Given their unique properties, tremendous progress is realized in the use of nanostructured materials for various applications. However, their incorporation and fabrication into prototypic devices remain challenging due to their limited ability to form hierarchical 3D structures through the use of large scale, low cost, and facile processes. Herein, this challenge is addressed and the growth of unique hierarchical structures is demonstrated by coating calcareous foraminiferal shells with metal oxide materials via simple and inexpensive processes conducted on a large scale. Foraminifera are highly diverse and abundant marine unicellular protists surrounded by large, ranging from 0.1 mm to more than 200 mm in size, identical porous, and complex hierarchical shells. In the present study, these hierarchal structures are investigated in electrochemical water oxidation reactions and tested in terms of their ability to purify water from inorganic (metal ions) contaminates. The remarkable performances of the prototype filters and catalysts developed here, among the best recorded values in both fields, are reported. These findings thus open new perspectives for catalytic and water purification applications.

An oil-based composite is employed to monitor the exposure to oxygen inside food packaging, aiming at evaluating the package integrity and the freshness of food. The composite is an oxygen-sensitive printable ink consisting of electrically conductive silver microflakes, embedded in a vegetable oil matrix. The sensitivity of the oil to oxygen is driven by its high content of unsaturated fatty acids that polymerize and shrink upon exposure to atmospheric oxygen. Shrinkage increases the silver concentration and induces percolation, manifested by a steep increase in the electrical conductivity of the composite. We found that the electrical conductivity of the composite is related to its exposure time to air. Employing linseed oil as a matrix demonstrates an increase in electrical conductivity from 10–11 to 10–3 S/cm after only 6 days of exposure to air. We also show that this time span could be modified by changing the oil type to fit various expiration periods of food products.

The determination of food freshness along manufacturer-to-consumer transportation lines is a challenging problem that calls for cheap, simple, reliable, and nontoxic sensors inside food packaging. We present a novel approach for oxygen sensing in which the exposure time to oxygen—rather than the oxygen concentration per se—is monitored. We developed a nontoxic hybrid composite-based sensor consisting of graphite powder (conductive filler), clay (viscosity control filler) and linseed oil (the matrix). Upon exposure to oxygen, the insulating linseed oil is oxidized, leading to polymerization and shrinkage of the matrix and hence to an increase in the concentration of the electrically conductive graphite powder up to percolation, which serves as an indicator of food spoilage. In the developed sensor, the exposure time to oxygen (days to weeks) is obtained by measuring the electrical conductivity though the sensor. The sensor functionality could be tuned by changing the oil viscosity, the aspect ratio of the conductive filler, and/or the concentration of the clay, thereby adapting the sensor to monitoring the quality of food products with different sensitivities to oxygen exposure time (e.g., fish vs grain).

The solution–liquid–solid (SLS) mechanism is a well-established method for forming one-dimensional (1D) nanostructures in a solution. Herein, an SLS mechanism is explored for the formation of metal oxides for the first time. Two key synthetic achievements allow this synthesis: (i) the design of a tailored catalyst with a low melting point and high stability and (ii) control over the reactivity and the oxidation of the precursors. Once these conditions are achieved, the SLS growth of indium and tin oxides ensues. Structural characterization of the products at various stages of the growth confirms the formation of 1D In2O3 and SnO2 nanoscale heterostructures using AuIn2 and Au7Sn3 as catalysts. Furthermore, SLS growth was easily adopted to insert SnO2 rods selectively between two domains of an Au/ZnO heterodimer, demonstrating the potential of achieving highly complex multicomponent metal-oxide nanostructures.

No abstract