Robin N. Klupp Taylor

Analysis of Optical Absorbance Spectra for the Determination of ZnO Nanoparticle Size Distribution, Solubility, and Surface Energy

We present a model to calculate particle size distributions (PSDs) of colloidal ZnO nanoparticles from their absorbance spectra. Using literature values for the optical properties of bulk ZnO and correlating the measurement wavelengths in the UV-visible regime with distinct particle sizes by a tight binding model (TBM), an algorithm deconvolutes the absorbance spectra into contributions from size fractions. We find an excellent agreement between size distributions determined from TEM images and the calculated PSDs. For further validation, bimodal PSDs have been investigated and an approach to determine not only particle size but also solid concentration is introduced. We will show the applicability of our model by the determination of temperature-dependent ripening rates, which enables the calculation of solubilities, surface tensions, and the activation enthalpy of ripening. In principle, our methodology is applicable to different semiconductor nanoparticles in various solvents as long as their bulk properties are known and scattering is negligible.

Mesoporous Organosilicas With Large Cage‐Like Pores for High Efficiency Immobilization of Enzymes

Periodic mesoporous organosilicas (PMOs) are a novel branch of ordered hybrid mesoporous materials in which the organic fragments are regularly distributed within the framework. [ 1 ] In comparison with pure silica mesoporous materials, PMOs not only maintain a highly ordered structure, high surface area, and pore volume, but also exhibit high hydrothermal and mechanical stability due to their hydrophobicity as a consequence of the organic moieties in the framework. [ 2 ] Additionally, compared to regular hybrid mesoporous materials obtained by simple anchoring of the organic moiety to the surface of the pores, the main advantage of PMOs is that the organic groups reside in the pore wall, presenting a rather lower steric hindrance to further introduction of other guest molecules. [ 3 ] With these specifi c properties, PMOs are considered to have high application potential for the immobilization of large guest molecules such as bulky complexes and enzymes. However, to date most PMOs are limited by their relatively small (2–6 nm) pore sizes to the adsorption of small molecules. In fact, there are only a few reports on large pore PMOs, [ 4 ] which would be required as supports for more bulky molecules. Moreover, in many applications increasing the diffusion rate of guest molecule and the exposed number of active sites can greatly improve the performance of the functional material. In general two approaches have been employed to meet these demands, namely the generation of hierarchical porous structures in mesoporous materials [ 5 ]

Determination of the Quantum Dot Band Gap Dependence on Particle Size from Optical Absorbance and Transmission Electron Microscopy Measurements

This work addresses the determination of arbitrarily shaped particle size distributions (PSDs) from PbS and PbSe quantum dot (QD) optical absorbance spectra in order to arrive at a relationship between band gap energy and particle size over a large size range. Using a modified algorithm which was previously developed for ZnO, we take only bulk absorption data from the literature and match the PSDs derived from QD absorbance spectra with those from transmission electron microscopical (TEM) image analysis in order to arrive at the functional dependence of the band gap on particle size. Additional samples sized solely from their absorbance spectra with our algorithm show excellent agreement with TEM results. We investigate the influence of parameters of the TEM image analysis such as threshold value on the final result. The band gap versus size relationship developed from analysis of just two samples lies well within the bounds of a number of published data sets. We believe that our methodology provides an attractive shortcut for the study of various novel quantum-confined direct band gap semiconductor systems as it permits the band gap energies of a broad size range of QDs to be probed with relatively few synthetic experiments and without quantum mechanical simulations.

One‐Pot Colloidal Synthesis of Plasmonic Patchy Particles

templated self-assembly, [ 9 ] interface-masking, [ 10 ] facet-selective crystal growth, [ 11 ] and microcontact printing. [ 12 ] To the best of our knowledge, there exist no reports of one-pot colloidal routes in homogeneous solution to high yields of patchy particles which do not involve templating in some form. Patchy and Janus particles with gold or silver patches with nanoscale thickness are proving to be a particularly interesting class of materials, mainly due to their tunable optical properties and potential for further chemical functionalization. [ 8 ] c, [ 9 ] b] They are also a closely related asymmetric analogue to the symmetric metal nanoshell system, which permits a very large tunability of visible and infrared electromagnetic behaviour through variation of the dielectric core diameter and metal shell thickness. [ 13 ]

Influence of the Counterion on the Synthesis of ZnO Mesocrystals under Solvothermal Conditions

Polymers and coordinating solvents have been shown to serve as templating agents to assist the precipitation of ZnO nanoparticles and address their morphology. In this work we show for the first time that a difference in the coordination strength between the polymer (poly-N-vinylpyrrolidone (PVP)) and the two Zn(II) precursor salts (nitrate and acetate) is able to promote or suppress the formation of mesocrystalline structures and even more importantly to tune their three-dimensional organization. On the basis of FTIR and (13)C NMR spectroscopic studies, we propose that not only the polymer (PVP) but also the solvent (DMF) play a key role as directing agents.

The synthesis of luminescent adenosine triphosphate passivated cadmium sulfide nanoparticles

A simple method of preparing luminescent cadmium sulfide nanoparticles passivated with the biological molecule adenosine triphosphate (ATP) is reported. The biological molecule ATP is used as a materials chemistry synthon rather than a biological entity and its interaction with a semiconductor quantum dot surface is investigated.

Covalent Immobilization of Imidazolium Cations Inside a Silica Support: Palladium-Catalyzed Olefin Hydrogenation

Mesoporous organosilica materials with different contents of bistrialkoxysilyl imidazolium salts in the framework were synthesized by a one‐step synthesis. Textural characterization of the materials confirmed that the morphology and surface properties of the imidazolium‐bridged organosilicas depended critically on the amount of organic groups in the framework, whereas solid‐state NMR characterization showed that the imidazolium fragments were integrated covalently into the framework. Further reaction of these materials with Pd(OAc)2, followed by reduction with NaBH4 yielded palladium nanoparticles stabilized in the mesoporous organosilicas. The stabilizing effect of the imidazolium cations and the mesostructure contributed to the high activity, selectivity, and stability of the palladium nanoparticles and allowed olefin hydrogenation under mild reaction conditions.

Facile Route to Morphologically Tailored Silver Patches on Colloidal Particles

Here we demonstrate, for the first time, the heterogeneous nucleation and growth of silver patches on submicrometer silica spheres. While patches can be grown directly onto native silica particles, it is shown that a higher patch yield can be obtained by first treating the silica with a mixture of an alkanolamine and silver nitrate. Variation of the pretreatment and subsequent coating reactions allowed the patch yield, number, size, thickness, and shape to be adjusted. The patchy particles were shown to possess plasmon modes extending from the visible into the near-IR region, making these structures highly interesting for both their asymmetric morphological and functional properties.

Shedding light on the growth of gold nanoshells.

Nanostructured particles containing noble metals can have highly tunable localized surface plasmon resonances and are therefore of particular interest for numerous applications. Nanoshells comprising a dielectric core and gold or silver shell are a widely researched systems because of the strong dependence of their optical properties on the ratio of core diameter to shell thickness. Although seeded-growth procedures have been developed to produce these particles, the many reported studies show significant variation in the nanoshell morphologies and hence optical properties. In order to establish processes that reproducibly synthesize nanoshells with high optical quality, it is necessary to develop techniques that monitor changes at the core particle surface during shell growth. For that purpose, we have carried out in situ nonlinear second-harmonic scattering (SHS) and linear vis-NIR extinction spectroscopy simultaneously during the seeded growth of gold nanoshells on silica core particles. Our SHS measurements show a striking variation in the nonlinear optical properties of the growing gold nanoshells. In comparison with linear optical measurements and with scanning electron microscopy (SEM) images made of gold nanoshells produced with varying shell completenesses, the SHS signal was observed to reach a peak intensity at a stage prior to shell closure. We attribute this high sensitivity of the SHS signal to the incomplete nanoshell surface morphology to the generation and subsequent degeneration of regions of electric field enhancement at gaps between isolated gold islands, which grow and coalesce. This conclusion is corroborated by finite-difference time-domain simulations of incomplete nanoshells. We suggest that the in situ analytical approach demonstrated here offers significant promise for future activities regarding the in-process optimization of the morphology and optical properties of metal nanoshells and other nanostructured plasmonic particles.

Painting by Numbers: Nanoparticle‐Based Colorants in the Post‐Empirical Age

The visual appearance of the artificial world is largely governed by films or composites containing particles with at least one dimension smaller than a micron. Over the past century and a half, the optical properties of such materials have been scrutinized and a broad range of colorant products, based mostly on empirical microstructural improvements, developed. With the advent of advanced synthetic approaches capable of tailoring particle shape, size and composition on the nanoscale, the question of what is the optimum particle for a certain optical property can no longer be answered solely by experimentation. Instead, new and improved computational approaches are required to invert the structure-function relationship. This progress report reviews the development in our understanding of this relationship and indicates recent examples of how theoretical design is taking an ever increasingly important role in the search for enhanced or multifunctional colorants.