Perfluorinated carboxylic acids (PFCAs) of different carbon chain lengths are chemicals of concern to human health and their removal, using conventional remediation technologies, is challenging. The present paper pursuits thermal and photo-induced degradation of PFCAs (F(CF₂)_nCOOH, n = 1–9) under various concentrations of four different acids (HNO₃, H₂SO₄, HCl, and H₃PO₄) covering a range of strong acidic to basic pH. For thermal-induced experiments, the temperature was set at 40 °C, 60 °C, and 80 °C at acid strengths of 0.04–18.4 M. Photo-induced experiments were conducted at pH 0.5, 7.0, and 13.0 under a light intensity of (150 ± 10) × 100 μW/cm². The degradation first-order rate constant (k_1, h⁻¹) as a function of [H⁺] was modeled by considering equilibrium of nondissociated (F(CF₂)_nCOOH, HX) and dissociated (F(CF₂)_nCOO⁻, X⁻) species of PFCAs (HX ⇌ X⁻ + H⁺, pK_a = −0.1). Species-specific rate constants, k₁^HX, reasonably described the trend of thermal and photo decay of PFCAs, where k₁^HX increased with acidity of solution and the carbon chain length of PFCAs. Mechanism of degradation of PFCAs (e.g. perfluorooctanoic acid (PFOA)) involved homolytic breakage of CC bond between alkyl and carboxyl groups, which produced radicals and subsequently decarboxylation to perfluoroheptene-1. Density functional theory (DFT) calculations supported the mechanism. The calculations indicated that a breaking of CC bond is more feasible with nondissociated HX than dissociated X⁻ species of PFCAs and also with increase in chain length. The potential of a combination of thermal- and photo-induced processes under acidic conditions to enhance degradation of PFOA in water is presented.

中文翻译：

---

热和光诱导的全氟羧酸降解：动力学和机理

不同碳链长度的全氟化羧酸（PFCA）是人类健康所关注的化学物质，使用传统的修复技术将其去除是具有挑战性的。本文研究了在四种不同酸（HNO ₃，H ₂ SO ₄，HCl和H ₃ PO ₄）的不同浓度下，PFCA（F（CF ₂）_n COOH，n = 1–9）的热降解和光诱导降解。）涵盖了从强酸性到碱性pH的范围。对于热诱导实验，温度设置为40°C，60°C和80°C，酸强度为0.04-18.4M。在光强下，在pH 0.5、7.0和13.0下进行光诱导实验的（150±10）×100μW/ cm²。降解一级速率常数（ķ _1， ħ ^-1），为[H的函数的⁺ ]通过考虑的nondissociated（F（CF平衡建模₂）_Ñ COOH，HX）和离解（F（CF ₂）_Ñ COO ^-，X ^-全氟羧酸的）物种（HX⇌X ^-  + H ⁺，p ķ_一个 = -0.1）。特定物种的速率常数k ₁ ^HX合理地描述了PFCA的热衰变和光衰变趋势，其中k ₁ ^HX随着溶液酸度和PFCAs碳链长度的增加而增加。PFCA（例如全氟辛酸（PFOA））的降解机理涉及C的均质裂解烷基和羧基之间的C键产生自由基，随后脱羧为全氟庚烯-1。密度泛函理论（DFT）的计算支持该机制。计算表明，C的破坏C键与nondissociated HX比解离X更可行^-种全氟羧酸的并且还与在链长度的增加。提出了在酸性条件下热诱导和光诱导过程相结合以增强水中PFOA降解的潜力。