Ultrafine microporous and mesoporous activated carbon fibers from alkali lignin

Abstract

A facile and sustainable approach has been successfully devised to fabricate ultrafine (100-500 nm) highly porous activated carbon fibers (ACFs) by electrospinning of aqueous solutions of predominantly alkali lignin (low sulfonate content) followed by simultaneous carbonization and activation at 850 C under N 2 . Incorporating a polyethylene oxide (PEO) carrier with only up to one ninth of lignin not only enabled efficient electrospinning into fibers but also retained fibrous structures during heating, alleviating the need for a separate thermal stabilization step. In situ impregnation of alkali hydroxide activating chemicals with only up to 50% of the lignin carbon precursor, i.e., merely one tenth to one quarter of the quantities used in manufacturing activated carbon particulates, allowed simultaneous carbonization and activation in a single heating step. A range of micropore-dominant to mesoporedominant ACFs were successfully fabricated to achieve superior specific surface (>1400 m 2 g À1) and porosity (>0.7 cm 3 g À1) tuned by varying the type and contents of alkali hydroxides. This streamlined approach was robust and demonstrated the feasibility and versatility in processing and converting a readily available renewable carbon precursor, lignin, into highly porous activated carbon fibers.

Holistic Rice Straw Nanocellulose and Hemicelluloses/Lignin Composite Films

“…The two stage mass losses corresponded to two major exotherms at 310 and 455°C, indicative of the respective hemicelluloses and lignin decomposition. Assuming complete decomposition of hemicelluloses into volatiles and 60% alkali lignin char at 600°C, 43 HL was estimated to contain 65% hemicelluloses and 35% lignin, similar to their proportion in raw rice straw.…”

“…These lignin peaks resembled those derived from softwood via commercial alkali pulping process. 43 The EDX elemental analysis of HL showed 61.5% C and 38.5% O in mass (Figure 2b) with C content in between that of lignin (58 to 65%) 44−46 and hemicelluloses (38 to 42%). 44,47 ACNF consisted of 47.2% C, 50.6% O and 2.2% Na in mass, with a 1.24 C/O atomic ratio very close to the 1.2 C/O ratio of pure cellulose.…”

1D Lignin-Based Solid Acid Catalysts for Cellulose Hydrolysis to Glucose and Nanocellulose

“…The ultrafine ACFs were electrospun from lignin and simultaneously carbonized and activated at 900°C to high specific surface (1400 m 2 /g) and pore volume (0.7 cm 3 /g). 31 The solid acid catalysts from ligninbased ACFs have several advantages and desired attributes over other solid acid catalysts for hydrolysis of crystalline cellulose. Lignin, an abundant and underutilized biomass fraction, is an excellent carbon precursor, and lignin chars are less recalcitrant than rigid graphitic carbons, such as carbon nanotubes, 18 to be readily sulfonated by concentrated sulfuric acid, a much safer alternative than the commonly used fuming sulfuric acid for sulfonation of graphitic carbons.…”

“…Both carbon fibers (CFs) and activated carbon fibers (ACFs) were synthesized according to a previously reported approach. 31 Briefly, aqueous 9:1 w/w AL ls /PEO (10 wt % total concentration) mixtures without and with NaOH at a 1:2 w/w NaOH/lignin ratio were electrospun into CF and ACF precursor fibers, respectively. The precursor fibers were placed in a quartz tube (2 cm inner diameter) of an electric furnace (Mini-Mite, Lindberg/Blue), heated at 10°C min −1 under flowing N 2 at 100 mL min −1 to 105°C, held for 0.5 h to drive off moisture, and then to 600 (CFs) or 900°C (CFs and ACFs), held for another 0.5 h, and finally cooled to ambient temperature under flowing N 2 at 100 mL min −1 .…”

Preparation of Different Carbon Materials by Thermochemical Conversion of Lignin

“…Some authors studied the electrospinning of n-fractionated SKL solutions together with various concentrations of suspended MWCNTs (Lin et al, 2013;Teng et al, 2013). Furthermore, it has been reported that the presence of 10 wt% PEO enables the efficient electrospinning of aqueous NaOH or KOH/Alcali-lignin (AL ls ) solutions into fibers (Hu and Hsieh, 2013;Hu et al, 2014). Another outstanding method to assist the spinning of advanced fine lignin fibers is the emulsion electrospinning (Lin et al, 2013).…”