Facile and "green" techniques for hydrogel fabrication are in high demand to satisfy a wide range of practical applications. To the best of our knowledge, this report presents the first description of an efficient, one-flask method for preparing a guar gum (GG)-based self-assembling hydrogel, which takes advantage of the formation of cyclic acetals between the vicinal hydroxyl groups and carbonyl groups, as introduced via the regioselective oxidation of GG using sodium periodate (NaIO4). The final product was achieved without the addition of any crosslinking agents. The self-assembling hydrogel was rapidly formed under ambient conditions, and demonstrated remarkable self-healing performance, as well as thermally responsive properties associated with sol-gel transitions. Furthermore, the GG hydrogel had the ability to remove copper ions (Cu2+) from the surrounding aqueous solution. This removal can be accounted for due to the large number of active sites (i.e., hydroxyl groups) within its porous three-dimensional structure. The adsorption equilibrium was achieved after 5 h, and the amount of adsorbed Cu2+ was 944 mg/g GG when an initial concentration of 25 mg/mL CuSO4 in solution was used. The adsorption isotherm data correlated well with the Freundlich model (R-2 > 0.99), suggesting that the Cu2+ was removed through multilayered and complex adsorption mechanisms.