The separation and storage of CO₂ in geological form as mineral carbonates has been seen as a viable method to reduce the concentration of CO₂ from the atmosphere. Mineralization of CO₂ to mineral salts like calcium carbonate provides a stable storage of CO₂. Reversible hydration of CO₂ to carbonic acid is the rate limiting step in the mineralization process. We report catalysis of the reversible hydration of CO₂ using nickel nanoparticles (NiNPs) at room temperature and atmospheric pressure. The catalytic activity of the NiNPs is pH independent and as they are water insoluble and magnetic they can be magnetically separated for reuse. The reaction steps were characterized using X-ray photoemission spectroscopy and a possible reaction mechanism is described.

A reduced graphene oxide/bismuth (rGO/Bi) composite was synthesized for the first time using a polyol process at a low reaction temperature and with a short reaction time (60 °C and 3 hours, respectively). The as‐prepared sample is structured with 20–50 nm diameter bismuth particles distributed on the rGO sheets. The rGO/Bi composite displays a combination of capacitive and battery‐like charge storage, achieving a specific capacity value of 773 C g⁻¹ at a current density of 0.2 A g⁻¹ when charged to 1 V. The material not only has good power density but also shows moderate stability in cycling tests with current densities as high as 5 A g⁻¹. The relatively high abundance and low price of bismuth make this rGO/Bi material a promising candidate for use in electrode materials in future energy storage devices.

The presence of nanoparticles in many industrial applications and daily products is making it nowadays crucial to assess their impact when exposed to the environment. Metallic nickel nanoparticles (Ni NPs) are of high industrial interest due to their ability to catalyze the reversible hydration of CO2 to carbonic acid at ambient conditions. We characterized metallic Ni NPs by XRD, HRTEM and EDS and determined the solubility of free nickel ions from 3 mg/L metallic Ni NPs in seawater by ICP-MS over 96 h, which was below 3%. Further, embryonic development of the sea urchin Paracentrotus lividus was investigated for 48 h in the presence of metallic Ni NPs (0.03 mg/L to 3 mg/L), but no lethal effects were observed. However, 3 mg/L metallic Ni NPs caused a size reduction similar to 1.2 mg/L NiCl2*6 H2O. The obtained results contribute to current studies on metallic Ni NPs and point to their consequences for the marine ecosystem.

Hydration reaction of CO₂ is one of the rate limiting steps for CO₂ absorption (in aqueous solutions) and aqueous CO₂ mineralization. The catalytic activity of nickel nanoparticles (NiNPs) for CO₂ hydration is studied at different temperatures, pH, and low CO₂ partial pressures to mimic the true flue gas conditions. Results show that NiNPs can work as active catalyst for hydration of CO₂ in applications such as CO₂ separation and CO₂ mineralization. The NiNPs display optimum activity within 20–30°C and at pH value <8. NiNPs show catalytic activity even at low CO₂ partial pressures (12 vol%). In 50 wt% K₂CO₃ solution, an enhancement of 77% is observed in the rate of CO₂ absorption with NiNPs. Commercially, CO₂ saturated K₂CO₃ solutions are usually regenerated at 150°C; at these conditions, NiNPs show no considerable surface oxidation. They still exhibit catalytic activity for hydration reaction of CO₂. CO₂ absorption and mineralization (as CaCO₃) in DI water are three times higher in presence of NiNPs. Calcite (CaCO₃) particles precipitated in presence of NiNPs are spherical in morphology.

In this work, wavy nickel nanowires (NiNWs) were immobilized on mesoporous silica (SiO₂) aerogels by the sol–gel method. We measured the catalytic activity of pure NiNWs and NiNW–SiO₂ aerogel composites toward the CO₂ hydration reaction (CHR) when they are in water. Dynamic vapor sorption (DVS) analysis was performed at levels of 50% CO₂ and 50% H₂O vapor for SiO₂ aerogels, immobilized nickel nanoparticles (NiNPs) on silica aerogel and NiNW–SiO₂ aerogel composites, in order to determine catalytic activity for CHR in the gaseous phase. The results from DVS analysis (gaseous phase) and CHR (aqueous phase) showed that NiNW–SiO₂ aerogel composites are good heterogeneous catalysts for CHR in both gaseous and aqueous phases but they are less active than NiNP–SiO₂ aerogel composites.