Supramolecular assemblies of carbon nanocoils and tetraphenylporphyrin derivatives for sensing of catechol and hydroquinone in aqueous solution

Non-enzymatic electrochemical detection of catechol (CC) and hydroquinone (HQ), the xenobiotic pollutants, was carried out at the surface of novel carbon nanocoils/zinc-tetraphenylporphyrin (CNCs/Zn-TPP) nanocomposite supported on glassy carbon electrode. The synergistic effect of chemoresponsive activity of Zn-TPP and a large surface area and electron transfer ability of CNCs lead to efficient detection of CC and HQ. The nanocomposite was characterized by using FT-IR, UV/vis. spectrophotometer, SEM and energy dispersive X-ray spectroscopy (EDS). Cyclic voltammetry, differential pulse voltammetry (DPV) and electrochemical impedance spectroscopy were used for the electrochemical studies. CNCs/Zn-TPP/GCE nanosensor displayed a limit of detection (LOD), limit of quantification (LOQ) and sensitivity for catechol as 0.9 µM, 3.1 µM and 0.48 µA µM-1 cm-2, respectively in a concentration range of 25-1500 µM. Similarly, a linear trend in the concentration of hydroquinone detection was observed between 25 and 1500 µM with an LOD, LOQ and sensitivity of 1.5 µM, 5.1 µM and 0.35 µA µM-1 cm-2, respectively. DPV of binary mixture pictured well resolved peaks with anodic peak potential difference, ∆Epa(CC-HQ), of 110 mV showing efficient sensing of CC and HQ. The developed nanosensor exhibits stability for up to 30 days, better selectivity and good repeatability for eight measurements (4.5% for CC and 5.4% for HQ).

A Calixarene Promotes Disaggregation and Sensing Performance of Carboxyphenyl Porphyrin Films

The aggregation of a free base porphyrin, meso-tetrakis(4-carboxyphenyl)porphyrin and its Zn(II) derivative have been studied at the air/water interface in the presence of a p-tert-butylcalyx[8]arene matrix. The mixed Langmuir films were obtained either by premixing the compounds (cospreading) or by sequential addition. The negative deviation from the additivity rule of the cospread films is indicative of a comparatively good miscibility that was further confirmed by Brewster angle microscopy. The images of the cospread mixed films showed a more homogeneous morphology in comparison with those of pure porphyrin that is attributed to a deeper and earlier self-aggregation state at the interface of the latter. These results were similar for both porphyrins and revealed the disaggregating effect of the calixarene matrix. The orientation and association of the porphyrins were studied by UV-visible reflection spectroscopy at the interface. A different aggregation behavior can be inferred from the resulting spectra, and a higher orientational freedom was observed when the molecules were less aggregated in mixed cospreaded films. The disaggregating effect was retained when the films were transferred to solid supports as demonstrated by UV-visible spectroscopy. Finally, the potential use of these Langmuir-Blodgett films as optical gas sensors was tested against ammonia and amine vapors. The changes in the spectrum in the presence of the volatile compounds are higher for the Zn-porphyrin. The presence of calixarene enhances the sensor response due to the higher accessibility of volatiles to disaggregated porphyrins in the mixed films. The resulting changes were mapped into a numerical matrix that can be transformed into a color pattern to easily discriminate among these gases.

Highly Sensitive Detection of Benzene, Toluene, and Xylene Based on CoPP-Functionalized TiO2 Nanoparticles with Low Power Consumption

Among various metal oxides, titanium dioxide (TiO₂) has received considerable interest as a gas-sensing material owing to its high reliability at high operating temperatures. Nonetheless, TiO₂ generally has low sensitivity to target gases. In particular, TiO₂-based sensors have difficulty in sensitively detecting benzene, toluene, and xylene (referred to as BTX). Moreover, the reported TiO₂-based sensors have not simultaneously satisfied the demand for tens of ppb BTX detection and operation with low power consumption. This work proposes a BTX sensor using cobalt porphyrin (CoPP)-functionalized TiO₂ nanoparticles as a sensing material on a suspended microheater fabricated by bulk micromachining for low power consumption. TiO₂ nanoparticles show an enhanced sensitivity (245%) to 10 ppm toluene with CoPP functionalization. The proposed sensor exhibits high sensitivity to BTX at concentrations ranging from 10 ppm down to several ppb. The high reliability of the sensor is also explored through the long-time operation with repeated exposure to 10 ppm toluene for 14 h.

A tetraphenylporphyrin/WO3/exfoliated graphite nanocomposite for the photocatalytic degradation of an acid dye under visible light irradiation

Charge carrier separation in visible light photocatalytic degradation of a dye was achieved by the fabrication of a tetraphenylporphyrin/WO₃/exfoliated graphite nanocomposite.

Anchoring of carboxyl-functionalized porphyrins on MgO, TiO2, and Co3O4 nanoparticles

Hybrid materials consisting of functional organic molecules on metal oxide nanomaterials are key components in emerging technologies, for example in energy conversion and molecular electronics. In this work, we present the results of a comparative study of carboxyl-functionalized porphyrins on different oxide nanomaterials. Specifically, we investigated the interaction of 5(3-carboxyphenyl)-10,15,20-triphenyl-21,23H-porphyrin (2H-3-MCTPP) and 5(4-carboxyphenyl)-10,15,20-triphenyl-21,23H-porphyrin (2H-4-MCTPP), on MgO, TiO2, and Co3O4 nanoparticles (NPs) using isothermal and temperature-programmed diffuse reflection infrared Fourier transform spectroscopy (DRIFTS). We show that both porphyrins bind to the NPs, yielding stable monolayer films consisting of tilted surface carboxylates. In all cases, anchoring through the carboxylic acid group suppresses self-metalation of the porphyrin unit. Upon annealing, all anchored porphyrin films undergo metalation. The position of the acid group has no major influence on the reactivity. The same is true for the nature of the metal oxide, suggesting that the observed behaviour is general for most anchored porphyrin films on oxide nanomaterials.

Porphyrins in troubled times: a spotlight on porphyrins and their metal complexes for explosives testing and CBRN defense

A critical perspective on (metallo)porphyrins in security-related applications: the past, present and future of explosives detection, CBRN defense, and beyond.

Preparation of Cu(ii) porphyrin–TiO2 composite in one-pot method and research on photocatalytic property

A promising strategy for porphyrin–TiO₂ photocatalyst preparation by using sol–gel process and solvothermal condition showed prospective utilization in the field of dye pollutant photodegradation.

Optical Gas Sensing of Ammonia and Amines Based on Protonated Porphyrin/TiO₂ Composite Thin Films

Open porous and transparent microcolumnar structures of TiO₂ prepared by physical vapour deposition in glancing angle configuration (GLAD-PVD) have been used as host matrices for two different fluorescent cationic porphyrins, 5-(N-methyl 4-pyridyl)-10,15,20-triphenyl porphine chloride (MMPyP) and meso-tetra (N-methyl 4-pyridyl) porphine tetrachloride (TMPyP). The porphyrins have been anchored by electrostatic interactions to the microcolumns by self-assembly through the dip-coating method. These porphyrin/TiO₂ composites have been used as gas sensors for ammonia and amines through previous protonation of the porphyrin with HCl followed by subsequent exposure to the basic analyte. UV–vis absorption, emission, and time-resolved spectroscopies have been used to confirm the protonation–deprotonation of the two porphyrins and to follow their spectral changes in the presence of the analytes. The monocationic porphyrin has been found to be more sensible (up to 10 times) than its tetracationic counterpart. This result has been attributed to the different anchoring arrangements of the two porphyrins to the TiO₂ surface and their different states of aggregation within the film. Finally, there was an observed decrease of the emission fluorescence intensity in consecutive cycles of exposure and recovery due to the formation of ammonium chloride inside the film.

Porphyrinoids for Chemical Sensor Applications

Porphyrins and related macrocycles have been intensively exploited as sensing materials in chemical sensors, since in these devices they mimic most of their biological functions, such as reversible binding, catalytic activation, and optical changes. Such a magnificent bouquet of properties allows applying porphyrin derivatives to different transducers, ranging from nanogravimetric to optical devices, also enabling the realization of multifunctional chemical sensors, in which multiple transduction mechanisms are applied to the same sensing layer. Potential applications are further expanded through sensor arrays, where cross-selective sensing layers can be applied for the analysis of complex chemical matrices. The possibility of finely tuning the macrocycle properties by synthetic modification of the different components of the porphyrin ring, such as peripheral substituents, molecular skeleton, coordinated metal, allows creating a vast library of porphyrinoid-based sensing layers. From among these, one can select optimal arrays for a particular application. This feature is particularly suitable for sensor array applications, where cross-selective receptors are required. This Review briefly describes chemical sensor principles. The main part of the Review is divided into two sections, describing the porphyrin-based devices devoted to the detection of gaseous or liquid samples, according to the corresponding transduction mechanism. Although most devices are based on porphyrin derivatives, seminal examples of the application of corroles or other porphyrin analogues are evidenced in dedicated sections.

Functionalized Porphyrins on an Atomically Defined Oxide Surface: Anchoring and Coverage-Dependent Reorientation of MCTPP on Co3O4(111)

We have studied the adsorption of tetraphenylporphyrin (2HTPP) and its carboxylated counterpart mono-para-carboxyphenyltriphenylporphyrin (MCTPP) on an atomically defined Co3O4(111) film under ultrahigh vacuum (UHV) conditions. Using time-resolved infrared reflection absorption spectroscopy (TR-IRAS), we show that 2HTPP adsorbs molecularly in a flat-lying orientation, whereas MCTPP binds to the surface via formation of a chelating bidentate carboxylate upon deposition at 400 K. Combining TR-IRAS and density-functional theory (DFT), we determine the molecular tilting angle as a function of coverage. We show that the MCTPP adsorption geometry changes from a nearly flat-lying orientation (tilting angle <30°) at low coverage to a nearly perfectly upright-standing orientation (tilting angle of approximately 80°) in the full monolayer.

Free-Base Carboxyphenyl Porphyrin Films Using a TiO₂ Columnar Matrix: Characterization and Application as NO₂ Sensors

The anchoring effect on free-base carboxyphenyl porphyrin films using TiO₂ microstructured columns as a host matrix and its influence on NO₂ sensing have been studied in this work. Three porphyrins have been used: 5-(4-carboxyphenyl)10,15,20-triphenyl-21H,23H-porphyrin (MCTPP); 5,10,15,20-tetrakis(4-carboxyphenyl)-21H,23H-porphyrin (p-TCPP); and 5,10,15,20-tetrakis(3-carboxyphenyl)-21H,23H-porphyrin (m-TCPP). The analysis of UV-Vis spectra of MCTPP/TiO₂, p-TCPP/TiO₂ and m-TCPP/TiO₂ composite films has revealed that m-TCPP/TiO₂ films are the most stable, showing less aggregation than the other porphyrins. IR spectroscopy has shown that m-TCPP is bound to TiO₂ through its four carboxylic acid groups, while p-TCPP is anchored by only one or two of these groups. MCTPP can only be bound by one carboxylic acid. Consequently, the binding of p-TCPP and MCTPP to the substrate allows them to form aggregates, whereas the more fixed anchoring of m-TCPP reduces this effect. The exposure of MCTPP/TiO₂, p-TCPP/TiO₂ and m-TCPP/TiO₂ films to NO₂ has resulted in important changes in their UV-Vis spectra, revealing good sensing capabilities in all cases. The improved stability of films made with m-TCPP suggests this molecule as the best candidate among our set of porphyrins for the fabrication of NO₂ sensors. Moreover, their concentration-dependent responses upon exposure to low concentrations of NO₂ confirm the potential of m-TCPP as a NO₂ sensor.

Effects of number and position of meta and para carboxyphenyl groups of zinc porphyrins in dye-sensitized solar cells: structure-performance relationship

Porphyrin sensitizers containing meta- and para-carboxyphenyl groups in their meso positions have been synthesized and investigated for their performance in dye-sensitized solar cells (DSSCs). The superior performance of para-derivative compared to meta-derivative porphyrins was revealed by optical spectroscopy, electrochemical property measurements, density functional theory (DFT) calculations, attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy, incident photon-to-current conversion efficiency (IPCE), electrochemical impedance spectroscopy (EIS), and stability performance. Absorption spectra of para-carboxyphenyl-substituted porphyrins on TiO2 show a broader Soret band compared to meta-carboxyphenyl-substituted porphyrins. ATR-FTIR spectra of the studied porphyrins on TiO2 were applied to investigate the number and mode of carboxyl groups attached to TiO2. The VOC, JSC, and IPCE values of para-series porphyrins were distinctly superior to those of meta-series porphyrins. The Nyquist plots of the studied porphyrins show that charge injection in para-series porphyrins is superior to that in meta-series porphyrins. The orthogonally positioned para derivatives have more efficient charge injection and charge transfer over charge recombination, whereas the efficiencies of flat-oriented meta derivatives are retarded by rapid charge recombination. Photovoltaic measurements of the studied meta- and para-carboxyphenyl-functionalized porphyrins show that the number and position of carboxyphenyl groups play a crucial role in the performance of the DSSC. Our results indicate that para-carboxyphenyl derivatives outperform meta-carboxyphenyl derivatives to give better device performance. This study will serve as a guideline for the design and development of organic, porphyrin, and ruthenium dyes in DSSCs.

Self assembled nanocages from DNA–protoporphyrin hybrid molecules

DNA–organic hybrid molecular building blocks are generated by covalent conjugation of the carboxyl groups of protoporphyrin IX with the amine functional groups of modified DNA oligomers.