Certain metal ions accelerate deterioration of secondary polyamide reverse osmosis membranes during hypochlorite treatment. However, the mechanisms underlying this metal ion–mediated membrane deterioration have not been clarified. Here, we examined the deterioration of a secondary polyamide reverse osmosis membrane during hypochlorite treatment at various pHs by Ca²⁺, one of the most abundant ions in surface water. In the presence of Ca²⁺, accelerated membrane deterioration was observed after chlorination and hydrolysis treatment. In addition, the greater membrane deterioration was observed under neutral and alkaline conditions than under acidic conditions, suggesting that Ca²⁺ might accelerate hydrolysis rather than chlorination. X-ray photoelectron spectroscopy analysis confirmed that the Cl atomic concentration in the active layer was increased by hypochlorite treatment; however, the presence of Ca²⁺ did not enhance chlorination of the membrane. In addition, measurement of the water contact angle of the active layer of membranes treated by hypochlorite in the presence of Ca²⁺ showed a significant increase of wettability. Together, these results provided the evidence that Ca²⁺ increased hydrolysis rather than chlorination. Solid-state ¹³C nuclear magnetic resonance spectra of the membranes after hypochlorite treatment showed a signal attributed to the -C*-NH₂ of phenylenediamine structures in the active layer, the intensity of which was increased in the presence of Ca²⁺, indicating that the presence of Ca²⁺ in hypochlorite treatment resulted in increased hydrolysis of the polyamide structure. In addition, evolved gas analysis–mass spectrometry analysis provided further evidence supporting the production of ions with an m/z of 108, which corresponds to phenylenediamine. Together, the present results showed that deterioration of polyamide membrane by hypochlorite is increased in the presence of Ca²⁺ via acceleration of hydrolysis but not of chlorination. Based on these findings, we proposed a mechanism for the accelerated degradation of polyamide membrane by Ca²⁺.

在次氯酸盐处理过程中，某些金属离子会加速次级聚酰胺反渗透膜的降解。但是，这种金属离子介导的膜变质的潜在机制尚未阐明。在这里，我们研究了Ca ²⁺（地表水中最丰富的离子之一）在各种pH下的次氯酸盐处理过程中，次级聚酰胺反渗透膜的劣化。在Ca ²⁺存在下，氯化和水解处理后观察到膜加速加速降解。此外，在中性和碱性条件下比在酸性条件下观察到的膜劣化更大，表明Ca ²⁺可能会加速水解而不是氯化。X射线光电子能谱分析证实，次氯酸盐处理增加了活性层中的Cl原子浓度。然而，Ca ²⁺的存在并未增强膜的氯化作用。另外，在Ca ²⁺存在下，用次氯酸盐处理过的膜的活性层的水接触角的测量表明润湿性显着增加。总之，这些结果提供了Ca ²⁺增加水解而不是氯化作用的证据。次氯酸盐处理后膜的固态¹³ C核磁共振光谱显示归因于-C * -NH ₂的信号活性层中苯二胺结构的强度，其强度在Ca ²⁺存在下增加，表明在次氯酸盐处理中Ca ²⁺的存在导致聚酰胺结构水解增加。另外，演化气体分析-质谱分析提供了进一步的证据，支持产生m / z为108的离子，该离子对应于苯二胺。总之，目前的结果表明，在Ca ²⁺存在下，通过加速水解而不是通过氯化作用，次氯酸盐会加剧聚酰胺膜的劣化。基于这些发现，我们提出了Ca ²⁺加速聚酰胺膜降解的机理。