Photoreduction of CO2 into sustainable and green solar fuels is generally believed to be an appealing solution to simultaneously overcome both environmental problems and energy crisis. The low selectivity of challenging multi-electron CO2 photoreduction reactions makes it one of the holy grails in heterogeneous photocatalysis. This Review highlights the important roles of cocatalysts in selective photocatalytic CO2 reduction into solar fuels using semiconductor catalysts. A special emphasis in this review is placed on the key role, design considerations and modification strategies of cocatalysts for CO2 photoreduction. Various cocatalysts, such as the biomimetic, metal-based, metal-free, and multifunctional ones, and their selectivity for CO2 photoreduction are summarized and discussed, along with the recent advances in this area. This Review provides useful information for the design of highly selective cocatalysts for photo(electro)reduction and electroreduction of CO2 and complements the existing reviews on various semiconductor photocatalysts.

Cocatalysts for Selective Photoreduction of CO2 into Solar Fuels.

The increase in the global atmospheric CO2 concentration resulting from over a century of combustion of fossil fuels has been associated with significant global climate change. With the global population increase driving continued increases in fossil fuel use, humanity’s primary reliance on fossil energy for the next several decades is assured. Traditional modes of carbon capture such as precombustion and postcombustion CO2 capture from large point sources can help slow the rate of increase of the atmospheric CO2 concentration, but only the direct removal of CO2 from the air, or “direct air capture” (DAC), can actually reduce the global atmospheric CO2 concentration. The past decade has seen a steep rise in the use of chemical sorbents that are cycled through sorption and desorption cycles for CO2 removal from ultradilute gases such as air. This Review provides a historical overview of the field of DAC, along with an exhaustive description of the use of chemical sorbents targeted at this application. Solv...

Direct Capture of CO2 from Ambient Air

The burning of our diminishing fossil fuel reserves is accompanied by a large anthropogenic CO2 release, which is outpacing nature's CO2 recycling capability, causing significant environmental harm. Much is being done to avert this crisis including more efficient technology for usage, savings and replacing carbon fuels with alternatives whenever feasible. The capture of CO2 followed by sequestration (CCS) into geologic formation or under the seas has also been proposed and in some cases implemented. Carbon capture and recycling (CCR) to fuels and materials is another promising approach. At first, capturing carbon dioxide from concentrated sources such as fossil fuel burning power plants, industrial plants and natural sources might be the most practical. However, the capture of CO2 from the atmosphere is also technically feasible despite its low concentration (∼390 ppm) and presents even some benefits compared to point source CO2 capture. The present article reviews methods developed for the capture of CO2 directly from the air as well as their advantages and drawbacks. While strong bases such as sodium hydroxide and potassium hydroxide could be used, their regeneration is energy intensive, requiring high temperatures. Amines either physically or chemically immobilized on solid supports require much lower temperatures for their regeneration and are therefore promising candidates.

Air as the renewable carbon source of the future: an overview of CO2 capture from the atmosphere

Solubility of CO2 in water from −1.5 to 100 °C and from 0.1 to 100 MPa: evaluation of literature data and thermodynamic modelling

In mammals, cadmium is widely considered as a non-genotoxic carcinogen acting through a methylation-dependent epigenetic mechanism. Here, the effects of Cd treatment on the DNA methylation patten are examined together with its effect on chromatin reconfiguration in Posidonia oceanica. DNA methylation level and pattern were analysed in actively growing organs, under short- (6 h) and long- (2 d or 4 d) term and low (10 mM) and high (50 mM) doses of Cd, through a Methylation-Sensitive Amplification Polymorphism technique and an immunocytological approach, respectively. The expression of one member of the CHROMOMETHYLASE (CMT) family, a DNA methyltransferase, was also assessed by qRT-PCR. Nuclear chromatin ultrastructure was investigated by transmission electron microscopy. Cd treatment induced a DNA hypermethylation, as well as an up-regulation of CMT, indicating that de novo methylation did indeed occur. Moreover, a high dose of Cd led to a progressive heterochromatinization of interphase nuclei and apoptotic figures were also observed after long-term treatment. The data demonstrate that Cd perturbs the DNA methylation status through the involvement of a specific methyltransferase. Such changes are linked to nuclear chromatin reconfiguration likely to establish a new balance of expressed/repressed chromatin. Overall, the data show an epigenetic basis to the mechanism underlying Cd toxicity in plants.

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In Posidonia oceanica cadmium induces changes in DNA methylation and chromatin patterning

Carbon Dioxide Solubility in Water

Gas Absorption - Absorption of Carbon Dioxide from Air by Sodium and Potassium Hydroxides.

Concurrent flow in gas absorption may be used to practical advantage when liquid partial pressure is minor. The higher transfer coefficients of this operation are reported and analyzed in reference to pertinent variables.

Concurrent gas absorption mass transfer

This work presents initial information useful to concurrent gas-absorption design. Data are reported on the variation of pressure drop and liquid holdup obtained with various flow rates, packings, and liquids.

Leroy F. Stutzman

Papers

Carbon Dioxide Solubility in Water

Gas Absorption - Absorption of Carbon Dioxide from Air by Sodium and Potassium Hydroxides.

Concurrent gas absorption mass transfer

Pressure drop and liquid holdup in concurrent gas absorption

Temperature Gradients and Eddy Diffusivities in Turbulent Fluid Flow