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In this study, DDR membranes with a layer thickness of approximately 700 nm were studied for separation feeds comprising mixtures of CO 2 and CH 4. The membranes displayed the highest CO 2 over CH 4 permselectivity and CO 2 permeability reported in literature. This was ascribed to a defect-free and ultra-thin zeolite film as well as an open and highly permeable support. For equimolar mixtures, the highest CO 2 over CH 4 permselectivity of 727 was observed when the pressure at the feed side was 5 bar(a) and the permeate pressure was 1 bar(a) at 25 °C. At these conditions, the CO 2 permeability was very high at 45 × 10−7 mol/(m2 s Pa). Separation experiments for 80/20 and 20/80 mixtures were also performed, and in these cases, CO 2 over CH 4 permselectivities of 1011 and 622 were observed, respectively. For all feeds, the membrane permselectivity decreased slightly at higher temperature and in all cases, higher permselectivity was observed when vacuum was applied at the permeate side. One-stage membrane processes for upgrading biogas to biomethane at three different operating pressures were designed based on the experimental data. In all cases, a quite low membrane area, methane slip and power need were observed. [Display omitted] • DDR membranes with ultrahigh CO 2 permeance for CO 2 /CH 4 separation. • One-stage DDR membrane processes for biogas upgrading. • Low membrane area, CH 4 slip, and power use for these processes. [ABSTRACT FROM AUTHOR]

We developed a series of molecule-scale hybrid amine-silica membranes synthesized from organoalkoxysilane precursors of 3-(triethoxysilyl)propan-1-amine (PA-Si) and 3-(triethoxysilyl)-N-methylpropan-1-amine (SA-Si), and made these functional using either unhindered amines or a 3-(triethoxysilyl)-N,N-dimethylpropan-1-amine (TA-Si) that is sterically hindered. CO 2 adsorption-desorption measurements of amine-silica powdered xerogels were conducted to observe the effect of amine type on CO 2 adsorption and desorption/diffusion properties. The results revealed that TA-Si xerogel powders demonstrated faster kinetics for both adsorption and desorption processes compared with those of the PA-Si and SA-Si samples due to the steric hindrance effect of the amine, which reduced the CO 2 binding energy and thereby boosted both the forward and reverse reaction rates of CO 2 -amine. In single-gas permeation performances, all the membranes exhibited excellent molecular sieving at higher temperatures and all the gases considered, except CO 2 , tended to permeate the membranes via activated diffusion. The effect of amine type on CO 2 separation performance was compared using CO 2 permeance, CO 2 /N 2 selectivity, activation energy for permeation ( E p ) of CO 2 [ E p (CO 2 ) ], and differences in E p between CO 2 and N 2 [ E p (CO 2 )-E p (N 2 ) ]. The TA-Si membrane demonstrated superior CO 2 separation performance, and achieved the highest values for both CO 2 permeance and selectivity. A relatively smaller difference in CO 2 separation performance was observed between PA-Si and SA-Si membranes despite some differences in basicity. This suggests that, rather than the basicity, it was the steric hindrance effect that played the greatest role in CO 2 transport performance across amine-silica membranes. [ABSTRACT FROM AUTHOR]

A novel pyrimidine-bridged organoalkoxysilane precursor, 4,6-bis(3-triethoxysilyl-1-propoxy)-1,3-pyrimidine (BTPP), was synthesized via a platinum-catalyzed reaction and subsequently a BTPP membrane was developed via a sol-gel process. This new membrane exhibits great potential for improved CO 2 separation compared with common amine-functionalized organosilica membranes. Possible CO 2 transport mechanisms across amine-functionalized organosilica membranes were explored by comparing the CO 2 sorption behaviors of organoalkoxysilane materials with both strong and mild affinities. The results showed that a membrane with strong affinity to CO 2 does not lead to a superior CO 2 separation capability. Hence, the concept of a “mild-affinity membrane” was proposed, which describes membranes with intermediate-to-low CO 2 binding energy that exhibits an improved level of CO 2 transport efficiency. The concept of a mild-affinity membrane offers the development of technological innovation leading to the realization of highly efficient CO 2 separation membranes. [ABSTRACT FROM AUTHOR]

Producing formate via electrochemical carbon dioxide reduction reaction (CO 2 RR) is an attractive approach to carbon neutrality but suffers from low selectivity and energy conversion efficiency. Herein, we develop an efficient CO 2 RR electrocatalyst composed of Bi nanoparticles supported on N-doped carbon aerogel (Bi@NCA). Based on experimental and computational results, the carbon support serves as dual roles, one is to stabilize Bi nanoparticles by nitrogen dopants, the other function is to provide high porosity with abundant active sites to enhance CO 2 adsorbability. Because of the synergistic effect between Bi nanoparticles and N-doped carbon framework, the as-obtained Bi@NCA delivers remarkable performance with moderate overpotential, and high selectivity towards formate with Faradaic efficiency surpassing 95% in a wide potential range. [Display omitted] • Ultrasmall bismuth nanoparticles are synthesized on nitrogen-doped carbon aerogel via facile thermal treatment. • Nitrogen-doped carbon nanosheets with defective structures are essential to stabilize ultrasmall bismuth nanoparticles. • The electrocatalyst can efficiently catalyze CO2 reduction to produce formate with high selectivity. • High current density is achieved in flow cell for CO2 reduction. [ABSTRACT FROM AUTHOR]

The adsorption and mass transport of CO 2 and CH 4 in CHA zeolite were studied experimentally. First, large and well-defined CHA crystals with varying Si/Al ratios and morphologies ideal for adsorption studies were prepared. Then, adsorption isotherms were measured, and adsorption parameters were estimated from the data. In the next step, permeation experiments for pure components and mixtures were conducted for a defect-free CHA membrane with a Si/Al ratio of 80 and a thickness of 600 nm over a wide temperature range. A maximum selectivity of 243 in combination with a CO 2 permeance of 70 × 10−7 mol/(m2 s Pa) was observed for a feed of an equimolar CO 2 /CH 4 mixture at 273 K and 5.5 bar. Finally, a simple model accounting for adsorption and diffusion through the surface barriers and the interior of the pores of the membrane was fitted to the permeation data. The fitted model indicated that the surface barrier was a surface diffusion process at the pore mouth with higher activation energy than the diffusion process within the pores. The model also showed that the highly selective mass transport in the membrane was mostly a result of a selective surface barrier and, to a lesser extent, a result of adsorption selectivity. [Display omitted] • CHA crystals with various Si/Al ratios were studied for gas adsorption. • The adsorption were performed in a wide temperature range of 150–350 K. • Single gas and CO 2 /CH 4 permeation were measured over an ultra-thin CHA membrane. • Adsorption parameters were used to model mass transport through the CHA membrane. • High CO 2 /CH 4 selectivity is mostly due to high surface permeability selectivity. [ABSTRACT FROM AUTHOR]

In the present work, single channel tubular zeolite CHA membranes with a length of 50 cm and a membrane area of 100 cm2 were evaluated by SEM and permeation experiments with single components and industrially relevant humid mixtures. The membranes comprised well-intergrown and smooth CHA films with a thickness of <500 nm supported on the inside of a highly porous tube. For single component permeation, a very low SF 6 permeance of 4.5 × 10−10 mol/(m2‧s‧Pa) was observed, which indicated nearly defect free membranes. On the contrary, the membranes displayed a very high CO 2 permeance of 128 × 10−7 mol/(m2‧s‧Pa), which illustrated the very high permeability of the CHA pores. Finally, the membranes displayed excellent selectivity for separation of industrially relevant CO 2 /CH 4 /H 2 O mixtures, which was attributed to selective interaction between the CO 2 molecules and the polar water molecules in the pores. The highest observed CO 2 /CH 4 separation selectivity was as high as 198 in combination with a CO 2 permeance of 14 × 10−7 mol/(m2‧s‧Pa) at a feed pressure of 600 kPa (including 2.2 kPa water) and 293K. The corresponding CO 2 flux was 0.39 mol/(m2‧s) and the corresponding CO 2 /CH 4 separation factor was 162. The observed membrane performance was reduced by concentration polarisation due to the limited feed flow in the experimental setup. The corresponding selectivity and CO 2 permeance corrected for concentration polarisation were as high as 236 and 16 × 10−7 mol/(m2‧s‧Pa), and the corrected CO 2 flux was 0.44 mol/(m2‧s) and corrected separation factor was 198. An estimate showed that even at a low feed pressure of 500 kPa, it would be sufficient with as few as 64 membranes for processing of a feed of 100 Nm3/h raw biogas, i.e. the capacity of a typical biogas plant at a large farm, to biomethane with high purity. These results illustrated that the membranes are promising candidates for industrial separation of CO 2 from e.g. natural gas and biogas. [Display omitted] • The first report described industrially relevant CHA membranes. • The membrane was a single channel tube with a membrane area of 100 cm2. • CO 2 single gas permeances was as high as 128 × 10−7 mol/(m2‧s‧Pa). • The highest observed CO 2 /CH 4 separation factor was 169. • Effect of concentration polarisation on separation was discussed. [ABSTRACT FROM AUTHOR]

• High-performance adsorbents with diamine-functionalized mesoporous support (P/D-SD) effectively remove trace CO 2 from C 2 H 2. • P/D-SD shows high CO 2 adsorption capacity (1.76 mmol/g at 298 K and 0.0004 bar) and CO 2 /C 2 H 2 IAST selectivity surpassing 105. • P/D-SD produces highly pure C 2 H 2 (>99.9 %) from CO 2 /C 2 H 2 mixtures, with adsorption performance unaffected by moisture. • P/D-SD shows fast CO 2 adsorption kinetics and excellent cycling stability. The removal of trace carbon dioxide (CO 2) from acetylene (C 2 H 2) through adsorption poses a significant challenge due to their similar kinetic diameters and physical properties. Here, we report a novel solid amine adsorbent, polyethyleneimine-diethanolamine functionalized silica dioxide (termed P/D-SD), which exhibited a remarkable CO 2 adsorption capacity of 1.76 mmol/g at 298 K and 0.0004 bar. The IAST selectivity of the CO 2 /C 2 H 2 (1/99, v/v) mixture of P/D-SD was 7.98E + 05. The exceptional separation performance of P/D-SD is demonstrated through breakthrough experiments, producing ultra-high purity C 2 H 2 (greater than 99.9 %) from CO 2 /C 2 H 2 (1/99) mixtures. Its CO 2 adsorption performance remains largely unaffected under different humidity condition. Furthermore, P/D-SD exhibited excellent stability in the adsorption–desorption cycle and rapid CO 2 adsorption kinetics at different temperatures when compared with P-SD. The adsorption mechanism of P/D-SD with CO 2 was studied as a chemisorption process via in situ DRIFTS. [ABSTRACT FROM AUTHOR]

The abatement of defects in zeolite membranes is essential for achieving high selectivity. In the present work, a simple and effective method for blocking defects in ultra-thin (ca. 0.5 μm) MFI zeolite membranes has been developed. The method is based on deposition of an ultra-thin (~15 nm) layer of amorphous silica on the top surface of the membrane. Permporometry data indicated that the amount of defects, especially defects larger than 4 nm, in the membranes was significantly reduced after the modification. In mixture separation experiments, the CO 2 /H 2 separation factor increased dramatically after blocking the defects in a defective membrane that was selected for the experiments. For instance, at 263 K and 9 bar feed pressure, the CO 2 /H 2 separation factor increased from 8.5 to 36 after modification of the membrane, whereas the CO 2 flux only decreased by ca. 40%. [ABSTRACT FROM AUTHOR]

[Display omitted] • Based on the USPEX screening more stable SiCP 4 allotropes was obtained. • A high carrier mobility of 106 cm2 V−1 s−1 is observed for SiCP 4 allotrope. • The maximum η S T H ′ and η S T F ′ of SiCP 4 allotrope can reach 21.89% and 23.90% • Two SiCP 4 allotropes can trigger HER spontaneously. • SiCP 4 allotropes have the potential to reduce CO 2 to CH 4 or HCOOH. Two-dimensional metal-free photocatalysts are catching the attention of researchers. Here, we present several allotrope SiCP 4 monolayers with high stability, high carrier mobility, and excellent photocatalytic performance. Using a searching method based on the universal structure predictor evolutionary xtallography, together with assessing the energy and thermodynamic stabilities, and matching the potentials of band edges with the photocatalytic conditions for achieving overall water splitting, we successfully identify 5 highly favorable configurations (including the previously reported one) from a pool of 1056 allotrope SiCP 4 monolayers. The results show that the largest solar-to-hydrogen efficiency of the considered monolayers can reach 21.89 %, while a high mobility of 2.7677 × 105 cm2 V−1 s−1 is observed, both are superior to those of the previously reported one. The Gibbs free energies for hydrogen or oxygen evolutions, and CO 2 reduction reactions indicate they are thermodynamically feasible. Moreover, the hydrogen evolution reaction can proceed spontaneously with two allotrope SiCP 4 monolayers. Therefore, the newfound allotrope SiCP 4 monolayers are expected to have potential applications in the field of photocatalytic water splitting for hydrogen generation and carbon dioxide reduction. [ABSTRACT FROM AUTHOR]

Monolithic binder-free CO 2 adsorbents with high adsorption capacity, selectivity, adsorption-desorption kinetics, and regenerability are highly desired to both reduce the environmental impact of anthropogenic CO 2 emissions and purify valuable gases from CO 2. Herein, we report a strategy to prepare monolithic carbonaceous CO 2 adsorbents from low-cost and underutilized bioresources, which enabled the formation of a delicate anisotropic, hierarchical porous structure. With optimized material composition and processing conditions, the biobased carbon adsorbent demonstrated a CO 2 adsorption capacity of 4.49 mmol g-1 at 298 K and 100 kPa, relatively weak adsorbent-adsorbate affinity, good CO 2 /N 2 selectivity, and advantageous hydrophobicity against water vapor. Moreover, the unique anisotropic porous structure provided high stiffness and good flexibility to the adsorbent in the axial and radial directions, respectively. We confirmed that this type of carbon adsorbent could be packed in a column for dynamic CO 2 capture independent of any binders, indicating its promising future for further development toward widespread utilization. [Display omitted] • Biocarbon aerogels with anisotropic, hierarchical porous structure were prepared. • Carbon aerogels reached CO 2 adsorption capacity of 4.49 mmol g−1 (298 K, 100 kPa). • Carbon aerogels showed good CO 2 /N 2 selectivity and low water vapor adsorption. • Carbon aerogels exhibited strong and unique anisotropic mechanical properties. • Carbon aerogels were packed in a column without binders for large-scale CO 2 capture. [ABSTRACT FROM AUTHOR]

In the present work, a biosynthesis route for the preparation of hierarchical pompon-like SAPO-34 was developed. Commercially available bacterial cellulose aerogel was used as template. SiO 2 loaded bacterial cellulose aerogel was used as silica source and a simple hydrothermal treatment was used for crystallization. XRD, FT-IR, SEM, TEM, N 2 adsorption-desorption and TG techniques were employed to characterize the obtained samples. The hierarchical pompon-like SAPO-34 showed a spherical morphology that was comprised of nanosheets with a thickness less than 30 nm. The specific surface area of the hierarchical pompon-like SAPO-34 was 498 m2/g that was higher than the trigonal SAPO-34 crystals of 465 m2/g. The ultrasonic treatment experiment indicated a high stability of the pompon-like structure. In addition, the hierarchical pompon-like SAPO-34 exhibited a CO 2 adsorption capacity of 2.26 mmol/g at 100 kPa and 298K and the corresponding CO 2 /CH 4 ideal separation factor was 5.7, which was higher than that of trigonal SAPO-34 crystals. The saturated adsorption capacity and b-value were estimated using single site Langmuir, Toth and Sips adsorption isotherm models and the observed results were constant. Compared with trigonal SAPO-34, hierarchical pompon-like SAPO-34 displayed a higher saturated adsorption capacity, but a lower b-value. [Display omitted] • A biosynthesis route was developed for the synthesis of hierarchical SAPO-34. • Economical bacterial cellulose aerogel was used as the template. • The hierarchical SAPO-34 crystals were comprised of ultrathin zeolite nanosheets. • A higher surface area and a higher CO 2 adsorption capacity were observed. [ABSTRACT FROM AUTHOR]

This study developed a green and efficient process for simultaneous extraction and enrichment of phytochemicals from plant waste using a novel CO 2 - responsive surfactant (CRS) aqueous with ultrasound assistance. This extraction process was optimized. using single-factor experiments combined with Box-Behnken design. The tris (2-hydroxyethyl) ammonium palmitate (THAP) aqueous was selected as extraction solvent. The optimal conditions were ultrasound time of 120 min, R(S/L) of 20 mg/mL and CRS concentration of 54 mmol/L, the extraction yields for target compounds increased 1.1 folds to 5 folds compared with other surfactants. The results showed that THAP could be guaranteed at least 5 cycles with relatively stable extraction yields of target compounds. Moreover, the mechanism study using density functional theory was applied to investigate physicochemical properties of THAP and extraction mechanism. The presented method is a promising, nontoxic, lower-cost, and sustainable alternative to extract and enrich valuable components from plant materials. [Display omitted] • The CO 2 -responsive surfactant- aqueous (CRS) is environmentally friendly. • The CRS as an alternative is used for extraction components from Cili leaves. • The mechanism study investigated the CRS the solubilization characters. [ABSTRACT FROM AUTHOR]