Preparation of amino functionalized imidazolium-modified silicas by different coupling agents for removal of 2,4-dinitrophenol from aqueous solutions

Amino group exhibits alkaline properties. Amino functionalized imidazole-modified silicas would benefit the adsorption of phenolic compounds. Coupling agent between the silica and the imidazolium ring has an effect on adsorption performance. In this paper, two adsorbents were synthesized for the surface bonding of N-(3- aminopropyl)-imidazole onto silicas modified by 3-chloropropyltriethoxysilane and 3-mercaptopropyltrimethoxysilane, respectively. Infrared spectra, elemental analysis, thermogravimetric analysis and N₂ adsorption–desorption isotherms were used to characterize the two adsorbents, and their adsorption capacities of 2,4-dinitrophenol from aqueous solutions were investigated in detail. The experimental results indicated that amino group plays an important role in the enhancement of adsorption capacities of 2,4-dinitrophenol. The adsorbent with 3-mercaptopropyltrimethoxysilane as coupling agent exhibited lower adsorption capacity due to a weak electron–electron repulsion between the non-bonding electrons of sulfur atom and π electrons of benzene ring of 2,4-dinitrophenol. The adsorption kinetics fitted well with pseudo-second-order model. The two adsorbents could be regenerated and reused eight times at least by washing with HCl. The adsorption mechanism was also discussed.