Toward Tunable Adsorption Properties, Structure, and Crystallinity of Titania Obtained by Block Copolymer and Scaffold-Assisted Templating

Nanostructured titania and composite titania materials were synthesized for the first time by a one-pot strategy in an aqueous solution containing Pluronic P123 block copolymer and suitable precursors. The strategy can be considered as more facile, environmentally friendly, and less expensive as compared to the existing ones that require use of organic solvents. In the case of composites, silica and alumina particles were used as a structure protecting scaffold and composite components. This synthesis strategy allowed tuning of adsorption and structural properties of the resulting materials; namely, the specific surface area was varied from 84 to 250 m² g^–1, total pore volume from 0.11 to 0.46 cm³ g^–1, and the pore width from 5.6 to 11.2 nm. All samples studied but one showed exclusively anatase phase, and the composites obtained with silica scaffold showed tunable degree of crystallinity. The proposed approach to tailoring the surface and structure properties of titania is especially important for the development of high performance materials for photocatalysis, lithium-based batteries, and dye-sensitized solar cells

Mesoporous Organosilica with Amidoxime Groups for CO₂ Sorption

Incorporation of basic species such as amine-containing groups into porous materials is a well-established strategy for achieving high uptake of acidic molecules such as CO₂. This work reports a successful use of the aforementioned strategy for the development of ordered mesoporous organosilica (OMO) with amidoxime groups for CO₂ sorption. These materials were prepared by two-step process involving: (1) synthesis of OMO with cyanopropyl groups by co-condensation of (3-cyanopropyl)­triethoxysilane and tetraethylorthosilicate in the presence of Pluronic P123 triblock copolymer under acidic conditions, and (2) conversion of cyanopropyl groups into amidoxime upon treatment with hydroxylamine hydrochloride under suitable conditions. The resulting series of amidoxime-containing OMO was prepared and used for CO₂ sorption at low (25 °C) and elevated (60, 120 °C) temperatures. These sorbents exhibited relatively high adsorption capacity at ambient conditions (25 °C, 1 atm) and remarkable high sorption uptake (∼3 mmol/g) at 60 and 120 °C. This high CO₂ uptake at elevated temperatures by amidoxime-containing OMO sorbent makes it a noticeable material for CO₂ capture

Activated Carbon Spheres for CO₂ Adsorption

A series of carbon spheres (CS) was prepared by carbonization of phenolic resin spheres obtained by the one-pot modified Stöber method. Activated CS (ACS), having diameters from 200 to 420 nm, high surface area (from 730 to 2930 m²/g), narrow micropores (<1 nm) and, importantly, high volume of these micropores (from 0.28 to 1.12 cm³/g), were obtained by CO₂ activation of the aforementioned CS. The remarkably high CO₂ adsorption capacities, 4.55 and 8.05 mmol/g, were measured on these AC spheres at 1 bar and two temperatures, 25 and 0 °C, respectively

Mesoporous Alumina with Amidoxime Groups for CO₂ Sorption at Ambient and Elevated Temperatures

Development of various mesostructures with introduced basic species such as amine groups represents a viable strategy for enhancing adsorption of acidic molecules such as CO₂. To follow this strategy, mesoporous alumina-based materials with incorporated amidoxime functionality were prepared by evaporation induced self-assembly of commercial boehmite nanoparticles as an alumina precursor, (3-cyanopropyl)­triethoxysilane as an organosilica precursor, and Pluronic P123 triblock copolymer as a soft template under acidic conditions. In the next synthesis step, the resulting mesoporous materials with cyanopropyl groups were subjected to hydrothermal reaction with hydroxylamine hydrochloride at slightly basic conditions and 80 °C to convert cyanopropyl groups to amidoxime functionalities. The latter sorbents showed fairly high CO₂ uptake at ambient conditions (25 °C, 1.2 atm) and remarkably high sorption capacity (3.84 mmol/g) at 120 °C. Good thermal and chemical stabilities of these materials combined with high CO₂ uptake at elevated temperatures make them of potential interest for sorption of acidic gaseous molecules such as CO₂

Synergetic Effect of MoS₂ and Graphene as Cocatalysts for Enhanced Photocatalytic H₂ Production Activity of TiO₂ Nanoparticles

The production of H₂ by photocatalytic water splitting has attracted a lot attention as a clean and renewable solar H₂ generation system. Despite tremendous efforts, the present great challenge in materials science is to develop highly active photocatalysts for splitting of water at low cost. Here we report a new composite material consisting of TiO₂ nanocrystals grown in the presence of a layered MoS₂/graphene hybrid as a high-performance photocatalyst for H₂ evolution. This composite material was prepared by a two-step simple hydrothermal process using sodium molybdate, thiourea, and graphene oxide as precursors of the MoS₂/graphene hybrid and tetrabutylorthotitanate as the titanium precursor. Even without a noble-metal cocatalyst, the TiO₂/MoS₂/graphene composite reaches a high H₂ production rate of 165.3 μmol h^–1 when the content of the MoS₂/graphene cocatalyst is 0.5 wt % and the content of graphene in this cocatalyst is 5.0 wt %, and the apparent quantum efficiency reaches 9.7% at 365 nm. This unusual photocatalytic activity arises from the positive synergetic effect between the MoS₂ and graphene components in this hybrid cocatalyst, which serve as an electron collector and a source of active adsorption sites, respectively. This study presents an inexpensive photocatalyst for energy conversion to achieve highly efficient H₂ evolution without noble metals

Microwave-Assisted Synthesis of Porous Carbon–Titania and Highly Crystalline Titania Nanostructures

Porous carbon–titania and highly crystalline titania nanostructured materials were obtained through a microwave-assisted one-pot synthesis. Resorcinol and formaldehyde were used as carbon precursors, triblock copolymer Pluronic F127 as a stabilizing agent, and titanium isopropoxide as a titania precursor. This microwave-assisted one-pot synthesis involved formation of carbon spheres according to the recently modified Stöber method followed by hydrolysis and condensation of titania precursor. This method afforded carbon–titania composite materials containing anatase phase with specific surface areas as high as 390 m² g^–1. The pure nanostructured titania, obtained after removal of carbon through calcination of the composite material in air, was shown to be the anatase phase with considerably higher degree of crystallinity and the specific surface area as high as 130 m² g^–1. The resulting titania, because of its high surface area, well-developed porosity, and high crystallinity, is of great interest for catalysis, water treatment, lithium batteries, and other energy-related applications

Structural Stability of Si–C Bonds in Periodic Mesoporous Thiophene-Silicas Prepared under Acidic Conditions

Periodic mesoporous thiophene-silicas with hexagonal (<i>p</i>6<i>mm</i>) symmetry were synthesized using a 2,5-bis­(triethoxysilyl)­thiophene (BTET) precursor in the presence of Pluronic P123 (EO₂₀PO₇₀EO₂₀) and PLGE (EO₁₇(L₂₈G₇)­EO₁₇) triblock copolymers at different acidic conditions. P123-templated mesoporous thiophene-silicas with <i>p</i>6<i>mm</i> ordered structure were prepared in the presence of hydrochloric acid and iron­(III) chloride hexahydrate used as acid catalysts. However, it was found that a relatively large fraction of the Si–C bonds in thiophene-bridging groups were decomposed during the synthesis process. On the other hand, thiophene-silicas synthesized at lower acidic conditions were disordered and nonporous structures. In contrast, PLGE-templated thiophene-silicas with <i>p</i>6<i>mm</i> ordered mesostructure were prepared using copper­(II) perchlorate hexahydrate and boric acid as well as hydrochloric acid. Importantly, up to 97.3% of the Si–C bonds in mesoporous thiophene-silica prepared in the presence of boric acid were retained. Solid state ²⁹Si MAS NMR clearly showed that the structural stability of the Si–C bond is dependent on the acidity and time of the initial self-assembly stage. Also, the thermal stability of the thiophene-bridging groups was shown to be dependent on the acidity of the synthesis gel

Microemulsion-Assisted Synthesis of Mesoporous Aluminum Oxyhydroxide Nanoflakes for Efficient Removal of Gaseous Formaldehyde

Mesoporous aluminum oxyhydroxides composed of nanoflakes were prepared via a water-in-oil microemulsion-assisted hydrothermal process at 50 °C using aluminum salts as precursors and ammonium hydroxide as a precipitating agent. The microstructure, morphology, and textural properties of the as-prepared materials were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), nitrogen adsorption, and X-ray photoelectron spectroscopy (XPS) techniques. It is shown that the aluminum oxyhydroxide nanostructures studied are effective adsorbents for removal of formaldehyde (HCHO) at ambient temperature, due to the abundance of surface hydroxyl groups, large specific surface area, and suitable pore size. Also, the type of aluminum precursor was essential for the microstructure formation and adsorption performance of the resulting materials. Namely, the sample prepared from aluminum sulfate (Al-s) exhibited a relatively high HCHO adsorption capacity in the first run, while the samples obtained from aluminum nitrate (Al-n) and chloride (Al-c) exhibited high adsorption capacity and relatively stable recyclability. A combination of high surface area and strong surface affinity of the prepared aluminum oxyhydroxide make this material a promising HCHO adsorbent for indoor air purification

Synthesis of Porous Crystalline Doped Titania Photocatalysts Using Modified Precursor Strategy

We propose a new strategy for the synthesis of porous crystalline doped titania materialsdubbed the modified precursor strategy. The modified precursors are prepared by reacting generic titania precursors with organic acids in order to introduce “carbonizable” groups into the precursor’s structure, so that carbon–titania composites can form upon carbonization. The resulting carbon framework serves as a scaffold for TiO₂ and supports the structure during crystallization. Afterward, removal of the carbon scaffold through calcination results in titania with a well-developed structure and high crystallinity. The titanias synthesized according to this strategy, using common organic acids as the modifiers, have specific surface areas reaching 100 m² g^–1 and total pore volumes exceeding 0.20 cm³ g^–1, even after crystallization at temperatures from 500 to 1000 °C. The materials possess high crystallinity and tunable phase composition, and some show visible light absorption and significantly narrowed band gaps (2.3–2.4 eV). Photocatalytic degradation of methylene blue proved that these photocatalysts are active under visible light. All tested titanias show an excellent photocatalytic performance due to the combined effects of the well-developed structure, high crystallinity, and narrow band gap. This strategy can easily be adopted for the preparation of other porous crystalline materials

Highly Active Mesoporous Ferrihydrite Supported Pt Catalyst for Formaldehyde Removal at Room Temperature

Ferrihydrite (Fh) supported Pt (Pt/Fh) catalyst was first prepared by combining microemulsion and NaBH₄ reduction methods and investigated for room-temperature removal of formaldehyde (HCHO). It was found that the order of addition of Pt precursor and ferrihydrite in the preparation process has an important effect on the microstructure and performance of the catalyst. Pt/Fh was shown to be an efficient catalyst for complete oxidation of HCHO at room temperature, featuring higher activity than magnetite supported Pt (Pt/Fe₃O₄). Pt/Fh and Pt/Fe₃O₄ exhibited much higher catalytic activity than Pt supported over calcined Fh and TiO₂. The abundance of surface hydroxyls, high Pt dispersion and excellent adsorption performance of Fh are responsible for superior catalytic activity and stability of the Pt/Fh catalyst. This work provides some indications into the design and fabrication of the cost-effective and environmentally benign catalysts with excellent adsorption and catalytic oxidation performances for HCHO removal at room temperature