Universidad Nacional Autónoma de México, Instituto de Ciencias Nucleares, Circuito Exterior, Cd. Universitaria, Cd de México, C.P. 04510, México E-mail:
Universidad Nacional Autónoma de México, Instituto de Ciencias Nucleares, Circuito Exterior, Cd. Universitaria, Cd de México, C.P. 04510, México.
Water Sci Technol. 2024 Jun;89(12):3178-3191. doi: 10.2166/wst.2024.167. Epub 2024 May 24.
The radiolytic degradation of 4-hydroxybenzoate (4-HBA) in aerated, oxygen-free and NO-saturated aqueous solutions at concentrations of 0.10 and 0.25 mmol/dm were gamma irradiated at different doses in a source of Co-60. The results show that ·OH adds predominantly to the 3 position of the aromatic ring, and elimination of the acid group leads to the degradation of 4-HBA. With an NO-saturated 0.10 mmol/dm 4-HBA solution, total degradation occurred at 1.6 kGy, and with a 0.25 mmol/dm solution, total degradation occurred at 3.5 kGy. In the aerated and oxygen-free 0.25 mmol/dm 4-HBA solutions, the behavior was similar, degradation occurring at a dose of 13.1 kGy. At the concentration of 0.10 mmol/dm, total degradation occurred at 7.0 kGy, with small amounts of radiolytic products and byproducts. We propose a mechanism for the degradation of 4-HBA caused by water radicals produced in the three environments, leading to formation of the identified stable products. Oxidation was followed by chemical oxygen demand (COD), which decreased as the 4-HBA concentration increased. The kinetics showed a pseudo-first-order behavior. The rate constant of degradation was similar for the solutions with and without oxygen.
在有氧、无氧和 NO 饱和的水溶液中，浓度为 0.10 和 0.25 mmol/dm 的 4-羟基苯甲酸（4-HBA）在 Co-60 源中进行不同剂量的γ辐照，发生辐解降解。结果表明，·OH 主要加成到芳环的 3 位，酸基消除导致 4-HBA 降解。在 0.10 mmol/dm 的 NO 饱和 4-HBA 溶液中，1.6 kGy 时可完全降解，而在 0.25 mmol/dm 的溶液中，3.5 kGy 时可完全降解。在有氧和无氧的 0.25 mmol/dm 4-HBA 溶液中，行为相似，在 13.1 kGy 时发生降解。在 0.10 mmol/dm 的浓度下，7.0 kGy 时可完全降解，产生少量的辐解产物和副产物。我们提出了在三种环境中产生的水自由基导致 4-HBA 降解的机制，生成了鉴定出的稳定产物。COD 随氧化而降低，随 4-HBA 浓度的增加而降低。动力学表现出拟一级行为。有氧气和无氧气的溶液的降解速率常数相似。
