Colorimetric Identification of Colorless Acid Vapors using a Metal-Organic Framework-Based Sensor

Colorimetric Identification of Colorless Acid Vapors using a Metal-Organic Framework-Based Sensor | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Article Colorimetric Identification of Colorless Acid Vapors using a Metal-Organic Framework-Based Sensor Jin Yeong Kim, Wonhyeong Jang, Hyejin Yoo, Dongjun Shin, Seokjin Noh This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-4505436/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 04 Jan, 2025 Read the published version in Nature Communications → Version 1 posted You are reading this latest preprint version Abstract In terms of safety and emergency response, identifying hazardous gaseous acid chemicals is crucial for ensuring effective evacuation and administering proper first aid. However, current studies struggle to distinguish between different acid vapors and remain in the early stages of development. In this study, we propose a novel on-site monitorable acid vapor decoder, MOF-808-EDTA-Cu, integrating the robust MOF-808 with Cu-EDTA, functioning as a proton-triggered colorimetric decoder that translates the anionic components of corrosive acids into visible colors. The sensor exhibits a remarkable cyan-to-yellow shift when exposed to HCl vapor and can visually differentiate various acidic vapors (HF, HBr, and HI) through unique color changes. Furthermore, the compatibility of the MOF-based sensor with multiple metal ions having atomic-level dispersion broadens its discrimination range, enabling the identification of six different colorless acid vapors within a single sensor domain. Additionally, by incorporating a flexible polymer, the MOF-808-EDTA-Cu has been successfully processed into a portable miniaturized acid sensor, exhibiting distinct color changes that can be easily monitored by the naked eye and camera sensors. This provides experimental validation as a practical sensor capable of on-site 24-hour monitoring in the real world. Physical sciences/Chemistry/Materials chemistry/Metal–organic frameworks Physical sciences/Chemistry/Green chemistry/Chemical safety Figures Figure 1 Figure 2 Figure 3 Introduction Acids are essential reagents in modern chemical processes and are used to produce various chemicals, such as fertilizers, detergents, batteries, and pharmaceuticals, as well as to remove impurities from many products 1 – 6 . Despite their versatility, acids pose significant risks owing to their corrosive and chemically reactive nature, which can cause irritation or severe damage to the eyes, skin, and respiratory system upon exposure to high concentrations or prolonged exposure 7 – 8 . The required emergency response and first-aid protocols depend on the type of acid exposed 9 – 10 ; hence, the detection and identification of hazardous acid chemicals is of paramount importance for applications ranging from health diagnostics to public safety and environmental protection 1–2,11−12 . Electrochemical acid vapor sensors, some of which are already commercially available, exhibit high sensitivity, however, their acid vapors identification efficiency is limited 13 – 14 . Moreover, traditional acid vapor identification methods, including infrared and mass spectrometry, require complex and expensive instrumentation, rendering on-site identification of acid vapors challenging 15 – 17 . One of the most attractive approaches in this field involves the construction of colorimetric molecular decoders that offer simplicity in identifying acid vapors with the naked eye, cost efficiency, and the potential for on-site identification of multiple targets. Recently, several colorimetric sensors have been reported utilizing organic dyes 18 – 19 , polymers 20 , covalent organic frameworks (COFs) 21 – 22 , and metal-organic frameworks (MOFs) 8 , 23 . However, most studies have focused on detecting single HCl vapors by relying on a protonation mechanism, which cannot differentiate between various acid vapors. Recent studies on colorimetric sensor arrays have demonstrated that integrating the detection results from multiple sensor domains can distinguish various chemical vapors, including some acid vapors; however, this requires additional complex data processing 24 – 25 . Consequently, despite their importance, research on sensor materials capable of visually identifying acidic gases remains in the preliminary stages. To develop a true optical molecular decoder for the identification of colorless acidic vapors, an anion-participating colorimetric sensing mechanism is required. Transition-metal chelate complexes are attractive candidates for use in visual identification sensors. Chelating ligands such as ethylenediaminetetraacetic acid (EDTA), which form a stable metal complex, can release chelated metal ions under acidic conditions 26 – 28 . The de-chelated transition metal ion acts as a colorimetric center, displaying characteristic colors depending on the coordinating ligands and coordination geometry, thus enabling the visualization of acidic vapors in a single-domain sensor. However, most pure metal-chelate complexes exist as non-porous powders, which impedes their direct exposure to acid vapors and their processing into practical sensors. Herein, we report a novel MOF-based acid vapor decoder, MOF-808-EDTA-Cu, capable of visually identifying exposed colorless acid vapors (Scheme 1 ). MOF-808, a robust and porous Zr-based MOF, was selected as the platform, and Cu-chelated EDTA (Cu-EDTA) was incorporated as the proton-triggered colorimetric center. Direct exposure of the Cu-EDTA colorimetric center to HCl vapors facilitated the cyan-to-yellow color transition at HCl concentrations as low as 120 ppm. Interestingly, the Cu-EDTA colorimetric center could be regenerated up to three times via a simple immersion in water. Furthermore, the Cu-EDTA-grafted MOF-808 exhibited characteristic color changes from cyan to pale green, dark purple, and brown upon exposure to different acid vapors (HF, HBr, and HI), whereas it did not react to interfering gases, humidity, or temperature variations. This unique acid-selective colorimetric behavior originates from the de-chelation of metal ions from the stable Cu-EDTA, triggered by protons, followed by a color- change mechanism involving anions in the acid vapors. To the best of our knowledge, it is the first approach to specifically identify acid vapor using both protonation and anion dependent systems in a single domain sensor. Due to the strong chelating properties of EDTA, multiple metal ions could be easily incorporated into a single sensor domain with atomic-level dispersion, expanding the decoding capability to identify six different acidic vapors. Additionally, by introducing a flexible polymer, the Cu-EDTA-decorated MOF-808 was successfully processed into a portable miniaturized acid decoder, exhibiting distinct color changes detectable by the naked eye and monitored by camera sensors. This proves its practicality and versatility as an acid vapor-triggered colorimetric decoder for 24-hour on-site monitoring applications. Results Preparation and characterization of MOF-808-EDTA-Cu To develop an acid vapor decoder system featuring a fully exposed colorimetric decoder, EDTA-coordinated MOF-808 (designated as MOF-808-EDTA) was prepared following a previously reported method 29 – 30 (Supplementary Figs. 1 and 2). The colorimetric center Cu 2+ was introduced by soaking MOF-808-EDTA in a 100 mM Cu 2+ solution for 24 h, affording a cyan-colored powder. The Cu-ion-incorporated MOF-808-EDTA was denoted as MOF-808-EDTA-Cu (Fig. 1 a). The X-ray powder diffraction (XRPD) patterns of MOF-808-EDTA-Cu confirmed that the framework structure was maintained even after post-synthetic treatments (Fig. 1 b). Inductively coupled plasma-atomic emission spectrometry (ICP-AES) confirmed that the Cu 2+ ions capable of chelating up to 82% of EDTA were successfully incorporated into MOF-808-EDTA-Cu. Concurrently, the Fourier transform-infrared (FT-IR) spectrum of MOF-808-EDTA-Cu showed the absence of peaks associated with NO 3 − constituting the Cu precursor, ruling out the possibility of the physical inclusion of Cu precursors into the MOF pores (Supplementary Fig. 3) 31 – 32 . Upon the inclusion of Cu ions into MOF-808-EDTA, the ultraviolet visible near-infrared (UV-vis-NIR) spectrum revealed a new absorption peak at 13140 cm − 1 , corresponding to the d-d transition 2 E g → 2 T 2g of an octahedral six-coordinated Cu ion, which is the same as in the previously reported [Cu(EDTA)(H 2 O)] 33 , suggesting the presence of Cu-chelated EDTA in the MOF-808-EDTA-Cu system (Supplementary Fig. 4). X-ray photoelectron spectroscopy (XPS) of MOF-808-EDTA-Cu (Supplementary Fig. 5) revealed a significant shift in the Zr 3d binding energy compared to MOF-808, with the monocarboxylate ligand removed, indicating that the EDTA molecule chelating the Cu ion remained grafted to the Zr 6 cluster of MOF-808-EDTA-Cu 29 , 34 . Nitrogen sorption measurements of MOF-808-EDTA-Cu showed a decrease both in surface area and pore size of larger cavity (1127 m 2 /g and 0.79 nm) compared to that of the pristine MOF-808 (2108 m 2 /g and 1.30 nm), indicating that Cu chelated EDTA, the colorimetric center, exists in accessible internal pores of MOF-808 rather physical mixed (Fig. 1 c and Supplementary Fig. 6). Therefore, MOF-808-EDTA-Cu containing fully exposed Cu-EDTA within its accessible pores, was successfully prepared as a colorimetric sensor via a simple post-synthetic modification. Colorimetric response of MOF-808-EDTA-Cu to HCl vapor An interesting naked-eye detectable color change from cyan to yellow was observed in MOF-808-EDTA-Cu within 20 s of exposure to HCl vapors evaporated from a concentrated HCl solution (Fig. 1 e). Remarkably, this transition occurred without any structural changes in the MOF-808 framework, suggesting that the eye-detectable color shift did not originate from structural decomposition (Fig. 1 b). Further analysis confirmed the incorporation of chlorine into MOF-808-EDTA-Cu after exposure, as evidenced by scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (SEM-EDS) (Fig. 1 d) and the XPS spectra of Cl 2p (Supplementary Fig. 7). The emergence of a Cu–Cl stretching vibration peak at ~ 289 cm − 1 in the Raman spectra (Supplementary Fig. 8) indicated the formation of new bonds between Cu and Cl 35 . Upon exposure to HCl, UV–vis–NIR spectroscopy showed new absorption peaks at 34364 and 25316 cm⁻¹, suggesting that the coordination environment of the Cu 2+ ion is changed (Fig. 1 f). Interestingly, these peaks align with the LMCT characteristics reported for tetrahedrally structured CuCl 4 2 − 2,36−37 , implying that free Cu 2+ ions de-chelated from EDTA forming a new yellow Cu-Cl complex (Fig. 1 f). Importantly, MOF-808-EDTA-Cu demonstrated selectivity towards acid gas, maintaining its colorimetric response unchanged when exposed to potentially interfering air gases such as N₂, O₂, and CO₂, as well as variations in humidity and temperature within a substantial range (Supplementary Fig. 9). This highlights its potential as a reliable acid-vapor-selective sensor for practical applications. An intriguing colorimetric response was observed upon exposure of MOF-808-EDTA-Cu to HCl vapor, which was detectable even at concentrations as low as 120 ppm, although a longer detection time was required. Cu-EDTA and Cu(CH₃COO)₂, characterized by non-porous and densely packed structures, displayed gradual color changes after acidic exposure for 1 h at 120 ppm. Conversely, MOF-808-EDTA-Cu exhibited a visible color shift within 5 min, underscoring the significance of grafting Cu-EDTA onto MOF-808 and directly expose it to external acidic vapors for efficient acid sensing (Supplementary Fig. 10). Upon immersion in water, the yellow color of the HCl-exposed MOF-808-EDTA-Cu immediately changed to cyan and was recovered as a cyan powder through filtration (Fig. 1 e). The recovered MOF exhibited the same UV-Vis-NIR spectrum as that of MOF-808-EDTA-Cu (Supplementary Fig. 11). This intriguing regeneration of the sensor is attributed to the characteristics of EDTA, which is known to efficiently chelate various metal ions even at low concentrations in aqueous solutions 30 , 38 – 39 . Consequently, the EDTA-decorated MOF-808 demonstrated an ability to re-chelate approximately 80% of Cu²⁺ ions during the regeneration process, as confirmed by ICP-AES analysis. Furthermore, during three cycles of alternating exposure to HCl and water, MOF-808-EDTA-Cu continued to exhibit reversible cyan-yellow color variations, highlighting the reusability of the sensor (Fig. 1 e). Acid-triggered colorimetric decoding mechanism To reveal the underlying mechanism of the formation of yellow Cu-Cl complexes from highly stable cyan-colored Cu-EDTA complexes, a series of controlled experiments were conducted with MOF-808-EDTA-Cu. First, to elucidate the formation conditions of the Cu-Cl complexes from MOF-808-Cu-EDTA, three types of aqueous solutions containing the same 4 M Cl − ions were prepared: two neutral (NaCl and KCl) and one acidic (HCl) solution. In the 4M Cl − solution, a portion of the introduced free Cu 2+ ions formed a yellow Cu-Cl complex, leading to a color change from blue to greenish-yellow (Supplementary Fig. 12a). Notably, MOF-808-EDTA-Cu turned greenish-yellow only in the acidic HCl solution, while retaining its cyan color in the other solutions, indicating the generation of free Cu 2+ ions from Cu-EDTA only under acidic conditions (Supplementary Fig. 12b). This unique acid-condition-selective color transformation stems from alterations in the functional groups of EDTA, as evidenced by the FT-IR spectra of MOF-808-EDTA-Cu before and after exposure to HCl (Fig. 1 g). Compared to MOF-808-EDTA-Cu, the HCl-exposed MOF-808-EDTA-Cu showed decreased intensity of the peak at 1566 cm − 1 , corresponding to the ν as,COO− of EDTA 40 – 43 , while the emergence of a new peak at 1719 cm − 1 was attributed to the ν C=O of carboxylic acids, indicating the protonation of the carboxylate in EDTA 27 , 44 . XPS spectra of the HCl-exposed MOF-808-EDTA-Cu compared to MOF-808-EDTA-Cu revealed new peaks at 401.6 and 533.1 eV corresponding to the N 1s of the protonated amine (-HN + -) and O 1s of the carboxylic acid in EDTA 45 – 47 , respectively, further supporting the protonation of EDTA which hardly chelates the Cu 2+ ion, resulting in the release of free Cu ions (Fig. 1 h and Supplementary Fig. 13). Therefore, both Cl − and H + are essential for the colorimetric decoding of acid vapors by MOF-808-EDTA-Cu. These unique acid-selective color transition mechanism demonstrates the potential of MOF-808-EDTA-Cu as a true colorimetric acid sensor that can selectively react with anions in acidic environments. MOF decoder to visualize exposed acid vapors Building on the unique acid-triggered and anionic participation in the colorimetric sensing mechanism, we explored the potential of MOF-808-EDTA-Cu as a colorimetric sensor for the visualization of colorless hydrohalic acid vapors. The MOF-808-EDTA-Cu sensor distinctly visualized the exposed hydrohalic acid vapors, namely HF, HBr, and HI, as white, dark purple, and brown, respectively (Fig. 2 a). Interestingly, these observed color changes were aligned with the expected colors resulting from the interaction of free Cu ions with halide ions, suggesting that the de-chelated Cu 2+ ions from the protonated EDTA in MOF-808-EDTA-Cu reacted with hydrohalic acids (Supplementary Fig. 14). Specifically, the UV-vis-NIR spectra of MOF-808-EDTA-Cu after exposure to HF and HBr were consistent with those of CuF 2 and CuBr 4 2− , respectively 48 , implying the formation of white CuF 2 and purple CuBr 4 2− within the MOF sensor following acid exposure (Supplementary Figs. 15 and 16). Furthermore, exposure to HI resulted in the formation of white CuI(s) and brown I 2 (aq), as confirmed by PXRD and UV-vis-NIR spectra, suggesting that the brown color of the HI-exposed MOF-808-EDTA-Cu originated from I 2 (aq) rather than CuI(s) (Supplementary Fig. 17). The exceptionally strong chelation of EDTA in MOF-808 renders it versatile and enables the incorporation of various metal ions into the MOF-808 sensor. To further explore our methodology, we prepared Fe 3+ -chelated MOF-808-EDTA (referred to as MOF-808-EDTA-Fe) as a colorimetric sensor, which exhibited a distinct color change from ivory to yellow and orange upon exposure to HCl and HBr, respectively (Fig. 2 b and Supplementary Fig. 18). Furthermore, the strong chelation capability of EDTA allowed MOF-808-EDTA to effectively integrate multiple metal ions (Cu 2+ and Co 2+ ) with atomic-level dispersion, thereby expanding the scope of visually-identifiable acid vapors within a single-domain sensor (Fig. 2 c). MOF-808-EDTA-Cu/Co, featuring Cu-chelated EDTA and Co-chelated EDTA, exhibited a unique ability to differentiate between six acidic vapors within a single-domain sensor (Fig. 2 d). This capability arises from the co-presence of Cu-chelated EDTA, adept at decoding hydrohalic acid and Co-chelated EDTA, proficient at decoding nitric acid and trifluoroacetic acid (TFA). Such findings demonstrate the versatility and resilience of our sensor platform, providing visual identification of a variety of acid vapors with a single sensor domain. To exploit the outstanding properties of the MOF-808-EDTA-Cu platform for the visualization of colorless acid vapors, the fabrication of miniaturized portable acid vapor sensors that could be used for real-time on-site monitoring was explored (Fig. 3 a). For transformation into a portable acid vapor decoding sensor, a MOF sensor-based ink was fabricated by combining MOF-808-EDTA-Cu with polyvinylidene fluoride (PVDF) in a dimethylformamide (DMF) solution, which can be applied to various substrates, including foil, paper, fabric, and glass (Supplementary Fig. 19). When exposed to HCl vapor evaporating from a concentrated HCl solution (approximately 15,500 ppm) 49 – 50 , the MOF-808-EDTA-Cu portable sensor underwent a distinct color shift from cyan to yellow, which was detectable by the naked eye and recorded by a camera sensor (Fig. 3 b). This color change was further translated into RGB channel values, allowing the quantification of the color changes and 24-hour real-time monitoring. Notably, when exposed to low concentrations of HCl where the color change is not saturated, the sensor exhibited a reduced transition from cyan to yellow within the same exposure timeframe, suggesting its potential as an acid–gas concentration analyzer (see Fig. 3 c). This transition can be precisely quantified using the equation |dB|/B 0 , where |dB| denotes the absolute value of change in the blue channel value from the initial blue channel value B 0 . Correlation of the |dB|/B 0 ratio with different HCl vapor concentrations can establish a linear range spanning from 120 to 740 ppm, providing experimental validation of the portable sensor as a colorimetric sensor capable of quantifying the concentration of exposed HCl vapor. Additionally, when exposed to an atmosphere with high relative humidity (RH) 85%, no color change was detected both with the naked eye or even with RGB values, demonstrating its practical use as a portable sensor capable of selectively visualizing acidic vapors, even in the presence of humidity interference (Fig. 3 d). Based on the obtained results, we extended our investigation on the color changes of sensors upon exposure to various acid vapors. In experiments with hydrohalic acid vapors, including HF, HBr, and HI, the color change of the MOF-808-EDTA-Cu portable sensor was not complete until 25 min, however, changes detectable by the naked eye appeared within 10 min (Supplementary Fig. 20). Interestingly, when monitoring the color shifts of the portable sensor via the RGB channel values, distinct trends in the RGB channel values depending on the exposed acid vapors were observed, even in the early stages when they were barely detectable by the naked eye (Fig. 3 e). Furthermore, these acid-dependent distinct color alterations enable the statistical validation of exposure to hydrohalic acid vapor within 2 min by applying principal component analysis (PCA) and hierarchical cluster analysis (HCA) methods. As shown in Fig. 3 f, the 12 datasets of dR, dG, and dB obtained from three repeated 2-min exposure experiments with four different hydrohalic acids formed distinct clusters that were well-spaced apart, implying efficient identification. HCA-based data classification using Ward's method revealed that when the closest data points were clustered, three points originating from the same acid vapor exposure experiments were successfully grouped together, confirming the ability of the sensor to discriminate between acids (Fig. 3 g). Moreover, this versatile portable sensor platform can incorporate various transition metals, such as Co and Fe, to broaden the decoding range of acid vapors to up to six types or to adjust the detection color (Supplementary Fig. 21), providing experimental validation of its applicability to diverse industrial requirements. Conclusions We successfully fabricated a colorimetric acid vapor sensor capable of on-site differentiation between various acid vapors, leveraging the color-changing attributes of a built-in colorimetric center, Cu-EDTA, in the robust and porous MOF-808-EDTA-Cu. Cu-EDTA grafted in MOF-808-EDTA-Cu was directly exposed to acid vapors, enhancing its effectiveness in identifying acid vapors and translating the different anion components of corrosive acids into visible colors. Notably, MOF-808-EDTA-Cu was unresponsive to interfering gases, humidity, and temperature variations, rendering it a practical and versatile acid-triggered sensor for on-site applications. This distinctive acid-selective colorimetric behavior stems from the proton-triggered de-chelation of metal ions from the stable Cu-EDTA, which is followed by a color-change mechanism that involves anions present in the acid vapors. Further, the strong chelating properties of EDTA in MOF-based sensors enable the easy extension to other metal ions, such as Fe and Co, broadening its ability to detect various acid vapors in a single-domain sensor as well as its potential customization for specific industrial needs. The integration of a polymer into the MOF sensor led to the development of a portable miniaturized sensor capable of visually identifying six different colorless acid vapors, highlighting its versatility in practical 24-hour on-site monitoring of acid vapor sensor applications. This simple yet sophisticated decoding method using wireless communication technology enables the development of a novel gas sensors capable of detection and identification of hazardous acid chemicals, providing comprehensive and real-time data for large-scale environmental monitoring. Methods Materials and Characterization All chemicals and solvents were of reagent grade and used without further purification. X-ray powder diffraction (XRPD) patterns were collected on a Bruker D2 PHASER at 30 kV and 10 mA for Cu K α (λ = 1.54050 Å), with a step size of 0.02° in 2 θ . Fourier transform-Infrared (FT-IR) spectra were recorded on a Bruker ALPHA II FT-IR spectrometer using the attenuated total reflection (ATR) mode. 1 H nuclear magnetic resonance (NMR) spectra were measured on a Bruker Avance III HD 300 MHz. The nitrogen adsorption-desorption isotherm was obtained using a Quantachrome Instruments Autosorb-iQ at 77 K. All samples (~ 60 mg) were activated under ultra-high vacuum at 130°C for 24 h prior to each measurement. Scanning electron microscopy (SEM) images and energy dispersive X-ray spectroscopy (EDS) mapping were taken using JSM 7800F Prime operating at 15 kV. For SEM imaging, the samples were placed on the carbon tape on an aluminum sample holder and coated using carbon-sputter coating. X-ray photoelectron spectroscopy (XPS) data were obtained by using an AXIS SUPRA and spectra were analyzed using XPSPEAK 4.1. Inductively coupled-atomic emission spectroscopy (ICP-AES) data were collected on a Perkin Elmer Optima 8300. For ICP-AES sample preparation, 0.01 g of samples were digested with 60 µL of hydrofluoric acid. The hydrofluoric acid was completely removed by vaporization before the samples were further dissolved with 4 mL of nitric acid. The acid digested samples were diluted with deionized water before measurement. UV-Vis-NIR spectra were recorded with a PerkinElmer Lambda 365 UV/Vis spectrophotometer for reflectance measurement. Raman spectroscopy data were obtained using a Thermo Fischer Scientific DXR2xi Raman imaging microscope with 532 nm laser source. Synthesis of MOF-808-EDTA MOF-808-EDTA was prepared based on the methods reported on previous literature studies 29 – 30 . 1,3,5-Benzentricarboxylic acid (0.786 g, 3.7 mmol) and ZrOCl 2 \(\bullet\) 8H 2 O (1.209 g, 3.7 mmol) were dissolved in the mixture of N,N-Dimethylformamide (DMF) (150 mL) and formic acid (150 mL) in a 500 mL lab bottle, and the bottle was heated in an oven at 130°C for 24 h. The white powder was collected by filtration and washed with DMF, water and acetone for three days respectively, during which time the solvents were replaced two times per day. The MOF-808 was activated by heating at 150°C for 24 h in vacuum condition. Yield: 0.834 g (67%), 1 H-NMR (DMSO-d 6 ): δ 8.56 (s, 3H), FT-IR (ATR, cm − 1 ): ν as (carboxylate, BTC) = 1605(s), ν as (carboxylate, formate) = 1564(s), ν O−C=O(aromatic carboxylate, sym) = 1445(s), ν O−C=O(aliphatic carboxylate, sym) = 1379(s). Then 0.100 g of activated MOF-808 and 1.860 g of ethylenediaminetetraacetic acid disodium salt (EDTA-2Na) were dissolved in 50 mL water. The contents were placed in a 100 mL lab bottle and heated at 80°C for 24 h. The powder was filtered and washed with water for several times to remove unreacted EDTA. It was then washed several times with fresh acetone. The solid was dried overnight at 100°C under vacuum. 1 H-NMR (DMSO-d 6 ): δ 8.56 (s, 3H), δ 4.10 (s, 8H), δ 3.60 (s, 4H), FT-IR (ATR, cm − 1 ): ν O−C=O(aromatic carboxylate, asym) = 1615(s), ν O−C=O(aliphatic carboxylate, asym) = 1566(s), ν O−C=O(aromatic carboxylate, sym) = 1445(s), ν O−C=O(aliphatic carboxylate, sym) = 1381(s), ν C−N(EDTA) = 1214(sh). Synthesis of MOF-808-EDTA-Metal To prepare MOF-808-EDTA-M (M = Cu or Fe), MOF-808-EDTA (0.100 g) was added into a glass vial containing 10 mL aqueous solution of 0.1 M metal nitrate (Cu(NO 3 ) 2 \(\bullet\) 3H 2 O and Fe(NO 3 ) 3 \(\bullet\) 9H 2 O for MOF-808-EDTA-Cu and MOF-808-EDTA-Fe, respectively). The mixture was stirred at room temperature for 24 h and filtered through a 0.2 µm polytetrafluoroethylene (PTFE) membrane filter. The resulting powder was activated by heating at 100°C for 24 h in vacuum condition and stored at ambient condition. To prepare MOF-808-EDTA-Cu/Co, MOF-808-EDTA (0.100 g) was added into 10 mL of mixed metal solution containing equal concentration (50 mM) of Cu(NO 3 ) 2 \(\bullet\) 3H 2 O and Co(NO 3 ) 2 \(\bullet\) 6H 2 O. The mixture was stirred at room temperature for 24 h and filtered through a 0.2 µm PTFE membrane filter. The resulting powder was activated by heating at 100°C for 24 h in vacuum condition and stored at ambient condition. Acid Vapor Detection and Regeneration of MOF-808-EDTA-Metal A 3 cm glass dish containing 0.010 g of MOF-808-EDTA-Metal was placed inside a 5 cm glass dish with 2 mL of acid solution, ensuring no direct contact between the MOF-808-EDTA-metal and the acid solution. The 5 cm dish was covered with a 7 cm glass dish to detect vaporized acid. Different concentrations of HCl vapor were prepared using HCl solutions with various wt% based on a previously reported method 49 – 50 ; 15460 ppm, 740 ppm, 590 ppm, 300 ppm and 120 ppm HCl vapor were prepared using 37.1 wt%, 24.7 wt%, 22.0 wt% 21.6 wt% and 18.5 wt% HCl solutions, respectively. To regenerate the acid vapor-exposed MOF-808-EDTA-Metal, the powder was added to 10 mL of DI water and stirred for 5 minutes. It was then filtered through a 0.2 µm membrane filter. The resulting powder was dried overnight at 100°C under vacuum. Preparation of Portable and Miniaturized MOF-808-EDTA-Metal Sensor The portable and miniaturized MOF-808-EDTA-Metal sensor was fabricated by combining MOF-808-EDTA-Metal with polyvinylidene fluoride (PVDF) based on the previous literature with minor modifications 51 . 0.048 g of MOF-808-EDTA-Metal was dispersed in 2.4 mL of acetone and sonicated for 30 minutes in a vial. Then, 0.6 mL of a DMF solution containing 0.012 g of PVDF (M w ~ 534,000) was added to the MOF suspension. The suspension was further sonicated for 30 minutes, and the acetone was removed using rotary evaporation, resulting in MOF sensor-based ink. This ink was applied to various substrates, including foil, paper, fabric, and glass, and then dried at 80°C for 1 hour. On-site Monitoring of Portable and Miniaturized MOF-808-EDTA-Metal Sensor Combined with Smartphone Camera The MOF-808-EDTA-Metal portable sensor was prepared by coating 200 µL of MOF sensor-based ink onto a 1.8 cm x 1.8 cm cover glass. This prepared MOF portable sensor was exposed to acid vapors under the same conditions as the acid vapor detection for MOF-808-EDTA-Metal, replacing the MOF-808-EDTA-Metal powder with the MOF portable sensor. During the acid vapor exposure, the color change of MOF portable sensor was recorded as a video using the standard camera application on the Galaxy S20. The camera’s auto-focus and exposure settings were locked during recording. The video was taken in a commercially available photobox with a white LED light (6000 K color temperature and 95 color rendering index (CRI)) to ensure consistent conditions and minimize the influence of surrounding light. To quantify the color changes of the portable sensor recorded in the video, a Python script utilizing the OpenCV library was run in Linux to crop the video featuring the MOF portable sensor and calculate the mean RGB channel values of the cropped frames as a function of exposure time. Discrimination analysis Principal component analysis (PCA) and hierarchical cluster analysis (HCA) was performed by using R 4.3.3 programming language, operating with R studio. Matrix with a size of 12 × 3 (three trial of four different acids x dR, dG, dB value) was entered as input data without relying on sample labels. For PCA, ‘prcomp’ function was mainly used to decrease the dimensionality of data, forming new principal components. The new principal component space was plotted to show as score plot. For HCA, ‘hclust’ function was mainly used to facilitates data categorization. The dendrogram was generated for distance method as Euclidean and cluster method as Ward’s method. Declarations Author contributions W.J. and J.Y.K. conceived the idea and designed the experiments. W.J. synthesized the molecular structures, carried out the experimental work, and analyzed the data; H.Y. and D.S. helped the synthesis of molecular structures experiments. H.Y., and S.N. helped in the N 2 sorption isotherms and PXRD measurements. W.J. and J.Y.K. co-wrote the manuscript. All authors discussed and analyzed the results. Acknowledgements This work was supported by the National Research Foundation (NRF) of Korea funded by the Ministry of Science and ICT, South Korea (NRF-2022R1C1C101022013). 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J Forensic Leg Med 15:450–453 Cui S et al (2021) Highly sensitive sensing of polarity, temperature, and acid gases by a smart fluorescent molecule. Sens Actuators B Chem 344:130120 Li XC et al (2016) A T-shaped triazatruxene probe for the naked-eye detection of HCl gas with high sensitivity and selectivity. Chem Commun 52:2748–2751 Imaya H, Ishiji T, Takahashi K (2005) Detection properties of electrochemical acidic gas sensors using halide-halate electrolytic solutions. Sens Actuators B Chem 108:803–807 Zang Y et al (2014) Specific and reproducible gas sensors utilizing gas-phase chemical reaction on organic transistors. Adv Mater 26:2862–2867 Mann DE, Acquista N, White D (1966) Infrared spectra of HCl, DCl, HBr, and DBr in solid rare-gas matrices. J Chem Phys 44:3453–3467 Perchard JP, Murphy WF, Bernstein HJ (1972) Raman and Rayleigh spectroscopy and molecular motions: I. Liquid hydrochloric and hydrobromic acids and their deuterated analogues. Mol Phys 23:499–517 Marcy TP et al (2005) Using chemical ionization mass spectrometry for detection of HNO 3 , HCl, and ClONO 2 in the atmosphere. Int J Mass Spectrom 243:63–70 Nam YS et al (2014) Photochromic spiropyran-embedded PDMS for highly sensitive and tunable optochemical gas sensing. Chem Commun 50:4251–4254 Guo J, Wei X, Fang X, Shan R, Zhang X (2021) A rapid acid vapor detector based on spiropyran-polymer composite. Sens Actuators B Chem 347:130623 Genovese ME et al (2017) Light responsive silk nanofibers: an optochemical platform for environmental applications. ACS Appl Mater Interfaces 9:40707–40715 Ascherl L et al (2019) Perylene-based covalent organic frameworks for acid vapor sensing. J Am Chem Soc 141:15693–15699 Gong W et al (2022) Dual-function fluorescent hydrazone-linked covalent organic frameworks for acid vapor sensing and iron (iii) ion sensing. J Mater Chem C 10:3553–3559 Goswami R, Das S, Seal N, Pathak B, Neogi S (2021) High-performance water harvester framework for triphasic and synchronous detection of assorted organotoxins with site-memory-reliant security encryption via pH-triggered fluoroswitching. ACS Appl Mater Interfaces 13:34012–34026 Feng L et al (2010) Colorimetric sensor array for determination and identification of toxic industrial chemicals. Anal Chem 82:9433–9440 Jin K, Moon D, Chen YP, Park J (2023) Comprehensive qualitative and quantitative colorimetric sensing of volatile organic compounds using monolayered metal-organic framework films. Adv Mater Early View, 2309570 Weakliem HA, Hoard JL (1959) The structures of ammonium and rubidium ethylenediaminetetraacetatocobaltate (III). J Am Chem Soc 81:549–555 Nakamoto K, Morimoto Y, Martell AE (1963) Infrared spectra of aqueous solutions. III. Ethylenediaminetetraacetic acid, N-hydroxyethylethylenediamine triacetic acid and diethylenetriaminepentaacetic acid. J Am Chem Soc 85:309–313 Ji C et al (2021) High-efficiency and sustainable desalination using thermo-regenerable MOF-808-EDTA: temperature-regulated proton transfer. ACS Appl Mater Interfaces 13:23833–23842 Furukawa H et al (2014) Water adsorption in porous metal-organic frameworks and related materials. J Am Chem Soc 136:4369–4381 Peng Y et al (2018) A versatile MOF-based trap for heavy metal ion capture and dispersion. Nat Commun 9:187–195 Castro PM, Jagodzinski PW (1991) FTIR and Raman spectra and structure of Cu(NO 3 ) + in aqueous solution and acetone. Spectrochim Acta - A: Mol Biomol Spectrosc 47:1707–1720 Goebbert DJ et al (2009) Infrared spectroscopy of the microhydrated nitrate ions NO 3 -(H 2 O) 1–6. J Phys Chem A 113:7584–7592 Baker AT (1998) The ligand field spectra of copper (II) complexes. J Chem Educ 75:98–99 Wu J et al (2019) Efficient removal of metal contaminants by EDTA modified MOF from aqueous solutions. J Colloid Interface Sci 555:403–412 Khan MU, Rather RA, Siddiqui ZN (2020) Design, characterization and catalytic evaluation of halometallic ionic liquid incorporated Nd 2 O 3 nanoparticles ([smim][FeCl 4 ]-@ Nd 2 O 3 ) for the synthesis of N-aryl indeno pyrrole derivatives. RSC Adv 10:44892–44902 Helmholz L, Kruh RF (1952) The crystal structure of cesium chlorocuprate, Cs 2 CuCl 4 , and the spectrum of the chlorocuprate ion. J Am Chem Soc 74:1176–1181 Mereshchenko AS et al (2014) Photochemistry of copper (II) chlorocomplexes in acetonitrile: Trapping the ligand-to-metal charge transfer excited state relaxations pathways. Chem Phys Lett 615:105–110 Stein J, Fackler Jr JP, McClune GJ, Fee JA, Chan LT (1979) Superoxide and manganese (III). Reactions of manganese-EDTA and manganese-CyDTA complexes with molecular oxygen. X-ray structure of potassium manganese-EDTA 2 water. Inorg Chem 18:3511–3519 Lee A, Kim I, Kang SM (2024) Zr IV complexation for stability enhancement of polydopamine coatings and rapid grafting of amine compounds. Bull Korean Chem Soc 44:939–942 Sawyer DT, Paulsen PJ (1959) Properties and Infrared Spectra of Ethylenediamine tetraacetic Acid Complexes. II. Chelates of Divalent Ions. J Am Chem Soc 81:816–820 Brownson JR, Tejedor-Tejedor MI, Anderson MA (2006) FTIR spectroscopy of alcohol and formate interactions with mesoporous TiO 2 surfaces. J Phys Chem B 110:12494–12499 Balakrishnan T, Lee MJ, Dey J, Choi SM (2019) Sub-nanometer scale size-control of iron oxide nanoparticles with drying time of iron oleate. CrystEngComm 21:4063–4071 Lyu H et al (2022) Carbon dioxide capture chemistry of amino acid functionalized metal-organic frameworks in humid flue gas. J Am Chem Soc 144:2387–2396 Langer HG (1963) Infrared spectra of ethylenediamine tetraacetic acid (EDTA). Inorg Chem 2:1080–1082 Tao CA et al (2012) Fabrication of pH-sensitive graphene oxide-drug supramolecular hydrogels as controlled release systems. J Mater Chem 22:24856–24861 Li H, Gan S, Wang H, Han D, Niu L (2015) Intercorrelated superhybrid of AgBr supported on graphitic-C 3 N 4 ‐decorated nitrogen‐doped graphene: high engineering photocatalytic activities for water purification and CO 2 reduction. Adv Mater 27:6906–6913 Chen D et al (2021) A tandem strategy for enhancing electrochemical CO 2 reduction activity of single-atom Cu‐S 1 N 3 catalysts via integration with Cu nanoclusters. Angew Chem Int Ed 60:24022–24027 Furlani C, Morpurgo G (1963) Properties and electronic structure of tetrahalogenocuprate (II)-complexes. Theoret Chim Acta 1:102–115 Fritz JJ, Fuget CR (1956) Vapor pressure of aqueous hydrogen chloride solutions, 0° to 50°C. Ind Eng Chem 1:10–12 Zeisberg FC, van Arsdel WB, Blake FC, Greenwalt CH, Taylor GB (1928) The vapor pressures of aqueous solutions of commercial acids. International Critical Tables, vol III. McGraw-Hill, New York, p 301 Denny MS, Kalaj M, Bentz KC, Cohen SM (2018) Multicomponent metal–organic framework membranes for advanced functional composites. Chem Sci 9:8842–8849 Schemes Scheme 1 is available in the Supplementary Files section Additional Declarations There is NO Competing Interest. Supplementary Files supplementaryinformation.docx Scheme1.png Scheme 1. Schematic of the preparation of MOF-808-EDTA-Cu as an acid vapor decoder and visual identification of colorless acid vapors. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-4505436","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":311783789,"identity":"9d6add31-b010-48fb-9c57-b666058f128d","order_by":0,"name":"Jin Yeong Kim","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA80lEQVRIiWNgGAWjYBACCYYDjA8+VEjw8LM3ALkGFkRpYTacccZGTrLnAEiLBDFaGNikedvSjA1uJED5hIBk4xljYx62w4kNN59f3fCjQIKBv707Aa8WaYYzhg/n8BxObJydU3azB+gwiTNnN+DVIsdwxtjgjcThxGbpnLQbPEAtBhK5BLWYSfAYHE5skzyTdvMPMVqADjOT5ElIM+aRYD92myhbJBuOFRvOOGAjJ8GTw3ZbxkCCh6BfJG4c3vjg4z8JHvvjx5/dfPPHRo6/vRe/FgaJEwZQFg+YwYNfOQjwtz+Astgf4FIzCkbBKBgFIxwAAKL1TP7gm020AAAAAElFTkSuQmCC","orcid":"https://orcid.org/0000-0003-2250-8780","institution":"Seoul National University","correspondingAuthor":true,"prefix":"","firstName":"Jin","middleName":"Yeong","lastName":"Kim","suffix":""},{"id":311783790,"identity":"a25c557c-0e6e-4109-a689-69c2c8eb6b86","order_by":1,"name":"Wonhyeong Jang","email":"","orcid":"https://orcid.org/0000-0002-6641-5044","institution":"Seoul National University","correspondingAuthor":false,"prefix":"","firstName":"Wonhyeong","middleName":"","lastName":"Jang","suffix":""},{"id":311783791,"identity":"245f3a82-f3db-4b96-8b64-d223a3aa345e","order_by":2,"name":"Hyejin Yoo","email":"","orcid":"https://orcid.org/0009-0007-3097-9175","institution":"Seoul National University","correspondingAuthor":false,"prefix":"","firstName":"Hyejin","middleName":"","lastName":"Yoo","suffix":""},{"id":311783792,"identity":"72d7a054-a711-41e7-a1ce-c9bade6cc097","order_by":3,"name":"Dongjun Shin","email":"","orcid":"","institution":"Seoul National University","correspondingAuthor":false,"prefix":"","firstName":"Dongjun","middleName":"","lastName":"Shin","suffix":""},{"id":311783793,"identity":"331b1a74-5f6c-4fe4-979f-1a81da060b0f","order_by":4,"name":"Seokjin Noh","email":"","orcid":"","institution":"Seoul National University","correspondingAuthor":false,"prefix":"","firstName":"Seokjin","middleName":"","lastName":"Noh","suffix":""}],"badges":[],"createdAt":"2024-05-31 00:45:11","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-4505436/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-4505436/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1038/s41467-024-55774-x","type":"published","date":"2025-01-04T05:00:00+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":58029022,"identity":"0d2d4911-336d-4f1b-9c50-d2e10f6841b5","added_by":"auto","created_at":"2024-06-10 07:26:09","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":743162,"visible":true,"origin":"","legend":"\u003cp\u003e(a) Schematic illustration of the preparation of MOF-808-EDTA-Cu as an acid vapor decoder and its visual identification of hydrochloric acid vapor. (b) XRPD patterns of MOF-808-EDTA-Cu (blue) and MOF-808-EDTA-Cu (HCl) (red) with simulated XRPD pattern of MOF-808 (black). (c) N\u003csub\u003e2\u003c/sub\u003e sorption isotherms of MOF-808 (black) and MOF-808-EDTA-Cu (blue) measured at 77 K. (d) SEM images and the EDS elemental mapping images of MOF-808-EDTA-Cu (top) and MOF-808-EDTA-Cu (HCl) (bottom). (e) Photographs of MOF-808-EDTA-Cu with hydrochloric acid vapor exposure and regeneration series. (f) Diffuse reflectance UV-vis-NIR spectra of MOF-808-EDTA-Cu and MOF-808-EDTA-Cu (HCl). Inset: Suggested coordination system of Cu\u003csup\u003e2+\u003c/sup\u003e, copper (teal), oxygen (red), nitrogen (violet), and chlorine (yellow). (g) FT-IR spectra of MOF-808-EDTA-Cu (blue) and MOF-808-EDTA-Cu-HCl (red). (h) N 1s XPS spectra of MOF-808 EDTA-Cu (top) and MOF-808 EDTA-Cu (HCl) (bottom).\u003c/p\u003e","description":"","filename":"floatimage2.png","url":"https://assets-eu.researchsquare.com/files/rs-4505436/v1/1659d99e44fefe54a6178389.png"},{"id":58029027,"identity":"ba65d343-d2aa-47fe-87f2-2925ad6f2281","added_by":"auto","created_at":"2024-06-10 07:26:10","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":546311,"visible":true,"origin":"","legend":"\u003cp\u003e(a) Photographs of MOF-808-EDTA-Cu for identifying HCl, HBr, and HI vapors. (b) Photographs of MOF-808-EDTA-Fe after exposure to HCl and HBr vapors. (c) SEM images and the EDS elemental mapping images of MOF-808-EDTA-Cu/Co (Cu atomic%=2.91%, Co atomic%=1.34%). (d) Photographs of MOF-808-EDTA-Cu/Co after exposure to HF, HCl, HBr, HI, HNO\u003csub\u003e3\u003c/sub\u003e, and trifluoroacetic acid vapors.\u003c/p\u003e","description":"","filename":"floatimage3.png","url":"https://assets-eu.researchsquare.com/files/rs-4505436/v1/0c2b167ef20e03f73d58e703.png"},{"id":58029026,"identity":"62ea6840-67d0-4d45-9f11-274df6bb8a49","added_by":"auto","created_at":"2024-06-10 07:26:10","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":359267,"visible":true,"origin":"","legend":"\u003cp\u003e(a) Schematic illustration of the preparation of MOF-808-EDTA-Cu film and process for the extraction of RGB (Red, Green, Blue) channel value of film. (b) Time-dependent RGB curves of MOF-808-EDTA-Cu portable sensor exposed to 15500 ppm HCl vapor. Inset: Photographs of MOF-808-EDTA-Cu portable sensor under 15500 ppm HCl vapor exposure. (c) Response curve by relationship between |dB|/dB\u003csub\u003e0\u003c/sub\u003e value and concentration of HCl vapor (120, 300, and 740 ppm) after 3 min of acid expose. Error bar states the standard error based on three experimental trials. (d) Time-dependent RGB curves of MOF-808-EDTA-Cu portable sensor exposed to 85% RH water vapor. Inset: Photographs of MOF-808-EDTA-Cu portable sensor under 85% RH water vapor exposure. (e) Time-dependent RGB curves of MOF-808-EDTA-Cu portable sensors exposed to HF, HBr, and HI vapor. Inset: Photographs of the MOF-808-EDTA-Cu portable sensor after exposure to HF, HBr, and HI vapors for 25 min, 35 min, and 60 min, respectively (top), and after 2 min of exposure (bottom) (f) Principal component analysis (PCA) result for discrimination of hydrohalic acids, based on three experimental trials. (g) Hierarchical cluster analysis (HCA) dendrogram designed for categorizing hydrohalic acids, based on three experimental trials.\u003c/p\u003e","description":"","filename":"floatimage4.png","url":"https://assets-eu.researchsquare.com/files/rs-4505436/v1/8722715c52f9cc00e0996396.png"},{"id":72985865,"identity":"be8e603f-d0ed-4ad0-88ec-a247aac23c63","added_by":"auto","created_at":"2025-01-05 08:06:09","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":2402675,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-4505436/v1/12eac0f7-4354-4da8-a32d-b62d30dd217c.pdf"},{"id":58029024,"identity":"71fb0ef9-aa44-4c23-8b48-bf1e377b102c","added_by":"auto","created_at":"2024-06-10 07:26:09","extension":"docx","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":6122281,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cbr\u003e\u003c/p\u003e","description":"","filename":"supplementaryinformation.docx","url":"https://assets-eu.researchsquare.com/files/rs-4505436/v1/49b80397bb3818b492ca62ac.docx"},{"id":58029023,"identity":"f446de1e-5ed1-497e-8b16-5de5b6295608","added_by":"auto","created_at":"2024-06-10 07:26:09","extension":"png","order_by":2,"title":"","display":"","copyAsset":false,"role":"supplement","size":246008,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eScheme 1.\u003c/strong\u003e Schematic of the preparation of MOF-808-EDTA-Cu as an acid vapor decoder and visual identification of colorless acid vapors.\u003c/p\u003e","description":"","filename":"Scheme1.png","url":"https://assets-eu.researchsquare.com/files/rs-4505436/v1/2fc95e5857f1e48e34f18101.png"}],"financialInterests":"There is \u003cb\u003eNO\u003c/b\u003e Competing Interest.","formattedTitle":"Colorimetric Identification of Colorless Acid Vapors using a Metal-Organic Framework-Based Sensor","fulltext":[{"header":"Introduction","content":"\u003cp\u003eAcids are essential reagents in modern chemical processes and are used to produce various chemicals, such as fertilizers, detergents, batteries, and pharmaceuticals, as well as to remove impurities from many products\u003csup\u003e\u003cspan additionalcitationids=\"CR2 CR3 CR4 CR5\" citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e\u003c/sup\u003e. Despite their versatility, acids pose significant risks owing to their corrosive and chemically reactive nature, which can cause irritation or severe damage to the eyes, skin, and respiratory system upon exposure to high concentrations or prolonged exposure\u003csup\u003e\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e\u003c/sup\u003e. The required emergency response and first-aid protocols depend on the type of acid exposed\u003csup\u003e\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e\u003c/sup\u003e; hence, the detection and identification of hazardous acid chemicals is of paramount importance for applications ranging from health diagnostics to public safety and environmental protection\u003csup\u003e1\u0026ndash;2,11\u0026minus;12\u003c/sup\u003e. Electrochemical acid vapor sensors, some of which are already commercially available, exhibit high sensitivity, however, their acid vapors identification efficiency is limited\u003csup\u003e\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e\u003c/sup\u003e. Moreover, traditional acid vapor identification methods, including infrared and mass spectrometry, require complex and expensive instrumentation, rendering on-site identification of acid vapors challenging\u003csup\u003e\u003cspan additionalcitationids=\"CR16\" citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eOne of the most attractive approaches in this field involves the construction of colorimetric molecular decoders that offer simplicity in identifying acid vapors with the naked eye, cost efficiency, and the potential for on-site identification of multiple targets. Recently, several colorimetric sensors have been reported utilizing organic dyes\u003csup\u003e\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e\u003c/sup\u003e, polymers\u003csup\u003e\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e\u003c/sup\u003e, covalent organic frameworks (COFs)\u003csup\u003e\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e\u003c/sup\u003e, and metal-organic frameworks (MOFs) \u003csup\u003e\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e,\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e\u003c/sup\u003e. However, most studies have focused on detecting single HCl vapors by relying on a protonation mechanism, which cannot differentiate between various acid vapors. Recent studies on colorimetric sensor arrays have demonstrated that integrating the detection results from multiple sensor domains can distinguish various chemical vapors, including some acid vapors; however, this requires additional complex data processing\u003csup\u003e\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e\u003c/sup\u003e. Consequently, despite their importance, research on sensor materials capable of visually identifying acidic gases remains in the preliminary stages.\u003c/p\u003e \u003cp\u003eTo develop a true optical molecular decoder for the identification of colorless acidic vapors, an anion-participating colorimetric sensing mechanism is required. Transition-metal chelate complexes are attractive candidates for use in visual identification sensors. Chelating ligands such as ethylenediaminetetraacetic acid (EDTA), which form a stable metal complex, can release chelated metal ions under acidic conditions\u003csup\u003e\u003cspan additionalcitationids=\"CR27\" citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e\u003c/sup\u003e. The de-chelated transition metal ion acts as a colorimetric center, displaying characteristic colors depending on the coordinating ligands and coordination geometry, thus enabling the visualization of acidic vapors in a single-domain sensor. However, most pure metal-chelate complexes exist as non-porous powders, which impedes their direct exposure to acid vapors and their processing into practical sensors.\u003c/p\u003e \u003cp\u003eHerein, we report a novel MOF-based acid vapor decoder, MOF-808-EDTA-Cu, capable of visually identifying exposed colorless acid vapors (Scheme \u003cspan refid=\"Sch1\" class=\"InternalRef\"\u003e1\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eMOF-808, a robust and porous Zr-based MOF, was selected as the platform, and Cu-chelated EDTA (Cu-EDTA) was incorporated as the proton-triggered colorimetric center. Direct exposure of the Cu-EDTA colorimetric center to HCl vapors facilitated the cyan-to-yellow color transition at HCl concentrations as low as 120 ppm. Interestingly, the Cu-EDTA colorimetric center could be regenerated up to three times via a simple immersion in water. Furthermore, the Cu-EDTA-grafted MOF-808 exhibited characteristic color changes from cyan to pale green, dark purple, and brown upon exposure to different acid vapors (HF, HBr, and HI), whereas it did not react to interfering gases, humidity, or temperature variations. This unique acid-selective colorimetric behavior originates from the de-chelation of metal ions from the stable Cu-EDTA, triggered by protons, followed by a color- change mechanism involving anions in the acid vapors. To the best of our knowledge, it is the first approach to specifically identify acid vapor using both protonation and anion dependent systems in a single domain sensor. Due to the strong chelating properties of EDTA, multiple metal ions could be easily incorporated into a single sensor domain with atomic-level dispersion, expanding the decoding capability to identify six different acidic vapors. Additionally, by introducing a flexible polymer, the Cu-EDTA-decorated MOF-808 was successfully processed into a portable miniaturized acid decoder, exhibiting distinct color changes detectable by the naked eye and monitored by camera sensors. This proves its practicality and versatility as an acid vapor-triggered colorimetric decoder for 24-hour on-site monitoring applications.\u003c/p\u003e"},{"header":"Results","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003ePreparation and characterization of MOF-808-EDTA-Cu\u003c/h2\u003e \u003cp\u003eTo develop an acid vapor decoder system featuring a fully exposed colorimetric decoder, EDTA-coordinated MOF-808 (designated as MOF-808-EDTA) was prepared following a previously reported method\u003csup\u003e\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e\u003c/sup\u003e (Supplementary Figs.\u0026nbsp;1 and 2). The colorimetric center Cu\u003csup\u003e2+\u003c/sup\u003e was introduced by soaking MOF-808-EDTA in a 100 mM Cu\u003csup\u003e2+\u003c/sup\u003e solution for 24 h, affording a cyan-colored powder. The Cu-ion-incorporated MOF-808-EDTA was denoted as MOF-808-EDTA-Cu (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ea). The X-ray powder diffraction (XRPD) patterns of MOF-808-EDTA-Cu confirmed that the framework structure was maintained even after post-synthetic treatments (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eb). Inductively coupled plasma-atomic emission spectrometry (ICP-AES) confirmed that the Cu\u003csup\u003e2+\u003c/sup\u003e ions capable of chelating up to 82% of EDTA were successfully incorporated into MOF-808-EDTA-Cu. Concurrently, the Fourier transform-infrared (FT-IR) spectrum of MOF-808-EDTA-Cu showed the absence of peaks associated with NO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e constituting the Cu precursor, ruling out the possibility of the physical inclusion of Cu precursors into the MOF pores (Supplementary Fig.\u0026nbsp;3)\u003csup\u003e\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e\u003c/sup\u003e. Upon the inclusion of Cu ions into MOF-808-EDTA, the ultraviolet visible near-infrared (UV-vis-NIR) spectrum revealed a new absorption peak at 13140 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, corresponding to the d-d transition \u003csup\u003e\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e\u003c/sup\u003eE\u003csub\u003eg\u003c/sub\u003e \u0026rarr; \u003csup\u003e\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e\u003c/sup\u003eT\u003csub\u003e2g\u003c/sub\u003e of an octahedral six-coordinated Cu ion, which is the same as in the previously reported [Cu(EDTA)(H\u003csub\u003e2\u003c/sub\u003eO)]\u003csup\u003e\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e\u003c/sup\u003e, suggesting the presence of Cu-chelated EDTA in the MOF-808-EDTA-Cu system (Supplementary Fig.\u0026nbsp;4). X-ray photoelectron spectroscopy (XPS) of MOF-808-EDTA-Cu (Supplementary Fig.\u0026nbsp;5) revealed a significant shift in the Zr 3d binding energy compared to MOF-808, with the monocarboxylate ligand removed, indicating that the EDTA molecule chelating the Cu ion remained grafted to the Zr\u003csub\u003e6\u003c/sub\u003e cluster of MOF-808-EDTA-Cu\u003csup\u003e\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e,\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e\u003c/sup\u003e. Nitrogen sorption measurements of MOF-808-EDTA-Cu showed a decrease both in surface area and pore size of larger cavity (1127 m\u003csup\u003e2\u003c/sup\u003e/g and 0.79 nm) compared to that of the pristine MOF-808 (2108 m\u003csup\u003e2\u003c/sup\u003e/g and 1.30 nm), indicating that Cu chelated EDTA, the colorimetric center, exists in accessible internal pores of MOF-808 rather physical mixed (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ec and Supplementary Fig.\u0026nbsp;6). Therefore, MOF-808-EDTA-Cu containing fully exposed Cu-EDTA within its accessible pores, was successfully prepared as a colorimetric sensor via a simple post-synthetic modification.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003eColorimetric response of MOF-808-EDTA-Cu to HCl vapor\u003c/h2\u003e \u003cp\u003eAn interesting naked-eye detectable color change from cyan to yellow was observed in MOF-808-EDTA-Cu within 20 s of exposure to HCl vapors evaporated from a concentrated HCl solution (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ee). Remarkably, this transition occurred without any structural changes in the MOF-808 framework, suggesting that the eye-detectable color shift did not originate from structural decomposition (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eb). Further analysis confirmed the incorporation of chlorine into MOF-808-EDTA-Cu after exposure, as evidenced by scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (SEM-EDS) (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ed) and the XPS spectra of Cl 2p (Supplementary Fig.\u0026nbsp;7). The emergence of a Cu\u0026ndash;Cl stretching vibration peak at ~\u0026thinsp;289 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e in the Raman spectra (Supplementary Fig.\u0026nbsp;8) indicated the formation of new bonds between Cu and Cl \u003csup\u003e\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e\u003c/sup\u003e. Upon exposure to HCl, UV\u0026ndash;vis\u0026ndash;NIR spectroscopy showed new absorption peaks at 34364 and 25316 cm⁻\u0026sup1;, suggesting that the coordination environment of the Cu\u003csup\u003e2+\u003c/sup\u003e ion is changed (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ef). Interestingly, these peaks align with the LMCT characteristics reported for tetrahedrally structured CuCl\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e2\u0026thinsp;\u0026minus;\u0026thinsp;2,36\u0026minus;37\u003c/sup\u003e, implying that free Cu\u003csup\u003e2+\u003c/sup\u003e ions de-chelated from EDTA forming a new yellow Cu-Cl complex (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ef). Importantly, MOF-808-EDTA-Cu demonstrated selectivity towards acid gas, maintaining its colorimetric response unchanged when exposed to potentially interfering air gases such as N₂, O₂, and CO₂, as well as variations in humidity and temperature within a substantial range (Supplementary Fig.\u0026nbsp;9). This highlights its potential as a reliable acid-vapor-selective sensor for practical applications.\u003c/p\u003e \u003cp\u003eAn intriguing colorimetric response was observed upon exposure of MOF-808-EDTA-Cu to HCl vapor, which was detectable even at concentrations as low as 120 ppm, although a longer detection time was required. Cu-EDTA and Cu(CH₃COO)₂, characterized by non-porous and densely packed structures, displayed gradual color changes after acidic exposure for 1 h at 120 ppm. Conversely, MOF-808-EDTA-Cu exhibited a visible color shift within 5 min, underscoring the significance of grafting Cu-EDTA onto MOF-808 and directly expose it to external acidic vapors for efficient acid sensing (Supplementary Fig.\u0026nbsp;10). Upon immersion in water, the yellow color of the HCl-exposed MOF-808-EDTA-Cu immediately changed to cyan and was recovered as a cyan powder through filtration (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ee). The recovered MOF exhibited the same UV-Vis-NIR spectrum as that of MOF-808-EDTA-Cu (Supplementary Fig.\u0026nbsp;11). This intriguing regeneration of the sensor is attributed to the characteristics of EDTA, which is known to efficiently chelate various metal ions even at low concentrations in aqueous solutions\u003csup\u003e\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e,\u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e\u003c/sup\u003e. Consequently, the EDTA-decorated MOF-808 demonstrated an ability to re-chelate approximately 80% of Cu\u0026sup2;⁺ ions during the regeneration process, as confirmed by ICP-AES analysis. Furthermore, during three cycles of alternating exposure to HCl and water, MOF-808-EDTA-Cu continued to exhibit reversible cyan-yellow color variations, highlighting the reusability of the sensor (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ee).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003eAcid-triggered colorimetric decoding mechanism\u003c/h2\u003e \u003cp\u003eTo reveal the underlying mechanism of the formation of yellow Cu-Cl complexes from highly stable cyan-colored Cu-EDTA complexes, a series of controlled experiments were conducted with MOF-808-EDTA-Cu. First, to elucidate the formation conditions of the Cu-Cl complexes from MOF-808-Cu-EDTA, three types of aqueous solutions containing the same 4 M Cl\u003csup\u003e\u0026minus;\u003c/sup\u003e ions were prepared: two neutral (NaCl and KCl) and one acidic (HCl) solution. In the 4M Cl\u003csup\u003e\u0026minus;\u003c/sup\u003e solution, a portion of the introduced free Cu\u003csup\u003e2+\u003c/sup\u003e ions formed a yellow Cu-Cl complex, leading to a color change from blue to greenish-yellow (Supplementary Fig.\u0026nbsp;12a). Notably, MOF-808-EDTA-Cu turned greenish-yellow only in the acidic HCl solution, while retaining its cyan color in the other solutions, indicating the generation of free Cu\u003csup\u003e2+\u003c/sup\u003e ions from Cu-EDTA only under acidic conditions (Supplementary Fig.\u0026nbsp;12b). This unique acid-condition-selective color transformation stems from alterations in the functional groups of EDTA, as evidenced by the FT-IR spectra of MOF-808-EDTA-Cu before and after exposure to HCl (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eg). Compared to MOF-808-EDTA-Cu, the HCl-exposed MOF-808-EDTA-Cu showed decreased intensity of the peak at 1566 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, corresponding to the ν\u003csub\u003eas,COO\u0026minus;\u003c/sub\u003e of EDTA\u003csup\u003e\u003cspan additionalcitationids=\"CR41 CR42\" citationid=\"CR40\" class=\"CitationRef\"\u003e40\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e43\u003c/span\u003e\u003c/sup\u003e, while the emergence of a new peak at 1719 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e was attributed to the ν\u003csub\u003eC=O\u003c/sub\u003e of carboxylic acids, indicating the protonation of the carboxylate in EDTA\u003csup\u003e\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e,\u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e44\u003c/span\u003e\u003c/sup\u003e. XPS spectra of the HCl-exposed MOF-808-EDTA-Cu compared to MOF-808-EDTA-Cu revealed new peaks at 401.6 and 533.1 eV corresponding to the N 1s of the protonated amine (-HN\u003csup\u003e+\u003c/sup\u003e-) and O 1s of the carboxylic acid in EDTA\u003csup\u003e\u003cspan additionalcitationids=\"CR46\" citationid=\"CR45\" class=\"CitationRef\"\u003e45\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e47\u003c/span\u003e\u003c/sup\u003e, respectively, further supporting the protonation of EDTA which hardly chelates the Cu\u003csup\u003e2+\u003c/sup\u003e ion, resulting in the release of free Cu ions (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eh and Supplementary Fig.\u0026nbsp;13). Therefore, both Cl\u003csup\u003e\u0026minus;\u003c/sup\u003e and H\u003csup\u003e+\u003c/sup\u003e are essential for the colorimetric decoding of acid vapors by MOF-808-EDTA-Cu. These unique acid-selective color transition mechanism demonstrates the potential of MOF-808-EDTA-Cu as a true colorimetric acid sensor that can selectively react with anions in acidic environments.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec6\" class=\"Section2\"\u003e \u003ch2\u003eMOF decoder to visualize exposed acid vapors\u003c/h2\u003e \u003cp\u003eBuilding on the unique acid-triggered and anionic participation in the colorimetric sensing mechanism, we explored the potential of MOF-808-EDTA-Cu as a colorimetric sensor for the visualization of colorless hydrohalic acid vapors. The MOF-808-EDTA-Cu sensor distinctly visualized the exposed hydrohalic acid vapors, namely HF, HBr, and HI, as white, dark purple, and brown, respectively (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ea). Interestingly, these observed color changes were aligned with the expected colors resulting from the interaction of free Cu ions with halide ions, suggesting that the de-chelated Cu\u003csup\u003e2+\u003c/sup\u003e ions from the protonated EDTA in MOF-808-EDTA-Cu reacted with hydrohalic acids (Supplementary Fig.\u0026nbsp;14). Specifically, the UV-vis-NIR spectra of MOF-808-EDTA-Cu after exposure to HF and HBr were consistent with those of CuF\u003csub\u003e2\u003c/sub\u003e and CuBr\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e2\u0026minus;\u003c/sup\u003e, respectively\u003csup\u003e\u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e48\u003c/span\u003e\u003c/sup\u003e, implying the formation of white CuF\u003csub\u003e2\u003c/sub\u003e and purple CuBr\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e2\u0026minus;\u003c/sup\u003e within the MOF sensor following acid exposure (Supplementary Figs.\u0026nbsp;15 and 16). Furthermore, exposure to HI resulted in the formation of white CuI(s) and brown I\u003csub\u003e2\u003c/sub\u003e(aq), as confirmed by PXRD and UV-vis-NIR spectra, suggesting that the brown color of the HI-exposed MOF-808-EDTA-Cu originated from I\u003csub\u003e2\u003c/sub\u003e(aq) rather than CuI(s) (Supplementary Fig.\u0026nbsp;17). The exceptionally strong chelation of EDTA in MOF-808 renders it versatile and enables the incorporation of various metal ions into the MOF-808 sensor. To further explore our methodology, we prepared Fe\u003csup\u003e3+\u003c/sup\u003e-chelated MOF-808-EDTA (referred to as MOF-808-EDTA-Fe) as a colorimetric sensor, which exhibited a distinct color change from ivory to yellow and orange upon exposure to HCl and HBr, respectively (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eb and Supplementary Fig.\u0026nbsp;18).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eFurthermore, the strong chelation capability of EDTA allowed MOF-808-EDTA to effectively integrate multiple metal ions (Cu\u003csup\u003e2+\u003c/sup\u003e and Co\u003csup\u003e2+\u003c/sup\u003e) with atomic-level dispersion, thereby expanding the scope of visually-identifiable acid vapors within a single-domain sensor (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ec). MOF-808-EDTA-Cu/Co, featuring Cu-chelated EDTA and Co-chelated EDTA, exhibited a unique ability to differentiate between six acidic vapors within a single-domain sensor (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ed). This capability arises from the co-presence of Cu-chelated EDTA, adept at decoding hydrohalic acid and Co-chelated EDTA, proficient at decoding nitric acid and trifluoroacetic acid (TFA). Such findings demonstrate the versatility and resilience of our sensor platform, providing visual identification of a variety of acid vapors with a single sensor domain.\u003c/p\u003e \u003cp\u003eTo exploit the outstanding properties of the MOF-808-EDTA-Cu platform for the visualization of colorless acid vapors, the fabrication of miniaturized portable acid vapor sensors that could be used for real-time on-site monitoring was explored (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ea). For transformation into a portable acid vapor decoding sensor, a MOF sensor-based ink was fabricated by combining MOF-808-EDTA-Cu with polyvinylidene fluoride (PVDF) in a dimethylformamide (DMF) solution, which can be applied to various substrates, including foil, paper, fabric, and glass (Supplementary Fig.\u0026nbsp;19). When exposed to HCl vapor evaporating from a concentrated HCl solution (approximately 15,500 ppm)\u003csup\u003e\u003cspan citationid=\"CR49\" class=\"CitationRef\"\u003e49\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR50\" class=\"CitationRef\"\u003e50\u003c/span\u003e\u003c/sup\u003e, the MOF-808-EDTA-Cu portable sensor underwent a distinct color shift from cyan to yellow, which was detectable by the naked eye and recorded by a camera sensor (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eb). This color change was further translated into RGB channel values, allowing the quantification of the color changes and 24-hour real-time monitoring. Notably, when exposed to low concentrations of HCl where the color change is not saturated, the sensor exhibited a reduced transition from cyan to yellow within the same exposure timeframe, suggesting its potential as an acid\u0026ndash;gas concentration analyzer (see Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ec). This transition can be precisely quantified using the equation |dB|/B\u003csub\u003e0\u003c/sub\u003e, where |dB| denotes the absolute value of change in the blue channel value from the initial blue channel value B\u003csub\u003e0\u003c/sub\u003e. Correlation of the |dB|/B\u003csub\u003e0\u003c/sub\u003e ratio with different HCl vapor concentrations can establish a linear range spanning from 120 to 740 ppm, providing experimental validation of the portable sensor as a colorimetric sensor capable of quantifying the concentration of exposed HCl vapor. Additionally, when exposed to an atmosphere with high relative humidity (RH) 85%, no color change was detected both with the naked eye or even with RGB values, demonstrating its practical use as a portable sensor capable of selectively visualizing acidic vapors, even in the presence of humidity interference (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ed).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eBased on the obtained results, we extended our investigation on the color changes of sensors upon exposure to various acid vapors. In experiments with hydrohalic acid vapors, including HF, HBr, and HI, the color change of the MOF-808-EDTA-Cu portable sensor was not complete until 25 min, however, changes detectable by the naked eye appeared within 10 min (Supplementary Fig.\u0026nbsp;20). Interestingly, when monitoring the color shifts of the portable sensor via the RGB channel values, distinct trends in the RGB channel values depending on the exposed acid vapors were observed, even in the early stages when they were barely detectable by the naked eye (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ee). Furthermore, these acid-dependent distinct color alterations enable the statistical validation of exposure to hydrohalic acid vapor within 2 min by applying principal component analysis (PCA) and hierarchical cluster analysis (HCA) methods. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ef, the 12 datasets of dR, dG, and dB obtained from three repeated 2-min exposure experiments with four different hydrohalic acids formed distinct clusters that were well-spaced apart, implying efficient identification. HCA-based data classification using Ward's method revealed that when the closest data points were clustered, three points originating from the same acid vapor exposure experiments were successfully grouped together, confirming the ability of the sensor to discriminate between acids (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eg). Moreover, this versatile portable sensor platform can incorporate various transition metals, such as Co and Fe, to broaden the decoding range of acid vapors to up to six types or to adjust the detection color (Supplementary Fig.\u0026nbsp;21), providing experimental validation of its applicability to diverse industrial requirements.\u003c/p\u003e \u003c/div\u003e"},{"header":"Conclusions","content":"\u003cp\u003eWe successfully fabricated a colorimetric acid vapor sensor capable of on-site differentiation between various acid vapors, leveraging the color-changing attributes of a built-in colorimetric center, Cu-EDTA, in the robust and porous MOF-808-EDTA-Cu. Cu-EDTA grafted in MOF-808-EDTA-Cu was directly exposed to acid vapors, enhancing its effectiveness in identifying acid vapors and translating the different anion components of corrosive acids into visible colors. Notably, MOF-808-EDTA-Cu was unresponsive to interfering gases, humidity, and temperature variations, rendering it a practical and versatile acid-triggered sensor for on-site applications. This distinctive acid-selective colorimetric behavior stems from the proton-triggered de-chelation of metal ions from the stable Cu-EDTA, which is followed by a color-change mechanism that involves anions present in the acid vapors. Further, the strong chelating properties of EDTA in MOF-based sensors enable the easy extension to other metal ions, such as Fe and Co, broadening its ability to detect various acid vapors in a single-domain sensor as well as its potential customization for specific industrial needs. The integration of a polymer into the MOF sensor led to the development of a portable miniaturized sensor capable of visually identifying six different colorless acid vapors, highlighting its versatility in practical 24-hour on-site monitoring of acid vapor sensor applications. This simple yet sophisticated decoding method using wireless communication technology enables the development of a novel gas sensors capable of detection and identification of hazardous acid chemicals, providing comprehensive and real-time data for large-scale environmental monitoring.\u003c/p\u003e"},{"header":"Methods","content":"\u003cdiv id=\"Sec9\" class=\"Section2\"\u003e \u003ch2\u003eMaterials and Characterization\u003c/h2\u003e \u003cp\u003eAll chemicals and solvents were of reagent grade and used without further purification. X-ray powder diffraction (XRPD) patterns were collected on a Bruker D2 PHASER at 30 kV and 10 mA for Cu K\u003csub\u003eα\u003c/sub\u003e (λ\u0026thinsp;=\u0026thinsp;1.54050 \u0026Aring;), with a step size of 0.02\u0026deg; in 2 \u003cem\u003eθ\u003c/em\u003e. Fourier transform-Infrared (FT-IR) spectra were recorded on a Bruker ALPHA II FT-IR spectrometer using the attenuated total reflection (ATR) mode. \u003csup\u003e\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u003c/sup\u003eH nuclear magnetic resonance (NMR) spectra were measured on a Bruker Avance III HD 300 MHz. The nitrogen adsorption-desorption isotherm was obtained using a Quantachrome Instruments Autosorb-iQ at 77 K. All samples (~\u0026thinsp;60 mg) were activated under ultra-high vacuum at 130\u0026deg;C for 24 h prior to each measurement. Scanning electron microscopy (SEM) images and energy dispersive X-ray spectroscopy (EDS) mapping were taken using JSM 7800F Prime operating at 15 kV. For SEM imaging, the samples were placed on the carbon tape on an aluminum sample holder and coated using carbon-sputter coating. X-ray photoelectron spectroscopy (XPS) data were obtained by using an AXIS SUPRA and spectra were analyzed using XPSPEAK 4.1. Inductively coupled-atomic emission spectroscopy (ICP-AES) data were collected on a Perkin Elmer Optima 8300. For ICP-AES sample preparation, 0.01 g of samples were digested with 60 \u0026micro;L of hydrofluoric acid. The hydrofluoric acid was completely removed by vaporization before the samples were further dissolved with 4 mL of nitric acid. The acid digested samples were diluted with deionized water before measurement. UV-Vis-NIR spectra were recorded with a PerkinElmer Lambda 365 UV/Vis spectrophotometer for reflectance measurement. Raman spectroscopy data were obtained using a Thermo Fischer Scientific DXR2xi Raman imaging microscope with 532 nm laser source.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec10\" class=\"Section2\"\u003e \u003ch2\u003eSynthesis of MOF-808-EDTA\u003c/h2\u003e \u003cp\u003eMOF-808-EDTA was prepared based on the methods reported on previous literature studies\u003csup\u003e\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e\u003c/sup\u003e. 1,3,5-Benzentricarboxylic acid (0.786 g, 3.7 mmol) and ZrOCl\u003csub\u003e2\u003c/sub\u003e\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\bullet\\)\u003c/span\u003e\u003c/span\u003e8H\u003csub\u003e2\u003c/sub\u003eO (1.209 g, 3.7 mmol) were dissolved in the mixture of N,N-Dimethylformamide (DMF) (150 mL) and formic acid (150 mL) in a 500 mL lab bottle, and the bottle was heated in an oven at 130\u0026deg;C for 24 h. The white powder was collected by filtration and washed with DMF, water and acetone for three days respectively, during which time the solvents were replaced two times per day. The MOF-808 was activated by heating at 150\u0026deg;C for 24 h in vacuum condition. Yield: 0.834 g (67%), \u003csup\u003e\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u003c/sup\u003eH-NMR (DMSO-d\u003csub\u003e6\u003c/sub\u003e): δ 8.56 (s, 3H), FT-IR (ATR, cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e): \u003cem\u003eν\u003c/em\u003e\u003csub\u003eas (carboxylate, BTC)\u003c/sub\u003e\u0026thinsp;=\u0026thinsp;1605(s), \u003cem\u003eν\u003c/em\u003e\u003csub\u003eas (carboxylate, formate)\u003c/sub\u003e\u0026thinsp;=\u0026thinsp;1564(s), \u003cem\u003eν\u003c/em\u003e\u003csub\u003eO\u0026minus;C=O(aromatic carboxylate, sym)\u003c/sub\u003e\u0026thinsp;=\u0026thinsp;1445(s), \u003cem\u003eν\u003c/em\u003e\u003csub\u003eO\u0026minus;C=O(aliphatic carboxylate, sym)\u003c/sub\u003e\u0026thinsp;=\u0026thinsp;1379(s). Then 0.100 g of activated MOF-808 and 1.860 g of ethylenediaminetetraacetic acid disodium salt (EDTA-2Na) were dissolved in 50 mL water. The contents were placed in a 100 mL lab bottle and heated at 80\u0026deg;C for 24 h. The powder was filtered and washed with water for several times to remove unreacted EDTA. It was then washed several times with fresh acetone. The solid was dried overnight at 100\u0026deg;C under vacuum. \u003csup\u003e\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u003c/sup\u003eH-NMR (DMSO-d\u003csub\u003e6\u003c/sub\u003e): δ 8.56 (s, 3H), δ 4.10 (s, 8H), δ 3.60 (s, 4H), FT-IR (ATR, cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e): \u003cem\u003eν\u003c/em\u003e\u003csub\u003eO\u0026minus;C=O(aromatic carboxylate, asym)\u003c/sub\u003e\u0026thinsp;=\u0026thinsp;1615(s), \u003cem\u003eν\u003c/em\u003e\u003csub\u003eO\u0026minus;C=O(aliphatic carboxylate, asym)\u003c/sub\u003e\u0026thinsp;=\u0026thinsp;1566(s), \u003cem\u003eν\u003c/em\u003e\u003csub\u003eO\u0026minus;C=O(aromatic carboxylate, sym)\u003c/sub\u003e\u0026thinsp;=\u0026thinsp;1445(s), \u003cem\u003eν\u003c/em\u003e\u003csub\u003eO\u0026minus;C=O(aliphatic carboxylate, sym)\u003c/sub\u003e\u0026thinsp;=\u0026thinsp;1381(s), \u003cem\u003eν\u003c/em\u003e\u003csub\u003eC\u0026minus;N(EDTA)\u003c/sub\u003e\u0026thinsp;=\u0026thinsp;1214(sh).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec11\" class=\"Section2\"\u003e \u003ch2\u003eSynthesis of MOF-808-EDTA-Metal\u003c/h2\u003e \u003cp\u003eTo prepare MOF-808-EDTA-M (M\u0026thinsp;=\u0026thinsp;Cu or Fe), MOF-808-EDTA (0.100 g) was added into a glass vial containing 10 mL aqueous solution of 0.1 M metal nitrate (Cu(NO\u003csub\u003e3\u003c/sub\u003e)\u003csub\u003e2\u003c/sub\u003e\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\bullet\\)\u003c/span\u003e\u003c/span\u003e3H\u003csub\u003e2\u003c/sub\u003eO and Fe(NO\u003csub\u003e3\u003c/sub\u003e)\u003csub\u003e3\u003c/sub\u003e\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\bullet\\)\u003c/span\u003e\u003c/span\u003e9H\u003csub\u003e2\u003c/sub\u003eO for MOF-808-EDTA-Cu and MOF-808-EDTA-Fe, respectively). The mixture was stirred at room temperature for 24 h and filtered through a 0.2 \u0026micro;m polytetrafluoroethylene (PTFE) membrane filter. The resulting powder was activated by heating at 100\u0026deg;C for 24 h in vacuum condition and stored at ambient condition.\u003c/p\u003e \u003cp\u003eTo prepare MOF-808-EDTA-Cu/Co, MOF-808-EDTA (0.100 g) was added into 10 mL of mixed metal solution containing equal concentration (50 mM) of Cu(NO\u003csub\u003e3\u003c/sub\u003e)\u003csub\u003e2\u003c/sub\u003e\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\bullet\\)\u003c/span\u003e\u003c/span\u003e3H\u003csub\u003e2\u003c/sub\u003eO and Co(NO\u003csub\u003e3\u003c/sub\u003e)\u003csub\u003e2\u003c/sub\u003e\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\bullet\\)\u003c/span\u003e\u003c/span\u003e6H\u003csub\u003e2\u003c/sub\u003eO. The mixture was stirred at room temperature for 24 h and filtered through a 0.2 \u0026micro;m PTFE membrane filter. The resulting powder was activated by heating at 100\u0026deg;C for 24 h in vacuum condition and stored at ambient condition.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec12\" class=\"Section2\"\u003e \u003ch2\u003eAcid Vapor Detection and Regeneration of MOF-808-EDTA-Metal\u003c/h2\u003e \u003cp\u003eA 3 cm glass dish containing 0.010 g of MOF-808-EDTA-Metal was placed inside a 5 cm glass dish with 2 mL of acid solution, ensuring no direct contact between the MOF-808-EDTA-metal and the acid solution. The 5 cm dish was covered with a 7 cm glass dish to detect vaporized acid. Different concentrations of HCl vapor were prepared using HCl solutions with various wt% based on a previously reported method\u003csup\u003e\u003cspan citationid=\"CR49\" class=\"CitationRef\"\u003e49\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR50\" class=\"CitationRef\"\u003e50\u003c/span\u003e\u003c/sup\u003e; 15460 ppm, 740 ppm, 590 ppm, 300 ppm and 120 ppm HCl vapor were prepared using 37.1 wt%, 24.7 wt%, 22.0 wt% 21.6 wt% and 18.5 wt% HCl solutions, respectively.\u003c/p\u003e \u003cp\u003eTo regenerate the acid vapor-exposed MOF-808-EDTA-Metal, the powder was added to 10 mL of DI water and stirred for 5 minutes. It was then filtered through a 0.2 \u0026micro;m membrane filter. The resulting powder was dried overnight at 100\u0026deg;C under vacuum.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec13\" class=\"Section2\"\u003e \u003ch2\u003ePreparation of Portable and Miniaturized MOF-808-EDTA-Metal Sensor\u003c/h2\u003e \u003cp\u003eThe portable and miniaturized MOF-808-EDTA-Metal sensor was fabricated by combining MOF-808-EDTA-Metal with polyvinylidene fluoride (PVDF) based on the previous literature with minor modifications\u003csup\u003e\u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e51\u003c/span\u003e\u003c/sup\u003e. 0.048 g of MOF-808-EDTA-Metal was dispersed in 2.4 mL of acetone and sonicated for 30 minutes in a vial. Then, 0.6 mL of a DMF solution containing 0.012 g of PVDF (M\u003csub\u003ew\u003c/sub\u003e ~ 534,000) was added to the MOF suspension. The suspension was further sonicated for 30 minutes, and the acetone was removed using rotary evaporation, resulting in MOF sensor-based ink. This ink was applied to various substrates, including foil, paper, fabric, and glass, and then dried at 80\u0026deg;C for 1 hour.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec14\" class=\"Section2\"\u003e \u003ch2\u003eOn-site Monitoring of Portable and Miniaturized MOF-808-EDTA-Metal Sensor Combined with Smartphone Camera\u003c/h2\u003e \u003cp\u003eThe MOF-808-EDTA-Metal portable sensor was prepared by coating 200 \u0026micro;L of MOF sensor-based ink onto a 1.8 cm x 1.8 cm cover glass. This prepared MOF portable sensor was exposed to acid vapors under the same conditions as the acid vapor detection for MOF-808-EDTA-Metal, replacing the MOF-808-EDTA-Metal powder with the MOF portable sensor. During the acid vapor exposure, the color change of MOF portable sensor was recorded as a video using the standard camera application on the Galaxy S20. The camera\u0026rsquo;s auto-focus and exposure settings were locked during recording. The video was taken in a commercially available photobox with a white LED light (6000 K color temperature and 95 color rendering index (CRI)) to ensure consistent conditions and minimize the influence of surrounding light. To quantify the color changes of the portable sensor recorded in the video, a Python script utilizing the OpenCV library was run in Linux to crop the video featuring the MOF portable sensor and calculate the mean RGB channel values of the cropped frames as a function of exposure time.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec15\" class=\"Section2\"\u003e \u003ch2\u003eDiscrimination analysis\u003c/h2\u003e \u003cp\u003ePrincipal component analysis (PCA) and hierarchical cluster analysis (HCA) was performed by using R 4.3.3 programming language, operating with R studio. Matrix with a size of 12 \u0026times; 3 (three trial of four different acids x dR, dG, dB value) was entered as input data without relying on sample labels. For PCA, \u0026lsquo;prcomp\u0026rsquo; function was mainly used to decrease the dimensionality of data, forming new principal components. The new principal component space was plotted to show as score plot. For HCA, \u0026lsquo;hclust\u0026rsquo; function was mainly used to facilitates data categorization. The dendrogram was generated for distance method as Euclidean and cluster method as Ward\u0026rsquo;s method.\u003c/p\u003e \u003c/div\u003e"},{"header":"Declarations","content":"\u003ch2\u003eAuthor contributions\u003c/h2\u003e \u003cp\u003eW.J. and J.Y.K. conceived the idea and designed the experiments. W.J. synthesized the molecular structures, carried out the experimental work, and analyzed the data; H.Y. and D.S. helped the synthesis of molecular structures experiments. H.Y., and S.N. helped in the N\u003csub\u003e2\u003c/sub\u003e sorption isotherms and PXRD measurements. W.J. and J.Y.K. co-wrote the manuscript. All authors discussed and analyzed the results.\u003c/p\u003e\u003ch2\u003eAcknowledgements\u003c/h2\u003e \u003cp\u003eThis work was supported by the National Research Foundation (NRF) of Korea funded by the Ministry of Science and ICT, South Korea (NRF-2022R1C1C101022013). This research was supported by the 4th BK21 Science Education in Infosphere Program.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eZhao CW et al (2016) An in situ self-assembled Cu\u003csub\u003e4\u003c/sub\u003eI\u003csub\u003e4\u003c/sub\u003e-MOF-based mixed matrix membrane: a highly sensitive and selective naked-eye sensor for gaseous HCl. Chem Commun 52:5238\u0026ndash;5241\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eChen X et al (2017) CsPbBr\u003csub\u003e3\u003c/sub\u003e perovskite nanocrystals as highly selective and sensitive spectrochemical probes for gaseous HCl detection. 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Bull Korean Chem Soc 44:939\u0026ndash;942\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSawyer DT, Paulsen PJ (1959) Properties and Infrared Spectra of Ethylenediamine tetraacetic Acid Complexes. II. Chelates of Divalent Ions. J Am Chem Soc 81:816\u0026ndash;820\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eBrownson JR, Tejedor-Tejedor MI, Anderson MA (2006) FTIR spectroscopy of alcohol and formate interactions with mesoporous TiO\u003csub\u003e2\u003c/sub\u003e surfaces. J Phys Chem B 110:12494\u0026ndash;12499\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eBalakrishnan T, Lee MJ, Dey J, Choi SM (2019) Sub-nanometer scale size-control of iron oxide nanoparticles with drying time of iron oleate. CrystEngComm 21:4063\u0026ndash;4071\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLyu H et al (2022) Carbon dioxide capture chemistry of amino acid functionalized metal-organic frameworks in humid flue gas. 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International Critical Tables, vol III. McGraw-Hill, New York, p 301\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eDenny MS, Kalaj M, Bentz KC, Cohen SM (2018) Multicomponent metal\u0026ndash;organic framework membranes for advanced functional composites. Chem Sci 9:8842\u0026ndash;8849\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"},{"header":"Schemes","content":"\u003cp\u003eScheme 1 is available in the Supplementary Files section\u003c/p\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":true,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"nature-portfolio","isNatureJournal":true,"hasQc":false,"allowDirectSubmit":false,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"","title":"Nature Portfolio","twitterHandle":"","acdcEnabled":false,"dfaEnabled":false,"editorialSystem":"ejp","reportingPortfolio":"","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"","lastPublishedDoi":"10.21203/rs.3.rs-4505436/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-4505436/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eIn terms of safety and emergency response, identifying hazardous gaseous acid chemicals is crucial for ensuring effective evacuation and administering proper first aid. However, current studies struggle to distinguish between different acid vapors and remain in the early stages of development. In this study, we propose a novel on-site monitorable acid vapor decoder, MOF-808-EDTA-Cu, integrating the robust MOF-808 with Cu-EDTA, functioning as a proton-triggered colorimetric decoder that translates the anionic components of corrosive acids into visible colors. The sensor exhibits a remarkable cyan-to-yellow shift when exposed to HCl vapor and can visually differentiate various acidic vapors (HF, HBr, and HI) through unique color changes. Furthermore, the compatibility of the MOF-based sensor with multiple metal ions having atomic-level dispersion broadens its discrimination range, enabling the identification of six different colorless acid vapors within a single sensor domain. Additionally, by incorporating a flexible polymer, the MOF-808-EDTA-Cu has been successfully processed into a portable miniaturized acid sensor, exhibiting distinct color changes that can be easily monitored by the naked eye and camera sensors. This provides experimental validation as a practical sensor capable of on-site 24-hour monitoring in the real world.\u003c/p\u003e","manuscriptTitle":"Colorimetric Identification of Colorless Acid Vapors using a Metal-Organic Framework-Based Sensor","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-06-10 07:26:04","doi":"10.21203/rs.3.rs-4505436/v1","editorialEvents":[],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"nature-communications","isNatureJournal":true,"hasQc":false,"allowDirectSubmit":false,"externalIdentity":"NCOMMS","sideBox":"Learn more about [Nature Communications](http://www.nature.com/ncomms/)","snPcode":"","submissionUrl":"https://mts-ncomms.nature.com/","title":"Nature Communications","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"ejp","reportingPortfolio":"Nature Communications","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"fd4dd521-be6e-4aaa-894c-9ac3c4f3174b","owner":[],"postedDate":"June 10th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[{"id":32956657,"name":"Physical sciences/Chemistry/Materials chemistry/Metal\u0026#x2013;organic frameworks"},{"id":32956658,"name":"Physical sciences/Chemistry/Green chemistry/Chemical safety"}],"tags":[],"updatedAt":"2025-01-05T08:06:04+00:00","versionOfRecord":{"articleIdentity":"rs-4505436","link":"https://doi.org/10.1038/s41467-024-55774-x","journal":{"identity":"nature-communications","isVorOnly":false,"title":"Nature Communications"},"publishedOn":"2025-01-04 05:00:00","publishedOnDateReadable":"January 4th, 2025"},"versionCreatedAt":"2024-06-10 07:26:04","video":"","vorDoi":"10.1038/s41467-024-55774-x","vorDoiUrl":"https://doi.org/10.1038/s41467-024-55774-x","workflowStages":[]},"version":"v1","identity":"rs-4505436","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-4505436","identity":"rs-4505436","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}