One-step synthesis of nitrogen-grafted copper-gallic acid for enhanced methylene blue removal

Nitrogen-grafting through the addition of glycine (Gly) was performed on a metal- phenolic network (MPN) of copper (Cu²⁺) and gallic acid (GA) to increase its adsorption capacity. Herein, we reported a one-step synthesis method of MPN, which was developed according to the metal-ligand complexation principle. The nitrogen grafted CuGA (N_g-CuGA) MPN was obtained by reacting Cu²⁺, GA, and Gly in an aqueous solution at a molar ratio of 1:1:1 and a pH of 8. Several physicochemical measurements, such as Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), N₂ sorption, X-ray diffraction (XRD), and thermal gravimetry analysis (TGA), were done on N_g-CuGA to elucidate its characteristics. The analysis revealed that the N_g-CuGA has non-uniform spherical shaped morphology with a pore volume of 0.56 cc/g, a pore size of 23.25 nm, and thermal stability up to 205 °C. The applicational potential of the N_g-CuGA was determined based on its adsorption capacity against methylene blue (MB). The N_g-CuGA was able to adsorb 190.81 mg MB per g adsorbent at a pH of 6 and temperature of 30 °C, which is 1.53 times higher than the non-grafted CuGA. Detailed assessment of N_g-CuGA adsorption properties revealed their pH- and temperature-dependent nature. The adsorption capacity and affinity were found to decrease at a higher temperature, demonstrating the exothermic adsorption behavior.