Anatase and amorphous TiO2 nanoparticles were used to improve recovery of heavy oil from sandstone cores. Before performing core floods, the stability of nanoparticles at different salinities was tested using ζ potential and ultraviolet–visible (UV–vis) methods. While water recovered only 49% of the oil in the core flood experiments, 0.01% anatase structure solution recovered 80% of the oil after injecting two pore volumes at optimum conditions. To understand the mechanism responsible for improved recovery, contact angle measurements were performed on the rock surface before and after treatment with the nanoparticle solution. Contact angle measurements showed that the rock wettability changed from oil-wet to water-wet conditions after treatment with nanoparticles. In 0.01% concentration, scanning electron microscopy (SEM) results showed homogeneous deposition of nanoparticles onto the core plug surface and a few nanorods with a diameter about 60 nm were observed. Energy-dispersive spectrometry (EDS) confirms diffusion of nanoparticles in porous media and uniform distribution. When the nanoparticle concentration was increased, more nanorods with the same diameter were composed, which resulted in plugging to occur. These results indicated the possibility of TiO2 application in enhanced oil recovery (EOR); however, more investigation is required to overcome multi-nanoparticle deposition onto pores.

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Although application of nanoparticles in enhanced oil recovery has been reported, understanding the transport and retention of nanoparticles in the oilfield reservoir is still a crucial issue. In this research, behavior of low concentration of TiO 2 nanoparticles in core plug porous media and the mechanism of increasing oil recovery were investigated. Flooding test with a concentration of 0.01% TiO 2 nanoparticles showed improvement in sweeping heavy oil from 41% to 55%. Inductively coupled plasma results on the exiting effluent of the flooding test with a concentration of 0.05% TiO 2 nanoparticles showed the presence of only 0.5% of injected nanoparticles, which indicates high affinity of the nanoparticles for deposition in porous media. The total amount of deposited TiO 2 extracted from different cross sections of the core plug was consistent with the difference of injected and exited TiO 2 material. At the entrance side, the amount of deposited TiO 2 was high but decreased significantly in 0.1 cm depth, and reduces linearly versus distance. On the basis of surface area estimation of the core plug, only about 1% of the internal surface was deposited by nanoparticles. The viscosity, interfacial tension, and contact angle measurements showed that the main mechanism for increasing oil sweeping is changing the wettability of the rock surface from oil-wet to water-wet due to deposition of TiO 2 nanoparticles. The role of the low concentration nanofluid in rapidly displacing crude oil from the rock surface may be described by gradient pressure of nanoparticles in the three-phase contact wedge of oil, nanofluid, and rock surface.

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BackgroundPristine carbon dots (CDs) derived from citric acid pyrolysis are used in a variety of biomedical research such as imaging and drug delivery. However, potential cytotoxic effects of pyrolysis temperature on cells is underexplored. To address this need, we studied toxicity of the CDs to breast cancer cells using MTT and LDH assays. In addition, we investigated photo-induced cytotoxicity of the synthesized CDs in a wide concentration range under white light.ResultsOur results suggest little cytotoxicity of the CDs after 24 h exposure of cells. Only the high quantum yield CDs caused a significant toxicity to cells at the highest concentrations of 2.0 and 1.5 mg/ml compared to other CDs at similar concentrations. The synthesized CDs entered the cells without any significant cytotoxicity. The CDs also caused a concentration- and irradiation time-dependent photo-induced cytotoxicity.ConclusionThe optimization of synthesis conditions from this study may help develop safe and efficient CDs for imaging and drug delivery.