Monthly Archives: September 2023

Optimization of Biodiesel Production from Waste Cooking Oil Using Nano Calcium Oxide Catalyst

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Optimization of Biodiesel Production from Waste Cooking Oil Using Nano Calcium Oxide Catalyst

Biodiesel is an alternative to fossil diesel fuel derived from sustainable biological resources. Biodiesel production from waste cooking oil and methanol in the presence of a nanosized CaO catalyst was studied. Transesterification was performed at different times, temperatures, and methanol/oil ratios, and response surface methodology was used to predict optimum parameters for biodiesel production.


Abstract

The use of nano calcium oxide as a catalyst in biodiesel production has gained attention due to its high catalytic activity, low cost, and environmental friendliness. It efficiently converts triglycerides to fatty acids and methyl esters. In the present study, nano CaO was prepared by precipitation and characterized by various techniques. The results showed that the nano CaO has high purity, nanoscale crystal size, good thermal stability, and high specific surface area. Biodiesel was produced by transesterification from waste cooking oil, methanol, and the nano catalyst. Response surface methodology was applied to predict the optimum parameters for the production of the biodiesel based on its yield. The produced biodiesel was characterized by FTIR spectroscopy and GC-MS and evaluated according to ASTM D6571.

Theoretical Analysis of Metals Supported on Tungsten Oxide Nanowires (W18O49) for Water Dissociation Reaction

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Theoretical Analysis of Metals Supported on Tungsten Oxide Nanowires (W18O49) for Water Dissociation Reaction

Applying the density functional theory method, W18O49 was developed for catalyst support on Pt, Pd, Ni, Ir, Ag, and Rh metal atoms for the oxygen evolution reaction. Various adsorbates that are intermediate products in this reaction were tested for adsorption on metal catalysts. Gibbs free energy diagrams were also developed to analyze the potential of the catalyst and W18O49.


Abstract

Pt is the cause of the high total cost of fuel cells and electrolyzers, leading to difficult commercialization. Here, various types of metal atoms, i.e., Pt, Pd, Ni, Ir, Ag, and Rh, suitable for catalysts are used and supported by W18O49 nanowires for oxygen evolution reaction (OER) by the density functional theory (DFT) method. Four adsorbate molecules involved in OER were tested on adsorption energy: OH, O, OOH, and OO. Although the adsorption energy of these adsorbate molecules indicates that W18O49 has low adsorption energy, the Gibbs free energy diagram demonstrates that W18O49 has high OER reaction energy. Pt, Pd, Ni, and Rh have the lowest Gibbs energy to initiate the reaction and reasonable Gibbs free energy for other OER reactions. Bimetallic or trimetallic active sites can be developed along with selecting other metals with Pt, Pd, Rh, and Ni to reduce the Gibbs free energy difference for the decomposition of OH to O and OOH to H2O. Ag metal can also be applied as a second or third metal because Ag exhibits a relatively low Gibbs free energy difference in the O to OOH step. A selectivity study of each step on bimetallic and trimetallic active sites needs to be performed.

Structural Description of Chiral E‐Tiling DNA Nanotubes with the Chiral Indices (n,m) and Handedness Defined by Microscopic Imaging

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Structural Description of Chiral E-Tiling DNA Nanotubes with the Chiral Indices (n,m) and Handedness Defined by Microscopic Imaging

The chiral index theory, widely used in carbon nanotubes, has been introduced to describe the chiral structures of E-tiling DNA nanotubes precisely. In particular, we define a general equation of tube curvature with a clear physical picture by modifying its mathematical definition. Furthermore, we summarize the recent progress on defining the left- or right-handedness of E-tiling DNA nanotubes through differentiating their inside and outside surfaces by fluorescence or electron or atomic force microscopic imaging.


Abstract

In structural DNA nanotechnology, E-tiling DNA nanotubes are evidenced to be homogeneous in diameter and thus have great potential in biomedical applications such as cellular transport and communication, transmembrane ion/molecule channeling, and drug delivery. However, a precise structural description of chiral DNA nanotubes with chiral parameters was lacking, thus greatly hindering their application breadth and depth, until we recently raised and partly solved this problem. In this perspective, we summarize recent progress in defining the chiral indices and handedness of E-tiling DNA nanotubes by microscopic imaging, especially atomic force microscopy (AFM) imaging. Such a detailed understanding of the chiral structures of E-tiling DNA nanotubes will be very helpful in the future, on the one hand for engineering DNA nanostructures precisely, and, on the other, for realizing specific physicochemical properties and biological functions successfully.

Epimerization of trans‐Cycloalkenes with the X–C=C–SeR*‐Unit – The Steric Demand of X = H, F, Cl, Br, I, Me, Et and CF3

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Trans-cycloalkenes with the X–C=C–SeR*-unit and ring sizes from 9 to 20 have been synthesized. Bond the selenium atom is the chiral (S)-o-(1-Methoxypropyl)phenyl-residue R*, and X = H, F, Cl, Br, I, Me, Et and CF3. The planar-chiral trans-cycloalkenes in combination with the chiral residue R* exist as two diastereomers. These can be distinguished in principle by NMR spectroscopy. We have studied the epimerization of the trans-cycloalkenes, i.e., the 180° rotation of the X–C=C-unit through the cavity of the ring. The measurements were done with variable temperature 13C NMR spectroscopy in the range from –110 to 140°C. The obtained values of the Gibbs energy of activation ΔG‡C depend strongly on the ring size. Furthermore, the ΔG‡C values show dramatic steric effects due to the groups X. The steric requirement of X increases in the series H << F << Cl < Me < Br < I < Et < CF3. Here, F is significantly larger than H, and CF3 is larger than Et. The corresponding iPr-compounds could not be synthesized. The transition state structures of the ring inversion for ring sizes 8–20 were calculated at the DFT level of theory.

Investigating the Influence of Treatments on Carbon Felts for Vanadium Redox Flow Batteries

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Vanadium redox flow battery (VRFB) electrodes face challenges related to their long-term operation. We investigated different electrode treatments mimicking the aging processes during operation, including thermal activation, aging, soaking, and storing. Several characterization techniques were used to deepen the understanding of the treatment of carbon felts. Synchrotron X-ray imaging, electrochemical impedance spectroscopy (EIS) with the distribution of relaxation times analysis, and dynamic vapor sorption (DVS) revealed differences between the wettability of felts. The bulk saturation after electrolyte injection into the carbon felts significantly differed from 8% to 96%. DVS revealed differences in the sorption/desorption behavior of carbon felt ranging from a slight change of 0.8 wt% to over 100 wt%. Additionally, the interactions between the water vapor and the sample change from type V to type H2. After treatment, morphology changes were observed by atomic force microscopy and scanning electron microscopy. Cyclic voltammetry and EIS were used to probe the electrochemical performance, revealing different catalytic activities and transport-related impedances for the treated samples. These investigations are crucial for understanding the effects of treatments on the performance and optimizing materials for long-term operation.

Batch and flow green microwave‐assisted catalytic conversion of levulinic acid to pyrrolidones

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This paper reports a new sustainable protocol for the microwave-assisted catalytic conversion of levulinic acid into N-substituted pyrrolidones over tailor-made mono (Pd, Au) or bimetallic (PdAu) catalysts supported on either highly mesoporous silica (HMS) or titania-doped HMS, exploiting the advantages of dielectric heating. MW-assisted reductive aminations of levulinic acid with several amines were first optimized in batch mode under hydrogen pressure (5 bar) in solvent-free conditions. Good-to-excellent yields were recorded at 150 °C in 90 min over the PdTiHMS and PdAuTiHMS, that proved recyclable and almost completely stable after six reaction cycles. Aiming to scale-up this protocol, a MW-assisted flow reactor was used in combination with different green solvents. Cyclopentyl methyl ether (CPME) provided a 99% yield of N-(4-methoxyphenyl) pyrrolidin-2-one at 150 °C over PdTiHMS. The described MW-assisted flow synthesis proves to be a safe procedure suitable for further industrial applications, while averting the use of toxic organic solvents.

Spatiotemporal Changes in Trace Metal Bioavailability in The Sediment Porewater of a Constructed Wetland Using Passive Porewater Samplers

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ABSTRACT

Sediments in aquatic systems often act as a major sink for contaminants. Diffusive gradient in thin films (DGTs) and in situ equilibrium dialysis samplers (peepers) are two major in situ porewater sampling devices that overcome the problems associated with conventional porewater sampling methods. In this study, DGTs and peepers were used to study the spatial and seasonal effects (cool months: October-February, warm months: May-September) on metal bioavailability in the H-02 constructed wetland, and the sink vs. source role of the sediments by calculating the metal resupply capacity (R). Data showed similar seasonal trends in metal concentrations using both passive samplers, peepers and DGTs. Pooled Cu and Zn concentrations measured using DGTs were lower in warm months (1.67 ± 1.50 and 2.62 ± 0.68 μg.L-1, respectively, p < 0.001) vs. (2.12 ± 0.65 and 5.58 ± 1.33 μg.L-1, respectively, p < 0.001) in cool months (mean ± 95% Confidence Intervals). Sulfate (SO4 2-) concentrations were significantly (p = 0.0139) lower in warm months (averaged at 0.22 ± 0.05 mg.L-1) compared to (0.16 ± 0.05 mg.L-1) in cool months. The increase in SO4 2- concentration is an indicator of the lower activity of sulfate reducing bacteria (SRB) which need SO4 2- during the anaerobic respiration, in which SO4 2- is reduced to sulfide (S2-) which forms insoluble salts with Cu and Zn, which could partially explain higher bioavailability of these metals in the cool season. Metal resupply capacity of the sediments was mostly < 0.2 for Cu and Zn. Taken together, the H0-2 wetland sediments mostly acted as a sink to both Cu and Zn over the course of this study.