Showing papers in "Journal of Photochemistry and Photobiology A-chemistry in 2014"

Preparation and characterization of copper-doped anatase TiO2 nanoparticles with visible light photocatalytic antibacterial activity

Abstract: Anatase titanium dioxide (TiO 2 ) nanoparticles doped with copper (1.0–3.0 mole%) were synthesized by sol–gel method. The UV–visible diffused reflectance measurement revealed that the doping of the Cu 2+ ions in TiO 2 lattice extends its optical absorption in the visible region. XRD and XPS analysis revealed that the substitutions of the few sites of Ti 4+ ions by Cu 2+ ions. TEM analysis revealed the non-spherical nanoparticles size within the range 8–12 nm. The role of hydroxyl radicals during bacterial inactivation was studied by photoluminescence technique. The bactericidal activity of copper doped titanium dioxide nanoparticles was tested against pathogenic bacteria Escherichia coli and Staphylococcus aureus under visible light irradiation. The bacterial survival does not seem to be affected by in contact with nanoparticles in dark.

Photoactive TiO2–montmorillonite composite for degradation of organic dyes in water

Abstract: TiO 2 –montmorillonite composite (TiO 2 –M) was prepared by impregnation with TiCl 4 followed by calcination at 350 °C. The synthesized material was characterized by FTIR, TG–DTA, BET, XRD and SEM–EDX. The results show that TiO 2 was efficiently formed in Na–montmorillonite (Na–M) framework, and only a crystalline, pure anatase phase was produced. Photoactivity tests were carried out under UV-A irradiation using five selected organic dyes. The results indicate that the activity of TiO 2 –M is more important for cationic dyes, where the removal rates are in the order: crystal violet (97.1%) > methylene blue (93.20%) > rhodamine B (79.8%) > methyl orange (36.1%) > Congo red (22.6%). The results of the TiO 2 –M activity were compared with that of the commercial P25. The comparison demonstrates that the synthesized TiO 2 –M exhibits a higher adsorptive behavior and can be used as low-cost alternative to the commercial TiO 2 for wastewater treatment, showing also an extreme easiness to completely recover the composite catalyst at the end of the test.

Solar photocatalysis: A green technology for E. coli contaminated water disinfection. Effect of concentration and different types of suspended catalyst

Abstract: Photocatalytic and photolytic disinfection of Escherichia coli in water was studied under natural sunlight using different types of photocatalyst (TiO 2 P-25, PC500, Ruana and Bi 2 WO 6 ) at different concentrations. The solar photo-inactivation yielded complete inactivation results, which varied with the solar light intensity. Meanwhile, dark control samples in the lab (temperature constant at 25 °C) remained at constant concentration and dark samples outside laboratory showed a decrease due to the mild solar heating occurred during the experiments. The adding of any kind of photo-catalyst to the water accelerated the bactericidal action of solar irradiation and led to complete disinfection (until detection limit). The photocatalytic disinfection efficiency was not enhanced by the increase of catalyst concentration above 0.5 g/L for P-25, PC500 and Bi 2 WO 6 , where about 10 6 CFU/mL were completely inactivated within 5 min, 30 min and more than 150 min of solar exposure under clear sky, respectively. An increase of the concentration to 1 g/L slightly decreased the total inactivation time. Rutile (Ruana) catalyst behaves differently, optimal concentration was lower than for the other titania materials; agglomeration of particles occurred as the concentration of catalyst increases. Durability of photocatalytic treatment and chemicals analyses of inorganic anions and cations have also been investigated.

Synthesis and visible light photocatalytic antibacterial activity of nickel-doped TiO2 nanoparticles against Gram-positive and Gram-negative bacteria

Abstract: Nanocrystalline anatase titanium dioxide (TiO 2 ) nanoparticles doped with nickel ions (1.0–3.0 mol%) were synthesized by sol–gel method. XRD and XPS showed the proper substitutions of the few sites of Ti 4+ ions by Ni 2+ ions in titania host lattice. Particle size was estimated from TEM analysis and found in the range of 10–12 nm. UV–vis diffuse reflectance absorption measurement of doped titania nanoparticles shows the optical absorption in the visible region; which also confirms the incorporation of nickel ions in TiO 2 crystal lattice. For photocatalytic inactivation four common bacterial pathogens, Staphylococcus aureus , Bacillus subtilis , Escherichia coli , and Salmonella abony were illuminated with nickel doped-TiO 2 nanoparticles. This shows a substantial decrease in bacterial numbers. The decrease in photoluminescence intensity with increasing dopant content reveals the higher photocatalytic inactivation and lower recombination rate of photogenerated charge carriers. The survival number of all bacteria species is not affected in dark with nanoparticles and in light condition without nanoparticles.

Influence of crystallinity and OH surface density on the photocatalytic activity of TiO2 powders

Abstract: The aim of the work was to study the influence of crystallinity and OH surface density on the photocatalytic activity of two commercial and two home-prepared TiO 2 powders The samples were characterized by X-ray diffraction (XRD), thermogravimetric analysis (TG) and electron paramagnetic resonance (EPR) measurements The photoactivity of the powders was tested employing the photodegradation of 4-nitrophenol (4-NP) and the selective oxidation of 4-methoxybenzyl alcohol (4-MBA) to 4-methoxybenzaldehyde ( p -anisaldehyde) under UV irradiation An anti-correlation between oxidant power and selectivity of the various samples was found A higher rate of 4-NP degradation was exhibited by the most crystalline commercial samples, whereas the highest selectivity toward the synthesis of p -anisaldehyde was obtained in the presence of the least crystalline and most hydroxylated home-prepared powders

Effect of Al3+ substituted zinc ferrite on photocatalytic degradation of Orange I azo dye

Abstract: Aluminum substituted zinc ferrite catalysts were prepared by the sol–gel auto-combustion method and characterized by using Mossbauer spectroscopy and nitrogen adsorption–desorption isotherm measurements. The photocatalytic activity of ZnFe 2− x Al x O 4 (0 ≤ x ≤ 2) spinel ferrites was evaluated for the first time on Orange I azo dye degradation under UV light illumination. The results showed that the photocatalytic process was promoted when aluminum cations substituted iron cations located in octahedral sites of zinc ferrite lattice. Therefore, the Orange I azo dye best removal efficiency was observed when the Al 3+ and Fe 3+ are presents in equimolar amounts. The dye degradation performance of the ZnFe 2− x Al x O 4 (0 ≤ x ≤ 2) catalysts was related to the crystallite size than to the BET surface area values and to the presence of secondary phases, such as α-Fe 2 O 3 and ZnO.

Quinazoline copper(II) ensemble as turn-on fluorescence sensor for cysteine and chemodosimeter for NO

Abstract: A fluorescent quinazoline based chemosensor QHYN had been designed and synthesized. It exhibits high sensitivity and selectivity towards Cu 2+ over other metal ions in DMSO:H 2 O (1:9, v/v) at pH = 7.4 [HEPES buffer] by fluorescence quenching. Addition of nitric oxide to a solution of this QHYN·Cu(II) restores the fluorescence. This is attributed to the reduction of the Cu(II) centre by nitric oxide to diamagnetic Cu(I). The fluorescence response of QHYN·Cu(II) to NO is direct and specific, which is a significant improvement over commercially available small molecule-based chemodosimeter probe that are capable of detecting NO. The QHYN·Cu(II) also acts as an efficient “off–on” fluorescent sensor for cysteine with high sensitivity.

Photochemically produced quasi-linear copolymers for stable and efficient electrolytes in dye-sensitized solar cells

Abstract: Dye-sensitized solar cells are increasingly establishing themselves as third generation photovoltaic technology which can be manufactured with easily available materials and low-cost processes. In this context, the replacement of the liquid electrolyte with quasi-linear polymer electrolyte membranes is here proposed, with the aim of increasing the durability of the device. The membranes are photochemically produced starting from two methacrylic monomers, by means of a process that does not involve the use of solvents and catalysts. In order to ensure handling and durability, the membranes are partially crosslinked with a tunable opening of the epoxy ring of one of the two monomers, thus binding together different polymer chains and allowing an effective entrapment of the redox mediator within the network. The experimental conditions are investigated and optimized by means of a multivariate chemometric approach, and the characterization of materials and devices is presented. Quasi-solid cells able to maintain efficiency up to 4% after 500 h of accelerated ageing are successfully fabricated.

Fabrication of an oxysulfide of bismuth Bi2O2S and its photocatalytic activity in a Bi2O2S/In2O3 composite

Abstract: Oxide-chalcogenide semiconductors are proposed in order to attain a smaller band gap and improve efficiencies in comparison to oxides for light induced total water splitting. Dibismuthoxysulfide (Bi2O2S) was synthesized under relatively mild hydrothermal conditions. The synthesized compound was characterized by XRD, SEM and UV–vis DRS techniques. The band gap of 1.5 eV measured is smaller than 2.8 eV of bismuth oxide (Bi2O3). Photoelectrochemical studies showed that it is possible to utilize Bi2O2S and the Bi2O2S/In2O3 composite as n-type semiconductors. Dye modified Bi2O2S/In2O3 showed promise for the catalysis of water splitting.

Photocatalytic reduction of aromatic nitro compounds using CdS nanostructure under blue LED irradiation

Abstract: The aromatic nitro compounds reduced with a high selectivity to the corresponding amines under blue LED irradiation (3 W) using CdS nanostructure as photocatalyst. The reaction is relatively sensitive to the electron demands of the substituents. The nitro compounds with electron withdrawing groups (CN, COR, NO2) give higher yields than with the electron donating groups (OMe, Me). In the nitro compounds with low activity, the high yields of corresponding amines were achieved by the addition of ammonium format. The CdS nanostructure showed excellent photocatalytic performance for the reduction of nitrobenzene compared with commercial CdS (Aldrich) under visible LED irradiation. The results demonstrated that CdS nanostructure have potential to provide a promising visible light driven photocatalyst for the selective reduction of nitro compounds to corresponding amines under mild conditions. The excellent reusability of the photocatalyst was examined for six runs.

Enhancement of photocatalytic activity of zinc/cobalt spinel oxides by doping with ZrO2 for visible light photocatalytic degradation of 2-chlorophenol in wastewater

Abstract: ZrO2-doped ZnCo2O4 nanoparticles were synthesized by hydrothermal coprecipitation of sulphate precursors with Zn/Co atomic ratio of 0.5 followed by addition of 0.05 mmol of ZrO2 precursor and calcination at 250–650 °C for 3 h. Several characterization tools such as X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and UV–visible diffuse reflectance spectroscopy (UV–vis-DRS) were used for the morphological structure, chemical composition and optical properties of the catalysts. Doping with ZrO2 appeared to stabilize the ZnCo2O4 phase and suppress ZnO phase formation as evidenced by XRD. The produced ZrO2-doped ZnCo2O4 nanoparticles were evaluated as catalyst for visible light photodegradation of 2-chlorophenol (2-CP) in synthetic wastewater solutions. Presence of ZrO2 in the ZnCo2O4 structure was responsible for a significant shift in the UV absorption spectrum toward visible region and resulted in enhancing the visible light photocatalytic activity. The photocatalytic experiments were performed in a batch reactor under 150 W visible light irradiation (λ > 400 nm). Parameters affecting the photocatalytic activity of the catalyst such as the catalyst dose, solution pH, and 2-CP concentration were investigated and evaluated. Results indicated efficient degradation of 2-CP, the highest removal % was achieved by catalyst calcined at 350 °C.

Elements doping to expand the light response of SrTiO3

Abstract: Cr,B-codoped-SrTiO 3 was successfully synthesized by one-step hydrothermal method. XRD, FTIR, Raman and XPS results showed that B existed in the forms of both substitutional B for O and interstitial B in the bulk of SrTiO 3 . UV-Vis absorption spectra showed that Cr,B-codoped-SrTiO 3 had strong visible light absorption and small band gap (2.07 eV). Theoretical calculation pointed out that the strong p–d repulsion of substitutional B 2p with Cr 3d was responsible for the narrowing of band gap and enhanced visible light absorption. Our results indicate that the codoping of Cr and B offers a novel route to modify the light response of SrTiO 3 . The photocatalytic activity for hydrogen production over Cr,B-codoped SrTiO 3 photocatalyst is 15.4 μmol/h, which is higher than that over Cr-doped SrTiO 3 (9.3 μmol/h) synthesized by the similar method. The higher activity for Cr,B-codoped SrTiO 3 is attributed to its smaller band gap than Cr-doped SrTiO 3 .

TiO2 based nano-photocatalysis immobilized on cellulose substrates

Abstract: This work mainly aims at exploiting the photocatalytic reactivity of nano-TiO2 coatings immobilized on cellulose substrate to get self-cleaning textiles. The efficiency of three commercial nano-titania, in the photo-degradation of organics, was investigated in different experimental conditions. In order to identify different factors affecting the photocatalytic reactivity, various experimental settings were tested to represent the self-cleaning application: TiO2 nanoparticles in solution, TiO2-coated textile dipped in solution and stain on TiO2-coated textile. The degradation of Rhodamine B (RhB) was used as model reaction. The photocatalytic activity was evaluated by the determination of the kinetics of degradation, the photonic efficiency (ξ) and the photocatalytic activity expressed as percentage conversion. The different experimental set-ups let to assess interfaces where nano-TiO2 played its photocatalytic activity and provided information on self-cleaning mechanism.

Degradation of ciprofloxacin by UV/S2O82− process in a large photoreactor

Abstract: This study evaluates the effectiveness of the UV/S2O82− process in the degradation of ciprofloxacin in aqueous solutions without adjusting their pH using a large photoreactor. The effect of Na2S2O8 concentration on the efficiency of degradation of ciprofloxacin was examined. A larger Na2S2O8 concentration was associated with a higher efficiency of degradation of ciprofloxacin. However, excessive Na2S2O8 concentration inhibited the degradation of ciprofloxacin. UV/S2O82− process exhibited pseudo-first-order kinetics. SO4 − was detected by performing quenching studies using specific alcohols, revealing that SO4 − was found to be the predominant radical. Additionally, the presence of HCO3− inhibited the degradation of ciprofloxacin at a high concentration. An efficiency of degradation of ciprofloxacin was 95% within 30 min using an Na2S2O8 concentration of 1.92 g/L in the absence of inorganic anions. Comparison of both UV/S2O82− and heat/S2O82− processes demonstrates that the degradation of ciprofloxacin at ambient temperature can be enhanced by the UV/S2O82− process, leading to a reduced operating time. These promising results obviously reveal the potential of the UV/S2O82− process application for the effective degradation of ciprofloxacin in aqueous solutions without adjusting the pH.

Synthesis, characterization, DNA binding and cleavage, HSA interaction and cytotoxicity of a new copper(II) complex derived from 2-(2′-pyridyl)benzothiazole and glycylglycine

Abstract: A new copper(II) complex, [Cu(glygly)(pbt)(H2O)]ClO4 (glygly = glycylglycine anion and pbt = 2-(2′-pyridyl)benzothiazole) was synthesized and characterized by elemental analysis, molar conductivity, mass spectra, IR spectra, UV–vis spectra and thermogravimetric analysis (TGA). Spectroscopic titration, viscosity, and electrophoresis measurements revealed that the complex intercalated to calf thymus (CT)-DNA with moderate binding affinity (Kb = 5.64 × 104 M−1), and cleaved pBR322 DNA at a low concentration of 5 μM in the presence of ascorbic acid, presumably via an oxidative mechanism. Further, the protein-binding ability has been monitored by various spectroscopic techniques (UV–vis, fluorescence and CD) using human serum albumin (HSA) as a model protein. The complex displayed desired affinity to HSA in which hydrophobic interaction played a major role. In addition, the complex was subjected to cytotoxicity tests in vitro using three human cancer cells lines (HepG2, HeLa and A549) and showed prominent and selective cytotoxicity against HepG2 cell lines (IC50 ∼ 17.78 μM).

Neutral solar photo-Fenton degradation of 4-nitrophenol on iron-enriched hybrid montmorillonite-alginate beads (Fe-MABs)

Abstract: Hybrid montmorillonite-alginate beads (MABs) were prepared by the ion-gelation method from alginate and montmorillonite clay suspension dropped in a calcium chloride solution. Similarly, iron-enriched beads (Fe-MABs) were prepared using iron-exchanged montmorillonite. All beads were characterized by atomic absorption and Fourier-transform infrared spectroscopy. The efficiency of Fe-MABs as catalysts for the solar photo-Fenton performed at initial pH = 7.0 was evaluated by varying the catalyst amount and hydrogen peroxide concentration, and monitoring the removal of 4-nitrophenol (4-NP) at initial concentration of 10 ppm. A kinetic analysis showed that the removal of 4-NP by Fe-MABs followed a pseudo first-order kinetics model (R-2 = 0.966). High 4-NP removal (75%) was achieved with 25 Fe-MABs by using 150 ppm of hydrogen peroxide and 40 min of irradiation, while total 4-NP removal was obtained by using 500 ppm of hydrogen peroxide. Moreover, preliminary studies about beads' recycling showed good removal efficiencies for the first three cycles. (C) 2014 Elsevier B.V. All rights reserved.

Photochemical degradation of sulfadiazine, sulfamerazine and sulfamethazine: Relevance of concentration and heterocyclic aromatic groups to degradation kinetics

Abstract: Sulfonamides are often not satisfactorily removed in wastewater treatment plants, reaching surface and ground waters at low concentrations. Photo-oxidation treatments appear as a viable alternative for the remediation of water and wastewater containing these pollutants. Moreover, the use of solid phase extraction (SPE) techniques for the quantification of sulfonamides at very low levels during photo-oxidation treatments is not usually discussed. In this study, three different processes (UV photolysis, UV/H 2 O 2 and photo-Fenton) were investigated for the degradation of sulfadiazine (SDZ), sulfamerazine (SMR), and sulfamethazine (SMT) to final concentrations below mg L −1 . A tubular photochemical reactor with a concentric low pressure mercury vapor lamp emitting at 254 nm was used. Sulfonamide concentrations were determined using ultra-fast liquid chromatography (UFLC). Hydrogen peroxide consumption was monitored spectrophotometrically. In particular, we optimized the SPE technique for the quantification of the three sulfonamides and determined the most appropriate stationary phase cartridge and pH for sample extraction. In comparison to UV photolysis and H 2 O 2 /UV processes, the photo-Fenton reaction was able to degrade sulfonamides to final concentrations of nmol L −1 (μg L −1 ), attaining the method detection limit after 20, 12 and 6 min of irradiation for SMT, SMR and SDZ, respectively. SDZ is more hydrophilic than SMR and SMT, which is related to the presence of methyl groups bonded to the heterocyclic group. The increase in the number of CH 3 substituents in the heterocyclic group of SMT and the corresponding increased steric hindrance to radical addition, resulted in slower degradation rates in comparison with those observed for SMR and SDZ. The optimized SPE technique can be used in further studies of sulfonamides degradation by advanced oxidation processes at more realistic concentration levels as those detected in real wastewater and in the environment.

Preparation and characterization of ZnO–SiO2 thin films as highly efficient photocatalyst

Abstract: ZnO doped SiO2 thin films were prepared by the sol–gel method and annealed at different temperatures from 200 to 1100 °C. SiO2 matrix is selected as support due to their high flexibility, thermal stability and high porosity and surface areas. The XRD patterns showed that the hexagonal wurtzite structure of the ZnO film was formed for all the prepared samples. TEM images of ZnO synthesized nanoparticles are almost spherical with a relatively narrow size distribution in the range of 5–20 nm according to the annealing temperature. These images clearly show the (0 0 0 1) atomic planes (interplanner distance is 0.52 nm) perpendicular to the c-axis, thus indicating that (0 0 0 1) is the preferred growth direction of these wurtzite-type ZnO. The newly prepared photocatalysts ZnO–SiO2 films have been evaluated by the determination of their photonic efficiencies for degradation of methylene blue. The photonic efficiencies of 10 wt% ZnO–SiO2 increase from 0.9 to 2.3% with increasing annealing temperature from 200 to 600 °C and then gradually decrease to 1.56% at 1100 °C. The results indicate that 10 wt% ZnO–SiO2 annealed at 600 °C showed the highest photocatalytic activity for the MB photodegradation. Our work demonstrates the ability to reduce the working temperature as well as to increase the response of ZnO thin film as a highly efficient photocatalyst, which would be of great merit for commercialized applications.

Second- and third-order nonlinear optical properties of bis-chalcone derivatives

Abstract: Bis-chalcone derivatives: 2,5-bis(benzylidene)-cyclopentanone (CP-DBA), 2,5-bis(4-methoxy-benzylidene)-cyclopentanone (CP-POME), 2,5-bis(4-isopropyl-benzylidene)-cyclopentanone (CP-ISO) and 2,5-bis(cinnamylidene)-cyclopentanone (CP-CAL) are synthesized by Claisen–Schmidt reaction and characterized using, FT-IR, 1H NMR, 13C NMR, and mass spectroscopic techniques The second- and third-order nonlinear optical properties of these samples are studied using second harmonic generation and nanosecond open-aperture Z-scan methods CP-POME has shown a very high second harmonic generation (SHG) efficiency (53 times that of urea) These molecules reveal a strong third-order nonlinear absorption (NLA) that is of optical limiting type, due to their peculiar D–π–A–π–D structure that leads to high polarization of the delocalized electron cloud CP-CAL exhibits highest NLA activity with a β coefficient of 1 × 10−10 m/W Through numerical simulations, the mechanism of NLA is found to be a two-photon absorption process in the case of all the samples

Comparing the efficacy of UVC, UVC/ZnO and VUV processes for oxidation of organophosphate pesticides in water

Abstract: This study investigated the performance of UVC, UVC/ZnO and vacuum UV (VUV) processes for the degradation of diazinon as a model organophosphate pesticide. The highest diazinon degradation was obtained at a solution pH of 5 for UVC, 7.5 for UVC/ZnO, and 9 for VUV. At optimum pH and a reaction time of 30 min, the UVC process degraded 57.8% of the diazinon (10 mg/L) and the UVC/ZnO process degraded 93.3%. By comparison, the VUV process completely degraded 10 mg/L diazinon in a very short reaction time of 90 s. VUV produced a significantly greater degradation rate for diazinon than UVC and UVC/ZnO. Under similar operating conditions, the first-order degradation rate of 5 mg/L diazinon for VUV was 119 times greater than for UVC and 18 times greater than for UVC/ZnO. In continuous mode, the VUV process completely degraded 1 mg/L diazinon in natural water at a hydraulic retention time (HRT) of 2.2 min; complete mineralization was obtained at a HRT of 4.7 min. It was found that the VUV process is a very efficient and viable process for complete mineralization of organophosphate pesticides in water sources and is an appropriate technology for real scale applications.

π–π binding ability of different carbon nano-materials with aromatic phthalocyanine molecules: Comparison between graphene, graphene oxide and carbon nanotubes

Abstract: The π–π stacking ability of graphene sheets (GS), graphene oxide (GO), and single walled carbon nanotubes (SWCNT) with phthalocyanine (Pc) molecules was studied by the UV–vis absorption, steady state and time-resolved fluorescence spectra. Absorption spectra revealed that strong π–π binding with the Pc ground state (S0) occurred for GS and GO but not for SWCNT, the binding ability is GS ≫ GO ≫ SWCNT. However, when a Pc molecule is photoexcited, fluorescence study shows that the π–π interaction capability is changed to GS ≫ SWCNT ≫ GO. Although SWCNT exhibits low ability to bind Pc S0 state, it strongly interacts with Pc S1 state. The data analysis shows that the dynamic quenching for the nanoscaled carbon quenchers still obeys linear Stern–Volmer relationship, but the static quenching is not linear. An exponential expression is needed to fit the data for GS and SWCNT, which indicates that an effective quenching sphere model is valid for the nanoscaled fluorescence quenchers.

Tuning the electron donating ability in the triphenylamine-based D-π-A architecture for highly efficient dye-sensitized solar cells

Abstract: A new series of triphenylamine-based organic dye sensitizers, namely TPA1-TPA6 with introduced auxiliary donor groups including carbazole and diphenylamine moieties to triphenylamine core, and with inserted fluorene moiety between triphenylamine and auxiliary donor, was designed and theoretically investigated. The starburst triphenylamine dyes acting as electron donor groups capped with mono- and di-substituted auxiliary donors coded as D-D-π-A and 2D-D-π-A respectively, were studied for the propose of comparison with only one triphenylamine moiety as donor, namely TPA, in the D-π-A system. Density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations were conducted to investigate the molecular structures, frontier molecular orbitals, absorption spectra as well as dye-(TiO2)38 complexes of these dyes as implemented in the Gaussian 09 program. Among three dye architectures, the results suggested that the 2D-D-π-A system showed the largest absorption range. We found that different types of auxiliary donors provided different light-harvesting ability; the diphenylamine auxiliary donor can improve properties of red-shifted absorption region. In addition, the optimized geometries showed that adding of diphenylamine auxiliary donor provided smaller external dihedral angles (EDA) leading to wider absorption range with strong charge-transfer character compared to other dyes. Our results are suggested to be the possible reasons for the enhancement of conversion efficiency in dye-sensitized solar cells.

Photocatalytic degradation of dyes in water with micro-sized TiO2 as powder or coated on porcelain-grès tiles

Abstract: Some particular drawbacks due to the industrial use of nano-sized TiO 2 (safety, recovery) in photocatalytic processes for water remediation can be avoided choosing micro-sized TiO 2 . Tests on both micro-sized TiO 2 powder and industrially prepared photocatalytic tiles, having the surface of porcelain-gres tiles hot-coated with the same photocatalyst, were performed. Good photocatalytic performance in the degradation of three organic dyes (rhodamine B, crystal violet and methylene blue) in water phase were achieved. Photocatalytic tiles can really represent a good alternative to TiO 2 suspensions and pave the way for the fully industrial use of photocatalysis in environmental remediation.

Dual optical Hg2+-selective sensing through FRET system of fluorescein and rhodamine B fluorophores

Abstract: A “naked-eye” indicator and fluorescent chemosensor based on fluorescein connected to two rhodamine B fluorophores by hydrazide moieties, RF1, was designed and synthesized for highly sensitive and selective detection of Hg 2+ . The sensor system operated through the FRET process from the fluorescein energy donor to the ring-opened rhodamine B acceptors. The binding to Hg 2+ was observed through both fluorescence enhancement and a chromogenic change (from colorless to pink). The sensor is shown to discriminate various foreign metal ions, particularly Ag + , Pb 2+ and Cu 2+ , as well as Li + , Na + , Mg 2+ , Cd 2+ , K + , Al 3+ , Fe 3+ , Ca 2+ , Ba 2+ and Zn 2+ , with a detection limit of 2.02 × 10 −8 M or 4 ppb toward Hg 2+ .

Characterization and mechanistic study of Mo+6 and V+5 codoped TiO2 as a photocatalyst

Abstract: Undoped, mono and codoped TiO 2 nanoparticles were prepared with Mo +6 and V +5 dopants using ultrasonic-assisted sol–gel method. XRD diffraction revealed that photocatalyst powders calcined at 550 °C are composed of anatase with minor brookite and rutile phases. Codoped powders showed largest red shift in the band gap and the decrease in photoluminescence intensity demonstrated that electrons holes recombination has decreased. Mo +6 and V +5 have been detected by XPS analysis indicating that the dopants Mo +6 and V +5 substitute for titanium (Ti +4 ) in the lattice of TiO 2 . The activity tests reveal that codoped (TMo 0.125 V 0.125 ) powder has the best photocatalytic performance in the degradation of methylene blue (MB) dye and antibiotic sulfamethoxazole (SMX) under UV and visible light irradiations. Briefly, the enhanced activity of codoped TiO 2 is due to the synergistic effect of TiO 2 polymorphs, the Mo +6 and V +5 energy levels and their d-d transition with TiO 2 conduction band electrons, high specific surface area via small crystallite size, surface acidity, Ti +3 surface states and oxygen defects. The mechanistic study illustrates that the complex band structure of the codoped powders does not only improve visible light absorption and promote the separation of photoinduced electron hole pairs, but it also facilitates the enhanced formation of hydroxyl radicals (OH ) and superoxide anions (O 2 − ). Degradation of methylene blue (MB) and sulfamethoxazole (SMX) showed pseudo first order kinetics. With MB experiments under UV irradiation a rate constant ( k app ) of 0.064 min −1 was obtained with TMo 0.125 V 0.125 powder, which is higher than that of commercially available Degussa P25 (0.05 min −1 ) and twice as high than the undoped TiO 2 (0.031 min −1 ).

Facile fabrication of MoS2/PEDOT–PSS composites as low-cost and efficient counter electrodes for dye-sensitized solar cells

Abstract: A novel MoS 2 /PEDOT–PSS counter electrode (CE) is proposed and used for dye sensitized solar cells (DSCs). The MoS 2 /PEDOT–PSS composites were facilely obtained from the mechanical mixture of hydrothermal synthesized MoS 2 nanomaterial and poly(3,4-ethylenedioxythiophene)–poly(styrenesulfonate) (PEDOT–PSS) aqueous solution, and the composites are compatible to low temperature and cost-effective screen-printing fabrication technique. DSC with MoS 2 /PEDOT–PSS CE exhibits comparable power conversion efficiency and fill factor to the DSC with conventional Pt CE. The good photovoltaic performance of DSC using MoS 2 /PEDOT–PSS CE is primarily derived from the high electrocatalytic activity of nanosized MoS 2 and the high conductive feature of PEDOT–PSS. These results reveal the potential application of MoS 2 /PEDOT–PSS composite in the use of low-cost, printable and efficient Pt-free CEs.

Phosphorescence of BODIPY dyes

Abstract: The phosphorescence of BODIPY dyes was observed directly in glassy solvent matrix at 78 K. The phosphorescence occurred when Br substituents are present on the BODIPY core and the solvent temperature is lower than the freezing point. The phosphorescence quantum yield (Φp) and lifetime (τp) were measured. The substitution effect of Br atoms on the phosphorescence properties of 8-phenyl-BODIPY dyes is also studied. Upon the increase in the number of Br atoms on the BODIPY core, the phosphorescence emission maximum is varied from 720 to 780 nm, the corresponding excited triplet state energy changes from 1.71 to 1.62 eV, the lifetime τp is shortened from 5.8 to 3.7 ms, while the quantum yield Φp is decreased from 3.0 × 10−3 to 1.4 × 10−3. The mechanism for the effect of Br substitution on the phosphorescence properties is revealed by calculating the rate constants of related photophysical processes. The Br substitution at position 1 or 7 showed a dramatic difference from that at positions 2, 6, 3, and 5. The steric hindrance to the rotation of the phenyl leads to the deformation of BODIPY π-core such that the phosphorescence properties change toward a different direction.

Enhanced photoabsorption properties of composites of Ti/TiO2 nanotubes decorated by Sb2S3 and improvement of degradation of hair dye

Abstract: The present work illustrates the great potentiality of Ti/TiO2/Sb2S3 composite electrode prepared by electrochemical anodization of Ti foil in aqueous electrolyte (1 mol L−1 NaH2PO4 + 0.3 wt.% HF followed by chemical bath deposition of Sb2S3) in environmental electrochemistry. The electrodes are characterized by deposits of particles of 500 nm of diameter formed on the top of TiO2 nanotubes of 900 nm of length, 110 nm of diameter and 13 nm of wall thickness. The band gap obtained for Ti/TiO2/Sb2S3 composite electrode was 1.68 eV, contributing to strong photoabsorption properties of the material in the visible light region (λ < 740 nm). The photocurrent on this material is remarkably improved in relation to that obtained on comparable nanotubes TiO2 films. The electrodes promote complete degradation of the investigated hair dyeing commercialized as Arianor Tyrian Purple® after 120 min of photoelectrocatalytic oxidation under potential of 1.2 V and commercial light irradiating under UV/Visible light. Finally, the degradation products generated by photoelectrocatalysis were analyzed by HPLC–MS/MS.

Tracing TiO2 photocatalytic degradation of humic acid in the presence of clay particles by excitation–emission matrix (EEM) fluorescence spectra

Abstract: Excitation–emission matrix (EEM) fluorescence spectral features were evaluated for the elucidation of the photocatalytic degradation of sole humic acid (HA) and HA in the presence of clay minerals. Montmorillonite (Mt) or kaolinite (Kt) was selected to represent two different types of clay minerals. EEM fluorescence signatures displayed irradiation time dependent transformation of humic-like fluorophores to fulvic-like fluorophores in accordance with the photocatalytic mineralization of HA. The role of Ca 2+ ions on the photocatalytic degradation of HA could also be visualized through EEM under the specified conditions. Upon photocatalytic treatment, the role of Mt was more pronounced with respect to the effects observed in the presence of Kt in comparison to the results achieved for sole HA. Under prolonged irradiation conditions ( t irr = 180 min) almost complete removal of fluorophoric groups was detected in relation to a substantial degree of mineralization (>75% removal of dissolved organic carbon, DOC). As a correlative approach, fluorescence-derived index defined as fluorescence intensity (FI) represented by the ratio of the emission intensity at λ emis = 450 nm to that at λ emis = 500 nm, following excitation at λ exc = 370 nm was successfully employed. FI values were correlated to specified UV parameters (UV 254 and UV 280 ) revealing an inverse relationship. Moreover, through normalization of the specified UV parameters to DOC contents, the derived specific UV parameters (SUVA 254 and SUVA 280 ) could also be successfully correlated to FI. The obtained results indicated that besides photocatalytic mineralization efficiencies, UV–vis and fluorescence spectroscopic properties could also be employed to gain further information on the humic structural changes attained through non-selective oxidation mechanism in comparison to the data obtained under non-oxidative conditions.

Azobenzene based polymers as photoactive supports and micellar structures for applications in biology

Abstract: Azo-polymers have been investigated for the large structural modifications occurring under light excitation. Photo induced isomerizations of the azobenzene molecular units can provide cooperative forces able to affect self-assembling processes in the liquid state or leading to an efficient mass transport in the solid state, which results in large deformations of film surfaces. We introduce here our studies on azopolymers based on a polysiloxane matrix bearing specific chemical functions, whose composition can be finely tuned for applications in the biological field. Depending on their chemical structure, these materials are able to form photoactive surfaces with adjustable topographic properties or photosensitive micellar architectures in aqueous solvents. In the first case, the ability to control the surface shape at the optical wavelength scale aims to provide photoactive cell growth supports with tuneable properties, for the investigation of the environment influence on cell development. The optical properties of the materials are presented, as well as the preliminary studies showing the materials potential to modify the cell response to the surface. The stability of the films surface in contact with biological media and the implications on the cell behavior are also addressed. The second property involving formation of micellar structures is demonstrated by showing the ability of the materials to encapsulate and provide controlled release of small molecules pointing to their potential use in drug delivery applications.