Preparation Of High Adsorption Performance Carbon Nanomaterials Via Catalytic Co-pyrolysis Of Lignin And Polyethylene With The Aid Of Transition Metals

Lignin,a class of natural polymer,extensively exists in black liquor of papermaking and hydrolytic reside of biomass.The annual output of the lignin produced from black liquor and hydrolytic residue is more than 5 million tons in China.Unreasonable disposal techniques have seriously caused waste of resources and environmental pollution.The carbon content of lignin is50%-65%.It is of great significance to transform lignin into high value-added carbon functional nanomaterials for the high-quality utilization and large-scale disposal.Herein,we proposed that hydrogen-rich waste plastic(polyethylene)and low-cost transition metals(Ni,Co,Fe and Mn)were introduced to blend with lignin for catalytic co-pyrolysis for the fabrication of carbon nanoonions.Meanwhile,carbon nanotubes were produced via catalytic reforming the volatiles from the preparation of carbon nanoonions.The as-prepared carbon nanoonions and carbon nanotubes were subsequently employed as adsorbents to treat Cu(?)-contained wastewater including simulated wastewater and industrial effluents.The main research contents and conclusions are as follows:(1)The physico-chemical properties of lignin-based carbon materials obtained at different pyrolysis temperatures(100-1000 ?)were studied.It was found that the amorphous structure,thermal stability,pore structure and oxygen-containing functional groups of the lignin-based carbon materials decreased when the pyrolysis temperature exceeded 400 ?.(2)The preparation of carbon nanoonions via catalytic pyrolysis of the blends of transition metals and polyethylene with lignin were systematically studied.It was found that a mesopores and macropores-rich carbon material can be produced as the introduction of Ni into lignin while the introduction of polyethylene produced a carbon material with abundant micropores and small mesopores.No carbon nanomaterials-like can be found.Interestingly,the introduction of Ni and polyethylene resulted in the production of carbon nanoonion particles with relatively uniform size(with diameters about 30-50 nm).Thremogravimetric analysis,Fourier Transform Infrared spectrum and magnetic strength analysis showed that the carbon materials obtained from catalytic co-pyrolysis of lignin and polyethylene mixture contained 15% carbon nanoonions which were abundant in oxygen-containing surface functional groups,structure defects and possessed strong magnetic properties.Folded greaphene,carbon nanotubes and structured graphene cluster could be obtained when Co,Fe and Mn were employed as catalysts,respectively.The increase of the concentration of Ni and catalytic pyrolysis temperature were favorable for the preparation carbon nanoonions.The growth mechanism analysis revealed that Dissolution-Precipitation mechanism was responsible for the growth of carbon nanoonions.(3)The preparation of carbon nanotubes from catalytic reforming the volatiles of lignin-polyethylene blends were investigated.The results indicated that 600-700 ? was turned out to be the ideal catalytic reforming temperature range for the preparation of carbon nanotubes,and the optimal concentration of the active component in catalyst was 10%.As a result,interconnected,defect-rich,oxygen-containing surface functional groups cone-shaped carbon nanotubes with diameters and lengths of about 18-35 nm and 0.1-1?m,respectively,can be produced.(4)The adsorption performance of lignin based carbon nanomaterials(i.e.,carbon nanoonions and carbon nanotubes)towards Cu(?)-contained wastewater including simulated wastewater and industrial effluents was investigated.The results showed that the carbon nanoonions and carbon nanotubes possessed a favorable adsorption capability towards Cu(?),and the adsorption processes can be well described by Langmuir isotherm model and pseudo-second order kinetic model,indicating that the adsorption of Cu(?)onto carbon nanoonions and carbon nanotubes was mainly dominated by a chemical and homogeneous process.The calculated maximum adsorption capacity of carbon nanoonions and carbon nanotubes towards Cu(?)according to the Langmuir isotherm model was as high as 100.00 and 158.73 mg/g,respectively,which was about 2 folds and 3 folds of that of commercially available activated carbon.After five adsorption-desorption cycles,the removal efficiency of Cu(?)in solution by carbon nanoonions and carbon nanotubes was still close to 90%.The analysis of adsorption mechanism showed that complexation,electrostatic interaction,surface precipitation and C-? cation interaction were involved in the adsorption of Cu(?).