A green,
efficient, and facile ball-milling-assisted strategy was
proposed to design an SO3H-containing solid acid for biomass
valorization, where −SH groups were grafted on a natural clay
attapulgite by wet ball milling with 3-mercaptopropyltrimethoxysilane
(MTPS), followed by the oxidation of −SH to −SO3H with H2O2 at room temperature. The
mechanism of the −SO3H functionalization by the
ball-milling process was investigated, and the investigation indicated
that the MTPS was grafted on the attapulgite through hydrolysis and
condensation, which was induced by the mechanical forces of ball milling.
Characterization, including SEM, EDX (energy-dispersive X-ray spectrometry),
NH3-TPD, TGA, FT-IR, elemental analysis, and XPS, confirmed
the success of −SO3H modification on attapulgite
with a total acidity of 1.81 mmol/g. Harsh conditions involving a
corrosive sulfonating agent, organic solvent, or high temperature
in traditional methods are avoided in the developed approach. The
prepared catalyst displayed a high activity toward the transformation
of biomass-derived carbohydrates (glucose, fructose, cellobiose, sucrose,
starch, and cellulose) into the more valuable chemical 5-hydroxymethylfurfural
due to the synergy effect of MgO and −SO3H sites
on the catalyst. Moreover, the catalyst showed excellent stability
and recyclability for five recycles without loss of activity. This
study provides a novel green method for the preparation of an SO3H-containing heterogeneous catalyst, which should have great
application potential in other processes of biomass valorization.