Use 20ml GO (2mg/ml, 30% oxygenation) suspension in teflon lined up autoclave (180C for 2h). A hydrogel will be obtained without any additional chemicals neccesary. Than freeze it and dry in liophilizator afterwards(few days). To make the gelation easier you can use 100ul HCl to the GO suspension (for abovementioned volume), it will start to gelate even without hydrothermal synthesis. Higher temperature, bigger flakes, lower pH, higher concentration make gelation easier.