Cellulose Nanofiber-Based Aerogels from Wheat Straw: Influence of Surface Load and Lignin Content on Their Properties and Dye Removal Capacity

Abstract

Water pollution is one of the most serious problems worldwide. Nanocellulose-based aerogels usually show excellent adsorption capacities due to their high aspect ratio, specific surface area and surface charge, making them ideal for water purification. In this work, (ligno)cellulose nanofibers (LCNFs/CNFs) from wheat straw residues were obtained using two types of pre-treatments: mechanical (Mec) and TEMPO-mediated oxidization (TO), to obtain different consistency (0.2, 0.4, 0.6 and 0.8) bioaerogels, and their adsorption capacities as dye removers were further studied. The materials were characterized in terms of density, porosity and mechanical properties. An inversely proportional relationship was observed between the consistencies of the aerogels and their achieved densities. Despite the increase in density, all samples showed porosities above 99%. In terms of mechanical properties, the best results were obtained for the 0.8% consistency LCNF and CNF-Mec aerogels, reaching 67.87 kPa and 64.6 kPa for tensile strength and Young’s modulus, respectively. In contrast, the adsorption capacity of the aerogels was better for TEMPO-oxidized aerogels, reaching removal rates of almost 100% for the CNF-TO5 samples. Furthermore, the residual lignin content in LCNF-Mec aerogels showed a great improvement in the removal capacity, reaching rates higher than 80%, further improving the cost efficiency of the samples due to the reduction in chemical treatments.

Extraction and Characterization of Cellulose Nanofibers From Yellow Thatching Grass (Hyparrhenia filipendula) Straws via Acid Hydrolysis

“…The highest lignin removal was achieved for CNF1 (98 %), CNF 5.6 (97 %) and CNF3 (96 %).The highest hemicellulose removal was also observed for CNF1 (59 %), followed by CNF 5.6 (50 %) and CNF3 (38 %). This is in line with the common trend of observation due to the decrease of amorphous components like lignin and hemicellulose that easily absorb chemicals, whereas the compactness of the crystalline regions makes it difficult for chemical penetration [22,23]. The cellulose content increased significantly after acid hydrolysis.…”

Bioactive Absorbent Chitosan Aerogels Reinforced with Bay Tree Pruning Waste Nanocellulose with Antioxidant Properties for Burger Meat Preservation

“…The nanofibrillation yield (η, Table 2 ) for LCMNFs was 48%, while for CMNFs, it was 58%. The lower performance in LCMNFs is associated with the presence of lignin, which causes interference during TEMPO-mediated oxidation, leading to secondary oxidation reactions [ 44 ].…”

“…The fact that the reinforcing effect is greater with CMNFs than with LCMNFs can again be attributed to the presence of lignin in LCMNFs. It has been recently reported that the presence of lignin interferes with the primary activator (NaClO) during the bleaching process, resulting in aerogels with poorer mechanical properties [ 44 ]. Some authors have reported that a higher aspect ratio of CMNFs results in a higher Young’s modulus of the aerogels when the content of crosslinker employed is less than that of micro/nanofibers [ 55 ].…”

Down Fiber Reinforced Cellulose Nanofiber Aerogel toward Thermal Insulation and Pollutant Removal

“…. For example, Morcillo-Martín et al removed dyes through aerogels prepared from CNF oxidized by TEMPO, as its surface negative-charged carboxyl groups could remove cationic dyes . Despite these fascinating and unique characteristics, the inefficient network connection and discontinuity of cellulose based aerogels lead to an unsatisfactory mechanical property, − low thermal stability, and limited adsorption capacity, which greatly restricts their use in the field of thermal insulation.…”