Widespread microplastic pollution is raising growing concerns as to its detrimental effects upon living organisms. A realistic risk assessment must stand on representative data on the abundance, size ...distribution and chemical composition of microplastics. Raman microscopy is an indispensable tool for the analysis of very small microplastics (<20 μm). Still, its use is far from widespread, in part due to drawbacks such as long measurement time and proneness to spectral distortion induced by fluorescence. This review discusses each drawback followed by a showcase of interesting and easily available solutions that contribute to faster and better identification of microplastics using Raman spectroscopy. Among discussed topics are: enhanced signal quality with better detectors and spectrum processing; automated particle selection for faster Raman mapping; comprehensive reference libraries for successful spectral matching. A last section introduces non-conventional Raman techniques (non-linear Raman, hyperspectral imaging, standoff Raman) which permit more advanced applications such as real-time Raman detection and imaging of microplastics.
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•Raman is the method of choice for identifying small microplastics (<20 μm).•Automated mapping routines and library matching allow fast microplastic detection.•Nonlinear Raman techniques enable real-time monitoring of microplastics.
A thorough vibrational spectroscopy and molecular modeling study on poly(ethylene 2,5-furandicarboxylate) (PEF) explores its conformational preferences, in the amorphous and crystalline regions, ...while clarifying structure–property correlations. Despite the increasing relevance of PEF as a sustainable polymer, some of its unique characteristics are not yet fully understood and benefit from a deeper comprehension of its microstructure and intermolecular bonding. Results show that in the amorphous domains, where intermolecular interactions are weak, PEF chains favor a helical conformation. Prior to crystallization, polymeric chains undergo internal rotations extending their shape in a zigzag patternan energetically unfavorable geometry which is stabilized by C–H···O bonds among adjacent chain segments. The zigzag conformation is the crystalline motif present in the α and β PEF polymorphs. The energy difference among the amorphous and crystalline chains of PEF is higher than in PET poly(ethylene terephthalate) and contributes to PEF’s higher crystallization temperature. The 3D arrangement of PEF chains was probed using inelastic neutron scattering (INS) spectroscopy and periodic DFT calculations. Comparing the INS spectra of PEF with that of poly(ethylene terephthalate) (PET) revealed structure–property correlations. Several low-frequency vibrational modes support the current view that PEF chains are less flexible than those of PET, posing greater resistance to gas penetration and resulting in enhanced barrier properties. The vibrational assignment of PEF’s INS spectrum is a useful guide for future studies on advanced materials based on PEF.
In this work, the structural dynamics of the chloromethanes CCl4, CHCl3 and CH2Cl2 were evaluated through a computational spectroscopy approach by comparing experimental inelastic neutron scattering ...(INS) spectra with the corresponding simulated spectra obtained from periodic DFT calculations. The overall excellent agreement between experimental and calculated spectra allows a confident assignment of the vibrational features, including not only the molecular fundamental modes but also lattice and combination modes. In particular, an impressive overtone sequence for CHCl3 is fully described by the simulated INS spectrum. In the CCl4 spectrum, the splitting of the ν3 mode at ca. 765–790 cm−1 is discussed on the basis of the Fermi resonance vs. crystal splitting controversy.
The structure and dynamics of crystalline 4-(dimethylamino) benzaldehyde, 4DMAB, are assessed through INS spectroscopy combined with periodic DFT calculations. The excellent agreement between ...experimental and calculated spectra is the basis for a reliable assignment of INS bands. The external phonon modes of crystalline 4DMAB are quite well described by the simulated spectrum, as well as the modes involving low-frequency molecular vibrations. Crystal field splitting is predicted and observed for the modes assigned to the dimethylamino group. Concerning the torsional motion of methyl groups, four individual bands are identified and assigned to specific methyl groups in the asymmetric unit. The torsional frequencies of the four methyl groups in the asymmetric unit fall in a region of ca. 190 ± 20 cm
, close to the range of values observed for methyl groups bonding to unsaturated carbon atoms. The hybridization state of the X atom in X-CH
seems to play a key role in determining the methyl torsional frequency.
Solid‐state light‐emitting diodes (LEDs) are driving the lighting industry towards efficient and environmentally friendly lighting and displays. Current challenges encompass efficient and low‐cost ...down‐shifting phosphors with tuned emission colors. Green light lies on the low‐loss optical transmission window in plastic optical fibers and plays a special role in the regulation of the human and plant circadian rhythms. Moreover, green‐emitting phosphors may suppress the “green gap” found in semiconductor‐based LEDs. In this work, a UV‐photostable green‐emitting complex, Tb(NaI)3(H2O)2, with NaI = nalidixic acid (1‐ethyl‐1,4‐dihydro‐7‐methyl‐4‐oxo‐1,8‐naftiridine‐3‐carboxylic acid), was incorporated into tripodal organic‐inorganic hybrid materials. The hybrid hosts boost the absolute emission quantum yield from ≈ 0.11 (isolated complex) to ≈ 0.82 (doped hybrid), which is the largest value reported for Tb3+‐based hybrid phosphors. A green‐emitting LED was fabricated by coating a near‐UV LED (365 nm) with a Tb3+‐activated organic‐inorganic hybrid having pure‐green‐colored light with Commission International de l'Eclairage color coordinates and an efficacy value of (0.33, 0.59) and 1.3 lm W–1, respectively.
Green‐emitting LEDs were fabricated by coating commercial near‐UV‐emitting LEDs (365 nm) with high emission quantum yield (≈ 0.82) and photostable UV down‐shifting Tb3+‐activated organic‐inorganic hybrids prepared by the sol‐gel method. The fabricated devices revealed pure CIE colour coordinates in the green spectral region and luminous efficacy of ≈ 1.3 lm W–1.
Visible‐light‐excited Eu3+ complexes have received much attention in the last years due to the rapidly increasing demand for less‐harmful biomarkers and low‐voltage driven emitters in ...optoelectronics. Nevertheless, these complexes usually exhibit poor emission quantum yields, contrarily to the ones excited in the ultraviolet spectral region. To address this challenge, a series of complexes based on trivalent lanthanide ions, Eu(bpyO2)(CH3OH)2(H2O)(NO3)2(NO3) (1), Gd(bpyO2)(H2O)4(Cl)2Cl (4), Ln(tta)3(H2O)(C2H5OH) {Ln = Eu (2), Gd (5)} and Ln(tta)3(bpyO2) {Ln = Eu (3), Gd (6)}, were synthesized using 2‐thenoyltrifluoroacetone (Htta) as primary ligand and 2,2'‐dipyridyl N,N'‐dioxide (bpyO2) as neutral donor, and characterized, with special emphasis on their crystal structures and luminescence properties. Single crystal X‐ray diffraction revealed that the central metal ion has a coordination number of 9 in 1, and 8 in all other complexes. Complex 3 exhibited a broad excitation spectrum ranging from 250 to 480 nm, exhibiting, when compared to 1 and 2, higher absolute emission quantum yields of 0.46, 0.36 and 0.33, for excitation at 400, 425, and 450 nm, respectively. The theoretical intensity parameters, radiative and non‐radiative decay rates, and intrinsic and absolute emission quantum yields were assessed using the LUMPAC software displaying a very good accord with the experimental values. Moreover, organic light‐emitting diodes with a maximum efficiency of 5.7 × 10–2 cd A–1 at 14 V were fabricated using 3 as an emitting layer.
A novel visible‐light‐excitable Eu3+ complex has been synthesized. Its structural and optical characterizations are presented. The theoretical luminescence parameters assessed with LUMPAC software are in good accord with experimental values. Organic light‐emitting diodes with a maximum efficiency of 5.7 × 10–2 cd A–1 at 14 V were fabricated using the developed complex as an emitting layer.
The present work emphasizes the value of periodic density functional theory (DFT) calculations in the assessment of the vibrational spectra of molecular crystals. Periodic calculations provide a ...nearly one-to-one match between the calculated and observed bands in the inelastic neutron scattering (INS) spectrum of crystalline 4-phenylbenzaldehyde, thus validating their assignment and correcting previous reports based on single molecule calculations. The calculations allow the unambiguous assignment of the phenyl torsional mode at ca. 118-128 cm
, from which a phenyl torsional barrier of ca. 4000 cm
is derived, and the identification of the collective mode involving the antitranslational motion of CH···O bonded pairs, a hallmark vibrational mode of systems where C-H···O contacts are an important feature.
The biobased polyester poly(ethylene 2,4-furanoate) (2,4-PEF) is a potentially interesting yet insufficiently studied polymer whose resistance to crystallization fundamentally stems from the ...asymmetric nature of the 2,4-furandicarboxylic acid monomer. A combination of vibrational spectroscopy (infrared, Raman and inelastic neutron scattering) and ab initio calculations has been used to assess the conformational and regiochemistry preferences of 2,4-PEF. The latter polymerizes following a random distribution of monomer orientation, thereby rendering the formation of periodic interchain C–H···O contacts wholly unfeasible and ultimately favoring the formation of randomly coiled chains based on gauche-ethylene glycol segments. In the absence of C–H···O stabilization, the ordered crystalline arrangement is disfavored and polymer chainsadopting several quasi iso-energetic structuresprefer to solidify into an amorphous mess.
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