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

In this work, we have focused on the effect of highly acidic (0.2 M H 2 SO 4 ), neutral (H 2 O), and basic (0.2 M NaOH) solutions with and without the addition of 0.2 M (NH 4 ) 2 SO 4 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 (NH 4 ) 2 SO 4 varied considerably (11.34 wt % H 2 SO 4, 47.81 wt % H 2 O, and 3.54 wt % NaOH) as did spherical size (3.34, 4.57, and 6.63 nm for H 2 SO 4, H 2 O, and NaOH, respectively). The addition of (NH 4 ) 2 SO 4 increased product yields considerably in acidic and basic conditions (27.76 wt % H 2 SO 4 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 H 2 SO 4, H 2 O and NaOH respectively) the main oxygen functionality, although carbonyls, carboxylic acids, and ketones were also present. These oxygen functionalities fluctuated with the presence of (NH 4 ) 2 SO 4, 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 H 2 SO 4, H 2 O, and NaOH, respectively). GC-MS revealed that levulinic acid was the predominate byproduct.