Cheng Shuangshuang, Cui Rui, Sun Yuehong, Li Yuxin, Zhou Yangjian, Song Zilong, Yang Xin
School of Environmental Science and Engineering, Guangdong Provincial Key Laboratory of Environmental Pollution Control and Remediation Technology, Sun Yat-sen University, Guangzhou 510275, PR China.
School of Environmental Science and Engineering, Guangdong Provincial Key Laboratory of Environmental Pollution Control and Remediation Technology, Sun Yat-sen University, Guangzhou 510275, PR China.
Water Res. 2025 Oct 1;285:124132. doi: 10.1016/j.watres.2025.124132. Epub 2025 Jun 28.
The degradation kinetics and mechanism of four free bases were comparatively investigated during UV/HO and UV/PDS water treatment processes. The UV/PDS system demonstrated superior removal efficiency for all four bases compared to the UV/HO process. Pyrimidine bases (cytosine and thymine) exhibited notably faster degradation rates than purine bases (adenine and guanine) in both advanced oxidation systems. Guanine (G) was then selected as a representative free base to investigate the internal and external reverse-reduction process. The time-resolved transient spectra shows that key intermediate product G(-H) was formed in both processes, where this radical play critical role in initiating reverse-reduction process. During UV/HO process, the G's antioxidant intermediates (e.g. 8-oxoG) trigger an internal reverse-reduction process, which can reduce G(-H) back to their parent compounds. The second-order rate constant for the reaction between of G(-H) and 8-oxoG was quantitatively determined to be (2.60 ± 0.12) × 10 M s. Conversely, during the UV/PDS process, the reverse-reduction process of G(-H) is predominantly governed by external inhibition mediated by dissolved organic matter (DOM), with no competing internal pathway observed. Specifically, intrinsic intermediate products generated during UV/HO treatment initiate an internal reverse-reduction process, effectively suppressing DOM-driven external reduction. This may also explain why the degradation rates of free bases were lower in the UV/H₂O₂ system than in the UV/PDS system, and why DOM exhibited a stronger inhibitory effect on their degradation in the UV/PDS process compared to UV/H₂O₂. DFT calculations were conducted to verify the proposed mechanisms, which were applicable to the four studied bases. Studying both internal and external reverse-reduction processes can significantly enhance the understanding of compounds transformation pathways and enhance the accuracy of predicting degradation rates in real-world aqueous systems.
在UV/HO和UV/PDS水处理过程中，对四种游离碱的降解动力学和机理进行了比较研究。与UV/HO工艺相比，UV/PDS系统对所有四种碱均表现出更高的去除效率。在两种高级氧化系统中，嘧啶碱（胞嘧啶和胸腺嘧啶）的降解速率明显快于嘌呤碱（腺嘌呤和鸟嘌呤）。然后选择鸟嘌呤（G）作为代表性游离碱，研究其内部和外部的反向还原过程。时间分辨瞬态光谱表明，在两个过程中均形成了关键中间产物G(-H)，该自由基在引发反向还原过程中起关键作用。在UV/HO过程中，G的抗氧化中间体（如8-氧代鸟嘌呤）引发内部反向还原过程，可将G(-H)还原回其母体化合物。G(-H)与8-氧代鸟嘌呤之间反应的二级速率常数经定量测定为(2.60±0.12)×10 M s。相反，在UV/PDS过程中，G(-H)的反向还原过程主要受溶解有机物（DOM）介导的外部抑制作用控制，未观察到竞争性的内部途径。具体而言，UV/HO处理过程中产生的固有中间产物引发内部反向还原过程，有效抑制DOM驱动的外部还原。这也可以解释为什么游离碱在UV/H₂O₂系统中的降解速率低于UV/PDS系统，以及为什么DOM在UV/PDS过程中对其降解的抑制作用比UV/H₂O₂更强。进行了密度泛函理论（DFT）计算以验证所提出的机理，该机理适用于所研究的四种碱。研究内部和外部反向还原过程可以显著增强对化合物转化途径的理解，并提高预测实际水系统中降解速率的准确性。
