A topologically substituted boron nitride hybrid aerogel for highly selective CO<Subscript>2</Subscript> uptake

A topologically mediated synthesis of porous boron nitride aerogel has been experimentally and theoretically investigated for carbon dioxide (CO₂) uptake. Replacement of the carbon atoms in a precursor aerogel of graphene oxide and carbon nanotubes was achieved using an elemental substitution reaction, to obtain a boron and nitrogen framework. The newly prepared BN aerogel possessed a specific surface area of 716.56 m²/g and exhibited an unprecedented twentyfold increase in CO₂ uptake over N₂, adsorbing 100 cc/g at 273 K and 80 cc/g in ambient conditions, as verified by adsorption isotherms via the multipoint Brunauer-Emmett-Teller (BET) method. Density functional theory calculations were performed to give hints on the mechanism of such high selectivity of CO₂ over N₂ adsorption in BN aerogel, which may be due to the interaction between the intrinsic polar nature of B–N bonds and the high quadrupole moment of CO₂ over N₂.

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The size modulation of hollow mesoporous carbon spheres synthesized by a simplified hard template route

Hollow mesoporous carbon spheres (HMCSs) have been prepared by a simplified replication route from a solid silica core/mesoporous silica shell aluminosilicate (SCMS-Al) template, which was synthesized by directly incorporating aluminum species into the mesoporous framework during template synthesis. The size of HMCSs can be tuned between 80 and 470 nm by simply changing the diameters of SCMS-Al. The HMCSs have uniform mesopores with a narrow pore size distribution (3.4-4.1 nm), and high surface area, (890-1150 m²/g) and total pore volumes (0.75-1.15 cm³/g). The techniques of N₂ sorption isotherms, TEM, EDX and SEM were used to characterize the as-synthesized spheres.     

Hierarchical Porous O‐Doped g‐C3N4 with Enhanced Photocatalytic CO2 Reduction Activity

Artificial photosynthesis of hydrocarbon fuels by utilizing solar energy and CO₂ is considered as a potential route for solving ever‐increasing energy crisis and greenhouse effect. Herein, hierarchical porous O‐doped graphitic carbon nitride (g‐C₃N₄) nanotubes (OCN‐Tube) are prepared via successive thermal oxidation exfoliation and curling‐condensation of bulk g‐C₃N₄. The as‐prepared OCN‐Tube exhibits hierarchically porous structures, which consist of interconnected multiwalled nanotubes with uniform diameters of 20–30 nm. The hierarchical OCN‐Tube shows excellent photocatalytic CO₂ reduction performance under visible light, with methanol evolution rate of 0.88 µmol g^?1 h^?1, which is five times higher than bulk g‐C₃N₄ (0.17 µmol g^?1 h^?1). The enhanced photocatalytic activity of OCN‐Tube is ascribed to the hierarchical nanotube structure and O‐doping effect. The hierarchical nanotube structure endows OCN‐Tube with higher specific surface area, greater light utilization efficiency, and improved molecular diffusion kinetics, due to the more exposed active edges and multiple light reflection/scattering channels. The O‐doping optimizes the band structure of g‐C₃N₄, resulting in narrower bandgap, greater CO₂ affinity, and uptake capacity as well as higher separation efficiency of photogenerated charge carriers. This work provides a novel strategy to design hierarchical g‐C₃N₄ nanostructures, which can be used as promising photocatalyst for solar energy conversion.     

Ultrasonic-assisted synthesis of amorphous Bi<Subscript>2</Subscript>S<Subscript>3</Subscript> coupled (BiO)<Subscript>2</Subscript>CO<Subscript>3</Subscript> catalyst with improved visible light-responsive photocatalytic activity

A series of Bi₂S₃/(BiO)₂CO₃ composite photocatalysts with different loadings of amorphous Bi₂S₃ were successfully synthesized through an ultrasonic-assisted ion-exchange reaction between thioacetamide (CH₃CSNH₂) and (BiO)₂CO₃, and characterized by XRD, XPS, BET, EELS, EDX, SEM, TEM/HRTEM, UV–Vis, and photoluminescence (PL) techniques. The results of TEM/HRTEM, EELS, and EDX indicate that the composite catalyst Bi₂S₃/(BiO)₂CO₃ has been successfully synthesized with the deposited Bi₂S₃ present in amorphous state on the surface of (BiO)₂CO₃. The activities of the catalysts for RhB degradation under visible light show that the catalyst prepared under ultrasonic is more active than the one synthesized without ultrasonic. The optimized sample Bi₂S₃/(BiO)₂CO₃ (U5.0) exhibits a much higher activity, about 4.8 times to that of pure (BiO)₂CO₃. Based upon the band structures of Bi₂S₃/(BiO)₂CO₃, it is deduced that the migration of the visible light-induced electrons from the conduction band of Bi₂S₃ to that of (BiO)₂CO₃ should have facilitated the separation of photogenerated carriers, as confirmed by the suppressed photoluminescence spectra. Using different scavengers, the ·O₂ ^? and holes are clearly identified as the main oxidative species for RhB photodegradation. In light of these observations, a potential photocatalytic mechanism of RhB degradation over Bi₂S₃/(BiO)₂CO₃ is proposed.     

Mechanochemical synthesis of fine-particle γ-LiAlO<Subscript>2</Subscript>

We describe a new approach for the synthesis of fine-particle gamma lithium aluminate, γ-LiAlO₂, which involves mechanical activation of mixtures of Al(OH)₃ and Li₂CO₃ and heat treatment of the products. The formation of γ-LiAlO₂ was followed using x-ray diffraction, chemical analysis, thermal analysis, IR spectroscopy, and BET specific surface measurements. The specific surface of the synthesized γ-LiAlO₂, 10 to 33 m²/g, is large enough for this material to be used as an electrolyte matrix support for molten carbonate fuel cells.     

Formation of TiO<Subscript>2</Subscript> nanotubes by thermal decomposition of poly(vinyl alcohol)-titanium alkoxide hybrid nanofibers

Anatase type TiO₂ nanotubes were formed by calcination of poly(vinyl alcohol)-Ti alkoxide hybrid precursor nanofibers in air. The outer and inner diameters of the TiO₂ nanotubes calcined at 500 °C for 5 h were ca. 440 nm and ca. 270 nm, respectively. The specific surface area of the TiO₂ nanotubes was 38.8 m²/g, and the existence of mesopores (average pore diameter, 14.8 nm) on the nanotube wall was indicated by the nitrogen adsorption isotherm (−196 °C). The photocatalysis of the TiO₂ nanotubes was superior to that of commercially available anatase type TiO₂ nanoparticles.     

Hierarchical CuCo<Subscript>2</Subscript>O<Subscript>4</Subscript>/C microspheres assembled with nanoparticle-stacked nanosheets for sensitive non-enzymatic glucose detection

The hierarchical CuCo₂O₄/C microspheres have been fabricated via a two-step method involving hydrothermal and calcination processes. SEM, TEM, HRTEM, XRD and XPS were used to characterize the morphology, structure, and composition of the materials. The CuCo₂O₄/C microspheres have a hierarchically flower-like structure composed of nanoparticles-stacked nanosheets. Moreover, the as-prepared double-metal oxide hierarchical microsphere composites exhibit greatly improved electrochemical performance than that of pure CuCo₂O₄, owing to the synergistic effect of CuCo₂O₄ and carbon spheres. The CuCo₂O₄/C 5:1 modified electrode exhibited high sensitivity of 707.71 μA mM^?1cm^?2 in a wide linear range from 5 to 8000 μM with detection limit of about 1.5 μM. The outstanding glucose sensing performance of CuCo₂O₄/C 5:1 demonstrated that this kind of spinel bimetallic oxides composites can be favorable candidates for the development of non-enzymatic sensor.     

Synthesis and characterization of Cd-doped ZnMn<Subscript>2</Subscript>O<Subscript>4</Subscript> microspheres as supercapacitor electrodes

In this paper, we demonstrate the effects of Cd-doping ZnMn₂O₄ on structural and electrochemical performance. Cd-doped ZnMn₂O₄ spheres with diameters of about 2 μm were successfully synthesized by a facile hydrothermal method at 200 °C for 18 h. The fabricated Cd-doped ZnMn₂O₄ samples were characterized by X-ray diffraction, scanning electron microscopy, Brunauer Emmett Teller surface area analyzer and X-ray photoelectron spectroscopy. The electrochemical performance was investigated by cyclic voltammetry and electrochemical impedance spectrometry. The experimental results show that the synthesized spherical Cd-doped ZnMn₂O₄ exhibit far better rate capability and cyclic stability than that of pure spinel porous ZnMn₂O₄ microspheres. The result of cyclic voltammetry measurement indicates that the obtained Cd-doped ZnMn₂O₄ microspheres exhibited the high specific capacitance of 364 Fg^?1 at 2 mV/s.     

Lightweight glass/Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>-polyaniline composite hollow spheres with conductive and magnetic properties

Lightweight composite hollow spheres with conductive and magnetic properties were prepared by using Hollow Glass Spheres (HGS) as substrate. The morphology, composition, conductive, and magnetic properties of the resultant products were characterized by SEM, EDX, XRD, FTIR spectra, conductivity measurement, and vibrating-sample magnetometry. Polyaniline (PANI) were in situ polymerized on HGS with increasing ratios of PANI to HGS, resulting in the enhanced conductivity of HGS/PANI composites from 1.3 × 10⁻² S/cm to 4.4 × 10⁻² S/cm. Lightweight glass/Fe₃O₄-PANI composite hollow spheres (HGS/Fe₃O₄-PANI) with conductivity of 5.4 × 10⁻³ S/cm and magnetization of 9.25 emu/g were prepared by deposition of Fe₃O₄ nanoparticles onto HGS via electrostatic adsorption first, and then polymerization of aniline onto HGS/Fe₃O₄. The glass/PANI-Fe₃O₄ composite hollow spheres (HGS/PANI-Fe₃O₄) composed of Fe₃O₄ as the outmost layer and PANI as the inner layer were prepared for comparison. The conductivity and magnetization of HGS/PANI-Fe₃O₄ were 1.1 × 10⁻⁴ S/cm and 2.61 emu/g, respectively.     

Facile fabrication of hierarchical BiVO<Subscript>4</Subscript>/TiO<Subscript>2</Subscript> heterostructures for enhanced photocatalytic activities under visible-light irradiation

BiVO₄/TiO₂ nanocomposites were fabricated by a facile wet-chemical process, followed by the synthesis of TiO₂ hierarchical spheres via hydrothermal method. The BiVO₄/TiO₂ nanocomposites were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, UV–Vis diffuse reflectance spectroscopy and X-ray photoelectron spectroscopy. The results showed that prepared TiO₂ presented hierarchical spherical morphology self-assembled by nanoparticles and an anatase–brookite mixed crystal phase. The introduction of monoclinic BiVO₄ components retained the hierarchical structures and expanded the light response to around 510 nm. Type II BiVO₄/TiO₂ heterostructured nanocomposites exhibited improved photocatalytic degradation towards methylene blue under visible-light irradiation, especially for the composite photocatalysts with atomic Ti/Bi?=?10, which showed double degradation rate than that of pure BiVO₄. The enhanced photocatalytic mechanism of the heterostructured BiVO₄/TiO₂ nanocomposites was discussed as well.     

A Hierarchical Z‑Scheme α‐Fe2O3/g‐C3N4 Hybrid for Enhanced Photocatalytic CO2 Reduction

The challenge in the artificial photosynthesis of fossil resources from CO₂ by utilizing solar energy is to achieve stable photocatalysts with effective CO₂ adsorption capacity and high charge‐separation efficiency. A hierarchical direct Z‐scheme system consisting of urchin‐like hematite and carbon nitride provides an enhanced photocatalytic activity of reduction of CO₂ to CO, yielding a CO evolution rate of 27.2 µmol g^?1 h^?1 without cocatalyst and sacrifice reagent, which is >2.2 times higher than that produced by g‐C₃N₄ alone (10.3 µmol g^?1 h^?1). The enhanced photocatalytic activity of the Z‐scheme hybrid material can be ascribed to its unique characteristics to accelerate the reduction process, including: (i) 3D hierarchical structure of urchin‐like hematite and preferable basic sites which promotes the CO₂ adsorption, and (ii) the unique Z‐scheme feature efficiently promotes the separation of the electron–hole pairs and enhances the reducibility of electrons in the conduction band of the g‐C₃N₄. The origin of such an obvious advantage of the hierarchical Z‐scheme is not only explained based on the experimental data but also investigated by modeling CO₂ adsorption and CO adsorption on the three different atomic‐scale surfaces via density functional theory calculation. The study creates new opportunities for hierarchical hematite and other metal‐oxide‐based Z‐scheme system for solar fuel generation.     

Sol-gel synthesis of titania hollow spheres

TiO₂ hollow spheres are prepared by a convenient sol-gel method at room temperature. The products were characterized by XRD, FESEM, TEM and FT-IR. It was found that these spheres are hollow inside with outer diameters of 200-500 nm. The average mesoporous diameter is about 9.8 nm. And the BET surface area and specific pore volume are about 161.9 m²/g and 0.441 cm³/g, respectively.     

Optimization of TiO<Subscript>2</Subscript>/MWCNT composites for efficient dye sensitized solar cells

This paper deals with the effects of introducing multiwall carbon nanotubes (MWCNTs) into photoanodes of dye sensitized solar cells (DSSCs). Mesoporous titanium dioxide (TiO₂) nanoparticles were synthesized using sol–gel technique. TiO₂/MWCNT composites were prepared by adding functionalized MWCNTs to TiO₂ nanoparticles using two different surfactants (α-terpineol and Triton X-100). Nanoparticles and composites were characterized using Dynamic Light Scattering spectrophotometer, Raman spectrometer, X-ray diffractometer, field emission scanning electron microscope, Brunauer–Emmett–Teller surface area analyzer and UV–Vis spectrophotometer. FESEM depicted that particles were spherical in shape and their size decreased due to addition of MWCNTs. This was attributed to the decrease in the crystallite size which in turn confirmed by XRD. UV–Vis absorption spectra showed the better absorbance for the visible range of light, as the content of MWCNT is increased. From the Tauc plot optical band gap was calculated and noted that it declined gradually with the content of MWCNTs. BET surface area increased drastically which was attributed to the formation of more number of pores in the nanocomposites as visualized from FESEM. UV–Vis spectra of dye desorbed from the photoanode revealed that the dye adsorption increased as a function of MWCNT wt%. I–V studies were carried out under the illumination of 100 mW/cm² simulated sunlight. Photoanodes prepared by both the methods showed better performance compared to pristine TiO₂ photoanode, because of high conducting path and high surface area provided by MWCNTs. Photoanodes with 0.19 wt% MWCNTs in them were able to achieve maximum efficiency of 3.54 and 3.86% for method A and B respectively.     

Highly enhanced photocatalytic degradation of dye rhodamine B on the biogenic hierarchical porous TiO<Subscript>2</Subscript>/SiO<Subscript>2</Subscript> with 1D/3D-chain

A hybrid photocatalyst consisting of TiO₂ and nonporous SiO₂ (TiO₂/CS-RH) is prepared by loading TiO₂ sol on one-dimensional/three-dimensional chain (1D/3D-chain) which is synthesized from rice husk. The products are characterized by X-ray diffraction, N₂-adsorption–desorption analysis and scanning electron microscopy. Meanwhile, the corresponding photocatalytic activity is evaluated by measuring the photocatalytic oxidation of rhodamine B (RhB). The results reveal that TiO₂/CS-RH displays a hierarchical porous structure from micrometer to nanometer scale with high BET surface area (574.7–719.4 cm²/g). Meanwhile, the activity of TiO₂/CS-RH for the photocatalytic degradation of RhB in aqueous slurry is significantly higher than that of the unsupported TiO₂. The optimal TiO₂ loaded on the support was two times and then treated at 600 °C for 120 min to complete the conversion of RhB. In contrast, the unsupported TiO₂ photocatalyst could convert only 20% of RhB in the same irradiation time and condition.     

<Emphasis Type="Italic">Ab initio</Emphasis> studies on [bmim][PF<Subscript>6</Subscript>]-CO<Subscript>2</Subscript> mixture and CO<Subscript>2</Subscript> clusters

Ab initio molecular dynamics studies have been carried out on the room temperature ionic liquid, 1,n-butyl,3-methylimidazolium hexafluorophosphate ([bmim][PF₆]) and supercritical carbon dioxide mixture at room temperature and experimental density. Partial radial distribution functions (RDF) for different sites have been computed to see the organization of CO₂ molecules around the ionic liquid. Several partial RDFs around the carbon atom of CO₂ molecule are compared to find out that the CO₂ has specific interaction with a carbon atom present in the imidazolium ring. The CO₂ is also found to be very well organized around the terminal carbon atom of the butyl chain. The partial RDFs for the oxygen atoms around oxygen and carbon atoms of the CO₂ suggests that there is very good organization of CO₂ molecules around themselves even in the [bmim][PF₆]-CO₂ mixture. The instantaneous quadrupole moment tensor has been calculated for the anion and the cation. The ensemble average of diagonal components of quadrupole moment tensor of the cation have finite values, whereas the off-diagonal components of the cation and both the diagonal and off-diagonal components of the anion have the value of zero with a large standard deviation. The CPMD studies performed on CO₂ clusters reveals the greater tendency of the clusters with more CO₂ units, to deviate from the linear geometry.     

The unstructured two-dimensional grid-based computation of selective thermal radiation in CO<Subscript>2</Subscript>-N<Subscript>2</Subscript> mixture flows

The possibility of applying the P ₁ approximation of the spherical harmonics method to the computation of the radiant heat transfer in heterogeneous volumes of complicated geometry is investigated. This approximation is used to evaluate the radiant heating of the surface of a spacecraft descending in the Martian atmosphere. The chemical composition of the gas heated behind the shock wave is calculated by using a kinetic model including 79 chemical reactions and ten components, such as CO₂, CO, C, O, O₂, C₂, N, N₂, CN, and NO. The optical properties are set by a spectral multigroup model computed with the help of the ASTEROID computer code with averaging over the rotational molecular spectrum structure in each group. The mechanisms of the radiant heating of the surface of descent space vehicles in the Martian atmosphere are studied.     

Preparation of high-surface-area activated carbon from <Emphasis Type="Italic">Zizania latifolia</Emphasis> leaves by one-step activation with K<Subscript>2</Subscript>CO<Subscript>3</Subscript>/rarefied air

An activated carbon (AC) with high-porosity was prepared from Zizania latifolia leaves by a one-step method combining chemical and physical activation. K₂CO₃ was employed as a chemical reagent, and air as a physical agent. During the activation, several key parameters were discussed, including the effects of activation temperature, K₂CO₃ impregnation ratio, amount of introduced air on the surface area and pore volumes evolution of the ACs derived from the Zizania latifolia leaves. The synergistic effect between the chemical agent and the physical agent was also investigated. Under optimal activation conditions, the as-synthesized AC attained a maximum surface area up to 2481 m²/g, with 1.21 cm³/g pore volume, and it had a micro/meso porosity developed by the combining activation. The crystal sizes of the as-synthesized AC along the a- and c-axes were about 5 nm and 1–2 nm, respectively. The average thickness of the crystallites is 3–4 layers with about 0.37 nm interlayer spacing.     

Synthesis and characterization of a basic molecular sieve: Nitrogen-incorporated SAPO-34

Microporous nitrogen-incorporated SAPO-34 molecular sieves were synthesized by thermal post-treatment of SAPO-34 in flowing dry ammonia at elevated temperatures. The results of property characterized by DRIFTS of CO₂ adsorption and CO₂–TPD showed that basic sites existed on the surface of nitridized samples probably due to the presence of nitrogen-containing species incorporating into the framework of SAPO-34 molecular sieves. The changes in structure of nitrogen-incorporated samples were investigated by ²⁷Al MAS NMR, ³¹P MAS NMR spectra X-ray diffraction and BET surface area measurements. It was found that nitrogen-incorporated SAPO-34 still kept good crystallinity and high specific surface area of precursors. And N-containing species had incorporated into the framework of samples during nitridation, in which N atom presumably bounded to Al and P atoms formed N-containing groups, but unfortunately some of them were not ascribed.     

From Waste Paper Basket to Solid State and Li‐HEC Ultracapacitor Electrodes: A Value Added Journey for Shredded Office Paper

Hydrothermal processing followed by controlled pyrolysis of used white office paper (a globally collectable shredded paper waste) are performed to obtain high surface area carbon with hierarchical pore size distribution. The BET specific surface area of such carbon is 2341 m² g^?1. The interconnected macroporous structure along with the concurrent presence of mesopores and micropores makes the material ideal for ultracapacitor application. Such waste paper derived carbon (WPC) shows remarkable performance in all solid‐state supercapacitor fabricated with ionic liquid‐polymer gel electrolyte. At room temperature, the material exhibits a power density of 19 000 W kg^?1 with an energy capability of 31 Wh kg^?1. The Li‐ion electrochemical capacitor constructed using WPC as cathode also shows an excellent energy storage capacity of 61 Wh kg^?1.     

Synthesis of mesoporous Al2O3 macrospheres using the biopolymer chitosan as a template: A novel active catalyst system for CO2 reforming of methane

A new and simple method to prepare alumina containing mainly mesopores is described. This alumina has a high surface area (464 m²/g) and a large pore volume ranging from about 0.35 to 0.65 cm³/g. The present method was developed using a biopolymer (chitosan) and Al solution. The Al–chitosan solution was added to NH₄OH solution in the form of drops. A hybrid macrosphere compound of aluminum hydroxide and organic polymer is formed. Through polymer elimination by thermal treatment, porous Al₂O₃ spheres with a high specific surface area are obtained. The Ni-impregnated Al₂O₃ spheres showed a high catalytic activity and stability for dry reforming of methane at 650 °C and a CH₄ / CO₂ = 1 molar ratio.