CO2 Sorption Research Articles

Enhanced CO2/H2 separation by GO and PVA-GO embedded PVAm nanocomposite membranes

Membrane technology for CO2/H2 separation, especially when using CO2-selective membranes to keep H2 on the high-pressure retentate side, has been considered promising and energy-efficient for further H2 transport and utilization. This work prepared and optimized a CO2-selective membrane based on polyvinylamine (PVAm) with embedded graphene oxide (GO) and grafted GO for CO2/H2 separation. The facilitated transport effect of PVAm enhances CO2 transport, while the GO-based 2D nanosheets bring in a barrier effect to compensate for the high H2 diffusivity. The GO-modified surface with higher CO2 affinity also provides additional CO2 sorption sites. The membranes’ chemical structure, thermal stability, and morphology were characterized. The effects of GO and PVA-GO in the PVAm matrix and optimal loadings of GO or PVA-GO were investigated. Introducing GO into PVAm significantly increased CO2 permeance with a slight increase in CO2/H2 selectivity. While by adding 0.5 wt% PVA-GO, CO2/H2 selectivity significantly increased from 10 to 22. The selective layer thickness also greatly affects CO2/H2 separation. By increasing the coating layer thickness to approx. 11 μm, the CO2/H2 selectivity substantially increased. The separation performances of the studied membrane are far above the current CO2/H2 upper bound.

Synthesis of polyvinylpyrrolidone@dioctyl sodium sulfosuccinate (PVP@DSSS)via gamma radiation for Ce(III) and Co(II) separation

ABSTRACT By inducing gamma radiation at a dose of 25 kGy, vinylpyrrolidone (VP) was combined with dioctyl sodium sulfosuccinate, an anionic surfactant, to create PVP@DSSS. The sorption and recovery of Ce(III) and Co(II) from aqueous solutions were evaluated using PVP@DSSS. The physical and chemical characterisation of prepared sorbent was investigated by X-ray diffraction spectroscopy (XRD), Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX), and thermal analysis (TGA-DTA). The characterisations show that sorbents prepared using these techniques outperform conventional preparation methods. The PVP@DSSS was implanted for batch processing with the goal of studying the effect of different parameters on the sorption of the investigated metal ions, such as pH, contact time, metal ion concentration, and reaction temperatures. The results show that the maximum adsorption capacity of the PVP@DSSS adsorbent for Ce(III) and Co(III) were 9.8 and 0.9 mg/g, respectively. The adsorption of Ce(III) and Co(II) from aqueous suspension using PVP@DSSS was fit to Langmuir and pseudo second order equations well. The changes in the free energy (ΔG) and enthalpy (ΔH) values of Ce(III) confirm the endothermic nature of the adsorption reaction, whereas Co(II) adsorption was exothermic and spontaneous. The desorption efficiency was 95% for Co(II) and less than 10% for Ce(III) with HCl as good desorbing agent.The results show that PVP@DSSS is a promising adsorbent for the the recovery and separation process of Ce(III) ions from aqueous solution.

Sorption enhanced steam reforming of ethanol for hydrogen production, over Mg/Al hydrotalcites modified with K

Sorption-enhanced ethanol steam reforming is an interesting alternative, to produce high purity H2. In this study, potassium promoted hydrotalcites are compared for sorption-enhanced ethanol steam reforming reaction under cyclic operation, performing sorbent regeneration at reaction temperature which is a great advantage to reduce process energy requirements. It is found that potassium promoted hydrotalcites have higher CO2 sorption capacity compared to unpromoted ones, due to the higher concentration of intermediate and strong basic sites. The hydrotalcite modified with 15 wt% potassium shows the best performance on multicyclic CO2 sorption-desorption (sorption capacity = 0.167 molCO2/kgsorbent). Therefore, there is an optimum loading of potassium, for which the opposite effects of reduction in surface area and enhanced basicity are balanced. Finally, potassium promoted hydrotalcites are tested under cyclical ethanol reforming process with simultaneous adsorption of CO2 followed by regeneration in N2 at reaction temperature (500 °C). At short reaction times (<5 min), H2 purities higher than 95% are achieved, with CO2 purities near 0%.

CO2 solubility and diffusivity in poly(vinyl acetate) studied using the PC-SAFT and free volume theory

Poly (vinyl acetate) (PVAc) is a polymer used in various industrial applications, and the quantitative determination of CO2 solubility and diffusion coefficient is important for designing foaming processes involving supercritical CO2. In this study, these two physical properties were obtained experimentally and theoretically using the perturbed chain–statistical associating fluid theory (PC–SAFT) and free volume theory at temperatures between 353 K and 473 K and pressures up to 20 MPa. CO2 solubility increased almost linearly with pressure and could be correlated with the PC–SAFT equation of state and binary interaction parameter kij within the average relative deviation of 2.1%. Furthermore, the fitted plot of kij versus temperature can be used to predict CO2 solubility at lower temperatures. The diffusion coefficient of CO2 in PVAc was experimentally determined from CO2 sorption curves. Its value increased with increasing CO2 solubility and temperature, which was consistent with the free volume theory.

Application of composite construction and demolition debris in heavy metals removal from industrial wastewater

The utilization of construction and demolition debris in industrial wastewater treatment by sorption of Co2+ and Ni2+ ions was investigated. Selected waste composites are cost-effective and locally available, still their sorption characteristics and application are not sufficiently investigated. The samples of concrete, facade, ceramic materials, and asphalt were characterized in terms of mineral and surface composition, radioactivity, and stability at different pH values, as well as pH values of suspension and filtrate and electrical conductivity of the filtrate. The sorption capacities were determined in batch experimental conditions in one- and multi-component solutions. Characterization showed different crystal structures and mineralogical compositions of components. The results of gamma spectrometry confirmed the radiological safety of samples. Based on stability testing results, waste materials are suitable for further utilization and do not pose any risk to the environment. The overall sorption results suggested that cement-based materials, in addition to high affinity for the tested ions, represent a sorbent that binds contaminants firmly enough, reduces their mobility and bioavailability, and are suitable for removing Co2+ and Ni2+ ions from wastewaters.

Microscopic insight into the shaping of MOFs and its impact on CO2 capture performance.

The traditional synthesis method produces microcrystalline powdered MOFs, which prevents direct implementation in real-world applications which demand strict control of shape, morphology and physical properties. Therefore, shaping of MOFs via the use of binders is of paramount interest for their practical use in gas adsorption/separation, catalysis, sensors, etc. However, so far, the binders have been mostly selected by trial-and-error without anticipating the adhesion between the MOF and binder components to ensure the processability of homogeneous and mechanically stable shaped MOFs and the impact of the shaping on the intrinsic properties of the MOFs has been overlooked. Herein, we deliver a first systematic multiscale computational exploration of MOF/binder composites by selecting CALF-20, a prototypical MOF for real application in the field of CO2 capture, and a series of binders that cover a rather broad spectrum of properties in terms of rigidity/flexibility, porosity, and chemical functionality. The adhesion between the two components and hence the effectiveness of the shaping as well as the impact of the overall porosity of the CALF-20/binder on the CO2/N2 selectivity, CO2 sorption capacity and kinetics was analyzed. Shaping of CALF-20 by carboxymethyl cellulose was predicted to enable a fair compromise between excellent adhesion between the two components, whilst maintaining high CO2/N2 selectivity, large CO2 uptake and CO2 transport as fast as in the CALF-20. This multiscale computational tool paves the way towards the selection of an appropriate binder to achieve an optimum shaping of a given MOF in terms of processability whilst maintaining its high level of performance.

Enhanced CO2 sorption properties in a polarizable [WO2F4]2--pillared physisorbent under direct air capture conditions.

We report the CO2 capture properties of an ultramicroporous physisorbent [Ni(WO2F4)(pyrazine)2]n, WO2F4-1-Ni, which crystallizes in I4/mcm (a = 9.91785(6) Å, c = 15.71516(9) Å) and its structure is solved using laboratory X-ray powder diffraction. The WO2F4 anion is acentric with polarizable WO bonds offering unique potential properties within a porous structure. Despite isostructural compounds being previously reported, the effect of this distorted anion on CO2 capture properties has not been studied. In this context, at a 400 ppm partial pressure of CO2 (applicable for direct air capture), this primitive cubic (pcu) network captures 0.934 mmolCO2 gsorbent-1 under dry conditions and 0.685 mmolCO2 gsorbent-1 at 75%RH, the highest capacity for a physisorbent reported to date.

Unveiling the different physicochemical properties of M-doped β-NaFeO2 (where M = Ni or Cu) materials evaluated as CO2 sorbents: a combined experimental and theoretical analysis

A nickel-doped sodium ferrite presented oxygen vacancies and the highest CO2 sorption, while AIMD simulations evidenced high Na mobility.

Suitability of biochar as supplementary cementitious material (SCM) or filler: waste revalorization, a critical review

For decades, researchers on materials science have highlighted the potential of biochar as a CO2 adsorption medium and the possibility of its incorporation into other materials to reduce the overall carbon footprint. This present study is a critical review of a selection of articles about biochar potential as a material on the construction industry. Biochar is a promising material in order to mitigate GHG emissions when added to cementitious materials, reducing its carbon footprint through a dual effect: CO2 sorption and replacement of cement or aggregates. Literature evidenced that replacement ratios of around 2-8 of cement wt% improved or leveled with conventional cementitious composites. However, some recent studies have shown that the incorporation of biochar up to &gt;10% replacement ratios have the potential to improve the composites. Based on this premise, the present review emphasizes on the durability and long-term properties of biochar cementitious composites by providing up-to-date discussions of the studies on the matter and the future perspectives of the research in order to develop more eco-efficient concretes or mortars.

The role of biomass elemental composition and ion-exchange in metal sorption by algae

The use of macroalgae, microalgae and cyanobacteria for metal sorption has been widely reported. Still, there are no studies allowing a direct comparison of the performance of these biomasses, especially while evaluating metal competition. The simultaneous sorption of Co2+, Cu2+, Ni2+ and Zn2+ present in a multi-elemental solution by six macroalgae, two microalgae and three cyanobacteria was evaluated. Brown macroalgae were shown to be the most promising biosorbent, with Undaria pinnatifida having a total metal sorption capacity of 0.6 mmol g−1. Overall, macroalgae performed better than microalgae, followed by cyanobacteria. Carboxyl groups were identified as being the main functional groups involved in metal sorption, and all biomass samples were found to be selective to Cu2+. This was linked not only to its higher complexation constant value with relevant functional groups when compared to the remaining metals, but also the Irving-Williams series. The release of K+ and Ca2+ to the aqueous solution during the metal sorption was followed. The obtained results suggest they are readily exchanged with metals in the solution, indicating the occurrence of an ion-exchange mechanism in metal sorption by most biomass. Red macroalgae are an exception to the reported trends, suggesting that their metal sorption mechanism may differ from the other biomass types.

Multistep Transformation from Amorphous and Nonporous Fullerenols to Highly Crystalline Microporous Materials.

The structural and morphological properties of fullerenols upon exposure to heat treatment have yet to be understood. Herein, the temperature-driven structural and morphological evolutions of fullerenols C60 (OH) and C70 (OH) were investigated. In situ spectroscopic techniques, such as variable-temperature X-ray diffraction and coupled thermogravimetric Fourier-transform infrared analysis, were used to elucidate the structural transformation mechanism of fullerenols. Both fullerenols underwent four-step structural transformation upon heating and cooling, including amorphous-to-crystalline transition, thermal expansion, structural compression, and new crystal formation. Compared to the initially nonporous amorphous fullerenol, the crystalline product exhibited microporosity with a surface area of 114 m2 g-1 and demonstrated CO2 sorption capability. These findings show the potential of fullerene derivatives as adsorbents.

Open-Celled Foams from Polyethersulfone/Poly(Ethylene Glycol) Blends Using Foam Extrusion.

Polyethersulfone (PESU), as both a pristine polymer and a component of a blend, can be used to obtain highly porous foams through batch foaming. However, batch foaming is limited to a small scale and is a slow process. In our study, we used foam extrusion due to its capacity for large-scale continuous production and deployed carbon dioxide (CO2) and water as physical foaming agents. PESU is a high-temperature thermoplastic polymer that requires processing temperatures of at least 320 °C. To lower the processing temperature and obtain foams with higher porosity, we produced PESU/poly(ethylene glycol) (PEG) blends using material penetration. In this way, without the use of organic solvents or a compounding extruder, a partially miscible PESU/PEG blend was prepared. The thermal and rheological properties of homopolymers and blends were characterized and the CO2 sorption performance of selected blends was evaluated. By using these blends, we were able to significantly reduce the processing temperature required for the extrusion foaming process by approximately 100 °C without changing the duration of processing. This is a significant advancement that makes this process more energy-efficient and sustainable. Additionally, the effects of blend composition, nozzle temperature and foaming agent type were investigated, and we found that higher concentrations of PEG, lower nozzle temperatures, and a combination of CO2 and water as the foaming agent delivered high porosity. The optimum blend process settings provided foams with a porosity of approximately 51% and an average foam cell diameter of 5 µm, which is the lowest yet reported for extruded polymer foams according to the literature.

Sorption and oxidation of Co(II) at the surface of birnessite: Impacts of aqueous Mn(II)

The sorption of aqueous Mn(II) (1 mM) and Co(II) (50 and 200 μM) onto hexagonal birnessite (0.1 g L−1) was studied under anoxic conditions at pH 6.5 and 7.5 in binary and ternary experiments using batch kinetic experiments and XRD, ATR-FTIR, and Co K-edge EXAFS analyses. In the binary systems, sorption of Co(II) was accompanied by partial oxidation to Co(III) yielding a mixture of corner-sharing Co(II) and edge-sharing Co(III) complexes at both pH values, while Mn(II)-birnessite interaction resulted in coordination of Mn(II/III) at layer vacancy sites at pH 6.5, and led to reductive transformation of birnessite into feitknechtite at pH 7.5. In the ternary systems, strong mutual interferences between Co(II) and Mn(II) co-sorbates reduced the rate and extent of sorption relative to the binary experiments. The introduction of Mn(II)aq into the high-Co systems (200 μM) halted the slow sorption of Co(II) that was attributed to the incorporation of Co(III) into layer vacancies, while Co(II)aq prevented Mn(II)-driven transformation of birnessite into feitknechtite at pH 7.5. In the low-Co system (50 μM), reductive transformation of birnessite by Mn(II)aq at pH 7.5 produced Co(II)-substituted feitknechtite, a conversion that was accompanied by reduction of sorbed Co(III) to Co(II) which was partially released to solution. The strong effects of co-sorption are attributed to the similarity in sorption mechanisms of Co(II) and Mn(II), which both sorb as a mixture of di- and trivalent species. The results of this work demonstrate that aqueous Mn(II) may significantly affect the reactivity of phyllomanganate sorbents towards dissolved Co(II), and therefore impact the speciation and solubility of this trace metal in anoxic and suboxic geochemical environments.

Linear and Non Linear Recognition for the Sorption of 60Co and 152+154Eu Radionuclides onto Bio CuO Nanocomposite

A novel nanocomposite was prepared by hybridizing polyacrylic acid/maleic acid with nano copper oxide (PAACMA/CuO) for the sorption of 60Co (II) and 152+154Eu (III) radionuclides from an aqueous solution. Nano-CuO was biochemically produced by hydrolysing its salt in the presence of the Aspergillus terreus fungus. The PAACMA/CuO nanocomposite was characterized using a variety of analytical techniques. The optimum sorption conditions (pH 4.5 for 60Co and pH 3.53 for 152+154Eu, 24 h of equilibrium time at 20 oC) were applied. The kinetic mechanism of the sorption reaction was controlled by pseudo second order based on residual charts, coefficient of determination (R2), and corrected Akaike information Criterion (AICc). The sorption reaction mechanism was controlled by Langmuir model for linear regression using the coefficient of determination and the Dubinin-Radushkevich D-R model for the AICc and residual plots error functions. The reaction mechanism throughout non-linear regression was controlled by the D-R model due to the coefficient of determination, AICc, and residual charts. The PAACMA/CuO nanocomposite had a mono-layer adsorption capacity of 11.04 mg g− 1 for Co (II) and 21.54 mg g− 1 for Eu (III). According to desorption studies, Co (II) and Eu (III) could be recovered by 0.1 mol L− 1 EDTA with efficiencies 55.46% and 95.044%, respectively. According to thermodynamic studies, the sorption of Co (II) and Eu (III) on the prepared composite was endothermic and spontaneous.

Graphene as a promising additive to hierarchically porous carbon monoliths for enhanced H2 and CO2 sorption

This study aimed to examine a synthesis of hierarchically porous carbon monoliths (HPCM) doped with graphene oxide (GO) for H2 and CO2 sorption applications. The synthesis procedure combining the sol-gel process with soft-templating was tuned by adding different quantities of GO (0.5; 2 and 10 wt% of the total amount of polycondensation mixture), as well as different carbonization temperatures (500 °C, 900 °C) of the composite materials during which the reduction of GO to graphene occurs. The degree of GO reduction to graphene and its incorporation into the HPCM matrix of prepared materials were characterized by Raman, FTIR, SEM, TEM, and elemental analysis. Although incorporation was successful, the higher pyrolysis temperature of 900 °C promotes the reduction of GO to graphene, which enhances the (ultra)microporosity (proven by gas physisorption experiments) of the samples, especially of the one with 10% GO addition. The effectivity of materials towards H2 and CO2 sorption was examined by sorption of H2 (77 K, up 1 bar) and CO2 (273 K, up 1 bar), respectively. Addition of any amount of GO together with the used lower pyrolysis temperature of 500 °C reduced the adsorption capacity of the samples for CO2 (from 2.4 to 1.8 mmol g−1) and H2 (from 5.8 to 3.6 mmol g−1) compared to the original HPCM. On the bright side, a 10% addition of GO in combination with a pyrolysis temperature of 900 °C results in industrially perspective material with an H2 and CO2 adsorption capacity of 9.6 mmol g−1 and 4.6 mmol g−1, respectively.

Amine-doped PEBA membrane for CO2 capture

In recent years, mixed matrix membranes (MMMs) have been used more often in separation processes due to their excellent properties. These membranes combine the advantages of two main components, the polymer continuous and the nanoparticle dispersion phases. Block copolymers such as poly(ether-block-amide, PEBA) seems to be excellent materials for the membranes synthesis. This work aims to provide an overview of membranes made of PEBA doped with two different aminocompounds of various concentrations and their effect for CO2 sorption and separation. Most samples indicated the CO2 sorption improvement compared to the pristine PEBA. It strongly depends on concentration. The most significant changes were observed at MMM doped with 2.5% TEPA or 1% HDA. Samples were tested for the separation of binary CO2/CH4 mixture and that proved the effect on separation efficiency.

Quantification of gas-accessible microporosity in metal-organic framework glasses

Metal-organic framework (MOF) glasses are a new class of glass materials with immense potential for applications ranging from gas separation to optics and solid electrolytes. Due to the inherent difficulty to determine the atomistic structure of amorphous glasses, the intrinsic structural porosity of MOF glasses is only poorly understood. Here, we investigate the porosity features (pore size and pore limiting diameter) of a series of prototypical MOF glass formers from the family of zeolitic imidazolate frameworks (ZIFs) and their corresponding glasses. CO2 sorption at 195 K allows quantifying the microporosity of these materials in their crystalline and glassy states, also providing excess to the micropore volume and the apparent density of the ZIF glasses. Additional hydrocarbon sorption data together with X-ray total scattering experiments prove that the porosity features of the ZIF glasses depend on the types of organic linkers. This allows formulating design principles for a targeted tuning of the intrinsic microporosity of MOF glasses. These principles are counterintuitive and contrary to those established for crystalline MOFs but show similarities to strategies previously developed for porous polymers.

Molecular Dynamics and Nuclear Magnetic Resonance Studies of Supercritical CO2 Sorption in Poly(Methyl Methacrylate).

The study of supercritical carbon dioxide sorption processes is an important and urgent task in the field of "green" chemistry and for the selection of conditions for new polymer material formation. However, at the moment, the research of these processes is very limited, and it is necessary to select the methodology for each polymer material separately. In this paper, the principal possibility to study the powder sorption processes using 13C nuclear magnetic resonance spectroscopy, relaxation-relaxation correlation spectroscopy and molecular dynamic modeling methods will be demonstrated based on the example of polymethylmethacrylate and supercritical carbon dioxide. It was found that in the first nanoseconds and seconds during the sorption process, most of the carbon dioxide, about 75%, is sorbed into polymethylmethacrylate, while on the clock scale the remaining 25% is sorbed. The methodology presented in this paper makes it possible to select optimal conditions for technological processes associated with the production of new polymer materials based on supercritical fluids.

Nuclear magnetic resonance studies of carbon dioxide capture

Carbon dioxide capture is an important greenhouse gas mitigation technology that can help limit climate change. The design of improved capture materials requires a detailed understanding of the mechanisms by which carbon dioxide is bound. Nuclear magnetic resonance (NMR) spectroscopy methods have emerged as a powerful probe of CO2 sorption and diffusion in carbon capture materials. In this article, we first review the practical considerations for carrying out NMR measurements on capture materials dosed with CO2 and we then present three case studies that review our recent work on NMR studies of CO2 binding in metal–organic framework materials. We show that simple 13C NMR experiments are often inadequate to determine CO2 binding modes, but that more advanced experiments such as multidimensional NMR experiments and 17O NMR experiments can lead to more conclusive structural assignments. We further discuss how pulsed field gradient (PFG) NMR can be used to explore diffusion of adsorbed CO2 through the porous framework. Finally, we provide an outlook on the challenges and opportunities for the further development of NMR methodologies that can improve our understanding of carbon capture.

CO2 Capture Improvement in Polyetherimide Membranes: Effect of Ionic Liquid on the Molecular Mobility

The research described here was aimed at the development of polymeric membranes based on polyetherimide (PEI) containing the ionic liquid (IL) 1-butyl-2,3-dimethylimidazolium hexafluorophosphate ([BMMIM]PF6). The preparation of the PEI-based membranes was carried out via casting of solutions with the incorporation of the IL. The prepared membranes were characterized by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) for thermal and free volume properties. CO2 sorption and permeation properties were measured to evaluate the CO2 capture performance of the membranes. The fractional free volume (FFV) of the membranes was around 15%. The incorporation of IL increased the CO2 sorption capacity, promoting an increase of 330% in the solubility coefficient (KD) and resulted in a decrease of 96% in CO2 permeability when compared to the control membrane. The presence of IL in the PEI matrix significantly altered the structural and transport characteristics of the analyzed membranes, being efficient for CO2 capture, as they showed a high CO2 solubility and a decrease in CO2 permeation.