Improving Surface Adsorption via Shape Control of Hematite α-Fe₂O₃ Nanoparticles for Sensitive Dopamine Sensors

Abstract

α-FeO nanoparticles (NPs) with morphologies varying from shuttle to drum were synthesized through an anion-assisted and surfactant-free hydrothermal method by simply varying the ratios of ethanol and water in solvent. Control experiments show that the structural evolution can be attributed to a small-molecular-induced anisotropic growth mechanism in which the growth rate of α-FeO NPs along the a-, b-, or c-axis was well-controlled. The detailed structural analysis through the high-resolution transmission electron microscope (HRTEM) indicated that shuttle-like FeO NP surface was covered by high-density atomic steps, which endowed them with the enhanced adsorption and sensor ability toward dopamine (DA). The XPS characterizations indicated that the percentages of the O component follow the order of shuttle-like FeO (S-FeO for short) > pseudoshuttle-like FeO (Ps-FeO for short) > polyhedron-like FeO (Ph-FeO for short) > drum-like FeO (D-FeO for short). Benefits from these structural advantages, the S-FeO NPs-Nafion composite electrode exhibited remarkable electrochemical detection ability with a wide liner range from 0.2 μM to 0.107 mM and a low detection limit of 31.25 nM toward DA in the presence of interferents.

Morphologically Tunable MnO2 Nanoparticles Fabrication, Modelling and Their Influences on Electrochemical Sensing Performance toward Dopamine

“…As presented in Figure 5B, the oxidation peak currents (i pa ) increase linearly with scanning rate (v), suggesting the electrochemical oxidation of dopamine is an adsorption-controlled process. This result is consistent with previous reports [34,[37][38][39][40][41], and also favors our assumption for model simulation. …”

“…As is well known, electrocatalytic oxidation of dopamine on the surface of modified electrodes is mainly controlled by the adsorption process [34,[37][38][39][40][41]. Hence, the response peak current can be calculated according to the Laviron Equation [45]:…”

“…For example, the surface adsorption is tuned via controlled preparation of various shapes of hematite α-Fe 2 O 3 (shuttle-like, pseudo-shuttle-like, polyhedron-like, and drum-like α-Fe 2 O 3 ), and shuttle-like Fe 2 O 3 exhibits better electrochemical detection ability than other shapes of Fe 2 O 3 nanoparticles [34]. Various morphologies of manganese dioxide (MnO 2 ) electrocatalysts, including nanoflowers, nanorods, nanotubes, nanoplates, nanowires, and microspheres were prepared via facile hydrothermal synthesis and precipitation methods, and their electrochemical properties were found to be strongly dependent on the morphology [35].…”

“…The response peak currents and peak current densities among three various morphologies of MnO 2 -RGO/GCE have been compared to find out the main factors on the enhancement of electrochemical response. The response peak current is supposed to be proportional to the surface area of the modified electrode, because of the presence of an adsorption-controlled process during electrochemical oxidation of dopamine [34,[37][38][39][40][41]. Based on the hypothesis, spatial models for three various morphologies of nano-MnO 2 were established to compare their specific surface area, and find the main factors on the specific surface area.…”

Enhancing the Adsorption Capacity of Hematite by Manganese Doping: Facile Synthesis and its Application in the Removal of Congo Red

“…The overall XPS spectrum of sample MF4 is shown as Figure (a), which clearly indicates the presence of elements Mn, Fe, and O. The binding energy of O 1s is measured to be 529.4 eV (Figure (b)), which is consistent with the previous reports for hematite nanostructures . The XPS spectrum of Mn 2p can be fitted when considering the two spin‐orbit doublet characteristics of Mn 3+ and Mn 2+ (Figure (c)), suggesting the existence of Mn with different valence states.…”