*3.6. Stability and Reusability of the Prepared Materials*

The reusability of the prepared materials is investigated and evaluated. The AC-based adsorbent is tested for various adsorption cycles, and the results are displayed in Figure 8.

From the recyclability test, it was established that the system could work with a removal efficiency close to 50% for the studied molecules (AT, 46%; PR, 58%) for a minimum of four cycles. After each adsorption cycle, the adsorbent AC-OH is used for the desorption system, in which the leaching solvent is methanol. The histogram of the removal of AT and PR after each cycle is represented in Figure 8. As seen, for the PR removal, in the first cycle, percent recovery rates of 92% were reached in 2 h, while the second cycle shifted to 87%, which can be considered appreciable results for the recycled adsorbent. The same trend was observed for the removal of AT, which presents a slight decrease from 70% to 65%. Importantly, the developed materials had good recyclability, reaching 52% of PR removal

over the fourth cycle. Accordingly, the obtained results could be considered a suitable and stable adsorbent for removing pharmaceutical products.

The adsorption capacities of the pharmaceutical molecules were compared with data already published using other adsorbents. Table 1 summarizes the maximum adsorption capacity over various adsorbents for treating AT and PR. Comparatively, it was found that AC-OH showed a better adsorption capacity for AT (288 mg/g) and PR (339 mg/g) compared to the other adsorbents, such as granular activated carbon, hematite nanoparticles, and activated carbon fiber. Interestingly, this finding can open a new prospect to evaluate the prepared materials for other toxic molecules on a large scale, like the industrial scale.

In addition, it will be important to evaluate the efficiency of AC-TiO2 on the photodegradation uptake. It was clear that AC-TiO2 performs well on the photodegradation of AT and PR in liquid solution. Table 2 reports the photocatalytic degradation capacity using AC-TiO2 compared to other commercial photocatalysts reported in the literature. However, the photocatalytic degradation of pollutants by TiO2 has been extensively studied, while there are few reports of utilizing AC-TiO2 to degrade atenolol and propranolol (Table 2). It can be observed that AC-TiO2 is an efficient candidate to eliminate AT and PR, as compared to the other catalysts. It is interesting to note that AC-TiO2 is efficient in treating concentrated solutions of AT and PR in a short time compared to data already published in the literature. It should also be reminded that AC-TiO2 is inexpensive as it is prepared from a lignocellulosic agro-waste.

#### *3.7. Comparison between the Adsorption and the Photocatalysis Methods*

As mentioned in the introduction, this work comprehensively compared two methods for the water treatment, i.e., adsorption and photodegradation techniques, using the same support like AC-OH and AC-TiO2 for adsorption and photodegradation, respectively. Despite the interesting results obtained in the above section for both processes, a distinguishing difference can be illustrated in many aspects, particularly the reusability and the cost. Accordingly, the most useful and more suitable methods for wastewater treatment can be selected. On the one hand, the photocatalytic degradation of pharmaceutical products is based on utilizing TiO2 nanoparticles, which represents one of the most promising methods to decontaminate water containing organic pollutants, such as AT and PR. In its nanometric form, titanium dioxide is considered the first interesting catalyst for photocatalytic wastewater treatments, as it presents high stability. Also, in light of the results obtained in this work, it was found that TiO2 incorporated over AC is attractive due to its highly reactive surfaces, which make them a good photocatalyst of pollutants. Unlike the high energy consumption caused by the UV light during the sorbent activation, nanoparticle powders can be released in treated water, contaminating the environment. As the toxicity of the environment is not accepted to any degree, photodegradation via AC-TiO2 is limited

and cannot be developed on a large scale, including any industrialization of the process. However, the adsorption process represents an appreciable removal capacity of up to 89% of AT and PR pharmaceutical pollutants. Likewise, the adsorption methods are widely employed since it provides many advantages, such as low energy consumption, strong reusability, cost-effectiveness, and easy handling.


**Table 1.** Comparison of the adsorption capacity of AT and PR over various adsorbents.

**Table 2.** Comparison between photocatalytic degradation of (AT and PR) in this study with other catalysts reported in the literature.


Interestingly, no secondary contamination can be caused by this eco-friendly adsorption during water treatment. To date, wastewater treatment by adsorption can be used in full-scale applications, and very effective results are obtained using this method [15,16,46,47]. On the other, to assess the possible environmental impact and the safety of the whole process, the absence of toxic effects of the process effluents must be guaranteed. Accordingly, the adsorption process is more efficient than photodegradation methods.

#### **4. Conclusions**

We have compared the adsorption and the photodegradation methods in wastewater treatment, particularly the removal of pharmaceutical products (AT and PR). In this regard, biomasses based on date stem were activated and calcinated to prepare an activated carbon (AC). The AC materials were modified by a hydroxylation strategy to increase the hydroxyl

groups over the AC surface, resulting in AC-OH. In addition, to ensure the photodegradation methods, AC was impregnated into TiO2 solution to produce AC-TiO2. The prepared materials were characterized and tested for the removal of AT and PR. The results show that the obtained adsorbent exhibited high adsorption capacity for both molecules. The core of the adsorption mechanism involved interactions such as an electrostatic attraction between adsorbate pharmaceutical molecules and AC-OH adsorbent in the aqueous medium. AC-OH regeneration was studied through four adsorption–desorption cycles and found to have a recovery rate of more than 50% after adsorption. A comparison between the treatment methods proved that adsorption is more suitable for removing pollutants from water, as it presents low energy consumption. The study facilitates the preparation of recyclable and stable adsorbent material for wastewater treatment.

**Supplementary Materials:** The following supporting information can be downloaded at: https: //www.mdpi.com/article/10.3390/app13148074/s1, Table S1: Properties of atenolol and propranolol; Figure S1: Chemical structure of propranolol and atenolol; Figure S2: The effect of temperature on the adsorption capacity of AT and PR; Figure S3: Effect of concentration variation in the adsorption capacity of AT and PR; Figure S4: The effect of pH variation in the removal of (**a**) atenolol and (**b**) propranolol; Table S2: Thermodynamic parameters for Langmuir and Freundlich models; Figure S5: Thermodynamic adsorption of AT and PR on AC-OH; Table S3: Thermodynamic adsorption parameters for AT and PR; Figure S6: Removal capacity of (**a**) PR and (**b**) AT by AC doped with various % TiO2.

**Author Contributions:** B.S., P.N.F., J.C. and V.M. were involved in the investigation. B.S., N.B., J.V. and G.L.D. were involved in the writing, supervision, and funding acquisition. F.L.D. was involved in the supervision. All authors have read and agreed to the published version of the manuscript.

**Funding:** This work was financially supported by the University of Rouen Normandy, INSA Rouen Normandy, the Centre National de la Recherche Scientifique (CNRS), the European Regional Development Fund (ERDF), Labex SynOrg (ANR-11-LABX-0029), the Carnot Institut I2C, the Graduate School for Research Xl-Chem (ANR-18-EURE-0020 XL CHEM), and by the Region Normandie and the Grand Evreux Agglomeration.

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** Complementary data can be obtained upon request.

**Conflicts of Interest:** The authors declare no conflict of interest.
