Waste-polystyrene foams-derived magnetic carbon material for adsorption and redox supercapacitor applications

The current impact of plastic waste on the environment and nature pushes for coming up with methods for their efficient reuse and recycle. Expanded polystyrene waste, massively produced worldwide, is presented in this work as a novel precursor of magnetic activated carbons (MAC) for the first time. A simple methodology based on the impregnation of EPS samples with Fe3+ in solution, followed by pyrolysis under Ar pressure and chemical activation is proposed. The as-prepared carbonaceous magnetic materials present nanometric phases of Fe0, Fe3C, and Fe3O4, and showed high specific surface area (672 m2 g−1) and total pore volume (0.35 cm3 g−1), one of the highest found in the carbonaceous magnetic materials literature. Their excellent textural, chemical and electrical properties, combined with the possibility of magnetically collection and regeneration after operation guaranteed an excellent performance of MAC in two different applications: as adsorbents of organic contaminants and as electrodes of redox supercapacitors.The authors would like to thank the Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) and Fundação de Amparo à Pesquisa do Estado de Minas Gerais (FAPEMIG) for the financial support. P.F.R. Ortega acknowledges the FAPEMIG (DOF nº. 2720262/2018). The authors are also grateful to Rede Mineira de Química. R.L. Lavall is recipient of fellowship from CNPq (grant number 313304/2017-3). N. C. F. Machado, K. H. A. Mendes, and L. A. M. de Jesus would like to thank CEFET-MG and FAPEMIG for scholarships receivedPeer reviewe

The effects of functionalization on graphene oxide for organic dye adsorption: An experimental-theoretical study using electronic structure calculations and statistical mechanical modeling

In this work, an alternative theoretical–experimental approach was combined to investigate the influence of the degree of functionalization of reduced graphene oxides (rGO) on the capacity and adsorption mechanisms of two model organic dyes. The experimental adsorption equilibrium data for methylene blue (MB) and indigo carmine (IC) were adjusted and studied using an efficient Multi-Layer Finite Model (MLFM) based on statistical mechanics. Additionally, density functional calculations (DFTB and DFT) were carried out to study the molecular interaction geometry and adsorption energies. With this approach, a greater amount of information about the adsorption process can be obtained in relation to commonly used methodologies for adsorption at a solid–liquid interface. Herein, kinetic and adsorption equilibrium experiments were conducted on rGOs prepared via thermal reduction at different temperatures (300, 700, and 1000 °C) in order to obtain very different contents of oxygenated functional groups. The highest adsorbed amounts are obtained for rGO1000, reaching 208 and 320 mg g−1 for MB and IC, respectively. The MLFM results revealed that the rGO-dye interaction occurs preferentially via π-stacking, and with the formation of up to two adsorption layers. The elimination of functional groups from the surface of rGOs is also revealed to be favorable, decreasing the adsorption energy and increasing the amount and fraction of molecules adsorbed in parallel orientation.This work was supported by Brazilian agencies CNPq (grant numbers 309720/2020-6 and 311508-2021-9), FAPEMIG (grant numbers APQ-02780-18, APQ-00210-21, and APQ-04537-22) and CAPES. Danielle D. Justino acknowledges the scholarship received from FAPEMIG.Peer reviewe