| Biomass-derived porous carbons are widely used in absorption, separation, catalysis and energy storage due to their highly developed porosity, large specific surface area, abundant surface chemistry, and environmentally sustainable sources. Their application performances are mainly influenced by surface area, pore size distribution and surface chemistry, which rely on precursors and preparation process. Choosing suitable biomass precursor and preparation method is significant to control the physicochemical properties of products, as well as to build structure-activity relationships. In the present study, four types of porous carbons with various characteristics are prepared from hemp stem and pigskin collagen through different processes. Effects of experimental conditions on porous structure and surface chemistry, and further the structure-performance relationship are investigated.First of all, crosslinked cellulose spheres are synthesized by crosslinking cellulose extracted from hemp stems with HDI, and the carbon from these spheres can not keep spherical shape as a result of the structure collapse during carbonization. Instead, carbonaceous spheres are successfully prepared by dilute acid catalyzing hydrothermal carbonization of alkali-extracted hemicellulose from hemp stems, and well-shaped porous carbon spheres with large surface area of up to 3062 m2/g are obtained after pre-carbonization and KOH activation. Influences of acid species, concentrations, hydrothermal temperatures and times on the yield, morphology and chemical composition of carbonaceous spheres, and effects of KOH/carbon ratio on porous structure and surface chemistry of activated carbon spheres are studied by using SEM, FTIR, XRD, N2 adsorption-desorption and etc. It can be found that a relatively low hydrothermal temperature is needed in the presence of dilute acid, and carbonaceous spheres from dilute sulphuric acid catalysis possess higher yield and better morphology. Increasing the concentration of sulphuric acid, hydrothermal temperature and time leads to higher yield, better morphology, more carbon and less oxygen content in products. Pre-carbonization strategy can effectively avoids morphology destruction resulting from KOH activation. The oxygen content, surface area, total pore volume, micropore volume and mesopore volume of porous carbon spheres all increase with KOH/carbon ratio increasing. The porous carbon spheres show the highest specific capacitance of 318 and 255 F/g in three-electrode and symmetrical electrode system with 6 M KOH as electrolyte, respectively, and exhibit good rate capability and cycling stability, contributed from double layer capacitance on large surface, faradaic pseudocapacitance induced by rich oxygen groups and appropriate pore size distribution. The plentiful micropores also result in good CO2 and CH4 adsorption performance of carbon spheres at O ℃ and ambient pressure.Secondly, biomass-based mesoporous carbon with mesopore percentage of 76% and surface area of 828 m2/g is synthesized by assembly of hemp stem hemicellulose and silica species. Influences of raw material dosage on the morphology and porous structure of products are investigated by using SEM, N2 adsorption-desorption and etc. The results indicate that the carbon morphology changes from spherical particles to irregular blocks with a foam texture with the amount of hemp stem hemicellulose increasing. The specific surface area, total pore volume, mesopore volume and average pore size of products first increase and then decrease with the amount of hemicellulose increasing, while the micropore volume keeps decreasing. When used as electrode material in supercapacitors, the as-prepared mesoporous carbon shows a lower capacitance fading and better rate capability owing to its lower ion transfer resistance caused by more abundant mesopores.This thesis also develops a novel in situ carbonization reduction method using hemp stem as the carbon precursor and ferrisulfas as the iron source to prepared FeS/Fe nano particles loaded porous carbon. Effects of carbonization temperature and ferrisulfas dosage on the phase composition and porous structure are studied by using HRTEM, XRD, XPS, N2 adsorption-desorption and etc. The Cr(VI) removal performance of as-prepared materials at different pH values and Cr(VI) removal mechanism are further discussed. The results indicate that under the reductive atmosphere generated from hemp stem carbonization, ferrisulphas can be in situ directly decomposed and reduced into FeS/Fe at 800 ℃ existing in the form of nanoparticles embedded in a carbon matrix, and temperature is the main factor affecting the phase composition. Increasing temperature will develop the porosity, and increasing ferrisulfas dosage will enlarge the pores but meanwhile reduce the surface area and total pore volume. A lower pH can enhance Cr(VI) removal capacity but give rise to release more Fe into water. A pH value at around 4-5 is optimal to realize the best application performance of C/FeS/Fe. The synergy between surface adsorption and FeS/Fe reduction makes the FeS/Fe loaded porous carbon exhibit a maximum Cr(VI) removal capacity of 127 mg/g at pH 5.In the last part, a N-doped porous carbon is prepare by the carbonization and KOH-activation of collagen-rich biomass resource pigskin. Influences of carbonization and activation temperatures and KOH/carbon ratio on the surface chemistry and porous structure are systematically investigated by using XPS, elemental analysis, N2 adsorption-desorption and etc. It is found that the N and O content of products decrease with the increasing carbonization and activation temperature, but the effect of carbonization temperature is relatively weak. N content decreases and O content increases with the increase of KOH/carbon ratio. N content is most severely affected by activation temperature. The specific surface area, total pore volume, average pore size, mesopore volume and micropore volume all show an increasing trend firstly and then a decreasing one with the increase of KOH/carbon ratio. However, when activation temperature increases, the surface area and total pore volume first increase and then decrease, the average pore size and mesopore volume gradually increase, and the micropore volume continuously decreases. Porous structure is most significantly affected by KOH/carbon ratio. Low-temperature activation of pigskin collagen with high KOH/carbon ratio will make for a porous carbon with high N and O content and large surface area. The sample activated with KOH/carbon ratio of 4.5:1 at 600 ℃ has relatively high N and O content of 3.77 wt.% and 12.28 at.%, respectively, and a specific surface area of 2209 m2/g. The sample activated with KOH/carbon ratio of 4.5:1 at 800 ℃ possesses the highest specific surface area of 3465 m2/g but low N content of less than 1 wt.%. The former sample shows a very high specific capacitance of 547 F/g and excellent high rate performance with a specific capacitance of 224 F/g at 50 A/g current density due to its most micropores, appropriate mesopores and high N and O content. It is also found that high N content can enhance H2 adsorption on porous carbon at low pressure, while the adsorption capacity is eventually restricted by surface area and pore structure. A high specific surface area and more pores less than 3 nm is beneficial to H2 adsorption. N-containing functionalities can also enhance CO2 adsorption, and micropores less than 1 nm determine the adsorption capacity. CH4 adsorption on as-prepared porous carbons depends on narrow micropore content, and the sample activated with KOH/carbon ratio of 4.5:1 at 600 ℃ shows a better CO2/CH4 adsorption selectivity. |
