| Lignocellulose biomasses are green renewable resources with wide varieties and high carbon content.As our global are facing with resource shortage,environmental crisis,studies on biomass high-value transformation are attracting more and more attentions.Thermal chemical treatment is an effective way for biomass converting into high value-added products.Hydrothermal carbonization is a new bio-thermal chemical method that exhibit great future in biomass high-value transformation.Hydrothermal carbonization is a reaction react in closed system,using water as solution,at a mild temperature(130?250 ?)and self-generated pressure,raw materials can form carbon materials via series complex reactions.In this paper,different lignocellulose was chosen as raw material to prepare carbon materials via hydrothermal carbonization,analysis the influence rule of experiment factors on solid carbon,liquid carbon dots,realize controllable preparation on morphology and structure of biomass-based carbon materials,illustrate formation and carbon structure control mechanism.Including:morphology and pore structure controllable preparation and functional modification of bio-based solid products,liquid carbon dots properties study and parameter optimization;finally discuss on solid-liquid products composition and reaction mechanism.In the research,SEM,TEM,XPS,XRD,TGA,N2 adsorption-desorption,and VSM techniques were used to characterize the morphology,structure for those spherical carbon materials and composite materials,ultraviolet and fluorescence spectrophotometer are used to characterize the optical properties for carbon nanodots solid/liquid nuclear magnetic resonance(NMR)were used for structure and mechanism formation discussion.The main work are shown as following:Carbon microspheres rich in oxygen-containing functional groups were synthesized by hydrothermal carbonization of pentosan,which was separated from BHKP as a by-product of pulp refining at 190?210 ?.The spheres show a wide diameter distribution with good dispersion and thermal stability.Increasing the preparation temperature to 210 ? narrowed the size distribution of the spheres to 150-1200 nm.Abundant carbonyl groups on the surface of the spheres promoted anion exchange and complexation,enhancing their ability to adsorb Pb(II)and Cd(II)from aqueous solution.The prepared carbon microspheres exhibited maximum adsorption capacities of 380.1 mg/g and 100.8 mg/g for Pb(II)and Cd(?),respectively.The results revealed that Pb(II)and Cd(II)were chemically adsorbed as multilayers onto the carbon spheres.Novel carbon microspheres with tunable surface morphologies were synthesized from CMC via a soft-template/hydrothermal process.Influences of F127 amount on carbon morphology were discussed.Results showed:the obtained carbon microspheres are transformed from walnut-like,to strawberry-like and cage-like structures when the mass of F127 is increased from 0.5 to 1.0 g.After carbonization,the F127 in the carbon skeleton decomposes,leading to generation of mesopores.Perfect cage-like carbon spheres with a specific surface area of 326.2 m2/g and a cubic mesoporous structure was obtained for CSF1.0,their unique ordered mesoporous structure contributes to the carbon spheres exhibit high adsorption capacity for Vitamin B12 of 103 mg/g?When amount of F127 was 1.0 g,the effect of reaction time on both ordered mesoporous structure formation and structural properties were further investigated in details.When reaction time was 10 h,20 h and 30 h respectively,cooperative assembly of inorganic species with F127 contributed to the formation of mesoporous structures,space groups and pore orientations differed depending on different reaction times.An intermediate liquid crystal phase of rod-like and ball-like micelles can be formed,producing a mesoporous structure that varies from stripe-like hexagonal,mixed hexagonal and cubic,to cubic.The specific surface areas and mesoporous percentages were 326.2-1035.1 m2/g and 29.7-38.2%,respectively,leaving CSFn with a favorable structure and thermal stability.Carbon adsorbents with high specific surface areas and controlled developed micro-pore structures were prepared by hydrothermal carbonization of CMC,followed by KOH activation in N2 atmosphere.Influences of activation ratio and temperature on pore structures were discussed.Mild conditions(CSc-2)led to development of more micropores,especially pores narrower than 1 nm with lower SBET in the range of 1200?1700 m2/g,harsh conditions(CSc-4)generated high surface areas(1750-2300 m2/g)with developed micro-mesoporous structures.The adsorption capacities of these adsorbents depend strongly on their pore structures and surface areas,as well as the adsorption conditions.For samples prepared using the same activation ratio,higher specific surface areas led to higher CO2 capture capacities.However,when samples prepared with different activation ratios are compared,the CO2 capture capacity is dominated by the microporosity,in particular the micropore volume(d=0.4-0.9 nm).For further adjust chemical properties and structure of obtained carbon,Ni and N were selected as doping sources to discuss influences of doping on carbon structures:Ni-doped mesoporous CSs with high adsorption capacity were prepared via the hydrothermal treatment of CMC and nickel acetate,and subsequent carbonization at 800 ?.Crystalline metallic nickel and nickel oxide with hexagonal lattice structures were doped into the carbon matrix upon carbonization.Diameter distribution of Ni was 2-5 nm,the specific surface area of the CSn-800 samples decreased with increasing Ni content while the saturation magnetization strength increased from 4.3 to 11.8,21.6 and 29.2 emu/g.The mesoporous structure enhanced the samples' adsorption capacities.The highest adsorption capacity of 103 mg/g was achieved for CS4-800.Adsorbents could be separated on account of their magnetism.Solid hydrochar and water-soluble nanodots were obtained by one-pot HTC of CMC using urea as nitrogen source.The doping directly influences structure rearrangement,functional groups and thermal properties of obtained solid carbon.Urea can react with carbonyl,and present in the form of amidogen,imido groups,pyridine(N-6),pyrrolic/pyridone(N-5)and quaternary(N-Q)nitrogen after HTC at 210 ?.Activation at higher temperature contributes to generation of pyridine,quaternary nitrogen with graphite-like structure,higher thermal stability and electrical-conductivity.N can increase carrier density around carbon,that influence electronic band structure,increasing electrical conductivity.When amount of N is 0.2 g,the obtained carbon exhibited highest conductivity,reached to 166 S/m,1.8 times that of undoped materials.CNDs were spherical particles with excellent photoluminescence,excitation-dependence and pH-sensitivity abilities.CNDs can act as an effective photosensitizer in photocatalyst system,spectral response range of the CNDs/TiO2 can be expanded to visible light region,nearly 100%of MB degradation under visible irradiation can be achieved.Water-soluble carbon nano dots(CNDt)synthesized at different temperatures were discussed for influences of temperatures on their chemical and optical properties.Increasing reaction temperature from 200 ? to 260 ?,average diameter of obtained nanodots decreased from 20.35 nm to 6.48 nm,while PL efficiency increased from 13.4%to 18.1%,and was accompanied by variation in their ordered lattice structure from an obvious stripe-like hexagonal structure to a cubic structure.An obvious blue shift of the excitation and emission peaks was also observed,which arose from the differences in size and surface properties.Effective degradation of tetracycline hydrochloride(TCH)was achieved under visible-light irradiation.CNDt with smaller size,higher quantum yield and shorter excitation characteristic peak wavelength were found to be more beneficial as a photosensitizer in the CND/TiO2 system.Structural properties for both solid and liquid products as well as the reaction pathway of hydrothermal carbonization of loblolly pine were investigated in details via NMR analysis method.The solid hydro-carbon were condensed polyaromatic and furan structures,with yield of 41.93?48.54%,HHV of 26.52?30.58 MJ/kg and fixed carbon content of 50.43?52.18%.There were oligosaccharides and large amount of carboxyl-based organic acid exist in liquid,and they are value-added chemicals mainly consist of furfural and condensed polyaromatic structure connected via ether groups.It can be derived that at initial reaction stage,hydrolysis,ring-opening and aldol condensation were the main reactions,while aryl-condensation,polymerization and etherification reaction were mainly for last reaction.Further discuss structure properties and vary rules of different carbon products obtained at different temperatures.High temperature can benefit for generation of condensed aromatic structure,the content of aryl-ether,aliphatic ether,also show increase trend with increase of reaction temperature.There are many differences on structure variation between solid and liquid products:Solid products were carbon materials,carbonyl and carboxyl contents are low,methoxy content reduced at higher temperature while aliphatic side-chains content increased;Liquid products were water-soluble products,with high content of carbonyl and carboxyl groups,methoxy content increased at higher temperature while aliphatic side-chains content decreased,.CSP240 exhibit high content for all kinds of phenolic hydroxyl groups,while CSP260 exhibit some ether bond as etherification reaction mainly occured at 260 ?,indicating high reaction temperature can benefit for etherification and substitution reaction. |
PDF Full Text Request