Visible Light Photocatalysis Research Articles

Formation of 3-Alkynylidenephthalides by Gold(I)-Catalyzed Alkynylative Cyclization of o-Alkynylbenzoic Acids under Visible Light Irradiation.

Herein, we report a Csp2-Csp cross-coupling process involving the merger of gold catalysis and visible light photocatalysis leading to the alkynylative cyclization of o-alkynyl benzoic acids. The corresponding and previously undescribed alkynylidenephthalide products were obtained as mixtures of E:Z isomers. The key C-C bond formation is based on the photoactivation of the oxidative addition of an alkynyliodide to a vinylgold(I) intermediate resulting from an initial 5-exo-dig cyclization pathway, as supported by mechanistic studies including DFT calculations.

Regulation of Exciton Effects in Functionalized Conjugated Polymers by B-N Lewis Pairs for Visible-Light Photocatalysis.

Strong excitonic effects are common in organic conjugated polymer semiconductors, severely hindering the generation of free charge carriers for conducting photocatalysis. Therefore, exploring new channels to modulate exciton dissociation in polymers is far-reaching in facilitating photocatalysis. A series of B-N Lewis pair functionalized conjugated polymers have been developed to minimize exciton effects by modulating charge transfer pathways. Theoretical studies have shown that introducing B-N Lewis pairs can dramatically increase the distance of charge transfer (D index) and the amount of electron transfer and reduce the Coulomb attraction energy (EC), which contributes to breaking the equilibrium of the coexistence of excitons and charge carriers. Further experimental results show that the singlet excitons are efficiently dissociated into more free-charge carriers under photoexcitation to participate in surface reactions. The optimized polymer PyPBM shows an exponential increase in photocatalytic hydrogen and hydrogen peroxide production performance by visible light illumination.

Visible Light Excitation of Poly-(para-Phenylene Ethynylene) Enables Heterogeneous Photocatalytic Oxidations of Amines in Flow.

Heterogeneous visible light photocatalysis is a compelling approach to address sustainability in synthetic photochemistry. However, the use of solid-state photocatalysts remains very unpopular in organic synthesis because of their limited accessibility and the black-box effect associated to the lack of rational between their molecular structure and their photochemical properties. Herein, we disclose the synthesis, characterization, photocatalytic properties and synthetic applications of a simple and readily available solid-state conjugated organic polymer, poly-(para-phenylene ethynylene) 1, which exhibits a strong oxidative power upon irradiation with visible light (E(1*/1•-) = +1.67 V vs SCE). Comparisons with structural analogues highlighted the superior photocatalytic activity of this linear semiconductor, on account of its fully conjugated architecture. The associated excited-state reactivity enabled the transformation of various amines into imines in batch and continuous flow reactors together with straightforward photocatalyst recycling. Mechanistic investigations revealed concomitant photoredox and energy transfer pathways, that led to the formation of the desired products. Ultimately, the inline generation of imines was exploited in telescoped three-component Ugi reactions (3CR) in batch and flow toward biologically relevant α-acylaminoamides.

Visible Light Excitation of Poly‐(para‐Phenylene Ethynylene) Enables Heterogeneous Photocatalytic Oxidations of Amines in Flow.

Heterogeneous visible light photocatalysis is a compelling approach to address sustainability in synthetic photochemistry. However, the use of solid‐state photocatalysts remains very unpopular in organic synthesis because of their limited accessibility and the black‐box effect associated to the lack of rational between their molecular structure and their photochemical properties. Herein, we disclose the synthesis, characterization, photocatalytic properties and synthetic applications of a simple and readily available solid‐state conjugated organic polymer, poly‐(para‐phenylene ethynylene) 1, which exhibits a strong oxidative power upon irradiation with visible light (E(1*/1•–) = +1.67 V vs SCE). Comparisons with structural analogues highlighted the superior photocatalytic activity of this linear semiconductor, on account of its fully conjugated architecture. The associated excited‐state reactivity enabled the transformation of various amines into imines in batch and continuous flow reactors together with straightforward photocatalyst recycling. Mechanistic investigations revealed concomitant photoredox and energy transfer pathways, that led to the formation of the desired products. Ultimately, the inline generation of imines was exploited in telescoped three‐component Ugi reactions (3CR) in batch and flow toward biologically relevant α‐acylaminoamides.

Vinylene-Linking of Polycyclic Aromatic Hydrocarbons to π-Extended Two-Dimensional Covalent Organic Framework Photocatalyst for H2O2 Synthesis.

Polycyclic aromatic hydrocarbons (PAHs) hold the predominant role either as individual molecules or building blocks in the field of organic semiconductors or nanocarbons. Connecting PAHs via sp2-carbon bridges to form high-crystalline p-extended structures is highly desired not only for enlarging the regimes of two-dimensional materials but also for achieving exceptional properties/functions. In this work, we developed 5,10-dimethyl-4,9-diazapyrene as a key monomer, whose two methyl groups at the positions adjacent to nitrogen atoms, can helpfully increase the solubility, and serve as the active connection sites. In the presence of organic acids, this monomer enables smoothly conducting Knoevenagel condensation to form two vinylene-linked PAH-cored COFs, which show high-crystalline honeycomb structures with large surface areas up to 1238 m2 g-1. Owing to the direct connection mode of PAH building blocks with vinylene, the as-prepared COFs possess spatially extended p-conjugation and substantial semiconducting properties. Consequently, their visible-light photocatalysis with exceptional activity and durability was manifested to generate H2O2 up to 3820 µmol g-1 h-1 in pure water, and even 17080 µmol g-1 h-1 using benzyl alcohol as a hole sacrificial agent.

Photochemically Induced Approaches to the Syntheses of β‐Lactams

The synthesis of β‐lactam scaffolds is of paramount importance due to their extensive applications in pharmaceuticals, particularly as antibiotics. Visible light photocatalysis has emerged as a revolutionary approach in this domain, providing a sustainable and efficient pathway for β‐lactam construction. In this review, we meticulously discuss the recent developments in the synthesis of photocatalysed β‐lactam frameworks.A key focus is the Staudinger reaction, traditionally a cornerstone in β‐lactam synthesis, and its adaptation to visible light photocatalysis. We explore the mechanistic intricacies of the Staudinger reaction under photochemical conditions, along with other pivotal cyclization strategies enabled by visible light. By illuminating the novel photocatalytic routes to β‐lactams, this review provides a thorough understanding of the state‐of‐the‐art techniques and sets the stage for future innovations in the green synthesis of these critical compounds.

The excellent electrocatalytic HER activity and photogalvanic effect of WS2/Ga2O3 based on Density Functional Theory

This study is based on density functional theory, studied structure and electronic properties, optical properties, electrocatalytic water splitting to produce H2, and electrical properties of the WS2/Ga2O3 heterojunction. By analyzing the photoelectric characteristics, we find that the WS2/Ga2O3 heterojunction has built-in electric field, which can separate photogenerated carriers and effectively capture visible light for visible light photocatalysis. In addition, the change of Gibb free energy (ΔG) tends to 0, so when the WS2/Ga2O3 heterojunction is used as a catalyst, the hydrogen evolution reaction tends to proceed spontaneously. Interestingly, by analyzing the electrical properties, we find that the large and obviously changed photogalvanic effect photocurrent is produced with the change of polarization angle and photon energy of the WS2/Ga2O3 heterojunction, and it has the potential to become high-sensitivity optoelectronic detector.

Conversion of Acids to S-Alkyl Dithiocarbamates by Decarboxylative Sulfuration Using Visible-Light Photocatalysis.

S-Alkyl dithiocarbamates, as an important class of sulfur-containing compounds, play pivotal roles in diverse fields, yet methods for the synthesis that start from simple, readily available feedstocks and exhibit mild conditions and structurally diverse products are scarce. In this work, we developed an efficient approach for the synthesis of various S-alkyl dithiocarbamates via visible-light photocatalysis with readily available and structurally diverse alkyl carboxylic acids (primary, secondary, and tertiary acids, amino acids, etc.) and disulfide tetraalkylthiuram as the starting materials. This protocol features high efficiency, mild reaction conditions, a broad substrate scope, and good functional group tolerance. Potential applications are further demonstrated by a sunlight experiment, H2O as a solvent, gram-scale synthesis, and facile synthesis of bioactive molecules.

Bottom-up construction of defective TiO2 microspheres with hierarchical architectures and controlled crystallites for visible-light photocatalysis

Defect-engineering of TiO2 materials has emerged as an effective strategy to enhance the light adsorption and improve the photocatalytic activity under visible-light. However, the designing and fabricating of hierarchically structured TiO2 with controllable crystalline phases and stable structure defects is challenging and rarely reported. Herein, we present a novel bottom-up synthesis strategy to prepare defective TiO2 microspheres with hierarchical architecture and abundant phase junctions. The phase composition and defect concentration of the obtained TiO2 can be easily adjusted by regulating the amount of urea. Moreover, the formation mechanism of hierarchical defective TiO2 microspheres has been investigated. Notably, compared with the defective TiO2 prepared with traditional top-down strategies, more bulk Ti3+ and oxygen vacancies can be generated, which is crucial for the stability of materials. Such integration of unique hierarchical architecture, stable structure defects as well as abundant anatase/rutile phase junctions not only result in the narrowed band gap and improved visible-light absorption, but also allow the fast interfacial electron transfer and better charge separation, leading to enhanced photocatalytic activities in RhB degradation and hydrogen generation under visible light (λ>400 nm) irradiation.

Orientation-Dependent Photocatalysis of Imine-Linked Covalent Organic Frameworks Based on Thienothiophenes for Oxidation of Amines to Imines.

Toward visible light photocatalysis, covalent organic frameworks (COFs) have recently garnered growing attention. The effect of different orientations of imine of imine-linked COFs on photocatalysis should be elucidated. Here, two COFs are developed with 2,5-diphenylthieno[3,2-b]thiophene (DPTT) and 1,3,6,8-tetraphenylpyrene (Py) linked by imine, affording DPTT-Py-COF and Py-DPTT-COF, respectively. Distinctly, DPTT-Py-COF and Py-DPTT-COF have high crystallinity and porosity, paving the way to highly efficient photocatalysis. Theoretical calculations demonstrate that both DPTT-Py-COF and Py-DPTT-COF are of similar bandgaps but of varied energy positions due to the different orientations of imine. Besides, characterizations disclose that DPTT-Py-COF delivers more enhanced charge separation and transfer than Py-DPTT-COF. Probed by the oxidation of amine to imine, DPTT-Py-COF exhibits a blue light photocatalytic performance superior to that of Py-DPTT-COF. DPTT-Py-COF, a highly recyclable photocatalyst, enables the oxidation of various amines to imines with oxygen. This work highlights that tuning the microenvironment of COFs unravels tenable performances in photocatalysis.

Selective incorporation of antimony into gallium nitride

Dilute concentrations of antimony (Sb) incorporation into GaN induce strong bandgap bowing and tunable room-temperature photoluminescence from the UV to the green spectral regions. However, the atomistic details of the incorporation of Sb into the GaN host remain unclear. In this work, we use first-principles calculations to understand the thermodynamics of Sb substitution into GaN and its effect on the optical and Raman spectra. Although it is empirically considered that Sb is preferentially incorporated as an anion (Sb3−) into the N sublattice, we demonstrate that Sb can also be incorporated as a cation (Sb3+, Sb5+) into the metal sublattice. Our thermodynamic analysis demonstrates that SbN0, SbGa2+, and SbGa0 can co-exist under Ga-rich conditions in n-type samples. We further confirm the dual incorporation of Sb by calculating the vibrational frequencies of different anionic and cationic substitutions to explain the origins of experimentally observed additional Raman peaks of Sb-doped GaN. Moreover, the calculated band structures of different Sb substitutions into GaN explain the experimental photoluminescence and optical absorption spectra. Overall, our analysis suggests that the coexistence of Sb3−, Sb3+, and Sb5+ substitutions into GaN explains the totality of experimental measurements. Our results demonstrate that the selective incorporation of Sb into GaN (and potentially other group-V elements such as As, P, or Bi) by tuning the growth conditions can drastically modify the electronic properties, for applications in visible light emitters and photocatalysis.

A Nickel-Catalyzed Nozaki–Hiyama–Kishi Reaction under Visible Light Photocatalysis

A Nickel-Catalyzed Nozaki–Hiyama–Kishi Reaction under Visible Light Photocatalysis

Biosynthesis of bimetallic Au-Ag nanoparticles using Abrus precatorius seed Extract: Analysis of photocatalytic, cytotoxic, and antibacterial activities

The present investigation aims to examine the bio-route preparation of gold-silver bimetallic nanoparticles using an aqueous seed extract of the Abrus precatorius plant. The bio-synthesized gold-silver bimetallic nanoparticles (AP-Au-Ag NPs) were characterized by various spectroscopic techniques. The surface plasmon resonance (SPR) peak at 555 nm for Au, 433 nm for Ag, and 546 nm for the Au-Ag alloy indicates that bimetallic NPs have been formed. FTIR data provided evidence of functional groups such as OH, CO, and NH2 (proteins, flavonoids, and carbohydrates). When making a bimetallic Au-Ag alloy, carbohydrates are useful as a capping agent and proteins as a reducing agent. The AP-Au-Ag NPs’ stability was assessed by looking at their negative zeta potential value of −21.5 mV. The spherical-shaped crystalline alloy AP-Au-Ag NPs was produced with an average particle size of 10 nm. The TEM images verified the presence of polydispersity in the AP-Au-Ag NPs. The synthesized alloy nanoparticles have a potential cytotoxic effect against MCF-7 cancer cell lines with an IC50 value of 25 ± 1.5 μg/mL and the AP-Au-Ag NPs were found to be a good antibacterial agent against gram-positive and gram-negative bacteria. During visible light photocatalysis, ciprofloxacin was not removed after 60 min of exposure when employing materials made of a pure monometallic nanoparticle. However, the use of bi-metallic nanoparticles made of gold and silver resulted in the breakdown of over 90% of the ciprofloxacin into minerals. The produced bi-metallic nanoparticles, composed of Au-Ag showed exceptional catalytic efficiency. The gold-silver alloyed nanoparticles showed the most promise and efficiency when compared to others.

3D Lead-Organoselenide-Halide Perovskites and their Mixed-Chalcogenide and Mixed-Halide Alloys.

We incorporate Se into the 3D halide perovskite framework using the zwitterionic ligand: SeCYS (+NH3(CH2)2Se-), which occupies both the X- and A+ sites in the prototypical ABX3 perovskite. The new organoselenide-halide perovskites: (SeCYS)PbX2 (X=Cl, Br) expand upon the recently discovered organosulfide-halide perovskites. Single-crystal X-ray diffraction and pair distribution function analysis reveal the average structures of the organoselenide-halide perovskites, whereas the local lead coordination environments and their distributions were probed through solid-state 77Se and 207Pb NMR, complemented by theoretical simulations. Density functional theory calculations illustrate that the band structures of (SeCYS)PbX2 largely resemble those of their S analogs, with similar band dispersion patterns, yet with a considerable band gap decrease. Optical absorbance measurements indeed show band gaps of 2.07 and 1.86 eV for (SeCYS)PbX2 with X=Cl and Br, respectively. We further demonstrate routes to alloying the halides (Cl, Br) and chalcogenides (S, Se) continuously tuning the band gap from 1.86 to 2.31 eV-straddling the ideal range for tandem solar cells or visible-light photocatalysis. The comprehensive description of the average and local structures, and how they can fine-tune the band gap and potential trap states, respectively, establishes the foundation for understanding this new perovskite family, which combines solid-state and organo-main-group chemistry.

Biogenic Synthesis Based on Cuprous Oxide Nanoparticles Using Eucalyptus globulus Extracts and Its Effectiveness for Removal of Recalcitrant Compounds

Recalcitrant compounds resulting from anthropogenic activity are a significant environmental challenge, necessitating the development of advanced oxidation processes (AOPs) for effective remediation. This study explores the synthesis of cuprous oxide nanoparticles on cellulose-based paper (Cu2O@CBP) using Eucalyptus globulus leaf extracts, leveraging green synthesis techniques. The scanning electron microscopy (SEM) analysis found the average particle size 64.90 ± 16.76 nm, X-ray diffraction (XRD) and Raman spectroscopy confirm the Cu2O structure in nanoparticles; Fourier-transform infrared spectroscopy (FTIR) suggests the reducing role of phenolic compounds; and ultraviolet–visible diffuse reflectance spectroscopy (UV-Vis DRS) allowed us to determine the band gap (2.73 eV), the energies of the valence band (2.19 eV), and the conduction band (−0.54 eV) of Cu2O@CBP. The synthesized Cu2O catalysts demonstrated efficient degradation of methylene blue (MB) used as a model as recalcitrant compounds under LED-driven visible light photocatalysis and heterogeneous Fenton-like reactions with hydrogen peroxide (H2O2) using the degradation percentage and the first-order apparent degradation rate constant (kapp). The degradation efficiency of MB was pH-dependent, with neutral pH favoring photocatalysis (kapp = 0.00718 min−1) due to enhanced hydroxyl (·OH) and superoxide radical (O2·−) production, while acidic pH conditions improved Fenton-like reaction efficiency (kapp = 0.00812 min−1) via ·OH. The reusability of the photocatalysts was also evaluated, showing a decline in performance for Fenton-like reactions at acidic pH about 22.76% after five cycles, while for photocatalysis at neutral pH decline about 11.44% after five cycles. This research provides valuable insights into the catalytic mechanisms and supports the potential of eco-friendly Cu2O nanoparticles for sustainable wastewater treatment applications.

Superoxide Ion-Assisted Radical Cascade Reaction: Synthesis of 3-nitro-4-aryl-2H-chromen-2-ones from Aryl Alkynoate Esters under Methylene Blue Visible Light Photocatalysis

Background: From an industries and academic perspective, there is a need for a method for producing 3-nitro-4-aryl-2H-chromen-2-ones from aryl alkynoate esters that is both economic and environmental benign. In this context, superoxide ion-assisted radical cascade reaction can be an efficient and greener protocol. Objective: Herein, we have demonstrated an unprecedented methylene blue (MB) visible light photocatalysis for the production of a series of 3-nitro-4-aryl-2H-chromen-2-ones from readily available aryl alkynoate esters and a nitrating agent in solution. Methods: Synthesis of 3-nitro-4-aryl-2H-chromen-2-ones has been performed in the presence of aryl alkynoate ester, TBAN, DIPEA, solvent, catalyst and molecular oxygen under visible light irradiation at room temperature. The products were purified by column chromatography using silica gel, and the mixture of ethyl acetate/petroleum ether as an eluting solvent and characterized by IR, NMR and mass spectroscopic analysis. Results: A series of aryl alkynoate esters were successfully nitrated into corresponding 3-nitro-4- aryl-2H-chromen-2-ones with good isolated yields by this protocol, in which the key NO2-radicals formed by the action of superoxide ion (O2−·). Conclusion: In contrast to the literature-reported methods of synthesis of 3-nitro-4-aryl-2Hchromen- 2-ones, the process described here for making 3-nitro-4-aryl-2H-chromen-2-ones uses methylene blue visible light photocatalysis, is inexpensive, mild, does not require a metal precursor or high temperatures, and is successful when using the direct sunlight.

Facile construction of a bifunctional Eu-MOF for selective fluorescence sensing and visible light photocatalysis of tetracycline

Contamination detection and removal are important steps in environmental monitoring and cleanup. In this study, europium metal-organic framework structures (Eu-MOF) were designed and prepared that can act as fluorescent probes and photocatalysts for the detection and removal of tetracycline (TC) antibiotics. Eu-MOF was generated by a one-step solvothermal method using europium ion as the metal ion and terephthalic acid as the organic ligand source. The red fluorescence of Eu-MOF is selectively enhanced by TC due to the antenna effect. Eu-MOF, which has a linear range of 0.5–60 μM, can be utilized as a fluorescent probe for tetracycline detection based on this phenomena. In particular, Eu-MOF was found to be able to effectively photocatalyze the degradation of TC, with tetracycline removal rates of about 70 % and 55 % after 180 min of irradiation under ultraviolet light (UV) light and simulated visible light, respectively. The photocatalytic ability of Eu-MOF originated from the generation of hydroxyl radicals (•OH), superoxide radicals (•O2−) and electron holes (h+) under light irradiation. This study innovatively proposed a bifunctional Eu-MOF for TC fluorescence detection and photocatalytic degradation, which provides a novel method for the quick and easy identification and elimination of pharmaceutical contaminants. It can also provide some reference value for the construction of ratiometric fluorescent probes and heterojunction photocatalysts and their application in the treatment of water pollution.

Dye-sensitization on rosette-shaped BiOBr/Biochar photocatalyst for simultaneous removal of emerging pollutants and dyes

This study presents the fabrication of rosette-shaped bismuth oxybromide/biochar (BiOBr/BC) photocatalysts supported on biochar via a straightforward solvothermal approach. This BiOBr/BC photocatalyst demonstrates remarkable efficiency in degrading 17α-ethinylestradiol (EE2). The incorporation of the photosensitizer Rhodamine B (RhB) significantly enhances the degradation rate of EE2, while RhB itself undergoes degradation during visible-light photocatalysis. Biochar serves as a substrate, offering several advantages such as improved adsorption, facilitated electron transfer, and increased production of free radicals, all contributing to the enhanced degradation of EE2 by BiOBr/BC. Under 20 min of visible light irradiation, the degradation rate of EE2 by the RhB-sensitized BiOBr/BC system reaches 99.28%. Furthermore, the incorporation of RhB improves the stability and recyclability of the BiOBr/BC system, maintaining an EE2 degradation rate of 92.00% after seven consecutive degradation cycles. Our photocatalytic system exhibits strong degradation activity towards a mixed-pollutant solution of EE2 and various dyes. LC-MS analysis identified the degradation products and computational predictions indicated their lower ecotoxicity compared to the parent compound. Overall, this study provides new insights and possibilities for the treatment of environmental pollutants, leveraging the concept of “curing waste with waste”.

Photocatalytic Perfluoroalkylation of Disulfides and Diselenides. Syntheses of Perfluoroalkyl Thio- and Seleno-ethers.

The synthesis of alkyl(aryl)-fluoroalkyl sulfanyl [R(Ar)-S-RF] and aryl-fluoroalkyl selenolyl (Ar-Se-RF) ethers through visible-light photocatalysis has been successfully carried out. This process involves disulfides, and diselenides [R(Ar)-X-X-R(Ar), where X = S or Se], and fluoroalkyl iodides (RF-I) in the presence of a base as an additive under photocatalysis. The photocatalyst Eosin Y and green light-emitting diodes are utilized for irradiation of R(Ar)-S-RF and Ar-Se-RF syntheses. Our method integrates low-energy visible-light photocatalysis, commercially available perfluoroalkylating reagents (RF-I), and easily obtainable disulfides and diselenides as starting materials. Mechanistic studies and a detailed synthetic procedure for (Ar)-S-RF on a large scale are presented.

Visible light-induced chemoselective 1,2-diheteroarylation of alkenes

Visible-light photocatalysis has evolved as a powerful technique to enable controllable radical reactions. Exploring unique photocatalytic mode for obtaining new chemoselectivity and product diversity is of great significance. Herein, we present a photo-induced chemoselective 1,2-diheteroarylation of unactivated alkenes utilizing halopyridines and quinolines. The ring-fused azaarenes serve as not only substrate, but also potential precursors for halogen-atom abstraction for pyridyl radical generation in this photocatalysis. As a complement to metal catalysis, this photo-induced radical process with mild and redox neutral conditions assembles two different heteroaryl groups into alkenes regioselectively and contribute to broad substrates scope. The obtained products containing aza-arene units permit various further diversifications, demonstrating the synthetic utility of this protocol. We anticipate that this protocol will trigger the further advancement of photo-induced alkyl/aryl halides activation.