The microstructural evolution of C-(A)-S-H gel in Portland cement pastes immersed in pure water and 5.0 wt% Na2SO4 solution for different ages was comparatively investigated, by means of ^(29) Si NMR spectroscopy,...The microstructural evolution of C-(A)-S-H gel in Portland cement pastes immersed in pure water and 5.0 wt% Na2SO4 solution for different ages was comparatively investigated, by means of ^(29) Si NMR spectroscopy, and SEM-EDS analysis. Additionally, molecular dynamics simulation was performed to study the aluminum coordination status and interaction of sulfate ions in C-(A)-S-H gel. The results showed significant changes in the microstructural evolution of C-(A)-S-H gel in Portland cement paste. Sulfate attack has decalcifying and dealuminizing effect on C-(A)-S-H gel which is evident from increase in mean chain length(MCL) and decrease in Ca/Si & Al[4]/Si ratios of C-(A)-S-H gel. Additionally, Molecular dynamics simulation proves that Al[4] substituted in silicate chains of C-(A)-S-H gel is thermodynamically metastable, which may explain its migration from the silicate chains and transformation to Al[6], thus lowering the Al[4]/Si ratio of C-(A)-S-H gel. SO4^(2-)ions can carry the interfacial Ca^(2+) ions into the pore solution by the diffusion-absorption-desorption process, which unravels the mechanism of sulfate attack on C-(A)-S-H gel.展开更多
TiO2 films have received increasing attention for the removal of organic pollutants via photocatalysis. To develop a simple and effective method for improving the photodegradation efficiency of pollutants in surface w...TiO2 films have received increasing attention for the removal of organic pollutants via photocatalysis. To develop a simple and effective method for improving the photodegradation efficiency of pollutants in surface water, we herein examined the preparation of a P25-TiO2 composite film on a cement substrate via a sol–gel method. In this case, Rhodamine B(Rh B)was employed as the target organic pollutant. The self-generated TiO2 film and the P25-TiO2 composite film were characterized by X-ray diffraction(XRD), N2 adsorption/desorption measurements, scanning electron microscopy(SEM), transmission electron microscopy(TEM), and diffuse reflectance spectroscopy(DRS). The photodegradation efficiencies of the two films were studied by Rh B removal in water under UV(ultraviolet) irradiation. Over 4 day exposure, the P25-TiO2 composite film exhibited higher photocatalytic performance than the self-generated TiO2 film. The photodegradation rate indicated that the efficiency of the P25-TiO2 composite film was enhanced by the addition of the rutile phase Degussa P25 powder. As such, cooperation between the anatase TiO2 and rutile P25 nanoparticles was beneficial for separation of the photo-induced electrons and holes. In addition, the influence of P25 doping on the P25-TiO2 composite films was evaluated. We found that up to a certain saturation point, increased doping enhanced the photodegradation ability of the composite film. Thus, we herein demonstrated that the doping of P25 powders is a simple but effective strategy to prepare a P25-TiO2 composite film on a cement substrate, and the resulting film exhibits excellent removal efficiency in the degradation of organic pollutants.展开更多
基金Funded by National Natural Science Foundation of China(Nos.51778513,51578004,51608004)the Major State Basic Research Development Program of China("973"Program)(No.2015CB655101)
文摘The microstructural evolution of C-(A)-S-H gel in Portland cement pastes immersed in pure water and 5.0 wt% Na2SO4 solution for different ages was comparatively investigated, by means of ^(29) Si NMR spectroscopy, and SEM-EDS analysis. Additionally, molecular dynamics simulation was performed to study the aluminum coordination status and interaction of sulfate ions in C-(A)-S-H gel. The results showed significant changes in the microstructural evolution of C-(A)-S-H gel in Portland cement paste. Sulfate attack has decalcifying and dealuminizing effect on C-(A)-S-H gel which is evident from increase in mean chain length(MCL) and decrease in Ca/Si & Al[4]/Si ratios of C-(A)-S-H gel. Additionally, Molecular dynamics simulation proves that Al[4] substituted in silicate chains of C-(A)-S-H gel is thermodynamically metastable, which may explain its migration from the silicate chains and transformation to Al[6], thus lowering the Al[4]/Si ratio of C-(A)-S-H gel. SO4^(2-)ions can carry the interfacial Ca^(2+) ions into the pore solution by the diffusion-absorption-desorption process, which unravels the mechanism of sulfate attack on C-(A)-S-H gel.
基金supported by the National Science Funds for Creative Research Groups of China (No. 51421006)the National Major Projects of Water Pollution Control and Management Technology (No. 2017ZX07204003)+2 种基金the National Key Plan for Research and Development of China (2016YFC0502203)the Key Program of National Natural Science Foundation of China (No. 91647206)the Qing Lan Project of Jiangsu Province, and PAPD
文摘TiO2 films have received increasing attention for the removal of organic pollutants via photocatalysis. To develop a simple and effective method for improving the photodegradation efficiency of pollutants in surface water, we herein examined the preparation of a P25-TiO2 composite film on a cement substrate via a sol–gel method. In this case, Rhodamine B(Rh B)was employed as the target organic pollutant. The self-generated TiO2 film and the P25-TiO2 composite film were characterized by X-ray diffraction(XRD), N2 adsorption/desorption measurements, scanning electron microscopy(SEM), transmission electron microscopy(TEM), and diffuse reflectance spectroscopy(DRS). The photodegradation efficiencies of the two films were studied by Rh B removal in water under UV(ultraviolet) irradiation. Over 4 day exposure, the P25-TiO2 composite film exhibited higher photocatalytic performance than the self-generated TiO2 film. The photodegradation rate indicated that the efficiency of the P25-TiO2 composite film was enhanced by the addition of the rutile phase Degussa P25 powder. As such, cooperation between the anatase TiO2 and rutile P25 nanoparticles was beneficial for separation of the photo-induced electrons and holes. In addition, the influence of P25 doping on the P25-TiO2 composite films was evaluated. We found that up to a certain saturation point, increased doping enhanced the photodegradation ability of the composite film. Thus, we herein demonstrated that the doping of P25 powders is a simple but effective strategy to prepare a P25-TiO2 composite film on a cement substrate, and the resulting film exhibits excellent removal efficiency in the degradation of organic pollutants.