sulfonamide-functionalized melamine-based covalent organic framework for simultaneous removal of metal ions from aqueous solutions

Over the past decade, interest in the field of nanoporous materials as regular organic or inorganic frameworks has grown tremendously because of their excellent porous properties and broad applications. as an emerging kind of crystalline porous materials, covalent organic frameworks (cofs) pioneered by yaghi and co-workers in 2005 are composed of two organic moieties via strong covalent bonds between light atoms (e.g., h, b, c, n, o, si) to generate long-range ordered two-dimensional (2d) or three-dimensional (3d) network structures [1]. disposal of industrial effluents and wastewaters is considered as one of the most important challenges in the industrial world today. due to the toxic ingredients of these effluents such as, heavy metal ions and dyes, they are the main cause of pollution of rivers, lakes and underground waters. the most notorious heavy metals that cause significant environmental pollution are lead, chromium, mercury, cadmium, arsenic, zinc, copper, and nickel. accumulation of these ions in the human body lead to various health consequences, such as: anorexia, gastrointestinal colic, anemia, neurasthenia, kidney and liver damage, and even cancer. therefore, their removal before release into the environment using a suitable adsorbents is a necessity [2, 3].herein, we report the sulfonamide-functionalized covalent organic framework (cof-so3h) prepared from melamine and terephthalaldehyde as a new adsorbent for the removal of some heavy metal ions ions from environmental water and wastewater samples. the studied ions include cu(ii), cd(ii), pb(ii), ni(ii) and zn(ii). the physicochemical properties of cof-so3h adsorbent was characterized by x-ray diffraction analysis (xrd), scanning electron microscopy (fesem), transmission electron microscopy (tem), energy-dispersive x-ray spectroscopy (edax), thermo-gravimetric analysis (tga) and fourier-transform infrared spectroscopy (ft-ir) analysis. in this method, the batch removal process were designed by response surface methodology (rsm) based on a central composite design (ccd) model. under the optimized conditions, the removal efficiency of metal ions were > 90 % at ph of 5.5, and maximum adsorption capacities of all ions was above 100 mg/g. adsorption data showed that investigated ions uptake on cof-so3h followed the langmuir isotherm model equation and pseudo-second order kinetic model. the proposed method was successfully used to remove the studied ions from some environmental water samples and satisfactory results was achieved.