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.
