Synthesis and Characterization of Free and Grafted N-Halamine Nanoparticles for Decomposition of Organic Dyes in an Aqueous Continuous Phase

Synthetic organic dyes constitute a major pollutant in wastewater. Here, we describe the synthesis and characterization of N-halamine nanoparticles (NPs) for decomposition of organic dyes from contaminated wastewater. Cross-linked poly(methacrylamide) (PMAA) NPs of hydrodynamic diameters ranging from 11 ± 1 to 161 ± 31 nm were synthesized at room temperature by redox surfactant-free dispersion copolymerization of methacrylamide and the cross-linking monomer N,N′-methylenebis(acrylamide) in an aqueous continuous phase. The effect of various polymerization parameters on the diameter and size distribution of the formed NPs was studied. Additionally, thin coatings composed of cross-linked PMAA NPs were grafted onto oxidized corona-treated polypropylene (PP) films by redox graft polymerization of the monomers in the presence of oxidized PP films. The free and grafted NPs were converted to N-halamine species by chlorination with sodium hypochlorite. The decomposition kinetics of two model organic dyes, methylene blue (MB) and crystal violet (CV), was evaluated for both free and grafted PMAA-Cl NPs. Free cross-linked PMAA-Cl NPs at room temperature, with concentrations of 5 and 0.5 mg/mL, illustrated full decomposition of CV and approximately 90% decomposition of MB after 42 and 97 h. In order to enhance the dye decomposition, the mixtures were heated to 70 °C. Complete decomposition of CV and MB at PMAA-Cl NP concentrations of 5 and 0.5 mg/mL required 60 and 240 min for CV, respectively, and 180 and 420 min for MB, respectively. Similarly, the PP/PMAA-Cl films also demonstrated a high reduction in the MB concentration after 150 min. Due to the highly efficient dye decomposition, these free and immobilized chlorinated NPs may be utilized as new reagents for decomposition of organic materials from contaminated wastewater.