The extended Kubelka–Munk theory and its application to spectroscopy

Order-to-Disorder Transition and Hydrogen Bonding in the Jahn-Teller Active NH4CrF3 Fluoroperovskite

Large quantities of high-purity NH4CrF3 have been synthesized using a wet-chemical method, and its structural chemistry and magnetic properties are investigated in detail for the first time. NH4CrF3 is a tetragonal fluoroperovskite that displays an ordering of the ammonium (NH4+) groups at room temperature and C-type orbital ordering. The ammonium groups order and display distinct signs of hydrogen bonds to nearby fluoride anions by buckling the Cr-F-Cr angle away from 180°. The ammonium ordering remains up to 405 K, much higher than in other ammonium fluoroperovskites, indicating a correlation between the flexibility of the Jahn-Teller ion, the hydrogen bond formation, and the ammonium ordering. At 405 K, an order-to-disorder transition occurs, where the ammonium groups disorder, corresponding to a transition to higher symmetry. This is accompanied by a contraction of the unit cell from breaking hydrogen bonds, similar to the phenomenon observed in water ice melting. The compound orders antiferromagnetically with a Neél temperature of 60 K, an effective paramagnetic moment of 4.3 μB, and a Weiss temperature of -33 K. An A-type antiferromagnetic structure is identified by neutron diffraction, with an ordered moment of 3.72(2) μB.

Bismuth-Based Perovskite Derivates with Thermal Voltage Exceeding 40 mV/K

Heat is an inexhaustible source of energy, and it can be exploited by thermoelectronics to produce electrical power or electrical responses. The search for a low-cost thermoelectric material that could achieve high efficiencies and can also be straightforwardly scalable has turned significant attention to the halide perovskite family. Here, we report the thermal voltage response of bismuth-based perovskite derivates and suggest a path to increase the electrical conductivity by applying chalcogenide doping. The films were produced by drop-casting or spin coating, and sulfur was introduced in the precursor solution using bismuth triethylxanthate. The physical-chemical analysis confirms the substitution. The sulfur introduction caused resistivity reduction by 2 orders of magnitude, and the thermal voltage exceeded 40 mV K-1 near 300 K in doped and undoped bismuth-based perovskite derivates. X-ray diffraction, Raman spectroscopy, and grazing-incidence wide-angle X-ray scattering were employed to confirm the structure. X-ray photoelectron spectroscopy, elemental analysis, scanning electron microscopy, and energy-dispersive X-ray spectroscopy were employed to study the composition and morphology of the produced thin films. UV-visible absorbance, photoluminescence, inverse photoemission, and ultraviolet photoelectron spectroscopies have been used to investigate the energy band gap.

Sulfur-Doped g-C3N4 Heterojunctions for Efficient Visible Light Degradation of Methylene Blue

The discharge of synthetic dyes from different industrial sources has become a global issue of concern. Enormous amounts are released into wastewater each year, causing concerns due to the high toxic consequences. Photocatalytic semiconductors appear as a green and sustainable form of remediation. Among them, graphitic carbon nitride (g-C3N4) has been widely studied due to its low cost and ease of fabrication. In this work, the synthesis, characterization, and photocatalytic study over methylene blue of undoped, B/S-doped, and exfoliated heterojunctions of g-C3N4 are presented. The evaluation of the photocatalytic performance showed that exfoliated undoped/S-doped heterojunctions with 25, 50, and 75 mass % of S-doped (g-C3N4) present enhanced activity with an apparent reaction rate constant (kapp) of 1.92 × 10-2 min-1 for the 75% sample. These results are supported by photoluminescence (PL) experiments showing that this heterojunction presents the less probable electron-hole recombination. UV-vis diffuse reflectance and valence band-X-ray photoelectron spectroscopy (VB-XPS) allowed the calculation of the band-gap and the valence band positions, suggesting a band structure diagram describing a type I heterojunction. The photocatalytic activities calculated demonstrate that this property is related to the surface area and porosity of the samples, the semiconductor nature of the g-C3N4 structure, and, in this case, the heterojunction that modifies the band structure. These results are of great importance considering that scarce reports are found concerning exfoliated B/S-doped heterojunctions.

Magnetically Controlled and Addressable Photoelectrochemical Sensor Array with Self-Calibration for the Label-Free Detection of Amyloid β-Proteins

A label-free addressable photoelectric immunosensor array was designed for the detection of amyloid β-proteins based on magnetic separation and self-calibration strategies. In this paper, Na2Ti6O13 with a flower-like morphology was prepared by the hydrothermal method; after continuously combining Fe3O4 and CdS, it was endowed with magnetism and better photoelectric activity. Subsequently, a series of reactions occurred in the solution, and the magnetic separation method was used to enrich the target. On the other hand, the ITO glass was separated into eight sites (2 × 4) using magnets, and a light shield was utilized to prevent light exposure, resulting in addressable and continuous detection. After the uniform preparation of magnetic photoelectric materials and precise control of testing conditions, the relative errors among different sites have been effectively reduced. Moreover, incorporating a self-calibration strategy has allowed the sensor array to achieve greater accuracy. The proposed photoelectrochemical biosensor exhibits a good relationship with amyloid β-protein ranging from 0.01 to 100 ng mL-1 with a limit of detection of 1.1 pg mL-1 and exhibits excellent specificity, reproducibility, and stability.

Halide Complexes of 5,6-Dicyano-2,1,3-Benzoselenadiazole with 1 : 4 Stoichiometry: Cooperativity between Chalcogen and Hydrogen Bonding

The [M4 -Hal]- (M=the title compound; Hal=Cl, Br, and I) complexes were isolated in the form of salts of [Et4 N]+ cation and characterized by XRD, NMR, UV-Vis, DFT, QTAIM, EDD, and EDA. Their stoichiometry is caused by a cooperative interplay of σ-hole-driven chalcogen (ChB) and hydrogen (HB) bondings. In the crystal, [M4 -Hal]- are connected by the π-hole-driven ChB; overall, each [Hal]- is six-coordinated. In the ChB, the electrostatic interaction dominates over orbital and dispersion interactions. In UV-Vis spectra of the M+[Hal]- solutions, ChB-typical and [Hal]- -dependent charge-transfer bands are present; they reflect orbital interactions and allow identification of the individual [Hal]- . However, the structural situation in the solutions is not entirely clear. Particularly, the UV-Vis spectra of the solutions are different from the solid-state spectra of the [Et4 N]+ [M4 -Hal]- ; very tentatively, species in the solutions are assigned [M-Hal]- . It is supposed that the formation of the [M4 -Hal]- proceeds during the crystallization of the [Et4 N]+ [M4 -Hal]- . Overall, M can be considered as a chromogenic receptor and prototype sensor of [Hal]- . The findings are also useful for crystal engineering and supramolecular chemistry.

X-ray and Neutron Diffraction Studies of SrTe2FeO6Cl, an Oxide Chloride with Rare Anion Ordering

The oxychloride SrTe2FeO6Cl is obtained by high-temperature solid-state synthesis under inert conditions in closed reaction vessels. The compound crystallizes in a novel monoclinic crystal structure that is described in the space group P121/n1 (No. 14). The unit cell parameters, a = 10.2604(1) Å, b = 5.34556(5) Å, c = 26.6851(3) Å, and β = 93.6853(4)°, and atomic parameters were determined from synchrotron diffraction data, starting from a model that was obtained from single-crystal X-ray diffraction data. The anion lattice exhibits a rare ordering of oxide and chloride ions: one-dimensional zig-zag ladders of chlorine (squarelike motif) are surrounded by an oxygen matrix. Two different iron sites coordinated solely to oxygen are present in the structure, one octahedral and one square pyramidal, both distorted. Similarly, two different strontium coordinations are present; the first homoleptic coordinated to eight oxygen atoms and the second heteroleptic coordinated to four oxygen and four chlorine atoms in a fac-like manner. The lone pair of Te(IV) is directed toward the larger chlorine atoms. Magnetic susceptibility measurements confirm that Fe is +3 (d5) in the high-spin electronic configuration, exhibiting an almost ideal spin-only moment, μeff = 5.65 μB Fe-1. The slightly negative Weiss constant (θCW = -39 K) suggests dominating antiparallel spin-to-spin coupling in the paramagnetic temperature range, agreeing with an observed long-range antiferromagnetic spin ordering below Néel temperature, TN ∼ 13 K, and a broad second order-like anomaly in the specific heat measurement data. Low-temperature neutron diffraction data reveal that the antiferromagnetic ordered phase is C-type, with a k-vector (1/2, 1/2, 0) and ordered moment of 4.14(7) μB. The spin structure can be described as antiferromagnetic ordered layers stacked along the a-axis, forming layers of squares that alternate along the c-axis.

Green synthesize of copper nanoparticles on the cotton fabric as a self-regenerating and high-efficient plasmonic solar evaporator

Harvesting solar energy, as a clean and abundant resource, in the photothermal process, is the winning point of solar steam generation (SSG) systems. Herein, copper plasmonic nanoparticles were synthesized through a green method via red sanders extraction on the cotton fabric as the reducing matrix. The prepared fabrics were analyzed using FESEM, EDS, XRD, PL, Raman, and contact angle. The treated fabric on the stitched PU foam with cotton yarns with bio-inspired jellyfish structure was used for heat localization and water transmission, simultaneously. The evaporation rate, enhancement, and conversion efficiency of the plasmonic SSG were 1.73 kg m-2 h-1, 179%, and ~ 98%, under one sun irradiation, respectively. The quality of the collected water was investigated via induced coupled plasma which presents the proper solar desalination (> 99.83% for filtration of Na+ ion). Regenerating features of the treated fabric along with the simple and cost-effective preparation method promises viable aspects of our system for large-scale applications.

Influence of particle size of flame-synthesized carbon nanoparticles on band gap and photoluminescence properties

Band gap and photoluminescence (PL) properties were investigated for flame-synthesized carbon nanoparticles (CNPs) of four different particle size distributions. The particles were collected by varying the flow rates of fuel and oxidizer in a controllable co-flow diffusion flame. The results indicated the possibility of both direct and indirect band gaps in the synthesized CNPs. The band gaps were found to increase with a decrease in the particle size, thereby exhibiting the quantum confinement effect. The PL properties observed with the pure powdered sample showed strong emission in the green region. However, for samples dispersed in isopropyl alcohol, the emission wavelength shifts towards the blue region, showing strong solvent dependence. The particle size of CNPs, however, only affects the emission peak intensities.

Liquid-Ammonia-Mediated Dyeing Process of Wool at a Lower Temperature

Liquid ammonia as a non-aqueous medium has many physical properties close to water, such as small molecular weight and strong permeability. It has been widely used for the ecological processing of cellulosic fibers to improve their luster, softness and dyeing properties. However, there are few reports on the dyeing of wool treated with liquid ammonia, especially at a lower temperature. Herein, a continuous liquid ammonia finishing machine was used to batch process wool followed by dyeing in a commonly-used wool dyeing machine. The results showed that many scale flakes and some cuticle cracking were seen on the fiber surface, and the disulfide bonds of cystine were broken down after liquid ammonia treatment, which promoted the diffusion of dyestuff into the fiber. Moreover, the uptakes and K/S value of wool dyed with Lanaset and Lanasol CE dyes were higher than the untreated wool, and the dyeing temperature could decrease to 85 °C, while the degree of fiber strength reduction merely decreased by 3–5%. Furthermore, for the reactive dyes, the dyeing temperature can reduce to 70 °C with the chemical auxiliaries Miralan LTD, while the degree of strength reduction decrease by 8–10%. Liquid ammonia treatment can be used for dyeing at a lower temperature than boiling temperature (100 °C), reduce energy consumption and reduce the degree of fiber strength reduction of wool. The method shows considerable to great value and is significant in providing a feasible approach for the industrial application of low-temperature dyeing technology.

The world of inorganic pigments

Abstract

Inorganic pigments have been very important substances for human life for thousands of years. They have contributed and continue to contribute to the beautification of our daily life and habitat and to the accentuation and differentiation of objects, and influence thoughts, moods, and feelings. The industrial manufacture of inorganic pigments based on growing chemical and physical knowledge started around 1800. Before that, pigments based on natural materials or manufactured by mostly empirical processes were used. Most of the technically relevant inorganic pigments were developed and first produced on an industrial scale in the nineteenth and twentieth centuries. Ongoing developments are aiming to improve existing conventional pigments as well as synthesize new, innovative colorants, especially in the classes of effect pigments and functional pigments. The objective of this text is to present comprehensive knowledge about inorganic pigments, including definitions, types of pigments and their properties, historical pigments, modern inorganic pigments, synthesis methods, and applications. It is also intended to show the current status of new pigment developments.

Graphical abstract

Collection of samples of inorganic pigments

Spectral Properties of Foams and Emulsions

The optical and spectral properties of foams and emulsions provide information about their micro-/nanostructures, chemical and time stability and molecular data of their components. Foams and emulsions are collections of different kinds of bubbles or drops with particular properties. A summary of various surfactant and emulsifier types is performed here, as well as an overview of methods for producing foams and emulsions. Absorption, reflectance, and vibrational spectroscopy (Fourier Transform Infrared spectroscopy-FTIR, Raman spectroscopy) studies are detailed in connection with the spectral characterization techniques of colloidal systems. Diffusing Wave Spectroscopy (DWS) data for foams and emulsions are likewise introduced. The utility of spectroscopic approaches has grown as processing power and analysis capabilities have improved. In addition, lasers offer advantages due to the specific properties of the emitted beams which allow focusing on very small volumes and enable accurate, fast, and high spatial resolution sample characterization. Emulsions and foams provide exceptional sensitive bases for measuring low concentrations of molecules down to the level of traces using spectroscopy techniques, thus opening new horizons in microfluidics.

Pyrithione metal (Cu, Ni, Ru) complexes as photo-catalysts for styrene oxide production

Selective photochemical oxidation of styrene was performed in an active acetonitrile medium, using H₂O₂ with or without ultraviolet (UV) light radiation. Pyrithione metal complexes (M-Pth: M = Cu(II), Ni(II), Ru(II); Pth = 2-mercaptopyridine-N-oxide) were used as catalysts. Catalytic testing measurements were done by varying the time, chemical reaction temperature and H₂O₂ concentration with or without UV energy. Epoxide styrene oxide (SO), benzaldehyde and acetophenone were the major synthesized products. A high batch rate, conversion and selectivity towards SO was shown in the presence of UV. A minor constant formation of CO₂ was observed in the stream. Coordinated Ru-based compounds demonstrated the highest process productivity of SO at 60 °C. The effect of the functional alkyl substituent on the ligand Pth, attached to the specific ruthenium(II) centre, decreased the activity of the substance. Ni-Pth selectively yielded benzaldehyde. The stability of the catalysts was examined by applying nuclear magnetic resonance (NMR) spectroscopy and thermogravimetric analysis coupled with mass spectrometry. Tested metal complexes with pyrithione (M-Pth) exhibited excellent reuse recyclability up to 3 cycles.

Photocatalytic Degradation of Thiacloprid Using Tri-Doped TiO2 Photocatalysts: A Preliminary Comparative Study

Different tri-doped TiO2 photocatalysts (Fe-N-P/TiO2, Fe-N-S/TiO2, Fe-Pr-N/TiO2, Pr-N-S/TiO2, and P-N-S/TiO2) were successfully prepared and tested in the photocatalytic removal of thiacloprid (THI) under UV-A, visible, and direct solar light irradiation. The physical-chemical properties of the prepared catalysts were analyzed by different characterization techniques, revealing that dopants are effectively incorporated into the anatase TiO2 lattice, resulting in a decrease of the energy band gap. The reduction of photoluminescence intensity indicates a lower combination rate and longer lifespan of photogenerated carriers of all doped samples in comparison with the un-doped TiO2. The doped photocatalysts not only significantly promote the photodegradation under UV-A light irradiation but also extend the optical response of TiO2 to visible light region, and consequently improve the visible light degradation of THI. Fe-N-P tri-doped TiO2 sample exhibits the highest THI photodegradation degree (64% under UV-A light, 29% under visible light and 73% under solar light).

Photonic Crystal of Polystyrene Nanomembrane: Signal Amplification and Low Triggered Potential Electrochemiluminescence for Tetracycline Detection

In this work, a low triggered potential electrochemiluminescence strategy based on gold-filled photonic crystals (GPCs) electrodes composed of photonic crystals self-assembled with polystyrene spheres and gold nanoparticles embedded in the gaps of the photonic crystals was proposed. The GPCs electrodes served as the detection platform to bind antigen, and Ru(bpy)₃²⁺-COOH as a luminophore was labeled on the antibody (Ab). Then, Ru(bpy)₃²⁺-COOH/Ab was connected to the immobilized antigen on the surface of the photonic crystals by the immunoreaction to avoid direct contact with the gold nanoparticles surface. ECL emission can only be initiated by electrochemical oxidation of tripropylamine (TPrA) since Ru(bpy)₃²⁺-COOH cannot be oxidized directly on the electrode surface. The TPrA^·+ and TPrA^· radicals generated by the oxidation of TPrA can spread to the vicinity of Ru(bpy)₃²⁺-COOH over a short distance and react with the Ru(bpy)₃²⁺-COOH, eventually producing ECL emission. The potential of ECL emission caused by TPrA oxidation was about 300 mV lower than that caused by Ru(bpy)₃²⁺-COOH oxidation because the oxidation potential of TPrA (0.95 V vs SCE) was lower than Ru(bpy)₃²⁺-COOH (1.25 V vs SCE). Furthermore, the photonic crystals nanomembrane has the capability to enhance electrochemiluminescence. Thereafter, tetracycline antibiotic as a model compound was successfully detected via competitive immunoassay on GPCs electrodes with a detection limit of 0.075 pg/mL (S/N = 3), which has broad application prospects in the field of analysis and detection.

Industrial research on evolution and prediction of hardwood color

Color prediction in dyed wood is a difficult task since it involves the analysis of light propagation through a complex media where scattering and absorption processes are present. Kubelka-Munk-based models are usually proposed to make those predictions. Here, an oak wood color prediction tool is presented with the Kubelka-Munk theory and self-learning procedures as the basis of the model. Color prediction lies on the joint contribution of both the dying material and the wood substrate, each characterized by their previously obtained colorimetric and spectral properties. An identification of wood and dyes through the study of their optical properties is shown, from which the necessary parameters are obtained for the different applications. The model allows us to predict with good accuracy the resulting color in wood through the L^∗C^∗h^∘ coordinates when mixing either water or solvent-based dyes in different proportions for dying a wood substrate. Furthermore, the influences of applying dye mixtures either by hand with a brush or by machine with a roller coating and also that of varnishing are studied.

The Polychromatic Woodburytype-Colour Tracking in Translucent, Patterned Gelatin/Pigment Films

The Woodburytype is a 19th century photomechanical technique capable of producing high-quality continuous-tone prints. It uses pigment dispersed in gelatin to produce a 2.5D print, in which the effect of varying tone is produced by a variation in the print height. We propose a method of constructing full colour prints in this manner, using a CMY colour model. This involves the layering of multiple translucent pigmented gelatin films and tracking how the perceived colour of these stacks changes with varying height. A set of CMY inks is constructed, taking into account the optical properties of both the pigment and gelatin, and a method of translating images into these prints is detailed.