Search

Abstract: The pyrolysis behavior of polyvinyl chloride (PVC) in the presence of commercially available oxides catalysts was investigated using thermogravimetry. The pyrolysis proceeded under a heating rate of 5°C/min in the temperature range of 200–650°C. The thermogravimetric properties in terms of reduction in maximum degradation temperature and percent conversion were studied. The silica gel mesoporous catalyst, with a greater pore size and surface area, was found to be the most active materials in terms of reduction in maximum degradation temperature and increase in percent conversion. The alumina acidic, silica ppt, and alumina neutral catalysts also showed good results; however, their effects were less pronounced as compared to silica gel. The effects of these different catalysts show that surface area, pore size, and number of acidic sites are found to be the major factors for the energy efficient degradation of polymers. [ABSTRACT FROM AUTHOR]

Abstract: The thermal degradation kinetics of powder isotactic polypropylene was investigated in a thermobalance system, at non‐isothermal heating conditions with heating rate of 5, 10, 15, and 20°C min−1 in the temperature range of 30–600°C under nitrogen atmosphere. The apparent activation energy (Ea) was determined using Ozawa–Flynn–Wall, Tang Wanjun, and Coats–Redfern (modified) methods. The apparent activation energies range from 61.3 to 110.9 kJ mol−1. Increasing the heating rate shifted the Tmax to a higher level. The lower activation energy observed indicates the breakage of the bonds at weak links. Moreover, the values of activation energy are significantly controlled by the heating rate, level of conversion, and calculation technique. A comparison among the different techniques has been made on the basis of the apparent activation energy from the TG data. The activation energies determined by all the three methods are in good agreement with each other. Furthermore, the pyrolysis of model polypropylene was carried out over the temperature range 350–415°C in a salt bath using Pyrex reaction vessel. The gaseous fraction produced was collected in gas sampling bag and monitored gas chromatographically. The major hydrocarbons detected were methane, propylene, propane, 2‐methylpentane, 2,4 dimethylpentane, and 2,4 dimethylheptane. [ABSTRACT FROM AUTHOR]

In the present research work the degradation of acid yellow 17 (AY 17) by H2O2/Fe2+ was investigated. The effect of various conditions such as pH value, temperature, conc. of H2O2, Fe2+, conc. of AY 17 were studied. Additionally the scavenging effects of various anions such as Cl−, SO42−, CO32− and HCO3−, on percent degradation of AY 17 were examined. It was found that these anions decrease percent degradation as well as rate of degradation reaction. The optimum conditions were determined as [AY 17]=[Fe2+]=0.06 mM [H2O2]=0.9 mM, and pH 3.0 for 60 min of reaction time. It was found that at optimum conditions 89% degradation of AY17 was achieved. The degradation kinetics of AY17 followed pseudo-first-order reaction kinetics. Thermodynamic studies under natural conditions showed positive value of ∆H (enthalpy) which indicates the degradation process is endothermic. [ABSTRACT FROM AUTHOR]

This study investigates the decomposition of clofibric acid (CLF) by different advanced oxidation processes (AOPs), such as UV (254nm), VUV (185 nm), UV / TiO2 and VUV / TiO2. The removal efficiencies of applied AOPs were compared in the presence and absence of dissolved oxygen. The removal efficiency of the studied AOPs towards degradation of CLF were found in the order of VUV / TiO2 + O2 > VUV/TiO2 + N2 > VUV alone > UV / TiO2 + O2 > UV / TiO2 +N2 > UV alone. The decomposition kinetics of CLF was found to follow pseudo-first order rate law. VUV / TiO2 process was found to be most cheap and effective one for decomposition of CLF as compared to other applied AOPs in terms of electrical energy per order. Degradation products resulting from the degradation processes were also investigated using UPLC-MS /MS, accordingly degradation pathway was proposed. [ABSTRACT FROM AUTHOR]

This study reports the efficiency of gamma-ray irradiation to degrade quinolone antibiotic, norfloxacin, in aqueous solution. Laboratory batch experiments were conducted to determine the 'pseudo-first' order degradation kinetics of norfloxacin in the concentration ranges of 3.4-16.1 mg L by gamma-ray irradiation. The dose constant was found to be dependent on the initial concentration of norfloxacin and gamma-ray irradiation dose rate ( D). The saturation of norfloxacin sample solutions with N, air or NO, and the presence of tert-butanol and 2-propanol showed that OH played more crucial role in the degradation of norfloxacin. The second order rate constants of OH, e, and H with norfloxacin were calculated to be 8.81 × 10, 9.54 × 10, and 1.10 × 10 M s, respectively. The effects of various additives including CO, HCO, NO, NO, and thiourea and the pH of the medium on the degradation of norfloxacin were also investigated. Norfloxacin degradation was lower in surface water and wastewater than in ultrapure water. Several degradation byproducts of norfloxacin were identified from which the possible degradation pathway was proposed. [ABSTRACT FROM AUTHOR]

The present study elaborates the removal of endosulfan, an emerging water pollutant and potential carcinogenic, in aerated solution. The influence of Cl, NO, NO, CO, HCO, SO, and humic acid was assessed on the radiolytic degradation of endosulfan. A strong inhibition on the radiolytic degradation of endosulfan was observed in the presence of NO, NO, and SO. Instead, a slight increase in the removal efficiency of endosulfan was observed at high concentrations of CO and HCO. The formation of CO in radiolytic degradation of endosulfan in the presence of CO and HCO was demonstrated by adding SO that rapidly react with CO. The results indicate that CO formed from the reactions of CO and HCO and commonly found in natural water can play an important role in the degradation of endosulfan and other sulfur containing electron-rich compounds. The study showed faster degradation of endosulfan at lower concentration compared to high concentration and removal was found to follow pseudo-first-order kinetic. Endosulfan ether was found as the main degradation product and degradation pathway was found to be initiated at the S=O bond of endosulfan. The efficiency of gamma irradiation in the removal of endosulfan was examined in terms of formation of short chain organic acids and chloride ion accumulation. [ABSTRACT FROM AUTHOR]

In the present study, a novel TiO2/Ti film with enhanced {001} facets was synthesized by the hydrothermal technique followed by calcination for studying the removal of bezafibrate (BZF), from an aqueous environment. The synthesized photocatalyst was characterized by FE-SEM, XRD, HR-TEM, and PL-technique. The second-order rate constant of •OH with BZF was found to be 5.66 × 109 M-1 s-1. The steady state [•OH] was measured as 1.16 × 10-11 M, on the basis of oxidation of terephthalic acid. The photocatalytic degradation of BZF followed pseudo-first-order kinetics according to the Langmuir-Hinshelwood model (k1 = 2.617 mg L-1 min-1 and k2 = 0.0796 (mg L-1)−1). The effects of concentration and the nature of various additives including inorganic anions (NO3-, NO2-, HCO3-, CO32-, Cl-) and organic species (fulvic acid) and initial solution pHs (2, 4, 6, 9) on photocatalytic degradation of BZF were investigated. It was found that the nature and concentration of studied additives significantly affected the photocatalytic degradation of BZF. The efficiency of the photocatalytic degradation process in terms of electrical energy per order was estimated. Degradation schemes were proposed on the basis of the identified degradation byproducts by ultraperformance liquid chromatography. [ABSTRACT FROM AUTHOR]

Titanium dioxide (TiO2) films with dominant {001} facets coated on a titanium sheet (Ti) were synthesized with the simple hydrothermal method by using Ti as the precursor and substrate. The effect of addition of isopropanol into the hydrothermal solution on the structure, photocatalytic activity, and stability of as-synthesized TiO2 films was investigated. The presence of isopropanol obviously influenced the microstructure of as-synthesized TiO2 films, which was converted from microspheres into irregular close stack of truncated tetrahedrons. And the percentage of exposed {001} facets calculated from the Raman spectra increased from 48.2% to 57%. Accordingly, the TiO2 films prepared with addition of isopropanol showed high and stable photocatalytic activity, which is nearly 2.6 times as that of the conventional P25 TiO2 coated on Ti-substrate. In addition, the photocatalytic activity of as-synthesized TiO2 films was greatly enhanced after calcination treatment at 600°C, which can be attributed to removal of fluoride ions and organic residuals adsorbed on the surface of the catalyst. Photoluminescence (PL) technique was used for the detection of produced hydroxyl radicals COH) on the surface of UV-illuminated TiO2 using terephthalic acid as probe molecule. The photocatalytic degradation intermediates of bezafibrate were analyzed by an ultraperformance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS), and accordingly the degradation pathways were proposed. [ABSTRACT FROM AUTHOR]

The removal of brilliant green (BG), a toxic organic and cationic dye, has been examined by UV/S 2 O 8 2− (PS), UV/HSO 5 − (PMS) and UV/H 2 O 2 processes. BG showed insignificant direct photolysis at 254 nm (i.e., 8.6% after 30 min). However, enhanced BG degradation was observed in UV/PS, UV/PMS and UV/H 2 O 2 systems as revealed from 63.1, 47.0 and 34.8% BG degradation, respectively, at 30 min of reaction time, using 0.05 mM BG and 1.0 mM oxidant initial concentration. The bimolecular rate constants of OH and SO 4 − with BG were determined to be 2.35 × 10 9 and 2.21 × 10 9 M −1 s −1 , respectively. Electrical energy per order (EE/O) values for UV/PS, UV/PMS and UV/H 2 O 2 processes were calculated to be 5.4, 6.8, and 7.8 KWh/m 3 /order, respectively. The addition of humic acid (HA) and inorganic anions inhibited the degradation of BG by UV/PS in the order of NO 2 −  > HA > HCO 3 −  > Cl −   > NO 3 −  ≈ SO 4 2− . The results of frontier electron densities (FEDs) showed that C-atom holding the three rings (C7), and C-atoms at para positions to N-alkyl groups of the two rings (C4 and C14) are the predominant sites for radical addition. Furthermore, nine degradation products (DPs) of BG were detected experimentally using LC/MS/MS. [ABSTRACT FROM AUTHOR]