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

Characterization, agricultural potential, and perspectives for the management of light soils in Brazil

Os solos leves ocupam cerca de 8% do território brasileiro e são epecialmente expressivos na nova e na última fronteira agrícola do país: a região de Matopiba, nos estados do Maranhão, do Tocantins, do Piauí e da Bahia, onde representam 20% da área. Esses solos enquadram-se nas classes texturais areia e areia franca ou francoarenosa, até a profundidade de 0,75 m ou mais, e são representados principalmente pelos Neossolos Quartzarênicos e, em parte, por Latossolos e Argissolos. O entendimento do funcionamento desses solos depende do estabelecimento de critérios distintivos sobre: dinâmica da matéria orgânica; teor e mineralogia da fração argila; teores de areia grossa e de areia total, em relação aos de areia fina; diâmetro médio da fração areia; e capacidade de retenção de água. Esses critérios podem contribuir para o zoneamento e para o manejo conservacionista e da fertilidade dos solos leves, bem como para estimação de seu potencial agrícola. Sistemas integrados de produção, como os de integração lavoura-pecuária e lavoura-pecuária-floresta, além do plantio direto com rotação de culturas, dos plantios florestais mistos com espécies leguminosas, e do uso de adubos verdes e cultivos de cobertura, são relevantes para o manejo adequado desses solos. O objetivo deste artigo de revisão foi caracterizar os solos leves e apontar os principais desafios em relação a seu potencial agrícola, a seu manejo e conservação e sua fertilidade, frente à expansão e à consolidação da nova fronteira agrícola.Light soils occupy 8% of the Brazilian territory and are especially expressive in the new and last agricultural frontier in Brazil: the Matopiba region – in the states of Maranhão, Tocantins, Piauí, and Bahia –, where they represent 20% of the area. These soils fit into the textural classes of sand, loamy sand, and sandy loam, down to 0.75-m soil depth or deeper, and they are mainly represented by Entisols (Quartzipsamments), and partly by Oxisols and Ultisols. The understanding of soil functioning depends on the establishment of distinguishing criteria for: organic matter dynamics; content and mineralogy of the clay fraction; coarse sand and total sand contents, in relation to those of fine sand; mean diameter of the sand fraction; and water retention capacity. These criteria can contribute for the zoning and for the conservationist and fertility management of light soils, as well as for the estimation of their agricultural potential. Integrated production systems, such as, crop-livestock and crop-livestock-forestry integration, besides no-tillage with crop rotation, mixed forestry planting with legumes, and the use of green manure and cover crops, are relevant for the proper management of these soils. The objective of this review was to characterize light soils and to highlight the main challenges regarding their agricultural potential and their conservation and fertility managements, in face of the expansion and consolidation of the new Brazilian agricultural frontier