processes Article Visible Light-Driven Photocatalytic Rhodamine B Degradation Using CdS Nanorods Haseeb Ullah 1, * , Eva Viglašová 2 and Michal Galamboš 2, *   Citation: Ullah, H.; Viglašová, E.; Galamboš, M. Visible Light-Driven Photocatalytic Rhodamine B Degradation Using CdS Nanorods. Processes 2021, 9, 263. https:// doi.org/10.3390/pr9020263 Academic Editor: Olivier Monfort Received: 30 November 2020 Accepted: 24 January 2021 Published: 29 January 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 Chemistry, Quaid-i-Azam University, Islamabad 45320, Pakistan 2 Department of Nuclear Chemistry, Faculty of Natural Sciences, Comenius University in Bratislava, Mlynská Dolina, Ilkoviˇ cova 6, 84215 Bratislava, Slovakia; eva.viglasova@uniba.sk * Correspondence: chemist.ktk.06@gmail.com (H.U.); michal.galambos@uniba.sk (M.G.) Abstract: In this work, highly crystalline CdS nanorods (NRs) were successfully synthesized by a facile, one-step solvothermal method. The as-prepared CdS NRs powder was characterized by XRD, FESEM, Raman, PL, XPS, BET, and UV-visible techniques to evaluate the structural, mor- phological, and optical properties. The photocatalytic performance of the as-synthesized CdS NRs was investigated for the photodegradation of RhB dye under visible light irradiations. It has been found that CdS NRs show maximum RhB degradation efficiency of 88.4% in 120 min. The excellent photodegradation ability of the CdS NRs can be attributed to their rod-like structure together with their large surface area and surface state. The kinetic study indicated that the photodegradation process was best described by the pseudo-first-order kinetic model. The possible mechanism for the photodegradation of RhB dye over CdS NRs was proposed in this paper. Keywords: CdS; rhodamine B; photocatalysis; pseudo-first order kinetics 1. Introduction In recent years, the ever-increasing global population, unplanned urbanization, and rapid industrialization have caused enormous environmental pollution, becoming an in- creasingly serious threat to the survival of human beings [1,2]. Organic dyes are considered a major class of environmental hazards, extensively produced by some industries such as the manufacture of plastics, papers, textile, food, cosmetic, drugs, and printing indus- tries [3–5]. Most of the dyes have xenobiotic properties and complex aromatic structures and are resistant to degradation. Inhalation of organic dyes can cause eye burns, profuse sweating, vomiting, nausea, and mental confusion [6,7]. Nowadays, around 100,000 differ- ent types of synthetic dyes are produced with a production rate of 7 × 10 5 tons per year, and around 15% of the dyes are released into the natural ambiance [8]. The presence of dyes in waterbodies, even in a small amount, is a very concerning problem, as it not only affects the aesthetic nature but also reduces the photosynthetic activity of aquatic plants and algae in aqueous environments [9]. Various treatment methods, e.g., advanced oxidation processes [10], ion flotation [11], ozonation [12], membrane separation [13], anaerobic and aerobic treatment [14], biolog- ical treatment [15], and adsorption [16] have been used to treat wastewater containing organic dyes. However, these methods have several limitations, such as high cost, slow kinetics, and low performance. Therefore, it is important to develop an efficient and cost-effective technique for the decontamination of wastewater containing organic dyes. Recently, semiconductor-based photocatalysis has shown great potential in the remediation of the degradation of organic dyes as it can partially mineralize macromolecular organic dyes into small molecules such as H 2 O and CO 2 [17]. During the photocatalysis process under visible light irradiation, the electrons excites from the filled valence band (VB) of a semiconductor to the empty conduction band (CB), generates excited electron-hole pairs, which reacts with the oxygen and hydroxyl ions to generate active radicals that can degrade Processes 2021, 9, 263. https://doi.org/10.3390/pr9020263 https://www.mdpi.com/journal/processes