Xuetao Guo

Sorption behavior of tylosin and sulfamethazine on humic acid: kinetic and thermodynamic studies

With the aim to investigate the kinetics and thermodynamics of tylosin (TYL) and sulfamethazine (SMT) sorption on humic acid (HA), batch sorption experiments were performed using batch reactor systems. The results indicated that the Freundlich model was much more suitable for explaining the sorption of TYL/SMT on HA, where the sorption rates for TYL/SMT decreased with the initial concentration and the sorption equilibrium could be attained within 24 h. Based on the intraparticle diffusion model, the sorption process of TYL and SMT on HA could be divided into the fast sorption stage and the slow sorption stage. The kinetic data were well-fitted to the compartment pseudo first order model, where both surface diffusion and intraparticle diffusion may play an important role in rate-controlling processes. At a specific aqueous concentration, the single-point sorption distribution coefficient (kd) of TYL and SMT decreased when the solution pH and ionic strength increased, which suggested that the sorption of TYL and SMT on HA might be dominated by both ion exchange, surface complexation and hydrophobic interactions. Meanwhile, thermodynamic calculations of sorption of TYL and SMT on HA revealed that the sorption was endothermic and spontaneous at different temperatures and the transportation abilities of TYL and SMT might be weak for soils rich in HA.

Sorption and photodegradation of tylosin and sulfamethazine by humic acid-coated goethite

Humic acid and mineral oxides are simultaneously present in soils and can form organomineral complexes. These complexes could influence the transport and fate of antibiotics in the environment. The objective of this study was to investigate the sorption and photodegradation of TYL and SMT on these complexes. The results showed that HA tended to interact with goethite via hydrophobic and π–π interactions. The sorption capacity and sorption rate gradually increased with the increasing concentrations of HA and the equilibrium time for TYL and SMT was 7 h and 24 h, respectively, on HA–goethite complexes. The sorption isotherms of TYL were more nonlinear and SMT were less nonlinear on HA–goethite complexes with the increasing concentrations of HA, which implies a more heterogeneous distribution of the sorption sites for TYL and more rigid and porous structures developed for SMT. The photodegradation of TYL and SMT by HA–goethite complexes increased with increasing the concentration of HA. An iron redox cycle couple should be a common phenomenon in the system, since both Fe(III) and HA are ubiquitous in the natural environment. The influence of HA and goethite on the fate of antibiotics in the environment is worth noting. This study is helpful in understanding the potential of toxic organic pollutants migration and transformation in the natural environment.

Sorption of tylosin and sulfamethazine on solid humic acid.

Tylosin (TYL) and sulfamethazine (SMT) are ionizable and polar antimicrobial compounds, which have seeped into the environment in substantial amounts via fertilizing land with manure or sewage. Sorption of TYL and SMT onto humic acid (HA) may affect their environmental fate. In this study, the sorption of TYL and SMT on HA at different conditions (pH, ionic strength) was investigated. All sorption isotherms fitted well to the Henry and Freundlich models and they were highly nonlinear with values of n between 0.5 and 0.8, which suggested that the HA had high heterogeneity. The sorption of TYL and SMT on HA decreased with increasing pH (2.0-7.5), implying that the primary sorption mechanism could be due to cation exchange interactions between TYL(+)/SMT(+) species and the functional groups of HA. Increasing ionic strength resulted in a considerable reduction in the Kd values of TYL and SMT, hinting that interactions between H bonds and π-π EDA might be an important factor in the sorption of TYL and SMT on HA. Results of Fourier transform infrared (FT-IR) and (13)C-nuclear magnetic resonance (NMR) analysis further demonstrated that carboxyl groups and O-alkyl structures in the HA could interact with TYL and SMT via ionic interactions and H bonds, respectively. Overall, this work gives new insights into the mechanisms of sorption of TYL and SMT on HA and hence aids us in assessing the environmental risk of TYL and SMT under diverse conditions.

Rates and equilibria of perfluorooctanoate (PFOA) sorption on soils from different regions of China

Understanding sorption of PFOA on soil particles is crucial to evaluate its environmental risk. Here, sorption of PFOA onto ten agricultural soils was examined. The influence of soil physico-chemical properties on PFOA sorption was investigated. The sorption rate of PFOA followed a pseudo-second-order kinetics. Isotherm data of PFOA sorption was fitted with both Freundlich and linear models and the latter fitted better. The sorption-desorption of PFOA onto ten soil samples depended on soil organic carbon content and composition of soil minerals. The sorption and desorption isotherms of PFOA on ten soils were linear, except for the sorption of PFOA onto a few soils, which was described by the Freundlich equation with the parameter N >1. The main sorption mechanism of PFOA was hydrophobic interaction between the perfluorinated carbon chain and the organic matter of soil, as evidenced by the correlation between the solid-liquid distribution coefficient and the fraction of soil organic carbon. The sorption of PFOA in soils was highly irreversible.

An efficient method for tylosin removal from an aqueous solution by goethite modified straw mass

Renewable agricultural residues are produced in large quantities as waste, and their storage and management create environmental problems. Similarly, antibiotics could cause harm to the ecosystem and to the growth of plants and animals. As one of the widely used antibiotics in the world, the environmental risks of tylosin (TYL) are receiving increasing attention. In order to find a clean and effective method for TYL removal from an aqueous solution, maize straw (MS) is modified by goethite and the sorption capacity of the natural and modified forms (MSF) is determined for TYL removal. The characterisations of MS and MSF were carried out by XRD, FTIR, XPS and SEM-EDS. The characteristics of the sorption behavior of TYL on MS and MSF are systematically investigated. The results indicate that the sorption capacity of TYL on MSF is significantly higher than MS, and the sorption kinetics data of TYL on MS and MSF well fits the pseudo-second-order kinetics model and the sorption isotherms data well fits the linear model. Moreover, the sorption thermodynamics of TYL on MSF and MS indicate that a high temperature could favor the sorption of TYL on MS and MSF. In addition, the sorption of TYL on MS and MSF can be affected by pH and ionic strength of the solution. The sorption mechanisms of TYL on MS mainly involve electrostatic interactions and hydrophobic interactions, whereas electrostatic interactions, H bonding, hydrophobic interactions and surface complexation play a primal role in the sorption of TYL on MSF.

Effect of ions on sorption of tylosin on clay minerals

A widely used veterinary antibiotic tylosin is associated with a fast increase in the prevalence of genes for macrolide resistance. Therefore, there are growing concerns of its potentially adverse effects on natural ecosystems, and a study on the sorption of tylosin is an important step in this direction. As a weak base, prior studies pointed out that cation exchange was the main sorption mechanism for tylosin in soil, and minerals were important factors in influencing the sorption. However, the ionic effect on the tylosin sorption process on minerals has not been systematically conducted. In this study, the sorption of tylosin on pure clay minerals was investigated in different ionic strength solutions. Moreover, the interlayer interaction of tylosin on different types of montmorillonite was preliminarily studied. All of the sorption data were fitted with the Langmuir–Freundlich–Hill sorption model. The results showed that the variation tendency of tylosin sorption capacity on montmorillonite and kaolinite were nearly the same. The sorption capacity of tylosin at different ionic strengths decreased with the order: 0.008 M > 0.051 M > 0.108 M > 0.508 M. In different ion solutions, the sorption capacity of tylosin decreased in the following order: K+ > Na+ > Ca2+ Mg2+. However, the sorption of tylosin on montmorillonite at low initial concentration of tylosin displayed a different tendency. When the initial concentration of tylosin was low, its sorption capacities on montmorillonite at different ionic strengths decreased with the order: 0.051 M 0.108 M > 0.008 M > 0.508 M. For different ionic solutions, the sorption of tylosin decreased in the order of Mg2+ Ca2+ > K+ > Na+. The cation effect on tylosin sorption in the interlayers of montmorillonite was also investigated. The sorption of tylosin on different montmorillonites decreased in the order of Ca-montmorillonite > Na-montmorillonite > K-montmorillonite. These indicated that the hydration of inorganic ions influenced the sorption of tylosin. The results provide a more comprehensive understanding about the sorption of tylosin on minerals.

A eutectic mixture of choline chloride and urea as an assisting solvent in the synthesis of flower-like hierarchical BiOCl structures with enhanced photocatalytic activity

Flower-like hierarchical BiOCl structures were successfully synthesized in the presence of a eutectic mixture of choline chloride and urea through a solvothermal process. The as-prepared sample was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), N2 adsorption–desorption analysis, photo-electrochemical analysis and UV-vis diffuse reflectance spectroscopy (DRS). During the reaction process, the eutectic mixture of choline chloride and urea acted not only as the solvent and the template, but also as a chlorine source for the fabrication of flower-like BiOCl. In addition, the photocatalytic activity toward the degradation of RhB in aqueous solution was also investigated. The results showed that the flower-like BiOCl exhibited enhanced photocatalytic activity for the degradation of RhB under sunlight illumination. Meanwhile, the flower-like BiOCl catalyst performed without obvious decrease in activity after five cycles. Furthermore, the main reactive species in the catalytic oxidation reaction were detected through radical trapping experiments.

Preparation of SnO2–TiO2/Fly Ash Cenospheres and its Application in Phenol Degradation

SnO2–TiO2/fly ash cenospheres (FAC) were prepared via hydrothermal method and used as an active photocatalyst in a photocatalytic system. Scanning electron microscopy, X‐ray diffraction analysis, UV–Vis diffuse reflectance spectroscopy, Fourier transform infrared spectroscopy and N2 adsorption–desorption measurements were used to determine the structure and optical property of SnO2–TiO2/FAC. Phenol was selected as the model substance for photocatalytic reactions to evaluate catalytic ability. Results showed that the degradation efficiency of phenol by SnO2–TiO2/FAC was 90.7% higher than that decomposed by TiO2/FAC. Increased efficiency could be due to the enhanced synergistic effect of semiconductors and FAC could provide more adsorption sites for the pollutant in the photocatalytic reaction. Furthermore, SnO2–TiO2/FAC composites exhibited excellent photocatalytic stability in four reuse cycles. Radical‐trapping experiments further revealed the dominating functions of holes in the photocatalytic reaction.