CO2 capture and sequestration in stable Ca-oxalate, via Ca-ascorbate promoted green reaction

High-energy X-ray diffraction experiment employing a compact synchrotron X-ray source based on inverse Compton scattering

X-ray diffraction (XRD) is an important material analysis technique with a widespread use of laboratory systems. These systems typically operate at low X-ray energies (from 5 keV to 22 keV) since they rely on the small bandwidth of K-lines like copper. The narrow bandwidth is essential for precise measurements of the crystal structure in these systems. Inverse Compton X-ray source (ICS) could pave the way to XRD at high X-ray energies in a laboratory setting since these sources provide brilliant energy-tunable and partially coherent X-rays. This study demonstrates high-energy XRD at an ICS with strongly absorbing mineralogical samples embedded in soft tissue. A quantitative comparison of the measured XRD patterns with calculations of their expected shapes validates the performance of ICSs for XRD. This analysis was performed for two types of kidney stones of different materials. Since these stones are not isolated in a human body, the influence of the surrounding soft tissue on the XRD pattern is investigated and a correction for this soft tissue contribution is introduced.

Vitamin C-induced CO2 capture enables high-rate ethylene production in CO2 electroreduction

High-rate production of multicarbon chemicals via the electrochemical CO2 reduction can be achieved by efficient CO2 mass transport. A key challenge for C-C coupling in high-current-density CO2 reduction is how to promote *CO formation and dimerization. Here, we report molecularly enhanced CO2-to-*CO conversion and *CO dimerization for high-rate ethylene production. Nanoconfinement of ascorbic acid by graphene quantum dots enables immobilization and redox reversibility of ascorbic acid in heterogeneous electrocatalysts. Cu nanowire with ascorbic acid nanoconfined by graphene quantum dots (cAA-CuNW) demonstrates high-rate ethylene production with a Faradaic efficiency of 60.7% and a partial current density of 539 mA/cm2, a 2.9-fold improvement over that of pristine CuNW. Furthermore, under low CO2 ratio of 33%, cAA-CuNW still exhibits efficient ethylene production with a Faradaic efficiency of 41.8%. We find that cAA-CuNW increases *CO coverage and optimizes the *CO binding mode ensemble between atop and bridge for efficient C-C coupling. A mechanistic study reveals that ascorbic acid can facilitate *CO formation and dimerization by favorable electron and proton transfer with strong hydrogen bonding.

Polymers without Petrochemicals: Sustainable Routes to Conventional Monomers

Access to a wide range of plastic materials has been rationalized by the increased demand from growing populations and the development of high-throughput production systems. Plastic materials at low costs with reliable properties have been utilized in many everyday products. Multibillion-dollar companies are established around these plastic materials, and each polymer takes years to optimize, secure intellectual property, comply with the regulatory bodies such as the Registration, Evaluation, Authorisation and Restriction of Chemicals and the Environmental Protection Agency and develop consumer confidence. Therefore, developing a fully sustainable new plastic material with even a slightly different chemical structure is a costly and long process. Hence, the production of the common plastic materials with exactly the same chemical structures that does not require any new registration processes better reflects the reality of how to address the critical future of sustainable plastics. In this review, we have highlighted the very recent examples on the synthesis of common monomers using chemicals from sustainable feedstocks that can be used as a like-for-like substitute to prepare conventional petrochemical-free thermoplastics.

CO2 Adsorption over 3d Transition-Metal Nanoclusters Supported on Pyridinic N3-Doped Graphene: A DFT Investigation

CO₂ adsorption on bare 3d transition-metal nanoclusters and 3d transition-metal nanoclusters supported on pyridinic N₃-doped graphene (PNG) was investigated by employing the density functional theory. First, the interaction of Co₁₃ and Cu₁₃ with PNG was analyzed by spin densities, interaction energies, charge transfers, and HUMO-LUMO gaps. According to the interaction energies, the Co₁₃ nanocluster was adsorbed more efficiently than Cu₁₃ on the PNG. The charge transfer indicated that the Co₁₃ nanocluster donated more charges to the PNG nanoflake than the Cu₁₃ nanocluster. The HUMO-LUMO gap calculations showed that the PNG improved the chemical reactivity of both Co₁₃ and Cu₁₃ nanoclusters. When the CO₂ was adsorbed on the bare 3d transition-metal nanoclusters and 3d transition-metal nanoclusters supported on the PNG, it experienced a bond elongation and angle bending in both systems. In addition, the charge transfer from the nanoclusters to the CO₂ molecule was observed. This study proved that Co₁₃/PNG and Cu₁₃/PNG composites are adequate candidates for CO₂ adsorption and activation.

Circular Economy: A Comprehensive Review of Eco-Friendly Wollastonite Applications

The growing increase in greenhouse gases, especially carbon dioxide (CO2), by anthropogenic activities can be linked to extreme climate events, such as intensive droughts, floods, or hurricanes, and has led to several studies focused on reducing the concentration of this greenhouse gas in the atmosphere. Some technologies, such as carbon capture and storage (CCS), can potentially sequester billions of tons of CO2 per year. One of the promising methods is the use of carbon mineralization as a CCS methodology. For this approach, some minerals can be investigated, such as wollastonite, which can be obtained from agricultural waste recovery. One topic of interest in these studies is agriculture, demonstrating that it can play an important role in climate change mitigation. This work presents a critical review of the studies of rice waste use for potential synthesizing wollastonite as a path for CO2 storage, promoting the circular economy. Several works were analyzed and presented, addressing eco-friendly wollastonite use, such as in the cement industry, and they can contribute to a lower global warming potential. There is a promising way to explore, once there are few studies in the literature about CO2 capture and storage of wollastonite by carbon mineralization.

Thermal Stability of Calcium Oxalates from CO2 Sequestration for Storage Purposes: An In-Situ HT-XRPD and TGA Combined Study

Calcium oxalates are naturally occurring biominerals and can be found as a byproduct of some industrial processes. Recently, a new and green method for carbon capture and sequestration in stable calcium oxalate from oxalic acid produced by carbon dioxide reduction was proposed. The reaction resulted in high-quality weddellite crystals. Assessing the stability of these weddellite crystals is crucial to forecast their reuse as solid-state reservoir of pure CO2 and CaO in a circular economy perspective or, eventually, their disposal. The thermal decomposition of weddellite obtained from the new method of carbon capture and storage was studied by coupling in-situ high-temperature X-ray powder diffraction and thermogravimetric analysis, in order to evaluate the dehydration, decarbonation, and the possible production of unwanted volatile species during heating. At low temperature (119–255 °C), structural water release was superimposed to an early CO2 feeble evolution, resulting in a water-carbon dioxide mixture that should be separated for reuse. Furthermore, the storage temperature limit must be considered bearing in mind this CO2 release low-temperature event. In the range 390–550 °C, a two-component mixture of carbon monoxide and dioxide is evolved, requiring oxidation of the former or gas separation to reuse pure gases. Finally, the last decarbonation reaction produced pure CO2 starting from 550 °C.

Towards Sustainable Oxalic Acid from CO2 and Biomass

To quickly and drastically reduce CO2 emissions and meet our ambitions of a circular future, we need to develop carbon capture and storage (CCS) and carbon capture and utilization (CCU) to deal with the CO2 that we produce. While we have many alternatives to replace fossil feedstocks for energy generation, for materials such as plastics we need carbon. The ultimate circular carbon feedstock would be CO2 . A promising route is the electrochemical reduction of CO2 to formic acid derivatives that can subsequently be converted into oxalic acid. Oxalic acid is a potential new platform chemical for material production as useful monomers such as glycolic acid can be derived from it. This work is part of the European Horizon 2020 project "Ocean" in which all these steps are developed. This Review aims to highlight new developments in oxalic acid production processes with a focus on CO2 -based routes. All available processes are critically assessed and compared on criteria including overall process efficiency and triple bottom line sustainability.

A review on ex situ mineral carbonation

The increased CO₂ quantities in the environment have led to many harmful effects. Therefore, it is very important to decrease the CO₂ levels in the environment. CO₂ capture along with safe and permanent storage using mineral CO₂ sequestration method can play an important role to reduce carbon emissions into the environment. Mineral sequestration is a stable storage method that provides long-term storage and an appropriate substitute for the more popular geological storage method. The process is most suited for places where there is a lack of underground cavities for underground geological storage. Minerals rich in Ca and Mg are used predominantly in carbonation reactions. In addition, those alkaline wastes that are rich in Mg and Ca such as cement waste, steel slag and many process ashes can also be employed in CO₂ sequestration. Mineral carbonation could be used for the sequestration of billions of tonnes of CO₂ every year. However, various drawbacks related to mineral carbonation still need to be addressed, such as resolving the slow rate of reactions, necessity of large amounts of feedstock, decreasing the high overall cost of CO₂ sequestration and reducing the huge energy requirements to accelerate the carbonation reaction. This study explores a number of carbonation methods, parameters that control the process and future potential applications of carbonated products.

Performance and potential mechanism of Cr(VI) reduction and subsequent Cr(III) precipitation using sodium borohydride driven by oxalate

The method of treating high concentrations of Cr(VI) alone by NaBH4 has proved feasible, but the effects of the coexistence of Cr(VI) and organic compounds have not been evaluated. The objective of this study was to explore the potential mechanism by which oxalate affects the reduction of high concentrations of Cr(VI) treated by sodium borohydride (NaBH4) and the subsequent precipitation of Cr(III). The results show that Cr(VI) reduction could be gradually promoted by oxalate (1.0-10 mM). Compared with the control solution, the reduction of Cr(VI) in a 10 mM oxalate solution could be increased from 56.6% to 99.1%. Particularly, the promotion of Cr(VI) reduction attributed to the enhancement of OH- production from NaBH4 hydrolysis due to the increasing concentration of C2O42- species, forming conjugated acid-base pairs in the form HC2O4--C2O42-, which provided an effective buffer. In 0.10-0.40 mM oxalate-Cr(VI)-NaBH4 systems, the resulting Cr(III) could precipitate at different levels within 20 h, and showed settlement rates in the range of 8.8% and 95.8%, but no precipitate was found in 1.0-10 mM oxalate-Cr-NaBH4 systems. This is related to whether there was a sufficient oxalate dosage, which could be complexed with Cr (III) at a molar ratio of 1:1. The precipitates were analysed by means of electron spin resonance (ESR), atomic force microscopy (AFM), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR), indicating that Cr (III) could support oxalate coprecipitation. The results of the present study reveal the influence of oxalate on Cr(VI) reduction and subsequent Cr (III) precipitation, which are of great significance to the application of NaBH₄ in the treatment of industrial wastewater containing Cr(VI)-oxalate.