Mesoporous anodic α-Fe2O3 interferometer for organic vapor sensing application

Advances in Optical Biosensors and Sensors Using Nanoporous Anodic Alumina

This review paper focuses on recent progress in optical biosensors using self-ordered nanoporous anodic alumina. We present the fabrication of self-ordered nanoporous anodic alumina, surface functionalization, and optical sensor applications. We show that self-ordered nanoporous anodic alumina has good potential for use in the fabrication of antibody-based (immunosensor), aptamer-based (aptasensor), gene-based (genosensor), peptide-based, and enzyme-based optical biosensors. The fabricated optical biosensors presented high sensitivity and selectivity. In addition, we also showed that the performance of the biosensors and the self-ordered nanoporous anodic alumina can be used for assessing biomolecules, heavy ions, and gas molecules.

Formation of Nanoporous Mixed Aluminum-Iron Oxides by Self-Organized Anodizing of FeAl3 Intermetallic Alloy

Nanostructured anodic oxide layers on an FeAl3 intermetallic alloy were prepared by two-step anodization in 20 wt% H2SO4 at 0 °C. The voltage range was 10.0-22.5 V with a step of 2.5 V. The structural and morphological characterizations of the received anodic oxide layers were performed by field emission scanning electron microscopy (FE-SEM). Therefore, the formed anodic oxide was found to be highly porous with a high surface area, as indicated by the FE-SEM studies. It has been shown that the morphology of fabricated nanoporous oxide layers is strongly affected by the anodization potential. The oxide growth rate first increased slowly (from 0.010 μm/s for 10 V to 0.02 μm/s for 15 V) and then very rapidly (from 0.04 μm/s for 17.5 V up to 0.13 μm/s for 22.5 V). The same trend was observed for the change in the oxide thickness. Moreover, for all investigated anodizing voltages, the structural features of the anodic oxide layers, such as the pore diameter and interpore distance, increased with increasing anodizing potential. The obtained anodic oxide layer was identified as a crystalline FeAl2O4, Fe2O3 and Al2O3 oxide mixture.

Synthesis, structure, magnetism and photocatalysis of α-Fe2O3 nanosnowflakes

In this work, a simple one-step hydrothermal method was developed to synthesize high-quality α-Fe₂O₃ nanoparticles with a snowflake-like microstructure. First, a series of binary supramolecular aggregates were prepared by a non-covalent combination between a polymer such as polyvinylpyrrolidone (PVP) and a complex such as potassium ferrocyanide (PF). Then, the aggregates were used as the precursors of the one-step hydrothermal reactions. The snowflake-like nanostructure has six-fold symmetry as a whole, and each petal is symmetric. This synthesis method has the characteristics of simplicity, rapidity, reliance, and high yield, and can be used for creating high-quality α-Fe₂O₃ nanoparticles. Moreover, our results show that the molar ratio of PVP to PF, reaction time and temperature play important roles in the generation of a complete snowflake structure from different angles. Also, the snowflake-like α-Fe₂O₃ nanostructure exhibits a much higher coercivity (2997 Oe) compared to those reported by others, suggesting a strong hysteresis behaviour, which promises potential applications in memory devices, and other fields. Further, the α-Fe₂O₃ nanosnowflakes show a much higher photocatalytic degradation activity for cationic organic dyes such as crystal violet, rhodamine 6G than for anionic dyes such as methyl orange. A possible photocatalytic mechanism was proposed for explaining the selectivity of the photocatalytic oxidation reaction of organic dyes. We believe that this study provides a direct link among coordination compounds of transition metals, their supramolecular aggregates with polymers, and controlled hydrothermal synthesis of high-quality inorganic metal oxide nanomaterials.

α-Fe₂O₃ nanosnowflakes exhibit enhanced coercivity and improved photocatalytic performance for organic dyes.