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To date, little information is available regarding the impacts of the widespread anionic surfactants on the adsorption behaviors of antibiotics onto typical iron oxides. Herein, we have investigated the effects of two typical surfactants (sodium dodecyl sulfate (SDS) and sodium dodecylbenzene sulfonate (SDBS)) on the adsorption of two widely used antibiotics (i.e., levofloxacin (LEV) and ciprofloxacin (CIP)) onto ferrihydrite. Results of kinetic experiments showed that the adsorption of antibiotics was well fitted by the pseudo-second-order kinetic models, indicating that the adsorption process might be controlled by chemisorption. The affinity of ferrihydrite toward CIP was greater than that toward LEV, which was ascribed to the higher hydrophobicity of CIP than LEV. Both surfactants enhanced antibiotic adsorption owing to SDS or SDBS molecules as bridge agents between ferrihydrite particles and antibiotics. Interestingly, the extent of the enhanced effects of surfactants on antibiotic adsorption declined as the background solution pH increased from 5.0 to 9.0, which was mainly due to the weaker hydrophobic interactions between antibiotics and the adsorbed surfactants on the iron oxide surfaces as well as the greater electrostatic repulsion between the anionic species of antibiotics and the negatively charged ferrihydrite particles at higher pH. Together, these findings emphasize the importance of widespread surfactants for illustrating the interactions between fluoroquinolone antibiotics and iron oxide minerals in the natural environment. [ABSTRACT FROM AUTHOR]

With the broadly application of antibiotics to treat infectious diseases in humans and animals, antibiotic contaminants such as tetracycline (TC) and ciprofloxacin (CIP) have been detected in soil environments, where iron oxide minerals and phosphate are ubiquitous. To date, the influence of phosphate on the adsorption behaviors of TC/CIP onto iron oxides is still poorly understood. In this study, the effects of phosphate on the adsorptions of TC and CIP onto iron oxide minerals were investigated. Adsorption isotherms showed that the adsorption affinities of TC and CIP onto the three iron oxide minerals were in the order of goethite > hematite > magnetite with or without phosphate, the trend was dominated by different surface area and amount of surface hydroxyl groups of iron oxide minerals. Meanwhile, TC contains more functional groups than CIP for bonding, which resulted in greater adsorption affinity of three iron oxides to TC than that to CIP. Interestingly, phosphate weakened TC adsorption, while enhanced CIP adsorption, on the three iron oxides. This observation was ascribed to that phosphate anion enhanced the surface negative charge of iron oxides, which reinforced the electrostatic repulsion between iron oxides and negatively charged TC, also reinforced the electrostatic attraction between iron oxides and positively charged CIP. Furthermore, the inhibitory effect of phosphate on TC adsorption was dramatically enhanced at high pH, while the promoting effect of phosphate on CIP adsorption was slightly changed with various pH. Our results highlight the importance of phosphate in exploring the environmental fate of antibiotics in natural environment. Image 1 • The affinity to adsorb TC/CIP followed the order: goethite > hematite > magnetite. •Phosphate inhibited TC adsorption, while promoted CIP adsorption. •Phosphate affected TC/CIP adsorption mainly by changing electrostatic interactions. •The effect of phosphate on TC adsorption was more pH dependent as compared with CIP. [ABSTRACT FROM AUTHOR]

The ionic liquids may have an impact on the interactions between fluoroquinolone antibiotics and clay minerals, which are widespread in nature. This work evaluated the adsorption properties of levofloxacin onto three clay minerals (i.e., montmorillonite, vermiculite, and kaolinite) affected by three types of soluble imidazolium-based ionic liquids with different chain lengths of cations ([C 2 mim]Cl, [C 4 mim]Cl, and [C 6 mim]Cl). The results demonstrated that the levofloxacin-binding capacity varied according to clay type (i.e., montmorillonite > vermiculite > kaolinite) regardless of ionic liquids-free or ionic liquids-addition. The observation was made concerning the physical-chemical characteristics of different clay minerals (e.g., physical structure, surface functional groups, specific surface area, and cation exchange capacity). Interestingly, ionic liquids suppressed levofloxacin adsorption on the three test clay minerals because of steric hindrance effects induced by the adsorbed ionic liquids as well as the site competition during co-adsorption of levofloxacin molecules and cations of ionic liquids. Additionally, the inhibitory impacts of ionic liquids in the sequence of [C 6 mim]Cl > [C 4 mim]Cl > [C 2 mim]Cl stemmed from steric hindrance and site competition during co-adsorption of ionic liquids and levofloxacin increased with chain lengths of ionic liquids. Another interesting finding was that the extent of inhibitory effects of [C 4 mim]Cl increased with the rise of pH values from 5.0 to 9.0, owing to the greater adsorption competition and steric effects derived from more adsorbed [C 4 mim]+ at higher pH conditions. The findings of this study are critical in assessing the effects of emerging contaminants on the fate of antibiotics in eco-environmental systems. [Display omitted] • The affinities of clays towards LEV are montmorillonite > vermiculite > kaolinite. • ILs inhibit LEV adsorption onto clays due to steric effect and site competition. • Adsorption-inhibition effects of ILs are dependent on the alkyl chain lengths. • The extent of adsorption-inhibition effects is solution pH-dependent. [ABSTRACT FROM AUTHOR]

The ionic liquids (ILs) can influence the adsorption of antibiotics on minerals but there was ambiguity about mechanisms. Herein, we demonstrated the adsorption characteristics of ciprofloxacin (CIP) onto ferrihydrite and montmorillonite by various soluble ILs. Five imidazolium-based ILs with different alkyl chain lengths ([C 2 mim]Cl, [C 4 mim]Cl, [C 6 mim]Cl) and counteranions ([C 4 mim][TOS] and [C 4 mim][PF 6 ]) were employed. The results validated that ILs could suppress CIP adsorption on both minerals due to the adsorption site competition between cations and CIP molecules, steric hindrance induced by long alkyl chains of ILs, and electrostatic interaction. Interestingly, the adsorption-inhibition effects of ILs were almost unchanged with the lengthening alkyl chain for ferrihydrite, which were ascribed to the comparable adsorption capacities of the three ILs on ferrihydrite. Whereas, the effects of ILs on CIP adsorption onto montmorillonite followed the order of [C 6 mim]Cl > [C 4 mim]Cl > [C 2 mim]Cl owing to the adsorption site competition and steric hindrance effects on the ILs increased with the lengthening alkyl chain. Furthermore, the inhibitory effects of ILs on CIP adsorption onto both studied minerals were also dependent on the counteranions (kept the same cation ([C 4 mim]+)) and in the following order of [C 4 mim][PF 6 ] > [C 4 mim][TOS] > [C 4 mim]Cl, which was mainly ascribed to the differences of anions in the ion sizes and the binding affinities to minerals. Additionally, the extent of the inhibitory impact of [C 4 mim][TOS] on CIP adsorption onto ferrihydrite declined with increasing solution pH from 5.0 to 9.0, which was attributed to the amounts of adsorbed [TOS]– declined with increasing pH. Contrarily, for montmorillonite, the extent increased with increasing pH, owing to increase in adsorption site competition and steric effect at higher pH conditions. Our findings emphasize the significance of emerging contaminants in understanding the antibiotic environmental behavior in eco-environmental systems. [Display omitted] • Adsorption-inhibition mechanisms of ILs on CIP adsorption varies with mineral types. • The adsorption-inhibition effects of ILs are less controlled by alkyl chain length. • Effects of ILs on CIP adsorption onto montmorillonite depend on alkyl chain length. • Adsorption-inhibition effects of ILs are counter anions-dependent. • The extent of adsorption-inhibition effects strongly varies with solution pH. [ABSTRACT FROM AUTHOR]

Tetracycline (TC) is known to be one of the most widely used antibiotics and is released into the natural environment, where amounts of iron oxides exist. Low-molecular-weight organic acids (LMWOAs), widespread water-soluble organic substances in the eco-environment systems, may affect the interactions between iron oxides and TC molecules. Nevertheless, our knowledge about the impacts of LMWOAs on the adsorption process of TC onto iron oxides still remains incomplete. In this study, we investigated the adsorption characteristics of TC onto hematite (as a model iron oxide) with various LMWOAs (i.e., acetic acid, glycolic acid, oxalic acid, malic acid, and citric acid). The results clearly showed that LMWOAs suppressed TC adsorption onto hematite particles at pH 7.0 (e.g., the maximum adsorption amounts (q max) decreased from 9.05 mg/g (without LMWOAs) to 5.90 mg/g (with 0.5 mM citric acid)), which was mainly ascribed to the competitive adsorption between TC and LMWOAs on the hematite surface, the increased electrostatic repulsion between negatively charged iron oxide particles and TC– species, and the steric hindrance. Additionally, divalent cations (Ca2+ and Cu2+) enhanced the adsorption-inhibition effects by forming cation-bridging with deprotonated LMWOAs. Interestingly, different mechanisms were involved in the adsorption process with increasing pH from 3.0 to 10.0. At pH < 5.0, electrostatic repulsion, adsorption site competition, and steric effect co-controlled the inhibitory effects. Differently, at pH > 5.0, electrostatic repulsion solely dominated the adsorption-inhibition effects. The findings of this study reveal that ubiquitous LMWOAs are critical factors controlling the fate of antibiotics in the natural environment. [Display omitted] • Effects of LMWOAs on TC adsorption onto hematite was studied. • LMWOAs inhibited TC adsorption onto hematite via multi-mechanisms. • The extent of adsorption-inhibition effects depended on organic acid species. • Cation-bridging contributed to inhibitory effects in the presence of Ca2+/Cu2+. • Different mechanisms were involved in the adsorption process with increasing pH. [ABSTRACT FROM AUTHOR]

Inorganic ligands, ubiquitous in the natural environment, can interact with iron oxide minerals. To date, our knowledge regarding the effects of inorganic ligands on the adsorption properties of antibiotics onto iron oxides is still limited. In this work, the influences of different inorganic ligands (chosen iodate, silicate, and phosphate as the model ligands) on the adsorption of tetracycline (TC) onto hematite were examined. Adsorption isotherms indicated that inorganic ligands inhibited TC adsorption. The observations were attributed to the increase of electrostatic repulsion between anionic species (i.e., TC–) and negatively charged hematite particles as well as the competition between TC– species and inorganic ligand anions for the adsorption sites on hematite surfaces. Interestingly, the inhibitory effects of the three inorganic ligands were in the order of phosphate > silicate > iodate; the trend was stemmed from their differences in the binding affinities to hematite and the molecular size. When the background solutions contained divalent cations (e.g., Ca2+), surface precipitation of Ca-inorganic ligand compounds on hematite was another important mechanism for the inhibitory effects. Furthermore, adsorption of TC onto hematite with or without inorganic ligands was strongly affected by solution pH, which was due to the combination of the amphoteric behavior of TC and highly pH-dependent surface charges of the hematite mineral. Current results highlight the critical roles of ubiquitous inorganic ligands in revealing the fate of tetracycline antibiotics in natural systems. [Display omitted] • Inorganic ligands inhibited TC adsorption onto hematite. • The inhibitory effects followed the order phosphate > silicate > iodate. • Surface precipitation was another important mechanism in the presence of Ca2+. • Adsorption of TC with or without inorganic ligands was strongly dependent on pH. [ABSTRACT FROM AUTHOR]

Biochar, a cost-effective carbonaceous material, has shown great promise in many applications such as soil remediation and wastewater treatment. Citric acid in soil and water environments may affect interactions between biochar and organic contaminants (e.g., tetracycline). To evaluate the effect of citric acid on the adsorption of tetracycline onto biochars, this study investigated the adsorption behavior of tetracycline onto biochars of two different pyrolysis temperatures (300 and 450 °C, referred to as BC_300 and BC_450) in the present of citric acid, accompanying with the effects of solution pH and Cu2+. The results indicated that citric acid significantly inhibited the adsorption of tetracycline onto both biochars, that was mainly due to the multi-mechanisms including pore blocking effect, surface adsorption sites competition, and steric hindrance induced by citric acid. Moreover, citric acid more significantly suppressed the adsorption of tetracycline onto the two biochars at pH 9.0 than at pH 5.0 and 7.0. Because increasing pH could promote electrostatic repulsion between the negative tetracycline and the negatively charged surface of biochars. Cu2+ had greater enhancing effect on the sorption of tetracycline onto BC_300 than BC_450 via cation-bridging effect. Meanwhile, citric acid inhibited the adsorption of tetracycline onto BC_300 to a larger extent than the adsorption onto BC_450 in the presence of Cu2+. That is possibly due to BC_300 has more surface oxygen-containing functional groups than BC_450. Thus, the effect of coexisting citric acid needs to be taken into account when biochar is increasingly used as an amendment in soil and water systems. [ABSTRACT FROM AUTHOR]