High-performance and wearable hazardous gases sensor based on n-n heterojunction film of NGO and tetrakis(1-pyrenyl)porphyrin

Flexible and wearable electrochemical sensors for health and safety monitoring

Environmental safety monitoring is a crucial process that involves continuous and systematic observation and analysis of various pollutants in the environment to ensure its quality and safety. This monitoring encompasses a wide range of areas, including physical indicator monitoring (pertaining to parameters such as temperature, humidity, and wind speed), chemical indicator monitoring (focused on detecting harmful substances in environmental media such as air, water, and soil), and ecosystem monitoring (including biodiversity assessments and judgments on the health status of ecosystems). This review delves deeply into the significant advancements achieved in the field of flexible and wearable electrochemical sensors (FWESs) over the past fifteen years (from 2010 to 2024). It emphasizes the broad application of these sensors in health and environmental safety monitoring, with health monitoring primarily focusing on exhaled breath and sweat, and environmental monitoring covering temperature, humidity, and pollutants in air and water. By seamlessly integrating electrochemical principles, advanced sensor manufacturing technologies, and sensor functionalization, FWESs have opened up new avenues for non-invasive real-time monitoring of human health and environmental safety. This review highlights key developments in sensor structures, including flexible substrates, printed electrodes, and active materials. It also underscores the remarkable progress made in healthcare and environmental monitoring through the utilization of FWES. Despite these promising advancements, this emerging field still faces numerous challenges, such as improving sensor accuracy, enhancing durability, and reducing costs. The review concludes by discussing the future directions in this field, including ongoing research efforts aimed at overcoming these challenges and expanding the applications of FWESs in various sectors.

Two-Dimensional Covalent Organic Frameworks in Organic Electronics

Two-dimensional covalent organic frameworks (2DCOFs) are a unique class of crystalline porous materials interconnected by covalent bonds, which have attracted significant attention in recent years due to their chemical and structural diversity, as well as their applications in adsorption, separation, catalysis, and drug delivery. However, research on the electrical properties of 2DCOFs remains limited, despite their potential in organic electronics. Early studies recognized the poor electrical conductivity of 2DCOFs as a significant obstacle to their application in this field. To overcome this challenge, various strategies have been proposed to enhance conductivity. This review first introduces the concept of computational screening for 2DCOFs and explores approaches to improve their intrinsic conductivity, with a focus on four key aspects: in-plane and out-of-plane charge transport, topology, bandgap, and morphology. It then examines the application of pristine 2DCOFs in organic electronics, including applications in field-effect transistors, memristors, photodetectors, and chemiresistive gas sensors. We support these strategies with detailed statistical data, providing a comprehensive guide for the design and development of novel 2DCOFs for organic electronics. Finally, we outline future research directions, emphasizing the challenges that remain to be addressed in this emerging area.

Tetraiodo Fe/Ni phthalocyanine-based molecular catalysts for highly efficient oxygen reduction reaction and oxygen evolution reaction: Constructing a built-in electric field with iodine groups

In this paper, we report on the preparation and catalysis of a bifunctional molecular catalyst (Fe[Pc(I)4]+Ni[Pc(I)4]@NCPDI) for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) in rechargeable Zn-air batteries. This catalyst is prepared by self-assembling tetraiodo metal phthalocyanines (Fe[Pc(I)4] and Ni[Pc(I)4]) on a 2D N-doped carbon material (NCPDI) through π-π interactions. The introduction of iodine groups in the edge of phthalocyanines controls the density of electron cloud and electrostatic potential around Fe-N/Ni-N sites and constructs a built-in electric field that facilitates directional transport of charges, enhancing the catalytic activity of the catalyst. Density functional theory (DFT) calculations support this mechanism by showing a reduced energy barrier for the ORR rate-determining step (RDS). The Fe[Pc(I)4]+Ni[Pc(I)4]@NCPDI exhibits excellent performance outperforming 20 wt% Pt/C and single-molecule self-assembled Fe[Pc(I)4]@NCPDI and Ni[Pc(I)4]@NCPDI, with a half-wave potential of E1/2 = 0.940 V in the ORR process under alkaline condition. During the OER process, Fe[Pc(I)4]+Ni[Pc(I)4]@NCPDI exhibited a low overpotential of 298 mV at 10 mA cm-2 under the alkaline condition, which is much better than RuO2, Fe[Pc(I)4]@NCPDI and Ni[Pc(I)4]@NCPDI. The catalyst also demonstrates excellent catalysis and durability in rechargeable Zn-air batteries. This work provides a simple and specific method to develop efficient multifunctional molecular electrocatalysts.

Self-Healing, Laminated, and Low Resistance NH3 Sensor Based on 6,6',6″-(Nitrilotris(benzene-4,1-diyl))tris(5-phenylpyrazine-2,3-dicarbonitrile) Sensing Material Operating at Room Temperature

With the rapid development of the concept of the Internet of Things (IoT), gas sensors with the function of simulating the human sense of smell became irreplaceable as a key element. Among them, ammonia (NH3) sensors played an important role in respiration tests, environmental monitoring, safety, and other fields. However, the fabrication of the high-performance device with high stability and resistance to mechanical damages was still a challenge. In this work, polyurethane (PU) with excellent self-healing ability was applied as the substrate, and the sensor was designed from new sensitive material design and device structure optimization, through applying the organic molecule with groups which could absorb NH3 and the laminated structure to shorten the electronic transmission path to achieve a low resistance state and favorable sensing properties. Accordingly, a room temperature flexible NH3 sensor based on 6,6',6″-(nitrilotris(benzene-4,1-diyl))tris(5-phenylpyrazine-2,3-dicarbonitrile) (TPA-3DCNPZ) was successfully developed. The device could self-heal by means of a thermal evaporation assisted method. It exhibited a detection limit of 1 ppm at 98% relative humidity (RH), as well as great stability, selectivity, bending flexibility, and self-healing properties. The improved NH3 sensing performance under high RH was further investigated by complex impedance plots (CIPs) and density functional theory (DFT), attributing to the enhanced adsorption of NH3. The TPA-3DCNPZ based NH3 sensors proved to have great potential for application on simulated exhaled breath to determine the severity of kidney diseases and the progress of treatment. This work also provided new ideas for the construction of high-performance room temperature NH3 sensors.

Porphyrin/phthalocyanine-based porous organic polymers for pollutant removal and detection: Synthesis, mechanisms, and challenges

The growing global concern about environmental threats due to environmental pollution requires the development of environmentally friendly and efficient removal/detection materials and methods. Porphyrin/phthalocyanine (Por/Pc) based porous organic polymers (POPs) as a newly emerging porous material are prepared through polymerizing building blocks with different structures. Benefiting from the high porosity, adjustable pore structure, and enzyme-like activities, the Por/Pc-POPs can be the ideal platform to study the removal and detection of pollutants. However, a systematic summary of their application in environmental treatment is still lacking to date. In this review, the development of various Por/Pc-POPs for pollutant removal and detection applications over the past decade was systematically addressed for the first time to offer valuable guidance on environmental remediation through the utilization of Por/Pc-POPs. This review is divided into two sections (pollutants removal and detection) focusing on Por/Pc-POPs for organic, inorganic, and gaseous pollutants adsorption, photodegradation, and chemosensing, respectively. The related removal and sensing mechanisms are also discussed, and the methods to improve removal and detection efficiency and selectivity are also summarized. For the future practical application of Por/Pc-POPs, this review provides the emerging research directions and their application possibility and challenges in the removal and detection of pollutants.

Metalloporphyrin-Based Metal-Organic Frameworks for the Ultrasensitive Chemiresistive Detection of NO2: Effect of the Central Metal on Tuning the Sensing Performance

The highly sensitive and selective detection of trace hazardous gases at room temperature is very promising for health protection and environmental safety. Herein, chemiresistive sensors for NO2 were fabricated based on self-assembled films of the four metalloporphyrin (MPor)-based metal-organic frameworks PCN-222-M (M = Cu, Ni, Co, Fe) by the quasi-Langmuir-Shäfer method. It is found that the relative responses of the four PCN-222-M films are linearly related to the NO2 concentration, and the PCN-222-Cu possessed an unprecedented high response to NO2 with a sensitivity of 2209% ppm-1 in the 4-20 ppb range and a low limit of detection (LOD) of 0.93 ppb, achieving the best performance reported so far for NO2 detection at room temperature. Meanwhile, PCN-222-Ni showed the fastest recovery among the four PCN-222-M films, which can be used for the rapid detection of NO2. Excellent reproducibility, stability, selectivity, and moisture resistance are shown for both PCN-222-Cu and PCN-222-Ni. Combining the experimental study and density functional theory (DFT) calculation, the essential roles of MPor units and the MPor/Zr6 cluster hybrid material in tuning the Fermi level and the electron transfer between PCN-222-M and NO2 were further proved. These were less considered topics in previous studies on MOFs. This work explores the application of MPor-based MOFs in gas sensing by selecting appropriate MPor units, thus providing guidance for the development of MOF-based chemiresistive sensors.

Microgravimetric Modeling-A New Method for Extracting Adsorption Parameters of Functionalized MIL-101(Cr)

As a volatile air pollutant, formaldehyde can enter people's living environment through interior decoration, furniture and paint, causing serious harm to human health. Therefore, it is necessary to develop a sensor for the real-time detection of formaldehyde in low concentrations. According to the chemical interaction between amino groups and formaldehyde, a MIL-101(Cr) aminated-material-based formaldehyde cantilever sensor was prepared, of which ethylenediamine- functionalized MIL-101(Cr) named ED-MIL-101(Cr)) showed the best gas sensing performance. Using quasi-in situ infrared spectroscopy, ED-MIL-101(Cr) was found bound to formaldehyde through a Schiff base. The adsorption enthalpy of formaldehyde-bound ED-MIL-101(Cr) was -52.6 kJ/mol, which corresponds to weak chemical adsorption, so the material showed good selectivity. In addition, ED-MIL-101(Cr) has the most active sites, so its response value to formaldehyde is larger and it takes longer to reach saturation adsorption than bare MIL-101(Cr). Through the research on the gas sensing performance of functionalized MIL-101(Cr) material, we found that it has a strong application potential in the field of formaldehyde monitoring, and the material performance can be quantitatively and accurately evaluated through combining calculation and experimentation for understanding the gas sensing mechanism.

Solution-Processed Functionalized Graphene Film Prepared by Vacuum Filtration for Flexible NO2 Sensors

Large-scale production of graphene nanosheets (GNSs) has led to the availability of solution-processable GNSs on the commercial scale. The controlled vacuum filtration method is a scalable process for the preparation of wafer-scale films of GNSs, which can be used for gas sensing applications. Here, we demonstrate the use of this deposition method to produce functional gas sensors, using a chemiresistor structure from GNS solution-based techniques. The GNS suspension was prepared by liquid-phase exfoliation (LPE) and transferred to a polyvinylidene fluoride (PVDF) membrane. The effect of non-covalent functionalization with Co-porphyrin and Fe-phthalocyanines on the sensor properties was studied. The pristine and functionalized GNS films were characterized using different techniques such as Raman spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), atomic force microscopy (AFM), X-ray diffraction (XRD), and electrical characterizations. The morphological and spectroscopic analyses both confirm that the molecules (Co-porphyrin and Fe-phthalocyanine) were successfully adsorbed onto the GNSs surface through π-π interactions. The chemiresistive sensor response of functionalized GNSs toward the low concentrations of nitrogen dioxide (NO2) (0.5-2 ppm) was studied and compared with those of the film of pristine GNSs. The tests on the sensing performance clearly showed sensitivity to a low concentration of NO2 (5 ppm). Furthermore, the chemical modification of GNSs significantly improves NO2 sensing performance compared to the pristine GNSs. The sensor response can be modulated by the type of adsorbed molecules. Indeed, Co-Por exhibited negative responsiveness (the response of Co-Por-GNS sensors and pristine GNS devices was 13.1% and 15.6%, respectively, after exposure to 0.5 ppm of NO2). Meanwhile, Fe-Phc-GNSs induced the opposite behavior resulting in an increase in the sensor response (the sensitivity was 8.3% and 7.8% of Fe-Phc-GNSs and pristine GNSs, respectively, at 0.5 ppm NO2 gas).