catalysts Article Photocatalytic Degradation of Valsartan by MoS 2 /BiOCl Heterojunctions Eleni Grilla 1 , Maria Nefeli Kagialari 1 , Athanasia Petala 1 , Zacharias Frontistis 2 and Dionissios Mantzavinos 1, *   Citation: Grilla, E.; Kagialari, M.N.; Petala, A.; Frontistis, Z.; Mantzavinos, D. Photocatalytic Degradation of Valsartan by MoS 2 /BiOCl Heterojunctions. Catalysts 2021, 11, 650. https://doi.org/10.3390/ catal11060650 Academic Editor: Pedro Modesto Alvarez Pena Received: 5 May 2021 Accepted: 20 May 2021 Published: 21 May 2021 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2021 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/). 1 Department of Chemical Engineering, University of Patras, Caratheodory 1, GR-26504 Patras, Greece; elen.grilla@gmail.com (E.G.); nefkg97@gmail.com (M.N.K.); natpetala@chemeng.upatras.gr (A.P.) 2 Department of Chemical Engineering, University of Western Macedonia, GR-50150 Kozani, Greece; zfrontistis@uowm.gr * Correspondence: mantzavinos@chemeng.upatras.gr; Tel.: +30-261-099-6136; Fax: +30-261-099-1527 Abstract: In the present study, the removal of valsartan (VLS), an antihypertensive agent, under simulated solar radiation with the use of molybdenum sulfide-bismuth oxychloride composites (MoS 2 /BiOCl), of variable MoS 2 content (0.1–10.0 wt.%) was investigated. The physicochemical properties of the photocatalysts were examined by XRD, DRS, BET and TEM/HRTEM. Preliminary tests were conducted to examine the photocatalytic efficiency of the synthesized MoS 2 /BiOCl com- posites towards VLS degradation in ultrapure water (UPW). It was found that the activity of pure BiOCl is improved with the addition of MoS 2 . The degradation rate was maximized with the use of the catalyst containing 0.25 wt.% MoS 2 . It was also found that the increase in catalyst concentration (50–1000 mg/L) enhances VLS degradation. It was found that VLS removal decreased by increasing VLS concentration. The effect of the water matrix on VLS removal was studied by carrying out experiments in real and synthetic water matrices. VLS degradation in UPW was faster than in bottled water (BW) and wastewater (WW), mainly due to the existence of organic matter in real aqueous media. Lastly, 0.25 wt.% MoS 2 /BiOCl showed great stability after 360 min of irradiation, serving as a promising catalyst for water remediation of emerging contaminants under solar irradiation. Keywords: bismuth oxychloride; antihypertensive; valsartan; water matrix; photocatalysis 1. Introduction The ubiquity of pharmaceutically active compounds (PhACs) in aqueous media is one the biggest topics of concern for the 21st century [1–3]. PhACs mainly end up in waters through direct uncontrolled discharge from hospitals, households and industries, as well as through excretion from humans and animals’ faeces or urine [2,3]. According to some studies, antihypertensive compounds are one of the PhACs groups that have high total average concentration in influent wastewaters. One of the compounds that is frequently prescribed is VLS, which is a highly selective and orally active Angiotensin II receptor antagonist (ARA-II) for hypertension and heart failure treatment [4,5]. VLS is mainly recovered in faeces and urine when given as an oral solution. Approximately 20% of the dose is recovered as metabolites, so the recovery is more as an unchanged compound [6]. There have been reports of its presence in wastewater treatment plants all over the world, at concentrations between 11 ng/L and 6 μg/L [7–10]. These levels prove VLS minor degradation by conventional wastewater treatments plants. Therefore, alternative treatments need to be developed to remove VLS from waters. Advanced oxidation processes (AOPs) can be a viable choice for the elimination of compounds of this type, as they have shown a great potential in treating pollutants of low or high concentration of organic compounds [11,12]. These technologies are based on hydroxyl radical (·OH) production, which can be activated by ozone, hydrogen peroxide, heat, etc. These radicals are highly reactive and can oxidize a large number of organic Catalysts 2021, 11, 650. https://doi.org/10.3390/catal11060650 https://www.mdpi.com/journal/catalysts