In real engineering applications, nanoparticles can face hurdles of complex behavior of pollutants, for which electrostatic forces and background electrolyte can prove to be one of the robust mechanisms to remove pollutants from wastewater. In the present work, magnetite (Fe₃O₄) nanoparticles (NPs) and trioctyl phosphine oxide (TOPO) coated Fe₃O₄ NPs were synthesized and characterized for removing divalent Ni²⁺ and Cd²⁺ ions. Morphological and chemical analysis of both NPs was performed, and batch adsorption experiments were performed to study the influence of different pH ranges, concentrations of adsorbents and different contact timings. TOPO functionalized magnetite nanoparticles were found to have better adsorption capacities as compared to Fe₃O₄ at higher pH values. Isotherm models were run to identify the adsorption process. Langmuir isotherm model data fitted best for both metal ions adsorption, while Freundlich data suited best only for Ni²⁺ ions. The regression values for kinetic models confirmed that pseudo-second-order fitted best to the adsorption of both Ni²⁺ and Cd²⁺. Higher adsorption values were noticed for Ni²⁺ at higher dosages of both bare and TOPO-coated iron oxide NPs. Cadmium was found to have no influence of adsorbent dosage. Contact time was found to impact sorption values, i.e., adsorption was greater initially and then decreased with the passage of time. The study concludes that TOPO decorated Fe₃O₄ NPs can be more efficiently used for wastewater treatment. Furthermore, the presence of alkyl chains in TOPO can be immobilized at surface of metals to undergo adsorption more efficiently.

To overcome limitations of existing air-cleaning filters in capturing and deactivating aerosolized microorganisms, this study was embarked to evaluate novel Ag, Zn, and Fe nanoparticle-doped cotton filters (AgCt, ZnCt, FeCt), as biocidal filters for bioaerosol attenuation. To evaluate the biocidal activity of the nanocomposite filters, the survival of lab-generated E. coli after collection on each filter material was compared to collection on an undoped cotton control filter and in a BioSampler. Relative humidity (RH) affected the survival of bacteria on the filters, and the optimal RH was found to be 50 ± 5%. The physical removal efficiency (PRE) determined by an optical particle counter was 99.9 ± 0.7% for ZnCt, 97.4 ± 1.2% for AgCt, and 97.3 ± 0.6% for FeCt, where the control showed only 77.4 ± 6.3% for particles > 500 nm. The doped filters showed 100% viable removal efficiency (VRE). Importantly, the VRE of the nanocomposite filters after four cycles remained nearly 99% and was greater than the cotton control filter at 76.6 ± 3.2%. Adding to its benefits, the AgCt filters had a lower pressure drop than the FeCt and ZnCt filters and the cotton control. The permeability for the cotton control filter was 3.38 × 10⁻¹¹ m² while that for the AgCt filter was slightly higher (3.64 × 10⁻¹¹ m²) than the other filters as well. Overall, these results suggest that nanocomposite-doped filter media, particularly AgCt, can provide effective protection against airborne pathogens with a lower pressure drop, elevated collection efficiency, and better disinfection capability as compared to untreated cotton filters, which are all important features for practical biocidal applications. Graphical abstract