  Citation: Mohammed Ali, H.S.H.; Sumiya; Anwar, Y.; Al-Ghamdi, Y.O.; Fakieh, M.; Khan, S.A. Revealing the Effect of MnO 2 , Activated Carbon and MnO 2 /Activated Carbon on Chitosan Polymer Host Fabricated Co NPs: Antibacterial Performance and Degradation of Organic Compounds. Polymers 2022, 14, 627. https://doi.org/10.3390/ polym14030627 Academic Editor: Alina Sionkowska Received: 23 December 2021 Accepted: 29 January 2022 Published: 6 February 2022 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2022 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/). polymers Article Revealing the Effect of MnO 2 , Activated Carbon and MnO 2 /Activated Carbon on Chitosan Polymer Host Fabricated Co NPs: Antibacterial Performance and Degradation of Organic Compounds Hani S. H. Mohammed Ali 1,2 , Sumiya 4 , Yasir Anwar 1,2 , Youssef O. Al-Ghamdi 6 , Muhammad Fakieh 1 and Shahid Ali Khan 3,4,5, * 1 Department of Biological Sciences, Faculty of Science, King Abdulaziz University, P.O. Box 80203, Jeddah 21589, Saudi Arabia; haniolfat@gmail.com (H.S.H.M.A.); yasirpcsir2006@gmail.com (Y.A.); mf1881@yahoo.com (M.F.) 2 Princess Dr. Najla Bint Saud Al-Saud Center for Excellence Research in Biotechnology, King Abdulaziz University, P.O. Box 80203, Jeddah 21589, Saudi Arabia 3 Center of Excellence for Advanced Materials Research (CEAMR), King Abdulaziz University, P.O. Box 80203, Jeddah 21589, Saudi Arabia 4 Department of Chemistry, University of Swabi, Anbar, Swabi 23561, Pakistan; ssumiya208@gmail.com 5 Department of Chemistry, School of Natural Sciences, National University of Science and Technology (NUST), Islamabad 44000, Pakistan 6 Department of Chemistry, College of Science Al-Zulfi, Majmaah University, Al-Majmaah 11952, Saudi Arabia; Yo.alghamdi@mu.edu.sa * Correspondence: skhan@uoswabi.edu.pk or shahid.ali@sns.nust.edu.pk Abstract: MnO 2 and MnO 2 blended with 1 and 2 weight percent of activated carbon (AC), MnO 2 /AC1 and MnO 2 /AC2 were synthesized through the sol–gel method. The pure chitosan (CS) films were cast in the form of films. Similarly, 5 weight% of each MnO 2 , AC, MnO 2 /AC1 and MnO 2 /AC2 was intermingled with the CS to produce different films, such as CS-AC, CS-MnO 2 , CS-MnO 2 /AC1 and CS-MnO 2 /AC2. Zero-valent Co NPs were then supported on these films through the chemical reduction method and expressed as CS@Co, CS-AC@Co, CS-MnO 2 @Co, CS-MnO 2 /AC1@Co and CS-MnO 2 /AC2@Co NPs. All the catalysts were characterized by field emission scanning electron microscopy (FESEM), energy-dispersive spectroscopy (EDS) and X-ray diffraction (XRD) techniques. The synthesized catalysts were used as a dip catalyst against the hydrogenation of 4-nitrophenol (4NP), and for the degradation of methyl orange (MO) and Congo red (CR) dyes. The k app and R 2 values were deduced from pseudo-first-order kinetics for 4NP and MO and zero-order kinetics for CR dye. The k app values of CS-AC@Co and CS-MnO 2 /AC1@Co NPs for 4NP hydrogenation were higher than those for any other member of the series, at 1.14 × 10 −1 and 1.56 × 10 −1 min −1 respectively. Similarly, the rate of CR degradation was highest with CS-AC@Co. The R 2 values for 4NP, MO and CR dyes were above 0.9, which indicated that the application of pseudo-first- and zero-order models were appropriate for this study. Furthermore, the antibacterial activity of all the catalysts was evaluated against Pseudomonas aeruginosa and Escherichia coli. The CS-AC@Co NPs exhibited the highest zone of inhibition compared to other catalysts against P. aeruginosa, while all the catalysts were inactive against E. coli. This study reveals that the catalyst can be used for the degradation of other pollutants and for microbial inhibition. Keywords: chitosan; activated carbon; MnO 2 ; Co NPs; antibacterial activity; degradation 1. Introduction A dramatic increase in the anthropogenic activities, such as industrialization, mod- ernization and urbanization, has contaminated water bodies to a serious extent. These Polymers 2022, 14, 627. https://doi.org/10.3390/polym14030627 https://www.mdpi.com/journal/polymers