The morphologies of the samples
were examined by a field emission scanning electron
microscope (FESEM, Quanta 400, FEI Company, USA)
equipped with a energy dispersive X-ray spectroscope (EDS,
Noran 623M-3SUT, Thermo Electron Corporation, Japan). The
Brunauer-Emmett-Teller (BET) surface areas and porosities of
the samples were studied with a nitrogen adsorption instrument
(Micrometrics ASAP 2020).