Hybrid nanostructures composed of semiconductor and plasmonic metal components are receiving extensive attention. They display extraordinary optical characteristics that are derived from the simultaneous existence and close conjunction of localized surface plasmon resonance and semiconduction, as well as the synergistic interactions between the two components. They have been widely studied for photocatalysis, plasmon-enhanced spectroscopy, biotechnology, and solar cells. In this review, the developments in the field of (plasmonic metal)/semiconductor hybrid nanostructures are comprehensively described. The preparation of the hybrid nanostructures is first presented according to the semiconductor type, as well as the nanostructure morphology. The plasmonic properties and the enabled applications of the hybrid nanostructures are then elucidated. Lastly, possible future research in this burgeoning field is discussed.

Metal/Semiconductor Hybrid Nanostructures for Plasmon-Enhanced Applications

The controlled synthesis of nanohybrids composed of noble metals (Au, Ag, Pt and Pd, as well as AuAg alloy) and metal oxides (ZnO, TiO2, Cu2O and CeO2) have received considerable attention for applications in photocatalysis, solar cells, drug delivery, surface enhanced Raman spectroscopy and many other important areas. The overall architecture of nanocomposites is one of the most important factors dictating the physical properties of nanohybrids. Noble metals can be coupled to metal oxides to yield diversified nanostructures, including noble metal decorated-metal oxide nanoparticles (NPs), nanoarrays, noble metal/metal oxide core/shell, noble metal/metal oxide yolk/shell and Janus noble metal–metal oxide nanostructures. In this review, we focus on the significant advances in tailored nanostructures of noble metal–metal oxide nanohybrids. The improvement in performance in the representative solar energy conversion applications including photocatalytic degradation of organic pollutants, photocatalytic hydrogen generation, photocatalytic CO2 reduction, dye-sensitized solar cells (DSSCs) and perovskite solar cells (PSCs) are discussed. Finally, we conclude with a perspective on the future direction and prospects of these controllable nanohybrid materials.

Noble metal–metal oxide nanohybrids with tailored nanostructures for efficient solar energy conversion, photocatalysis and environmental remediation

Photocatalysis has been attracting much research interest because of its wide applications in renewable energy and environmental remediation. There are many materials that are found to show good photocatalytic activity in the presence of ultraviolet (UV) and visible light. However, the applications of these materials are limited to the UV portion of sunlight. α-Fe 2 O 3 has an advantage over the other conventional materials like TiO 2 , ZnO, etc . in using solar energy for photocatalytic applications due to its lower band gap ∼2.2 eV value. As a result of which Fe 2 O 3 is capable of absorbing a large portion of the visible solar spectrum (absorbance edge ∼600 nm). Also its good chemical stability in aqueous medium, low cost, abundance and nontoxic nature makes it a promising material for photocatalytic water treatment and water splitting applications. Except these advantages the usage of Fe 2 O 3 has been restricted by many anomalies such as higher e–h recombination effect, low diffusion length and VB positioning (VB is positive with respect to H + /H 2 potential). This article reviews the research that has been carried out to overcome these basic limitations and to enhance the photocatalytic activity of α-Fe 2 O 3 .

α-Fe2O3 as a photocatalytic material: A review

Controllable integration of noble metals (e.g., Au, Ag, Pt, and Pd) and metal oxides (e.g., TiO2, CeO2, and ZrO2) into single nanostructures has attracted immense research interest in heterogeneous catalysis, because they not only combine the properties of both noble metals and metal oxides, but also bring unique collective and synergetic functions in comparison with single-component materials. Among many strategies recently developed, one of the most efficient ways is to encapsulate and protect individual noble metal nanoparticles by a metal oxide shell of a certain thickness to generate the core–shell or yolk–shell structure, which exhibits enhanced catalytic performance compared with conventional supported catalysts. In this review article, we summarize the state-of-the art progress in synthesis and catalytic application of noble metal nanoparticle@metal oxide core/yolk–shell nanostructures. We hope that this review will help the readers to obtain better insight into the design and application of well-defined nanocomposites in both the energy and environmental fields.

Noble metal nanoparticle@metal oxide core/yolk-shell nanostructures as catalysts: recent progress and perspective.

The facet-engineered surface and interface design for photocatalytic materials has been proven as a versatile approach to enhance their photocatalytic performance. This review article encompasses some recent advances in the facet engineering that has been performed to control the surface of mono-component semiconductor systems and to design the surface and interface structures of multi-component heterostructures toward photocatalytic applications. The review begins with some key points which should receive attention in the facet engineering on photocatalytic materials. We then discuss the synthetic approaches to achieve the facet control associated with the surface and interface design. In the following section, the facet-engineered surface design on mono-component photocatalytic materials is introduced, which forms a basis for the discussion on more complex systems. Subsequently, we elucidate the facet-engineered surface and interface design of multi-component photocatalytic materials. Finally, the existing challenges and future prospects are discussed.

https://onlinelibrary.wiley.com/doi/pdf/10.1002/advs.201600216

Facet-Engineered Surface and Interface Design of Photocatalytic Materials

We studied the chemical, optical and catalytic properties of metal (Pt, Pd, Ag, Au)–Cu2O core–shell nanoparticles grown via a simple and reproducible approach which utilizes aqueous-phase reactions at room temperature. We were able to control the thickness of the Cu2O shell and examine the effect of the core's shape and size on the structure and properties of the hybrid nanocrystals. We also studied the optical properties of the hybrid nanocrystals, in particular the effect of the Cu2O shell thickness on the frequency of the plasmon of gold nanorods. In addition, the catalytic activity of the hybrid nanostructures was examined by testing the reduction reaction of 4-nitrophenol with NaBH4. Finally, the hybrid metal–Cu2O nanostructures were used as templates to form the yolk–shell of metal–Cu2S materials. The interface and the crystalline structures of the four hybrid nanostructures were extensively characterized by high resolution transmission electron microscopy (HRTEM), energy-filtered TEM (EFTRM) and X-ray diffraction (XRD).

Studying the chemical, optical and catalytic properties of noble metal (Pt, Pd, Ag, Au)–Cu2O core–shell nanostructures grown via a general approach

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 produ...

Thermal Decomposition Approach for the Formation of α-Fe2O3 Mesoporous Photoanodes and an α-Fe2O3/CoO Hybrid Structure for Enhanced Water Oxidation

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.

Bioinspired Hierarchical Porous Structures for Engineering Advanced Functional Inorganic Materials.

A simple one-step approach for the formation of close packed films of copper and copper oxide nanoparticles is described. Thermal decomposition of copper cupferrate, a single-source precursor, on silicon produces a well-controlled, assembled film of Cu nanocrystals. Upon oxidation, Cu2O is formed with retention of the assembly. Similarly, the thermal decomposition of manganese cupferrate results in the formation of porous MnO nanowires. Various solvents were used to examine their influence on the composition and assembly of the nanoparticles. This approach enables an easy and reproducible process for the synthesis and assembly of metal oxide nanostructures.

A facile one-step approach for the synthesis and assembly of copper and copper-oxide nanocrystals

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.

Mahmud Diab

Papers

Studying the chemical, optical and catalytic properties of noble metal (Pt, Pd, Ag, Au)–Cu2O core–shell nanostructures grown via a general approach

Thermal Decomposition Approach for the Formation of α-Fe2O3 Mesoporous Photoanodes and an α-Fe2O3/CoO Hybrid Structure for Enhanced Water Oxidation

Bioinspired Hierarchical Porous Structures for Engineering Advanced Functional Inorganic Materials.

A facile one-step approach for the synthesis and assembly of copper and copper-oxide nanocrystals

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