Naturally Occurring Allotropes of Carbon

Carbon is one of the most important chemical elements, forming a wide range of important allotropes, ranging from diamond over graphite to nanostructural materials such as graphene, fullerenes, and carbon nanotubes (CNTs). Especially these nanomaterials play an important role in technology and are commonly formed in laborious synthetic processes that often are of high energy demand. Recently, fullerenes and their building blocks (buckybowls) have been found in natural fossil materials formed under geological conditions. The question arises of how diverse nature can be in forming different types of natural allotropes of carbon. This is investigated here, using modern analytical methods such as ultrahigh-resolution mass spectrometry and transmission electron microscopy, which facilitate a detailed understanding of the diversity of natural carbon allotropes. Large fullerenes, fullertubes, graphene sheets, and double- and multiwalled CNTs together with single-walled CNTs were detected in natural heavy fossil materials while theoretical calculations on the B3LYP/6-31G(d) level of theory using the ORCA software package support the findings.

Unveiling the Quantitative Relationships between Electron Distribution and Steric Hindrance of Organic Amines and Their Reaction Rates with Carbonyl Sulfur: A Theoretical Calculation Investigation

The removal of carbonyl sulfide (COS) commonly contained in natural gas is of great significance but still very challenging via a widely employed absorption process due to its low reactivity and solubility in various commercial solvents. Artificial intelligence (AI) is playing an increasingly important role in the exploration of desulfurization solvents. However, practically feasible AI models still lack a thorough understanding of the reaction mechanisms. Machine learning (ML) models established on chemical mechanisms exhibit enhanced chemical interpretability and prediction performance. In this study, we constructed a series of solvent molecules with varying functional groups, including linear aliphatic amines, cyclic aliphatic amines, and aromatic amines and proposed a three-step reaction pathway to dissect the effects of charge and steric hindrance of different substituents on their reaction rates with COS. Chemical descriptors, based on electrostatic potential (ESP), average local ionization energy (ALIE) theory, Hirshfeld charges, and Fukui functions, were used to correlate and predict the electrophilic reactivity of amine groups with COS. Substituents influence the reaction rate by changing the attraction interaction of amine groups to COS molecules and the electron rearrangement in the electrophilic reaction. Furthermore, they have more pronounced steric effects on the reaction rate in the linear amines. The descriptors N_ALIE and q(N) were found to be crucial in predicting the reactivity of amine groups with COS. Present study provides a comprehensive understanding of the reaction mechanisms of COS with amine compounds, offers specific chemical principles for the development of chemistry-driven ML models, sheds light on other types of electrophilic reactions occurring on amine and phosphine groups, and guides the development of chemical solvents in gas absorption processes.

Atomically Dispersed Aluminum Sites in Hexagonal Boron Nitride Nanofibers for Boosting Adsorptive Desulfurization Performance

The exploitation of highly efficient and cost-effective selective adsorbents for adsorptive desulfurization (ADS) remains a challenge. Fortunately, single-atom adsorbents (SAAs) characterized by maximized atom utilization and atomically dispersed adsorption sites have great potential to solve this problem as an emerging class of adsorption materials. Herein, aiming at improving the efficiency of ADS performance via the economical and feasible strategy, the desirable SAAs have been fabricated by uniformly anchoring aluminum (Al) atoms on hexagonal boron nitride nanofibers (BNNF) via an in situ pyrolysis method. Remarkably, Al-BN-1.0 exhibited a superior adsorption capacity of 46.1 mg S/g adsorbent for dibenzothiophene, with a 45% increase in adsorption capacity compared to the pristine BNNF. Additionally, it demonstrated excellent adsorption of other thiophene sulfides. Moreover, the ADS mechanisms have been investigated through special adsorption experiments combined with density functional theory (DFT) calculations. It was demonstrated that the superior ADS performance and selectivity of Al-BN-1.0 originate from the sulfur-aluminum (S-Al) and π-π interactions cooperating synergistically. This work would cast light on a novel fabrication strategy for the SAAs based on the two-dimensional material with a tunable metal site configurations and densities for varied selective adsorption and separation.

Universal N2O Reaction Gas To Remove Spectral Interferences of Nonmetallic Impurity Elements by Inductively Coupled Plasma Tandem Mass Spectrometry Analysis of High-Purity Magnesium Alloys

Using N₂O as a universal reaction gas, a new strategy was proposed for the highly sensitive interference-free simultaneous determination of nonmetallic impurity elements in high-purity magnesium (Mg) alloys by ICP-MS/MS. In the MS/MS mode, through O-atom and N-atom transfer reactions, ²⁸Si⁺ and ³¹P⁺ were converted to the oxide ions ²⁸Si¹⁶O₂⁺ and ³¹P¹⁶O⁺, respectively, while ³²S⁺ and ³⁵Cl⁺ were converted to the nitride ions ³²S¹⁴N⁺ and ¹⁴N³⁵Cl⁺, respectively. The ion pairs formed via the ²⁸Si⁺ → ²⁸Si¹⁶O₂⁺, ³¹P⁺ → ³¹P¹⁶O⁺, ³²S⁺ → ³²S¹⁴N⁺, and ³⁵Cl⁺ → ¹⁴N³⁵Cl⁺ reactions by the mass shift method could eliminate spectral interferences. Compared with the O₂ and H₂ reaction modes, the present approach delivered much higher sensitivity and lower limit of detection (LOD) of the analytes. The accuracy of the developed method was evaluated via standard addition method and comparative analysis by sector field ICP-MS (SF-ICP-MS). The study indicates that in the MS/MS mode, use of N₂O as reaction gas can provide interference-free conditions and sufficiently low LODs for analytes. The LODs of Si, P, S, and Cl could reach down to 17.2, 4.43, 10.8, and 31.9 ng L^-1, respectively, and the recoveries were in the range of 94.0-106%. The determination results of the analytes were consistent with those obtained by SF-ICP-MS. This study presents a systematic method for the precise and accurate quantification of Si, P, S, and Cl in high-purity Mg alloys by ICP-MS/MS. The developed method provides valuable reference that can be expanded and applied to other fields.

Development of a Novel HPLC-MS Method to Separate Polar and Non-Polar Compounds in Biodiesel/Petrodiesel Mixtures

Due to a trend to higher sustainability, biodiesel is often mixed into petrodiesel. The analysis of these blends on a molecular level is not trivial, since huge differences in concentrations and polarity of the analytes require a large dynamic range of the analytical method, as well as the ability to investigate molecules of widely different polarities. A combination of high-performance liquid chromatography (HPLC) with high resolution mass spectrometry (HRMS) was identified as a promising method and a normal-phase (NP)-HPLC using amino-functionalized silica gel-based stationary phase delivered the best results with very fast (under 4 min) measurements, with distinct separation of the compounds and clean mass spectra of singular compounds. This method can also be easily modified to elute all FAMEs (fatty acid methyl esters) in one singular peak, thus making the separation even faster (under 3 min).

Investigating Molecular Transformation Processes of Biodiesel Components During Long-Term Storage Via High-Resolution Mass Spectrometry

Biodiesel is an important building block in renewable energy transformation. The main issue is that during storage biodiesel will undergo transformation processes that can lead to molecular changes, which then can cause applicational problems such as severe motor damage. To prevent this, a detailed understanding of the involved molecules and the emerging aging products is necessary. Biodiesel samples were stored for up to 12 months to monitor molecular changes, and all mixtures were investigated by using ultrahigh-resolution mass spectrometry (HRMS) with electrospray ionization (ESI). The data revealed that during storage large numbers of oxygen atoms were incorporated into the fatty acid methyl esters (FAMEs). This process was dominant for the first quarter of aging but then became overshadowed by dimerization of oxygenated FAMEs. This means that there are two main pathways for aging in biodiesel: polyoxygenation and oligomerization. These findings greatly pin down the possible causes for sedimentation giving a solid foundation for aging inhibition development.

Catalytic cracking of acidified oil and modification of pyrolytic oils from soap stock for the production of a high-quality biofuel

Soap stocks are by-products obtained during the refining process of vegetable oil, and are mainly feedstocks to produce acidified oil. In this work, an efficient process was developed to convert soap stock to a high-quality biofuel with low impurity content.

Getting a better overview of a highly PAH contaminated soil: A non-targeted approach assessing the real environmental contamination

Over the last 40 years, soils contaminated with polycyclic aromatic hydrocarbons (PAH) were monitored according to a list of 16 PAH, established by the U.S. Environmental Protection Agency (EPA). This, however, is underestimating the danger to the environment and humanity because other high molecular weight PAHs, heterocycles (PAXH, X = N, O, S) and alkylated derivatives can also occur at the contaminated site. Here, a new non-targeted approach of highly contaminated soil (64.5 ± 9.5 g kg^-1 solvent extractable organics from the German Ruhrgebiet) is introduced, where ultrahigh resolution mass spectrometry is combined with multiple ionization methods to get a better overview of anthropogenic contamination at a former industrial site. In total, 21,958 elemental compositions were assigned for positive and negative mode measurements. The approach is strongly increasing the amount of data that can be obtained from a single contaminated soil, making an assessment of the real environmental risk possible. In addition to highly aromatized and (alkylated) high molecular weight PAH, other PAXH especially basic and neutral PANH with very high aromaticity were also detected. This shows that while regulations and routine analysis are still stuck in the 1960 s, modern analytical methods are present in the 21st century.

Studying the Complexity of Biomass Derived Biofuels

Biofuel produced from biomass pyrolysis is a good example of a highly complex mixture. Detailed understanding of its composition is a prerequisite for optimizing transformation processes and further upgrading conditions. The major challenge in understanding the composition of biofuel derived from biomass is the wide range of compounds with high diversity in polarity and abundance that can be present. In this work, a comprehensive analysis using mass spectrometry is reported. Different operation conditions are studied by utilizing multiple ionization methods (positive mode atmospheric pressure photo ionization (APPI), atmospheric pressure chemical ionization (APCI) and electrospray ionization (ESI) and negative mode ESI) and applying different resolving power set-ups (120 k, 240 k, 480 k and 960 k) and scan techniques (full scan and spectral stitching method) to study the complexity of a pyrolysis biofuel. Using a mass resolution of 960 k and the spectral stitching scan technique gives a total of 21,703 assigned compositions for one ionization technique alone. The number of total compositions is significantly expanded by the combination of different ionization methods.

Studying Natural Buckyballs and Buckybowls in Fossil Materials

Buckyballs (fullerenes) were first reported over 30 years ago, but still little is known regarding their natural occurrence, since they have so far only been found at sites of high-energy incidents, such as lightning strikes or meteor impacts, but have not been reported in low-energy materials like fossil fuels. Using ultrahigh-resolution mass spectrometry, a wide range of fullerenes from C30 to C114 was detected in the asphaltene fraction of a heavy crude oil, together with their building blocks of C10n H10 stoichiometry. High-level DLPNO-CCSD(T) calculations corroborate their stability as spherical and hemispherical species. Interestingly, the maximum intensity of the fullerenes was found at C40 instead of the major fullerene C60 . Hence, experimental evidence supported by calculations show the existence of not only buckyballs but also buckybowls as 3-dimensional polyaromatic compounds in fossil materials.

GC-ICP-MS/MS Instrumental Setup for Total and Speciation Sulfur Analysis in Gasolines using Generic Standards

Quantitative characterization of sulfur-containing petroleum derivatives is mainly limited by the large number of potential targets present and the matrix effects suffered due to the high-carbon-containing matrices. Herein we describe the instrumental modifications required in a commercial GC-ICP-MS/MS instrument, and their corresponding optimization, for turning it into a compound-independent quantitative technique for both total and speciation sulfur analysis in gasolines. Additionally, carbon-derived matrix effects were made negligible for direct and fast total S analysis, making the use of relatively complex isotope-dilution strategies not necessary anymore. An absolute detection limit of 0.3 pg of S was achieved, which is, to the best of our knowledge, more than 1 order of magnitude below the ones reported for other sulfur GC selective detectors. The precision was below 3% RSD. Total analysis was performed by flow-injection analysis through a transfer line and external calibration, whereas speciation analysis was carried out by chromatographic separation and internal standardization. In both cases, simple generic standards were used, which enabled us to get rid of specific S-containing standards, which were sometimes not available or unstable. The proposed method was successfully applied to total and speciation sulfur analysis of a commercial gasoline sample and validated with a certified-reference-material (ERM-EF213) gasoline. The approach has proved to be simple, fast, robust, and convenient for implementation in routine laboratories, as demonstrated by the successive analyses of 50 gasoline samples in 3 h without any instrumental drift.

High-resolution GC/MS studies of a light crude oil fraction

The continuous development in analytical instrumentation has brought the newly developed Orbitrap-based gas chromatography / mass spectrometry (GC/MS) instrument into the forefront for the analysis of complex mixtures such as crude oil. Traditional instrumentation usually requires a choice to be made between mass resolving power or an efficient chromatographic separation, which ideally enables the distinction of structural isomers that is not possible by mass spectrometry alone. Now, these features can be combined, thus enabling a deeper understanding of the constituents of volatile samples on a molecular level. Although electron ionization is the most popular ionization method employed in GC/MS analysis, the need for softer ionization methods has led to the utilization of atmospheric pressure ionization sources. The last arrival to this family is the atmospheric pressure photoionization (APPI), which was originally developed for liquid chromatography / mass spectrometry (LC/MS). With a newly developed commercial GC-APPI interface, it is possible to extend the characterization of unknown compounds. Here, first results about the capabilities of the GC/MS instrument under high or low energy EI or APPI are reported on a volatile gas condensate. The use of different ionization energies helps matching the low abundant molecular ions to the structurally important fragment ions. A broad range of compounds from polar to medium polar were successfully detected and complementary information regarding the analyte was obtained.

Studying the fragmentation mechanism of selected components present in crude oil by collision-induced dissociation mass spectrometry

RATIONALE

Structural characterization of individual compounds in very complex mixtures is difficult to achieve. One important step in structural elucidation is understanding the mass spectrometric fragmentation mechanisms of the compounds present in such mixtures. Here, different individual compounds presumed to be present in a complex crude oil mixture have been synthesized and structurally characterized by tandem mass spectrometry (MS/MS) studies.

METHODS

Model compounds with different aromatic cores and various substitutents were synthesized. Major effort has been put into producing isomerically pure compounds to better understand the fragmentation pattern. Each synthesized compound has been subjected to MSⁿ studies using either a triple quadrupole or a linear ion trap mass spectrometer with electrospray or atmospheric pressure photoionization. The results are used to analyze individual compounds from a complex vacuum gas oil (VGO).

RESULTS

The synthesized compounds and a chromatographically simplified vacuum gas oil were used for structural analysis. The major fragmentation mechanism is the benzylic cleavage of the aliphatic side chain. Each side chain can be separately removed from the aromatic core by using MSⁿ methods. At the end of a series of fragmentations, the base aromatic core structure remains and can be chararcterized.

CONCLUSIONS

By defining the fragmentation mechanism in complex oil samples it was possible to structurally characterize individual compounds present in a chromatographically simplified VGO. The compounds consist of an aromatic core with aliphatic side chains. Cleavage of all side chains can be achieved by MSⁿ measurements, allowing characterization of the remaining core structure.