92 research outputs found

    Towards a circular economy: fabrication and characterization of biodegradable plates from sugarcane waste

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    Bagasse pulp is a promising material to produce biodegradable plates. Bagasse is the fibrous residue that remains after sugarcane stalks are crushed to extract their juice. It is a renewable resource and is widely available in many countries, making it an attractive alternative to traditional plastic plates. Recent research has shown that biodegradable plates made from Bagasse pulp have several advantages over traditional plastic plates. For example, they are more environmentally friendly because they are made from renewable resources and can be composted after use. Additionally, they are safer for human health because they do not contain harmful chemicals that can leach into food. The production process for Bagasse pulp plates is also relatively simple and cost-effective. Bagasse is first collected and then processed to remove impurities and extract the pulp. The pulp is then molded into the desired shape and dried to form a sturdy plate. Overall, biodegradable plates made from Bagasse pulp are a promising alternative to traditional plastic plates. They are environmentally friendly, safe for human health, and cost-effective to produce. As such, they have the potential to play an important role in reducing plastic waste and promoting sustainable practices. Over the years, the world was not paying strict attention to the impact of rapid growth in plastic use. As a result, uncontrollable volumes of plastic garbage have been released into the environment. Half of all plastic garbage generated worldwide is made up of packaging materials. The purpose of this article is to offer an alternative by creating bioplastic goods that can be produced in various shapes and sizes across various sectors, including food packaging, single-use tableware, and crafts. Products made from bagasse help address the issue of plastic pollution. To find the optimum option for creating bagasse-based biodegradable dinnerware in Egypt and throughout the world, researchers tested various scenarios. The findings show that bagasse pulp may replace plastics in biodegradable packaging. As a result of this value-added utilization of natural fibers, less waste and less of it ends up in landfills. The practical significance of this study is to help advance low-carbon economic solutions and to produce secure bioplastic materials that can replace Styrofoam in tableware and food packaging production

    Full-dimensional potential energy surface development and dynamics for the HBr + C2H5 → Br(2P3/2) + C2H6 reaction

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    We report a full-dimensional spin-orbit-corrected analytical potential energy surface (PES) for the HBr + C2H5 → Br + C2H6 reaction and a quasi-classical dynamics study on the new PES. For..

    Towards Automatic Generation of Chemistry Sets for Plasma Modeling Applications

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    Every technique for numerical modeling of low-temperature plasmas usually needs to be centered around a chemistry set (also referred to in the literature as reaction set, reaction mechanism, kinetic mechanism, etc.) Chemistry sets describe the kinetics of volumetric interactions between all the species tracked in the model, and additionally, the kinetics of the interactions between the species, and the surfaces of the modeling domain. Assembling self-consistent chemistry sets is a non-trivial task, mostly addressed by scientists with extensive experience in the field. This work envisions the Automatic Chemistry Set Generator; a method for algorithmic assembling of chemistry sets for low-temperature plasma modeling applications, based on a set of feed gas species and plasma parameters supplied by a user. In particular, two parts of this work detail two distinct steps necessary to be part of such a chemistry generator. I present a method for fast regression of kinetic parameters for reactions with unknown kinetics, and a method for skeletal reduction of detailed chemistry sets, by identifying redundant species and reactions

    Automated full-dimensional potential energy surface development and quasi-classical dynamics for the HI(X 1 Σ + ) + C 2 H 5 → I( 2 P 3/2 ) + C 2 H 6 reaction

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    We develop a high-level spin–orbit-corrected analytical ab initio potential energy surface and perform quasi-classical trajectory simulations to study the dynamics of the 9-atomic HI + C 2 H 5 → I + C 2 H 6 reaction in full (21) dimensions

    Chemical Kinetics

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    Chemical Kinetics relates to the rates of chemical reactions and factors such as concentration and temperature, which affects the rates of chemical reactions. Such studies are important in providing essential evidence as to the mechanisms of chemical processes. The book is designed to help the reader, particularly students and researchers of physical science, understand the chemical kinetics mechanics and chemical reactions. The selection of topics addressed and the examples, tables and graphs used to illustrate them are governed, to a large extent, by the fact that this book is aimed primarily at physical science (mainly chemistry) technologists. Undoubtedly, this book contains "must read" materials for students, engineers, and researchers working in the chemistry and chemical kinetics area. This book provides valuable insight into the mechanisms and chemical reactions. It is written in concise, self-explanatory and informative manner by a world class scientists in the field

    Химия и химическая технология в XXI веке : материалы XXI Международной научно-практической конференции студентов и молодых ученых имени выдающихся химиков Л. П. Кулёва и Н. М. Кижнера, посвященной 110-летию со дня рождения профессора А. Г. Стромберга, 21–24 сентября 2020 г., г. Томск

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    В сборнике представлены материалы XXI Международной научно-практической конференции студентов и молодых ученых «Химия и химическая технология в XXI веке» имени выдающихся химиков Л. П. Кулёва и Н. М. Кижнера, посвященной 110-летию со дня рождения профессора А. Г. Стромберга. В материалах сборника обсуждаются проблемы химии и химической технологии, актуальные для современной экономики. Большое внимание уделено синтезу специальных органических соединений, исследованию их свойств. Многие работы студентов и молодых ученых посвящены региональным проблемам экологии и переработки углеводородного сырья. Также в сборнике затронуты проблемы исследований современных материалов. Значительное внимание уделено нанотехнологиям в химической науке

    New Methods for Data Analysis of Complex Chemical Systems With Practical Applications for Atmospheric Studies

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    The hydroxyl radical, OH, is the most important oxidizing agent in the troposphere during daylight periods. This radical, which is predominantly produced from the photolysis of ozone initiates the gas-phase oxidation of the vast majority of volatile organic compounds emitted in the atmosphere. This thesis is focused on the development and exploitation of useful methods of analysis for the study of atmospherically-relevant processes via direct OH measurements. However, the flexibility of the technique makes it also suitable for the study of high temperature combustion-related chemistry. For example, OH recycling can be an important process for the high temperature oxidation of ethers, a class of oxygenated species often used as fuel additives. Such methods provide the necessary tools for the exploration of complex competing processes, stretching the limits of the conventional bimolecular analysis for measuring rate coefficients. Among them, a new method based on Master Equation calculations via global analysis allows the direct analysis of the temporal evolution of OH radicals undergoing temperature and pressure dependent processes. Such unprecedented analysis can not only provide mechanistic information, but also enables a robust evaluation of the thermochemistry of elementary reactions. The method is very useful in situations where a reaction of interest cannot be isolated from competing processes, as required by conventional analysis techniques. For example, for the high temperature oxidation of alkenes which involve both an OH addition and a hydrogen abstraction mechanism, the global technique is capable of discriminating and quantifying the contribution of each channel. The reaction of OH radicals with sulphur dioxide (SO2) was investigated via classical Master Equation analysis. The role of a weakly bound pre-reaction complex formation (~7.2 kJ mol^-1) was tested and a comparison of Leeds experimental data with the literature was undertaken. The results indicated that the pre-reaction complex formation is not significant under atmospheric conditions and much of literature data may have been influenced by secondary chemistry associated with SO2 photolysis. A transition state submerged below the reagents ( 1.0 kJ mol^-1) was required to describe the Leeds measurements, which appear to be more consistent than the rest of the literature. The analysis of high temperature equilibration data (OH + SO2 ⇄ HO-SO2), allowed the enthalpy of reaction to be determined (110.5 ± 6.6 kJ mol^-1). This experimental determination is in excellent agreement with the highest-level theoretical predictions found in the literature (~111.5 kJ mol^-1). The OH + isoprene reaction in the absence of oxygen was explored over a wide range of temperatures (298-794 K) and pressures (~60-1500 Torr). At high enough temperatures (T > 700 K), direct observations of the established isoprene + OH ⇄ isoprene-OH equilibrium were collected. The study also generated unprecedented rate coefficients which were subsequently employed for the study of OH recycling in the presence of O2. The equilibration data were exploited via a bi-exponential analysis of both experimental and Master Equation-simulated traces and used for the determination of the well-depth for OH addition to carbon C1 (153.5 ± 6.2 kJ mol^-1), which is in excellent agreement with our theoretically derived estimate (154.1 kJ mol^-1). This experimental value, however, is dependent on the level of theory at which the vibrational modes of the involved species are treated. The equilibration data also indicated a significant OH loss in the system, incompatible with the reaction of OH with its precursor or diffusion. This process was rationalized as a competing hydrogen abstraction, which interfered in the non-exponential equilibration traces. A global analysis of the data was capable of extracting information about both the OH addition (k_addition_∞(T) = (9.5 ± 1.2) × (10^-11) × (T/298 K)^(-1.33 ± 0.32) cm^3 molecule^-1 s^-1) and the abstraction channel, (k_abstraction_∞(T) = (1.3 ± 0.3) × (10^-11) × exp((-3.61 kJ mol^-1)/RT) cm^3 molecule^-1 s^-1). With respect to the OH addition, a comparison with previous investigations suggests that only our measurements at T>700 K were in the fall-off region, contradicting some literature studies. A new method of analysis via a global multi-temperature, multi-pressure fitting procedure was developed and used for the study of the ethylene + OH reaction. The method relied on the Master Equation modelling of the OH addition, and a subsequent incorporation of new consumption and formation terms to the rate laws of the involved species. With effect, the simulated traces become comparable to experimental observations and a direct trace analysis is possible. The reaction of OH with ethylene was studied over a range of temperatures (563 – 723 K) and pressures (~60 220 Torr), which included pressure dependent data, to test the limits of this global direct trace analysis. Excellent descriptions of OH traces were obtained when the Master Equations were modified to incorporate a hydrogen abstraction and a unimolecular loss of the adduct. A simultaneous fit of 96 traces where direct ethylene + OH ⇄ adduct equilibration was observed enabled the determination of the well-depth of the adduct (111.8 ± 0.20 kJ mol^-1). This value is in excellent agreement with our theoretical prediction (111.4 kJ mol^-1), calculated at the CCSD(T)/CBS//M06-2X/ aug cc pVTZ level of theory. The high pressure limiting rate coefficient for the OH addition extracted from the experimental traces by this technique (k_addition_∞(T)=(8.13 ± 0.86) × (10^-12) × (T/298 K)^(-0.99 ± 0.18) cm^3 molecule^-1 s^-1), is in very good agreement with the IUPAC recommendation for the 100 - 500 K temperature range (k_1a_∞(T)= 9 × (10^-12) × (T/300 K)^-0.85 cm^3 molecule^-1 s^-1). Furthermore, the experimentally derived abstraction rate coefficients k_abstraction(T) = (3.5 ± 0.75) × (10^-11) × exp((-26.2 ± 1.3 kJ mol^-1)/RT) cm^3 molecule^-1 s^-1 are in excellent agreement with previous investigations. The method proved to be robust enough to discriminate and quantify the competing processes influencing the shapes of the experimental OH profiles. This novel analysis was employed for the study of LIM1, a promising mechanism for the description of OH recycling via isoprene peroxy chemistry. Experiments were undertaken at elevated temperatures (400 <T<600 K) and large concentrations of O2 were employed ([O2]~10^17 molecules cm^-3) so as to promote the recycling to the millisecond timescale, compatible with direct experimental techniques for OH detection. Rate coefficients measured in the absence of O2 were incorporated to help constrain the analysis of the data. The LIM1 mechanism proved to be capable of accurately describing non-exponential traces collected under such experimental conditions. The OH recycling involves crucial hydrogen shifts, whose barriers were adjusted in unison to provide a good fit to the data. However, very small modifications were necessary for this purpose (~ 2 kJ mol^-1). The incorporation of these findings in an atmospheric model enabled the description of approximately 50% of the OH concentration measured in a field campaign performed in a Borneo rainforest, an environment dominated by biogenic volatile organic compounds emissions. Finally, the thesis concludes in Chapter 7 with a summary of the results of each experimental chapter including suggestions for further areas of study

    Speciation of gaseous oxidized mercury molecules relevant to atmospheric and combustion environments

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    Mercury is a pervasive and highly toxic environmental pollutant. Major anthropogenic sources of mercury emissions include artisanal gold mining, cement production, and combustion of coal. These sources release mostly gaseous elemental mercury (GEM), which upon entering the atmosphere can travel long distances before depositing to environmental waters and landforms. The deposition of GEM is relatively slow, but becomes greatly accelerated when GEM is converted to gaseous oxidized mercury (GOM) because the latter has significantly higher water solubility and lower volatility. Modeling GOM deposition requires the knowledge of its molecular identities, which are poorly known because ultra-trace (tens to hundreds part per quadrillion) level of GOM in the atmosphere makes its experimental detection and analysis a formidable task. It is here where computational methods can help address the GOM molecular identity problem. Accordingly, the two major goals of this work are to (a) develop a computationally inexpensive approach for assessing accurate thermochemistry of GOM species and (b) investigate ion-molecule reactions of GOM species in order to assist experimentalists in the development of a novel detection method. The first goal addresses the question of what are some of the molecular identities of GOM species that could be present in combustion and atmospheric environments. Ab initio and density functional theory calculations are used in combination with the methods of isodesmic and isogyric work reactions in order to calculate accurate heats of formation for GOM species that can form in reactions of GEM with atomic halogens, OH, OCl, and OBr. The accuracy of the calculations is assessed by comparing the calculated values against experimental data and also data from rigorous and computationally expensive state-of-the-art ab initio calculations. Bond dissociation energies (BDE) are determined from the heats of formation and used as a measure of the stability of the GOM species studied. The second goal of this work addresses the question of how can GOM species be measured in the atmosphere in real-time while retaining speciation information, using chemical ionization mass spectrometry. Ab initio and density functional theory calculations are used to determine structures of products of ion-molecule reactions and calculate associated reaction enthalpies and Gibbs free energies. The obtained data are used to identify reagent ions that can be used for atmospheric detection of GOM. The calculations provide an understanding of the complex ion-molecule chemistry that occurs during the chemical ionization process. The implications of this body of work are as follows. A low computational cost methodology is established that can be used to study a wide range of GOM species outside the scope of this work. The thermochemistry of the GOM species calculated in this work can serve as the foundation for future kinetic studies with the goal of improving the reaction mechanism in global transport models to provide a better understanding of the global mercury budget. Reagent ions identified in this work can be used for real-time speciation of GOM in the atmosphere, using chemical ionization mass spectrometry

    Area selective atomic layer deposition of Si-based materials

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    Modern electronics are very small and light yet extremely powerful. This is possible due to the constant integration of new techniques and novel materials into the electronics fabrication process. In the current project we are focusing on one of the most precise deposition fabrication techniques for microchip fabrication, called atomic layer deposition (ALD). In particular, we are interested in the applications of ALD for area-selective deposition, where the material is deposited only where it is needed allowing the lateral control of the grown film. We are using the quantum mechanical modelling, density functional theory (DFT) to investigate the chemical mechanism of the area-selective ALD processes for Si-based materials (SiC, SiO2 and SiNx ), which are widely used in the semiconductor microchip fabrication process. We are also focusing on the possible SiC ALD mechanism in more detail, as this mechanism is very challenging and still not implemented in high-volume manufacturing in the semiconductor industry. In order to investigate the possibility of area-selective deposition of Si-based materials on Si, SiC, SiO2 and SiNx substrates, the difference in adsorption energies of various aminosilane precursors was first analyzed by DFT. From DFT calculations we found that it is thermodynamically favorable for aminosilane precursors to react with SiNx and SiO2 substrates but not with SiC and Si. We further experimentally corroborate these results by depositing SiNx on Si, SiO2 and SiC substrates using di(sec-butylamino)silane precursor and N2 plasma ALD and measuring the apparent SiNx thickness by spectroscopic ellipsometry. Both DFT calculations and experiment show that the aminosilane precursor adsorbs selectively on SiO2 not on Si and SiC substrates, however, after N2 plasma pulse this selectivity is lost. Further, we investigated the possibility of the ALD of SiC. First, we used DFT to screen various precursors in order to select the most favourable for SiC ALD. Then we expanded this study by analyzing how these precursors react with H-terminated and bare SiC surfaces. We predicted that precursors disilane (Si2H6 ), silane (SiH4 ) or monochlorosilane (SiH3Cl) with ethyne (C2H2 ), carbontetrachloride (CCl4 ) or trichloromethane (CHCl3 ) are the most promising for ALD of SiC. All of these precursors are predicted to react thermodynamically with bare SiC but not with the passivated surface. An additional activation step would be needed to sustain an ALD process. In order to analyze how silane plasma fragments will react with the passivated surface, the reaction pathways of neutral silane plasma fragments SiH3 and SiH2 with the H-terminated surface were analyzed. Counterintuitively, it was found that silane plasma fragments SiH3 and SiH2 react selectivity with the Si-H bond rather than with the C-H bond of the H-terminated SiC surface. Lastly, as a part of collaboration with Prof. Adrie Mackus from Plasma Materials Process group in Eindhoven Technological University, Netherlands, we used a DFT screening approach to determine the non-growth surface during ALD of transition metal oxides via a ligand-exchange mechanism in the precursor pulse. Two different precursors reacting with various OH-terminated metal surfaces were compared: a heteroleptic amidometallocene and a homoleptic alkoxide. A sample result is that HfO2 , SiO2 and GeO2 are predicted to show nucleation delay in ALD on OH-terminated W, Co and Cu surfaces. Depending on the ligands used in the ALD precursor, Ru-based or W-based substrates were predicted to resist the nucleation of all the metal oxides that were studied

    The Kinetics of the Reaction C2H5• + HI → C2H6 + I• over an Extended Temperature Range (213-623 K): Experiment and Modeling

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    The present study reports temperature dependent rate constants k1 for the title reaction across the temperature range 213 to 293 K obtained in a Knudsen flow reactor equipped with an external free radical source based on the reaction C2H5I + H• → C2H5• + HI and single VUV-photon ionization mass spectrometry using Lyman-α radiation of 10.2 eV. Combined with previously obtained high-temperature data of k1 in the range 298-623 K using the identical experimental equipment and based on the kinetics of C2H5• disappearance with increasing HI concentration we arrive at the following temperature dependence best described by a three-parameter fit to the combined data set: k1 = (1.89 ± 1.19)10−13(T/298)2.92±0.51 exp ((3570 ± 1500)/RT), R = 8.314 J mol-1 K-1 in the range 213-623 K. The present results confirm the general properties of kinetic data obtained either in static or Knudsen flow reactors and do nothing to reconcile the significant body of data obtained in laminar flow reactors using photolytic free radical generation and suitable free radical precursors. The resulting rate constant for wall-catalyzed disappearance of ethyl radical across the full temperature range is discussed. Highly correlated ab initio quantum chemistry methods and canonical transition state theory were applied for the reaction energy profiles and rate constants. Geometry optimizations of reactants, products, molecular complexes, and transition states are determined at the CCSD/cc-pVDZ level of theory. Subsequent single-point energy calculations employed the DK-CCSD(T)/ANO-RCC level. Further improvement of electronic energies has been achieved by applying spin-orbit coupling corrections towards full configuration interaction and hindered rotation analysis of vibrational contributions. The resulting theoretical rate constants in the temperature range 213-623 K lie in the range E-11-E-12 cm3 molecule-1 s-1, however experiments and theoretical modelling seem at great odds with each other
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