Design and synthesis of pyrophosphate acid/graphene composites with wide stacked pores for methylene blue removal

• Stacked pore size is noticeably improved by aggregation of functionalized sheets.
• The average interlayer spacing of the product is wider than that of RGO.
• Modified graphene has high adsorption capacity for methylene blue.

Pyrophosphate acid/graphene composites were prepared by using graphite oxide and phosphorus trichloride as raw materials. Phosphorus-based groups and residual oxygenated functional groups may reduce graphene sheet restacking to form graphite. The stacked pore size and binding site of the composites are noticeably improved by aggregation of functionalized sheets. The average interlayer spacing of the composites is wider than that of reduced graphene oxide (RGO). Compared with the high surface area of the adsorbent, the porosity and pore size of the materials exert significantly greater influence on the adsorption capacity of the composites. The adsorption process follows second-order rate. The adsorption of methylene blue preferably fitting the Langmuir adsorption isotherm suggests monolayer coverage of adsorbed molecules. The adsorption capacity of the composites for methylene blue is 200.0 mg g−1, which is significantly higher than those of RGO (80.0 mg g−1) and active carbon (46.7 mg g−1).

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