Degradation of amoxicillin in aqueous solution using nanolepidocrocite chips/H2O2/UV: Optimization and kinetics studies

Degradation of amoxicillin (AMX) by nanolepidocrocite chips/H₂O₂/UV method as a new photo-Fenton like process was investigated and optimized by response surface methodology (RSM). The optimal conditions were initial AMX concentration of 10 mg l⁻¹ and initial H₂O₂ concentration of 60 mg l⁻¹ at pH of 2 under UV radiation for 120 min. The general photo-Fenton process mechanism was applied to propose a new kinetic model for AMX degradation. According to this model, the reaction constant between AMX and OH was obtained 4.55 × 10⁵ M⁻¹ s⁻¹. Also, nanolepidocrocite showed good catalytic activity even after four successive degradation cycles.     

Colour removal of three reactive dyes by UV light exposure after electrochemical treatment

This study applies UV light irradiation after a low current density electrochemical treatment to degrade reactive dyes to remove wastewater colour. The combination of these two techniques improves the quality of the treated effluent with respect to only an electrochemical treatment. Synthetic dyeing effluents containing a reactive dye (C.I. Reactive Orange 4, C.I. Reactive Black 5 or Procion Navy H-EXL) and Na₂SO₄ were studied. Ti/Pt oxides electrodes and UV irradiation lamp (6 W, 254 nm maximum emission) were used. Kinetic constants of the UV irradiation step were calculated. The influence of chloride ion at 3 and 6 mA/cm² was evaluated. Results showed that, with a very small Cl^? concentration (in the order of the net water content) the combined techniques provided full decolourization. The possible presence of 25 organic halogenated compounds was studied by gas chromatography–mass spectrophotometry (GCMS). Only four of them were detected after the electrochemical treatment at low intensity, mainly chloroform. Its concentration was found to be highly dependent of the Cl^? concentration, being much lower when reducing the amount of chloride ion. In all cases, the chloroform concentration was dramatically reduced by further UV irradiation which destroyed it up to a 75%.     

Photocatalytic degradation of methyl tert-butyl ether (MTBE) by Fe-TiO2 nanoparticles

Nowadays, since the underground waters are known as the main source for supplying the drinking water, their pollution to the organic contaminants such as methyl tert-butyl ether (MTBE) is a very significant issue. Therefore, in this study, photocatalytic degradation of MTBE was investigated in the aqueous soloution of Fe-TiO₂ nanoparticale under UV irradiation (wavelenght 254 nm) in a batch reactor. The Fe-TiO₂ mixed oxides were prepared by sol–gel impregnation method. The samples were characterized by X-ray diffraction (XRD), UV–vis diffuse reflectance spectroscopy (DRS), scanning electron microscopy (SEM) and BET specfic surface area. Then, the effect of various operational parameters namely pH, catalyst loading, molar ratio of [H₂O₂]₀/[MTBE]₀ and UV light intensity on degradation of aqueous MTBE were evaluated in a batch reactor. The optimal condition to achieve the best degradation for the initial concentration of 75 ppm MTBE was found at pH 7, catalyst concentration 2 g/L, molar ratio of [H₂O₂]₀/[MTBE]₀ 4, and UV irradiation 24 W. Total degradation of MTBE with initial concentration of 75 ppm was reached in optimal condition after 70 min. In addition, investigations were also carried out to determine the appropriate kinetics of MTBE degradation using UV/Fe-TiO₂/H₂O₂ process in optimal condition.     

Removal of metsulfuron methyl by Fenton reagent

The removal of metsulfuron methyl (MeS)—a sulfonyl urea herbicide from contaminated water was investigated by advanced oxidation process (AOP) using Fenton method. The optimum dose of Fenton reagent (Fe²⁺/H₂O₂) was 10 mg/L Fe²⁺ and 60 mg/L H₂O₂ for an initial MeS concentration ([MeS]₀) range of 0–80 mg/L. The Fenton process was effective under pH 3. The degradation efficiency of MeS decreased by more than 70% at pH > 3 (pH 4.5 and 7). The initial Fe²⁺ concentration ([Fe²⁺]₀) in the Fenton reagent affected the degradation efficiency, rate and kinetics. The degradation of MeS at optimum dose of Fenton reagent was more than 95% for [MeS] ₀ of 0–40 mg/L and the degradation time was less than 30 min. The determination of residual MeS concentration after Fenton oxidation by UV spectrophotometry was affected by the interferences from Fenton reagent. The estimation of residual MeS concentration after Fenton oxidation by high pressure/performance liquid chromatograph (HPLC) was interference free and represented the actual concentration of MeS and does not include the by-products of Fenton oxidation. The degradation kinetics of MeS was modelled by second order reactions involving 8 rate constants. The two reaction constants directly involving MeS were fitted using the experimental data and the remaining constants were selected from previously reported values. The model fit for MeS and the subsequent prediction of H₂O₂ were found to be within experimental error tolerances.     

Photodegradation of 2-naphthol in water by artificial light illumination using TiO2 photocatalyst: Identification of intermediates and the reaction pathway

The kinetics of the photocatalytic degradation of 2-naphthol has been investigated in aqueous suspensions of titanium dioxide (TiO₂) under a variety of conditions, which is essential from application point of view. The degradation was studied using different parameters such as types of TiO₂, catalyst concentration, substrate concentration, reaction pH and in the presence of different electron acceptors such as hydrogen peroxide (H₂O₂), potassium bromate (KBrO₃) and potassium persulphate (K₂S₂O₈) besides molecular oxygen. The degradation rates were found to be strongly influenced by all the above parameters. The photocatalyst “Degussa P-25” was found to be more efficient as compared with other photocatalysts. The degradation kinetics fit well to the Langmuir–Hinshelwood rate law. It was found that an optimal concentration of 5 × 10⁻⁴ mol/l Ag⁺ in TiO₂ achieved the fastest 2-naphthol degradation under the experimental conditions. However, with the addition of Na⁺, K⁺, Mg²⁺, Ca²⁺, Zn²⁺, Co²⁺ and Ni²⁺, there are no obvious effects on the reactions. An analysis of total organic carbon (TOC) showed that a complete mineralization of 2-naphthol can be easily achieved. The intermediate products were identified by HPLC–MS technique. A detailed degradation pathway could be proposed.     

Morphology controlled hydrothermal synthesis and photocatalytic properties of ZnFe2O4 nanostructures

The present work is focused on studying morphology dependent catalysis of spinel ZnFe₂O₄ nanostructures. Different morphologies i.e. porous nanorods, nanoparticles, nanoflowers and hollow microspheres were designed hydrothermally. The as prepared nanomaterials were characterized using Fourier Transform Infra-Red (FTIR), field emission scanning electron microscopy (FE-SEM), high resolution transmission electron microscopy (HR-TEM), powder X-ray diffraction (XRD), vibrating sample magnetometer (VSM), Brunauer–Emmett–Teller (BET) technique and UV–visible spectrophotometer. The results confirmed formation of desired morphologies of cubic spinel ZnFe₂O₄ with high surface areas (92–138 m²/g) and narrow band gaps (1.76–1.97 eV). It suggested the use of ZnFe₂O₄ nanostructures as potential visible light photocatalysts. Therefore, the application of synthesized ZnFe₂O₄ nanostructures was studied in photo-Fenton degradation of dyes. The results indicated shape dependent relationship with photocatalytic activity as the degradation of dyes followed the order porous nanorods>nanoparticles>nanoflowers>hollow microspheres. The role of main active species in the reaction i.e. ^∙OH was also confirmed. All the materials exhibited stability and magnetic separability hence could act as potential photo-Fenton catalysts for wastewater treatment.     

Photocatalytic degradation of 17-β-oestradiol on immobilised TiO2

Micro-molar concentrations of aqueous 17-β-oestradiol were 98% destroyed in 3.5 h by photocatalysis over the titanium dioxide powder immobilised on Ti-6Al-4V alloy. The concentration of oestradiol was determined by HPLC with fluorescence detection. The degradation kinetics were fitted to a Langmuir–Hinshelwood model with k(S) = 4.4 × 10⁻² μmol dm⁻³ min⁻¹ and K(S) = 0.347 dm³ μmol⁻¹. The pseudo-first-order rate constant (1.57 × 10⁻² min⁻¹) was in line with the 50% degradation time of 40 min. The apparent quantum yield per electron was φ_e′  = 0.41%. The effect of pH on the initial rate of degradation was similar to that reported for phenol.     

UV/S2O82− process for degrading polyvinyl alcohol in aqueous solutions

This investigation evaluates the effectiveness of the UV/S₂O₈²⁻ process in the degradation of polyvinyl alcohol (PVA) in aqueous solutions without adjusting their pH. The effects of UV wavelength and Na₂S₂O₈ dosage on the efficiency of degradation of PVA were examined. The efficiency of degradation of PVA under UV-254 nm exceeded that under UV-365 nm. A larger Na₂S₂O₈ dosage was associated with a higher efficiency of degradation of PVA under UV-254 nm irradiation. However, an excessive Na₂S₂O₈ dosage inhibited the degradation of PVA by the UV-365 nm/S₂O₈²⁻ process. Both UV-254 nm/S₂O₈²⁻ and UV-365 nm/S₂O₈²⁻ processes 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 in the UV-254 nm/S₂O₈²⁻ process. Additionally, the presence of inorganic anions with various effects inhibited the degradation of PVA by the UV-254 nm/S₂O₈²⁻ process. Complete degradation of PVA (20 mg/L) was achieved within 5 min under UV-254 nm using an Na₂S₂O₈ dosage of 0.12 g/L in the absence of inorganic anions, indicating that UV irradiation to activate S₂O₈²⁻ promotes the degradation of PVA in aqueous solutions without adjusting their pH.     

Optimization of flocculation conditions for the separation of TiO2 particles in coagulation-photocatalysis hybrid water treatment

TiO₂ mediated photocatalysis can decompose organic micropollutants (e.g., 1,4-dioxane) in water, but the removal of used TiO₂ particles is challenging. Although retrofitting enhances the particle separation efficiency, optimizing a coagulation/flocculation process should be most suitable for existing treatment plants. Therefore, the present study investigated the separation characteristics of TiO₂ particles added to drinking water treatment processes along with a polyaluminum coagulant. TiO₂ photocatalysts were able to achieve significant degradation of 1,4-dioxane (∼100% within 50 min) as well as dissolved organic matter (∼75% within 150 min) at a TiO₂ dose of 1.0 g/L under UV irradiation. Although the TiO₂ particle separation efficiency was sensitive to G values, maximal removal occurred at a G value of <34 s⁻¹ with a coagulant concentration of >8 mg/L as Al₂O₃. Sand filters had the capability to remove residual turbid materials and thus, the turbidity of the final product water dropped to as low as 0.1 NTU when the coagulation/flocculation process was preceded. The final effluent quality was comparable to that of a 0.45-μm membrane filter. The post separation of the TiO₂ photocatalysts dispersed for emergency water treatment to degrade 1,4-dixoane was successfully achieved with an optimal coagulant dose, proper flocculation, and sand filtration.     

Anodic oxidation of isothiazolin-3-ones in aqueous medium by using boron-doped diamond electrode

Electrochemical degradation of biocide compound, isothiazolin-3-ones, was studied in aqueous medium, with Na₂SO₄ supporting electrolyte using boron-doped diamond (BDD) anode. The redox response of isothiazolin-3-ones at BDD was examined by cyclic voltammetric study. The degradation of isothiazolin-3-ones and its mineralization trend were monitored by UV–vis spectrophotometric method and total organic carbon (TOC) analyzer, respectively. The effect of operating parameters such as applied current density, biocide concentration, electrolyte pH and nature of supporting electrolytes (Na₂SO₄, NaNO₃ and NaCl) on degradation rate was studied in detail. It was established that the hydroxyl radicals (OH) generated at BDD surface were responsible for the degradation and the mineralization of the biocide contaminant. The rate of degradation was almost independent of electrolyte pH but became faster as the applied current density increased and the biocide concentration decreased. The kinetic studies revealed that the biocide decay follows a pseudo-first-order rate. The apparent rate constant for the oxidation of isothiazolin-3-ones was determined to be 2.65 × 10^− 4 s^− 1 at an applied current density of 25 mA cm^− 2 in the presence of 0.1 mol dm^− 3 Na₂SO₄ at pH 6.0. A poor mineralization efficiency was observed in the case of NaCl as supporting electrolyte which cause in-situ generation of chlorine based mediated oxidants such as Cl₂ and OCl⁻ which have negligible influence in mineralizing the isothiazolin-3-ones compared to peroxodisulfate (S₂O₈^2 −) oxidants that formed in the case of Na₂SO₄. The oxidizing ability of the BDD anode was compared with those of Pt and glassy carbon anodes under similar experimental conditions.     

Thermodynamic parameters of activation for photodegradation of phenolics

The photocatalytic degradation of three phenolics namely phenol, 4-chlorophenol and 4-nitrophenol were carried out in aerated aqueous suspension of TiO₂ irradiated by ultraviolet light. The influence of temperature at optimized pH and TiO₂ concentration was studied. The degradation kinetics were somewhat accelerated by increase in temperature in the range 25–45 °C and apparent activation energy was calculated to be 9.68–21.44 kJ mol^?1. Thermodynamic parameters of activation were also assessed for the degradation process. Formation of acidic species results in decrease in pH of solution. The appearance and the evolution of main intermediate species like hydroquinone, benzoquinone and catechol during the degradation process were computed by UV–vis spectral analysis.     

Azo dyes sulphur-bridged ruthenium–molybdenum complexes: Synthesis,spectroscopic and electrochemical characterization of [(α/β-NaiR′)2Ru(μ-S)2Mo(OH)2]

The reaction of azo dye complexes ctc-[Ru(α/β-NaiR′)₂Cl₂] (1) [α/β-NaiR′ = 1-alkyl-2-α/β-(naphthylazo)imidazole, C₁₀H₇–NN–C₃H₂NN(1)–R′, R′ = Me (2), Et (3), Bz (4)] with (NH₄)₂MoS₄ in aqueous MeOH afforded reddish violet colour mixed ligand complexes of the type [(α/β-NaiR′)₂Ru(μ-S)₂Mo(OH)₂] (2–4). In complexes 2–4 the terminal MoS bonds of the MoS₄²⁻ unit become hydroxylated and the molybdenum ion is reduced from the starting Mo^VI in MoS₄²⁻ to Mo^IV in the final product (2–4). The solution electronic spectra exhibit a strong MLCT band at 550–570 nm in DCM. Cyclic voltammograms show a Ru(III)/Ru(II) couple at 1.10–1.4 V, irreversible Mo(IV)/Mo(V) oxidations in the 1.66–1.72 V range, along with four successive reversible ligand reductions in the range −0.45 to −0.67 V (one electron), −0.82 to −1.12 V (one electron), and −1.44 to −1.90 V (simultaneously two electrons).     

Theoretical investigation of mechanical and thermal properties of MPO4 (M = Al,Ga)

Minimum lattice thermal conductivities and mechanical properties of polymorphous MPO₄ (M = Al, Ga) are investigated by first principles calculations. The theoretical minimum thermal conductivities are found to be 1.02 W (m K)^?1 for α-AlPO₄, 1.20 W (m K)^?1 for β-AlPO₄, 0.87 W (m K)^?1 for α-GaPO₄ and 0.88 W (m K)^?1 for β-GaPO₄. The lower thermal conductivities in comparison to YSZ can be attributed to the lattice phonon scattering due to the framework of heterogeneous bonds. In addition, the low shear-to-bulk modulus ratio for both β-AlPO₄ (0.38) and β-GaPO₄ (0.30) is observed. Our results suggest their applications as light-weight thermal insulator and damage-tolerant/machinable ceramics.     

Syntheses,structures and properties of two copper-2-picolinic-acid germanomolybdate hybrids with mixed organic components

Two inorganic–organic hybrids based on saturated α-Keggin-type germanomolybdates with mixed organic components [H₂DAP]₂[Cu(PA)₂][α-GeMo₁₂O₄₀]·8H₂O (1) and [NH₄]₂[H₈L] [Cu(PA)₂][α-GeMo₁₂O₄₀]·8H₂O (2) (DAP = 1.2-diaminopropane, HPA = 2-picolinic acid, H₆L = 1,3-bis[tris(hydroxymethyl)methylamino]propane) have been obtained via the conventional aqueous solution method and structurally characterized by elemental analysis, IR spectra, thermogravimetric (TG) analysis and single-crystal X-ray diffraction. 1 stands for an one-dimensional linear organic–inorganic hybrid germanomolybdate chain constructed from classical Keggin [α-GeMo₁₂O₄₀]^4 − units supported by [Cu(PA)₂] linkers, whereas 2 represents the first hybrid germanomolybdate containing the H₆L component and consists of a saturated α-Keggin polyanion [α-GeMo₁₂O₄₀]^4 −, a diprotonated [H₈L]^2 + cation, a copper coordination complex [Cu(PA)₂], two ammonium cations [NH₄]⁺ and eight lattice water molecules. Furthermore, the electrochemical and electrocatalytic properties of 1 and 2 have also been investigated in detail.     

Enrichment of Nigella damascena extract with volatile compounds using supercritical fluid extraction

β-Elemene, germacrene A and damascenine were extracted from lady-in-a-mist (Nigella damascena L.) seeds with supercritical carbon dioxide at 10–30 MPa and 40–60 °C. The influence of supercritical fluid extraction (SFE) conditions on the yield and concentration of volatiles in the extract and the extraction kinetics were studied. The extraction yields and the apparent solubility of volatile compounds increased with increasing density of CO₂. The highest total yield was obtained at 30 MPa and 40 °C but the selectivity for volatiles was low under these conditions. With respect to both yield of volatiles and their concentration in extract, the best results were at 12 MPa and 40 °C, either with one separator or with additional separator maintained at 5 MPa and 25 °C. The yields of β-elemene, germacrene A and damascenine reached 0.72, 3.31 and 3.65 mg g⁻¹ and their concentration in the extract was 2.62, 12.04 and 13.28 wt.%, respectively. Though the yields of germacrene A and damascenine were by about 20% higher using Soxhlet extraction with hexane than using SFE, their concentration in the extract where fatty oil prevailed was only 1.19 and 1.20 wt.%, respectively. Under the conditions of hydrodistillation, partial conversion of germacrene A to β-elemene occurred and its yield was higher than using the other methods but the composition of volatiles in the SFE extracts better corresponds to the original raw material.     

Effect of carbon doping on WO3/TiO2 coupled oxide and its photocatalytic activity on diclofenac degradation

The improved photocatalyst carbon-doped WO₃/TiO₂ mixed oxide was synthesized in this study using the sol–gel method. The catalyst was thoroughly characterized by X-ray diffraction (XRD), diffuse reflectance UV–vis spectroscopy, N₂ adsorption desorption analysis, scanning electron microscopy coupled with energy dispersive X-ray analysis (SEM/EDX), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The photocatalytic efficiency of the prepared materials was evaluated with respect to the degradation of sodium diclofenac (DCF) in a batch reactor irradiated under simulated solar light. The progress of the degradation process of the drug was evaluated by high-performance liquid chromatography (HPLC), whereas mineralization was monitored by total organic carbon analysis (TOC) and ion chromatography (IC). The results of the photocatalytic evaluation indicated that the modified catalyst with tungsten and carbon (TWC) exhibited higher photocatalytic activity than TiO₂ (T) and WO₃/TiO₂ (TW) in the degradation and mineralization of diclofenac (TWC>TW>T). Complete degradation of diclofenac occurred at 250 kJ m⁻² of accumulated energy, whereas 82.4% mineralization at 400 kJ m⁻² was achieved using the photocatalytic system WO₃/TiO₂-C. The improvement in the photocatalytic activity was attributed to the synergistic effect between carbon and WO₃ incorporated into the TiO₂ structure.     

Syntheses,crystal structures,spectroscopy, and catalytic properties of two nickel-based hexaazamacrocyclic complexes with carboxylate ligands

Two new hexaazamacrocyclic nickel(II) complexes with the formula [NiL¹(4-nba)₂] (1) and [NiL²(sal)₂] (2) (L¹ = 3,10-dioctyl-1,3,5,8,10,12-hexaazacyclotetradecane, L² = 3,10-diisobutyl-1,3,5,8,10,12-hexaazacyclotetradecane, 4-nba = p-nitrobenzoate, and sal = salicylate) were synthesized at room temperature. These complexes were characterized by physico-chemical and spectroscopic methods as well as single-crystal X-ray diffraction analysis. The coordination geometry in complexes 1 and 2 exhibit a distorted octahedron around the nickel(II) ion with hexaazamacrocyclic unit in the equatorial positions and two p-nitrobenzoate (or salicylate) anions in the axial positions. The degradation of methyl orange by potassium persulfate (KPS) in the presence of complex 1 (or 2) oxidation system occurred to near completion in 60 min compared to only 55% with KPS alone under UV light irradiation. Thus, both complexes in cooperation with KPS could be an attractive choice for degradation of organic pollutants for environmental remediation.     

Sol–gel preparation of titania multilayer membrane for photocatalytic applications

The main goal of the present study is to prepare a titania membrane with high permeability and photocatalytic activity for environmental applications. In this investigation a mesoporous titania multilayer membrane on alumina substrate is successfully fabricated via the sol–gel processing method. The prepared titania polymeric sol for the membrane top layer has an average particle size of 11.7 nm with a narrow distribution. The resulting TiO₂ multilayer membrane exhibits homogeneity with no cracks or pinholes, small pore size (4 nm), large specific surface area (83 m²/g), and small crystallite size (10.3 nm).The permeability and photocatalytic properties of the titania membrane were measured. The photoactivity of the titania membrane was examined to be 41.9% after 9 h UV irradiation based on methyl orange degradation. This measurement indicates high photocatalytic activity per unit mass of the catalyst. Through multilayer coating procedure, the photocatalytic activity of the membrane improved by 60% without sacrificing the membrane permeation. The prepared TiO₂ photocatalytic membrane has a great potential in developing high efficient water treatment and reuse systems due to its multifunctional capability such as decomposition of organic pollutants and physical separation of contaminants.     

Degradation of hydrophobic organic pollutants by titania pillared fluorine mica as a substrate specific photocatalyst

The photocatalytic degradation of a highly hydrophobic and stable organic pollutant, γ-hexachlorocyclohexane (γ-HCH), was performed in aqueous suspended mixture of TiO₂-containing catalysts. Unlike most of the organic pollutants, γ-HCH was very stable under the conventional photocatalytic condition with TiO₂ (P25). Among various catalysts, TiO₂ pillared fluorine mica (Ti-mica) showed highest activity. The effect of preparation method of Ti-mica was also examined. The hydrothermal treatment increased the crystallinity of anatase pillar of Ti-mica, though the treatment at high temperature resulted in a decrease in the surface area and an increase in the pore size. Consequently, Ti-mica treated at lowest temperature (373 K), Ti-mica-373, was the most effective photocatalyst. The catalytic activity of TiO₂ and Ti-mica-373 was compared for 13 kinds of organic compounds with various hydrophobicity. Ti-mica-373 showed 5–66 times higher rate than TiO₂ for the degradation of hydrophobic organic pollutants (α, β, γ and δ-HCH, trans- and cis-chlordane, DDE, DDD and DDT) of low concentration (10 ppb). In contrast, TiO₂ showed higher rate than Ti-mica-373 for the degradations of less hydrophobic compounds (benzonitrile, chlorobenzene, 4-chloroacetophenone and 4-chloronitrobenzene). Over TiO₂-mica-373, organic compounds with higher log P_OW value, i.e. more hydrophobic compounds, were decomposed with higher rate. A positive effect of the fluorine mica support is suggested to be caused by the interaction of hydrophobic reactant with the hydrophobic interlayer surface of pillared-clay.     

A new polymorph telluridoindate [In(en)3][In5Te9(en)2] with photocatalytic properties

A new polymorph telluridoindate [In(en)₃][In₅Te₉(en)₂] (denoted as β-type, en = ethylenediamine) has been solvothermally synthesized and characterized. The crystal data for the β-type are listed as follows: monoclinic, space group Cc (No. 9), a = 11.642(2), b = 20.421(4), c = 17.577(4) Å, β = 92.20(3)°, V = 4175.7(14) Å³, Z = 4. The β-type contains organic-decorated [In₄Te₉(en)]^6 − supertetrahedral cluster and [InTe₃(en)]^3 − tetrahedron, which are interconnected to form an organic-decorated 2-D telluridoindate layer of [In₅Te₉(en)₂^3 −]_n with 9-membered rings. Two relevant conformers of telluridoindates are compared with each other. The β-type indicates absorption edge at 2.23 eV and exhibits photocatalytic activity for degradation of methyl orange (MO).