A vertical-style quartz tube furnace was employed for the pyrolysis of BM samples (BM1, BM2, and BM3), where an inert gas (N2) was pumped into the quartz tube from top to bottom. The temperature was first increased to 110 °C and then held there for 3 hours to remove all the air and moisture from the furnace. Then the temperature was increased to 600 °C at a heating rate of 10 °C/min. Once the temperature had reached 600 °C, it was held there for 1 hour and then gradually cooled down to room temperature.