Highly Efficient Photocatalytic Degradation of Organic Pollutants Using a Polyvinylidene Fluoride/Polyvinylpyrrolidone-Cuprous Oxide Composite Membrane.

Enhancing the efficiency of photocatalysts in the removal of organic pollutants is of vital importance in wastewater treatment. In this work, a set of composite membranes that can be used for efficient removal of the organic dyes, such as methyl orange (MO), methylene blue (MB), and Congo red (CR), were prepared through coblending/electrospinning techniques using polyvinylidene fluoride (PVDF) as the substrate, polyvinylpyrrolidone (PVP) as the dispersing agent and wettability regulator, and cuprous oxide (Cu2O) as the photocatalyst. The results showed that Cu2O particles were well encapsulated in the electrospun PVDF/PVP fibers, and the composite membranes exhibited apparently enhanced hydrophilicity. Furthermore, compared with the pure Cu2O particles, the composite membranes not only showed a higher photocatalytic degradation ratio for MO (93.6%) but also showed a much higher degradation rate (62.4 mg/(mg·h)) in comparison with the other reported Cu2O-based composite photocatalytic materials in the literature. In addition, the membrane sample also had excellent recycling stability, and the retention rate of its removal ability maintained 92.1% after 5 times of recycling. Furthermore, the composite membranes also showed high removal ability toward MB and CR, with photocatalytic degradation ratios of 81.4 and 76.1%, respectively. This work indicates that the prepared PVDF/PVP-Cu2O composite membranes possess promising application prospects in 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.

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.

Chitosan-assisted MOFs dispersion via covalent bonding interaction toward highly efficient removal of heavy metal ions from wastewater.

Metal organic frameworks (MOFs) have been considered to be robust adsorbent for the removing heavy metal ions from wastewater due to their unique properties such as large active sites, high specific surface area and high porosity, etc., however, their practical engineering application faces the problem of serious agglomeration. In this work, a new strategy of chitosan (CS) assisting MOF dispersion was proposed to develop the new generation of MOF-based adsorbents, namely, CS grafted UiO-66-NH2 composite materials (CGUNCM). The UiO-66-NH2 was selected and it was grafted onto the main chains of CS through covalent bonding interaction with the aid of glutaraldehyde, which was totally different from the common method that grafting molecular chains on the surface of MOFs resulting in the dramatic reduction of active adsorption sites. The results show that grafting MOFs onto CS main chains not only greatly improves the dispersion of MOFs but also reserves the morphology of MOFs as much as possible. The adsorption performances toward Cu(II) and Pb(II) were intensively studied by varying adsorbate concentration, ionic strength, the contact time, adsorption temperature and pH value of solution. The results show that the composite adsorbent exhibits high adsorption efficiency and the adsorption equilibrium can be reached within 45 min, and the maximum adsorption capacity toward Cu(II) and Pb(II) achieve 364.96 mg/g and 555.56 mg/g, respectively. Furthermore, the composite adsorbent shows good reusability. This work provides a new method of fabricating the MOF-based adsorbent and paves the way for the practical application of such adsorbents in wastewater treatment.