Formation of Copper Oxide Nanotextures on Porous Calcium Carbonate Templates for Water Treatment.

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.

Novel easy to fabricate liquid crystal composite with potential for electrically or thermally controlled transparency windows.

Switchable liquid crystal (LC) composites are a unique and attractive class of functional materials due to their extensive use in various applications including smart and privacy windows. Demand for developing smart windows with good switchable performance has steadily increasing in the past decades due to their importance in energy saving. Herein, we present the use of novel and highly active switchable LC composite material-octadecanol-doped LC-prepared via a facile, low-cost, and scalable process, for thermally or electrically controlled transparency windows. A systematic study of the switchable behavior reveals the formation of a reversible molecular arrangement between the LC and the octadecanol, which allows control of the transparency through scattering modulation of the device by voltage or temperature. The devices fabricated by sandwiching the LC composite material between two ITO-covered glass slides present switchable performance with high potential for cost-effective utilization in various applications, such as light shutters, smart or privacy windows.

Thermal decomposition approach for the formation of α-Fe2O3 mesoporous photoanodes and an α-Fe2O3/CoO hybrid structure for enhanced water oxidation.

Hematite (α-Fe2O3) is one of most investigated oxides for energy applications and specifically for photocatalysis. Many approaches are used to prepare well-controlled films of hematite with good photocatalytic performance. However, most of these methods suffer from a number of disadvantages, such as the small quantities of the product, and the assembly of the nanostructures is usually a secondary process. Herein, we present a facile and large-scale synthesis of mesoporous hematite structures directly on various substrates at moderate temperature and study their photoelectrochemical (PEC) properties. Our approach is based on thermal decomposition of iron acetate directly on a substrate followed by an annealing process in air to produce a continuous mesoporous film of α-Fe2O3, with good control of the size of the pores. Improving the PEC properties of iron oxide was achieved by deposition of CoO domains, which were formed by thermal decomposition of cobalt acetate directly onto the hematite surface to produce α-Fe2O3/CoO nanostructures. PEC measurements of the hematite film before and after CoO growth were tested. Two methods were used to deposit the cobalt material: (a) thermal decomposition and (b) the most typically used method, adsorption of cobalt salt. The photocurrent of pure hematite was 0.25 mA/cm(2) at 1.23 V versus reversible hydrogen electrode (RHE), while modification of the hematite surface using the thermal decomposition method showed 180% improvement (0.7 mA/cm(2) at 1.23 V vs RHE) and 40% improvement (0.35 mA/cm(2) at 1.23 V vs RHE) via the adsorption method. Moreover, the onset potential was shifted by 130 and 70 mV when the surface of the hematite was modified by the thermal decomposition and adsorption methods, respectively.

Calcareous Foraminiferal Shells as a Template for the Formation of Hierarchal Structures of Inorganic Nanomaterials.

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.

Bioinspired Hierarchical Porous Structures for Engineering Advanced Functional Inorganic Materials.

Tremendous efforts have been directed at designing functional and well-defined 3D structures in recent decades. Many approaches have been devised and are currently used to create 3D structures, including lithography, 3D printing, assembly, and template-mediated (natural or synthetic) methods. Natural scaffolds offer some unique traits, as compared to their artificial counterparts, presenting highly ordered, porous, identical, abundant, and diverse structures. Various organisms, such as viruses, bacteria, diatoms, foraminifera, and others, are used as templates to form 3D structures. Herein, advancements made in using the shell of marine microorganisms, diatoms, and foraminifera, as scaffolds for designing functional 3D structures are reported. Furthermore, a succinct overview of various synthetic methods used to coat these scaffolds with inorganic materials (i.e., metals, metal oxides, and metal sulfides) is provided. Finally, the use of such fabricated functional 3D structures in a wide range of applications, such as catalysis, sensing, drug delivery, photo-electrochemical uses, batteries, and others, is considered.

Electrophoretic deposition of single-source precursors as a general approach for the formation of hybrid nanorod array heterostructures.

HYPOTHESIS: Subjecting colloids to electric fields often results in (electrophoretic) deposition on conductive substrates. Dispersing a single-source precursor (SSP) of choice in an appropriate solvent, should allow its deposition on different substrates. The SSP-solvent interaction might play a role in the deposition (e.g., direction, rate, coverage). After thermal decomposition, the SSPs convert to the designed material, thus allowing formation of thin films or hybrid nanostructures. EXPERIMENTS: Electrophoretic deposition (EPD) was applied on two representative SSPs in different solvents. These SSPs were deposited onto substrates covered with vertically-aligned ZnO nanorod (NR) arrays. After thermal decomposition, hybrid nanostructures were obtained and their morphology and interfaces were characterized by electron microscopy, X-ray diffraction, UV-vis, and electrochemistry. FINDINGS: Tuning the organic dispersant-SSP interaction allows control over the final film morphology, which can result in coating and filling of NRs with metal-sulfides or metal-oxides after thermal decomposition of the SSP. These findings introduce a new facile method for a fast and large-scale uniform deposition of different (nanostructured) thin film semiconductors on a variety of substrates. We discuss the influence of the dispersant medium on the deposition of metallo-organic SSPs. As an example, the formed ZnO-CdS interface supports charge transfer upon illumination.

Ternary hybrid nanostructures of Au-CdS-ZnO grown via a solution-liquid-solid route using Au-ZnO catalysts.

Multi-component nanostructures of Au-CdS-ZnO with a novel morphology were synthesized by a non-conventional strategy where seeded growth is combined with solution-liquid-solid (SLS) growth. Each of these synthetic routes is used for growing a different domain of the final heterostructure, where ZnO rods are grown first on Au nanoparticles via heterogeneous nucleation while CdS is later grown between these two domains via SLS, using the Au tip of the preformed Au-ZnO as a catalyst. The in situ alloying of the Au tip with Cd enabled the metal tip to function as an SLS catalyst at a relatively mild reaction temperature which is lower than the melting point of pure Au.

Organic phase synthesis of noble metal-zinc chalcogenide core-shell nanostructures.

Multi-component nanostructures have been attracting tremendous attention due to their ability to form novel materials with unique chemical, optical and physical properties. Development of hybrid nanostructures that are composed of metal-semiconductor components using a simple approach is of interest. Herein, we report a robust and general organic phase synthesis of metal (Au or Ag)-Zinc chalcogenide (ZnS or ZnSe) core-shell nanostructures. This synthetic protocol also enabled the growth of more compositionally complex nanostructures of Au-ZnSxSe1-x alloys and Au-ZnS-ZnSe core-shell-shell. The optical and structural properties of these hybrid nanostructures are also presented.

Selective growth of metal particles on ZnO nanopyramids via a one-pot synthesis.

Hybrid nanostructures of metal (Cu, Au, Ag)-ZnO nanopyramids were synthesized. These hybrid nanostructures possess two distinct morphologies where the metal can be selectively attached to either the base or the tip of the ZnO pyramids. This is the first time that such morphologies are reported for Cu-ZnO and Ag-ZnO hybrid nanostructures.

Coating and enhanced photocurrent of vertically aligned zinc oxide nanowire arrays with metal sulfide materials.

Hybrid nanostructures combining zinc oxide (ZnO) and a metal sulfide (MS) semiconductor are highly important for energy-related applications. Controlled filling and coating of vertically aligned ZnO nanowire arrays with different MS materials was achieved via the thermal decomposition approach of single-source precursors in the gas phase by using a simple atmospheric-pressure chemical vapor deposition system. Using different precursors allowed us to synthesize multicomponent structures such as nanowires coated with alloy shell or multishell structures. Herein, we present the synthesis and structural characterization of the different structures, as well as an electrochemical characterization and a photovoltaic response of the ZnO-CdS system, in which the resulting photocurrent upon illumination indicates charge separation at the interface.