Photocatalytic degradation of hazardous Food Yellow 13 in TiO2 and ZnO aqueous and river water suspensions

Enhanced reactivity of the CuO-Fe2O3 intimate heterojunction for the oxidation of quinoline yellow dye (E104)

This research work describes the degradation of quinoline yellow (QY) in aqueous solutions by the heterogeneous Fenton and photo-Fenton processes in the presence of CuO/Fe₂O₃ photocatalyst. CuO/Fe₂O₃ derived from LDH structure was synthesized by the co-precipitation method. The physiochemical characteristics of CuO/Fe₂O₃ were described by XRD, TEM/SEM, BET surface area, and FTIR techniques. The effects of pH, H₂O₂ concentration, dye concentration, catalyst dose, reaction temperature, and reusability of catalyst on the QY decolorization efficiency were studied. The results indicated that a complete removal of QY was achieved within 150 min, when the H₂O₂ and QY concentrations were 27.6 mM and 100 mg/L, respectively. The rate constants for QY removal by the heterogeneous Fenton system were calculated, and the experimental data were found to fit the pseudo-first order model. Under optimal conditions, the rate constants were, respectively, 0.02032 and 0.01715 min^-1 for the photo-Fenton and Fenton systems; this means that the addition of light has not a noticeable effect.

Livistona jekinsiana fabricated ZnO nanoparticles and their detrimental effect towards anthropogenic organic pollutants and human pathogenic bacteria

An environment-friendly and economically sound method was developed to achieve a multi-functional ZnO nanoparticles (ZnO NPs) using water extract of Livistona jekinsiana. The ZnO NPs absorbed maximum wavelength of light at 332 nm in UV-Visible spectroscopy (UV/Vis). X-Ray Diffraction (XRD) pattern revealed the crystallinity of the nanoparticles with the crystallite size around 22.45 nm. The geometry, shape, size, and elemental composition were determined by Transmission Electron Microscope (TEM) and Energy Dispersive Spectroscopy (EDS). The presence of phytochemicals and the typical zinc-oxygen group in the ZnO NPs was implied by Fourier Transform Infrared spectroscopy (FTIR). Photo luminescence spectroscopy (PL), and Dynamic Light Scattering (DLS) techniques were also used to characterize and study the different features of ZnO NPs. The multifunctional ZnO NPs showed an efficient photodegradative effect towards the degradation of two anthropogenic dyes, methyl orange (MO) and methylene blue (MB) under solar radiation. The degradation reaction of MO and MB was compliantwithzero-order kinetics and first-order kinetics respectively. Also, Livistona jekinsiana fabricated ZnO NPs showed potential Antibacterial activity against S. aureus, B. subtilis, E. coli and K. pneumonia bacteria and effective antioxidant activity using DPPH scavenging assay. The mechanism of the antibacterial activity was established by estimating the ROS generation and percentage of DNA in K. pneumonia cell. The study illustrated the reducing and stabilizing property of the Livistona jekinsiana extract as a novel source and potential photodegradative and therapeutic effects of the ZnO NPs.

Degradation of the mixture of the ketoprofen, meloxicam and tenoxicam drugs using TiO2/metal photocatalysers supported in polystyrene packaging waste

The solution mixture of the non-steroidal anti-inflammatory drugs ketoprofen, meloxicam and tenoxicam was degraded through systems, composed of different photocatalysts based on TiO₂ (Fe and Cu) and the hydrogen peroxide oxidant. The monitoring was performed by UV-Vis spectroscopy. Under sunlight radiation, a reduction in peaks was observed with the use of impregnated photocatalysts. After 60 min, the sun/H₂O₂/Fe-TiO₂ system reached degradations of 46.5% and 93.2% at 260 and 367 nm, respectively, and was selected for further studies. The degradation kinetic reached 92 and 96% of degradation after 180 min, for the λ of 260 and 367 nm, respectively. The kinetic curve could be represented by the empirical model proposed by Nichela and co-authors, indicating that besides the heterogeneous photocatalysis that occurs at the surface of the TiO₂ there is also the joint effect of the photo-Fenton process. After the treatment, there was no toxicity to cress and lettuce seeds. However, a sensitivity of the thyme seeds to the compounds formed during the treatment was verified. After the fifth treatment cycle, the supported photocatalyst showed degradation higher than 82%. These results indicate that this system is suitable for the treatment of effluents containing pharmaceutical compounds.

Photocatalytic Degradation of Quinoline Yellow over Ag3PO4

In this study, the ability of Ag3PO4 to achieve the photocatalytic degradation of quinoline yellow (QY) a hazardous and recalcitrant dye, under UVA and visible light was investigated. The photocatalyst Ag3PO4 was synthesized through a precipitation method, and characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), BET Brunauer–Emmett-Teller (BET) analysis, UV-Differential Reflectance Spectroscopy (DRS) and Fourier transform infrared spectroscopy (FTIR). Ag3PO4 could successfully induce the photocatalytic degradation of QY under UVA and visible light. Optimal parameters were 0.5 g·L−1 of the catalyst, 20 ppm of QY and pH~7. Ag3PO4 was 1.6-times more efficient than TiO2 Degussa P25 under UVA light in degrading QY. Total organic carbon (TOC) analyses confirmed the almost complete QY mineralization. At least eight intermediate degradation products were identified by liquid chromatography coupled to high resolution mass spectrometry. The stability of Ag3PO4 was satisfactory as less than 5% Ag metal appeared in XRD analyses after 3 reuse cycles. These results show that under optimized conditions Ag3PO4 can efficiently achieve quinolone yellow mineralization.

Rare-Earth Metals-Doped Nickel Aluminate Spinels for Photocatalytic Degradation of Organic Pollutants

Visible-light-activated photocatalysts based on samarium-doped, europium-doped, and gadolinium-doped nickel aluminates (SmNA, EuNA, GdNA) were synthesized. The spinel crystalline structures of the doped mixed metal oxides were demonstrated by X-ray diffraction (XRD) and transmission electron microscopy (TEM) analysis. The presence of the rare-earth metals (REMs) was confirmed by the energy-dispersive X-ray (EDX) studies. Ultraviolet-visible-near-infrared (UV-Vis-NIR) spectra revealed that the REMs-doped catalysts absorb in the full solar spectrum range covering both visible and near infrared wavelengths. Scanning electron microscopy (SEM) visualized the profound morphological alterations of the doped nickel aluminate samples. Consequently, the pore volume and the Brunauer-Emmett-Teller (BET) surface area decreased, while nanoparticles sizes increased. Fourier-transform infrared spectroscopy (FTIR) exposed that surfaces of REMs-doped nickel aluminates are rich in hydroxyl groups. Finally, the photocatalytic performance was notably increased through doping nickel aluminate (NA) with REMs; the highest activity was observed for EuNA.

Cobalt phthalocyanine-TiO2 nanocomposites for photocatalytic remediation of textile dyes under visible light irradiation

CoPc(COOH)[Formula: see text]-TiO[Formula: see text] nanocomposites to be used as efficient visible light photocatalysts were obtained by modifying TiO2 nanoparticles with cobalt(II) tetracarboxyphthalocyanine (CoPc(COOH)[Formula: see text]). The photocatalyst was then characterized by ultra-violet diffuse reflectance spectroscopy (UV-DRS), Fourier transform infrared spectroscopy (FT-IR) and X-ray diffraction (XRD). The UV-DRS spectra showed that the absorbance spectrum of the modified catalyst was shifted to the visible region. Different textile dye solutions of Reactive Red 180, Acid Red 88 and Direct Orange 46 were efficiently degraded under visible light. Color removal rates were established to be 30%, 53% and 47% after 180 min for RR180, AR88 and DO46 dyes, respectively. The optimum catalyst concentration was determined to be 1 g/L of CoPc(COOH)[Formula: see text]-TiO[Formula: see text]. Development of the CoPc(COOH)[Formula: see text]-TiO[Formula: see text] nanocomposite photocatalyst enabled the utilization of visible light irradiation for efficient photodegradation of organic textile dye solutions.

Use of TiO2 photocatalyst supported on residues of polystyrene packaging and its applicability on the removal of food dyes

This work proposes the use of plastic residues, more specifically polystyrene packaging, to support TiO₂, used as a photocatalyst in the degradation of erythrosine and Brilliant Blue food dyes. The scanning electron microscopy and Fourier transform infrared spectroscopy analyses exhibited the surface coating and the presence of TiO₂ in the material, respectively. The UV/H₂O₂/TiO_{2 ((SP)supported)} process was used in the preliminary study, given the high percentage of degradation, operational advantages and greater reductions in peaks related to the aromatic rings when compared to the other processes studied. For the factorial design, the highest efficiency was reached for 150 mg of TiO₂, a H₂O₂ concentration of 11.2 mmol L^-1 and pH of 5.0. These conditions were used in the degradation kinetics, which was rapid during the first 30 min, with the concentration of dyes in the solution reaching values close to zero after 180 min. Based on the mechanism proposed, the pseudo-first order kinetic model presented the best adjustment to the experimental data. After treatment, the solution presented greater biodegradability and lower toxicity, verified by the lettuce seed germination test (Lactuca sativa). Thus, the UV/H₂O₂/TiO_{2((SP)supported)} process showed great potential in the treatment of industrial effluents contaminated by these food dyes, as well as in reusing discarded polystyrene packaging to support the photocatalyst.

Shedding new light on an old molecule: quinophthalone displays uncommon N-to-O excited state intramolecular proton transfer (ESIPT) between photobases

Excited state dynamics of common yellow dye quinophthalone (QPH) was probed by femtosecond transient absorption spectroscopy. Multi-exponential decay of the excited state and significant change of rate constants upon deuterium substitution indicate that uncommon nitrogen-to-oxygen excited state intramolecular proton transfer (ESIPT) occurs. By performing density functional theory (DFT) and time-dependent density functional theory (TDDFT) calculations, we found that adiabatic surface crossing between the S₁ and S₂ states takes place in the photoreaction. Unlike most cases of ESIPT, QPH does not exhibit tautomer emission, possibly due to internal conversion or back-proton transfer. The ESIPT of QPH presents a highly interesting case also because the moieties participating in ESIPT, quinoline and aromatic carbonyl, are both traditionally considered as photobases.