In the last few decades of industrialization, the concentration of CO 2 in the atmosphere had increased rapidly. Different organizations have invested considerable funds in research activities worldwide for CO 2 capture and storage. To date, significant work has been done and various technologies have been proposed for CO 2 capture and storage. Both adsorption and absorption are promising techniques for CO 2 capture, but low-temperature adsorption processes using solid adsorbents are the prevailing technique nowadays. In this review paper, a variety of adsorbents such as carbonaceous materials, dry alkali metal-based sorbents, zeolites, metal-organic frameworks (MOFs) and microporous organic polymers (MOPs) have been studied. Various methods of chemical or physical modification and the effects of supporting materials have been discussed to enhance CO 2 capture capacity of these adsorbents. Low-temperature (\100°C) adsorption processes for CO 2 capture are critically analyzed and concluded on the basis of information available so far in the literature. All the information in CO 2 adsorption using different routes has been discussed, summarized and thoroughly presented in this review article. The most important comparative study of relatively new material MOFs and MOPs is carried out between the groups and with other sorbent as well.

NH 2 -MIL-125 has been investigated as a water adsorbent because of its high hydrothermal stability and S-shaped water adsorption isotherm. Herein, we report the synthesis of NH 2 -MIL-125 with high surface area and water capacity for an adsorption heat transformation (AHT) system. NH 2 -MIL-125 derived from Ti(BuO) 4 shows higher surface area and water uptake than those of Ti(iPrO) 4 -derived samples regardless of the synthesis method. In a sense of crystallinity, a solvothermal method with static conditions generated more distinct crystalline properties than the one synthesized by a reflux reaction as confirmed from powder X-ray diffraction analysis, UV−vis absorbance spectra, and scanning electron microscopy images. Considering it as an adsorbent for an AHT system, the Ti(BuO) 4 -derived sample synthesized by a solvothermal method shows an ideal S-shaped isotherm with a steep rise in water uptake at lower relative pressure (0.550 g/g at P/P 0 = 0.30), which is attributed to narrow triangle apertures and hydrophilic functional groups. This material shows the dynamic water adsorption/ desorption cycle without any noticeable weight change.

Isostructural [M 2 (DOBDC)(EG) 2 ] (M = Mg, Co, Ni) frameworks are first synthesized by controlling the pH* in the reaction medium. Coordinated ethylene glycols form a hexagonal OH cluster, which works as a template to grow single crystals with high crystallinity. After the liberation of solvated molecules, [M 2 (DOBDC)] shows notably higher surface areas than the reported values and completely different CO 2 and CO separation properties depending on the kinds of unsaturated metal. Therefore, breakthrough experiments using a CO 2 /CO mixed gas show that Mg-MOF has a longer breakthrough time for CO 2 than for CO, whereas Co/Ni-MOFs have longer breakthrough times for CO than for CO 2 . Apart from CO 2 and CO, other gases such as CH 4 , H 2 , and N 2 were almost not adsorbed at all in these materials at 298 K. To reveal the role of unsaturated metal sites, CO 2 and CO adsorption sites are unequivocally determined by single-crystal X-ray diffraction analysis. One of very interesting discoveries is that there are two CO 2 and CO adsorption positions (sites A and B) in the hexagonal channels. Site A is the unsaturated metal center working as Lewis acidic sites, and site B is the secondary adsorption site located between two A sites. A close inspection of crystal structures reveals that unsaturated Co(II) and Ni(II) sites adsorb both CO 2 and CO, whereas the unsaturated Mg(II) sites strongly capture only CO 2 , not CO. Density functional theory calculations elucidate the discrepancy in CO affinity: Co(II) and Ni(II) form strong π-backdonating bonds with CO via electron transfer from the d orbitals of the transition metals to the antibonding molecular orbitals of CO, whereas Mg(II) does not participate in electron transfer or orbital overlap with CO. This observation provides new insight into the synthesis of novel functional materials with high CO 2 /CO separation performance.

No abstract

Novel hybrid composites of NH 2 -MIL-125(Ti) and ZnCr-layered double hydroxide nanosheets (ZnCr-LDH NSs) are developed for use as visible-light-active photocatalysts for hydrogen production based on water photolysis. The hybrid composites are obtained by growing NH 2 -MIL-125(Ti) in the presence of exfoliated ZnCr-LDH NSs using a solvothermal reaction. Hybridization of NH 2 -MIL-125(Ti) with exfoliated ZnCr-LDH NSs leads to significant effects on the morphology and optical properties of NH 2 -MIL-125(Ti). To find the optimum photocatalytic activity for hydrogen production by the hybrid composite photocatalysts, the content of ZnCr-LDH in this work is controlled. Compared to that of pristine NH 2 -MIL-125(Ti) and ZnCr-LDH, the hybrid composites exhibit an improved photocatalytic activity for hydrogen production under visible-light irradiation. In addition, the hybrid composite photocatalyst shows excellent photo-chemical stability. The improved photocatalytic activity is believed to benefit from the synergy of strong electronic coupling between NH 2 -MIL-125(Ti) and ZnCr-LDH NSs, expanded light absorption and band alignment to enhance the lifetime of photo-induced electrons and holes.

No abstract

No abstract

Defect-free mixed-matrix membranes (MMMs) were prepared by incorporating hydrophilic metal-organic polyhedra (MOPs) into cross-linked polyethylene oxide (XLPEO) for efficient CO separation. Hydrophilic MOPs with triethylene glycol pendant groups, which were assembled by 5-tri(ethylene glycol) monomethyl ether isophthalic acid and Cu ions, were uniformly dispersed in XLPEO without particle agglomeration. Compared to conventional neat XLPEO, the homogenous dispersion of EG -MOPs in XLPEO enhanced CO permeability of MMMs. Upon increasing the amount of EG -MOPs, the membrane performance such as CO /N selectivity was steadily improved because of unsaturated Cu sites at paddle-wheel units, which was confirmed by Cu K-edge XANES and TPD analysis. Therefore, such defect-free MMMs with unsaturated metal sites would contribute to enhance CO separation performance.