Nitrogen Doping of Hydrochars Produced Hydrothermal Treatment of Sucrose in H₂O, H₂SO₄, and NaOH

Abstract

In this work, we have focused on the effect of highly acidic (0.2 M H2SO4), neutral (H2O), and basic (0.2 M NaOH) solutions with and without the addition of 0.2 M (NH4)2SO4 on the chemical and structural morphologies of hydrothermally formed carbon spheres (hydrochar) from sucrose at 200 °C for 4 h. Hydrolysis product yields without the addition of (NH4)2SO4 varied considerably (11.34 wt % H2SO4, 47.81 wt % H2O, and 3.54 wt % NaOH) as did spherical size (3.34, 4.57, and 6.63 nm for H2SO4, H2O, and NaOH, respectively). The addition of (NH4)2SO4 increased product yields considerably in acidic and basic conditions (27.76 wt % H2SO4 and 14.73 wt % NaOH). Chemically, the hydrochars had a carbon content between 60 and 70 wt % and oxygen content between 22% and 29% with alcohol groups (12.29, 15.44, 11.26 atom % for H2SO4, H2O and NaOH respectively) the main oxygen functionality, although carbonyls, carboxylic acids, and ketones were also present. These oxygen functionalities fluctuated with the presence of (NH4)2SO4, with reductions in alcohols (1–3 atom %) and ketones (1–3 atom %), and increases in carboxylic acids. Nitrogen was located in pyridinic, pyrrolyic, and quaternary groups (6.24, 3.22, and 9.41 atom % for H2SO4, H2O, and NaOH, respectively). GC-MS revealed that levulinic acid was the predominate byproduct.