Potassium permanganate (KMnO4) has been proved to be an efficient oxidant for converting graphite into graphite oxide, but its slow diffusion in the interlayer of graphite seriously restricts the production of graphene oxide (GO). Here, we demonstrate that the preoxidation of graphite by impure manganese dioxide (MnO2) in a mixture of concentrated sulfuric acid (H2SO4) and phosphorus pentoxide (P2O5) can efficiently improve the synthesis of GO when KMnO4 is employed as the oxidant. The prepared honey-like GO hydrogels possess a high yield of single-layer sheets, large sizes (average lateral size up to 20 μm), wide ranges of stable dispersion concentrations (from dilute solutions, viscous hydrogels, to dry films), and good conductivity after reduction (~2.9 × 10(4) S/m). The mechanism for the improved synthesis of GO by impure MnO2 was explored. The enhanced exfoliation and oxidation of graphite by oxidative Mn ions (mainly Mn(3+)), which are synergistically produced by the reaction of impure MnO2 with H2SO4 and P2O5, are found to be responsible for the improved synthesis of such GO hydrogels. Particularly, preoxidized graphite (POG) can be partially dispersed in water with sonication, which allows the facile construction of flexible and highly conductive graphene nanosheet film electrodes with excellent electrochemical sensing properties.

中文翻译：

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通过用不纯的二氧化锰进行预氧化将石墨完全转化为氧化石墨烯水凝胶。

高锰酸钾（KMnO4）已被证明是将石墨转化为氧化石墨的有效氧化剂，但其在石墨中间层中的缓慢扩散严重限制了氧化石墨烯（GO）的生产。在这里，我们证明了当使用KMnO4作为氧化剂时，在浓硫酸（H2SO4）和五氧化二磷（P2O5）的混合物中不纯的二氧化锰（MnO2）对石墨的预氧化可以有效地改善GO的合成。制备的蜂蜜状GO水凝胶具有高产量的单层片材，大尺寸（平均横向尺寸最大20μm），宽范围的稳定分散液浓度（从稀溶液，粘性水凝胶到干膜），并且质量良好。还原后的电导率（〜2.9×10（4）S / m）。探索了不纯MnO2促进GO合成的机理。发现通过不纯MnO2与H2SO4和P2O5反应协同产生的氧化Mn离子（主要是Mn（3+））增强的石墨剥落和氧化作用，是这种GO水凝胶合成方法改进的原因。特别是，预氧化的石墨（POG）可以通过超声处理部分分散在水中，从而可以轻松构建具有出色的电化学感应特性的柔性，高导电性石墨烯纳米片薄膜电极。