Synthesis of graphene derivatives from asphaltenes and effect of carbonization temperature on their structural parameters.

A method for synthesizing graphene derivatives from asphaltene is proposed in this work. The graphene derivatives are mainly composed of few-layer graphene-like nano-sheets of randomly distributed heteroatoms; mainly sulfur and nitrogen. The proposed method is based on a thermal treatment in which asphaltene is carbonized in a rotating quartz-tube furnace under an inert atmosphere at a temperature in the range of 400-950 °C. Asphaltenes from different origins were employed to verify the synthesis method. The results indicate that graphene derivatives obtained at high carbonization temperature have similar structural parameters, despite the evident differences in parent asphaltenes structures and compositions. The transformation of asphaltene to graphene derivatives mainly occurred due to three factors: the reduction in the average number of aromatic layers (n), the expansion in aromatic sheet diameter (L a), and the elimination of alkyl side chains. The reduction in the number of aromatic sheets per stack is primarily ascribed to thermal exfoliation, while the increase in the aromatic sheet diameter is attributed to secondary reactions in the aromatic core of asphaltene. The elimination of side chains, on the other hand, is mainly credited to thermal cracking. The quantification of defect density (L D) in the graphene derivatives suggests an association between defects and heteroatoms presence.

Epitaxial synthesis of Ni-MoS2/Ti3C2T x MXene heterostructures for hydrodesulfurization.

Hierarchical structures of 2D layered Ti3C2T x MXene hold potential for a range of applications. In this study, catalysts comprising few-layered MoS2 with Ti3C2T x have been formulated for hydrodesulfurization (HDS). The support Ti3C2T x was derived from MAX phases (Ti3AlC2) via a liquid-phase exfoliation process, while MoS2 was obtained from synthesized aqueous ammonium tetrathiomolybdate (ATM). Furthermore, a series of catalysts with different architectures was synthesized by confinement of ATM and/or the promoter Ni in Ti3C2T x at different mole ratios, through a thermal conversion process. The synthesized MoS2/Ti3C2T x and Ni-MoS2/Ti3C2T x catalysts were characterized using X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET), scanning electron microscopy coupled with energy dispersive X-ray spectroscopy (SEM-EDS), high-resolution transmission electron microscopy (HRTEM), and temperature-programmed reduction (TPR) measurements. The number of MoS2 layers formed on the Ti3C2T x support was calculated using Raman spectroscopy. The heterostructured few-layered MoS2/Ti3C2T x catalysts were applied in sulfur removal efficiency experiments involving thiophene. The active MoS2 sites confined by the Ti3C2T x enhanced hydrogen activation by proton saturation, and the electron charge stabilized the sulfur atom to facilitate hydrogenation reactions, leading to predominant formation of C4 hydrocarbons. The Ni-MoS2/Ti3C2T x showed the best activity at a promoter molar ratio of 0.3 when compared to the other catalysts. In particular, it is evident from the results that ATM and Ti3C2T x are potential materials for the in situ fabrication of hierarchical few-layered MoS2/Ti3C2T x catalysts for enhancing hydrodesulfurization activity in clean fuel production.