Phosphorus pentoxide

Graphene oxide (GO) was prepared by modified two steps Hummers’ method. 200 mesh natural graphite oxide flakes (Alfa Aesar), sulfuric acid (Beijing Chemical works), and phosphorus pentoxide (Beijing Chemical works) were used for synthesizing preoxidized GO. Then, they were further oxidized in the sodium nitrate (Beijing Chemical works) and potassium permanganate (Aladdin Industrial Corporation) under low temperature (less than 20 °C), and further oxidized under middle temperature (35 °C) and high temperature (90 °C). Then, the solution was diluted with distilled water, followed by adding 30% hydrogen peroxide, purified in dialysis tubes for a week, and dried through freeze drying method. GO was exfoliated in distilled water for 5 h by bath sonication (80 W), followed by centrifugation, 2 times, at 3500 r.p.m to remove the un‐exfoliated GO, finally GO dispersions with concentrations of about 1 mg mL⁻¹ were obtained. Three GO samples with different oxidation degree were obtained by modifying the reaction time for middle and high temperature.

Graphene oxide (GO) was prepared by the modified two steps Hummers’ method^{49 (link),50 (link)}. In a typical synthesis protocol, 4.0 g of 200 mesh natural graphite oxide flakes (Alfa Aesar), 48 mL of concentrated sulfuric acid (Beijing Chemical Works), 8.0 g of potassium permanganate (Shanghai Aladdin Biochemical Technology Co., Ltd), and 8.0 g of phosphorus pentoxide (Beijing Chemical Works) were added in turn to synthesize pre-oxidized GO, which was then washed by deionized water till the vacuum filtrate becomes neutral. Then, 3.0 g of the pre-oxidized GO was dried in an oven at 60 °C for 12 h and was further oxidized with 3.0 g sodium nitrate (Beijing Chemical Works) and 18.2 g potassium permanganate (Shanghai Aladdin Biochemical Technology Co., Ltd.) in an ice bath. The mixed solution was then transferred to a 35 °C water bath for 2 h. After that, the solution was diluted with 300 mL of deionized water, followed by adding 10 mL of 30% hydrogen peroxide (Shanghai Aladdin Biochemical Technology Co., Ltd.) to completely react the excess potassium permanganate. The mixture was purified in dialysis tubes for a week, and followed by centrifugation at 8000 r/min twice to remove the liquid supernatant. The retained sticky GO dispersion was diluted to a suspension with 0.06 g/L GO.