电子级超纯水是半导体工业的基础原料，水量需求大，水质要求高。尿素可穿透超纯水生产线，易导致产水有机碳（DOC）超标，造成芯片生产良率下降，是超纯水制备中面临的技术难题。本研究旨在阐明双波长紫外线（VUV/UV）和氯对尿素的协同去除特性，掌握影响因素、反应机理和降解产物，明确VUV/UV和氯协同工艺应用于超纯水制备的效能，为电子级超纯水制备提供理论指导和技术支持。本研究发现，与单独VUV/UV、单独氯和UV/氯相比，VUV/UV/氯对尿素的去除效率可分别提升至5.13倍、7倍和1.54倍。pH值的降低和氯离子浓度的增加可以提升VUV/UV/氯去除尿素的效果。本研究从尿素氯化反应和自由基反应两个角度揭示了VUV/UV与氯协同去除尿素的机理。在酸性条件下，尿素与氯反应生成易被氧化分解的氯脲，同时VUV/UV/氯体系中·Cl和·OH进一步强化了氯脲的去除，这是尿素去除的关键机制。基于尿素的氯取代反应和氯代产物氯脲的高效氧化降解，本研究提出了氯化预处理-双波长紫外线（预氯化-VUV/UV）工艺，以强化尿素去除。与VUV/UV/氯相比，预氯化-VUV/UV工艺去除尿素的能耗可降低78%，药耗可降低50%。预氯化时间的延长，pH值的降低，活性氯浓度的增加以及氯离子可促进尿素向氯脲的转化和提高自由基浓度，从而提高预氯化-VUV/UV工艺去除尿素的效果。与预氯化-UV工艺相比，预氯化-VUV/UV工艺中·Cl的浓度提升了26倍，·Cl是氯脲分解中起主要作用的自由基。·Cl氧化、·OH氧化和光解对氯脲降解的贡献率分别为60%、23%和17%，氯脲与·OH和·Cl的反应速率常数分别为3.62×107 L·mol-1·s-1和2.26×109 L·mol-1·s-1。此外，预氯化-VUV/UV工艺在去除尿素的同时，可以高效脱氮除碳，可去除79%的DOC和54%的总氮，溶液中未脱除的氮以无机氮形式存在。与VUV/UV/过氧化氢、VUV/UV/臭氧和VUV/UV/过硫酸盐等典型高级氧化技术相比，预氯化-VUV/UV工艺去除尿素的效率更高，且可同时实现尿素与醇类、醛酮类、羧酸类和卤代消毒副产物等典型小分子有机污染物的高效去除。预氯化-VUV/UV连续处理系统在0.5分钟紫外辐照时间下可实现对尿素的完全去除。与VUV/UV/氯和VUV/UV/过硫酸盐连续处理相比，成本分别可下降86%和66%。
Ultrapure water is a fundamental raw material in the semiconductor industry, with high demands on both volume and quality. Urea can penetrate ultrapure water production lines, resulting in excessive dissolved organic carbon (DOC) in the produced water, which reduces chip production yields. This represents a significant technical challenge in ultrapure water production. This study aims to elucidate the synergistic removal characteristics of urea by vacuum ultraviolet/ultraviolet (VUV/UV) and chlorine, understand the influencing factors, reaction mechanisms, and degradation products, and clarify the effectiveness of the VUV/UV and chlorine synergistic process in ultrapure water production. This research provides theoretical guidance and technical support for the preparation of electronic-grade ultrapure water.The study found that the urea removal efficiency of VUV/UV/chlorine increased by 4.13 times, 6 times, and 0.54 times compared to VUV/UV alone, chlorine alone, and UV/chlorine, respectively. Lowering the pH and increasing the chloride ion concentration enhanced the urea removal efficiency of the VUV/UV/chlorine process.From the perspectives of urea chlorination and radical reactions, this study revealed the mechanisms of synergistic urea removal by VUV/UV and chlorine. Under acidic conditions, urea reacts with chlorine to form chlorourea, which is easily oxidized and decomposed. Simultaneously, ·Cl and ·OH in the VUV/UV/chlorine system further enhanced the removal of chlorourea, which is the key mechanism for urea removal. Based on the chlorination reaction of urea and the efficient oxidative degradation of chlorourea, this study proposes a pre-chlorination dual-wavelength ultraviolet (pre-chlorination-VUV/UV) process to enhance urea removal.Compared to VUV/UV/chlorine, the pre-chlorination-VUV/UV process reduces energy consumption by 78% and chemical consumption by 50%. Extending the pre-chlorination time, lowering the pH, increasing the active chlorine concentration, and the presence of chloride ions can promote the conversion of urea to chlorourea and increase the concentration of radicals, thereby improving the urea removal efficiency of the pre-chlorination-VUV/UV process.Compared to the pre-chlorination-UV process, the concentration of ·Cl in the pre-chlorination-VUV/UV process increased by 26 times. ·Cl is the primary radical responsible for chlorourea decomposition. The contributions of ·Cl oxidation, ·OH oxidation, and photolysis to chlorourea degradation were 60%, 23%, and 17%, respectively. The reaction rate constants of chlorourea with ·OH and ·Cl were determined to be 3.62×107 L·mol-1·s-1 and 2.26×109 L·mol-1·s-1, respectively. Additionally, the pre-chlorination-VUV/UV process efficiently removes nitrogen and carbon, removing 79% of DOC and 54% of total nitrogen, with the remaining nitrogen in the solution present as inorganic nitrogen.Compared to typical advanced oxidation techniques such as VUV/UV/hydrogen peroxide, VUV/UV/ozone, and VUV/UV/persulfate, the pre-chlorination-VUV/UV process exhibits higher efficiency in urea removal. It also effectively removes typical small molecule organic pollutants such as alcohols, aldehydes, ketones, carboxylic acids, and halogenated disinfection byproducts. The continuous pre-chlorination-VUV/UV treatment system can achieve complete urea removal within 0.5 minutes of UV irradiation. Compared to continuous VUV/UV/chlorine and VUV/UV/persulfate treatments, the cost can be reduced by 86% and 66%, respectively.
