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 N2. 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 mesopore-dominant ACFs were successfully fabricated to achieve superior specific surface (>1400 m2 g-1) and porosity (>0.7 cm 3 g-1) 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. © 2013 The Royal Society of Chemistry.

Lignin has proven to be highly effective "green" multi-functional binding, complexing and reducing agents for silver cations as well as capping agents for the synthesis of silver nanoparticles on ultra-fine cellulose fibrous membranes. Silver nanoparticles could be synthesized in 10min to be densely distributed and stably bound on the cellulose fiber surfaces at up to 2.9% in mass. Silver nanoparticle increased in sizes from 5 to 100nm and became more polydispersed in size distribution on larger fibers and with longer synthesis time. These cellulose fiber bound silver nanoparticles did not agglomerate under elevated temperatures and showed improved thermal stability. The presence of alkali lignin conferred moderate UV absorbing ability in both UV-B and UV-C regions whereas the bound silver nanoparticles exhibited excellent antibacterial activities toward Escherichia coli.

Silver nanoparticles (AgNPs) were robustly synthesized from aqueous AgNO3 with alkali lignin (low sulfonate) (ALls) severing as dual reducing and capping agent. The AgNP synthesis mechanisms were highly pH dependent. Under neutral and acidic conditions, polydispersed AgNPs were synthesized via the self-catalyzed reduction of Ag(+) on instantaneously formed Ag2O surfaces followed by the slower pseudo-first order reduction. The Ag2O nanoparticles functioned as the nucleating sites for the reduction of remaining silver cations to form AgNPs whose size and size distribution strongly dependent of lignin concentrations. AgNPs were optimally synthesized by reducing 2 mmol/L AgNO3 with 0.16 wt% ALls at pH 10 and 85°C in 30 min to near 100% yield in bimodal distributed sizes with 23% and 77% in feret diameters of 7.3 (± 2.2)nm and 14.3 (± 1.8)nm, respectively.

An efficient three-step process using toluene/ethanol, NaClO2, and KOH has been successfully devised to isolate pure cellulose from rice straw while generating two filtrates as activated carbon and silica precursors. The NaClO2 dissolution filtrate contains oxidized lignin and hemicellulose as carbon precursors as well as sodium carbonates as activating agents for direct carbonization (800 °C) into highly porous (0.90 cm 3/g), high specific surface area (997 m2/g), activated carbon particles (100-500 nm). The KOH dissolution filtrate contains mainly potassium silicate that could be precipitated by dilute acidified poly(ethylene oxide) and calcinated (500 °C) to pure, uniformly sized (100-120 nm), nonporous silica nanospheres. Deriving these additional activated carbon and silica particles along with nanocellulose creates advance materials while fully utilizing all major components in rice straw, the highest quantity agricultural crop byproduct in the world. © 2014 American Chemical Society.

Microporous and mesoporous particulate activated carbons (PACs) with unique hierarchical microstructures were facilely synthesized from alkali lignin via simultaneous carbonization and alkali hydroxide activation. Both NaOH and KOH activated PACs contained slit-like micropores and carbon microstructures with circular nanoplates of graphite-like basal planes and amorphous carbon clusters. The micropores broadened with increasing temperatures, holding time and alkaline hydroxides. The basal planes sizes and order were enhanced with increasing temperatures and holding time but lowering impregnation ratios, while amorphous carbon showed no particular patterns due to its much higher reactivity toward alkali hydroxides. The PACs with the highest micropore surface area and pore volume (1100 m2 g-1, 0.43 cm3 g-1) were obtained at 900 °C, 30 min and an impregnation ratio of 1 and fabricated into electrical supercapacitors to exhibit excellent 226 F g-1 specific capacitance, 7.8 W h kg-1 energy density and 47 kW kg-1 power density as well as over 92% capacitance retention after 5000 cycles.

Cellulose nanofibrils (CNF)-silica aerogels have been facilely synthesized via a one-step in situ aqueous sol-gel process of polymerizing and aging the silica precursor in the presence of CNFs to encompass the superior dry compressive strength and flexibility of CNF aerogels and the thermal stability of silica aerogels. Sodium silicate (Na2SiO3) was hydrolyzed and polymerized in the presence of CNFs at varied ratios to synthesize hydrogels whose storage and loss modulus confirmed CNFs to function as the structural skeleton. At the optimal 8:2 CNFs/Na2SiO3 composition, the hydrogels with homogeneously dispersed silica and CNF can be freeze-dried into hierarchically mesoporous aerogels with ultralow density of 7.7 mg/cm3, high specific surface of 342 m2/g, and pore volume of 0.86 cm3/g. This robust sol-gel approach employs naturally abundant silica and cellulose in aqueous system to generate improved CNF-silica aerogels that had much higher compressive strength and modulus of up to 28.5 and 177 kPa and structural flexibility than silica aerogel and enhanced thermal stability and specific surface over CNF aerogel. Further functionalization of CNF-silica aerogels via organosilane reaction introduced primary amine groups capable of capturing CO2 with an adsorption capacity of 1.49 mmol/g. ©

One-dimensional (1D) solid acid catalysts have been synthesized from lignin-based activated carbon fibers via sulfonation and hydrothermal treatment to be mesoporous and contain 0.56 mmol/g sulfonic and 0.88 mmol/g total acid for direct hydrolysis of highly crystalline rice straw cellulose (CrI = 72.2%). Under optimal hydrothermal conditions of 150°C and 5 atm, 69.8% of cellulose was hydrolyzed in three consecutive runs, yielding 64% glucose at 91.7 selectivity as well as 8.1% cellulose nanofibrils (2.1 nm thick, 3.1 nm wide, and up to 1 μm long). These 1D acid catalysts could be used repetitively to hydrolyze the remaining cellulose as well as be easily separated from products for hydrolysis of additional cellulose. In essence, complete valorization of rice straw cellulose has been demonstrated by direct hydrolysis with these 1D acid catalysts to superior glucose selectivity while generating high value cellulose nanofibrils.

Rice straw was dewaxed and optimally separated into cellulose-rich solid and hemicelluloses/lignin (HL)-rich aqueous suspension with two 5 min alkali immersions (4% NaOH, 70 °C). Alkaline cellulose nanofibrils (ACNFs) were derived, at 36.5% yield from the original rice straw, by TEMPO-mediated oxidation and mechanical defibrillation of cellulose-rich portion whereas HL was isolated at 18.1% yield from the aqueous suspension. Aqueous HL solutions containing up to 30% ACNF as well as three other nanocelluloses, i.e., cellulose nanocrystals (CNC), TEMPO oxidized and aqueous counter collision generated CNFs (OCNF and ACCNF) were cast into films to exhibit significantly improved flexibility, transparencies, mechanical and moisture barrier properties. The structure-properties relations of these holistic composite films were analyzed systematically, in particular regarding to the types and loadings of the different nanocelluloses.

Highly porous submicron activated carbon fibers (ACFs) were robustly generated from low sulfonated alkali lignin and fabricated into supercapacitors for capacitive energy storage. The hydrophilic and high specific surface ACFs exhibited large-size nanographites and good electrical conductivity to demonstrate outstanding electrochemical performance. ACFs from KOH activation, in particular, showed very high 344 F g-1 specific capacitance at low 1.8 mg cm-2 mass loading and 10 mV s-1 scan rate in aqueous electrolytes. Even at relatively high scan rate of 50 mV s-1 and mass loading of 10 mg cm-2, a decent specific capacitance of 196 F g-1 and a remarkable areal capacitance of 0.55 F cm-2 was obtained, leading to high energy density of 8.1 Wh kg-1 based on averaged electrodes mass. Furthermore, over 96% capacitance retention rates were achieved after 5000 charge/discharge cycles. Such excellent performance demonstrated great potential of lignin derived carbons for electrical energy storage. © 2014 Elsevier B.V. All rights reserved..