Density Functional Theory (DFT) study on the pyrolysis of cellulose: The pyran ring breaking mechanism

Characterization of the degradation products of lignocellulosic biomass by using tandem mass spectrometry experiments, model compounds, and quantum chemical calculations

Biomass-derived degraded lignin and cellulose serve as possible alternatives to fossil fuels for energy and chemical resources. Fast pyrolysis of lignocellulosic biomass generates bio-oil that needs further refinement. However, as pyrolysis causes massive degradation to lignin and cellulose, this process produces very complex mixtures. The same applies to degradation methods other than fast pyrolysis. The ability to identify the degradation products of lignocellulosic biomass is of great importance to be able to optimize methodologies for the conversion of these mixtures to transportation fuels and valuable chemicals. Studies utilizing tandem mass spectrometry have provided invaluable, molecular-level information regarding the identities of compounds in degraded biomass. This review focuses on the molecular-level characterization of fast pyrolysis and other degradation products of lignin and cellulose via tandem mass spectrometry based on collision-activated dissociation (CAD). Many studies discussed here used model compounds to better understand both the ionization chemistry of the degradation products of lignin and cellulose and their ions' CAD reactions in mass spectrometers to develop methods for the structural characterization of the degradation products of lignocellulosic biomass. Further, model compound studies were also carried out to delineate the mechanisms of the fast pyrolysis reactions of lignocellulosic biomass. The above knowledge was used to assign likely structures to many degradation products of lignocellulosic biomass.

Gas Phase Conformation of Trisaccharides and Core Pentasaccharide: A Three-Step Tree-Based Sampling and Quantum Mechanical Computational Approach

As an important component of N-linked glycoproteins, the core pentasaccharide is highly crucial to the potential application prospect of glycoprotein. However, the gas phase conformation study is a challenging one due to the size and complexity of the molecule, together with the necessity to rely on quantum chemistry modeling for relevant energetics and structures. In this paper, the structures of the trisaccharides and core pentasaccharides in N-linked glycans in the gas phase were constructed by a three-step tree-based (TSTB) sampling. Since single point energies of all the conformers are calculated at the temperature of zero, it is necessary to evaluate the stability at a high temperature. We calculate the Gibbs free energies using the standard thermochemistry model (T = 298.15 K). For trimannose, the energetic ordering at 298.15 K can be strongly changed compared to 0 K. Moreover, two structures of trimannose with high energies at 0 K are considered to provide a much better match of IR vibration signatures with the low Gibbs free energies. On this basis, the core pentasaccharide was constructed in three ways. The building configurations of core pentasaccharide were optimized to obtain reasonable low-energy stable conformers. Fortunately, the lowest-energy structure of core pentasaccharide is eventually the minimum at 0 K and 298.15 K. Furthermore, spectrum analysis of core pentasaccharide was carried out. Although poorly resolved, its contour from the experiment was in qualitative correspondence with the computed IR spectrum associated with its minimum free energy structure. A large number of strongly and weakly hydrogen-bonded hydroxyl and acetylamino groups contribute to a highly congested set of overlapping bands. Compared with traditional conformation generators, the TSTB sampling is employed to efficiently and comprehensively obtain preferred conformers of larger saccharides with lower energy.

Adsorption of chitosan combined with nicotinamide-modified eupatorium adenophorum biochar to Sb3+: Application of DFT calculation

The pollution and harm of Sb³⁺ to aquatic systems is a global problem, so Sb³⁺ removal from the water environment to make sure environment safety and human beings wellbeing is of urgency. This study explored the effect of chitosan combined with nicotinamide-modified eupatorium adenophorum biochar (CEBC) on adsorbing Sb³⁺ through batch adsorption experiments. The experiments indicated CEBC's maximum adsorption capacity to Sb³⁺ is 170.15 mg·g^-1. Meanwhile, the capacity of the original biochar (EBC) is only 9.97 mg·g^-1. Compared with EBC, CEBC contains more functional groups, such as CO, -OH and -NH₂. In addition, the pseudo-second-order kinetic model and the Langmuir model are fit to describe the kinetics and isotherms of adsorption of CEBC to Sb³⁺, which suggests that the adsorption of CEBC to Sb³⁺ is dominated by monolayer chemisorption. Density functional theory (DFT) calculations confirmed that the chelation between -NH₂ and Sb³⁺ is of significance in the adsorption process of CEBC. DFT calculations also found that the newly added -OH and CO in EBC have a synergistic enhancement effect on the absorption of Sb³⁺. The mechanism of CEBC absorbing Sb³⁺ includes electrostatic interactions, pore filling, Л-Л interactions, hydrogen bonding, functional group complexation, chelation, and oxidation. CEBC has an excellent anti-interference ability for inorganic anions (NO₃^-, SO₄^2- and Cl^-) and can also use the coexisting HA to improve its adsorption performance. In addition, CEBC has better mitigation of Sb³⁺ on the performance of Sb³⁺ about its secondary release and good reproducibility, which indicates that CEBC is a viable Sb³⁺ adsorbent.

Preparation, Properties, and Application of Lignocellulosic-Based Fluorescent Carbon Dots

Carbon dots (CDs) are a relatively new type of fluorescent carbon material with excellent performance and widespread application. As the most readily available and widely distributed biomass resource, lignocellulosics are a renewable bioresource with great potential. Research into the preparation of CDs with lignocellulose (LC-CDs) has become the focus of numerous researchers. Compared with other carbon sources, lignocellulose is low cost, rich in structural variety, exhibits excellent biocompatibility,^[1] and the structures of CDs prepared by lignin, cellulose, and hemicellulose are similar. This Review summarized research progress in the preparation of CDs from lignocellulosics in recent years and reviewed traditional and new preparation methods, physical and chemical properties, optical properties, and applications of LC-CDs, providing guidance for the formation and improvement of LC-CDs. In addition, the challenges of synthesizing LC-CDs were also highlighted, including the interaction of different lignocellulose components on the formation of LC-CDs and the nucleation and growth mechanism of LC-CDs; from this, current trends and opportunities of LC-CDs were examined, and some research methods for future research were put forward.

Forest Fuel Drying, Pyrolysis and Ignition Processes during Forest Fire: A Review

Forest ecosystems perform several functions that are necessary for maintaining the integrity of the planet’s ecosystem. Forest fires are thus a significant danger to all living things. Forest fire fighting is a foreground task for modern society. Forest fire prediction is one of the most effective ways to solve this urgent issue. Modern prediction systems need to be developed in order to increase the quality of prediction; therefore, it is necessary to generalize knowledge about the processes occurring during a fire. This article discusses the key features of the processes prior to forest fuel ignition (drying and pyrolysis) and the ignition itself, as well as approaches to their experimental and mathematical modeling.

Understanding Plant Biomass via Computational Modeling

Plant biomass, especially wood, has been used for structural materials since ancient times. It is also showing great potential for new structural materials and it is the major feedstock for the emerging biorefineries for building a sustainable society. The plant cell wall is a hierarchical matrix of mainly cellulose, hemicellulose, and lignin. Herein, the structure, properties, and reactions of cellulose, lignin, and wood cell walls, studied using density functional theory (DFT) and molecular dynamics (MD), which are the widely used computational modeling approaches, are reviewed. Computational modeling, which has played a crucial role in understanding the structure and properties of plant biomass and its nanomaterials, may serve a leading role on developing new hierarchical materials from biomass in the future.

Catalytic Production of Oxygenated and Hydrocarbon Chemicals From Cellulose Hydrogenolysis in Aqueous Phase

As the most abundant polysaccharide in lignocellulosic biomass, a clean and renewable carbon resource, cellulose shows huge capacity and roused much attention on the methodologies of its conversion to downstream products, mainly including platform chemicals and fuel additives. Without appropriate treatments in the processes of cellulose decompose, there are some by-products that may not be chemically valuable or even truly harmful. Therefore, higher selectivity and more economical and greener processes would be favored and serve as criteria in a correlational study. Aqueous phase, an economically accessible and immensely potential reaction system, has been widely studied in the preparation of downstream products of cellulose. Accordingly, this mini-review aims at making a related summary about several conversion pathways of cellulose to target products in aqueous phase. Mainly, there are four categories about the conversion of cellulose to downstream products in the following: (i) cellulose hydrolysis hydrogenation to saccharides and sugar alcohols, like glucose, sorbitol, mannose, etc.; (ii) selective hydrogenolysis leads to the cleavage of the corresponding glucose C-C and C-O bond, like ethylene glycol (EG), 1,2-propylene glycol (PG), etc.; (iii) dehydration of fructose and further oxidation, like 5-hydroxymethylfurfural (HMF), 2,5-furandicarboxylic acid (FDCA), etc.; and (iv) production of liquid alkanes via hydrogenolysis and hydrodeoxygenation, like pentane, hexane, etc. The representative products were enumerated, and the mechanism and pathway of mentioned reaction are also summarized in a brief description. Ultimately, the remaining challenges and possible further research objects are proposed in perspective to provide researchers with a lucid research direction.

Investigation into the reaction mechanism underlying the atmospheric low-temperature plasma-induced oxidation of cellulose

Atmospheric low-temperature plasma has been widely applied in surface modification of lignocellulose for manufacturing lightweight, strong composites. This study is aimed at elaborating the structural changes of cellulose after plasma treatment and further understanding the mechanism underlying plasma-induced oxidation of cellulose. Experiments suggested that atmospheric low-temperature plasma exhibits strong capacity to cleave covalent bonds, leading to oxidation and degradation of cellulose. Theoretical analysis revealed that cleavage of C₄O covalent bond is the first-step reaction during plasma-induced oxidation due to its low bond dissociation energy (229.2 kJ mol^-1). Subsequent pyranose ring-breaking reaction dominates dynamically and thermodynamically. Obtained outcomes are vital for fundamentally understanding the plasma-lignocellulose interaction. On that basis, plasma treatment for activation and oxidation of lignocellulose can be optimized and designed for improved efficiency. Wettability of lignocellulose can be thus improved in a short time, providing an opportunity to manufacture lignocellulose-based composites with enhanced efficiency and mechanical properties in future.

A mass spectrometric stochastic dynamic diffusion approach to selective quantitative and 3D structural analyses of native cyclodextrins by electrospray ionization and atmospheric pressure chemical ionization methods

The paper addressed shortcoming with highly precise and selective 3D structural analysis of native cyclodextrins in mixture using ions observable at low m/z-region by ESI- and APCI-mass spectrometry. Because of, the quantitative and structural analyses of CDs, in general, are vexed by a set of complications. The study outlines our own stochastic dynamic approaches to the latter issues based on new model relations, quantifing the measurable MS outcome intensity. They introduce the so-called stochastic dynamic mass spectrometric diffusion "D_SD" parameter, exhibiting high accuracy, precision, sensitivity and selectivity, respectively. It is linearly connected with the so-called quantum chemical diffusion parameter "D_QC" according to Arrhenius's theory. The most important upshot is that statistical parameters r = 0.99₆₃₉-0.99₉₈₁ has been obtained correlating between D_SD and D_QC parameters. Therefore, we determine high accurately 3D molecular and electronic structures of analytes by mass spectrometry. Fragment peaks at m/z 313, 279, 272, 252, 231, 214, 198, 171, 158 and 141 are examined. Mixtures of CDs and monomeric and acyclic oligomer carbohydrates glucose (1), sucrose (2), raffinose (3), melezitose (4) and cellotriose (5) are also studied. Our method is able to account precisely for the effect of the temperature under ESI- and APCI-MS conditions, as well. Correlative analysess between D_SD parameters of ESI- and APCI-MS measurements under different temperatures is also shown. Chemometric tests are used. Another important results and conclusions, among others, to draw from this research are: (i) excellent linear correlation between D_SD and D_QC parameters of r = 0.99₆₃₆ is found looking at common ions at m/z 141, 158 and 171, belonging to 2-formyl-3,4-dihydroxy-pyranylium, 4,5,6-trihydroxy-6H-pyran-2-carbaldehyde and 3,4,5-trihydroxy-6-oxo-6H-pyran-2-ylmethylidyne-oxonium ions. Thus, we distinguish precisely between the last structure and 3-formyl-4,5-dihydroxy-2,7-dioxa-8-oxonia-bicyclo[4.2.0]octa-1(8),3,5-triene cation. In the case of ion at m/z 141 subtle electronic effects are distinguished between the mentioned structure and the charged 3,4-dihydroxy-6H-pyran-2-carbaldehyde one. The method determines precisely very similar structurally poly-OH-substituted derivatives. Because of, (ii) absolute reproducibility (r = 1) of D_SD parameters of ESI-MS spectra is obtained studying the shown in point (i) MS peaks of β-CD between j^th and j^th numbers of experiments. The statistical equation is Dⁱ_SD = (0.51 ± 3.1.10^-5) × D^j_SD; (iii) the APCI- and ESI-MS provide identical results studying common MS ions of CDs and the correlation between D^APCI_SD and D^ESI_SD parameters excludes from error, due to, experiment; and (iv) The correlation between theory and experiment accounting for the factor temperature within our model equations shows r = 0.98₂₈ looking at the MS peaks at m/z 313 280, 279, 274 and 252, respectively. The effect of the temperature under both ESI- and APCI-MS conditions on the 3D molecular and electronic structures of CDs is precisely studied, respectively.

Quantitative study of the pyrolysis of levoglucosan to generate small molecular gases

In this paper, we studied 23 possible reaction paths for levoglucosan pyrolysis to generate small molecular gases and 51 compounds (including reactants, intermediates, and products), and quantified the 47 transition states involved in the pathway.

The removal of mercury ion pollution by using Fe3O4-nanocellulose: Synthesis, characterizations and DFT studies

In this study, we have attempted to extract cellulose from Cystoseria myricaas algae. Nanocellulose, Fe₃O₄ and Fe3O4-nanocellulose compounds are synthesized by acid hydrolysis and co-precipitation as well as sol-gel methods The synthesized compounds are characterized by x-ray diffraction, transmission electron microscopy, particle size distribution (PSD), scanning electron microscopy (SEM),energy dispersive x-ray spectroscopy, vibrating sample magnetometer and Fourier transform infrared spectroscopy. The Hg (II) uptake on Fe3O4-nanocellulose is investigated by 14 isotherm models, 12 kinetic models, adsorption activation energy as well as thermodynamic of adsorption. The polymers of algae and the interactions between Hg (II) and cellulose are investigated by density functional theory (DFT) in various conditions. The results of both simulations show a good agreement with experimental data.

Value-added organonitrogen chemicals evolution from the pyrolysis of chitin and chitosan

Thermogravimetric characteristics of chitin and chitosan and their potentials to produce value-added organonitrogen chemicals were separately evaluated via TG/DSC-FTIR and Py-GC/MS. Results shown that chitin had the better thermal stability and higher activation energy than chitosan because of the abundant acetamido group. Furthermore, the dominated volatilization in active pyrolysis of chitin contributed to its endothermic property, whereas the charring in chitosan led to the exothermal. During fast pyrolysis, the acetamido group in chitin and chitosan was converted into acetic acid or acetamide. Typical products from chitosan pyrolysis were aza-heterocyclic chemicals, i.e. pyridines, pyrazines, and pyrroles, with the total selectivity of 50.50% at 600°C. Herein, selectivity of pyrazine compounds was up to 22.99%. These aza-heterocyclic chemicals came from the nucleophilic addition reaction of primary amine and carbonyl. However, main reaction during chitin pyrolysis was ring-opening degradation, which led to the formation of acetamido chemicals, especially acetamido acetaldehyde with the highest selectivity of 27.27% at 450°C. In summary, chitosan had the potential to produce aza-heterocyclic chemicals, and chitin to acetamido chemicals.