Search

Synthetic dyes are widely used in various industries, which inevitably leads to increased water pollution. One of the recognized and waste-free techniques for water treatment is photocatalytic purification using semiconductor nanoparticles. However, the debate on how photocatalytic properties can be tuned through structural and morphological parameters using nanoparticle synthesis procedures remains open. In the present work, an approach to regulate UV-light-driven photocatalytic activity of spherical SnO2 nanoparticles using different structural parameters is demonstrated for the first time. Complex characterization of nanoparticles was provided using physicochemical methods with the help of computational methods. Special attention was paid to the development of a protocol of oxygen vacancy accounting within computer calculations for more realistic modeling of the interaction energy between nanoparticle surfaces and organic dye molecules of different natures. The photocatalysis mechanism was investigated according to the developed protocol, including the study of dye mixture kinetic degradation, dye-photocatalyst complex formation, and the ratio of oxygen vacancies and defects. It was shown that 93% of single dye decomposed in 7 min, and degradation of the dye mixture in a real water sample from Neva River achieved 60% after 40 min. It was possible to establish that this proof-of-concept study based on the combination of experimental and computational approaches can help develop the strategy of the rational design of photocatalysts promising for purification of real water samples. [ABSTRACT FROM AUTHOR]

The design of efficient photocatalysts for dye degradation is a challenging task for the scientific community. Semiconductor-based photocatalysts such as g-C3N4 and oxides, utilizing solar energy, have been proven to be effective and promising approaches to resolve this issue to some extent. Constructing Z-scheme heterostructures by coupling g-C3N4 with suitable oxide semiconductors has shown substantial enhancement of the photocatalytic performance. In this article, perovskite-type CeMnO3 (5, 15, 25%) nanoparticle-decorated g-C3N4 nanosheets are fabricated as heterostructures, using a hydrothermal synthesis process, for efficient photocatalysis of organic dyes. The formations of heterostructures are confirmed through structural, microstructural, and elemental state analysis. Brunauer–Emmett–Teller (BET) and Barrett–Joyner–Halenda (BJH) characterization techniques exhibited enhanced surface area and pore sizes, respectively. Ultraviolet–visible (UV–vis) diffuse reflectance spectroscopy (DRS), Mott–Schottky, and linear sweep voltammetry (LSV) analyses along with density functional theory (DFT) calculations predicted a p–n junction heterostructure. Electron paramagnetic resonance (EPR) studies revealed a broad spectrum with sextet hyperfine lines corresponding to Mn4+ and Mn2+ ions and enhanced intensity as compared to the parent ones, signifying the creation of oxygen vacancies in the heterostructure. The CeMnO3 (25 wt %)/g-C3N4 heterostructure showed highly efficient photocatalytic degradation of methylene blue under direct sunlight irradiation, with up to 99% degradation achieved in 120 min and excellent recyclability. The robustness of this photocatalyst was tested by adopting a similar process for methylene orange dye degradation, exhibiting 94% yield in 120 min. A tentative degradation mechanism is proposed based on the enhanced photodegradation efficiency and results obtained from electrochemical impedance (EIS), photoluminescence (PL), LSV, and first principal studies, which provides more insights into the photogenerated charge separation, enhanced photocurrent, and interfacial transfer efficiency through the Z-scheme charge transfer process. This study offers opportunities for designing high-performance Z-scheme hybrid photocatalysts for environmental remediation. [ABSTRACT FROM AUTHOR]

The same carbon-based nanomaterials have shown their potential photocatalytic applications toward environmental and energy-related problems based on their excellent light absorption abilities. Herein, we summarized the findings associated with visible light and sunlight-induced photocatalysis, specifically using carbon dots (CD), doped-CD, and their nanocomposite as an advanced photocatalytic material. Doped-CD and CD-based composite have improved light absorption abilities compared to bare CD, which is the essential parameter for photocatalysis applications. Various parameters, such as fabrication methodologies, efficiency, and stability, have also been discussed. The possible mechanistic insights involving the photocatalysis method applied in multiple chemical reactions have been discussed in detail, including degradation of organic dye, reduction of higher toxic oxidation states of metal ions, CO2 conversion, water splitting, organic transformation reaction, and NOx removal, etc. [ABSTRACT FROM AUTHOR]

Facet-engineered anatase TiO2 with NiO nanoparticles heterocontacts were successfully prepared by selective photodeposition of NiO nanoparticles onto the {101} facet of the top-truncated bipyramidal TiO2 anatase nanocrystals coexposed with {001} and {101} facets. The morphology and electronic properties of the resulting 0.1-10 wt % NiO-decorated TiO2 were investigated by X-ray diffraction, high-resolution electron microscopy, N2 sorption analysis, and UV-vis spectroscopy. Furthermore, a careful determination of the energy band alignment diagram was conducted by a model experiment using XPS and UPS to verify charge separation at the interface of the NiO-TiO2 heterostructure. The model experiment was performed by stepwise deposition of NiO onto oriented TiO2 substrates and in-situ photoelectron spectroscopy measurements without breaking vacuum. Core levels showed shifts of 0.58 eV toward lower binding energies, meaning an upward band bending in TiO2 at the NiO-TiO2 interface. Furthermore, 0.1 wt % NiO-TiO2 exhibited 50% higher activities than the pure TiO2 for methylene blue (MB) photodecomposition under UV irradiation. This enhanced photocatalytic activity of NiO- TiO2 nanocomposites was related to the internal electric field developed at the p-n NiO-TiO2 heterojunction, leading to vectorial charge separation. Finally, mechanistic studies conducted in the presence of carrier or radical scavengers revealed that holes dominantly contributed to the photocatalytic reactions in the case of NiO- TiO2 photocatalysts while electrons played the main role in photocatalysis for the pure TiO2 materials. [ABSTRACT FROM AUTHOR]

Treatment of N,N-bis(diphenylphosphanylmethyl)-3-aminopyridine (3-bdppmapy) with AgX (X = Br, I, CN, SCN, dicyanamide (dca)) under different reaction conditions afforded seven mononuclear, dinuclear, and polymeric coordination complexes including [Ag4I4(3-bdppmapy)2] n (1), [Ag2I2(3-bdppmapy)3]·CH3OH (2·CH3OH), [Ag2Br(3-bdppmapy)3]Br·4CH3OH (3·4CH3OH), [Ag4(CN)4(3-bdppmapy)3]·2CH3OH (4·2CH3OH), [Ag(3-bdppmapy)2]SCN (5), [Ag(3-bdppmapy)2](dca) (6), and {[Ag4(dca)4(3-bdppmapy)2]·4DMF} n (7). Compound 1 contains a unique two-dimensional (2D) network in which chairlike [Ag4I4] units are interconnected by μ3-3-bdppmapy bridges. Compounds 2 and 4 hold a similar centrosymmetric framework in which two [(3-bdppmapy)AgI] (2) or [(3-bdppmapy)Ag2(CN)2] (4) units are linked by a μ-3-bdppmapy. Compound 3 has a batlike cationic structure in which two Ag/3-bdppmapy units are joined by a pair of μ-Br and μ-3-bdppmapy bridges. Compounds 5 and 6 have a similar cationic mononuclear structure in which the Ag(I) center is chelated by two 3-bdppmapy ligands. Compound 7 possesses a 2D layer structure in which each one-dimensional (1D) chain [Ag4(dca)4(3-bdppmapy)2]n is connected to its equivalent ones by μ3-dca bridges. Compound 1 as a representative example exhibited excellent catalytic activity toward the photodecomposition of a spectrum of 11 organic dyes in water under UV light irradiation and can be reused five times without noticeable decay of its catalytic efficiency. [ABSTRACT FROM AUTHOR]

Hyper-cross-linked polynaphthalene nanoparticles (PNNs) capable of catalyzing the degradation of organic pollutants upon exposure to visible light have been developed. The nascent and metal-free PNNs with a porous structure, high specific surface area, and narrow bandgap are chemically and thermally stable in the catalytic system, which make it promising as a kind of excellent photocatalytic material compared to conventional photocatalysts. The photocatalytic activity of the as-obtained PNNs exhibits remarkable photocatalytic performance for the degradation of rhodamine B (RhB) and methyl blue (MB) under the irradiation of visible light. The easy preparation, high catalytic activity, and recyclability of the PNNs open new opportunities in the visible-light-promoted degradation of organic pollutants. [ABSTRACT FROM AUTHOR]

Conspectus: The majority of organic reactions are commonly carried out inside a lab, under a fume hood. A particular case is that of photochemical reactions, a field where the pioneering experiments by Giacomo Ciamician demonstrated more than one century ago that different processes can be carried out outdoors, for example, on the balcony of his own department, upon exposure of the reacting mixtures to sunlight. The main problem related to this chemistry of the "window ledge" is that most organic compounds are colorless and their absorption in the solar light region is in most cases negligible. Recently, the impressive development in the use of visible light absorbing photocatalysts (e.g., RuII or IrIII complexes, as well as organic dyes) made light-induced processes convenient even for non-photochemistry practitioners. It is thus possible to easily perform the reactions by simply placing the reaction vessel in a sunny place outside the lab. However, most of these processes are based on single electron transfer (SET) reactions (photoredox catalysis). Other photocatalysts able to activate substrates via alternative paths, such as hydrogen atom transfer (HAT), are emerging. In the last years, we were deeply involved in the use of the decatungstate anion ([W10O32]4-, a polyoxometalate) in synthesis. Indeed, such a versatile species is able to promote the photocatalytic C-H activation of organic compounds via either SET or HAT reactions. Interestingly, though the absorption spectrum of [W10O32]4- does not extend into the visible region, it shows an overlap with solar light emission. In this Account, we provide an overview on the application of decatungstate salts as photocatalysts in window ledge chemistry. We initially discuss the nature of the photogenerated species involved in the mechanism of action of the anion, also supported by theoretical simulations. The first-formed excited state of the decatungstate anion decays rapidly to the active species, a dark state tagged wO, featuring the presence of electron-deficient oxygen centers. Next, we describe the main applications of decatungstate chemistry. A significant part of this Account is devoted to photocatalyzed synthesis (C-X bond formation, with X = C, N, O, and oxidations) carried out by adopting sunlight (or simulated solar light). This synthetic approach is versatile, and most of the reactions involved C-H activation in cycloalkanes, alkylaromatics, amides, ethers (1,4-dioxane, oxetane, benzodioxole, and THF), aldehydes, nitriles, and cyclopentanones, and the ensuing addition of the resulting radicals onto electron-deficient olefins. Finally, the increasing role of the decatungstate anion in water depollution and polymerization is briefly discussed. [ABSTRACT FROM AUTHOR]

We have demonstrated a template-free large-scale synthesis of nanostructured CdxZn1-xS by a simple and a low-temperature solid-state method. Cadmium oxide, zinc oxide, and thiourea in various concentration ratios are homogenized at moderate temperature to obtain nanostructured CdxZn1-xS. We have also demonstrated that phase purity of the sample can be controlled with a simple adjustment of the amount of Zn content and nanocrystalline CdxZn1-xS (x = 0.5 and 0.9) of the hexagonal phase with 6-8 nm sized and 4-5 nm sized Cd0.1Zn0.9S of cubic phase can be easily obtained using this simple approach. UV-vis and PL spectrum indicate that the optical properties of as synthesized nanostructures can also be modulated by tuning their compositions. Considering the band gap of the nanostructured CdxZn1-xS well within the visible region, the photocatalytic activity for H2 generation using H2S and methylene blue dye degradation is performed under visible-light irradiation. The maximum H2 evolution of 8320 μmol h-1g-1 is obtained using nanostructured Cd0.1Zn0.9S, which is four times higher than that of bulk CdS (2020 μmol h-1 g-1) and the reported nanostructured CdS (5890 μmol h-1g-1). As synthesized Cd0.9Zn0.1S shows 2-fold enhancement in degradation of methylene blue as compared to the bulk CdS. It is noteworthy that the synthesis method adapted provides an easy, inexpensive, and pollution-free way to synthesize very tiny nanoparticles of CdxZn1-xS with a tunnable band structure on a large scale, which is quite difficult to obtain by other methods. More significantly, environmental benign enhanced H2 production from hazardous H2S using CdxZn1-xS is demonstrated for the first time. [ABSTRACT FROM AUTHOR]

New phenothiazine based organic dyes were prepared for visible-light-driven organic transformations. The 3,7-disubstituted phenothiazine derivatives showed visible light absorption and reversible one-electron oxidation behavior. In the presence of 0.5 mol % of 3,7-disubstituted phenothiazines, primary benzylamines showed oxidative coupling under visible light irradiation from a blue LED. The electronic effect of substituents in phenothiazine dyes was observed in catalytic activities. The mechanistic pathway of oxidative coupling was discussed based on the detection of H2O2after the reaction. [ABSTRACT FROM AUTHOR]

Nanoporous SnO2--ZnO heterojunction nanocatalyst was prepared by a straightforward two-step procedure involving, first, die synthesis of nanosized SnO2 particles by homogeneous precipitation combined with a hydrothermal treatment and, second, the reaction of the as-prepared SnO2 particles with zinc acetate followed by calcination at 500 °C. The resulting nanocatalysts were characterized by X-ray diffraction (XRD), FTIR, Raman, X-ray photoelectron spectroscopy (XPS), nitrogen adsorption--desorption analyses, transmission electron microscopy (TEM), and UV--vis diffuse reflectance Timeinun) spectroscopy. The SnO2--ZnO photocatalyst was made of a mesoporous network of aggregated wurtzite ZnO and cassiterite SnO2 nanocrystallites, the size of which was estimated to be 27 and 4.5 nm, respectively, after calcination. According to UV--visible diffuse reflectance spectroscopy, the evident energy band gap value of the SnO2--ZnO photocatalyst was estimated to be 3.23 eV to be compared with those of pure SnO2 that is, 3.7 eV, and ZnO, that is, 3.2 eV, analogues. The energy band diagram of the SnO2--ZnO heterostructure was directly determined by combining XPS and the energy band gap values. The valence band and conduction band offsets were calculated to be 0.70 ± 0.05 eV and 0.20 ± 0.05 eV, respectively, which revealed a type-II band alignment. Moreover, the heterostructure SnO2--ZnO photocatalyst showed much higher photocatalytic activities for die degradation of methylene blue dian those of individual SnO2 and ZnO nanomaterials. This behavior was rationalized in terms of better charge separation and the suppression of charge recombination in the SnO2--ZnO photocatalyst because of the energy difference between the conduction band edges of SnO2 and ZnO as evidenced by the band alignment determination. Finally, this mesoporous SnO2--ZnO heterojunction nanocatalyst was stable and could be easily recycled several times opening new avenues for potential industrial applications. [ABSTRACT FROM AUTHOR]

Organic dye degradation was achieved via direct oxidation by bismuth silver oxide coupled with visible light photocatalysis by sodium bismuthate. Crystal violet dye decomposition by each reagent proceeded via two distinct pathways, each involving different active oxygen species. A comparison of each treatment method alone and in combination demonstrated that using the combined methods in sequence achieved a higher degree of degradation, and especially mineralization, than that obtained using either method alone. In the combined process direct oxidation acts as a pretreatment to rapidly bleach the dye solution which substantially facilitates subsequent visible light photocatalytic processes. The integrated sequential direct oxidation and visible light photocatalysis are complementary manifesting α > 100% increase in TOC removal, compared to either isolated method. The combined process is proposed as a novel and effective technology based on one primary material, sodium bismuthate, for treating wastewaters contaminated by high concentrations of organic dyes. [ABSTRACT FROM AUTHOR]

Elucidation of photoinduced charge transfer behavior in organic dye/metal hybrids is important for developing photocatalytic systems for solar energy conversion. We report the synthesis and photophysical characterization of a perylene-3,4:9,10-bis(dicarboximide) (PDI)–ruthenium(II) complex, bis-PDI-2,2′-bipyridineRu(II)Cl2(CNtbutyl)2, which has favorable energetics, ΔGCS≈ −1.0 eV, for singlet electron transfer from the Ru complex to PDI. Time-resolved optical spectroscopy reveals that upon selective photoexcitation of PDI, ultrafast charge transfer (<150 fs) from the Ru complex to 1*PDI generates the Ru(III)–PDI–•ion pair. The resulting vibrationally hot Ru(III)–PDI–•ion pair exhibits fast relaxation (τ = 3.9 ps) and charge recombination (τCR= 63 ps). Our experimental and computational (DFT and TDDFT) studies show that energy-preserving photodriven singlet electron transfer can dominate in properly designed organic dye/metal complexes, making them of particular interest for use in artificial photosynthetic systems for solar fuels formation. [ABSTRACT FROM AUTHOR]

Two isomeric two-dimensional copper(I) coordination polymer materials based on an in situ generated 5-(3-pyridyl) te trazole ligand show similar layer structures but distinct photoluminescent and photo-catalytic properties, which present an interesting com-parative study on the structure--property correlation between isomeric materials. [ABSTRACT FROM AUTHOR]

The article presents a study which describes the new homogeneous system for the photocatalytic production of H2 from aqueous protons using high absorbing organic dyes and a cobalt molecular catalyst. It states that a homogeneous photocatalytic hydrogen evolving system has been constructed form earth abundant and inexpensive components. The effect of pH on the initial rate of photocatalytic H2 production from a system composed of 1,5, and TEOA and MeCN/H2O 1:1.