EDTA-Cross-Linked β‑Cyclodextrin: An Environmentally Friendly Bifunctional Adsorbent for Simultaneous Adsorption of Metals and Cationic Dyes

The discharge of metals and dyes poses a serious threat to public health and the environment. What is worse, these two hazardous pollutants are often found to coexist in industrial wastewaters, making the treatment more challenging. Herein, we report an EDTA-cross-linked β-cyclodextrin (EDTA-β-CD) bifunctional adsorbent, which was fabricated by an easy and green approach through the polycondensation reaction of β-cyclodextrin with EDTA as a cross-linker, for simultaneous adsorption of metals and dyes. In this setting, cyclodextrin cavities are expected to capture dye molecules through the formation of inclusion complexes and EDTA units as the adsorption sites for metals. The adsorbent was characterized by FT-IR, elemental analysis, SEM, EDX, ζ-potential, and TGA. In a monocomponent system, the adsorption behaviors showed a monolayer adsorption capacity of 1.241 and 1.106 mmol g^–1 for Cu­(II) and Cd­(II), respectively, and a heterogeneous adsorption capacity of 0.262, 0.169, and 0.280 mmol g^–1 for Methylene Blue, Safranin O, and Crystal Violet, respectively. Interestingly, the Cu­(II)–dye binary experiments showed adsorption enhancement of Cu­(II), but no significant effect on dyes. The simultaneous adsorption mechanism was further confirmed by FT-IR, thermodynamic study, and elemental mapping. Overall, its facile and green fabrication, efficient sorption performance, and excellent reusability indicate that EDTA-β-CD has potential for practical applications in integrative and efficient treatment of coexistenting toxic pollutants

Green Synthesis of Magnetic EDTA- and/or DTPA-Cross-Linked Chitosan Adsorbents for Highly Efficient Removal of Metals

The present paper describes a green and economic approach to explore EDTA/DTPA-functionalized magnetic chitosan as adsorbents for the removal of aqueous metal ions, such as Cd­(II), Pb­(II), Co­(II), and Ni­(II). EDTA and DTPA play roles not only as cross-linkers but also as functional groups in chelating metal ions. The morphology, structure, and property of the magnetic adsorbents were characterized by SEM, TEM, XRD, EDS, FT-IR, TGA, and VSM techniques. Their adsorption properties for the removal of metal ions by varying experimental conditions were also investigated. The kinetic results revealed that the transportation of adsorbates from the bulk phase to the exterior surface of adsorbents was the rate-controlling step. The obtained maximum adsorption capacities of magnetic adsorbents for the metal ions ranged from 0.878 to 1.561 mmol g^–1. Bi-Langmuir and Sips isotherm models fitting well to the experimental data revealed the surface heterogeneity of the adsorbents. More significantly, the resulting EDTA-/DTPA-cross-linked magnetic chitosan adsorbents had selectivity to Cu, Pb, Zn, Fe, and Ni from a practical industrial effluent. Furthermore, their good reusability and convenient magnetic separation makes them viable alternatives for real wastewater treatment

Carboxymethyl Chitosan and Its Hydrophobically Modified Derivative as pH-Switchable Emulsifiers

The emulsification properties of carboxymethyl chitosan (CMChi) and hydrophobically modified carboxymethyl chitosan (h-CMChi) were studied as a function of pH and dodecane/water ratio. The pH was varied between 610, and the oil/water ratio between 0.12.0. In CMChi solution, the emulsion stability increased as the pH was lowered from 10 to 7, and the phase inversion was shifted from oil/water ratio 1.0 to 1.8, respectively. The system behaved differently in pH 6 due to the aggregation of CMChi and the formation of nanoparticles (∼200300 nm). No phase inversion was observed and the maximum amount of emulsified oil was reached at oil/water ratio 1.2. The h-CMChi showed similar behavior as a function of pH but, due to hydrophobic modification, the phase inversion was shifted to higher values in pH 710. In pH 6, the behavior was similar, but the maximum amount of emulsified oil was higher compared to CMChi. The amount of adsorbed particles correlated with the emulsified amount of oil. Reversible emulsification of dodecane was demonstrated by pH adjustment using CMChi and h-CMChi solutions. The formed emulsions were gel-like, suggesting particle–particle interaction

Versatile Cellulose-Based Carbon Aerogel for the Removal of Both Cationic and Anionic Metal Contaminants from Water

Hydrothermal carbonization of cellulose in the presence of the globular protein ovalbumin leads to the formation of nitrogen-doped carbon aerogel with a fibrillar continuous carbon network. The protein plays here a double role: (i) a natural source of nitrogen functionalities (2.1 wt %) and (ii) structural directing agent (<i>S</i>_BET = 38 m²/g). The applicability in wastewater treatment, namely, for heavy metal removal, was examined through adsorption of Cr­(VI) and Pb­(II) ion solely and in a mixed bicomponent aqueous solutions. This cellulose-based carbogel shows an enhanced ability to remove both Cr­(VI) (∼68 mg/g) and Pb­(II) (∼240 mg/g) from the targeted solutions in comparison to other carbon materials reported in the literature. The presence of competing ions showed little effect on the adsorption efficiency toward Cr­(VI) and Pb­(II)