Michal Marszewski

Semiconductor-based photocatalytic CO2 conversion

Climate change and its impact on the Earth and Society has been recently reassessed by the International Panel on Climate Change. The panel estimates that the greenhouse gas emissions should be reduced by half by 2030 to mitigate climate change. Photocatalytic CO2 conversion is one of the promising technologies that can help with this modest goal. This review discusses the theoretical and practical aspects of CO2 conversion over semiconducting photocatalysts and overviews the recently reported CO2 conversion photocatalysts. A spectrum of photocatalysts reviewed in this work includes titania and its composites with metal oxides, metals, and advanced carbon allotropes; other solid photocatalysts, mostly based on germanium, gallium, tungsten, and niobium; graphitic carbon nitride; silver–silver halide plasmonic systems; photocatalytically active metal–organic frameworks; and graphene-based systems. Finally, a summary of the current state and an outlook for the future are provided.

New opportunities in Stöber synthesis: preparation of microporous and mesoporous carbon spheres

The recent extension of the Stober recipe to the synthesis of carbon particles creates tremendous opportunities in the design of novel carbon spheres having micropores, mesopores, or both, as well as composite carbon spheres with incorporated inorganic nanoparticles such as silica and silver.

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 m(2) g(-1), total pore volume from 0.11 to 0.46 cm(3) 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.

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 m(2) 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 m(2) 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.

Highly microporous polymer-based carbons for CO2 and H2 adsorption

A series of microporous carbons has been obtained through carbonization and KOH activation of a commercially available styrene divinylbenzene resin with sulfonate functional groups, Amberjet 1200 H. The resulting carbons featured very high specific surface areas: from 725 m2 g−1 to 3870 m2 g−1, large total pore volumes: from 0.44 cm3 g−1 to 2.07 cm3 g−1, and exceptionally developed microporosity: from 0.2 cm3 g−1 to 1.16 cm3 g−1. The controlled activation process afforded high amounts of ultramicropores (micropores < 0.75 nm) reaching 0.32 cm3 g−1. Physisorption measurements showed very high uptakes of CO2 and H2 reaching 356 mg g−1 of CO2 (0 °C, 800 mmHg), 209 mg g−1 of CO2 (25 °C, 850 mmHg), and 39 mg g−1 of H2 (−196 °C, 850 mmHg).

Organic acid-assisted soft-templating synthesis of ordered mesoporous carbons

A series of soft-templated ordered mesoporous carbons (OMCs) was synthesized by using resorcinol and formaldehyde as carbon precursors, triblock copolymer Pluronic F127 as a soft-template, and an organic acid (acetic, benzoic, citric, oxalic, or succinic) as a polymerization reaction catalyst. The aforementioned organic acids were strong enough to facilitate the formation of ordered mesophases by the block copolymer template used and to catalyze the polymerization reaction of resorcinol and formaldehyde in this template. The use of weak organic acids instead of strong inorganic acids such as HCl eliminated inorganic anions from the reaction environment and resulted in high surface area OMCs. Basically, the resulting carbons showed the surface areas and pore volumes comparable to those reported for the carbons prepared under similar conditions but in the presence of strong inorganic acids. Electron microscopy analysis proved the presence of ordered mesopores, whereas thermogravimetric analysis showed a good thermal stability of these carbons.

Benzene and Methane Adsorption on Ultrahigh Surface Area Carbons Prepared from Sulphonated Styrene Divinylbenzene Resin by KOH Activation

A commercially available styrene divinylbenzene ion-exchange resin, Amberjet 1200 H, was used to prepare a series of activated carbons through carbonization and subsequent activation with varying amounts of KOH. The resulting activated carbons showed a well-developed porous structure with specific surface area in the range of 730–3870 m2 g−1, total pore volume in the range of 0.44–2.07 cm3 g−1 and micropore volume in the range of 0.30–1.59 cm3 g−1. Importantly, these structural parameters can be changed by varying the amount of KOH used for the activation. These carbons showed extremely good adsorption properties towards benzene and methane at 20°C. The best uptakes for benzene and methane (19.6 and 1.68 mmol g−1, respectively) were obtained for the carbon activated using the KOH/C ratio of 4. These values correspond to the gravimetric adsorptions of 1.53 g/g and 27 mg/g, respectively. Benzene adsorption was analyzed using the Dubinin–Radushkevich (DR) equation. The micropore volume calculated using the DR equation based on benzene adsorption corresponds well with the micropore volume calculated from nitrogen adsorption by the αs comparative method. The high values of the structural parameters and the resulting high benzene and methane uptakes render the obtained activated carbons as prospective materials for use in environmental remediation and energy-related applications such as volatile organic compound adsorption and methane storage.

Scaffold-assisted synthesis of crystalline mesoporous titania materials

This work explores the scaffold-assisted synthesis of titania materials, in which the scaffold protects the titanias mesostructure during the calcination-induced crystallization that normally leads to its collapse. Two scaffold materials were examined: silica and alumina. The scaffolds were delivered either: (1) in the form of nanoparticles: Nanosol 3014D colloidal silica or Catapal A boehmite; or (2) through hydrolysis and condensation of suitable precursors: tetraethyl orthosilicate or aluminum isopropoxide. Titania was prepared by hydrolysis and condensation of titanium isopropoxide under acidic conditions, resulting in 4–8 nm TiO2 nanoparticles aggregated into mesoporous structures. Incorporation of even 10 wt% of the scaffold resulted in a substantial improvement of the structural properties and the higher scaffold amounts yielded even better results. It is shown that the structural properties of titania depend on the scaffolds structure: the nanoparticle-composed scaffolds are condensed and more suitable for development of large pore volume, whereas the precursor-generated scaffolds are more dispersed and better for achieving titania with large surface area. The final titania materials are crystalline (almost or exclusively anatase phase, depending on the scaffold) and possess a specific surface area reaching 260 m2 g−1 and pore volume reaching 0.60 cm3 g−1.