Highly Sensitive and Selective In-Situ SERS Detection of Pb(2+), Hg(2+), and Cd(2+) Using Nanoporous Membrane Functionalized with CNTs.

Mohamed Shaban,A R Galaly

doi:10.1038/srep25307

Abstract

Porous Anodic Alumina (PAA) membrane was functionalized with CoFe2O4 nanoparticles and used as a substrate for the growing of very long helical-structured Carbon Nanotubes (CNTs) with a diameter less than 20 nm. The structures and morphologies of the fabricated nanostructures were characterized by field emission- scanning electron microscopy (FE-SEM), energy dispersive X-ray (EDX), and Raman spectroscopy. By uploading the CNTs on PAA, the characteristic Raman peaks of CNTs and PAA showed 4 and 3 times enhancement, respectively, which leads to more sensitive Surface-Enhanced Raman Spectroscopy (SERS) substrates. For comparison, PAA and CNTs/PAA arrays were used as SERS substrates for the detection of Hg2+, Cd2+, and Pb2+. The proposed sensor demonstrated high sensitivity and selectivity between these heavy metal ions. CNTs/PAA sensor showed excellent selectivity toward Pb2+ over other metal ions, where the enhancement factor is decreased from ~17 for Pb2+ to ~12 for Hg2+ and to ~4 for Cd2+. Therefore, the proposed CNTs/PAA sensor can be used as a powerful tool for the determination of heavy metal ions in aqueous solutions.

Highlights

Carbon Nanotubes (CNTs) are attracting much interest owing to their novel commercial optoelectronic applications such as flat panel displays, ultra-sensitive electromechanical and chemical sensors, and hydrogen storage devices[1,2,3,4]
Multi-walled (MW) CNTs can be grown inside Porous anodic alumina (PAA) membrane by chemical vapor deposition (CVD) from transition metal nanoparticles (NPs) and nanowires (NWs) deposited inside its pores
The surface properties of the blank and CNTs- coated PAA membrane were characterized by field emission- scanning electron microscopy (FE-SEM)

Summary

Introduction

Carbon Nanotubes (CNTs) are attracting much interest owing to their novel commercial optoelectronic applications such as flat panel displays, ultra-sensitive electromechanical and chemical sensors, and hydrogen storage devices[1,2,3,4]. Deposition of CNTs inside the pores of PAA membranes has gained much attention in recent years due to their potential use as a surface-enhanced Raman scattering (SERS) substrate[13]. Multi-walled (MW) CNTs can be grown inside PAA membrane by CVD from transition metal nanoparticles (NPs) and nanowires (NWs) deposited inside its pores. Frost et al.[30] employed the metal-affinity properties of a citrate functionalized gold nanoparticle (AuNP) to detect Pb2+ ions based on SERS. This detector showed a linear behavior between 50 ng/L and 1000 ng/L. The fabricated blank PAA and CNTs/PAA membranes are used as ultra-high sensitive sensors for the detection of traces concentrations of Hg+2, Pb+2, and Cd+2 ions in water. The sensing principle is based on in-situ SERS spectroscopy

Methods

Results

Conclusion