Enhanced recognition of a nitrogen containing organic compound by adjusting the acidity of the porous organic frameworks base (JUC-Z2)

Abstract

Nitrogen containing organic compounds are very useful in industry but they often act as organic pollutants and are very difficult to selectively recover. Normal porous adsorbents such as porous organic frameworks show almost no selectivity to them because of the insensitivity between their pore size and the pollutants' molecular size. So a method of adjusting acidity was applied to modify the porous organic frameworks to enhance their selectivity to nitrogen containing organic compounds. In this research, a sulfonate grafted JUC-Z2, JUC-Z2-SO₃H was prepared and exhibited high chemical stability (weight loss of 5% at 333 °C), and showed a type-I nitrogen gas adsorption/desorption isotherm. The Brunauer–Emmett–Teller surface area for this network was determined to be 1027 m² g⁻¹. The pore size of the JUC-Z2-SO₃H, calculated by appropriate fitting of the quenched solid density functional theory model to the isotherm yielded a value of 1.0 nm. JUC-Z2-SO₃H could effectively adsorb the amines better than JUC-Z2, and then JUC-Z2-SO₃H could be selectively recovered and reused. Furthermore, solvents with different polarities, such as carbon tetrachloride (CCl₄), ethanol and methanol, were chosen to conduct amine binding measurements with JUC-Z2 and JUC-Z2-SO₃H. The formation constant K_f for JUC-Z2 and JUC-Z2-SO₃H in CCl₄, ethanol, and methanol drastically decreased with increasing in polarity, thus illustrating the solvent effect in amine binding. Other nitrogen containing organic compounds such as aniline, dimethylformamide, and N-methyl-2-pyrrolidone could not be adsorbed by either JUC-Z2 or JUC-Z2-SO₃H.