Chi Wang

The sorption of organic contaminants on biochars derived from sediments with high organic carbon content.

Biochars were produced using a Dianchi Lake sediment at different temperatures and their sorption characteristics with five organic contaminants (with solubilities varied three orders of magnitude) were compared. Freundlich model showed satisfying fitting results of the sorption isotherms. Distinct decrease of nonlinear factors was observed for all five contaminants with pyrolysis suggesting wider energy distribution of the sorption sites after pyrolysis. No clear trend was observed between K(d) and the chemical properties of the five chemicals. Phenanthrene and sulfamethoxazole (SMX) showed increased sorption with increased pyrolysis temperature, while the sorption of bisphenol A (BPA), ofloxacin (OFL) and norfloxacin (NOR) in the original sediment was comparable to those in the thermally treated samples. Electrostatic repulsion played an important role in SMX sorption as suggested by its lowest hydrophobicity-normalized sorption coefficients among the five chemicals. Possible sorption mechanisms were discussed and the sorption of SMX and PHE on the produced biochars were compared with natural adsorbents (including soils, sediments, and inorganic mineral particles).

The sorption of heavy metals on thermally treated sediments with high organic matter content.

A sediment sample with organic matter higher than 60% was thermally treated and the sorption of Cu(II), Cd(II), and Pb(II) was investigated and compared to evaluate the potential use of sediments with high organic matter content to produce biochar. Cu(II) and Cd(II) sorption generally decreased with increasing pyrolysis temperature, concurred with decreased oxygen-containing functional groups of the adsorbents. Sediment particles pyrolyzed at 400 and 500 °C showed higher sorption to Pb(II) than other temperatures. The small hydrated ionic radius of Pb(II) may enable its close contact with solid particles and thus facilitated the diffusion of Pb(II) into the pores and the formation of cation-π bond with aromatic structures generated by pyrolysis. The sorption of heavy metals in thermally treated sediment showed comparable sorption to or higher sorption than natural adsorbents and biochars from biomass, suggesting their possible significant impact on the transport and risk of heavy metals.

Sorption and solubility of ofloxacin and norfloxacin in water-methanol cosolvent.

Prediction of the properties and behavior of antibiotics is important for their risk assessment and pollution control. Theoretical calculation was incorporated in our experimental study to investigate the sorption of ofloxacin (OFL) and norfloxacin (NOR) on carbon nanotubes and their solubilities in water, methanol, and their mixture. Sorption for OFL and NOR decreased as methanol volume fractions (fc) increased. But the log-linear cosolvency model could not be applied as a general model to describe the cosolvent effect on OFL and NOR sorption. We computed the bond lengths of possible hydrogen bonds between solute and solvent and the corresponding interaction energies using Density Functional Theory. The decreased OFL solubility with increased fc could be attributed to the generally stronger hydrogen bond between OFL and H2O than that between OFL and CH3OH. Solubility of NOR varied nonmonotonically with increasing fc, which may be understood from the stronger hydrogen bond of NOR-CH3OH than NOR-H2O at two important sites (-O18 and -O21). The interaction energies were also calculated for the solute surrounded by solvent molecules at all the possible hydrogen bond sites, but it did not match the solubility variations with fc for both chemicals. The difference between the simulated and real systems was discussed. Similar sorption but different solubility of NOR and OFL from water-methanol cosolvent suggested that sorbate-solvent interaction seems not control their sorption.

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

The Kd of sulfamethoxazole (SMX) on activated carbon (AC) was larger than that of SMX on single-walled carbon nanotubes (SC), but the competition of SMX with carbamazepine (CBZ) for adsorption sites was weaker on AC than SC. Thus, a large Kd value does not necessarily reflect a high affinity. The analysis of the apparent sorption, competition, desorption hysteresis, and the sorption thermodynamics for SMX and CBZ did not provide sufficient information to distinguish their sorption affinities. The release of the adsorbed CBZ was not altered with SMX as the competitor, but SMX release increased significantly after CBZ addition. The higher sorption affinity of CBZ may be explained by the interactions of the CBZ benzene rings with the aromatic structures of the adsorbents. Although the thermodynamic meaning cannot be described, the release ratio of the adsorbed pollutants provides useful information for understanding pollutant sorption strength and associated risks.

Co-contaminant effects on ofloxacin adsorption onto activated carbon, graphite, and humic acid

Given their voluminous application, significant amounts of fluoroquinolones are discharged into the environment through wastewater effluent. Adsorption has been shown to be a critical process controlling the environmental behaviors of fluoroquinolones. Competition between ofloxacin (OFL) and naphthalene (NAP)/bisphenol A (BPA) and their adsorption on activated carbon (AC), graphite (GP), and humic acid (HA) were investigated. The suppressed adsorption of OFL was observed on AC and GP, but not on HA, by NAP or BPA. Moreover, for AC, the competition by NAP was slightly stronger than that by BPA. However, for GP, the competition with BPA was higher than that with NAP. These observations indicate that competitive adsorption of OFL with respect to NAP/BPA depends on the degree of overlap of adsorption sites, as interpreted by the following: (i) AC can provide overlapping adsorption sites for OFL, BPA, and NAP, which include non-specific adsorption sites, such as hydrophobic sites, π-π interactions, and micropore filling; (ii) π-π interactions and hydrogen bonding might be responsible for the strong competitive adsorption between BPA and OFL on GP; and (iii) OFL adsorbs on HA through specific adsorption force—electrostatic attraction, with which NAP and BPA cannot compete.

Dissolved Organic Matter-Ofloxacin Interaction as Affected by Metal Ions

A dialysis equilibrium system was applied to investigate the roles of Cu(II) and Mg(II) on DOM-ofloxacin (OFL) interaction. The binding behavior of both cations and OFL were studied. The introduction of Cu(II) increased DOM-OFL interaction, while Mg(II) decreased DOM-OFL binding. Cu(II) binding to DOM was also increased by OFL, while Mg(II) binding was decreased by OFL. The change in OFL binding amount in the absence and presence of cations (ΔC b) was calculated and compared with cation binding \( (C_{\mathrm{ b}}^{\mathrm{ m}}) \). \( \varDelta {C_{\mathrm{ b}}}/C_{\mathrm{ b}}^{\mathrm{ m}} \) was in the range of 1–3 for Cu(II), depending on the applied Cu concentration. Two ternary complexes of DOM-OFL-Cu and DOM-Cu-OFL were proposed. For Mg(II), \( \varDelta {C_{\mathrm{ b}}}/C_{\mathrm{ b}}^{\mathrm{ m}} \) was around −1 at Mg(II) concentrations lower than 1 mM but decreased to −5 with increasing Mg(II) concentration. The competitive effect of Mg(II) to OFL was thus proposed.