| Biochar is a carbon-rich solid product prepared from biomass under oxygen-limited conditions.It has great potential in energy production,relieving climate change,improving soil carbon fixation,increasing soil fertility and soil remediation.In this dissertation,the structural properties,applications and their relationships were summarized with special focus on applications in four different areas:climate,carbon sequestration;agriculture,fertilizers;environment,sorbents;and materials,functionalization.Therefore,we suggested that the biochar structures should be interpreted from element,to phases,to surface and to molecules.And the quantitative structure-applications need to be built gradually,especially considering that sorbates and sorbents both have great effect in biochars sorption system.Thus,a series of studies were conducted in the light of the singleness on biochar elements study(mostly carbon),the unclarity on the variation mechanisms of surface functional groups,the unknown molecular structures,the insufficiency on quantitative structure-application relationships,the complicated sorption behavior of different organic pollutants within natural samples and the unclear high sorption-performance biochars structure design and sorption mechanisms.Biochars under different pyrolysis temperatures were obtained from rice straw and pine needle,via dissolving experiments,Fourier transform infrared spectroscopy(FT-IR),X-ray diffraction(XRD),and scanning electron microscope with energy dispersive spectroscopy attached(SEM+EDX),the dissolution characters,morphologies and species of carbon and silicon within rice straw derived biochars were explored.The titration experiments were applied to monitor the surface functional groups variation mechanisms.To obtain in-situ aromatic cluster observation,solvents dispersion,mineral removal treatment,and HR-TEM were used.The quantitative structure-sorption relationships were developed based on H/C atomic ratio by selecting naphthalene(NAPH)and phenanthrene(PHE)as the typical organic pollutants.By choosing a natural groundwater with a series of new emerging contaminants(poly-and per-fluoroalkyl substances,PFASs)as the sorbates,we analyzed the effects of sorbates structures on their sorption kinetics.A water-stable and graphene-like biochar material was successfully synthetized by co-graphitization and activation,its sorption ability and mechanism towards organic pollutants was further discussed.These results are of great significance for the future biochar design and precise applications.The main innovation points are listed as follows:(1)The species,morphologies and dissolution of carbon and silicon within rice straw derived biochars under different pyrolysis temperatures was investigated as well as the surface functional groups variation mechanisms and the mineral effects on surface functional groups.Specially,under increasing pyrolysis temperatures,we found that the silicon species transformed from amorphous to crystal;while the carbon species transformed from aliphatic to aromatic carbon.Considering the special C-Si-C layered structure,the SEM+EDX results clearly indicated that the C-Si relationship was shifted from carbon protects silicon under low pyrolysis temperature to silicon protects carbon under high pyrolysis temperature.The methods to evaluate the surface functional groups and buffering ability of biochars were developed based on proton uptake curves.We found that the buffering range of biochars remarkable narrowed down after mineral removal.And aromatization increased phenolic hydroxyl percentages and the amount of total functional groups.(2)The atomic aromatic cluster structures of high pyrolysis temperature derived rice straw derived biochars(mineral removed)was firstly reported,a gaussian model to describe the distribution of different size aromatic clusters was proposed and a quaternary structural model of biochars was further developed,including heterogeneous phase,graphene-like aggregates,aromatic clusters,and atomic arrangement.Combine solvents dispersion and HR-TEM,the nanocrystals,graphite bulk and carbon black dots were observed.And the calculated size of the black carbon dots for DRS500 and DRS700(de-ashing from RS500 and RS700,respectively)was about 1.97 nm and 2.56 nm,respectively.(3)The quantitative relationships based on H/C atomic ratio to predict the pyrolysis temperatures,aromatic cluster structures,and the sorption ability to NAPH and PHE were built,which will greatly benefit the global biochars from different precursors comparable.Results show that pyrolysis temperature was the key factors to H/C atomic ratio,while the precursors and treatment methods have little effect on H/C atomic ratio.Moreover,the consistence between the H/C based rectangle-like polycyclic aromatic cluster model prediction and TEM observation of DRS500 and DRS700 provided a strong proof that the aromatic clusters existed in high-pyrolysis temperature derived biochars.(4)A water-stable and graphene-like biochar material(FZS900)was successfully synthetized and its ultra-high sorption ability and mechanisms towards aromatic pollutants was further illustrated.Results show that the surface area of FZS900 is 2280m2 g-1,close to the theoretical surface area of single graphene.The sorption ability for naphthalene,phenanthrene,and 1-naphthol were 615.8,413.2 and 2040 mg g-1,respectively,which are the highest sorption amount for these pollutants ever reported.TEM images indicated that the nonpolar aromatic organic pollutants could induce the spherical turbostratic nanosheets into 2-11 layered nanoloops,while polar organic pollutants will induce the graphene nanosheet to be more dispersed or more aggregated.Therefore,we proposed a new sorption mechanism which is the nano size effect induced co-assembly sorption. |
PDF Full Text Request