A polyethyleneimine-coated thermally-oxidized graphitic-carbon nitride adsorbent for the removal of organic...

Negatively charged organic pollutants in water are responsible for a large range of public health and ecological issues. Low-cost and low-toxicity graphitic carbon nitride (CN), with its abundant functional groups and surface defects, is a promising material for the removal of organic molecules by adsorption. However, basic synthesis methods for CN often result in a material with morphology and electric charge that are suboptimal for interacting with negatively charged pollutants. Here, an adsorbent was prepared by thermally oxidizing a tubular CN precursor and then coating the resulting flake-shaped material (FCNO) with the polycationic polymer polyethyleneimine (PEI). The resulting adsorbent, FCNO₅₅₀-PEI, removed humic acid (HA), a widespread problematic organic molecule, as well as the common toxic anionic dye Congo red (CR). FCNO₅₅₀-PEI was superior to other CN-based adsorbents previously reported in the literature with maximum adsorption capacities according to the Sips isotherm model for HA and CR of 437.1 mg/g and 1430.3 mg/g, respectively. In addition, FCNO₅₅₀-PEI could adsorb HA and CR from different types of water and was reusable. Besides electrostatic interactions and hydrogen bonds between PEI and the pollutants, HA and CR adsorption was enabled by π-π interactions with the FCNO support itself. The high efficiency of FCNO₅₅₀-PEI for the removal of HA and CR highlights its potential for water treatment applications.