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Journal articleShankar R, Sachs M, Francas L, et al., 2019, , Journal of Materials Chemistry A, Vol: 7, Pages: 23931-23940, ISSN: 2050-7488
Porous 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, , Industrial & Engineering Chemistry Research, Vol: 58, Pages: 18336-18344, ISSN: 0888-5885
Carbon 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 articleCrake A, Christoforidis K, Gregg A, et al., 2019, , Small, Vol: 15, Pages: 1-12, ISSN: 1613-6810
CO2 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, , Applied Catalysis B: Environmental, Vol: 242, Pages: 369-378, ISSN: 0926-3373
In 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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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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Journal articleStafford JP, Patapas A, Uzo N, et al., 2018, , AIChE Journal, Vol: 64, Pages: 3246-3276, ISSN: 0001-1541
Graphene, the twodimensional form of carbon, has received a great deal of attention across academia and industry due to its extraordinary electrical, mechanical, thermal, chemical, and optical properties. In view of the potential impact of graphene on numerous and diverse applications in electronics, novel materials, energy, transport, and healthcare, largescale graphene production is a challenge that must be addressed. In the past decade, top–down production has demonstrated high potential for scaleup. This review features the recent progress made in top–down production methods that have been proposed for the manufacturing of graphenebased products. Fabrication methods such as liquidphase mechanical, chemical and electrochemical exfoliation of graphite are outlined, with a particular focus on nonoxidizing routes for graphene production. Analysis of exfoliation mechanisms, solvent considerations, key advantages and issues, and important production characteristics including production rate and yield, where applicable, are outlined. Future challenges and opportunities in graphene production are also highlighted.
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Journal articleChristoforidis KC, Syrgiannis Z, La Parola V, et al., 2018, , NANO ENERGY, Vol: 50, Pages: 468-478, ISSN: 2211-2855
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Journal articleHerdes C, Petit C, Mejia A, et al., 2018, , Energy and Fuels, Vol: 32, Pages: 5750-5762, ISSN: 0887-0624
An experimental, theoretical, and molecular simulation consolidated framework for the efficient characterization of the adsorption and fluid-phase behavior of multi-component hydrocarbon mixtures within tight shale rocks is presented. Fluid molecules are described by means of a top-down coarse-grained model where simple Mie intermolecular potentials are parametrized by means of the statistical associating fluid theory. A four-component (methane, pentane, decane, naphthalene) mixture is used as a surrogate model with a composition representative of commonly encountered shale oils. Shales are modeled as a hierarchical network of nanoporous slits in contact with a mesoporous region. The rock model is informed by the characterization of four distinct and representative shale core samples through nitrogen adsorption, thermogravimetric analysis, and contact angle measurements. Experimental results suggest the consideration of two types of pore surfaces: a carbonaceous wall representing the kerogen regions of a shale rock, and an oxygenated wall representing the clay-based porosity. Molecular dynamics simulations are performed at constant overall compositions at a temperature of 398.15 K (257 °F) and explore pressures from 6.9 MPa up to 69 MPa (1000–10000 psi). Simulations reveal that it is the organic nanopores of 1 and 2 nm that preferentially adsorb the heavier components, while the oxygenated counterparts show little selectivity between the adsorbed and free fluid. Upon desorption, this trend is intensified, as the fluid phase in equilibrium with a carbon nanopore becomes increasing leaner (richer in light components) and almost completely depleted of the heavy components which remain trapped in the nanopores and surfaces of the mesopores. Oxygenated pores do not contribute to this unusual behavior, even for the very tight pores considered. The results presented elucidate the relative importance of considering both the pore size distribution and the heterogen
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Journal articleBui M, Adjiman CS, Bardow A, et al., 2018, , Energy and Environmental Science, Vol: 11, Pages: 1062-1176, ISSN: 1754-5692
Carbon capture and storage (CCS) is broadly recognised as having the potential to play a key role in meeting climate change targets, delivering low carbon heat and power, decarbonising industry and, more recently, its ability to facilitate the net removal of CO2 from the atmosphere. However, despite this broad consensus and its technical maturity, CCS has not yet been deployed on a scale commensurate with the ambitions articulated a decade ago. Thus, in this paper we review the current state-of-the-art of CO2 capture, transport, utilisation and storage from a multi-scale perspective, moving from the global to molecular scales. In light of the COP21 commitments to limit warming to less than 2 °C, we extend the remit of this study to include the key negative emissions technologies (NETs) of bioenergy with CCS (BECCS), and direct air capture (DAC). Cognisant of the non-technical barriers to deploying CCS, we reflect on recent experience from the UK's CCS commercialisation programme and consider the commercial and political barriers to the large-scale deployment of CCS. In all areas, we focus on identifying and clearly articulating the key research challenges that could usefully be addressed in the coming decade.
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Journal articleMarchesini S, McGilvery CM, Bailey J, et al., 2017, , ACS Nano, Vol: 11, Pages: 10003-10011, ISSN: 1936-0851
Production of biocompatible and stable porous materials, e.g., boron nitride, exhibiting tunable and enhanced porosity is a prerequisite if they are to be employed to address challenges such as drug delivery, molecular separations, or catalysis. However, there is currently very limited understanding of the formation mechanisms of porous boron nitride and the parameters controlling its porosity, which ultimately prevents exploiting the material’s full potential. Herein, we produce boron nitride with high and tunable surface area and micro/mesoporosity via a facile template-free method using multiple readily available N-containing precursors with different thermal decomposition patterns. The gases are gradually released, creating hierarchical pores, high surface areas (>1900 m2/g), and micropore volumes. We use 3D tomography techniques to reconstruct the pore structure, allowing direct visualization of the mesopore network. Additional imaging and analytical tools are employed to characterize the materials from the micro- down to the nanoscale. The CO2 uptake of the materials rivals or surpasses those of commercial benchmarks or other boron nitride materials reported to date (up to 4 times higher), even after pelletizing. Overall, the approach provides a scalable route to porous boron nitride production as well as fundamental insights into the material’s formation, which can be used to design a variety of boron nitride structures.
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Journal articleCrake A, Christoforidis KC, Kafizas A, et al., 2017, , Applied Catalysis B: Environmental, Vol: 210, Pages: 131-140, ISSN: 0926-3373
TiO2 nanosheets and metal-organic framework (NH2-UiO-66) were effectively coupled via an insitu growth strategy to form bifunctional materials for the combined capture and photocatalytic reduction of CO2 under UV–vis light irradiation. This was done to take advantage of the high CO2 adsorption capacity of the MOF and the photocatalytic properties of pre-formed TiO2 nanosheets in a single material. The prepared materials were thoroughly characterized using a variety of techniques. They were subsequently tested for CO2 adsorption and CO2 photocatalytic reduction using a heterogeneous gas/solid set-up to imitate both CO2 capture and fixation in a single process. The adopted synthesis process allowed the development of a tight interaction between TiO2 and NH2-UiO-66 forming a heterojunction, while maintaining both the high CO2 uptake and porosity of NH2-UiO-66. The nanocomposites were proven durable and significantly more efficient in reducing CO2 to CO than their single components. Photocatalytic activity was greatly affected by the nanocomposites composition with the optimum TiO2 content doubling the CO evolution rate compared with the pure TiO2. The improved photoactivity was assigned to the enhanced abundance of long lived charge carriers, as revealed by transient absorption spectroscopy (TAS). This most likely occurred due to the effective charge transfer via interface. A possible mechanism is discussed on the basis of the combined catalytic, spectroscopic and CO2 adsorption results.
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Journal articleLeeson D, Mac Dowell N, Shah N, et al., 2017, , International Journal of Greenhouse Gas Control, Vol: 61, Pages: 71-84, ISSN: 1750-5836
In order to meet the IPCC recommendation for an 80% cut in CO2 emissions by 2050, industries will be required to drastically reduce their emissions. To meet these targets, technologies such as carbon capture and storage (CCS) must be part of the economic set of decarbonisation options for industry. A systematic review of the literature has been carried out on four of the largest industrial sectors (the iron and steel industry, the cement industry, the petroleum refining industry and the pulp and paper industry) as well as selected high-purity sources of CO2 from other industries to assess the applicability of different CCS technologies. Costing data have been gathered, and for the cement, iron and steel and refining industries, these data are used in a model to project costs per tonne of CO2 avoided over the time period extending from first deployment until 2050. A sensitivity analysis was carried out on the model to assess which variables had the greatest impact on the overall cost of wide-scale CCS deployment for future better targeting of cost reduction measures. The factors found to have the greatest overall impact were the initial cost of CCS at the start of deployment and the start date at which large scale deployment is started, whilst a slower initial deployment rate after the start date also leads to significantly increased costs.
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Journal articleWoodward RT, Jobbe-Duval A, Marchesini S, et al., 2017, , Polymer, Vol: 115, Pages: 146-153, ISSN: 0032-3861
Hierarchically porous carbon foams were produced by carbonization of hypercrosslinked polymerized high internal phase water-in-styrene/divinylbenzene emulsions (HIPEs). The hypercrosslinking of these poly(ST-co-DVB)HIPEs was achieved using a dimethoxymethane external crosslinker to ‘knit’ together aromatic groups within the polymers using FriedelCrafts alkylation. By varying the amount of divinylbenzene (DVB) in the HIPE templates and subsequent polymers, the BET surface area and micropore volume of the hypercrosslinked analogues can be varied systematically, allowing for the production of carbon foams, or ‘carboHIPEs’, with varied surface areas, micropore volumes and pore-size distributions. The carboHIPEs retain the emulsion-templated macropores of the original polyHIPE, display excellent electrical conductivities and have surface areas of up to 417 m2/g, all the while eliminating the need for inorganic templates. The use of emulsion templates allows for pourable, mouldable precursors to designable carbonaceous materials.
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Journal articleMarchesini S, Regoutz A, Payne D, et al., 2017, , Microporous and Mesoporous Materials, Vol: 243, Pages: 154-163, ISSN: 1873-3093
Boron nitride (BN) has applications in a number of areas: it can be used as lubricant, as insulating thermoconductive filler or UV-light emitter. BN can also capture large amounts of hydrocarbons and gaseous molecules, provided that it exhibits a porous structure. This porous structure also enables its application as a drug-delivery nanocarrier. Little if anything is known on controlling the porosity of BN, even though it has tremendous implications in terms of adsorption performance and drug delivery properties. To address this aspect, we provide for the first time an in-depth investigation of the effects of the synthesis conditions on the formation of porous BN. The material was also tested for CO2 capture. We found that the intermediate preparation is of paramount importance and can in fact be used to tune the porosity of BN. Owing to a combination of spectroscopic and thermal analyses, we attributed this phenomenon to the variation of the thermal decomposition pattern of the intermediates. The most microporous BN produced was able to capture CO2 while not retaining N2. Overall, this study opens the route for the design of well-controlled porous BN structures to be applied as adsorbents and drug-delivery carriers.
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Journal articleSmit B, Graham R, Styring P, et al., 2016, , Faraday Discussions, Vol: 192, Pages: 303-335, ISSN: 1359-6640
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Journal articleHong J, Chen C, Bedoya FE, et al., 2016, , Catalysis Science & Technology, Vol: 6, Pages: 5042-5051, ISSN: 2044-4753
Heterogeneous photocatalysis plays a key role in the implementation of novel sustainable technologies, e.g. CO2 conversion into fuel, H2 production from water or organics degradation. The progress of photocatalysis relies on the development of tuneable photocatalysts and particularly the ability to build nanocomposites exhibiting synergistic properties with reduced electron–hole recombination rates. We report for the first time the in situ synthesis of nanocomposites of carbon nitride nanosheets (CNNSs) and metal–organic frameworks (MOFs) for application as photocatalysts. This approach leads to the ‘nano-scale mixing’ of the components, thereby enabling a greater performance compared to other types of 2D materials/MOF composites typically obtained via physical mixing. The objective is to take advantage of the complementary features of the materials while forming a heterojunction. The structural, chemical, photophysical and electrochemical properties of the nanocomposites are characterized and compared to those of the parent materials and their physical mixture. The nanocomposites retain the high specific surface area and strong visible light absorbance of MIL-100(Fe). The intimate contact between the CNNSs and the MOF particles is found to promote the electron–hole separation significantly due to the formation of a heterojunction. Hence, more efficient photocatalytic dye degradation is achieved over the composites than the physical mixture.
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Journal articleCalvez CL, Zouboulaki M, Petit C, et al., 2016, , RSC Adv., Vol: 6, Pages: 17314-17317
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Journal articleWoodward RT, Fam DWH, Anthony DB, et al., 2016, , Carbon, Vol: 101, Pages: 253-260, ISSN: 0008-6223
Carbon foams were produced from a macroporous poly(divinylbenzene) (poly(DVB) precursor, synthesized by polymerizing the continuous but minority phase of water-in-oil high internal phase emulsions (HIPEs) stabilized by molecular and/or particulate emulsifiers. Both permeable and non-permeable hierarchically porous carbon foams, or ‘carboHIPEs’, were prepared by carbonization of the resulting macroporous polymers at 800 °C. The carbon yields were as high as 26 wt.% of the original polymer. CarboHIPEs retain the pore structure of the macroporous polymer precursor, but with surface areas of up to 505 m2/g and excellent electrical conductivities of 81 S/m. Contrary to some previous reports, the method does not require further modification, such as sulfonation or additional crosslinking of the polyHIPE prior to carbonization, due to the inherently crosslinked structure of poly(DVB). The use of a pourable, aqueous emulsion-template enables simple moulding, minimises waste and avoids the strong acid treatments used to remove many conventional solid-templates. The retention of the macroporous structure is coupled with the introduction of micropores during carbonization, producing hierarchically porous carboHIPEs, suitable for a wide range of applications as sorbents and electrodes.
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Journal articlePetit C, Bhatnagar S, Park A-HA, 2013, , Journal of Colloid and Interface Science, Vol: 407, Pages: 102-108, ISSN: 0021-9797
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Journal articlePetit C, Bandosz TJ, 2012, , Dalton Transactions, Vol: 41, Pages: 4027-4035, ISSN: 1477-9226
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