•MIL-101(Cr)/natural polymer composites possess enhanced separability from water.•MIL-101(Cr)/chitosan composite beads exhibit high adsorption capacity.•Cr centers of MOFs and NH2 of chitosan have charge attraction with contaminants.•Strong π-π interaction also contributes to the adsorption.Porous metal-organic frameworks (MOFs) have great potential as high-effective adsorbents for water treatment. However, poor separability restricts their practical application. To overcome the drawback, both MIL-101(Cr)/sodium alginate (MIL-101(Cr)/SA) and MIL-101(Cr)/chitosan (MIL-101(Cr)/CS) composite beads were prepared and characterized. Adsorption of three selected pharmaceuticals and personal care products (PPCPs) (benzoic acid (BEN), ibuprofen (IBU) and ketoprofen (KET)) onto the two composite beads was investigated and compared with pristine SA and CS beads. Kinetic plots, pH dependence, isotherm data, and influences of ionic strength were reported. The MIL-101(Cr)/CS beads exhibit much higher adsorption capacity than SA, CS and MIL-101(Cr)/SA, and the adsorption amounts of three PPCPs onto MIL-101(Cr)/CS follow the order of KET > IBU > BEN. The adsorption amounts of the three PPCPs on the MIL-101(Cr)/CS increased quickly during the first 60 min of contact time and then achieved the adsorption equilibrium after ∼180 min. Not only the protonated amine groups but also the Cr center of the adsorbents exerted electrostatic attraction with the deprotonated carboxyl groups of contaminants, as elucidated by X-ray photoelectron spectroscopy (XPS). Based on the adsorption isotherms and π-energy analysis of three PPCPs, π-π interaction of aromatic groups between adsorbents and contaminants also contributed to the adsorption. The MIL-101(Cr)/CS beads exhibited good regenerability over several repeated adsorption/desorption cycles. Overall, this study is believed to enlarge the application of MOFs on the removal of emerging contaminants from waters.Download high-res image (231KB)Download full-size image

•New nanocomposite adsorbent ZIF-67/D201 is prepared by an alternate deposition method.•ZIF-67/D201 exhibits enhanced adsorption capacity to BTA.•ZIF-67/D201 has selective affinity to BTA when BTA with similar structure coexists.•Density functional theory (DFT) calculation is used to clarify adsorption mechanism.•A strategy for precise separation of pollutants with similar structure is provided.A new nanocomposite adsorbent ZIF-67/D201, in which nanocrystalline ZIF-67 were immobilized inside the networking pores of a commercial polystyrene anion exchanger D201 by an alternate deposition method, with high capacity and enhanced selective affinity toward benzotriazole (BTA) was fabricated and characterized. ZIF-67/D201 demonstrated precise selective adsorption of BTA when benzimidazole (BMA), with very similar chemical structure to BTA, coexisted. After the uptake of BTA, ZIF-67/D201 could be regenerated for repeated use with slight capacity loss. According to kinetics data, two diffusion steps driven by electrostatic attraction were found prior to adsorption equilibrium: a fast diffusion of the contaminant into mesopores of D201 and then a relatively slow diffusion into micropores of ZIF-67. The underlying mechanism for the enhanced selective adsorption was revealed by spectral analysis and density functional theory (DFT) calculations. Three sorts of interactions (coordination, electrostatic attraction and π-π interaction) contributed to the fixing of contaminants. Among them, coordination was the predominant effect. For each sort of interaction, the binding energy of adsorbent-BTA was always larger than that of adsorbent-BMA, which was the intrinsic reason of the high selectivity in molecular level. The above results provided a strategy for precise separation of components with similar structures in water.Download high-res image (155KB)Download full-size image

•Sulfamic/amino acids modified polyaspartic acid scale inhibitors are prepared.•The scale inhibitors have high scale inhibition capacities against calcium sulfate.•DFT calculation gives quantitative explanation of inhibition mechanism.•Inhibitors prevent the growth of crystal planes ({040}, {041} and {113}).•Differential UV spectra show Ca2 + is controlled by carboxylic and phenolic hydroxyl.Modified polyaspartic acid (PASP) scale inhibitors, Tyr-SA-PASP and Trp-SA-PASP, were prepared through grafting copolymerization on PASP with sulfamic/amino acids, and then applied for the inhibition of calcium sulfate from cooling water. Scale inhibition performance evaluation demonstrated Tyr-SA-PASP and Trp-SA-PASP were two cost-effective scale inhibitors for the inhibition of calcium sulfate: Compared to PASP and two commercial scale inhibitors (PAPEMP and JH-907), both modified PASP scale inhibitors exhibited higher inhibition performance, due to coordination between the deprotonation of carboxylic acid and phenolic hydroxyl groups of Tyr-SA-PASP and carboxylic acid groups of Trp-SA-PASP and Ca2 +. Scale inhibition mechanism was investigated from microscopic viewpoints: coordination was the intrinsic driving force; Modified PASP scale inhibitors significantly damaged the crystalline structure of calcium sulfate scale, which resulted from coordination between functional groups on modified PASP scale inhibitors and Ca2 +; The scale inhibition ability of modified PASP scale inhibitors came from the prevention of the growth of crystal planes ({040}, {041} and {113}). The current study provided a strategy for the design of scale inhibitors from the viewpoint of chemical structures.Download high-res image (110KB)Download full-size image

Complex interactions between antibiotics and graphene-based materials determine both the adsorption performance of graphene-based materials and the transport behaviors of antibiotics in water. In this work, such interactions were investigated through adsorption experiments, instrumental analyses and theoretical DFT calculations. Three typical antibiotics (norfloxacin (NOR), sulfadiazine (SDZ) and tetracycline (TC)) and different graphene-based materials (divided into two groups: graphene oxides-based ones (GOs) and reduced GOs (RGOs)) were employed. Optimal adsorption pHs for NOR, SDZ, and TC are 6.2, 4.0, and 4.0, respectively. At corresponding optimal pHs, NOR favored RGOs (adsorption capability: ∼50 mg/g) while SDZ preferred GOs (∼17 mg/g); All adsorbents exhibited similar uptake of TC (∼70 mg/g). Similar amounts of edge carboxyls of both GOs and RGOs wielded electrostatic attraction with NOR and TC, but not with SDZ. According to DFT-calculated most-stable-conformations of antibiotics-adsorbents complexes, the intrinsic distinction between GOs and RGOs was the different amounts of sp2 and sp3 hybridization regions: π–π electron donor–acceptor effect of antibiotic-sp2/sp3 and H-bonds of antibiotic-sp3 coexisted. Binding energy (BE) of the former was larger for NOR; the latter interaction was stronger for SDZ; two species of TC at the optimal pH, i.e., TC+ and TC0, possessed larger BE with sp3 and sp2 regions, respectively.Keywords: antibiotics; electrostatic attraction; graphene derivatives; hydrogen bond; interactions; π−π electron donor−acceptor effect

A pH- and temperature-responsive magnetic adsorbent [poly(N-isopropylacrylamide) grafted chitosan/Fe3O4 composite particles, CN-MCP], was synthesized for the removal of the endocrine-disrupting chemical nonylphenol. According to the structural characteristics (changeable surface-charge and hydrophilic/hydrophobic properties) of the targeted contaminant, CN-MCP was designed owning special structure (pH- and temperature-responsiveness for the changeable surface-charge and adjustable hydrophilic/hydrophobic properties, respectively). Compared to chitosan magnetic composite particles without grafting modification (CS-MCP) and several other reported adsorbents, CN-MCP exhibited relatively high adsorption capacity for nonylphenol under corresponding optimal conditions (123 mg/g at pH 9 and 20 °C; 116 mg/g at pH 5 and 40 °C). Meanwhile, high selectivity of the novel adsorbent in selective adsorption of nonylphenol from bisolute solution of nonylphenol and phenol was found. Effects of grafting ratio of the grafted polymer branches and coexisting inorganic salts on the adsorption were systematically investigated. Moreover, CN-MCP demonstrated desired reusability during 20 times of adsorption–desorption recycling. The high adsorption capacity, high selectivity, and desired reusability aforementioned revealed the significant application potential of CN-MCP in the removal of NP. On the basis of the adsorption behaviors, isotherms equilibrium, thermodynamics and kinetics studies, and instrumental analyses including X-ray photoelectron spectroscopy, BET specific surface area, zeta potential, and static water contact angle measurements, distinct adsorption mechanisms were found under various conditions: charge attraction between CN-MCP and the contaminant, as well as binding between polymeric branches of CN-MCP and nonyls, contributed to the adsorption at pH 9 and 20 °C; whereas hydrophobic interaction between CN-MCP and nonylphenol played a dominant role at pH 5 and 40 °C. The current study provided a strategy for the structural design of adsorbents according to the features of targeted emerging contaminants, and the continuity of the work was discussed and proposed.Keywords: adsorption mechanism; dual-responsive adsorbent; endocrine-disrupting chemicals; magnetic composite particles; nonylphenol

•Cu(II) plays a “bridge” role in promoting removal of antibiotics, but Zn(II) cannot.•One factor for the “bridge” role is tightly binding of flocculant–heavy metals.•The other key factor is strong coordination of heavy metals–antibiotics.•Hard–Soft-Acid–Base theory and steric effect determine the coordination intensity.Previous research found that certain types of heavy metals could play a “bridge” role in promoting removal of antibiotics in flocculation, but details (i.e. under what conditions and how heavy metals wielded this effect) were not clear. To investigate this point, two sorts of combined pollution [Cu(II)–tetracycline and Zn(II)–sulfadiazine] were selected in synthetic wastewaters for flocculation, to give a comparative study. A flocculant with high capacity to coordinate with heavy metals was applied. The flocculation performance declared that, Cu(II) improved removal of coexisted antibiotic molecules whereas Zn(II) did not. Analyses of macro- and micro-scopic properties of flocs demonstrated that, (i) tightly binding of the flocculant with heavy metals, and (ii) strong coordination of heavy metals–antibiotics when the two contaminants were suitably matched according to Hard–Soft-Acid–Base theory and steric effect, were two factors for heavy metals to perform the “bridge” role, and to achieve high co-removal efficiencies of both contaminants. The finding had operational significance for both promoted removal of antibiotics with the coexistence of heavy metals and mutual promotion in the removal of the combined contaminants from water.Graphical abstractCu(II) played the “bridge” role in promoting antibiotic removal due to strong coordination effect, whereas Zn(II) could not, when MAC was applied as the flocculant.

In the current work, an environmentally friendly chitosan-based flocculant (carboxyethyl chitosan, denoted as CEC) was prepared to flocculate copper(II) and tetracycline (TC) simultaneously for the first time. The effects of flocculant dosage, pH, and initial contaminant concentration were systematically studied. For a single contaminant system, CEC demonstrates the desired flocculation performance for copper(II) removal, whereas its TC removal efficiency is poor. However, it is notable to find that the removal of TC can be significantly enhanced when copper(II) coexists in the binary contaminant system. Compared to the commercial flocculants polyaluminum chloride and polyacrylamide, CEC enjoys the advantages of lower dosage requirement, higher removal efficiency, and better floc properties. The flocculation mechanism was investigated via pH monitoring, zeta potential, and floc property measurements. The results indicate that charge neutralization predominates for single contaminant copper(II) removal, while for binary contaminant removal, TC can be embedded in copper(II) hydroxides through coordination with the metal, and finally synergistically eliminated with copper(II). This work gives a new approach to treating livestock wastewater and extends the application fields of flocculation.

The presence of tetracycline antibiotics (TCs) in aquatic environments poses potential risks to human health and ecosystems. In the present study, hypercrosslinked resins MN-200 and NDA-150 and aminated polystyrene resins MN-150 and MN-100 were selected as adsorbents for removing two tetracyclines, TC and oxytetracycline, OTC, from aqueous solutions. Despite the different surface properties and pore structures of the resins, similar patterns of pH-dependent adsorption were observed. The TCs adsorption on the resins exhibited ionic strength dependence, which is consistent with their adsorption mechanism. OTC presented stronger adsorption at pH 2.0 compared with TC; this is ascribed to the enhancement by H-bonding. The proposed mechanisms for TCs adsorption at lower pH are dependent on H-bonding, hydrophobic effect, and π–π electron donor–acceptor (EDA) interaction, whereas those at higher pH are regarded as the coordination of π–π EDA interaction and hydrophobic effect. The findings indicate that the hypercrosslinked resin is a promising adsorbent for the removal of antibiotics from aqueous solutions.

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 SO42 − suppressed 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.Download full-size image