Highlights from the selected publications by our group.
Molten alkali-borates are a new class of high-temperature liquid CO2 absorbents
that exhibit high capacity, fast kinetics and exceptional stability. We
herein demonstrate the high working capacity and versatility of these materials
through an assessment of their compatibility with system configurations
involving both temperature swing and steam-based partial pressure swing
regeneration, revealing the suitability of these sorbents for use in a
large variety of CO2-emitting industries. The favorable physico-chemical
properties of these materials coupled to an effective and stable working
capacity of 3 mmol g−1 reached within 10-min cycles past 575 °C and using
15 v% CO2 for carbon capture and pure steam for regeneration further substantiates
the high potential of molten borates as alternatives to commercially available
carbon capture sorbents.
As part of CO2 capture strategies, ionic liquid-based CO2 absorbents have
gained attention for their tunable properties to lower the energy costs
for CO2 capture. In this study, a series of borate-based nonamine functionalized
ionic liquids (ILs), incorporated with magnesium acetylacetonate, were
developed and investigated for its CO2 capture capability at moderate temperature
under ambient pressure. Nuclear magnetic resonance and Fourier transform
infrared spectroscopy confirmed the successful incorporation of acetylacetonate
ligands into the fluorinated-lithium borate ionic liquids. Comprehensive
analyses of the physical and thermochemical properties revealed that the
synthesized ILs remain stable below 200 °C, with the borate structure and
acetylacetonate ligands intact. The ILs functionalized with fluorinated
alcohol and magnesium acetylacetonate enhance the CO2 uptake capacity by
55% in comparison with the original lithium borate ILs, suggesting the
enhanced cooperative interactions responsible for improved CO2 capture
performance. The carbon capture mechanism was identified to proceed via
physical absorption, as evidenced by minimal changes in the characterization
results and viscosity after CO2 absorption. The enthalpy of CO2 absorption
(ΔHa) for the synthesized ILs were determined experimentally by using differential
scanning calorimetry to be in the range from −12.4 kJ mol–1 to −18.9 kJ
mol–1, which are much lower than that of conventional amine solutions (e.g.,
MEA: −82 kJ mol–1) and amine-based ILs ((e.g., [Bmim][Ac]: −45.8 kJ mol–1).
These findings suggest that lithium borate-acetylacetonate ILs offer a
promising approach for a CO2 capture system under ambient conditions.
The crystalline structure of Li3NaB4O8, a reaction product resulting from
CO2 absorption by lithium–sodium orthoborate ((Li0.5Na0.5)3BO3), a recently
developed sorbent for high-temperature carbon capture, is herein elucidated.
The compound crystallizes to form a peculiar isolate borate fundamental
building block consisting of six 3-membered borate rings interlinked through
mutual tetrahedral borates to form a nonplanar 6-membered borate ring of
chemical formula B12O24. The identification of this structure allows closing
of the loop regarding the reaction mechanism characterizing CO2 capture
by lithium–sodium orthoborate, sheds light on previously made observations
regarding the evolution of the physicochemical properties of the melt during
carbon capture, and provides valuable information for future studies and
process simulations involving this promising new material for carbon capture.
The structural complexity of alkali borates, evident in the wide range
of distinct structures that typically comprise these compounds, is responsible
for the significant differences observed in the physicochemical properties
of their corresponding melts. In this work, the structural transformations
arising from carbon capture using molten lithium-sodium orthoborate ((Li0.5Na0.5)3BO3), a promising new alkali borate sorbent for carbon capture, are investigated
to better understand the evolution of various physicochemical properties
of the melt by employing in situ high-temperature Fourier transform infrared
spectroscopy in conjunction with density functional theory. The carbon
capture mechanism is shown to proceed via polymerization of small orthoborate
segments (BO33-) into larger structural units, ultimately reaching the metaborate composition
(BO2-) in the form of Li3NaB4O8 and Na3B3O6 upon complete CO2 saturation. The introduction of carbonate ions in the non-polymerized
orthoborate melt via CO2-capture has a substantial diluting effect on the density and viscosity
of the resulting polymerized CO2-saturated melt. Investigations into the melting points associated with
the various compounds involved in the capture mechanism and the discovery
of an apparent second-order phase transition of lithium-sodium pyroborate
(Li2Na2B2O5) past 520 ℃ further provide new and valuable information as
to potential energetically favorable operating conditions for this absorber/regenerator-based
carbon capture technology.
Alkali metal borate molten salts have emerged as efficient high-temperature
liquid CO2 sorbents, advancing carbon reduction for energy-intensive industrial
chemical processes. This work investigated the relationship between the
liquidus behavior and CO2 uptake characteristics of lithium–sodium borates,
MxB1–xO1.5–x (M = Li0.5Na0.5), over a composition range of 0.50 ≤ x ≤ 0.80.
Differential Scanning Calorimetry (DSC) measurements revealed detailed
phase–transition profiles, with liquidus temperatures ranging from 500
to 650 °C. Composition-dependent liquidus behavior governs the CO2 sorption
characteristics during the early sorption stages, transitioning from “solid-to-liquid”
in low-alkali to “liquid-to-liquid” in high-alkali regions. Optimal working
capacities and reaction rates consistently correspond to the liquidus transition
range, minimizing energy demands for preserving molten state in the cyclic
CO2 capture-release operations. These findings establish temperature–composition
operating windows tailored to industrial needs, providing critical liquidus
diagrams and demonstrating their potential as versatile sorbents for high-temperature
CO2 capture.
The oxidation and subsequent dissolution of nickel was investigated in
molten lithium–sodium orthoborate ((Li0.5Na0.5)3BO3) to assess the scaling-up
potential of this modern sorbent for carbon capture through its compatibility
with typical reactor materials used in processes involving molten salts.
Results indicate the oxidation process to be diffusion-limited and to proceed
through the chemical dissolution of oxygen in the melt via reaction with
oxide ions, showcasing the decisive role of the oxide-ion activity on the
oxidation rate. Additionally, an observed loss in carbon capture capacity
over time is explained by the reaction of the sorbent with nickel oxide,
thus encouraging reactor designs in which the ratio between the metal/melt
interfacial area and the bulk volume is minimized. The dissolution of nickel
appears to partially follow an acidic regime, with the upper solubility
limits approaching 1000 ppm. These results mirror previously reported mechanisms
on lithium–sodium carbonate and shed further light on the scale-up potential
of this innovative class of sorbents for carbon capture.
Photocatalytic conversion of CO2 into fuel feed stocks is a promising method
for sustainable fuel production. A highly attractive class of materials,
inorganic-core@metal–organic-framework heterogeneous catalysts, boasts
a significant increase in catalytic performance when compared to the individual
materials. However, due to the ever-expanding chemical space of inorganic-core
catalysts and metal–organic frameworks (MOFs), identification of these
optimal heterojunctions is difficult without appropriate computational
screening. In this work, a novel high-throughput screening method of nano-hybrid
photocatalysts is presented by screening 65 784 inorganic-core materials
and 20 375 MOF-shells for their ability to reduce CO2 based on their synthesizability,
aqueous stability, visible light absorption, and electronic structure;
the passing materials were then paired based on their electronic structure
to create novel heterojunctions. The results showed 58 suitable inorganic-core
materials and 204 suitable MOFs ranging from never-before-synthesized catalysts
to catalysts that have been overlooked for their photocatalytic ability.
These materials lay a new foundation of photocatalysts that have passed
theoretical requirements and can significantly increase the rate of catalyst
discovery.
Contact angle measurements were conducted on lithium–sodium orthoborate,
an alkali-metal borate-based high-temperature carbon capture sorbent, in
contact with nickel and stainless steel under air, N2, and CO2 atmospheres
at 600 °C in order to assess the compatibility of this innovative sorbent
with packed-bed reactors, typically used in the commercial carbon capture
industry. On nickel, the results reveal the melt to be wetting (contact
angle θ ≤ 90°), albeit with a contact angle reaching an apparent equilibrium
over the experimental time considered. It was found that θ was lower under
N2 than under CO2, which was explained as a consequence of the oxide-ion
activity difference between the CO2-lean and saturated melts. On stainless
steel, however, the melt rapidly spreads, tending toward complete wetting
of the metal sheet (θ = 0°) in all atmospheres. For the two metals investigated,
the results indicate high to very high wettability, hence the adequacy
of using lithium–sodium orthoborate in conventional gas–liquid contactors,
further backing this sorbent as a potential alternative to existing sorbents
for CO2 capture.
This paper reports on the structural changes occurring within the lithium–sodium
orthoborate crystal lattice during the solid-state absorption of CO2. Results
derived from Fourier transform infrared measurements indicate that the
CO2-saturated mixed-alkali metal orthoborate and its CO2-lean metaborate
counterpart essentially present the same spectral profile, suggesting that
CO2 capture results in a fundamental shift of the orthoborate composition
to the metaborate one. The implications of such a structural transformation
were examined in the molten state at elevated temperatures through rheological
measurements, and although confirming that the CO2-lean metaborate exhibits
a higher viscosity than the CO2-lean orthoborate, the results suggest that
incorporation of CO2 in the orthoborate ionic lattice dilutes the melt,
leading to a remarkable reduction in its overall viscosity, despite causing
a structural transformation from the less viscous orthoborate form to the
more viscous metaborate one.
Journal of Materials Chemistry A, 2019, 7, 21827-21834
Takuya Harada, Cameron Halliday, Aqil Jamal, and T. Alan Hatton
The development of efficient low cost CO2 capture systems is a critical challenge for mitigating climate change
while meeting global energy demand. Herein, we demonstrate the first liquid
absorbents for CO2 capture at medium to high temperatures (500 to 700 °C). Molten ionic oxides
based on sodium borate and the mixed alkali-metal borates show remarkably
fast kinetics and intrinsic regenerability, with no observable deterioration
in performance over multiple absorption–desorption cycles under both temperature-
and pressure-swing operations. The behavior of the molten ionic oxides
is ascribed to the instantaneous formation of carbonate ions in the molten
oxides without the diffusional transport restrictions imposed by solid
product layers characteristic of solid adsorbents. The new liquid absorbents
will enable continuous processing and thermal integration via a simple
absorber–desorber arrangement, thereby overcoming the challenges previously
restraining high temperature CO2 capture and opening up new opportunities in clean energy production.
ACS Sustainable Chemistry and Engineering, 2019, 7, 7979-7986
Takuya Harada, Paul Brown, and T. Alan Hatton
The establishment of advanced CO2 capture, utilization, and storage (CCUS) technology is a crucial challenge
for the mitigation of serious ongoing climate change. Herein, we report
nonaqueous colloidal dispersions of MgO nanoparticles in molten salts as
a new class of fluid absorbents for continuous CO2 capture at intermediate temperatures ranging from 200 to 350 °C. The colloidal
absorbents were developed by dispersion of the nanoparticles in three different
types of thermally stable low-melting point salts: ternary-eutectic alkali-metal
nitrates ((Li–Na–K)NO3), tetraphenylphosphonium bis(trifluoromethane)sulfonimide ([P(Ph)4][NTf2]), and their mixtures. The new absorbents show high CO2 uptake performance with acceptable rheological properties at the target
temperatures. The analysis of reaction rate kinetics in the uptake of CO2 revealed that CO2 can diffuse quickly into the molten salts to initiate the rapid formation
of carbonates on the surfaces of MgO nanoparticles dispersed in these molten
salts. These results demonstrate that the new colloidal dispersions could
be used as fluid absorbents for advanced continuous CO2capture processes at the temperatures of exhausts from fossil fuel combustion
reactors without the energy losses incurred upon cooling of the gases as
required for traditional absorption systems.
Journal of Materials Chemistry A, 2017, 5, 22224-22233
Takuya Harada, T. Alan Hatton
A lithium-borate oxide, Li3BO3, is proposed as a next generation high capacity CO2 adsorbent operative over the intermediate temperature range of 500 to
650 °C. This adsorbent shows high CO2 uptake capacity (e.g., 11.3 mmol g−1 at 520 °C) with excellent cyclic
regenerability in the presence of alkali-metal nitrite salts as a reaction
facilitator. The high CO2 uptake is attributed to the dissociative formation of lithium carbonate
(Li2CO3) and different compositions of lithium borates (Li6B4O9, LiBO2 and Li2B4O7) during the reaction of Li3BO3 with CO2. The excellent performance of the new CO2 adsorbents is discussed in terms of rapid gas–solid reactions on Li3BO3 mediated by the molten nitrite salts and pinning effects that prevent
the sintering of particle grains.
Chemistry of Materials, 2015, 27, 1943-1949
Takuya Harada, Fritz Simeon, Esam Z. Hamad, and T. Alan Hatton
(*This work was press released as ACS News by American Chemical Society, and featured in Phys. Org . Science Daily
, and others media.)
Regenerable high capacity CO2sorbents are desirable for the establishment of widespread carbon capture
and storage (CCS) systems to reduce global CO2emissions. We report on the marked effects of molten alkali metal nitrates
on CO2uptake by MgO particles and their impact on the development of highly regenerable
CO2adsorbents with high capacity (>10.2 mmol g–1) at moderate temperatures (∼300 °C) under ambient pressure. The molten
alkali metal nitrates are shown to prevent the formation of a rigid, CO2-impermeable, unidentate carbonate layer on the surfaces of MgO particles
and promote the rapid generation of carbonate ions to allow the high rate
of CO2uptake.
Physical Chemistry Chemical Physics (PCCP), 2010, 12, 11938-11943
Takuya Harada, Fritz Simeon, John B. Vander Sande, and T. Alan Hatton
(This work was selected to the Front Cover of Vol.12, Issue 38, PCCP)
Single- and double-walled magnetic nanotubes are obtained in a one-step
liquid phase reaction by the cooperative self-assembly of chiral amphiphiles
and nanoparticles on cooling of heated mixtures of N-dodecanoyl-L-serine
and Fe3O4 nanoparticles in toluene. The nanotubes are composed of well-ordered,
close-packed nanoparticle assemblies, and can be transformed into chiral
magnetic nanostructures, such as helical coils, by subsequent calcination.
The nanoparticle assemblies and their variations on calcination are attributed
to the collective organization of the surfactant molecules adsorbed on
the nanoparticles and the freely dispersed chiral molecules, and the dewetting
effects guided by the primitive constitution of the chiral amphiphilic
molecular assemblies.
Langmuir, 2009, 25, 6407-6412
Takuya Harada, T. Alan Hatton
We demonstrate the formation of highly ordered twofold symmetric rectangular
nanoparticle superlattices by the slow evaporation of solvent from colloidal
dispersions of oleic acid/oleylamine-coated Fe3O4 nanoparticles on a water surface. These superlattices covered regions
of micrometers in size without any noticeable disorders or defects, with
size controlled by the amount of oleic acid added to the colloidal dispersions.
The superlattices were transformed into arrays of nanowires by subsequent
calcination. The peculiar nanoparticle assemblies are discussed in terms
of the cooperative self-assembly of nanoparticles and fatty molecules during
the slow evaporation of solvent.