Engineering green MOF-based superhydrophobic sponge for efficiently synchronous removal of microplastics and pesticides from high-salinity water

Abstract

Microplastics (MPs) and pesticides are becoming an intractable environmental issue due to their wide spreading and non-degradable nature, posing serious threat to ecosystem and human health. To settle such dilemma, this work reasonably designed a superhydrophobic MOF-based coated sponge (ODSOSS/TiO₂/Ni-MOF/PDA@Sponge) through the combination of an environmentally friendly in-situ supersaturated coprecipitation and polysesiloxane modification method. Among them, (I) the introduction of polydopamine (PDA) not only improves the adhesion between coatings and sponge, but also enhances the growth of MOF structure through complexation. (II) The obtained Ni-MOF shows large-area microscale anthemy structure with multilayered flaky texture, forming heterogeneously hierarchical structure with the deposited TiO₂ nanoparticles, which promotes photodegradation ability of TiO₂ owing to great specific surface area of Ni-MOF. (III) The high specific large area Ni-MOF supplies sufficient action sites for linkage of PDA and polysesiloxane molecules with unique nanocage-like structure, thus further greatly increasing adsorption force for various pollutants. (IV) The superhydrophobicity protect the porous channels of MOF from contamination of various absorbed pollutants, while TiO₂ nanoparticles effectively photodegrade the absorbed organic pollutants, endowing the sponge superior recyclability. The superhydrophobic sponge selectively rapidly and synchronously adsorbs various MPs (maintained almost 100% after 60 cycles) and pesticides (adsorption rates 71.6%-95.1%) from high-salinity water. The large-area sponge (9 cm × 6 cm × 1 cm) simultaneously removes almost 100% MPs (40 mg/L), Sudan Ⅲ (10 mg/L), kerosene (30 mL/L), and four pesticides (10 mg/L) within 1 min. Particularly, four pesticides are quickly photocatalytic degraded by the coated sponge. The free radical capture trials show that hydroxyl radicals (·OH) are the main active species of pesticide degradation. Furthermore, we reveal the negative centers where pesticide molecules are most vulnerable to ·OH attack, on basis of the charge distribution and molecular electrostatic potential (MEP) analysis. The adsorption mechanisms are carefully clarified through theoretical calculation and experimental data. This work not only provide an effective superhydrophobic candidate for MPs and pesticides removal in a broad applicable scope (especially in high-salinity wastewater), but also opens a new strategy for environmental remediation.

Keywords: In-situ adsorption; Microplastics; Ni-MOF; Pesticides; Superhydrophobicity.