CO2 Capture at Low Temperatures (30–80 °C) and in the Presence of Water Vapor over a Thermally Activated Mg–Al Layered Double Hydroxide

Ca-Based Layered Double Hydroxides for Environmentally Sustainable Carbon Capture

The process of carbon dioxide capture typically requires a large amount of energy for the separation of carbon dioxide from other gases, which has been a major barrier to the widespread deployment of carbon capture technologies. Innovation of carbon dioxide adsorbents is herein vital for the attainment of a sustainable carbon capture process. In this study, we investigated the electrified synthesis and rejuvenation of calcium-based layered double hydroxides (Ca-based LDHs) as solid adsorbents for CO2. We discovered that the particle morphology and phase purity of the LDHs, along with the presence of secondary phases, can be controlled by tuning the current density during electrodeposition on a porous carbon substrate. The change in phase composition during carbonation and calcination was investigated to unveil the effect of different intercalated anions on the surface basicity and thermal stability of Ca-based LDHs. By decoupling the adsorption of water and CO2, we showed that the adsorbed water largely promoted CO2 adsorption, most likely through a sequential dissolution and reaction pathway. A carbon capture capacity of 4.3 ± 0.5 mmol/g was measured at 30 °C and relative humidity of 40% using 10 vol % CO2 in nitrogen as the feed stream. After CO2 capture occurred, the thermal regeneration step was carried out by directly passing an electric current through the conductive carbon substrate, known as the Joule-heating effect. CO2 was found to start desorbing from the Ca-based LDHs at a temperature as low as 220 °C as opposed to the temperature above 700 °C required for calcium carbonate that forms as part of the Ca-looping capture process. Finally, we evaluated the cumulative energy demand and environmental impact of the LDH-based capture process using a life cycle assessment. We identified the most environmentally concerning step in the process and concluded that the postcombustion CO2 capture using LDH could be advantageous compared with existing technologies.

Review of the Application of Hydrotalcite as CO2 Sinks for Climate Change Mitigation

In recent decades, the environmental impact caused by greenhouse gases, especially CO2, has driven many countries to reduce the concentration of these gases. The study and development of new designs that maximise the efficiency of CO2 capture continue to be topical. This paper presents a review of the application of hydrotalcites as CO2 sinks. There are several parameters that can make hydrotalcites suitable for use as CO2 sinks. The first question is the use of calcined or uncalcined hydrotalcite as well as the temperature at which it is calcined, since the calcination conditions (temperature, rate and duration) are important parameters determining structure recovery. Other aspects were also analysed: (i) the influence of the pH of the synthesis; (ii) the molar ratio of its main elements; (iii) ways to increase the specific area of hydrotalcites; (iv) pressure, temperature, humidity and time in CO2 absorption; and (v) combined use of hydrotalcites and cement-based materials. A summary of the results obtained so far in terms of CO2 capture with the parameters described above is presented. This work can be used as a guide to address CO2 capture with hydrotalcites by showing where the information gaps are and where researchers should apply their efforts.

Layered double hydroxides for removing and recovering phosphate: Recent advances and future directions

Eutrophication is a widespread environmental challenge caused by excessive phosphate. Thus, wastewater engineers primarily aim to limit the phosphate concentration in water bodies. Layered double hydroxides (LDHs) are lamellar inorganic materials containing tunable brucite-like structures. This review discusses the fundamental aspects and latest developments in phosphate removal using LDH-based materials. Based on the divalent cations, Ca, Mg, and Zn-containing LDHs are largely used along with trivalent cations such as Al and Fe owing to their limited toxicities. However, classical LDHs are affected by the presence of co-existing anions, have a narrow working pH range, and have moderate adsorption capacities. Binary LDHs have been designed to be selective towards phosphate by the addition of a third metal such as Zr⁴⁺. Developing LDH composites with magnetic, polymeric or carbon materials are feasible approaches for increasing adsorption capacity, stability, and reusability of LDHs. Biochar as a carrier material for LDHs achieved remarkable phosphate adsorption performance and improved LDH dispersion, anion exchange capacity, and ease of separation. The use of recovered phosphate as an SRF, which is a type of bioavailable fertilizer, is a promising approach.

LDH Nanocubes Synthesized with Zeolite Templates and Their High Performance as Adsorbents

In this work, the efficiency of the adsorptive removal of the organic cationic dye methylene blue (MB) from polluted water was examined using three materials: natural clay (zeolite), Zn-Fe layered double hydroxide (LDH), and zeolite/LDH composite. These materials were characterized via X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, high-resolution transmission electron microscopy (HRTEM), energy dispersive X-ray (EDX) diffraction (XRF), low-temperature N2 adsorption, pore volume and average pore size distribution and field emission scanning electron microscopy (FE-SEM). The properties of the applied nanomaterials regarding the adsorption of MB were investigated by determining various experimental parameters, such as the contact time, initial dye concentration, and solution pH. In addition, the adsorption isotherm model was estimated using the Langmuir, Freundlich, and Langmuir-Freundlich isotherm models. The Langmuir model was the best-fitting for all applied nanomaterials. In addition, the kinetics were analyzed by using pseudo-first-order, pseudo-second-order, and intraparticle diffusion models, and the pseudo-second-order model was an apparent fit for all three applied nanomaterials. The maximum Adsorption capacity toward MB obtained from the materials was in the order zeolite/LDH composite > zeolites > Zn-Fe LDH. Thus, the zeolite/LDH composite is an excellent adsorbent for the removal of MB from polluted water.

Water steam effect during high CO2 chemisorption in lithium cuprate (Li2CuO2) at moderate temperatures: experimental and theoretical evidence

Li₂CuO₂ is able to chemisorb high quantities of CO₂ in the presence of water steam at low temperatures.

Probing Local Structure of Layered Double Hydroxides with (1)H Solid-State NMR Spectroscopy on Deuterated Samples

By using a simple and efficient deuteration process, (2)H has been successfully introduced into layered double hydroxides (LDHs). Due to significantly less (1)H-(1)H homonuclear dipolar coupling, high-resolution (1)H solid-state NMR spectra can now be obtained conveniently at medium to low spinning speed to extract the information of cation ordering in LDHs. Furthermore, we show that double-resonance experiments can be applied easily to investigate internuclear proximities and test possible cation-ordered superstructure models. This approach can be readily extended to LDHs with different compositions to explore the local structure and the key interactions between the cations in the layer and interlayer anions.