Understanding the relationship between synthetic conditions, porosity and CO2 uptake capacity of turbostratic carbons

As of 2021, the atmospheric concentration of CO2 is 412 ppm and continues to rise. It is well established that these concentrations are resulting in rising temperatures, an increased incidence of extreme weather, and thus unspeakably disastrous consequences for all life. It follows then that CO2 capture and removal technologies must be rapidly developed to ensure the longevity of human society. One area of research is CO2 capture via physisorption onto porous materials and in particular on the easily synthesised turbostratic carbon. This application requires fine control over porosity (surface area, pore volume, pore size) according to conditions of sorption, and it therefore follows that both the ability to precisely measure pore sizes, as well as a definitive knowledge of the relationship between CO2 uptake capacity and pore size is needed. This thesis attempts to address all three of these issues. In terms of routes to activated carbons, this work investigates two principal synthetic methods. Firstly in chapter 4 - developing on the author's previous work - a simplification of the production of turbostratic carbons from unwrapped used cigarette filters (UCFs) was attempted by activation of whole used cigarette butts (UCBs) with KOH. The simplified method resulted in much less porosity as compared to the previous work (maximal A_{BET} of 4300 compared with 1960 m^2 g^{-1} and the samples derived by this method possess a hierarchical - as opposed to narrow, microporous - pore size distribution (PSD). Nevertheless, these new materials may perform well for CO2 capture in Pressure Swing Adsorption (PSA) applications. Pyrolysis of UCB in the absence of a porogen created minimal porosity, perhaps as a result of contaminants present from the ucb wrapping paper. The other approach to activation used (chapter 5) is a set of methods which have been collectively coined as impregnation routes, i.e. methods which attempt to achieve close contact between precursor and the activating species whilst maintaining a homogeneous distribution of the latter throughout the former. Impregnation was achieved through (i) the hydrothermal carbonisation of sawdust (SD) with KOH prior to pyrolysis, as well as (ii) direct activation of a polymeric sodium salt, sodium carboxymethyl cellulose (NC). In both cases, PSDs achieved were generally narrow and situated principally in the small micropore region, making the products potential candidates for low pressure CO2 capture. Both sets of materials also showed unexpected features, SD-derived samples having extremely low bulk density, and those obtained from NC exhibiting reduction in porosity at surprisingly low porogen:precursor ratios. The latter of these suggests pore formation effects outside of the caustic nature of porogenesis with Na compounds, and is a potential route for further investigation of activation mechanisms. For materials derived through the synthetic routes mentioned above, reliable, accurate, and efficient isothermal porosimetry proved difficult due to poor diffusion of N2 into the materials' pores. As such, alternative porosimetric techniques were investigated in chapter 6. It was found that dual isotherm porosimetry using O2 and H2 isotherms measured at -196 C results not only in more expedient equilibration of the sorptive-sorbent system, but allows the measurement of sub-angstrom level developments in porosity associated with changes in quantity of porogen used. These subtle developments in porosity are not measurable through traditional porosimetry using N2. As for improving the understanding of the relationship between CO2 uptake as a function of pressure and pore size, chapter 7 details the development and deployment of the pyPUC which, using experimental PSDs and gravimetric gas uptake isotherms applies a brute force approach to determine the correlation between porosity within some pore width range and CO2 uptake at a given pressure. This is performed for all user-defined pore width ranges and pressures, and correlation coefficients are compared to give optimum pore size ranges, Ω at each pressure. When applied to CO2 uptake on turbostratic carbons, it was confirmed that Ω broadens with increasing pressure. In addition, the relationship between Ω and pressure-dependent CO2 uptake was calculated to a more granular level of detail than has been previously reported. Furthermore, following on from findings in chapter 6 it was found that these relationships at low pressures are best described using dual isotherm O2/H2 porosimetry

Understanding the relationship between synthetic conditions, porosity and CO2 uptake capacity of turbostratic carbons

As of 2021, the atmospheric concentration of CO2 is 412 ppm and continues to rise. It is well established that these concentrations are resulting in rising temperatures, an increased incidence of extreme weather, and thus unspeakably disastrous consequences for all life. It follows then that CO2 capture and removal technologies must be rapidly developed to ensure the longevity of human society. One area of research is CO2 capture via physisorption onto porous materials and in particular on the easily synthesised turbostratic carbon. This application requires fine control over porosity (surface area, pore volume, pore size) according to conditions of sorption, and it therefore follows that both the ability to precisely measure pore sizes, as well as a definitive knowledge of the relationship between CO2 uptake capacity and pore size is needed. This thesis attempts to address all three of these issues. In terms of routes to activated carbons, this work investigates two principal synthetic methods. Firstly in chapter 4 - developing on the author's previous work - a simplification of the production of turbostratic carbons from unwrapped used cigarette filters (UCFs) was attempted by activation of whole used cigarette butts (UCBs) with KOH. The simplified method resulted in much less porosity as compared to the previous work (maximal A_{BET} of 4300 compared with 1960 m^2 g^{-1} and the samples derived by this method possess a hierarchical - as opposed to narrow, microporous - pore size distribution (PSD). Nevertheless, these new materials may perform well for CO2 capture in Pressure Swing Adsorption (PSA) applications. Pyrolysis of UCB in the absence of a porogen created minimal porosity, perhaps as a result of contaminants present from the ucb wrapping paper. The other approach to activation used (chapter 5) is a set of methods which have been collectively coined as impregnation routes, i.e. methods which attempt to achieve close contact between precursor and the activating species whilst maintaining a homogeneous distribution of the latter throughout the former. Impregnation was achieved through (i) the hydrothermal carbonisation of sawdust (SD) with KOH prior to pyrolysis, as well as (ii) direct activation of a polymeric sodium salt, sodium carboxymethyl cellulose (NC). In both cases, PSDs achieved were generally narrow and situated principally in the small micropore region, making the products potential candidates for low pressure CO2 capture. Both sets of materials also showed unexpected features, SD-derived samples having extremely low bulk density, and those obtained from NC exhibiting reduction in porosity at surprisingly low porogen:precursor ratios. The latter of these suggests pore formation effects outside of the caustic nature of porogenesis with Na compounds, and is a potential route for further investigation of activation mechanisms. For materials derived through the synthetic routes mentioned above, reliable, accurate, and efficient isothermal porosimetry proved difficult due to poor diffusion of N2 into the materials' pores. As such, alternative porosimetric techniques were investigated in chapter 6. It was found that dual isotherm porosimetry using O2 and H2 isotherms measured at -196 C results not only in more expedient equilibration of the sorptive-sorbent system, but allows the measurement of sub-angstrom level developments in porosity associated with changes in quantity of porogen used. These subtle developments in porosity are not measurable through traditional porosimetry using N2. As for improving the understanding of the relationship between CO2 uptake as a function of pressure and pore size, chapter 7 details the development and deployment of the pyPUC which, using experimental PSDs and gravimetric gas uptake isotherms applies a brute force approach to determine the correlation between porosity within some pore width range and CO2 uptake at a given pressure. This is performed for all user-defined pore width ranges and pressures, and correlation coefficients are compared to give optimum pore size ranges, Ω at each pressure. When applied to CO2 uptake on turbostratic carbons, it was confirmed that Ω broadens with increasing pressure. In addition, the relationship between Ω and pressure-dependent CO2 uptake was calculated to a more granular level of detail than has been previously reported. Furthermore, following on from findings in chapter 6 it was found that these relationships at low pressures are best described using dual isotherm O2/H2 porosimetry

Symposium Proceedings—Coyotes in the Southwest: A Compendium of Our Knowledge [complete work, 185 pp.]

This is the complete volume, containing all 40+ articles and presentations. Each article is also hosted here separately under its individual title and authors

Confirmation of pore formation mechanisms in biochars and activated carbons by dual isotherm analysis

In this study biochars and activated carbons were synthesized either directly via the pyrolysis of sodium carboxymethyl cellulose (NC) or via hydrothermal carbonization of sawdust (SD) in an aqueous solution of KOH. The amount of porogen was varied by modulating the degree of sodium carboxymethyl substitution on NC or the amount of KOH mixed in solution with SD. Pore size distributions (PSDs) of these carbons were determined from the dual fit of kernels based on the two-dimensional version of the nonlocal density functional theory (2D-NLDFT) heterogeneous surface models to either N2 and H2 or O2 and H2 isotherms measured at 196 1C. By comparing PSDs of carbons from the same starting material at increasing degrees of activation, we show that those derived using O2 and H2 isotherms not only give more detail of variations in pore size but that the results also fit better with current understandings of porosity development in carbons derived through oxidative activation. This is likely a result of superior diffusion of O2 into ultramicropores at low pressure relative to N2

Ultra-high surface area ionic-liquid-derived carbons that meet both gravimetric and volumetric methane storage targets

The storage of methane, to enable vehicular use, may be achieved in porous solids, but to date, there is no material that meets the gravimetric and volumetric targets (for example those set by the US Department of Energy, DOE) for such use. Here, in an effort to address this challenge, we explore the use of carbonised N-rich crosslinkable imidazolium-based ionic liquid (IL), 1-butyl-3-methylimidazolium tricyanomethanide, ([BMIm][C(CN)3]), as a precursor for porous carbons. On carbonisation, the IL yields carbonaceous matter (IL-C) with the unusual combination of high N content and low O content (i.e., low O/C atomic ratio). Activation of the IL-derived carbonaceous matter (IL-C) with KOH generates activated carbons with a mix of microporosity and mesoporosity, ultra-high surface area of up to ∼4000 m2 g−1, pore volume of up to 3.3 cm3 g−1, and relatively high packing density. The enhanced porosity and comparatively high packing density of the activated carbons is a consequence of the elemental composition of the IL-C precursor. The presence of N, which acts as a porogen, favours generation of carbons with high mesoporosity and high surface area while a low O/C ratio acts in a reverse manner favouring the formation of microporous carbons with high packing density. The overall effect is that the carbons have porosity and packing density that is suited for optimising both the gravimetric and volumetric uptake of methane, which reaches 0.53 g g−1 and 289 cm3 (STP) cm−3, respectively, at 25 °C and 100 bar. The uptake, therefore, surpasses both the gravimetric and volumetric methane storage targets that would enable widespread use for vehicular transport. The IL-derived activated carbons are the first porous materials (carbon or MOF) to meet both gravimetric and volumetric methane storage targets for experimentally determined values

A simple, sustainable route to flexible microporous carbon cloth for energy storage applications

Activated carbon cloth can be synthesised through a simple carbonisation and activation process, and its porosity tuned to either carbon dioxide capture or methane storage

Distribution of subglacial sediments across the Wilkes Subglacial Basin, East Antarctica

Topography, sediment distribution, and heat flux are all key boundary conditions governing the dynamics of the East Antarctic Ice Sheet (EAIS). EAIS stability is most at risk in Wilkes Land across vast expanses of marine-based catchments including the 1400 km × 600 km expanse of the Wilkes Subglacial Basin (WSB) region. Data from a recent regional aerogeophysical survey (Investigating the Cryospheric Evolution of the Central Antarctic Plate (ICECAP)/IceBridge) are combined with two historical surveys (Wilkes basin/Transantarctic Mountains System Exploration-Ice-house Earth: Stability or DYNamism? (WISE-ISODYN) and Wilkes Land Transect (WLK)) to improve our understanding of the vast subglacial sedimentary basins impacting WSB ice flow and geomorphology across geologic time. Analyzing a combination of gravity, magnetic and ice-penetrating radar data, we present the first detailed subglacial sedimentary basin model for the WSB that defines distinct northern and southern subbasin isopachs with average sedimentary basin thicknesses of 1144 m ± 179 m and 1623 m ± 254 m, respectively. Notably, more substantial southern subbasin sedimentary deposition in the WSB interior supports a regional Wilkes Land hypothesis that basin-scale ice flow and associated glacial erosion is dictated by tectonic basement structure and the inherited geomorphology of preglacial fluvial networks. Orbital, temperate/polythermal glacial cycles emanating from adjacent alpine highlands during the early Miocene to late Oligocene likely preserved critical paleoclimatic data in subglacial sedimentary strata. Substantially thinner northern WSB subglacial sedimentary deposits are generally restricted to fault-controlled, channelized basins leading to prominent outlet glacier catchments suggesting a more dynamic EAIS during the Pliocene

Small instream infrastructure: Comparative methods and evidence of environmental and ecological responses

1. Around the globe, instream infrastructures such as dams, weirs, and culverts associated with roads are wide‐spread and continue to be constructed. There is limited documentation of smaller infrastructure because of mixed regulation and laws related to instream construction, as well as difficulty in documentation because of their size and frequency in waterscapes. 2. We reviewed evidence of different methods used to quantify environmental and ecological responses (positive, negative, or neutral) to dams, weirs, and culverts. 3. Most studies (78% of 87) in our review evaluated dams or weirs, and more than half evaluated environmental or ecological responses at more than one of these structures. More than half of the studies used spatial (disturbed–undisturbed in the same or a different catchment) rather than temporal (before–after construction or before–after destruction) comparative methods. Evaluations also tended to focus on ecological variables, most specifically on fish community responses (just over a quarter) to infrastructure. 4. More than half (58%) of the evaluations at dams, weirs, or culverts reported negative environmental or ecological responses. Discrepancies in responses recorded for different infrastructure types could be partially explained by the focus on ecological responses in reviewed studies and related metrics used for evaluations (e.g. biotic groups, richness, and abundance), the imbalance of studies at different infrastructure types, and discrepancies in spatial and temporal scales of evaluations compared to those at which the variables respond to infrastructure. 5. Despite the abundance of road culverts greatly exceeding the number of small or large dams worldwide, they were evaluated in only 22% of studies that we reviewed. Our findings underscore the need for studies to not only better understand local but also cumulative impacts of these smaller infrastructure, as these could be greater than those caused by large infrastructure depending on their location, density, and type, among other factors. Such studies are needed to inform infrastructure planning and watershed management