Copper sorption on a straw lignin: experiments and EPR characterization.

Area of Science:

• Materials Science
• Environmental Chemistry
• Biomass Valorization

Background:

• Lignocellulosic biomass is an abundant, renewable resource.
• Understanding metal-binding properties of biomass is crucial for remediation and resource recovery.
• Straw-derived ligno-cellulosic substrate (LS) presents potential for adsorbing metal ions.

Purpose of the Study:

• To characterize the ligno-cellulosic substrate (LS) from straw.
• To investigate the copper(II) binding capacity and mechanism of LS.
• To determine the stability and structural properties of copper(II) surface complexes on LS.

Main Methods:

• Physicochemical analysis including X-ray photoelectron spectroscopy (XPS), solid-state NMR, GC/MS, surface area, and acidity.
• Copper(II) adsorption studies at varying pH.
• Electron paramagnetic resonance (EPR) spectroscopy for structural characterization of surface complexes.
• Correlation of thermodynamic data with EPR parameters.

Main Results:

• LS possesses carboxylic and phenolic binding sites with high affinity for copper(II).
• Maximum copper(II) adsorption of approximately 4 mg g(-1) occurs at pH 6.
• EPR spectroscopy revealed a CuO(4) chromophore in a distorted square geometry for inner-sphere complexes.
• Simultaneous surface oxidation led to semiquinonic radicals.
• A surface complexation constant (log beta) of 12.6 indicates stable copper(II) complexes.

Conclusions:

• Straw-derived ligno-cellulosic substrate is effective for copper(II) adsorption.
• The binding involves carboxylic and phenolic groups, forming stable inner-sphere complexes.
• Surface complexation is accompanied by substrate oxidation, forming semiquinonic radicals.