Styrofoam modified paper as a low-cost platform for qualitative and semi-quantitative determination of Ni2+ ions in wastewater

Abstract

In the present article we have demonstrated a swift and low-cost method to design hydrophobic paper and its potential applications for the determination of Ni²⁺ ions in wastewater. Styrofoam was used as a precursor to fabricate pristine filter paper into a low wetting substrate. The water contact angle (θ) of the modified paper was ∼111° whereas atomic force microscopy analysis ensured a uniform coating of the polymer onto cellulose fibers. Metal specific reagent 1-(2-mercaptophenyl)iminomethyl naphthalen-2-ol (MPMN) was manually arrayed and one-step assay for the determination of Ni²⁺ was demonstrated on the aforementioned substrates. The end-result was observed in the form of a distinct color change which was easily readable via the naked eye. We also quantitated the concentration of Ni²⁺ ions through flatbed scanning and scoring their pixel gray volume using image analysis software. On Styrofoam modified paper, the limit of detection was improved to 10⁻² μg mL⁻¹, which was 3-orders of magnitude lower than that observed on pristine filter paper. The MPMN reagent was highly selective towards Ni²⁺ in the presence of a high concentration of commonly diverse heavy metals (Ag⁺, Al³⁺, As³⁺, Ba²⁺, Cd²⁺, Cr³⁺, Fe³⁺, Pb²⁺ and Mn²⁺) and some other ions (Na⁺, Ca²⁺, K⁺ and Cl⁻) in water. Our developed method successfully demonstrated the semi-quantitative determination of Ni²⁺ ions in tap and municipal wastewater samples. Due to good specificity as well as accuracy towards Ni²⁺ ions, our low-cost sensor will be useful in point-of-use applications.