Zheng Li, Eka Sutandar, Thomas Goihl, Xiao Zhang, and Xuejun Pan. Cleavage of ethers and demethylation of lignin in acidic concentrated lithium bromide (ACLB) solution. Green Chemistry, 2020, 22, 7989-8001. https://doi.org/10.1039/D0GC02581J
Open access at https://pubs.rsc.org/en/content/articlepdf/2020/gc/d0gc02581j
The methoxyl group is the most abundant functional group of lignin and affects the properties, reactivity, and application of lignin. Efficient demethylation is always of interest in the area of lignin chemistry and application. This study demonstrated a new method for cleaving ether compounds and demethylating lignin in acidic concentrated lithium bromide (ACLB) solution under mild conditions. It was found that the ACLB system could universally cleave ether compounds except for diaryl ethers. The study on lignin model compounds (creosol, syringol, and 1,2,3-trimethoxybenzene) verified that ACLB could demethylate them to corresponding phenols. Four real lignin samples produced from various sources by different methods were also efficiently demethylated by 69–82% in ACLB. The lignin demethylation resulted in more phenolic hydroxyl groups, which benefits some downstream applications of lignin. This study also provided new insights into the cleavage of the ether bonds in lignin. In addition to the methyl–aryl ether bond, ACLB could cleave other ether bonds of lignin in β-O-4, β-5, and β-β structures except for the 4-O-5 bond in the diphenyl structure. The ether bonds were cleaved via the SN2 substitution except for the β-O-4 bond, which was primarily cleaved via the benzyl cation and enol ether intermediates, leading to Hibbert’s ketones. Some of the β-O-4 structures were transformed into benzodioxane (BD) structures, which were stable in the ACLB system.
Meijun Zeng and Xuejun Pan. Insights into solid acid catalysts for efficient cellulose hydrolysis to glucose: progress, challenges, and future opportunities. Catalysis Reviews-Science and Engineering, 2020, https://doi.org/10.1080/01614940.2020.1819936
Lei Zhang, Yang Liao, Yi-Cheng Wang, Steven Zhang, Weiqing Yang, Xuejun Pan, and Zhong Lin Wang. Cellulose II aerogels based triboelectric nanogenerator. Advanced Functional Materials, 2020, 30 (28), 2001763. https://doi.org/10.1002/adfm.202001763.
Cellulose II aerogels, with the features of high flexibility, porosity, and surface area, are integrated with triboelectric nanogenerators to yield green, sustainable energy harvesting, and sensing devices. By blending other natural polysaccharides to introduce electron‐donating and electron‐withdrawing groups, the performance of the cellulose II aerogel‐based triboelectric nanogenerators can be significantly improved and used for mechanical energy harvesting and motion monitoring.
Yang successfully defended his PhD thesis on April 20, 2020. Congratulations! The title of his thesis is “Fabrication, functionalization and application of cellulose 3D hierarchical materials (hydrogels and aerogels)”. Due to the Covid-19 pandemic, in-person meeting was not allowed. Yang became the first PhD student in the department history who defended thesis virtually. Wish Yang a successful and bright career.
Tianjiao Qu successfully defended her Master thesis on July 23, 2019. Congratulations! Tianjiao did an excellent job both in course work and lab research. In particular, Tianjiao is an “A” student, maintaining a cumulative GPA 4.0! Wish Tianjiao a successful and bright future career.
N. Li, Z.N. Wang, T.J. Qu, J. Kraft, J.-H. Oh, J.P. van Pijkeren, G.W. Huber, and X.J. Pan. High-yield synthesis of glucooligosaccharides (GlOS) from glucose via non-enzymatic glycosylation as potential prebiotics. Green Chemistry, 2019, 21, 2686-2698. https://doi.org/10.1039/C9GC00663J
This study demonstrated a high-yield process to synthesize glucooligosaccharides (GlOS) from glucose via non-enzymatic glycosylation in an acidic lithium bromide trihydrate (ALBTH, a concentrated aqueous solution of LiBr containing a small amount of acid) system. The single-pass yield of the GlOS was up to 75%, which was the highest yield ever reported. The synthesized GlOS consisted of 2-9 glucose units linked predominantly via α/β–1,6 glycosidic bonds (69%), followed by α/β–1,3, α/β–1,2, α/β–1,1, and α–1,4 glycosidic bonds. Preliminary in-vitrofermentation tests indicated that GlOS could be utilized by select gut probiotic strains, suggesting that GlOS had the potential as prebiotics. Theenhanced glucose glycosylation in ALBTH was attributedto the unique properties of the solvent system, including water-deficient nature, extra-highcapacity of dissolving glucose,and enhanced acid catalysis. The LiBr salt could be recovered after separating the GlOS by anti-solvent precipitation and directly reused.