A Comparative Evaluation of TiO 2

The most important parameters affecting the efficiency of catalysts for the oxidation of the surrounding materials are considered to be the thickness and uniformity of the catalyst layer. The present method for the determination of thickness used in most studies is the analysis of cross-sectional pictures from SEM imaging. This method, however, has several restrictions. This study proposes a feasible and simple method for evaluating the optimal thickness and uniformity using UVA light transmitted through the samples. Three techniques for catalyst deposition have been investigated in this study using UVA light transmitted through the samples and by measuring the photocatalytic activity. These methods include lowering, dip coating, and spraying, which showed coefficients of variation for the coated catalyst weight of 28.4%, 13.6%, and 3.24%, respectively. The samples from the lowering, dip coating, and spraying techniques showed UVA transmissions of 95.02%, 68.8%, and 15.6%, respectively. The spraying technique displayed the lowest values for both. The estimated removal efficiencies (%RE/mgcm−2) for lowering, dip coating, and spraying were 18.42, 16.84, and 24.15, respectively. Using these analyses it was determined that the spraying technique yielded the best photocatalytic oxidation performance of the three techniques studied

Highly dispersed atomic layer deposited CrOx on SiO2 catalyst with enhanced yield of propylene for CO2 –mediated oxidative dehydrogenation of propane

The increasing worldwide demand for propylene and the necessity of CO2 mitigation attracted the attention of scientists to focus on CO2-oxidative dehydrogenation of propane (CO2-ODHP). In this regard, CrOx/SiO2 catalyst is an important and conventional option. Herein, we studied the atomic layer deposition (ALD) of CrOx on silica to increase the propylene production by increasing the dispersion of the catalyst. For ALD synthesis of CrOx/SiO2 catalyst, Cr(acac)3 and synthetic air were used as metal precursor and oxidant. The catalysts were examined in the CO2-ODHP reaction and their characteristics were compared to their impregnation counterparts using UV–Vis DRS, Raman, XANES, HRTEM and STEM-EDS mapping, H2-TPR, NH3-TPD and TPO. The ALD catalysts have shown up to 2 times higher acidity and enhanced reducibility compared to the impregnation catalysts. The presence of mainly Cr(VI) with a pre-edge peak at 5.994 keV in both series of catalysts was confirmed by XANES. UV–Vis DRS and Raman spectroscopy revealed the higher contents of active polymeric Cr(VI) species in the ALD ones. The dark field HRTEM and STEM-EDS mapping represented higher dispersion of chromium oxide particles in ALD catalysts. In CO2-ODHP, the ALD catalysts showed up to 18 and 15% promotion in propane conversion and propylene yield.Peer reviewe

Efficient synergistic chemical fixation of CO2 by simple metal-free organocatalysts : Mechanistic and kinetic insights

Background: Carbon dioxide is a versatile, non-toxic, and renewable C1 building block source to produce valuable chemicals such as cyclic carbonates. The purpose of this research is development of efficient, metal free and affordable catalysts for cycloaddition reaction of CO2 with epoxides at mild conditions. Methods: In the present work, a group of novel bifunctional organocatalysts consisting of different hydrogen bond donors (HBDs) and halogen ion is simply synthesized. Under the optimized conditions, the reaction is kinetically and thermodynamically studied. Additionally, the catalytic active species are determined, and a mechanism is proposed with the help of electrospray-ionization time-of -flight mass spectrometry (ESITOF MS). Significant findings: The most active catalytic system is obtained by chemically interaction of 3-bromopropionic acid (BPA) with DMF at 80 degrees C (BPA-DMF). An excellent product yield of 98% and a high TOF value are obtained with 0.99 mol% of BPA-DMF, which is attributed to the synergistic effects of carboxyl functional groups and halide ions. The activation energy was found to be 50.75 kJ/mol. The positive value of Gibbs free activation energy (DGt) and negative value of activation entropy (DSt) confirm a non-spontaneous, endergonic and kinetically controlled reaction. (c) 2021 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V. All rights reserved.Peer reviewe

Abatement of trichloroethylene using DBD plasma

Dielectric barrier discharge plasma was used to oxidize trichloroethylene (TCE) in 21% of O2 in carriers of N2 and He. The degradation products of TCE were analyzed using gas chromatography mass spectrometry. TCE was decomposed completely at optimum energy density of 260 and 300 J/l for He and N2, respectively and its conversion followed zero order reaction. The TCE removal efficiency is decreased in humid air due to interception of reactive intermediates by OH radicals

H2O/air plasma-functionalized carbon nanotubes decorated with MnO2 for glucose sensing

Multi-walled carbon nanotubes (MWCNTs) were functionalized using dielectric barrier discharge plasma in water vapor-saturated air at 70 °C. MnO2 was deposited on the MWCNTs by chronoamperometry, followed by glucose oxidase (GOx) immobilization, and the resulting GOx/MnO2/MWCNTs electrode was used for electrochemical detection of glucose. Structural, morphological, and elemental microanalysis was performed. Plasma-induced oxygen-based functional groups were confirmed on the MWCNT surfaces and improved their dispersion in aqueous solutions. The maximum amount of these groups was created at the optimum exposure time of 4 min. The GOx immobilized on the MnO2/MWCNTs hybrid showed a well-defined, reversible and surface-controlled redox wave around −0.45 V and a peak to peak separation of 0.04 V. The coefficient and rate constant for electron transfer of GOx were calculated as 0.41 and 1.08 s−1, respectively. The GOx/MnO2/MWCNT-modified electrode exhibited a linear behavior in the range of 0.1–3.2 mM glucose concentration with the competitive detection limit of 3.0 μM and a sensitivity of 24.2 μA mM−1 cm−2. This highly-stable glucose sensing electrode retained more than 76% of its initial faradic current value after 71 days. These results are relevant to the development of next-generation glucose sensors for diverse health- and food-related applications