Photooxidation of 4-chlorophenol sensitised by iron meso-tetrakis(2,6-dichloro-3-sulfophenyl)porphyrin in aqueous solution

Photodegradation of metoprolol using a porphyrin as photosensitizer under homogeneous and heterogeneous conditions

Porphyrins are known as effective photosensitizers and can be an interesting key in phototreatment of water contaminated with micropollutants such as pharmaceuticals. They already showed to be efficient photocatalysts for the degradation of dyes, chlorophenols and other pollutants. This work demonstrates the applicability of 5,10,15,20-tetrakis(pentafluorophenyl)porphyrin (H₂TF₅PP) as photosensitizer for treatment of water contaminated with metoprolol, a highly prescribed β-blocker, which is not completely removed in sewage treatment plants. Studies were firstly developed under homogeneous conditions with simulated solar radiation and porphyrin was found to be efficient in the photodegradation of metoprolol, following a pseudo-first order kinetics with ca. 90% metoprolol degradation after 12 h. Experiments in presence of scavengers confirmed the mechanism of degradation via singlet oxygen. Appearance of several new peaks in HPLC chromatograms indicates the formation of products, identified by HPLC-MSⁿ. Furthermore, the porphyrin was immobilized on a silica support and used as heterogeneous photocatalyst in degradation of metoprolol. Experiments using this heterogeneous photocatalyst under real solar irradiation were also performed, and similar results were obtained. Kinetic comparison of metoprolol photodegradation in buffer solution and in real wastewater treatment plant effluent showed that the efficiency of the immobilized porphyrin was not decreased by the complex matrix of the effluent.

Nitrobenzene method: A keystone in meso-substituted halogenated porphyrin synthesis and applications

This review article briefly describes the available synthetic approaches for meso-arylporphyrins giving particular emphasis for one-pot nitrobenzene and nitrobenzene/NaY methods regarding the synthesis of meso-halogenated arylporphyrins. The review also describes the relevant applications of these halogenated porphyrins and their metalloporphyrin counterparts, prepared via nitrobenzene method, as photosensitizers for therapy (PDT and PDI), diagnostic (molecular contrast agents) and also for catalytic oxidation and CO2 cycloaddition reactions to epoxides.

Kinetic and mechanistic aspects of solid state, nanostructured porphyrin diacid photosensitizers in photooxidation of sulfides

The kinetics and mechanism of aerobic photooxidation of sulfides in the presence of a series of electron-rich and electron-deficient porphyrins immobilized on Amberlyst 15 nanoparticles in the form of porphyrin diacids are reported.

A diphenylacrylonitrile conjugated porphyrin with near-infrared emission by AIE–FRET

The strong aggregation induced emission–fluorescence resonance energy transfer (AIE–FRET) effect was observed for diphenylacrylonitrile units and porphyrin units.

Chlorophyll catalyse the photo-transformation of carcinogenic benzo[a]pyrene in water

Algal blooms cause great damage to water quality and aquaculture. However, this study showed that dead algal cells and chlorophyll could accelerate the photo-transformation of benzo[a]pyrene (BaP), a ubiquitous and persistent pollutant with potently mutagenic and carcinogenic toxicities, under visible light irradiation. Chlorophyll was found to be the major active substance in dead algal cells, and generated a high level of singlet oxygen to catalyse the photo-transformation of BaP. According to various BaP metabolites formed, the degradation mechanism was proposed as that chlorophyll in dead algal cells photo-oxidized BaP to quinones via photocatalytic generation of singlet oxygen. The results provided a good insight into the role of chlorophyll in the photo-transformation of organic contaminants and could be a possible remediation strategy of organic pollutants in natural environment.

Hollow and sulfonated microporous organic polymers: versatile platforms for non-covalent fixation of molecular photocatalysts

Sulfonated hollow microporous organic polymers showed excellent heterogenization ability towards various cationic photocatalysts through ionic interaction.

New hybrid materials based on halogenated metalloporphyrins for enhanced visible light photocatalysis

The impregnation of TiO₂ with functionalized halogenated (metallo)porphyrins leads to novel materials with a superior photocatalytic activity.

Zinc(II) phthalocyanines immobilized in mesoporous silica Al-MCM-41 and their applications in photocatalytic degradation of pesticides

In the present study the authors investigated a set of three new zinc(II) phthalocyanines (zinc(II) tetranitrophthalocyanine (ZnTNPc), zinc(II) tetra(phenyloxy)phthalocyanine (ZnTPhOPc) and the tetraiodide salt of zinc(II)tetra(N,N,N-trimethylaminoethyloxy) phthalocyaninate (ZnTTMAEOPcI)) immobilized into Al-MCM-41 prepared via ship-in-a-bottle methodology. The samples were fully characterized by diffuse reflectance-UV-vis spectroscopy (DRS-UV-vis), luminescence, thermogravimetric analysis (TG/DSC), N(2) adsorption techniques and elemental analysis. A comparative study was made on the photocatalytic performance upon irradiation within the wavelength range 320-460nm of these three systems in the degradation of pesticides fenamiphos and pentachlorophenol. ZnTNPc@Al-MCM-41 and ZnTTMAEOPcI@Al-MCM-41 were found to be the most active systems, with the best performance observed with the immobilized cationic phthalocyanine, ZnTTMAEOPcI@Al-MCM-41. This system showed high activity even after three photocatalytic cycles. LC-MS product characterization and mechanistic studies indicate that singlet oxygen ((1)O(2)), produced by excitation of these immobilized photosensitizers, is a key intermediate in the photocatalytic degradation of both pesticides.

Tin(IV) porphyrin functionalization of electrochemically active fluoride-doped tin-oxide (FTO) via Huisgen [3+2] click chemistry

A novel tetra-alkyne terminated tin(IV) porphyrin 3 was synthesized in good yields and characterized using NMR spectroscopy, high resolution mass spectrometry and X-ray crystallography, the latter revealing interactions with hexane molecules that stabilize the crystal structure of the tin(IV) porphyrin 3. It was then linked to a conductive fluorine-doped tin oxide (FTO) surfaces using Huisgen [3+2] click chemistry. The attachment of the tin(IV) porphyrin to the FTO surface 6 was characterized by X-ray photoelectron spectroscopy (XPS), indicating the presence of the 1,2,3-triazole unit. Electrochemical measurements of the tin(IV) porphyrin modified FTO surface 7 show that it is still electrochemically active with oxidation (Epa) and reduction peaks (Epc) for the ferricyanide redox couple observed at Epc and Epa of -0.144 and +0.568 V vs. Ag | AgCl respectively, representing a modest shift of ca . +/- 0.1–0.15 V, compared to unmodified FTO.

Structural, electrochemical and photochemical investigation of the water-soluble tin(IV) tetrakis(2-N-hydroxyethyl-4-pyridinium)porphyrin photocatalyst

The water-soluble tin(IV) tetrakis(2-N-hydroxyethyl-4-pyridinium)porphyrin 1 photocatalyst was synthesized in good yield and its structure determined by single crystal X-ray crystallography. Electrochemical measurements on tin(IV) porphyrin 1 reveal a range of complex redox processes that are highly dependent on the pH and electrode used. The cathodic processes at ca. -0.6 to -0.8 V were assigned to electrochemical processes on the pyridyl moiety following differential pulse voltammetry and spectroelectrochemical investigation into the electrochemical properties of tin(IV) porphyrin. Photocatalytic experiment on tin(IV) porphyrin 1 under anaerobic conditions using triethanolamine (TEAO) as a sacrifical donor reveal a phlorin species as the main product which rapidly disappears upon exposure to oxygen. These results suggest that tin(IV) porphyrin π-radical anion is perhaps not the species responsible for the apparent ability tin(IV) porphyrins to photocatalytically reduce various substrates, including water to hydrogen.

Removal efficiency and toxicity reduction of 4-chlorophenol with physical, chemical and biochemical methods

Chlorophenols are well-known priority pollutants and many different treatments have been assessed to facilitate their removal from industrial wastewater. However, an absolute and optimum solution still has to be practically implemented in an industrial setting. In this work, a series ofphysical, chemical and biochemical treatments have been systematically tested for the removal of 4-chlorophenol, and their results have been compared in order to determine the most effective treatment based on removal efficiency and residual by-product formation. Chemical treatments based on advanced oxidation processes (AOP) produced the best results on rate and extent of pollutant removal. The non-chemical technologies showed advantages in terms of complete (in the case of adsorption) or easy (enzymatic treatments) removal of toxic treatment by-products. The AOP methods led to the production of different photoproducts depending on the chosen treatment. Toxic products remained in most cases following treatment, though the toxicity level is significantly reduced with combination treatments. Among the treatments, a photochemical method combining UV, produced with a KrCl excilamp, and hydrogen peroxide achieved total removal of chlorophenol and all by-products and is considered the best treatment for chlorophenol removal.

Determination of the thermodegradation of deoxyArbutin in aqueous solution by high performance liquid chromatography

Tyrosinase is the key and rate-limiting enzyme responsible for the conversion of tyrosine into melanin. Competitive inhibition of tyrosinase enzymatic activity results in decreased or absent melanin synthesis by melanocytes in human skin. DeoxyArbutin (4-[(tetrahydro-2H-pyran-2-yl)oxy]phenol), a novel skin whitening agent, was synthesized through the removal of hydroxyl groups from the glucose side-chain of arbutin. DeoxyArbutin not only shows greater inhibition of tyrosinase activity but is also safer than hydroquinone and arbutin. Hence, deoxyArbutin is a potential skin whitening agent for cosmetics and depigmenting drugs; however, stability of this compound under some conditions remains a problem. The lack of stability poses developmental and practical difficulties for the use of deoxyArbutin in cosmetics and medicines. Improving the thermostability of deoxyArbutin is an important issue for its development. In this research, we established an analytical procedure to verify the amount of deoxyArbutin in solutions using a high performance liquid chromatographic (HPLC) method. The results indicate that this novel skin whitening agent is a thermolabile compound in aqueous solutions. Additionally, the rate constant for thermodegradation (k) and the half-life (t(1/2)) of deoxyArbutin were determined and can be used to understand the thermodegradation kinetics of deoxyArbutin. This information can aid in the application of deoxyArbutin for many future uses.

A comparative study of water soluble 5,10,15,20-tetrakis(2,6-dichloro-3-sulfophenyl)porphyrin and its metal complexes as efficient sensitizers for photodegradation of phenols

5,10,15,20-Tetrakis(2,6-dichloro-3-chlorosulfophenyl)porphyrin and its tin and zinc complexes were synthesized with high yields and fully characterized. The corresponding water-soluble 5,10,15,20-tetrakis(2,6-dichloro-3-sulfophenyl)porphyrins were obtained by hydrolysis with water. An extensive photophysical study of the new water soluble porphyrinic compounds was carried out including absorption and fluorescence spectra, fluorescence quantum yields, triplet absorption spectra, triplet lifetimes, triplet and singlet oxygen quantum yields. These sensitizers were successfully used in the photodegradation of 4-chlorophenol and 2,6-dimethylphenol. A comparison is made of their efficiencies, and some mechanistic considerations are highlighted.

Kinetics and mechanism of the sensitized photodegradation of lignin model compounds

The kinetics of the sensitized photodegradation of a variety of well-defined lignin model compounds was studied to determine the mechanisms responsible for lignin's photochemically-mediated oxidation. Monomeric and dimeric models representing lignin's phenolic end groups and nonphenolic dimers representing its inner core were studied. It was determined that the rate constants for the reaction of the deprotonated phenolic models with singlet oxygen (1O2) range from 0.96 to 7.2 x 10(7) M(-1) s(-1). The models were substituted with zero, one, or two electron-donating methoxy groups on both aryl rings and, while the rate constants showed little dependence on the substitution of the nonphenolic ring, the rate constants increased dramatically with increasing methoxy substitution of the phenol. Reaction between these deprotonated models and 1O2 is thus proposed to occur at the phenolate ring. Under neutral conditions, it was observed that the phenolic models react with excited state sensitizer, with this reaction also occuring at the phenol ring. The sum of the rate constants for quenching of and reaction with excited state sensitizer by lignin model compound ranges from 5.4 to 75 x 10(7) M(-1) s(-1). This study corrects previous reports that attribute the sensitized degradation of neutral lignin model compounds to reaction with 1O2. A nonphenolic aromatic ketone inner-core model was observed to undergo direct photolysis, and its reduced analog was not degraded by direct photolysis or reaction with 1O2 or excited state sensitizer. The oxidized inner-core model was also shown to be able to act as a sensitizer for the degradation of a phenolic lignin model compound.