Polymethyl Methacrylate-templating Research Articles

3DOM BiVO4 supported silver bromide and noble metals: High-performance photocatalysts for the visible-light-driven degradation of 4-chlorophenol

Three-dimensionally ordered macroporous (3DOM) photocatalysts BiVO4 (denoted as 3D-BiV), AgBr/3D-BiV, and 0.17wt% M/AgBr/3D-BiV (MAu, Pt, and Pd) were prepared using the polymethyl methacrylate-templating, low-temperature deposition, and polyvinyl alcohol-protected reduction methods, respectively. The as-prepared BiVO4 possessed a good-quality 3DOM structure and a high surface area. It is found that the AgBr and noble metals were uniformly distributed on the surface of 3D-BiV. Among the M/AgBr/3D-BiV samples, the 0.17wt% Pd/AgBr/3D-BiV sample showed the highest photocatalytic activity for the degradation of 4-chlorophenol (4-CP) under visible light illumination (i.e., complete 4-CP degradation could be achieved within 150min), which was associated with its good 3DOM structure, high surface oxygen adspecies concentration, easy transfer and separation of photogenerated carriers, and synergistic effect between AgBr or Pd nanoclusters and BiVO4.

Au–Pd/3DOM Co3O4: Highly active and stable nanocatalysts for toluene oxidation

The polymethyl methacrylate-templating and polyvinyl alcohol-protected reduction routes were adopted to prepared three-dimensionally ordered macroporous (3DOM) Co3O4 and its supported gold–palladium alloy (xAuPd/3DOM Co3O4, x=0.50–1.99wt% and Au/Pd mass ratio=1:1) nanocatalysts. The 3DOM Co3O4 supported Au–Pd samples performed much better than supported single Au or Pd samples, with the 1.99AuPd/3DOM Co3O4 sample showing the best performance: the T10%, T50%, and T90% (temperatures required for achieving toluene conversions of 10%, 50%, and 90%) were 145, 164, and 168°C at a space velocity of 40,000mL/(gh), respectively. The 3DOM Co3O4 supported Au–Pd nanocatalysts also exhibited better catalytic stability and more moisture-tolerant ability than the supported Au or Pd samples for toluene oxidation. The apparent activation energies (33–41kJ/mol) over xAuPd/3DOM Co3O4 were much lower than those (52–112kJ/mol) over 3DOM Co3O4 and supported single Au or Pd samples, with the 1.99AuPd/3DOM Co3O4 sample exhibiting the lowest apparent activation energy (33kJ/mol). It is concluded that better oxygen activation ability and stronger noble metal–3DOM Co3O4 interaction were responsible for the excellent catalytic performance of 1.99AuPd/3DOM Co3O4.

Fabrication and high photocatalytic performance of noble metal nanoparticles supported on 3DOM InVO4–BiVO4 for the visible-light-driven degradation of rhodamine B and methylene blue

Three-dimensionally ordered macroporous (3DOM) InVO4–BiVO4 (InBi-3D) and its supported noble metal M nanoparticles (xM/InBi-3D; x=0.08–0.13wt%; M=Au, Ag, Pd, Pt) were prepared using the polymethyl methacrylate-templating and polyvinyl alcohol- or polyvinyl pyrrolidone-assisted reduction methods, respectively. Physical properties of the materials were characterized by a number of analytical techniques. Photocatalytic activities of the xM/InBi-3D samples were evaluated for the degradation of rhodamine B (RhB), methylene blue (MB), and their mixture. It is found that the as-fabricated samples possessed a surface area of 17–30m2/g, a M particle size of 2.5–3.8nm, and a bandgap energy of 2.50–2.56eV. The xM/InBi-3D photocatalysts showed high activities for the degradation of RhB, MB, and RhB+MB in the presence of a small amount of H2O2 under visible-light irradiation, among which complete degradation of RhB, MB, and RhB+MB was achieved within 50, 90, and 120min over 0.08wt% Au/InBi-3D, respectively. The degradation of MB and RhB fellow the zero- and first-order reaction mechanisms with respect to dye concentration, respectively. It is concluded that the high photocatalytic efficiency of the Au-loaded sample in the removal of organic dyes was associated with its high surface area, high-quality 3DOM hierarchical architecture, InVO4–BiVO4 composite, and high dispersion of gold nanoparticles.

Preparation and high catalytic performance of Au/3DOM Mn2O3 for the oxidation of carbon monoxide and toluene

Three-dimensionally ordered macroporous (3DOM) Mn2O3 and its supported gold (xAu/3DOM Mn2O3, x=1.9−7.5wt%) nanocatalysts were prepared using the polymethyl methacrylate-templating and polyvinyl alcohol-protected reduction methods, respectively. The 3DOM Mn2O3 and xAu/3DOM Mn2O3 samples exhibited a surface area of 34−38m2/g. The Au nanoparticles (NPs) with a size of 3.0−3.5nm were uniformly dispersed on the skeletons of 3DOM Mn2O3. The 5.8Au/3DOM Mn2O3 sample performed the best, giving the T90% (the temperature required for a conversion of 90%) of −15°C at space velocity (SV)=20,000mL/(gh) for CO oxidation and 244°C at SV=40,000mL/(gh) for toluene oxidation. The apparent activation energies (30 and 54kJ/mol) over 5.8Au/3DOM Mn2O3 were much lower than those (80 and 95kJ/mol) over 3DOM Mn2O3 for CO and toluene oxidation, respectively. The effects of SV, water vapor, CO2, and SO2 on catalytic activity were also examined. It is concluded that the excellent catalytic performance of 5.8Au/3DOM Mn2O3 was associated with its high oxygen adspecies concentration, good low-temperature reducibility, and strong interaction between Au NPs and 3DOM Mn2O3 as well as high-quality porous architecture.

3DOM InVO4-supported chromia with good performance for the visible-light-driven photodegradation of rhodamine B

Three-dimensionally ordered macroporous (3DOM) monoclinic InVO4 and its supported chromia (yCrOx/3DOM InVO4, y denotes as the weight percentage of Cr2O3, y = 5, 10, 15, and 20 wt%) photocatalysts were fabricated using the ascorbic acid-assisted polymethyl methacrylate-templating and incipient wetness impregnation methods, respectively. Physicochemical properties of the materials were characterized by means of a number of analytical techniques. Photocatalytic activities of the samples were evaluated for the degradation of rhodamine B (RhB) in the presence of H2O2 under visible-light illumination. Compared to 3DOM InVO4 and 15CrOx/bulk InVO4, yCrOx/3DOM InVO4 showed much better visible-light-driven photocatalytic performance for RhB degradation, with the 15CrOx/3DOM InVO4 sample performing the best. It is concluded that the CrOx loading, higher surface area and surface oxygen vacancy density and lower bandgap energy as well as the better quality of 3DOM structure were responsible for the good photocatalytic performance of 15CrOx/3DOM InVO4 for the degradation of RhB.

Au/3DOM La0.6Sr0.4MnO3: Highly active nanocatalysts for the oxidation of carbon monoxide and toluene

Three-dimensionally ordered macroporous (3DOM) La0.6Sr0.4MnO3 (LSMO) and its supported gold (xAu/LSMO, x=3.4–7.9wt%) catalysts were prepared using the polymethyl methacrylate-templating and gas-bubble-assisted polyvinyl alcohol-protected reduction methods, respectively. There were good correlations of surface-adsorbed oxygen species concentration and low-temperature reducibility with the catalytic activity of the sample for CO and toluene oxidation. Among the LSMO and xAu/LSMO samples, 6.4Au/LSMO performed the best, giving T50% and T90% values of −19 and 3°C for CO oxidation and 150 and 170°C for toluene oxidation, respectively. The apparent activation energies (31–32 and 44–48kJ/mol) obtained over xAu/LSMO were much lower than those (45 and 59kJ/mol) obtained over LSMO for the oxidation of CO and toluene, respectively. It is concluded that higher oxygen adspecies concentration, better low-temperature reducibility, and strong interaction between Au and LSMO are responsible for the excellent catalytic performance of 6.4Au/LSMO.

Au/3DOM LaCoO3: High-performance catalysts for the oxidation of carbon monoxide and toluene

Rhombohedrally crystallized three-dimensionally ordered macroporous (3DOM) LaCoO3 and its supported Au (xAu/3DOM LaCoO3, x=0–7.63wt%) catalysts were prepared using the polymethyl methacrylate-templating and polyvinyl alcohol-protected reduction methods, respectively. Physicochemical properties of the materials were characterized by means of numerous analytical techniques, and their catalytic activities were evaluated for the oxidation of toluene and CO. It is shown that the xAu/3DOM LaCoO3 samples displayed a 3DOM architecture and a high surface area of 24–29m2/g. The 7.63Au/3DOM LaCoO3 sample exhibited the highest adsorbed oxygen species concentration and the best low-temperature reducibility, and hence the best catalytic performance. Over 7.63Au/3DOM LaCoO3, the T10%, T50%, and T90% (corresponding to the temperatures required for achieving a reactant conversion of 10%, 50%, and 90%) were 136, 188, and 202°C for toluene oxidation at space velocity (SV)=20,000mL/(gh), and −61, −6, and 42°C for CO oxidation at SV=10,000mL/(gh), respectively. Over xAu/3DOM LaCoO3, the apparent activation energies were 31.4–37.4kJ/mol for toluene oxidation and 16.6–19.4kJ/mol for CO oxidation. We believe that the high oxygen adspecies concentration, good low-temperature reducibility, and strong interaction between Au and 3DOM LaCoO3 might account for the excellent catalytic performance of 7.63Au/3DOM LaCoO3.

Three-dimensionally ordered macroporous InVO4: Fabrication and excellent visible-light-driven photocatalytic performance for methylene blue degradation

Three-dimensionally ordered macroporous (3DOM) monoclinic InVO4 with nanovoid-like skeletons and high surface areas (35–52m2/g) were fabricated using the citric acid-, tartaric acid- or ascorbic acid-assisted polymethyl methacrylate-templating strategy. Photocatalytic activities of the 3DOM-structured materials were evaluated for the degradation of methylene blue (MB) under visible-light illumination. Compared to the bulk InVO4, the 3DOM-structured InVO4 showed much better visible-light-driven photocatalytic performance for MB degradation. It is concluded that the excellent photocatalytic activity of 3DOM-structured InVO4 were associated with their higher surface areas and surface oxygen vacancy density and lower bandgap energy as well as the better 3DOM structure. We are sure that the 3DOM-structured materials are promising photocatalysts for the removal of organics from wastewater under visible-light illumination.

PMMA-templating generation and high catalytic performance of chain-like ordered macroporous LaMnO3 supported gold nanocatalysts for the oxidation of carbon monoxide and toluene

Rhombohedrally crystallized chain-like LaMnO3 and its supported gold (xAu/LaMnO3; x=1.4, 3.1, and 4.9wt%) catalysts have been prepared using the poly(ethylene glycol)-assisted polymethyl methacrylate-templating and gas bubble-assisted polyvinyl alcohol-protected reduction methods, respectively. It is shown that there were good correlations of surface adsorbed oxygen species concentration and low-temperature reducibility with catalytic activity of the samples for the oxidation of CO and toluene. Among the LaMnO3 and xAu/LaMnO3 samples, 4.9Au/LaMnO3 performed the best, giving the T50% and T90% of 61 and 91°C for CO oxidation, and of 201 and 226°C for toluene combustion, respectively. The apparent activation energies (29–50 and 47–62kJ/mol) of the chain-like LaMnO3 and xAu/LaMnO3 samples were much smaller than those (63 and 97kJ/mol) of the bulk LaMnO3 sample for the oxidation of CO and toluene, respectively. We believe that the higher surface area and oxygen adspecies concentration and better low-temperature reducibility as well as the strong interaction between Au nanoparticles and chain-like LaMnO3 support might account for the high catalytic performance of 4.9Au/LaMnO3.

Preparation of High Weight Loading Lithium Borohydride in Carbon Aerogels

We describe approaches using modified carbon aerogels for increasing the weight loading of LiBH4. Large pore volume carbon aerogels were prepared with a sol-gel method and a polymethyl methacrylate (PMMA) microsphere template. Compared to those without using templates, the pore volume has been up to 3.8 times with a PMMA template. After incorporation into carbon aerogels, the weight loading of LiBH4 has reached 80%. Nitrogen absorption/desorption measurements show that more than 95% free space of carbon aerogels has been incorporated with LiBH4. Rama spectra suggest that there is no PMMA or chemical reaction during the synthesis of LiBH4/carbon aerogel composites.

Au/3DOM Co3O4: highly active nanocatalysts for the oxidation of carbon monoxide and toluene

Three-dimensionally ordered macroporous Co3O4 (3DOM Co3O4) and its supported gold (xAu/3DOM Co3O4, x = 1.1-8.4 wt%) nanocatalysts were prepared using the polymethyl methacrylate-templating and bubble-assisted polyvinyl alcohol-protected reduction methods, respectively. The 3DOM Co3O4 and xAu/3DOM Co3O4 samples exhibited a surface area of 22-27 m(2) g(-1). The Au nanoparticles with a size of 2.4-3.7 nm were uniformly deposited on the macropore walls of 3DOM Co3O4. There were good correlations of oxygen adspecies concentration and low-temperature reducibility with catalytic activity of the sample for CO and toluene oxidation. Among 3DOM Co3O4 and xAu/3DOM Co3O4, the 6.5Au/3DOM Co3O4 sample performed the best, giving a T90% (the temperature required for achieving a conversion of 90%) of -35 °C at a space velocity of 20 000 mL g(-1) h(-1) for CO oxidation and 256 °C at a space velocity of 40 000 mL g(-1) h(-1) for toluene oxidation. The effect of water vapor was more significant in toluene oxidation than in CO oxidation. The apparent activation energies (26 and 74 kJ mol(-1)) over 6.5Au/3DOM Co3O4 were lower than those (34 and 113 kJ mol(-1)) over 3DOM Co3O4 for CO and toluene oxidation, respectively. It is concluded that the higher oxygen adspecies concentration, better low-temperature reducibility, and strong interaction between Au and 3DOM Co3O4 were responsible for the excellent catalytic performance of 6.5Au/3DOM Co3O4.

Fabrication of macroporous titanium dioxide film using PMMA microspheres as template

A novel synthetic procedure is described for the fabrication of macroporous titanium dioxide (TiO2) films with an ordered, uniform pore framework comprised of nanocrystalline anatase mainly. The synthetic approach involved several processes. First, polymethyl methacrylate (PMMA) microspheres (87nm) were synthesized by using a dispersion polymerization technique in the presence of Fenton reagent (FeSO4/H2O2) as a novel initiator, which has advantages such as simple and fast polymerization process without deoxygenation. Next, the templates of PMMA microspheres were assembled on clean substrates by dip-drawing technique. Finally, the macroporous TiO2 films with the average size of pores about 87nm were obtained by sol-dipping template method and calcination to remove the templates at 550°C. The test results of X-ray diffraction indicate that the nanocrystalline of anatase formed after calcination. The mechanisms of PMMA polymerization and template formation were proposed. Furthermore, both structures and morphologies of the composite films were investigated with field emission scanning electron microscope, and the processes of the thermal decomposition of PMMA and TiO2 gel were also discussed with thermo gravimetric analysis. This ordered and uniform pore framework could be used as the promising ultrafilter membranes showing active photocatalysis without intensive fouling.

Gold mesoflower arrays with sub-10 nm intraparticle gaps for highly sensitive and repeatable surface enhanced Raman spectroscopy

Self-assembling Au mesoflower arrays are prepared using a polymethylmethacrylate (PMMA) template on an iron substrate via a combined top-down/bottom-up nanofabrication strategy. The PMMA template with the holes around 300–500 nm in diameter is first fabricated by using polymer blend lithography on iron substrates, and the highly homogeneous Au mesoflower arrays with less than 10 nm intraparticle gaps are subsequently obtained by an in situ galvanic reaction between HAuCl4 solution and the iron substrate under optimal stirring of the solution as well as reaction time. Owing to the unique mesostructures and uniformity, Raman measurements show that the gold mesoflower arrays obtained demonstrated a strong and reproducible surface enhanced Raman scattering (SERS) enhancement on the order of ∼107–108. The development of a SERS substrate based on the Au mesoflowers with high spatial density of hot spots, relatively low cost and facial synthesis provides a novel strategy for applications in chemical and biomolecular sensing.

Template-assisted formation of microsized nanocrystalline CeO2 tubes and their catalytic performance in the carboxylation of methanol

Polymethylmethacrylate (PMMA)/ceria composite fibres were synthesized by using a sequential combination of polymer electrospinning, spray-coating with a sol, and a final calcination step to yield microstructured ceria tubes, which are composed of nanocrystalline ceria particles. The PMMA template is removed from the organic/inorganic hybrid material by radio frequency (rf) plasma etching followed by calcination of the ceramic green-body fibres. Microsized ceria (CeO2) tubes, with a diameter of ca. 0.75 µm, composed of nanocrystalline agglomerated ceria particles were thus obtained. The 1-D ceramic ceria material was characterized by X-ray diffraction, scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), UV–vis and photoluminescence spectroscopy (PL), as well as thermogravimetric analysis (TGA). Its catalytic performance was studied in the direct carboxylation of methanol with carbon dioxide leading to dimethyl carbonate [(CH3O)2CO, DMC], which is widely employed as a phosgene and dimethyl sulfate substitute, and as well as a fuel additive.

Controllable fabrication of enclosed micro/nanochannels via polymethyl methacrylate pattern as sacrificial template and capillary effect

High quality rectangular micro- to nanochannels with SiO2 shells have been fabricated by using optimized preparation parameters. Various dimensions of cross section of channels have been effectively controlled via the polymethyl methacrylate template as a suitable sacrificial layer in the processes of pattern formation and nanolithography. And, the fabricated channels have excellent shape uniformity, smooth inner surface, and vertical sidewalls along the longitudinal axis, which is confirmed by the good agreement between the experimental data and theoretical values of the mean filling speeds of liquids in the confined space. This technique exhibits the potential advantage for the controllable fabrication of various micro- to nanofluidic devices.

Photonic stop band effect in ZnO inverse photonic crystal

Three-dimensional photonic crystals are fabricated using inward-growing self-assembly technique from polymethyl methacrylate (PMMA) colloids. Their air voids are infiltrated with zinc oxide (ZnO) by sol–gel method and the PMMA template is removed by the two independent processes of heat treatment and wet chemical method resulting in ZnO inverse photonic crystal. The inversion is confirmed from the structural characterization. In X-ray diffraction (XRD) experiment, the ZnO inverse photonic crystals obtained by both the techniques do not show any signature of single-crystalline ZnO. The inverse photonic crystals obtained by chemical method are further heated at different temperatures and XRD confirms crystalline nature of ZnO for temperature treatment at 400°C. Laser-induced emission studies on ZnO inverse photonic crystals are carried out at two different excitation wavelengths. Excitation with 355nm enables the observation of the stop band effect for emission at 45° from the inverse crystal obtained by the inexpensive chemical method.

Synthesis and Characterization of Ordered Meso-Macro-Porous Silica Membranes on a Porous Alumina Support

Macroporous silica materials with ordered three-dimensional pore structure can be easily prepared by the template-directed sol-gel process. However, it is still a challenge to prepare them in membrane form on a porous support, which limits their applications. In this work, we have demonstrated the feasibility of obtaining a three-dimensional ordered macroporous silica membrane on macroporous alumina support using poly-methyl methacrylate (PMMA) spheres as the template. PMMA spheres were packed on the top of an Anopore-alumina support by filtration of a PMMA aqueous suspension. Silica sol obtained by an acid-catalyzed sol-gel process was infiltrated into the voids among the spheres. Drying induced stress caused the membrane to crack or peel off from the top of the support. This can be minimized by annealing the PMMA template layer before the introduction of silica sol which increases the mechanical strength of the template. Calcination or solvent extraction to remove the template produced a highly ordered three-dimensional macroporous silica membrane with spherical pores connected by windows in the mesoporous range. The results show that the PMMA-templated infiltration method is effective in preparing three-dimensional ordered macroporous silica membranes on a porous support.

Fabrication of porous alumina ceramics having cell windows with controlled size by PMMA template method

Highly porous alumina compacts have been prepared by filling alumina slurry into opening of a specially designed template block prepared by cross-linked (cl-) polymethylmethacrylate (PMMA) microspheres (mean particle size: 98.6 μm) under reduced pressure, followed by firing to remove the template and then sintering at 1600 °C. The template blocks were prepared by utilizing cl-PMMA and acetone solution dissolving noncrosslinked (Ncl-) PMMA as an adhesive to make partial connection among the cl-PMMA microspheres. Furthermore, the effects of the addition of other chemicals (two types of triblockcopolymers and a nonionic surfactant) to the Ncl-PMMA adhesive solution were tested to improve the wettability of the solution to cl-PMMA and then to control the cell windows among the cl-PMMA-originated cells after the firing. By employing the template block, prepared with the adhesive solution containing an appropriate amount of triblockcopolymer, a highly porous alumina compact having an open porosity of 77.2%, a mean cell window diameter of 28.8 μm, and strong alumina skeleton could be fabricated.

Study of multi-step X-ray exposures to fabricate microstructure

Compared with single-step exposure of X-ray light source of high-power synchrotron radiation, lithographic process using multi-step exposures with a conformal mask has some advantages such as a thinner absorption layer, better heat dissipation, and shorter developing time. In this study, a conformal mask with an aurum (Au) absorber is fabricated using traditional ultraviolet (UV) lithography and Au electroplating process. For X-ray exposure, an analytical model of the absorption dosage (exposure dosage) along the exposed depth of x is developed. It can estimate accurately the time and dosage required for exposure. Based on the calculated dosage, 2-mm-thick PMMA (Polymethylmethacrylate) template with high-aspect ratio of 20 is fabricated by this multi-step exposures and developing process. With this template, nickel-cobalt (Ni–Co) alloy electroplating process is applied to fabricate a metallic mold with high hardness. For high-aspect-ratio microstructures, hardness and internal stress of the metallic mold by electroplating is a key factor to the quality. Experimentally, it is found that changing the ratio of Ni sulfamate to Co sulfamate can affect hardness and internal stress of the deposit. Though the hardness of the electroplated alloy is improved due to Co sulfamate, internal stress is induced at the same time. Thus, it is necessary to add a stress reducer to reduce internal stress. The currently result shows that the hardness of the mold of about 550 Hv with about 25 wt.% of Co and zero internal stress can be made successfully after adding a stress reducer. With this electroplating technique, the 2-mm-thick and 100-μm-wide microstructure with high hardness is fabricated.

Fabrication of Macroporous Pt Film Electrode

Colloidal crystal template films have been prepared on a Pt-sputtered Si substrate by a dip-coating method with suspensions containing 870 nm polymethylmethacrylate (PMMA) microspheres. The mostly-packed PMMA template films could be obtained from the ethanol-ultra pure water suspensions containing P123 as a surfactant. Macroporous Pt films could be fabricated successfully by electrolytic deposition of Pt on the PMMA template film and subsequent removal of PMMA by thermal treatment. The use of the thick template film prepared from a suspension containing higher PMMA concentration resulted in a thinner wall of Pt framework and destruction of pore structure during the firing process to remove the PMMA template. Similar phenomena were observed for Pt films prepared by non-electrolytic deposition of Pt on the PMMA film. In contrast, firm Pt porous structure with thicker framework was maintained after removal of PMMA when electrolytic deposition of Pt was conducted on a thin template film prepared from a suspension containing lower concentration.