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•Typical porous materials for VOCs adsorption were carefully overviewed.•Adsorption mechanism was intensively discussed between adsorbate and adsorbent.•Different modification ...technologies were introduced for enhancing VOCs adsorption.
Volatile organic compounds (VOCs) have attracted world-wide attention regarding their serious hazards on ecological environment and human health. Industrial processes such as fossil fuel combustion, petrochemicals, painting, coatings, pesticides, plastics, contributed to the large proportion of anthropogenic VOCs emission. Destructive methods (catalysis oxidation and biofiltration) and recovery methods (absorption, adsorption, condensation and membrane separation) have been developed for VOCs removal. Adsorption is established as one of the most promising strategies for VOCs abatement thanks to its characteristics of cost-effectiveness, simplicity and low energy consumption. The prominent progress in VOCs adsorption by different kinds of porous materials (such as carbon-based materials, oxygen-contained materials, organic polymers and composites is carefully summarized in this work, concerning the mechanism of adsorbate-adsorbent interactions, modification methods for the mentioned porous materials, and enhancement of VOCs adsorption capacity. This overview is to provide a comprehensive understanding of VOCs adsorption mechanisms and up-to-date progress of modification technologies for different porous materials.
The structural characteristics of softwood (Chinese fir) lignin and hardwood (Maple) lignin prepared by Klason method were identified by elemental analysis and Fourier transform infrared (FTIR) ...spectrometry, and the pyrolytic behaviors of lignin were examined by means of thermogravimetric-Fourier transform infrared spectrometry (TG-FTIR) and Pyrolylisis-gas chromatography/mass spectrometry (Py-GC/MS). It was found that maple (hardwood) lignin contained more methoxyl groups than Chinese fir (softwood) lignin due to the enrichment of syringol units, presenting the chemical formula as C4.64H4.017O2.482 against C4.939H5.255O2.219 for Chinese fir lignin. The amounts of phenolics, methanol and CH4 evolved from pyrolysis of maple lignin were all remarkably larger than that of Chinese fir lignin through TG-FTIR analysis. For both two lignins, aromatic compounds (such as benzene, toluene and xylene) were predominantly released between 650 °C and 800 °C, due to the intensive cleavage of aryl-O-R linkages and dehydroxylation reaction on benzene-ring. The distribution of produced volatiles during lignin fast pyrolysis against furnace temperature was intensively discussed, finding that the cleavage of typical inter-unit linkages under relatively low temperature produced the guaiacol-type and syringol-type compounds, whereas the elevated temperature facilitated the cracking of methoxyl group, giving rise to the notable increase of phenol-type, catechol-type compounds and aromatic hydrocarbons.
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•Methane production were improved with addition of biochar, magnetic biochar and Fe3O4.•The cumulative methane yield was increased by 60.47% with 5 g/kg of Fe3O4.•The direct ...interspecies electron transfer (DIET) was enhanced by Fe3O4.•The strategy of recycling Fe3O4 additive has the best economic benefit.
The co-digestion of corn straw and sewage sludge with different additives (biochar, magnetic biochar, Fe3O4) were investigated. The highest cumulative methane yield of 245.15 mL/g VSadded was obtained with the Fe3O4 addition ratio of 5 g/kg, which was 60.47% higher than that of the control run (without additives). The lag phase time was shortened from 5.46 to 3.82 days with a biochar dosage of 5 g/kg. The performance of Fe3O4 on methane production from the co-digestion process was better than that of the biochar and magnetic biochar. The direct interspecies electron transfer (DIET) was enhanced with regard to the increased concentration of acetic acid and decreased concentration of propionic acid. Microbial community analysis showed that the Geobacter and Methanosarcina were selectively enriched on the surface of Fe3O4, promoting the DIET and acetoclastic methanogenesis pathway. The cost-benefit analysis proved that the strategy of recycling Fe3O4 additive has the best economic benefit.
Biomass charcoal is dominantly made from lignin. It is necessary to study lignin carbonization process to improve the quality of biomass charcoal. A Thermo-Gravimetric Analyzer coupled with a Fourier ...Transform Infrared Spectrometry (TG-FTIR) was applied to investigate the kinetics of lignin carbonization. Three mass loss stages (drying, pyrolysis and carbonization) were observed below 900°C and another stage (structural rearrangement stage) with a slight mass loss was noticed between 900 and 1200°C. Charcoal obtained at different temperatures was analyzed by FTIR to track the variation of functional groups. The pyrolysis of lignin started at 200°C and charcoal was initially formed till 500°C together with the intensive evolution of volatiles including various phenyl compounds. Amorphous carbon was formed between 500 and 900°C, while most benzene rings structures were transformed into aromatic structures with emission of CO. When the temperature increased from 900°C to 1400°C, most CC bonds were cleaved and a new charcoal structure, between amorphous carbon and graphite structures, was probably formed. The activation energies of the above three stages were estimated to be 54kJ/mol, 70kJ/mol and 178kJ/mol.
► Pyrolysis, amorphous carbon forming and structure reforming are important stages. ► Amorphous carbon formed at 500~900°C as benzene rings became aromatic structure. ► A structure between amorphous carbon and graphite appeared at 900~1400°C. ► Most CC bonds broke when the temperature increased from 900 to 1400°C.
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•Biomass derived carbon material is a potential electrocatalyst for hydrogen evolution.•Metal-involved modification significantly enhanced the electrocatalytic activity of ...biomass-based carbon.•The challenges and future development of biomass-derived carbon applicated in hydrogen evolution are addressed.
Hydrogen evolution reaction (HER) involving electrocatalytic process is established as a promising and non-pollution method for hydrogen production. The cheap alternatives of precious-metal electrocatalysts with high activity and robust stability is essential for the high-scale application of electrocatalytic hydrogen evolution. Recently, carbon-based electrocatalysts derived from biomass have attracted more and more attentions with thanks to their characteristics as low-cost, renewable, abundantly distributed and environmentally friendly. In this work, the original carbon material derived from biomass and the one doped with N and/or S as HER electrocatalysts are intensively overviewed regarding to the electrochemical performance and hydrogen yield. The overpotential at 10 mA cm−2 (η10) is generally greater than 100 mV, which is far inferior to Pt-based catalysts. Consequently, biomass-based carbon materials decorated by transition metal and/or trace amount precious metal were introduced for improving the HER performance. The synergistic effect between metals and heteroatoms can significantly enhance the electrocatalytic activity, and the smallest value of η10 is 10 mV. The limitations and challenges in this area were also addressed as (1) the in-depth investigation of conversion and electrocatalytic mechanism, (2) metal modification via in-situ growth, (3) the reproducibility for biomass transformation, and (4) the catalyst assembly with renewable energy equipment.
Pyrolysis is estimated to be one of the most promising methods to convert biomass to diverse products (such as
syn
-gas, liquid fuel and charcoal), while its application has the potential for ...alleviating the fossil fuel crisis and environmental deterioration. Cellulose, a linear homopolymer of glucopyranose residues linked by
β
-1, 4-glycosidic bonds, is the most principal component in biomass (accounting for more than 50% by weight). The research on the pyrolytic behavior of cellulose is particularly beneficial for achieving a better understanding of the pyrolytic behavior of biomass, also promoting its direct applications in terms of fuels, chemicals and bio-materials. The studies on pyrolysis of cellulose are extensively reported in the categories of the following four issues: (1) the physico-chemical properties of cellulose in lignocellulosic biomass; (2) the on-line pyrolysis study of cellulose; (3) the off-line pyrolysis study of cellulose; (4) the interactions with other chemical components under pyrolytic conditions. The information on pyrolysis of cellulose concerning the configuration of cellulose in biomass, the mass loss along with the evolution of volatiles against temperature, the yield of products, the proposed chemical pathways for cellulose decomposition and secondary cracking of the fragments would be vigorously discussed as well as the way-forward in this field, with thanks to the valuable contributions from the leading global researchers and their groups.
The information concerning the configuration of cellulose in biomass, on-line pyrolysis and off-line pyrolysis of cellulose is extensively introduced, with thanks to the outstanding contributions from global leading research groups.
► Structural characteristics of lignin were identified by FTIR, 1H and 13C NMR. ► Evolved volatiles corresponding to main mass loss stages were analyzed by TG-FTIR. ► A global kinetic model provids ...activation energies for BEL and AL.
Structural characteristics of benzene–ethanol-extracted lignin (BEL) and acetone-extracted lignin (AL) precipitated from black liquor were identified by elemental analysis, FTIR, 13C NMR, and 1H NMR, while the thermal behaviors were examined with thermogravimetric-Fourier transform infrared spectroscopy (TG-FTIR). The frequency of β-O-4 bonds per 100 C9 monomeric units was 28 and 17 for BEL and AL. Two-stage pyrolysis processes were observed for the two lignins. The mass loss rate of the initial solvent evolution stage (110–180°C) of BEL was greater than that of AL. The two lignins presented slightly different mass loss curves and evolution profiles of gases in the main pyrolysis stage (280–500°C). A global kinetic model was proposed for lignin pyrolysis and activation energies of 39.5 and 38.8kJ/mol was obtained for BEL and AL. The results enhance understanding of lignin pyrolysis and facilitate commercial utilization of black-liquor lignin.
The transformation of lignin with natural aromatic structure into value-added carbon dots (CDs) achieves a win-win situation for low-cost production of novel nanomaterials and reasonable disposal of ...biomass waste. However, it remains challenging to produce multi-emission CDs from biomass for advanced applications. Herein, a green and facile approach to preparing multi-emission CDs from alkali lignin via N and B co-doping is developed. The obtained N and B co-doped CDs (NB-CDs) show multi-emission fluorescence centers at 346, 428 and 514 nm under different excitations. As the doping amount of N and B increases, the fluorescence emission band gradually shifts to 428 and 514 nm, while that at 346 nm decreases. The fluorescence mechanism is explored through the research of the structure, composition and optical performance of NB-CDs in combination with density functional theory (DFT) calculations. It demonstrates that the effect of doping with B-containing functional groups on the fluorescence emission behavior is multivariate, which may be the crucial contribution to the unique multi-emission fluorescence of CDs. The multi-emission NB-CDs with prominent stability are applied for multilevel anti-counterfeiting printing. It provides a promising direction for the sustainable and advanced application of biomass-derived CDs, and the theoretical results highlight a new insight into the deep understanding of the multi-emission fluorescence mechanism.
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