Microwave Radiation Preparation Of Tobacco Stems Wood Ceramics And Its Application

With more and more concerns on the environmental protection, developing resource utilization ratio and enviromental-friendly materials, which have no side effect on environment and have great properties, has been a focusing subject in material science. Woodceramics is a new kind of ecomaterials being developed in recent years, which has many excellent performances such as good electrical, friction and wear resistance, corrosion resistance, high strength, lightweight, porousness, electromagnetic shielding ability and so on. Therefore, it has great potential application in many industries. However, there are many problems exsiting in the preparation process reported, such as using wood as raw materials, preparation time longer and energy consumption costly. So the development and expanding application fields of woodceramics have been obstructed.In order to solve above mentioned problems, a novel technology for preparing woodceramics has been put forward. Tobacco stems as raw materials were carbonized at a lower temperature, then milled and mechanically sieved to obtain 150μm tobacco stem carbon powders, and then mixed with phenolic resin. To mold to be samples with a certain dimension at a certain pressure and solidified to obtain tobacco stem carbon/phenolic resin composites. The composite was put into the carbonizing furnace and sintered in the atmosphere of nitrogen. After that, put the sample into the microwave furnace chamber in the atmosphere of nitrogen instantly to heat, then cooled with furnace naturally to the room temperature to get the woodceramics samples. The effects of the mass fraction of phenolic resin, microwave irradiation time and power on the woodceramics properites were investigated systemically. The evolution of microstructure of woodceramics were performed by X-ray diffraction, Raman spectroscopy and Scanning Electron Microscopy in order to elucidate the changing reasons of the properties of the sample. Furthermore, woodceramics have been used successfully for the removal of heavy metals in wastewater for the first time. The thermodynamics, kinetics and the mechanism of adsorption were studied and analyzed.In the present study, the effects of microwave irradiation power and time and the mass fraction of phenolic resin on the properties including the mass loss ratio, volume shrinkage ratio, apparent density, open porosity and volume electrical resistivity of the woodceramics were investigated. The experiments showed that the preparation time by microwave irradiation is 0.6% compared to that of the conventional processing. The experimenta results showed that the mass loss ratio, volume shrinkage ratio and apparent density increased, while the volume electrical resistivity and open porosity decreased with increasing microwave irradiation time. The apparent density increased, while the mass loss ratio, volume shrinkage ratio, volume electrical resistivity and open porosity decreased with increasing the mass fraction of phenolic resin. The mass loss ratio, volume shrinkage ratio and open porosity increased, while apparent density and volume electrical resistivity decreased with increasing the microwave power.The structures of a series of woodceramics prepared under different conditions were studied by the XRD, the Laser Raman spectroscopy and SEM. The result of the XRD analysis showed that woodceramics was a kind of non-graphitic carbon materials. With increasing the microwave irradiation time, the mass fraction of phenolic resin and microwave irradiation power, the interlayer spacing of graphene sheets in microcrystal of woodceramics, d₀₀₂ was decreasing, but the dimension of the crystallites, L_c and L_a, were increasing. Laser Raman spectra showed that line-D and line-G appeared at 1360cm^-1 and 1580cm^-1, respectively and didn't appear the line for the diamond at 1332cm^-1, indicating the woodceramics was a C/C composite material like the graphite. It can be found from the photo of SEM that the woodceramics was a new porous carbon hybrid material and made up of glass-like carbon generated from phenolic resin and amorphous carbon derived from tobacco stems. The prolonging time of microwave irradiation made more and more extent of phenol resin changing into hard glassy carbon, and more ordered structure of the woodceramics.A systematic study was carried out for the disposal of wastewater containing lead ion by woodceramics prepared with the ratio of phenolic resin of 50%, the microwave irradiation time of 80s and power of 800W. Adsorption of Pb(II) ions from aqueous solution onto woodceramics has been investigated to evaluate the effects of initial lead ion concentration, adsorbent dosage, contact time, pH and temperature on the removal of Pb(II) systematically and obtained the optimal process parameters. Thermodynamic parameters such as standard Gibbs free energy (ΔG⁰), standard enthalpy (ΔH⁰), and standard entropy (ΔS⁰) were evaluated by applying the Van't Hoff equation, which describes the dependence of equilibrium constant on temperature and the equilibrium data at different temperatures were analyzed using Langmuir and Freundlich isotherms. The calculated Langmuir adsorption capacity of lead ion was 6.5518 mg/g. The experimental results were analyzed by pseudo-second-order kinetics model of solid-liquid phase, obtaining the initial sorption rate and rate constants. It was found that the sorption kinetics fit the pseudo-second-order kinetics model well. It was shown from the adsorption mechanism analyses and investigations of the controlling step of adsorption that the adsorptions of heavy metals onto woodceramics were all film diffusion controlling processes.Generally, a novel process of preparing woodceramics by microwave irradiation was put forward successfully and high-quality woodceramics samples from carbonzied tobacco stems and phenol resin were obtained using microwave irradiation, which may replace conventional heating method. Furthermore, woodceramics has been used for the removal of Pb ions in the wastewater for the first time. Above-mentioned process could make use of agricultural and forestry wastes effectively, reduce the cost of production and the energy consumption, and shorten the processing time of woodceramics prepared. Furthermore, the prepared woodceramics provided a new path for the treatment of the wastewater containing heavy metals. The research results might provide the pilot-scale production and application of woodceramics with theory basis.