**1. Introduction**

The rise in environmental concerns and pollution issues in recent years has prompted the search for new and sustainable green sources for the production of environmentally friendly materials for environmental applications. The use of biomass as precursors for the production of carbon materials received important attention from many researchers since this is a widely available and abundant source compared to traditional petroleum-based materials, which are polluting, toxic and non-biodegradable [1,2]. Currently, increasing focus is being paid to plant biomass as a raw material, and many industrial companies are following this trend with a major interest in developing economic bio-based products and materials from these renewable materials. Thus, the valorization of biomass into activated carbon is the subject of various works [3–7]. The global activated carbon market is expected to garner 2776 kilotons and 5129 million USD by 2022, registering a compound annual growth rate of 6.83% and 9.32% during the forecast period 2016–2020 [8]. The extensive use of activated carbon is mainly due to its large number of industrial applications, including water and wastewater treatment [9–11], wastewater reclamation [12], gas purification [13–15], or as adsorbents for either CO<sup>2</sup> capture or high-pressure CH<sup>4</sup>

**Citation:** Madani, N.; Moulefera, I.; Boumad, S.; Cazorla-Amorós, D.; Gandía, F.J.V.; Cherifi, O.; Bouchenafa-Saib, N. Activated Carbon from *Stipa tenacissima* for the Adsorption of Atenolol. *C* **2022**, *8*, 66. https://doi.org/10.3390/c8040066

Academic Editors: Indra Pulidindi, Pankaj Sharma and Aharon Gedanken

Received: 28 October 2022 Accepted: 19 November 2022 Published: 22 November 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/).

storage [16,17] and also as catalysts [18–20] and catalyst supports [21,22]. Among the large variety of activation processes, chemical activation with phosphoric acid of biomass is one of the most employed methods for the preparation of activated carbon with enhanced physico-chemical properties [23,24]. It presents multiple advantages being the phosphoric acid not toxic compared to other impregnating chemicals [25], the low activating temperature required [25], a high yield obtained [26], and a well-developed mesoporosity [27]. Many factors, during preparation, play an important role in obtaining high-quality activated carbon. The knowledge and control of those variable factors during the activation process is very important in developing the porous texture of the activated carbon that is sought for given applications [9], as this last depends strongly on both, the activation process [16,28] and the nature of the precursor [29–31]. Hence, the influence of the preparation condition parameters such as impregnation ratios and activation temperature was deeply analyzed by many researchers [32,33].

Although there are many applications of activated carbon in different industries, adsorption still remains an effective process that results in extensive use of activated carbons. Consequently, the production of activated carbons with specific pore size distributions from low-cost materials at moderate temperatures is an important challenge on both, economical and energetical aspects [24]. Nowadays, ACs can be produced from a wide range of natural and synthetic substances and lignocellulosic materials being this last one the most used precursors [34–36]. The important content of cellulose and lignin in lignocellulosic materials has promoted them to be the most desired precursors for the preparation of activated carbon, being those two indispensables for getting a high carbon yield [37,38].

Removal of emergent pollutants from wastewater by different methods has been an important challenge for recent society and the subject of several studies over the last years [39–41]. Among them, pharmaceutical products have been widely reported due to their harmful effects on the environment such as paracetamols, clofenac, and some β-blocker species [42–44]. Atenolol is a beta blocker medicament usually used to treat high blood pressure or hypertension, heart rhythm problems, and angina [45]. Around 50% of the dose is not fully metabolized by the human body and is disposed of unchanged through urine [46]. Therefore, it has been extensively detected in concentrations ranging from about 0.78 µg/L to 6.6 µg/L in wastewater and hospital sewage [46,47].

In our previous study [48], the preparation of activated carbons from Stipa tenacissima leaves (STLs), a lignocellulosic plant widely abundant in Southern Algeria, through chemical activation with H3PO<sup>4</sup> has been reported. It has been shown that relatively low temperatures are preferred for the preparation of activated carbons. For this purpose and with the attempt to obtain a well-developed porous texture at low temperatures, this study, on one hand, investigated the preparation of activated carbons from STLs by chemical activation with H3PO<sup>4</sup> at different impregnation ratios (R) and activation temperatures (T). These factors were extensively examined. The study range varied from 400 to 600 ◦C and from 1 to 3 for both activation temperature and impregnation ratio, respectively. To check further the quality of our obtained ACs, atenolol medicament removal was used as a test to verify the adsorption capacities of three activated carbons, compared with commercial activated carbon from Darco (commercial DARCO G60 derived from lignin delivered by Fluka Chemika (ref. 05100), where the kinetics study was investigated and Freundlich and Langmuir models were reported as well.
