Multiwall carbon nanotube-encapsulated algina micro-beads for extractions of lead(II) and methylene blue from water samples

Abstract

Aquatic heavy metals and dyes have been extensively-studied due to their toxicity that threatens human health and the environment. However, most of the methods are technologically disadvantageous and not cost effective from an economic point of view. This study investigates the application of multiwall carbon nanotube encapsulated alginate (MWCNT-Alg) micro-beads as adsorbent in solid phase microextraction (µSPE) for the determination of selected heavy metal ion, Pb(II) and methylene blue in water samples. MWCNT-Alg micro-beads were prepared by dissolving sodium alginate in warm water and add appropriate amount of MWCNT. The mixture was stirred until it turned into a viscous black mixture. The mixture obtained was added dropwise into a stirred 500-mL CaCl₂ solution (1% v/w) using a syringe and solid gel was immediately formed. The material was characterized using scanning electron microscopy (SEM) and attenuated total reflection (ATR) spectroscopy. Three parameters were optimized for the extraction of metal and the condition were: sample solution of pH 7, extraction time, 60 min and hydrochloric acid solution (0.05 M) as desorption solvent. Metal ion was determined using atomic absorption spectroscopy (AAS) while ultraviolet-visible spectroscopy (UV-Vis) was used to determine methylene blue in the water sample. For dye, the optimized extraction parameters were 4 min extraction time, 4 min desorption time and acetyl nitrile as a desorption solvent. Pb(II) ions were successfully extracted from the water samples. The method shows good linearity for Pb(II) and methylene blue with r² > 0.9965. Overall, the proposed MWCNT-Alg-mSPE combined with AAS and UV-Vis has proved satisfactory for the determination of aquatic heavy metal ions and dyes with good linearity  r² >  0.9969 and satisfactory LODs of 0.20 and 0.43 ppm for lead(II) and methylene blue, respectively.