**Raghad M. Omer 1, Emaad T. B. Al-Tikrity 1, Gamal A. El-Hiti 2,\*, Mohammed F. Alotibi 3,\*, Dina S. Ahmed <sup>4</sup> and Emad Yousif 5,\***


Received: 28 November 2019; Accepted: 19 December 2019; Published: 20 December 2019

**Abstract:** High energy demand has led to excessive fuel consumption and high-concentration CO2 production. CO2 release causes serious environmental problems such as the rise in the Earth's temperature, leading to global warming. Thus, chemical industries are under severe pressure to provide a solution to the problems associated with fuel consumption and to reduce CO2 emission at the source. To this effect, herein, four highly porous aromatic Schiff bases derived from melamine were investigated as potential media for CO2 capture. Since these Schiff bases are highly aromatic, porous, and have a high content of heteroatoms (nitrogen and oxygen), they can serve as CO2 storage media. The surface morphology of the Schiff bases was investigated through field emission scanning electron microscopy, and their physical properties were determined by gas adsorption experiments. The Schiff bases had a pore volume of 0.005–0.036 cm3/g, an average pore diameter of 1.69–3.363 nm, and a small Brunauer–Emmett–Teller surface area (5.2–11.6 m2/g). The Schiff bases showed remarkable CO2 uptake (up to 2.33 mmol/g; 10.0 wt%) at 323 K and 40 bars. The Schiff base containing the 4-nitrophenyl substituent was the most efficient medium for CO2 adsorption and, therefore, can be used as a gas sorbent.

**Keywords:** porosity properties; adsorption capacity; carbon dioxide storage; melamine Schiff bases; surface area; energy
