Shaomei Cao

Integrated Fast Assembly of Free-Standing Lithium Titanate/Carbon Nanotube/Cellulose Nanofiber Hybrid Network Film as Flexible Paper-Electrode for Lithium-Ion Batteries

A free-standing lithium titanate (Li4Ti5O12)/carbon nanotube/cellulose nanofiber hybrid network film is successfully assembled by using a pressure-controlled aqueous extrusion process, which is highly efficient and easily to scale up from the perspective of disposable and recyclable device production. This hybrid network film used as a lithium-ion battery (LIB) electrode has a dual-layer structure consisting of Li4Ti5O12/carbon nanotube/cellulose nanofiber composites (hereinafter referred to as LTO/CNT/CNF), and carbon nanotube/cellulose nanofiber composites (hereinafter referred to as CNT/CNF). In the heterogeneous fibrous network of the hybrid film, CNF serves simultaneously as building skeleton and a biosourced binder, which substitutes traditional toxic solvents and synthetic polymer binders. Of importance here is that the CNT/CNF layer is used as a lightweight current collector to replace traditional heavy metal foils, which therefore reduces the total mass of the electrode while keeping the same areal loading of active materials. The free-standing network film with high flexibility is easy to handle, and has extremely good conductivity, up to 15.0 S cm(-1). The flexible paper-electrode for LIBs shows very good high rate cycling performance, and the specific charge/discharge capacity values are up to 142 mAh g(-1) even at a current rate of 10 C. On the basis of the mild condition and fast assembly process, a CNF template fulfills multiple functions in the fabrication of paper-electrode for LIBs, which would offer an ever increasing potential for high energy density, low cost, and environmentally friendly flexible electronics.

Luminescent and transparent nanopaper based on rare-earth up-converting nanoparticle grafted nanofibrillated cellulose derived from garlic skin.

Highly flexible, transparent, and luminescent nanofibrillated cellulose (NFC) nanopaper with heterogeneous network, functionalized by rare-earth up-converting luminescent nanoparticles (UCNPs), was rapidly synthesized by using a moderate pressure extrusion paper-making process. NFC was successfully prepared from garlic skin using an efficient extraction approach combined with high frequency ultrasonication and high pressure homogenization after removing the noncellulosic components. An efficient epoxidation treatment was carried out to enhance the activity of the UCNPs (NaYF4:Yb,Er) with oleic acid ligand capped on the surface. The UCNPs after epoxidation then reacted with NFC in aqueous medium to form UCNP-grafted NFC nanocomposite (NFC-UCNP) suspensions at ambient temperature. Through the paper-making process, the assembled fluorescent NFC-UCNP hybrid nanopaper exhibits excellent properties, including high transparency, strong up-conversion luminescence, and good flexibility. The obtained hybrid nanopaper was characterized by transmission electron microscopy (TEM), atomic force microscope (AFM), Fourier transform infrared spectroscopy (FTIR), field emission-scanning electron microscope (FE-SEM), up-conversion luminescence (UCL) spectrum, and ultraviolet and visible (UV-vis) spectrophotometer. The experimental results demonstrate that the UCNPs have been successfully grafted to the NFC matrix with heterogeneous network. And the superiorly optical transparent and luminescent properties of the nanopaper mainly depend on the ratio of UCNPs to NFC. Of importance here is that, NFC and UCNPs afford the nanopaper a prospective candidate for multimodal anti-counterfeiting, sensors, and ion probes applications.

Fast fabrication of transparent and multi-luminescent TEMPO-oxidized nanofibrillated cellulose nanopaper functionalized with lanthanide complexes

We designed an easy-to-fabricate multi-luminescent nanopaper with high transparency, for the first time, by grafting lanthanide complexes [Eu(dbm)3(H2O)2, Sm(dbm)3(H2O)2, Tb(tfacac)3(H2O)2] on TEMPO mediated oxidized nanofibrillated cellulose (ONFC). The lanthanide complex functionalized ONFC nanopaper (Ln–ONFC nanopaper, Ln = Eu, Sm, Tb) with uniform luminescence was rapidly fabricated after solvent exchange using a press-controlled extrusion papermaking method. The new TEMPO-induced carboxyl groups on the surface of ONFC provided the possibility to participate in the coordination with lanthanide ions and then to construct heterogeneous network architectures. The fluorescent properties of the Ln–ONFC hybrid nanopaper were significantly influenced by the amount of lanthanide complexes and the solvent medium during the extrusion. Based on simple manipulation and mild conditions, a highly transparent NFC template provided a soft matrix and afforded the high thermal stability and excellent luminescent properties of the Ln–ONFC nanopaper, which yields ever increasing potential to supersede petroleum-based materials for diverse applications.

In Situ Carbonized Cellulose-Based Hybrid Film as Flexible Paper Anode for Lithium-Ion Batteries

Flexible free-standing carbonized cellulose-based hybrid film is integrately designed and served both as paper anode and as lightweight current collector for lithium-ion batteries. The well-supported heterogeneous nanoarchitecture is constructed from Li4Ti5O12 (LTO), carbonized cellulose nanofiber (C-CNF) and carbon nanotubes (CNTs) using by a pressured extrusion papermaking method followed by in situ carbonization under argon atmospheres. The in situ carbonization of CNF/CNT hybrid film immobilized with uniform-dispersed LTO results in a dramatic improvement in the electrical conductivity and specific surface area, so that the carbonized paper anode exhibits extraordinary rate and cycling performance compared to the paper anode without carbonization. The flexible, lightweight, single-layer cellulose-based hybrid films after carbonization can be utilized as promising electrode materials for high-performance, low-cost, and environmentally friendly lithium-ion batteries.

Transparent nanocellulose hybrid films functionalized with ZnO nanostructures for UV-blocking

Transparent, nanocellulose–ZnO (NC–ZnO) hybrid films were fabricated via a pressure controlled extrusion process using NC fibrils and sheet-like ZnO (s-ZnO) or belt-like ZnO (b-ZnO) nanostructures. The s-ZnO and b-ZnO conjoined with the NC fibrils to form a heterogeneous, fibrous network structure. The NC–ZnO hybrid films with different amounts of ZnO nanostructures showed a synergic feature of high optical transparency and excellent UV-blocking. The results indicated that NC assembled with s-ZnO hybrid film possessed excellent UV-blocking ability in a wide range from 200 to 375 nm, in contrast to NC–b-ZnO. Moreover, the prominent thermal and photo stability of transparent NC–ZnO hybrid films enhanced extensibility and ease of use for diverse biological applications, which require tolerance of temperature changes.

Easy synthesis of photoluminescent N-doped carbon dots from winter melon for bio-imaging

N-doped carbon dots were successfully synthesized via a one-step hydrothermal method by using edible winter melon as the source material. Mono-dispersed CDs 4.5–5.2 nm in diameter were achieved in a quantum yield (QY) of 7.51%. The photoluminescent CDs were demonstrated to be effective bio-imaging agents for hepG2 (liver hepatocellular carcinoma) cells.

Combined bleaching and hydrolysis for isolation of cellulose nanofibrils from waste sackcloth

A convenient and low cost process to prepare cellulose nanofibrils (CNF) from waste sackcloth by using H2O2/HNO3 solution as both bleaching agent and hydrolysis medium was recommended. The resultant CNF with high crystallinity was initially synthesized by the chemical disintegration process for the removal of non-cellulosic components and the crystallinity of CNF was 68.11% compared with that of sackcloth fibers (48.28%). The decomposition temperature of CNF was about 340°C, which indicated that the thermal stability of the fibers was increased after the combined bleaching and hydrolysis. Subsequently, the homogenous CNF colloidal suspensions in water, ethanol and acetone were obtained after sonication treatment. The CNF in water suspensions with 20-50nm in width and hundreds of nanometers in length was ultimately prepared under the conditions of different ultrasonic time.

Synthesizing nano-sized (∼20 nm) Li4Ti5O12 at low temperature for a high-rate performance lithium ion battery anode

In this paper, we developed a novel strategy to synthesize nano-sized Li4Ti5O12 (LTO) by hydrothermal method and calcination. X-ray diffraction and high resolution transmission electron microscopy were performed to characterize the structures and morphologies of these samples. Highly crystalline and pure-phase Li4Ti5O12 synthesized at low calcination temperature of 500 °C has been reported for the first time. This nanocrystalline LTO was tested as the anode material for lithium ion batteries, and exhibited excellent reversible capacities of 166, 162, 155, 142 and 123 mAh g−1 at current densities of 1 C, 2 C, 5 C, 10 C and 20 C, respectively. It also demonstrated good capacity retention and high coulombic efficiency values at all current rates. This excellent electrochemical performance makes our LTO a promising anode material for high energy/power density lithium ion batteries.

Use of carbon dots to enhance UV-blocking of transparent nanocellulose films

High-efficient transparent UV-blocking nanocellulose (NC) films were successfully assembled by pressured-extrusion of the composites of carbon dots (CDs), 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) radical mediated oxidized nanocellulose (ONC) and ZnO nanostructures. ONC nanofibrils were firstly extracted from bamboo fibers and subsequently prepared by applying TEMPO oxidation. The as-obtained CDs-ONC-ZnO films exhibited high visible light transparency, excellent thermal stability and enhanced UV-blocking properties. Compared to the previously designed NC-ZnO films, CDs-ONC-ZnO films presented significant increase of UV-blocking ratio (UVR) with the same amounts of ZnO. Moreover, the UVR of CDs-ONC-s-ZnO film with 4wt% sheet-like ZnO (s-ZnO) at 300nm and 225nm is 92.74% and 98.99%, better than the same condition of CDs-ONC-b-ZnO film added with belt-like ZnO (b-ZnO) and CDs-ONC-p-ZnO film added with commercial particulate ZnO (p-ZnO). An interesting discovery is that when adding 4wt% p-ZnO, the UVR of CDs-ONC-p-ZnO film is very close to the value of NC-s-ZnO film with the same amount of s-ZnO.