Cheng-Kang Lee

Enhanced enzymatic hydrolysis of sugarcane bagasse by N-methylmorpholine-N-oxide pretreatment

The cellulose dissolution solvent used in Lyocell process for cellulose fiber preparation, N-methylmorpholine-N-oxide (NMMO) monohydrate, was demonstrated to be an effective agent for sugarcane bagasse pretreatment. Bagasse of 20wt% was readily dissolved in NMMO monohydrate at 130 degrees C within 1h. After dissolution, bagasse could be regenerated by rapid precipitation with water as a porous and amorphous mixture of its original components. The regenerated bagasse exhibited a significant enhancement on enzymatic hydrolysis kinetic. Not only the reducing sugars releasing rate but also hydrolysis yield was enhanced at least twofold as compared with that of untreated bagasse. The cellulose fraction of regenerated bagasse was nearly hydrolyzed to glucose after 72h hydrolysis with Cellulase AP3. The recycled NMMO demonstrated the same performance as the fresh one on bagasse pretreatment for hydrolysis enhancement. The regenerated bagasse was directly used in simultaneous saccharification and fermentation (SSF) for ethanol production by Zymomonas mobilis. No negative effect on ethanol fermentation was observed and ethanol yield approximately 0.15 g ethanol/g baggasse was achieved.

Stepwise assembly of multimetallic nanoparticlesvia self-polymerized polydopamine

Without using polyelectrolytes and reducing agents, a multilayer of multimetal nanoparticles was built-up with the help of exceptional adhesive and reductive self-polymerized polydopamine (Pdop). Uniformly distributed multilayer Ag nanoparticles (SNPs) were generated on the surface of polymer film by simply alternative dipping the film in dopamine and silver nitrate solution. The multilayered SNPs demonstrated a significant enhancement in antibacterial and catalytic performance. Multilayer of multimetal nanoparticles (SNPs followed by Au NPs or vice versa) could also be generated. The surface density of metal nanoparticles in each layer could be tuned by varying the Pdop coating time.

Facile preparation of magnetic carbonaceous nanoparticles for Pb2+ ions removal

Magnetic carbonaceous nanoparticles were prepared by a facile two-step solution phase thermal synthesis. Magnetic nanoparticles (MNPs) with size less than 100 nm were first generated from FeCl(3) in a solvothermal reaction. The size could be significantly reduced to approximately 30 nm when 1,6-hexanediamine was employed in the reaction solution to functionalize the surface of MNPs with amine. Both the plain and amine-functionalized MNPs (MH) were effectively encapsulated in the carbonaceous shell by hydrothermal treatment in 0.5 M glucose solution. The saturation magnetization of MH decreased significantly from 70 to 25 emu/g after carbonaceous shell was formed. The as-prepared magnetic carbonaceous nanoparticles (MH@C) carries a negative surface charge (-30 mV) at neutral pH and has a point of zero charge (PZC) at pH 2. The carbonaceous shell not only can protect the magnetic nanoparticles (MNP) from the corrosive environment but also possesses a high adsorption capacity towards Pb(II). The adsorption isotherm at room temperature can be well-fitted by Langmuir model with a maximum adsorption capacity of 123 mg/g.

One-pot preparation of amine-rich magnetite/bacterial cellulose nanocomposite and its application for arsenate removal

Surface functionalization of bacterial cellulose (BC) nanofibrils with aminated magnetite nanoparticles (MH) was carried out by one-pot solvothermal reaction of 1,6-hexanediamine, FeCl3·6H2O and BC pellicle in ethylene glycol at 200 °C for 6 h. The presence of amine surface-functionalized magnetite nanoparticles on the surface of cellulose nanofibrils not only significantly enhanced the thermal and mechanical properties but also the amine content of the nanostructured bacterial cellulose pellicle. Approximately 10.5 mmol g−1 of amine was measured in the aminated magnetite-BC nanocomposite (BC@MH) which is about 14.3 fold higher than its counterpart (MH) prepared in the absence of BC pellicle. The never-dried BC@MH nanocomposite demonstrated a high adsorption capacity towards As(V) ions because of its high iron-oxide and amine content. Approximately 90 mg of As(V) can be adsorbed per gram of BC@MH.

Carbonaceous hydrogels based on hydrothermal carbonization of glucose with chitin nanofibers

Carbonaceous hydrogels can be generated with good mechanical strength by hydrothermal carbonization of glucose dissolved in a dilute (0.08%, w/v) chitin nanofiber viscose. Carbonaceous nanoparticles were observed along the surface of the nano-fibrous structure of the hydrogels. The carbonaceous materials also cross-link the entangled nanofibers and lead to durable 3D hydrogel formation. Hydrothermal carbonization of 0.2 M glucose with chitin nanofibers at 180 °C for 4 h resulted in a carbonaceous hydrogel with optimal strength and 99.3% water content.

β-Chitin nanofibrils for self-sustaining hydrogels preparation via hydrothermal treatment.

A transparent nanofibril suspension could be readily obtained by treating purified squid pen powder in water with ultrasonic irradiation. The obtained suspension is consisted of β-chitin nanofibrils (CNF) with 3-10 nm in width and several micrometers in length. The degree of acetylation (DA) of CNF was found to be 84% which is about 10% lower than that of untreated sample. The CNF suspension could be transformed into a durable 3-D hydrogels (CH) by simply heating to 180 °C for 1-4 h in an autoclave. Hydrophobic interaction between CNF was believed to play the major role for CNF self-assembling into hydrogels, since the as-prepared chitin hydrogels readily dissolved in a typical chaotropic solution (8 M urea) under room temperature. The hydrothermal duration and CNF concentration (0.3-2% (w/v)) strongly affected the physical properties of CH. The suspension of 1% (w/v) CNF treated with 4 h, 180 °C hydrothermal heating generated a CH with 99.3% water content, CNF with 87% crystallinity and an mechanical strength of 0.7 N breaking force.

Bactericidal magnetic nanoparticles with iodine loaded on surface grafted poly(N-vinylpyrrolidone)

Bactericidal magnetic nanoparticles were prepared by complexing iodine with poly(N-vinylpyrrolidone) (PVP) grown at the surface of silica coated magnetic nanoparticles (MNPs) via surface-initiated atom transfer radical polymerization (SI-ATRP). Approximately, 10 mg of iodine could be loaded onto one gram of the PVP-grafted MNPs to form bactericidal MNPs@PVP-I. At a concentration of 5 g L-1, MNPs@PVP-I could achieve 100% bactericidal rate for both Gram-negative Escherichia coli and Gram-positive Staphylococcus aureus with a concentration of ∼1 × 1010 CFU mL-1 within 3 min. After being used for killing the bacteria in solution, the bactericidal rate of the MNPs@PVP-I decreased to <10% due to the consumption of iodine. The bactericidal rate could be tuned back to 100% when the used MNPs@PVP-I was recharged in a 15 g L-1 iodine solution for 12 h. The as-prepared bactericidal MNPs@PVP-I could be reused at least 4 times with 100% bactericidal rate by repeatedly recharging it with iodine.

A chitin nanofibril reinforced multifunctional monolith poly(vinyl alcohol) cryogel

A highly porous and spongy monolith cryogel was prepared by a single freeze-thawing cycle of a PVA solution containing chitin nanofibrils (CNFs) as the nanofiller and glutaraldehyde (GA) as the cross-linker. The presence of CNFs significantly reinforced the spongy structure of the cryogel so that repeated squeezing-releasing did not deteriorate its spongy structure. The in situ self-polymerized polydopamine was formed inside the spongy cryogel by soaking the cryogel in a dopamine solution. The polydopamine modified cryogel (PVA-CNF-D) showed a very good antioxidant activity in that approximately 49% of free radicals of DPPH˙ was consumed within 2 min. Silver nanoparticles (SNPs) could be spontaneously reduced from silver nitrate solution and deposited onto the polydopamine modified surface without an exogenous reducing reagent. The SNP incorporated spongy cryogel demonstrated a very effective antibacterial activity against E. coli.

Knock-out of glucose dehydrogenase gene in Gluconacetobacter xylinus for bacterial cellulose production enhancement

Glucose dehydrogenase (GDH) locates in the cytoplasmic membrane of Gluconacetobacter xylinus oxidizes glucose to gluconic acid that decreases the conversion of glucose to bacterial cellulose (BC). In this study, a mutant of G. xylinus was generated by knocking-out the membrane bound GDH gene via homologous recombination of a defect GDH gene. The production of BC by G. xylinus mutant (GDH-KO strain) using glucose as a carbon source was investigated. Without the membrane bound GDH activity, the mutant strain still produces BC and increases glucose utilization efficiency for cellulose biosynthesis. In contrast, the wild-type strain oxidized a large fraction of glucose to gluconic acid that decreased the conversion yield of glucose to BC. Our results showed that the BC production from GDH-KO strain was about 40 and 230% higher than that of wild-type strain in static and shaken culture, respectively.

Facile preparation of a robust and flexible antioxidant film based on self-polymerized dopamine in a microporous battery separator

The microslits of a microporous polyethylene (PE) separator membrane were filled with polydopamine (Pdop) via auto-oxidation and self-polymerization of dopamine to generate a robust, antioxidant, and free standing flexible thin film. Multifunctional groups present on the Pdop act as strong anti-oxidative agents and can induce in situ formation of noble metal nanoparticles on the film surface. The superior antioxidant property of the film was well maintained even after harsh ultrasonic irradiation, tape peeling, and extreme pH treatment.