Rapid urbanization and industry expansion have caused massive public health and water quality. As a result, various industries discharge their heavy metals and organic dyes into the aquatic systems without a proper purification process. Based on literature studies, hexavalent chromium [Cr(VI)] is intensively used in the tannery, textile and steel fabrication, while arsenic is discharged into environmental surroundings via geothermal processes and mineral deposits. The maximum permissible concentrations of arsenic and chromium regulated by the World Health Organization (WHO) are 10 and 50 ppb in drinking water. Additionally, dyes originate from various industrial activities such as textile, cosmetics, leather, food, pharmaceutical, paper productions (pulp), paint and varnish. These discharged dyeing effluents are carcinogenic, and mutagenic which are highly toxic to humans and ecological organisms. Hence, it’s vital to treat them before their discharge. In this regard, a group of academic principle investigators from multiple countries (Poland, Taiwan and India) offered a significant contribution toward developing a promising adsorbent (magnetic aerogel, PEI-h-BNNSs@Fe₃O₄NPs) for environmental remediation with high adsorption efficiency.

Herein we fabricated thermal polycondensation of melamine and boric acid, and pyrolysis of the resultant products which allowed to exfoliate by ultra-sonication process further functionalization with PEI-mediated modification of h-BNNSs. The as-formed PEI-h-BNNSs allowed the in-situ formation of magnetite nanoparticles (Fe₃O₄ NPs) decorated on their surfaces, which are turned to be PEI-h-BNNSs@Fe₃O₄ NPs. The lyophilization treatment of PEI-h-BNNSs@Fe₃O₄ NPs-loaded PVA hydrogels generated the magnetic hybrid aerogel (MHAs) with a large surface area to volume ratio and good super-paramagnetic behaviour. The as-made MHAs exhibited a three-dimensional porous structure with diverse functional groups (−N, −NH, −NH₂, and −OH) and zero net charge.

Additionally, incorporating magnetic nanoparticles into aerogels (3-dimensional porous structure) had the added advantages of simplicity, low cost and rapidity in the recycling process. These features enabled the as-made MHAs to serve as a powerful adsorbent to remove Cr(VI), As(V), MB and AO from an aqueous solution and their adsorption behaviour which follows the Freundlich isotherm model and a pseudo-second-order model. In contrast to the PEI-h-BNNSs-loaded PVA aerogels, Fe₃O₄ NPs-loaded PVA aerogels and other previously reported adsorbents, the MHAs provide numerous distinct advantages, including (1) the presence of highly mesoporous structures with a large specific surface area of 104.6 m² g^-1, (2) the possession of diverse and abundant functional groups (−N, −NH, −NH₂, and −OH) on the surface, (3) outstanding adsorption capacity for capturing of Cr(VI) (833 mg g^-1), As(V) (426 mg g^-1), MB (415 mg g^-1) and AO (286 mg g^-1), (4) in-situ reduction of Cr(VI) to Cr(III) and As(V) to As(III), (5) The adsorption performance of MHAs allows the removal of >95% for Cr(VI) and As(V) in contaminated soil-sludge samples, (6) more than three successive adsorption-desorption cycles for >80% uptake of Cr(VI), As(V), MB, and AO and (7) the accessible collection of MHAs by applying an external magnetic field. Accordingly, our research work discloses that the as-made aerogels composed of magnetic nanoparticles and h-BNNSs-based materials cross-linked with PVA polymers have a great potential candidate (adsorbent) in the large-scale water purification process.

For more details on this work, please see: https://doi.org/10.1038/s41545-022-00175-0