Co-production of xylooligosaccharides and activated carbons from Camellia oleifera shell treated by the catalysis and activation of zinc chloride

Catalytically Active Carbon for Oxygen Reduction Reaction in Energy Conversion: Recent Advances and Future Perspectives

The shortage and unevenness of fossil energy sources are affecting the development and progress of human civilization. The technology of efficiently converting material resources into energy for utilization and storage is attracting the attention of researchers. Environmentally friendly biomass materials are a treasure to drive the development of new-generation energy sources. Electrochemical theory is used to efficiently convert the chemical energy of chemical substances into electrical energy. In recent years, significant progress has been made in the development of green and economical electrocatalysts for oxygen reduction reaction (ORR). Although many reviews have been reported around the application of biomass-derived catalytically active carbon (CAC) catalysts in ORR, these reviews have only selected a single/partial topic (including synthesis and preparation of catalysts from different sources, structural optimization, or performance enhancement methods based on CAC catalysts, and application of biomass-derived CACs) for discussion. There is no review that systematically addresses the latest progress in the synthesis, performance enhancement, and applications related to biomass-derived CAC-based oxygen reduction electrocatalysts synchronously. This review fills the gap by providing a timely and comprehensive review and summary from the following sections: the exposition of the basic catalytic principles of ORR, the summary of the chemical composition and structural properties of various types of biomass, the analysis of traditional and the latest popular biomass-derived CAC synthesis methods and optimization strategies, and the summary of the practical applications of biomass-derived CAC-based oxidative reduction electrocatalysts. This review provides a comprehensive summary of the latest advances to provide research directions and design ideas for the development of catalyst synthesis/optimization and contributes to the industrialization of biomass-derived CAC electrocatalysis and electric energy storage.

Efficient production of xylooligosaccharides from Camellia oleifera shells pretreated by pyruvic acid at lower temperature

XOS production from lignocellulose using organic carboxylic acids and alkyd acids has been widely reported. However, it still faces harsh challenges such as high energy consumption, high cost, and low purity. Pyruvic acid (PYA), a carbonyl acid with carbonyl and carboxyl groups, was used to produce XOS due to its stronger catalytic activity. In this work, XOS was efficiently prepared from COS in an autoclave under the condition of 0.21 M PYA-121 °C-35 min. The total yield of XOS reached 68.72 % without producing any toxic by-products, including furfural (FF) and 5-hydroxymethylfurfural (5-HMF). The yield of xylobiose (X2), xylotriose (X3), xylotetraose (X4), and xylopentaose (X5) were 20.58 %, 12.47 %, 15.74 %, and 10.05 %, respectively. Meanwhile, 89.05 % of lignin was retained in the solid residue, which provides a crucial functional group for synthesizing layered carbon materials (SRG-a). It achieves excellent electromagnetic shielding (EMS) performance through graphitization, reaching -30 dB at a thickness of 2.0 mm. The use of a PYA catalyst in the production of XOS has proven to be an efficient method due to lower temperature, lower acid consumption, and straightforward operation.

Glycolic acid-based deep eutectic solvents boosting co-production of xylo-oligomers and fermentable sugars from corncob and the related kinetic mechanism

BACKGROUND

Xylo-oligomers are a kind of high value-added products in biomass fractionation. Although there are several chemical methods to obtain xylo-oligomers from biomass, the reports about the deep eutectic solvents (DESs)-mediated co-production of xylo-oligomers and fermentable sugars and the related kinetic mechanism are limited.

RESULTS

In this work, glycolic acid-based DESs were used to obtain xylo-oligomers from corncob. The highest xylo-oligomers yield of 65.9% was achieved at 120 °C for 20 min, of which the functional xylo-oligosaccharides (XOSs, DP 2-5) accounted for up to 31.8%. Meanwhile, the enzymatic digestion of cellulose and xylan in residues reached 81.0% and 95.5%, respectively. Moreover, the addition of metal inorganic salts significantly accelerated the hydrolysis of xylan and even the degradation of xylo-oligomers in DES, thus resulting in higher selectivity of xylan removal. AlCl3 showed the strongest synergistic effect with DES on accelerating the processes, while FeCl2 is best one for xylo-oligomers accumulation, affording the highest xylo-oligomers yield of 66.1% for only 10 min. Furthermore, the kinetic study indicates that the 'potential hydrolysis degree' model could well describe the xylan hydrolysis processes and glycolic acid/lactic acid (3:1) is a promising solvent for xylo-oligomers production, in particular, it worked well with FeCl2 for the excellent accumulation of xylo-oligomers.

CONCLUSIONS

Glycolic acid-based deep eutectic solvents can be successfully applied in corncob fractionation with excellent xylo-oligomers and fermentable sugars yields on mild conditions, and the large amount of xylo-oligosaccharides accumulation could be achieved by specific process controlling. The strategies established here can be useful for developing high-valued products from biomass.

Efficient co-production of xylooligosaccharides and glucose from lignocelluloses by acid/pentanol pretreatment: Synergetic role of lignin removal and inhibitors

A novel technology for co-production of xylooligosaccharides (XOS) and glucose from Monterey pine sawdust and wheat straw was introduced using dilute acid (DA)/pentanol pretreatment. Effects of pretreatment severity (PS), lignin removal, and inhibitors with byproduct concentrations on XOS production were investigated. Optimal identified conditions (PS: 3.71; 170 °C, 45 min) resulted in maximum XOS of 48.65 % (pine sawdust) and 46.85 % (wheat straw), due to appropriate lignin removal (pine sawdust, 88.5 %; wheat straw, 89.7 %) and formation of small amounts of inhibitors and byproducts. Enzymatic hydrolysis of optimal pretreated solid residues yielded 88.65 % and 93.34 % glucose in pine sawdust and wheat straw, respectively. Biomass characterization revealed that DA/pentanol pretreatment enhanced porosity and pore size along with removal of amorphous fractions in both samples, thereby increasing cellulose accessibility and glucose yield. This study demonstrated lignin removal and low formation of inhibitors and byproducts, effectively enhancing XOS and glucose production from lignocellulosic biomass.

Production of xylooligosaccharides from Camellia oleifera Abel fruit shell using a shell-based solid acid catalyst

This study aimed to produce xylooligosaccharides (XOS) from Camellia oleifera Abel fruit shell (CFS) using a shell-based solid acid derived from CFS (CFS-BSA). CFS-BSA preparation was optimized by incomplete carbonization at 450 °C for 1 h, followed by sulfonation at 130 °C for 8 h to yield a -SO₃H functional group concentration of 1.04 mmol/g. When CFS-BSA was used to hydrolyze CFS with a 1:5 ratio of CFS-BSA to CFS at 170 °C for 20 min, a maximum XOS yield (X₂-X₅) of 51.41 % was achieved, which was notably higher than when using subcritical H₂O solely. CFS-BSA can be recycled and reused at least six times by sieving without a substantial loss in its catalytic activity. CFS-BSA can also be used to produce XOS from other lignocellulosic materials such as corncob (41.04 %), sugarcane bagasse (45.03 %), corn stalk (45.89 %), birchwood (46.05 %), and poplar (40.10 %).

BCOFGs loaded with nano-FexSy for the catalytic degradation of QNC: Contribution and mechanism of OFGs for reductive iron regeneration

Biochar currently served as the support for dispersed metal nanoparticles and cooperated with pyrite to generate more reactive radicals in organic pollution degradation system. But the mechanism of interaction between biochar and pyrite has not been elucidated. In this paper, biochar with oxygen-containing functional groups (OFGs) served as a stable dispersant to prepare nano-Fe_xS_y loaded biochar materials (BC_OFGs@nano-Fe_xS_y). BC_OFGs coordinated with nano-Fe_xS_y to overcome its drawbacks, boosting QNC removal efficiency from 28.64% to 100%. The XPS and the linear sweep voltammetry (LSV) results revealed higher Fe(II) content and higher electron transfer rate on used BC_OFGs@nano-Fe_xS_y, further validating that hydroxyl functional groups on biochar surface provided electrons to Fe(III) to achieve efficient Fe(II)/Fe(III) cycling. Based on comparative experiments and studies on the roles of iron, S(II) species and OFGs, we clearly revealed that OFGs on biochar materials surface coordinated with nano-Fe_xS_y to catalyze the degradation of QNC. The degradation efficiency of BC_OFGs@nano-Fe_xS_y for QNC was still as high as 91.39% after five cycles, providing full demonstrations that OFGs and S(II) as the abundant electron donor coordinated with Fe species for QNC catalytic degradation and further enhanced the catalytic performance and stability of nano-Fe_xS_y.

Coproduction xylo-oligosaccharides with low degree of polymerization and glucose from sugarcane bagasse by non-isothermal subcritical carbon dioxide assisted seawater autohydrolysis

High pretreatment temperature is necessary to obtain xylo-oligosaccharides (XOS) with low degree of polymerization (DP). However, traditional isothermal pretreatment for XOS production may increase the generation of xylose and furfural with the reaction time extending (10-100 min). In this study, non-isothermal subcritical CO₂-assisted seawater autohydrolysis (NSCSA) firstly used seawater and CO₂ for the coproduction of XOS with low DP and glucose. 51.44% XOS was obtained at 205 °C/5 MPa, and low-DP (2-4) XOS accounted for 79.13% of the total XOS. Furthermore, the specific surface area and total pore volume of the pretreated sugarcane bagasse (SCB) were 1.96 m²/g and 0.011 cm³/g, respectively, increased by 148% and 83% than that of nature SCB. Compared with subcritical CO₂ pretreatment, NSCSA is an efficient method for the coproduction of XOS with low DP and glucose through inorganic salts in seawater and H₂CO₃ formed from CO₂.

Coproduction of xylo-oligosaccharides and glucose from sugarcane bagasse in subcritical CO2-assisted seawater system

Abundant seawater resources can replace the shortage of freshwater resources. The co-production of xylo-oligosaccharides and glucose from sugarcane bagasse by subcritical CO2-assisted seawater pretreatment was studied in this paper. We investigated the effects of pretreatment conditions of temperature, CO2 pressure and reaction time on the yield of xylo-oligosaccharides in subcritical CO2-assisted seawater systems. The maximum xylo-oligosaccharide yield of 68.23% was obtained at 165 °C/2 MPa/5 min. After further enzymatic hydrolysis of the solid residue, the highest glucose yield of 94.45% was obtained. In this system, there is a synergistic effect of mixed ions in seawater and CO2 to depolymerize xylan into xylo-oligosaccharides with a lower degree of polymerization. At the same time, the addition of CO2 increased the pore size and porosity of sugarcane bagasse, improved the efficiency of enzymatic hydrolysis and increased the yield of glucose. Therefore, this study provides a more environmentally friendly and sustainable process for the co-production of xylo-oligosaccharides and glucose from sugarcane bagasse, and improves the utilization of seawater resources.

Combining impregnation and co-pyrolysis to reduce the environmental risk of biochar derived from sewage sludge

Sewage sludge derived biochar has great potential for agricultural application, whereas the risk of heavy metals in sewage sludge is a key challenge for utilization. This study investigated the synergetic effect of co-pyrolysis and ZnCl₂ impregnation treatment on the surface characteristics and potential ecological risk of heavy metals in sewage sludge derived biochar. It was concluded that ZnCl₂ impregnation led to an increase in biochar yield, O and S content, but decrease the ash content and pH. Additionally, the thermal stability of ZnCl₂-added biochar was decreased. Semi-quantitive specific functional groups analysis suggested that ZnCl₂ impregnation had a negative effect on the content of CO and C-O, while promoted the formation of aromatic CC. And the functional group of CO was retained in biochar by co-pyrolysis with Camellia oleifera shell due to its high content of potassium. For heavy metal passivation, ZnCl₂ impregnation decreased total content of heavy metals by chlorination, while the oxidizable fraction (F3) of heavy metals showed an increasing tendency. Results of potential ecological risk assessment indicated that combining ZnCl₂ impregnation and co-pyrolysis had great potential to reduce the ecological risk of heavy metals in sewage sludge derived biochar.

Xylo-oligosaccharides and lignin production from Camellia oleifera shell by malic acid hydrolysis at mild conditions

Camellia oleifera shell (COS), a by-product of processing woody vegetable oil, is rich in hemicellulose and lignin. In this study, we investigated the effects of acid concentration, pretreatment temperature and reaction time on the concentration and yield of xylo-oligosaccharides (XOS) and the degree of polymerization (DP) distribution of XOS when pretreating COS with malic acid (MA). Under moderate condition (2 M MA, 120 ℃, 30 min), the maximum yield of XOS with DP 2-4 was 48.78% (based on the initial xylan) with low xylose, 5-hydroxymethylfurfural (HMF) and furfural, in which xylobiose (X₂), xylotriose (X₃) and xylotraose (X₄) concentrations were 5.22 g/L, 2.75 g/L and 2.91 g/L, respectively. In addition, acid-insoluble lignin (AIL) in the residue after MA pretreatment and milling wood lignin (MWL) were mainly composed of guaiacyl and syringyl. AIL has higher thermal stability than MWL, which can be the stabilizer for producing flame-resistant materials.

The Effect of Temperature on the Properties of Hydrochars Obtained by Hydrothermal Carbonization of Waste Camellia oleifera Shells

Hydrothermal carbonization (HTC) is a thermochemical conversion technique that can produce renewable solid biofuel by all types of waste. Waste Camellia oleifera shells (WCOSs) can be used to produce hydrochars via HTC. The effect of HTC temperature on the physicochemical properties and combustion behaviors of hydrochars was analyzed by varying from 150 to 300 °C. The mass yield of hydrochars decreased from 72.45% at 150 °C to 41.88% at 300 °C with the increase in temperature, and the higher heating value increased from 19.22 MJ/kg at 150 °C to 29.97 MJ/kg at 300 °C. The H/C and O/C values reduced from 1.30 and 0.66 of HTC150 to 0.77 and 0.27 of HTC300, respectively. Fourier transform infrared spectroscopy analysis indicated that the functional groups of hydrochar have changed because of the dehydration and decarboxylation reaction. The surface structure of hydrochars was rougher, and many pore structures were found at 240-300 °C by scanning electron microscopy analysis. The combustion behaviors of WCOSs and their hydochars are distinct via thermogravimetric analysis, and the stability of hydrochars was strengthened with the increase in HTC temperature.

Synthesis, characterization, and selective dye adsorption by pH- and ion-sensitive polyelectrolyte galactomannan-based hydrogels

Three novel polyelectrolyte galactomannan hydrogels (PGHs) were fabricated by chemically crosslinking quaternary ammonium galactomannan (QAG) and carboxymethyl galactomannan (CMG), and employed for the removal of Congo Red (CR) and Methylene Blue (MB). Physicochemical characterization revealed that the PGHs are chemically and physically crosslinked. The PGHs are pH- and ion-sensitive, and their physical crosslinking can be destroyed by artificial urine; water swelling capacity (100.6-321.9 g/g dry gel) and artificial urine swelling capacity (35.9-80.5 g/g dry gel). The adsorption of CR and MB was studied and found to be pH-dependent and selective. The maximum adsorption capacities of CR and MB on the QAG and CMG gels are 1441 and 94.52 mg/g, respectively, and their adsorption kinetics and isotherm behavior obey the pseudo-second-order kinetics model and Langmuir isotherm model, respectively. The adsorption mechanism is dominated by electrostatic interactions and hydrogen bonding. Further, the PGHs have excellent salt resistance and are reusable.

Zeolitic imidazolate framework-8/graphene oxide/magnetic chitosan nanocomposites for efficient removal of Congo red from aqueous solution

A novel bio-adsorbent toward Congo red with large adsorption capacity.

Effects of temperature, oxygen and steam on pore structure characteristics of coconut husk activated carbon powders prepared by one-step rapid pyrolysis activation process

Activated carbon powders made from coconut husk (CHCs) were prepared by one-step rapid pyrolysis activation process. Effects of temperature, oxygen and steam on the pore structure of CHCs were investigated. Results showed that high temperature, oxygen and steam all motivated the development of the CHCs pore structure. High temperature accelerated the evaporation of volatiles and led to more micropore structures. Oxygen promoted the development of both micropores and mesopores. CHCs' porosity separately presented a linear and a logarithmic growth with the increase of the preparation temperature and oxygen content. CHCs prepared under 1000 ℃ with activation agents of 6% oxygen and 20% steam exhibited the largest specific surface area and total pore volume of 415.85 m²/g and 0.1748 cm³/g. Steam can diffuse into the CHC matrix and enhance the formation of more mesopores. Steam over 20% would over-burn the substance and lead to the collapse of some pore structures.