Enhanced CO2 Uptake Research Articles

Molecular Dye-Sensitized Photocatalysis with Metal-Organic Framework and Metal Oxide Colloids for Fuel Production

Colloidal dye-sensitized photocatalysis is a promising route toward efficient solar fuel production by merging properties of catalysis, support, light absorption, and electron mediation in one. Metal-organic frameworks (MOFs) are host materials with modular building principles allowing scaffold property tailoring. Herein, we combine these two fields and compare porous Zr-based MOFs UiO-66-NH2(Zr) and UiO-66(Zr) to monoclinic ZrO2 as model colloid hosts with co-immobilized molecular carbon dioxide reduction photocatalyst fac-ReBr(CO)3(4,4′-dcbpy) (dcbpy = dicarboxy-2,2′-bipyridine) and photosensitizer Ru(bpy)2(5,5′-dcbpy)Cl2 (bpy = 2,2′-bipyridine). These host-guest systems demonstrate selective CO2-to-CO reduction in acetonitrile in presence of an electron donor under visible light irradiation, with turnover numbers (TONs) increasing from ZrO2, to UiO-66, and to UiO-66-NH2 in turn. This is attributed to MOF hosts facilitating electron hopping and enhanced CO2 uptake due to their innate porosity. Both of these phenomena are pronounced for UiO-66-NH2(Zr), yielding TONs of 450 which are 2.5 times higher than under MOF-free homogeneous conditions, highlighting synergistic effects between supramolecular photosystem components in dye-sensitized MOFs.

CO2 Capture by Low-Cost Date Pits-Based Activated Carbon and Silica Gel.

The rising levels of CO2 in the atmosphere are causing escalating average global temperatures. The capture of CO2 by adsorption has been carried out using silica gel type III and prepared activated carbon. The date pits-based activated carbon was synthesized using a tubular furnace by physical activation. The temperature of the sample was increased at 10 °C/min and the biomass was carbonized under N2 flow maintained continuously for 2 h at 600 °C. The activation was performed with the CO2 flow maintained constantly for 2 h at 600 °C. The temperature, feed flow and adsorbate volume were the parameters considered for CO2 adsorption. The success of CO2 capture was analyzed by CO2 uptake, efficiency based on column capacity, utilization factors and the mass transfer zone. The massively steep profiles of the breakthrough response of the AC demonstrate the satisfactory exploitation of CO2 uptake under the conditions of the breakthrough. The SG contributed to a maximal CO2 uptake of 8.61 mg/g at 298 K and Co = 5% with F = 5 lpm. The enhanced CO2 uptake of 73.1 mg/g was achieved with a column efficiency of 0.94 for the activated carbon produced from date pits at 298 K. The AC demonstrated an improved performance with a decreased mass transfer zone of 1.20 cm with an enhanced utilization factor f = 0.97 at 298 K. This finding suggests that a date pits-based activated carbon is suitable for CO2 separation by adsorption from the feed mixture.

Mn-promoted CaO-based adsorbents with enhanced CO2 uptake performance

The adsorption of CO2 over CaO-based adsorbents has been an effective way to capture CO2 at high temperature, but the adsorption capacity was hampered and the cycle durability was poor. To address the said problems, this paper reported the effect of Mn doping on the structure, morphology and CO2 adsorption performances of CaO-based adsorbents synthesized by a sol-gel method. The characterization results showed that the addition of Mn was helpful to form abundant micropores and mesopores in the doped CaO-based adsorbent, and Mn can effectively prevent the sintering and agglomeration of CaO particles. Moreover, electron transfer occurred on the modified CaO-based absorbents. These findings suggested that Mn species induced both structural and electronic promotion effect, resulting in smaller particle, higher dispersion and specific surface area of CaO-based adsorbents and formation of some electron-rich oxygen and Ca species, ultimately boosting CO2 adsorption performance. Especially, with the molar ratio of Ca/Mn being 20, the adsorbent Ca/Mn-20 presented the best CO2 uptake and excellent cycle stability (up to 10 cycles). In addition, it can be concluded that the adsorption process of CO2 was more obedient to the pseudo-second-order kinetic model, indicating the adsorption process was dominated by chemical adsorption.

Fluorocarbon-Functionalized Superhydrophobic Metal-Organic Framework: Enhanced CO2 Uptake via Photoinduced Postsynthetic Modification.

The design and synthesis of porous materials for selective capture of CO2 in the presence of water vapor is of paramount importance in the context of practical separation of CO2 from the flue gas stream. Here, we report the synthesis and structural characterization of a photoresponsive fluorinated MOF {[Cd(bpee)(hfbba)]·EtOH}n (1) constructed by using 4,4'-(hexafluoroisopropylidene)bis(benzoic acid) (hfbba), Cd(NO3)2, and 1,2-bis(4-pyridyl)ethylene (bpee) as building units. Due to the presence of the fluoroalkyl -CF3 functionality, compound 1 exhibits superhydrophobicity, which is validated by both water vapor adsorption and contact angle measurements (152°). The parallel arrangement of the bpee linkers makes compound 1 a photoresponsive material that transforms to {[Cd2(rctt-tpcb)(hfbba)2]·2EtOH}n (rctt-tpcb = regio cis,trans,trans-tetrakis(4-pyridyl)cyclobutane; 1IR) after a [2 + 2] cycloaddition reaction. The photomodified framework 1IR exhibits increased uptake of CO2 in comparison to 1 under ambient conditions due to alteration of the pore surface that leads to additional weak electron donor-acceptor interactions with the -CF3 groups, as examined through periodic density functional theory calculations. The enhanced uptake is also aided by an expansion of the pore window, which contributes to increasing the rotational entropy of CO2, as demonstrated through force field based free energy calculations.

Efficient electrochemical synthesis of a manganese-based metal–organic framework for H2 and CO2 uptake

Electrochemical synthesis, from manganese strips and dissolved linker, of a new amine-containing manganese-based metal–organic framework with enhanced CO2 uptake.

Tree—Open Grassland Structure and Composition Drive Greenhouse Gas Exchange in Holm Oak Meadows of the Iberian Peninsula

Iberian holm oak meadows are savannah-like ecosystems that result from traditional silvo-pastoral practices. However, such traditional uses are declining, driving changes in the typical tree—open grassland structure of these systems. Yet, there are no studies integrating the whole ecosystem—including the arboreal and the herbaceous layer—as drivers of greenhouse gas (GHG: CO2, CH4 and N2O) dynamics. Here, we aimed at integrating the influence of tree canopies and interactions among plant functional types (PFT: grasses, forbs, and legumes) of the herbaceous layer as GHG exchange drivers. For that purpose, we performed chamber-based GHG surveys in plots dominated by representative canopy types of Iberian holm oak meadows, including Quercus species and Pinus pinea stands, the last a common tree plantation replacing traditional stands, and unraveled GHG drivers through a diversity-interaction model approach. Our results show the tree–open grassland structure, especially drove CO2 and N2O fluxes, with higher emissions under the canopy than in the open grassland. Emissions under P. pinea canopies are higher than those under Quercus species. In addition, the inclusion of diversity and compositional terms of the herbaceous layer improve the explained variability, with legumes enhancing CO2 uptake and N2O emissions. Changes in the tree cover and tree species composition, in combination with changes in the structure and composition of the herbaceous layer, will imply deep changes in the GHG exchange of Iberian holm oak meadows. These results may provide some guidelines to perform better management strategies of this vast but vulnerable ecosystem.

A general way to transform Ti3C2Tx MXene into solvent-free fluids for filler phase applications

The emerging two-dimensional transition metal carbides (MXenes) have been gradually coming into the limelight due to excellent mechanical properties, electrical conductivity performance and versatile surface chemistry. However, the oxidation instability and poor processability of MXenes impede further scalable applications. Toward this end, we have for the first time proposed a general and facile strategy to transform Ti3C2Tx MXene into a novel class of homogenous, stable solvent-free liquids (MX-fluid) with core-corona-canopy structure via covalent linkage surface engineering strategy. The as-prepared MX-liquid exhibited rather stable antioxidant ability after setting for 540 days. Moreover, the MX-fluid presented macroscopic flow behaviors at room temperature, remarkably improving processability and showing extensive potential in addressing the daunting dispersion issue when blending the Ti3C2Tx with other polymer matrixes. Furthermore, the generality of constructing solvent-free MXene fluids using covalent corona-canopy linkage strategy was verified. As two proof-of-concept demonstrations, the MX-fluid was first utilized as a filler phase of mixed matrix membranes (MMMs). The MX-fluid exhibited greatly enhanced CO2 uptake compared with that of N2, which was also confirmed by molecular simulation. Next, the MX-fluid was incorporated into Pebax-1657 matrix, and improved CO2 selective separation (CO2/N2 selectivity of 69.2) was obtained, where the CO2 permeability increased by 179.9% compared with pristine Pebax-1657 membrane. Second, the MX-fluid was demonstrated a good reinforcement phase of epoxy-based composites. Remarkably, the rich library of MXenes family and oligomer species provides more convenience for the further optimization of structures of solvent-free MXene liquids for task-specific applications, thus paving new ways to advance the development of novel solvent-free MXene liquids into scale-up and practical applications

In Situ Coating CsPbBr3 Nanocrystals with Graphdiyne to Boost the Activity and Stability of Photocatalytic CO2 Reduction.

The instability and low inferior catalytic activity of metal-halide perovskite nanocrystals are crucial issues for promoting their practical application in the photocatalytic field. Herein, we in situ coat a thin graphdiyne (GDY) layer on CsPbBr3 nanocrystals based on a facile microwave synthesis method, and employ it as a photocatalyst for CO2 reduction. Under the protection of GDY, the CsPbBr3-based photocatalyst delivers significantly improved stability in a photocatalytic system containing water concomitant with enhanced CO2 uptake capacity. The favorable energy offset and close contact between CsPbBr3 and GDY trigger swift photogenerated electron transfer from CsPbBr3 to doping metal sites in GDY, boosting a remarkable improvement in the photocatalytic performance for CO2 reduction. Without adding traditional sacrificial reductants, the cobalt-doped photocatalyst achieves a high yield of 27.7 μmol g-1 h-1 for photocatalytic CO2 conversion to CO based on water as a desirable electron source, which is about 8 times higher than that of pristine CsPbBr3 nanocrystals.

A Selenophene-Incorporated Metal-Organic Framework for Enhanced CO2 Uptake and Adsorption Selectivity.

A new metal–organic coordination polymer [Zn2(sedc)2(dabco)] (1se; sedc2− = selepophene-2,5-dicarboxylate; dabco = 1,4-diazabicyclo[2.2.2]octane) was synthesized and characterized by single-crystal X-ray diffraction analysis. This MOF is based on {Zn2(OOCR)4N2} paddle wheels and is isoreticular to the family of [Zn2(bdc)2(dabco)] derivatives (1b; bdc2− = 1,4-benzenedicarboxylate) with pcu topology. The gas adsorption measurements revealed that 1se shows a 15% higher CO2 volumetric uptake at 273 K and 28% higher CO2 uptake at 298 K (both at 1 bar) compared to the prototypic framework 1b. Methane and nitrogen adsorption at 273 K was also investigated, and IAST calculations demonstrated a pronounced increase in CO2/CH4 and CO2/N2 selectivity for 1se, compared with 1b. For example, the selectivity factor for the equimolar CO2/CH4 gas mixture at 1 bar = 15.1 for 1se and 11.9 for 1b. The obtained results show a remarkable effect of the presence of selenium atom on the carbon dioxide affinity in the isoreticular metal–organic frameworks with very similar geometry and porosity.

Guest-Responsive Reversal in Structural Transformation after a [2 + 2] Topochemical Reaction in a 3D Pillared Layer MOF: Uncovering the Role of C-H···O Interaction.

Here, we report the influences of the C-H···O interaction, weaker than other conventional noncovalent interactions, on the guest-responsive structural modification of a photoactive metal-organic framework (MOF) and the impact on gas sorption properties. A photoactive pillared-layer three-dimensional MOF {[Cd(pzdc)(bpee)]2·3H2O}n (1) (where bpee = 1,2-bis(4-pyridyl)ethylene and pzdc = 2,3-pyrazinedicarboxylate) was synthesized and characterized. Compound 1 shows guest-responsive structural contraction by the movement of two-dimensional layers supported by the C-H···O interaction between the pillar (bpee) and layer (pzdc) linkers. Further, 1 was postsynthetically modified using light by exploiting the parallel arrangement of the olefinic double bondsof the bpee pillars based on a [2 + 2] cycloaddition reaction to produce {[Cd2(pzdc)2(rctt-tpcb)]·3H2O}n, (1IR) (rctt-tpcb = regio cis,trans,trans-tetrakis(4-pyridyl)cyclobutane) in a single-crystal-to-single-crystal transformation (SCSC) manner. The C-H···O interaction between the two linkers is not possible in the photomodified framework, and thus guest-responsive structural expansion is realized. Such a reversal of the structural transformation facilitates the enhanced CO2 uptake in 1IR with respect to 1 at their dehydrated states. Further, the photomodified compound 1IR does not uptake N2 and CH4 at 273 K and shows high selectivity as realized by an ideal adsorbed solution theory calculation. The facile diffusion of CO2 in the irradiated framework is also supported by the kinetic measurements based on MeOH adsorption isotherms at 293 K. Here, postsynthetic modification by a [2 + 2] photochemical reaction is the key to control the structural change for enhanced CO2 uptake capacity.

The CO2 -equivalent balance of freshwater ecosystems is non-linearly related to productivity.

Eutrophication of fresh waters results in increased CO2 uptake by primary production, but at the same time increased emissions of CH4 to the atmosphere. Given the contrasting effects of CO2 uptake and CH4 release, the net effect of eutrophication on the CO2 -equivalent balance of fresh waters is not clear. We measured carbon fluxes (CO2 and CH4 diffusion, CH4 ebullition) and CH4 oxidation in 20 freshwater mesocosms with 10 different nutrient concentrations (total phosphorus range: mesotrophic 39µg/L until hypereutrophic 939µg/L) and planktivorous fish in half of them. We found that the CO2 -equivalent balance had a U-shaped relationship with productivity, up to a threshold in hypereutrophic systems. CO2 -equivalent sinks were confined to a narrow range of net ecosystem production (NEP) between 5 and 19mmolO2 m-3 day-1 . Our findings indicate that eutrophication can shift fresh waters from sources to sinks of CO2 -equivalents due to enhanced CO2 uptake, but continued eutrophication enhances CH4 emission and transforms freshwater ecosystems to net sources of CO2 -equivalents to the atmosphere. Nutrient enrichment but also planktivorous fish presence increased productivity, thereby regulating the resulting CO2 -equivalent balance. Increasing planktivorous fish abundance, often concomitant with eutrophication, will consequently likely affect the CO2 -equivalent balance of fresh waters.

Hierarchically nanoporous copolymer with built-in carbene-CO2 adducts as halogen-free heterogeneous organocatalyst towards cycloaddition of carbon dioxide into carbonates

A serial of porous polymers incorporating N‑heterocyclic carbene-CO2 adducts (designated as NHC-CO2 adducts) were facilely synthesized via radical polymerization of N-vinylimidazolate and ethyleneglycol dimethacrylate plus post-treatment with dimethyl carbonate (DMC). The polymers possessed tunable chemical structure, large surface area along with abundant meso-macropores and enhanced CO2 uptake which functioned as metal-halogen-free heterogeneous organocatalysts for solvent-free cycloaddition of CO2 to styrene oxide under 10 bar CO2 pressure, exhibiting highly catalytic activity and stable recyclability. Further, turnover frequency (TOF) of 7.1 h−1 (94.3% yield, 12 h) was obtainable under ambient condition, much higher than those of reported metal-halogen-free heterogeneous catalysts, even comparable with existing halogen-containing ones. Furthermore, the catalyst could efficiently convert various epoxides including internal epoxides into corresponding cyclic carbonates under mild condition (1 bar, 70–120 °C). The excellent catalytic performance was ascribed to the appropriate proportion of NHC-CO2 adducts in porous skeleton structure triggered by DMC. A plausible reaction mechanism was proposed to understand NHC-catalyzed fixation of CO2. This study highlights porous organic polymer is a versatile platform of NHC-CO2 adducts to construct eco-friendly solid catalyst towards efficient CO2 conversion.

Hydroxyl-functionalized microporous polymer for enhanced CO2 uptake and efficient super-capacitor energy storage

In recent years, porous organic polymers (POPs) have received increasing attention and research interest due to their formidable potential applications in gas storage/separation, heterogeneous catalysis, photoelectricity, energy storage and conversion, etc. In this work, we report the design and synthesis of a hydroxyl-functionalized porous organic polymer (PCz-res) by conventional FeCl3-facilitated oxidative polymerization for gas adsorption and energy storage applications. The precursor Cz-res was designed and synthesized by the imidization of anhydride bearing twisted carbazole units with 4,6-diaminoresorcinol. The prepared PCz-res polymer was completely characterized by the usual analytical techniques. PCz-res exhibited a high specific surface area of 1015 m2/g and reversibly adsorbed 20.53 wt% (273 K) and 14.92. wt% (295 K) CO2 at 1 bar with a moderate isosteric heat of CO2 adsorption (22.39 kJ/mol). The favourable properties of PCz-res were attributed to the uniform pore size distribution (0.8 nm), high surface area, rich nitrogen content and presence of polar CO2-philic hydroxyl groups in the polymeric network. These features make the investigated polymer a plausible emerging material in the field of gas adsorption and separation. Moreover, PCz-res was applied in supercapacitor energy storage and exhibited a specific capacitance as high as 434 F g−1 in 1 M H2SO4 at a 2 mV/s scan rate and 367 F g−1 at a current density of 0.5 A g−1. Additionally, PCz-res retained 91% of the initial specific capacitance after 2000 charge/discharge cycles at a current density of 10 A g−1. The structural characteristics of PCz-res lead to a larger accessible surface area and a redox-active structure, resulting in efficient charge energy storage.

Squaramide-derived framework modified periodic mesoporous organosilica: A robust bifunctional platform for CO2 adsorption and cooperative conversion

Novel periodic mesoporous organosilica with different concentrations of squaramide-derived framework (PMO-SAF) were prepared and structurally characterized. They were applied to CO2 capture and conversion into cyclic carbonates under mild and metal/solvent-free conditions. The PMO-SAFs as prepared possess favorable structure features of high specific surface area, Lewis basic units and dual hydrogen bond donor groups, they showed interesting synergistic effects for both CO2 adsorption and epoxide activation. By regulating structure of the PMO-SAFs, an enhanced CO2 uptake capacity was obtained under a low CO2 pressure. The catalytic behaviors of PMO-SAFs on the model cycloaddition of CO2 to propylene oxide, including reaction parameters optimization, catalyst reusability and versatility were investigated in detail, and excellent yield (98%) and selectivity (99%) to propylene carbonate were obtained under the optimized reaction conditions of 90 °C and 2.0 MPa for 7.0 h. Moreover, the PMO-SAF-catalyzed reaction mechanism was proposed according to the results obtained. The special design of the PMO-SAFs endows the material with robust structure, dual-functions of CO2 adsorption and transformation, displaying great significance to the design of multi-functional nanomaterials.

Accelerated carbonation of biochar reinforced cement-fly ash composites: Enhancing and sequestering CO2 in building materials

Biochar produced from the pyrolysis of corn stover biomass was added as a filler material in the cement-fly ash blocks as 2%, 4%, 6% and 8% of total weight. The resultant blocks were subjected to two hours mineral carbonation at (3 day) after demoulding to enhance the CO2 uptake and sequester carbon in the blocks. Along with that, 28 days compressive strength of un-carbonated blocks was determined to gauge the effect of biochar as the filler material on the strength of the specimens. Results showed that there was an enhanced CO2 uptake on 3 days compressive strength and biochar dosage was optimised at 4% and 6% depending on the chosen mix. The 28 days compressive strength of un-carbonated blocks showed that there was an increase in the strength as biochar addition increased to a certain extent, however, thereafter it decreased with the further addition of biochar.

Encapsulation of a Porous Organic Cage into the Pores of a Metal-Organic Framework for Enhanced CO2 Separation.

We present a facile approach to encapsulate functional porous organic cages (POCs) into a robust MOF by an incipient‐wetness impregnation method. Porous cucurbit[6]uril (CB6) cages with high CO2 affinity were successfully encapsulated into the nanospace of Cr‐based MIL‐101 while retaining the crystal framework, morphology, and high stability of MIL‐101. The encapsulated CB6 amount is controllable. Importantly, as the CB6 molecule with intrinsic micropores is smaller than the inner mesopores of MIL‐101, more affinity sites for CO2 are created in the resulting CB6@MIL‐101 composites, leading to enhanced CO2 uptake capacity and CO2/N2, CO2/CH4 separation performance at low pressures. This POC@MOF encapsulation strategy provides a facile route to introduce functional POCs into stable MOFs for various potential applications.

Encapsulation of a Porous Organic Cage into the Pores of a Metal–Organic Framework for Enhanced CO2 Separation

AbstractWe present a facile approach to encapsulate functional porous organic cages (POCs) into a robust MOF by an incipient‐wetness impregnation method. Porous cucurbit[6]uril (CB6) cages with high CO2 affinity were successfully encapsulated into the nanospace of Cr‐based MIL‐101 while retaining the crystal framework, morphology, and high stability of MIL‐101. The encapsulated CB6 amount is controllable. Importantly, as the CB6 molecule with intrinsic micropores is smaller than the inner mesopores of MIL‐101, more affinity sites for CO2 are created in the resulting CB6@MIL‐101 composites, leading to enhanced CO2 uptake capacity and CO2/N2, CO2/CH4 separation performance at low pressures. This POC@MOF encapsulation strategy provides a facile route to introduce functional POCs into stable MOFs for various potential applications.

Fine-Tuning the Porosities of the Entangled Isostructural Zn(II)-Based Metal-Organic Frameworks with Active Sites by Introducing Different N-Auxiliary Ligands: Selective Gas Sorption and Efficient CO2 Conversion.

Three new pairs of 2-fold interpenetrated and self-entangled three-dimensional isostructural porous metal-organic frameworks (MOFs), [Zn(L1)(x)0.5]·0.5H2O (x = bipy for 1, bpa for 2, and bpe for 3) and [Zn(L2)(x)0.5]·0.5H2O (x = bipy for 4, bpa for 5, and bpe for 6) [bipy = 4,4'-bipyridine, bpa = 1,2-bis(4-pyridyl)ethylene, and bpe = 1,2-bis(4-pyridyl)ethylene], have been created and fine-tuned via similar skeleton ligands 2-(imidazol-1-yl)terephthalic acid (H2L1) and 2-(1H-1,2,4-triazol-1-yl)terephthalic acid (H2L2) and N-auxiliary coligands with different linking groups. Interestingly, the porosities of the MOFs can be effectively increased via the insertion of -CH2CH2- or -CH═CH- spacers into the N-auxiliary bipy ligand. As a result, complexes 5 and 6 displayed highly enhanced CO2 uptake capacities. Furthermore, complex 5 also had a higher C2/C1 selectivity as well as great CO2 cycloaddition efficiency.

Mechano-chemical stability and water effect on gas selectivity in mixed-metal zeolitic imidazolate frameworks: a systematic investigation from van der Waals corrected density functional theory.

A series of Zn/Cu Zeolitic Imidazolate Frameworks (ZIFs) ZIF-202, -203, and -204 are systematically investigated by Density Functional Theory (DFT) with and without van der Waals (vdW) corrections. The elastic constants for non-solvent structures indicate that ZIF-202 and -204 are mechanically stable while ZIF-203 is unstable, which arises from the stiffness along the x-axis under a uniaxial strain in the PBE-D3 method. By considering the presence of solvents in ZIF-203, a structural phase transformation from a monoclinic to a triclinic structure is found which could be explained by the Jahn-Teller distortion. From the chemical bonding point of view, it is found that vdW interactions and hybridization between d-orbitals (copper) and p-orbitals (imidazolate) are the main-driving forces in stabilizing ZIF-202 and -204, respectively. The electronic structure calculations predict the presence of two optical transitions in the visible region in agreement with the experimental observation for ZIF-204 both without and with water. The DFT simulations reveal that CO2 molecules prefer to locate near imidazolate and water in dry and hydrated ZIF-204, respectively. The analysis of Canonical Monte Carlo (GCMC) simulations reveals that Coulomb interaction between CO2 and H2O molecules is mainly responsible for the enhanced CO2 uptake and selectivity under humid conditions compared to dry ones.

Marine CO2 system variability in a high arctic tidewater-glacier fjord system, Tempelfjorden, Svalbard

The marine CO2 system in Tempelfjorden (Svalbard) was investigated between August 2015 and December 2017 using total alkalinity, pH, temperature, salinity, oxygen isotopic ratio, and nutrient data. Primary production resulted in the largest changes that were observed in the partial pressure of CO2 (pCO2, 140 μatm) and the saturation state of aragonite (ΩAr, 0.9). Over the period of peak freshwater discharge (June to August), the freshwater addition and air-sea CO2 uptake (on average 15.5 mmol m−2 day−1 in 2017) governed the surface pCO2. About one fourth of the uptake was driven by the freshening. The sensitivity of ΩAr to the freshwater addition was investigated using robust regressions. If the effect of air-sea CO2 exchange was removed from ΩAr, a freshwater fraction larger than 50% (lower range of uncertainty) was needed to provide aragonite undersaturated waters. This study shows that ΩAr and freshwater fraction relationships that are derived from regression techniques and the interpretation thereof are sensitive to the effect of air-sea CO2 exchange. Since the freshening in itself only drives a fraction of the air-sea CO2 uptake, studies that do not account for this exchange will overestimate the impact of freshwater on ΩAr. Finally, in the summer an excess in the salinity normalized dissolved inorganic carbon, corrected for aerobic primary production/respiration, of on average 86 μmol kg−1 was found in the deepest water of the fjord. This excess is suggested to be a result of enhanced CO2 uptake and brine release during the period of sea ice growth.