Gas Chromatography Measurements Research Articles

Water-Insoluble Copper Complexes As Electrocatalysts for CO2 Reduction

The electrochemical reduction of carbon dioxide (CO2R) constitutes a promising CO2 utilization technology, allowing the production of valuable fuels and chemicals by using electrical energy from renewable sources. Nevertheless, poor selectivity and high required overpotentials hamper practical applications of the CO2R, which highlights the need for the development of more efficient electrocatalysts. Different copper-based materials have been extensively studied as electrocatalysts for CO2R. Particularly, copper complexes exhibited interesting properties under operational conditions: many of them undergo structural modifications (e.g. changes in oxidation state and/or coordination number), which potentially affect activity, selectivity and stability. Interestingly, some complexes exhibit reversible restructuring under specific conditions, which can be an interesting property to reach higher stability. In this presentation, we will show the results obtained for the electrocatalysis of water-insoluble copper complexes for the CO2R. The activity, selectivity and stability of both [Cu(bzimpy)Cl2] and [Cu(pyrben)2(NO3)]NO3 were investigated in K2SO4 0.1 mol L-1 (CO2 sat.) under different electrochemical conditions. Here, bzimpy and pyrben stand for 2,6-bis(2-benzimidazolyl)pyridine and 2-(2-pyridyl)benzimidazole, respectively. Qualitative EC-MS (Electrochemistry Coupled to Mass Spectrometry) analysis evidenced that both complexes are active for CO2 reduction and that product distribution changes according to the applied potential. Quantitative gas chromatography measurements revealed that, at -1.24 V vs. RHE, [Cu(bzimpy)Cl2] promotes the formation of H2, CO, CH4 and C2H4 with faradaic efficiencies of 26, 3.4, 9.2 and 31%, respectively. On the other hand, [Cu(pyrben)2(NO3)]NO3 shows FE values of 24, 8.8, 15 and 24% for H2, CO, CH4 and C2H4, respectively. After 1.6 h of electrolysis, the former exhibited stable current and FE of ~42% towards ethylene formation.

Exploring the possibility of aluminum plating/stripping from a non‐corrosive Al(OTf)3‐based electrolyte

Rechargeable aluminum batteries offer a promising candidate for energy storage systems, due to the Aluminum (Al) abundance source. However, the development of non‐corrosive electrolytes, facilitating reversible Al plating/stripping, is a critical challenge to overcome. This study investigates the feasibility of aluminum plating on a platinum substrate using a non‐corrosive trifluoromethanesulfonate (Al(OTf)3)/N‐methylacetamide (NMA)/urea electrolyte. This electrolyte was proposed earlier as an alternative chloroaluminate‐based ionic liquid, but Al plating/stripping was not proved. In this work, various techniques, including cyclic voltammetry, scanning electron microscope/energy‐dispersive X‐ray spectroscopy, operando optical microscopy and electrochemical quartz crystal microbalance (EQCM), gas chromatography (GC), and X‐ray photoelectron spectroscopy were employed to understand the Aluminum plating and stripping behavior. While cyclic voltammetry indicates redox activity on Pt, further analysis reveals no significant plating. Instead, hydrogen evolution reaction, promoted by the water‐residue, dominates the observed current, confirmed by operando microscopy and GC measurements. EQCM studies suggest the concurrent adsorption/desorption of Al(OH)2+ and Al3+ ions on the Pt electrode. Further drying the electrolyte reduces the hydrogen evolution, but plating of metallic Al remains elusive. These findings highlight the need for further optimization of the electrolyte composition to achieve efficient Al plating/stripping.

The effect of fat model variation on muscle fat fraction quantification in a cross-sectional cohort.

Spectroscopic imaging, rooted in Dixon's two-echo spin sequence to distinguish water and fat, has evolved significantly in acquisition and processing. Yet precise fat quantification remains a persistent challenge in ongoing research. With adequate phase characterization and correction, the fat composition models will impact measurements of fatty tissue. However, the effect of the used fat model in low-fat regions such as healthy muscle is unknown. In this study, we investigate the effect of assumed fat composition, in terms of chain length and double bond count, on fat fraction quantification in healthy muscle, while addressing phase and relaxometry confounders. For this purpose, we acquired bilateral thigh datasets from 38 healthy volunteers. Fat fractions were estimated using the IDEAL algorithm employing three different fat models fitted with and without the initial phase constrained. After data processing and model fitting, we used a convolutional neural net to automatically segment all thigh muscles and subcutaneous fat to evaluate the fitted parameters. The fat composition was compared with those reported in the literature. Overall, all the observed estimated fat composition values fall within the range of previously reported fatty acid composition based on gas chromatography measurements. All methods and models revealed different estimates of the muscle fat fractions in various evaluated muscle groups. Lateral differences changed from 0.5% to 5.3% in the hamstring muscle groups depending on the chosen method. The lowest observed left-right differences in each muscle group were all for the fat model estimating the number of double bonds with the initial phase unconstrained. With this model, the left-right differences were 0.64% ± 0.31%, 0.50% ± 0.27%, and 0.50% ± 0.40% for the quadriceps, hamstrings, and adductors muscle groups, respectively. Our findings suggest that a fat model estimating double bond numbers while allowing separate phases for each chemical species, given some assumptions, yields the best fat fraction estimate for our dataset.

Chemical Analysis of Exhaled Vape Emissions: Unraveling the Complexities of Humectant Fragmentation in a Human Trial Study.

Electronic cigarette smoking (or vaping) is on the rise, presenting questions about the effects of secondhand exposure. The chemical composition of vape emissions was examined in the exhaled breath of eight human volunteers with the high chemical specificity of complementary online and offline techniques. Our study is the first to take multiple exhaled puff measurements from human participants and compare volatile organic compound (VOC) concentrations between two commonly used methods, proton-transfer-reaction time-of-flight mass spectrometry (PTR-ToF-MS) and gas chromatography (GC). Five flavor profile groups were selected for this study, but flavor compounds were not observed as the main contributors to the PTR-ToF-MS signal. Instead, the PTR-ToF-MS mass spectra were overwhelmed by e-liquid thermal decomposition and fragmentation products, which masked other observations regarding flavorings and other potentially toxic species associated with secondhand vape exposure. Compared to the PTR-ToF-MS, GC measurements reported significantly different VOC concentrations, usually below those from PTR-ToF-MS. Consequently, PTR-ToF-MS mass spectra should be interpreted with caution when reporting quantitative results in vaping studies, such as doses of inhaled VOCs. Nevertheless, the online PTR-ToF-MS analysis can provide valuable qualitative information by comparing relative VOCs in back-to-back trials. For example, by comparing the mass spectra of exhaled air with those of direct puffs, we can conclude that harmful VOCs present in the vape emissions are largely absorbed by the participants, including large fractions of nicotine.

Feedback control of an experimental electrically-heated steam methane reformer

Steam methane reforming (SMR) is the most common industrial process to produce hydrogen (H2) from methane and water vapor. The SMR reactions are overall highly endothermic and traditionally, fossil fuels are burned to provide the necessary heat of reaction. However, it was found that electrifying the tubular SMR reactors using renewable electrons instead of conventional heating gives the opportunity of producing H2 with lower carbon emissions, lower reactor volumes, and higher carbon conversion. While current studies in this new technology focus on improving the catalysts or heating sources, a more efficient process control scheme can also significantly contribute to the understanding of potential challenges and opportunities of combining renewables and natural gas in the production of H2 at industrial scales. In order to further develop the electrically-heated SMR process and the associated control strategies, we have constructed an experimental Joule-heated SMR system at UCLA. The system contains a tubular reactor with a washcoated Ni/ZrO2 catalyst, two thermocouples connected to the top and bottom of the reactor, a power supply for providing electrical heating, and an on-line gas chromatograph (GC) for measuring outlet gas concentrations. The synthesis procedure of the catalyst, SMR data collection, and thermal considerations for catalyst degradation are described in this paper and are all accounted for experimentally when using a proportional integral (PI) controller to gradually increase the reactor temperature without harming the catalyst. Advanced control strategies, such as model predictive control (MPC), require a process model that uses measurement feedback to make predictions of the process time-evolution in order to optimize the control actions in real-time. We have previously developed a lumped-parameter modeling strategy for the SMR process. The MPC objective is to control the H2 production rate by manipulating the current flowing through the outer reactor shell. However, to use this model in an MPC, feedback values for all state variables should be provided by the sensors. In our experimental system, the on-line GC only gives discrete measurements with a long sampling period. To this end, the process model is incorporated into an extended Luenberger observer (ELO) that uses the reactor temperature and GC measurements to provide estimates of all the variables needed by the MPC. The ELO-based MPC system is then experimentally implemented on the process and it is demonstrated to be more efficient in terms of speed of the closed-loop response than the PI controller using delayed, measurement feedback by the GC.

A mechanistic model to predict headspace concentration profile of carvacrol for controlled release packaging

The efficacy of an antimicrobial agent in food packaging depends largely on its concentration profile in the package headspace. In this study, a mechanistic mathematical model was developed to predict the headspace concentration profile of carvacrol, a prominent antimicrobial agent, using the physical principles that govern the movement of carvacrol molecules in a controlled release packaging system. The model and its estimated parameter values were validated using three different sets of gas chromatography measurements—this rigorous process confirms the accuracy and reliability of the model. Advancing beyond existing models, our model enhances the understanding of the dynamics between the concentration profile and its interacting processes including evaporation, adsorption, and gas transmission. It provides packaging developers with a superior alternative to the trial-and-error approach to tailor concentration profiles for optimizing antimicrobial efficacy. It leads to more efficient and better design of controlled release packaging.

The driving force of water absorption in cementitious materials: An analysis of surface-free energies and pore structure

Upon the initial contact of hydrophilic cementitious materials with water, capillary absorption becomes the dominant phenomenon leading to durability deterioration of structures. The water absorption characteristics of such materials are governed by the interplay between pore structure and surface-free energies, with the latter being a factor often overlooked. In this study, advanced inverse gas chromatography (IGC) measurement techniques were employed to investigate the one-dimensional capillary water absorption of ordinary Portland cement (OPC) and alkali-activated slag (AAS). Results revealed water sorptivity values for OPC, AAS(NaOH), and AAS(Waterglass) as 0.0112, 0.0137, and 0.0187 mm/s0.5, respectively. This phenomenon can be attributed to the higher total surface-free energies observed at the liquid-solid interface in AAS materials, measuring 100.10 and 119.56 mJ/m2, compared with 74.25 mJ/m2 for OPC, consequently increasing capillary pressures. Moreover, it is observed that OPC exhibited a more complex pore tortuosity in comparison to AAS. This study underscores the dual role played by both capillary pressures and pore tortuosity in determining the water absorption characteristics of cementitious materials.

Identifying and correcting interferences to PTR-ToF-MS measurements of isoprene and other urban volatile organic compounds

Abstract. Proton-transfer-reaction time-of-flight mass spectrometry (PTR-ToF-MS) is a technique commonly used to measure ambient volatile organic compounds (VOCs) in urban, rural, and remote environments. PTR-ToF-MS is known to produce artifacts from ion fragmentation, which complicates the interpretation and quantification of key atmospheric VOCs. This study evaluates the extent to which fragmentation and other ionization processes impact urban measurements of the PTR-ToF-MS ions typically assigned to isoprene (m/z 69, C5H8H+), acetaldehyde (m/z 45, CH3CHO+), and benzene (m/z 79, C6H6H+). Interferences from fragmentation are identified using gas chromatography (GC) pre-separation, and the impact of these interferences is quantified using ground-based and airborne measurements in a number of US cities, including Las Vegas, Los Angeles, New York City, and Detroit. In urban regions with low biogenic isoprene emissions (e.g., Las Vegas), fragmentation from higher-carbon aldehydes and cycloalkanes emitted from anthropogenic sources may contribute to m/z 69 by as much as 50 % during the day, while the majority of the signal at m/z 69 is attributed to fragmentation during the night. Interferences are a higher fraction of m/z 69 during airborne studies, which likely results from differences in the reactivity between isoprene and the interfering species along with the subsequent changes to the VOC mixture at higher altitudes. For other PTR masses, including m/z 45 and m/z 79, interferences are observed due to fragmentation and O2+ ionization of VOCs typically used in solvents, which are becoming a more important source of anthropogenic VOCs in urban areas. We present methods to correct these interferences, which provide better agreement with GC measurements of isomer-specific molecules. These observations show the utility of deploying GC pre-separation for the interpretation PTR-ToF-MS spectra.

Temperature‐Mediated Dynamic Lithium Loss and its Implications for High‐Efficiency Lithium Metal Anodes

AbstractLithium (Li) metal has been strongly regarded as the ultimate anode option for next‐generation high‐energy‐density batteries. Nevertheless, the insufficient Coulombic efficiency induced by the extensive active Li loss largely hinders the practical operation of Li metal batteries under wide temperature range. Herein, the temperature‐mediated dynamic growth of inactive Li from −20 to 60°C via titration gas chromatograph measurements is quantitatively decoupled. Combined X‐ray photoelectronic spectroscopy, cryo‐transmission electronic microscopy, and scanning electronic microscopy methods depicted that both solid electrolyte interphase (SEI) characteristics and Li deposition compactness can be profoundly manipulated by working temperature. The elevation of temperature is found to fundamentally aggravate the parasitic reactions and deteriorate the spatial uniformity of SEI, yet promote the lateral growth of Li by kinetic reason. The opposite effects of temperature on SEI properties and Li deposition compactness can properly explain the intricate temperature‐dependent growth rates of SEI‐Li+ and dead Li0 capacity loss observed under titration gas chromatograph measurements. Design implications towards more stable Li metal anodes with higher reversibility can thus be yielded.

A simple dip-coating-co-firing fabricated anode supported tubular solid oxide fuel cells for bio-ethanol carbon dioxide internal dry reforming and power generation

Direct internal dry reforming of hydrocarbon is a promising way for the growth of solid oxide fuel cells (SOFCs) due to the convenient storage and transportation of hydrocarbon fuels. Herein, NiO-YSZ (Y2O3-stabilized ZrO2) anode supported tubular SOFCs (T-SOFCs) are successfully fabricated by a simple dip-coating-co-firing method with NiFe2O4–Gd0.1Ce0.9O2-δ(NFO-GDC) internal reforming layer, and the electrochemical and carbon resistance are characterized under three different bio-ethanol carbon dioxide components (40 %, 50 %, 60 % ethanol partial pressure). The maximum power density of the T-SOFC in H2 atmosphere is 434.08 mW cm−2. With CO2–C2H5OH mixture as the fuel, the maximum power density is obtained at 50 % C2H5OH -CO2 atmosphere. This difference in performance is attributed to the varying levels of carbon dioxide affecting the dry reforming of ethanol. Distribution of relaxation times (DRT) analysis of T-SOFCs are carried out to explore the contribution of different electrode reactions. Long-term stability studies, gas chromatography measurements of exhaust gases and Raman scanning results are collected under three ethanol partial pressures to obtain the stability of single cell, catalytic reactions and carbon tolerance of fuel electrode. All experiments are designed to investigate the optimal performance of bio-ethanol carbon dioxide fueled single cells in terms of electrochemical performance and stability.

Variability of internal standard method calibration factors estimated with a multifactorial Taguchi experiment in the analysis of alcoholic products by gas chromatography with flame ionization detection.

This study compares the variability of relative response factors (RRFs) using Taguchi's multifactorial analysis for two internal standard (IS) methods in gas chromatography (GC) for quality control of alcoholic products. Methods where either ethanol or pentan-1-ol was used as an IS were compared. For ten volatile substances prescribed by legislation, the RRFs of both methods were compared under 27 different experimental conditions. The influence of parameters (control factors) such as ethanol content in the matrix, analyte concentration, injected volume, injector temperature, split ratio, and flame ionization detector temperature was evaluated. The selected control factors had values at one of the three levels to cover the commonly used ranges of their settings in the measuring system and to characterize the majority of alcoholic products commonly analyzed in practice. The obtained results showed that the biggest differences in the variability of the results between the two methods were found for the most strictly controlled substances in alcoholic products, acetaldehyde, and methanol, where the application of ethanol as an IS provides clearly better results. For both methods, the way control factors affect the repeatability of GC measurements expressed in the form of relative deviation was also evaluated.

Irradiated animal bedding material derived from cattail leaves and rice straw with orthophosphoric acid activation for amplified ammonia absorption

This scientific study investigates the suitability of cattail leaves and rice straw as biomass materials for animal bedding. Cattail, an invasive plant species known for its ability to thrive in nutrient-rich environments, offers high cellulose content for absorption. In combination with rice straw, which is readily available and cost-effective, the aim is to achieve optimal carbon-to-nitrogen ratios that suppress the growth of microorganisms. To resist bacterial growth, the mixed cattail leaves and rice straw samples undergo treatment with orthophosphoric acid at concentration of 25%, 30%, and 35% v/v, followed by gamma irradiation at 25 kGy. A comprehensive evaluation of the materials, focusing on surface morphology, water absorption, ammonia absorption, and bacterial resistance was conducted. SEM images provide evidence of dramatic surface restructuring. Samples treated with 30% v/v orthophosphoric acid exhibit enhanced water absorption capacities, and can absorb water equivalent to 2.2 times their own weight. Also, samples containing a 1:1 ratio of cattail leaves and rice straw demonstrate superior ammonia absorptions as evidenced by gas chromatography (GC) measurements compared to other samples. After sample irradiation, less bacterial growth was observed by optical density measurements. These findings support the potential utilization of a 1:1 ratio of cattail leaves and rice straw, treated with orthophosphoric acid of 30% v/v and irradiated with gamma radiation, as an effective animal bedding material. This combination offers advantages in terms of waste absorption and microbial control, making it a promising option for use in animal husbandry and laboratory settings.

Effect of Incorporation Techniques and Soil Properties on NH3 and N2O Emissions after Urea Application

Ammonia (NH3) emissions affect the environment, the climate, and human health and originate mainly from agricultural sources like urea fertilizers. Such losses from urea fertilizer can be avoided by different application techniques like incorporation. However, the knowledge of the effect of these techniques on NH3 emissions is very limited and ambiguous since incorporation can also promote nitrous oxide (N2O) emissions. Three different principles of fertilizer incorporation methods were compared in three different soils (sandy, loamy, and clayey) at two moisture levels of 70% and 30% water-holding capacity (WHC), shallow mixing at 2 cm, injection with the slit technique at 5 cm, and deep complete incorporation at 5 cm simulating plow incorporation. The laboratory study was conducted with open dynamic incubation chambers where NH3 emissions were monitored with washing bottles while N2O emissions were studied with gas chromatographic (GC) measurements. The highest cumulative NH3 emissions occurred at low soil moisture levels in sandy soil (34% of the N applied). A maximum reduction in emissions by 87% was achieved with slit injection and 82% with deep injection compared to standard surface application. The reduction effect was positively related to increasing clay content. N2O emissions were delayed and highest from sandy soil. Overall, all urea incorporation techniques showed great potential for mitigating NH3 emissions on the clayey soil; for sandy and drier soils, only deeper or closed slot injection were consistently effective. However, connected to the surface incorporation at the higher moisture level, a relevant increase in N2O emissions compared to surface application was observed. Therefore, an increase in N2O emissions by urea incorporation may rule out specific incorporation techniques for NH3 emissions reduction from field-applied urea. In agricultural practice, a lower reduction in NH3 by fertilizer incorporation can be assumed in sandy soils or under dry soil conditions, as well as a more challenging technical implementation.

Effects of Different TiO2/CNT Coatings of PVDF Membranes on the Filtration of Oil-Contaminated Wastewaters.

Six different TiO2/CNT nanocomposite-coated polyvinylidene-fluoride (PVDF) microfilter membranes (including -OH or/and -COOH functionalized CNTs) were evaluated in terms of their performance in filtering oil-in-water emulsions. In the early stages of filtration, until reaching a volume reduction ratio (VRR) of ~1.5, the membranes coated with functionalized CNT-containing composites provided significantly higher fluxes than the non-functionalized ones, proving the beneficial effect of the surface modifications of the CNTs. Additionally, until the end of the filtration experiments (VRR = 5), notable flux enhancements were achieved with both TiO2 (~50%) and TiO2/CNT-coated membranes (up to ~300%), compared to the uncoated membrane. The irreversible filtration resistances of the membranes indicated that both the hydrophilicity and surface charge (zeta potential) played a crucial role in membrane fouling. However, a sharp and significant flux decrease (~90% flux reduction ratio) was observed for all membranes until reaching a VRR of 1.1-1.8, which could be attributed to the chemical composition of the oil. Gas chromatography measurements revealed a lack of hydrocarbon derivatives with polar molecular fractions (which can act as natural emulsifiers), resulting in significant coalescent ability (and less stable emulsion). Therefore, this led to a more compact cake layer formation on the surface of the membranes (compared to a previous study). It was also demonstrated that all membranes had excellent purification efficiency (97-99.8%) regarding the turbidity, but the effectiveness of the chemical oxygen demand reduction was slightly lower, ranging from 93.7% to 98%.

Electrochemical CO2 Reduction Using a Free-Standing Porous Cu Framework as Catalyst

Due to fossil fuel combustion, the CO2 concentration in the atmosphere has reached around 410 ppm, causing major climate change on our planet. It thus becomes increasingly important to limit CO2 emissions or even remove CO2 from our atmosphere. One promising pathway to transform CO2 into useful chemicals is electrochemical reduction. However, electrochemical CO2 reduction is a challenging process that requires robust, low cost and stable catalysts. Copper is a promising candidate, at which CO2 can be reduced to several types of hydrocarbons.In this contribution, CO2 reduction was performed with a free-standing porous copper catalyst that was prepared using an inexpensive hydrogen assisted electroplating process [1]. The porous copper framework has good mechanical stability and a large internal surface area. Furthermore, it can easily be manufactured on a large scale. Due to its porous nature with tunable pore sizes this copper framework is at the same time gas diffusion layer and catalyst. A porous sample with a 10 cm2 geometric surface area was assembled in a custom-made electrochemical cell consisting of an open cell anode compartment, a closed compact cell for the cathode, separated by a cation-exchange membrane. CO2 mixed with water vapor is transported to the free-standing porous Cu in the closed compact cell for the CO2 reduction process. The electrochemical cell is connected to a gas chromatograph (GC) for further gas phase product analysis. The experiments were performed in the potential range between -0.3 V vs RHE and -1.7 V vs RHE in 0.5 M KHCO3 as the anolyte. GC measurements show a considerable amount of methane (CH4), ethylene (C2H4), ethane (C2H6), and propane (C3H8) which indicates a successful reduction reaction of the CO2 on the porous copper framework surface.[1] M. Kurniawan, M. Stich, M. Marimon, M. Camargo, R. Peipmann, T. Hannappel, A. Bund: "Electrodeposition of cuprous oxide on a porous copper framework for an improved photoelectrochemical performance." J. Mater Sci. 56 (2021) 11866-11880

Effect of Crosslink Density on Thermal Aging of Bio-Based Rigid Low-Density Closed-Cell Polyurethane Foams

Gradual replacement of the traditional raw materials in polyurethane (PU) synthesis by bio-based ones and introduction of environmentally friendly physical blowing agents (PBAs) motivate the analysis of thermal aging of bio-based foams in order to optimize the chemical structure of the PU matrix so that its permeability to PBA is minimized. With the aim of elucidating the effect of the PU chemical structure on thermal aging of foams, rigid low-density closed-cell PU foams were produced solely from bio-based polyols. The effective diffusivities of PBA and atmospheric gasses were evaluated based on the measured thermal conductivity aging of foams and validated by gas chromatography measurements of gas composition in foam cells. Gas permeability of the PU polymer was estimated based on effective diffusivity in foams and foam morphology and found to decrease with increasing crosslink density, apparently due to reduction in the fractional free volume in the polymers.

Estimation of retention parameters from temperature programmed gas chromatography

A fast and reliable method is presented to evaluate retention parameters of the distribution-centric 3-parameter model from temperature programed gas chromatographic measurements. Based on a fully differentiable model of the migration of solutes in a gas chromatographic (GC) system, Newton's method with a trust region is used to determine the three parameters, respectively the three parameters and the column diameter, of several solutes as the minima of the difference between measured and calculated retention times. The determined retention parameters can then be used in method development, using the simulation of GC separation. The results of the retention parameters are compared to the parameters determined using isothermal GC measurements and show good agreement, with deviations of less than 0.5% (1.8 K) for the most important parameter of characteristic temperature Tchar. Using the estimated retention parameters, additional GC separations are simulated and compared with measurements. Retention times in additional temperature programmed measurements could be predicted with less than 0.7% deviation. Four to five different temperature programs are enough to determine reliable retention parameters. Unless the column diameter and the column length are exactly known, it is preferable to also estimate the diameter (more precisely the L/d-ratio) together with the retention parameters.

The Influence of Antioxidant Plant Extracts on the Oxidation of O/W Emulsions

The demand for natural cosmetics has steadily increased in recent years. However, challenges occur especially in quality preservation regarding oxidative spoilage of natural cosmetic products, as the use of synthetic preservatives and antioxidants is limited. Therefore, it is important to find nature-based ingredients to ensure shelf life in natural cosmetic formulations. As a result, potential is seen in the use of plant-based antioxidant extracts. The aim of this work was to determine the suitability of the method combination by measuring the antioxidant activity, oxygen concentration, and volatile oxidation products via gas chromatography (hexanal) for the characterization of the influence of some plant extracts on the oxidative stability of natural cosmetic emulsions. Plant extracts of Riesling (Vitis vinifera) pomace, apple (Malus domestica) pomace, coffee (Coffea arabica) grounds, cocoa (Theobroma cacao) husk, and coffee (Coffea arabica) powder extract were incorporated in stable O/W emulsion formulations, while an emulsion without extract functioned as blank. Afterwards, the emulsions were subjected to 3-month accelerated storage tests with and without light exposure. Their oxygen uptake was investigated, and headspace gas chromatography measurements were performed to detect the fatty acid oxidation products formed during oxidative processes in the samples. The results showed that all emulsion samples under light exposure had a higher oxygen uptake and an increase in the characteristic fatty acid oxidation products compared with those stored under light exclusion. However, differences in oxygen uptake under light exposure were observed depending on the plant extract. Therefore, for O/W emulsions, the daily oxygen consumption rate correlated exponentially with the antioxidant activity, and the hexanal concentration correlated linearly with the daily oxygen consumption rate.

Sepiolite- rosemary oil combination as an environmentally oriented insecticide

Pest management is essential for cost-effective agriculture, however, due to the pests' ability to develop resistance to pesticides and the environmental and health considerations, there is a need for new and less hazardous alternatives. Certain essential oils that are regularly consumed by humans, are known to be lethal to specific pests and may serve as an alternative to traditional pesticides, even though their rapid volatility and potential phytotoxicity limit their direct use. Clays and organoclays were suggested as matrices for controlled-or slow-release of organic compounds, and thus might increase the pesticide efficiency and reduce the phytotoxicity of essential oils, by influencing their release. This study combined in vitro studies evaluating the rate of evaporation of rosemary (Rosmarinus officinalis) or lemongrass (Cymbopogon citratus) essential oils (ROEO and CCEO, respectively) from clay-based formulations, with in vivo experiments of essential oil-sepiolite insecticides on onion thrips (Thrips tabaci) while avoiding phytotoxicity damage to chives' (Allium schoenoprasum) crops. Fourier transform infrared spectroscopy (FTIR) and gravimetric kinetic measurements of the evaporation led to the conclusion that sepiolite increased the half-life evaporation period when compared to the raw essential oils or oils pre-adsorbed to other clays or even organoclays. Gas chromatography measurements showed that the interaction with the clay yielded differences in evaporation for the different components in the ROEO oil. Lethality tests of canola:essential oil combinations indicated that ROEO is effective at very low ratios, whereas CCEO activity required higher ratios. Plant tests showed that while the efficiency of CCEO formulation was not very significant, binding ROEO to sepiolite reduced its phytotoxicity yielding efficient pesticidal activity on thrips with less damage to chives' plants even one month after application.

Anion-Directed Self-Assembly of Calix[4]arene-Based Silver(I) Coordination Polymers and Photocatalytic Degradation of Organic Pollutants

Coordination polymers (CPs) have recently emerged as promising candidates for heterogeneous photocatalysis due to their structural designability and tunable properties. Herein, we developed two novel Ag(I)-calix[4]arene coordination polymers with the formula {[Ag2(μ-NO3)L1]}n (CP 1) and {[AgL1]·PF6}n (CP 2) (L1 = 2-mercapto-5-methyl-1,3,4-thiadiazole resorcinol calix[4]arene). Crystallography revealed that anion coordination and self-inclusion behavior induced the cavitand and silver ions to self-assemble into well-defined CPs 1 and 2 with different topological coordination frameworks, respectively. Furthermore, CPs 1 and 2 display high photocatalytic activity for the photodegradation of rhodamine B (RhB) and methyl orange (MO) in an aqueous solution under mild conditions (WLED and UV irradiation). The comparison results demonstrate that CP 1 exhibited better photocatalytic performance than CP 2, which correlated well with the differences in their molecular structure and HOMO-LUMO energy gaps. The photocatalysis products and possible intermediates were successfully monitored and determined using mass spectrum, gas chromatography, and electron paramagnetic resonance measurements. The rational photocatalysis mechanism was further investigated and proposed.