Yefei Wang

Nowadays, carbon dots (CDs) with a variety of structures and compositions are widely applied in the petroleum industry, including tracers, modification of interfacial properties and regulation of rheological properties due to their excellent modifiability, environmental compatibility, straightforward synthesis, and outstanding photoluminescent properties. In this review, we summarize the applications of CDs in the petroleum industry and elucidate the effects of CDs based on the classification of application scenarios. In addition, we briefly analyze the relationship between the structure of CDs and their performance, identify the challenges we are currently facing, and discuss the structural characteristics of high-performance CDs along with their potential future applications. The discussion presented in this article is based on research on CDs and the petroleum industry. By combining these two areas, this review is expected to provide guidance to researchers working in related areas. Meanwhile, we also hope this review can offer innovative ideas for further applications of CDs in the petroleum industry.

Due to the fact that more conventional heavy oil recovery methods (heating, emulsification, dilution, and other methods) have many shortcomings, they cannot meet the demand of heavy oil exploitation. Therefore, there is a need for new recovery methods. In this paper, the surface of nano SiO₂ was modified with a silane coupling agent, KH-560, to prepare a nanoviscosity reducer (NRV), which has high-temperature resistance (300 °C), calcium and magnesium resistance (Ca²⁺ + Mg²⁺ > 900 mg/L) and high viscosity reduction rate (>99%). FTIR and SEM measurements showed that KH560 has been successfully connected to the surface of SiO₂. The particle size distribution of NRV is mainly distributed in 50-80 nm, which matches the results of SEM. The experimental results showed that the viscosity reduction rates of 1 wt % NRV on M-1 heavy oil before and after aging were 99.73% and 99.71%, respectively. The viscosity reduction effect of 1% NRV on M-1 heavy oil and the bleeding rate of emulsion formation were investigated when the oil-water ratio ranged from 9:1 to 1:9. The results showed that when the oil-water ratio was between 7:3 and 1:9, the viscosity reduction rate was greater than 99%. Besides, the bleeding rate of emulsion increases with the decrease of the oil-water ratio. What's more, static and dynamic adsorption experiments showed that the adsorption capacity of 1 wt % NRV was 1.746 mg/g and 1.668 mg/g sand, respectively. The interfacial tension experiment showed that the interfacial tension (IFT) between 1 wt % NRV and M-1 heavy oil was 0.052 mN/m, and low interfacial tension was beneficial to displace the oil in the formation pores. At the same time, the displacement effect of NRV on M-1 heavy oil at different concentrations (0.5, 1.0, and 1.5 wt %) and temperatures (200, 250, and 300 °C) was investigated by core flooding experiments. The results showed that the recovery rate increases with the increase of NRV concentration, and 1 wt % NRV at 300 °C will improve the recovery rate of M-1 heavy oil by 27.3% compared to steam flooding. NRV could reduce the viscosity of crude oil, which provides technical guidelines for the exploitation of heavy oil and extra heavy oil.

Nanoparticles have been widely applied to treat emulsion-containing wastewater in the form of chemical demulsifiers, such as SiO₂, Fe₃O₄, and graphene oxide (GO). Owing to their asymmetric structures and selective adsorption, Janus nanoparticles show greater application potential in many fields. In the present work, the novel magnetic Janus graphene oxide (MJGO) nanoparticle was successfully prepared by grafting magnetic Fe₃O₄ to the surface of the JGO, and its demulsifying ability to treat a crude oil-in-water emulsion was evaluated. The MJGO structure and its magnetic intensity were verified by Fourier-transform infrared spectra (FTIR), transmission electron microscopy (TEM), X-ray diffraction (XRD), and magnetization saturation (MS) tests. Compared with GO and JGO, MJGO displayed the superior efficiency (>96%) to demulsify the crude oil-in-water emulsion, which can be attributed to the reduced electrostatic repulsion between MJGO and the emulsion droplets. Furthermore, the effects of pH and temperature on the demulsification performance of MJGO were also studied. Lastly, the recyclability of MJGO largely reduced the cost of demulsifiers in separating crude oil and water. The current research presents an efficient and recyclable demulsifier, which provides a new perspective for the structural design of nanomaterials and their application in the field of demulsification.

二维InSe半导体材料由于其优异的电学性能以及适中可调的带隙等优点, 引起了研究者的关注. 材料中的空位缺陷不仅影响材料的光电学特性, 还影响材料的环境稳定性. 相比于InSe材料中的其他相, δ-InSe具有更优异的材料性能, 然而关于对该材料环境稳定性影响的研究未见报道. 本文基于密度泛函理论, 系统研究了氧气环境下二维δ-InSe材料的稳定性问题. 结果表明: 1)在氧气环境下, 完美δ-InSe表面具有良好的惰性和稳定性, O₂分子在其表面从物理吸附到解离吸附需要克服1.827 eV的势垒; 2) Se空位(V_Se)的存在则会促进δ-InSe的氧化反应, 被氧化的过程仅需克服0.044 eV的势垒, 说明V_Se的存在使δ-InSe在氧气环境下的稳定性显著下降, 此外被O₂分子氧化的δ-InSe单层有利于H₂O分子的解离吸附; 3)含有In空位(V_In)的δ-InSe被氧化的速率较慢, O₂分子在V_In表面的物理吸附的吸附能和电荷转移与完美表面基本一致, 被氧化的过程需克服1.234 eV的势垒. 这一研究结果将为更好地理解单空位缺陷对δ-InSe单层的氧化行为提供理论指导, 同时为高可靠二维δ-InSe器件的实验制备提供参考.