Controlled Preparation Of Porous Carbon-Based Materials And Study On Behavior And Mechanism Of High-Efficiency Antibiotic Separation

Porous carbon materials, as a class of porous material consist of carbon skeleton,have been widely studied by researchers, because of their excellent properties, such as a large specific surface area, developed pore structure, high chemical stability(acid resistance), high mechanical properties and adjustable pore structure and size.The porous carbon materials were widely used in environmental remediation, gas storage and capture, energy storage and conversion as well as catalyst carrier etc. In recent years, antibiotics have been recognized as a new pollution because of their have high biological activity, persistence and bio-accumulation, which can cause serious impacts to human health and ecosystems. Porous carbon materials as the adsorbents used for antibiotics pollution treatment is one of the best choices, but large-scale preparation and application are still limited by the following points: low adsorption performance, in order to improve adsorption capacity and adsorption rate;high cost and difficult recycle; adsorption separation mechanism research is not thorough enough, no in-depth analysis of structure-activity relationship between pore structure and surface chemistry characteristics and adsorption properties.This paper focused on the increasingly serious problem of antibiotic pollutions currently and controlled preparation of a class porous carbon materials using natural biomass, industrial lignin and organic carboxylic acid potassium as carbon precursor by alkali activated method, self-template method, colloidal crystal template method and direct carbonization method. The as-prepared materials were used for highly efficient separation of antibiotics. The physical and chemical properties including the pore structure, morphology and surface properties, stability, magnetism of materials were characterized by scanning electron microscope(SEM), transmission electron microscope(TEM), specific surface analyzer(BET), Raman spectrum analyzer(Raman), X-ray diffraction(XRD), Fourier infrared spectrometer(FT-IR), X-ray photoelectron spectroscopy(XPS), thermogravimetric analysis/differential thermal analyzer(TG/DSC), contact angle analyzer instruments. The separation behavior and mechanism of typical antibiotics in the process were studied systematically. And then build a system of porous carbon materials suitable for antibiotics efficient separation.The main study results of this thesis are as follows:1. Controlled preparation and performance study of biomass-based hierarchical porous carbon materials for highly efficient separation of antibiotics(1) Based on two aspects of low cost and high performance and inspired by upside-down wicker branch, in this experiment wicker-based hierarchically porous carbon(WBHPC) was prepared using wicker as carbon precursor via a two-step carbonization and KOH activation method. The composition, morphology, pore structure and crystallization properties of WBHPC were systematically characterized by SEM, TEM, BET, XRD, Raman, XPS and FT-IR. The properties of WBHPC were controlled by adjusting the activation temperature and the mass ratio of KOH and wicker-based carbon(WBC). And the results indicated the optimal preparation condition was the mass ratio of 4:1(KOH: WBC) and temperature of 850 o C. The porosity analysis results indicated the WBHPC-850-4 with ultrahigh BET surface area(3342 cm2 g-1) and large pore volume(1.912 cm3 g-1), suggesting the existence of the long-range macropore channel of wicker, micropores and mesoporous form the hierarchical structure. WBHPC-850-4 displayed the excellent adsorption properties:ultrahigh adsorption capacity(the saturated adsorption amount of 1292 mg g-1 at 298K) and fast adsorption rate. Pseudo-second-order kinetic model and Langmuir isotherm model were well-fitted to describe the adsorption process. Thermodynamic analysis results showed that the process was spontaneous, endothermic and the physical adsorption was main adsorption process. It was found that it had a good linear relationship between adsorption capacity and pore structure parameters(specific surface area, micropore surface area, pore volume and micropore volume).In addition, micropore filling was main adsorption mechanism, but also involved in Waals force, π-π EDA and electrostatic interaction.(2) Taking the enhancement of adsorption rate for antibiotic as starting point, the paper towel-based hierarchically porous carbon(PTHPC) was prepared using paper towels as the carbon precursor via a carbonization and KOH activation two-step method. The paper towel is rich in loose porous structure, which is conducive to the full activation and the content of KOH played an important role. PTHPC-4 presented fold layered short fiber structure and enriched in micro-mesoporous with the specific surface area of 3524 m2 g-1 and pore volume of 1.839 cm3 g-1. The equilibrium adsorption capacity of TC onto PTHPC-4 reached 1130, 1537 and 1648 mg g-1 at 298,308 and 318 K, respectively, which was much higher than adsorption property previously reported. More importantly, PTHPC-4 had an ultrafast adsorption rate for TC: when the TC initial concentration(Co) was 100 and 150 mg L-1, the adsorption could reach equilibrium within 5.0 and 10 min at 298 K, respectively. When Co=100mg L-1, the pseudo-second-order kinetic constants k2 values of PTHPC-4 for TC at298, 308 and 318 K were 1.055×10-2, 5.731×10-2 and 8.916×10-2 g mg-1 min-1,respectively, which were higher 1-3 magnitude than those adsorbents previously reported. The ultrafast kinetics property was caused by the synergistic effect of high specific surface area, pore volume, fold layered structure and good water wettability(water contact angle of 84.2o). In addition, PTHPC-4 has excellent regeneration performance, and provides ideas for the resource utilization of waste paper products.2. Controlled preparation and performance study of industrial lignin-based hierarchical porous carbons for highly efficient separation of antibiotics(1) Inspired by the heuristics of inorganic salt template method and alkali activation, lignin-based hierarchical porous carbon materials(LHPC) was prepared from industrial lignin(SLS) using KOH as inorganic templates and activation agent.LHPC-3 showed a well sheet-like morphology and KOH template activation produced a rich hierarchical pore structure, with SBET of 2235 m2 g-1, micropore area of 1831 m2 g-1 and VP value of 1.512 cm3 g-1, respectively. Static adsorption experiment of sulfamethazine(SMZ) onto LHPC-3 was carried out and LHPC-3showed the largest single molecule layer adsorption capacity Qm of 854.7 mg g-1 at the optimum temperature of 288 K. The van der Waals forces, π-π EDA interactions and electrostatic interactions were the main mechanism of SMZ adsorption onto LHPC-3. This method provided a simple method for the preparation of porous carbon materials.(2) 3D continuous hierarchical porous carbon materials(3DLHPC) was synthesized form a three-dimensional ordered complexes by centrifugation accumulation SLS precursor and monodispersed silica template via confinement carbonization and etching template and KOH in-situ activation. the morphology,composition, pore structure, crystallinity and stability of 3DLHPC were well characterized. 3DLHPC showed a clear 3D continuous macropore structure, high specific surface area of 2784 m2 g-1, total pore volume of 1.382 cm3 g-1 and the ratio of micropore volume of 85.96%. Also, we explored the effects of contact time, initial concentration, temperature and solution p H on the adsorption properties of SMZ. At308 K, the maximum adsorption capacity of 3DLHPC could reach 869.6 mg g-1.When Co=80 mg L-1, adsorption could reached equilibrium within 30 min at 298 K.Importantly, the k2 value of LHPC(1.41×10-3 g mg-1 min-1) was 3.2 times larger than the k2 value of disordered structure(4.332×10-4 g mg-1 min-1) under the same condition. It can be concluded that the ordered structure provide fast and effective flow path.(3) In this section, we used layer graphene oxide as intercalation template, SLS as carbon source, through π-π stacking, hydrogen bonding and so on by volatilization induced assembly to form layered complexes, which were treated by lamellar confinement carbonization and KOH activation, to prepare graphene/lignin composite hierarchical porous carbon(GLHPC) with high specific surface area. The incorporation of GO obviously changed the morphology and properties of GLHPC to construct a laminated sheet structure. With the increase of GO quality percentage, the more thin layers got. The SBET and VP of GLHPC-1 were up to 3223 m2 g-1 and 2.275cm3 g-1 and the micropore surface area and pore volume were 2054 m2 g-1 and 1.343cm3 g-1, pore structure in micropore containing both mesoporous(2.0-5.0 nm).GLHPC-1 had the best adsorption performance of ciprofloxacin(CIP), and the influence factors, equilibrium, isothermal adsorption, kinetics and thermodynamic properties were further studied. The Langmuir model well fitted GLHPC-1 adsorption isotherm. At 298, 308 and 318 K, the adsorption capacity Qm values for CIP were 675.7, 925.9 and 980.4 mg g-1. The regeneration experiment shows that GLHPC-1 had good reusability.3. Controlled preparation and performance study of porous carbon-based materials using organic acid potassium salt as precursor for highly efficient separation of antibiotics(1) Hierarchical porous carbon materials EHPCs-xM-T were synthesized using ethylenediamine tetraacetate(EDTA-x M) as carbon precursors via direct self-template and self-activation. The morphology, structure and composition of EHPCs-x M-T were characterized by SEM, TEM, XRD, Raman, XPS and other instruments. All the EHPCs-x M-T samples had good porous structure. Meanwhile, it was found that specific surface area and pore volume of porous carbon prepared from potassium salt precursor was much higher than the sodium salt precursor, especially to EDTA-3K as carbon source, SBET and VP of EHPCs-3K-850 were as high as 2898m2 g-1 and 1.80 cm3 g-1, respectively, when compared with the previous literatures,EHPCs-3K-850 had get the highest value. The adsorption capacity of EHPCs-3K-850 for TC at 298 K reached 1131 mg g-1, the equilibrium could be reached within 45 min when TC initial concentration was 100 mg L-1. Additionally, nitrogen content of EHPCs-x M-T was confirmed in the carbon framework. At 298 K, and EHPCs-2K-750 were 5.80 g-1 mmol and 5.45 g-1 CO2 at, respectively. The CO2 adsorption amount of EHPCs-2K-750 and EHPCs-3K-800 reached 5.80 mmol g-1 and5.45 mmol g-1(298 K, 1 bar), respectively.(2) EHPCs@CMCS microspheres was prepared from EHPCs-2K-750 used sodium carboxymethyl cellulose(CMC) as cross-linker by trivalent metal Fe3+. By means of SEM, TEM, BET, XRD, Raman, XPS and FT-IR, the composition,morphology, structural characteristics were investigated. EHPCs@CMCS also has better pore structure, SBET is 1501 m2 g-1 and showed good adsorption performance for TC of 132.9 mg g-1 at 298 K. The pseudo-second-order kinetic model and Langmuir isotherm model could better fit the adsorption process. Although the adsorption capacity is significantly lower than EHPCs-2K-750, but it has obvious advantages of easy-separation in the process. The possible mechanism included hydrogen bonding, van der Waals forces and π-π EDA interactions.(3) In order to achieve the aim of magnetic separation, the magnetic mesoporous carbon materials(MHPC) was prepared used EDTA-3K as carbon source and ferric nitrate as magnetic precursor via carbonization at high temperature. The morphology,size, magnetic properties, pore structure characteristics of MHPC was characterized by a series of technique. It was found that the good linear correlation between the surface area, pore volume, saturation magnetic strength and the ratio of ferric salt:EDTA3K. MHPC-20 possess the most developed pore, SBET and Vp are still as high as 1688 m2 g-1 and 0.884 cm3 g-1. When chloramphenicol(CAP) used as the target antibiotic, the MHPC-20 displayed best adsorption performance. The Langmuir model and the pseudo-second kinetic model could good description the process of CAP onto MHPC-20. In addition, MHPC-20 also showed that the magnetic separation performance and excellent regeneration performance.