No abstract

In the past few years, cellulose nanomaterials obtained from lignocellulose have attracted extensive attention as functional nanomaterials with excellent properties and great application potentials in a variety of high-tech fields....

No abstract

Cellulose nanocrystals (CNCs) and cellulose nanofibrils (CNFs) are of great interest to researchers due to their outstanding properties and wide application potentials. However, green and sustainable production of CNCs and CNFs is still challenging. In this work, the integrated and sustainable production of functional CNCs and CNFs was achieved by formic acids (FA) hydrolysis. Kinetic study for FA hydrolysis of cellulosic pulp was performed to investigate the hydrolysis mechanism. FA concentration of 80–98 wt %, reaction temperature of 70–100 °C, and reaction duration up to 24 h were employed to capture the feature of the coexistence of a diversity of reaction products, i.e., CNCs, cellulose solid residue (CSR), cellulose formate (CF), xylose, glucose, and furfural. The separated CSR was further fibrillated to CNFs by homogenization. It was found that the yield, morphology, crystallinity, thermal stability, and degree of esterification of CNCs and CNFs were significantly affected by hydrolysis conditions (particularly for acid concentration). Detailed characterization indicated that the as-prepared CNCs exhibited high thermal stability (maximal weight loss temperature of 375 °C) and high crystallinity index of 79%. Both the resultant CNCs and CNFs showed good dispersibility in dimethylacetamide due to the introduction of ester groups on cellulose surface during FA hydrolysis. More interestingly, the regenerated CF was also a kind of functional CNFs with more ester groups. These ester groups would enable the CNCs/CNFs to be potentially used in polymeric materials due to the hydrophobic surface. Therefore, this study provided fundamental knowledge for the sustainable and integrated production of thermally stable and functional CNCs and CNFs with tailored characteristics.

It has previously been shown that ex situ phosphorus-doped polycrystalline silicon on silicon oxide (poly-Si/SiO x ) passivating contacts can suffer a pronounced surface passivation degradation when subjected to a firing treatment at 800 °C or above. The degradation behavior depends strongly on the processing conditions, such as the dielectric coating layers and the firing temperature. The current work further studies the firing stability of poly-Si contacts and proposes a mechanism for the observed behavior based on the role of hydrogen. Secondary ion mass spectrometry is applied to measure the hydrogen concentration in the poly-Si/SiO x structures after firing at different temperatures and after removing hydrogen by an anneal in nitrogen. While it is known that a certain amount of hydrogen around the interfacial SiO x can be beneficial for passivation, surprisingly, we found that the excess amount of hydrogen can deteriorate the poly-Si passivation and increase the recombination current density parameter J 0. The presence of excess hydrogen is evident in selected poly-Si samples fired with silicon nitride (SiN x ), where the injection of additional hydrogen to the SiO x interlayer leads to further degradation in the J 0, while removing hydrogen fully recovers the surface passivation. In addition, the proposed model explains the dependence of firing stability on the crystallite properties and the doping profile, which determine the effective diffusivity of hydrogen upon firing and hence the amount of hydrogen around the interfacial SiO x after firing.