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  • Author or Editor: Yan Wang x
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Abstract

Na-montmorillonites were exchanged with Li+, K+, Rb+, Cs+, Mg2+, Ca2+, Sr2+, and Ba2+, while Ca-montmorillonites were treated with alkaline and alkaline earth ions except for Ra2+ and Ca2+. Montmorillonites with interlayer cations Li+ or Na+ have remarkable swelling capacity and keep excellent stability. It is shown that metal ions represent different exchange ability as follows: Cs+ > Rb+ > K+ > Na+ > Li+ and Ba2+ > Sr2+ > Ca2+ > Mg2+. The cation exchange capacity with single ion exchange capacity illustrates that Mg2+ and Ca2+ do not only take part in cation exchange but also produce physical adsorption on the montmorillonite. Although interlayer spacing d 001 depends on both radius and hydration radius of interlayer cations, the latter one plays a decisive role in changing d 001 value. Three stages of temperature intervals of dehydration are observed from the TG/DSC curves: the release of surface water adsorbed (36–84 °C), the dehydration of interlayer water and the chemical-adsorption water (47–189 °C) and dehydration of bound water of interlayer metal cation (108–268 °C). Data show that the quantity and hydration energy of ions adsorbed on montmorillonite influence the water content in montmorillonite. Mg2+-modified Na-montmorillonite which absorbs the most quantity of ions with the highest hydration energy has the maximum water content up to 8.84%.

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Abstract  

The calorimetric data of binders containing pure Portland cement, 20% fly ash, 20% slag and 10% silica fume respectively are determined at different initial casting temperatures using an adiabatic calorimeter to measure the adiabatic temperature rising of concrete. The calorimetric data of binders with different dosages of fly ash at two water binder ratios (w/b) are determined, too. Elevation of initial casting temperature decreases the heat evolution of binder, enhances the heat evolution rate of binder and increases the heat evolution rate of binder at early age. The dosage of fly ash in concrete has different effects on the heat evolution of binder with different w/b. At high w/b ratio the heat evolution of binder decreases when dosage of fly ash increases. At low w/b ratio the heat evolution of binders increases when dosage of fly ash increases from 0 to 40% of total binder quantity. The heat evolution of binder decreases after the dosage of fly ash over 40%. An appropriate dosage of fly ash in binder benefits the performance of concrete at low w/b ratio.

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Abstract  

Herein, hydroxyapatite (HAP) was prepared by aqueous precipitation technique and was characterized by using FT-IR and XRD to determine its chemical functional groups and micro-structure. The removal of cobalt from aqueous solution to HAP was studied by batch technique as a function of various environmental parameters such as contact time, pH, ionic strength, foreign ions, fulvic acid (FA), and temperature under ambient conditions. The results indicated that the sorption of Co(II) on HAP was strongly dependent on pH and ionic strength. The presence of FA enhanced the sorption of Co(II) on HAP at low pH, whereas reduced Co(II) sorption on HAP at high pH. The Langmuir, Freundlich and D-R models were used to simulate the sorption isotherms at three different temperatures of 303.15, 323.15 and 343.15 K. The thermodynamic parameters (ΔH°, ΔS° and ΔG°) calculated from the temperature dependent sorption isotherms indicated that the sorption process of Co(II) on HAP was spontaneous and endothermic. The sorption of Co(II) was dominated by outer-sphere surface complexation and ion exchange at low pH, whereas inner-sphere surface complexation or surface precipitation was the main sorption mechanism at high pH values. The results suggest that the HAP is a suitable material in the preconcentration and solidification of Co(II) from large volumes of aqueous solutions.

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Abstract  

In this work, hydroxyapatite (HAP) was prepared by aqueous precipitation technique and was characterized by using FT-IR to determine its chemical functional groups. A series of batch experiments were carried out to investigate the effect of various environmental factors such as contact time, pH, ionic strength, foreign ions, fulvic acid (FA) and temperature on the sorption behavior of HAP towards radionuclide 109Cd(II). The results indicated that the sorption of 109Cd(II) on HAP was strongly dependent on pH and ionic strength. A positive effect of FA on 109Cd(II) sorption was found at pH <7.0, whereas a negative effect was observed at pH >7.0. The Langmuir, Freundlich and D-R models were used to simulate the sorption isotherms at three different temperatures of 298.15, 323.15 and 343.15 K. The thermodynamic parameters (ΔH0, ΔS0 and ΔG0) calculated from the temperature dependent sorption isotherms indicated that the sorption process of 109Cd(II) on HAP was spontaneous and endothermic. At low pH, the sorption of 109Cd(II) was dominated by outer-sphere surface complexation and ion exchange on HAP surfaces, whereas inner-sphere surface complexation was the main sorption mechanism at high pH. From the experimental results, it is possible to conclude that HAP has good potentialities for cost-effective treatments of 109Cd(II)-contaminated wastewaters.

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Background and aims

Although smartphone use brings many benefits for adolescents, it is also associated with many serious health problems. This study examined the relationship between problematic smartphone use (PSU) and clinical health symptoms (e.g., body dysfunction) and the mediating effects of sleep quality on this relationship in adolescents.

Methods

Participants in this cross-sectional survey were 686 middle- and high-school students (girls = 55.7%, M age = 12.98 ± 1.38 years). Participants completed self-report measures of PSU, sleep quality, and physical symptoms. Correlation analyses and structural equation modeling between adolescents’ PSU and the variables of interest were conducted.

Results

This study indicated that there was a significant positive correlation between PSU and health symptoms. Furthermore, sleep quality mediated the relationship between PSU and health symptoms.

Discussion and conclusions

Findings suggest that to promote health and wellness in adolescents, individuals should be encouraged to place boundaries on smartphone use, especially at bedtime. Reducing adolescents’ exposure to smartphone use in this way may hold promise for improving the efficacy of PSU prevention efforts for adolescents.

Open access

Abstract

Background and aims

The working memory (WM) ability of internet addicts and the topology underlying the WM processing in internet addiction (IA) are poorly understood. In this study, we employed a graph theoretical framework to characterize the topological properties of the IA brain network in the source cortical space during WM task.

Methods

A sample of 24 subjects with IA and 23 matched healthy controls (HCs) performed visual 2-back task. Exact Low Resolution Electromagnetic Tomography was adopted to project the pre-processed EEG signals into source space. Subsequently, Lagged phase synchronization was calculated between all pairs of Brodmann areas, the graph theoretical approaches were then employed to estimate the brain topological properties of all participants during the WM task.

Results

We found better WM behavioral performance in IA subjects compared with the HCs. Moreover, compared to the HC group, more integrated and hierarchical brain network was revealed in the IA subjects in alpha band. And altered regional centrality was mainly resided in frontal and limbic lobes. In addition, significant relationships between the IA severity and the significant altered graph indices were found.

Conclusions

In conclusion, these findings provide evidence to support the notion that altered topological configuration may underline changed WM function observed in IA.

Open access

Abstract  

A calorimetric investigation was performed on the partition ofn-pentanol in the external oil phase and in the interfacial layer of the water-in-oil microemulsion system sodium dodecyl-benzenesulfonate(DDBS)/n-pentanol/n-heptane/water. The results show that fine changes can be observed in the structure of the water-in-oil emulsion and microemulsion droplets, such as then-pentanol/DDBS mole ratio increase in the interfacial layer; further, the alcohol/surfactant mole ratio α in the interfacial layer of the droplets, and also the standard thermodynamic functions of the alcohol transition from the external phase to the interfacial phase (ΔG e→s o , ΔH c→s o and ΔS e→s o ), can be derived from calorimetric data.

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Abstract  

Emf measurements were made on the cell without liquid junction: Li−ISE LiCl(m1), Li2SO4(m2) Ag/AgCl. The performances of the electrode pairs constructed in our laboratory were tested and exhibited near-Nernstian behavior. The mean activity coefficients of LiCl for the system Li+−Cl−SO 4 2− −H2O have been investigated by the emf values at temperatures of 0, 15, 35°C and constant total ionic strengths of 0.05, 0.1, 0.5, 1.0, 2.0, 3.0 and 5.0 mol·kg−1. The activity coefficients decrease with increasing temperature and the ionic strength fraction of Li2SO4 in the mixtures. The thermodynamic properties are interpreted by use of Harned's empirical equations and Pitzer's ion interaction approach including the contribution of higher order electrostatic terms. The experimental results obey Harned's rule and are described by using Pitzer equations satisfactorily. The activity coefficients of Li2SO4, the osmotic coefficients and the excess free energies of mixing for the system in the experimental temperature range were reported.

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Abstract  

Immobilized Saccharomyces cerevisiae (ISC) was prepared by the sodium alginate–gelatin embedding method after dry cells had been cross-linked by formaldehyde. Adsorption of uranium(VI) by incompletely and completely dry ISC was studied. The results indicated that incompletely dry ISC had greater adsorption capacity for U(VI), with physical adsorption being the primary mechanism, whereas completely dry ISC exhibited much greater rigidity and much smaller volume. Therefore, initial absorption of U(VI) by incompletely dry ISC followed by heating could be compared with glass solidification for disposal of radioactive waste. The influence of solution pH, temperature, and contact time on U(VI) absorption was also studied, with pH being found to be the main influencing factor. The adsorption mechanism of completely dry ISC was explored by scanning electron microscopy (SEM) and Fourier-transform infrared (FTIR) spectroscopy, indicating that the main adsorption mechanism is chemical adsorption.

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