TEMPO-Oxidized Spruce Galactoglucomannan–Biopolymer with Enhanced Antioxidant Activity and Selective Heavy-Metal Sorption

This study examines galactoglucomannan, a well-studied biopolymer isolated from Siberian spruce (<i>Picea obovata</i> Ledeb). Due to its structure, abundant with hydroxyl groups, galactoglucomannan's properties, such as heavy-metal ion affinity, are considered to be mediocre. Nevertheless, there are various ways to enhance its functionality via oxidative TEMPO/NaBr/NaOCl processing. This work is concerned with the determination of the oxidation effect on the structure and performance properties, such as thermal decomposition behavior, antioxidant activity, and selective heavy-metal sorption. In the results, TEMPO-oxidized galactoglucomannan yields vary in the range of 78.3 ± 6.4 wt.%. The carboxylate group in the oxidized derivative represents up to 0.084 g/1 g of the sample. According to antioxidant activity tests, the oxidized galactoglucomannan exceeds the initial sample in terms of hydroxyl radical scavenging ability. The spectral characteristics of the initial and oxidized galactoglucomannan samples reveal the differences in absorption units (1725, 1610, and 1371 cm^-1). The preservation of the polymeric structure was confirmed by the gel permeation chromatography analysis results. The heavy-metal ion capacity of galactoglucomannan is higher for the oxidized derivative, which demonstrated Cd²⁺, Fe²⁺, Cu²⁺, and Pb²⁺ adsorption values of 166.8 mg/g, 142.8 mg/g, 150.0 mg/g, and 199.2 mg/g, accordingly. The obtained result of the competitive heavy-metal ion adsorption of oxidized galactoglucomannan also exceeds its initial form, as characterized by its summary 143.1 mg/g capacity.