Model Pembelajaran Asam Basa Berbasis Scs (Science Process Skills) Melalui Kegiatan Laboratorium Sebagai Wahana Pendidikan Sains Siswa Mts

Tujuan penelitian ini adalah untuk memperkenal- kan dan mengetahui efektivitas Model Pembelajaran SCS ( Science Process Skills ) melalui kegiatan Laboratorium Sebagai Wahana Pendidikan Sains yang cocok bagi siswa MTs agar meningkatkan: penguasaan konsep kimia, ke- mampuan berpikir kreatif, dan keterampilan sains siswa. Metode yang digunakan adalah metode penelitian kelas, dan difokuskan pada pokok bahasan asam basa. Penelitian ini dilakukan di salah satu MTs Negeri di kota Semarang dengan subyek sebanyak 40 siswa kelas III. Instrumen yang digunakan dalam penelitian ini meliputi model pembelaja- ran, soal-soal tes, pedoman wawancara, pedoman obser- vasi dan angket, sedang LKS digunakan pada saat kegiatan laboratorium. Dalam model pembelajaran dikembangkan empat jenis konsep yaitu konsep kongkret, konsep yang menyatakan sifat, konsep yang melibatkan penggambaran simbol, dan konsep berdasarkan prinsip. Model pembela- jaran ini dapat meningkatkan pemahaman konsep pada setiap kelompok kemampuan siswa, mengembangkan ke- mampuan berpikir kreatif dengan hasil tertinggi pada as- pek membangun konsep di atas pengetahuan yang telah ada pada diri siswa dan terendah pada aspek memilih hal- hal yang mungkin tidak relevan, serta keterampilan sains mengatasi kurangnya waktu pembelajaran, bagian-bagian pembelajaran tertentu dapat dilaksanakan di luar jam ke- las

Hybrid methylammonium lead halide perovskite nanocrystals confined in gyroidal silica templates

We successfully synthesized hybrid methylammonium lead halide nanocrystals confined in a gyroidal mesoporous silica template. The nanocrystals adopted the same crystal structure as their bulk perovskite counterparts, highlighting the ability to control the bandgap by tuning the pore-size of the template. Besides providing more accessible spaces for the materials to diffuse within the channels, the 3D mesh of the gyroidal template should also allow easier escape of the solvent and pinning of the particles at different points, thus promoting the formation of isolated nanoparticles over larger structures (e.g., nanowires, nanorods)

Stable blue luminescent CsPbBr3 Perovskite nanocrystals confined in mesoporous thin films

Creating CsPbBr perovskite nanocrystals with bright blue emission is challenging because their optical properties depend sensitively on structure. Growing perovskites in mesoporous templates bypasses some of these purification issues because the size of the nanocrystal is governed by the dimensions of the pores. Mesoporous silica consisting of aligned channels with tunable diameter can be easily synthesized and used as a template. When the perovskite solution evaporates and retreats, some of the liquid remains trapped in the interconnecting pores by discontinuous dewetting. The precursor crystallizes, generating stable ca. 3.1 nm blue-emitting perovskite nanocrystals. The mesoporous template also serves as a protective barrier to preserve the optical properties of the CsPbBr from atmospheric conditions. Compared to the bulk crystals and the powder composite, the strong blue-shift of the emission peak in the film is accompanied by a decrease in the longer lifetime component and an 8-fold increase in the external quantum efficiency

Electrochemically in situ controllable assembly of hierarchically-ordered and integrated inorganic-carbon hybrids for efficient hydrogen evolution

Inorganic-carbon hybrid materials are an emerging class of nanostructured catalysts that can enhance various energy-oriented electrochemical reactions. Despite recent progress, it is still very challenging to controllably generate the hybrid carbon architecture and its inorganic components with a single approach. Inspired by the flexible redox properties of conductive polyaniline (PANI) polymer, we develop a redox-unit cooperative assembly strategy to synthesize hierarchically-ordered and integrated inorganic-carbon hybrids by electrochemically constructing the nanostructures of PANI and then modifying their redox states to controllably bond different metal complexes. The needle-branched PANI nanofibers are assembled in situ into a three-dimensional (3D) hierarchical framework on carbon paper by an anion induced electrochemical polymerization. Interestingly, tuning the redox states of PANI with a potentiostatic method achieves a controllable metal complex loading. The theoretical calculations show that the oxidized units can strongly bond metal complexes while reduced units don\u27t react significantly due to a high formation energy. Both units with proper proportions can cooperatively control the concentration and spatial distribution of metal complexes in the PANI framework. After thermal treatment, the metal/PANI composites are transformed into a series of inorganic-carbon hybrids including metals and metal oxides, carbides, and sulfides. This novel strategy not only significantly improves the catalytic performance of non-noble metal hybrid materials but also greatly increases the utilization efficiency of noble metal catalysts in the hydrogen evolution reaction. Surprisingly, the optimized Pt@NC catalyst exhibits an ultrahigh mass activity that is ∼5.3-times better than the commercial Pt/C catalyst

Temperature-Dependent Electronic Structure of Bixbyite α-Mn2O3 and the Importance of a Subtle Structural Change on Oxygen Electrocatalysis

α-Mn2O3 is an inexpensive Earth-abundant mineral that is used as an electrode material in various kinds of electrochemical devices. The complex bixbyite structure of α-Mn2O3, and its subtle orthorhombic → cubic phase transformation near room temperature has made it challenging to accurately determine its electronic proper- ties. We used high-resolution X-ray diffraction to study the temperature-dependent structures of phase-pure α-Mn2O3 prisms. Our measurements show a clear change in the crystal phase from orthorhombic → cubic between 293K and 300K. We input the Rietveld refined high-resolution crystal structures collected at various temperatures (273, 293, 300, 330K) directly into density functional theory (DFT) calculations to model their electronic properties. These calculations indicate that the orthorhombic phase α-Mn2O3 is a narrow bandgap semiconductor as expected. However, temper- atures higher than 300K transform the α-Mn2O3 into the cubic phase, causing the molecular orbitals of the Mn 3d and O 2p bands to overlap and mix covalently, mak- ing the material behave as a semimetal. This subtle change in crystal structure will affect the bulk conductivity of the material as well as Mn-O-Mn bond distances that influence the quality of its catalytic active sites for oxygen electrochemistry. Elec- trochemical oxygen evolution (OER) and oxygen reduction reaction (ORR) experi- ments performed at various temperatures (∼ 288K to 323K) using the same prepared electrode show a marked enhancement in both OER and ORR performance that is attributed to the higher activity of the cubic phase.</div

Controlled chemical vapor deposition for synthesis of nanowire arrays of metal-organic frameworks and their thermal conversion to carbon/metal oxide hybrid materials

Metal-organic frameworks (MOFs) can serve as high-surface-area templates to generate hierarchically ordered nanoporous carbon electrodes for high-performance supercapacitor devices. Here we describe a simple chemical approach to synthesize dense three-dimensional (3D) arrays of core-shell ZnO@ZIF-8 and Co(CO)(OH)·0.11HO@ZIF-67 nanowires on a conductive carbon cloth. Annealing the core-shell structures at high temperatures converted the MOF shell into a composite of nanoporous carbon (NC) mixed with conductive metal oxides. The conformal nature of the MOF-coating process generates a NC film with continuous conductive paths from the outer surfaces of the nanowires down to the flexible carbon electrode. Carbonization of ZIF-67 transforms the material into conductive sp type carbon mixed with CoO nanostructures. Because CoO is a faradic metal oxide with a high theoretical capacitance, these CoO/NC hybrid heterostructure arrays are a promising candidate material for use in an electrochemical supercapacitor device. The CoO/NC hybrid electrodes had good performance and exhibited a high areal capacitance of 1.22 F·cm at 0.5 mA·cm. Conformal deposition of MOFs via the chemical vapor method offers a promising new platform to design conductive, ultrahigh surface area electrodes that preserve the 3D morphology for applications in supercapacitors and electrocatalysis

Morphosynthesis of nanoporous pseudo Pd@Pt bimetallic particles with controlled electrocatalytic activity

Nanoporous pseudo Pd@Pt bimetallic particles were prepared using a facile one-step synthetic approach. The morphologies of the resultant particles are changed from spheres to cubes by increasing the molar ratio of the Pd/Pt precursor solution. Compared to commercially available Pt black and Pt/C-20%, the nanoporous pseudo Pd@Pt bimetallic particles were up to 7 times and 2.1 times more active for the methanol oxidation reaction on the basis of equivalent Pt, respectively. This excellent electrocatalytic activity is caused by a combination of the high surface area of the nanoporous architecture in addition to the bimetallic synergetic effect. Through this work, we demonstrate a general approach for the creation of nanoporous bimetallic Pt-based particles with controlled shape, composition and size for enhanced catalytic activity

Self-assembly of uniform polyhedral silver nanocrystals into densest packings and exotic superlattices

Understanding how polyhedra pack into extended arrangements is integral to the design and discovery of crystalline materials at all length scales. Much progress has been made in enumerating and characterizing the packing of polyhedral shapes, and the self-assembly of polyhedral nanocrystals into ordered superstructures. However, directing the self-assembly of polyhedral nanocrystals into densest packings requires precise control of particle shape, polydispersity,interactions and driving forces. Here we show with experiment and computer simulation that a range of nanoscale Ag polyhedra can self-assemble into their conjectured densest packings. When passivated with adsorbing polymer, the polyhedra behave as quasi-hard particles and assemble into millimetre-sized three-dimensional supercrystals by sedimentation.We also show, by inducing depletion attraction through excess polymer in solution, that octahedra form an exotic superstructure with complex helical motifs rather than the densest Minkowski lattice. Such large-scale Ag supercrystals may facilitate the design of scalable three-dimensional plasmonic metamaterials for sensing, nanophotonics, and photocatalysis