Degradation and statistical optimization of 3,5,6-trichloro-2-pyridinol by zero valent iron-activated persulfate

Pyrite-activated persulfate to degrade 3,5,6-trichloro-2-pyridyl in water: Degradation and Fe release mechanism

TCP (3,5,6-trichloro-2-pyridinol), the main recalcitrant degradation product of chlorpyrifos, poses a high risk to human health and ecological systems. This study provided a comprehensive exploration of the pyrite-activated persulfate (PS) system for the removal of TCP in water and placed particular emphasis on the pyrite oxidation process that releases Fe. The results showed that the pyrite-activated PS system can completely degrade TCP within 300 min at 5.0 mmol/L PS and 1000 mg/L pyrite at 25 °C, wherein small amounts of PS (1 mmol/L) can effectively facilitate TCP removal and the oxidation of pyrite elements, while excessive PS (>20 mmol/L) can lead to competitive inhibitory effects, especially in the Fe release process. Aimed at the dual effects, the evident positive correlation (R2 > 0.90) between TCP degradation (kTCP) and Fe element release (kFe), but the value of k (0.00237) in the pyrite addition variable experiment was less than that in the PS experiment (k = 0.00729), further indicating that the inhibition effect of excessive addition consists of PS but not notably pyrite. Moreover, the predominant free radicals and non-free radicals produced in the pyrite/PS system were tested, with the order of significance being •OH < Fe (Ⅳ) < SO4•- < •O2- < 1O2, wherein 1O2 emerged as the principal player in both TCP degradation and Fe release from the pyrite oxidation process. Additionally, CO32- can finitely activate PS but generally slows TCP degradation and inhibit pyrite oxidation releasing Fe process. This study provides a theoretical basis for the degradation of TCP using pyrite-activated PS.

Activation of persulfate by heterogeneous nano zero-valent iron/halloysite nanotubes: reaction behavior, mechanism, and implication for tetracycline hydrochloride degradation

A novel composite (nZVI/HNTs) was prepared via incorporating nano zero-valent iron (nZVI) on halloysite nanotubes (HNTs) for degrading tetracycline hydrochloride (TCH) with existence of persulfate (PS). The adsorption process of nZVI/HNTs to TCH conformed to the Freundlich isotherm model and pseudo-second-order kinetic model, and its maximum adsorption capacity was 76.62 mg·g-1. Furthermore, the nZVI/HNTs + PS system exhibited satisfactory degradation efficiency (84.21%) for TCH, and stable nZVI/HNTs (Fe leaching < 0.001 mg·L-1) could be reused. When nZVI/HNTs dosage, PS dosage and temperature increased, TCH degradation could be enhanced. After four cycling, nZVI/HNTs + PS system had still 65.8% degradation for TCH. The quenching tests and EPR analysis evidenced that SO4•- was predominant instead of •OH in such system. Three possible pathways of TCH degradation were provided through the liquid chromatograph-mass spectrometer (LC-MS) determination. Meanwhile, the biological toxicity prediction analysis indicated that the nZVI/HNTs + PS system would be an environment friendly treatment method toward TCH pollution.