P phenylenediamine ppd

GO suspensions (5 mg/ml) were first fabricated according to the modified Hummer’s method^{43 (link),44 (link)}. A solution of 1.92 g (6.6 mmol) of Ni(NO₃)·6H₂O in 28 ml of Milli-Q water was mixed with 32 ml GO suspension in a sealed three-necked flask. Another solution of 1.57 g (14.5 mmol) of p-phenylenediamine (pPD) (Sigma Aldrich) in 60 ml of Milli-Q water was also prepared in a sealed flask. Two solutions were separately stirred and purged with Ar gas for 1 h to exclude any external oxygen sources in the solutions. Two solutions were then mixed together in the three-necked flask and 20 ml of concentrated NH₄OH solution was added drop by drop to initiate the reaction. During the reaction, the mixture was stirred in a sealed flask with Ar gas bubbling for over 10 h at room temperature. The resulted black powders were filtered and then washed with Milli-Q water and ethanol thoroughly. Finally, the solids were redispersed into 200 ml Milli-Q water to make Ni-pPD@rGO suspensions (0.6 mg ml^–1). For comparison, Ni(OH)₂@GO nanosheets were also synthesized by treating GO only with Ni(NO₃)₂ and NH₄OH (without adding the pPD solution).