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Concurrent Sensing of CO2 and H2O from Air Using Ultra-microporous Fluorinated MOFs: Effect of Transduction Mechanism on the Sensing Performance Mohamed Rachid Tchalala, Youssef Belmabkhout, Karim Adil, karumbaiah chappanda, Amandine Cadiau, Prashant M. Bhatt, Khaled N. Salama, and Mohamed Eddaoudi ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.8b18327 • Publication Date (Web): 10 Dec 2018 Downloaded from http://pubs.acs.org on December 13, 2018

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ACS Applied Materials & Interfaces

Concurrent Sensing of CO2 and H2O from Air Using Ultra-microporous Fluorinated MOFs: Effect of Transduction Mechanism on the Sensing Performance Mohamed Rachid Tchalala ‡, Youssef Belmabkhout ‡, Karim Adil ‡, Karumbaiah Nanaiah Chappanda ¥, Amandine Cadiau ‡, Prashant Bhatt‡, Khaled Nabil Salama¥, Mohamed Eddaoudi ‡*

‡ Functional

Materials Design, Discovery & Development Research Group (FMD3), Advanced

Membranes & Porous Materials Center, Division of Physical Sciences and Engineering, King Abdullah University of Science and Technology (KAUST), Thuwal 23955-6900, Kingdom of Saudi Arabia ¥

Sensors Lab, Advanced Membranes & Porous Materials Center, Division of Physical Sciences

and Engineering, King Abdullah University of Science and Technology (KAUST), Thuwal 23955-6900, Kingdom of Saudi Arabia KEYWORDS. Transduction technique, fluorinated Metal Organic Framework, Concurrent sensing, Confined space,

ACS Paragon Plus Environment

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ABSTRACT. Conventional materials for gas/vapor sensing are limited to a single probe detection ability for specific analytes. However, materials capable of concurrent detection of two different probes in their respective harmful levels and using two types of sensing modes have yet to be explored. In particular, the concurrent detection of uncomfortable humidity levels and CO2 concentration (400-5000ppm) in confined spaces is of extreme importance in a great variety of fields such as submarine technology, aerospace, mining, and rescue operations. Herein we report the deliberate construction and performance assessment of extremely sensitive sensors using an interdigitated-electrode (IDE) -based capacitor and a quartz crystal microbalance (QCM) as transducing substrates. The unveiled sensors are able to simultaneously detect CO2 within a 4005000 ppm range, and relative humidity (RH) levels below 40% and above 60%, using two fluorinated metal-organic frameworks (MOFs), namely NbOFFIVE-1-Ni and AlFFIVE-1-Ni, fabricated as a thin film. Their subtle difference in a structure-adsorption relationship for H2O and CO2 were analyzed to unveil the corresponding structural-sensing properties relationships using both QCM and IDE based sensing modes.

INTRODUCTION Maintaining safe levels of CO2 and humidity in indoor environments or confined spaces is a top priority, but often also a major challenge, for environmental technologies 1. Consequently, major research efforts have recently been devoted to developing new technologies and processes that can effectively detect and measure indoor levels of CO2 and relative humidity

2-8.

Technologies

currently available for the detection of CO2 are based on either non-dispersive infrared (NDIR) sensors or chemical CO2 gas sensors

2, 9-11.

These technologies even if they can operate at low

temperature and their lifetime can be quite long, present many drawbacks, such as elevated


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working-temperatures (300-800 οC), prohibitive costs and relatively shortened lifetimes

12.

Transduction techniques, including acoustic, resistance, magnetic, resonance, optical, impedance, delay-line, capacitance, thermal, and QCM techniques,

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have allowed the development of

efficient humidity sensors. However, the presence of large amounts of CO2 (found mainly in confined spaces) can alter the measure of relative humidity levels by sensors14. It is therefore imperative to develop robust and inexpensive sensors with the ability of simultaneously detecting CO2 and H2O, in a precise and reliable manner. Metal-organic frameworks (MOFs) are a unique class of porous materials that have shown great potential for gas separation/storage, catalysis and sensing

15-24.

Recently, the use of a

fluorinated MOF, namely AlFFIVE-1-Ni, as adsorbent offered the ability to simultaneously remove H2O and CO2 from various gas streams. This distinctive property is distinctive and remarkable as the capture of both gases usually follows a competitive adsorptive mechanism 25. In fact, the presence of two distinct actives sites, those on open metal sites for the adsorption of H2O, and those within cavities for the adsorption of CO2 explains this unique simultaneous adsorption process of the AlFFIVE-1-Ni adsorbent 26. Here, we present the development of the first sensing device with the ability to simultaneously detect and measure CO2 and H2O. In our study, harmful levels of CO2 (between 400 ppm and 5,000 ppm) and uncomfortable levels of humidity (below 40%RH and higher than 60%RH) commonly present in indoor environments were established as targets for ranges of detection. Gas sensitivity performances were analyzed using two different transduction techniques: one measuring changes in mass (using QCM) and the other measuring changes in dielectric properties (using an IDE capacitor). The performance of AlFFIVE-1-Ni 26 was compared with those obtained


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using another fluorinated MOF, NbOFFIVE-1-Ni, which displayed a competitive adsorption process of CO2 and H2O 27-28. RESULTS AND DISCUSSION Preparation and characterization of sensing materials Recently, reticular chemistry allowed us to fabricate a series of fluorinated MOF materials with the ability to capture CO2 from air or to dehydrate gas streams 27. The structure of these materials can be described as having a pcu underlying topology where a square-grid Ni(pyrazine)2 is pillared by inorganic building blocks, either [NbOF5]2- or [AlF5(H2O)] 2-, to generate a channel-based MOF with a periodic array of fluorine moieties (Figure 1) 26-28. The structural differences between these two fluorinated MOFs resulted from the presence of an open metal site in the case of AlFFIVE1-Ni. Markedly, gas adsorption experiments on AlFFIVE-1-Ni revealed the simultaneous adsorption of CO2 and H2O molecules26. In-situ single-crystal X-ray diffraction and DFT calculations showed that the open metal sites were the preferred adsorption sites for H2O molecules, whereas CO2 preferably adsorbed within the cavities 26. Desorption experiments at set temperatures conducted after adsorption of a mixture of CO2 and H2O confirmed the concomitant nature of the adsorption mechanism 26. Similar experiments conducted with NbOFFIVE-1-Ni, an analogue with no open metal site, confirmed the competitive nature of the adsorption mechanism, with preferential adsorption of CO2 to one single site located within the cavity 27. Based on these remarkable adsorptive properties, AlFFIVE-1-Ni and NbOFFIVE-1-Ni are expected to be excellent candidates for addressing challenges faced by many chemical sensors in the concurrent detection of CO2 and H2O detection. In order to do so, there is a need for establishing a signal transduction process that will enable the use of NbOFFIVE-1-Ni and AlFFIVE-1-Ni for chemical sensing.


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In recent years, quartz microbalance (QCM) and interdigitated electrode (IDE) technologies have been proposed as new effective tools for the rapid detection of gases, VOCs, and humidity, due to their simplicity, small size, low cost, high sensitivity, shorter time of analysis and suitability for label-free measurements 29. The resonant frequency of QCM substrates depends on the amount of adsorbed material. QCM can detect the change in a mass of sub-nanograms. The relation between the shift in frequency and the mass loading is described by the Sauerbery equation 8. Capacitive interdigitated electrodes (IDEs) are widely used to sense the change in sensing film permittivity, upon gas adsorption, and are seen as attractive candidates, from a power consumption perspective 30. The key element of any chemical sensor is the sensitive layer that captures the analyte gases 31. MOF films are generally grown on surfaces that have been functionalized with self-assembled monolayers, or by seeding with small MOFs crystal. The nanostructures of these thin films have not been yet well characterized, and sometimes lead to improper growth of the desired thin film 32, 33.

In this context, we developed, for the first time, a new synthesis method to obtain a soft

homogenous MOF solution with a paste-like consistency, making it well-suited for the preparation of a wide range of homogeneous thin film. Indeed, the method can easily be adapted to the deposition or spin coating of thin films, from a chemical solution. A representation of this is presented in (Figure 2), which shows a good uniformity in the deposition of the crystals, along with an improved adhesion to the substrates. AlFFIVE-1-Ni and NbOFFIVE-1-Ni films contain close-packed crystal domains exhibiting a good coalescence of microcrystals with small intergranular voids leading to compact, uniform MOF films of excellent crystallinity. NbOFFIVE-1-Ni films consist of small cubic crystallites of approximately 150 nm, whereas


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larger crystallites of about 7m are found for AlFFIVE-1-Ni. The purity and crystallinity of the deposited MOF films were confirmed by powder x-ray diffraction experiments (Figure S1).

Gas-sensing properties 1. Concurrent sensing of CO2 and H2O The use of MOF thin films for sensing application requires a critical activation step, permitting the attainment of a guest-free thin film before any sensing signal measurement is performed. For this reason, we fully reactivated the MOF adsorbent at 105 oC, prior each new cycle of analyte exposure, using in situ heating provided by HT24S metal ceramic heater from Thorlabs. The output temperature of the heater was calibrated and monitored using a LM35DZ/NOPB commercial temperature sensor from Texas Instruments (Figure S2). This calibration is of prime importance to preserve the integrity of the MOF adsorbent, and to ensure that guest-free activated NbOFFIVE-1-Ni and AlFFIVE-1-Ni are obtained, prior to sensing experiments. The sensing characteristics and performance of NbOFFIVE-1-Ni and AlFFIVE-1-Ni were investigated, at variable CO2 concentration, in dry and humid conditions, to verify the potential application of the newly fabricated sensors. Interestingly, NbOFFIVE-1-Ni and AlFFIVE-1-Ni coated on IDE and QCM as sensors show a nonlinear change in the signal over several orders magnitude of CO2 concentration (from 400 to 5000 ppm). The capacitive properties of the IDE exhibited a dielectric constant dependency of the material, due to the change in CO2 concentration. The capacitance can be calculated using the standard capacitance equation 36. The exposure of all the sensors to different dry CO2 concentrations led to a sharp decrease of the capacitance (Figure 3(a,b)). Additionally, the interaction of CO2 with NbOFFIVE-1-Ni and AlFFIVE-1-Ni changed


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the local dielectric properties of the thin films, resulting in a decrease in capacitance. Remarkably, the interdigitated sensor devices coated with NbOFFIVE-1-Ni showed a significantly higher change in capacitance (about 100 times, for 400-5000 ppm of CO2), when compared to AlFFIVE1-Ni. These observations are in agreement with the remarkably favorable selectivity of CO2 obtained from calorimetric and co-adsorption tests. Figure 3(c,d) depicts the

concentration-dependent responses of NbOFFIVE-1-Ni or

AlFFIVE-1-Ni coated on QCMs, as sensors, to different concentrations of CO2, at room temperature and under dry conditions. We observed that when the gas enters in contact with the QCM-based sensors, CO2 molecules were adsorbed into the sensitive film, the mass increases in a proportional manner, negative shift in resonance frequency. Namely, the decrease in resonant frequency (Figure3 (c,d)), as the CO2 concentration increases, can be seen very clearly, showing a good response of the QCM to CO2. In case of QCM devices, the maximum shifts in frequency are -84.85 Hz for NbOFFIVE-1Ni, and -3.5 Hz for AlFFIVE-1-Ni, at CO2 concentrations ranging from 400 to 5000ppm. These results are in good agreement with NbOFFIVE-1-Ni exhibiting a higher interaction with CO2 at low loading (53kJ/mol) vs. a weaker interaction (45 kJ/mol) for AlFFIVE-1-Ni. In the case of IDE- sensing mode under dry CO2 conditions, a high adsorptive selectivity was observed at low CO2 loadings and concentrations for NbOFFIVE-1-Ni vs. AlFFIVE-1-Ni. Interestingly, MOF- coated mass-sensitive QCMs devices exhibited a lower sensitivity towards CO2, under dry conditions, compared to the IDE capacitors. Part of the reason for this difference is that IDE capacitors can detect larger effects of CO2 on dielectric properties of the thin films, whereas the mass- sensitive QCM devices are only able to detect small mass changes.


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2. Effect of synthetic air on concurrent sensing of CO2 and H2O In general, the moisture from the environment has a considerable impact on the sensitivity of the gas sensor and must be taken into consideration for practical deployment of any sensor. Therefore, we investigated the concentration-dependent response of the IDE and QCM devices coated with NbOFFIVE-1-Ni or AlFFIVE-1-Ni to CO2, under humid conditions. The relationship between the resonant frequencies of the QCM sensors and the relative humidity (60%) is shown in Figure S3. The sensitivity of NbOFFIVE-1-Ni coated on QCM, as a sensor, was reduced in the presence of moisture and was easily distinguishable from the response of CO2 in the air. However, the sensitivity was considerably reduced with AlFFIVE-1-Ni coated QCM, and its frequency was reduced even more, especially at low CO2 concentrations. In the case of IDE type sensing, NbOFFIVE-1-Ni and AlFFIVE-1-Ni coated IDEs sensors were greatly affected by the presence of moisture. In fact, an often-heard objection to capacitive sensor technology is that it is sensitive to humidity, yet the capacitive sensor is based on dielectric changes of the thin film upon water vapor uptake. Practically, humidity and condensable vapors are shown to have a significant effect on the IDE-based sensors because water has a dielectric constant of 𝜀𝑟 = 78.3, 𝑖.𝑒.  48 times larger than that of CO2 ( 𝜀𝑟 = 1.60). The presence of moisture often interferes with the IDE sensory signal of CO2, and thereby can hamper its qualitative identification and quantification. Accordingly, the results presented here show that QCM- based sensors are a good alternative to compensate the loss of performance in IDE-based sensors, due to the presence of humidity.


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A detailed analysis of the sensitivity to H2O, as a function of relative humidity (26% to 60% RH), was performed to further delineate the water vapor adsorptive based sensing performance. After an initial activation cycle at 105οC, the sensors were cooled to room temperature and subsequently exposed to different levels of relative humidity, using N2 as a gas carrier. The relative humidity level was varied by changing the carrier flow (0 to 200 ml/min) bubbling through the water. One should note that an ideal sensor swiftly senses water vapor, in the optimal range of 2665% RH. This is the desired range of humidity levels for confined spaces; conform to the standards set by the occupational health safety. The humidity sensing behavior of the AlFFIVE-1-Ni/ NbOFFIVE-1-Ni coated IDE- and QCM- based sensors, as shown in Figure4, reveals a response in a non-linear fashion with good sensitivity in the recommended range of humidity levels (2665% RH). Notably, AlFFIVE-1-Ni and NbOFFIVE-1-Ni have an almost simultaneous response to change in humidity levels; however, as expected, the presence of an open metal site in highly confined pores, in the case of AlFFIVE-1-Ni thin films, offers a greater sensitivity to humidity. In fact, the exposed Al3+ of the AlFFIVE-1-Ni framework serves as the initial preferable adsorption site for water molecules, when exposed to different levels of relative humidity levels. Humidity levels above 60% have a considerable impact on the sensitivity, which is related to the nature of the MOF adsorbent. AlFFIVE-1-Ni shows a sensitivity five times higher than that of NbOFFIVE-1-Ni, for a 26%- 60% RH range. On the other hand, a comparison of the effects of the transduction mechanisms on the sensing performance, in humid conditions, clearly shows that QCM- based sensors are more reluctant to changes, in comparison to IDE-based devices.


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It is to be noted that the shift in frequency and capacitance decreased more steeply, when RH exceeded 60%, a phenomenon that can be explained by the aggregation of water molecules on thin films. To mimic the real conditions (atmospheric conditions), experiments were also performed in the presence of 500 ppm CO2, using both transduction techniques (Figure S4). After an initial exposure to 500 ppm of CO2, both samples exhibited a decrease in their sensing signals, as a function of the subsequent exposure to humidity. In the case of AlFFIVE-1-Ni, this decrease was almost two times higher than that observed for NbOFFIVE-1-Ni. Interestingly, changes in CO2 levels had a lower impact (four times lower) for NbOFFIVE-1Ni than for AlFFIVE-1-Ni. This suggests that a partial desorption of non-coordinated water molecules occurs easily for NbOFFIVE-1-Ni, due to their relatively weak interactions occurring with the framework, compared to those of CO2 with the framework.26 In the case of AlFFIVE-1Ni, the water molecules coordinated to the open metal site could not be desorbed because of their stronger interaction with the open metal sites in the presence of CO2, therefore causing unchanged performances for water detection. Although both QCM and IDE responded to variable H2O and CO2 concentrations, the sensitivities were not identical. Accordingly, the detection of CO2, in the presence of variable humidity levels, under real (atmospheric) conditions, could be directly observed by a shift in the resonance frequency of QCM. However, the capacitive sensor could much better reflect the changes in humidity levels in the presence of 500 ppm CO2. 3. Stability studies The most important parameters for a given sensing device are its stability and reproducibility. These parameters were investigated by cyclic exposure, every 48 hours, at room temperature, for


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over a period of 12 days (Figure5). It was clearly shown that both sensors response did not vary significantly with time, confirming their long-term stability. These results pinpoint some of the most important elements required for the choice of materials granting comfortable/healthy indoor conditions; they also shed light on the associated transduction mechanisms required for the concurrent detection of harmful levels of CO2 and humidity, in a condition akin to atmospheric condition and confined environments. The response of the sensors to humidity and CO2 showed that sensitivity and resolution were dependent on both the transduction mechanism and the sensing material. However, the response, stability, selectivity, detection limit, and lifecycle were found to depend only on the intrinsic properties of the sensing material.

CONCLUSION In summary, we report, for the first time, the use of both IDE- and QCM- based sensors for the simultaneous detection of CO2 and H2O, using ultra-microporous fluorinated MOFs exhibiting unprecedented structural CO2-H2O adsorption properties. The sensors have excellent selectivity for sensing CO2, at variable humidity levels; they can also detect humidity levels at variable CO2 concentrations. We show that isostructural fluorinated MOF-based capacitance sensitive sensors possess good CO2-sensing properties, under dry conditions. When working under real conditions (atmospheric conditions), the change in the dielectric constant over the change in the CO2 concentrations, and at a constant humidity level of 60%RH, results in a decrease in capacitance. The detection of CO2, under real conditions, can be directly observed on the QCM frequency shift. However, the capacitive sensor can better reflect the changes in humidity, in the presence of CO2. At room temperature, all the sensor’s properties reported here make the reported sensor a


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promising candidate for the detection of CO2 and water vapor, when used for indoor and confined spaces. MATERIALS AND METHODS Materials All solvents and reagents were used without further purification: Ni(NO3)2·6H2O (Acros), Al(NO3)3·9H2O (Aldrich), Pyrazine (Aldrich), Nb2O5 (Aldrich), Ni(NO3)2· 6H2O (Acros), HF (Aldrich). AlFFIVE-1-Ni Pyrazine (384.40 mg, 4.80 mmol), Ni(NO3)2·6H2O (174.50 mg, 0.60 mmol), Al(NO3)3·9H2O (225.0 mg, 0.6 mmol) and HFaq 48% (0.26 ml, 7.15 mmol) were mixed in a 20 ml Teflon liner. After dilution of the mixture with 3 ml deionized water, the autoclave was sealed and heated to 85 °C, for 24h. After cooling of the reaction mixture to room temperature, the obtained blue-violet square-shaped crystals, suitable for single crystal X-ray structure determination, were collected by filtration, washed with 5 ethanol, and dried in air. Elemental analysis: N%: 13.76 (theo: 14.19), C%: 21.73 (theo: 24.33), H%: 3.16 (theo: 3.57). NiAlF5(H2O)(pyr)2·2(H2O) (called AlFFIVE-1Ni) was activated at 105 oC, for one night, under high vacuum (3 mTorr), before each adsorption measurements[26]. NbOFFIVE-1-Ni Pyrazine (384.40 mg, 4.80 mmol), Ni(NO3)2·6H2O (174.50 mg, 0.60 mmol), Nb2O5 (79.70 mg, 0.30 mmol), and HF (aqueous, 48%, 0.26 mL, 7.15 mmol) were mixed in a 20 mL Teflon liner. The mixture was diluted with 3 mL of deionized water, and the autoclave was then sealed and heated to 130 °C, for 24 h. After cooling of the reaction mixture to room temperature, the obtained


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violet square-shaped crystals, suitable for single crystal X-ray structure determination, were collected by filtration, washed with ethanol and dried in air. Elemental anal. C8H12O2N4F5NiNb: N, 11.88 (theo: 12.21), C, 20.58 (theo: 20.54), H, 2.54 (theo: 2.64), O, 11.42 (theo: 10.46). NiNbOF5 (pyr)2·(H2O)2 (called NbOFFIVE-1-Ni) was activated at 105 °C, for 12 h, under high vacuum (3 mTorr), before each adsorption experiment[27-28]. QCM and IDE electrodes (IDE)- based capacitors were fabricated on a highly resistive silicon wafer using complementary metal-oxide semiconductor processes. A 2μm silicon dioxide layer was grown, using wet thermal oxidation for electrical isolation. A layer of 10/300 nm Ti/Au was subsequently sputtered- deposited via physical vapor deposition (PVD), in a ESC metal sputter system. Photolithography was used in the next step of the process, in order to define the interdigitated electrodes (4 μm fingers with 5μm spaces). The metal layer was then etched, using a ion sputtering system PlasmaLab System from Oxford Intruments, with the patterned photoresist acting as the mask layer. 10 MHz AT-cut (QCM) with a 6 mm diameter electrodes from open QCM were used as substrates for the mass-based sensing technique. Fabrication of NbOFFIVE-1-Ni and AlFFIVE-1-Ni coated IDE/QCM: Electrodes were rinsed with acetone/ethanol and dried in air. MOFs paste was then deposited on one of the electrode of QCMs/IDEs by spin-coating method (2m thick). No prior modification of the sensors surface was required with this method of deposition. The method is simple in yielding good quality and uniform films. The coated electrodes were then dried at 60 oC for 2 hours under vacuum to obtain thin films of sensing materials on the electrodes.


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The sensors were then characterized in a custom built sealed chamber. Prior to any measurements the fresh coated MOFs film on the sensors were activated in situ for 4 hours to have a guest free framework. The resulting coatings are ultrathin and reproducible so that the absorbed CO2 and/or water vapor induces an effective change in the mass/dielectric properties of change of the thin films. Apparatus: Scheme S1 shows the schematic of the setup used in this study for real-time gas sensing measurements. MFCs (Mass flow controllers) from Alicat scientific Inc. were used to control the flow rate of gases from certified bottles. Stainless steel or perfluoroalkoxy alkane, PFA tubing (in regions requiring flexibility) along with Vernier metering valves (from Swagelok) as a flow regulator were used as delivery lines in the setup. A commercial humidity sensor (Honeywell HIH4000-003, error less than 0.5%RH) was used to monitor the humidity levels inside the test chamber. The QCM/IDE- based sensors were exposed to the analyte stream until a stable response was attained. Two-port impedance analyzer (Keysight E5071C ENA) circuit was used for monitoring the change in resonance frequency. A LabVIEW interface was used for synchronization and data acquisition by controlling the LCR meter and the multi-meter. This minimized the possibility of data loss.


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Figure 1. Crystal structure details for NbOFFIVE-1-Ni and AlFFIVE-1-Ni. a) square-grid resulting from the connection of Ni2+ cations and pyrazine that are further pillared by either (b) (AlF5 (H2O)) 2- pillar or (c) (NbOF5)2- pillar.


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Figure 2. SEM images of a) NbOFFIVE-1-Ni and b) AlFFIVE-1-Ni thin films.


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Figure 3. Capacitive sensor response for a) NbOFFIVE-1-Ni and b) AlFFIVE-1-Ni. Comparison of frequency shifts as a function of the CO2 concentration, for c) NbOFFIVE-1-Ni and d) AlFFIVE-1-Ni.


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Figure4. Variation in capacitance with RH change in a) NbOFFIVE-1-Ni and b) AlFFIVE-1Ni. Frequency shift as function of RH for QCM coated with c) NbOFFIVE-1-Ni and d) AlFFIVE-1-Ni

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Figure5. Long-term stability properties of a) H2O upon prior exposure to 500 ppm CO2 of the AlFFIVE-1-Ni/IDE sensor, b) CO2 upon prior exposure to 60% RH of the NbOFFIVE-1Ni/QCM sensor.


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ASSOCIATED CONTENT Supporting Information. Thin film Synthesis, Powder X-ray diffraction, sensing apparatus and additional sorption data (breakthrough measurements) are available in the Supporting Information. This material is available free of charge via the Internet at http://pubs.acs.org.

AUTHOR INFORMATION Corresponding Author * Functional Materials Design, Discovery & Development Research Group (FMD3), Advanced Membranes & Porous Materials Center, Division of Physical Sciences and Engineering, King Abdullah University of Science and Technology (KAUST), Thuwal 23955-6900, Kingdom of Saudi Arabia. E-mail: [email protected] Author Contributions K. A. and A. C. carried out the synthetic experiments; K. A. and M. R. T contributed to the conceptual approach in designing the MOF deposition on the electrode. Y. B. and P.B analyzed gas adsorption-sensing properties. P. B. and Y. B; Y. B., M. R. T., and K. A. conceptualized the set of sensing testing. Y. B., M. R. T., K. A., K. N. S., and K. N. C. conducted and interpreted the sensing results. K. A., Y. B., and M. E. conceived, designed, and guided the whole project. M. R. T., Y. B., K. A. and M. E. wrote the manuscript.


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ACKNOWLEDGMENT The research reported in this publication was supported by funding from King Abdullah University of Science and Technology (KAUST), under award number CCF/1/1972-25-01, CCF/1/1972-27-01, and OSR-2017-CPF-3325.

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Concurrent Sensing of CO2 and H2O from Air ... - ACS Publications

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