The physical properties of two-dimensional nanosheet materials make them promising candidates as active materials in the areas of photoelectronics, fuel cells, sensors, water splitting, solar energy conversion, CO2 reduction, and heterogeneous catalysis. Among two-dimensional nanosheet materials, graphitic carbon nitride due to its electronic structure and high chemical and thermal stability possesses unique properties. Covalent functionalization of graphitic carbon nitride could be the key step in modifying its ability and significantly improving its properties. To this purpose, a novel strategy for the covalent functionalization of g-C3N4 nanosheets (CN) with vitamin B1 (VB1) by using 1,3-dibromopropane as a covalent linker for the first time is demonstrated. The obtained CN-Pr-VB1 exhibits increased thermal stability compared to the VB1 which is important in the practice application and can be easily dispersed in common organic solvents. The efficacy of the CN-Pr-VB1 as a heterogeneous organocatalyst was evaluated in the quinoxaline synthesis under solvent-free conditions and afforded good isolated yield with high purity. Moreover, the prepared catalyst could be facilely recycled and reused for seven consecutive cycles without a noticeable decrease in the catalytic activity. Extensive characterization confirmed the stability of morphology and chemical structure after recyclability of the CN-Pr-VB1.