Elucidation of methyl tert-butyl ether degradation with Fe/H2O2 by purge-and-trap gas chromatography-mass spectrometry

Degradation of methyl tert-butyl ether (MTBE) with Fe²⁺/H₂O₂ was studied by purge-and-trap gas chromatography-mass spectrometry. MTBE was degraded 99% within 120 min under optimum conditions. MTBE was firstly degraded rapidly based on a Fe²⁺/H₂O₂ reaction and then relatively slower based on a Fe³⁺/H₂O₂ reaction. The dissolved oxygen decreased rapidly in the Fe²⁺/H₂O₂ reaction stage, but showed a slow increase in the Fe³⁺/H₂O₂ reaction stage. tert-Butyl formate, tert-butyl alcohol, methyl acetate and acetone were identified as primary degradation products by mass spectrometry. A preliminary reaction mechanism involving two different pathways for the degradation of MTBE with Fe²⁺/H₂O₂ was proposed. This study suggests that degradation of MTBE can be achieved using the Fe²⁺/H₂O₂ process.     

Thermal degradation mechanism of highly filled nano-SiO2 and polybenzoxazine

Effects of high nano-SiO₂ loading (up to 30 mass%) on polybenzoxazine (PBA-a) thermal degradation kinetics have been investigated using nonisothermal thermogravimetric analysis (TG). The DTG curves revealed three stages of thermal decomposition process in the neat PBA-a, while the first peak at low temperature was absent in its nanocomposites. As a consequence, the maximum degradation temperature of the nanocomposites shifted significantly to higher temperature as a function of the nano-SiO₂ contents. Moreover, the degradation rate for every degradation stage was found to decrease with the increasing amount of the nano-SiO₂. From the kinetics analysis, dependence of activation energy (E _a) of the nanocomposites on conversion (α) suggests a complex reaction with the participation of at least two different mechanisms. From Coats–Redfern and integral master plot methods, the average E _a and pre-exponential factor (A) of the nanocomposites showed systematically higher value than that of the PBA-a, likely from the shielding effect of the nanoparticles. The main degradation mechanism of the PBA-a was determined to be a random nucleation type with one nucleus on the individual particle (F1 model), while that of the PBA-a nanocomposite was the best described by diffusion-controlled reaction (D3 model).     

Full factorial experimental design applied to oxalic acid photocatalytic degradation in TiO2 aqueous suspension

Full factorial experimental design technique was used to study the main effects and the interaction effects between operational parameters in the photocatalytic degradation of oxalic acid in a batch photo-reactor using TiO₂ aqueous suspension. The important parameters which affect the removal efficiency of oxalic acid such as agitation, initial concentration, volume of the solution and TiO₂ dosage were investigated. The parameters were coded as X₁, X₂, X₃ and X₄, consecutively, and were investigated at two levels (−1 and +1). The effects of individual variables and their interaction effects for dependent variables, namely, photocatalytic degradation efficiency (%) were determined. From the statistical analysis, the most effective parameters in the photocatalytic degradation efficiency were initial concentration and volume of solution. The interaction between initial concentration, volume of solution and TiO₂ dosage was the most influencing interaction. However, the interaction between agitation, initial concentration and volume of solution was the least influencing parameter.     

Effect of Salts (NaCl and Na2CO3) on Callus and Suspension Culture of Stevia rebaudiana for Steviol glycoside Production

Steviol glycosides are natural non-caloric sweeteners which are extracted from the leaves of Stevia rebaudiana plant. Present study deals the effect of salts (NaCl and Na₂CO₃) on callus and suspension culture of Stevia plant for steviol glycoside (SGs) production. Yellow-green and compact calli obtained from in vitro raised Stevia leaves sub-cultured on MS medium supplemented with 2.0 mg l^?1 NAA and different concentrations of NaCl (0.05–0.20 %) and Na₂CO₃ (0.0125–0.10 %) for 2 weeks, and incubated at 24?±?1 °C and 22.4 μmol m^?2 s^?1 light intensity provided by white fluorescent tubes for 16 h. Callus and suspension biomass cultured on salts showed less growth as well as browning of medium when compared with control. Quantification of SGs content in callus culture (collected on 15th day) and suspension cultures (collected at 10th and 15th days) treated with and without salts were analyzed by HPLC. It was found that abiotic stress induced by the salts increased the concentration of SGs significantly. In callus, the quantity of SGs got increased from 0.27 (control) to 1.43 and 1.57 % with 0.10 % NaCl, and 0.025 % Na₂CO₃, respectively. However, in case of suspension culture, the same concentrations of NaCl and Na₂CO₃ enhanced the SGs content from 1.36 (control) to 2.61 and 5.14 %, respectively, on the 10th day.     

Application of NO2/supercritical CO2 system for safe and selective nitration of adamantanes and tertiary alkyl bromides

A concise safe approach for selective nitration and nitroxylation of tert-alkanes, in particular adamantane, and tert-alkyl bromides utilizing NO₂ in supercritical CO₂ medium has been established. Major reaction products were tert-alkyl nitro compounds and tert-alkyl nitrates depending on the reaction conditions.     

Photodegradation of aromatic amines by Ag-TiO2 photocatalyst

The photocatalytic degradation of ortho, para and meta-nitroanilines (ONA, PNA and MNA) was investigated by Ag-TiO₂ suspension. The effect of some parameters such as the amount of photocatalyst, irradiation time of UV light, flow rate of O₂, pH, and temperature for the Ag-TiO₂ photocatalyst was also examined. Degradation of amines was small when the reaction was carried out in the absence of photocatalyst, and negligible in the absence of the UV light. Degradation rate of aniline derivatives decreases with increasing O₂ in the system. The effect of pH indicated that effective degradation occurred in alkaline conditions. Degradation kinetics of these aromatic amines can be described by Langmuir-Hinshelwood equation and shows pseudo-first order law.     

γ-Radiolysis of aqueous 2-chloroanisole

The radiation-induced degradation of 2-chloroanisole (2-ClAn) is investigated under various experimental conditions in neutral aqueous media as a function of absorbed radiation dose. The initial yields (G_i-values) of substrate degradation as well as those of the resulting major products were determined by HPLC analysis. Probable reaction mechanisms are suggested.     

Preparation of meso-substituted trans-A2B-corroles in ionic liquids

A new and simple method for the preparation of meso-substituted trans-A₂B-corroles was developed by using ionic liquid as reaction medium. The reaction can be performed to offer the desired corroles with reasonable to satisfied yields.     

Ultrasound-assisted fabrication and characterization of a novel UV-light-responsive Er2Cu2O5 semiconductor nanoparticle Photocatalyst

The photocatalytic procedure is one of the most favorable methods for the elimination of poisonous organic dyes to achieve clean drinking water. In this research, a fast sonochemistry method was accomplished to attain Er₂Cu₂O₅ (ECO) nanoparticles with a progressive photo-degradation catalytic routine. Tetraethylenepentamine (TEPA) was operated as both alkaline and complexing agents to control growth of designed nuclei due to the formation of hydrogen bonds between active surface groups of TEPA and nuclei and, lastly stop nano-product accumulation. The ultrasonic time and power factors in sonochemistry reaction were improved to control the final nanostructures properties. The surface features of products were measured via diverse characterization systems of spectroscopic and microscopic. The elimination of dissimilar artificial dyes was carried out through Er₂Cu₂O₅ nanoparticle catalysts. The outcome of altering of artificial pollutant, pollutant concentration, scavenger, nano-catalyst dosage and solution pH was titled on the proficiency of nano-catalyst utility. Optimized Er₂Cu₂O₅ nanoparticles have an efficiency of 97% for degradation of erythrosine dye in an acidic medium. The possible mechanism of deletion dye by photocatalytic purpose was studied and concluded that ^?O₂^– radicals help UV-degradation of contamination.     

[bmim]BF4/[Cu(Im12)2]CuCl2 as a novel catalytic reaction medium for click cyclization

Herein, a new application of an ionic liquid containing copper (I), ([Cu(Im¹²)₂]CuCl₂), is introduced. This ionic liquid was used as an efficient catalyst for the click cyclization between organic azides and terminal alkynes in various solvents. Then, the mixture of [bmim]BF₄/[Cu(Im¹²)₂]CuCl₂ was used as a green catalytic medium for the multicomponent click synthesis of 1,4-disubstituted-1H-1,2,3-triazoles from α-halo ketones. The reactions were performed efficiently in this mixture and excellent yields were obtained in all cases. This catalytic reaction medium was recycled five times without significant loss of activity.     

ZnO-Bi2O3/graphitic carbon nitride photocatalytic system with H2O2-assisted enhanced degradation of Indigo carmine under visible light

Indigo carmine in aqueous solution was effectively degraded using ZnO-Bi₂O₃/Graphitic Carbon Nitride heterojunction structure by visible light/H₂O₂ system. The mechanism of photocatalytic degradation of Indigo carmine shows the responsible species for the degradation of Indigo carmine in the ZnO-Bi₂O₃-xC₃N₄/H₂O₂/visible light system (x = 0, 1, 2, and 3) is the hydroxyl radicals which were generated from the reaction of e⁻ and h⁺ with H₂O₂. Under optimal conditions, ZnO-Bi₂O₃-2C₃N₄/H₂O₂/Vis system degraded more than 93% of Indigo carmine in 180 min. Besides, the kinetic of the photocatalytic process was detailed. These results demonstrate that the ZnO-Bi₂O₃-2C₃N₄/H₂O₂/visible light system may become a promising approach to achieve efficient environmental remediation as an environmentally friendly oxidant.     

Kinetics of tartrazine photodegradation by UV/H2O2 in aqueous solution

In the present work, kinetics of tartrazine decay by UV irradiation and H₂O₂ photolysis, and the removal of total organic carbon (TOC) under specific experimental conditions was explored. Irradiation experiments were carried out using a photoreactor of original design with a low-pressure Hg vapour lamp. The photodegradation rate of tartrazine was optimised with respect to the H₂O₂ concentration and temperature for the constant dye concentration of 1.035 × 10^?5 M. Tartrazine degradation and the removal of TOC followed the pseudo-first-order kinetics. The much higher k _obs value for tartrazine degradation (7.91 × 10^?4 s^?1) as compared with the TOC removal (2.3 × 10^?4 s^?1) confirmed the presence of reaction intermediates in the solution.     

The preparation,characterization, photoelectrochemical and photocatalytic properties of lanthanide metal-ion-doped TiO2 nanoparticles

Lanthanide metal-ion-doped TiO₂ nanoparticles were prepared with hydrothermal method and characterized with X-ray diffraction (XRD), transmission electron microscopy (TEM), inductively coupled plasma (ICP) and fluorescence spectrum. The results showed that a small part of metal ions entered into the lattice of TiO₂ and others adsorbed on the surface of TiO₂. The photoelectrochemical and photocatalytic properties of these lanthanide metal-ion-doped TiO₂ nanoparticles were investigated and the results showed that the photoresponse of Eu³⁺-, La³⁺-, Nd³⁺- and Pr³⁺-doped TiO₂ electrodes were much larger and that of Sm³⁺-doped TiO₂ electrode was a little larger than that of undoped TiO₂ electrode, indicating that the photogenerated carriers were separated more efficiently in Eu³⁺-, La³⁺-, Nd³⁺- and Pr³⁺-doped TiO₂ nanoparticles than in undoped TiO₂ nanoparticles. The photocatalytic degradation of rhodamine B (RB) was conducted in the suspension of lanthanide metal-ion-doped TiO₂ nanoparticles, and its first-order reaction rate constant (k) and average initial rate (r_ini) were significantly higher in the presence of Eu³⁺-, La³⁺-, Nd³⁺- and Pr³⁺-doped TiO₂ nanoparticles than those in the presence of undoped TiO₂ nanoparticles. The enhanced photocatalytic degradation rate of RB in the presence of Eu³⁺-, La³⁺-, Nd³⁺- and Pr³⁺-doped TiO₂ nanoparticles is attributed to increased charge separation in these systems. The effect of the content of La³⁺ on the reaction parameters (k and r_ini) was also investigated and the result showed that there was an optimal value (ca. 0.5%) of the content of La³⁺ to make the rate constant (k) and average initial rate (r_ini) reach the maxima.     

Degradation of n-butylparaben and 4-tert-octylphenol in H2O2/UV system

The degradation of two endocrine disrupting compounds: n-butylparaben (BP) and 4-tert-octylphenol (OP) in the H₂O₂/UV system was studied. The effect of operating variables: initial hydrogen peroxide concentration, initial substrate concentration, pH of the reaction solution and photon fluency rate of radiation at 254 nm on reaction rate was investigated. The influence of hydroxyl radical scavengers, humic acid and nitrate anion on reaction course was also studied. A very weak scavenging effect during BP degradation was observed indicating reactions different from hydroxyl radical oxidation. The second-order rate constants of BP and OP with OH radicals were estimated to be 4.8×10⁹ and 4.2×10⁹ M^?1 s^?1, respectively. For BP the rate constant equal to 2.0×10¹⁰ M^?1 s^?1was also determined using water radiolysis as a source of hydroxyl radicals.     

Response Surface Methodology: Photocatalytic Degradation Kinetics of Basic Blue 41 Dye Using Activated Carbon with TiO2

Water decontamination still remains a major challenge to some developing countries not having centralized wastewater systems. Therefore, this study presents the optimization of photocatalytic degradation of Basic Blue 41 dye in an aqueous medium by an activated carbon (AC)-TiO₂ photocatalyst under UV irradiation. The mesoporous AC-TiO₂ synthesized by a sonication method was characterized by X-ray diffraction (XRD) and Fourier-transform infrared (FTIR) spectroscopy for crystal phase identification and molecular bond structures, respectively. The efficiency of the AC-TiO₂ was evaluated as a function of three input variables viz. catalyst load (2–4 g), reaction time (15–45 min) and pH (6–9) by using Box-Behnken design (BBD) adapted from response surface methodology. Using color and turbidity removal as responses, a 17 run experiment matrix was generated by the BBD to investigate the interaction effects of the three aforementioned input factors. From the results, a reduced quadratic model was generated, which showed good predictability of results agreeable to the experimental data. The analysis of variance (ANOVA), signposted the selected models for color and turbidity, was highly significant (p < 0.05) with coefficients of determination (R²) values of 0.972 and 0.988, respectively. The catalyst load was found as the most significant factor with a high antagonistic impact on the process, whereas the interactive effect of reaction time and pH affected the process positively. At optimal conditions of catalyst load (2.6 g), reaction time (45 min), and pH (6); the desirability of 96% was obtained by a numerical optimization approach representing turbidity removal of 93% and color of 96%.     

Degradation and detoxification mechanisms of organophosphorus flame retardant tris(1,3-dichloro-2-propyl) phosphate (TDCPP) during electrochemical oxidation process

Electrochemical oxidation of aqueous tris(1,3-dichloro-2-propyl) phosphate (TDCPP) by using Ti/SnO₂-Sb/La-PbO₂ as anode was investigated for the first time, and the degradation mechanisms and toxicity changes of the degradation intermediates were further determined. Results suggested that electrochemical degradation of TDCPP followed pseudo-first-order kinetics, and the reaction rate constant (k) was 0.0332 min⁻¹ at the applied current density of 10 mA/cm² and Na₂SO₄ concentration of 10 mmol/L. There was better TDCPP degradation performance at higher current density. Free hydroxy radical (^•OH) was proved to play dominant role in TDCPP oxidation via quenching experiment, with a relative contribution rate of 60.1%. A total of five intermediates (M1, C₆H₁₁Cl₄O₄P; M2, C₃H₇Cl₂O₄P; M3, C₉H₁₆Cl₅O₅P; M4, C₉H₁₄Cl₅O₆P; M5, C₆H₁₀Cl₃O₆P) were identified, and the intermediates were further degraded prolonging with the reaction time. Flow cytometer results suggested that the toxicity of TDCPP and degradation intermediates significantly reduced, and the detoxification efficiency was achieved at 78.1% at 180 min. ECOSAR predictive model was used to assess the relative toxicity of TDCPP and the degradation intermediates. The EC₅₀ to green algae was 3.59 mg/L for TDCPP, and the values raised to 84, 574, 54.6, 391, and 8920 mg/L for M1, M2, M3, M4, and M5, respectively, indicating that the degradation intermediates are less toxic or not toxic. Electrochemical advanced oxidation process is a valid technology to degrade TDCPP and pose a good detoxification effect.     

Synthesis and properties of titanium glycolate Ti(OCH2CH2O)2

A new efficient method for the synthesis of extended micro-and nano-sized crystals (whiskers, fibers) of titanium glycolate Ti(OCH₂CH₂O)₂ has been suggested. The method implies the reaction of hydrated titanium dioxide with ethylene glycol on heating in air. Thermolysis of Ti(OCH₂CH₂O)₂ in air gives titanium dioxide as anatase (400–500°C) and rutile (T > 700°C), the morphology of titanium glycolate crystals being inherited by the oxide. The pseudocrystals of the thermolysis product in an inert gas medium (T = 500–950°C) represent aglomeration of nano-sized titanium dioxide particles and amorphous carbon. At temperatures up to 1300°C, the formation of the TiO_2?x C _x phase with a rutile structure is probable. In a wet air environment, titanium glycolate is partially hydrolyzed to give TiO _x (OCH₂CH₂O)_2?2x (OH)_2x ·xH₂O (0 ≤ x ≤ 1) and on keeping in water at room temperature, ethylene glycol is completely displaced from the crystals. This process is also not accompanied by changes in the particle morphology.     

Hydroesterification of styrene using an in situ formed Pd(OTs)2(PPh3)2 complex catalyst

Hydroesterification of styrene to 3-phenyl propionate 1, and 2-phenyl propionate 2, has been studied using a Pd(OTs)₂(PPh₃)₂ catalyst formed in situ from Pd(OAc)₂, PPh₃ and p-toluenesulfonic acid (p-tsa). Because of the weakly coordinating properties of the TsO⁻ ligand, the catalyst has vacant coordination sites capable of easy activation of reactants. The presence of water is found to be necessary for the reaction and hydrogen enhances the catalytic activity under certain conditions (with Pd:p-tsa=1). The beneficial effect of hydrogen, p-tsa and water is discussed in terms of favoring the formation of a Pd–H species, which initiates the catalytic cycle through the insertion of styrene into this bond with formation of a Pd-alkyl intermediate, which inserts CO to give a Pd-acyl intermediate, which, upon nucleophilic attack of the alkanol on the carbon atom of the acyl ligand, yields the final product and the starting hydride back to the catalytic cycle. p-tsa would favor the formation of a Pd–H species by reactivating any Pd(0) species that may form during the course of catalysis. Water would favor the formation of a Pd–H species through a reaction closely related to the water–gas shift reaction. The effect of various ligands, promoters, solvents and alcohols on catalytic activity as well as selectivity pattern has been studied. Regioselectivity to the branched product, 2, increases with decrease in basicity of the phosphorous ligands as well as steric bulk around the palladium center and polarity of the medium.     

Cooperative coupling of photocatalytic production of H2O2 and oxidation of organic pollutants over gadolinium ion doped WO3 nanocomposite

This work reported the lanthanide ion (Gd³⁺) doped tungsten trioxide (Gd-WO₃) nanocrystal for remarkable promoted photocatalytic degradation of organic pollutants and simultaneous in-situ H₂O₂ production. With doped lanthanide ion (Gd³⁺), Gd-WO₃ showed a much broad and enhanced solar light absorption, which not only promoted the photocatalytic degradation efficiency of organic compounds, but also provided a suitable bandgap for direct reduction of oxygen to H₂O₂. Additionally, the isolated Gd³⁺ on WO₃ surface can efficiently weaken the *OOH binding energy, increasing the activity and selectivity of direct reduction of oxygen to H₂O₂, with a rate of 0.58 mmol L⁻¹ g⁻¹ h⁻¹. The in-situ generated H₂O₂ can be subsequently converted to ^•OH based on Fenton reaction, further contributed to the overall removal of organic pollutants. Our results demonstrate a cascade photocatalytic oxidation-Fenton reaction which can efficiently utilize photo-generated electrons and holes for organic pollutants treatment.     

Kinetic studies of direct blue photodegradation over flower-like TiO<Subscript>2</Subscript>

The kinetics of photocatalytic oxidation reaction for direct blue solution was studied by using flower-like TiO₂ under the irradiation of ultraviolet (UV) light. A series of possible affecting factors were studied, including pH value, the additive amount of light catalyst, H₂O₂ and with or without Ag modification. The kinetics of photocatalytic degradation under UV was found following a pseudo-second-order reaction kinetic model with high regression coefficients (R ²). It has been demonstrated that the initial concentration and its related factors have influenced the photocatalytic degradation efficiency and corresponding kinetic parameters. Also, the kinetic parameter k is increasing with the degradation efficiency.