RESUMEN
[This corrects the article DOI: 10.1021/acsomega.0c00358.].
RESUMEN
The catalytic esterification of free fatty acids is an important reaction pathway for chemical synthesis and biodiesel production, wherein efficient heterogeneous catalysts are sought to replace mineral acids. Herein, the esterification of oleic acid together with some familiar fatty acids is demonstrated with methanol over a heterogeneous heteropolyacid-functionalized zeolite imidazolate framework [H6-n P2W18O62 n-/ZIF(H n His.)+n ]. This new heterogeneous catalyst (named as HPA/ZIF(His.) throughout the text) with an average particle size of 80 nm was prepared via condensation of histamine with zinc chloride and characterized by means of Fourier transform infrared (FT-IR), X-ray diffraction (XRD), UV-vis, energy-dispersive X-ray spectrometry, Brunauer-Emmett-Teller, thermogravimetric analysis (TGA), inductively coupled plasma - optical emission spectrometry (ICP-OES), and scanning electron microscopy. According to the performed characterizations, an HPA loading of 40.5 wt % is obtained for HPA/ZIF(His.) from ICP-OES analysis. Moreover, a typical type-IV isotherm with similar adsorption-desorption properties as seen for ZIF-8 is attained. In addition, TGA measurement confirms less stability of HPA/ZIF(His.) compared to that of pure ZIF(His.). The catalytic performance of the nanomaterial is evaluated with respect to temperature, catalyst loading, and methanol/oleic acid ratio and leads to a high yield of methyl ester (>90%) under reflux for 4 h. The preliminary kinetic studies confirm a pseudo-first-order kinetic model for the esterification of oleic acid. To explore the scope of the HPA/ZIF(His.) catalyst in methyl ester production, other free fatty acids with various chain lengths are also successfully tested. Although the nanocatalyst loses a part of its activity during reuse, however, it is stable over at least four recycles as confirmed by XRD and FT-IR. Eventually, the response surface methodology (RSM) is used as a statistical modeling approach to get the best-optimized reaction conditions compared to the performed single-variable benchmarking experiments. Therefore, the central composite design (CCD) and RSM attained a platform to determine the relationship among the reaction time, acid/methanol molar ratio, and catalyst dosage.
RESUMEN
As a highly efficient adsorbent, the zinc-based metal-organic framework has been successfully synthesized from zinc as the metal ion and histamine as an organic linker under solvothermal conditions. The structure of nanocomposite was characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), and Fourier transform infrared (FTIR) analysis. The synthesized sorbent was applied for dispersive solid-phase extraction (DSPE) of organophosphorus pesticides (OPPs) in fruit juice and water samples. The gas chromatography-flame ionization detector (GC-FID) was used as instrument detection. The main experimental factors affecting the extraction efficiency such as the desorption conditions, sorbent amount and extraction time were evaluated and optimized. Good linearity exhibited for all of the target analytes in the 0.1-100 ng mL-1 concentration range. The enrichment factors (EFs) ranged from 803 to 914. The limits of detection (LODs) for the established DSPE-GC-FID method were found to be 0.03-0.21 ng mL-1. The DSPE-GC-FID method can be used for the analysis of OPPs in water and fruit juice samples with recoveries of the analytes in the range of 91.9% to 99.5%.
