Organic photocatalysts for the oxidation of pollutants and model compounds

Photocatalytic fixation and oxygenation of NAD+/NADP+ and sulfides using solar light: Exploring mechanistic investigations and their impact on synthetic applications

Sulfur-doped Eosin-B (SDE-B) photocatalysts were synthesized for the first time utilizing sublimed sulfur (S8) as a dopant in an in situ thermal copolymerization technique. Sulfur doping not only increased Eosin-B (E-B) absorption range for solar radiation but also improved fixation and oxygenation capabilities. The doped sulfur bridges the S-S bond by substituting for the edge bromine of the E-B bond. The improved photocatalytic activity of SDE-B in the fixation and oxygenation of NAD+/NADP+ and sulfides using solar light is attributed to the photo-induced hole of SDE-B's high fixation and oxygenation capacity, as well as an efficient suppression of electron and hole recombination. The powerful light-harvesting bridge system created using SDE-B as a photocatalyst works extremely well, resulting in high NADH/NADPH regeneration (79.58/76.36%) and good sulfoxide yields (98.9%) under solar light. This study focuses on the creation and implementation of a sulfur-doped photocatalyst for direct fine chemical regeneration and organic transformation.

Photocatalytic systems: reactions, mechanism, and applications

The photocatalytic field revolves around the utilization of photon energy to initiate various chemical reactions using non-adsorbing substrates, through processes such as single electron transfer, energy transfer, or atom transfer. The efficiency of this field depends on the capacity of a light-absorbing metal complex, organic molecule, or substance (commonly referred to as photocatalysts or PCs) to execute these processes. Photoredox techniques utilize photocatalysts, which possess the essential characteristic of functioning as both an oxidizing and a reducing agent upon activation. In addition, it is commonly observed that photocatalysts exhibit optimal performance when irradiated with low-energy light sources, while still retaining their catalytic activity under ambient temperatures. The implementation of photoredox catalysis has resuscitated an array of synthesis realms, including but not limited to radical chemistry and photochemistry, ultimately affording prospects for the development of the reactions. Also, photoredox catalysis is utilized to resolve numerous challenges encountered in medicinal chemistry, as well as natural product synthesis. Moreover, its applications extend across diverse domains encompassing organic chemistry and catalysis. The significance of photoredox catalysts is rooted in their utilization across various fields, including biomedicine, environmental pollution management, and water purification. Of course, recently, research has evaluated photocatalysts in terms of cost, recyclability, and pollution of some photocatalysts and dyes from an environmental point of view. According to these new studies, there is a need for critical studies and reviews on photocatalysts and photocatalytic processes to provide a solution to reduce these limitations. As a future perspective for research on photocatalysts, it is necessary to put the goals of researchers on studies to overcome the limitations of the application and efficiency of photocatalysts to promote their use on a large scale for the development of industrial activities. Given the significant implications of the subject matter, this review seeks to delve into the fundamental tenets of the photocatalyst domain and its associated practical use cases. This review endeavors to demonstrate the prospective of a powerful tool known as photochemical catalysis and elucidate its underlying tenets. Additionally, another goal of this review is to expound upon the various applications of photocatalysts.

Natural Sunlight-Mediated Emodin Photoinactivation of Aeromonas hydrophila

Aeromonas hydrophila can be a substantial concern, as it causes various diseases in aquaculture. An effective and green method for inhibiting A. hydrophila is urgently required. Emodin, a naturally occurring anthraquinone compound, was exploited as a photo-antimicrobial agent against A. hydrophila. At the minimum inhibitory concentration of emodin (256 mg/L) to inactivate A. hydrophilia in 30 min, an 11.32% survival rate was observed under 45 W white compact fluorescent light irradiation. In addition, the antibacterial activity under natural sunlight (0.78%) indicated its potential for practical application. Morphological observations demonstrated that the cell walls and membranes of A. hydrophila were susceptible to damage by emodin when exposed to light irradiation. More importantly, the photoinactivation of A. hydrophila was predominantly attributed to the hydroxyl radicals and superoxide radicals produced by emodin, according to the trapping experiment and electron spin resonance spectroscopy. Finally, a light-dependent reactive oxygen species punching mechanism of emodin to photoinactivate A. hydrophila was proposed. This study highlights the potential use of emodin in sunlight-mediated applications for bacterial control, thereby providing new possibilities for the use of Chinese herbal medicine in aquatic diseases prevention.

Photocatalytic oxygenation of sulfide using solar light and ingenious GQDs@AQ catalyst: Mechanistic and synthetic investigations

The combination of excellent electronic properties and thermal stability positions orange-derived graphene quantum dots (GQDs) as promising materials for solar light-based applications. Researchers are actively exploring their potential in fields such as photovoltaics, photocatalysis, optoelectronics, and energy storage. Their abundance, cost-effectiveness, and eco-friendly nature further contribute to their growing relevance in cutting-edge scientific research. Furthermore, only GQDs are not much more effective in the UV-visible region, therefore, required band gap engineering in GQDs material. In this context, we designed GQDs-based light harvesting materials, which is active in UV-visible region. Herein we synthesized GQDs coupled with 2,6-diaminoanthrquninone (AQ), that is, GQDs@AQ light harvesting photocatalyst the first time for the oxidation of sulfide to sulfoxide under visible light. For the integrating reactions of sulfide in aerobic conditions under visible light by GQDs@AQ photocatalyst exhibit utmost higher photocatalytic activity than simple GQDs due to low molar extinction coefficient and slow recombination charges. The use of GQDs@AQ light harvesting photocatalyst, showed the excellent organic transformation efficiency of sulfide to sulfoxide with excellent yield (94%). The high efficiency and excellent yield of 94% indicate the effectiveness of GQDs@AQ as a photocatalyst for these specific organic transformations.

Consecutive π-Lewis acidic metal-catalysed cyclisation/photochemical radical addition promoted by in situ generated 2-benzopyrylium as the photoredox catalyst

A π-Lewis acidic metal-catalysed cyclisation/photochemical radical addition sequence was developed, which utilises in situ generated 2-benzopyrylium cation intermediates as photoredox catalysts and electrophilic substrates to form 1H-isochromene derivatives in good yields in most cases. The key 2-benzopyrylium intermediates were generated through the activation of the alkyne moiety of ortho-carbonyl alkynylbenzene derivatives by such π-Lewis acidic metal catalysts as AgNTf2 and Cu(NTf2)2, and the subsequent intramolecular cyclisation and proto-demetalation using trifluoroacetic acid. Further photo-excitation of the 2-benzopyrylium intermediates facilitated single-electron transfer from a benzyltrimethylsilane derivative as a donor molecule to promote the radical addition of arylmethyl radicals to the 2-benzopyrylium intermediates.

A novel eco-friendly polymeric photosensitizer based on chitosan and flavin mononucleotide

Flavin mononucleotide (FMN) is a dye belonging to the flavin family. These dyes produce photosensitized degradation of organic compounds via reaction with the excited states of the dye or with reactive oxygen species photogenerated from the triplet of the dye. This article presents a new polymeric dye (FMN-CS) composed of the photosensitizer FMN covalently bonded to chitosan polysaccharide (CS). FMN-CS obtained has a molecular weight of 230 × 103 g mol-1 and a deacetylation degree of 74.8%. The polymeric dye is an environmentally friendly polymer with spectroscopic and physicochemical properties similar to those of FMN and CS, respectively. Moreover, under sunlight, it is capable of generating 1O2 with a quantum yield of 0.31. FMN-CS, like CS, is insoluble in basic media. This allows easy recovery of the polymeric dye once the photosensitized process has been carried out and makes FMN-CS a suitable photosensitizer for the degradation of pollutants in contaminated waters. To evaluate whether FMN-CS may be used for pollutant degradation, the photosensitized degradation of two trihydroxybenzenes by FMN-CS was studied.

A Plant Dye for Photocatalytic Methane Conversion

A metal-free natural dye has been developed to selectively convert methane to methyl trifluoroacetate (CH3 TFA) using visible light, probably due to the formation of a chloride-bridged dimer undergoing fast intra-complex charge transfer.

Facile and Simple Post Treatment Ball Milling Strategy for the Production of Low-Cost TiO2 Composites with Enhanced Photocatalytic Performance and Applicability to Construction Materials

A facile and cost-effective approach assisted by ball milling (BM) of commercial titanium dioxide (TiO₂), has been utilized to develop cheaper and efficient construction materials. At least three of the commercial and cheaper TiO₂ samples (BA01-01, BA01-01+ and R996, designated as A1, A4 and R1, respectively) were selected and subjected to BM treatment to enhance their photocatalytic efficiencies, if possible. It was noted, that the samples A1, A4 and R1 were typical composites of TiO₂ and calcium carbonate (CaCO₃) and contained varying proportions of anatase, and rutile phases of TiO₂ and CaCO₃. Two of the highly efficient commercial TiO₂ samples, Degussa P25 (simply designated as P25) and ST01 (Ishihara Ind.) were selected for making benchmark comparisons of photocatalytic efficiencies. The BM treated TiO₂ samples (designated as TiO₂-BM with respect to A1, A4 and R1) were evaluated for photocatalytic efficiencies both in both aqueous (methylene blue (MB)) and gaseous (NO_x) photodegradation reactions. Based on detailed comparative investigations, it was observed that A1-BM photocatalyst exhibited superior photocatalytic performances over A4-BM and R1-BM, towards both MB and NO_x photodegradation reactions. The difference of NO_x photodegradation efficiency between the mortar mixed with A1-BM and that mixed with ST01, and P-25 at 15% were 16.6%, and 32.4%, respectively. Even though the mortar mixed with A1-BM at 15% composition exhibited a slightly lower NO_x photodegradation efficiency as compared to mortar mixed with the expensive ST01 and P-25 photocatalysts, the present work promises an economic application in the eco-friendly construction materials for air purification considering the far lower cost of A1. The reasons for the superior performance of A1-BM were deduced through characterization of optical properties, surface characteristics, phase composition, morphology, microstructure and particle size distribution between pristine and BM treated A1 using characterization techniques such as diffuse reflectance spectroscopy, X-ray photoelectron spectroscopy, X-ray diffraction analysis, field emission scanning electron microscopy and particle size analysis.

Plasmon Chemistry on Ag Nanostars: Experimental and Theoretical Raman/SERS Study of the Pesticide Thiacloprid Bond Cleavage by the Plasmon Deactivation Effect

Silver nanoparticles (AgNPs) were synthetized and employed in surface-enhanced Raman scattering measurements to study the chemical behavior when thiacloprid (Thia) interacts with the surface of Ag nanospheres (AgNSp) and Ag nanostars (AgNSt) upon excitation of the system with a 785 nm laser. Experimental results show that the deactivation of the localized surface plasmon resonance induces structural changes in Thia. When AgNSp are used, it is possible to observe a mesomeric effect in the cyanamide moiety. On the other hand, when AgNSt are employed, it promotes the cleavage of the methylene (-CH₂-) bridge in Thia to produce two molecular fragments. To support these results, theoretical calculations based on topological parameters described by the atoms in molecules theory, Laplacian of the electron density at the bond critical point (∇²ρ BCP), Laplacian bond order, and bond dissociation energies were made, confirming that the bond cleavage is centered at the -CH₂- bridge in Thia.

Divergent Functionalization of Alkynes Enabled by Organic Photoredox Catalysis

Direct functionalization of alkynes under oxidative conditions is challenging, as alkynes are usually recalcitrant towards typical oxidants. Herein, we communicate a strategy for the divergent functionalization of alkynes with photoexcited acridinium organic dyes, presumably via the formation of vinyl cation radicals as key intermediates. Based on the nature of the nucleophiles, different types of difunctionalized products were obtained in moderate to good yields. Addition of lithium Lewis acids resulted in a surprising reversal of diastereocontrol.

Development of water-soluble phenazine-2,3-diol-based photosensitizers for singlet oxygen generation

Phenazine-2,3-diol-based dyes, KY-1Na and KY-2Na bearing one and two carboxylic acid sodium salts, respectively, have been newly developed as water-soluble photosensitizers (PSs) possessing the ability to generate singlet oxygen (¹O₂). In order to evaluate the solubility of KY-1Na and KY-2Na in water, the hydrophobicity/hydrophilicity of the two PSs was investigated by experimental measurement of the logarithms (log P_o/w) of the 1-octanol/water partition coefficient (P_o/w) for the PS. The log P_o/w values of both KY-1Na and KY-2Na were determined to be -0.9, indicating that both the PSs are more hydrophilic than Rose Bengal (-0.6) and have hydrophilicity equivalent to methylene blue (-0.9). Both the PSs in water show a broad photoabsorption band in the range of 500 to 600 nm. Thus, we estimated the ¹O₂ quantum yields (Φ_Δ) of KY-1Na and KY-2Na in water by using 9,10-anthracenediyl-bis(methylene)dimalonic acid (ABDA) as a water-soluble ¹O₂ scavenger. It was found that in water the Φ_Δ value (0.19) of KY-2Na is higher than that of KY-1Na (0.06). Density functional theory (DFT) calculations suggested that the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) distributions for the molecular structure of KY-2Na are adequately separated, leading to a decrease in the energy gap (ΔE_ST) between the singlet state (S₁) and the triplet state (T₁) that causes efficient intersystem crossing (ISC), compared to that for the molecular structure of KY-1Na. Indeed, time-dependent DFT (TD-DFT) calculations demonstrated that the ΔE_ST(S₁-T₁) value (0.82 eV) of KY-2Na is smaller than that (0.98 eV) of KY-1Na, resulting in a relatively high Φ_Δ value of KY-2Na. Consequently, we demonstrate that phenazine-2,3-diol-based PSs bearing carboxylic acid salts possess high solubility and moderate ¹O₂ generation ability in water.

Visible-Light-Induced Diradical-Mediated ipso-Cyclization towards Double Dearomative [2+2]-Cycloaddition or Smiles-Type Rearrangement

When mono-radical ipso-cyclization of aryl sulfonamides tend to undergo Smiles-type rearrangement through aromatization-driven C-S bond cleavage, diradical-mediated cyclization must perform in a distinct reaction pathway. It is interesting meanwhile challenging to tune the rate of C-S bond cleavage to achieve a chemically divergent reaction of (hetero) aryl sulfonamides in a visible-light induced energy transfer (EnT) reaction pathway involving diradical species. Herein a chemically divergent reaction based on the designed indole-tethered (hetero)arylsulfonamides is reported which involves a diradical-mediated ipso-cyclization and a controllable cleavage of an inherent C-S bond. The combined experimental and computational results have revealed that the cleavage of the C-S bond in these substrates can be controlled by tuning the heteroaryl moieties: a) If the (hetero)aryl is thienyl, furyl, phenanthryl, etc., the radical coupling of double dearomative diradicals (DDDR) precedes over C-S bond cleavage to afford cyclobutene fused indolines by double dearomative [2+2]-cycloaddition; b) if the (hetero)aryl is phenyl, naphthyl, pyridyl, indolyl etc., the cleavage of C-S bond in DDDR is favored over radical coupling to afford biaryl products.

Heterogeneous vs homogenous photocatalysis: what dominates in the degradation of methyl orange and methylene blue mixtures?

Photocatalysis has been oft proposed as a green solution for pollution remediation, however, majority of the existing literature only studies the degradation of solitary analytes. The degradation of mixtures of organic contaminants is inherently more complicated due to a variety of photochemical processes that occur in parallel. Here, we describe a model system comprised of methylene blue and methyl orange dyes whose degradation carried out by two common photocatalysts, P25 TiO₂ and g-C₃N₄. With P25 TiO₂ as the catalyst, the degradation rate of methyl orange slowed by 50% when degraded in a mixture compared to when alone. Control experiments with radical scavengers showed this to occur due to competition between the dyes for oxidative photogenerated species. In the presence of g-C₃N₄, methyl orange's degradation rate in the mixture increased by 2300% due to two homogeneous photocatalysis processes sensitized by methylene blue. Homogenous photocatalysis was found to be fast relative to heterogeneous photocatalysis by g-C₃N₄ but slow relative to photocatalysis by P25 TiO₂ and explains the change observed between the two catalysts. Changes in dye adsorption to the catalyst when in a mixture were also explored but not found to coincide with changes in degradation rate.

Noble Metal Nanoparticle-Loaded Porphyrin Hexagonal Submicrowires Composites (M-HW): Photocatalytic Synthesis and Enhanced Photocatalytic Activity

Surface plasmon resonance (SPR) photocatalysts have attracted considerable attention because of their strong absorption capacity of visible light and enhanced photogenic carrier separation efficiency. However, the separate production of metal nanoparticles (NPs) and semiconductors limits the photogenic charge transfer. As one of the most promising organic photocatalysts, porphyrin self-assemblies with a long-range ordered structure-enhance electron transfer. In this study, plasmonic noble metal-based porphyrin hexagonal submicrowires composites (M-HW) loaded with platinum (Pt), silver (Ag), gold (Au), and palladium (Pd) NPs were synthesized through a simple in situ photocatalytic method. Homogeneous and uniformly distributed metal particles on the M-HW composites enhanced the catalytic or chemical properties of the organic functional nanostructures. Under the same loading of metal NPs, the methyl orange photocatalytic degradation efficiency of Ag-HW [k_Ag-HW (0.043 min^-1)] composite was three times higher than that of HW, followed by Pt-HW [k_Pt-HW (0.0417 min^-1)], Au-HW [k_Au-HW (0.0312 min^-1)], and Pd-HW [k_Pd-HW (0.0198 min^-1)]. However, the rhodamine B (RhB) and eosin B photocatalytic degradations of Pt-HW were 4 times and 2.6 times those of HW, respectively. Finally, the SPR-induced electron injection, trapping, and recombination processes of the M-HW system were investigated. These results showed that M-HW plasmonic photocatalysts exhibited excellent photocatalytic performances, making them promising materials for photodegrading organic pollutants.

Metal-Catalyzed, Photo-Assisted Selective Transformation of Tertiary Alkylbenzenes and Polystyrenes into Carbonyl Compounds

Every year, thousands of tons of polystyrene are produced and discarded, filling landfills and polluting the marine environment. Although several degradation alternatives have been proposed, the need for an effective procedure for the chemical recycling of polystyrene still remains. Here, a vanadium-catalyzed reaction, assisted by visible light, promoted the direct, selective conversion of tertiary alkylbenzenes into acetophenone and other ketone derivatives. Likewise, standard polystyrene samples as well as polystyrenes from insulation and packaging waste could be chemically recycled into acetophenone in a scalable way regardless of their molecular weight, polydispersity, or form. Preliminary mechanistic investigations revealed the participation of singlet oxygen, superoxide, and hydroxyl radical species in this homogenously catalyzed process. Acetophenone could be used as an additive to accelerate the reaction and to increase the yields in some cases.

Enhancement of photoactivity and cellular uptake of (Bu4N)2[Mo6I8(CH3COO)6] complex by loading on porous MCM-41 support. Photodynamic studies as an anticancer agent

The incorporation by ionic assembly of the hexanuclear molybdenum cluster (Bu₄N)₂[Mo₆I₈(CH₃CO₂)₆] (1) in amino-decorated mesoporous silica nanoparticles MCM-41, has yielded the new molybdenum-based hybrid photosensitizer 1@MCM-41. The new photoactive material presents a high porosity, due to the intrinsic high specific surface area of MCM-41 nanoparticles (989 m² g^-1) which is responsible for the good dispersion of the hexamolybdenum clusters on the nanoparticles surface, as observed by STEM analysis. The hybrid photosensitizer can generate efficiently singlet oxygen, which was demonstrated by using the benchmark photooxygenation reaction of 9,10-anthracenediyl-bis(methylene)dimalonic acid (ABDA) in water. The photodynamic therapy activity has been tested using LED light as an irradiation source (λ_irr ~ 400-700 nm; 15.6 mW/cm²). The results show a good activity of the hybrid photosensitizer against human cervical cancer (HeLa) cells, reducing up to 70 % their viability after 20 min of irradiation, whereas low cytotoxicity is detected in the darkness. The main finding of this research is that the incorporation of molybdenum complexes at porous MCM-41 supports enhances their photoactivity and improves cellular uptake, compared to free clusters.

Porous Photo-Fenton Catalysts Rapidly Triggered by Levodopa-Based Mussel-Inspired Coatings for Enhanced Dye Degradation and Sterilization

The advanced oxidation process of the photo-Fenton reaction can produce hydroxyl radicals with extremely strong oxidizing properties for the efficient and green degradation of various chemical and microbial pollutants. Herein, we report an approach to fabricating heterogeneous Fenton catalysts of β-FeOOH nanorods on porous substrates triggered by mussel-inspired coatings of levodopa (3,4-dihydroxy-phenyl-l-alanine, l-DOPA) and polyethylenimine (PEI) for efficient photocatalytic dyes' degradation and sterilization. The l-DOPA-based coatings not only promote the formation and immobilization of β-FeOOH nanorods on the porous substrates by strong coordination between catechol/carboxyl groups and Fe³⁺ but also improve the energy band structure of the Fenton catalysts through a valence band blue shift and band gap narrowing. The photo-Fenton catalysts prepared by the l-DOPA-based coatings exhibit high electron transport efficiency and improved utilization of sunlight. Only 2 h of mineralization is needed to fabricate these catalysts with excellent photocatalytic efficiency, in which the degradation efficiency of methylene blue can reach 99% within 30 min, whereas the sterilization efficiency of E. coli/S. aureus can reach 93%/94% within 20 min of the photo-Fenton reaction. Additionally, the prepared catalysts reveal a high photodegradation performance for various dyes including methylene blue, methyl blue, methyl orange, direct yellow, and rhodamine B. Furthermore, the catalysts retain high dye degradation efficiencies of above 90% after five photodegradation cycles, indicating cycling performance and good stability.

Perylene diimide growth on both sides of carbon nanotubes for remarkably boosted photocatalytic degradation of diclofenac

Perylene diimide and its derivatives are promising photocatalysts for clean and efficient production, but their practical application in the field of photocatalysis is still limited by the rapid photogenerated charge recombination. In this work, the confined photocatalysts were synthesized by using a gas-phase self-assembly method and comparing the morphology and photocatalytic properties of different photocatalysts after the confinement of carbon nanotubes. The confinement effect of carbon nanotubes acts to stabilize perylene diimide. Electrostatic interaction formed by a wide range of dispersion forces is dominant in the process of stabilization. Benefitting from the three-dimensional electron transfer pathway formed by the conjugation of perylene diimide with a large number of π electrons to the carbon nanotubes plane, the confined photocatalyst shows the pseudo-first-order kinetic constant k of 1.106 h^-1 for the photocatalytic degradation of diclofenac under light, which is 6.11 times higher than that of perylene diimide. The electron transfer created an internal electric field at the interface from carbon nanotubes to perylene diimide, which greatly accelerated the separation of photogenerated electron-hole pairs and improved the photocatalytic activity. This study further expands the applicability of perylene diimide in the field of photocatalysis and provides a new approach for water environment treatment.

Methyl Viologens of Bis-(4'-Pyridylethynyl)Arenes - Structures, Photophysical and Electrochemical Studies, and their Potential Application in Biology

A series of bis-(4'-pyridylethynyl)arenes (arene=benzene, tetrafluorobenzene, and anthracene) were synthesized and their bis-N-methylpyridinium compounds were investigated as a class of π-extended methyl viologens. Their structures were determined by single crystal X-ray diffraction, and their photophysical and electrochemical properties (cyclic voltammetry), as well as their interactions with DNA/RNA were investigated. The dications showed bathochromic shifts in emission compared to the neutral compounds. The neutral compounds showed very small Stokes shifts, which are a little larger for the dications. All of the compounds showed very short fluorescence lifetimes (<4 ns). The neutral compound with an anthracene core has a quantum yield of almost unity. With stronger acceptors, the analogous bis-N-methylpyridinium compound showed a larger two-photon absorption cross-section than its neutral precursor. All of the dicationic compounds interact with DNA/RNA; while the compounds with benzene and tetrafluorobenzene cores bind in the grooves, the one with an anthracene core intercalates as a consequence of its large, condensed aromatic linker moiety, and it aggregates within the polynucleotide when in excess over DNA/RNA. Moreover, all cationic compounds showed highly specific CD spectra upon binding to ds-DNA/RNA, attributed to the rare case of forcing the planar, achiral molecule into a chiral rotamer, and negligible toxicity toward human cell lines at ≤10 μM concentrations. The anthracene-analogue exhibited intracellular accumulation within lysosomes, preventing its interaction with cellular DNA/RNA. However, cytotoxicity was evident at 1 μM concentration upon exposure to light, due to singlet oxygen generation within cells. These multi-faceted features, in combination with its two-photon absorption properties, suggest it to be a promising lead compound for development of novel light-activated theranostic agents.

Efficient peroxymonosulfate activation by N-rich pyridyl-iron phthalocyanine derivative for the elimination of pharmaceutical contaminants under solar irradiation

It is of great significance for improving electron transmission performance by changing of the outer ring structure of iron phthalocyanine. Herein, 4 (pyridine-2, 3-yl) iron phthalocyanine (FepyPc), as N-rich pyridyl-iron phthalocyanine derivative, was introduced to degrade pharmaceutical contaminants. The catalytic degradation of organic pollutants with FepyPc was studied by activating peroxymonosulfate (PMS) at room temperature. The results clarified that the removal rate of carbamazepine (CBZ) was close to 100% within 60 min and the calculated apparent rate constant was about 2 times larger than FePc, which proved that FepyPc had superior performance. Four active species were identified for the degradation of CBZ, including superoxide radical (•O₂^-), singlet oxygen (¹O₂), sulfate radical (SO₄•^-) and hydroxyl radical (•OH). In addition, the possible reaction mechanism was inferred in FepyPc/PMS/sunlight system for CBZ removal. Finally, the CBZ degradation pathway was proposed by using ultra-performance liquid chromatography and high definition mass spectrometry (UPLC/HDMS). This research provided a meaningful and efficient method for the elimination of pharmaceutical contaminants.

Photocatalytic Degradation of Recalcitrant Pollutants of Greywater

These days, many countries have a water shortage and have limited access to clean water. To overcome this, a new treatment is emerging, namely, the photocatalytic processing of greywater. Photocatalytic processes to remove the organic matter from different greywater sources are critically reviewed. Their efficiency in degrading the organic matter in greywater is scrutinized along with factors that can affect the activity of photocatalysts. Modified TiO2, ZnO and TiO2 catalysts show great potential in degrading organic materials that are present in greywater. There are several methods that can be used to modify TiO2 by using sol-gel, microwave and ultrasonication. Overall, the photocatalytic approach alone is not efficient in mineralizing the organic compounds, but it works well when the photocatalysis is combined with oxidants and Fe3+. However, factors such as pH, concentration and catalyst-loading of organic compounds can significantly affect photocatalytic efficiency.

Biomimetic photooxidation of noscapine sensitized by a riboflavin derivative in water: The combined role of natural dyes and solar light in environmental remediation

Noscapine (NSC) is a benzyl-isoquinoline alkaloid discovered in 1930 as an antitussive agent. Recently, NSC has also been reported to exhibit antitumor activity and, according to computational studies, it is able to attack the protease enzyme of Coronavirus (COVID-19) and thus could be used as antiviral for COVID-19 pandemic. Therefore, an increasing use of this drug could be envisaged in the coming years. NSC is readily metabolized with a half-life of 4.5 h giving rise to cotarnine, hydrocotarnine, and meconine, arising from the oxidative breaking of the CC bond between isoquinoline and phthalide moieties. Because of its potentially increasing use, high concentrations of NSC but also its metabolites will be delivered in the environment and potentially affect natural ecosystems. Thus, the aim of this work is to investigate the degradation of NSC in the presence of naturally occurring photocatalysts. As a matter of fact, the present contribution has demonstrated that NSC can be efficiently degraded in the presence of a derivative of the natural organic dye Riboflavin (RFTA) upon exposure to visible light. Indeed, a detailed study of the mechanism involved in the photodegradation revealed the similarities between the biomimetic and the photocatalyzed processes. In fact, the main photoproducts of NSC were identified as cotarnine and opianic acid based on a careful UPLC-MS² analysis compared to the independently synthesized standards. The former is coincident with one of the main metabolites obtained in humans, whereas the latter is related to meconine, a second major metabolite of NSC. Photophysical experiments demonstrated that the observed oxidative cleavage is mediated mainly by singlet oxygen in a medium in which the lifetime of ¹O₂ is long enough, or by electron transfer to the triplet excited state of RFTA if the photodegradation occurs in aqueous media, where the ¹O₂ lifetime is very short.

Exploring metallic and plastic 3D printed photochemical reactors for customizing chemical synthesis

Visible light photocatalysis is a rapidly developing branch of chemical synthesis with outstanding sustainable potential and improved reaction design. However, the challenge is that many particular chemical reactions may require dedicated tuned photoreactors to achieve maximal efficiency. This is a critical stumbling block unless the possibility for reactor design becomes available directly in the laboratories. In this work, customized laboratory photoreactors were developed with temperature stabilization and the ability to adapt different LED light sources of various wavelengths. We explore two important concepts for the design of photoreactors: reactors for performing multiple parallel experiments and reactors suitable for scale-up synthesis, allowing a rapid increase in the product amount. Reactors of the first type were efficiently made of metal using metal laser sintering, and reactors of the second type were successfully manufactured from plastic using fused filament fabrication. Practical evaluation has shown good accuracy of the temperature stabilization in the range typically required for organic synthesis for both types of reactors. Synthetic application of 3D printed reactors has shown good utility in test reactions-furan C-H arylation and thiol-yne coupling. The critical effect of temperature stabilization was established for the furan arylation reaction: heating of the reaction mixture may lead to the total vanishing of photochemical effect.

Self-assembly hybridization of COFs and g-C3N4: Decipher the charge transfer channel for enhanced photocatalytic activity

Organic semiconductors have been recognized as a new generation of photocatalysts for pollutants degradation and energy production. Herein, organic heterojunction (TpMa/CN) consisting of carbon nitride and β-ketoenamine-based covalent organic framework is fabricated via a controllable self-assembly approach. The as-prepared TpMa/CN heterojunctions show enlarged visible-light absorption. The optimum TpMa/CN-5 photocatalyst achieves the highest photocatalytic activity towards tetracycline degradation, and its photocatalytic degradation rate is improved by 2.3 and 4.3 times than TpMa and CN, respectively. As a multifunctional photocatalyst, TpMa/CN-5 sample also shows remarkable photocatalytic activity for hydrogen peroxide production (880.494 μM h^-1), which is 49 times higher than that of CN. Experimental and theoretical investigations indicate that a built-in electric field is formed at the interface of composite, which enables an accelerated charge transfer and separation. This work develops an effective strategy to design difunctional photocatalyst and deciphers the electronic properties and mechanisms of g-C₃N₄-based organic photocatalysts, which spurs further interests for organic heterojunction photocatalysts in the future.

A Photosensitized Singlet Oxygen (1O2) Toolbox for Bio-Organic Applications: Tailoring 1O2 Generation for DNA and Protein Labelling, Targeting and Biosensing

Singlet oxygen (1O2) is the excited state of ground, triplet state, molecular oxygen (O2). Photosensitized 1O2 has been extensively studied as one of the reactive oxygen species (ROS), responsible for damage of cellular components (protein, DNA, lipids). On the other hand, its generation has been exploited in organic synthesis, as well as in photodynamic therapy for the treatment of various forms of cancer. The aim of this review is to highlight the versatility of 1O2, discussing the main bioorganic applications reported over the past decades, which rely on its production. After a brief introduction on the photosensitized production of 1O2, we will describe the main aspects involving the biologically relevant damage that can accompany an uncontrolled, aspecific generation of this ROS. We then discuss in more detail a series of biological applications featuring 1O2 generation, including protein and DNA labelling, cross-linking and biosensing. Finally, we will highlight the methodologies available to tailor 1O2 generation, in order to accomplish the proposed bioorganic transformations while avoiding, at the same time, collateral damage related to an untamed production of this reactive species.

2,11-Dimethoxyldipyridopurinone as an efficient reducing visible-light photocatalyst for organic transformations

2,11-Dimethoxyldipyridopurinone (DP4) was demonstrated as a potent reducing visible-light PC that can efficiently catalyze three prototypic photoreactions: the redox-neutral, net oxidative and reductive reactions via oxidative-quenching mechanisms.

POM-based metal–organic compounds: Assembly, structures and properties

Four POM-based inorganic-organic hybrid compounds, which are {[(Cu·L1’·H2O)·(α-Mo8O26)0.5]·H2O}n (1), {(Cu·L2’·H2O)·(α-Mo8O26)0.5}n (2), {[(Cu·L3’·H2O)·(β-Mo8O26)0.5]·5H2O}n (3), {(Cu·L4’·H2O)·(β-Mo8O26)}n (4)[L1’ = 1,5-bis (4-carboxylpyridine) pentane dibromide, L2’ = 1,7-bis (4-carboxylpyridine) heptane dibromide, L3’ = 1,2-bis [(4-carboxylpyridine) - N-methylene] benzene dibromide, L4’ = 1,4-bis [(4-carboxylpyridine) - N-methylene] benzene dibromide] have been successfully synthesized under hydrothermal conditions by tuning ligands. Compounds 1–4 were characterized by single crystal X-ray diffraction, infrared spectrum (IR), powder X-ray diffraction (PXRD), and thermogravimetric (TG). The transformation of ligands have a momentous effect on the [Mo8O26]4 - structures of this series. In addition, the adsorption and photocatalytic properties of organic dyes for compounds 1–4 have been investigated.

Enhanced Nitrite Production from the Aqueous Photolysis of Nitrate in the Presence of Vanillic Acid and Implications for the Roles of Light-Absorbing Organics

A prominent source of hydroxyl radicals (^•OH), nitrous acid (HONO) plays a key role in tropospheric chemistry. Apart from direct emission, HONO (or its conjugate base nitrite, NO₂^-) can be formed secondarily in the atmosphere. Yet, how secondary HONO forms requires elucidation, especially for heterogeneous processes involving numerous organic compounds in atmospheric aerosols. We investigated nitrite production from aqueous photolysis of nitrate for a range of conditions (pH, organic compound, nitrate concentration, and cation). Upon adding small oxygenates such as ethanol, n-butanol, or formate as ^•OH scavengers, the average intrinsic quantum yield of nitrite [Φ(NO₂^-)] was 0.75 ± 0.15%. With near-UV-light-absorbing vanillic acid (VA), however, the effective Φ(NO₂^-) was strongly pH-dependent, reaching 8.0 ± 2.1% at a pH of 8 and 1.5 ± 0.39% at a more atmospherically relevant pH of 5. Our results suggest that brown carbon (BrC) may greatly enhance the nitrite production from the aqueous nitrate photolysis through photosensitizing reactions, where the triplet excited state of BrC may generate solvated electrons, which reduce nitrate to NO₂ for further conversion to nitrite. This photosensitization process by BrC chromophores during nitrate photolysis under mildly acidic conditions may partly explain the missing HONO in urban environments.

Strong Pyro-Electro-Chemical Coupling of Elbaite/H2O2 System for Pyrocatalysis Dye Wastewater

Elbaite is a natural silicate mineral with a spontaneous electric field. In the current study, it was selected as a pyroelectric catalyst to promote hydrogen peroxide (H2O2) for dye decomposition due to its pyro-electro-chemical coupling. The behaviors and efficiency of the elbaite/H2O2 system in rhodamine B (RhB) degradation were systematically investigated. The results indicate that the optimal effective degradability of RhB reaches 100.0% at 4.0 g/L elbaite, 7.0 mL/L H2O2, and pH = 2.0 in the elbaite/H2O2 system. The elbaite/H2O2 system exhibits high recyclability and stability after recycling three times, reaching 94.5% of the degradation rate. The mechanisms of RhB degradation clarified that the hydroxyl radical (·OH) is the main active specie involved in catalytic degradation in the elbaite/H2O2 system. Moreover, not only does elbaite act as a pyroelectric catalyst to activate H2O2 in order to generate the primary ·OH for subsequent advanced oxidation reactions, but it also has the role of a dye sorbent. The elbaite/H2O2 system shows excellent application potential for the degradation of RhB.

Harnessing selective PET and EnT catalysis by chlorophyll to synthesize N-alkylated quinoline-2(1H)-ones, isoquinoline-1(2H)-ones and 1,2,4-trioxanes

Photocatalytic syntheses of quinoline-2(1H)-ones, isoquinoline-1(2H)-ones and 1,2,4-trioxanes were achieved by selective photo-induced electron transfer (PET) and energy transfer (EnT), respectively, by chlorophyll under visible light irradiation. Quinoline-2(1H)-ones, isoquinoline-1(2H)-ones and 1,2,4-trioxanes are biologically potent scaffolds and their syntheses following mild reaction protocols are highly sought after. This work showcases the divergent photocatalytic roles of chlorophyll viz., electron transfer in the case of quinolines or isoquinolines and energy transfer with allyl alcohols as substrates, affording their aerobic oxidation under green reaction conditions. The mechanistic investigations affirm that the catalytic cycle follows the electron-transfer pathway in carrying out the oxidation of N-alkyl(iso)quinolinium salts. Furthermore, the method provides an environmentally benign, simple reaction strategy for organic transformations of (N)-heterocycles.

Fe-based single-atom catalysis for oxidizing contaminants of emerging concern by activating peroxides

We prepared a single-atom Fe catalyst supported on an oxygen-doped, nitrogen-rich carbon support (SAFe-OCN) for degrading a broad spectrum of contaminants of emerging concern (CECs) by activating peroxides such as peroxymonosulfate (PMS). In the SAFe-OCN/PMS system, most selected CECs were amenable to degradation and high-valent Fe species were present for oxidation. Moreover, SAFe-OCN showed excellent performance for contaminant degradation in complex water matrices and high stability in oxidation. Specifically, SAFe-OCN, with a catalytic center of Fe coordinated with both nitrogen and oxygen (FeN_xO_4-x), showed 5.13-times increased phenol degradation kinetics upon activating PMS compared to the catalyst where Fe was only coordinated with nitrogen (FeN₄). Molecular simulations suggested that FeN_xO_4-x, compared to FeN₄, was an excellent multiple-electron donor and it could potential-readily form high-valent Fe species upon oxidation. In summary, the single-atom Fe catalyst enables efficient, robust, and sustainable water and wastewater treatment, and molecular simulations highlight that the electronic nature of Fe could play a key role in determining the activity of the single-atom catalyst.

Photocatalytic degradation of drugs in water mediated by acetylated riboflavin and visible light: A mechanistic study

There is a current concern, among the scientific community, on the pollutants classified as "persistent organic pollutants (POPs)". Pharmaceuticals and personal care products (PPCPs) belong to this family of contaminants; therefore, it is necessary to find more efficient techniques able to achieve their removal from the environment. This study focuses on two different pharmaceuticals: carbamazepine and atenolol, chosen for their widespread use and their different chemical and medical properties. In this work, an organic dye, acetylated riboflavin, has been used in combination with visible light to achieve the photodegradation of these two POPs in <2 h. Moreover, photophysical experiments demonstrated the involvement of the singlet and triplet excited states of acetylated riboflavin and the generated singlet oxygen in the removal of these drugs. Besides, a detailed UFLC-MS-MS analysis of the photoproducts confirmed the oxidation of the drugs. Finally, a plausible mechanism has been postulated.

Phthalocyanines: An Old Dog Can Still Have New (Photo)Tricks!

Phthalocyanines have enjoyed throughout the years the benefits of being exquisite compounds with many favorable properties arising from the straightforward and diverse possibilities of their structural modulation. Last decades appreciated a steady growth in applications for phthalocyanines, particularly those dependent on their great photophysical properties, now used in several cutting-edge technologies, particularly in photonic applications. Judging by the vivid reports currently provided by many researchers around the world, the spotlight remains assured. This review deals with the use of phthalocyanine molecules in innovative materials in photo-applications. Beyond a comprehensive view on the recent discoveries, a critical review of the most acclaimed/considered reports is the driving force, providing a brief and direct insight on the latest milestones in phthalocyanine photonic-based science.

Photogenerated-hole-induced rapid elimination of solid tumors by the supramolecular porphyrin photocatalyst

The rapid, complete, targeted and safe treatment for tumors remains a key issue in cancer therapy. A novel treatment of solid tumors by supramolecular photocatalyst Nano-SA-TCPP with the irradiation of 600-700 nm wavelength is established. Solid tumors (100 mm3) can be eliminated within 10 min. The 50-day mouse survival rate was increased from 0% to 100% after the photocatalytic therapy. The breakthrough was owing to the cell membrane rupture and the cytoplasmic loss caused by photogenerated holes inside cancer cells. The porphyrin-based photocatalysts can be internalized in a targeted manner by cancer cells due to the size selection effect, without entering the normal cells. The therapy has no toxicity or side effects for normal cells and organisms. Moreover, the photocatalytic therapy is effective for a variety of cancer cell lines. Because of its high efficiency, safety and universality, the photocatalytic therapy provides us with a new lancet to conquer the tumor.