Effect of Interaction of Non-residual Fractions on Adsorption of Atrazine onto Surficial Sediments and Natural Surface Coating Samples

To quantify the effect of the interaction of non-residual fractions[Fe oxides（Fe）, Mn oxide（Mn）, organic materials（OMs）] in the surficial sediments and the natural surface coating samples on the adsorption of atrazine（AT）, an AT multiple regression adsorption model（AT-MRAM） was developed. The AT-MRAM improves upon the previous AT additional adsorption model（AT-AAM） with superior goodness-of-fit test（adjusted R2=ca.1.000）, F-test and t-test（P〈0.01）, and reveals the effect of the interaction among the components in the surficial sediments（SSs） and na- tural surface coatings samples（NSCSs） on the adsorption of AT, which was neglected by the AT-AAM. Meanwhile, the AT-MRAM was also verified through adsorption experiments of AT and the relative deviation between predicted maximum adsorption of AT and the experimental one is less than 15%. The resulted information shows that Mn is prone to interact with other non-residual components, the total maximum adsorption of AT is inversly proportional to the level of Mn, and Fe and OMs facilitate the adsorption of AT. The results also indicate that the adsorption of AT is not only dominated by Fe, OMs, Fe/OMs, but also restrained by Fe/Mn, Fe/Mn/OMs, with lesser roles attributed to Mn, and the estimated AT distributions among the components do not agree with that previously predicted by the AT-AAM, especially with the relative contribution of Mn to the adsorption of AT, revealing significant contribution of the interactions among non-residual components in controlling the behavior of AT in aquatic environments.

Adsorption of Poly(L-lysine) on Surface-attached Poly(methacrylic acid) Monolayers

Adsorption of poly（L-lysine） on surface-attached poly（methacrylic acid） monolayers formed through in situ free radical polymerization was investigated. A strong ＂template effect＂ was observed for the adsorption of poly（L-lysine） on poly（methacrylic acid） layers, which were perpendicularly grown from the surface of substrates. The adsorbed amount of poly（amino acid） increases linearly with the increase in initial layer thickness of poly（methacrylic acid） monolayers. In addition, the adsorbed poly（amino acid） is relatively stable in medium concentration of salt solution but can be completely released from the brush in high salt concentration.

Interaction mechanism between carboxylmethyl cellulose and iron ore concentrates in iron ore agglomeration

Carboxylmethyl cellulose(CMC) has become a commercial organic binder in agglomeration of iron ore concentrates. The relative molecular mass and degree of substitution(DS) of CMC have a large impact on its binding performance. The interaction mechanism between CMC and iron ore particles was analyzed through Zeta potential measurements, adsorption measurements and infrared spectra. The results show that the interaction is chemical adsorption-oriented and the CMC's adsorption performance is related to the properties of CMC as well as the type of iron oxides. CMC has a greater affinity to Fe2O3 than Fe3O4, and CMC with higher relative molecular mass shows a higher adsorption isotherm. Pelletization of practical iron ore concentrates added with CMC further illustrates that CMC with higher relative molecular mass or DS exhibits a better binding performance, which is consistent with the results of adsorption tests.

Adsorption of three pharmaceuticals on two magnetic ion-exchange resins

The presence of pharmaceuticals in aquatic environments poses potential risks to the ecology and human health. This study investigated the removal of three widely detected and abundant pharmaceuticals, namely, ibuprofen（IBU）, diclofenac（DC）, and sulfadiazine（SDZ）, by two magnetic ion-exchange resins. The adsorption kinetics of the three adsorbates onto both resins was relatively fast and followed pseudo-second-order kinetics. Despite the different pore structures of the two resins, similar adsorption patterns of DC and SDZ were observed, implying the existence of an ion-exchange mechanism. IBU demonstrated a combination of interactions during the adsorption process. These interactions were dependent on the specific surface area and functional groups of the resin. The adsorption isotherm fittings verified the differences in the behavior of the three pharmaceuticals on the two magnetic ion-exchange resins. The presence of Cl-and SO2-4suppressed the adsorption amount, but with different inhibition levels for different adsorbates. This work facilitates the understanding of the adsorption behavior and mechanism of pharmaceuticals on magnetic ion-exchange resins.The results will expand the application of magnetic ion-exchange resins to the removal of pharmaceuticals in waters.

Electronic-property dependent interactions between tetracycline and graphene nanomaterials in aqueous solution

Understanding the interactions between graphene nanomaterials（GNMs） and antibiotics in aqueous solution is critical to both the engineering applications of GNMs and the assessment of their potential impact on the fate and transport of antibiotics in the aquatic environment. In this study, adsorption of one common antibiotic, tetracycline, by graphene oxide（GO） and reduced graphene oxide（RGO） was examined with multi-walled carbon nanotubes（MWCNTs） and graphite as comparison. The results showed that the tetracycline adsorption capacity by the four selected carbonaceous materials on the unit mass basis followed an order of GO ＆gt; RGO ＆gt; MWCNTs ＆gt; graphite. Upon normalization by surface area,graphite, RGO and MWCNTs had almost the same high tetracycline adsorption affinity while GO exhibited the lowest. We proposed π-electron-property dependent interaction mechanisms to explain the observed different adsorption behaviors. Density functional theory（DFT） calculations suggested that the oxygen-containing functional groups on GO surface reduced its π-electron-donating ability, and thus decreased the π-based interactions between tetracycline and GO surface. Comparison of adsorption efficiency at different p H indicated that electrostatic interaction also played an important role in tetracycline-GO interactions. Site energy analysis confirmed a highly heterogeneous distribution of the binding sites and strong tetracycline binding affinity of GO surface.

Adsorption of chlorophenols from aqueous solutions by pristine and surface functionalized single-walled carbon nanotubes

The adsorption of six kinds of chlorophenols on pristine, hydroxylated and carboxylated single-walled carbon nanotubes（SWCNTs） has been investigated. Pseudo-first order and pseudo-second order models were used to describe the kinetic data. All adsorption isotherms were well fitted with Langmuir, Freundlich and Polanyi–Manes models, due to surface adsorption dominating the adsorption process. The close linear relationship between log Kowand log Kdsuggested that hydrophobicity played an important role in the adsorption. The SWCNTs＇ adsorption capacity for chlorophenols was weakened by addition of oxygen-containing functional groups on the surface, due to the loss of specific surface area, the increase of hydrophilicity and the reduction of π–π interaction. The best adsorption capacity of pristine SWCNTs, SWCNT-OH and SWCNT-COOH for six chlorophenols varied from 19 to 84 mg/g, from 19 to 65 mg/g and from 17 to 65 mg/g,respectively. The effect of pH on the adsorption of 2,6-dichlorophenol（2,6-DCP）, was also studied. When p H is over the pK aof 2,6-dichlorophenol（2,6-DCP）, its removal dropped sharply. When ionic strength increased（Na Cl or KCl concentration from 0 to 0.02 mmol/L）,the adsorption capacity of 2,6-DCP on pristine SWCNTs decreased slightly. The comparison of chlorophenols adsorption by SWCNTs, MWCNTs and PAC was made, indicating that the adsorption rate of CNTs was much faster than that of PAC. The results provide useful information about the feasibility of SWCNTs as an adsorbent to remove chlorophenols from aqueous solutions.

Removal of ammonium ion from water by Na-rich birnessite:Performance and mechanisms

Na-rich birnessite（NRB） was synthesized by a simple synthesis method and used as a high-efficiency adsorbent for the removal of ammonium ion（NH＋4） from aqueous solution.In order to demonstrate the adsorption performance of the synthesized material,the effects of contact time,pH,initial ammonium ion concentration,and temperature were investigated.Adsorption kinetics showed that the adsorption behavior followed the pseudo second-order kinetic model.The equilibrium adsorption data were fitted to Langmuir and Freundlich adsorption models and the model parameters were evaluated.The monolayer adsorption capacity of the adsorbent,as obtained from the Langmuir isotherm,was 22.61 mg NH＋4-N/g at283 K.Thermodynamic analyses showed that the adsorption was spontaneous and that it was also a physisorption process.Our data revealed that the higher NH＋4adsorption capacity could be primarily attributed to the water absorption process and electrostatic interaction.Particularly,the high surface hydroxyl-content of NRB enables strong interactions with ammonium ion.The results obtained in this study illustrate that the NRB is expected to be an effective and economically viable adsorbent for ammonium ion removal from aqueous system.