Sixiao Hu

Bio: Sixiao Hu is an academic researcher from University of California, Davis. The author has contributed to research in topics: Cellulose & Nanocellulose. The author has an hindex of 3, co-authored 3 publications receiving 115 citations.

1D Lignin-Based Solid Acid Catalysts for Cellulose Hydrolysis to Glucose and Nanocellulose

Abstract: 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.

Preparation of Activated Carbon and Silica Particles from Rice Straw

Abstract: 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 cm3/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.

Holistic Rice Straw Nanocellulose and Hemicelluloses/Lignin Composite Films

Abstract: 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.

Utilization of Waste Straw and Husks from Rice Production: A Review

Abstract: As a staple food for much of the world, rice production is widespread. However, it also results in the generation of large quantities of non-food biomass, primarily in the form of straw and husks. Although they have been little utilized and much rice straw is still simply burned, these lignocellulosic materials potentially have considerable values. This review considers the composition of rice straw and husks, the various processes involved in the production of valuable products, and a range of uses to which they can be put. These include agricultural amendments, energy production, environmental adsorbents, construction materials, and various speciality products.

Highly Pure Silica Nanoparticles with High Adsorption Capacity Obtained from Sugarcane Waste Ash.

Abstract: Silica nanoparticles (SiO2NPs) from renewable sources can be used in very different materials, such as paints, membranes for fuel cells, Li-ion batteries, adsorbents, catalysts, and so on. Brazil is the world's largest producer of sugarcane and generates huge amounts of sugarcane waste ash (SWA), which is a Si-rich source. This study investigates a method to produce highly pure SiO2NPs from SWA. The SiO2NPs were characterized by inductively coupled plasma optical emission spectroscopy, scanning and transmission electron microscopy (TEM), X-ray diffraction analyses, specific surface area and pore distribution, UV and Fourier transform infrared spectroscopy, and thermogravimetric analyses and applied as an adsorbent material in the removal of acid orange 8 (AO8) dye from aqueous solution. The SiO2 content was 88.68 and 99.08 wt % for SWA and SiO2NPs, respectively. TEM images of SWA and SiO2NPs exhibit drastic alterations of the material size ranging from several micrometers to less than 20 nm. The SiO2NPs showed a specific surface area of 131 m2 g-1 and adsorption capacity of around 230 mg g-1 for acid orange 8 dye. Furthermore, the recycling of the SiO2NPs adsorbent after AO8 adsorption was very satisfactory, with reuse for up to five cycles being possible. The results indicate that it was possible to obtain highly pure silica in a nanosize from the waste material and produce an adsorbent with high adsorption capacity and the possibility of reuse.

Synergetic Effects of Alcohol/Water Mixing on the Catalytic Reductive Fractionation of Poplar Wood

Abstract: One of the foremost challenges in lignocellulose conversion encompasses the integration of effective lignin valorization in current carbohydrate-oriented biorefinery schemes. Catalytic reductive fractionation (CRF) of lignocellulose offers a technology to simultaneously produce lignin-derived platform chemicals and a carbohydrate-enriched pulp via the combined action of lignin solvolysis and metal-catalyzed hydrogenolysis. Herein, the solvent (composition) plays a crucial role. In this contribution, we study the influence of alcohol/water mixtures by processing poplar sawdust in varying MeOH/water and EtOH/water blends. The results show particular effects that strongly depend on the applied water concentration. Low water concentrations enhance the removal of lignin from the biomass, while the majority of the carbohydrates are left untouched (scenario A). Contrarily, high water concentrations favor the solubilization of both hemicellulose and lignin, resulting in a more pure cellulosic residue (scenario B)...