Research Article Chromium Ion Accumulations from Aqueous Solution by the Eichorinia crassipes Plant and Reusing in the Synthesis of Cr- Doped ZnO Photocatalyst Osman Ahmed Zelekew , 1 Paulos Asefa Fufa, 1 Fedlu Kedir Sabir , 2 Dinsefa Mensur Andoshe, 1 Noto Susanto Gultom , 3 Hairus Abdellah, 3 Dong-Hau Kuo, 3 Xiaoyun Chen, 4 and Gopal Krishna Devulapalli 2 1 Department of Materials Science and Engineering, Adama Science and Technology University, Adama, Ethiopia 2 Department of Applied Chemistry, Adama Science and Technology University, Adama, Ethiopia 3 Department of Materials Science and Engineering, National Taiwan University of Science and Technology, Taipei 10607, Taiwan 4 College of Materials Engineering, Fujian Agriculture and Forestry University, Fuzhou 350002, China Correspondence should be addressed to Osman Ahmed Zelekew; osmax2007@gmail.com Received 23 October 2021; Revised 9 February 2022; Accepted 24 February 2022; Published 8 March 2022 Academic Editor: Van Viet Pham Copyright © 2022 Osman Ahmed Zelekew et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. The Cr-doped ZnO photocatalysts were synthesized through the chromium ion accumulations by water hyacinth (Eichhornia crassipes). In the preparation process, the plant tissues were immersed in different sample flasks containing chromium precursors for 1, 2, 4, 6, and 8 days. The plant tissue containing chromium ion was mixed with zinc precursor followed by calcinations. For simplicity, the prepared Cr-doped ZnO samples with the plant immersed for 1, 2, 4, 6, and 8 days were abbreviated as D1, D2, D4, D6, and D8, respectively. Moreover, pure ZnO was also prepared without the water hyacinth plant accumulated with chromium ion for comparison purposes. The powder sample characterizations were performed and evaluated in the degradation of methylene blue (MB). The Cr-doped ZnO sample (D1) degrades 80% of MB dye while the D2, D4, D6, D8, and pure ZnO samples degrade only 74, 76, 79, 73, and 25%, respectively. On the other hand, without the addition of catalysts (blank), there was no significant degradation of MB dye within 90 min irradiation. Therefore, the degradation performance of Cr-doped ZnO in the presence of optimum amount of chromium dopant and water hyacinth is highly improved than that of pure ZnO. The catalytic improvement may be as a result of reducing the photogenerated electron and hole recombination rates due to the presence of dopants. Moreover, the presence of the Eichhornia crassipes plant in the synthesis of Cr-doped ZnO could also prevent further aggregations and particle size growth and enhance the porosity after calcination. 1. Introduction Currently, the disposals of industrial effluents without proper treatment are the major threat and the utmost research areas in the world [1, 2]. Mainly, organic and inorganic wastes released from different sectors such as textile industries, dye- ing, paintings, and other sources are the potential causes of water pollutions [3, 4]. Hence, proper controls of pollutants discharged from different sources with appropriate removal techniques should be the primary activity [5–8]. One of the techniques used in the wastewater treatment technology is photocatalysis. In the photocatalysis process, semiconductors such as ZnO can be used due to the ability to absorb the light, nontoxicity, and stability [9–11]. However, the activity of the ZnO semiconductor on the visible light source is not good due to its larger band gap energy (3.2 eV) [12, 13]. Due to this Hindawi Journal of Nanomaterials Volume 2022, Article ID 4943844, 10 pages https://doi.org/10.1155/2022/4943844