Polyoxometalate (POM)-aided modification of lignin from wheat straw biorefinery

Abstract

Abstract:The oxidative modification of Biolignin (BL) has been investigated to make it more suitable as an adsorbent for transition/heavy metals. BL is a by-product of a wheat straw organosolv process for the production of pulp, ethanol, and pentoses (CIMV S.A. pilot plant, Levallois Perret, France). It was subjected to oxidation by a polyoxometalate (POM) H 3 [PMo 12 O 40 ], aiming at the increment of oxygen-containing adsorption-active sites. The POM oxidation of BL was performed under moderate conditions (1 bar, 60 -90 ° C, and 200 ° C) with the co-oxidants O 2 or H 2 O 2 . The resulting lignin functionality and structure was evaluated by pyrolysis-gas chromatography/mass spectrometry, solid-state 13 C nuclear magnetic resonance, Fourier transform infrared, and chemical analysis. The condensation degree of BL and its COOH and aliphatic OH group contents increased significantly, whereas the polymer structure was maintained. Under optimal conditions with POM/H 2 O 2 , the sorption capacity of lignins toward Cd(II) and Pb(II) was increased threefold and twofold, respectively.

Pretreatment of Wheat Straw with Phosphoric Acid and Hydrogen Peroxide to Simultaneously Facilitate Cellulose Digestibility and Modify Lignin as Adsorbents

“…These changes indicated that -OH and -COOH were involved in the adsorption process [46,47]. Generally, the -OH of lignin linkages with cations groups through electrostatic attractions or surface exchanges, while the -COOH groups were ionized as -COO − groups at higher pH, and provided potential sites for coordinative linkages with cations groups [38,40,48]. Based on these results, the enhanced adsorption capacity of PHPLs on MB can be greatly attributed to the increased -OH and -COOH on the surfaces of PHPLs, which was mainly resulted from the oxidative modification in the pretreatment.…”

“…The degree of modification on lignin can be control by changing the addition of H 2 O 2 input. The resultant PHP lignin has abundant oxygen-containing functional groups, and can potentially work as a functional adsorbent to remove some cationic substances from aqueous solution [17,38].…”

“…Moreover, the linear fitting of carboxyl group with adsorption capacity (R 2 = 0.946) was better than that of total phenol hydroxyl group (R 2 = 0.822), suggesting that the carboxylic of the lignin surface played a dominant role in the MB adsorption. Actually, a similar report has indicated the -COOH, usually as the main functional groups, was introduced on lignin and other carriers by additional modification to improve adsorption capability [17,38,41]. Apparently, PHP pretreatment demonstrated the advantage of producing PHPLs with the key functional -COOH groups by a one-step fractionation and modification compared with other methods [17,38].…”

“…Actually, a similar report has indicated the -COOH, usually as the main functional groups, was introduced on lignin and other carriers by additional modification to improve adsorption capability [17,38,41]. Apparently, PHP pretreatment demonstrated the advantage of producing PHPLs with the key functional -COOH groups by a one-step fractionation and modification compared with other methods [17,38]. In order to further verify the adsorption function of lignin modification by PHP pretreatment, typical cationic heavy metal substances (Pb 2+ and Cu 2+ ) were also tested for adsorption investigation.…”

Advances in Metal Recovery from Wastewaters Using Selected Biosorbent Materials and Constructed Wetland Systems

“…The first category is oxygen-containing functional groups where acid treatment increases the naturally occurring fraction of oxygen groups as well as the hydrophobicity of the lignins. This process can significantly increase the adsorption rates for metals such as Cd and Pb ( [95], Table 9) provided the pH is also controlled. In general, oxidised lignins have been shown to exhibit stronger adsorption capabilities than unmodified lignins due to the higher amounts of carboxyl groups present [96].…”