Co-hydrothermal carbonization of fruit peel with sugars or furfural impacts structural evolution of hydrochar

Both fruit peel and food waste are wet carbonaceous feedstock and they may be processed together via a process such as hydrothermal carbonization. During the co-HTC, the sugars/furfural derived from starch-rich food waste might interact with the fruit peel or its derivatives, influencing the nature of hydrochar and its further activation. This was investigated herein via co-HTC of grapefruit peel with glucose, xylose, or furfural at 180 degrees C and the subsequent activation of the resulting hydrochars by K2C2O4 at 750 degrees C. The results showed that the sugars and furfural reacted with GP and/or the derivatives, enhancing the hydrochar yields. The presence of furfural rendered the hydrochar from the co-HTC more "densified", aromatic, and resistant to cracking/gasification during activation, producing the activated carbon of higher yield but with main micropores. The aliphatic glucose and xylose reacted with GP or the derivatives via cross-polymerization through consumption of carbonyl functionality, increasing aromaticity of hydrochar as well but also retaining abundant aliphatic structures, especially glucose. The abundant aliphatic structures in the hydrochar obtained from the co-HTC of GP and glucose facilitated the pore generations in the activation. The specific surface area increased from 753.6 m(2)g(-1) of the control sample to 919.1 m(2)g(-1), which was also accompanied with an increase in mesopore percentage from 48 % to 63 %. The dominance of mesopores facilitated the mass transfer and achieved efficiently the methyl blue adsorption and the capacitance performance over the AC obtained with the co-presence of glucose.