The Preparation And Adsorption Study Of Nitrogen-doped Mesoporous Carbon Material Synthesis

Mesoporous carbon（MC） materials show good performance in the fields of dye and heavy metal ions adsorption due to its outstanding properties such as high specific surface area, large pore volume, adjustable pore structure and uniform pore size. However, MC lack of active sites and render hydrophobicity, which limit its adsorption applications, and nitrogen-doped mesoporous carbon material can reforme surface defects and improve the adsorption properties. In this paper, two nitrogen-containing mesoporous carbon with different nitrogen content and structure were prepared using two different benzoxazine as precursor and two kinds of mesoporous Si O₂ as hard templates. What’s more, adsorption performance of methyl orange dye and heavy metal ions Cu（Ⅱ）, Pb（Ⅱ）, Cd（Ⅱ） and Ni（Ⅱ） from aqueous solution on two kinds of material was studied..Using ionic liquid [C12mim]Br as soft template, with water and ethanol as co-solvent, TEOS as precursor, mesoporous silica spheres were prepared in alkaline conditions. Using scanning electron microscopy（SEM）and N2 adsorption/desorption as characterization methods, the factors of influence on morphology and structure of samples containing the ethanol/water volume ratio temperature, ammonia water concentration and concentrations of [C12mim]Br were investigated, and ordered mesoporous Si O₂ can be obtained with adjustable particle size（350 nm-667 nm）,narrow pore size distribution（2.0 nm）, and high specific surface area（312-1016 m2/g）.Mesoporous Si O₂ materials with similar pore structure and increased pore size were prepared using ionic liquid [C8mim]Br, [C16mim]Br and [C18mim]Br as template,respectively. According to the applications of composite mesoporous carbon material mesoporous Si O₂-12 and Si O₂-16 were selected to synthesis different nitrogen-containing mesoporous carbon for the adsorption of methyl orange and heavy metals ions.Using mesoporous Si O₂-16 spheres as hard templates, benzoxazine BOZ-DETA and phenolic resin as precursor, nitrogen-doped mesoporous carbon spheresNMCS-DETA and mesoporous carbon spheres MCS were prepared by a liquid impregnation route. The NMCS-DETA and MCS were characterized by SEM,transmission electron microscopy（TEM）, N2 adsorption/desorption, XRD, elemental analysis, energy dispersive spectrometry（EDS） and FT-IR. The results show that NMCS-DETA and MCS are amorphous spherical nanoparticles with worm-like mesoporous channels, particle size of 244 nm and 345 nm, pore diameter of 3.5 nm and 3.7 nm, specific surface area of 789 m2/g and 953 m2/g, pore volume of 0.49cm3/g and 0.66 cm3/g, respectively. The nitrogen content of NMCS-DETA is3.50%（wt）, and mainly in the form of C-N. The maximum adsorption capacity of MO adsorption on as-prepared NMCS-DETA and MCS was 352.1 mg/g and 251.9 mg/g,respectively. Experimentally obtained two materials as methyl orange（MO） dye adsorbent, maximum adsorption capacity was 352.1 mg/g and 251.9 mg/g.NMCS-DETA isotherm data MO of the Langmuir adsorption model. MO adsorption on NMCS-DETA was well fitted with the Langmuir adsorption isothermal. The thermodynamic parameters indicated MO adsorption was a spontaneous, endothermic feasible and entropy effect process. MO adsorption kinetics was found to follow the pseudo-second-order kinetic model, and rate-controlling step of adsorption was determined simultaneously by external mass transfer and intra-particle diffusion.Moreover, after four adsorption-desorption cycles, the adsorption capacity of NMCS-DETA can reach 89.04% of raw materials, exhibiting good recycling capability. MO adsorption should be mainly controlled by π = π and electrostatic attraction mechanism.Nitrogen-doped mesoporous carbon spheres NMCS-PEA were prepared by a hard template method using mesoporous Si O₂-12 as hard template and benzoxazine resins BOZ-PEA as precursor of nitrogen and carbon. The NMCS were characterized by SEM, N2 adsorption/desorption, XRD, elemental analysis and FT-IR. The results show that NMCS-PEA are spherical and the surface area, particle size, most probable aperture, pore volume and nitrogen contents is 845 m2/g, 470 nm, 2.06 nm, 0.40cm3/g and 2.32%（wt）, respectively. The form of N elements is C-N and C-H. The static adsorption studies of heavy metal ions Cu（Ⅱ）, Pb（Ⅱ）, Cd（Ⅱ） and Ni（Ⅱ） on NMCS-PEA showed that Pb（Ⅱ） and Ni（Ⅱ） adsorption on NMCS-PEA were wellfitted with the Langmuir adsorption isothermal, Cd（Ⅱ） and Cu（Ⅱ） adsorption were well fitted with the Freundlich adsorption isothermal, the maximum adsorption capacity of Pb（Ⅱ）, Ni（Ⅱ）, Cd（Ⅱ） and Cu（Ⅱ） was 217.7 mg/g, 82.2 mg/g, 525.7mg/g and 185.2 mg/g, respectively. The thermodynamic study indicated heavy metal ions Pb（Ⅱ）, Ni（Ⅱ）, Cd（Ⅱ） and Cu（Ⅱ） adsorption on NMCS-PEA were spontaneous,exothermic, entropy increase and enthalpy effect process.