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Journal articleLow M-YA, Barton LV, Pini R, et al., 2023,
Analytical review of the current state of knowledge of adsorption materials and processes for direct air capture
, Chemical Engineering Research and Design, Vol: 189, Pages: 745-767, ISSN: 0263-8762Significant research interest has been directed towards the deployment of direct air capture (DAC) as a net-negative CO2 emissions technology to help limit global temperature rise to below 2 °C. The scope of this review is to outline the advancement of adsorption-based DAC technologies, as well as to highlight the still-existing data gaps, for both materials’ development and process design in the period 2016 – 2021. On the material side, we highlight the available and missing data on adsorbent properties in relation to what is needed for process modelling and design. We cover material densities, textural properties, thermal properties, adsorption isotherms (i.e. CO2, N2, O2, H2O), adsorption kinetics, and adsorbent stability towards humidity, oxidation, and cycling. On the process side, we provide a detailed look at key process studies conducted in the same time frame by considering the trade-offs to be expected in the design of the adsorption-based DAC process. We focus on process configuration and contactor design, desorption processes, and the need for systematic reporting of key performance indicators to allow for accurate comparisons and benchmarking. Throughout the review, we identify the lack of synergy between material and process development which must be addressed to advance the field of DAC by adsorption.
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Journal articleXiong Y, Tian T, L'Hermitte A, et al., 2022,
Using silver exchange to achieve high uptake and selectivity for propylene/ propane separation in zeolite Y
, Chemical Engineering Journal, Vol: 446, ISSN: 1385-8947Adsorptive separation of propylene and propane, an important step of polypropylene production, is more energy-efficient than distillation. However, the challenge lies in the design of an adsorbent which exhibits both high selectivity and uptake. Herein, we hypothesise that enhancing the propylene affinity of the adsorption sites while keeping a suitable pore size can address this challenge. To do so, we performed silver exchange of a commercial zeolite Y, thereby making the adsorbent design easily scalable. We characterised the adsorbent using analytical, spectroscopic and imaging tools, tested its equilibrium and dynamic sorption properties using volumetric and gravimetric techniques and compared its performance to those of state-of-the-art adsorbents as well as other silver-functionalised adsorbents. The silver-exchanged zeolite Y (Ag-Y) exhibited one of the best selectivity vs uptake performances reported so far. Ag-Y also displayed fast adsorption kinetics and reversible propylene sorption, making it a promising new benchmark for propylene/propane separation. Synchrotron-based pair distribution function analyses identified the silver cations’ location which confirmed that the silver sites are easily accessible to the adsorbates. This aspect can, in part, explain the propylene/propane separation performance observed. The overall design strategy proposed here to enhance sorption site affinity and maintain pore size could be extended to other adsorbents and support the deployment of adsorption technology for propylene/propane separation.
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Journal articleSchukraft GEM, Itskou I, Woodward RT, et al., 2022,
Evaluation of CO2 and H2O adsorption on a porous polymer using DFT and in situ DRIFT spectroscopy
, The Journal of Physical Chemistry B, Vol: 126, Pages: 8048-8057, ISSN: 1520-6106Numerous hyper-cross-linked polymers (HCPs) have been developed as CO2 adsorbents and photocatalysts. Yet, little is known of the CO2 and H2O adsorption mechanisms on amorphous porous polymers. Gaining a better understanding of these mechanisms and determining the adsorption sites are key to the rational design of improved adsorbents and photocatalysts. Herein, we present a unique approach that combines density functional theory (DFT), in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), and multivariate spectral analysis to investigate CO2 and H2O adsorption sites on a triazine–biphenyl HCP. We found that CO2 and H2O adsorb on the same HCP sites albeit with different adsorption strengths. The primary amines of the triazines were identified as favoring strong CO2 binding interactions. Given the potential use of HCPs for CO2 photoreduction, we also investigated CO2 and H2O adsorption under transient light irradiation. Under irradiation, we observed partial CO2 and H2O desorption and a redistribution of interactions between the H2O and CO2 molecules that remain adsorbed at HCP adsorption sites.
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Journal articleTian T, Xu J, Xiong Y, et al., 2022,
Cu-functionalised porous boron nitride derived from a metal–organic framework
, Journal of Materials Chemistry A, Vol: 10, Pages: 20580-20592, ISSN: 2050-7488Porous boron nitride (BN) displays promising properties for interfacial and bulk processes, e.g. molecular separation and storage, or (photo)catalysis. To maximise porous BN's potential in such applications, tuning and controlling its chemical and structural features is key. Functionalisation of porous BN with metal nanoparticle represents one possible route, albeit a hardly explored one. Metal–organic frameworks (MOFs) have been widely used as precursors to synthesise metal functionalised porous carbon-based materials, yet MOF-derived metal functionalised inorganic porous materials remain unexplored. Here, we hypothesise that MOFs could also serve as a platform to produce metal-functionalised porous BN. We have used a Cu-containing MOF, i.e. Cu/ZIF-8, as a precursor and successfully obtained porous BN functionalised with Cu nanoparticles (i.e. Cu/BN). While we have shown control of the Cu content, we have not yet demonstrated it for the nanoparticle size. The functionalisation has led to improved light harvesting and enhanced electron–hole separation, which have had a direct positive impact on the CO2 photoreduction activity (production formation rate 1.5 times higher than pristine BN and 12.5 times higher than g-C3N4). In addition, we have found that the metal in the MOF precursor impacts porous BN's purity. Unlike Cu/ZIF-8, a Co-containing ZIF-8 precursor led to porous C-BN (i.e. BN with a large amount of C in the structure). Overall, given the diversity of metals in MOFs, one could envision our approach as a method to produce a library of different metal functionalised porous BN samples.
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Journal articleTaddei M, Petit C, 2022,
Engineering metal-organic frameworks for adsorption-based gas separations: from process to atomic scale (vol 6, pg 841, 2021)
, MOLECULAR SYSTEMS DESIGN & ENGINEERING, Vol: 7, Pages: 1162-1162, ISSN: 2058-9689 -
Journal articleAzzan H, Rajagopalan AK, L'Hermitte A, et al., 2022,
Simultaneous estimation of gas adsorption equilibria and kinetics of individual shaped adsorbents
, Chemistry of Materials, Vol: 34, Pages: 6671-6686, ISSN: 0897-4756Shaped adsorbents (e.g., pellets, extrudates) are typically employed in several gas separation and sensing applications. The performance of these adsorbents is dictated by two key factors, their adsorption equilibrium capacity and kinetics. Often, adsorption equilibrium and textural properties are reported for materials. Adsorption kinetics are seldom presented due to the challenges associated with measuring them. The overarching goal of this work is to develop an approach to characterize the adsorption properties of individual shaped adsorbents with less than 100 mg of material. To this aim, we have developed an experimental dynamic sorption setup and complemented it with mathematical models, to describe the mass transport in the system. We embed these models into a derivative-free optimizer to predict model parameters for adsorption equilibrium and kinetics. We evaluate and independently validate the performance of our approach on three adsorbents that exhibit differences in their chemistry, synthesis, formulation, and textural properties. Further, we test the robustness of our mathematical framework using a digital twin. We show that the framework can rapidly (i.e., in a few hours) and quantitatively characterize adsorption properties at a milligram scale, making it suitable for the screening of novel porous materials.
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Journal articleXiao F-S, Azevedo D, Nicholas CP, et al., 2022,
Preface for Special Issue on Engineered Methodologies for CO<sub>2</sub> Utilization
, INDUSTRIAL & ENGINEERING CHEMISTRY RESEARCH, Vol: 61, Pages: 10295-10297, ISSN: 0888-5885- Author Web Link
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- Citations: 2
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Journal articleHwang J, Azzan H, Pini R, et al., 2022,
H2, N2, CO2, and CH4 unary adsorption isotherm measurements at low and high pressures on zeolitic imidazolate framework ZIF-8
, Journal of Chemical & Engineering Data, Vol: 67, Pages: 1674-1686, ISSN: 0021-9568Excess adsorption of CO2, CH4, N2, and H2 on ZIF-8 was measured gravimetrically in the pressure range ranging from vacuum to 30 MPa at 298.15, 313.15, 333.15, 353.15, and 394.15 K using a magnetic suspension balance. The textural properties of the adsorbent material─i.e., skeletal density, surface area, pore volume, and pore-size distribution─were estimated by helium gravimetry and N2 (77 K) physisorption. The adsorption isotherms were fitted with the Sips isotherm model and the virial equation, and the values of isosteric heat of adsorption and Henry constants for the gases were determined using the latter.
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Journal articleOsterrieth JWM, Rampersad J, Madden D, et al., 2022,
How reproducible are surface areas calculated from the BET equation?
, Advanced Materials, Vol: 34, ISSN: 0935-9648Porosity and surface area analysis play a prominent role in modern materials science. At the heart of this sits the Brunauer–Emmett–Teller (BET) theory, which has been a remarkably successful contribution to the field of materials science. The BET method was developed in the 1930s for open surfaces but is now the most widely used metric for the estimation of surface areas of micro- and mesoporous materials. Despite its widespread use, the calculation of BET surface areas causes a spread in reported areas, resulting in reproducibility problems in both academia and industry. To prove this, for this analysis, 18 already-measured raw adsorption isotherms were provided to sixty-one labs, who were asked to calculate the corresponding BET areas. This round-robin exercise resulted in a wide range of values. Here, the reproducibility of BET area determination from identical isotherms is demonstrated to be a largely ignored issue, raising critical concerns over the reliability of reported BET areas. To solve this major issue, a new computational approach to accurately and systematically determine the BET area of nanoporous materials is developed. The software, called “BET surface identification” (BETSI), expands on the well-known Rouquerol criteria and makes an unambiguous BET area assignment possible.
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Journal articleShankar RB, Mistry EDR, Lubert-Perquel D, et al., 2022,
A response surface model to predict and experimentally tune the chemical, magnetic and optoelectronic properties of oxygen-doped boron nitride
, ChemPhysChem: a European journal of chemical physics and physical chemistry, Vol: 23, ISSN: 1439-4235Porous boron nitride (BN), a combination of hexagonal, turbostratic and amorphous BN, has emerged as a new platform photocatalyst. Yet, this material lacks photoactivity under visible light. Theoretical studies predict that tuning the oxygen content in oxygen-doped BN (BNO) could lower the band gap. This is yet to be verified experimentally. We present herein a systematic experimental route to simultaneously tune BNO's chemical, magnetic and optoelectronic properties using a multivariate synthesis parameter space. We report deep visible range band gaps (1.50–2.90 eV) and tuning of the oxygen (2–14 at.%) and specific paramagnetic OB3 contents (7–294 a.u. g−1). Through designing a response surface via a design of experiments (DOE) process, we have identified synthesis parameters influencing BNO's chemical, magnetic and optoelectronic properties. We also present model prediction equations relating these properties to the synthesis parameter space that we have validated experimentally. This methodology can help tailor and optimise BN materials for heterogeneous photocatalysis.
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Journal articleSchukraft GEM, Moss B, Kafizas AG, et al., 2022,
Effect of band bending in photoactive MOF-based heterojunctions.
, ACS Applied Materials and Interfaces, Vol: 14, Pages: 19342-19352, ISSN: 1944-8244Semiconductor/metal-organic framework (MOF) heterojunctions have demonstrated promising performance for the photoconversion of CO2 into value-added chemicals. To further improve performance, we must understand better the factors which govern charge transfer across the heterojunction interface. However, the effects of interfacial electric fields, which can drive or hinder electron flow, are not commonly investigated in MOF-based heterojunctions. In this study, we highlight the importance of interfacial band bending using two carbon nitride/MOF heterojunctions with either Co-ZIF-L or Ti-MIL-125-NH2. Direct measurement of the electronic structures using X-ray photoelectron spectroscopy (XPS), work function, valence band, and band gap measurements led to the construction of a simple band model at the heterojunction interface. This model, based on the heterojunction components and band bending, enabled us to rationalize the photocatalytic enhancements and losses observed in MOF-based heterojunctions. Using the insight gained from a promising band bending diagram, we developed a Type II carbon nitride/MOF heterojunction with a 2-fold enhanced CO2 photoreduction activity compared to the physical mixture.
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Journal articleHeiba HF, Bullen JC, Kafizas A, et al., 2022,
The determination of oxidation rates and quantum yields during the photocatalytic oxidation of As(III) over TiO2
, Journal of Photochemistry and Photobiology A: Chemistry, Vol: 424, Pages: 113628-113628, ISSN: 1010-6030The determination of reaction rates for the photocatalytic oxidation (PCO) of arsenite (As(III)) using TiO2 under UV radiation is challenging due to the numerous experimental processes. This includes chemical processes running simultaneously with PCO (e.g. adsorption of arsenic species, direct UV photolysis of As(III)) and the analytical approach used (e.g. whether As(III) or As(V) are measured and used in the calculation of the PCO rate). The various experimental approaches used to date have led to oxidation rates and rate constants which vary by orders of magnitude and contradicting information on rate laws. Here we present the results of a critical examination of possible controls affecting the experimental determination of PCO rates. First, we demonstrate that the choice of analytical technique is not critical, provided that the rate constants are calculated based on the depletion of As(III) after correction of the directly adsorbed As(III). Second, we show the correction of the directly adsorbed As(III) at each time interval is best done by running two parallel experiments (one under UV and the other in dark) instead of running sequential experiment (i.e. running the experiment in the dark then turning on the UV lamp). These findings are supported by XPS analysis of the oxidation state of TiO2-sorbed As. Third, we demonstrate that photolysis by the light source itself, as well as the chemical composition of the solution (i.e. the effect of HEPES and the ionic strength), can significantly increase As(III) oxidation rates and need to be corrected. Finally, to determine the quantum yield of As(III) oxidation, we measured the photon absorption by the TiO2 photocatalyst. Our results showed that the quantum yield (Ø) for this oxidation reaction was low, and in the region of 0.1 to 0.2 %.
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Journal articleRajagopalan AK, Petit C, 2021,
Material Screening for Gas Sensing Using an Electronic Nose: Gas Sorption Thermodynamic and Kinetic Considerations
, ACS SENSORS, Vol: 6, Pages: 3808-3821, ISSN: 2379-3694- Author Web Link
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- Citations: 3
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Journal articleButler EL, Reid B, Luckham PF, et al., 2021,
Interparticle Forces of a Native and Encapsulated Metal-Organic Framework and Their Effects on Colloidal Dispersion
, ACS APPLIED MATERIALS & INTERFACES, Vol: 13, Pages: 45898-45906, ISSN: 1944-8244- Author Web Link
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- Citations: 2
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Journal articleRampal N, Ajenifuja A, Tao A, et al., 2021,
The development of a comprehensive toolbox based on multi-level, high-throughput screening of MOFs for CO/N2 separations
, Chemical Science, Vol: 12, Pages: 12068-12081, ISSN: 2041-6520The separation of CO/N2 mixtures is a challenging problem in the petrochemical sector due to the very similar physical properties of these two molecules, such as size, molecular weight and boiling point. To solve this and other challenging gas separations, one requires a holistic approach. The complexity of a screening exercise for adsorption-based separations arises from the multitude of existing porous materials, including metal–organic frameworks. Besides, the multivariate nature of the performance criteria that needs to be considered when designing an optimal adsorbent and a separation process – i.e. an optimal material requires fulfillment of several criteria simultaneously – makes the screening challenging. To address this, we have developed a multi-scale approach combining high-throughput molecular simulation screening, data mining and advanced visualization, as well as process system modelling, backed up by experimental validation. We have applied our recent advances in the engineering of porous materials' morphology to develop advanced monolithic structures. These conformed, shaped monoliths can be used readily in industrial applications, bringing a valuable strategy for the development of advanced materials. This toolbox is flexible enough to be applied to multiple adsorption-based gas separation applications.
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Journal articleTaddei M, Petit C, 2021,
Engineering metal-organic frameworks for adsorption-based gas separations: from process to atomic scale
, Molecular Systems Design & Engineering, Vol: 6, Pages: 841-875, ISSN: 2058-9689Metal-organic frameworks (MOFs) are the object of intense research targeting their deployment as adsorbents for a wide range of gas separations, such as CO2 capture, biogas upgrading, air separation and small hydrocarbons separation. The scope of this review is to provide chemists, material scientists and engineers with an overview of the state-of-the-art and of the main challenges in the field of adsorption-based gas separations using MOFs. To do so, we first discuss current gas separation challenges for which adsorption could play a role. The following three sections of the paper describe process-level considerations in the design, selection and deployment of MOFs as sorbents and subsequently focus on material-level considerations. Both the process and the material aspects cover experimental and computational work. Going from the process scale to the atomic scale, we aim to highlight the links and synergies between the two and identify the current barriers that hamper the development of adsorption-based gas separations using MOFs as sorbents. Throughout the article, we also provide fundamental and technical information related to MOFs design, synthesis, characterisation and sorption testing.
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Journal articleXiong Y, Woodward RT, Danaci D, et al., 2021,
Understanding trade-offs in adsorption capacity, selectivity and kinetics for propylene/propane separation using composites of activated carbon and hypercrosslinked polymer
, CHEMICAL ENGINEERING JOURNAL, Vol: 426, ISSN: 1385-8947 -
Journal articleDanaci D, Bui M, Petit C, et al., 2021,
En route to zerio emissions for power and industry with amine-based post-combustion capture
, Environmental Science and Technology (Washington), Vol: 55, Pages: 10619-10632, ISSN: 0013-936XAs more countries commit to a net-zero GHG emission target, we need a whole energy and industrial system approach to decarbonization rather than focus on individual emitters. This paper presents a techno-economic analysis of monoethanolamine-based post-combustion capture to explore opportunities over a diverse range of power and industrial applications. The following ranges were investigated: feed gas flow rate between 1–1000 kg ·s–1, gas CO2 concentrations of 2–42%mol, capture rates of 70–99%, and interest rates of 2–20%. The economies of scale are evident when the flue gas flow rate is <20 kg ·s–1 and gas concentration is below 20%mol CO2. In most cases, increasing the capture rate from 90 to 95% has a negligible impact on capture cost, thereby reducing CO2 emissions at virtually no additional cost. The majority of the investigated space has an operating cost fraction above 50%. In these instances, reducing the cost of capital (i.e., interest rate) has a minor impact on the capture cost. Instead, it would be more beneficial to reduce steam requirements. We also provide a surrogate model which can evaluate capture cost from inputs of the gas flow rate, CO2 composition, capture rate, interest rate, steam cost, and electricity cost.
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Journal articleTian T, Hou J, Ansari H, et al., 2021,
Mechanically stable structured porous boron nitride with high volumetric adsorption capacity
, JOURNAL OF MATERIALS CHEMISTRY A, Vol: 9, Pages: 13366-13373, ISSN: 2050-7488 -
Journal articleSchukraft GEM, Woodward RT, Kumar S, et al., 2021,
Hypercrosslinked polymers as a photocatalytic platform for visible-light-driven CO2 photoreduction using H2O
, ChemSusChem: chemistry and sustainability, energy and materials, Vol: 14, Pages: 1720-1727, ISSN: 1864-5631The design of robust, high‐performance photocatalysts is key for the success of solar fuel production by CO2 conversion. In this study, hypercrosslinked polymer (HCP) photocatalysts have been developed for the selective reduction of CO2 to CO, combining excellent CO2 sorption capacities, good general stabilities, and low production costs. HCPs are active photocatalysts in the visible light range, significantly outperforming the benchmark material, TiO2 P25, using only sacrificial H2O. It is hypothesized that superior H2O adsorption capacities facilitate access to photoactive sites, improving photocatalytic conversion rates when compared to sacrificial H2. These polymers are an intriguing set of organic photocatalysts, displaying no long‐range order or extended π‐conjugation. The as‐synthesized networks are the sole photocatalytic component, requiring no added cocatalyst doping or photosensitizer, representing a highly versatile and exciting platform for solar‐energy conversion.
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