Citation: Márta, V.; Pap, Z.; Bárdos, E.; Gyulavári, T.; Veréb, G.; Hernadi, K. Effect of Urea as a Shape-Controlling Agent on the Properties of Bismuth Oxybromides. Catalysts 2023, 13, 616. https:// doi.org/10.3390/catal13030616 Academic Editors: Petros Kokkinos and Dionissios Mantzavinos Received: 15 February 2023 Revised: 10 March 2023 Accepted: 14 March 2023 Published: 20 March 2023 Copyright: © 2023 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/). catalysts Article Effect of Urea as a Shape-Controlling Agent on the Properties of Bismuth Oxybromides Viktória Márta 1,† , Zsolt Pap 1,2,3,† , Enik ˝ oBárdos 1 , Tamás Gyulavári 1 ,Gábor Veréb 4, * and Klara Hernadi 5, * 1 Department of Applied and Environmental Chemistry, University of Szeged, Rerrich Béla Sqr. 1, H-6720 Szeged, Hungary 2 Centre of Nanostructured Materials and Bio-Nano-Interfaces, Institute for Interdisciplinary Research on Bio-Nano-Sciences, Babes-Bolyai University, Treboniu Laurian 42, RO-400271 Cluj-Napoca, Romania 3 Laboratory for Advanced Materials and Applied Technologies, Institute for Research, Development and Innovation in Applied Natural Sciences, Babes-Bolyai University, Fântânele Str. 30, RO-400294 Cluj-Napoca, Romania 4 Department of Biosystems Engineering, Faculty of Engineering, University of Szeged, Moszkvai Blvd. 9, H-6725 Szeged, Hungary 5 Institute of Physical Metallurgy, Metal Forming and Nanotechnology, Faculty of Materials and Chemical Engineering, University of Miskolc, Miskolc-Egyetemváros, C/2-5, H-3515 Miskolc, Hungary * Correspondence: verebg@mk.u-szeged.hu (G.V.); klara.hernadi@uni-miskolc.hu (K.H.); Tel.: +36-62-546-582 (G.V.); +36-46-565-111 (ext. 1339) (K.H.) † These authors contributed equally to this work. Abstract: Bismuth oxybromides were prepared via a solvothermal method by applying different urea amounts during synthesis. The effects of the urea ratio on the morpho–structural properties and photocatalytic activity of the samples were investigated. X-ray diffraction, diffuse reflectance spectroscopy, infrared spectroscopy, Raman spectroscopy, scanning electron microscopy, and sur- face tension measurements were carried out to characterize the samples. Their photoactivity was evaluated by the photocatalytic degradation of rhodamine B and ibuprofen under UV and visible light irradiations. The urea ratio notably influenced morphology, particle size distribution, and photoactivity. However, it only had a limited effect on the crystalline composition, primary crystallite size, and band gap of bismuth oxybromides. The formation of Bi-based complexes and degraded urea-based products were observed, which were deduced to influence band gap energies and hence, photoactivity. Predominantly, samples prepared at low urea ratios proved to be the best for both rhodamine B and ibuprofen degradations under both irradiations. Keywords: bismuth oxybromide; photocatalysis; urea; ibuprofen; rhodamine B 1. Introduction Due to increasing environmental contamination by various industrial processes, the amount of consumable water has been decreasing, while wastewater treatment is a growing problem. These problems are usually tackled via traditional water treatment technologies. However, they are mostly limited to eliminating only one contaminant during a single purification process. Low-cost, highly efficient advanced oxidation techniques may be an al- ternative solution. These techniques are based upon oxidative chemical reactions, in which highly reactive free radicals (such as • OH or • O 2 − ) interact with organic compounds [1]. As a result, hazardous compounds can be degraded or converted into harmless products such as water or carbon dioxide. A widely investigated field since the 1970s, heterogeneous photocatalysis encompasses chemical reactions that occur under UV–visible light. TiO 2 , the most frequently investigated photocatalyst, can be activated by UV photons; however, they account for only ~4% of the solar spectrum. In comparison, the visible region covers ~43%; consequently, photocatalysts that can be activated by visible light, and methods to increase photoactivity [2,3] have been increasingly investigated over the last few decades. Catalysts 2023, 13, 616. https://doi.org/10.3390/catal13030616 https://www.mdpi.com/journal/catalysts