A functional lignin for heavy metal ions adsorption and wound care dressing

Recently, the application of lignin activation by demethylation to improve reactivity and enrich multiple functions has intensively attracted attention. However, it is still challenge up to now due to the low reactivity and complexity of lignin structure. Here, an effective demethylation way was explored by microwave-assisted method for substantially enhancing the hydroxyl (-OH) content and retaining the structure of lignin. Then, the optimum demethylated lignin was used to removal heavy metal ions and promote wound healing, respectively. In detail, for microwave-assisted demethylated poplar lignin (M-DPOL), the contents of phenolic (Ar-OH) and total hydroxyl (Tot-OH) groups reached the maximum for 60 min at 90 °C in DMF with 7.38 and 9.13 mmol/g, respectively. After demethylation, with this M-DPOL as lignin-based adsorbent, the maximum adsorption capacity (Q_max) for Pb²⁺ ions reached 104.16 mg/g. Based on the isotherm, kinetic and thermodynamic models analyses, the chemisorption occurred in monolayer on the surface of M-DPOL, and all adsorption processes were endothermic and spontaneous. Meanwhile, M-DPOL as a wound dressing had excellent antioxidant property, outstanding bactericidal activity and remarkable biocompatibility, suggesting that it did not interfere with cell proliferation. Besides, the wounded rats treated with M-DPOL significantly promoted its formation of re-epithelialization and wound healing of full-thickness skin defects. Overall, microwave-assisted method of demethylated lignin can offer great advantages for heavy metal ions removal and wound care dressing, which facilitates high value application of lignin.

Rapid Conversion of Methane to Hydrogen Stimulated by Microwave Irradiation on the Surface of a Carbon Adsorbent

Abstract

The paper presents the results on the rapid production of H2 from CH4 by its direct decomposition in a plasma-catalytic mode stimulated by microwave irradiation (MWI) at 600°C. Methane was passed through a bed of iron-containing carbon adsorbent obtained from gas coal characterized by a large dielectric loss tangent. Under MWI, intense breakdown effects with plasma generation appear on the surface of the iron–carbon system. Methane in the plasma converts to hydrogen and carbon. A method has been developed for the rapid regeneration of the catalyst by water vapor with the removal of carbon under microwave stimulation. Short-cycle experiments have shown that the catalytic system provides high conversions of methane and its almost complete regeneration.