Layered Double Hydroxides-Based Mixed Metal Oxides: Development of Novel Structured Sorbents for CO2 Capture Applications

Utilizing Gelatin Waste for Efficient Bimodal Porous Silica Adsorbents for Carbon Dioxide Capture

This study explores the modification of pore structures in porous silica materials synthesized using sodium silicate and waste gelatin, under varying silica-to-gelatin ratios. At ratios of 1.0-1.5, bimodal porous silica with mesopores and macropores emerged due to spaces between silica nanoparticles and clusters, following gelatin elimination. The study further evaluated the obtained bimodal porous silica as polyethyleneimine (PEI) supports for CO2 capture, alongside PEI-loaded unimodal porous silica and hollow silica sphere for comparison. Notably, the PEI-loaded bimodal silica showcased superior CO2 uptake, achieving 145.6 mg g-1 at 90 °C. Transmission electron microscopy (TEM) revealed PEI's uniform distribution within the pores of bimodal silica, unlike the excessive surface layering seen in unimodal silica. Conversely, PEI completely filled the hollow porous silica's interior, extending gas molecule diffusion distance. All sorbents displayed nearly constant CO2 adsorption across 20 cycles, demonstrating outstanding stability. Notably, the bimodal porous silica displayed a negligible capacity loss, underscoring its robust performance.

Multifaceted potential applicability of hydrotalcite-type anionic clays from green chemistry to environmental sustainability

Hydrotalcite-like anionic clays (HTs) also known as Layered double hydroxides (LDHs) have been developed as multifunctional materials in numerous applications related to catalysis, adsorption, and ion-exchange processes. These materials constitute an important class of ionic lamellar solid clays of Brucite-like structure which comprise of consecutive layers of divalent and trivalent metal cations with charge balancing anions and water molecules in interlayer space. These materials have received increasing attention in research due to their interesting properties namely layered structure, ease of preparation, flexible tunability, ability to intercalate different types of anions, electronic properties, high thermal stability, high biocompatibility, and easy biodegradation. Moreover, HTs/LDHs have unique tailorable and tuneable characteristics such as both acidic and basic sites, anion exchange capability, surface area, basal spacing, memory effect, and also exhibit high exchange capacities, which makes them versatile materials for a wide range of applications and extended their horizons to diverse areas of science and technology. This study enlightens the various rational researches related to the synthetic methods and features focusing on synthesis and/or fabrication with other hybrids and their applications. The diverse applications (namely catalyst, adsorbent to toxic chemicals, agrochemicals management, non-toxic flame retardants, and recycling of plastics) of these multifunctional materials related to a clean and sustainable environment were also summarized.

A Review on SAPO-34 Zeolite Materials for CO2 Capture and Conversion

Among several known zeolites, silicoaluminophosphate (SAPO)-34 zeolite exhibits a distinct chemical structure, unique pore size distribution, and chemical, thermal, and ion exchange capabilities, which have recently attracted considerable research attention. Global carbon dioxide (CO₂ ) emissions are a serious environmental issue. Current atmospheric CO₂ level exceeds 414 parts per million (ppm), which greatly influences humans, fauna, flora, and the ecosystem as a whole. Zeolites play a vital role in CO₂ removal, recycling, and utilization. This review summarizes the properties of the SAPO-34 zeolite and its role in CO₂ capture and separation from air and natural gas. In addition, due to their high thermal stability and catalytic nature, CO₂ conversions into valuable products over single metal, bi-metallic, and tri-metallic catalysts and their oxides supported on SAPO-34 were also summarized. Considering these accomplishments, substantial problems related to SAPO-34 are discussed, and future recommendations are offered in detail to predict how SAPO-34 could be employed for greenhouse gas mitigation.

Efficient, scalable, closed-loop synthesis of highly crystalline pure phase MgAl-layered double hydroxides intercalated with hydroxyl anions

Layered double hydroxides (LDHs) can play an important role in various areas, but conventional LDHs synthesis often causes product agglomeration and generates plenty of high-salt wastewater, and requires a time-consuming aging process to reach the desired purity and crystalline state. Herein, we report the synthesis of MgAl-LDH, a representative of these kinds of ionic lamellar inorganic solids, with a novel method involving the reaction of magnesium oxide (MgO) with aluminate ions (Al(OH)₄^-) in a strongly alkaline environment. The formation of MgAl-LDH follows a mechanism of interfacial dissolution-reprecipitation (IDR), i.e., Mg²⁺ ions released at the interface of dissolved MgO react immediately with Al(OH)₄^- ions to reprecipitate as MgAl-LDH. The obtained MgAl-LDH has no impurity phases and shows high crystallinity, high specific surface area, and a narrow particle size distribution. Moreover, MgAl-LDH is intercalated with OH^- anions, so it can be directly used as a Brønsted base catalyst and ion exchanger. The novel method requires no time-consuming aging process and is highly scalable. It is also shown that a closed-loop synthesis of MgAl-LDH without waste discharge can be achieved with an appropriate Al source, e.g., Al(OH)₃, and a recycled NaOH solution.

Roles of London Dispersive and Polar Components of Nano-Metal-Coated Activated Carbons for Improving Carbon Dioxide Uptake

Adsorption using carbonaceous materials has been considered as the prevailing technology for CO2 capture because it offers advantages such as high adsorption capacity, durability, and economic benefits. Activated carbon (AC) has been widely used as an adsorbent for CO2 capture. We investigated CO2 adsorption behaviors of magnesium oxide-coated AC (MgO-AC) as a function of MgO content. The microstructure and textural properties of MgO-AC were characterized by X-ray diffraction and nitrogen adsorption–desorption isotherms at 77 K, respectively. The CO2 adsorption behaviors of MgO-AC were evaluated at 298 K and 1 atm. Our experimental results revealed that the presence of MgO plays a key role in increasing the CO2 uptake through the interaction between an acidic adsorbate (e+) and an efficient basic adsorbent (e−).