Distribution Of Au Nanoparticles Research Articles

Fabrication of MoO3/rGO/Au composite for increased photocatalytic degradation of methylene blue

Water line purification and wastewater treatment have become challenging in the fast-growing industry, infrastructure, textile, manufacturing world, etc. with this challenge, photocatalysis has gained substantial attention as an environmentally friendly process on which researchers are working aggressively and, in this progress, two-dimensional (2D) are in focus because of their good photocatalytic ability. Therefore, in this study, we present the synthesis of one such ternary composite material comprising molybdenum trioxide nanorods (MoO3NR), reduced graphene oxide (rGO) and gold nanoparticles (AuNR), with a specific focus on its enhanced photocatalytic performance. The ternary composite is prepared via a combination of in situ hydrothermal and laser ablation methods allowing for precise control over the growth and integration of the constituent materials. The structural and morphological properties of the MoO3 nanorods, rGO and Au ternary material were systematically characterized using various techniques, including UV-vis spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS). The obtained results suggest the successful formation of a composite, revealing the presence of uniformly dispersed MoO3 nanorods on the rGO sheets and evenly distributed Au nanoparticles throughout the structure. Photocatalysis evaluations conducted to assess the material performance under visible light irradiation exhibited significantly enhanced methylene blue degradation efficiency of 85.91% in 90[Formula: see text]min in comparison with individual MoO3 nanorods and rGO counterparts. The improved efficiency can be attributed to the combined effects arising from the integration of MoO3 nanorods, rGO and Au nanoparticles, which facilitate efficient light absorption, charge separation and catalytic reactions, which in turn reduces electron–hole recombination and improve photocatalytic performance. Also, the tunable morphology and collective effects of MoO3 nanorods, rGO and Au offer new avenues for designing highly efficient and stable photocatalytic materials.

Understanding the Plasmonic Effect of Enhanced Photodegradation with Au Nanoparticle Decorated ZnO Nanosheet Arrays under Visible Light Irradiation.

Plasmonic-enhanced photocatalysis using visible light is considered a promising strategy for pollution photodegradation. However, there is still a lack of comprehensive and quantitative understanding of the underlying mechanisms and interactions involved. In this study, we employed a two-step process to fabricate arrays of ZnO nanosheets decorated with Au nanoparticles (Au-ZnO NS). Various characterization techniques were used to examine the morphological, structural, and chemical properties of the fabricated Au-ZnO NS array. Furthermore, we systematically investigated the photocatalytic degradation of methyl orange under visible light irradiation using Au-ZnO NS arrays prepared with varying numbers of photochemical reduction cycles. The results indicated that as the number of photochemical reduction cycles increased, the photodegradation efficiency initially increased but subsequently decreased. Under visible light irradiation, the Au-ZnO NS array obtained via four cycles of photochemical reduction exhibits the highest photocatalytic degradation rate of methyl orange 0.00926 min-1, which is six times higher than that of the ZnO NS array. To gain a better understanding of the plasmonic effect on photodegradation performance, we utilized electromagnetic simulations to quantitatively investigate the enhancement of electric fields in the Au-ZnO NS array. The simulations clearly presented the nonlinear dependencies of electric field intensity on the distribution of Au nanoparticles and the wavelength of radiation light, leading to a nonlinear enhancement of hot electron injection and eventual plasmonic photodegradation. The simulated model, corresponding to four cycles of photochemical reduction, exhibits the highest electric field intensity at 550 nm, which can be attributed to its strong plasmonic effect. This work provides mechanistic insights into plasmonic photocatalysts for utilizing visible light and represents a promising strategy for the rational design of high-performance visible light photocatalysts.

Electrostatically enabled dye reduction using laser synthesized gold nanoparticles

The size and shape-dependent catalytic activities of noble metal nanoparticles (NPs) have been well studied. However, the effect of the surface coating on their catalytic performance is relatively less explored. Herein, we demonstrate that the catalytic activity of NPs has a marked dependence on the type of their surfactant coating. Gold NPs were synthesized by pulsed laser ablation and subsequently coated with different surfactants such as cetyltrimethylammonium bromide (CTAB), sodium dodecyl sulfate (SDS), and polyvinylpyrrolidone (PVP). This enabled us to keep the size, size distribution, and concentration of Au NP the same for the comparative catalysis study. The bare and coated NPs were employed as a catalyst to carry out the reduction of methylene blue (MB) and methyl orange (MO). The results showed remarkable dependence of the reaction rates on the type of surfactant coating of the catalyst NPs. Bare NPs were found to be far superior to the coated NPs for both reactions. In the case of bare NPs both the dyes were completely reduced in less than 5 mins. Whereas, for coated NPs, the zeta potential values determined their effectiveness for a certain reaction. For instance, the reduction of the cationic dye MB was relatively more effective with NPs with a negative zeta potential value, whereas the reduction of anionic dye MO was better for NPs possessing a positive zeta potential. The apparent rate constant of SDS-coated NPs was 40 times higher than that of the CTAB-coated NPs for the reduction of MB. Conversely, the rate constant is 27-fold higher for CTAB-coated NPs compared to SDS-coated NPs for the reduction of MO. These results imply that there is a strong dependence of the catalytic reaction rates on the relative charge of reactants and NPs. Moreover, the better catalytic performance of bare NPs in both cases highlights the significance of the availability of the unhindered surface for catalysis. These results signify the importance of engineering the right surface coating for NPs for their best catalytic performance.

Fate of Gold Nanoparticles in Laser Desorption/Ionization Mass Spectrometry: Toward the Imaging of Individual Nanoparticles

This study focuses on mapping the spatial distribution of Au nanoparticles (NPs) by laser desorption/ionization mass spectrometry imaging (LDI MSI). Laser interaction with NPs and associated phenomena, such as change of shape, melting, migration, and release of Au ions, are explored at the single particle level. Arrays of dried droplets containing low numbers of spatially segregated NPs were reproducibly prepared by automated drop-on-demand piezo-dispensing and analyzed by LDI MSI using an ultrahigh resolution orbital trapping instrument. To enhance the signal from NPs, an in source gas-phase chemical reaction of generated Au ions with xylene was employed. The developed technique allowed the detecting, chemical characterization, and mapping of the spatial distribution of Au NPs; the ion signals were detected from as low as ten 50 nm Au NPs on a pixel. Furthermore, the Au NP melting dynamics under laser irradiation was monitored by correlative atomic force microscopy (AFM) and scanning electron microscopy (SEM). AFM measurements of Au NPs before and after LDI MSI analysis revealed changes in NP shape from a sphere to a half-ellipsoid and total volume reduction of NPs down to 45% of their initial volume.

Strain-induced exciton localized states in quantum well

We use AlAs sacrificial layer etching technology to peel a film of In0.15Ga0.85As/GaAs single quantum wells (QWs) from a GaAs substrate and transfer the film to a Si wafer covered with randomly distributed Au nanoparticles. In this way, local strains are introduced into the QW film, which leads to the formation of the exciton confinement potential. From them, we have observed very sharp emission lines in photoluminescence (PL) spectra and local PL bright spots in space. The PL is proved to be from localized exciton emission in a potential energy funnel. We can also introduce the localized strain in the QW film using a micropillar array of an electron beam resist and observe similar narrow emission lines. The method to achieve localized exciton states is a controllable way and it will further expand the application of traditional semiconductor QWs in optical quantum devices.

Structure Formation and Regulation of Au Nanoparticles in LiTaO3 by Ion Beam and Thermal Annealing Techniques.

The size uniformity and spatial dispersion of nanoparticles (NPs) formed by ion implantation must be further improved due to the characteristics of the ion implantation method. Therefore, specific swift heavy ion irradiation and thermal annealing are combined in this work to regulate the size and spatial distributions of embedded Au NPs formed within LiTaO3 crystals. Experimental results show that small NPs migrate to deeper depths induced by 656 MeV Xe35+ ion irradiation. During thermal annealing, the growth of large Au NPs is limited due to the reductions in the number of small Au NPs, and the migrated Au NPs aggregate at deeper depths, resulting in a more uniform size distribution and an increased spatial distribution of Au NPs. The present work presents a novel method to modify the size and spatial distributions of embedded NPs.

Catalytic degradation of methylene blue by biosynthesized Au nanoparticles on titanium dioxide (Au@TiO2).

The degradation of methylene blue is a critical procedure in its wastewater remediation and thus has inspired wide catalysis research with semiconductors such as titanium dioxide (TiO2) and rare metals such as gold (Au). In this study, we report bacterial cells assisting biosynthesis for Au@TiO2 as an efficient catalyst for the catalytic degradation of methylene blue. Multiple complementary characterization for bio-Aux@TiO2 evidenced the evenly distributed Au nanoparticles (NPs) on the bio-TiO2 layers. Meanwhile, bio-Au2@TiO2 displayed the superior catalytic activity in the degradation of methylene blue with the highest kinetics constant (kapp) value of 0.195 min-1. In addition, bio-Au2@TiO2 keeps stable catalytic activity for up to 10 cycles. The origin of the catalytic activity was investigated by the hydroxyl radical fluorescence quantitative analysis and optical band gap analysis. In the bio-Au2@TiO2 catalytic system, Au NPs decreased the band gap energy of TiO2 and enabled the generation of abundant photogeneration hydroxyl radicals, resulting in an enhanced photocatalytic activity. Our microbial synthesized bio-TiO2 and bio-Aux@TiO2 study would be useful for developing green synthesis catalyst technology.

Growing and stabilizing metallic nanoparticles inside mesoporous oxide thin films

<h2>Abstract</h2> Metallic nanoparticles (NPs) have interesting size-dependent optical properties and a high surface to volume ratio that make them appealing for many different applications, such as sensing, catalysis, energy conversion and storage, biomedicine, etc. These applications require avoiding NPs degradation, coarsening and/or aggregation. The use of porous templates has become a promising strategy to attain this objective. In particular, ordered mesoporous oxides prepared by sol-gel reactions combined with supramolecular templates are highly appealing supports, due to their high specific surface and regular and accessible porosity. Moreover, if these oxides are prepared as thin films, the manipulation and integration in portable devices is straightforward. In this work, different alternatives to obtain metallic NPs stabilized within mesoporous oxide thin films are discussed. Firstly, the major effect of mesoporous TiO₂ thin films pores ordering over the amount and distribution of Au NPs obtained within is presented, along with the discussion of the architecture effect over the materials sensing capabilities. Afterwards, the use of hybrid mesoporous thin films containing carboxylic and phosphonate groups as templates to form and stabilize Cu and Ag nanoparticles is presented. In all cases, the key effect of the surface chemistry over synthesis of the composites and their applications is highlighted.

Spin-casting of Micron-Scale Thick PMMA Films with Embedded Au Nanoparticles Formed by Laser Ablation in Liquid

Background: A Facile, scalable approach to fabrication of organic thin films with an embedded layer of nanoparticles in the ambient environment. The approach is based on step-bystep spin-coating of polymethylmethacrylate (PMMA) films and a nanoparticle layer. Objective: The goal of the present work is to fabricate a sandwich structure of the PMMA films for the top and bottom layers of a sandwich structure as well as a middle layer of nanoparticles formed in solution by the Laser Ablation in Liquid (LAL) method. Methods: First, a PMMA thin film was fabricated by spin-casting of PMMA solution in ethylacetate. Secondly, a solution of Au nanoparticles synthesized by laser ablation in ethanol was spin-cast on a prefabricated PMMA film. The distribution of Au nanoparticles and the morphology of the resulting film were analyzed using scanning electron microscopy (SEM), optical microscopy, and atomic microscopy (AFM). Finally, another PMMA layer was spin-cast on the nanoparticle-decorated film. Results: A hybrid organic film with the embedded layer of nanoparticles was fabricated using the spin-casting method for top and bottom layers as well as for the middle layer of Au nanoparticles fabricated by laser ablation in ethanol by a pulsed UV laser. Statistical and fractal analysis shows uniform distribution of nanoparticles on length scale above ten microns. Conclusion: Spin-cast-based layer-by-layer approach to fabrication of sandwich structures of organic films with embedded nanoparticlesis a facile and scalable method for hybrid organic - nanoparticle films. This approach can be extended for the fabrication of multi-layered hybrid structures.

Bottom-up colloidal synthesis of PMMA@Au core–shell based metallodielectric photonic crystals as substrates for surface-enhanced Raman spectroscopy

The bottom-up colloidal synthesis of photonic band gap (PBG) materials or photonic crystals (PCs) has attracted considerable interest in comparison to top-down approaches due to the relatively simple processing steps involved, the potential for large area sample production and the relatively low-costs associated with this approach for the fabrication of complex 3-dimensional (3D) structures.This research focuses on the colloidal synthesis of poly(methyl methacrylate) (PMMA)@Au core–shell (CS) structures, their bottom-up assembly into 3D metallodielectric PCs (MDPCs) and the demonstration of their potential to be used as surface enhanced Raman substrates (SERS) using the commonly deployed SERS reporter molecule, 4- aminothiolphenol. Here, monodispersed spherical PMMA particles were used both as a host material for Au nanoparticles (NPs) and as a crystal template to produce the MDPC structures. The materials engineering employed which involved combining the synthesis of monodispersed CS particles and the fabrication of their corresponding MDPCs enabled us to control the distribution of Au NPs in the PC structure and thereby investigate their light scattering, reflection and transmission properties including Raman scattering.

Optical limiting applications of resonating plasmonic Au nanoparticles in a dielectric glass medium

Plasmonic nanostructures exhibiting high optical nonlinearities are widely used in the rapidly growing modern nanotechnology of nonlinear optics including biomedical applications due to their tunable plasmonic behavior. In this work, we investigate the nonlinear optical properties of uniformly distributed Au nanoparticles (NPs) embedded in pre-synthesized sodium−zinc borate glass by the well-known ion-exchange technique for optical limiting (OL) applications. Various techniques such as optical absorption spectroscopy, x-ray photoelectron spectroscopy, Transmission Electron Microscope (TEM), Photoluminescence, Time of Flight secondary mass spectroscopy and the Z scan technique were used for the characterization of these NPs. TEM confirmed spherically shaped Au NPs with varying sizes of up to 16 nm, in agreement with optical absorption spectroscopy. Nonlinear optical (NLO) properties of these Au NPs were investigated by using an open as well as close aperture Z scan technique which exhibited enhanced optical nonlinearities. The two-photon absorption (2PA) coefficients demonstrated an increasing trend while the OL threshold values demonstrated a decreasing trend as a function of heat treatment. The improved 2PA coefficients and decreased OL threshold values endorsed the Au NPs containing glasses as contending materials for the fabrication of promising optical limiters for the protection of eyes and other sensitive instruments from laser induced damages.

Fabrication of Bovine Serum Albumin@Au Particles for Colorimetric Detection of Glutathione.

Abnormal concentrations of glutathione (GSH) are important indicators of many human diseases such as cancers, liver damage, AIDS, and Alzheimer's disease. In this work, a kind of bovine serum albumin (BSA)@Au core-shell particles were fabricated using 110 nm BSA aggregates as a template, onto which gold shells composed of Au nanoparticles (NPs) were grown through a seeded growth approach. The morphology of the Au shells deposited on BSA aggregates was tuned from sparse to dense distribution of Au NPs by increasing the concentration of silver ions contained in the growth solutions. Surface plasmon resonance (SPR) peaks of BSA@Au particles were tunable in the range from 550 to 620 nm, corresponding to evolution in color from red to blue due to the enhanced plasmonic coupling among the Au NPs in the shell. The blue BSA@Au particles were qualified for colorimetric detection of GSH since GSH may act as a swelling agent for BSA@Au particles by breaking the intermolecular disulfide bonds in BSA aggregates. With an increased amount of GSH presented, the color of BSA@Au particles evolved from blue to red attributed to gradual swelling of BSA@Au particles and thus increased the distance among the Au NPs in the shell, which was readily recognized by naked eyes or recorded by ultraviolet-visible (UV-vis) spectroscopy. This colorimetric method exhibited good selectivity and anti-interference capability in the analysis of GSH in real samples. In addition, a solid sensing system for the detection of GSH was designed and fabricated by dispersing BSA@Au particles into an agarose hydrogel.

Tunable Raman scattering enhancement due to self-assembled Au nanoparticles layer on porous AAO: The influence of the alumina support

In this investigation, SERS substrates were synthesized based on the growth of Au nanoparticles (AuNPs) layer over porous support of anodized aluminum oxide (AAO). The enhancement factor (EF) of the SERS substrates was determined by the measurement of Rhodamine 6G (R6G) allowed a detection limit of 10−11 (measured over molar concentration). The AAO was grown by a two-stage anodizing method, and subsequently, an Au precursor layer in different thicknesses was sputtered on each alumina support. The coated samples were heat-treated under nitrogen to promote different spatial distributions of AuNPs on the surface. Au-Np layer was achieved with disordered pore-like as demonstrated by low-pressure Nitrogen adsorption and BET analysis (isotherm curve type IV-H3). The sample that exhibited the strongest SERS effect consisted of a 50 nm Au precursor layer on the AAO support. The method reported in this work is highly reproducible, given its simplicity, with a homogeneous size distribution compared to other methods and other substrates such as Silicon.

Quantifying Electrocatalytic Reduction of CO2 on Twin Boundaries

Summary A protocol relying on the use of silver nanostructures with well-defined dimensions and morphologies (e.g., nanocubes and nanowires) has been developed to differentiate and quantitatively determine the atom-specific activities of different surface atoms toward catalyzing electrochemical CO2 reduction reaction (CO2RR). The atom-specific activity of the twin-boundary edges (TBEs) is comparable to (or slightly higher than) that of the single-crystal edges (SCEs) formed from the crossing of two {100} surfaces, and it is on the order of ∼16 attoampere/atom (aA/atom) toward electrochemical CO2RR. This value is more than two orders higher than the atom-specific activity of the {100} surface atoms, i.e., ∼0.1 aA/atom. The high catalytic activity of the TBEs, which represent a class of commonly existing surface defects in stable metal nanostructures with face-centered cubic lattices, is consistent with the DFT calculations, in which the bridge-type binding configuration of COOH∗ at the TBEs stabilizes this intermediate to promote overall CO2RR.

Nanoscale Spatial Distribution of Supported Nanoparticles Controls Activity and Stability in Powder Catalysts for CO Oxidation and Photocatalytic H2 Evolution.

Supported metal nanoparticles are essential components of high-performing catalysts, and their structures are intensely researched. In comparison, nanoparticle spatial distribution in powder catalysts is conventionally not quantified, and the influence of this collective property on catalyst performance remains poorly investigated. Here, we demonstrate a general colloidal self-assembly method to control uniformity of nanoparticle spatial distribution on common industrial powder supports. We quantify distributions on the nanoscale using image statistics and show that the type of nanospatial distribution determines not only the stability, but also the activity of heterogeneous catalysts. Widely investigated systems (Au-TiO2 for CO oxidation thermocatalysis and Pd-TiO2 for H2 evolution photocatalysis) were used to showcase the universal importance of nanoparticle spatial organization. Spatially and temporally resolved microkinetic modeling revealed that nonuniformly distributed Au nanoparticles suffer from local depletion of surface oxygen, and therefore lower CO oxidation activity, as compared to uniformly distributed nanoparticles. Nanoparticle spatial distribution also determines the stability of Pd-TiO2 photocatalysts, because nonuniformly distributed nanoparticles sinter while uniformly distributed nanoparticles do not. This work introduces new tools to evaluate and understand catalyst collective (ensemble) properties in powder catalysts, which thereby pave the way to more active and stable heterogeneous catalysts.

Au-Decorated Ce-Ti Mixed Oxides for Efficient CO Preferential Photooxidation.

We investigated the photocatalytic behavior of gold nanoparticles supported on CeO2–TiO2 nanostructured matrixes in the CO preferential oxidation in H2-rich stream (photo-CO-PROX), by modifying the electronic band structure of ceria through addition of titania and making it more suitable for interacting with free electrons excited in gold nanoparticles through surface plasmon resonance. CeO2 samples with different TiO2 concentrations (0–20 wt %) were prepared through a slow coprecipitation method in alkaline conditions. The synthetic route is surfactant-free and environmentally friendly. Au nanoparticles (<1.0 wt % loading) were deposited on the surface of the CeO2–TiO2 oxides by deposition–precipitation. A benchmarking sample was also considered, prepared by standard fast coprecipitation, to assess how a peculiar morphology can affect the photocatalytic behavior. The samples appeared organized in a hierarchical needle-like structure, with different morphologies depending on the Ti content and preparation method, with homogeneously distributed Au nanoparticles decorating the Ce–Ti mixed oxides. The morphology influences the preferential photooxidation of CO to CO2 in excess of H2 under simulated solar light irradiation at room temperature and atmospheric pressure. The Au/CeO2–TiO2 systems exhibit much higher activity compared to a benchmark sample with a non-organized structure. The most efficient sample exhibited CO conversions of 52.9 and 80.2%, and CO2 selectivities equal to 95.3 and 59.4%, in the dark and under simulated sunlight, respectively. A clear morphology–functionality correlation was found in our systematic analysis, with CO conversion maximized for a TiO2 content equal to 15 wt %. The outcomes of this study are significant advancements toward the development of an effective strategy for exploitation of hydrogen as a viable clean fuel in stationary, automotive, and portable power generators.

Controllable in situ fabrication of portable AuNP/mussel-inspired polydopamine molecularly imprinted SERS substrate for selective enrichment and recognition of phthalate plasticizers

A bio-inspired polydopamine (PDA) molecularly imprinted substrate is fabricated by one-step oxidative self-polymerization of dopamine and template molecules in weakly alkaline medium on screen-printed electrode (SPE). Through the catechol and amine groups on PDA surface, Au nanoparticles (AuNPs) can be easily anchored and growth on PDA-MIP coating, thereby forming a three-dimensional (3D) architecture. By adjusting the reaction conditions, the particle size and distribution of PDA and AuNPs can be well controlled. Benefiting from the “hot spots” generated by AuNPs and recognition sites produced by MIP, the AuNP/PDA-MIP nanocomposite can serve as excellent SERS substrate enabling selective enrichment and identification of phthalate plasticizers (PAEs). Using this substrate, an enhancement factor (EF) up to 1.70 × 107 for dimethyl phthalate (DMP) is achieved with a detection limit as low as 1.0 × 10−10 M. Furthermore, the rebinding kinetics study demonstrates that the portable MIP-based SERS substrate can promptly reach the adsorption equilibrium within 10 min. Thanks to its highly selectivity, the substrate exhibits low SERS interference for structural analogues benzyl butyl phthalate (BBP) and di(2-ethylhexyl) phthalate (DEHP). Besides, the straightforward SERS recognition of DMP in surface water, commercial bottled water and liquor samples are successfully realized using this substrate. This green and environmental-friendly fabrication method is promising for synthesis of highly performance sensing substrate, adsorbent or catalysts. Combining with portable Raman spectrometer, the fabricated MIP-based SERS substrate has exhibited a great potential as on-site device for environmental monitoring, food safety and homeland security.

Photocatalytic enhancement of hydrogen production in water splitting under simulated solar light by band gap engineering and localized surface plasmon resonance of ZnxCd1-xS nanowires decorated by Au nanoparticles

Excellent photocatalytic properties for hydrogen production in water splitting under simulated solar light (with AM1.5G filter) with Au nanoparticles (NPs)/ZnxCd1-xS nanowires (NWs) have been demonstrated. The ZnxCd1-xS NWs photocatalyst shows much higher photocatalytic activity for H2-production than ZnS and CdS NWs with Na2S and Na2SO3 as sacrificial reagents. The high photocatalytic H2-production activity, as high as 57.07 mmol g−1h−1, is attributed to appropriate band gap width and suitable conduction band edge potential of the ZnxCd1-xS NWs. The H2-production efficiency was further significantly enhanced to 96.04 mmol g−1h−1 by decorating ZnxCd1-xS NWs with appropriate size and distribution of Au NPs to induce localized surface plasmon resonances (LSPR) in visible and near infrared region. The work represents significant advance with a totally green and novel approach of enhancing H2-production efficiency in water splitting under simulated solar light (with AM1.5G filter).

Optimal Conditions for the Deposition of Gold Nanofilms on a Silicon by Galvanic Replacement Method

The formation conditions of gold nanofilms on silicon (Si) substrate by galvanic replacement in a dimethyl sulfoxide (DMSO) solvent and their subsequent use for the fabrication of Si nanostructures by metal-assisted chemical etching (MACE) method were under study. It was found that the average size and number of Au nanoparticles increase with an increase in the reducible metal ion concentration from 2 to 8 mM HAuCl4 in DMSO, whereas the distribution of Au nanoparticles in height remains low for all concentrations of the reducible metal. In the temperature range 40 - 70°C, a different morphology of the deposited Au nanofilms observed. In particular, at 40 °C, the film is porous mainly homogeneous, whereas at a temperature of 50°C the film is rougher. The subsequent rise in temperature from 60°C to 70°C results in the formation of Au nanofilm with a discontinuous morphology. It was established that regardless of the morphology of deposited Au nanofilms, the Si nanostructures maintain a vertical orientation to the plane of the Si substrate during MACE-etching. The produced Si nanostructures were 1.5 - 2.5 μm in height and their average diameter ranged from 100 to 300 nm.

Exploration of accessibility of internal pore surface by using rigid nanoparticles as a probe for constructing the integrated nanocomposites

Many mesoporous materials with different morphologies, dimensions, pore sizes and structures have been fabricated and served as carriers to load a wide range of guest species. The high accessibility of pore interiors should be of very significance for efficient loading in the nanocarriers and resultant performance of the formed nanocomposites. In this work, by electrostatic self-assembly, the rigid nanoparticles (NPs) were used as probes to detect the accessibility of internal surface of different pore channels of two typical porous materials, i.e., conventional mesoporous silica nanospheres (MSNs) with uniform hexagonal ordered mesopores and recently created dendritic porous silica NPs (DPSNs) with center-radial porous structure. Interestingly, even 1.6 ± 0.4 nm of ultrafine Au NPs have an uneven and low density distribution on the internal pore surface of MSNs owing to small tubular pores with only two openings. On the contrary, the rigid NPs with different particle sizes from 1.6 ± 0.4 nm to 7.8 ± 1.9 nm can enter DPSNs through open center-radial large pores with 360° diffusion direction, and achieve a high density and well-dispersed loading on the surface of internal pore channels. Besides, based on the size effect, the integrated DPSNs-NH2@Au@Pt nanocomposite with hierarchical spatial distributions of large Au NPs on particle surface and small Pt NPs on both internal pore surface and particle surface were successfully constructed. These results provide an important insight into the accessibility of internal pore surface toward rigid NPs and the smart construction of multifunctional nanocomposites.