Optical CO(2) sensor of the combination of colorimetric change of alpha-naphtholphthalein in poly(isobutyl methacrylate) and fluorescent porphyrin in polystyrene

An optical CO₂ sensor based on the overlay of the CO₂ induced absorbance change of pH indicator dye α-naphtholphthalein in poly(isobutyl methacrylate) (polyIBM) layer with the fluorescence of tetraphenylporphyrin (TPP) in polystyrene layer is developed. The observed luminescence intensity from TPP at 655 nm increased with increasing the CO₂ concentration. The ratio I₁₀₀/I₀ value of the sensing film consisting of α-naphtholphthalein in polyIBM and TPP in polystyrene layer, where I₀ and I₁₀₀ represent the detected luminescence intensities from a layer exposed to argon and CO₂ saturated conditions, respectively, that the sensitivity of the sensor, is estimated to be 192. The response and recovery times of the sensing film are less than 6.0 s for switching from argon to CO₂, and for switching from CO₂ to argon. The signal changes are fully reversible and no hysterisis is observed during the measurements. The highly sensitive optical CO₂ sensor based on fluorescence intensity changes of TPP due to the absorption change of α-naphtholphthalein in polyIBM layer with CO₂ is achieved.     

Optical sensor for carbon dioxide combining colorimetric change of a pH indicator and a reference luminescent dye

A new optical CO₂ sensor based on the luminescence intensity change of the europium(III) complex tris(thenoyltrifluoroacetonato) europium(III) dihydrate ([Eu(tta)₃]) caused by the absorption change of various pH indicators—thymol blue, phenol red, or cresol red—with CO₂ was developed and its CO₂ sensing properties were investigated. For all the CO₂ sensors using pH indicators the observed luminescence intensity from [Eu(tta)₃] at 613 nm increased with increasing CO₂ concentration. The linear calibration method based on the plot of (I₁₀₀–I₀)/(I–I₀) versus the inverse of CO₂ concentration was suggested, where I₀ and I₁₀₀ were luminescence intensities at 613 nm of the CO₂ sensor film in 100% nitrogen and 100% gaseous CO₂. In all cases the plots showed good linearity and the correlation factors of the plots, r², were 0.991 for thymol blue, 0.990 for phenol red, and 0.998 for cresol red. The slopes of the plots (A/B) for thymol blue, phenol red, and cresol red were 2.2, 5.2, and 9.0%, respectively. The response times of the CO₂ sensor film were 4.0 s for thymol blue, 4.4 s for phenol red, and 8.8 s for cresol red for switching from nitrogen to CO₂, and the recovery times of films were 36 s for thymol blue, 39.2 s for phenol red, and 56.6 s for cresol red for switching from CO₂ to nitrogen. The signal changes were fully reversible and hysteresis was not observed during the measurements. The highly sensitive CO₂ sensor was developed using thymol blue as an indicator for the CO₂-sensing probe.     

A reagent-free SIA module for monitoring of sugar, color and dissolved CO2 content in soft drinks

This work presents a new sequential injection analysis (SIA) method and a module for simultaneous and real-time monitoring of three key parameters for the beverage industry, i.e., the sugar content (measured in Brix), color and dissolved CO₂. Detection of the light reflection at the liquid interface (the schlieren effect) of sucrose and water was utilized for sucrose content measurement. A near infrared LED (890 ± 40 nm) was chosen as the light source to ensure that all the ingredients and dyes in soft drinks will not interfere by contributing light absorption. A linear calibration was obtained for sucrose over a wide concentration range (3.1-46.5 Brix). The same module can be used to monitor the color of the soft drink as well as the dissolved CO₂ during production. For measuring the color, the sample is segmented between air plugs to avoid dispersion. An RGB-LED was chosen as the light source in order to make this module applicable to a wide range of colored samples. The module also has a section where dissolved CO₂ is measured via vaporization of the gas from the liquid phase. Dissolved CO₂, in a flowing acceptor stream of water resulting in the change of the acceptor conductivity, is detected using an in-house capacitively coupled contactless conductivity detector (C⁴D). The module includes a vaporization unit that is also used to degas the carbonated drink, prior the measurements of sucrose and color within the same system. The method requires no chemicals and is therefore completely friendly to the environment.     

Development of a volatile amine sensor for the monitoring of fish spoilage

A sensor with potential for the development of a “chemical barcode” for real-time monitoring of fish freshness is described. This on-package sensor contains a pH sensitive dye, bromocresol green, that responds through visible colour change to basic volatile spoilage compounds, such as trimethylamine (TMA), ammonia (NH₃) and dimethylamine (DMA) collectively known as Total Volatile Basic Nitrogen (TVB-N). The sensor characteristics were studied as well as its response with standard ammonia gas. Trials on cod and under-utilised species have verified that the sensor response correlates with bacterial growth patterns in fish samples thus enabling the “real-time” monitoring of spoilage in various fish species. The sensor response can be interrogated with a simple, inexpensive reflectance colorimeter that we have developed based on two light emitting diodes (LEDs) and a photodetector.     

Optical sensors for dissolved sulfur dioxide

Colorimetric sensing membranes for the determination of sulfur dioxide were developed and characterized. These films can be used for sensing trace amounts of sulfur dioxide both in the gas phase and in aqueous solutions. Lipophilic pH indicator ion pairs were immobilized in hydrophobic gas-permeable silicone and phenyl substituted ormosil. On exposure to SO₂ the films undergo a visually detectable color change from blue to yellow. No cross-sensitivity to pH and CO₂ was observed. Response times depend on the thickness of the sensing membranes, the indicator concentration in the film as well as on the respective SO₂ concentration. Membranes with response times of < 1 min (t₉₀) were developed. The sensitivity to sulfur dioxide depends on the pK_a of the indicator. An increase in the pK_a results in a lower detection limit. The new optical SO₂ sensors are chemically and mechanically stable and are easy to manufacture. The storage stability of the membranes is at least 7 months if stored in the dark. Received: 17 December 1997 / Revised: 12 June 1998 / Accepted: 15 June 1998     

CO2 regulates phase transition of sodium oleate and 3-(diethylamino)-propylamine in aqueous solution

We reported that the phase conversion of the micelles in aqueous solution prepared by sodium oleate (NaOA) and 3-(diethylamino)-propylamine (DEAPA) in the presence of carbon dioxide. This micellar structure is very sensitive to CO₂ and the pH value of the solution is continuously reduced with the continuous introduction of carbon dioxide. When pH?>?10.2, the mixed solution of NaOA and DEAPA is mainly in the form of spherical micelles; when the 10.2?>?pH?>?9.6, the mixed solution mainly in the worm-like micelles (WLM), where the solution has a significant viscosity change; when the 9.6?>?pH?>?9.1, the NaOA and DEAPA mixed solution becomes the aqueous two-phase system (ATPS), which is composed of two layers, the upper layer is the vesicle structure and the lower layer is the WLM structure; when the pH between 9.1?>?pH?>?9.0, NaOA and DEAPA mixed solution form vesicles, thus realizing the regulation of CO₂ on the micellar structure transition of NaOA and DEAPA mixed solution. Such these microstructures transition could be confirmed by Rheology measurement, DLS and Cryo-TEM.     

Luminescent dual sensor for time-resolved imaging of pCO2 and pO2 in aquatic systems

An optical dual sensor for the two-dimensional detection of pCO₂ and pO₂ is described. Tris(tetraoctylammonium)-8-hydroxypyrene-1,3,6-trisulfonate ((TOA)₃HPTS) acting together with the lipophilic buffer tetraoctylammonium hydrogen carbonate ((TOA)HCO₃) as pCO₂-sensing system along with the oxygen indicator tris(4,7-diphenyl-1,10-phenanthroline) ruthenium(II) bis(3-(trimethylsilyl)-1-propanesulfonate) (Ru(dpp)₃TMS₂) are incorporated into a single layer ethyl cellulose matrix. A second layer of black silicone rubber served as an optical isolation. The two indicators were simultaneously excited with a 460-nm LED, and a fast-gateable CCD camera was used as the detector. The time-gated imaging scheme enables the mapping of pCO₂ and pO₂ within one measurement, where images in three different time windows during and after a series of square-shaped excitation pulses are recorded. A numerical evaluation method for the resolution of the single parameter maps from these three overall images is described. The response of the sensor has been optimized for use in aquatic systems.     

Sensitively electrochemical detection of the DNA damage in situ by electro-Fenton reaction based on Fe@Fe2O3 core-shell nanonecklace and multi-walled carbon nanotube composite

An electrochemical biosensor for mimicking the metal-mediated DNA damage pathway in situ was presented. The Fenton reagents (H₂O₂ and iron ion) for the DNA damage were generated in situ with a constant rate from the sensing film. H₂O₂ and iron ion reacted further together to yield hydroxyl radical, which attacked DNA in the film. These courses of DNA damage were just like those happened in organism. The DNA damage was detected by monitoring the differential pulse voltammetric response of an electrochemical indicator, Co(phen)₃³⁺. Another electrochemical indicator, Ru(NH₃)₆³⁺, was also used for monitoring the DNA damage as a complementary means and the minimal detectable amount of DNA damage was 0.16 μg. The biosensor had good reproducibility. After this biosensor was used for 11 times, 90% of the first detection signal was obtained.     

碱金属助剂类型及前驱物对改性NiAl复合氧化物催化分解N2O活性的影响

制备了不同Ni/Al原子比的NiAl类水滑石样品,焙烧获得NiAl复合氧化物,用于N₂O分解反应,研究了NiAl复合氧化物组成对催化活性的影响。在活性较高的NiAl复合氧化物表面浸渍碱金属碳酸盐溶液,制备改性NiAl复合氧化物,考察了碱金属类型（Na、K、Cs）和钾前驱物（K₂CO₃、K₂C₂O₄、CH₃COOK、KNO₃）对改性催化剂活性的影响。用XRD、ICP-AES、FT-IR、BET、H₂-TPR、XPS技术表征了催化剂的组成结构。结果表明,Ni/Al原子比为2.7的NiAl复合氧化物催化活性较高;Na、K、Cs碳酸盐改性NiAl复合氧化物均提高了催化剂活性,其中K的助剂效应最强。钾前驱物对K改性NiAl复合氧化物的催化活性有显著影响,其中碳酸钾、醋酸钾、草酸钾的加入明显提高了改性催化剂的催化活性,而加入硝酸钾反而降低了催化剂活性。     

Assessing respiratory complications by carbon dioxide sensing platforms: Advancements in infrared radiation technology and IoT integration

Respiratory illness demands pragmatic clinical monitoring and diagnosis to curb numerous fatal diseases in all aged groups. Due to the complicated instrumentation, long amplification periods, and restricted number of simultaneous detections, present clinically available multiplex diagnostic technologies are difficult to deploy the onsite diagnostic platforms. The futuristic assessment of medical diagnosis eases the respiratory monitoring using exhaled breath, due to the simple and comfort non-invasive detecting techniques. Carbon dioxide (CO₂) stands as a promising biomarker and has been identified in exhaled breath samples that distinguish different respiratory issues. State-of-the-art CO₂ gas sensing strategies are recognized with the growth of modern telecommunication technologies for real-time respiratory illness monitoring and diagnosis using exhaled breath. The presented article reviews the existing CO₂ gas sensors and their developments towards medical applications. With that, the advancement of infrared (IR) CO₂ gas sensors with distinguished light and sensing properties in detecting respiratory disorders are overviewed. The development of optimal CO₂ gas sensing strategy incorporated with Internet of Things (IoT) technology is over-reviewed. The hurdles encountered in the existing research and future preference with real-time CO₂ monitoring and diagnosing respiratory disorders with the advancement attained in IR sensing technology and IoT networking are highlighted.     

Rapid monitoring of intermediate states and mass balance of nitrogen during denitrification by means of cavity enhanced Raman multi-gas sensing

The comprehensive investigation of changes in N cycling has been challenging so far due to difficulties with measuring gases such as N₂ and N₂O simultaneously. In this study we introduce cavity enhanced Raman gas spectroscopy as a new analytical methodology for tracing the stepwise reduction of ¹⁵N-labelled nitrate by the denitrifying bacteria Pseudomonas stutzeri. The unique capabilities of Raman multi-gas analysis enabled real-time, continuous, and non-consumptive quantification of the relevant gases (¹⁴N₂, ¹⁴N₂O, O₂, and CO₂) and to trace the fate of ¹⁵N-labeled nitrate substrate (¹⁵N₂, ¹⁵N₂O) added to a P. stutzeri culture with one single measurement. Using this new methodology, we could quantify the kinetics of the formation and degradation for all gaseous compounds (educts and products) and thus study the reaction orders. The gas quantification was complemented with the analysis of nitrate and nitrite concentrations for the online monitoring of the total nitrogen element budget. The simultaneous quantification of all gases also enabled the contactless and sterile online acquisition of the pH changes in the P. stutzeri culture by the stoichiometry of the redox reactions during denitrification and the CO₂-bicarbonate equilibrium. Continuous pH monitoring – without the need to insert an electrode into solution – elucidated e.g. an increase in the slope of the pH value coinciding with an accumulation of nitrite, which in turn led to a temporary accumulation of N₂O, due to an inhibition of nitrous oxide reductase. Cavity enhanced Raman gas spectroscopy has a high potential for the assessment of denitrification processes and can contribute substantially to our understanding of nitrogen cycling in both natural and agricultural systems.     

Dry Potassium-Based Sorbents for CO<Subscript>2</Subscript> Capture

Dry potassium-based sorbents were prepared by impregnation with potassium carbonate on supports such as activated carbon (AC), TiO₂, Al₂O₃, MgO, CaO, SiO₂ and various zeolites. The CO₂ capture capacity and regeneration property of various sorbents were measured in the presence of H₂O in a fixed bed reactor, during multiple cycles at various temperature conditions (CO₂ absorption at 50–100 °C and regeneration at 130–400 °C). The KAlI30, KCaI30, and KMgI30 sorbents formed new structures such as KAl(CO₃)₂(OH)₂, K₂Ca(CO₃)₂, K₂Mg(CO₃)₂, and K₂Mg(CO₃)₂·4(H₂O), which did not completely convert to the original K₂CO₃ phase at temperatures below 200 °C, during the CO₂ absorption process in the presence of 9 vol.% H₂O. In the case of KACI30, KTiI30, and KZrI30, only a KHCO₃ crystal structure was formed during CO₂ absorption. The formation of active species, K₂CO₃·1.5H₂O, by the pretreatment with water vapor and the formation of the KHCO₃ crystal structure after CO₂ absorption are important factors for absorption and regeneration, respectively, even at low temperatures (130–150 °C). In particular, the KTiI30 sorbent showed excellent characteristics with respect to CO₂ absorption and regeneration in that it satisfies the requirements of a large amount of CO₂ absorption (87 mg CO₂/g sorbent) without the pretreatment with water vapor, unlike KACI30, and a fast and complete regeneration at a low temperature condition (1 atm, 150 °C). In addition, the higher total CO₂ capture capacity of KMgI30 (178.6 mg CO₂/g sorbent) than that of the theoretical value (95 mg CO₂/g sorbent) was explained through the contribution of the absorption ability of MgO support. In this review, we introduce the CO₂ capture capacities and regeneration properties of several potassium-based sorbents, the changes in the physical properties of the sorbents before/after CO₂ absorption, and the role of water vapor and its effects on CO₂ absorption.     

Online analysis of products from a direct ethanol fuel cell

Methodology for the online analysis of the main products from a direct ethanol fuel cell (DEFC) has been developed. The liquid exhaust from the fuel cell is first passed through a conductivity cell to determine the concentration of acetic acid and then CO₂ is extracted into a nitrogen stream for determination with a flow-through infrared-based CO₂ sensor. The other major product, acetaldehyde can be obtained by difference from the current. The continuous measurement of these products allows monitoring of changes in product distributions with time and operating conditions, resulting in a simple online system for rapid evaluation of anode catalysts in DEFCs.     

The solubility of CO2 and N2O in olive oil

The solubility of CO₂ and N₂O in olive oil has been measured at temperatures of about 298, 310, and 323 K with a gravimetric microbalance under pressures up to 2 MPa. The molecular weight of olive oil has been analyzed and found to be about 882 g mol⁻¹ as a mixed oil compound. The observed solubility data have been correlated with a cubic equation of state (EOS) model. N₂O has a larger solubility than CO₂ in olive oil based on either the mole or mass fraction. The present results clarify some ambiguities from the previous N₂O solubility data in the literature.     

一种检测CO32-比率荧光探针的合成及其在细胞成像中的应用

本文设计开发了一种以2,6-二甲酰基对甲苯酚为母体的新型荧光探针HMI,可用于高效识别EtOH-H₂O (8/2, v/v, HEPES 10 mM, pH =7.4)体系中的CO_3^2-。HMI在660 nm处显示发射带,加入CO_3^2-后,在600 nm的等吸收点激发时,原来在660 nm处的荧光淬灭,而以540 nm为中心的新发射带荧光显着增加,为比率型荧光探针。HMI对CO_3^2-表现出高选择性且具有较强的抗干扰能力。此外,荧光探针HMI对CO_3^2-荧光响应的检测限较低,可达到3.938×10^_-6 M。更具有意义的是,HMI探针对CO_3^2-的检测能够在实际水样中起到很好的应用,而且细胞成像研究表明,HMI可用于活体MCF-7细胞中CO_3^2-的成像。     

Efficient ensemble and IDA system based on the metal binding motif for highly sensitive and selective detection and determination of carbonate and citrate ions

Herein, we have reported a novel naked eye detection method which is based on the analyte competing for a metal reporter with a chromogenic indicator. This assay is based on the highly specific interaction between the anions and the metal ions and murexide (Mure) probe in a competition assay format. The resulting high sensitivity and selectivity for citrate and carbonate were achieved by changing the metal ions. The indicator is set free due to its displacement from the Mure/Cu²⁺ complex by citrate (Cit³ˉ) and the change in absorbance may be due to the further complexation of carbonate (CO₃²ˉ) with the additional coordination sites present in the zinc atom of Mure/Zn²⁺ complex. The dye-based ensemble systems are expected to be a potential and practical way for the detection of nanomolar concentrations of analytes in 100% aqueous solutions. The chemosensor enabled sensitive and selective detection of Cit³ˉ and CO₃²ˉ with detection limits of 19.1 and 9.4 nmol L^?1, respectively. These systems are simple in design, fast in operation and are more promising than previous methods. This novel method eliminated the need for separation processes, chemical modifications, organic cosolvents, and sophisticated instrumentations. Chiefly, the protocol offers high selectivity for the determination of Cit³ˉ and CO₃²ˉ among anions found in human urine samples in the presence of some biological species, including K⁺, Mg²⁺, Fe³⁺, Ca²⁺, Zn²⁺, Na⁺, glucose, urea, uric acid and ascorbic acid. Further, NAND and INHIBIT molecular logic gates were obtained using chemical inputs and UV–Vis absorbance signal as the output.     

In situ FT-IR spectroscopic study on the conformational changes of isotactic polypropylene in the presence of supercritical CO2

The conformational changes of isotactic polypropylene (iPP) under supercritical CO₂ condition with different pressure and temperature have been carefully studied by in situ Fourier-transform infrared spectroscopy (FT-IR). Analysis of the corresponding spectra shows that the conformational ordering by supercritical CO₂ results in the intensity enhancement of the regularity bands of iPP. Due to the high CO₂ concentration and strong intermolecular interaction, iPP can reach an equilibrium state in a short time at high CO₂ pressure. The equilibrium time increases with soaking temperature. After supercritical CO₂ treatment, two mechanisms, the formation of short helix from amorphous phase and the extension of short helix into long one, happen simultaneously. The latter mechanism undergoes quickly at the beginning of induced conformational changes and then slows down, resulting in the slight increase of crystallinity. At the same time, the conformational ordering in amorphous phase happens continuously until a thermodynamic equilibrium. In summary, in the presence of supercritical CO₂, the conformational ordering of iPP chains occurs exclusively in the amorphous region, with no impact on the crystal part.     

Apparent low surface areas in microporous SiO2-xerogels

Nitrogen adsorption at −195°C serves as routine method for the measurement of surface area of porous materials derived by sol-gel procedures. In a systematic study of the simultaneous effect of the pH and water-silane ratio of the starting solutions of preparation of SiO₂ xerogels on their surface areas, it was found that conditions of high acidity and low water/silane ratio result in microporous materials, the surface of which cannot be accessed by N₂ at −195°C, within a realistic time scale, but only by CO₂ at 0°C. In a typical result for TMOS/water/methanol = 1/2/3 at pH=1.0, the apparent N₂-area was zero, while the CO₂-area was 414 m²/gr. It is recommended to recheck apparent N₂-low surface areas of sol-gel materials by CO₂ adsorption. The behavior of pyrene-doped xerogels of this type is in agreement with the structural characterization by adsorption.     

Soybean-Oil-Based CO2-Switchable Surfactants with Multiple Heads

Oligomeric surfactants display the novel properties of low surface activity, low critical micellar concentration and enhanced viscosity, but no CO₂ switchable oligomeric surfactants have been developed so far. The introduction of CO₂ can convert tertiary amine reversibly to quaternary ammonium salt, which causes switchable surface activity. In this study, epoxidized soybean oil was selected as a raw material to synthesize a CO₂-responsive oligomeric surfactant. After addition and removal of CO₂, the conductivity analyzing proves that the oligomeric surfactant had a good response to CO₂ stimulation. The viscosity of the oligomeric surfactant solution increased obviously after sparging CO₂, but returned to its initial low viscosity in the absence of CO₂. This work is expected to open a new window for the study of bio-based CO₂-stimulated oligomeric surfactants.     

采用复合锂源制备的LiFePO4/C材料及其碳含量优化

采用Li_2CO_3与Li OH·H_2O为复合锂源制备LiFePO_4/C材料,同时优化了材料中的碳含量。由于氢氧化锂的熔点低于碳酸锂,在同样的烧结温度下,采用复合锂源可以获得更佳的熔融状态,在高温合成过程中使锂离子具有更高的扩散性,能够更顺利地得到高纯度的LiFePO_4晶相。通过优化碳包覆量达到提高导电性与控制晶粒尺寸的目的,使材料晶相结构完整,纯度高,表现出优秀的加工性能与电化学性能。所制得的LiFePO_4/C材料放电克容量达到158.2 m Ah·g~(-1),在全电池中经过100 d存储后容量保持率仍然高于94.0%,具有优异的长期可靠性。