Design, Synthesis And Adsorption Performance Of Several Novel Adsorbents For The Antibiotics Contaminants In Aquatic Environment

The pharmaceutical antibiotics in environments are the main bioactive emerging contaminants in the group of the "pharmaceuticals and personal care products (PPCPs)". Because of their continuous introduction into the environment via effluents from sewage treatment facilities and from septic systems, contaminants antibiotics show the characteristics of "pseudo-persistent" and are constantly enriched in varied water bodies, soils and sediments. Increasing concern has been raised regarding their potential risks to ecological and human health. And their efficient treatment methods are proved to be one of the research hotspots. The nondestructive treatment technology of adsorption is considered to be one of the most promising measures for its easy control, low cost, high efficiency and no high-toxic degradation products. In this paper, a series of novel adsorbents with different structures and characters were produced and applied to the adsorptive removal of antibiotics from aqueous solution.Firstly, a kind of quasi-two-dimensional graphene-like layered hexagonal boron nitride (g-BN) adsorbent was prepared and characterized by N2adsorption-desorption, XRD, SEM, TEM, XPS, EDS and AFM. The adsorption performance of g-BN for removal of antibiotics was evaluated. The results showed that few-layered g-BN exhibited excellent adsorption capability with about95%removal ratio for fluoroquinolone antibiotics gatifloxacin (GTF) and levofloxacin (LOF), and more than85%removal ratio for tetracycline antibiotics tetracycline (TC) and doxycycline (DC), while commercial BN displayed only less than10%antibiotics removal. The adsorption performance of g-BN for antibiotic GTF was evaluated systematically. The sorption was fast and arrived equilibrium around45min. The effect of pH was generally not observable, and the adsorption capacity (qe) was74.2～74.7mg/g in a wide range of pH3-11. The ionic strength of Na+and Ca2+decreased qe by7%and8%, respectively. The adsorption data were well described by Langmuir isotherm model with the maximum adsorption capacity (gm) of89mg/g at288K. The adsorption was a spontaneous, exothermic and physisorption process,π-π interaction, hydrophobic effect and electrostatic interaction may dominate the adsorption.Then, another kind of quasi-two-dimensional few-layered adsorbent, which containing transitional metal element molybdenum, graphene-like layered molybdenum disulfide (g-MoS2) was prepared and characterized by AFM, XRD, TEM, XPS, BET and UV. The performance of using g-MoS2as an adsorbent for removal of antibiotics from aqueous solution was investigated. Compared with the commercial MoS2, the prepared g-MoS2demonstrated a much better capability in the removal of antibiotics from aqueous solution, the removal ratio of TC and DC was96～97%, greater than GTF and LOF (the removal ratio was about86%).The adsorption behavior of g-MoS2for TC and DC was investigated systematically. The qe was325and312mg/g at the equilibrium of16and24h for TC and DC, respectively. The adsorption was influenced by solution pH, the optimum pH for the sorption of TC and DC was2-9and4-9, respectively. Na+in the solution could promote the adsorption, the qe increased by31%(pH=6.4) for TC, and increased by24%(pH=3.8) and16%(pH=7.0) for DC. Pseudo-second-order kinetics model and Langmuir isotherm model provided the best fit to the adsorption data. The main step limiting the adsorption rat might be the diffusion transferred through the boundary liquid layer surrounding g-MoS2but not the interlayer mass transfer. The monolayer qm was435and556mg/g for TC and DC at303K, respectively. The adsorption process was spontaneous, endothermic, physisorption and chemisorptions coexisted. The adsorption mechanism was probably π-π interaction, hydrophobic effect and electrostatic interaction.Next, six economical macroporous polystyrene ion-exchange resins D201, D370, D001, D061, D072and NKC-9were introduced and compared their adsorbability for antibiotics. The removal ratio of antibiotics TC, DC, GTF and LOF was91-100%when using strong-basic anion-exchange resin D201and alkalescent anion-exchange resin D370as adsorbents, which was much greater than the four strong-acid cation-exchange resins D001, D061, D072, and NKC-9(only removed17-58%antibiotics) at the experiment condition of initial pH and pH=7. The adsorption ability of the six resins for antibiotic TC and DC was studied systematically. The results showed that the sorption equilibrium could be reached after about96h. Solution pH and ionic strength had significant effects on the sorption. Basic resins D201and D370exhibited strong sorption capability under pH4-7, but strong-acid resins only at acid condition of pH2-3showed good sorption ability. The inhibitory effect of Na+for sorption was much greater on D201than on D370. The qe of TC and DC decreased by72.9%and67.3%on D201, but only decreased by37.5%and18.6%on D370, respectively. The sorption was mainly well fitted by Langmuir isotherm and pseudo-second-order kinetics models. Intra-particle diffusion and external mass transfer both controlled the sorption rate. The Langmuir monolayer qm was222,233and123mg/g for TC, and256,122and149mg/g for DC on D001(pH=3), D201and D370(pH=7), respectively, at the optimal temperature. The sorption was spontaneous and endothermic (DC sorption on D001was exothermic). The mechanism was deduced to be the interaction of ion-exchange, hydrophobic effect and π-π effect.Then, the macroporous strong-acid cation-exchange resin D001was modified by metal ions Fe3+, Cu2+and Zn2+to obtain the new adsorbents of metal ions impregnated D001resins (M-D001, M:Fe3+, Cu2+and Zn2+), the properties of the adsorbents were characterized by N2sorption-desorption, XRD and FTIR. The adsorption performance of three M-D001for antibiotics was evaluated. The results showed that excellent sorption capability with more than90%removal ratio of TC, DC, GTF and LOF was observed for these resins after modification (the removal ratio of TC and DC was above98%). A much better suitability in fluctuation of pH was exhibited for M-D001, and extremely strong sorption capability with qe of more than200mg/g was shown under a wide range of pH2～8. The sorption rate was also enhanced with equilibrium time of12～72h. The ionic strength of NaCl exhibited obviously inhibitory effect for the sorption. The qe on Fe-D001, Cu-D001and Zn-D001decreased by29%,35%and66%for TC, and36%,51%and73%for DC. Pseudo-second-order kinetic equation and Langmuir isotherm model provided the best match to the sorption data. Intra-particle diffusion was not the only rate-controlling step, the external mass transfer process also influenced the sorption rate. The monolayer qm was417-625mg/g under288-318K. The sorption was spontaneous and endothermic. The main mechanism was proposed to be surface complexation, cation bridge and electrostatic interaction.Finally, the mesoporous adsorbent of metal Fe3+doped mesoporous silica (Fe-SiO2) was synthesized with metal based ionic liquid as the soft template. The properties were characterized by N2adsorption-desorption, XRD, SEM, EDS, TEM and XPS, and the adsorption performance of Fe-SiO2for antibiotics was investigated. Compared with SiO2, Fe-SiO2demonstrated a much better adsorption capability with more than90%antibiotics removal for TC, DC, GTF and LOF. The adsorption behavior of TC and LOF were studied systematically. The perfect pH for the adsorption of TC and LOF was4-9and5-11, respectively. With the increase of NaCl the sorption capacity increased slightly for TC but decreased for LOF, while CaCl2decreased the sorption both for TC and LOF, and the qe decreased by16.5%and33.5%, respectively. The sorption data were well described by Langmuir isotherm equation and pseudo-second-order kinetic model. The sorption rate was not only controlled by intra-particle diffusion, but also influenced by external film diffusion. The monolayer qm was385and104mg/g for TC and LOF at initial pH and288K, respectively. The sorption process was thermodynamically feasible, spontaneous and favorable at lower temperature. The interactions of surface complexation, cation bridge and electrostatic attraction were proposed as the main sorption mechanism.