# Optimization of Organic Content Removal from Aqueous Solutions by Fenton-Ozonation
## 1 Introduction  
Activated carbons (ACs) have been widely used for many years as adsorbent materials for gas and liquid separation and purification. For each of these applications and the associated chemical species to be separated or purified, a suitable material is required. This is particularly true when treating natural aqueous matrices such as polluted water [1, 2]. In order to treat the latter, it is necessary to have a material with an optimum porous texture for which the performance of the adsorption process will be maximized for a given type of molecule, while considering other influencing factors such as surface chemistry and environmental conditions [3, 4, 5]. In addition to their use in liquid-phase adsorption processes, ACs can be integrated into advanced oxidation processes by acting as pseudo-catalysts for hydroxyl radicals [6, 7, 8, 9, 10]. Hydroxyl radicals are powerful oxidizers of organic compounds. As a result, they can lead to their total mineralization in the form of carbon dioxide. While these hydroxyl radicals can be generated by ozone reacting with activated carbon in the presence of hydrogen peroxide (known as the peroxone system), they canalso be generated by hydrogen peroxide reacting with metals such as iron (in the Fe\({}^{2+}\) form), and in particular its oxide (known as the Fenton system) [11, 12, 13]. However, the efficiency of mineralization strongly depends on the operational conditions specific to the applied oxidation process. In this context, [PERSON] and [PERSON] (2023) compared various oxidative and reductive approaches for the treatment of mordant blue 9, a chlorinated azo dye, and highlighted the critical influence of reagent selection and the molecular properties of the pollutant on the overall performance of the process [13]. Nevertheless, coupling these two reaction systems, peroxone and Fenton, should enable optimum mineralization of certain organic pollutants in the aqueous phase. Within the framework of these advanced oxidation processes (AOPs) couplings, it is important to identify the most efficient carbonaceous material for these specific applications for the degradation and mineralization of persistent organic molecules present in water, and to optimize the experimental parameters of these processes. This study focuses on 2,4-dichlorophenoxyoxyacetic (2,4-D), a widely used herbicide in agriculture and gardening to control broad-leaved weeds [14; 15]. Its use is favored due to its low cost and effectiveness in controlling weeds in corn, coffee, and soybean crops [14; 15]. Although its use in France, for example, has been steadily decreasing since 2011 (674 tons of 2,4-D sold in 2011 compared to 350 tons in 2019), this product can still be considered relatively commonly used [16]. 2,4-D is a low-dissociation phenoxy-acid herbicide characterized by an electron density of \(\pi\) on its phenyl ring. However, its low pKa of 2.8 indicates that it is predominantly anionic (2,4-dichlorophenoxyoxyacetate) at pH above 2.8, while it takes a neutral form below this value. The environmental problem linked to the use of this product is that its presence in the environment increases the risk of soil and aquatic pollution (surface water and groundwater). This pollution is the result of the transfer of these products from the soil to the water via the phenomena of bursting and infiltration into the soil. 2,4-D, being highly soluble in water (900 mg\(\cdot\)L\({}^{-1}\)) [17; 18], is easily transported in aquatic environments and in the soil. In addition, since 2015, 2,4-D has been classified as a probable carcinogen for humans (carcinogenic group 2B) by the International Agency for Research on Cancer (IARC) and the World Health Organization (WHO) [19]. However, the use of this herbicide is still allowed in the European Union. This highlights the importance of removing this pollutant from water.