Synthesis of Acidic Heterogeneous Catalysts with High Stability Based on Graphene Oxide/Activated Carbon Composites for the Esterification of Lactic Acid

Table 1

Specific surface areas and sulfonic acid group (-SO₃H) content of the catalysts.

Catalysts	SBET (m^2·g^−1)	-SO3H content (mmol g^−1)
Sulfonated biochar	423.4	1.14
Sulfonated biochar after 4 cycles of reaction	—	0.64
Activated carbon	721.1	0
Graphene oxide	215.9	0.92
GO/AC	570.3	0.35
GO/AC after 6 cycles of reaction	618.9	0.29