Research Article Adsorptive Performance of Polypyrrole-Based KOH-Activated Carbon for the Cationic Dye Crystal Violet: Kinetic and Equilibrium Studies Abdulaziz Ali Alghamdi , 1 Abdel-Basit Al-Odayni , 2 Naaser A. Y. Abduh , 1 Safiah A. Alramadhan , 1 Mashael T. Aljboar , 1 and Waseem Sharaf Saeed 2 1 Department of Chemistry, College of Science, King Saud University, P.O. Box 2455, Riyadh 11451, Saudi Arabia 2 Engineer Abdullah Bugshan Research Chair for Dental and Oral Rehabilitation, College of Dentistry, King Saud University, Riyadh 11545, Saudi Arabia Correspondence should be addressed to Abdel-Basit Al-Odayni; aalodayni@ksu.edu.sa Received 14 May 2020; Accepted 25 February 2021; Published 20 March 2021 Academic Editor: Danina Krajišnik Copyright © 2021 Abdulaziz Ali Alghamdi 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 aim of this work was to investigate the adsorptive performance of the polypyrrole-based KOH-activated carbon (PACK) in the removal of the basic dye crystal violet (CV) using a batch adsorption system. The equilibrium data, obtained at different initial CV concentrations (C 0 = 50 – 500 mg/L) and temperatures (25–45 ° C), were interpreted using the Langmuir, Freundlich, Temkin, and Dubinin-Radushkevich isotherms, with the Langmuir model providing a better fit(R 2 ≥ 0:9997) and a maximum adsorption capacity of 497.51 mg/g at 45 ° C. Under the examined conditions, the values of the thermodynamic parameters free energy, enthalpy, and entropy indicate a spontaneous, endothermic, and physisorption adsorption process. The kinetic data of the adsorption process were very well described by a pseudo-second-order model (R 2 ≥ 0:9996). However, surface diffusion seems to be the main rate-controlling step. Thus, we concluded that PACK shows commercial potential for the removal of cationic dyes such as CV from industrial effluent. 1. Introduction Water pollution is a major environmental problem world- wide and requires urgent solutions. Industrial discharge is the main source of aquatic pollution [1] and results in the release of various physical, chemical, and biological pollut- ants, including suspended elements, dissolved gasses, mineral and organic solutes, and microorganisms [2]. The effluents from the paper, textile, leather, food, plastic, pharmaceutical, and printing industries typically contain large quantities of dyes that are used to color their products. Although many of the dyes used are not highly toxic, they cause visual pollu- tion via aesthetic changes to the natural environment. Fur- thermore, they cause a reduction in light penetration into water, impinging on the photosynthesis of aquatic organ- isms. Nevertheless, many dyes have long-lasting hazardous and toxic effects on aquatic life, largely due to their high water solubility and nondegradability under natural condi- tions [3]. Crystal violet (CV), also known as gentian violet, is a synthetic cationic dye belonging to the triphenylmethane group. Compared with anionic dyes, cationic dyes are more toxic to mammalian cells due to their ability to interact with negatively charged cell membrane surfaces, which enables them to penetrate into cells and concentrate in the cytoplasm [4]. CV is used in a variety of applications, including textile, plastic, and paper coloring; biological staining; and veteri- nary and animal medicine. However, researchers have reported that CV is a mutagen and mitotic poison that is toxic to mammalian cells and may exhibit carcinogenic effects [5–8]. Moreover, it can cause irritation to the skin and digestive tract. In extreme cases, CV can cause kidney Hindawi Adsorption Science & Technology Volume 2021, Article ID 5527594, 11 pages https://doi.org/10.1155/2021/5527594