UV-assisted degradation of propiconazole in a TiO2 aqueous suspension: identification of transformation products and the reaction pathway using GC/MS

Photocatalytic degradation of propiconazole, a triazole pesticide, in the presence of titanium dioxide (TiO₂) under ultraviolet (UV) illumination was performed in a batch type photocatalytic reactor. A full factorial experimental design technique was used to study the main effects and the interaction effects between operational parameters in the photocatalytic degradation of propiconazole in a batch photo-reactor using the TiO₂ aqueous suspension. The effects of catalyst concentration (0.15–0.4 gL^?1), initial pH (3–9), initial concentration (5–35 mg L^?1) and light conditions were optimised at a reaction time duration of 90 min by keeping area/volume ratio constant at 0.919 cm² mL^?1. Photocatalytic oxidation of propiconazole showed 85% degradation and 76.57% mineralisation under UV light (365 nm/30 Wm^?2) at pH 6.5, initial concentration 25 mg L^?1 and constant temperature (25 ± 1 °C). The Langmuir–Hinshelwood kinetic model has successfully elucidated the effects of the initial concentration on the degradation of propiconazole and the data obtained are consistent with the available kinetic parameters. The photocatalytic transformation products of propiconazole were identified by using gas chromatography–mass spectrometry (GC/MS). The pathway of degradation obtained from mass spectral analysis shows the breakdown of transformation products into smaller hydrocarbons (m/z 28 and 39).     

Synthesis of N-TiO2: Stability and Visible Light Activity for Aqueous Styrene Degradation

Nitrogen-doped TiO₂ (N-TiO₂) were prepared by the impregnation method using urea as a nitrogen source and TiO₂-P25 as precursor. N-TiO₂ was characterized by x-ray diffraction (XRD), UV–vis diffusion reflectance spectra (UV–vis DRS), Fourier transform infrared spectroscopy (FTIR), and x-ray photoelectron spectroscopy (XPS) techniques. XPS analysis indicates the incorporation of nitrogen in TiO₂ lattice as O–Ti–N linkage. DRS spectra reveal the extended absorption to the visible range. Photocatalytic performance of the N-TiO₂ was studied by testing the degradation rate of aqueous styrene under visible light. Also, the degradation kinetics of aqueous styrene and possibility of cyclic usage of N-TiO₂ were investigated.     

Degradation of ofloxacin by UVA-LED/TiO<Subscript>2</Subscript> nanotube arrays photocatalytic fuel cells

The degradation of ofloxacin (OFX) at low concentration in aqueous solution by UVA-LED/TiO₂ nanotube arrays photocatalytic fuel cells (UVA-LED/TiO₂ NTs PFCs) was investigated. TiO₂ nanotube arrays (TiO₂ NTs) photoanode prepared by anodization-constituted anatase–rutile bicrystalline framework. The results indicated that the degradation efficiency of OFX by UVA-LED/TiO₂ NTs PFC was significantly enhanced by 14.3% compared with UVA-LED/TiO₂ NTs photocatalysis. The pH affected the degradation efficiency markedly; the highest degradation efficiency (95.0%) and the pseudo-first-order reaction rate constant k value (0.049 min^?1) were achieved in neutral condition (pH 7.0). The degradation efficiency increased with the increasing concentration of dissolved oxygen (DO) in the UVA-LED/TiO₂ NTs PFC. The main reactive species of OFX degradation are positive holes (h⁺) and superoxide ion radicals (O ₂ ^·? ) in a DO sufficient condition. Furthermore, the possible pathways of OFX degradation were proposed.     

Photocatalytic degradation kinetics of methyl orange in TiO2–SiO2–NiFe2O4 aqueous suspensions

Photocatalytic degradation of methyl orange by TiO₂–SiO₂–NiFe₂O₄ suspensions was investigated. Adsorption studies revealed photocatalytic degradation occurred mainly on the surface of the TiO₂–SiO₂–NiFe₂O₄. The disappearance of the compound followed the zero-order kinetics according to the Langmuir–Hinshelwood model and the rate constant was 0.0035 mg L^?1 min^?1. The rate constant depended on the amount of photocatalyst, initial pH, and the presence of additional scavengers. ^?OH radicals and h⁺ had important roles in the photocatalytic degradation of methyl orange by TiO₂–SiO₂–NiFe₂O₄.     

Heterogeneous photocatalyzed degradation of a pesticide derivative, 3-chloro-4-methoxyaniline, in aqueous suspensions of titania

The photocatalyzed degradation of a pesticide derivative, 3-chloro-4-methoxyaniline (1), has been investigated in aqueous suspensions of titanium dioxide (TiO₂) and air as a function of irradiation time under a variety of conditions using UV?CVis spectroscopic and HPLC analysis techniques. The degradation kinetics were studied under different conditions such as types of TiO₂ powders, reaction pH, catalyst loading, substrate, and H₂O₂ concentrations. The photocatalyst Degussa P25 showed better photocatalytic activity for the degradation of the compound 1. Addition of hydrogen peroxide as an electron acceptor in addition to oxygen greatly enhanced the degradation rate of the compound 1. Higher degradation rates were observed at lower and higher pH values, i.e., 3.15 and 9.15, respectively. The optimal substrate concentration and catalyst loading for the degradation was found to be 0.6?mM with 1.5?g?L^?1. A probable pathway for the decomposition of compound 1 is proposed.     

Separation and Extraction of Uranium from Leach Liquor Containing Uranium and Molybdenum by Solvent Extraction with LIX 622N

The leach liquor (0.5 g/L Mo, 0.05 g/L U) obtained from the leaching process of molybdenum-uranium ore material was treated using solvent extraction to recover U(VI) by LIX 622N, which is a salicylaldoxime derivative. The influence of various basic variables such as pH, concentration of LIX 622N, temperature, different stripping reagents, phase ratio, and diluents was examined. Using 10% LIX 622N with the aqueous solution of equilibrium pH 6.0 and a phase ratio organic phase:aqueous phase (O:A) = 1:1, a two-stage McCabe-Thiele plot was constructed, which showed 99.9% of U extraction with no co-extraction of molybdenum. This was confirmed by a 6-cycle counter current simulation (CCS) study. The obtained data of temperature on the extraction of uranium showed that the extraction process is exothermic with enthalpy change of ?20.949 kJ mol^?1. The stripping of U(VI) was quantitative using 4 M H₂SO₄. The stable complex UO₂(HSO₄)R_org formed during extraction, which supports the cation exchange mechanism, and was confirmed by FTIR spectral analysis.      

Photocatalytic degradation of triazine dyes over N-doped TiO2 in solar radiation

Photocatalytic degradation of the reactive triazine dyes Reactive Yellow 84 (RY 84), Reactive Red 120 (RR 120), and Reactive Blue 160 (RB 160) on anatase phase N-doped TiO₂ in the presence of natural sunlight has been carried out in this work. The effect of experimental parameters like initial pH and concentration of dye solution and dosage of the catalyst on photocatalytic degradation have also been investigated. Adsorption of dyes on N-doped TiO₂ was studied prior to photocatalytic studies. The studies show that the adsorption of dyes on N-doped TiO₂ was high at pH 3 and follows the Langmuir adsorption isotherm. The Langmuir monolayer adsorption capacity of dyes on N-doped TiO₂ was 39.5, 86.0, and 96.3 mg g^?1 for RY 84, RR 120, and RB 160, respectively. The photocatalytic degradation of the dyes follows pseudo first-order kinetics and the rate constant values are higher for N-doped TiO₂ when compared with that of undoped TiO₂. Moreover, the degradation of RY 84 on N-doped TiO₂ in sunlight was faster than the commercial Aeroxide^® P25. However, the P25 has shown higher photocatalytic activity for the other two dyes, RR 120 and RB 160. The COD of 50 mg l^?1 Reactive Yellow-84, RR 120 and RB 160 was reduced by 65.1, 73.1, and 69.6 %, respectively, upon irradiation of sunlight for 3 h in the presence of N-doped TiO₂. The photocatalyst shows low activity for the degradation of RY 84 dye, when its concentration was above 50 mg l^?1, due to the strong absorption of photons in the wavelength range 200–400 nm by the dye solution. LC–MS analysis shows the presence of some triazine compounds and formimidamide derivatives in the dye solutions after 3 h solar light irradiation in the presence of N-doped TiO₂.     

Synthesis,Characterization, and Photocatalytic Properties of Ag/TiO2 Composite Nanofibers Prepared by Electrospinning

Ag nanoparticles (Ag NPs) embedded titanium dioxide (TiO₂) nanofibers were fabricated by colloidal sol process, electrospinning, and calcination technique. Calcination of the electrospun nanofibers were heat treated at 600°C for 180 minutes in air atmosphere. X-ray diffraction patterns exhibited that the anatase phase and silver coexisted in the resulted Ag NPs/TiO₂ nanofibers; transmission electron microscopy demonstrated Ag NPs well spread in the porous microstructure of composite fibers. The prepared nanofibers were utilized as photocatalyst for degradation of methyl orange. The degradation rate of methyl orange dye solution containing Ag/TiO₂ composite nanofibers is 99% only after irradiation for 3 hours. It is proposed that these new Ag NPs/TiO₂ composite nanofibers will have potential application in water pollution treatment.      

Direct fabrication of anatase TiO<Subscript>2</Subscript> hollow microspheres for applications in photocatalytic hydrogen evolution and lithium storage

Hollow titanium dioxide (TiO₂) microspheres were synthesized in one step by employing tetrabutyl orthotitanate (TBOT) as a precursor through a facile solvothermal method in the presence of NH₄HCO₃. XRD analysis indicated that anatase TiO₂ can be obtained directly without further annealing. TiO₂ hollow microspheres with diameters in the range of 1.0–4.0 μm were confirmed through SEM and TEM measurements. The specific surface area was measured to be 180 m² g^?1 according to the nitrogen adsorption–desorption isotherms. Superior photocatalytic performance and good lithium storage properties were achieved for resultant TiO₂ samples. The H₂ evolution rate of the optimal sample is about 0.66 mmol h^?1 after loaded with 1 wt.% Pt (20 mg samples). The reversible capacity remained 143 mAh g^?1 at a specific current of 300 mA g^?1 after 100 charge–discharge cycles. This work provides a facile strategy for the preparation of hollow titanium dioxide microspheres and demonstrates their promising photocatalytic H₂ evolution and the lithium storage properties.

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Graphical abstract Hollow titanium dioxide spheres are directly synthesized via a facile template-free solvothermal method with the presence of NH₄HCO₃ based on inside-out Ostwald ripening (see picture), and demonstrated both as a photocatalyst for water splitting and a promising anode material for lithium-ion batteries. Superior photocatalytic performance and excellent lithium storage properties are achieved for resultant TiO₂ hollow microspheres.

     

Extended Cauchy Model for Tunable Refractive Index of Titania Nanoparticles at Visible Region

The extended Cauchy model is derived based on the experimental data for describing the mass fraction-, crystallite size-, and calcination-dependent refractive index of anatase and rutile TiO₂ nanoparticles. This model fits the experimental data of TiO₂ nanoparticles well in the visible spectral region. There is a tunable correlation between the refractive index of TiO₂ nanoparticle and the anatase nanoparticle size at visible region. Moreover, there is a near correlation between experimental and calculated Abbe number at 588 nm.     

The role of counter-anions in photocatalytic reduction of Ni(II) with a trace amount of titania nanoparticles

The reduction of Ni(II) ion, originated from nitrate or sulfate salts, was investigated based on photo-generated electrons in UV-irradiated TiO₂ aqueous suspensions. Design of experiments, modeling, and process optimization were performed using central composite design of response surface methodology. Influence of pH, temperature, and nickel concentration was investigated based on percentage of reduction efficiency (RE). Under operating conditions of pH = 9.3, T = 40 °C, [Ni(II)]_o = 5 mg L^?1, [TiO₂] = 100 mg L^?1 and after 90 min treatments, 64.8 and 76.1 % RE were achieved for nitrate and sulfate counter-anions, respectively. The higher efficiency obtained with sulfate anion was attributed to the more ionic strength and its interaction with titania nanoparticles. Rate of Ni(II) ions reduction, originated from both of the nickel salts, obeys pseudo-first-order kinetic model. As a relevant criterion, the electrical energy consumption and other criteria were evaluated and were compared with other previously reported processes.     

HPLC Method for Monitoring of Degradation Products in Picoplatin Stability Study

An analytical method combining high-performance liquid chromatography (HPLC) with UV detection was developed for an easy and rapid assay determination of the anticancer drug picoplatin (=cis-[Pt(NH₃)(2-methylpyridine)Cl₂]) and its degradation products. An ion exchanger was used as the stationary phase with an aqueous solution of NaH₂PO₄ with pH adjusted to 3.0 with H₃PO₄ as the mobile phase. The calibration curve was linear within the concentration range of 0.10–0.50 g L^?1 (R ² ≥ 0.998). The limit of detection was 0.05 g L^?1 and limit of quantification was 0.09 g L^?1. The developed method was characterized with a high precision (≤6.0%, determined as RSD), an acceptable accuracy (the values of recovery were from intervals 98–103%). The developed method was used for assessing the stability of picoplatin during a stability study.     

Evaluation of gamma irradiation effect on physico-chemical properties of a mixed beverage based in soy milk and grape juice

The effects of the main operation variables on the electrochemical oxidation of simulated tributyl phosphate (TBP) waste by a boron-doped diamond anode are individually studied. The optimum operating conditions are obtained as follows: 4 g L^?1 initial TBP concentration, 180 min degradation time, 40 mA cm^?2 current density, 0.5 mol L^?1 Na₂SO₄ as the supporting electrolyte, and unadjusted pH of the aqueous phase. Under such conditions, a chemical oxygen demand (COD) removal ratio of 82.3% is achieved, and the energy consumption is 26.16 kWh m^?3. A degradation mechanism of TBP is tentatively proposed.     

Preconcentration and spectrophotometric determination of trace amount of formaldehyde using hollow fiber liquid-phase microextraction based on derivatization by Hantzsch reaction

Formaldehyde is known as a highly toxic compound to humans and identified as a carcinogenic substance. In this study, Hantzsch reaction was utilized for the derivatization of trace amounts of formaldehyde in aqueous samples with acetylacetone in the presence of ammonia to form an extractable colored product named 3,5-diacetyl 1,4-dihydrolutidine (DDL) and its further extraction using two-phase hollow fiber liquid-phase microextraction. The main experimental variables affecting the extraction performance were investigated and optimized. Under the optimum conditions (sample volume 12 mL; reaction temperature 70 °C; ammonium acetate buffer solution 4 mL 0.1 mol L^?1; acetylacetone 5 mL 0.15 mol L^?1; solvent octanol, salt concentration 20% (w/v) NaCl; pH of donor phase 7.0; stirring speed 400 rpm and extraction time 30 min), the linear dynamic range, limit of detection (LOD as 3S _b/m) and relative standard deviation (RSD %) of the proposed method were obtained as 5–250 μg L^?1 (r ² = 0.9979), 3.6 μg L^?1 and 2.5%, respectively. Finally, the applicability of the proposed method was examined, and very good results were obtained. The results confirmed the applicability of the proposed method as a versatile, low-cost and sensitive preconcentration method for determination of low concentrations of formaldehyde in aqueous solutions.     

Magnetic solid-phase extraction of Zineb by C18-functionalised paramagnetic nanoparticles and determination by first-derivative spectrophotometry

Fe₃O₄-SiO₂-C₁₈ paramagnetic nanoparticles have been synthesised and used as magnetic solid-phase extraction (MSPE) sorbent for the extraction of Zineb from agricultural aqueous samples under ultrasonic condition and quantified through a first-derivative spectrophotometric method. The produced magnetic nanoparticles were characterised by using scanning electron microscopy, X-ray diffraction spectroscopy, Fourier transform infrared spectroscopy and zeta potential reader. The Fe₃O₄-SiO₂-C₁₈ paramagnetic nanoparticles had spherical structures with diameters in the range of 198–201 nm. Further, MSPE was performed by dispersion of Fe₃O₄-SiO₂-C₁₈ paramagnetic nanoparticles in a buffered aqueous solution accompanied by sonication. Next, the sorbents were accumulated by applying an external magnetic field and were washed with 4-(2-pyridylazo) resorcinol-dimethyl sulfoxide solution, for the purpose of desorbing the analyte. The extraction conditions (sample pH, washing and elution solutions, amount of sorbents, time of extraction, sample volume and effect of diverse ions), as well as Zineb-PAR first-order derivative spectra, were also evaluated. The calibration curve of the method was linear in the concentration range of 0.055–24.3 mg L^?1 with a correlation coefficient of 0.991. The limit of detection and limit of quantification values were 0.022 and 0.055 mg L^?1, respectively. The precision of the method for 0.27 mg L^?1 solution of the analyte was found to be less than 3.2%. The recoveries of three different concentrations (0.27, 1.37 and 13.7 mg L^?1) obtained 98.3%, 98.5% and 96.0%, respectively. The proposed Fe₃O₄-SiO₂-C₁₈ paramagnetic nanoparticles were found to have the capability of reusing for 7.0 times.