Preparation of Amine-Modified Cu-Mg-Al LDH Composite Photocatalyst

Cu-Mg-Al layered double hydroxides (LDHs) with amine modification were prepared by an organic combination of an anionic surfactant-mediated method and an ultrasonic spalling method using N-aminoethyl-γ-aminopropyltrimethoxysilane as a grafting agent. The materials were characterized by elemental analysis, XRD, SEM, FTIR, TGA, and XPS. The effects of the Cu2+ content on the surface morphology and the CO2 adsorption of Cu-Mg-Al LDHs were investigated, and the kinetics of the CO2 adsorption and the photocatalytic reduction of CO2 were further analyzed. The results indicated that the amine-modified method and appropriate Cu2+ contents can improve the surface morphology, the increase amine loading and the free-amino functional groups of the materials, which were beneficial to CO2 capture and adsorption. The CO2 adsorption capacity of Cu-Mg-Al N was 1.82 mmol·g−1 at 30 °C and a 0.1 MPa pure CO2 atmosphere. The kinetic model confirmed that CO2 adsorption was governed by both the physical and chemical adsorption, which could be enhanced with the increase of the Cu2+ content. The chemical adsorption was suppressed, when the Cu2+ content was too high. Cu-Mg-Al N can photocatalytically reduce CO2 to methanol with Cu2+ as an active site, which can significantly improve the CO2 adsorption and photocatalytic conversion.

CO2 Reduction to Valuable Chemicals on TiO2-Carbon Photocatalysts Deposited on Silica Cloth

A new photocatalyst for CO2 reduction has been presented. The photocatalyst was prepared from a combination of a commercial P25 with a mesopore structure and carbon spheres with a microporous structure with high CO2 adsorption capacity. Then, the obtained hybrid TiO2-carbon sphere photocatalysts were deposited on a glass fiber fabric. The combined TiO2-carbon spheres/silica cloth photocatalysts showed higher efficiency in the two-electron CO2 reduction towards CO than in the eight-electron reaction to methane. The 0.5 g graphitic carbon spheres combined with 1 g of TiO2 P25 resulted in almost 100% selectivity to CO. From a practical point of view, this is promising as it economically eliminates the need to separate CO from the gas mixture after the reaction, which also contains CH4 and H2.

Tailoring Amine-Functionalized Ti-MOFs via a Mixed Ligands Strategy for High-Efficiency CO2 Capture

Amine-functionalized metal-organic frameworks (MOFs) are a promising strategy for the high-efficiency capture and separation of CO2. In this work, by tuning the ratio of 1,3,5-benzenetricarboxylic acid (H3BTC) to 5-aminoisophthalic acid (5-NH2-H2IPA), we designed and synthesized a series of amine-functionalized highly stable Ti-based MOFs (named MIP-207-NH2-n, in which n represents 15%, 25%, 50%, 60%, and 100%). The structural analysis shows that the original framework of MIP-207 in the MIP-207-NH2-n (n = 15%, 25%, and 50%) composites remains intact when the mole ratio of ligand H3BTC to 5-NH2-H2IPA is less than 1 to 1 in the resulting MOFs. By the introduction of amino groups, MIP-207-NH2-25% demonstrates outstanding CO2 capture performance up to 3.96 and 2.91 mmol g−1, 20.7% and 43.3% higher than those of unmodified MIP-207 at 0 and 25 °C, respectively. Furthermore, the breakthrough experiment indicates that the dynamic CO2 adsorption capacity and CO2/N2 separation factors of MIP-207-NH2-25% are increased by about 25% and 15%, respectively. This work provides an additional strategy to construct amine-functionalized MOFs with the maintenance of the original MOF structure and a high performance of CO2 capture and separation.

Effect of Thermal Stabilization on PAN-Derived Electrospun Carbon Nanofibers for CO2 Capture

Carbon capture is amongst the key emerging technologies for the mitigation of greenhouse gases (GHG) pollution. Several materials as adsorbents for CO2 and other gases are being developed, which often involve using complex and expensive fabrication techniques. In this work, we suggest a sound, easy and cheap route for the production of nitrogen-doped carbon materials for CO2 capture by pyrolysis of electrospun poly(acrylonitrile) (PAN) fibers. PAN fibers are generally processed following specific heat treatments involving up to three steps (to get complete graphitization), one of these being stabilization, during which PAN fibers are oxidized and stretched in the 200–300 °C temperature range. The effect of stabilization temperature on the chemical structure of the carbon nanofibers is investigated herein to ascertain the possible implication of incomplete conversion/condensation of nitrile groups to form pyridine moieties on the CO2 adsorption capacity. The materials were tested in the pure CO2 atmosphere at 20 °C achieving 18.3% of maximum weight increase (equivalent to an uptake of 4.16 mmol g−1), proving the effectiveness of a high stabilization temperature as route for the improvement of CO2 uptake.

Activated Carbon from Palm Date Seeds for CO2 Capture

The process of carbon dioxide capture and storage is seen as a critical strategy to mitigate the so-called greenhouse effect and the planetary climate changes associated with it. In this study, we investigated the CO2 adsorption capacity of various microporous carbon materials originating from palm date seeds (PDS) using green chemistry synthesis. The PDS was used as a precursor for the hydrochar and activated carbon (AC). Typically, by using the hydrothermal carbonization (HTC) process, we obtained a powder that was then subjected to an activation step using KOH, H3PO4 or CO2, thereby producing the activated HTC-PDS samples. Beyond their morphological and textural characteristics, we investigated the chemical composition and lattice ordering. Most PDS-derived powders have a high surface area (>1000 m2 g−1) and large micropore volume (>0.5 cm3 g−1). However, the defining characteristic for the maximal CO2 uptake (5.44 mmol g−1, by one of the alkaline activated samples) was the lattice restructuring that occurred. This work highlights the need to conduct structural and elemental analysis of carbon powders used as gas adsorbents and activated with chemicals that can produce graphite intercalation compounds.

CO2 Adsorption Performance and Kinetics of Ionic Liquid-Modified Calcined Magnesite

CO2 is a major contributor to global warming, and considerable efforts have been undertaken to capture and utilise it. Herein, a nanomaterial based on ionic liquid (IL)–modified calcined magnesites was investigated for CO2 capture. The synthesised nanomaterial (magnesite modified using [APMIM]Br) exhibited the best adsorption performance of 1.34 mmol/g at 30% IL loading amount, 50 °C, 0.4 MPa and 150 mL/min. In particular, the obtained nanomaterial could be regenerated at a low temperature of 90 °C for 3 h, and its CO2 adsorption capacity of 0.81 mmol/g was retained after eight cycles. FT-IR results showed that the imidazole ring and C–N group are directly related to CO2 adsorption capacity. Moreover, improving the conjugative effect of the imidazole ring enhanced the adsorption performance. Further, CO2 was adsorbed on the adsorbent surface and incomplete desorption decreased the BET surface area and CO2 adsorption capacity. Additionally, four models were selected to fit the adsorption kinetics. The results show that the adsorption mechanism fits the pseudo-first-order model well.

Physical and Chemical Activation of Graphene-Derived Porous Nanomaterials for Post-Combustion Carbon Dioxide Capture

Activation is commonly used to improve the surface and porosity of different kinds of carbon nanomaterials: activated carbon, carbon nanotubes, graphene, and carbon black. In this study, both physical and chemical activations are applied to graphene oxide by using CO2 and KOH-based approaches, respectively. The structural and the chemical properties of the prepared activated graphene are deeply characterized by means of scanning electron microscopy, Raman spectroscopy, Fourier transform infrared spectroscopy, X-ray photoelectron spectrometry and nitrogen adsorption. Temperature activation is shown to be a key parameter leading to enhanced CO2 adsorption capacity of the graphene oxide-based materials. The specific surface area is increased from 219.3 m2 g−1 for starting graphene oxide to 762.5 and 1060.5 m2 g−1 after physical and chemical activation, respectively. The performance of CO2 adsorption is gradually enhanced with the activation temperature for both approaches: for the best performances of a factor of 6.5 and 9 for physical and chemical activation, respectively. The measured CO2 capacities are of 27.2 mg g−1 and 38.9 mg g−1 for the physically and chemically activated graphene, respectively, at 25 °C and 1 bar.