Facile Synthesis, Characterization, Catalytic and Photocatalytic Activity of Multiferroic BiFeO3 Perovskite Nanoparticles

We report the synthesis of multiferroic BiFeO3 perovskite nanoparticles using the microwave combustion technique. Phase evolution is investigated by X-ray diffraction (XRD), which confirms that the formation of a secondary α-Bi2O3 phase with a monoclinic structure along with the existing rhombohedral (BiFeO3) structure. The average crystalline size has been found at 50 nm. The optical band gap was calculated from the Tauc’s plot it has been found 2.18 eV, as measured by diffuse reflectance spectroscopy (DRS). The appearances of Fourier transform infrared spectroscopy (FT-IR) absorption bands at 550 and 444 cm-1 were correlated to the rhombohedral stretching modes of bismuth ferrite nanostructure. The morphology observations using scanning electron microscopy (SEM) showed the formation of nanosized grains with pores. Energy-dispersive X-ray analysis (EDX) was done to confirm the extent of Bi3+, Fe3+, and O2- in the samples. The magnetization-Field (M-H) hysteresis curves recorded from the vibrating sample magnetometer (VSM) revealed the appearance of ferrimagnetic behavior at room temperature. The specific surface area characterized by N2 adsorption-desorption isotherm is found 44.86 m2 g-1 using Brunauer-Emmett-Teller (BET) technique. The as-fabricated BiFeO3 perovskite nanoparticles were investigated for their superior catalytic activity in two applications, which include (i) the conversion of glycerol to formic acid in a selective liquid phase batch reactor at atmospheric pressure. This bismuth-based nanoparticles exhibit as an efficient multifunctional catalyst with high conversion and selectivity efficiency around 99.2% and 98.5%, respectively, (ii) the photocatalytic degradation of rhodamine B under visible light irradiation is found maximum efficiency (99.9%), when a small amount of H2O2 was added during photocatalysis, indicating the samples possessed photo-Fenton like catalytic activity. Finally, we concluded that the BiFeO3 perovskite nanoparticles' high performance in future multifunctional devices is demonstrated by the simultaneous enhancement of catalytic and photocatalytic activities.

Probing dissolved CO2(aq) in aqueous solutions for CO2 electro-reduction and storage

CO2 dissolved in aqueous solutions is of wide ranging importance from CO2 capture, storage and photo-/electro-reduction in the fight against global warming, to CO2 analysis in various liquids including natural waterbodies and consumer drinking products. Here we developed micro-scale infrared (IR) spectroscopy for in-situ dynamic monitoring and quantitating CO2(aq) in aqueous solutions with high time resolutions under various conditions including CO2 gas bubbling and high pressures. The quantized CO2(g) rotational state transitions were observed to quench when dissolved in water to form CO2(aq) solvated by water molecules, accompanied by increased H2O IR absorption. An accurate CO2 molar extinction coefficient ε was derived for in-situ CO2(aq) quantification up to 58 atm. For the first time, we directly measured CO2(aq) concentrations in electrolytes under CO2(g) bubbling and high pressure conditions. In KHCO3 electrolytes with CO2(aq) > ~ 1 M, CO2 electroreduction (CO2RR) to formate reaches > 98% Faradaic efficiencies on copper (Cu2O/Cu) based electrocatalyst. Further, we probed CO2 dissolution/desolvation kinetics important to energy and environmental applications dynamically, revealing large hysteresis and ultra-slow reversal of CO2(aq) supersaturation in water, with implications to CO2 capture, storage and supersaturation phenomena in natural water bodies.

Direct Observation of Peptide Hydrogel Self-Assembly

The characterization of self-assembling molecules presents significant experimental challenges, especially when associated with phase separation or precipitation. Transparent window infrared (IR) spectroscopy leverages site-specific probes that absorb in the “transparent window” region of the biomolecular IR spectrum. Carbon-deuterium (C-D) bonds are especially compelling transparent window probes since they are non-perturbative, can be readily introduced site selectively into peptides and proteins, and their stretch frequencies are sensitive to changes in the local molecular environment. Importantly, IR spectroscopy can be applied to a wide range of molecular samples regardless of solubility or physical state, making it an ideal technique for addressing the solubility challenges presented by self-assembling molecules. Here, we present the first continuous observation of transparent window probes following stopped-flow initiation. To demonstrate utility in a self-assembling system, we selected the MAX1 peptide hydrogel, a biocompatible material that has significant promise for use in tissue regeneration and drug delivery. C-D labeled valine was synthetically introduced into five distinct positions of the twenty-residue MAX1 β-hairpin peptide. Consistent with current structural models, steady-state IR absorption frequencies and linewidths of C-D bonds at all labeled positions indicate that these side chains occupy a hydrophobic region of the hydrogel and that the motion of side chains located in the middle of the hairpin is more restricted than those located on the hairpin ends. Following a rapid change in ionic strength to initiate gelation, the peptide absorption spectra were monitored as function of time, allowing determination of site-specific time constants. We find that within the experimental resolution, MAX1 gelation occurs as a cooperative process. These studies suggest that stopped-flow transparent window FTIR can be extended to other time-resolved applications, such as protein folding and enzyme kinetics.

The Infrared Complex Refractive Index of Amorphous Ammonia Ice at 40 K (1.43–22.73 μm) and Its Relevance to Outer Solar System Bodies

A near-IR absorption band at 2.2 μm linked to ammonia-containing ice has been detected on icy bodies throughout the solar system and appears in the extensive volume of data for Pluto and Charon returned by New Horizons. This band is an important clue for understanding the abundance of ammonia and ammoniated compounds on the surface of outer solar system bodies and requires new laboratory data for its full analysis. To satisfy this data need, the complex refractive index of amorphous ammonia ice was calculated from experimental infrared transmission spectra with ice deposition and measurements conducted at 40 K, a characteristic surface temperature for outer solar system bodies. The measured imaginary part of the complex refractive index and associated band strength calculations are generally larger than prior published values for amorphous ammonia ice at 30 K. The complex refractive index for amorphous ammonia at 40 K computed in the mid-infrared region (2.5–22.73 μm) will also be valuable for interpreting observations of both solar system and astrophysical sources anticipated with the Near InfraRed Spectrograph and Mid-Infrared Instrument on the James Webb Space Telescope.

Fabrication and Characterization of a Dye-Sensitized Solar Cell using Natural Dye Extract of Rosella (Hibiscus sabdariffa L.) as Photosensitizer

The relatively low energy conversion efficiency of dye-sensitized solar cells (DSSCs) is a key challenge hindering the commercialization of the solar cell. The photochemical performance of the dye used as a photosensitizer for the DSSC greatly determines the efficiency of the solar cell. This study demonstrates the suitability of dye extracted from rosella (Hibiscus sabdariffa L.) flowers as a photosensitizer for a DSSC. The natural dye was extracted using the acid water extraction method and was characterized using FTIR spectroscopy and UV–vis spectrophotometry. The absorption spectra of the dye were examined to determine the aptness of the dye as a photosensitizer in DSSCs. The IR absorption spectra of the extracted dye confirmed both amine and hydroxyl compounds as functional groups in the natural dye, which established the suitability of the dye as a photosensitizer in DSSCs.The UV-vis absorption spectra of the natural dye within the visible region illustrate that the aqueous extract from rosella flowers has stable absorption of visible light, thus validating the natural dye as a good candidate for photosensitizer in a DSSC. The fabricated DSSC delivered a short-circuit current of 5 ?A and an open-circuit voltage of 0.637 V.

Measuring in situ CO2 and H2O in apatite via ATR-FTIR

We present a new approach to determine in situ CO2 and H2O concentrations in apatite via attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR). Absolute carbon and hydrogen measurements by nuclear reaction analysis (NRA) and elastic recoil detection (ERD) are used to calibrate ATR-FTIR spectra of CO2 and H2O in apatite. We show that CO2 and H2O contents in apatite can be determined via linear equations (r2 > 0.99) using the integrated area of CO2 and H2O IR absorption bands. The main benefits of this new approach are that ATR-FTIR analyses are non-destructive and can be conducted on polished sample material surfaces with a spatial resolution of ~ 35 μm. Furthermore, the wavenumber of the phosphate IR absorption band can be used to determine the crystallographic orientation of apatite, which allows for accurate quantification of CO2 and H2O in randomly orientated apatite grains. The limit of quantification of H2O in apatite is ~ 400 ppm and ~ 100 ppm for CO2. Via two examples, one from a carbonatite and one from a metasedimentary rock, we show that this new technique opens up new possibilities for determining volatile concentrations and behavior in a wide range of hydrothermal, igneous, and metamorphic systems.

Nanosilver Immobilized in Carbonaceous Particles Derived from Hydrothermal Carbonization of Eleusine indica Leaf Extract

In this study, for the first time, hydrothermal treatment of Eleusine indica leaf extract and silver nitrate produced nanosilver immobilized in hydrothermal carbon synthesized at different reaction times (RT) - 6, 12, 24 and 48 h. The surface morphology of nanosilver hydrochar (AgNP@hydrochar) composites was studied using SEM, while their chemical functionalities were investigated using FT-IR, UV-Vis, XRF and EDX spectroscopy. The AgNP@hydrochar were observed to be agglomerated spherical particles with size ranges from 128 to 171 nm. Varying C=O and C=C IR absorption peaks at different RT suggested that the plant extract reduced Ag+ into Ag0 in solution. Elemental analysis using EDX showed that Ag is dominant in the composite (84.07 %) supported by the Ag spatial distribution as demonstrated by the EDX elemental mapping. HIGHLIGHTS For the first time, hydrothermal treatment of Eleusine indica leaf extract with silver nitrate resulted in nanosilver trapped in hydrothermal carbon HTC process of E. indica extract produced composite having agglomerated spherical particles EDX elemental mapping showed an abundant silver in the synthesized composite GRAPHICAL ABSTRACT

Engineering of defects in fast neutron irradiated synthetic diamonds

Chemical vapor deposited (CVD) diamonds have been irradiated with fast reactor neutrons at fluencies F = 1·1018 and 3 · 1018 cm-2 and then heated at temperatures up to 1600 °C. The processes of annealing in and annealing out of various complexes of intrinsic defects responsible for vibrational and electron-vibrational bands in the IR absorption spectra have been studied in detail. Some tens of local vibrational modes and zero-phonon lines with rather small width caused by numerous complexes of intrinsic defects were observed in the 400-11000 cm-1 range.

Colloidal Cu-Zn-Sn-Te Nanocrystals: Aqueous Synthesis and Raman Spectroscopy Study

Cu-Zn-Sn-Te (CZTTe) is an inexpensive quaternary semiconductor that has not been investigated so far, unlike its intensively studied CZTS and CZTSe counterparts, although it may potentially have desirable properties for solar energy conversion, thermoelectric, and other applications. Here, we report on the synthesis of CZTTe nanocrystals (NCs) via an original low-cost, low-temperature colloidal synthesis in water, using a small-molecule stabilizer, thioglycolic acid. The absorption edge at about 0.8–0.9 eV agrees well with the value expected for Cu2ZnSnTe4, thus suggesting CZTTe to be an affordable alternative for IR photodetectors and solar cells. As the main method of structural characterization multi-wavelength resonant Raman spectroscopy was used complemented by TEM, XRD, XPS as well as UV-vis and IR absorption spectroscopy. The experimental study is supported by first principles density functional calculations of the electronic structure and phonon spectra. Even though the composition of NCs exhibits a noticeable deviation from the Cu2ZnSnTe4 stoichiometry, a common feature of multinary NCs synthesized in water, the Raman spectra reveal very small widths of the main phonon peak and also multi-phonon scattering processes up to the fourth order. These factors imply a very good crystallinity of the NCs, which is further confirmed by high-resolution TEM.

The potential of spectroscopy in the diagnosis of hepatocellular carcinoma – a pilot study

Summary: None of the bio­markers studied so far in the HCC area has yielded higher sensitivity and specificity in the early-stage dia­gnosis than the liver ultrasonography examination. There is an urgent clinical need for establishing a laboratory marker for HCC that meets the requirements for high sensitivity and specificity for the screening and early dia­gnosis of at-risk patients. As a variety of pathological processes, including carcinogenesis, may cause changes in both the concentration and the structure and spatial arrangement of body bio­molecules, the spectroscopic analysis of blood-based derivatives appears to be an appropriate tool for the early detection thereof. In our research, the focus is on the identification of novel bio­markers in blood plasma, which would exhibit sufficient sensitivity and specificity to detect early and potentially curable HCC stages, and which would be potentially useful for routine screening of this disease in well-defined at-risk groups. For this purpose, we utilised a unique combination of two chiroptical methods – electronic circular dichroism (ECD) and Raman optical activity (ROA) – supplemented by non-polarised variants – infrared (IR) absorption and Raman spectroscopy. Methods: Blood plasma of 18 selected patients with liver cirrhosis, 8 of which also suffered from HCC, was analysed by a combination of ECD, ROA, IR and Raman spectroscopy. Results: The obtained spectral data were processed by a multivariate statistical evaluation using principal component analysis (PCA) and linear discriminant analysis (LDA). The visualisation of the LDA results showed the separation of the two monitored groups with only a slight overlap. Based on the spectral analysis within this preliminary study, sensitivity and specificity for the discrimination between cirrhotic individuals with and without HCC reached 88% and 90% after leave-one-out cross validation, respectively. The area under the ROC curve of 0.975 proved high reliability of the established model. Conclusion: Based on our findings, the combination of advanced spectroscopic methods for the analysis of blood plasma might be a promising tool in HCC dia­gnosis and potentially in the screening thereof. Key words: hepatocellular carcinoma – blood plasma – spectroscopy – cirrhosis