An investigation of Al2O3 induced variations in the structural parameters in strontium borosilicate glasses using solid state NMR.

The physical properties of oxide glasses are crucially dependent on the atomistic structural speciation. In this study, we investigate the variation in the local ordering in the glass network of strontium borosilicate glasses (34.82 SrO, 51.84 B2O3, 13.34 SiO2 in mol%) with a progressive substitution of B2O3 by Al2O3 and estimate the structural parameters: the oxygen packing fraction, and the average network coordination number. The coordination of the network forming cations at various glass compositions is determined using 11B, 27Al, and 29Si solid-state nuclear magnetic resonance (SSNMR). The SSNMR reveals that at the higher substitution of B2O3 by Al2O3 in the glass composition, the coordination network of Al3+ exists predominantly in the 4 coordinated state, the network forming B3+ cations transform from a tetrahedral BO4 to a trigonal BO3 structure, and the Q4 form of silicates is dominant. The average coordination number and the oxygen packing fraction were calculated using the parameters obtained from the SSNMR results, and it is observed that the average coordination number decreases, and the oxygen packing fraction increases on incorporating Al. It is interesting to note that some of the thermophysical properties of these compositions closely follow the pattern shown by the average coordination number and the oxygen packing fraction.

Ionic Conductivity of Na3Al2P3O12 Glass Electrolytes-Role of Charge Compensators.

In glasses, a sodium ion (Na+) is a significant mobile cation that takes up a dual role, that is, as a charge compensator and also as a network modifier. As a network modifier, Na+ cations modify the structural distributions and create nonbridging oxygens. As a charge compensator, Na+ cations provide imbalanced charge for oxygen that is linked between two network-forming tetrahedra. However, the factors controlling the mobility of Na+ ions in glasses, which in turn affects the ionic conductivity, remain unclear. In the current work, using high-fidelity experiments and atomistic simulations, we demonstrate that the ionic conductivity of the Na3Al2P3O12 (Si0) glass material is dependent not only on the concentration of Na+ charge carriers but also on the number of charge-compensated oxygens within its first coordination sphere. To investigate, we chose a series of glasses formulated by the substitution of Si for P in Si0 glass based on the hypothesis that Si substitution in the presence of Na+ cations increases the number of Si-O-Al bonds, which enhances the role of Na as a charge compensator. The structural and conductivity properties of bulk glass materials are evaluated by molecular dynamics (MD) simulations, magic angle spinning-nuclear magnetic resonance, Raman spectroscopy, and impedance spectroscopy. We observe that the increasing number of charge-imbalanced bridging oxygens (BOs) with the substitution of Si for P in Si0 glass enhances the ionic conductivity by an order of magnitude-from 3.7 × 10-8 S.cm-1 to 3.3 × 10-7 S.cm-1 at 100 °C. By rigorously quantifying the channel regions in the glass structure, using MD simulations, we demonstrate that the enhanced ionic conductivity can be attributed to the increased connectivity of Na-rich channels because of the increased charge-compensated BOs around the Na atoms. Overall, this study provides new insights for designing next-generation glass-based electrolytes with superior ionic conductivity for Na-ion batteries.

Distribution of water in the pores of periodic mesoporous organosilicates - a proton solid state MAS NMR study.

Solid state proton (1H) magic angle spinning (MAS) NMR has been employed to study the distribution of confined water in ethane substituted periodic mesoporous organosilicate (PMOE) materials. Proton spectra acquired at different hydration levels are analysed and interpreted in terms of water clusters of various sizes and distributions of water layers on the pore surface. For comparison, we also performed similar experiments on SBA-15. The formation of larger clusters at lower hydration suggests that the pores of PMOE are getting filled with water at lower hydration levels than those in SBA-15. For PMOE, the simultaneous presence of two major resonances in the ranges 3.6-4.1 ppm and 4.4-5.2 ppm and their behaviour upon hydration imply a water layer distribution that is the sum of two contributions, corresponding to fully filled and partially filled pores or pore segments. Furthermore, the behaviour mentioned above suggests that both radial and axial filling mechanisms play a significant role in the hydration process. For SBA-15, as a function of hydration, we observed a smooth variation in the proton chemical shift of the main dynamic resonance. In accordance with previous studies, this is attributed to the gradual increase in the average thickness of water layers with an increase in hydration, and to a pore filling mechanism that is predominantly radial.

Preparation of colourless phosphate glass by stabilising higher Fe[II] in microwave heating.

Iron impurity in raw material remains a major challenge in producing colourless glass. In this investigation, we report microwave (MW) heating capable of altering Fe-redox ratio (Fe2+/∑Fe) enabling preparation of colourless phosphate glass. The effect of Sn concentration in retention of Fe[II] in glass melted in MW was compared with conventional glasses. Colourimetric study developing Fe2+-ferrozine colour complex reveals Fe-redox ratio ≥0.49 required to obtain colourless phosphate glass. In microwave heating, addition of 1 wt.% Sn metal powder can impart the desired effect whereas addition of 1.9 wt.% Sn metal powder is required in conventional heating. The correlation equation of Fe-redox ratio with concentration of Sn metal is found to be different in microwave and conventional heating. Thus, exploiting this different redox changes in MW heating optical properties can be tailored. Preservation of higher Fe[II] in MW melted glass is also confirmed by XPS and TGA. 31P MAS NMR spectra suggest that transition from cross linked ultra phosphate to linear polymer metaphosphate network in incorporation of Sn is found different in glass prepared adopting microwave irradiation. 27A1 MAS NMR spectra suggest higher relative content of Al6+ in glass obtained from MW heating. Energy consumption analysis revels 3.4 kWh in MW heating while 14 kWh in conventional glass melting using resistance heating. Further, glass melting in MW can be completed within 2 h unlike ~5 h needed in conventional. MW heating plays a significant role in improving properties to make colourless phosphate glass in addition to significant energy and time saving.

Structural elucidation of NASICON (Na3Al2P3O12) based glass electrolyte materials: effective influence of boron and gallium.

Understanding the conductivity variations induced by compositional changes in sodium super ionic conducting (NASICON) glass materials is highly relevant for applications such as solid electrolytes for sodium (Na) ion batteries. In the research reported in this paper, NASICON-based NCAP glass (Na2.8Ca0.1Al2P3O12) was selected as the parent glass. The present study demonstrates the changes in the Na+ ion conductivity of NCAP bulk glass with the substitution of boron (NCABP: Na2.8Ca0.1Al2B0.5P2.7O12) and gallium (NCAGP: Na2.8Ca0.1Al2Ga0.5P2.7O12) for phosphorus and the resulting structural variations found in the glass network. For a detailed structural analysis of NCAP, NCABP and NCAGP glasses, micro-Raman and magic angle spinning-nuclear magnetic resonance (MAS-NMR) spectroscopic techniques (for 31P, 27Al, 23Na, 11B and 71Ga nuclei) were used. The Raman spectrum revealed that the NCAP glass structure is more analogous to the AlPO4 mesoporous glass structure. The 31P MAS-NMR spectrum illustrated that the NCAP glass structure consists of a high concentration of Q0 (3Al) units, followed by Q0 (2Al) units. The 27Al MAS-NMR spectrum indicates that alumina exists at five different sites, which include AlO4 units surrounded by AlO6 units, Al(OP)4, Al(OP)5, Al(OAl)6 and Al(OP)6, in the NCAP glass structure. The 31P, 27Al and 11B MAS-NMR spectra of the NCABP glass revealed the absence of B-O-Al linkages and the presence of B3-O-B4-O-P4 linkages which further leads to the formation of borate and borophosphate domains. The 71Ga MAS-NMR spectrum suggests that gallium cations in the NCAGP glass compete with the alumina cations and occupy four (GaO4), five (GaO5) and six (GaO6) coordinated sites. The Raman spectrum of NCAGP glass indicates that sodium cations have also been substituted by gallium cations in the NCAP glass structure. From impedance analysis, the dc conductivity of the NCAP glass (∼3.13 × 10-8 S cm-1) is slightly decreased with the substitution of gallium (∼2.27 × 10-8 S cm-1) but considerably decreased with the substitution of boron (∼1.46 × 10-8 S cm-1). The variation in the conductivity values are described based on the structural changes of NCAP glass with the substitution of gallium and boron.

Targeted Drug Delivery in Covalent Organic Nanosheets (CONs) via Sequential Postsynthetic Modification.

Covalent organic nanosheets (CONs) have emerged as a new class of functional two-dimensional (2D) porous organic polymeric materials with a high accessible surface, diverse functionality, and chemical stability. They could become versatile candidates for targeted drug delivery. Despite their many advantages, there are limitations to their use for target specific drug delivery. We anticipated that these drawbacks could be overturned by judicious postsynthetic modification steps to use CONs for targeted drug delivery. The postsynthetic modification would not only produce the desired functionality, it would also help to exfoliate to CONs as well. In order to meet this requirement, we have developed a facile, salt-mediated synthesis of covalent organic frameworks (COFs) in the presence of p-toluenesulfonic acid (PTSA). The COFs were subjected to sequential postsynthetic modifications to yield functionalized targeted CONs for targeted delivery of 5-fluorouracil to breast cancer cells. This postsynthetic modification resulted in simultaneous chemical delamination and functionalization to targeted CONs. Targeted CONs showed sustained release of the drug to the cancer cells through receptor-mediated endocytosis, which led to cancer cell death via apoptosis. Considering the easy and facile COF synthesis, functionality based postsynthetic modifications, and chemical delamination to CONs for potential advantageous targeted drug delivery, this process can have a significant impact in biomedical applications.

M-Au/TiO2 (M = Ag, Pd, and Pt) nanophotocatalyst for overall solar water splitting: role of interfaces.

M-Au/TiO2 (M = Ag, Pd, Pt) composites were prepared through a facile one-pot photodeposition synthesis and evaluated for solar water splitting (SWS) with and without a sacrificial agent. The M-Au combination exhibits a dominant role in augmenting the H2 generation activity by forming a bi-metallic system. Degussa P25 was used as a TiO2 substrate to photodeposit Au followed by Au + M (M = Ag/Pd/Pt). The SWS activity of the M-Au/TiO2 was determined through photocatalytic H2 production in the presence of methanol as a sacrificial agent under one sun conditions with an AM1.5 filter. The highest H2 yield was observed for Pt0.5-Au1/TiO2 and was around 1.3 ± 0.07 mmol h(-1) g(-1), with an apparent quantum yield (AQY) of 6.4%. Pt0.5-Au1/TiO2 also demonstrated the same activity for 25 cycles of five hours each for 125 h. Critically, the same Pt0.5-Au1/TiO2 catalyst was active in overall SWS (OSWS) without any sacrificial agent, with an AQY = 0.8%. The amount of Au and/or Pt was varied to obtain the optimum composition and it was found that the Pt0.5-Au1/TiO2 composition exhibits the best activity. Detailed characterization by physico-chemical, spectral and microscopy measurements was carried out to obtain an in-depth understanding of the origin of the photocatalytic activity of Pt0.5-Au1/TiO2. These in-depth studies show that gold interacts predominantly with oxygen vacancies present on titania surfaces, and Pt preferentially interacts with gold for an effective electron-hole pair separation at Pt-Au interfaces and electron storage in metal particles. The Pt in Pt0.5-Au1/TiO2 is electronically and catalytically different from the Pt in Pt/TiO2 and it is predicted that the former suppresses the oxygen reduction reaction.