Citation: Cruz, T.d.S.d.; Batista, W.V.F.d.C.; Oliveira, E.F.d.; Oliveira, W.L.d.; Pimentel, D.M.; Diab, G.A.A.; Teixeira, I.F.; Pereira, M.C.; Mesquita, J.P.d. A Coordination Polymer Based on Nickel(II)–Cyamelurate: A Robust Catalyst with Highly Dispersed Nickel Sites for Nitrophenol Reduction under Ambient Conditions. C 2024, 10, 27. https://doi.org/ 10.3390/c10010027 Academic Editors: Chi-Hui Tsou, Patrizia Savi and Gil Goncalves Received: 2 February 2024 Revised: 7 March 2024 Accepted: 14 March 2024 Published: 17 March 2024 Copyright: © 2024 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/). Journal of Carbon Research C Article A Coordination Polymer Based on Nickel(II)–Cyamelurate: A Robust Catalyst with Highly Dispersed Nickel Sites for Nitrophenol Reduction under Ambient Conditions Taís dos Santos da Cruz 1 , Walker Vinícius Ferreira do Carmo Batista 1 , Eduarda Ferreira de Oliveira 1 , Wanessa Lima de Oliveira 1 , Dilton Martins Pimentel 1 , Gabriel Ali Atta Diab 2 , Ivo Freitas Teixeira 2 , Marcio César Pereira 3 and João Paulo de Mesquita 1,2, * 1 Department of Chemistry, Federal University of Jequitinhonha and Mucuri Valleys, Rodovia MGT 367—Km 583, nº 5000, Alto da Jacuba, Diamantina 39100-000, MG, Brazil; tais.cruz@ufvjm.edu.br (T.d.S.d.C.); walker.vinicius@ufvjm.edu.br (W.V.F.d.C.B.); ferreira.eduarda@ufvjm.edu.br (E.F.d.O.); wanessa.oliveira@ufvjm.edu.br (W.L.d.O.); dilton.pimentel@ufvjm.edu.br (D.M.P.) 2 Department of Chemistry, Federal University of São Carlos, Rod. Washington Luís Km 235—SP-310, São Carlos 13565-905, SP, Brazil; gabrieldiab@estudante.ufscar.br (G.A.A.D.); ivo@ufscar.br (I.F.T.) 3 Instituto de Ciência, Engenharia e Tecnologia, Federal University of Jequitinhonha and Mucuri Valleys, Rua do Cruzeiro, nº 01-Bairro Jardim São Paulo, Teófilo Otoni 39803-371, MG, Brazil; marcio.pereira@ufvjm.edu.br * Correspondence: joao.mesquita@ufvjm.edu.br Abstract: Cyamelurate anions obtained from the hydrolysis of polymeric graphitic carbon nitride were used for the preparation of a water-stable and crystalline coordination polymer based on nickel(II)–cyamelurate. The polymer was prepared and applied as a catalyst for the reduction of 4-nitrophenol to 4-aminophenol in the presence of borohydride under ambient conditions. The catalyst was prepared by a simple and environmentally friendly method in an aqueous medium, and it was completely characterized by a variety of techniques, including FTIR, UV–Vis, XRD, TGA, TEM, and STEM. The obtained catalyst was able to catalyze the reaction of 4-nitrophenol to 4-aminophenol with a good kinetic constant. In addition, the catalyst proved to be significantly robust, maintaining a conversion rate greater than 80% after five minutes of reaction for eight consecutive catalytic cycles. In addition, the catalytic activity of the coordination polymer was much higher than that observed for a homogeneous catalyst based on aqueous Ni 2+ ions, suggesting the importance of the structure of the coordination sphere formed by the cyamelurate anions. The results presented here can contribute to the application of other coordination polymers anchored with cyamelurate-like ligands and derivatives, as well as to new catalyst designs based on this coordination site formed by oxygen and nitrogen donor atoms. Keywords: coordination polymer; carbon nitride; cyamelurate; nickel; 4-nitrophenol 1. Introduction The process of reducing global carbon emissions will require significant changes in the production sector, which will have a profound impact on the chemical industry. Catalysis will play a central role in this new industrial revolution as it has been estimated that 90% of all commercially produced chemicals go through some catalytic process during at least one stage of their production process. Therefore, catalysts must be redesigned to reduce production costs, minimize dependence on critical minerals, and operate efficiently under ambient conditions [1]. Over the past decade, there has been an increase in the use of coordination polymers (CPs) in various catalytic reactions. The outcomes of these experiments have shown that CPs have the potential to be used as effective heterogeneous catalysts in a range of organic reactions [2]. In fact, catalysts based on coordination polymers are considered very promising, since they are incorporated into the class of single-atom C 2024, 10, 27. https://doi.org/10.3390/c10010027 https://www.mdpi.com/journal/carbon