Hierarchical growth of ZnFe2O4 for sensing applications

Abstract

Mesoporous ZnFe₂O₄ nanoflowers (NFs) have been prepared using a modified hydrothermal (MHT) technique, developed in our laboratory. Urea has been brought in for hydrolysis of FeCl₃ and ZnSO₄ in solution to homogeneously precipitate ZnFe₂O₄. The precipitated product upon annealing at 450 °C results in mesoporous ZnFe₂O₄ NFs. Important physical methods have been used to characterize the NF material in the solid state. The growth mechanism of mesoporous NFs of evolution is confirmed by the adopted reaction strategy. The ZnFe₂O₄ NF finds application in peroxidase mimicking activity which in turn helps the selective naked eye detection of H₂O₂ and Hg²⁺ ions in solution. However, spectrophotometric detection limit goes down to 0.1 mM and 2.58 × 10⁻³ mM for H₂O₂ and Hg²⁺, respectively. To contemplate peroxidase like activity, colorless 3,3′,5,5′-tetramethylbenzidine (TMB) is employed which in turn oxidized to a blue solution by H₂O₂ in the presence of ZnFe₂O₄ rendering H₂O₂ sensing. It has been discovered that the blue color development is selectively held up by Hg²⁺ ion causing Hg²⁺ sensing possible. Judicious selection of Hg²⁺ ions once again indicates strong affinity of the nitrogen donor towards Hg²⁺. This makes Hg²⁺ sensing possible without the use of any noble metal. A strong and definite ‘–N–Hg–N’ binding interaction with nitrogen donors of the TMB substrate causes blue color bleaching. Herein we report the usefulness of an under-rated ZnFe₂O₄ nanoflower for the first time to detect Hg²⁺ spectrophotometrically and in a cost-effective way. On the other hand, a highly mesoporous nanoflower has been shown to be a selective sensor for acetone also. Based on the above reaction/interaction strategies it is expected that the as-synthesized ZnFe₂O₄ NFs would stand as cost effective sensor materials for biological applications and environmental remediation.