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.
Controlled assembly of nanostructures is a key challenge in nanotechnology. In this work, we introduce an approach for the controlled assembly of 1D nanodumbbellsAu-tipped semiconductor nanorodsinto arbitrary 2D higher architectures, by their chemical docking to nanopatterned functionalities. We realized the docking functionalities via nanoimprinted metallic nanodots functionalized with an organic monolayer, whose terminal thiol groups chemically bind the nanodumbbell tips. We demonstrated that the functional nanopattern encodes the nanodumbbell assembly and can be designed to deterministically position nanodumbbells in two possible modes. In the single-docking mode, the nanodot arrays are designed with a spacing that exceeds the nanodumbbell length, restricting each nanodumbbell to dock with one edge and physically connect with its free edge to one of the neighboring nanodumbbells. Alternatively, in the double-docking mode, the nanodots are spaced to exactly fit the nanodumbbell length, allowing nanodumbbell docking with both edges. We found that the docking kinetics can be described by a random attachment model, and verified that for the used docking chemistry, nanodumbbells that are docked to the same dot do not interact with each other. Our work demonstrates the possibility for massively parallel positioning of sub-100 nm 1D semiconductor nanostructures, and can potentially enable their future integration into functional nanodevices and nanosystems.
Two-dimensional CdS-based hybrid nanostructures are intriguing materials with an application prospect in different fields such as sensing (i. e., photoresistors) and solar energy harvesting (photocatalysis, photovoltaics, and so forth). We report herein a colloidal synthetic path for interfacing metal and semiconductor with 2D CdS nanoplates. Selective growth of Au, Pt, and a PtNi alloy as well as Cu 2−x S semiconductor is achieved on CdS nanoplates using controlled reduction of metallic precursors and thermal decomposition of a metal-sulfide single-source precursor using standard organic-phase colloidal chemistry.
The novel ensuing functionalities of complex nanostructures are driving the surging interest in their conceptualization and realization. Despite the significant synthetic developments in multicomponent hybrid nanostructure (HNS) formation, development of selective chemistry to tune the properties of HNSs will always be one of the major demands in colloidal synthesis. Synthesis of complex HNSs with a predicted morphology is particularly challenging using traditional strategies as the seeded growth due to surface chemistry limits. In the present work, we investigate the role of a metal oxide (MO) domain on the insertion of a CdS nanorod via a solution–liquid–solid mechanism between heterodimers of Au–MO. By choosing different compositions and crystalline structures for the MOs (namely, Fe3O4 and MnO), we demonstrate and explore the mechanism that allows the MO to dictate the chemoselective growth of the CdS domain. Additionally, a kinetic study unravels the role of the crystalline structure at a CdS–Fe3O4 interface on the final HNS shape.
A microorganism template approach has been explored for the fabrication of various well-defined three-dimensional (3D) structures. However, most of these templates suffer from small size (few μm), difficulty to remove the template, or low surface area, which affect their potential use in different applications or makes industrial scale-up difficult. Conversely, foraminifer’s microorganisms are large (up to 200 mm), consist of CaCO3 (easy to dissolve in mild acid), and have a relatively high surface area (≈5 m2 g–1). Herein, we demonstrate the formation of hierarchical structures of inorganic materials using calcareous foraminiferal shells such as Sorites, Globigerinella siphonifera, Lox-ostomina amygdaleformis, Calcarina baculatus or hispida, and Peneroplis planatus. Several techniques, such as thermal decomposition of single-source precursors of metal oxides or sulfides, reduction of metal salts directly on the surfaces, and redox reactions, were used for coating of different shell materials and several hybrid compositions, which possess nanofeatures. Finally, we examined the role of the prepared 3D structures on the reduction of 4-nitrophenol (4-NP), ethanol electrooxidation, and water purification. A remarkable performance was achieved in each application. The hierarchical structure leads to the reduction of 4-NP within several minutes, a 27 mA cm–2 current density peak was obtained for ethanol electrooxidation, and more than 95% of the organic dye contaminants were successfully removed. These results show that using foraminiferal shells offers a new way for designing complex hierarchical structures with unique properties.
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.
The necessity of providing clean water sources increases the demand to develop catalytic systems for water treatment. Good pollutants adsorbers are a key ingredient, and CuO is one of the candidate materials for this task. Among the different approaches for CuO synthesis, precipitation out of aqueous solutions is a leading candidate due to the facile synthesis, high yield, sustainability, and the reported shape control by adjustment of the counter anions. We harness this effect to investigate the formation of copper oxide-based 3D structures. Specifically, the counter anion (chloride, nitrate, and acetate) affects the formation of copper-based hydroxides and the final structure following their conversion into copper oxide nanostructures over porous templates. The formation of a 3D structure is obtained when copper chloride or nitrate reacts with a Sorites scaffold (marine-based calcium carbonate template) without external hydroxide addition. The transformation into copper oxides occurs after calcination or reduction of the obtained Cu2(OH)3X (X = Cl– or NO3–) while preserving the porous morphology. Finally, the formed Sorites@CuO structure is examined for water treatment to remove heavy metal cations and degrade organic contaminant molecules.
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