Synthesis and characterization of fibrous silica zsm-5 for methanol to olefin reaction

Olefins are one of the most important chemicals and raw materials in the petrochemical industry. However, because of the rapid increase in the price of crude oil and the oil shortage in the foreseeable future, alternative routes for production of light olefins from non-oil sources are desired. Catalytic conversion of methanol to light olefins (MTO) provides an alternative route for production of light olefins from a non- petroleum source. Protonated commercial ZSM-5 (HZSM-5) zeolite has been widely used in the MTO reaction. However, fast deactivation of HZSM-5 due to coke deposition has always been one of the key problems in MTO reaction. A novel ZSM- 5 catalyst with silica fibrous morphology (HSi@ZSM-5) was successfully prepared using a microemulsion system with ZSM-5 seed assisted crystallization followed by protonation for MTO reaction. X-ray diffraction and field emission scanning electron microscopy analyses showed that the HSi@ZSM-5 possesses ZSM-5 structure and a spherical morphology with evenly distributed dendrimeric silica fibers. In addition, HSi@ZSM-5 exhibited intrinsic mesopores at 3-5 and 10-20 nm, which led to an increase in the surface area up to 22% compared with HZSM-5. Ammonia Fourier transform infrared spectroscopy result showed a remarkable reduction of Brønsted acid sites in HSi@ZSM-5. This reduction of Brønsted acid sites suppressed side reactions which led to increased olefin selectivity. These were proven in the catalytic activity as the propylene selectivity of HSi@ZSM-5 was almost two-fold higher than that of HZSM-5. Besides, the catalytic lifetime was improved significantly up to 80 hours for HSi@ZSM-5 compared to about 30 hours for HZSM-5. The high selectivity towards propylene and long catalyst lifetime of HSi@ZSM-5 could be attributed to the unique morphology of HSi@ZSM-5 which facilitates the diffusion of reactant and product into and out of the catalyst. Lowering diffusion limitation reduces the possibility of coke accumulation on the catalyst that lead to the deactivation of the catalyst. This new protonated silica fibrous ZSM-5 catalyst opens a big potential in general heterogeneous catalytic reaction

Graphene oxide dispersed with ferrite nano - particles as magnetic solid phase extraction adsorbent for chlorpyrifos and diazinon

Magnetic graphene oxide, Fe3O4-GO has been synthesized through oxidation of graphite via modified Hummer’s method followed by a one step co-precipitation method. Fe3O4-GO was used in the extraction of two organophosphorus pesticides (OPPs), namely chlorpyrifos and diazinon using magnetic solid phase extraction (MSPE) technique. The GO and Fe3O4-GO synthesised was characterized using Fourier transform infrared spectroscopy (FT-IR), and field emission scanning electron microscopy (FESEM). Optimum conditions obtained from the optimization process were as follows: 80 mL sample volume, 50 mg of adsorbent, 10 min extraction time followed by desorption process using 500 µL of acetonitrile. Under the optimum conditions, Fe3O4-GO MSPE method showed excellent linearity in the range of 0.1-10 µg L-1 with coefficient of determination (R2) of 0.9997 for both OPPs. Precision studies found that the repeatability of this Fe3O4-GO MSPE method (RSD, n = 3) were 9.95% and 9.05% for chlorpyrifos and diazinon respectively. Meanwhile the reproducibility (RSD, n = 9) observed was 11.45% for chlorpyrifos and 13.35% for diazinon. The limit of detection (LOD = 3 S/N) for chlorpyrifos was 0.034 µg L-1 and 0.40 µg L-1 for diazinon. Lake water sample was spiked with 0.5 µg L-1 of each of the OPPs after confirming the non-detection in the sample using gas chromatography-electron capture detector (GC-ECD). Percentage recoveries of the two OPPs from lake water samples were found to be 57.71% for chlorpyrifos and 73.86% for diazinon. The Fe3O4-GO MSPE method was found to be susceptible to matrix effect from the lake water sample analysed. The Fe3O4-GO MSPE method was also applied to the determination of the two OPPs from tomato sample using matrix-matched calibration curve in the range of 1-50 µg L-1. Good coefficient of determination (R2) value of 0.9963 and 0.9897 for chlorpyrifos and diazinon respectively was observed. Both OPPs were found to be present in the tomato sample analysed (0.19 µg L-1 of chlorpyrifos and 7.88 µg L-1 of diazinon