Sorption affinities of sulfamethoxazole and carbamazepine to two sorbents under co-sorption systems

Adsorption characteristics of sulfonamide antibiotic molecules on carbon nanotube and the effects of environment

CONTEXT

In this paper, the adsorption characteristics of five sulfonamide antibiotic molecules on carbon nanotubes were investigated using density functional theory (DFT) calculations. The adsorption configurations of different adsorption sites were optimized, and the most stable adsorption configuration of each sulfonamide molecule was determined by adsorption energy comparison, and the relative adsorption stability of five sulfonamide molecules on carbon nanotubes was determined by comparing their adsorption energies, i.e., sulfamethazine > sulfadiazine > sulfamerazine > sulfamethoxazole > sulfanilamide. The electron densities of the adsorption configurations were then calculated to confirm that the adsorption of five sulfonamide drug molecules on carbon nanotubes should be physical adsorption. Moreover, the adsorption energy of five sulfonamide molecules on carbon nanotubes in the aqueous environment was larger than that in the vacuum even though the adsorption process remain to be physical adsorption. The adsorption characteristics of the five sulfonamide molecules in various acid-base environments were finally investigated. In contrast, the adsorption energies of the five drug molecules in acid-base environments were significantly reduced, indicating that carbon nanotubes may need to have a suitable pH range to achieve the optimal adsorption effect when they are used for the treatment of sulfonamide antibiotics.

METHODS

In this paper, we use density functional theory (DFT) with PBE functional to study the adsorption properties of five sulfonamides on carbon nanotubes. The structural optimization and the calculation of electronic structural properties are carried out by CP2K package (version 7.1), adopting the DZVP-MOLOPT-SR-GTH basis set and Goedeck-Teter-Hutter (GTH) pseudo potential. Grimme's D3 correction is used to during all the calculations to correctly capture the influence of the van der Waals interactions.

Competitive adsorption of sulfamethoxazole and bisphenol A on magnetic biochar: Mechanism and site energy distribution

Competitive adsorption and complementary adsorption between emerging pollutants has been observed in multiple studies. Investigation of the preference of pollutants for different types of adsorption sites can provide a supplementary perspective for understanding complementary adsorption. In this study, the simultaneous adsorption of two typical emerging pollutants, sulfamethoxazole (SMX) and bisphenol A (BPA), on magnetic biochar (MBC-1) was investigated. The results showed that the modification with ferric chloride optimized the surface properties of biochar (aromaticity, hydrophobicity, and oxygen-containing functional groups, etc.), and helped to remove SMX and BPA through various interactions. The equilibrium adsorption capacity of the two adsorbents was inhibited by competitive adsorption in the mixed solute systems, which was due to the same adsorption mechanism. When pH = 7, the SMX and BPA adsorption mainly involved pore filling, hydrophobic effect, π-π EDA, and hydrogen bonding. In addition, electrostatic force, surface coordination, and ion exchange have also been proven to be related to the adsorption of SMX and BPA. In the co-adsorption system, BPA's competitive advantage might be due to its superior hydrophobicity, charge property, and molecular diameter. In the competitive adsorption experiment, the total adsorption capacity (Q_i) of the competitive solute exceeded the adsorption inhibition (△Q_i) of the main solute, indicating that the two solutes occupied their preferred adsorption sites, which confirmed the complementary adsorption phenomenon. Complementary adsorption can be explained by the preference of SMX and BPA for different types of adsorption sites. BPA preferentially occupied high-energy sites in the co-adsorption system, such as π-π EDA interaction, ion exchange, and surface coordination. At the same time, SMX tended to be removed by hydrophobic interaction and hydrogen bonding.

Mechanism evolution and prediction of carbamazepine sorption by mangrove plant residue-derived biochars

A mechanism for carbamazepine (CBZ) sorption by mangrove plant residue-derived biochars pyrolyzed at 200-700 °C (referred as MPR200-MPR700) was elucidated in this study. The experimental results demonstrated that the dominant sorption mechanism of biochars for CBZ was evolved from partition to adsorption with increasing pyrolysis temperature. The CBZ concentration-dependent contributions of partition and adsorption were controlled by the relative noncarbonized and carbonized fractions of biochars. The partition medium changed from a polymeric aliphatic fraction (mangrove plant residue [MPR]200-MPR400) to a more condensed aromatic phase (MPR500-MPR600), which made the partition less favorable. Meanwhile, the adsorption was selectively regulated by polarity (MPR200-MPR300) and porosity (MPR400-MPR700) for different biochars. A pragmatic model including the sorbent aromaticity index (H/C) was put forward to predict CBZ sorption to MPR200-MPR700 and other carbonaceous materials reported in the literature. The findings can be helpful in understanding CBZ-biochar interactions and developing effective sorbents (such as biochars) for pollutant sequestration.

Enhanced adsorption of hydrophobic organic contaminants by high surface area porous graphene

The relatively low surface area and micropore volume of graphene nanosheets (GNS) limit their potential application as effective adsorbents for hydrophobic organic contaminants (HOCs). In this study, KOH etching was used to develop activated GNS (K-GNS) for adsorption of model HOCs such as naphthalene, phenol, nitrobenzene, and bisphenol A. After activation, the specific surface area (SSA) of K-GNS increased to 885 m²/g, which was three times larger than that of GNS. The micropore volume of K-GNS substantially increased and the C/O ratio was doubled. Accordingly, the adsorption capacity of these HOCs on K-GNS was larger than that of pristine GNS (P-GNS) by 2-8 times. The kinetic data was fitted by the pseudo-second-order model, and the adsorption isotherms of HOCs on P-GNS and K-GNS were fitted by the Freundlich model. The desorption studies showed the K-GNS had a lower rate of release than P-GNS. The high adsorption of naphthalene, phenol, nitrobenzene, and bisphenol A on P-GNS and K-GNS is dominated by hydrophobic and π-π interactions. Additionally, the π-π EDA interaction and hydrogen bond between K-GNS and substituents cannot be ignored.

Modeling adsorption of organic pollutants onto single-walled carbon nanotubes with theoretical molecular descriptors using MLR and SVM algorithms

Prediction of adsorption equilibrium coefficients (K) of organic compounds onto single walled carbon nanotubes (SWNTs) from in silico molecular descriptors is of importance for probing potential applications of SWNTs as well as for evaluating environmental behavior and ecological risks of organic pollutants and SWNTs. In this study, two models for predicting logK were developed with multiple linear regression (MLR) and support vector machine (SVM) algorithms. The two models have satisfactory goodness-of-fit, robustness and predictive ability, and the SVM model performs slightly better than the MLR model. The two models are based on the up-to-date experimental dataset consisting of 61 logK values, and the applicability domains cover diverse organic compounds with functional groups > CC<, CC, C₆H₅, >CO, COOH, C(O)O, OH, O, F, Cl, Br, NH₂, NH, >N, >NN<, NO₂, >NC(O)NH₂, >NC(O)NH, S and S(O)(O). The adsorption of organic compounds toward SWNTs is mainly determined by van der Waals forces and hydrophobic interactions. Since only in silico molecular descriptors were employed for the modeling, the developed models are beneficial for prediction purposes.

Adsorption of sulfamethoxazole by magnetic biochar: Effects of pH, ionic strength, natural organic matter and 17α-ethinylestradiol

Recent studies have shown the widespread occurrence of pharmaceuticals in the aquatic environment leading to increasing global concern on their potential adverse effects in the environment and public health. In this study, we evaluated the use of magnetic biochar derived from pine sawdust, one of New Zealand's major wood wastes, to remove an emerging contaminant, sulfamethoxazole (SMX), at different pH, ionic strength, natural organic matter (NOM) and a competing compound, 17α-ethinylestradiol (EE2). In single-solute system, the sorption of SMX onto magnetic biochar was found to be highly pH-dependent and slightly increased with increase in ionic strength. However, the effects of pH, ionic strength and NOM were relatively insignificant compared to the sorption inhibition caused by EE2 in binary-solute system. Both SMX and EE2 sorption onto the highly carbonised biochar in magnetic biochar were postulated to be due to the π-π electron donor acceptor and hydrophobic interaction. EE2 is more hydrophobic than SMX. Hence, strong competition between these compounds was identified where EE2 markedly inhibited the sorption of SMX onto magnetic biochar in all artificial environmental conditions studied.

Impact of mineral components in cow manure biochars on the adsorption and competitive adsorption of oxytetracycline and carbaryl

Knowledge about the impact of mineral component in biochar on the sorption of OTC and CBL is limited and need be systematically studied. The mineral component of cow manure biochar showed different effects on the sorption of OTC and CBL.

Adsorption mechanism of different organic chemicals on fluorinated carbon nanotubes

Multi-walled carbon nanotubes (MC) were fluorinated by a solid-phase reaction method using polytetrafluoroethylene (PTFE). The surface alteration of carbon nanotubes after fluorination (MC-F) was confirmed based on surface elemental analysis, TEM and SEM. The incorporation of F on MC surface was discussed as F incorporation on carbon defects, replacement of carboxyl groups, as well as surface coating of PTFE. The adsorption performance and mechanisms of MC-F for five kinds of representative organic compounds: sulfamethoxazole (SMX), ofloxacin (OFL), norfloxacin (NOR), bisphenol a (BPA) and phenanthrene (PHE) were investigated. Although BET-N2 surface area of the investigated CNTs decreased after fluorination, the adsorption of all five chemicals increased. Because of the glassification of MC-F surface coating during BET-N2 surface area measurement, the accessible surface area of MC-F was underestimated. Desorption hysteresis was generally observed in all the sorption systems in this study, and the desorption hysteresis of MC-F were stronger than the pristine CNTs. The enhanced adsorption of MC-F may be attributed the pores generated on the coated PTFE and the dispersed CNT aggregates due to the increased electrostatic repulsion after fluorination. The rearrangement of the bundles or diffusion of the adsorbates in MC-F inner pores were the likely reason for the strong desorption hysteresis of MC-F. The butterfly structure of BPA resulted in its high sorption and strong desorption hysteresis. The exothermic sorption character of OFL on CNTs resulted in its strong desorption hysteresis.

Simultaneous removal and degradation characteristics of sulfonamide, tetracycline, and quinolone antibiotics by laccase-mediated oxidation coupled with soil adsorption

The uses of laccase in the degradation and removal of antibiotics have recently been reported because of the high efficiency and environmental friendliness of laccase. However, these removal studies mostly refer to a limited number of antibiotics. In this study, soil adsorption was introduced into the laccase-oxidation system to assist the simultaneous removal of 14 kinds of sulfonamide, tetracycline, and quinolone antibiotics, which differed in structures and chemical properties. The complementary effects of laccase-mediated oxidation and soil adsorption enabled the simultaneous removal. Removal characteristics were determined by a comprehensive consideration of the separate optimum conditions for laccase oxidation and soil adsorption removal experiments. With concentrations of laccase, syringaldehyde (SA), and soil of 0.5mg/mL, 0.5mmol/L, and 50g/L, respectively, and at pH 6 and 25°C, the removal rates of each antibiotic exceeded 70% in 15min and were close to 100% in 180min. Sulfonamide antibiotics (SAs) were removed mainly by laccase oxidation and quinolone antibiotics (QUs) mainly by soil adsorption. Tetracycline antibiotics (TCs) were removed by both treatments in the coupled system, but laccase oxidation dominated. Electrostatic adsorption was speculated to be one of the adsorption mechanisms in soil adsorption with QUs and TCs.

Photolysis and photocatalytic decomposition of sulfamethazine antibiotics in an aqueous solution with TiO2

Photo-decomposition of sulfamethazine (SMT) involves photolytic and photo-catalytic reactions, which occur simultaneously.