Synthesis,characterization and photoactivity of bi-crystalline mesoporous TiO2

Mesoporous titania (meso-TiO₂) has received extensive attention owing to its versatile potential applications. This paper reports a low-temperature templating approach for the fabrication of meso-TiO₂ using the peroxo titanic acid (PTA) sol as precursor and Pluronic P123 as nonionic template. The TGA, XRD, N₂ sorption, FE-SEM and HRTEM were used to characterize the obtained samples. The results showed that meso-TiO₂ with high surface area up to 163 m²·g^–1 and large pore volume of 0.65 cm³·g^–1 can be obtained. The mesopore sizes can be varied between 13 and 20 nm via this synthesis approach. The amount of P123 and the calcination conditions were found to have great influence on the mesoporous and crystalline structures of meso-TiO₂. The photocatalytic activity testing clearly shows that the high surface area and bi-crystallinity phases of meso-TiO₂ play important roles in enhancing photocatalytic properties of meso-TiO₂ in photo-decomposing Rhodamine B in water.     

Facile and controllable preparation of mesoporous TiO<Subscript>2</Subscript> using poly(ethylene glycol) as structure-directing agent and peroxotitanic acid as precursor

This work demonstrated that mesoporous TiO₂ (meso-TiO₂) with controllable mesoporous and crystalline structures can be facilely prepared by using poly (ethylene glycol) (PEG) as structure-directing (SD) agent and peroxotitanic acid (PTA) as precursor. Meso-TiO₂ with high specific surface area (157 m²?g^-1), pore volume (0.45 cm³?g^-1) and large mesopore size of 13.9 nm can be obtained after calcination at 450°C. Such meso-TiO₂ also shows relatively high thermal stability. BET surface area still reaches 114 m²?g^-1 after calcination at 550°C. In the synthesis and calcination process, PEG that plays multiple and important roles in delivering thermally stable and tunable mesoporous and crystalline structures shows to be a suitable low-cost SD agent for the controllable preparation of nanocrystalline meso-TiO₂. The photocatalytic activity tests show that both high surface area and bi-crystallinity of obtained meso-TiO₂ are important in enhancing the performance in photo-decomposing Rhodamine B in water.     

Unexpected liquefaction under isotropic consolidation of idealized granular materials

The drained isotropic compression behaviour of very loose and fully saturated monodisperse glass beads in triaxial compression is investigated in this paper. Short cylindrical samples were prepared by moist-tamping technique and isotropically compressed in a classical axisymmetric triaxial machine. Very loose glass bead samples exhibit numerous local collapses with sudden volumetric compaction and axial contraction of very large amplitude and experience ultimately global collapse with spontaneous liquefaction under undetermined external isotropic stress. Excess pore pressure instantaneously generated at the beginning of the collapse phenomenon, and rapidly dissipated with the usual drainage system, shows a global complex system with local dynamic instability. The dynamic time evolution of the excess pore pressure \(\varDelta U\) consists in a first and fast transient phase I at constant volume and constant axial strain with large spikes \(\varDelta U^{peak}\), followed by an intermediate second phase II of large increase of volumetric compaction and axial contraction at stabilizing \(\varDelta U_{stable}\) or constant effective stress \(\sigma ^{\prime }\) and finally a third and longest phase III of excess pore water pressure dissipation at nearly constant axial strain toward the initial back-pressure. For local collapses, the second phase is totally missing. Upon ignoring the local collapses, very loose idealized granular materials have a unique and global isotropic compressibility behaviour, independently of the void ratio at the end of the fabrication stage; and liquefaction-free for dense state below a threshold void ratio at fabrication \(e_{30}^{liq}\), representing the transition from global instability with total failure to local instability with partial collapse. This paper provides the first reported spontaneous liquefaction instability under isotropic consolidation. It gives the necessarily conditions for an isotropic liquefaction and emphases some usually hidden or partially developed mechanisms underlying the diffuse instability phenomenon and adds a new intriguing layer to the complex behaviour of idealized granular materials in classical drained triaxial isotropic compression.     

Foreign Particle Promoted Crystalline Nucleation for Growing High‐Quality Ultrathin Rubrene Films

Introducing foreign particles or agents as nucleator is an efficient way to promote crystallization in the crystal growth field, with the advantage to speed up the crystallizing rate and control the growth process. However, in the field of organic crystalline film growth, where the crystallization and morphology modulation are of significant importance in optoelectronics, this method has rarely been utilized. Particularly, some potential high‐performance materials such as rubrene face the problem of crystallization during film formation. Here a strategy is reported to promote the crystallization of rubrene films in the initial stage assisted by foreign particles. Highly ordered thin film from the sub‐monolayer stage can be achieved. Efficient charge transport and high mobility up to 2.95 cm² V^?1 s^?1 are achieved on thus ultrathin crystalline films. Such a method enables the well controlling of the film growth from the very early stage and produces uniform crystalline films with good reproducibility, thus highly promising to yield desired optoelectrical properties and applications.     

Multifunctional Transmembrane Protein Ligands for Cell‐Specific Targeting of Plasma Membrane‐Derived Vesicles

Liposomes and nanoparticles that bind selectively to cell‐surface receptors can target specific populations of cells. However, chemical conjugation of ligands to these particles is difficult to control, frequently limiting ligand uniformity and complexity. In contrast, the surfaces of living cells are decorated with highly uniform populations of sophisticated transmembrane proteins. Toward harnessing cellular capabilities, here it is demonstrated that plasma membrane vesicles (PMVs) derived from donor cells can display engineered transmembrane protein ligands that precisely target cells on the basis of receptor expression. These multifunctional targeting proteins incorporate (i) a protein ligand, (ii) an intrinsically disordered protein spacer to make the ligand sterically accessible, and (iii) a fluorescent protein domain that enables quantification of the ligand density on the PMV surface. PMVs that display targeting proteins with affinity for the epidermal growth factor receptor (EGFR) bind at increasing concentrations to breast cancer cells that express increasing levels of EGFR. Further, as an example of the generality of this approach, PMVs expressing a single‐domain antibody against green fluorescence protein (eGFP) bind to cells expressing eGFP‐tagged receptors with a selectivity of ≈50:1. The results demonstrate the versatility of PMVs as cell targeting systems, suggesting diverse applications from drug delivery to tissue engineering.     

石墨烯的制备及其在能源方面的应用研究进展

近年来,石墨烯以其独特的二维结构和许多优异的性能吸引了物理、化学、材料等领域科学家的关注,并得到了多方面研究。至今,石墨烯的制备方法有多种,其研究取得了一定的进展,为石墨烯的理论研究和实践应用奠定了基础。本文综述了石墨烯的制备方法(固相法、液相法和气相法)及其在能源方面的应用研究现状,并比较了各种方法的优缺点。最后,对石墨烯的未来发展作了展望。     

Dyna-Q-based vector direction for path planning problem of autonomous mobile robots in unknown environments

Reinforcement learning (RL) is a popular method for solving the path planning problem of autonomous mobile robots in unknown environments. However, the primary difficulty faced by learning robots using the RL method is that they learn too slowly in obstacle-dense environments. To more efficiently solve the path planning problem of autonomous mobile robots in such environments, this paper presents a novel approach in which the robot’s learning process is divided into two phases. The first one is to accelerate the learning process for obtaining an optimal policy by developing the well-known Dyna-Q algorithm that trains the robot in learning actions for avoiding obstacles when following the vector direction. In this phase, the robot’s position is represented as a uniform grid. At each time step, the robot performs an action to move to one of its eight adjacent cells, so the path obtained from the optimal policy may be longer than the true shortest path. The second one is to train the robot in learning a collision-free smooth path for decreasing the number of the heading changes of the robot. The simulation results show that the proposed approach is efficient for the path planning problem of autonomous mobile robots in unknown environments with dense obstacles.