OH Vibrations Research Articles

Impact of pH Preparation on the Physical Nature and Metal Phase of Zeolite-Supported Metal Catalyst

The synthesis of CoMo/USY catalysts has been widely carried out. However, the bond strength between metal and USY is still a problem. Therefore, this research has synthesised the catalyst with the chelating agent ethylenediaminetetraacetate (EDTA). Apart from that, the effect of pH on the characteristics of the catalyst is also reviewed. This research aims to analyse the effect of preparation pH on catalyst characteristics. In the preparation process, the pH of the solution is set at values of 2, 7, and 8. Catalyst activation includes a calcination process and reduction. The catalyst characterisation uses XRD, GSA, and FTIR instruments to determine phase composition, specific surface area, and functional groups. The result showed that pH preparation significantly influenced the metal loading on the catalyst and reached a maximum at pH 8. The surface area is not directly related to the pH of the preparation but has the opposite property depending on the amount of metal added. Meanwhile, it was found that the CoO and MoO3 phases were achieved on the catalyst by all pH preparations. On the other hand, the CoMo alloys are present on the catalyst at pH 7 and 8, while the Co and Mo elements are visible at pH 2. The difference in pH during the synthesis process impacts the shift in the absorption wave number of the OH vibration.

PHENOLIC AND ANTIOXIDANT PROFILE: FTIR AND LC-MS ANALYSES OF SERAPIAS ORIENTALIS

Objective: The objective of this study is to characterize the aerial parts of S. orientalis using Fourier Transform Infrared (FTIR) spectroscopy, evaluate the phenolic content and antioxidant activity of seeds, stems, and flowers, and conduct quantitative analysis of phenolic compounds using LC-MS/MS. Material and Method: Fourier Transform Infrared (FTIR) spectroscopy was employed to characterize the aerial parts of S. orientalis. The analysis focused on identifying various functional groups such as -OH vibrations associated with polysaccharides, C-H vibrations from lipids and lignin compounds, and C=O vibrations related to cellulose derivatives. The total phenolic, flavonoid, flavanol, tannin, and proanthocyanidin contents of S. orientalis seeds, stems, and flowers were evaluated using standard analytical methods. DPPH radical scavenging activity was determined to assess antioxidant potential, with IC50 values calculated for each plant part. Quantitative analysis of phenolic compounds in the plant extract was conducted using LC-MS/MS. The abundance of various phenolic acids including P-coumaric acid, trans-ferulic acid, caffeic acid, and vanillic acid was determined. Additionally, other phenolic compounds such as gallic acid, chlorogenic acid, salicylic acid, (+) taxifolin, rutin hydrate, ellagic acid, quercetin dihydrate, and apigenin were also detected and quantified. Result and Discussion: The evaluation of phenolic content showed differences among different plant parts, with flowers exhibiting the highest total phenolic and proanthocyanidin content. Seeds demonstrated superior DPPH radical scavenging activity. Quantitative analysis of phenolic compounds using LC-MS/MS highlighted the abundance of various phenolic acids and other phenolic compounds in S. orientalis. These findings underscore the potential of S. orientalis as a valuable source of natural antioxidants. Overall, the results suggest that S. orientalis possesses significant phenolic diversity and antioxidant activity, which could contribute to its potential applications in various industries, including pharmaceuticals and nutraceuticals.

Near-Infrared Spectroscopic Study of Biotite–Phlogopite (Mg# = 30~99): OH-Stretching Modes and Mg# Content Prediction Equation

Biotite–phlogopite minerals are a complete Mg–Fe isomorphism series of phyllosilicates. A Fourier transform infrared spectroscopy (FTIR) and electron microprobe analysis (EMPA) were conducted on end-member phlogopite, Mg–biotite, and annite samples. In the mid-infrared region, absorption peaks were observed at 460, 1000, 3680, and 3710 cm−1 in the biotite group. Samples with higher Mg content exhibited stronger peaks assigned to OH vibrations and a weak absorption peak at 810 cm−1. In the near-infrared region, combination peaks were observed near 4200, 4300, and 4450 cm−1, with wavenumbers showing a linear inverse relationship with the Mg# [=100 × Mg/(Mg + FeT)] value. For annite, combination peaks occurred at 4173, 4292, and 4439 cm−1, decreasing by 10–15 cm−1 compared to end-member phlogopite. Judging the fundamental peaks of the combination band contributes to identifying suitable near-infrared characteristic peaks for quantitative research. The 4300 cm−1 absorption peak in biotite–phlogopite was assigned to OH-bending and -stretching vibrations, making it suitable for mineral identification and Mg# estimations across all biotite groups. The 4450 cm−1 characteristic peak, assigned to Al–O-stretching vibrations and OH-stretching vibrations, is suitable for accurately predicting Mg# values in high AlVI samples. The first overtones of biotite–phlogopite appeared at 7250 cm−1, with an average factor of 1.955 between the fundamental and corresponding overtones. This study aims to refine the patterns of OH-stretching vibrations and characteristic peak shifts in the near-infrared spectral region of phyllosilicate minerals, providing data references for planetary spectroscopy and ore deposit studies.

Mg doping effect on the properties of SnO2 thin films synthesized by dip-coating method

Undoped and Mg doped SnO2 thin films were deposited on glass substrates using dip-coating method for the first time. X-ray diffraction analysis of the films revealed a tetragonal rutile phase. A decrease in crystallite size is observed as the Mg doping increases. The transmittance spectrum exhibits a decrease in transmittance from 87% to 62% as the Mg content is increased. The optical band gap narrows from 3.97 eV to 3.93 eV with the increasing of Mg content. MEB showed an increase of grain sizes with increase in Mg concentration. The RMS roughness increases with Mg doping content. FTIR showd O–Sn–O, Sn–OH, Mg–O, and OH–Mg–OH vibration modes. PL spectra indicated that the incorporation of more Mg2+ into the lattice of SnO2 creates additional oxygen vacancies, leading to an increase in the PL emission intensity in the films. A transition from n-type to p-type conduction was observed at 9 wt% Mg doping.

Absorption of water molecules on the surface of stereocomplex-crystal spherulites of polylactides: An in-situ FT-IR spectroscopy investigation

The correlation between water molecules and polylactide was clarified. The crystallinity in stereocomplex (SC) crystal spherulites was investigated using microbeam wide-angle X-ray diffraction. The crystallinity was higher in the central region, and edge-on lamellae grew in a twisted manner. The hydrogen bonding in SC-crystal spherulites was evaluated via microbeam FT-IR spectroscopy in a humidity-controlled cell. The water-derived bands corresponding to OH vibration and HOH bending increased with increasing humidity. Microbeam FT-IR spectroscopy was used to evaluate the water absorption behavior of crystalline films depending on their position. Coarse-grained molecular dynamics simulations indicated that the number of adsorbed water molecules increased with decreasing crystallinity. In SC-crystal spherulites, water molecules are absorbed in both amorphous and crystalline regions but with greater difficulty in the crystalline regions. These insights into water molecule absorption on SC-crystal spherulite can facilitate the development of polylactide materials with controlled biodegradability for advanced medical and optical applications.

Chemical States of Water in Anion Exchange Membrane for Fuel Cells Using Raman and Coherent Anti-Stokes Raman Spectroscopies

Purpose Low membrane durability remains a major challenge in anion exchange membrane fuel cells (AEMFCs). This is despite the AEMFCs’ proven potential to eliminate the dependency of Fuel cells on Pt catalysts and bring about the mass commercialization of the technology. This problem can be effectively addressed through combined optimization of the AEMFCs’ operating conditions during evaluation, followed by finetuning of the membrane chemistry to address any observed weaknesses. After synthesis, water distribution is the primary operation condition determining a given AEM’s performance and lifespan [1]. This is partly because water affects the ionic conductivity and, thus, maximum current density, which is known to play a significant role in the longevity of membranes. Therefore, establishing the water distribution during power generation for any given membrane is highly desirable. For this to happen, suitable and reliable techniques must exist to measure and compare the water distribution in situ and operando. In this paper, we used in-house assembled Raman spectroscopy and coherent anti-Stokes Raman scattering spectroscopy (CARS) systems to measure the water in an operational AEMFC for the first time. CARS comes with a high time resolution of 0.1 s, which is essential in the transient response study of FCs. Experimental Method QPAF-4 membrane film (Fig. 1) of the thickness of 30 µm and IEC of 2.0 meq g-1 was solution cast as reported [2]. The cell was then assembled, as reported [3]. An airtight transparent quartz window 200 μm thick was mounted at the cathode endplate for optical access to the QPAF-4 membrane through a 500 mm pinhole in the GDE. A thin Pt disk was placed on the opposite side of the membrane to reflect the signal to the spectrometer through the ×50 objective lens used. For Raman spectroscopy, a 632 nm, 1 mW laser with 5.5 min total exposure was used. For CARS, an 11 mW 785nm pump laser and 16 mW Stokes laser with 200 ms total exposure were used. The flow rate was 100 ml min-1 for all gases. The cell temperature was maintained at 60 °C. The relative humidity of the gas varied from 30% to 100% in steps of 10% RH. The system was allowed to stabilize for 3 hours at each humidity level before measurement. Results and discussion Figures 2 and 3 show the normalized in situ spectra recorded at the center of the membrane at different relative humidity values using CARS and Raman, respectively. The peak positions are comparable. However, the OH peak in CARS is taller relative to C=C than in Raman. CARS signal intensity is generally stronger than Raman [3]. Within the CARS peak, the purely OH portion of the signal is more prominent relative to the rest of the peak than in Raman. This is attributed to the fact that the Infrared laser associated with the stokes light (817-1144nm) of CARS is known to be more sensitive to OH vibration than the lower wavelength laser (632nm) used in Raman [4]. Conclusion We successfully developed a 785nm CARS system capable of operando water measurement in AEMFCs. The results from this technique are comparable to those from micro-Raman spectroscopy but with better signal intensity and time resolution. This increases the number of practical methods available to researchers interested in measuring water content in AEMFCs allowing for faster development of the technology. The water distribution results during power generation will be discussed at the conference. With CARS, higher temporal/time resolution is achieved, which is advantageous when cell response needs to be studied.

Rapid discrimination of Panax ginseng powder adulterated with various root plants by FT-IR spectroscopy coupled with multivariate analysis

Panax ginseng powder adulterated with other root plants (arrowroot, bellflower, and lance asiabell) was discriminated using Fourier transform infrared (FT-IR) spectroscopy, combined with multivariate analysis. Principal component analysis visually diagnosed the adulteration by showing two distinct clusters based on presence of adulteration. Wavenumber regions (1000 cm−1 and 3300 cm−1) selected from the loading plot associated with the vibration of OH and CH bond in ginsenoside and aromatic compounds. A quantitative model for the content of ginsenosides and specific aromatic compounds as indicators of pure ginseng powder, was developed based on partial least square regression analysis. The performance of the prediction model preprocessed with the Savizky–Golay 1st derivative was improved to R2 of 0.9650, 0.9635, and 0.9591 for Rb1, Rc, and β-Panasinsene, respectively. Therefore, FT-IR technology makes it possible to rapidly authenticate pure ginseng product based on the ginsenoside contents and aroma compound.

Derivative of aminoresin as potent anti-virulence agent: Synthesis, spectral (FT-IR, UV, NMR) analysis, molecular docking, effect of polar solvation dynamics, and quantum chemical investigation

This work undertakes a comprehensive study encompassing the synthesis, spectral characterization (FT-IR, UV, 1HNMR , 13CNMR), exploration of polar solvation dynamics (DMSO, EtOH, MeOH) on the molecular structure, quantum chemical calculations, topological (ELF, NCI) analysis, and molecular docking investigation. The focal point is a derivative of amino terpolymer resin, synthesized via the condensation of 4,4′-diaminodiphenylmethane, 8-hydroxyquinoline, and formaldehyde (DHQF). Thorough examination of the compound was conducted to evaluate its responsiveness in varying solvents and investigate its viability as a key candidate for antivirulent therapy against toxins from Vibrio cholerae and Salmonella enterica. Simulation of solvation dynamics underscored the compound's robust thermodynamic stability even at lower temperatures. Primary vibrations noted within the compound encompassed CH, OH, NH, CH2, and CN vibrations, whereas UV spectroscopy unveiled an electronic shift from HOMO to LUMO, featuring peak absorption at 292.77 nm, influenced by its interaction with DMSO. The molecular docking analysis reveals the terpolymer's significant bioactivity against proteins 7EE6 (affinity: −6.7 kcal/mol) and 5V6f (affinity: -7.1 kcal/mol) associated with V. cholerae and S. enterica. The binding affinity of DHQF with S. enterica toxin protein (PDB: 7EE6) is comparable to that of standard drug Ciprofloxacin (affinity: −6.9 kcal/mol) and the toxin protein. However, the binding affinity between DHQF and V. cholerae toxin protein 5V5F considerably surpasses the binding affinity (−4.6 kcal/mol) between Doxycycline and the toxin protein. More so, the complex shows close binding affinities to both proteins and a higher number of conventional hydrogen bonds, this formed multiple favorable interactions, particularly conventional hydrogen bonds, contributing significantly to the stability of the ligand-protein complexes. In conclusion, the analyzed terpolymer displayed favorable qualities and interactions, which establish it as a strong candidate for addressing the targeted V. cholerae and S. enterica pathogens. These findings highlight the compound's impressive stability and its potential for various therapeutic applications in different areas.

ZnO nanocomposites containing Cd are synthesized with high photodegradation potential for wastewater treatment

The zinc oxide (ZnO) nanoparticle on a two - electron oxygen reduction reaction is a particularly promising candidate for in-situ application. Herein, we prepared the Cd doped ZnO nanocomposites through a simple hydrothermal method. The X-ray diffraction (XRD) analysis has been carried out to confirm the structure and size of the nanomaterial. The optical absorption and energy gap of the prepared nanoparticles have been identified by UV–vis-NIR studies. Photoluminescence (PL) studies on the synthesized nanomaterials confirm the characteristic existence of blue and green emission bands. Fourier transform infrared (FTIR) spectroscopy has been studied on the ZnO nanoparticles to analyze the -OH and CO-O vibrations. The structural and surface morphology analysis was inferred by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and energy dispersive X-ray (EDX) microanalysis. Cd doped ZnO nanocomposites are environmentally friendly and can be utilized to quickly remove contaminants from wastewater. The findings from the adsorption equilibrium fit the Brunauer-Emmett-Teller (BET) model very well, showing multi-layer adsorption. The photodegradation studies on Cd doped ZnO nanocomposites were carried out, which is an advanced oxidation process widely used for methylene blue removal. Therefore, the higher photocatalytic performance revealed that Cd doped ZnO nanocomposites could be a promising photocatalyst for environmental remediation applications.

Raman spectroscopy investigations of hydrated hydroxypropyl cellulose mixtures with low-soluble salicylic acid: Molecular interactions and the water-binding structure

Highly hydrophilic polymer matrices are limited their in use to the delivery of hydrophilic drugs, and are ineffective for hydrophobic compounds. Therefore, studying hydrogels that can effectively deliver hydrophobic drugs is still an important challenge. The molecular interactions occurring in model hydrated binary mixtures of hydroxypropyl cellulose (HPC) and low-soluble and hydrophobic salicylic acid (SA) (1:1 w/w) were investigated by means of Raman spectroscopy. During the study, the OH stretching vibrations region (in the 3600–3100 cm−1 range) was examined and bands for the three assessed fractions of water were assigned at the wavenumbers 3400 cm−1 (non-freezing water), 3320 cm−1 (freezing bound water) and 3220 cm−1 (free water). The contribution of the OH vibrations of SA (3205 cm−1) was also considered. A significant area for the analysis of changes in the HPC polymer is the glycosidic linkage vibration region ranging from 1250 cm−1 to 1000 cm−1 (at ∼1151 cm−1 and at ∼1093 cm−1) and the 3000–2850 cm−1 region due to the CH stretching of the CH2 and CH3 groups. SA is able to form hydrogen bonds to polymer chains and to water, as well as to another SA molecule to form a dimer. Therefore, bands derived from SA were observed to monitor these interactions (in the 1600–1500 cm−1 range).The obtained results were discussed and partially compared to the corresponding previously published spectroscopic and theoretical outcomes. All observed interactions between the components of the mixture and water molecules were also analyzed as a function of time, which is a novel approach providing a large amount of valuable information about the system. The applied methodology allowed for establishing that the stabilization of the hydrated HPC/SA system took place after one week. The greatest dynamics of changes were observed for the lowest studied water concentration. For the highest water concentration, several low-intensity bands in the CO vibration range seemed to indicate dimer-type interactions.

The FTIR image comparison of zirconium sulfate synthesis products from the pathways of Na2ZrO3 and zirconium oxychloride compounds

PSTA BATAN has synthesized zirconium sulfate (ZS) through two methods. Synthesis pathway (I) from Na2ZrO3 (CDZ) and (II) through zirconium oxychloride (ZOC). This research aimed to compare both pathways by utilizing FTIR. Path (I) was done using concentrations of H2SO4 65%, contact time of 30, 60, 90, and 150 min, and temperatures of 125, 150, 175, and 225 °C. While path II has been carried out in previous studies [1]. The FTIR image comparison was finished by tracing sulfate derivative functional groups from a wavenumber of 4000–400 cm−1. The O–H stretching at 3441.01 cm−1 as the Zr(OH)Zr group and OH vibration in 3425.68 cm−1 were found at each pathway. However, at pathway (II), we observed another vibration at 3132.40 cm−1 as the NH3 compound group. Furthermore, the track records of S–O and SO stretching on both pathways were checked at 1635.64, 1095.57, and 956.69 cm−1, respectively, as H3O+, SO42−, and SO32− species. The real difference in pathway (I) was revealed by the presence of H2SO4 residue at 802.39 cm−1. At the same time, the Zr–O–Zr and O–Zr–O stretching could be detected in both pathways at the wavenumber of 594.09 and 470.63 cm−1 consecutively. The form of synthesis pathway (I) product was predicted as Zr(SO4)2, while the product of path (II) forecasted as Zr(NH3)(SO4)2 compound.

Synthesis and Characterization of Silica Gel from Palm Shell and Coir Ash

This study aims to determine the composition of the oxide, the characteristics of palm shell and coir, and silica gel synthesized. The oxide composition, crystallinity, palm shell and coir ash functional groups were analyzed using XRF, XRD, and FTIR. Analysis of the functional groups and crystallinity using FT-IR and XRD. The results showed the composition of SiO2 in palm shell and coir ash was 76%, and SiO2 in the form of quartz and cristobalite was more dominant than amorphous SiO2. The synthesis success was indicated by the appearance of peaks with low intensity, not sharp, and resembling bumps on the synthesized silica gel diffractogram, which is an amorphous SiO2 characteristic. This result is confirmed by FT-IR, where absorption at wave number 455 cm-1 is a Si-O-Si bending vibration, 783 cm-1 is a stretching vibration of Si-O symmetry of Si-O-Si, 3454.51 cm-1, and 3568 cm-1 with fairly high intensity are characteristic of the -OH group from Si-OH. The wide and sharp absorption at 1083.99 cm-1 is a stretching vibration of the Si-O symmetry of Si-O-Si, 1625.99 cm-1 is -OH vibration of water molecule, 798.53 cm-1 is Si-O stretching vibration of Si-O-Si and absorption of 462.92 cm-1 indicates bending vibration of Si-O-Si.

Design of an Electrostatic Frequency Map for the NH Stretch of the Protein Backbone and Application to Chiral Sum Frequency Generation Spectroscopy.

We develop an electrostatic map for the vibrational NH stretch (amide A) of the protein backbone with a focus on vibrational chiral sum frequency generation spectroscopy (chiral SFG). Chiral SFG has been used to characterize protein secondary structure at interfaces using the NH stretch and to investigate chiral water superstructures around proteins using the OH stretch. Interpretation of spectra has been complicated because the NH stretch and OH stretch overlap spectrally. Although an electrostatic map for water OH developed by Skinner and co-workers was used previously to calculate the chiral SFG response of water structures around proteins, a map for protein NH that is directly responsive to biological complexity has yet to be developed. Here, we develop such a map, linking the local electric field to vibrational frequencies and transition dipoles. We apply the map to two protein systems and achieve much better agreement with experiment than was possible in our previous studies. We show that couplings between NH and OH vibrations are crucial to the line shape, which informs the interpretation of chiral SFG spectra, and that the chiral NH stretch response is sensitive to small differences in structure. This work increases the utility of the NH stretch in biomolecular spectroscopy.

Preparation of high‐strength, high‐modulus PVA fiber by synthesis of syndiotacticity‐rich high molecular weight PVA polymers with VAc and VBz via emulsifier‐free emulsion polymerization

AbstractDifferent vinyl acetate (VAc) and vinyl benzoate (VBz) monomer ratios have been chosen as monomers to create high polymerization degree (Pn) and high syndiotacticity‐diad content (S‐diad) poly(vinyl alcohol) (PVA) polymers via emulsifier‐free polymerization in order to address the problem of limited mechanical capabilities of PVA fibers prepared with low Pn and low S‐diad polymer. The variations in hydrogen bonding, Pn, S‐diad, and viscosity of different PVA polymers were investigated and evaluated using Fourier transform infrared spectroscopy, proton nuclear magnetic resonance, gel permeation chromatography, and a viscosity tester. Moreover, various PVA fibers with high strength and modulus have been manufactured using a synthetic polymer as the raw material for dry‐wet spinning. The effect of Pn and S‐diad on the mechanical and thermal characteristics of PVA fibers is evaluated using a variety of characterization techniques, such as the scanning electron microscope, differential scanning calorimetry, thermogravimetric analyzer, X‐ray diffraction, and tensile tester. As the ratio of VBz monomer increased, the results suggested that VBz may have a considerable impact on the Pn and S‐diad of PVA polymers, the OH vibration absorption peak reduced from 3491 to 3442 cm−1; the Pn increased from 2112 to 17,704; and the S‐diad rose from 51.2% to 60.1%. In addition to the fact that Pn and S‐diad significantly increased the fibers' strength and modulus, the crystallinity increased from 41.8% to 51.7%, and the orientation degree rose from 87.5% to 91.7%, as Pn and S‐diad increased; the tensile strength and highest elastic modulus increased from 9.71 ± 0.3 cN/dtex to 12.74 ± 0.5 cN/dtex (increased of 31.2%) and 264.52 ± 9.3 cN/dtex to 338.41 ± 8.6 cN/dtex (increased of 27.9%); the elongation at break decreased from 5.63 ± 0.3% to 2.92 ± 0.2%.

Temperature Dependence of Non-Condon Effects in Two-Dimensional Vibrational Spectroscopy of Water.

Non-Condon effects in vibrational spectroscopy refers to the dependence of a molecule's vibrational transition dipole and polarizability on the coordinates of the surrounding environment. Earlier studies have shown that such effects can be pronounced for hydrogen-bonded systems like liquid water. Here, we present a theoretical study of two-dimensional vibrational spectroscopy under the non-Condon and Condon approximations at varying temperatures. We have performed calculations of both two-dimensional infrared and two-dimensional vibrational Raman spectra to gain insights into the temperature dependence of non-Condon effects in nonlinear vibrational spectroscopy. The two-dimensional spectra are calculated for the OH vibration of interest in the isotopic dilution limit where the coupling between the oscillators is ignored. Generally, both the infrared and Raman line shapes undergo red shifts with decrease in temperature due to strengthening of hydrogen bonds and decrease in the fraction of OH modes with weaker or no hydrogen bonds. The infrared line shape is further red-shifted under the non-Condon effects at a given temperature, while the Raman line shape does not show any such red shift due to non-Condon effects. The spectral dynamics becomes slower on decrease of temperature due to slower hydrogen bond relaxation and, for a given temperature, the spectral diffusion occurs at a faster rate upon inclusion of non-Condon effects. The time scales of spectral diffusion extracted from different metrics agree well with each other and also with experiments. The changes in the spectrum due to non-Condon effects are found to be more significant at lower temperatures.

Utilization of Jengkol Peel (Pithecellobium jiringa) as an Adsorbent of Iron Metal

Cellulose, which has the active group OH, is found in Jengkol peel. Jengkol peel has the potential to be utilized as an adsorbent for Iron (Fe) metal because it contains these active groups. The FT-IR spectrophotometer instrument was used to confirm the presence of the -OH group in the Jengkol peel adsorbent, which was observed at the peak of the OH vibration at wave number 3293 cm1. Utilizing NaOH (0.1 M), the active group was activated. With an adsorption percentage of 96.24%, pH 7 was the optimum adsorption pH. With an adsorption percentage of 99.20%, 25 minutes was indeed the optimum contact time. With an adsorption capacity value of 8.581 mg/g, the binding of Fe metal by the adsorbent active group occurs in the complex formation mechanism, it was indicating a relatively high adsorption efficiency.

Vacuum-Assisted Strong Luminescence Thermal Enhancement in NaYF4:Ho3+/Yb3+ Upconverting Nanocrystals: A Conclusive Evidence for the Effect of Water Desorption

The luminescence thermal enhancement (LTE), in lanthanide-doped upconverting nanocrystals (UCNCs), has attracted extensive attention for its applications in anticounterfeiting, temperature sensing, and so on. Some mechanisms for LTE were proposed, including thermally induced water desorption from the surface of UCNCs, but conclusive evidence is absent for any of the mechanisms. Here, vacuumizing is employed in the experiment for the LTE in NaYF4:Ho3+/Yb3+ UCNCs, and significantly promoted LTE is observed. The 300–450–300 K temperature cycling experiment in vacuum shows continuous luminescence enhancement without luminescence intensity recovery as in the cooling process in moisture air, indicating the effect of water desorption because water readsorption is blocked in vacuum. It is found that the Ho3+ 5I6 level can be deexcited by direct long-range energy transfer to water adsorbed at the surface of nanocrystals due to resonant coupling between the Ho3+ 5I6 → 5I7 transition and the −OH vibration of water. As a result, water desorption suppresses the 5I6 depopulation and thus enhances the luminescence of Ho3+. Finally, the regulation of upconversion LTE is realized by adjusting the size of nanocrystals and Ho3+ or Yb3+ concentrations. Our findings indicate that the vacuumizing technique is an effective method to distinguish water-desorption-induced LTE. This work deepens the understanding of LTE and offers insights into the regulation of LTE.

Predicting Frequency from the External Chemical Environment: OH Vibrations on Hydrated and Hydroxylated Surfaces.

Robust correlation curves are essential to decipher structural information from IR-vibrational spectra. However, for surface-adsorbed water and hydroxides, few such correlations have been presented in the literature. In this paper, OH vibrational frequencies are correlated against 12 structural descriptors representing the quantum mechanical or geometrical environment, focusing on those external to the vibrating molecule. A nonbiased fitting procedure based on Gaussian process regression (GPR) was used alongside simple analytical functional forms. The training data consist of 217 structurally unique OH groups from 38 water/metal oxide interface systems for MgO, CaO and CeO2, all optimized at the DFT level, and the fully anharmonic and uncoupled OH vibrational signatures were calculated. Among our results, we find the following: (i) The intermolecular R(H···O) hydrogen bond distance is particularly strong, indicating the primary cause of the frequency shift. (ii) Similarly, the electric field along the H-bond vector is also a good descriptor. (iii) Highly detailed machine learning descriptors (ACSF, SOAP) are less intuitive but were found to be more capable descriptors. (iv) Combinations of geometric and QM descriptors give the best predictions, supplying complementary information.

Influence of Calcination Temperatures on Gunningite-Based Gelatin Template and Its Application as Ibuprofen Adsorption

Gunningite has been successfully synthesized using the soft template method with the Pluronic F127-gelatin template. Gunningite was calcined at diverse temperatures of 500, 600, and 700 °C for 12 h and characterized by XRD, SEM, and FTIR. A UV-Vis Spectrophotometer measured the adsorption capacity of Gunningite against ibuprofen. The XRD results showed that the crystal sizes of Gunningite decreased from 35.41 to 28.31 nm with the increasing calcination temperature from 500 to 700 °C. Besides, the crystallinity degrees also increased from 49.94% to 56.13% as calcination temperature increased from 500 to 700 °C. The Gunningite formed aggregates in the form of tiny particles that merge and experience agglomeration. The FTIR spectra of the Gunningite samples demonstrated the functional groups –OH, Zn-OH, Zn-O-Zn, and gunningite vibrations. The maximum adsorption capacities of Gunningite to adsorb ibuprofen were 233.161 mg g−1 (500 °C), 219.543 mg g−1 (600 °C), and 227.033 mg g-1 (700 °C). The kinetic model of Gunningite on the ibuprofen adsorption followed the kinetic model of Ho and McKay.

IR spectroscopic study of the hydrogen bond network in the water–3-amino-1-propanol system and its comparison with the spatial network of hydrogen bonds in the water–monoethanolamine system

IR spectroscopy was used to explore the water–3-amino-1-propanol (3AP) system in the range of 400–4000 cm-1. Based on the stretching vibrations of OH, NH2 and CH groups and skeletal bending vibrations of 3AP it was concluded that mixed spatial networks are formed in the water–3AP system that predominate at medium 3AP concentrations. The obtained results are similar to the IR spectroscopic data for the water–monoethanolamine system, viz., the networks of both amino alcohols are incorporated into the spatial