Novel nitrogen-containing mesoporous carbon with well-ordered pores (NMC-G) and high basicity is synthesized using a low-cost single-molecule precursor, gelatin biomolecule, and SBA-15 as a template via nanocasting method. The obtained materials are thoroughly characterized. It is found that the prepared materials have excellent textural properties such as high specific surface areas, huge pore volumes, and large pore diameters. The pore diameter of the materials can also be controlled with a simple adjustment of the pore diameter of the hard templates. The C/N ratio of the samples is calculated to be 6.01, which is slightly higher than that observed for mesoporous carbon nitride samples. X-ray photoelectron spectroscopy (XPS) reveals the presence of sp2 hybridized carbon in aromatic ring structure attached to amino groups. The materials could adsorb a huge quantity of CO2. The sensing capability of the materials with different pore diameters for different adsorbates including ethanol, acetic acid, aniline, toluene, and ammonia is also investigated. Among the materials with different pore diameters studied, the material with the highest basicity and the largest pore diameter (NMC-G-150) showed excellent sensing performance with a high selectivity of adsorption for acetic acid molecule.