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Precise control of quantum structures in hybrid nanocrystals requires advancements in scientific methodologies. Here, on the design of tunable CsPbBr3/Cs4PbBr6 quantum dots are reported by developing a unique discrete phase transformation approach in Cs4PbBr6 nanocrystals. Unlike conventional hybrid systems that emit solely in the green region, this current strategy produces adjustable luminescence in the blue (450 nm), cyan (480 nm), and green (510 nm) regions with high photoluminescence quantum yields up to 45%, 60%, and 85%, respectively. Concentration-dependent studies reveal that phase transformation mechanisms and the factors that drive CsBr removal occur at lower dilutions while the dissolution-recrystallization process dominates at higher dilutions. When the polymer-CsPbBr3/Cs4PbBr6 integrated into a field-effected transistor the resulting phototransistors featured enhanced photosensitivity exceeding 105, being the highest reported for an n-type phototransistor, while maintaining good transistor performances as compared to devices consisting of polymer-CsPbBr3 NCs.
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Sintering of ceramic electrolytes (CE) is the most efficient way to obtain a dense, all ceramic solid-state battery with oxide-based materials. However, the high temperature required for this process leads to detrimental reactivity between CE and the active material. Crystalline ceramics are necessary for highly conductive oxide materials. Still, thermomechanical properties of glass-phase materials can be used to obtain a denser and more conductive CE. Glass-phase CE can be produced with Nasicon-type CE. Here, Li1.5Al0.5Ge1.5(PO4)3 (LAGP) glass is used as a model to investigate the formability, densification, and conduction properties upon crystallization. A complete study of the crystallization mechanism is first performed to fully understand how a high conductivity of 6.3 × 10-5 S·cm-1 at 30 °C with 92% relative density is obtained at a sintering temperature of only 550 °C without pressure. This is approximately 200 °C below the usual sintering temperature of LAGP. X-ray diffraction is then used to calculate the amount of crystalline phase as a function of time. A combined study of reaction kinetics and conductivity evolution reveals an autocatalytic nucleation effect, which produces an early crystallization pathway. Density is studied to quantify the ability of the glass to flow during the crystallization process.
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Understanding of crystal formation and growth conditions in reverse osmosis membrane channels enables us to develop efficient tools to control scaling in membrane facilities and increase their recoveries. Crystals are formed in "dead areas" and subsequently get out of them and sediment on membrane surface. Adsorption of polymeric inhibitor molecules to crystal surface was investigated as well as antiscalant behaviour throughout nucleation in "dead areas" and growth of crystals sedimented on membrane surface. Experimental dependencies of antiscalant adsorption rates on the antiscalant dosage values were determined. Examination of SEM images of crystals demonstrated that their size and amount depend on the supersaturation value reached in the "dead areas". More efficient antiscalants delay the beginning of nucleation and reduce the rate of crystal growth due to adsorption and blockage of crystal growth process. Antiscaling property of inhibitors is also attributed to their ability to provide certain amount of adsorbent to block crystal growth during nucleation. A test procedure is described that enables us to predict concentrate composition in the "dead areas" and calculate supersaturation values that correspond to beginning of nucleation.
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Herein, a simple and green quasi-solid-phase (QSP) method for facile synthesis of proton-type ZSM-5 avoiding use of excessive water, dry gel, Na+ cation and fluoride is reported. Crystallization by using the stoichiometric amount of TPAOH (tetrapropylammonium hydroxide) at 180 °C for only 12â h gave well-structured HZSM-5 crystals with high specific surface area of 429â m2 g-1 and high thermal stability. 5MRs was observed to closely relate the formation of MFI structure and QSP method exhibits shorter induction period (t0 ), higher nucleation rate (Vn ), and faster growth rate (Vg ). Moreover, HZ-12-180 showed extremely better and rather stable catalytic activity for methanol-to-propylene reaction by comparison with commercial HZSM-5.
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This study investigated crystallization mechanisms for the formation of lead aluminosilicate by sintering lead stabilization with kaolin-based precursors. PbAl2Si2O8 was found to be the only stable lead aluminosilicate in low-PbO system and demonstrates its highly intrinsic resistance to acid attack in leaching test. A three-stage PbAl2Si2O8 formation mechanism was supported by the results of the changing temperature in the system. Amorphization of sintered products was observed in both PbO/kaolinite and PbO/mullite systems at 600-700°C. When the temperature was increased to 750-900°C, the crystallochemical formation of lead aluminosilicates (i.e., Pb4Al4Si3O16, Pb6Al6Si2O21, and PbAl2Si2O8) was observed. Pb4Al4Si3O16 and Pb6Al6Si2O21 were found to be the intermediate phases at 700-900°C. Finally, PbAl2Si2O8 was found to be the only crystallite phase to host Pb at above 950°C. A maximum of 80% and 96.7% Pb can be incorporated into PbAl2Si2O8 in PbO/kaolinite and PbO/mullite systems, respectively, but the final products exhibited different microstructures. To reduce environmental hazard of lead, this strategy demonstrated a preferred mechanism of immobilizing lead into PbAl2Si2O8 structure via kaolin-based precursors.
Asunto(s)
Silicatos de Aluminio , Plomo , Cerámica , CaolínRESUMEN
Novel 17-nuclear Zr/Hf oxide clusters ({Zr17 } and {Hf17 }) are isolated from aqueous systems. In the clusters, Zr/Hf ions are connected through µ3 -O, µ3 -OH, and µ2 -OH linkages into a pinwheel core which is wrapped with SO4 2- , HCOO- , and aqua ligands. Octahedral hexanuclear Zr/Hf oxide clusters ({Zr6 }oct and {Hf6 }oct ) are also isolated from the same hydrothermal system by decreasing the synthesis temperature. Structures, synthetic conditions, vibrational spectra, and ionic conductivity of the clusters are studied. Structural studies and synthesis inspection suggest that formation of {Zr6 }oct and {Zr17 } involves assembly of the same transferable building blocks, but the condensation degree and thermodynamic stability of the products increase with hydrothermal temperature. The role of {Zr6 }oct and {Zr17 } in the formation of ZrO2 nanocrystals are then discussed in the scenario of nonclassical nucleation theory. In addition, the Zr oxide clusters exhibit ionic conductivity owing to the mobility of protons. This study not only adds new members to the Zr/Hf oxide cluster family, but also establishes a connection from Zr4+ ions to ZrO2 in the hydrothermal preparation of zirconium oxide nanomaterials.
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The action of direct sonication (US) versus conventional hydrothermal method (HY) was investigated to determine the differences in the crystallization mechanism of zeolite formed from fly ash. The results showed that ultrasonic energy is decisive in very fast faujasite and A-type zeolite transformation into more stable sodalite phase. The data display the main presence of sodalite together with a low amount of faujasite and zeolite A after the first 3â¯h of sonication. The full transformation of the latter two phases into sodalite takes place after 1â¯h more of treatment. The samples incubated by hydrothermal process for 3â¯h, instead, are characterized by the main presence of faujasite and A-type zeolites. The progressive synthesis of sodalite at the expense of the other two phases begins only after 4â¯h of treatment. The conclusion is that the crystallization of zeolites by ultrasonic and hydrothermal method proceeds via two different mechanisms. The data also show that the two approaches affect the stability of the synthetic products in a different way over the years.
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Hematin crystallization is the primary mechanism of heme detoxification in malaria parasites and the target of the quinoline class of antimalarials. Despite numerous studies of malaria pathophysiology, fundamental questions regarding hematin growth and inhibition remain. Among them are the identity of the crystallization medium in vivo, aqueous or organic; the mechanism of crystallization, classical or nonclassical; and whether quinoline antimalarials inhibit crystallization by sequestering hematin in the solution, or by blocking surface sites crucial for growth. Here we use time-resolved in situ atomic force microscopy (AFM) and show that the lipid subphase in the parasite may be a preferred growth medium. We provide, to our knowledge, the first evidence of the molecular mechanisms of hematin crystallization and inhibition by chloroquine, a common quinoline antimalarial drug. AFM observations demonstrate that crystallization strictly follows a classical mechanism wherein new crystal layers are generated by 2D nucleation and grow by the attachment of solute molecules. We identify four classes of surface sites available for binding of potential drugs and propose respective mechanisms of drug action. Further studies reveal that chloroquine inhibits hematin crystallization by binding to molecularly flat {100} surfaces. A 2-µM concentration of chloroquine fully arrests layer generation and step advancement, which is â¼10(4)× less than hematin's physiological concentration. Our results suggest that adsorption at specific growth sites may be a general mode of hemozoin growth inhibition for the quinoline antimalarials. Because the atomic structures of the identified sites are known, this insight could advance the future design and/or optimization of new antimalarials.