Nano-gold diggers: Au-assisted SiO(2)-decomposition and desorption in supported nanocatalysts

Which is Better for Nanomedicines: Nanocatalysts or Single-Atom Catalysts?

With the rapid advancements in nanotechnology and materials science, numerous nanomaterials have been used as catalysts for nanomedical applications. Their design and modification according to the microenvironment of diseases have been shown to achieve effective treatment. Chemists are in pursuit of nanocatalysts that are more efficient, controllable, and less toxic by developing innovative synthetic technologies and improving existing ones. Recently, single-atom catalysts (SACs) with excellent catalytic activity and high selectivity have attracted increasing attention because of their accurate design as nanomaterials at the atomic level, thereby highlighting their potential for nanomedical applications. In this review, the recent advances in nanocatalysts and SACs are briefly summarized according to their synthesis, characterizations, catalytic mechanisms, and nanomedical applications. The opportunities and future scope for their development and the issues and challenges for their application as nanomedicine are also discussed. As far as it is known, the review is the systematic comparison of nanocatalysts and SACs, especially in the field of nanomedicine, which has promoted the development of nanocatalytic medicine.

Mapping the thermal entrenchment behavior of Pd nanoparticles on planar SiO2 supports

Thermal treatment of metal nanoparticles at temperatures above 1000 °C leads to the formation of nanopores in amorphous SiO₂ planar supports. In this work, we employ Pd/SiO₂ as a model system to investigate how the initial size and distribution of nanoparticles on the SiO₂ surface affects the behavior of the nanoparticles at high temperatures with respect to the formation of nanopores and related structures. We also examine the role of physical processing parameters such as heating temperature, ramp rate, and heating time in altering the type, size, and number density of features formed. These studies reveal that nanopore formation competes with other surface phenomena, including nanoparticle agglomeration and encapsulation, which also occur at high temperatures. We establish that the dominant behavior, among the many competing phenomena occurring at the metal-oxide interface, depends on the initial surface distribution of the nanoparticles. Using this knowledge, we show that the final nanopore diameter and surface density are highly tunable.

Self-assembly of strawberry-like organic–inorganic hybrid particle clusters with directionally distributed bimetal and facile transformation of the core and corona

Controllable structure of organic–inorganic hybrid particle clusters were successfully fabricated by self-assembly which derived from the strong interaction between carboxyl groups of the organic particles and amino groups of the inorganic particles.

Growth of nanowire arrays from micron-feature templates

Here, we present a two-step annealing procedure to imprint nanofeatures on SiO₂ starting from metallic microfeatures. The first annealing transforms the microfeatures into gold nanoparticles and the second imprints these nanoparticles into the SiO₂ layer with nanometric control. The resulting nanohole arrays show a high ensemble uniformity. As a potential application, the nanohole mask is used as a selective mask for the Ga self-assisted growth of GaAs nanowires (NWs). Thus, for the first time, a successful implementation of nano-self-imprinting that links high-throughput microlithography with bottom-up NW growth is shown. The beneficial hole morphology of the SiO₂ mask promotes high Ga droplet contact angles with the silicon substrate and the formation of single droplets in the mask holes. This droplet predeposition configuration enables a high vertical yield of NWs. Thus, this article describes a new protocol to grow NW devices that combines simultaneously nanosized holes and parallel processing.

Au-catalyzed desorption of GaAs oxides

Thermal desorption of native oxides on GaAs(100), (110) and (111)B surfaces around Au particles are studied in vacuum using in situ microspectroscopy. Two temperature-dependent desorption regimes, common to all surfaces, are identified. The low-temperature desorption regime spatially limited to the vicinity of some Au nanoparticles (NPs) is catalytically enhanced, resulting in oxide pinholes which expand laterally into macro holes many times the size of the catalyzing NPs and with shapes dictated by the underlying crystallography. The high-temperature desorption regime causes homogeneous oxides thinning and, ultimately, complete oxide desorption. The temperature difference between the two regimes is ∼25 °C-60 °C. After oxide desorption and depending on Au size and GaAs surface orientation, Au particles may dissolve the fresh GaAs surface and form mobile AuGa₂/Ga core/shell units, or form stationary AuGa₂ crystallites, or the catalyzing Au particles may run with minimal reaction with the GaAs surface. These results will add to the fundamental understanding of many Au-based nanofabrication processes, particularly the epitaxial growth of vertical and lateral nanowires.

New method for MBE growth of GaAs nanowires on silicon using colloidal Au nanoparticles

We present a new method for the deposition of colloidal Au nanoparticles on the surface of silicon substrates based on short-time Ar plasma treatment without the use of any polymeric layers. The elaborated method is compatible with molecular beam epitaxy, which allowed us to carry out the detailed study of GaAs nanowire synthesis on Si(111) substrates using colloidal Au nanoparticles as seeds for their growth. The results obtained elucidated the causes of the difference between the initial nanoparticle sizes and the diameters of the grown nanowires.

Effect of Systematic Control of Pd Thickness and Annealing Temperature on the Fabrication and Evolution of Palladium Nanostructures on Si (111) via the Solid State Dewetting

Si-based optoelectronic devices embedded with metallic nanoparticles (NPs) have demonstrated the NP shape, size, spacing, and crystallinity dependent on light absorption and emission induced by the localized surface plasmon resonance. In this work, we demonstrate various sizes and configurations of palladium (Pd) nanostructures on Si (111) by the systematic thermal annealing with the variation of Pd thickness and annealing temperature. The evolution of Pd nanostructures are systematically controlled by the dewetting of thin film by means of the surface diffusion in conjunction with the surface and interface energy minimization and Volmer-Weber growth model. Depending on the control of deposition amount ranging between 0.5 and 100 nm at various annealing temperatures, four distinctive regimes of Pd nanostructures are demonstrated: (i) small pits and grain formation, (ii) nucleation and growth of NPs, (iii) lateral evolution of NPs, and (iv) merged nanostructures. In addition, by the control of annealing between 300 and 800 °C, the Pd nanostructures show the evolution of small pits and grains, isolated NPs, and finally, Pd NP-assisted nanohole formation along with the Si decomposition and Pd-Si inter-diffusion. The Raman analysis showed the discrepancies on phonon modes of Si (111) such that the decreased peak intensity with left shift after the fabrication of Pd nanostructures. Furthermore, the UV-VIS-NIR reflectance spectra revealed the existence of surface morphology dependent on absorption, scattering, and reflectance properties.

Tailoring the Catalytic Properties of Metal Nanoparticles via Support Interactions

The development of new catalysts for energy technology and environmental remediation requires a thorough knowledge of how the physical and chemical properties of a catalyst affect its reactivity. For supported metal nanoparticles (NPs), such properties can include the particle size, shape, composition, and chemical state, but a critical parameter which must not be overlooked is the role of the NP support. Here, we highlight the key mechanisms behind support-induced enhancement in the catalytic properties of metal NPs. These include support-induced changes in the NP morphology, stability, electronic structure, and chemical state, as well as changes in the support due to the NPs. Utilizing the support-dependent phenomena described in this Perspective may allow significant breakthroughs in the design and tailoring of the catalytic activity and selectivity of metal nanoparticles.

Precise control of configuration, size and density of self-assembled Au nanostructures on 4H-SiC (0001) by systematic variation of deposition amount, annealing temperature and duration

Hexagonal Au nano-crystals, round dome-shaped droplets and irregular nano-mounds were fabricated on GaN (0001) based on the combinational effects of thermal dewetting and surface free energy minimization.

Using the M13 Phage as a Biotemplate to Create Mesoporous Structures Decorated with Gold and Platinum Nanoparticles

By taking advantage of the physical and chemical properties of the M13 bacteriophage, we have used this virus to synthesize mesoporous silica structures. Major coat protein p8 was chemically modified by attaching thiol groups. As we show, the resulting thiolated phage can be used as a biotemplate able to direct the formation of mesoporous silica materials. Simultaneously, this thiol functionality acts as an anchor for binding metal ions, such as Au(3+) and Pt(4+), forming reactive M13-metal ionic complexes which evolve into metal nanoparticles (NPs) trapped in the mesoporous network. Interestingly, Au(3+) ions are reduced to Au(0) NPs by the protein residues without requiring an external reducing agent. Likewise, silica mesostructures decorated with Au and Pt NPs are prepared in a one-pot synthesis and characterized using different techniques. The obtained results allow us to propose a mechanism of formation. In addition, gold-containing mesoporous structures are tested for the reduction of 4-nitrophenol (4-NP) and methylene blue (MB) in the presence of NaBH4. Although all of the gold-containing catalysts exhibit catalytic activity, those obtained with thiolated phages present a better performance than that obtained with M13 alone. This behavior is ascribed to the position of the Au NPs, which are partially embedded in the wall of the final mesostructures.

Au@Pd core–shell nanoparticles-decorated reduced graphene oxide: a highly sensitive and selective platform for electrochemical detection of hydrazine

An Au_core–Pd_shell-decorated reduced graphene oxide nanocomposite is successfully employed for the electrochemical detection of low-level hydrazine in an aqueous solution.

Real-time observation of self-limiting SiO2/Si decomposition catalysed by gold silicide droplets

Gold enhances the decomposition rate of thin SiO₂ layers on Si(001) in a self-limiting fashion.