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Journal articleTian T, Hou J, Ansari H, et al., 2021,
Mechanically Stable Monolithic Porous Boron Nitride with High Volumetric Adsorption Capacity
<jats:p>The development of adsorbents into structured and robust forms remains a challenge for emerging porous materials. In the context of porous boron nitride (BN), studies point to a tradeoff between mechanical stability, porosity, density, and adsorption kinetics. Approaches towards shaping and densification of porous BN have been mostly empirical since a detailed understanding of its formation mechanism, and how it impacts mechanical strength and porosity, is lacking. Here, we demonstrate a synthesis method that can directly produce a mechanically robust monolithic porous BN (mpBN) from an easily scalable polymeric precursor, which results in the highest volumetric surface area among porous BN samples to date. mpBN exhibits a high bulk density, 50% higher than BN powders and over ten times higher than the structured BN aerogels, while maintaining fast sorption kinetics. mpBN presents good mechanical strength, with hardness of 66.4 ± 4.5 MPa, <jats:italic>i.e. </jats:italic>one to two orders of magnitude higher than structured aerogels. We propose a mpBN formation mechanism which reveals that the crosslinked intermediates are responsible for the high mechanical strength of the final material. Our approach produces a form of BN that addresses the limitations of other adsorbents, and facilitate their application in gas separation and storage technologies. </jats:p><jats:p />
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Journal articleStafford J, Uzo N, Farooq U, et al., 2021,
Real-time monitoring and hydrodynamic scaling of shear exfoliated graphene
, 2D Materials, Vol: 8, Pages: 1-17, ISSN: 2053-1583Shear-assisted liquid exfoliation is a primary candidate for producing defect-free two-dimensional (2D) materials. A range of approaches that delaminate nanosheets from layered precursors in solution have emerged in recent years. Diverse hydrodynamic conditions exist across these methods, and combined with low-throughput, high-cost characterization techniques, strongly contribute to the wide variability in performance and material quality. Nanosheet concentration and production rate are usually correlated against operating parameters unique to each production method, making it difficult to compare, optimize and predict scale-up performance. Here, we reveal the shear exfoliation mechanism from precursor to 2D material and extract the derived hydrodynamic parameters and scaling relationship that are key to nanomaterial output and common to all shear exfoliation processes. Our investigations use conditions created from two different hydrodynamic instabilities—Taylor vortices and interfacial waves—and combine materials characterization, fluid dynamics experiments and numerical simulations. Using graphene as the prototypical 2D material, we find that scaling of concentration of few-layer nanosheets depends on local strain rate distribution, relationship to the critical exfoliation criterion, and precursor residence time. We report a transmission-reflectance method to measure concentration profiles in real-time, using low-cost optoelectronics and without the need to remove the layered precursor material from the dispersion. We show that our high-throughput, in situ approach has broad uses by controlling the number of atomic layers on-the-fly, rapidly optimizing green solvent design to maximize yield, and viewing live production rates. Combining the findings on the hydrodynamics of exfoliation with this monitoring technique, we unlock targeted process intensification, quality control, batch traceability and individually customizable 2D materials on-demand.
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Journal articleDanaci D, Webley PA, Petit C, 2021,
Guidelines for techno-economic analysis of adsorption processes
, Frontiers in Chemical Engineering, Vol: 2, ISSN: 2673-2718Techno-economic analyses (TEAs) of CO2 capture technologies have risen in popularity, due to growing interest in meeting CO2 emissions reduction targets. Adsorption processes are one of the technologies proposed for CO2 capture, and although difficult, standardisation of TEAs for adsorption should be attempted. The reason is that TEAs are often referred to as input data to other forms of modelling, to guide policy, and act as summaries for those unfamiliar with adsorption processes. Herein, we discuss the aspects that should be considered when conducting TEAs for CO2 adsorption processes, we present the implications of choices made at the TEA stage and offer guidance on best practice. Overall, our aim is to make TEAs of adsorption processes more widely accessible to the adsorption community, and also more generally to communities engaged in the evaluation of CCS technologies.
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Journal articleFarooq U, Stafford J, Petit C, et al., 2020,
Numerical simulations of a falling film on the inner surface of a rotating cylinder
, Physical Review E, Vol: 102, Pages: 043106 – 1-043106 – 13, ISSN: 2470-0045A flow in which a thin film falls due to gravity on the inner surface of a vertical, rotating cylinder is investigated. This is performed using two-dimensional (2D) and 3D direct numerical simulations, with a volume-of-fluid approach to treat the interface. The problem is parameterized by the Reynolds, Froude, Weber, and Ekman numbers. The variation of the Ekman number (Ek), defined to be proportional to the rotational speed of the cylinder, has a strong effect on the flow characteristics. Simulations are conducted over a wide range of Ek values (0≤Ek≤484) in order to provide detailed insight into how this parameter influences the flow. Our results indicate that increasing Ek, which leads to a rise in the magnitude of centrifugal forces, produces a stabilizing effect, suppressing wave formation. Key flow features, such as the transition from a 2D to a more complex 3D wave regime, are influenced significantly by this stabilization and are investigated in detail. Furthermore, the imposed rotation results in distinct flow characteristics such as the development of angled waves, which arise due to the combination of gravitationally and centrifugally driven motion in the axial and azimuthal directions, respectively. We also use a weighted residuals integral boundary layer method to determine a boundary in the space of Reynolds and Ekman numbers that represents a threshold beyond which waves have recirculation regions.
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Journal articleYe Z, Schukraft GEM, L'Hermitte A, et al., 2020,
Mechanism and stability of an Fe-based 2D MOF during the photoelectro-Fenton treatment of organic micropollutants under UVA and visible light irradiation
, WATER RESEARCH, Vol: 184, ISSN: 0043-1354- Author Web Link
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- Citations: 59
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Journal articleSchukraft GM, Woodward R, Kumar S, et al., 2020,
Hypercrosslinked Polymers as a Photocatalytic Platform for Visible-Light-Driven CO2 Photoreduction Using H2O
<jats:p>The design of robust, high-performance photocatalysts is key for the success of solar fuel production <jats:italic>via</jats:italic> CO<jats:sub>2</jats:sub>conversion. Herein, we present hypercrosslinked polymer (HCP) photocatalysts for the selective reduction of CO<jats:sub>2</jats:sub> to CO, combining excellent CO<jats:sub>2</jats:sub> sorption capacities, good general stabilities, and low production costs. HCPs are active photocatalysts in the visible light range, significantly out-performing the benchmark material, TiO<jats:sub>2</jats:sub> P25, using only sacrificial H<jats:sub>2</jats:sub>O. We hypothesise that superior H<jats:sub>2</jats:sub>O adsorption capacities led to concentration at photoactive sites, improving photocatalytic conversion rates when compared to sacrificial H<jats:sub>2</jats:sub>. These polymers are an intriguing set of organic photocatalysts, displaying no long-range order or extended pi-conjugation. The as-synthesised networks are the sole photocatalytic component, requiring no co-catalyst doping or photosensitiser, representing a highly versatile and exciting platform for solar-energy conversion.</jats:p>
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Journal articleButler EL, Petit C, Livingston AG, 2020,
Poly(piperazine trimesamide) thin film nanocomposite membrane formation based on MIL-101: Filler aggregation and interfacial polymerization dynamics
, JOURNAL OF MEMBRANE SCIENCE, Vol: 596, ISSN: 0376-7388- Author Web Link
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- Citations: 23
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Journal articleEvans A, Cummings M, Decarolis D, et al., 2020,
Optimisation of Cu+ impregnation of MOF-74 to improve CO/N2 and CO/CO2 separations
, RSC Advances: an international journal to further the chemical sciences, Vol: 10, Pages: 5152-5162, ISSN: 2046-2069Carbon monoxide (CO) purification from syngas impurities is a highly energy and cost intensive process. Adsorption separation using metal–organic frameworks (MOFs) is being explored as an alternative technology for CO/nitrogen (N2) and CO/carbon dioxide (CO2) separation. Currently, MOFs' uptake and selectivity levels do not justify displacement of the current commercially available technologies. Herein, we have impregnated a leading MOF candidate for CO purification, i.e. M-MOF-74 (M = Co or Ni), with Cu+ sites. Cu+ allows strong π-complexation from the 3d electrons with CO, potentially enhancing the separation performance. We have optimised the Cu loading procedure and confirmed the presence of the Cu+ sites using X-ray absorption fine structure analysis (XAFS). In situ XAFS and diffuse reflectance infrared Fourier Transform spectroscopy analyses have demonstrated Cu+–CO binding. The dynamic breakthrough measurements showed an improvement in CO/N2 and CO/CO2 separations upon Cu impregnation. This is because Cu sites do not block the MOF metal sites but rather increase the number of sites available for interactions with CO, and decrease the surface area/porosity available for adsorption of the lighter component.
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Journal articleDanaci D, Bui M, Mac Dowell N, et al., 2020,
Exploring the limits of adsorption-based CO2 capture using MOFs with PVSA – from molecular design to process economics
, Molecular Systems Design and Engineering, Vol: 5, Pages: 212-231, ISSN: 2058-9689Metal-organic frameworks (MOFs) have taken the materials science world by storm, with potentials of near infinite possibilities and the panacea for adsorption-based carbon capture. Yet, no pilot-scale (or larger-scale) study exists on MOFs for carbon capture. Beyond material scalability issues, this clear gap between the scientific and engineering literature relates to the absence of suitable and accessible assessment of MOFs in an adsorption process. Here, we have developed a simple adsorbent screening tool with process economics to evaluate adsorbents for post-combustion capture, while also considering factors relevant to industry. Specifically, we have assessed the 25 adsorbents (22 MOFs, 2 zeolites, 1 activated carbon) against performance constraints – i.e. CO2 purity and recovery – and cost. We have considered four different CO2 capture scenarios to represent a range of CO2 inlet concentrations. The cost is compared to that of amine-based solvents for which a corresponding model was developed. Using the model developed, we have conceptually assessed the materials properties and process parameters influencing the purity, recovery and cost in order to design the ‘best’ adsorbent. We have also set-up a tool for readers to screen their own adsorbent. In this contribution, we show that minimal N2 adsorption and moderate enthalpies of adsorption are key in obtaining good process performance and reducing cost. This stands in contrast to the popular approaches of maximizing CO2 capacity or surface area. Of the 22 MOFs evaluated, UTSA-16 shows the best performance and lowest cost for post-combustion capture, having performance in-line with the benchmark, zeolite 13X. Mg-MOF-74 performs poorly. The cost of using the adsorbents remains overall higher than that of an amine-based absorption process. Ultimately, this study provides specific directions for material scientists to design adsorbents and assess their performance at the process scale. This
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Book chapterSchukraft G, Petit C, 2020,
Green Synthesis and Engineering Applications of Metal-Organic Frameworks
, SUSTAINABLE NANOSCALE ENGINEERING: FROM MATERIALS DESIGN TO CHEMICAL PROCESSING, Editors: Szekely, Livingston, Publisher: ELSEVIER SCIENCE BV, Pages: 139-162, ISBN: 978-0-12-814681-1- Author Web Link
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- Citations: 8
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Journal articleThompson JF, Bellerjeau C, Marinick G, et al., 2019,
Intrinsic Thermal Desorption in a 3D Printed Multifunctional Composite CO2 Sorbent with Embedded Heating Capability
, ACS APPLIED MATERIALS & INTERFACES, Vol: 11, Pages: 43337-43343, ISSN: 1944-8244 -
Journal articleShankar R, Sachs M, Francas L, et al., 2019,
Porous boron nitride for combined CO2 capture and photoreduction
, Journal of Materials Chemistry A, Vol: 7, Pages: 23931-23940, ISSN: 2050-7488Porous and amorphous materials are typically not employed for photocatalytic purposes, like CO2 photoreduction, as their high number of defects can lead to low charge mobility and favour bulk electron–hole recombination. Yet, with a disordered nature can come porosity, which in turn promotes catalyst/reactant interactions and fast charge transfer to reactants. Here, we demonstrate that moving from h-BN, a well-known crystalline insulator, to amorphous BN, we create a semiconductor, which is able to photoreduce CO2 in the gas/solid phase, under both UV-vis and pure visible light and ambient conditions, without the need for cocatalysts. The material selectively produces CO and maintains its photocatalytic stability over several catalytic cycles. The performance of this un-optimized material is on par with that of TiO2, the benchmark in the field. For the first time, we map out experimentally the band edges of porous BN on the absolute energy scale vs. vacuum to provide fundamental insight into the reaction mechanism. Owing to the chemical and structural tunability of porous BN, these findings highlight the potential of porous BN-based structures for photocatalysis particularly solar fuel production.
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Journal articleEvans AD, Cummings MS, Luebke R, et al., 2019,
Screening metal–organic frameworks for dynamic CO/N2 separation using complementary adsorption measurement techniques
, Industrial & Engineering Chemistry Research, Vol: 58, Pages: 18336-18344, ISSN: 0888-5885Carbon monoxide (CO)/nitrogen (N2) separation is a particularly challenging separation, yet it is the one with great industrial relevance for its use in petrochemical synthesis. Although an expensive cryogenic step can be used to perform such separation, it remains ineffective in purifying CO from syngas streams with a significant N2 content. Taking advantage of the lower energy requirement of adsorption processes, we have explored the use of metal–organic frameworks (MOFs) as adsorbents for this difficult separation. We have screened a range of MOF candidates for CO/N2 separation covering a range of chemical and textural features, using the flux response technology to evaluate their dynamic performance for throughput testing alongside equilibrium uptake measurements. We have identified Ni-MOF-74 and Co-MOF-74 as the most promising candidates because of their high metal density and strong metal–CO interactions. We have investigated further the effect of N2 impurity concentrations upon CO/N2 separation using breakthrough adsorption testing and cyclic testing (up to 20 cycles). Overall, using multiple adsorption measurement techniques, this study demonstrates the CO/N2 dynamic separation performance of M-MOF-74 and its ability to be applied for an industrially relevant separation.
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Journal articleTaddei M, Schukraft GM, Warwick MEA, et al., 2019,
Band gap modulation in zirconium-based metal–organic frameworks by defect engineering
, Journal of Materials Chemistry A, Vol: 7, Pages: 23781-23786, ISSN: 2050-7488<p>A simple defect engineering approach to systematically tune the band gap of the prototypical zirconium-based metal–organic framework UiO-66 is reported. Defect engineered materials display enhanced photocatalytic activity.</p>
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Journal articleZhao D, Thallapally PK, Petit C, et al., 2019,
Advanced Porous Materials: Design, Synthesis, and Applications in Sustainability
, ACS SUSTAINABLE CHEMISTRY & ENGINEERING, Vol: 7, Pages: 7997-7998, ISSN: 2168-0485 -
Journal articleMarchesini S, Wang X, Petit C, 2019,
Porous boron nitride materials: Influence of structure, chemistry and stability on the adsorption of organics
, Frontiers in Chemistry, Vol: 7, ISSN: 2296-2646Porous boron nitride (BN) is structurally analogous to activated carbon. This materialis gaining increasing attention for its potential in a range of adsorption and chemicalseparation applications, with a number of recent proof-of-concept studies on the removalof organics from water. Today though, the properties of porous BN—i.e., surface area,pore network, chemistry—that dictate adsorption of specific organics remain vastlyunknown. Yet, they will need to be optimized to realize the full potential of the materialin the envisioned applications. Here, a selection of porous BN materials with varied porestructures and chemistries were studied for the adsorption of different organic molecules,either directly, through vapor sorption analyses or as part of a water/organic mixture in theliquid phase. These separations are relevant to the industrial and environmental sectorsand are envisioned to take advantage of the hydrophobic character of the BN sheets.The materials were tested and regenerated and their physical and chemical featureswere characterized before and after testing. This study allowed identifying the adsorptionmechanisms, assessing the performance of porous BN compared to benchmarks in thefield and outlining ways to improve the adsorption performance further.
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Journal articleCrake A, Christoforidis K, Gregg A, et al., 2019,
The effect of materials architecture in TiO2/MOF composites on CO2 photoreduction and charge transfer
, Small, Vol: 15, Pages: 1-12, ISSN: 1613-6810CO2 photoreduction to C1/C1+ energized molecules is a key reaction of solar fuel technologies. Building heterojunctions can enhance photocatalysts performance, by facilitating charge transfer between two heterojunction phases. The material parameters that control this charge transfer remain unclear. Here, it is hypothesized that governing factors for CO2 photoreduction in gas phase are: i) a large porosity to accumulate CO2 molecules close to catalytic sites and ii) a high number of “points of contact” between the heterojunction components to enhance charge transfer. The former requirement can be met by using porous materials; the latter requirement by controlling the morphology of the heterojunction components. Hence, composites of titanium oxide or titanate and metal–organic framework (MOF), a highly porous material, are built. TiO2 or titanate nanofibers are synthesized and MOF particles are grown on the fibers. All composites produce CO under UV–vis light, using H2 as reducing agent. They are more active than their component materials, e.g., ≈9 times more active than titanate. The controlled composites morphology is confirmed and transient absorption spectroscopy highlights charge transfer between the composite components. It is demonstrated that electrons transfer from TiO2 into the MOF, and holes from the MOF into TiO2, as the MOF induces band bending in TiO2.
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Journal articleCrake A, Christoforidis K, Godin R, et al., 2019,
Titanium dioxide/carbon nitride nanosheet nanocomposites for gas phase CO2 photoreduction under UV-visible irradiation
, Applied Catalysis B: Environmental, Vol: 242, Pages: 369-378, ISSN: 0926-3373In the field of photocatalysis and particularly that of CO2 photoreduction, the formulation of nanocomposites provids avenues to design a material platform with a unique set of structural, optoelectronic and chemical features thereby addressing shortcomings of single-phase materials and allowing synergistic effects. In this work, inorganic/organic composite photocatalysts for CO2 reduction comprised of titanium dioxide (TiO2) and carbon nitride nanosheets (CNNS) were synthesized using a hydrothermal in-situ growth method. Specifically, pre-formed CNNS were used to synthesize TiO2/CNNS heterostructures with control over the TiO2 facet formation. This synthesis approach improved the catalytic properties by increasing CO2 adsorption capacity and facilitating charge transfer. The materials were characterised by various spectroscopic, imaging, and analytical techniques to investigate their structural (from nano- to macroscale), chemical, and optical properties. TiO2 nanoparticles were efficiently grown on the CNNS. The CO2 adsorption capacity of the composites was measured, and they were tested for CO2 photoreduction under UV-Vis illumination with hydrogen as the reducing agent in a heterogeneous gas-solid system to combine CO2 capture and conversion into a single-step process. Catalytic tests were performed without adding any precious metal co-catalyst. The composites exhibited enhanced CO2 adsorption capacity and photocatalytic CO2 conversion compared to their constituent materials (> ten-fold increase) and outperformed the TiO2 P25 benchmark material. The TiO2/CNNS composite with more {001} TiO2 facets was the most catalytically active. Further investigations using transient absorption spectroscopy (TAS) revealed the control of facet formation improved interfacial transfer at the TiO2/CNNS junction. A photocatalytic mechanism was proposed based on the spectroscopic analyses as well as the CO2 adsorption, and CO2 conversion results.
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Journal articleShankar R, Marchesini S, Petit C, 2019,
Enhanced hydrolytic stability of porous boron nitride via the control of crystallinity, porosity, and chemical composition
, Journal of Physical Chemistry C, Vol: 123, Pages: 4282-4290, ISSN: 1932-7447Porous boron nitride is gaining significant attention for applications in molecular separations, photocatalysis, and drug delivery. All these areas call for a high degree of stability (or controlled stability) over a range of chemical environments, particularly under humid conditions. The hydrolytic stability of the various forms of boron nitride, including porous boron nitride, has been sparingly addressed in the literature. Here, we map the physical–chemical properties of the material to its hydrolytic stability for a range of conditions. Using analytical, imaging, and spectroscopic techniques, we identify the links between the hydrolytic instability of porous boron nitride and its limited crystallinity, high porosity, as well as the presence of oxygen atoms. To address this instability issue, we demonstrate that subjecting the material to a thermal treatment leads to the formation of crystalline domains of h-BN exhibiting a hydrophobic character. The heat-treated sample displays an enhanced hydrolytic stability, while maintaining a high porosity. This work provides an effective and simple approach to producing stable porous boron nitride structures and will progress the implementation of the material in applications involving interfacial phenomena.
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Conference paperDanaci D, Bui M, Dowell NM, et al., 2019,
An adsorbent screening tool with process economics for carbon capture by PVSA
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