Chemical conversion based on the crystal facet effect of transition metal oxides and construction methods for sharp-faced nanocrystals

Microwave-Assisted Hydrothermal Synthesis of {100} and {111} Faceted LiFeO2 Truncated Octahedra: Investigations on Volatile Organic Compound Sensing Performance

Growth of exposed crystal facets has received considerable attention because of their coordinatively unsaturated surface atoms and defect-related surface reactivities. Herein, LiFeO2 truncated octahedra exposed with 6 {100} facets and 8 {111} facets were prepared through a simple microwave-assisted hydrothermal method without using any additives, surfactants, and calcination processes. The detailed growth process revealed that the formation of LiFeO2 truncated octahedra occurred only at the optimized reaction temperature (180 °C), time (30 min), and reactant concentrations. The prepared LiFeO2 truncated octahedra showed excellent sensing responses toward aliphatic organic compounds compared to that against aromatic organic compounds and poor response to inorganic compounds. The response percentages of 150 ppm concentrations of acetone, ethanol, formaldehyde, and isopropyl alcohol are 81.84, 62.91, 62.68, and 69.41%, respectively, at a low operating temperature (100 °C). The presence of exposed facets with their coordinatively unsaturated Li/Fe surface atoms such as 5-fold {100}, 3-fold {111}, 3-fold {100}-{111}, 2-fold {111}-{111}, and 2-fold coordination with the O atom in the vertices facilitated more oxygen vacancies and led to improved surface reactivities as well as sensitivity.

Shape-specific MOF-derived Cu@Fe-NC with morphology-driven catalytic activity: Mimicking peroxidase for the fluorescent- colorimetric immunosignage of ochratoxin

Ochratoxin A (OTA), which has strong hepatotoxicity and nephrotoxicity, can accumulate in the human body through the food chain; thus, the selective and effective detection of OTA is urgently required for food security. Nanozymes with hyperfine size and shape control have attracted attention because of their controllable structure and intrinsic activity. Herein, CuFe-bimetal coordinated N-doped carbon (Cu@Fe-NC) with morphology-driven peroxidase-mimicking activity was synthesized using Cu₂O with specific polygonal cubes and fully exposed {111} crystalline facets as the template to produce a CuFe-bimetallic metal organic framework (MOF) and further treating CuFe-MOF with high-temperature pyrolysis. N-doping can confer electronegativity to exhibit high affinity, while the large surface area of the porous carbon support can facilitate rapid adsorption-desorption equilibrium. Using the peroxidase-mimicking Cu@Fe_0.5-NC as a carrier, a versatile immunoassay for the detection of OTA was implemented based on the ratiometric fluorescence and the localized surface plasmon resonance peak shift, achieving a detection limit of 0.52 ng/L in the range of 0.001-10 μg/L. Therefore, the strategy of enhancing enzyme-mimicking activity using specific shapes and crystalline facets may open new avenues for food and environmental analysis.

Water-induced stacked α-Fe2O3 hexagonal nanoplates along [001] direction and its facet-dependent catalytic performances

Controlling the growth of nanocrystal to expose a specific facet is of great significance for the rational design of effective crystal catalysts. Herein, a water-induced stacking process was developed to...