Surfactin-functionalized poly(methyl methacrylate) as an eco-friendly nano-adsorbent: from size-controlled scalable fabrication to adsorptive removal of inorganic and organic pollutants

Abstract

Poly(methyl methacrylate) (PMMA), a non-toxic, cheap and easy-to-obtain compatible polymer, has widespread applications in biomedical and environmental nanotechnology. This work presents an environmentally-friendly sonochemical approach to synthesizing PMMA nanoparticles surface-functionalized with surfactin to develop multifunctional polymer nanoparticles with enhanced sorption properties. The advantages of sonochemical emulsion polymerization over conventional polymerization included (i) higher monomer conversion, (ii) enhanced latex yield, (iii) better surfactin functionalization and (iv) higher colloidal stability. The TEM micrographs showed that spherical nanoparticles with average sizes of 60 and 72 nm were formed by sonochemical and conventional emulsion polymerization, respectively. These nanoparticles were used for the selective removal of Pb²⁺, Cd²⁺, Cu²⁺, Fe²⁺, Ni²⁺, Co²⁺, Zn²⁺ and Cr³⁺ from water. Metal ions were removed either by forming chelate complexes or by electrostatic interactions. The observed affinity order for adsorption was Co²⁺ > Zn²⁺ > Ni²⁺ > Cr³⁺ > Fe²⁺ > Cu²⁺ > Cd²⁺ > Pb²⁺ under single-component non-competitive conditions. These nanoparticles were suitable for four adsorption–desorption cycles without appreciable loss of adsorption capacity. The rate of adsorption was described well by a pseudo-second-order rate equation and the Sips and Redlich–Peterson isotherms provided the best theoretical correlation with the experimental equilibrium data. The quality of the results was measured and the most influential parameter in each model was identified by a sensitivity analysis of the fitted model parameters. The adsorption thermodynamics were spontaneous and exothermic. The nanoparticles were also a good adsorbent for phenol and β-naphthol, but not for 1-naphthylamine. Furthermore, the sonochemically synthesized and surfactin-functionalized PMMA exhibited bactericidal action (300 μg mL⁻¹) against E. coli, with 80% killing efficacy and low haemolytic toxicity (45%), even at high concentrations up to 500 μg mL⁻¹. Therefore, these nano-adsorbents care suitable for environmental engineering applications.