Chen Liu,Lu Bai,Jianming Zhang,Deng Hu,Meng Li,Gaofeng Zeng,Yanfeng Zhang,Wei Wei,Yuhan Sun
Rapid synthesis and characterization of all-silica Deca-Dodecasil 3 Rhombohedral (DD3R) zeolite were systematically studied with (NH 4 ) 2 SiF 6 as silica source. The effects of gel recipe, synthesis temperature and time, seeding, aging and silica source were investigated systematically. Big DD3R crystals (50–150 μm) with various morphologies (hexagonal plate, polyhedron and rhombohedron) were obtained by tuning the synthesis temperature, time, seeding and aging. Compared with other silica sources, (NH 4 ) 2 SiF 6 is very reactive which enhances the nucleation and crystal growth of DD3R zeolite significantly. At 220 °C, highly crystalline DD3R was obtained in 12 h without seeding, which is the fastest synthesis up to now. Aging and seeding reduced the synthesis time substantially and led to smaller crystals. With the help of seeding and aging, pure DD3R crystals were obtained in 6 d at 100 °C, which opens the door to synthesis at low temperature and ambient pressure. Mixed silica sources can reduce the consumption of expensive (NH 4 ) 2 SiF 6 . Higher calcination temperature is required for the complete template removal of the big DD3R crystals obtained in this study, which hinders the diffusion of oxidation products from the template. Zeolites SGT and DOH are competing phases in the synthesis of DD3R. The introduction of Al into the mother liquor led to the formation of zeolite SGT.
Pomegranate-like B@(NH 4 ) 2 SiF 6 @LiClO 4 enables ordered boron combustion. • Sequential fluorination–oxidation suppresses oxide re-passivation. • The optimized composite shows faster ignition and stronger flames. Boron suffers from severely limited combustion efficiency due to the kinetic barrier imposed by its native oxide layer. In this work, a pomegranate-inspired B@(NH 4 ) 2 SiF 6 @LiClO 4 composite was fabricated via a two-step solvent evaporation-induced self-assembly strategy, enabling highly dispersed reactive domains and intimate interfacial contact. The distinctive pomegranate-inspired architecture establishes particle-level spatial organization of the reactive components, while their distinct thermal activation windows provide the temporal basis for a proposed spatiotemporally coordinated reaction pathway. TG-DSC and TG-FTIR analyses reveal that fluorine-containing species derived from (NH 4 ) 2 SiF 6 evolve prior to LiClO 4 melting and major oxidizer release, supporting a proposed sequential fluorination-oxidation pathway involving early fluorine-mediated interfacial modification followed by oxidizer-driven boron oxidation. At an optimal (NH 4 ) 2 SiF 6 content of 10 wt%, the ignition delay and combustion duration are reduced by 15.47% and 68.22%, respectively, compared with B@LiClO 4 , demonstrating substantially improved ignition and combustion kinetics. Combined structural, thermal, and combustion analyses support the proposed spatiotemporally coordinated fluorination-oxidation pathway arising from the coupling of particle-level organization and temporally separated thermal events. This work provides a particle-level interfacial engineering strategy for coordinating fluorination and oxidation in high-performance boron-based energetic systems. A pomegranate-inspired B@(NH₄)₂SiF₆@LiClO₄ enables spatiotemporally ordered boron combustion by coupling fluorination and oxidation reactions within confined nanoscale domains. Sequential interfacial activation and molten-salt-mediated oxygen transport promote continuous reaction propagation and suppress oxide re-passivation, resulting in faster ignition, intensified flame propagation, and more efficient energy release compared with conventional physically mixed systems. Download: Download high-res image (176KB) Download: Download full-size image
Idowu Peter Babatunde,Wang Xiaohui,Ma Shuhua,Oduye Temitope Gabriel
A new process for the controlled-synthesis of large surface area mesoporous silica nanoparticles (MSNs) from the unique (NH 4 ) 2 SiF 6 -NH 4 F solution produced from coal fly ash was developed using template assisted rapid chemical precipitation method. This work achieved the synthesis of MSNs with specific surface area (SSA) (~ 500 m 2 /g—1064 m 2 /g), small particle size (~ 90 nm- 133 nm) with narrow pore size distribution ranging between (7.56 nm- 20.11 nm) and reduced agglomeration condition by proposing a unique reactant’s feeding pattern and studying other parameters aiding the controlled synthesis process. The effect of high concentration fluoride ion on cationic cetyltrimethylammonium bromide (CTAB) template was also investigated. A novel CTAB removal method from the highly porous cavities of the silica nanoparticles under mild conditions was proposed. At 50 °C and atmospheric pressure, the foam fractionation technique showed 61% efficiency of CTAB removal while maintaining the porous structure and surface silanol of the particles compared with the traditional calcination method, providing green, economic and sustainable method for surfactant removal in MSNs.
The synthesis procedures of red phosphors activated by Mn4+ that are carried out especially at room temperature, are significant to industrialization. Herein, we report a facile strategy to obtain two red micro-crystal phosphors: (NH4)2TiF6:Mn4+ (NTF:Mn) and (NH4)2SiF6:Mn4+ (NSF:Mn) through ion exchange at room temperature for a few hours. Raw materials NTF and NSF act as host lattices of red micro-crystal phosphors, and activator Mn4+ ions are from K2MnF6/HF and/or mixed KMnO4/HF solution. The reaction mechanism for the synthesis process has been comprehensively discussed in detail. The typical red emitting luminescence of Mn4+ with strong absorption in the blue region and the large size of about 200 μm of red micro-crystal phosphors NTF:Mn make it an attractive candidate material as a red compensator for resin-free white light-emitting diodes with high color rendering index. The dependence of emission intensity on concentration of HF and KMnO4, and measurement temperature has been investigated. The advantage of the proposed strategy is the ability to explore Mn4+ doped red phosphors from low-cost starting materials at room temperature for large scale industrial applications.
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