Raman Specrtoscopic Interpretation And Structure Discussion Of Aqueous Solution

Water is the origin of life on earth,there is no life without water.People’s exploration of water has never stopped,but they know little about water.The structure of liquid water is one of the most challenging scientific research problems in the world today.The exploration of hydrogen bond structure is the key to understanding the water structure.At present,a large number of experimental and theoretical studies have been carried out on the hydrogen bond structure in water.Among them,how to unify the experimental results and theoretical explanations has always been a scientific problem.Raman spectroscopy is an effective means to study water structure.In this paper,the Raman spectra of water were measured at 293–573 K with each 20 K as a gradient.Based on the five-peak fitting,the interaction between water molecules was analyzed by comparing isotope substitution and combining with the changes of peak position,bandwidth,symmetry and relative intensity of Raman spectra,and then the hydrogen bond structure of liquid water was discussed.After the basic structural details of water were determined,the Raman spectra of aqueous solutions at different temperatures,chloride concentrations and anion types were systematically compared.The variation law of the specific gravity of each hydrogen bond structure with temperature was obtained by peak-splitting fitting method,and the correlation interpretation mechanism between water structure and various conditions was established.The results show that:（1）Isotope substitution makes the hydrogen bond form in water transform from tetrahedral to non-tetrahedral.In the range of 293～573 K,the OD and OH stretching band characteristics of water show the main peak blue shift,the left shoulder peak decreases,the right shoulder peak increases and the peak width decreases with the increase of temperature.According to the Gaussian fitting analysis,the proportion of the five main hydrogen bonds in the water changed with temperature.On the whole,the proportion of tetrahedra decreased greatly,but the proportion of non-tetrahedra,especially the single hydrogen bond water increased significantly.The increase of temperature accelerated the thermal movement of molecules,resulting in the fracture of hydrogen bonds and the decrease of the coupling degree between water molecules.（2）The effect of chloride ion（Cl^-）on hydrogen bond varies at different temperatures.With the increase of Cl^-concentration at T<～473 K,the stretching band width of OD and OH decreases,and the main peak shifts to blue.The relative strength of the low frequency shoulder peak to the main peak decreases,while the relative strength of the main peak to the high frequency shoulder peak increases,indicating that Cl^-destroys the hydrogen bond structure.T≥～473 K,with the increase of temperature,the main peaks of OD and OH stretching bands redshift,and the bandwidth increases slightly.It reveals that Cl^-slightly promotes the tetrahedrality between water molecules,which hinders the destruction of hydrogen bonds by temperature.In addition,increasing Cl^-concentration can promote these effects.（3）Different ions have different effects on water structure.The influence of OD and OH stretching bands of SO₄^2-water is similar to that of Cl^-at low temperature,but the frequency shift caused by SO₄^2-is significantly less than that of Cl^-.Combined with Gaussian fitting analysis data,it shows that the damage ability of SO₄^2-to hydrogen bonds is weaker than that of Cl^-.T≥～473 K,with the increase of temperature,the main peaks of OD and OH stretching bands of SO₄^2-solution are obviously red-shifted relative to Cl^-,and the bandwidth increases,indicating that the binding ability of SO₄^2-with water molecules at high temperature is greater than that of Cl^-,which depends on ion electronegativity and charge density.The same spectral comparison and analysis showed that PO₄^3-always promoted the formation of hydrogen bonds at 293–573 K,but this promotion was small at room temperature,and gradually increased with the increase of temperature.However,it gradually weakened at≥～473 K,even significantly lower than that of SO₄^2-.This may be due to the strong binding ability of PO₄^3-to Na⁺at high temperature,and a large number of ion pairs were easily formed in the solution.Therefore,this study reveals that there are many hydrogen bond configurations in water.Temperature,isotope substitution and ion addition can affect the distribution of hydrogen bond configurations in water.Based on the experimental data of Raman spectroscopy under various conditions,this thesis discusses the hydrogen bond structure and interaction in water at the micro level,and establishes a method to explain the Raman spectroscopy characteristics of aqueous solutions under extensive conditions,which provides a theoretical basis for the study of water（solution）.In addition,collectors need to be added in the flotation process to improve the flotation efficiency.The essence of collectors is chemical adsorption and hydrogen bonding adsorption with minerals.Therefore,the research on the water structure of different salt solutions is of great significance to the flotation index.