Bio-inspired one-step structure adjustment and chemical modification of melamine foam toward highly efficient removal of hexavalent chromium ions

Hollow Biomass Adsorbent Derived from Platanus Officinalis Grafted with Polydopamine-Mediated Polyethyleneimine for the Removal of Eriochrome Black T from Water

Platanus officinalis fibers (PFs) taking advantage of high-availability, eco-friendly and low-cost characteristics have attracted significant focus in the field of biomaterial application. Polyethyleneimine grafted with polydopamine on magnetic Platanus officinalis fibers (PEI-PDA@M-PFs) were prepared through a two-step process of mussel inspiration and the Michael addition reaction, which can work as an effective multifunctional biomass adsorbent for anionic dye with outstanding separation capacity and efficiency. The as-prepared PEI-PDA@M-PFs possess desirable hydrophilicity, magnetism and positive charge, along with abundant amino functional groups on the surface, facilitating efficient adsorption and the removal of Eriochrome Black T (EBT) dyes from water. In addition to the formation mechanism, the adsorption properties, including adsorption isotherms, kinetics, and the reusability of the absorbent, were studied intensively. The as-prepared PEI-PDA@M-PFs achieved a theoretical maximum adsorption capacity of 166.11 mg/g under optimal conditions (pH 7.0), with 10 mg of the adsorbent introduced into the EBT solution. The pseudo-second-order kinetic and Langmuir models were well matched with experimental data. Moreover, thermodynamic data ΔH > 0 revealed homogeneous chemical adsorption with a heat-absorption reaction. The adsorbent remained at high stability and recyclability even after five cycles of EBT adsorption processes. These above findings provide new insights into the adsorption processes and the development of biologic material for sustainable applications.

Superior capacity and easy separation of zirconium functionalized chitosan melamine foam for antimony(III/V) removal

Nowadays, highly toxic antimony has severely posed threat to water sources and jeopardized human health. Fabricating adsorbents with the capability of easy separation, high efficiency and large adsorption capacity remains a major challenge. In this paper, zirconium functionalized chitosan melamine foam (ZCMF) was fabricated with zirconium and chitosan crosslinked onto melamine foam, then utilized for the removal of antimony(III/V) in water. The characterization of SEM and EDS collectively showed that ZCMF has a porous structure which could boost the mass transfer rate and zirconium ions on the surface could provide plentiful active adsorption sites. Systematic adsorption experiments demonstrated that the experimental data of Sb(III) and Sb(V) were consistent with the pseudo-second-order and Elovich kinetic models, respectively, and the Langmuir maximum adsorption capacities were separately 255.35 mg g-1 (Sb(III)) and 414.41 mg g-1 (Sb(V)), which displayed prominent performance among adsorbents derived from biomass. Combining the XPS and FTIR characterization with experimental data, it is rational to speculate that ZCMF could remove Sb from aqueous solution through ligand exchange, electrostatic attraction, and surface complexation mechanisms. ZCMF exhibited excellent performance, including large adsorption capacity, easy separation, facile preparation and eco-friendliness. It could be a promising new adsorbent for the treatment of antimony-containing wastewater.

High nitrogen content bimolecular co-functionalized graphene nanoflakes for hypertoxic Cr(VI) removal: Insights into adsorption behavior and mechanisms

The proven high carcinogenicity to humans and high destructive force to the environment determine the extreme urgency of eliminating hypertoxic Cr(VI) in water bodies. Herein, a route of room temperature synthesis and secondary grafting was proposed to fabricate graphene oxide-based nanoadsorbent co-functionalized with polydopamine and branched polyethyleneimine (GOPP) to remove Cr(VI). The flexible decoration of polydopamine and polyethyleneimine on GO flakes could gradually enhance the amount of N-containing functional groups and realize selective removal of Cr(VI) with the maximum experimental adsorption capacity of 564.7 mg/g, displaying a significantly high separation factor against alkali metal, alkaline earth metal, and other transition metal ions. Various combination mechanisms, such as electrostatic attraction, reduction, complexation, and hydrogen bonding, were demonstrated to be involved in the adsorption process of Cr(VI) by XPS, ESP, and DFT calculations. And the interaction energies of the five protonated configurations of primary amine, tertiary amine, secondary amine, imine, and secondary amine on the ring with HCrO4- were: -22.66, -12.08, -24.92, -24.26, -27.64 kcal/mol. In the actual industrial wastewater study, a Cr(VI) removal rate of 85.8% was realized. This work provided a viable idea for the elimination of Cr(VI) and was expected to be applied in the field of wastewater treatment.

Synchronously Enhanced Removal Ability and Stability of MXene through Biomimetic Modification

Increasing environmental problems intensify the demand for high-performance environmental purification materials. MXene is a typical transition-metal carbide/nitride material with a two-dimensional geometric feature and a good deal of functional groups, and it is considered as an efficient adsorbent for removing pollutants from wastewater. However, the easy oxidation and relatively low adsorption capacity greatly restrict its application. In this study, the MXene/polydopamine (PDA) composite particles were fabricated through the biomimetic modification method of inducing the self-polymerization of dopamine in an MXene aqueous solution. Microstructure characterizations demonstrate that PDA facilitates the exfoliation of MXene. Adsorption measurements show that MXene and PDA exhibit an apparent synergistic effect in removing chromium hexavalent Cr(VI) from aqueous solution, and more PDA content leads to a larger synergistic effect. Consequently, the composite particles exhibit an ultrahigh adsorption capacity (862.3 mg/g). Specifically, even if the composite particles were stored in aqueous solution for 2 months, they still exhibit high adsorption ability with only a 3.3% loss in adsorption capacity, indirectly confirming the enhanced stability of MXene induced by PDA. Furthermore, the composite particles also show reduction ability to Cr(VI) and about 54.3% Cr(VI) can be reduced to harmless chromium trivalent Cr(III). This study provides a new method for the preparation of MXene-based adsorbents with excellent adsorption capacity and high stability, which has broad application prospects in the field of wastewater treatment.

Biomimetic Polylactic Acid Electrospun Fibers Grafted with Polyethyleneimine for Highly Efficient Methyl Orange and Cr(VI) Removal

The rapid growth of industrialization has resulted in the release of large quantities of pollutants into the environment, especially dyes and heavy metals, which are environmentally hazardous for humans and animals. It is considered as the most promising and environmentally friendly route to develop green materials by using the green modification method, which has no negative impact on the environment. In this work, the green material of polylactic acid (PLA) was used as the substrate material, and a novel modification method of polydopamine (PDA)-assisted polyethyleneimine (PEI) grafting was developed. The electrospun PLA fibers are mainly composed of stereocomplex crystallites, which were achieved via the electrospinning of poly(l-lactic acid) and poly(d-lactic acid). The water-soluble PEI was grafted onto the PDA-modified PLA fibers through the glutaraldehyde-assisted cross-linking reaction. The prepared composite fibers can be degraded, which is environmentally friendly and meets the requirements of sustainable development. The potential application of such PLA composite fibers in wastewater treatment was intensively evaluated. The results show that at appropriate fabrication conditions (PDA concentration of 3 g·L^-1 and a PEI molecular weight of 70,000 g·mol^-1), the composite fibers exhibit the maximum adsorption capacities of 612 and 398.41 mg·g^-1 for methyl orange (MO) and hexavalent chromium [Cr(VI)], respectively. Simultaneously, about 64.79% of Cr(VI) adsorbed on the composite fibers was reduced to Cr(III). The above results show that the PLA composite fibers have a good development prospect in the field of wastewater treatment.

Polydopamine-assisted polyethylenimine grafting melamine foam and the application in wastewater purification

Melamine foam (MF) is a widely used commercial product and exhibits wide applications in many fields ranging from building, transportation to daily chemical product. Recent researches confirm that the special three-dimensional (3D) framework structure of MF can be an ideal substrate to prepare functional materials. In this work, the water-soluble polyethylenimine (PEI) was grafted onto the framework of MF to develop the water purification material toward heavy metal ions removal. The grafting of PEI on MF was achieved with the aids of polydopamine (PDA) coating and epoxy chloropropane (ECH) cross-linking successively. The 3D framework of MF could be well reserved and PEI was homogeneously grafted onto the framework surface. The adsorption capacity of the adsorbent was dependent upon the molecular wight of PEI. Lower PEI molecular weight endowed the adsorbent with better adsorption ability. The maximum adsorption capacity reached 328.95 mg/g, and the adsorbent exhibited extremely high adsorption stability with increasing cycling measurement numbers. Further results showed that the adsorbent also exhibited high reduction ability and induced about 62.5% toxic Cr(VI) to be reduced. This work confirms that the PEI-modified MF sample is a promising adsorbent in the removal of heavy metal ions and it can be used in wastewater treatment.