**1. Introduction**

With the continuous increase of human demand for the environment, many pollutants with low content in the environment but with great harm have gradually attracted people's attention, such as anti-inflammatories, antibiotics, etc., which are called emerging contaminants (ECs). ECs are a group of chemical pollutants that have potential threats to human health and the ecological environment. They are very complex organic matters and generally exist in water. ECs usually comes from medicines, personal care products, endocrine-disrupting chemicals, antibiotics, persistent organic pollutants, disinfection byproducts, and other industrial chemicals [1]. These ECs persist in the environment and last for a long time. Previous studies have found more than 30 ECs in untreated wastewater, treated wastewater, urban rainwater, agricultural rainwater, and fresh water. Among them, artificial sweeteners, pharmaceuticals, and personal care products were detected in various water samples [2]. ECs are constantly circulating, migrating, and transforming in environmental media. Although the concentration of these ECs in water is relatively low, they may have potential impacts on the environment and human health through the food chain after being accumulated by organisms [3]. Therefore, how to effectively remove ECs in water has received widespread attention.

**Citation:** Bouhcain, B.; Carrillo-Peña, D.; El Mansouri, F.; Ez Zoubi, Y.; Mateos, R.; Morán, A.; Quiroga, J.M.; Zerrouk, M.H. Removal of Emerging Contaminants as Diclofenac and Caffeine Using Activated Carbon Obtained from Argan Fruit Shells. *Appl. Sci.* **2022**, *12*, 2922. https:// doi.org/10.3390/app12062922

Academic Editors: Amanda Laca Pérez and Yolanda Patiño

Received: 21 January 2022 Accepted: 11 February 2022 Published: 12 March 2022

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**Copyright:** © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

This is the case of pharmaceutical drugs, and this is the main theme of this work. For example, in the case of painkillers and anti-inflammatory drugs such as diclofenac (Dic), their ecological toxicity and the removal capacity of conventional wastewater treatment plants are worrying. This drug has been frequently seen in wastewater and surface water at concentrations up to 2 μg/L [4], and its chronic effects need to be analyzed. Another example is caffeine (Caf), a psychostimulant and analeptic that is largely consumed by the human population and expelled basically in urine. It is frequently found in surface waters, and indeed at low concentrations caffeine can negatively affect the metabolism of fish, amphibians, and reptiles [5–8].

Diclofenac and caffeine have been removed by using different types of adsorbents which are listed in Table 1, along with percentage removal.

**Table 1.** Activated carbon performance from different agricultural waste toward caffeine and diclofenac.


At present, the methods generally used to remove ECs from water basically include the microbial method [30], electrochemical method [31], adsorption method, membrane process, and chemical oxidation process [32]. Among them, adsorption is extensively accepted because of its advantages such as low cost, high efficiency, and wide processing range. Generally used adsorbents include activated carbon [33–35]. The mechanisms of adsorption are usually non-specific which could be employed to eliminate or reduce a large variety of contaminants [36]. Adsorption is a widely acknowledged surface phenomenon which is also a method for equilibrium separation as an effective process for removal of pollutants from the wastewater [37–40]. Adsorption was observed to be advantageous over other wastewater treatment methods in terms of initial price, simple design, ease of use and non-sensitivity to harmful substances. Adsorption is therefore not allowing hazardous chemicals to form [41–43]. Presently, activated carbon is the most widely used adsorbent. It is substantially used to eliminate complex pollutants from wastewater, like dyes and heavy metals [44].

Activated carbon (AC) is a long-known adsorbent distinguished by, among other things, its large specific surface area, porous structure, and thermostability [45]. Activated carbon might be prepared from any solid material containing a high proportion of carbon often by carbonization followed by physical or chemical activation. However, a process combining both steps can be applied [46]. Carbonization is essentially aimed at enriching the material in carbon and creating the first pores, while activation aims at developing a porous structure [47]. Good-quality activated carbons are prepared by plant biomass using orthophosphoric acid H3PO4 as a chemical activating agent [48].

The AC resulting from these treatments acquires an adsorbing [49] and catalyzing capacity [50], which is highly sought after in several fields [46]: the pharmaceutical, food, and automotive industries. AC is widely used in water purification. It allows for the removal of organic (e.g., pesticides) and inorganic (e.g., heavy metals such as Pb) materials [51].

During the last decade, the ability of agricultural by-products to give ACs with a high adsorption capacity and very advantageous physicochemical properties including, among others, a low ash content, has not ceased to attract the attention of researchers [46]. Numerous works have been undertaken on the plant material of various origins: corn straw [52], olive pits [53], sunflower seed shells [54], sugarcane bagasse [55], almond shells [56], peach pits [57], grape seeds [58], apricot kernels [56], cherry pits [58], peanut shells [59], walnut shells [60], rice hulls [61], corn hulls [62], and barley seeds [63].

In Morocco, the agricultural activity attached to the production of argan fruit (Argania Spinosa) for oil extraction is rapidly emerging because of developing interest regarding its usages for culinary and cosmetic purposes worldwide. So far, the increased popularity of argan oil has prompted an annual production up to 4000 tons by Morocco, which leaves behind about 80,000 tons of hard shells [64]. The latter is currently considered as an agriculture by-product without any significant economic value and is mainly used by the local population as a domestic combustible [65]. Even more interesting, argan shells are well known by their rich lignocellulosic content [66], with high potential for use as raw material to produce activated carbons.

Indeed, we previously reported successful production of nanoporous activated carbon made from argan shells using optimal preparation conditions following an empirical approach [67]. The purpose of the present work was to initially obtain an activated carbon by chemical activation of argan fruit shells, then to investigate its capacity of adsorption on caffeine and diclofenac. This property is determined by the depollution of various industrial effluents.

## **2. Materials and Methods**

#### *2.1. Materials*

The argan nutshells studied were collected in September 2020 in the rural area of the region of Tafraout (29◦43 11.1 N 8◦58 51.7 W), southeast Morocco. These are waste fruits

from Argan trees that grow spontaneously but do not benefit from any valuation. Figure 1 shows the initial samples of argan fruit.

**Figure 1.** Initial samples of argan fruit and the process of preparation of activated carbon.

Caffeine anhydrous 98.5% (Caf) was supplied by PanReac AppliChem and diclofenac sodium 98% (Dic) was purchased from Acros Organics. Their chemical structure and other properties are shown in Table 2.

**Table 2.** Properties and chemical structures of the contaminants studied.

