Heteroatom doped carbon dots (CDs), with high photoluminescence quantum yield (PLQY), are of keen interest in various applications such as chemical sensors, bio-imaging, electronics, and photovoltaics. Zinc, an important element assisting the electron-transfer process and an essential trace element for cells, is a promising metal dopant for CDs, which could potentially lead to multifunctional CDs. In this contribution, we report a single-step, high efficiency, hydrothermal method to synthesize Zn-doped carbon dots (Zn-CDs) with a superior PLQY. The PLQY and luminescence characteristic of Zn-CDs can be tuned by controlling the precursor ratio, and the surface oxidation in the CDs. Though a few studies have reported metal doped CDs with good PLQY, the as prepared Zn-Cds in the present method exhibited a PLQY up to 32.3%. To the best of our knowledge, there is no report regarding the facile preparation of single metal-doped CDs with a QY more than 30%. Another unique attribute of the Zn-CDs is the high monodispersity and the resultant highly robust excitation-independent luminescence that is stable over a broad range of pH values. Spectroscopic investigations indicated that the superior PLQY and luminescence of Zn-CDs are due to the heteroatom directed, oxidized carbon-based surface passivation. Furthermore, we developed a novel and sensitive biosensor for the detection of hydrogen peroxide and glucose leveraging the robust fluorescence properties of Zn-CDs. Under optimal conditions, Zn-CDs demonstrated high sensitivity and response to hydrogen peroxide and glucose over a wide range of concentrations, with a linear range of 10-80 μM and 5-100 μM, respectively, indicating their great potential as a fluorescent probe for chemical sensing.

Asphaltenes-free vacuum resid derived deasphalted oils (DAOs) from Chinese Liaohe (LDAO) and Venezuela Orinoco (VDAO) were subjected to catalytic hydrotreating. Electrospray ionization (ESI) Fourier transform-ion cyclotron resonance mass spectrometry (FT-ICR MS) analyses were performed on LDAO and VDAO before and after hydrotreating to determine the structural composition transformation of nitrogen-containing compounds as a result of hydrotreating. The results showed that the basic nitrogen contents of the two DAO before and after hydrotreating were relatively constant. However, the neutral nitrogen contents of hydrotreated LDAO and VDAO were dramatically reduced. The LDAO had a higher neutral nitrogen conversion than VDAO, even though LDAO had a higher neutral nitrogen content than VDAO prior to hydrotreating. The significant difference in nitrogen removal for the DAOs was due to the structural variation of the neutral nitrogen compounds. By plotting the double bond equivalent (DBE) value as a function of carbon number for N1 class species, the hydrodenitrogenation reactivities of nitrogen compounds could be classified as easy- and hard-to-convert nitrogen compounds. The easy-to-convert nitrogen compounds have more unsaturated cores and have less and/or shorter alkyl side chains than the hard-to-convert nitrogen compounds which have long alkyl side chains.

A Venezuela Orinoco petroleum vacuum residue (VR) was subjected to supercritical fluid extraction fractionation (SFEF) and separated into 13 extractable fractions and an unextractable end-cut. Detailed molecular composition of polar heteroatom species in the SFEF subfractions were determined by electrospray ionization (ESI) Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). The SFEF subfractions were also subjected to high-temperature gas chromatography (GC) for their simulated distillation analysis, gel permeation chromatography (GPC) for their molecular distributions, and open column liquid chromatography for their saturates, aromatics, resins, and asphaltenes (SARA) compositions. In ESI FT-ICR analysis, the mass spectra showed that the mass range and maximum peak of the SFEF subfraction increased as the SFEF subfraction became heavier. Multifunctional group compounds, such as N

A novel methodology was extended for modeling the detailed composition of petroleum heavy vacuum resid fractions. The resid molecules were organized in terms of basic structural attributes: cores, intercore linkages, and side chains. The identities of the structural attributes were determined both from the extrapolation of chemical characteristics of light petroleum and the analysis of detailed mass spectrometric measurement of heavy resid fragmentation products. A building block library was constructed containing ∼600 attributes. The molecular composition was constructed by the combination of attributes, or building blocks, into discrete molecules. The quantitative abundance of each molecule was determined by the juxtaposition of a set of structural attribute probability density functions (PDFs) constraining pure hydrocarbon and heteroatom mixtures. Quantitative structure–property relationships (QSPRs) were applied to calculate the bulk properties of both the constructed molecules and the mixture. The adjustable parameters of the PDFs were determined using an optimization loop that employed an objective function that contained a term for each of the available analytical data points. The resulting optimal molecular compositions were in good agreement with the experimental structural information.