水体富营养化是目前普遍存在的环境问题，其中氮、磷浓度是进行富营养化风险预警和水质管理的重要依据。实时监测是提高水质管理效能的重要手段。其中，磷浓度的实时监测普遍采用磷钼蓝吸收光谱法，但由于方法原理的限制，分析结果仅能获得总磷浓度，无法得到与水体富营养化直接相关的磷酸阴离子（H2PO4 -、HPO4 2-、PO4 3-）的浓度。同时，在实时监测的长期运行中，该方法存在二次污染、设备复杂，仪器维护困难、能耗高等问题，不符合绿色化学理念。吸收光谱法是一种能够通过直接测定产生物质响应的分析方法，具有快速、无污染的优点，具备磷酸阴离子浓度实时监测的开发潜力。然而，目前采用吸收光谱法直接测定水中磷酸阴离子仍存在光谱特征尚不明确、信号响应弱、定量模型建立复杂等问题。据此，本论文采用含时密度泛函理论（TD-DFT），结合态密度和电荷转移光谱分析探究了磷酸阴离子的分子结构、分子轨道和电子激发特性；基于聚苯乙烯（PSM）散射介质以及反射膜和多次反射光学结构进行了磷酸阴离子的吸收增强研究；通过机器学习和吸收光谱建立了多参数磷酸阴离子定量模型；最后进行了混合体系中磷酸阴离子定量模型的优化、验证及方法对比分析。主要研究结果如下：（1）探明了磷酸阴离子的分子结构、分子轨道、电子激发特性以及吸收光谱行为。结果表明，磷酸阴离子的 HOMO 轨道主要由 O 原子的 p 轨道组成，LUMO 轨道由磷（P）原子的s 轨道和氧（O）原子的 p 轨道以反键作用产生。H2PO4 -、HPO4 2-、PO4 3-的特征波长均位于深紫外区域，分别由电子的局域激发和电荷转移激发产生。在吸收光谱行为研究中，对不同浓度（0~10 mmol/L）、光程（1~100 mm）以及光谱带宽（0.4~3 mm）条件下磷酸阴离子的吸收光谱进行了测定，结果表明随着浓度及光程的增大，吸光度增大的同时，最大吸收波长均会发生红移。同时，随着光谱带宽的增加，磷酸阴离子的吸光度逐渐减小，最大吸收波长发生蓝移，吸光度和浓度拟合的线性相关系数逐渐减小。多因子方差分析结果表明，光程是磷酸 阴离子吸收光谱行为最主要的影响因素，将为后续光谱特征响应的调节提供理论基础。（2）对比了散射及反射条件下磷酸阴离子的吸收增强效果。结果表明，散射介质能够有效增大磷酸阴离子的吸光度，且增强效果与 PSM 的浓度成正比，与 PSM 的粒径成反比。但基于散射未对传统吸收光谱法的方法性能产生影响。基于已有的吸收腔体设计了多次反射光学结构，结合膜层结构为 MgF2-Al-Ti 的反射膜，测定了不同浓度磷酸阴离子的多次反射增强吸收（MREA）光谱，并对吸收光谱的测定条件进行了优化。结果表明，相比于传统吸收光谱，MREA 方法能够有效增大磷酸阴离子的吸光度，提高方法灵敏度，降低方法检出限。相比于散射增强，多次反射具有更好的吸收增强效果，能够有效提高磷酸阴离子的响应信号。 （3）建立了磷酸阴离子的定量模型。结果表明，随着 pH 的降低，磷酸阴离子的吸光度、最大吸收波长以及半峰宽均发生了变化，这主要与磷酸阴离子的结构及其在水环境中的分布规律相关。基于上述吸收光谱，研究中分别基于原始光谱数据、导数光谱数据以及光谱特征参数结合 pH 进行了不同形态磷酸阴离子定量模型的建立。结果表明，随机森林（RF）算法 在依据光谱数据建立模型时表现最佳；CART 算法在依据光谱特征参数进行模型建立时表现最佳。相比于原始光谱数据和导数光谱数据，依据 187 nm 处的光谱特征参数建立的定量模型性能最优。同时，光程的优化能够进一步降低模型的浓度定量范围，MREA 条件下能够获得最大的光程，此时，H2PO4 -和 HPO4 2-的浓度定量范围最低，分别为 5.98×10 -6~4.20×10 -4 mol/L和 1.53×10 -6~7.43×10 -4 mol/L。（4）阐明了水体中常见干扰物质的电子激发特征和跃迁方式，分析了 15 种干扰物质对磷酸阴离子吸光度、吸收波长及半峰宽的影响水平和类型，据此得到定量模型的优化方法。在干扰物质种类和浓度已知的前提下，通过扣除不同干扰物质的吸光度能够减小其对磷酸阴离子定量的影响，并对优化后的定量模型进行了分析和验证。另外，将本研究中建立的定量方法与常用磷浓度分析方法的绿色化学指标进行了对比。结果表明，本方法在试剂添加种类、废液量产生以及能耗方面均具有优势，是一种符合绿色化学理念的分析方法。综上，本研究基于分子结构、轨道特征、电子激发特性探究了磷酸阴离子的吸收光谱行为；通过光的反射和散射实现了磷酸阴离子的吸收增强；结合机器学习算法建立了不同形态磷酸阴离子的定量模型，并对优化后的定量模型进行了验证分析。上述研究符合绿色化学理念，将为基于吸收光谱法进行磷酸阴离子实时监测技术的开发研究提供理论参考。

Eutrophication of water bodies is a common environmental problem. The nitrogen and phosphorus concentration is an important basis for eutrophication risk warning and water quality management. Real-time monitoring is an important means to improve the efficiency of water quality management. Among them, real-time monitoring of phosphorus concentration is generally carried out using phosphorus molybdenum blue absorption spectroscopy. But due to the limitations of the method principle, the analysis results only obtained the total phosphorus concentration, without the concentration of phosphate anions (H2PO4 -, HPO4 2-, PO4 3-) directly related to water eutrophication. Meanwhile, in the long-term operation of real-time monitoring, this method causes secondary pollution, complex equipment, difficult instrument maintenance, and high energy consumption, which is not in line with the concept of green chemistry. Absorption spectroscopy is an analytical method that directly determines the response of substances, which has the advantages of being fast and pollution-free, and has the potential for real-time monitoring of phosphate anions. However, currently, the direct determination of phosphate anions in water using absorption spectroscopy still faces issues such as unclear spectral characteristics, weak signal response, and complex quantitative model establishment. Accordingly, this study first used time-dependent density functional theory (TD-DFT), combined with density of states and charge transfer spectroscopy analysis, to explore the molecular structure, molecular orbitals, and electronic excitation characteristics of phosphate anions; The absorption enhancement of phosphate anions was studied based on polystyrene (PSM) scattering medium, reflective film, and multiple reflection optical structure; A quantitative model for multi parameter phosphate anions was established through machine learning and absorption spectroscopy; Finally, the optimization, validation, and method comparison analysis of the quantitative model for phosphate anions in the mixed system were carried out. The main research findings are as follows: (1) Explored the molecular structure, molecular orbitals, electronic excitation characteristics, and absorption spectral behavior of phosphate anions. The results showed that the HOMO orbitals of phosphate anions were mainly composed of the p orbitals of O atoms, while the LUMO orbitals were generated by anti bonding between the s orbitals of P atoms and the p orbitals of O atoms. The characteristic wavelengths of H2PO4 -, HPO4 2- and PO4 3- were all located in the deep ultraviolet region and were generated by localized electron excitation and charge transfer excitation, respectively. In the study of absorption spectroscopy behavior, the absorption spectra of phosphate anions were measured under different concentrations (0—10 mmol/L), optical pathlength (1—100 mm), and spectral bandwidth (0.4—3 mm). The results showed that as the concentration and optical path increased, the absorbance increased while the maximum absorption wavelength red-shifted. Meanwhile, as the spectral bandwidth increased, the absorbance of phosphate anions gradually decreased, the maximum absorption wavelength undergoes a blue shift, and the linear correlation coefficient between absorbance and concentration fitting gradually decreased. The results of multiple factor analysis of variance showed that optical pathlength was the most important influencing factor on the absorption spectral behavior of phosphate anions, which provided a theoretical basis for the regulation of subsequent spectral characteristic responses. (2) The absorption enhancement effect of phosphate anions under scattering and reflection conditions was compared. The results showed that the scattering medium effectively increased the absorbance of phosphate anions, and the enhancement effect was directly proportional to the concentration of PSM and inversely proportional to the particle size of PSM. However, based on scattering, the performance of traditional absorption spectroscopy methods remained unchanged. A multi reflection optical structure was designed based on the existing absorption cavity, and combined with a reflective film with an Al-MgF2-Ti film structure, the multi reflection enhanced absorption (MREA) spectra of different concentrations of phosphate anions were measured, and the measurement conditions of the absorption spectra were optimized. The results showed that compared to traditional absorption spectroscopy, the MREA method effectively increased the absorbance of phosphate anions, improve sensitivity, and reduced detection limits. Compared to scattering enhancement, multiple reflections have better absorption enhancement effects and effectively enhanced the response signal of phosphate anions. (3) A quantitative model for phosphate anions has been established. The results showed that with the decrease of pH, the absorbance, maximum absorption wavelength, and half peak width of phosphate anions all changed, which was mainly related to the structure and distribution of phosphate anions in the water environment. Based on the above absorption spectra, quantitative models for different forms of phosphate anions were established in the study using original spectral data, derivative spectral data, and spectral characteristic parameters combined with pH. The results showed that the quantitative model established based on spectral characteristic parameters performed better than the original spectral data and better than the derivative spectral data. The Random Forest (RF) algorithm performed the best when establishing models based on spectral data, and the CART algorithm performs best when modeling based on spectral characteristic parameters at 187 nm. At the same time, the optimization of optical pathlength further reduced the concentration range of the quantitative model. Under MREA conditions, the maximum optical pathlength was obtained, and the concentration quantitative range of H2PO4 - and HPO4 2- was the lowest, which was 5.98×10 -6—4.20×10 -4 mol/L and 1.53×10 -6—7.43×10 -4 mol/L, respectively. (4) The electronic excitation characteristics and transition modes of common interfering substances in water were elucidated. The impact levels and types of 15 interfering substances on the absorbance, absorption wavelength, and half peak width of phosphate anions absorption spectra were analyzed. Based on this, the optimization method of the quantitative model was obtained. Under the premise of knowing the type and concentration of interfering substances, the influence of interfering substances on the quantification of phosphate anions was eliminated by deducting the absorbance of different substances, and the optimized quantitative model was analyzed and validated. In addition, the quantitative method established in this study was compared with the green chemistry indicators of commonly used phosphorus analysis methods. The results showed that this method has advantages in the types of reagents added, the amount of waste liquid, and energy consumption, which was an analytical method that conforms to the concept of green chemistry. In summary, this study achieved absorption enhancement of phosphate anions based on their molecular structure, orbital characteristics, electronic excitation characteristics and absorption spectral behavior. A quantitative model for the concentration of different forms of phosphate anions was established using machine learning algorithms, which was validated and analyzed after optimization. The above research conforms to the concept of green chemistry and provide theoretical reference for the development of real-time monitoring technology for phosphate anions based on absorption spectroscopy.