This work applied molecular dynamics(MD)simulation to calculate densities of natural gas mixtures at extremely high pressure(>138 MPa)and high temperature(>200℃)conditions(x HPHT)to bridge the knowledge and tec...This work applied molecular dynamics(MD)simulation to calculate densities of natural gas mixtures at extremely high pressure(>138 MPa)and high temperature(>200℃)conditions(x HPHT)to bridge the knowledge and technical gaps between experiments and classical theories.The experimental data are scarce at these conditions which are also out of assumptions for classical predictive correlations,such as the Dranchuk&Abou-Kassem(DAK)equation of state(EOS).Force fields of natural gas components were carefully chosen from literatures and the simulation results are validated with experimental data.The largest relative error is 2.67%for pure hydrocarbons,2.99%for C1/C3 mixture,7.85%for C1/C4 mixture,and 8.47%for pure H2S.These satisfactory predictions demonstrate that the MD simulation approach is reliable to predict natural-and acid-gases thermodynamic properties.The validated model is further used to generate data for the study of the EOS with pressure up to 276 MPa and temperature up to 573 K.Our results also reveal that the Dranchuk&Abou-Kassem(DAK)EOS is capable of predicting natural gas compressibility to a satisfactory accuracy at x HPHT conditions,which extends the confidence range of the DAK EOS.展开更多
Structural control and element doping are two popular strategies to produce semiconductors with surface enhanced Raman spectroscopy(SERS)properties.For TiO2 based SERS substrates,maintaining a good crystallinity is cr...Structural control and element doping are two popular strategies to produce semiconductors with surface enhanced Raman spectroscopy(SERS)properties.For TiO2 based SERS substrates,maintaining a good crystallinity is critical to achieve excellent Raman scattering.At elevated temperatures(N600°C),the phase transition from anatase to rutile TiO2 could result in a poor SERS performance.In this work,we report the successful synthesis of TiO2 nanowhiskers with excellent SERS properties.The enhancement factor,an index of SERS performance,is 4.96×106 for methylene blue molecule detecting,with a detection sensitivity around 10-7 mol·L-1.Characterizations,such as XRD,Raman,TEM,UV–vis and Zeta potential measurement,have been performed to decrypt structural and chemical characteristics of the newly synthesized TiO2 nanowhiskers.The photo absorption onset of MB adsorbed TiO2 nanowhiskers was similar to that of bare TiO2 nanowhiskers.In addition,no new band was observed from the UV–vis of MB modified TiO2 nanowhiskers.Both results suggest that the high enhancement factor cannot be explained by the charge-transfer mechanism.With the support of ab initio density functional theory calculations,we reveal that interfacial potassium is critical to maintain thermal stability of the anatase phase up to 900°C.In addition,the deposition of potassium results in a negatively charged TiO2 nanowhisker surface,which favors specific adsorption of methylene blue molecules and significantly improves SERS performance via the electrostatic adsorption effect.展开更多
基金partial financial support from Ballard Petroleum Holdings and Yangtze Universitythe Schooner Supercomputing from the University of Oklahomathe startup support from the University of Oklahoma。
文摘This work applied molecular dynamics(MD)simulation to calculate densities of natural gas mixtures at extremely high pressure(>138 MPa)and high temperature(>200℃)conditions(x HPHT)to bridge the knowledge and technical gaps between experiments and classical theories.The experimental data are scarce at these conditions which are also out of assumptions for classical predictive correlations,such as the Dranchuk&Abou-Kassem(DAK)equation of state(EOS).Force fields of natural gas components were carefully chosen from literatures and the simulation results are validated with experimental data.The largest relative error is 2.67%for pure hydrocarbons,2.99%for C1/C3 mixture,7.85%for C1/C4 mixture,and 8.47%for pure H2S.These satisfactory predictions demonstrate that the MD simulation approach is reliable to predict natural-and acid-gases thermodynamic properties.The validated model is further used to generate data for the study of the EOS with pressure up to 276 MPa and temperature up to 573 K.Our results also reveal that the Dranchuk&Abou-Kassem(DAK)EOS is capable of predicting natural gas compressibility to a satisfactory accuracy at x HPHT conditions,which extends the confidence range of the DAK EOS.
基金supported by National Natural Science Foundation of China(21878143,21476106,and 21838004)Joint Research Fund for Overseas Chinese Scholars and Scholars in Hong Kong and Macao Young Scholars(21729601)+3 种基金the fund of State Key Laboratory of MaterialsOriented Chemical Engineering(ZK201702,KL16-01)the Priority Academic Program Development of Jiangsu Higher Education Institutions(PAPD)the U.S.National Science Foundation(NSF)for support through Grant No.CHE-1710102the High-Performance Computing Center of Nanjing Tech University for supporting the computational resources。
文摘Structural control and element doping are two popular strategies to produce semiconductors with surface enhanced Raman spectroscopy(SERS)properties.For TiO2 based SERS substrates,maintaining a good crystallinity is critical to achieve excellent Raman scattering.At elevated temperatures(N600°C),the phase transition from anatase to rutile TiO2 could result in a poor SERS performance.In this work,we report the successful synthesis of TiO2 nanowhiskers with excellent SERS properties.The enhancement factor,an index of SERS performance,is 4.96×106 for methylene blue molecule detecting,with a detection sensitivity around 10-7 mol·L-1.Characterizations,such as XRD,Raman,TEM,UV–vis and Zeta potential measurement,have been performed to decrypt structural and chemical characteristics of the newly synthesized TiO2 nanowhiskers.The photo absorption onset of MB adsorbed TiO2 nanowhiskers was similar to that of bare TiO2 nanowhiskers.In addition,no new band was observed from the UV–vis of MB modified TiO2 nanowhiskers.Both results suggest that the high enhancement factor cannot be explained by the charge-transfer mechanism.With the support of ab initio density functional theory calculations,we reveal that interfacial potassium is critical to maintain thermal stability of the anatase phase up to 900°C.In addition,the deposition of potassium results in a negatively charged TiO2 nanowhisker surface,which favors specific adsorption of methylene blue molecules and significantly improves SERS performance via the electrostatic adsorption effect.
