Abstract
In the present work, the degradation of p-nitrophenol (PNP) and its mineralization by a UV/Vis-based persulphate activation process was investigated. Firstly, a screening of processes as direct photolysis, persulphate alone and persulphate activated by radiation was performed. The incidence of radiation demonstrated to have an important role in the oxidant activation, allowing to achieve the highest PNP and total organic carbon (TOC) removals. The maximum PNP oxidation (100%) and mineralization (61.6%)—both after 2 h of reaction time—were reached when using T = 70 °C, (S2O82−) = 6.4 g/L and I = 500 W/m2. The influence of radiation type (ultraviolet/visible, visible or simulated solar light) was also evaluated, being found that the source with the highest emission of ultraviolet radiation (UV/visible) allowed to achieve the best oxidation efficiency; however, solar radiation also reached very-good performance. According to quenching experiments, the sulphate radical is key in the activated persulphate oxidation process, but the hydroxyl radical also plays an important role.
Highlights
This study was started with the use of UV-visible radiation (TQ150 lamp) and it was firstly aimed to compare the performance of direct photolysis, persulphate per se and persulphate activated with the artificial radiation
Direct photolysis proved to be inefficient in reducing the pollutant content and mineralising the organic matter, with overall removals below 8% after 2 h of irradiation, which allows concluding that PNP is not very sensitive to UV/visible radiation
The pH decrease is associated to the formation of H+ during the persulphate process, which was corroborated by the fact this parameter reduced in the blank run, and to the generation of intermediate compounds like carboxyl acids
Summary
It is applied both as raw material and as a process intermediary in numerous types of industrial activities, such as the production of pharmaceutical and petrochemical products, explosives, pesticides, pigments, dyes, plasticisers, wood preservatives, and rubber chemicals, among others [1,2,3]. Due such widespread use, small concentrations of this chemical compound have been detected in both water resources and soils due to improper wastewater discharges resulting from production, distribution, and application processes [4,5,6]. PNP has been considered by the US Environmental
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