In-situ analysis of trace components in proportioning distilled spirits using Raman integrating sphere spectroscopy.

In situ and on-site analysis of trace components, such as methanol and ethyl acetate, in distilled spirits poses significant challenges. In this study, we have proposed a simple, yet effective and rapid approach that combines Raman spectroscopy with Raman integrating sphere technology to accurately detect trace constituents in distilled spirits. An external standard method to effectively separate overlapping Raman peaks from different substances are developed. Experimental results demonstrate that with an exposure time of 180 s under normal temperature and pressure, the detection limits for methanol, acetic acid, and ethyl acetate in proportioned distilled spirits are below 0.1 g/L. Importantly, the detection limit of methanol and acetic acid remains unaffected by the concentration of distilled spirits and the types of trace substances. Notably, the concentration of trace solute exhibits a highly linear relationship with its corresponding Raman intensity, offering a reliable probe for identifying unknown components in distilled spirits.

Probing natural gas components with Raman integrating sphere technology.

Raman spectroscopy is a powerful method of probing natural gas components, but higher sensitivity, greater miniaturization, and lower cost techniques are required. Therefore, we designed a Raman integrating sphere-enhanced spectroscopy technology in a volume of 40 × 40 × 20 cm3 based on the principle of integrating sphere reflection. This technology consists of two parts: the first is an integrating sphere model to collect scattered signals, and the second is a right-angle light-boosting system to increase the optical path of the pump light in the sample. Raman integrating sphere technology has a detection limit of 0.5 ppm in the air with an exposure time of 600 s under room temperature and ambient pressure conditions. Experiments of natural gas detection display that the detection limits of ethane, propane, n-butane, isobutane, n-pentane, and isopentane are 28, 28, 95, 28, 189, and 95 ppm, respectively. In addition, there is a linear relationship between the relative Raman intensity and the concentration of each component in natural gas, which can be used as a probe for detecting unknown natural gas components in gas wells.

Trace Analysis of Gases and Liquids with Spontaneous Raman Scattering Based on the Integrating Sphere Principle.

Spontaneous Raman scattering is an attractive optical technique for the analysis of gases and liquids; however, their low densities and notoriously weak scattering cross sections demand an enhancement of the spontaneous Raman scattering signal for detection. Here, we have developed a simple but highly effective and fast technique to enhance the signal of spontaneous Raman scattering from gases and liquids. The technique is developed based on the principle of an integrating sphere, which realizes the multiple pass actions of low-energy pump light and the collection of all Raman scattered light for a sample volume of 2 mL. By measuring the ambient air sample with an exposure time of 180 s, we found the experimental detection limit of our spontaneous Raman scattering setup can reach 3 ppm. CH4 (<2 ppm) in air can be also examined by increasing the exposure time to 300 s. The performance of our setup used for the analysis of trace gases is further illustrated by characterizing ethane, propane, butane, and pentane in methane as well as isotopes of carbon dioxide. The results reveal that the detection limit of our setup for liquids can be improved by nearly 4 orders of magnitude compared to that of confocal Raman scattering spectroscopy with the same experimental conditions.

Mechanical response of surface wettability of Janus porous membrane and its application in oil-water separation.

Smart surfaces with switchable wettability are widely studied for environmental application. Although a large number of stimulation routes provide broad prospects for the development of smart surfaces, achieving high sensitivity, fast response and recovery, simple operation, security and good stability is still challenging. Herein, a Janus membrane via electrospinning, chemical bath deposition and heat treatment is constructed. By using the hydrophilic ZIF-L nanosheet to functionalize the hydrophobic thermoplastic polyurethane (TPU) substrate, a smart surface utilizes the ZIF-L crack induced by strain in the hydrophilic layer to control surface wettability is obtained. In the range of 0%-100% strain, the wettability of the smart surface presents an obvious change with stretching, and water contact angle of the surface shows a monotonic increase with a maximum tuning range from 47° to 114°. Due to local fusion of the TPU microfibers and good binding between the ZIF-L layer and the TPU substrate after heat treatment, the prepared Janus membrane exhibits consistent and symmetrical hydrophilic-hydrophobic-hydrophilic transition curves in 50 stretching-releasing cycles. Thanks to the porous and asymmetric architecture, the membrane shows good oil-water separation performance, and the separation flux increases with the increase of strain, while the separation efficiency is always higher than 98%. Because of the excellent structural stability, the robust membrane with 100% strain maintains its oil-water separation property for 50 stretching-releasing cycles. This study provides a new perspective for the development of smart material with stimuli responsive surface for oily wastewater purification.

Study of hydrogen bonding interactions in ethylene glycol-water binary solutions by Raman spectroscopy.

EG (ethylene glycol) is a good model system for the study of the fundamental hydrogen bonds in aqueous solutions. Using Raman spectroscopy, we have investigated the EG volume fraction induced variation in the hydrogen bonding interactions and conformations of EG-H2O (water) binary solutions. New hydrogen bonding networks is evidenced by the appearance of remarkable changes in Raman spectra and the full width at half maximum (FWHM) when the mixing volume ratio is 0.5. The H-bond in water molecules firstly strengthened and then weakened with the increasing concentration of EG. Meanwhile, the dominant association structure also changed from H2O-H2O to EG-H2O in binary solutions in this process. We provide a simple but effective method for studying EG-H2O binary solutions. It also has exciting potential prospects and can be easily extended to other mixing situations.

Estimating the effective pressure from nanosecond laser-induced breakdown in water.

Nanosecond laser-induced breakdown (LIB) in liquids (e.g., water) can produce dynamic high pressure and high temperature. However, since high pressure needs to negate the effect of high temperature to some degree, it is only partially effective. As a result, it is difficult to directly measure the effective pressure due to the transient and complex LIB process. Here, we presented a simple method based on Raman spectroscopy to indirectly determine the effective pressure caused by LIB in liquid pure H2O and low concentration H2O-H2O2 mixtures. By comparing the Raman shifts of the ice-VII mode for pure H2O and H2O-H2O2 mixtures under laser pumping and static high pressure, the LIB effective pressure can be first estimated. The empirical equation was then derived base on the correlation of the LIB effective pressure to ice-VII-point stimulated Raman scattering thresholds for pure and mixture water solutions, which can be used to estimate the LIB effective pressures for other different mixture water solutions with the uncertainty of 0.14-0.25 Gpa. Hopefully, our study here would advance the measurements of effective pressure in the LIB process.

Exploring the hydrogen bond kinetics of methanol-water solutions using Raman scattering.

Stimulated Raman scattering (SRS) and spontaneous Raman spectra are both used here to study the hydrogen bond (HB) structure and kinetics of methanol (MeOH)-water mixtures in different volume ratios. We have found that when the volume fraction of MeOH ranges from 0 to 0.27, the HB structure of water molecules is enhanced, originating from the cooperation of the hydroxyl-enhanced HBs in liquid water and the formation of an ice-like structure around the methyl groups. However, when the volume fraction of MeOH goes beyond 0.27, the main Raman peak of water becomes very weak and even disappeared, which reveals that the HB structure of liquid water is weakened. This weakening can be attributed to the H-H repulsion introduced by MeOH salvation derives. Furthermore, some HBs among water molecules are destroyed at a high MeOH volume fraction ([gt-or-equal]0.7) based on the change of C-H vibrations.

Enhanced stimulated Raman scattering of water by KOH.

Stimulated Raman scattering (SRS) of water and a 1 M KOH-H2O solution are investigated using a Nd:YAG laser in both forward and backward directions. An obvious enhanced SRS signal is realized by dissolving KOH in liquid water. Compared with pure water, the performance improvements include the appearance of low-wavenumber Raman peaks, higher Raman intensity, an increased Raman gain, and an enhanced hydrogen bonding network. In this paper, the SRS enhancement phenomenon is explained from both the hydrogen bonding structure and the mechanism of stimulated Raman scattering. We consider it to be a very important SRS enhancement technique, which is low cost, simple, but reliable. Meanwhile, it can easily be extended to other alkali hydroxides.

Enhanced Stimulated Raman Scattering by a Pressure-Controlled Shock Wave in Liquid Water.

Stimulated Raman scattering (SRS) is observed using a Nd:YAG laser in liquid water at both forward and backward directions under different pressures. The spectra at atmospheric pressure and high pressure exhibit different characteristic features. For high pressure, the main SRS peak (about 3400 cm-1) of liquid water shifts to low frequency. Interestingly, a new peak is observed in both directions. The position of the new peak is lower than that at atmospheric pressure, which belongs to strong hydrogen bonds. Especially, a low peak is obtained at around 3140 cm-1 in the backward direction at 400 MPa, indicating the formation of an ice-like structure. In addition, the normalized SRS intensity of high pressure is higher than that of atmospheric pressure. These results indicate that high pressure can significantly enhance the SRS of water molecules. The enhancement mechanism is attributed to the long duration and slightly slow velocity of the shock wave induced by high pressure.

Si quantum dots enhanced hydrogen bonds networks of liquid water in a stimulated Raman scattering process.

Stimulated Raman scattering (SRS) of silicon quantum dots (Si QD) water solutions of different sizes (2 and 5 nm) are investigated using Nd:YAG laser. Since strong and weak hydrogen bonds are formed by the charge transfer between water molecules and Si QDs, two SRS peaks of OH stretching vibrations of Si QDs solutions are observed in the forward direction. Simultaneously, characteristic feature peaks related to the interaction between OH groups and excess electrons are obtained in the backward SRS of 2 nm Si QDs solutions. The excess electrons induce a strong electrostatic field, leading to the transformation from water to an ice-VIII structure.

Raman spectra study hydrogen bonds network in ice Ih with cooling.

The Raman spectra of ice Ih (H2O and HDO) in the temperatures range from 253 to 83 K are measured. The results show that Raman peaks shift to low- or high-wavenumber due to the influence of temperature on hydrogen bonds dynamics. Importantly, Raman shifts are linear relationship with temperatures and its slope fully reflects the change of hydrogen bonds length. Finally, Raman intensity of ice Ih dependent on temperatures are also discussed.

A Raman spectroscopy study on the effects of intermolecular hydrogen bonding on water molecules absorbed by borosilicate glass surface.

The structural forms of water/deuterated water molecules located on the surface of borosilicate capillaries have been first investigated in this study on the basis of the Raman spectral data obtained at different temperatures and under atmospheric pressure for molecules in bulk and also for molecules absorbed by borosilicate glass surface. The strongest two fundamental bands locating at 3063cm-1 (2438cm-1) in the recorded Raman spectra are assigned here to the OH (OD) bond stretching vibrations and they are compared with the corresponding bands observed at 3124cm-1 (2325cm-1) in the Raman spectrum of ice Ih. Our spectroscopic observations have indicated that the structure of water and deuterated water molecules on borosilicate surface is similar to that of ice Ih (hexagonal phase of ice). These observations have also indicated that water molecules locate on the borosilicate surface so as to construct a bilayer structure and that strong and weak intermolecular hydrogen bonds are formed between water/deuterated molecules and silanol groups on borosilicate surface. In accordance with these findings, water and deuterated water molecules at the interface of capillary have a higher melting temperature.

Influence of the hydrogen bond quantum nature in liquid water and heavy water on stimulated Raman scattering.

Stimulated Raman scattering (SRS) of liquid water and heavy water have been investigated using Nd:YAG laser. The SRS spectra of liquid heavy water indicate that ice-VII and ice-VIII structures are formed by shock-induced compression (SIC) in forward and backward directions, respectively. Simultaneously, the SRS spectra reveal of liquid water that only ice-VII structure is formed in the backward direction. The difference in ice structures formed by SIC in liquid water and heavy water could be attributed to the effect of the hydrogen bond quantum nature with H+. SRS spectra of 2M NaOH water solution with ice-VII and ice-VIII structures have been successfully obtained in forward and backward, respectively, as OH- greatly reduce the quantum nature of hydrogen bonds by neutralizing H+ in water. The hydrogen bond quantum nature is important for understanding isotope calibration test structure and isotopic effect.

Study of hydrogen bonding in ethanol-water binary solutions by Raman spectroscopy.

Raman spectra of ethanol-water binary solutions have been observed at room temperature and atmospheric pressure. We find that with increasing ethanol concentration, the symmetric and asymmetric OH stretching vibrational mode (3286 and 3434cm-1) of water are shifted to lower frequency and the weak shoulder peak at 3615cm-1 (free OH) disappears. These results indicate that ethanol strengthens hydrogen bonds in water. Simultaneously, our experiment shows that Raman shifts of ethanol reverses when the volume ratio of ethanol and the overall solution is 0.2, which demonstrates that ethanol-water structure undergoes a phase transition.

Dynamic high pressure induced strong and weak hydrogen bonds enhanced by pre-resonance stimulated Raman scattering in liquid water.

355 nm pulsed laser is employed to excite pre-resonance forward stimulated Raman scattering (FSRS) of liquid water at ambient temperature. Due to the shockwave induced dynamic high pressure, the obtained Raman spectra begin to exhibit double peaks distribution at 3318 and 3373 cm-1 with the input energy of 17 mJ,which correspond with OH stretching vibration with strong and weak hydrogen (H) bonds. With laser energy rising from 17 to 27 mJ, the Stokes line at 3318 cm-1 shifts to 3255 and 3230 cm-1 because of the high pressure being enlarged. When the energy is up to 32 mJ, only 3373 cm-1 peak exists. The strong and weak H bond exhibit quite different energy dependent behaviors.

Structure of water molecules from Raman measurements of cooling different concentrations of NaOH solutions.

The Raman spectra of different concentrations of NaOH solutions have been successfully obtained at normal pressure by cooling. The results indicate that the icing point and the ice phase transition temperature of NaOH solutions decrease with increasing concentrations. Particularly, the different concentrations (2, 4, 6 or 8 and 12M) take place the liquid- III- Ih, liquid- V- Ih, liquid- VI- XV and liquid- IX- VI phase transition, respectively. In addition, the three peaks of around 3524, 3580 and 3624cm-1 appear spectra of the NaOH solutions at low temperature.