Textural and morphological characterization
Nitrogen adsorption isotherms were measured at – 196°C on a Micromeritics ASAP 2020 instrument. Prior to each measurement, each sample was outgassed overnight at 150°C until a constant vacuum of 10-7 kPa was reached. The Brunauer-Emmett-Teller (BET) method within a relative pressure range of 0.05-0.15 was used to calculate the specific area (S BET) while the total pore volume (V T) was calculated from the N2 uptake at relative pressure p/po of 0.998.
The Non-Local Density Functional Theory in its two-dimensional version, 2D-NLDFT, considering slit-shaped pores with energetically heterogeneous and rough walls [33], was used to estimate the volume of micropores,V mic, and ultramicropores (V <0.7 nm) and to obtain the pore size distributions (PSDs). The volume of mesopores,V mes, was calculated as a difference betweenV T and V mic.
X-ray diffraction (XRD) patterns were collected with a Philips PANalytical X’Pert X-ray diffractometer using CuKα (40 kV, 40 mA) radiation. All the measurements were acquired in the 2-theta (2θ ) range from 5° to 70°, in steps of 0.02°, and with a time of 0.5 s per step.
Scanning electron images were recorded using a Zeiss Supra 55 VP scanning electron microscope (SEM) with an electron beam of 5 keV.
Thermal analysis was performed using an SDT Q600 of TA Instruments. All the samples were analyzed under helium and air flow (100 mL/min), heating them up to 1000°C at 10°C/min. The two thermogravimetric (TG) curves were collected, and the corresponding differential thermal gravimetric (DTG) curves were calculated in order to determine the thermal behavior of the samples.