This work evaluated for the first time the effect of carbon chain size of different carboxylic acids (stearic and caprylic acid) and crystallization temperatures (60, 120, and 180 °C) on the structural, textural, morphological, basic, and mechanism properties of reaction in the synthesis of mesoporous aluminas (meso-Al₂O₃). Regarding the structure-directing agents (SDA) traditionally used in the synthesis of meso-Al₂O₃ (i.g. strong acids, strong bases, and synthetic polymers), carboxylic acids are non-toxic, biodegradable compounds of low commercial value, and can be obtained from renewable sources. The physical-chemical characterizations performed, including low and high-angle X-ray diffractometry (XRD), Fourier-transform infrared spectroscopy (FT-IR), thermal analysis (TG/DTG), nitrogen adsorption-desorption, temperature-programmed desorption of carbon dioxide (CO₂-TPD), scanning electron microscopy (SEM), and transmission (TEM), confirmed the formation of mesostructured γ-Al₂O₃. No pore organization was observed, but a system of interconnected channels was provided by the wormhole-like structure. Mesoporous aluminas synthesized at 180 °C showed an increase in structural, textural (higher of 68% in pore volume and 36% in pore diameter), and basic properties (around 19%) about materials synthesized at 60 °C. This can be attributed to the increased degree of coordination of the carboxylic acid with aluminum during the hydrolysis-condensation reactions. Furthermore, stearic acid (longer carbon chain carboxylic acid) tends to bend during micellar aggregation, leading to pore sizes 33% smaller than caprylic acid (shorter carbon chain acid). Therefore, the best condition for meso-Al₂O₃ synthesis was obtained at 180 °C and using caprylic acid (CAP-180°C) as SDA. The results of CO₂ adsorption showed that all materials correlate better with the pseudo-first order model in the entire temperature range studied (10 – 50 °C), suggesting that diffusion through the interface gas-solid (external diffusion) is the limiting step of the adsorption process. The adsorbent CAP-180°C showed high adsorption capacity (around 134.45 mg_CO2/g_ads at 10 °C under atmospheric pressure) and elevated stability after eight cycles of adsorption-desorption, reaching adsorption capacity superior to other meso-Al₂O₃.