Polystyrene Colloidal Crystal Templates Research Articles

A 3D ordered hierarchical crystalline porous organic salt for large-sized enzyme immobilization

Crystalline porous organic salts (CPOSs) are an emerging class of promising materials with intrinsic highly polar nanoconfined microporosity. However, their single microporous structure greatly hinders their development in the field of catalysis and adsorption. Constructing a hierarchical porous structure can effectively reduce the mass transport resistance, thus expanding the scope of their applications. Herein, we report the synthesis of a three-dimensional (3D) ordered macro-/microporous hierarchical CPOS (HCPOS-1) using a template-assisted approach for the first time. The as-synthesized HCPOS-1 prepared from a polystyrene colloidal crystal template showcases a 3D ordered macroporous structure while also preserving the microporous structure. The 3D ordered macroporous structure in such a hierarchical structure, together with its hydrophilic surface, endows HCPOS-1 with the ability to immobilize large-sized enzymes through physical adsorption under mild conditions. The resulting catalase/HCPOS-1 showcases a high enzyme immobilization capacity and avoids undesired conformational changes of enzymes during the immobilization process, thus exhibiting excellent catalytic activity for the decomposition of hydrogen peroxide.

An Electrochemical Sensor Based on Three-Dimensional Porous Reduced Graphene and Ion Imprinted Polymer for Trace Cadmium Determination in Water

Three-dimensional (3D) porous graphene-based materials have displayed attractive electrochemical catalysis and sensing performances, benefiting from their high porosity, large surface area, and excellent electrical conductivity. In this work, a novel electrochemical sensor based on 3D porous reduced graphene (3DPrGO) and ion-imprinted polymer (IIP) was developed for trace cadmium ion (Cd(II)) detection in water. The 3DPrGO was synthesized in situ at a glassy carbon electrode (GCE) surface using a polystyrene (PS) colloidal crystal template and the electrodeposition method. Then, IIP film was further modified on the 3DPrGO by electropolymerization to make it suitable for detecting Cd(II). Attributable to the abundant nanopores and good electron transport of the 3DPrGO, as well as the specific recognition for Cd(II) of IIP, a sensitive determination of trace Cd(II) at PoPD-IIP/3DPrGO/GCE was achieved. The proposed sensor exhibited comprehensive linear Cd(II) responses ranging from 1 to 100 μg/L (R2 = 99.7%). The limit of detection (LOD) was 0.11 μg/L, about 30 times lower than the drinking water standard set by the World Health Organization (WHO). Moreover, PoPD-IIP/3DPrGO/GCE was applied for the detection of Cd(II) in actual water samples. The satisfying recoveries (97–99.6%) and relative standard deviations (RSD, 3.5–5.7%) make the proposed sensor a promising candidate for rapid and on-site water monitoring.

In-situ fabrication of porous-silica-microsphere-supported platinum nanocluster catalyst by γ-ray radiation

The synthesis and stable loading of metal nanoclusters have always been a hot and difficult topic in the field of nano-metal catalysts. In this work, micron-sized inverse opal SiO2 microspheres (IO-SiO2) are firstly prepared as the carrier of platinum nanoclusters (PtNCs) through a sol-gel process of tetraethyl orthosilicate (TEOS) on sacrificed polystyrene (PS) colloidal crystal microspheres template. After the IO-SiO2 carriers are dispersed into the aqueous solution of H2PtCl6 and irradiated by 60Co γ-ray radiation for a certain absorbed dose in a deoxygenized atmosphere, PtNCs with a size of less than 2 nm are in situ synthesized based on a redox equilibrium of Pt(0)/Pt(IV) induced by effect of the reductive species (eaq−, H) and oxidizing radicals (HO) produced by the radiolysis of water, and immobilized on IO-SiO2 without the help of any stabilizer. Due to the large pore volume of the IO-SiO2, the loading capacity of PtNCs can reach as high as 18.63 μg/mgmicrosphere. The prepared IO-SiO2-supported PtNCs (PtNCs@IO-SiO2) show excellent catalytic activity and recyclability for the reduction of o-nitroaniline by NaBH4 as the model reaction. This work offers a new route to prepare stable and high-performance metal nanocluster catalysts loaded on porous microspheres using γ-ray radiation technique.

Effect of template on catalytic performance of La0.7Ce0.3Ni0.7Fe0.3O3 for ethanol steam reforming reaction

Perovskite-type oxides La0.7Ce0.3Ni0.7Fe0.3O3 (LCNF) were synthesized by polystyrene colloidal crystal templating (LCNF-CCT) and polystyrene polymer templating (LCNF-PS) through co-precipitation. The structure and physicochemical properties of the obtained oxides were investigated by scanning electron microscopy, X-ray diffraction, N2 adsorption-desorption, Fourier transform infrared spectrometry, H2 temperature-programmed reduction and H2 temperature-programmed desorption, as well as X-ray photoelectron spectroscopy. The results show that the as-synthesized LCNF-CCT perovskite possesses large specific surface area and regular pore size distribution. In addition, the formation of additional oxygen vacancies on the surface favors the migration of lattice oxygen from the bulk phase to the surface and production of more metallic sites, thus improving the activity and resistance to carbon deposition of catalysts in ethanol steam reforming reaction.

Synthesis of Three‐dimensionally Ordered Macroporous TiO2 and TiO2/WO3 Composites and Their Photocatalytic Performance

This work presents the characterization and preparation of three‐dimensionally ordered macroporous TiO2 and TiO2/WO3 composite nanoparticles with enhanced visible‐light‐responsive properties for rhodamine B (Rh B) photodegradation. The 3DOM TiO2 and TiO2/WO3 composites were prepared through a dip‐infiltrating sol‐gel process using a polystyrene (PS) colloidal crystal template. The materials were characterized by SEM, TEM, XRD, BET, XPS and UV/Vis. The 3DOM TiO2/WO3 composite structures ranged from well‐defined 3DOM structures, which are highly ordered and interconnected via small pore windows, to collapsed three‐dimensional structures as the WO3 content increased. The photoresponse range and specific surface area of the composite increased with less than 0.025 g of WCl6. The 3DOM TiO2/WO3 composite with less than 0.025 g of WCl6 exhibited a higher catalytic activity than 3DOM TiO2 for the photocatalytic degradation of Rh B under simulated sunlight illumination.

Gas sensing performance enhancement: Determining the role of active sites through colloidal lithography

Using colloidal lithography, gold honeycomb (AuHC) monolayer crystals with various degree of porosity were formed on quartz crystal microbalance (QCM) electrodes thus enabling the experimental determination of the important role that surface parameters (pore size, surface area etc.) play in the sensing of gaseous species such as mercury vapor. The pore size was controlled through altering the O2 plasma etching periods of the close-packed monodispersed polystyrene colloidal crystal templates. It was found that the reduced pore size (or increased surface area) of AuHC structures enhanced the sensitivity of the QCMs toward mercury vapor adsorption, however the enhancement could not be correlated to the surface area increase alone. For example, the QCM containing AuHC structures which had been etched for 12 min (AuHC12 min) had similar Au mass and surface area as the control QCM with its continuous thin film of Au (Au-Ctrl), yet exhibited around twice the response magnitude when exposed toward elemental mercury (Hg°) vapor at 30 °C. The increased response magnitude could only be explained by the increased number of available active sites undergoing Hg° sorption which are present around the edges of the honeycomb pores. The QCM data showed that the number density of these active sites increased with increasing plasma etching periods as evidenced by the AuHC12 min QCM showing 7.4 times higher response magnitude toward Hg° vapor over the AuHC0 min based QCM when operated at 30 °C. Furthermore, the selectivity of the AuHC12 min based QCM was shown to be operating temperature dependent when undergoing cross-interference tests against common industrial gases such as humidity, ammonia, mercaptans, ketones and aldehydes, where improved selectivity was observed at elevated operating temperature of 75 °C.

The structure-reactivity relationships of using three-dimensionally ordered macroporous LaFe1−xNixO3 perovskites for chemical-looping steam methane reforming

Chemical-looping steam methane reforming (CL-SMR) is a novel technology for syngas and hydrogen production without purification process. A series of three-dimensionally ordered macroporous (3DOM) LaFe1−xNixO3 (x = 0.05, 0.1, 0.15, 0.2, 0.25, 0.3) perovskite-type oxides were synthesized using the polystyrene colloidal crystal templating method. The structural and physico-chemical properties of the obtained oxides were investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD) and Brunauere-Emmette-Teller (BET) surface area technologies. The structure-reactivity relationships and effects of Ni-substitution on the improvement of reactivity and resistance to carbon formation were investigated in a thermo-gravimetric analyzer and a fixed-bed reactor. It was found that the as-prepared oxides obtained standard perovskite structures and the well-ordered skeleton was surrounded with uniform close-packed macroporous windows. Ni-substitution improved the ability for oxygen supply but simultaneously enhanced the methane dissociation. While the openness channel and large surface area of 3DOM perovskite allowed low mass-transfer resistances and provided high active sites for reaction. Complicated factors synergistically affected the reactivity and an optimal value for Ni-substitution is confirmed with x = 0.1 by comprehensively considering from the points of reactivity, resistance to carbon formation, as well as hydrogen generation capacity. During the following successive redox reactions, 3DOM LaFe0.9Ni0.1O3 exhibited good regenerability and thermo-stability probably converting 90% of CH4 into syngas in methane reforming stage and generating ∼210–220 ml hydrogen in steam splitting stage.

Synthesis of three-dimensionally ordered macroporous LaFe0.7Co0.3O3 perovskites and their performance for chemical-looping steam reforming of methane

Three-dimensionally ordered macroporous (3DOM) LaFe0.7Co0.3O3 perovskite-type oxides were synthesized using a polystyrene (PS) colloidal crystal templating method. The obtained 3DOM LaFe0.7Co0.3O3 perovskites were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and Brunauere-Emmette-Teller (BET) surface area. Its performance as oxygen carriers in chemical looping steam methane reforming (CL-SMR) to produce syngas (H2 + CO) and hydrogen were investigated in a fixed-bed reactor. The size of PS spheres obviously increases as the styrene addition increases. The calcination temperature is the major factor to affect the prepared 3DOM perovskite. SEM and TEM analysis show that the samples calcined at 500, 800 and 850°C exhibit good 3DOM structures which collapse when the sample is calcined at 900°C. XRD results suggest that the obtained 3DOM LaFe0.7Co0.3O3 perovskites are pure crystalline. Two kinds of oxygen species, bulk lattice oxygen and surface adsorbed oxygen, are found to exist on the 3DOM LaFe0.7Co0.3O3 perovskites. The surface oxygen contributes to the complete oxidization of methane to CO2 and H2O in beginning of the reaction, while the bulk lattice oxygen tends towards partial methane oxidation to H2 and CO. In the methane conversion step, methane is partially oxidized into syngas at a H2/CO molar ratio close to 2:1 by the 3DOM-LaFe0.7Co0.3O3 in a wide range of the reactions, suggesting that the sample exhibits a good resistance to carbon deposition. In the steam oxidation step, the reduced perovskites are oxidized by steam to generate hydrogen with hydrogen productivity about 4 mmol/g oxygen carriers.

Chemically Responsive Polymer Inverse-Opal Photonic Crystal Films Created by a Self-Assembly Method

The synthesis of poly-2-hydroxyethyl methacrylate inverse-opal hydrogel (IOHGPHEMA) was realized by capillary-force-induced in situ polymerization in a polystyrene colloidal crystal template. The created IOHGPHEMA films show brilliant blue-violet color when they are immersed in deionized water and reach swelling equilibrium. The stop band of the IOHGPHEMA films can be tuned within the entire visible wavelength range by immersing them into different chemical solutions, such as aldehydes, ketones, amides, dimethyl sulfoxide, and alcohols. The extent of the reflective peak shift not only depends on the number of hydrogen band donors but also on the chain length and structure of the chemicals and their concentration. Since the IOHGPHEMA films have different reflectance spectra and structural colors in response to different compounds of the same series, this provides a potential way to visually detect homologues and other compounds with similar structure and properties. This simple, yet effective, method also ...

Color Tunable and Upconversion Luminescence in Yb-Tm Co-Doped Yttrium Phosphate Inverse Opal Photonic Crystals.

For this paper, YPO4: Tm, Yb inverse opals with the photonic band gaps at 475 nm and 655 nm were prepared by polystyrene colloidal crystal templates. We investigated the influence of photonic band gaps on the Tm-Yb upconversion emission which was in the YPO4: Tm Yb inverse opal photonic crystals. Comparing with the reference sample, significant suppression of both the blue and red upconversion luminescence of Tm3+ ions were observed in the inverse opals. The color purity of the blue emission was improved in the inverse opal by the suppression of red upconversion emission. Additionally, mechanism of upconversion emission in the inverse opal was discussed. We believe that the present work will be valuable for not only the foundational study of upconversion emission modification but also the development of new optical devices in upconversion lighting and display.

Synthesis of Nano-Al with Fe<sub>2</sub>O<sub>3</sub> Nanowires to Realize Core-Shell Composite Materials Arrays Based on Colloidal Templates

Controlled composite materials arrays have been widely applied for their unique physical and chemical properties, with the aim of developing nanodevices functionality. Nanosphere lithography is a successful technique for fabricating highly ordered arrays of various materials. In this work, the polystyrene colloidal crystal template in large area on Si substrate was obtained via dipping method. The thickness of the single layer template fabricated can be precisely controlling the particle concentration and the film formation speed. The ordered arrays of Fe2O3 nanowires were obtained via convenient spin method on this template and heat treatment subsequently. Finally, the uniform Al/Fe2O3 arrays were produced by magnetron sputtering method. These periodic composite arrays cover large area substrates (of dimensions > 1 cm × 1 cm) and are uniform in terms of nanowire height and density. The arrays thickness and gaps between nanowires are easily controlled by either the diameter of colloidal crystal or the parameters of magnetron sputtering.

Fabrication of 3D Photonic Crystals from Chitosan That Are Responsive to Organic Solvents

Inspired by photonic nanostructures in nature, such as the hair-like chaetae on the body of sea mice, inverse opal photonic crystals films were fabricated with chitosan, a kind of biomacromolecule found in nature. First, monodispersed polystyrene (PS) colloidal crystal templates with different particle sizes were prepared. The inverse opal films (IOFs) were fabricated through in situ cross-linking of the PS templates. The IOFs contain periodically ordered interconnecting pores that endow the films with photonic stop bands and structural colors, which are visible to the naked eye. The IOFs exhibit rapid reversible changes in their structural colors and reflectance peaks in response to alcohols and phenols. Possible mechanisms for the shifts in the IOF's reflectance peaks are proposed. The changes in the IOFs in response to alcohols and phenols provide a potential way to visually detect these organic solvents.

Inverse Opal Structure Platinum Electrode for Improving a Membrane-Electrode Assembly Performance of Polymer Electrolyte Membrane Fuel Cell

The ordered macroporous inverse opal structures electrode would be attractive structure for various applications in electrochemical device. The inverse opal structured platinum electrode was directly fabricated for application of membrane-electrode assemblies (MEA) in polymer electrolyte membrane fuel cells (PEMFC). The electrode was prepared by pulse electro–deposition following polystyrene colloidal crystal template on gas diffusion layers, without any additional transfer process at the electrodes. The performance of the inverse opal electrode-based MEA in the PEMFC was higher than that of a traditional MEA with Pt/C catalyst because of the morphological advantages of inverse opal structure.

Enhancement of near-infrared to near-infrared upconversion emission in the CeO_2: Er^3+, Tm^3+, Yb^3+ inverse opals

In this Letter, CeO₂: Er³⁺, Tm³⁺, Yb³⁺ inverse opal with near-infrared to near-infrared upconversion emission was prepared by polystyrene colloidal crystal templates, and the influence of photonic bandgap on the upconversion emission was investigated. Comparing with the reference sample, suppression of the blue or red upconversion luminescence was observed in the inverse opals. It is interesting that the near-infrared upconversion emission located at about 803 nm was enhanced due to the inhibition of visible upconversion emission in the inverse opals. Additionally, the variety of upconversion emission mechanisms was observed and discussed in the CeO₂: Er³⁺, Tm³⁺, Yb³⁺ inverse opals.

Fabrication of bowl-like porous WO3 film by colloidal crystal template-assisted electrodeposition method

Large scale of bowl-like porous WO3 film was successfully fabricated by electrodeposition into two-dimensional (2D) polystyrene (PS) colloidal crystal template. The technological process involved the following steps: colloidal crystal template preparation, potentiostatic electrodeposition of WO3 into the template, and template removal. 1.5 μm PS spheres were used to prepare the 2D colloidal crystal template by means of spinning on indium-tin-oxide (ITO) glass. A two-electrode cell was used for electrodeposition, in which the anode was graphite and the cathode was PS-coated ITO glass. The electrodeposition solution consisted of 25 mM Na2WO4 and 30 % H2O2 acidified at pH 1.2. Via electrodeposition, the interstitial space of the densely packed PS colloidal crystal template was filled with WO3. Bowl-like porous WO3 film was obtained after the removal of the PS colloidal crystal template by a thermal treatment at 475 °C. Scanning electron microscopic, X-ray diffraction spectra and transmission electron microscopy were performed to analyze and compare bowl-like porous WO3 film with dense WO3 film. The homogeneous area of the obtained film was 25 × 15 mm2. The template-assisted electrodeposition method was simple and low-cost that can be completed within 30 min.

Optimal filling fraction of Ta2O5 inverse opals

Tantalum pentoxide (Ta2O5) inverse opals were prepared by combining the self-assembly process and sol–gel chemistry-based opal infiltration. The inverse opal was made by the infiltration of a tantalum(V) ethoxide solution in the interstices of the polystyrene colloidal crystal template, and then removing the original opal template by calcination. The infiltration process as well as the optimal precursor concentration has been investigated in order to obtain Ta2O5 inverse opals with the optimal filling fraction. The effects of processing, template sphere size, morphology, structural properties, filling fraction and composition of the inverse opal are provided by scanning electron microscopy (SEM), X-ray energy dispersive spectroscopy analysis (EDS) and powder X-ray diffraction (XRD). The results correlate the concentration of the precursor with the filling fraction of the template.

Investigation of upconversion and near infrared emission properties in CeO_2: Er^3+, Yb^3+ inverse opals

The upconversion emission of rare earth ions can be modified in photonic crystals, however, the influence of upconversion emission modification of rare earths on near infrared emission has not been investigated yet in the photonic crystals. In the paper, CeO₂: Er³⁺, Yb³⁺ inverse opals with the photonic band gaps at 545, 680 and 450 nm were prepared by polystyrene colloidal crystal templates. The upconversion and the near infrared emission properties of Er³⁺ ions were systematically investigated in the CeO₂: Er³⁺, Yb³⁺ inverse opals. Comparing with the reference sample, significant suppression of both the green and red upconversion luminescence of Er³⁺ ions were observed in the inverse opals. It is interesting that the infrared emission located at 1,560 nm was enhanced due to inhibition of upconversion emission in the inverse opals. Additionally, mechanism of upconversion emission of the inverse opal was discussed. The photon avalanche upconversion process is observed.

Preparation and characterization of electrodeposited Ag-doped ZnO inverse opals with a smooth surface

Ag-doped ZnO inverse opal structures were prepared by electrochemical deposition using polystyrene colloidal crystal templates. The Ag-doped ZnO structures had granular morphology, but this morphology became smooth using a three-dimensional (3D) porous template in the same electrolyte. The Ag-doped ZnO structures were characterized using energy-dispersive X-ray spectroscopy, and the lattice parameter was found to increase compared with undoped ZnO as verified by X-ray diffraction. Strong reflection photonic stop bands centered at 495 and 681 nm were detected from inverse opals templated from microspheres having diameters of 285 and 370 nm. The filling ratio of Ag-doped ZnO inverse opals using the template was lower than that of the uniform film growth of undoped ZnO. Moreover, photochemical cell analysis revealed that doped ZnO inverse opals with n- and p-type conductivities were successfully formed using electrolytes with different silver ion concentrations.

Fabrication of Combined One-Dimensional and Three-Dimensional Structure of Potassium Tungstate Crystal Layers by Spray Deposition with Polystyrene Colloidal Crystal Templates

Well-aligned honeycomb-designed layers of potassium tungstate (K0.33WO3.165) were successfully fabricated by spray deposition and microsphere lithography using polystyrene (PS) colloidal crystals as templates. A densely packed monolayer of monodisperse PS microspheres was formed on a silica glass surface, using the Langmuir–Blodgett thin film technique. Subsequently, a (NH4)10W12O41·5H2O-KCl aqueous solution was sprayed as a micromist on the PS templates. While the K0.33WO3.165 crystal layers were synthesized by chemical reaction between W and K sources during the heating, the PS templates were thermally decomposed, generating an inverse opal surface structure where the interstitial space of the densely hexagonal packed PS microspheres had been. Numerous hexagonal rodlike crystals were grown on the honeycomb-designed layer of K0.33WO3.165. X-ray diffraction analysis, energy-dispersive X-ray spectroscopy analyses, and X-ray photoelectron spectroscopy were performed to analyze the combined one-dimensional and three-dimensional honeycomb-designed structure.

Synthesis of three-dimensionally ordered macroporous LaFeO3 perovskites and their performance for chemical-looping reforming of methane

Three-dimensionally ordered macroporous (3DOM) LaFeO3 perovskite-type oxides were synthesized using a polystyrene colloidal crystal templating method. The obtained 3DOM LaFeO3 was characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR). The reactivity of the perovskite-type oxides was evaluated using temperature-programmed reduction and multicyclic redox reactions by exposing them to an alternating methane and air atmosphere. The methane oxidation performance of the oxides was investigated in a fixed-bed reactor. The effect of the self-assembly method on the structure of the polystyrene template was also studied. A vertical deposition method yielded a more uniform and orderly polystyrene template than those obtained by centrifugation and evaporation techniques. The solvent and concentration of the precursor solution were the major factors to affect the prepared 3DOM perovskite. SEM analysis showed that samples synthesized with ethanol precursor solvent exhibited a better 3DOM structure than those produced with ethylene glycol, and that 1.0 mol/L may be an optimal precursor solution concentration. XRD and FTIR results suggested that the obtained 3DOM LaFeO3 was pure crystalline perovskite. Two kinds of oxygen species were found to exist on the 3DOM perovskites: surface adsorbed oxygen and bulk lattice oxygen. The surface oxygen contributed to the complete oxidization of methane to CO2 and H2O because of its higher reactivity, while the bulk lattice oxygen tended towards partial methane oxidation to H2 and CO. The available oxygen in the 3DOM LaFeO3 was higher than that of the same mass of non-3DOM LaFeO3 during the partial oxidation of methane. Methane was partially oxidized into syngas with a H2/CO ratio of around 2:1 in a wide time range of the reactions. The generated H2/CO = 2 syngas was suitable for subsequent gas-to-liquids processes, such as Fischer-Tropsch and/or methanol synthesis. 采用超声波辐射法制备了具有介孔结构的高浓度氮掺杂TiO2纳米晶(N/TiO2). 采用N2物理吸附/X射线粉末衍射/X射线光电子能谱/透射电镜/光致发光谱和紫外-可见漫反射光谱等手段对N/TiO2进行了表征. 以波长为400–660 nm的可见光为光源, 以水体污染物邻苯二甲酸二甲酯为降解对象, 考察了不同制备方法对N/TiO2光催化性能的影响. 结果表明, 超声波辐射使氮掺杂浓度提高了2.2倍, 该法制备的N/TiO2同时具有较好的介孔结构, 表现了更高的光催化降解邻苯二甲酸二甲酯的活性. 其活性提高的主要原因是N/TiO2含有更高浓度的氮和对可见光具有更强的吸收能力.