Characterization and application of titanium tannate (Ti-TA) metallic phenolic network for removal of ammonia nitrogen

Metal-phenolic networks, despite their good ammonia nitrogen adsorption properties, have suffered from poor acid resistance and high oxidability in the past thus leading to ineffective treatment and the possible conversion of ammonia nitrogen into nitrate nitrogen. Research on the adsorption of ammonia nitrogen by titanium tannate (Ti-TA), which exhibits good resistance to ammonia nitrogen oxidation, is still unclear. A batch experiment was conducted to investigate the structural characteristics of Ti-TA, as well as its adsorption behaviors. Among them, advanced technologies such as Scanning Electron Microscopy, Fourier transform infrared spectroscopy, Brunauer-Emmett-Teller, X-ray diffraction, and X-ray photoelectron spectroscopy, were used for this investigation. The results showed that Ti-TA, prepared with a molar ratio of tannic acid to tetrabutyl titanate of 1:5 at a solution pH of 7, was able to form a rough surface and a microporous structure with a specific surface area up to 356.9 m 2 /g. The parameters, affecting the adsorption results, included pH and adsorbent dose, where lower adsorbent doses resulted in higher adsorption capacities, reaching up to 4.175 mg/g, and neutral to weakly acidic conditions were conducive to the adsorption process. For example, when the initial NH 4 + -N concentration was 28.45 mg/L, and the ratio of tannic acid to Ti was 1.5, the removal rate of ammonia nitrogen can exceed 95.78 % within a pH range of 6–7. The primary mechanisms underlying physicochemical adsorption involve electrostatic interaction between oxygen ions and NH 4 + -N, as well as hydrogen bonding. The adsorption process occurred spontaneously, following Pseudo-second-order kinetics and adhering to the Freundlich isotherm model, with a relatively low adsorption index (1/ n  < 0.5). For the first time, the findings of this study reveal the adsorption behaviors of Ti-TA and propose optimal preparation conditions, underscoring its significant potential for applications in nitrogen pollution treatment.