Luminescent polymethylmethacrylate (PMMA) films were prepared by the solvent-casting technique from polymer solution doped with different concentrations of red perylene dyestuffs (KREMER 94720 and KREMER 94739). The effect of the dye concentration on the structure and spectroscopic properties was studied using X-ray diffraction (XRD), transmission electron microscope (TEM) optical absorption, and fluorescence spectroscopy. The optimum dye concentration of photoselective PMMA films was determined by the fluorescence spectroscopy measurements and showed the best emission properties for the doping concentration 10⁻³ wt % of the investigated dyes. The accelerated photostability tests showed promising stability of the prepared films towards terrestrial solar ultraviolet radiation (UVA). The results endorsed a promising application of the investigated films in photoselective greenhouse cladding applications as the optimized film fluoresces at the action spectra of special chlorophyll a.

This study investigated the dielectric and photocatalytic properties of green-synthesized titanium dioxide nanoparticles (TiO₂ NPs), which are widely utilized semiconductor materials known for their excellent optical, structural, and electronic characteristics. The TiO₂ NPs were synthesized via a green precipitation method from the aqueous extract of Cymbopogon proximus. A comprehensive set of analytical techniques—UV–Vis spectroscopy, XRD, FTIR, TEM, EDX, and DLS—was employed to determine their optical response, crystalline structure, functional groups, morphology, elemental composition, and particle size distribution. UV–Vis analysis revealed a characteristic absorption peak at 327 nm, and the band gap energy, calculated via the Tauc plot method, was 3.16 eV. The XRD results confirmed the formation of a tetragonal TiO₂ phase with an average crystallite size of approximately 4 nm. TEM images further supported the spherical to quasitetragonal morphology and revealed that the aggregated clusters formed conjoint nanostructures. The photocatalytic activity of the TiO₂ NPs was evaluated using a 0.5 mM RhB dye solution under UV–visible irradiation. The synthesized nanoparticles achieved a photodegradation efficiency of 97% after 50 h, with a corresponding rate constant of 0.073402 h⁻¹, indicating their potential for effective photocatalytic pollutant removal. Furthermore, the dielectric behavior of the TiO₂ NPs was examined at room temperature. The material exhibited a high dielectric constant at low frequencies due to interfacial (Maxwell–Wagner) polarization, along with frequency-dependent AC conductivity attributed to charge-carrier hopping mechanisms. These dielectric properties, combined with strong photocatalytic performance, underscore the suitability of green-synthesized TiO₂ NPs for applications in environmental remediation, energy-storage devices, and advanced technologies.

In this study, a sensing device employing a gold-coated quartz tuning fork (QTF) modified with a self-assembled monolayer (SAM) of L-cysteine was evaluated for the sensitive detection of Cu²⁺ ions in aqueous solutions. Three copper (II) salts, CuSO₄, CuCl₂, and Cu(NO₃)₂, at four different concentrations (10⁻¹², 10⁻¹⁰, 10⁻⁸, and 10⁻⁶ M) in small (100 μL) water sample amounts were each used as analytes to investigate the influence of their counterions in the detection of the Cu²⁺ ions. It was found that, among the counterions, the sulfate anion had the largest effect upon the detection of Cu²⁺ in water, in the following order: SO₄²⁻ > Cl⁻ > NO₃⁻. The lower limit of detection of the Cu²⁺ ions detected was in the 10⁻¹² M range. The frequency shifts measured with the QTFs relative to deionized water were inversely proportional to the concentration/mass of the analytes. Density functional theory calculations were conducted to understand the effect of the counterions on the respective electronic interaction energies for the apparent host–guest binding of the analytes with L-cysteine and with gold surface-bound L-cysteine molecules. Gas phase (both with and uncorrected BSSE) and solution phase interaction energies (ΔIE) calculated at the B3LYP/LANL2DZ and ωB97XD levels of theory showed that the stability for the complexes were in the following order: [L-cysteine]⊃[CuSO₄] > [L-cysteine]⊃[CuCl₂] > [L-cysteine]⊃[Cu(NO₃)₂], which supports our experimental findings, as they were in the same order as the experimentally observed order for the copper salts tested: CuSO₄ > CuCl₂ > Cu(NO₃)₂.

Micromechanical sensors, in which the sensor response is created as a result of molecular interactions on the sensors’ surfaces, have been employed as a powerful technique for rapid and sensitive detection of low concentrations of chemical and biological materials. In the study reported herein, poly(methyl methacrylate) (PMMA)-coated microcantilever (MCL) sensors were used to detect the vapors of volatile alcohols (methanol, ethanol, and isopropanol) at three different concentrations. A vapor generator was used to generate and flow the alcohol vapor onto the PMMA coated MCL surface in a closed system chamber. The vapor adsorption onto the MCL surface results in a rapid and measurable deflection of the MCL. No significant deflections of the uncoated MCL occurred when the different vapors were passed through into the microcantilever chamber. Linear concentration–deflection responses were observed, with the highest sensitivity shown with methanol, followed by ethanol and then isopropanol. Density functional theory (DFT) quantum chemical calculations were conducted to estimate the electronic interaction energies (ΔIE) between the alcohol molecules and MMA and two different model tetrameric segments of PMMA. The computed ΔIEs were in the same order as the experimentally observed order: methanol > ethanol > isopropanol.

Quartz tuning forks (QTFs), which were coated with gold and with self-assembled monolayers (SAM) of a lower-rim functionalized calix[4]arene methoxy ester (CME), were used for the detection of benzene, toluene, and ethylbenzene in water samples. The QTF device was tested by measuring the respective frequency shifts obtained using small (100 µL) samples of aqueous benzene, toluene, and ethylbenzene at four different concentrations (10⁻¹², 10⁻¹⁰, 10⁻⁸, and 10⁻⁶ M). The QTFs had lower limits of detection for all three aromatic hydrocarbons in the 10⁻¹⁴ M range, with the highest resonance frequency shifts (±5%) being shown for the corresponding 10⁻⁶ M solutions in the following order: benzene (199 Hz) > toluene (191 Hz) > ethylbenzene (149 Hz). The frequency shifts measured with the QTFs relative to that in deionized water were inversely proportional to the concentration/mass of the analytes. Insights into the effects of the alkyl groups of the aromatic hydrocarbons on the electronic interaction energies for their hypothetical 1:1 supramolecular host–guest binding with the CME sensing layer were obtained through density functional theory (DFT) calculations of the electronic interaction energies (ΔIEs) using B3LYP-D3/GenECP with a mixed basis set: LANL2DZ and 6-311++g(d,p), CAM-B3LYP/LANL2DZ, and PBE/LANL2DZ. The magnitudes of the ΔIEs were in the following order: [Au4-CME⊃[benzene] > [Au4-CME]⊃[toluene] > [Au4-CME]⊃[ethylbenzene]. The gas-phase BSSE-uncorrected ΔIE values for these complexes were higher, with values of −96.86, −87.80, and −79.33 kJ mol⁻¹, respectively, and −86.39, −77.23, and −67.63 kJ mol⁻¹, respectively, for the corresponding BSSE-corrected values using B3LYP-D3/GenECP with LANL2dZ and 6-311++g(d,p). The computational findings strongly support the experimental results, revealing the same trend in the ΔIEs for the proposed hypothetical binding modes between the tested analytes with the CME SAMs on the Au-QTF sensing surfaces.