ClO•, and Cl• with CTZ were revealed using quantum chemical calculation. This study provided significant insights into the efficient degradation and the underlying mechanism for the removal of CTZ in the UV/chlorine system

Mechanistic Insight into Degradation of Cetirizine under UV/Chlorine Treatment: Experimental and Quantum Chemical Studies

UV/chlorine treatment is an efficient technology for removing organic pollutants in wastewater. Nevertheless, degradation of antihistamines in the UV/chlorine system, especially the underlying reaction mechanism, is not yet clear. In this study, the degradation of cetirizine (CTZ), a representative antihistamine, under UV/chlorine treatment was investigated. The results showed that CTZ could undergo fast degradation in the UV/chlorine system with an observed reaction rate constant (kobs) of (0.19 ± 0.01) min−1, which showed a first-increase and then-decrease trend with its initial concentration increased. The degradation of CTZ during the UV/chlorine treatment was attributed to direct UV irradiation (38.7%), HO• (35.3%), Cl• (7.3%), and ClO• (17.1%). The kobs of CTZ decreased with the increase in pH and the increase in concentrations of a representative dissolved organic matter, Suwannee River natural organic matter (SRNOM), due to their negative effects on the concentrations of reactive species generated in the UV/chlorine system. The detailed reaction pathways of HO•, ClO•, and Cl• with CTZ were revealed using quantum chemical calculation. This study provided significant insights into the efficient degradation and the underlying mechanism for the removal of CTZ in the UV/chlorine system

Machine Learning-Assisted Multifunctional Environmental Sensing Based on Piezoelectric Cantilever

Multifunctional environmental sensing is crucial for various applications in agriculture, pollution monitoring, and disease diagnosis. However, most of these sensing systems consist of multiple sensors, leading to significantly increased dimensions, energy consumption, and structural complexity. They also often suffer from signal interferences among multiple sensing elements. Herein, we report a multifunctional environmental sensor based on one single sensing element. A MoS2 film was deposited on the surface of a piezoelectric microcantilever (300 × 1000 μm2) and used as both a sensing layer and top electrode to make full use of the changes in multiple properties of MoS2 after its exposure to various environments. The proposed sensor has been demonstrated for humidity detection and achieved high resolution (0.3% RH), low hysteresis (5.6%), and fast response (1 s) and recovery (2.8 s). Based on the analysis of the magnitude spectra for transmission using machine learning algorithms, the sensor accurately quantifies temperatures and CO2 concentrations in the interference of humidity with accuracies of 91.9 and 92.1%, respectively. Furthermore, the sensor has been successfully demonstrated for real-time detection of humidity and temperature or CO2 concentrations for various applications, revealing its great potential in human–machine interactions and health monitoring of plants and human being