ENHANCING ACTIVITIES TYPES OF TEACHERS USING COOPERATIVE JIGSAW IN CLASS VIA

Application of jigsaw cooperative learning is done to increase the activity of teachers. The method used is qualitative descriptive method to describe the condition of the activity of teachers in the learning theme 8 sub themes 1. This type of research is "Classroom Action Research" or the classroom action research (PTK). This study was conducted using two cycles. The procedure of research include: (1) planning, (2) implementation, (3) observation (4) evaluation and (5) result. The technique of collecting data through observation / observation of teacher activities that take place in two cycles at the end of the lesson. The conclusion of this study is, activity increased teachers who in turn have an impact on student learning outcomes also increased

Monitoring the Coordination Modulator Shell at MOF Nanocrystals

A small angle neutron scattering (SANS) study is presented, which investigates the impact of a modulator on nucleation and growth of MOF-5 nanoparticles. Two DMF solutions, one with the secondary building unit Zn₄O­(C₆H₅COO)₆ (SBU) and one with terephthalic acid (BDC) as a linker, were mixed, and 5 min after generation of the mixture, monodentate 4-<i>n</i>-decylbenzoic acid was added as a modulator agent. Time-resolved SANS during the initial stages of the particle formation process offered insight into morphological transformations during the first hours. Subsequently, it could be demonstrated that a shell is formed by the modulator wrapping around the growing MOF-5 particles while directing the formation of MOF-5 nanoparticles. This has been made possible by an identification of a mixture of deuterated and hydrogenated solvent (DMF), which matches the scattering contrast of MOF-5, thus giving access to the scattering signal of the modulator

Impact of Sodium Polyacrylate on the Amorphous Calcium Carbonate Formation from Supersaturated Solution

A detailed in situ scattering study has been carried out on the formation of amorphous calcium carbonate (ACC) particles modulated by the presence of small amounts of sodium polyacrylate chains. The work is aiming at an insight into the modulation of ACC formation by means of two polyacrylate samples differing in their molecular weight by a factor of 50. The ACC formation process was initiated by an in situ generation of CO₃^2– ions via hydrolysis of 10 mM dimethylcarbonate in the presence of 10 mM CaCl₂. Analysis of the formation process by means of time-resolved small-angle X-ray and light scattering in the absence of any additives provided evidence for a monomer addition mechanism for the growth of ACC particles. ACC formation under these conditions sets in after a lag-period of some 350 s. In the presence of sodium polyacrylate chains, calcium polyacrylate aggregates are formed during the lag-period, succeeded by a modulated ACC growth in a second step. The presence of anionic polyacrylate chains changed the shape of the growing particles toward loose and less homogeneous entities. In the case of low amounts (1.5–7.5 mg/L) of the long chain additive with 97 kDa, the size of the aggregates is comparable to the size of the successively formed hybrid particles. No variation of the lag-period has been observed in this case. Use of the short chain additive with 2 kDa enabled increase of the additive concentration up to 100 mg/L and resulted in a significant increase of the lag-period. This fact, together with the finding that the resulting hybrid particles remained stable in the latter case, identified short chain sodium polyacrylates as more efficient modulators than long chain polyacrylates

Modulated Formation of MOF-5 NanoparticlesA SANS Analysis

MOF-5 nanoparticles were prepared by mixing a solution of [Zn₄O­(C₆H₅COO)₆] with a solution of benzene-1,4-dicarboxylic acid in DMF at ambient conditions. The former species mimics as a secondary building unit (SBU), and the latter acts as linker. Mixing of the two solutions induced the formation of MOF-5 nanoparticles in dilute suspension. The applied conditions were identified as suitable for a closer investigation of the particle formation process by combined light and small angle neutron scattering (SANS). Scattering analysis revealed a significant impact of the molar ratio of the two components in the reaction mixture. Excessive use of the building unit slowed down the process. A similar effect was observed upon addition of 4n-decylbenzoic acid, which is supposed to act as a modulator. The formation mechanism leads to initial intermediates, which turn into cubelike nanoparticles with a diameter of about 60–80 nm. This initial stage is followed by an extended formation period, where nucleation proceeds over hours, leading to an increasing number of nanoparticles with the same final size of 60–80 nm

Coordination polymer structure and revisited hydrogen evolution catalytic mechanism for amorphous molybdenum sulfide.

International audienceMolybdenum sulfides are very attractive noble-metal-free electrocatalysts for the hydrogen evolution reaction (HER) from water. The atomic structure and identity of the catalytically active sites have been well established for crystalline molybdenum disulfide (c-MoS2) but not for amorphous molybdenum sulfide (a-MoSx), which exhibits significantly higher HER activity compared to its crystalline counterpart. Here we show that HER-active a-MoSx, prepared either as nanoparticles or as films, is a molecular-based coordination polymer consisting of discrete [Mo3S13]2- building blocks. Of the three terminal disulfide (S22-) ligands within these clusters, two are shared to form the polymer chain. The third one remains free and generates molybdenum hydride moieties as the active site under H2 evolution conditions. Such a molecular structure therefore provides a basis for revisiting the mechanism of a-MoSx catalytic activity, as well as explaining some of its special properties such as reductive activation and corrosion. Our findings open up new avenues for the rational optimization of this HER electrocatalyst as an alternative to platinum

Crystal Growth Mechanisms and Morphological Control of the Prototypical Metal-Organic Framework MOF-5 Revealed by Atomic Force Microscopy

Crystal growth of the metal-organic framework MOF-5 was studied by atomic force microscopy (AFM) for the first time. Growth under low supersaturation conditions was found to occur by a two-dimensional or spiral crystal growth mechanism. Observation of developing nuclei during the former reveals growth occurs through a process of nucleation and spreading of metastable and stable sub-layers revealing that MOFs may be considered as dense phase structures in terms of crystal growth, even though they contain sub-layers consisting of ordered framework and disordered non-framework components. These results also support the notion this may be a general mechanism of surface crystal growth at low supersaturation applicable to crystalline nanoporous materials. The crystal growth mechanism at the atomistic level was also seen to vary as a function of the growth solution Zn/H2bdc ratio producing square terraces with steps parallel to the direction or rhombus-shaped terraces with steps parallel to the direction when the Zn/H2bdc ratio was &gt;1 or about 1, respectively. The change in relative growth rates can be explained in terms of changes in the solution species concentrations and their influence on growth at different terrace growth sites. These results were successfully applied to the growth of as-synthesized cube-shaped crystals to increase expression of the {111} faces and to grow octahedral crystals of suitable quality to image using AFM. This modulator-free route to control the crystal morphology of MOF-5 crystals should be applicable to a wide variety of MOFs to achieve the desired morphological control for performance enhancement in applications. Growth changes: Crystal growth mechanisms of the metal-organic framework MOF-5 were studied by atomic force microscopy and observed to occur through a process of nucleation and spreading of metastable and stable sub-layers, revealing that MOFs may be considered as dense phase structures in terms of crystal growth. Crystal growth rates were found to depend on the framework metal ion/organic linker ratio (see figure). Copyright © 2012 WILEY-VCH Verlag GmbH &amp; Co. KGaA, Weinheim