Polystyrene Colloidal Spheres Research Articles

3DOM SrTiO3-TiO2 composite material modified by CQDs with up-conversion characteristics: Enhanced photocatalytic degradation and photolysis of water for hydrogen production

Semiconductor photocatalysis is considered as an effective technology to ease the global energy shortage, designing efficient photocatalysts with enhanced light absorption, carrier separation and surface reaction is still one of the main strategies to solve its practical application. In this paper, the structure of the synthesized material was controlled by regular polystyrene (PS) colloidal spheres as templates, and the 3DOM SrTiO3-TiO2 composite modified by carbon quantum dots (CQDs) with three-dimensional ordered macroporous structure was prepared. In this composite, CQDs with up-conversion characteristics are used as photosensitizers to expand light absorption. The combination of SrTiO3 and TiO2 enhances the separation efficiency of charges, and the three-dimensional ordered macropore structure reduces the resistance of substances entering the catalyst, further improving the catalytic performance of the material. Under the irradiation of xenon lamp, the hydrogen evolution of the prepared CQDs/3DOM SrTiO3-TiO2 composite reached 578.95 μmol·g−1 after 8 h of photolysis, which is 14.5 times that of the monomer TiO2. In addition, with Rhodamine B (RhB) as the model molecule, the photocatalytic degradation activity of CQDs/3DOM SrTiO3-TiO2 was significantly better than that of other contrast systems under the experimental conditions of multimode photocatalytic degradation, showing enhanced photocatalytic degradation and hydrogen production from water photolysis. This study provides a feasible method for preparing three-dimensional ordered macroporous materials with excellent photocatalytic properties.

Phase stability of colloidal mixtures of spheres and rods.

We determined the phase boundaries of aqueous mixtures containing colloidal rod-like fd-viruses and polystyrene spheres using diffusing-wave spectroscopy and compared the results with free volume theory predictions. Excluded volume interactions in mixtures of colloidal rods and spheres lead to mediated depletion interactions. The strength and range of this attractive interaction depend on the concentrations of the particles, the length L and diameter D of the rods, and the radius R of the spheres. At strong enough attraction, this depletion interaction leads to phase separation. We experimentally determined the rod and sphere concentrations where these phase transitions occur by systematically varying the size ratios L/R and D/R and the aspect ratio L/D. This was done by using spheres with different radii and modifying the effective diameter of the rods through either the ionic strength of the buffer or anchoring a polymeric brush to the surface of the rods. The observed phase transitions were from a binary fluid to a colloidal gas/liquid phase coexistence that occurred already at very low concentrations due to the depletion efficiency of highly anisotropic rods. The experimentally measured phase transitions were compared to phase boundaries obtained using free volume theory (FVT), a well established theory for calculating the phase behavior of colloidal particles mixed with depletants. We find good correspondence between the experimental phase transitions and the theoretical FVT model where the excluded volume of the rod-like depletants was explicitly accounted for in both the reservoir and the system.

In situ growth of an opal-like TiO2 electron transport layer by atomic layer deposition for perovskite solar cells

Here, we use an atomic layer deposition system and different sizes of polystyrene colloidal spheres to in situ prepare an opal-like TiO2 mesoporous electron transport layer for perovskite solar cells.

Fabrication of polystyrene colloidal crystal film by electrophoretic deposition

Proper conditions for the formation of a colloidal crystal film by the electrophoretic deposition process were investigated in detail using monodisperse polystyrene (PS) colloidal spheres. Removal of the ionic contaminants and application of a pulsed current were effective in suppressing the electrolysis of water and obtaining a uniform film, but it was not possible to obtain colloidal crystals in which the particles were closely and periodically packed. Mixing EtOH at a high concentration with an aqueous PS suspension and withdrawing the substrate from the suspension at a moderate rate after the EPD process were found to be the key for the successful fabrication of colloidal crystal films. It was demonstrated that the formation of large area colloidal crystal films by the EPD technique was also possible. The advantage of the EPD process for scale up was successfully shown, taking into account the fast film fabrication rate.

Near field scattering for samples under forced flow

We describe a light scattering technique for characterizing colloidal samples under constant flow. It exploits the properties of speckles in the deep Fresnel region-the so-called near field speckles-providing absolute scattering measurements of the static form factor of the sample, as described extensively by Mazzoni et al. [Rev. Sci. Instrum. 84, 043704 (2013)] for static samples. We exploit a strongly astigmatic beam for illuminating the scattering volume with a light sheet a few microns thick. This largely improves the sensitivity of the method to small signals. Moreover, by flowing the sample in the direction perpendicular to the light sheet, the transit times are reduced to a minimum, allowing for fast measurements. We tested the instrument with suspensions of calibrated colloidal polystyrene spheres with a size comparable to the light wavelength. In particular, we recovered the static form factors of suspensions of spherical particles and the phase lag of the zero-angle scattering amplitude, which both compare well to Mie theory predictions. We then applied the method to colloidal fractal aggregates of sub-wavelength particles and measured their fractal dimension. The instrument is designed to be operational in continuous flow analysis systems.

Architecture design and applications of nanopatterned arrays based on colloidal lithography

Nanopatterned arrays have potential applications in diverse devices, including high-density memory, wettability control, electronic chips, biochips, plasmonics (such as plasmon sensors, plasmon-enhanced molecular spectroscopy, and plasmon-mediated chemical reactions), and so on. In this tutorial, we first introduce colloidal lithography (CL) technique as an important method to prepare nanopatterned arrays. Based on the formation of a mask by self-assembly of polystyrene (PS) colloid spheres, the nanopatterned arrays can be achieved by following a series of various deposition, etching, transfer, and their combination steps. According to the structural differences of the acquired surface patterns, diverse nanopatterned arrays are fabricated by controlling the fabrication routes. Technical issues are discussed in detail, such as preparation and modification of the large-area and ordered PS colloid sphere arrays and design and hybridization of nanostructured arrays of films with various shapes. In the meantime, the potential applications of these nanopatterned array films are reviewed and summarized. Hopefully, the present tutorial will inspire more ingenious designs of nanopatterned arrays and developments of using CL technique in potential applications.

Preparation of colloidal polydopamine/Au hollow spheres for enhanced ultrasound contrast imaging and photothermal therapy.

Development of functional theranostic platform for systemic contrast-enhanced diagnostic imaging and therapy is of great necessity in nanomedicine. However, synthesizing the biocompatible theranostic agents with enhanced merits in imaging and therapy via a facile and green way is still highly challenged. Here, we report a novel theranostic agent based on colloidal polydopamine/Au (PDA/Au) hollow spheres, which are synthesized with combined use of PDA chemistry and sacrificial template techniques. Colloidal polystyrene (PS) spheres serve as the templates with coatings of a PDA shell and Au nanoparticles in sequence, which are subsequently removed with trichloromethane, giving rise to colloidal PDA/Au hollow spheres. Colloidal PDA/Au hollow spheres exhibit excellent contrast enhancement for ultrasound imaging, and can serve as the near-infrared (NIR) photoabsorbers for the effective photothermal ablation of 4 T1 breast cancer cells in vitro with minor cytotoxicity to living cells. This method suggests a novel avenue for theranostic treatment in oncology.

Three-dimensional ordered hollow sphere composite Pt/TiO2-ZrO2: enhanced performance of photocatalytic degradation and photocatalytic hydrogen evolution

In this paper, a three-dimensional ordered hollow sphere (3DOH) structure composite Pt/TiO2-ZrO2 was prepared by using polystyrene (PS) colloidal spheres as the template and combining with two-step vacuum impregnation method, of which the composition, crystalline structure, morphology, and surface physicochemical properties were characterized by X-ray diffraction (XRD), UV-vis diffuse reflectance (UV-vis/DRS), photoluminescence (PL), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), and nitrogen adsorption-desorption measurements. The results illustrate the crystal type of 3DOH Pt/TiO2-ZrO2 is mainly anatase TiO2 and tetragonal ZrO2 phase, which exhibits a three-dimensional ordered hollow sphere structure. Hollow spheres are arranged orderly; moreover, the composite shows a strong absorption in the visible region due to the effect of surface plasmon absorption (SPA) after doping Pt nanoparticles. Meanwhile, the photocatalytic activity of 3DOH Pt/TiO2-ZrO2 was investigated by using Congo red as the model molecule. The results show that 3DOH Pt/TiO2-ZrO2 has good photocatalytic activity under multi-modes photocatalytic experiments, and its activity is higher than that of P25, ZrO2, and other Pt/TiO2-ZrO2 not treated by PS colloidal spheres. In addition, the total amount of hydrogen production of 3DOH Pt/TiO2-ZrO2 is 100 times as much as the commercial P25 in the photocatalytic hydrogen evolution experiment (8 h), which shows an excellent photolysis of water hydrogen production activity.

The Structural Colors of Photonic Glasses

AbstractThe color of materials usually originates from a combination of wavelength‐dependent absorption and scattering. Controlling the color without the use of absorbing dyes is of practical interest, not only because of undesired bleaching properties of dyes but also regarding minimization of environmental and health issues. Color control without dyes can be achieved by tuning the material's scattering properties in controlling size and spatial arrangement of scatterers. Herein, calibrated photonic glasses (PGs), which are isotropic materials made by random aggregation of nonabsorbing, monodisperse colloidal polystyrene spheres, are used to generate a wide spectral range of purely structural, angular‐independent colors. Experimental reflectance spectra for different sized spheres compare well with a recent theoretical model, which establishes the latter as a tool for color mapping in PGs. It allows to determine the range of visible colors accessible in PGs as function of size, packing fraction, and refractive index of scatterers. It also predicts color saturation on top of the white reflectance as function of the sample's optical thickness. Blue, green, and red are obtained even with low index, while saturated green, cyan, yellow, and magenta can be reached in higher index PGs over several orders of magnitude of sample thickness.

Aluminum film over nanosphere surface for Deep Ultraviolet plasmonic nanosensors

Deep ultraviolet (DUV) plasmonic nanosensors are emerging as potential candidates to detect biomolecules with enhanced sensitivity, as these molecules strongly absorb light in the DUV region. In the present work, we fabricated aluminium film over nanospheres surface (AlFON) and successfully demonstrated, for the first time, an AlFON based DUV plasmonic nanosensor for detecting volatile organic compounds (VOCs) such as ethanol, isopropyl alcohol (IPA) and toluene, and bovine serum albumin (BSA) protein. The AlFON was fabricated by thermally evaporating aluminium thin film onto a two-dimensional photonic crystal (2DPC). The 2DPC was prepared by drop casting colloidal polystyrene spheres (PSS) on quartz substrates that self-assembled to form a monolayer of hexagonally close packed PSS with periodic interstices. The optical reflection spectrum of 70 nm AlFON exhibited a sharp minimum at 289 nm in the DUV wavelength range which corresponds to strong absorption in V-shaped nanocavities due to excitation of localized cavity plasmons. The reflection minimum—or LSPR wavelength—is sensitive to the changes in the refractive index of the surrounding medium. The LSPR mode of the V-shaped nanocavities in 70 nm AlFON was exploited to sense VOCs and BSA. The 70 nm AlFON exhibited 244 nm/RIU sensitivity in detecting VOCs and was capable of sensing 1 mM concentration of BSA in water. The AlFON is physically stable and has a self-limiting Al2O3 oxide layer of less than 5 nm thickness as elucidated from x-ray photoelectron spectroscopy measurements. The effect of higher aluminum film thickness, i.e. 100 nm and 120 nm on the sensitivity of AlFON also was studied. The performance of AlFON based DUV plasmonic nanosensors is better than the previously reported Al nanostructure based nanosensors and can still be enhanced by optimizing the structure of 2DPC and AlFON.

Bimodally Porous WO3 Microbelts Functionalized with Pt Catalysts for Selective H2S Sensors

Bimodally meso- (2-50 nm) and macroporous (>50 nm) WO3 microbelts (MBs) functionalized with sub-3 nm Pt catalysts were fabricated via the electrospinning technique followed by subsequent calcination. Importantly, apoferritin (Apo), tea saponin and polystyrene colloid spheres (750 nm) dispersed in an electrospinning solution acted as forming agents for producing meso- and macropores on WO3 MBs during calcination. Particularly, mesopores provide not only numerous reaction sites for effective chemical reactions, but also facilitate gas diffusion into the interior of the WO3 MBs, dominated by Knudsen diffusion. The macropores further accelerate gas permeability in the interior and on the exterior of the WO3 MBs. In addition, Pt nanoparticles with mean diameters of 2.27 nm were synthesized by using biological protein cages, such as Apo, to further enhance the gas sensing performance. Bimodally porous WO3 MBs functionalized by Pt catalysts showed remarkably high hydrogen sulfide (H2S) response ( Rair/ Rgas = 61 @ 1 ppm) and superior selectivity to H2S against other interfering gases, such as acetone (CH3COCH3), ethanol (C2H5OH), ammonia (NH3), and carbon monoxide (CO). These results demonstrate a high potential for the feasibility of catalyst-loaded meso- and macroporous WO3 MBs as new sensing platforms for the possibility of real-time diagnosis of halitosis.

Design of Hybrid Nanostructural Arrays to Manipulate SERS-Active Substrates by Nanosphere Lithography.

An easy-handling and low-cost method is utilized to controllably fabricate nanopattern arrays as the surface-enhanced Raman scattering (SERS) active substrates with high density of SERS-active areas (hot spots). A hybrid silver array of nanocaps and nanotriangles are prepared by combining magnetron sputtering and plasma etching. By adjusting the etching time of polystyrene (PS) colloid spheres array in silver nanobowls, the morphology of the arrays can be easily manipulated to control the formation and distribution of hot spots. The experimental results show that the hybrid nanostructural arrays have large enhancement factor, which is estimated to be seven times larger than that in the array of nanocaps and three times larger than that in the array of nanorings and nanoparticles. According to the results of finite-difference time-domain simulation, the excellent SERS performance of this array is ascribed to the high density of hot spots and enhanced electromagnetic field.

Hollow graphene oxide spheres: facile synthesis and formation mechanism

In this work, we introduced a facile approach for preparing hollow graphene oxide spheres (HGOSs). By electrostatic self-assembly polystyrene (PS)/graphene oxide (GO), core/shell microspheres were synthesized. After removal of the sacrificial PS colloidal spheres by toluene solution treatment, HGOSs were prepared successfully. Based on the DLVO theory, van der Waals force and electric double layer repulsion were proposed to quantitatively analyze the self-assembly of the composite structure. The theoretical formulation for the resultant interaction force F versus separation between the surfaces d showed a significant low energy barrier for the aggregation of the GO and PS, which predicted the favorable HGOSs formation.

Highly Tunable Complementary Micro/Submicro-Nanopatterned Surfaces Combining Block Copolymer Self-Assembly and Colloidal Lithography.

Two kinds of large-area ordered and highly tunable micro/submicro-nanopatterned surfaces in a complementary manner were successfully fabricated by elaborately combining block copolymer self-assembly and colloidal lithography. Employing a monolayer of polystyrene (PS) colloidal spheres assembled on top as etching mask, polystyrene-block-poly(2-vinylpyridine) (PS-b-P2VP) or polystyrene-block-poly(4-vinylpyridine) (PS-b-P4VP) micelle films were patterned into micro/submicro patches by plasma etching, which could be further transferred into micropatterned metal nanoarrays by subsequent metal precursor loading and a second plasma etching. On the other hand, micro/submicro-nanopatterns in a complementary manner were generated via preloading a metal precursor in initial micelle films before the assembly of PS colloidal spheres on top. Both kinds of micro/submicro-nanopatterns showed good fidelity at the micro/submicroscale and nanoscale; meanwhile, they could be flexibly tuned by the sample and processing parameters. Significantly, when the PS colloidal sphere size was reduced to 250 nm, a high-resolution submicro-nanostructured surface with 3-5 metal nanoparticles in each patch or a single-nanoparticle interconnected honeycomb network was achieved. Moreover, by applying gold (Au) nanoparticles as anchoring points, micronanopatterned Au arrays can serve as a flexible template to pattern bovine serum albumin (BSA) molecules. This facile and cost-effective approach may provide a novel platform for fabrication of micropatterned nanoarrays with high tunability and controllability, which are promising in the applications of biological and microelectronic fields.

Optofluidic Switching of Nanoparticles Based on a WDM Tree Splitter

We demonstrate a silicon-based wavelength-division multiplexing (WDM) tree splitter for optofluidic switching of nanoparticles in a lab-on-a-chip or nanofluidic system. The gradient force and scattering force induced by the evanescent field can, respectively, lead to trapping and transportation of colloidal polystyrene (PS) spheres directly above the waveguide. Guiding of PS into any designated branch within a cascaded tree splitter is achieved by switching of the excitation wavelength. As compared to that based on microrings, an optimized design of the reported tree splitter approach offers a number of advantages in terms of device compactness, wavelength tolerance, response speed, and trap stability, while maintaining the inherent low-loss and low-power performance features of WDM splitters. A network of such splitters can readily lead to a platform for high-throughput and large-scale particle manipulation in nanofluidic systems.

One-pot Seedless Synthesis of Uniform Gold Nanoshells and Their Photothermal Conversion Property

Gold nanoshells have strongly tunable localized surface plasmon resonance and therefore attract considerable interest for numerous applications. Here, we present a facile one-pot seedless approach to rapidly and controllably prepare gold nanoshells. According to this approach, the continuous and uniform gold nanoshells were obtained directly by adding NaBH4, PVP, NaOH and ascorbic acid (AA) into the mixture solution of HAuCl4 and polyelectrolyte modified polystyrene (PS) colloidal spheres, sequentially. The obtained gold nanoshells showed structure-dependent localized surface plasmon resonance and their absorption wavelengths red-shifted as the gold nanoshells grew from incomplete to continuous gold layers. In terms of the photothermal conversion property, gold nanoshells could effectively convert 808 nm laser to heat and the temperature increase depended highly on the structure of gold nanoshells.

Synthesis of Rh/Macro-Porous Alumina Over Micro-Channel Plate and Its Catalytic Activity Tests for Diesel Reforming

Macro-porous Al2O3 as the catalytic support material was synthesized using colloidal polystyrene spheres over a micro-channel plate. The colloidal polystyrene spheres were used as a template for the production of an ordered macro porous material using an alumina nitrate solution as the precursor for Al2O3. The close-packed colloidal crystal array template method was applied to the formulation of ordered macro-porous Al2O3 used as a catalytic support material over a micro-channel plate. The solvent in the mixture solution, which also contained the colloidal polystyrene solution, aluminum nitrate solution and the precursor of the catalytic active materials (Rh), was evaporated in a vacuum oven at 50 degrees C. The ordered polystyrene spheres and aluminum salt of the solid state were deposited over a micro channel plate, and macro-porous Al2O3 was formed after calcination at 600 degrees C to remove the polystyrene spheres. The catalytic activity of the Rh/macro-porous alumina supported over the micro-channel plate was tested for diesel reforming.

Studies on the Characteristics of Vertical Organic Transistor with Nano Patterned Gate Using Block Copolymer.

In this study, we fabricated and studied the device characteristics of vertical organic transistors consisting of nano-patterned gates constructed from the self-assembly of block copolymer. The size of the gate opening made by the new method was 30~40 nm. The device was compared with those which had gate openings of 200 nm. These lager devices were constructed from monodispersed colloidal polystyrene spheres. The device which used block copolymer showed significant improvements in its on-off ratio. We also fabricated transistors with tungsten oxide buffer layer to increase the on current of the device. The devices were analyzed based on their current-voltage charac- teristics, impedance spectroscopy, atomic force microscope (AFM) images and scanning electron microscope (SEM) images.

One‐Step Self‐Assembly Fabrication of High Quality NixMg1‐xO Bowl‐Shaped Array Film and Its Enhanced Photocurrent by Mg,2+ Doping

A series of high quality NixMg1‐xO bowl‐shaped array films are successfully prepared by a simple one‐step assembly of polystyrene colloidal spheres and metal oxide precursors at oil–water interface, and further used to fabricate nanodevices. The doping of Mg2+ can greatly enhance the current and spectrum responsivity of NiO film‐based nanodevice. The maximum Rλ value of these bowl‐shaped NixMg1‐xO film‐based devices measured in the study shows 4–5 orders of enhancement than the previously reported NixMg1‐xO film at equal doping.

Improved performance of GaN-based light emitting diodes with nanopatterned sapphire substrates fabricated by wet chemical etching

The authors present a facile approach to the fabrication of nanopatterned sapphire substrates (NPSS) with concave pyramid structure by a wet etching method. The silica wet-etching mask on the sapphire substrate was prepared by using a colloidal monolayer templating strategy. NPSS with two different periods were prepared by employing 660 and 900 nm polystyrene colloidal spheres. Light emitting diode (LED) structure was epitaxially grown on the NPSS by the metal-organic chemical vapor deposition method. Both structural and optoelectronic properties of LEDs grown on flat sapphire substrate and NPSS were demonstrated and compared in detail. The calculations based on x-ray rocking curves revealed that the threading dislocation densities (TDDs) were decreased and the crystalline quality of epitaxial GaN film was improved when NPSS was used. Furthermore, the decrease in the edge TDDs was more prominent than that in the screw TDDs, which could be explained by the dislocation annihilation mechanism. The LEDs grown on 660- and 900-nm-NPSS exhibited 48% and 56% enhancement in light output power compared to that of a conventional LED on a flat sapphire substrate, arising from the nanoscale patterns in the sapphire which allowed more light to reflect from sapphire substrate onto the top direction.