Photocatalytic Reduction of CO2 with H2O on Ti-Containing Porous Silica Thin Film Photocatalysts

Two different Ti-containing porous silica thin films having a hexagonal and cubic pore structure were synthesized and used as photocatalysts for the reduction of CO₂ with H₂O at 323 K. UV irradiation of the Ti-containing porous silica thin films in the presence of CO₂ and H₂O led to the formation of CH₄ and CH₃OH with a high quantum yield of 0.28%. These porous silica thin film photocatalysts having a hexagonal pore structure exhibited higher reactivity than the Ti-MCM-41 powder photocatalysts with the same pore structure.     

Effect of electrochemical preparation methods on structure and properties of PbO2 anodic layer

PbO₂ anodic layers were formed by direct oxidation of lead electrodes galvanostatically (G) and potentiostatically (P), in attempt to study PbO₂ as positive active material for lead-acid batteries. The structural and electrochemical properties of PbO₂ anodic layers, prepared by the two methods, were examined and found to be different. Comparative studies indicated that PbO₂-G electrode exhibited a longer discharge time, corresponding to a higher capacity, and a lower charge transfer resistance than that of PbO₂-P. Through SEM observation it was established that the PbO₂-G had a compact structure, while the PbO₂-P surface showed a porous structure. Discharge capacity was related to the film structure and internal resistance of PbO₂ layer. The compact structure with higher degree of interconnected particles lead to lower internal resistance thus higher capacity, and the porous surface layer would result in high transfer resistance and diminished capacity. It was concluded that preparation methods could controllably affect the structure of PbO₂ films, which further played important roles in discharge capacity.     

Oxidative energy storage behavior of a porous nanostructured TiO2–Ni(OH)2 bilayer photocatalysis system

TiO₂–Ni(OH)₂ bilayer electrodes were prepared by the cathodic electrodeposition of Ni(OH)₂ layer on a TiO₂/ITO substrate. The porous Ni(OH)₂ layers were obtained at relatively high current densities (≥1.0 mA cm⁻²), and the particle size increased with increasing the deposition current density. A porous nanostructured TiO₂–Ni(OH)₂ bilayer was obtained at a current density of 1.0 mA cm⁻². The effects of OH⁻ concentration in the electrolyte and surface structure in the Ni(OH)₂ layer on storage of the oxidative energy of TiO₂ were investigated. In our experimental conditions the oxidative energy storage of an UV-irradiated TiO₂ photocatalyst in Ni(OH)₂ was obviously enhanced in the electrolyte with 1.0 M OH⁻. The porous nanostructured TiO₂–Ni(OH)₂ bilayer electrode showed the notably improved oxidative energy storage performance, resulting from its porous structure and nanostructured Ni(OH)₂ particles. The TiO₂–Ni(OH)₂ bilayer electrode during UV irradiation exhibited much higher potentials and larger photocurrent than the TiO₂/ITO electrode. The transition from Ni(OH)₂ to NiOOH under UV irradiation proceeded in the potential range of −0.5 to −0.2 V, much more negative than the Ni(OH)₂/NiOOH redox potential. A possible mechanism on the oxidative energy storage of an UV-irradiated TiO₂ photocatalyst in Ni(OH)₂ was proposed, and the related experimental results were discussed in terms of the suggested model.     

Effect of pore structure on anomalous behaviour of the lithium intercalation into porous V2O5 film electrode using fractal geometry concept

The effect of pore structure on anomalous behaviour of the lithium intercalation into porous V₂O₅ film electrode has been investigated in terms of fractal geometry by employing ac-impedance spectroscopy combined with N₂ gas adsorption method and atomic force microscopy (AFM). For this purpose, porous V₂O₅ film electrodes with different pore structures were prepared by the polymer surfactant templating method. From the analysis of N₂ gas adsorption isotherms and the triangulation analysis of AFM images, it was found that porous V₂O₅ surfaces exhibited self-similar scaling properties with different fractal dimensions depending upon amount of the polymer surfactant in solution and the spatial cut-off ranges. All the ac-impedance spectra measured on porous V₂O₅ film electrodes showed the non-ideal behaviour of the charge-transfer reaction and the diffusion reaction, which resulted from the interfacial capacitance dispersion and the frequency dispersion of the diffusion impedance, respectively. From the comparison between the surface fractal dimensions by using N₂ gas adsorption method and AFM, and the analysis of ac-impedance spectra by employing a constant phase element (CPE), it is experimentally confirmed that the lithium intercalation into porous V₂O₅ film electrode is crucially influenced by the pore surface irregularity and the film surface irregularity.     

Preparation of hollow porous Cu2O microspheres and photocatalytic activity under visible light irradiation

Cu₂O p-type semiconductor hollow porous microspheres have been prepared by using a simple soft-template method at room temperature. The morphology of as-synthesized samples is hollow spherical structures with the diameter ranging from 200 to 500 nm, and the surfaces of the spheres are rough, porous and with lots of channels and folds. The photocatalytic activity of degradation of methyl orange (MO) under visible light irradiation was investigated by UV-visible spectroscopy. The results show that the hollow porous Cu₂O particles were uniform in diameters and have an excellent ability in visible light-induced degradation of MO. Meanwhile, the growth mechanism of the prepared Cu₂O was also analyzed. We find that sodium dodecyl sulfate acted the role of soft templates in the synthesis process. The hollow porous structure was not only sensitive to the soft template but also to the amount of reagents.     

Porous polymers prepared via high internal phase emulsion polymerization for reversible CO2 capture

A series of porous polymers with different pore volumes, pore sizes, and crosslinking densities were synthesized by high internal phase emulsion (HIPE) polymerization. The crosslinked polymerized HIPEs (polyHIPEs) were formed by the copolymerization of 4-vinylbenzyl chloride and divinylbenzene using water droplets in conventional or Pickering HIPEs as the templates. These porous materials were further modified by quaternization and ion exchange to introduce quaternary ammonium hydroxide groups. The resulting polyHIPEs were utilized as sorbents for reversible CO₂ capture from air using the humidity swing. The effect of pore structure on the CO₂ adsorption and desorption processes was studied. The polyHIPEs containing large pores and interconnected porous structures showed improved swing sizes and faster adsorption/desorption kinetics of CO₂ compared to a commercial Excellion membrane with similar functional groups.     

A novel preparation method for NiCo2O4 electrodes stacked with hexagonal nanosheets for water electrolysis

In this paper, we describe the preparation of a porous nanosheet-stacked NiCo₂O₄ composite electrode using a novel electrophoretic deposition (EPD) calcination method. The effects of the deposition time and voltage, and of the calcination temperature have been investigated. The microstructure of the deposited films in the electrodes before and after calcination has also been investigated. The electrocatalytic properties of the electrodes have been investigated using cyclic voltammetry and polarization curves. The electrode films produced using this new technique have a porous structure composed of stacked hexagonal NiCo₂O₄ nanosheets. The resulting electrodes exhibit good electrocatalytic properties for water electrolysis.     

Foaming of polymers with supercritical CO2: An experimental and theoretical study

Microcellular polystyrene (PS) foams and porous structures of the biodegradable poly(d,l-lactic acid) (P_d,lLA) were prepared with the batch foaming technique (pressure quench) using supercritical CO₂ as blowing agent. The effect of pressure, temperature and depressurization rate on the final porous structure was investigated. The results revealed that the size of the pores decreases and their population density increases with pressure increase, or decrease of temperature, and/or increase of the depressurization rate. The results were correlated by combining nucleation theory with NRHB model in order to account for and emphasize the physical mechanism related to nucleation of bubbles inside the supersaturated polymer matrix. A satisfactory agreement between correlations and experimental data was obtained indicating that the nucleation theory yields quantitative correlations when variables such as sorption, degree of plasticization, and surface tension of the system polymer-supercritical fluid are accurately described.     

MICROPOROUS SOLIDS FROM SiO2-Al2O3

Polymeric Si-Al sols were prepared from Al(OBu^s)₃ and Si(OEt)₄ (TEOS). Acetylacetone and isoeugenol were employed separately to chelate the Al precursor in order to slow down the chemical reactivity, avoiding precipitation. The characterization techniques were Fourier Transform Infrared Spectroscopy (FTIR), nitrogen sorption measurements, Thermal Gravimetric (TGA) and Differential Thermal Analyses (DTA). The Si-O-Al bond vibration was detected by FTIR in the 1056-1074 cm^m1 region. From the N₂ adsorption, isotherms the surface area results obtained range between 15.8 to 408.4 m²/g. Corresponding average pore diameter are 3.397 to 1.417 nm. It is found that the porous texture of the materials mainly depends to the chelating agent in the sols. A strong influence of the molecular structure of the chelating agents in the sols was observed in the oxides by TGA and DTA studies.     

Space electric field concentrated effect for Zr:SiO2 RRAM devices using porous SiO2 buffer layer

To improve the operation current lowing of the Zr:SiO₂ RRAM devices, a space electric field concentrated effect established by the porous SiO₂ buffer layer was investigated and found in this study. The resistive switching properties of the low-resistance state (LRS) and high-resistance state (HRS) in resistive random access memory (RRAM) devices for the single-layer Zr:SiO₂ and bilayer Zr:SiO₂/porous SiO₂ thin films were analyzed and discussed. In addition, the original space charge limited current (SCLC) conduction mechanism in LRS and HRS of the RRAM devices using bilayer Zr:SiO₂/porous SiO₂ thin films was found. Finally, a space electric field concentrated effect in the bilayer Zr:SiO₂/porous SiO₂ RRAM devices was also explained and verified by the COMSOL Multiphysics simulation model.     

Preparation of porous PLGA/HA/collagen scaffolds with supercritical CO2 and application in osteoblast cell culture

Biocompatible three-dimensional scaffolds for cell culturing may facilitate methods for the repair of damaged human tissues. A novel hybrid porous scaffold of poly(lactic-co-glycolic acid), hydroxyapatite and collagen was prepared using a supercritical CO₂ saturation technique. Expansion factors of scaffolds with different compositions were studied after supercritical CO₂ treatment to choose the optimal composition for three-dimensional culture. The supercritical CO₂ process conditions, such as saturation temperature, saturation time and saturation pressure were varied to evaluate their influence on pore structure. The results showed that the pore size and porosity of the scaffold could be controlled by manipulating these process conditions. The porous samples were characterized by environmental scanning electron microscopy, energy-dispersive X-ray spectroscope, Fourier transform infrared spectroscopy and X-ray diffractometry. Finally, MG-63 cells were successfully cultured on the porous scaffold as assessed by electron and confocal microscopy, confirming the biocompatibility of this new hybrid porous scaffold.     

A comparative electrochemical study of LiMn2O4 spinel thin-film and porous laminate

Novel Electrostatic Spray Deposition (ESD) technique was used to fabricate LiMn₂O₄ spinel thin-films. Cyclic voltammograms of both the ESD and porous laminate films show the double peaks in the 4.0 V range characteristic of the LiMn₂O₄ spinel materials. The porous laminates exhibit two semicircles in the impedance spectra while the ESD films show only one single semicircle. The diffusion time constant in the laminate films was typically one order of magnitude larger than that in the ESD thin-films. The apparent lithium-ion chemical diffusion coefficient in LiMn₂O₄ was found to be of the order of 10⁻⁹ cm²/s for both the porous laminate film and the ESD films despite the difference in the diffusion time constants.     

Photocatalytic activity of transparent porous glass supported TiO2

A porous glass tube with a composition of 96SiO₂·4B₂O₃ (wt%) supported TiO₂ shows high photooxidation activity due to its transparency and large surface area. The surface area of the porous glass tube supported TiO₂ is 10,000 times larger than that of conventional materials. TiO₂ crystals supported are anatase type. Transparency of the porous glass tube is very important. Herein, sol–gel and chemical vapor deposition (CVD) processes were employed as TiO₂ supporting processes. CVD process is more effective. For instance, an aqueous methylene blue solution with 1 ppm concentration almost thoroughly decomposes at a contact time of 300 s using porous glass tube supported TiO₂ prepared by CVD process under irradiating with 10 W low-pressure mercury lamp, on the other hand, opaque porous alumina tube supported TiO₂ was only 25%. The smaller the pore size of the porous glass tube, the larger the transparency and the permeation resistance through porous glass tube. Hence, porous glass tube with ca. 40 nm pore diameter is suitable from the standpoint of a practical use.     

Adsorption of Cu(II) from Aqueous Solution by Porous Mn3[Co(CN)6]2 · nH2O Nanospheres

Prussian blue analogue of porous Mn₃[Co(CN)₆]₂ · nH₂O nanospheres with a large surface area were prepared by simple mixing K₃[Co(CN)₆]₂ and manganous nitrate solution at room temperature. The morphology and structure of the prepared products were characterized by XRD, FE-SEM, TEM, and BET. The results indicated that the product was composed of nanospheres with the diameter of ～250 nm, which was of porous structure with the pore diameter in the 2.5–4 nm range. The adsorption behavior of Cu(II) ions from aqueous solution onto porous nanospheres was investigated as a function of parameters, such as the equilibrium time, the pH, the initial concentration, and the temperature. A maximum adsorption capacity of 140.85 mg g^?1 of Cu(II) was achieved. Due to the simple synthetic method and its high adsorption capacity, the porous nanospheres had the potential to be utilized as an effective adsorbent for Cu(II) removal.     

Synthesis and photocatalytic properties of H2La2Ti3O10/TiO2 intercalated nanomaterial

H₂La₂Ti₃O₁₀/ TiO₂ intercalated nanomaterial was fabricated by successive intercalation reactions of H₂La₂Ti₃O₁₀ with n-C₆H₁₃NH₂/C₂H₅OH mixed solution and acid TiO₂ sol, followed by irradiating with a high-pressure mercury lamp. The intercalated materials possess a gallery height of 0.46 nm and a specific surface area of 31.58 m²·g⁻¹, which indicate the formation of a porous material. H₂La₂Ti₃O₁₀/TiO₂ shows photocatalytic activity for the decomposition of organic dye under irradiation with visible light and the activity of TiO₂ intercalated material was superior to the unsupported one.     

Formation of TiO2 nano fibers on a micro-channeled Al2O3-ZrO2/TiO2 porous composite membrane for photocatalytic filtration

In this study, needle-shape TiO₂ fibers were successfully fabricated inside a micro-channeled Al₂O₃-ZrO₂ composite porous membrane system using sol-gel method. The micro-channeled Al₂O₃-ZrO₂ composite was fabricated using the fibrous monolithic (FM) process. Pure anatase phase TiO₂ was crystallized from the as-coated amorphous phase during calcination at 510 °C. The TiO₂ fibers grew on the surface frame of the micro-channeled Al₂O₃-ZrO₂ composite membrane and fully covered the inside of the micro-channeled pores. The specific surface area of the TiO₂ coated membrane system was dramatically increased by over 100 fold compared to that of the non-coated system. The photocatalytic activity of the membrane was also assessed and was shown to very effectively convert organic materials. Thus, this novel membrane holds promise for use as an advanced filtration system.     

Fabrication of Porous TiO<Subscript>2</Subscript> Hollow Spheres and Their Application in Gas Sensing

In this work, porous TiO₂ hollow spheres with an average diameter of 100 nm and shell thickness of 20 nm were synthesized by a facile hydrothermal method with NH₄HCO₃ as the structure-directing agent, and the formation mechanism for this porous hollow structure was proved to be the Ostwald ripening process by tracking the morphology of the products at different reaction stages. The product was characterized by SEM, TEM, XRD and BET analyses, and the results show that the as-synthesized products are anatase phase with a high surface area up to 132.5 m²/g. Gas-sensing investigation reveals that the product possesses sensitive response to methanal gas at 200°C due to its high surface area.     

Effect of TiO2 addition on the microstructures,mechanical and dielectric properties of porous Si3N4-based ceramics

Porous Si₃N₄-based ceramics with different TiO₂ contents were prepared by gas pressure sintering method. The effects of TiO₂ addition ranging from 0 to 25?wt-% on the phase compositions, microstructures, mechanical performance and dielectric properties were investigated. The addition of TiO₂ significantly promoted the density which increased from 1.64 to about 2.3?g?cm^?3. The mechanical properties of porous Si₃N₄-based ceramics with TiO₂ addition decreased first and then increased with the increase of TiO₂ content, and the flexural strength and elastic modulus are more than 167.4?MPa and 72.8?GPa, respectively, which were higher than that of the Si₃N₄ ceramic without TiO₂ addition. With the increase of TiO₂ content, both the dielectric constant and dielectric loss increased, and the dielectric constant enhanced obviously. These results suggested that the TiO₂ was beneficial for the improvement of mechanical properties and dielectric constant of porous Si₃N₄-based ceramics.     

Novel porous TiO2 glass-ceramics with highly photocatalytic ability

A porous TiO₂ glass-ceramics with high photo-oxidative activity was successfully obtained from the SiO₂–Al₂O₃–B₂O₃–CaO–TiO₂ glass system. Rutile-type TiO₂ was observed in the crystallization temperature range of 973–1173 K. The band gap of the glass-ceramics coincided approximately with that of rutile-type TiO₂. The photocatalytic activity of this glass-ceramics was about four times larger than that of a TiO₂-coated photocatalyst fabricated by the sol–gel process. Furthermore, as this porous TiO₂ glass-ceramics contained TiO₂ in composition form, it could prevent peeling of the TiO₂ from the substrate. As well, this glass-ceramics can be easily shaped into sheets, tubes, rods, etc.     

Preparation of a highly microporous carbon from a carpet material and its application as CO2 sorbent

In order to increase the use of carpet wastes (pre- and/or post-consumer wastes), this work studies for the first time the preparation and characterisation of a microporous material from a commercial carpet (pile fiber content: 80% wool/20% nylon; primary and secondary backings: woven polypropylene; binder: polyethylene) and its application for CO₂ capture. The porous material was prepared from an entire carpet material using a standard chemical activation with KOH and then, characterised in terms of their porous structure and surface functional groups. Adsorption of CO₂ was studied using a thermogravimetric analyser at several temperatures (25-100 °C) and under different CO₂ partial pressures (i.e. pure CO₂ flow and a ternary mixture of 15% CO₂, 5% O₂ and 80% N₂). In order to examine the adsorbent regenerability, multiple CO₂ adsorption/desorption cycles were also carried out. The surface area and micropore volume of the porous adsorbent were found to be 1910.17 m² g^− 1 and 0.85 cm³ g^− 1, respectively. The CO₂ adsorption profiles illustrate that the maximum CO₂ capture on the sample was reached in less than 10 min. CO₂ adsorption capacities up to 8.41 wt.% and 3.37 wt.% were achieved at 25 and 70 °C, respectively. Thermal swing regeneration studies showed that the prepared adsorbent has good cyclic regeneration capacities.