Preparation of Graphene-Oxide/Polyamidoamine Dendrimers and Their Adsorption Properties toward Some Heavy Metal Ions

Graphene oxide/polyamidoamine dendrimers (GO/PAMAMs) were prepared via a “grafting to” method. The adsorption behavior of the GO/PAMAMs for Pb­(II), Cd­(II), Cu­(II), and Mn­(II) was studied, and the effects of solution pH, adsorption time, and initial metal ion concentration on adsorption capacity of the adsorbent were also investigated. The pseudo-first-order and pseudo-second-order kinetic models were used to describe the kinetic processes, and the results indicated that the adsorption of Pb­(II), Cd­(II), Cu­(II), and Mn­(II) followed a second-order type reaction kinetics and the adsorption of Pb­(II), Cd­(II), Cu­(II), and Mn­(II) onto GO/PAMAMs is a chemical adsorption. The adsorption capacities of GO/PAMAMs were found to be 568.18, 253.81, 68.68, and 18.29 mg/g for Pb­(II), Cd­(II), Cu­(II), and Mn­(II), respectively. The adsorption reached equilibrium within 60 min and characteristics of the adsorption process were evaluated by using the Langmuir and Freundlich isotherm models. The adsorption processes fit better with the Langmuir model for Cu­(II) and Mn­(II) than for Pb­(II) and Cd­(II); the adsorption of Cu­(II) and Mn­(II) on GO/PAMAMs was a typical monomolecular layer adsorption

Dynamic Compression Characteristics and Failure Mechanism of Water-Saturated Granite

For Fangshan granite in Beijing, the static compression and dynamic compression tests have been carried out separately under natural air drying and water saturation. It was found that the dynamic compressive strength of water-saturated granite is higher than that of air-dried granite, which is contrary to the result that the strength of water-saturated rock is lower than that of air-dried granite under static load. Furthermore, under the medium strain rate condition, when the strain rate is 85 s−1, the dynamic strength of natural air-dried granite could be increased by nearly 0.5 times compared with its static state. The dynamic strength of water-saturated granite could be increased by nearly 1–2 times compared with its static strength, which shows that water-saturated granite has stronger strain rate sensitivity than natural air-dried granite. Meanwhile, under impact loading, from the perspective of water-bearing granite the Bernoulli effect of fluid, the adhesion effect of free water and the Stefan effect of fluid in water-saturated granite were revealed, and found to be the essential reasons affecting the dynamic strength of water-saturated granite. The dynamic strength in different water-bearing states in the range of medium strain rate could then be analyzed in depth, providing a certain reference value for the strength design of water-bearing rock engineering

Dynamic Compression Characteristics and Failure Mechanism of Water-Saturated Granite

For Fangshan granite in Beijing, the static compression and dynamic compression tests have been carried out separately under natural air drying and water saturation. It was found that the dynamic compressive strength of water-saturated granite is higher than that of air-dried granite, which is contrary to the result that the strength of water-saturated rock is lower than that of air-dried granite under static load. Furthermore, under the medium strain rate condition, when the strain rate is 85 s−1, the dynamic strength of natural air-dried granite could be increased by nearly 0.5 times compared with its static state. The dynamic strength of water-saturated granite could be increased by nearly 1–2 times compared with its static strength, which shows that water-saturated granite has stronger strain rate sensitivity than natural air-dried granite. Meanwhile, under impact loading, from the perspective of water-bearing granite the Bernoulli effect of fluid, the adhesion effect of free water and the Stefan effect of fluid in water-saturated granite were revealed, and found to be the essential reasons affecting the dynamic strength of water-saturated granite. The dynamic strength in different water-bearing states in the range of medium strain rate could then be analyzed in depth, providing a certain reference value for the strength design of water-bearing rock engineering