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We report a systematic study of the controlled synthesis of new hybrid spherical TiO 2 nanoparticle cluster (TiO 2 -NPC) homogeneously decorated with noble metal nanoparticles (NPs) by gas-phase evaporation-induced self-assembly. Silver NP (AgNP) was used as the representative noble metal NP. The degradation of methyl blue (MB) in the aqueous solution was chosen as the representative system for the study of photocatalysis, which were tested and evaluated with respect to irradiation conditions and the presence of bovine serum albumin (BSA). The results show that particle size and chemical composition of the hybrid nanostructure were tunable by choosing the suitable concentration of precursors. The photocatalytic activity of AgNP-decorated TiO 2 -NPC was strongly affected by the light irradiation and the ligand-nanoparticle interfacial interaction. The presence of BSA influenced molecular conjugation to the surface of the hybrid nanostructure. Under conditions of simultaneous competitive adsorption of MB and BSA, the combination of AgNPs improved the photocatalytic activity of the TiO 2 -NPC-based catalysts. Our work describes a prototype methodology to fabricate TiO 2 -NPC homogeneously decorated with noble metal NPs with well-controlled material properties. The mechanistic understanding developed in this study can be useful for the future optimization of material properties of hybrid nanostructures versus interfacial interactions with the surrounding molecules., (Copyright © 2016 Elsevier Inc. All rights reserved.)

Dithiothreitol (DTT)-based displacement is widely utilized for separating ligands from their gold nanoparticle (AuNP) conjugates, a critical step for differentiating and quantifying surface-bound functional ligands and therefore the effective surface density of these species on nanoparticle-based therapeutics and other functional constructs. The underlying assumption is that DTT is smaller and much more reactive toward gold compared with most ligands of interest, and as a result will reactively displace the ligands from surface sites thereby enabling their quantification. In this study, we use complementary dimensional and spectroscopic methods to characterize the efficiency of DTT displacement. Thiolated methoxypolyethylene glycol (SH-PEG) and bovine serum albumin (BSA) were chosen as representative ligands. Results clearly show that (1) DTT does not completely displace bound SH-PEG or BSA from AuNPs, and (2) the displacement efficiency is dependent on the binding affinity between the ligands and the AuNP surface. Additionally, the displacement efficiency for conjugated SH-PEG is moderately dependent on the molecular mass (yielding efficiencies ranging from 60 to 80% measured by ATR-FTIR and ≈90% by ES-DMA), indicating that the displacement efficiency for SH-PEG is predominantly determined by the S-Au bond. BSA is particularly difficult to displace with DTT (i.e., the displacement efficiency is nearly zero) when it is in the so-called normal form. The displacement efficiency for BSA improves to 80% when it undergoes a conformational change to the expanded form through a process of pH change or treatment with a surfactant. An analysis of the three-component system (SH-PEG + BSA + AuNP) indicates that the presence of SH-PEG decreases the displacement efficiency for BSA, whereas the displacement efficiency for SH-PEG is less impacted by the presence of BSA.

Here we demonstrate a rapid and quantitative means to characterize the size and packing structure of small clusters of nanoparticles in colloidal suspension. Clustering and aggregation play important roles in a wide variety of phenomena of both scientific and technical importance, yet characterizing the packing of nanoparticles within small clusters and predicting their aerodynamic size remains challenging because available techniques can lack adequate resolution and sensitivity for clusters smaller than 100 nm (optical techniques), perturb the packing arrangement (electron microscopies), or provide only an ensemble average (light scattering techniques). In this article, we use electrospray-differential mobility analysis (ES-DMA), a technique that exerts electrical and drag forces on the clusters, to determine the size and packing of small clusters. We provide an analytical model to determine the mobility size of various packing geometries based on the projected area of the clusters. Data for clusters aggregated from nominally 10 nm gold particles and nonenveloped viruses of various sizes show good agreement between measured and predicted cluster sizes for close-packed spheres.

Highlights • Mechanistic understanding of CH 4 combustion via Cu Ce O interface at nanoscale. • Aerosol-based method to synthesize homogeneous Cu Ce O hybrid nanoparticle (NP). • Tunable oxidation state of NP directly by the gas-phase 2nd stage H 2 reduction. • High activity and operation stability by the Cu Ce O hybrid NP. • Activity and stability are independent of initial oxidation state of the hybrid NP. Abstract The synergistic effect of Cu Ce O hybrid nanostructure has shown the promise for catalytic methane combustion. In this study, we develop an aerosol-based two-stage thermal treatment method to (1) synthesize the Cu Ce O hybrid nanoparticle (NP) with a tunable oxidation state directly in gas phase, and (2) provide a mechanistic understanding of surface reduction of the Cu Ce O hybrid NP for catalysis of methane combustion. After evaporation-induced self-assembly followed by a thermal decomposition to form metal oxide NP at the 1st stage thermal treatment, a temperature-programmed, aerosol-based hydrogen reduction process was employed for direct tuning the oxidation state of the NP in the gas phase (the 2nd stage thermal treatment). Differential mobility analysis, x-ray diffractomery, x-ray photoelectron spectroscopy, and scanning electron microscopy were employed complementarily for characterization of particle size, morphology, crystallinity, elemental composition, and oxidation state of the NPs. The results show a successful surface reduction of Cu for both Cu-only NP and Cu Ce O hybrid NP by the aerosol-based two-stage thermal treatment method. Using the Cu Ce O hybrid nanoparticle as catalyst, our results show a successfully catalysis on methane combustion over various initial oxidation states of Cu. The results show a high activity with a low light-off temperature, a high light-off stability and operation stability toward catalytic methane combustion. The prototype method proposed in this study provides the mechanistic understanding of the synergistic catalysis of the surface-reduced Cu Ce O hybrid nanoparticle with different oxidation states. The method can be especially useful to fabricate a variety of nanocatalysts with different oxidation states of active metals by design for the study of methane-based energy and environmental applications (e.g., CO 2 dry reforming by methane). Graphical abstract Image, graphical abstract [ABSTRACT FROM AUTHOR]

An electrospray–differentialmobility analyzer (ES-DMA)was operated with an aerosol flow-mode, temperature-programmed approachto enhance its ability to characterize the particle size distributions(PSDs) of nanoscale particles (NPs) in the presence of adsorbed andfree ligands. Titanium dioxide NPs (TiO2-NPs) stabilizedby citric acid (CA) or bovine serum albumin (BSA) were utilized asrepresentative systems. Transmission electron microscopy (TEM) andinductively coupled plasma mass spectrometry were used to providevisual information and elemental-based PSDs, respectively. Resultsshow that the interference resulting from electrospray-dried nonvolatilesalt residual nanoscale particles (S-NPs) could be effectively reducedusing the thermal treatment process: PSDs were accurately measuredat temperatures above 200 °C for CA-stabilized TiO2-NPs and above 400 °C for BSA-stabilized TiO2-NPs.Moreover, TEM confirmed the volumetric shrinkage of S-NPs due to thermaltreatment and also showed that the primary structure of TiO2-NPs was relatively stable over the temperature range studied (i.e.,below 700 °C). Conversely, the shape factor for TiO2-NPs decreased after treatment above 500 °C, possibly due toa change in the secondary (aggregate) structure. S-NPs from BSA-stabilizedTiO2-NPs exhibited higher global activation energies towardinduced volumetric shrinkage than those of CA-stabilized TiO2-NPs, suggesting that activation energy is dependent on ligand size.This prototype study demonstrates the efficacy of using ES-DMA coupledwith thermal treatment for characterizing the physical state of NPs,even in a complex medium (e.g., containing plasma proteins) and inthe presence of particle agglomerates induced by interaction withbinding ligands. [ABSTRACT FROM AUTHOR]

In this study, a prototypical thiolated organic ligand, 3-mercaptopropionic acid (MPA), was conjugated on gold nanoparticles (AuNPs), and packing density was measured on an ensemble-averaged basis using inductively coupled plasma optical emission spectrometry. The effects of sample preparation, including centrifugation and digestion, as well as AuNP size and concentration, on recovery were investigated. For AuNPs with diameters of 5, 10, 30, 60, and 100 nm, calculated packing density is independent of size, averaging 7.8 nm and ranging from 6.7 to 9.0 nm, and is comparable to reported values for MPA and similar short-chain ligands on AuNPs. These preliminary data provide fundamental information on the advantages and limitations of ICP-based analyses of conjugated AuNP systems. Moreover, they provide necessary information for the development of more broadly applicable methods for quantifying nanoparticle-ligand conjugates of critical importance to nanomedicine applications. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]