RESUMEN
A fully automated on-line system for monitoring the TiO2-based photocatalytic degradation of dimethyl phthalate (DMP) and diethyl phthalate (DEP) using sequential injection analysis (SIA) coupled to liquid chromatography (LC) with UV detection was proposed. The effects of the type of catalyst (sol-gel, Degussa P25 and Hombikat), the amount of catalyst (0.5, 1.0 and 1.5 g L-1), and the solution pH (4, 7 and 10) were evaluated through a three-level fractional factorial design (FFD) to verify the influence of the factors on the response variable (degradation efficiency, %). As a result of FFD evaluation, the main factor that influences the process is the type of catalyst. Degradation percentages close to 100% under UV-vis radiation were reached using the two commercial TiO2 materials, which present mixed phases (anatase/rutile), Degussa P25 (82%/18%) and Hombikat (76%/24%). 60% degradation was obtained using the laboratory-made pure anatase crystalline TiO2 phase. The pH and amount of catalyst showed minimum significant effect on the degradation efficiencies of DMP and DEP. Greater degradation efficiency was achieved using Degussa P25 at pH 10 with 1.5 g L-1 catalyst dosage. Under these conditions, complete degradation and 92% mineralization were achieved after 300 min of reaction. Additionally, a drastic decrease in the concentration of BOD5 and COD was observed, which results in significant enhancement of their biodegradability obtaining a BOD5/COD index of 0.66 after the photocatalytic treatment. The main intermediate products found were dimethyl 4-hydroxyphthalate, 4-hydroxy-diethyl phthalate, phthalic acid and phthalic anhydride indicating that the photocatalytic degradation pathway involved the hydrolysis reaction of the aliphatic chain and hydroxylation of the aromatic ring, obtaining products with lower toxicity than the initial molecules.
RESUMEN
The preparation of hierarchical porous carbon sponges (HCS) from metal oxide nanoparticle@metal-organic frameworks is reported. ZnO nanoparticles are partially converted to zeolitic imidazolate framework-8 (ZIF-8) crystals in presence of n-butylamine to obtain ZnO@ZIF-8 porous hybrids. After direct carbonization, followed by ZnO acidic etching, ZnO@ZIF-8 crystals were converted to submicrometric HCS. Due to the high surface area and accessible porosity, combining micro- and mesoporosity of HCS, their application for the extraction of water pollutants was studied by preparing HCS/polymer membranes, and showed a high efficiency for the fast (650â L m-2 h-1 ) removal of plastic degradation by-products (DBP, dibutyl phthalate. DEHP, bis(2-n-ethylhexyl)phthalate). DBP and DEHP breakthroughs were lower than 3 % after the filtration of 100â mL of water containing simultaneously both phthalates at a high concentration level (300â µg L-1 , each). HCS/polymer membranes were reusable up to 5â times, maintaining their extraction capacity, with relative errors of 6 % for DBP, and <1 % for DEHP.
RESUMEN
An on-line solid phase extraction coupled to liquid chromatography with UV detection (SPE/LC-UV) method was automated by the multisyringe flow-injection analysis (MSFIA) system for the determination of three phthalic acid esters (PAEs). The PAEs determined in drinking water stored in polyethylene terephthalate (PET) bottles of ten commercial brands were dimethyl phthalate (DMP), diethyl phthalate (DEP) and dibutyl phthalate (DBP). C18-bonded silica membrane was used for isolation and enrichment of the PAEs in water samples. The calibration range of the SPE/LC-UV method was 2.5-100µgL-1 for DMP and DEP and 10-100µgL-1 for DBP with correlation coefficients (r) ranging from 0.9970 to 0.9975. Limits of detection (LODs) were between 0.7 and 2.4µgL-1. Inter-day reproducibility performed at two concentration levels (10 and 100µgL-1) expressed as relative standard deviation (%RSD) were found in the range of 0.9-4.0%. The solvent volume was reduced to 18mL with a total analysis time of 48min per sample. The major species detected in bottled water samples was DBP reaching concentrations between 20.5 and 82.8µgL-1. The recovery percentages for the three analytes in drinking water were 80-115%. The migration test showed a great variation in the sum of migrated PAEs level (10.2-50.6µgL-1) among the PET bottle brands analyzed indicating that the presence of these contaminants in the plastic containers may depend on raw materials and the conditions used during their production process.
