Chemphyschem最新文献

In this study, six activated carbons were synthesised using low-rank coal from Labin and Spitsbergen through single- and two-step KOH activation methods. The materials were evaluated for their ability to adsorb rhodamine B from aqueous solutions. The method of activation and impregnation ratio significantly affected the structural and sorption properties of the carbons. BET surface areas ranged from 602 to 855 m²/g. Surface functional groups varied depending on the precursor used. Adsorption experiments explored the effects of initial dye concentration, contact time, adsorbent mass, shaking speed and pH. Kinetic and isotherm models were applied to understand the adsorption mechanism. The linear Langmuir isotherm best fit the data, indicating uniform adsorption sites, while the process followed a pseudo-second-order kinetic model. Maximum adsorption capacities ranged from 100 to 294 mg/g. One adsorbent demonstrated excellent reusability, achieving up to 90% desorption efficiency after three cycles. These results highlight the material's strong potential for removing organic pollutants from water.

The precise positioning and manipulation of individual nanoclusters in ordered arrangements are essential prerequisites for both comprehensive understanding and mathematical formulation to generalize the intrinsic optical characteristics for the advent of nanoscale applications. In analogy with our long-standing understanding of molecular polymers, linear chains of metallic nanostructures have been coined as plasmonic polymers, where the individual particles can be considered as the monomeric building units. The possibility of plasmonic waveguiding in these well-defined strongly coupled plasmonic nanostructures has motivated their investigation as prototypical model systems to fulfill the modern demand of applications in photonics miniaturized at the nanoscale dimensions. 1D chain-like assemblies of nanostructures, because of their high symmetry, represent particular spatial arrangements for propagating surface plasmon polaritons that can venture directed energy transfer along the chain and to unravel short- and long-range electromagnetic coupling mechanisms in these oriented assemblies. The optical properties of these plasmonic polymers are dependent upon the structural characteristics, such as the aggregation number, interparticle distances, and mutual orientations that explicitly correlate with the degree of polymerization, bond lengths, and bond angles, respectively, in these lattice architectures. Moreover, the morphological characteristics, such as size, and geometry of the individual building blocks, are of paramount significance to the critical condensation of the intriguing optical features in these polymeric configurations. The cumulative effect of all these intrinsic physical observables associated with the polymeric configurations can reckon the complete story towards the observed plasmonic properties. As to the first initiative to distill this complex relationship, a theoretical formulation has been devised in simple intuitive terminologies to correlate the chain length dependence on the plasmonic characteristics and electric field distribution patterns in 1D aggregation of size-selective gold nanostructures. The complementarity of theoretical, experimental, and numerical simulation approaches has been adopted in bridging the interrelation between the associated physical parameters and optical characteristics of the periodic assemblies with varying chain lengths comprised of size-selective gold nanoparticles. The unique ability of plasmonic waveguiding and coherent exchange of near electric fields along these 1D chain-like assemblies can endow newer perspectives towards their potential applications in light-trapping in photovoltaic devices, nanoscale photonics, optical circuitry, chemical and biological sensing, and surface enhanced spectroscopies.

In this study, first-principles calculations were employed to systematically explore the stability and structural evolution of all-inorganic lead-free perovskites RbGeX₃ (X = I, Br, Cl) in three optically active phases: Pm$$m, R3m, and Pna2₁. Total energy and phonon spectra indicate that Pna2₁ is the most stable phase, followed by R3m and Pm$$m. Ab initio molecular dynamics (AIMD) simulations at 300 and 500 K further confirm the thermal robustness of RbGeX₃. The distortion parameters (D, σ², ψ) indicate that the R3m and Pna2₁ phases exhibit varying degrees of symmetry breaking compared to the Pm$$m phase. Analysis of the soft phonon modes reveals that instability in Pm$$m originates from off-center displacements of Ge atoms coupled with halide vibrations, whereas in R3m it is driven by X-site-induced tilting of GeX₆ octahedra. After AIMD simulations, the structures of both Pm$$m and R3m exhibit significant octahedral tilting, while the Pna2₁ phase shows minimal structural change, indicating greater thermal robustness. Finally, band structure calculations using the Heyd–Scuseria–Ernzerhof hybrid functional show a progressive bandgap increase with decreasing symmetry, offering theoretical guidance for the development of efficient lead-free perovskites.

Heavy-metal fluoride (HMF) glasses exhibit a combination of broad infrared transparency, low phonon energy, and potential fluoride-ion conductivity, rendering them promising candidates for optical and electrochemical applications. However, the atomic-scale environment of La³⁺ ions, which governs these properties, remains inadequately characterized. In this work, we systematically examine NaF–LaF₃ and LiF–LaF₃ binary mixtures as model systems using a suite of solid-state nuclear magnetic resonance (NMR) techniques. Our findings reveal markedly distinct behaviors of the alkali cations. NaF readily reacts with LaF₃ to form a crystalline NaLaF₄ phase, as unambiguously confirmed by ¹⁹F and ²³Na NMR, along with 2D ¹⁹F–²³Na HETCOR and CP/MAS experiments. In contrast, LiF exhibits no evidence of forming Li–La–F coordination structures, instead persisting as a phase-separated LiF/ LaF₃ composite. This divergence is attributed to the stronger Li–F bonding and the limited coordination flexibility of Li⁺, which hinders disruption of the LaF₃ lattice. These mechanistic insights highlight the critical influence of alkali cation identity on the structural evolution in mixed fluoride systems and offer valuable design principles for ZBLAN and related HMF glasses.

The conformational behavior of SH···S H-bonded ethanethiol (EtSH) dimer and trimer has been experimentally studied in cold and solid argon (Ar) and nitrogen (N₂) matrices via analysis of the $$ spectral region. Over 20 spectral bands were observed in both matrices exhibiting a wide range of $$ spectral shifts (4.8–87.5 cm⁻¹). Their spectral assignment was supported by normal mode frequencies calculated at the ωB97X-D/aug-cc-pV(D + d)Z level of theory, which displayed close match. Calculations predicted 24 (EtSH)₂ conformers belonging to four classes (GG, GG′, GA, and AA) and 45 (EtSH)₃ conformers from seven classes (GGG, GGG′, GG′G′, GGA, GG′A, GAA, and AAA) formed by gauche (G and G’) and anti (A) monomers. Experimentally, 16 dimers and 9 trimers were identified as the relative stability showed small variation; only 1.42 and 2.77 kcal mol⁻¹ for dimer and trimer. However, no AA dimer as well as GAA and AAA trimer could be identified in any matrix, due to the presence of multiple lesser stable A monomers. The most stable conformers were found to possess weaker and longer SH···S H-bonds, while the lesser stable conformers possessed stronger and shorter SH···S H-bonds. When compared against SH···S H-bonds in H₂S clusters, the ones in EtSH clusters showed markedly greater contribution of dispersion interaction.

The magic-angle spinning NMR technique, Centerband-Only Detection of EXchange (CODEX), can be used to determine the oligomerization state of molecules when combined with site-specific labeling. Calibrated with amino acid crystals, the method is successfully applied to proteins, primarily combined with ¹⁹F labeling. The use of ¹³C spins for CODEX-based oligomer determination in proteins is hampered by limited sensitivity of ¹³C spins due to the low gyromagnetic ratio of ¹³C and the presence of natural abundance background spins which contribute to the observed CODEX decay. The use of CODEX is proposed in conjunction with dynamic nuclear polarization (DNP) at low temperature to increase sensitivity. It is necessary to correct for effects of ¹³C present at natural abundance. A (PDSD) proton driven spin diffusion-based correction is demonstrated to be effective when the isotropic chemical shifts of the natural abundance background are distinct from the labeled site. Using a ¹³C-ζ-phenylalanine-labeled GB1 sample, it is demonstrated that the autocorrelation peak decay observed in a series of PDSD spectra can be utilized to correct for the additional dephasing and recover the expected CODEX decay curve. With ¹³C-γ-phenylalanine labeling and ¹³C-depleted background, mixing times up to 1500 s are demonstrated.

Oleyl-capped nanoparticles have been used in nonpolar dispersions and can form ordered assemblies, for which an understanding of their interactions from a theoretical perspective is relevant. Long-range comprehensive molecular dynamics runs (1000 ns) are performed on oleyl-capped gold nanoclusters in different environments: hexane as a nonpolar solvent, and ethanol and pentanol as polar solvents. The molecular dynamics results in ethanol medium demonstrate that oleyl-capped nanoclusters tend to form attractive interactions with themselves via hydrocarbon interdigitation of their oleyl ligands, which leads to their aggregation. On the contrary, the attractive interactions between these nanoclusters are compensated by the interactions with hexane molecules, so that the nanoclusters keep separated from each other, leading to stable dispersions. The behavior of pentanol with the oleyl-capped nanoclusters indicates presumably more similarities to hexane, despite of being a polar solvent. These three simulation cases provide an insightful overview about the stabilization effects of oleyl-capped nanoparticles in organic solvents.

Only very soluble electrolytes can form concentrated solutions. Some salts are so soluble that there are less than four water molecules per ion in saturated solution. Ions usually form clusters or networks with more than one counterion in their coordination sphere in these concentrated solutions. Do these ultraconcentrated solutions form because the counterions have high affinity for each other in liquid, or because they have a poor affinity for each other in solids? Here this question is addressed using the valence matching principle of the bond valence model by comparing the charge density mismatch between counterions to their solubility for a series of alkali fluorides, carboxylates, and oxyanions. The solubilities are plotted against the characteristic average bond valence of the alkali, and the lowest solubilities are those where alkali and anion had matching bond valences. Conversely, the highest solubilities are those with poorly matching bond valences. Available ion-pairing constants indicate that the weakest ion-pairs are those with the largest bond valence mismatch, indicating that the large water solubilities occur despite weak ion-pairing rather than because of strong ion-pairing. Therefore, a key characteristic of highly water-soluble salts is that the counterions have mismatched charge densities.

Lead-based halide perovskite solar cells represent a significant advancement in photovoltaic technology, achieving certified power conversion efficiencies of over 27%. However, the toxicity of lead poses a major barrier to widespread commercialization. The demand for environmentally safe alternatives has driven extensive research into Pb-free perovskites. Current efforts include replacing Pb with Sn or Ge; forming double perovskites in which Pb is substituted by a monovalent–trivalent cation pair; and developing chalcogenide perovskites where the B site (ABX₃) adopts tetravalent cations (rather than Pb) to balance the charge. This concept examines the recent progress in developing Pb-free alternatives, revealing fundamental performance bottlenecks, inherent material limitations, and persistent development challenges. Through a comparative assessment of material properties and device performance limitations, this work highlights the underlying dilemma between environmental safety and efficiency in perovskite photovoltaics. The analysis identifies fundamental material constraints that create substantial barriers to simultaneously achieving both objectives.

Quantum chemical methods are employed to investigate the complexation of CaX₂ with nNH₃ (X = H, F; n = 1–3). In the presence of CaX₂, NH₃ molecules engage in several types of noncovalent interactions, namely, hydrogen bonding (HB), calcium bonding (CB), and dihydrogen bonding (DHB). The CaX₂:nNH₃ complexes are primarily stabilized by Ca···N interactions, though other noncovalent contacts also contribute in stabilizing or destabilizing different conformers. Closed ring conformers in CaX₂:nNH₃ complexes show high degree of cooperativity together with a consistent increase in Ca···N bond length and decease in H⁺···H⁻/ H⁺···F⁻ bond length with increasing number of NH₃ molecules. Fragment-wise interaction energy analysis indicates that two-body ammonia–metal hydride/fluoride (A_i–CaX₂) interactions dominate the total interaction energy, while nonadditive terms contribute up to ∼10% in certain heterotrimer conformers but diminish as the number of ammonia molecules increases. Vibrational mode automatic relevance determination analysis (VMARD) of CaX₂:nNH₃ complexes shows unequal contributions from atomic motions within the three different bonds in NH₃ molecule, revealing that complexation induces different intermolecular force constants, leading to loss in symmetry of NH₃ molecules. Pronounced redshift of the symmetric NH stretching mode is consistently observed, accompanied by symmetry lowering of the degenerate asymmetric NH stretching mode.