Phosphorus-containing graphene-based hybrids are materials with outstanding properties for applications in the field of electrochemical devices. In this work, an easy route to produce phosphorus-graphene oxide hybrid materials is described,...

(GO) is investigated in the present work. Six different graphitic precursors were used to produce GO following a modified Hummers method, namely: natural graphite, commercial lubricant graphite, milled graphite, graphite flakes, high-purity graphite and graphite recycled from Li-ion batteries. The products were characterized by X-ray diffraction (XRD), thermogravimetry, solid-state 13 C nuclear magnetic resonance (NMR) and scanning electron microscopy (SEM). 13C NMR spectra revealed the presence of epoxy, hydroxyl, carbonyl and lactol groups in the synthesized GOs. However, the oxidation degree of each product was found to be dependent on the average crystallite size (L c ) and particle size of the graphitic precursors, with the best GO samples being produced from the milled graphite and the graphite recycled from ion-Li batteries. These results were rationalized in terms of the structural and microstructural differences among the graphitic precursors, as revealed by the XRD patterns and SEM images, evidencing the importance of the correct choice of the precursor aiming the achievement of a well-developed structure for the GO product.Keywords: graphite oxide; recycled graphite; ion-Li battery; solid-state 13 C NMR. INTRODUÇÃOEm 1859, Brodie relatou a descoberta de um material composto por carbono, hidrogênio e oxigênio, ao qual deu o nome de "ácido grafítico", após tentar promover a oxidação do grafite.1 Tal material viria a ser conhecido como óxido de grafite (OG) e, após Novoselov e colaboradores conseguirem isolar uma folha única de grafeno, o interesse em estudos sobre a produção e características do OG ressurgiu de forma intensa, devido ao seu papel como um precursor para a produção de baixo custo e em larga escala de materiais à base de grafeno.2,3 Além disso, a completa esfoliação do OG em meio aquoso permite a obtenção do material conhecido como óxido de grafeno, este também um material com aplicações promissoras em áreas como catálise, adsorção e eletroquímica, dentre outras. 4,5 Desde o estudo pioneiro de Brodie várias rotas químicas foram propostas para sintetizar o OG, como a sugerida por Staudenmaier, 40 anos após Brodie, e por Hummers e Offeman, um século após o primeiro relato.6,7 Os produtos das reações relatadas por esses pesquisadores apresentavam grandes variações em sua composição, em função não somente dos diferentes reagentes oxidantes utilizados em cada uma (KClO 3 /HNO 3 nos métodos de Brodie e Staudenmaier e H 2 SO 4 /KMnO 4 no método de Hummers) mas também da fonte de grafite empregada e das condições reacionais.8 Atualmente, o mé-todo de Hummers é o mais utilizado para síntese do OG. Contudo, as quantidades de cada reagente originalmente usadas eram muito altas, e com o passar dos anos surgiram variações desse método que modificavam não somente as proporções dos reagentes mas também parâmetros de temperatura e tempo reacional. Tais adaptações ao método de Hummers são comumente chamadas de "métodos de Hummers modificados". [8][9][10] A estrutura do OG permanece até os dias atuais obje...

Graphene quantum dots (GQDs) are nanosized systems that combine beneficial properties typical of graphenic materials (such as chemical stability, biocompatibility and ease of preparation from low-cost precursors) with remarkable photoluminescent features. GQDs are well-known for their low cytotoxicity and for being promising candidates in applications, such as bioimaging, optoelectronics, electrochemical energy storage, sensing and catalysis, among others. This work describes a simple and low-cost synthesis of GQDs, starting from an alcoholic aqueous suspension of graphene oxide (GO) and using a hydrothermal route. GO was prepared using graphite recycled from spent Li-ion batteries, via a modified Hummers method. The GO suspension was submitted to hydrothermal treatments at different temperatures using a homemade hydrothermal reactor that allows the control of the heating program and the assessment of the internal pressure generated in the reaction. The synthesized GQDs exhibited bright blue/green luminescence under UV light; showing the success of the chosen route and opening the way for future applications of these materials in the field of optoelectronic devices.

The reduction of graphene oxide (GO) by means of thermal and/or chemical treatments leads to the production of reduced graphene oxide (rGO)—a material with improved electrical conductivity and considered a viable and low-cost alternative to pure graphene in several applications, including the production of supercapacitor electrodes. In the present work, GO was prepared by the oxidation of graphite recycled from spent Li-ion batteries using mixtures of sulfuric and phosphoric acids (with different H2SO4/H3PO4 ratios), leading to the production of materials with significant S and P contents. These materials were then thermally reduced, resulting in rGO papers that were investigated by solid-state 13C and 31P nuclear magnetic resonance, along with other methods. The electrochemical properties of the produced rGO papers were evaluated, including the recording of cyclic voltammetry and galvanostatic charge–discharge curves, besides electrochemical impedance spectroscopy analyses. The samples obtained by thermal reduction at 150 °C exhibited good rate capability at high current density and high capacitance retention after a large number of charge–discharge cycles. The results evidenced a strong relationship between the electrochemical properties of the produced materials and their chemical and structural features, especially for the samples containing both S and P elements. The methods described in this work represent, then, a facile and low-cost alternative for the production of rGO papers using graphite recycled from spent batteries, with promising applications as supercapacitor electrodes.