Light Irradiation In Aqueous Solution Research Articles

Fabrication of Sn(IV)porphyrin-Imbedded Silica Aerogel Composite

Optoelectronic functional composite materials with porous structures are of great importance in various fields. A hybrid composite (SnP@SiA) composed of (trans-dihydroxo)(5,10,15,20-tetraphenylporphyrinato)tin(IV) (SnP) in silica aerogel (SiA) was successfully fabricated through the reaction of SnP with silanol groups of SiA in the presence of hexamethyldisilazane (HMDS). SnP@SiA was then characterized using various instrumental techniques. The zeta potential for SnP@SiA (−11.62 mV) was found to be less negative than that for SiA (−18.26 mV), indicating that the surface of SnP@SiA is covered by hydrophobic species such as SnP and trimethylsilyl groups. The Brunauer–Emmett–Teller (BET) surface area, pore volume, and average pore size of SnP@SiA are 697.07 m2/g, 1.69 cm3/g, and 8.45 nm, respectively, making it a suitable composite for catalytic applications. SnP@SiA, a photocatalyst with high porosity and a large surface area, yields promising performance in the photodegradation of acid orange 7 (AO7) under visible light irradiation in aqueous solution. This hybrid composite exhibited the desirable properties of aerogels along with the photoelectronic features of porphyrins. Therefore, this porphyrin-imbedded mesoporous material has valuable potential in various applications such as photocatalysis, light energy conversion, biochemical sensors, and gas storage.

Ionic liquids with reversible photo-induced conductivity regulation in aqueous solution

Stimulus-responsive ionic liquids have gained significant attention for their applications in various areas. Herein, three kinds of azobenzimidazole ionic liquids with reversible photo-induced conductivity regulation were designed and synthesized. The change of electrical conductivity under UV/visible light irradiation in aqueous solution was studied, and the effect of chemical structure and concentration of ionic liquids containing azobenzene to the regulation of photoresponse conductivity were discussed. The results showed that exposing the ionic liquid aqueous solution to ultraviolet light significantly increased its conductivity. Ionic liquids with longer alkyl chains exhibited an even greater increase in conductivity, up to 75.5%. Then under the irradiation of visible light, the electrical conductivity of the solution returned to its initial value. Further exploration of the mechanism of the reversible photo-induced conductivity regulation of azobenzene ionic liquids aqueous solution indicated that this may attributed to the formation/dissociation of ionic liquids aggregates in aqueous solution induced by the isomerization of azobenzene under UV/visible light irradiation and resulted the reversible conductivity regulation. This work provides a way for the molecular designing and performance regulation of photo-responsive ionic liquid and were expected to be applied in devices with photoconductive switching and micro photocontrol properties.

Photocatalytic Activity of CoO/ZnO Nanocrystalline for Dye Wastewater Treatment under UV Light

CoO nanocrystal is well-known photocatalyst for overall water splitting. However it suffers from a very short lifetime of only 1 h. The poor stability is derived from carrier recombination-induced thermal oxidation. This research will provide information about synthesis of CoO/ZnO nanocrystalline that can potentially enhance photocatalysts. CoO has been synthesized first under hydrothermal method, followed by calcination process. Thereafter, CoO has been used to produce CoO/ZnO under precipitation method. The samples were characterized using XRD (X-Ray Diffraction), FTIR (Fourier Transform Infrared Spectroscopy), and UV-VIS (UV–Visible Spectroscopy) to analyze their composition, chemical functional group, optical absorption, and band gap. The XRD spectrum showed that CoO/ZnO had cubic spinel and hexagonal phase structure with crystallite size of 69.0, 46.4, 32.8, and 32,4 nm. The bands in obtained FTIR spectrum at 586.36, 671.23, and 410-429 cm−1 were correlated with vibrations of the Co3+ in octahedral hole, the Co2+ in tetrahedral hole, and Zn-O, respectively. The band gap energy of CoO, CoO/ZnO with variation of 1:1 and 1:3 were 4.39, 4.14, and 3.65 eV, respectively. The photocatalytic activities of CoO/ZnO were confirmed by methylene blue dyes photodegradation of 663 nm under UV light irradiation in aqueous solution. The 22.4% methylene blue can be removed within 3 h. Overall, these findings reveal the potential of CoO/ZnO for practical application.

Enhanced activation of peroxymonosulfate by a floating Cu0-MoS2/C3N4 photocatalyst under visible-light assistance for tetracyclines degradation and Escherichia coli inactivation

Transition metal-based photocatalysts have recently attracted much attention in photo-induced Peroxymonosulfate (PMS) activation systems. Herein, a novel floating catalyst Cu0-MoS2/C3N4-expanded graphite (Cu-MSCN-EG) was prepared by a chemical reduction method and applied as a PMS activator to remove tetracyclines (TCs) and inactivate Escherichia coli under visible light irradiation in aqueous solution. Over 99.0 % of TCs and Escherichia coli could be removed and inactivated within 1 h in Vis/PMS/Cu-MSCN-EG system. Compared to the MoS2/C3N4-EG system, the loading of zero-valent copper in the Vis/PMS/Cu-MSCN-EG system increased the reaction rate by 278 %. Raman spectroscopy and density functional theory (DFT) calculations indicated that ·OH and 1O2 were generated via two different adsorption patterns between PMS and copper (≡Cu+-OSO3-–OH and ≡Cu+–OH-OSO3-). With the light assistance, the photo-induced electrons reduced the copper leaching and enhanced the generation of ·SO4- and ·O2–, leading to a high recyclability and mineralization rate. Overall, this study provides a new insight into the fabrication of copper-based PMS activator with high efficiency and durability for contaminants degradation and pathogen inactivation.

Design of TiO2/Ag3BiO3 n-n heterojunction for enhanced degradation of tetracycline hydrochloride under visible-light irradiation

Pharmaceutical residual contaminants in aquatic ecosystems have caused severe risks to human health. Affordable, eco-friendly and effective photocatalysts to deal with these pollutants has become a hot topic in the scientific community. In this research, Ag3BiO3 nanoparticles were embedded on TiO2 to form n-n heterojunction through a facile hydrothermal method. According to scanning electron microscopy (SEM), fourier transform infrared spectroscopy (FT-IR), brunauer emmett teller (BET), electrochemical impedance spectroscopy (EIS), X-ray photoelectron spectroscopy (XPS), energy-dispersive X-ray spectroscopy (EDS), photoluminescence (PL), X-ray diffraction (XRD), transmission electron microscopy (TEM), and UV–vis diffuse reflectance spectroscopy (UV–vis DRS) tests, the successful construction of TiO2/Ag3BiO3 heterojunction is proved. TiO2/Ag3BiO3 heterojunctions were employed as photocatalysts to remove tetracycline hydrochloride (TCH) under visible light irradiation in aqueous solution. Optimum TCH photodegradation efficiency was observed for TiO2/Ag3BiO3 (10%), 15.4 times superior to that of TiO2. The enhanced TCH photodegradation efficiency of TiO2/Ag3BiO3 results from improved light absorption capacity and the reduction of recombination of photogenerated charge carriers via generation of n-n heterojunctions. The mechanism of increasing the photodegradation efficiency of TCH was determined by employing reactive species quenching experiments. TiO2/Ag3BiO3 (10%) also exhibited an acceptable stability.

Kinetics, mechanism studies and antibacterial activity of pharmaceutical Sulfaguanidine under light irradiation in aqueous solution

The presence of pharmaceutical compounds in the environment worries several researchers for several years since their existence in aquatic systems leads to major environmental problems. These compounds are a unique category of pollutants and considered emerging contaminants in water supply systems. They have been found in groundwater and even in drinking water at concentrations ranging from ng to µg/L.In the present work, we investigated the photochemical behavior of a sulfonamide antibiotic, namely sulfaguanidine (SGD) in aqueous solutions as a function of pH and we examined the inhibitory activity of photoproducts SDG against E coli BLSE and S. aureus using the disc diffusion method, determination of minimum inhibitory concentration and cell viability percentage. Quantum yields were measured at 254 and 302 nm during irradiation in absence and presence of oxygen). In aerated conditions, they were evaluated to 2.3 x 10−2 and 2.5 x 10−3 respectively. However, the degradation process is not completely inhibited in the presence of oxygen due to sulfaguanidine photoreactivity, which is in agreement with the involvement of the singlet as well as the triplet excited states.Several photoproducts were elucidated using liquid chromatography coupled with positive mode mass spectroscopy LC/MS/ESI +. For bacterial activity, these photoproducts shows more toxic that the Sulfaguanidine and exhibited a higher inhibitory activity against E coli and S. aureus cells.

Phytogenic fabrication of ZnO and gold decorated ZnO nanoparticles for photocatalytic degradation of Rhodamine B

Pure Zinc Oxide (ZnO) nanoparticles (NPs) and gold (Au) decorated (Au-ZnO) hetero-nanostructures were synthesized using green-synthesis method employing pecan nuts (Carya illinoinensis) leaves extract as reducing agent. The structural and optical properties studied by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Scanning electron microscopy (SEM), Energy-dispersive X-ray spectroscopy (EDX), High-resolution transmission electron microscopy (HRTEM) and UV–vis spectrophotometer (UV–vis). Structural modification with the introduction of Au in ZnO have been confirmed by the XRD and TEM results. UV data confirmed the decrease in Au-ZnO energy band-gap Eg value, which validates the formation of hetero-structure. The modulation of energy band-gap causes visible light absorption and hence enhances the photodegradation activity of Au-ZnO. Photocatalytic activity was carried-out by degradation of RhB dye under UV light irradiation in aqueous solution. The maximum degradation of 95 % was obtained during the time of 180 min for the basic pH of the dye. The Enhanced degradation in Au-ZnO as compared with bare ZnO NPs, was attributed to Au, which controls the amount of electron and suppress electron-hole ratio at ZnO surface. In the recycling study of the Au-ZnO Photocatalyst, the hetero-structure showed good stability up to five cycles.

An Efficient and Stable MoS2 /Zn0.5 Cd0.5 S Nanocatalyst for Photocatalytic Hydrogen Evolution.

Photocatalytic hydrogen evolution by water splitting is highly important for the application of hydrogen energy and the replacement of fossil fuel by solar energy, which needs the development of efficient catalysts with long-term catalytic stability under light irradiation in aqueous solution. Herein, Zn0.5 Cd0.5 S solid solution was synthesized by a metal-organic framework-templated strategy and then loaded with MoS2 by a hydrothermal method to fabricate a MoS2 /Zn0.5 Cd0.5 S heterojunction for photocatalytic hydrogen evolution. The composition of MoS2 /Zn0.5 Cd0.5 S was fine-tuned to obtain the optimized 5 wt % MoS2 /Zn0.5 Cd0.5 S heterojunction, which showed a superior hydrogen evolution rate of 23.80 mmol h-1 g-1 and steady photocatalytic stability over 25 h. The photocatalytic performance is due to the appropriate composition and the formation of an intimate interface between MoS2 and Zn0.5 Cd0.5 S, which endows the photocatalyst with high light-harvesting ability and effective separation of photogenerated carriers.

Biosynthesis of zinc oxide nanoparticles by one-pot green synthesis using fruit extract of Amomum longiligulare and its activity as a photocatalyst

This paper presents a green biosynthetic approach of zinc oxide nanoparticles using co-precipitation method with dried fruit extract of Amomum longiligulare (A. longiligulare), as it is plant-derived reducing agent. For configuration of Al-ZnO NPs, the absorption of wavelength of nanoparticles was observed by UV–vis spectra at 354 nm. XRD (X-ray diffraction) micrograph and FE-TEM (Field-Emission Transmission Electron Microscopy) determined the morphological structure of green synthesized Al-ZnO. The chemical functional group, elemental mapping, and crystallization of nanoparticles were characterized by FTIR (Fourier Transform Infrared Spectroscopy), and EDX (Energy dispersive X-ray spectroscopy). The photocatalytic activity of Al-ZnO NPs was confirmed by photodegradation of methylene blue and malachite green dyes under 356 nm of UV light irradiation in aqueous solution. The degradation of MB with Al-ZnO NPs was completed with approximately 66 % in 60 min, whereas MG degradation was measured around 38.1 % by 60 min by Al-ZnO NPs respectively. The kinetic reaction rate as stated by first-order reaction of photocatalytic degradation of MB and MG with Al-ZnO NPs were found to be 0.014 min−1 and 0.008 min−1 respectively. Therefore, phytochemicals of A. longiligulare extract have capability to act as a reducing agent in biosynthesis of zinc nanoparticles and is suitable to produce cost-efficient and eco-friendly photocatalyst.

Preparation of fluorescent polystyrene nanoparticles mediated by a multi-functional amphiphilic iridium complex under visible light irradiation in aqueous solution

Amphiphilc iridium(iii) complex has been synthesized and served as both a photoinitiator and a surfactant for the preparation of nanoparticles with high fluorescence intensity and uniform morphology by visible light irradiation of styrene in aqueous.

Visible Light Induced Photodegradation of Methylene Blue in Sodium Doped Bismuth Barium Ferrite Nanoparticle Synthesized by Sol-gel Method

Perovskite-like BiFeO3 nanoparticles doped with barium and sodium ions were synthesized via the citric acid route by the sol-gel method. The as-prepared Bi0.65Na0.2Ba0.15FeO3 nanopowders were divided into three equal portions and separately annealed at various annealing temperatures of 600, 700 and 800°C. The powders were characterized using X-ray diffraction (XRD) and crystallized with a rhombohedral R3c space group. Scanning electron microscopy was used to determine the morphology of the crystal and Fourier transform infrared spectroscopy was conducted at room temperature to determine the phase purity and the B-site formation in the perovskite structure. The UV-vis diffuse reflectance spectroscopy of all the materials was investigated, showing strong photoabsorption (λ > 420 nm). The doping effect of BiFeO3 enhanced photocatalytic activity while it significantly reduced the energy bandgap to 2.05 eV (for BNBFO at 800°C) which showed strong visible light absorption. The photocatalytic activity of Bi0.65Na0.2Ba0.15FeO3 nanomaterials was tested by monitoring the degradation rate of methylene blue dye pollutant under visible light irradiation in aqueous solution. All powders showed photoactivity after 2 hours of visible light irradiation. The annealing temperature greatly affected the methylene blue degradation, showing the efficiencies of 57, 67 and 75 % for BNBFO at 600, 700 and 800°C, respectively. Kinetic studies were carried out and the rate constants of 6.70 x 10-3, 8.90 x 10-3 and 1.05 x 10-2 min-1 were obtained for powders annealed at 600, 700 and 800°C, respectively. The photocatalytic mechanism of the degradation process was proposed in this study.

Template free synthesis, characterization and application of nano ZnO rods for the photocatalytic decolourization of methyl orange

Zinc oxide (ZnO) nano rods were synthesized by utrasonication assisted chemical precipitation method without any templates. The influence of pH on the growth of ZnO rods was examined by adjusting the pH of the reaction mixture at values 7, 9 and 13. The as-synthesized rods were characterized by XRD, FT-IR, UV-DRS, SEM and Room Temperature Photoluminescence Spectroscopy. The photocatalytic activity of the synthesized ZnO rods was studied by photocatalytic decolourization of Methyl Orange (MO) dye in presence of UV (365nm) light irradiation in aqueous solution. The effects of operational parameters such as initial concentration of the MO dye, amount of photocatalyst and initial pH of the dye solution were analyzed. The photocatalytic decolourization of MO dye was confirmed from the decrease in intensity of UV–vis absorption peaks at 464nm due to lowering concentration of MO dye. Photocatalytic decolourization of MO dye followed pseudo-first order kinetics.

Low Temperature Hydrothermal Synthesis of Visible-Light-Activated I-Doped TiO2 for Improved Dye Degradation

Iodine doped TiO2 with different iodine/Ti molar ratios has been firstly synthesized with a low temperature hydrothermal route and has been studied systematically in photocatalysis under visible light condition. The resulting iodine doped TiO2 were characterized by X-ray diffraction (XRD), high resolution transmission electron microscopy (TEM), diffuse reflectance spectrum (DRS), and X-ray photoelectron spectroscopy (XPS). The photocatalytic performance investigations were conducted by means of the degradation of Rhodamine B (RhB) under the visible light irradiation in aqueous solution. Under an optimized I/Ti doping ratio of 10 mol%, the photocatalytic performance is greatly better, with degradation efficiency of 95%, which is almost double that of pure TiO2. The superior photocatalytic activity of iodine-doped TiO2 could be mainly attributed to extended visible light absorption originated from the formation of continuous states existed in the band gap of the doped TiO2 introduced by iodine. Active oxygen species, that is, *OH and O2-, were evidenced to be involved in the degradation process and a possible mechanism was also proposed.

Photochemical treatment of organic contaminations in wastewater with ag-containing TiO2/AC composite

Photocatalytic oxidation of organic contaminants under UV light irradiation in aqueous solution was studied using Ag-TiO2/activated carbon (AC) photocatalyst. Rhodamine B (RhB) and Methyl Orange (MO) were selected as the model compounds. The Ag-TiO2/AC composites with a single-phase (anatase) framework was synthesized by a facile sol–gel method using titanium isopropoxide as a TiO2 precursor and depositing metal Ag on the surface of TiO2 nanostructures via a facile chemical reduction process. The asobtained composite was characterized by X-ray diffraction (XRD), N2 adsorption-desorption measurements (BET), UV-vis diffuse reflectance spectroscopy (UV-vis DRS) and photoluminescence spectroscopy (PL). As compared with the pristine TiO2, the Ag-TiO2/AC hybrid material exhibited improved photocatalytic efficiency (90%) for the UV-light photooxidation of RhB and MO. Investigations demonstrated that the enhancement can be attributed to the increase of the adsorption effect of activated carbon and the efficient separation and preventing of the recombination of electron-hole pairs. Moreover, the hydroxyl radical was detected as the main active species generated in the oxidation reaction of RhB or MO over Ag-TiO2/AC composite photocatalyst. A corresponding mechanism was also proposed for the photocatalysis process.

UV photoinduced reduction of water to hydrogen in Na2S, Na2SO3, and Na2S2O4 aqueous solutions

Hydrogen was produced by ultraviolet (UV) light irradiation (>200nm) in an Na2S aqueous solution without photocatalysts. Water (protons) appeared to be directly reduced to hydrogen by excited electrons produced in photon absorption with sulfide ions (S2−). The maximum quantum efficiency for hydrogen formation, 8.9%, was obtained in a 25mmoldm−3 Na2S solution. Marked amounts of hydrogen were produced under UV light irradiation in the aqueous solutions of SO32− and S2O42− ions. S2− ion absorption began at 290nm, SO32− at 275nm, and S2O42− at 400nm. Hydrogen hardly formed at all, however, in SO42−, I−, and SCN− solutions.

Photocatalytic Oxidation of Toluene to Benzaldehyde by Molecular Oxygen

The visible light irradiation of aqueous solutions containing toluene, uranyl(VI) ions, and O2 results in the formation of benzaldehyde as a major product. Small amounts of PhCH2OH are also formed. The yields of benzaldehyde are 3 times greater for toluene-h8 than for toluene-d8, but the kinetic isotope effect for the quenching of the excited state *UO22+ by toluene is negligible (ktoluene-h8/ktoluene-d8 = 1.2). This and other evidence indicate that the quenching takes place in two parallel pathways. The major one involves the aromatic portion of toluene and leads to the recovery of the reactants. The minor, productive path takes place by hydrogen atom abstraction from the methyl group, followed by the oxidation of PhCH2•. Cumene, benzyl alcohol, and benzaldehyde react similarly.

Mechanism of the formation of dihydrogen from the photoinduced reactions of tris(bipyridine)ruthenium(II) with tris(bipyridine)rhodium(III)

Visible light irradiation of aqueous solutions of Ru(bpy)/sub 3//sup 2 +/, Rh(bpy)/sub 3//sup 3 +/, triethanolamine TEOA/TE OAH/sup +/ (pH 8.1), and K/sub 2/PtCl/sub 4/ (or K/sub 2/PtCl/sub 6/) yields dihydrogen with a quantum yield of up to 0.11 +- 0.01 mol einstein/sup -1/ depending on the conditions used. The dihydrogen is the end product of a sequence of electron-transfer reactions. Ru(bpy)/sub 3//sup 2 +/ formed by visible light absorption is oxidized by Rh(bpy)/sub 3//sup 3 +/ to produce Rh(bpy)/sub 3//sup 2 +/ and Ru(bpy)/sub 3//sup 3 +/. The latter is rapidly reduced by TEOA. In the absence of platinum, the rhodium(II) disproportionates to give rhodium(III) and rhodium(I); in the presence of platinum, the rhodium(II) may either disproportionate or yield dihydrogen. Observations on the photochemical and dark reactions in this system are reported. The rhodium system is more expensive than that based on methylviologen and is subject to efficiency-lowering side reactions. 1 figure. (DP)

Hydrogen Generation by Visible Light Irradiation of Aqueous Solutions of Metal Complexes. An approach to the photochemical conversion and storage of solar energy

AbstractWe describe a photochemical system for the generation of hydrogen by water reduction under visible light or sunlight irradiation of aqueous solutions containing the following components: a photosensitizer, the Ru (bipy) complex, for visible light absorption; a relay species, the Rh (bipy) complex, which mediates water reduction by intermediate storage of electrons via a reduced state; an electron donor, triethanolamine (TEOA) which provides the electrons for the reduction process and a redox catalyst, colloïdal platinum, which facilitates hydrogen formation. The conditions for efficient hydrogen production and the influence of the concentration of the components have been investigated; the metal complexes act as catalysts with high turnover numbers; excess bipyridine facilitates the reaction. The process contains two catalytic cycles: a ruthenium cycle and a rhodium cycle. The Ru cycle involves oxidative quenching of the *Ru(bipy) excited state by Rh(bipy) forming Ru(bipy) which is converted back to Ru(bipy) by oxidation of the electron donor TEOA, which is thus consumed. The Rh cycle comprises a complicated set of transformations of the initial Rh(bipy) complex. The reduced rhodium complex formed in the quenching process undergoes a series of transformations involving the Rh(bipy) complex and hydridorhodium‐bipyridine species, from which hydrogen is generated by reaction with the protons of water. In view of the storage of two electrons in the reduced rhodium species, the process is formally a dielectronic water reduction. The properties and eventual participation of [Rh(III)(bipy)2LL′]n+(L,L′ = H2O, OH−) species are investigated. It is concluded that at neutral pH in presence of excess bipyridine, the cycle involving regeneration of the Rh(bipy) complex is predominant. A number of experiments have been performed with modified systems. Hydrogen evolution is observed with other photosensitizers (like proflavin), other relay species (like Rh(dimethylbipy) or Co(II)‐bipyridine complexes), other donor species, or in absence of the platinum catalyst. It also occurs in absence of photosensitizer by sunlight of UV. irradiation of Rh(bipy) or by visible light irradiation of iridium (III)‐bibyridine complexes. These systems deserve further investigations. The present photochemical hydrogen generating system represents the reductive component of a complete water splitting process. Its role in solar energy conversion and in photochemical fuel production is discussed.