Reversible CO2 capture by ZnO slurry leading to formation of fine ZnO particles

Tailoring tea residue-derived nitrogen-doped activated carbon for CO2 adsorption: influence of activation temperature and activating agents

Embracing CO2 mitigation strategies, such as state-of-the-art CO2 capture technologies, is essential for effectively reducing atmospheric carbon levels and advancing global efforts toward a more sustainable future. In this context, adsorption sequestering techniques utilising carbon materials have emerged as promising candidates for CO2 capture. These materials have been extensively researched with a range of tuning methods to optimise their physicochemical features. In this study, an alteration of the N-doped activated carbon was successfully performed, utilizing tea residue as the carbon precursor and ammonia as the nitrogen source, facilitated through an impregnation procedure. With the objective of discovering the effect of diverse activation parameters on prepared adsorbent physicochemical properties, several selections of activating agents (AA) were investigated: KOH, H3PO4, ZnCl2, and NaOH, together with broad thermal activation temperature from 873 to 1173 K. The best-performed adsorbents from the respective AC group were subjected to several characterisation analyses and found to the enhanced structural features, heteroatom doped-rich surface (i.e. N and O); together with AA-induced metal/mineral functionalization, the NaOH-used AC (NAC-N-1173) was the optimum-performed adsorbent with a promising 4.12 mmol/g CO2 uptake capacity, higher than other prepared adsorbent including N-doped tea residue-derived char and commercialized AC with 175 and 325% higher, respectively.

CO2 capture and storage by metal and non-metal decorated silicon carbide nanotubes: a DFT study

This study addressed the nano-mechanism of CO2 capture by Al-doped, B-doped and N-doped single-walled silicon carbide nanotubes (SWSiCNTs) using the prominent density functional theory. The results showed absolute interactions between CO2 and B- and N- impurity atoms of the SWSiCNT surface with the highest adsorption energy of −1.85 eV and −1.83 eV respectively. Analysis of the binding energy of CO2 to Al-doped SWSiCNT revealed that chemisorption between them is stronger than B-doped and N-doped SWSiCNTs. Results from optical adsorption spectra revealed that both B-and N-doped systems adsorb CO2 in the visible region of the electromagnetic spectrum while B-doped SiCNT shows the highest adsorption. This study recommends B- and N-doped SiCNTs as candidates for CO2 capture and storage with higher efficiency by B-doped SiCNT, while the performance of the Al-doped system was underscored.

Interfacial Chemistry in the Electrocatalytic Hydrogenation of CO2 over C-Supported Cu-Based Systems

Operando soft and hard X-ray spectroscopic techniques were used in combination with plane-wave density functional theory (DFT) simulations to rationalize the enhanced activities of Zn-containing Cu nanostructured electrocatalysts in the electrocatalytic CO2 hydrogenation reaction. We show that at a potential for CO2 hydrogenation, Zn is alloyed with Cu in the bulk of the nanoparticles with no metallic Zn segregated; at the interface, low reducible Cu(I)-O species are consumed. Additional spectroscopic features are observed, which are identified as various surface Cu(I) ligated species; these respond to the potential, revealing characteristic interfacial dynamics. Similar behavior was observed for the Fe-Cu system in its active state, confirming the general validity of this mechanism; however, the performance of this system deteriorates after successive applied cathodic potentials, as the hydrogen evolution reaction then becomes the main reaction pathway. In contrast to an active system, Cu(I)-O is now consumed at cathodic potentials and not reversibly reformed when the voltage is allowed to equilibrate at the open-circuit voltage; rather, only the oxidation to Cu(II) is observed. We show that the Cu-Zn system represents the optimal active ensembles with stabilized Cu(I)-O; DFT simulations rationalize this observation by indicating that Cu-Zn-O neighboring atoms are able to activate CO2, whereas Cu-Cu sites provide the supply of H atoms for the hydrogenation reaction. Our results demonstrate an electronic effect exerted by the heterometal, which depends on its intimate distribution within the Cu phase and confirms the general validity of these mechanistic insights for future electrocatalyst design strategies.

Highly Active Nanocrystalline ZnO and Its Photo-Oxidative Properties towards Acetone Vapor

Zinc oxide is one of the well-known photocatalysts, the potential applications of which are of great importance in photoactivated gas sensing, water and air purification, photocatalytic synthesis, among others. However, the photocatalytic performance of ZnO strongly depends on its morphology, composition of impurities, defect structure, and other parameters. In this paper, we present a route for the synthesis of highly active nanocrystalline ZnO using commercial ZnO micropowder and ammonium bicarbonate as starting precursors in aqueous solutions under mild conditions. As an intermediate product, hydrozincite is formed with a unique morphology of nanoplates with a thickness of about 14-15 nm, the thermal decomposition of which leads to the formation of uniform ZnO nanocrystals with an average size of 10-16 nm. The synthesized highly active ZnO powder has a mesoporous structure with a BET surface area of 79.5 ± 4.0 m2/g, an average pore size of 20 ± 2 nm, and a cumulative pore volume of 0.507 ± 0.051 cm3/g. The defect-related PL of the synthesized ZnO is represented by a broad band with a maximum at 575 nm. The crystal structure, Raman spectra, morphology, atomic charge state, and optical and photoluminescence properties of the synthesized compounds are also discussed. The photo-oxidation of acetone vapor over ZnO is studied by in situ mass spectrometry at room temperature and UV irradiation (λmax = 365 nm). The main products of the acetone photo-oxidation reaction, water and carbon dioxide, are detected by mass spectrometry, and the kinetics of their release under irradiation are studied. The effect of morphology and microstructure on the photo-oxidative activity of ZnO samples is demonstrated.

Identification of Nano-Metal Oxides That Can Be Synthesized by Precipitation-Calcination Method Reacting Their Chloride Solutions with NaOH Solution and Their Application for Carbon Dioxide Capture from Air-A Thermodynamic Analysis

Several metal oxide nanoparticles (NPs) were already obtained by mixing NaOH solution with chloride solution of the corresponding metal to form metal hydroxide or oxide precipitates and wash-dry-calcine the latter. However, the complete list of metal oxide NPs is missing with which this technology works well. The aim of this study was to fill this knowledge gap and to provide a full list of possible metals for which this technology probably works well. Our methodology was chemical thermodynamics, analyzing solubilities of metal chlorides, metal oxides and metal hydroxides in water and also standard molar Gibbs energy changes accompanying the following: (i) the reaction between metal chlorides and NaOH; (ii) the dissociation reaction of metal hydroxides into metal oxide and water vapor and (iii) the reaction between metal oxides and gaseous carbon dioxide to form metal carbonates. The major result of this paper is that the following metal-oxide NPs can be produced by the above technology from the corresponding metal chlorides: Al₂O₃, BeO, CaO, CdO, CoO, CuO, FeO, Fe₂O₃, In₂O₃, La₂O₃, MgO, MnO, Nd₂O₃, NiO, Pr₂O₃, Sb₂O₃, Sm₂O₃, SnO, Y₂O₃ and ZnO. From the analysis of the literature, the following nine nano-oxides have been already obtained experimentally with this technology: CaO, CdO, Co₃O₄, CuO, Fe₂O₃, NiO, MgO, SnO₂ and ZnO (note: Co₃O₄ and SnO₂ were obtained under oxidizing conditions during calcination in air). Thus, it is predicted here that the following nano-oxides can be potentially synthesized with this technology in the future: Al₂O₃, BeO, In₂O₃, La₂O₃, MnO, Nd₂O₃, Pr₂O₃, Sb₂O₃, Sm₂O₃ and Y₂O₃. The secondary result is that among the above 20 nano-oxides, the following five nano-oxides are able to capture carbon dioxide from air at least down to 42 ppm residual CO₂-content, i.e., decreasing the current level of 420 ppm of CO₂ in the Earth's atmosphere at least tenfold: CaO, MnO, MgO, CdO, CoO. The tertiary result is that by mixing the AuCl₃ solution with NaOH solution, Au nano-particles will precipitate without forming Au-oxide NPs. The results are significant for the synthesis of metal nano-oxide particles and for capturing carbon dioxide from air.