Humidity effect on ammonia sensing properties of substituted and unsubstituted cobalt phthalocyanines

Microwave Gas Sensors Based on Electrodeposited Polypyrrole-Nickel Phthalocyanine Hybrid Films

Previous studies have shown that the incorporation of sulfonated metallophthalocyanines into sensitive sensor materials can improve electron transfer and thus species detection. Herein, we propose a simple and easy alternative to the use of generally expensive sulfonated phthalocyanines by electropolymerizing polypyrrole together with nickel phthalocyanine in the presence of an anionic surfactant. The addition of the surfactant not only helps the incorporation of the water-insoluble pigment into the polypyrrole film, but the obtained structure has increased hydrophobicity, which is a key property for developing efficient gas sensors with low sensitivity to water. The obtained results show the effectiveness of the materials tested for the detection of ammonia in the range of 100 to 400 ppm. It is shown by comparing the microwave sensor responses that the film without nickel phthalocyanine (hydrophilic) produces greater variations than the film with nickel phthalocyanine (hydrophobic). These results are consistent with the expected results since the hydrophobic film is not very sensitive to residual ambient water and therefore does not interfere with the microwave response. However, although this excess response is usually a handicap, as it is a source of drift, in these experiments the microwave response shows great stability in both cases.

Symmetrically Substituted Zn and Al Phthalocyanines and Polymers for Photodynamic Therapy Application

N4 macrocyclic complexes of Al and Zn phthalocyanines with symmetrical imine and imidazole moiety at the periphery were synthesized. The synthesized ligands, complexes, and polymers were purified and characterized to study the structure of the molecule. These synthesized complexes were used for photodynamic therapy application as the diamagnetic Zn and Al have the ability to produce and stabilize singlet oxygen species. The synthesized N4 molecules of aluminum iminomethoxy phenyl phthalocyanine and aluminum ethyl phenyl benzimidazolephthalocyanine showed better activity against MCF-7 cells. These results suggest that this assay may be used as an early biomarker of clinical response.

Fluorination vs. Chlorination: Effect on the Sensor Response of Tetrasubstituted Zinc Phthalocyanine Films to Ammonia

In this work, the effect of fluorine and chlorine substituents in tetrasubstituted zinc phthalocyanines, introduced into the non-peripheral (ZnPcR4-np, R = F, Cl) and peripheral (ZnPcR4-p, R = F, Cl) positions of macrocycle, on their structure and chemiresistive sensor response to low concentration of ammonia is studied. The structure and morphology of the zinc phthalocyanines films (ZnPcR4) were investigated by X-ray diffraction and atomic force microscopy methods. To understand different effects of chlorine and fluorine substituents, the strength and nature of the bonding of ammonia and ZnPcHal4 molecules were studied by quantum chemical simulation. It was shown on the basis of comparative analysis that the sensor response to ammonia was found to increase in the order ZnPcCl4-np < ZnPcF4-np < ZnPcF4-p < ZnPcCl4-p, which is in good agreement with the values of bonding energy between hydrogen atoms of NH3 and halogen substituents in the phthalocyanine rings. ZnPcCl4-p films demonstrate the maximal sensor response to ammonia with the calculated detection limit of 0.01 ppm; however, they are more sensitive to humidity than ZnPcF4-p films. It was shown that both ZnPcF4-p and ZnPcCl4-p and can be used for the selective detection of NH3 in the presence of carbon dioxide, dichloromethane, acetone, toluene, and ethanol.

A high-sensitive room temperature gas sensor based on cobalt phthalocyanines and reduced graphene oxide nanohybrids for the ppb-levels of ammonia detection

Highly sensitive gas sensing materials are of great importance for environmental pollution monitoring. In this study, four nanohybrid materials containing different phenoxyl substituents of cobalt phthalocyanines (tetra-β-carboxylphenoxylphthalocyanine cobalt (cpoPcCo), tetra-β-(4-carboxy-3-methoxyphenoxy)phthalocyanine cobalt (cmpoPcCo), tetra-β-phenoxylphthalocyanine cobalt (poPcCo), and tetra-β-(3-methoxyphenoxy)phthalocyanine cobalt (mpoPcCo)) and reduced graphene oxide (rGO) (RPcCo/rGO) were synthesized via non-covalent interactions as a high performance gas sensing materials for the ppb-level detection of ammonia (NH3). Various characterization techniques, including FT-IR, Raman, UV-vis, TGA, XPS and SEM, were used to confirm the structure, element information and morphology of the as-synthesized materials. The obtained materials were used in interdigital electrodes to fabricate the sensing device, and the gas sensing performance was investigated at room temperature. The obtained sensors exhibited excellent sensitivity, selectivity, good reproducibility and perfect response-concentration linearity towards NH3, which are mainly ascribed to the synergetic effects of RPcCo and rGO due to the specific surface area structure for NH3 diffusion, the abundant active sites to adsorb NH3, and excellent conductivity for efficient electron transport, particularly the effect of RPcCo. For example, the cpoPcCo/rGO-based sensor showed a higher and faster response for low concentration of NH3 (∼2.5 and 45 s for 100 ppb of NH3), a ppb level detection and superior stability over 60 days. Besides, the effect of different phenoxyl substituents of cobalt phthalocyanines on the sensing performance and the sensing mechanism for the sensitivity enhancement were discussed and confirmed by the first-principles density functional theory calculations and electrochemical impedance spectroscopy (EIS).

Sensing alcohol vapours with novel unsymmetrically substituted metallophthalocyanines

Unsymmetrically substituted phthalocyanines were synthesized by the well-known statistical condensation method using two differently substituted precursors, 4-tert-butylphthalonitrile and 4-(4-pyrrol-1-yl)phenoxyphthalonitrile.

The effects of amino substituents on the enhanced ammonia sensing performance of PcCo/rGO hybrids

Three reversible ammonia (NH3) gas sensors were fabricated using tetra-α-(p-aminobenzyloxy)phthalocyanine cobalt (ABOPcCo), tetra-α-aminophthalocyanine cobalt (APcCo) and substituent-free phthalocyanine cobalt (FPcCo) functionalized reduced graphene oxide (rGO), with cost-efficient, highly sensitive and stable sensing performance. These hybrid materials were prepared via a facile physical solution mixing self-assembly reaction with rGO and PcCo solutions. The obtained PcCo/rGO hybrid sensors exhibit excellent sensing performance; especially the ABOPcCo/rGO sensor, whose response is about 23.3% (50 ppm), with a limit of detection as low as 78 ppb, and response and recovery times about as fast as 225 s and 250 s. The performance of the PcCo/rGO hybrid sensors can be optimized by adjusting the concentrations of the PcCo/rGO aqueous dispersions. More importantly, the NH3-sensing performance of the PcCo/rGO sensors was tuned by adjusting the substituent structure of PcCo. The enhanced NH3-sensing performance may be attributed to synergistic effects between PcCo and rGO, e.g., stronger adsorption interactions between PcCo with an aminophenoxy substituent and NH3, the high electrical conductivity of rGO, and fast charge transfer between PcCo and rGO. These are further confirmed via first-principle density functional theory (DFT) calculations and electrochemical impedance spectra (EIS) measurements.

Multi-mode humidity sensing with water-soluble copper phthalocyanine for increased sensitivity and dynamic range

Aqueous solubility of copper phthalocyanine-3,4',4″,4″'-tetrasulfonic acid tetrasodium salt (CuPcTs) enables fabrication of flexible electronic devices by low cost inkjet printing. We (1) investigate water adsorption kinetics on CuPcTs for better understanding the effects of relative humidity (RH) on hydrophilic phthalocyanines, and (2) assess CuPcTs as a humidity-sensing material. Reaction models show that H2O undergoes 2-site adsorption which can be represented by a pair of sequentially-occurring pseudo-first order reactions. Using high frequency (300-700 THz) and low frequency (1-8 MHz) dielectric spectroscopy combined with gravimetric measurements and principal component analysis, we observe that significant opto-electrical changes in CuPcTs occur at RH ≈ 60%. The results suggest that rapid H2O adsorption takes place at hydrophilic sulfonyl/salt groups on domain surfaces at low RH, while slow adsorption and diffusion of H2O into CuPcTs crystallites leads to a mixed CuPcTs-H2O phase at RH > 60%, resulting in high frequency dielectric screening of the film by water and dissociation of Na+ from CuPc(SO3-)4 ions. The CuPcTs-H2O interaction can be tracked using a combination of gravimetric, optical, and electrical sensing modes, enabling accurate ( ± 2.5%) sensing in the ~0-95% RH range with a detection limit of less than 0.1% RH.

The effect of rigid phenoxyl substituent on the NH3-sensing properties of tetra-α-(4-tert-butylphenoxyl)-metallophthalocyanine/reduced graphene oxide hybrids

We report an enhanced NH₃ sensing material formed by functionalization of reduced graphene oxide (rGO) with 1,8,15,22-tetra(4-tert-butylphenoxyl)metallophthalocyanine (TBPOMPc; M = Cu, Ni, Pb) via a solution self-assembly method based on π–π stacking interactions.

The effects of central metals on ammonia sensing of metallophthalocyanines covalently bonded to graphene oxide hybrids

Stably dispersed aPcM–GO hybrids were prepared by a facile amidation reaction with excellent NH₃ sensing properties at room temperature, which rely to the aPcM functionalization on GO.

Elaboration of ammonia gas sensors based on electrodeposited polypyrrole--cobalt phthalocyanine hybrid films

The electrochemical incorporation of a sulfonated cobalt phthalocyanine (sCoPc) in conducting polypyrrole (PPy) was done, in the presence or absence of LiClO4, in order to use the resulting hybrid material for the sensing of ammonia. After electrochemical deposition, the morphological features and structural properties of polypyrrole/phthalocyanine hybrid films were investigated and compared to those of polypyrrole films. A gas sensor consisting in platinum microelectrodes arrays was fabricated using silicon microtechnologies, and the polypyrrole and polypyrrole/phthalocyanine films were electrochemically deposited on the platinum microelectrodes arrays of this gas sensor. When exposed to ammonia, polymer-based gas sensors exhibited a decrease in conductance due to the electron exchange between ammonia and sensitive polymer-based layer. The characteristics of the gas sensors (response time, response amplitude, reversibility) were studied for ammonia concentrations varying from 1 ppm to 100 ppm. Polypyrrole/phthalocyanine films exhibited a high sensitivity and low detection limit to ammonia as well as a fast and reproducible response at room temperature. The response to ammonia exposition of polypyrrole films was found to be strongly enhanced thanks to the incorporation of the phthalocyanine in the polypyrrole matrix.

Ammonia sorption studies into thin layers of hexadecafluorinated cobalt phthalocyanine using optical techniques

In the present work, the optical response of CoPcF16 films upon exposure to ammonia vapor in the concentration range 50 to 1000 ppm was measured by total internal reflection ellipsometry. It was demonstrated that the sorption of NH3 molecules causes substantial shift of the Δ(λ) spectrum which is determined by the increase in film thickness and change of its optical parameters. It was found that the CoPcF16 films deposited at substrate temperature of 220 °C are characterized by larger grains and more developed surface demonstrating higher optical response than films deposited at substrate temperature of 60 °C. In order to gain an insight into the sorption mechanism at molecular level, we have studied the interaction of ammonia vapor with hexadecafluorinated cobalt phthalocyanine using infrared spectroscopy. It was shown that the detection of ammonia was found to be governed primarily by coordination to the metal center.