Tannin-diethylenetriamine based adsorbents with exceptional adsorption capacity of Chromium(VI) in aqueous solution

Background: In order to remedy the pollution of chromium(VI), it is of great significance to develop high-efficiency adsorbents. Methods: Heren, excellent adsorbents poly(polyethyleneimine-tannin-diethylenetriamine) (PPTD) were synthesized using a simple route and utilized for the removal of Cr (VI) from aqueous solutions. The effect of various factors on the adsorption behavior of PPTD was studied, such as polyethyleneimine content, temperature, initial pH, initial concentration, adsorbent dosage, contact time, and foreign ions. The optimized experiments were performed under the conditions of polyethyleneimine content (35%), temperature (30 °C), initial pH (2), initial concentration (200 mg L−1), and contact time (24 h) using 25 mg PPTD to remove Cr(VI) for 100 mL solution. Significant Findings: The results not only showed rapid removal efficiency which is close to 100% at low concentrations (20∼120 mg L−1), but also exhibited favorable selectivity for Cr (VI) even in the presence of coexisting ions (such as Cl−, Cd (II), and Cu (II)). Its maximum capacity reached the value of 757.6 mg g−1 at 30 °C, which was close to the experiment data (751.6 mg g−1). Besides, the adsorption behavior of Cr (VI) can be described by the pseudo-second-order kinetic model and the Langmuir isothermal model. Following satisfactory fitting with the Langmuir isotherm model.