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Atluri, Rambabu
Publications (10 of 10) Show all publications
Atluri, R., Bacsik, Z., Hedin, N. & Garcia-Bennett, A. E. (2010). Structural variations in mesoporous materials with cubic Pm3n symmetry. Microporous and Mesoporous Materials, 133(1-3), 27-35
Open this publication in new window or tab >>Structural variations in mesoporous materials with cubic Pm3n symmetry
2010 (English)In: Microporous and Mesoporous Materials, ISSN 1387-1811, E-ISSN 1873-3093, Vol. 133, no 1-3, p. 27-35Article in journal (Refereed) Published
Abstract [en]

The fine structural details of mesoporous materials possessing Pm3n symmetry prepared with varying amphiphilic surfactants under acid and alkaline conditions are investigated using electron crystallography and sorption studies. The structural data derived is used to understand the parameters that govern the formation of cavity-windows and to propose synthetic strategies in order to control independently the size of the cavities and cavity-windows. Results support that whilst attainment of Pm3n cubic packing is due to the overall surfactant geometry, the formation of cavity-windows is associated with the hydration layer formed at the interphase between the surfactant and the silica wall.  The charge density at the micelle surface may be tailored using two strategies: (i) using dicationic gemini surfactants at low pHs resulting in an increase in the hydration layer; or (ii) by using co-structure directing agents such as organoalkoxysilanes which reduce the hydration layer surrounding the micelles. The latter leads to the formation of higher cavity sizes and may be useful for tuning fine structural details of mesoporous materials when considering their use in important applications such as gas separation.

Keywords
Amphiphilic surfactants, Mesoporous materials, Electron microscopy, Structural solutions, Gas separation
National Category
Materials Engineering
Research subject
Materials Science
Identifiers
urn:nbn:se:uu:diva-121984 (URN)10.1016/j.micromeso.2010.04.007 (DOI)000279061000004 ()
Available from: 2010-04-06 Created: 2010-04-03 Last updated: 2017-12-12Bibliographically approved
Bacsik, Z., Atluri, R., Garcia-Bennett, A. E. & Hedin, N. (2010). Temperature-Induced Uptake of CO2 and Formation of Carbamates in Mesocaged Silica Modified with n-Propylamines. Langmuir, 26(12), 10013-10024
Open this publication in new window or tab >>Temperature-Induced Uptake of CO2 and Formation of Carbamates in Mesocaged Silica Modified with n-Propylamines
2010 (English)In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 26, no 12, p. 10013-10024Article in journal (Refereed) Published
Abstract [en]

Adsorption-mediated CO2 separation can reduce the costs of carbon capture and storage. The reduction in cost requires adsorbents with high capacities for CO2 sorption and high CO2-over-N2 selectivity. Amine-modified sorbents are promising candidates for carbon capture. To investigate the details of CO2 adsorption in such materials, we studied mesocaged (cubic, Pm3n symmetry) silica adsorbents with tethered propylamines using Fourier transform infrared (FTIR) spectroscopy and volumetric uptake experiments. The degree of heterogeneity in these coatings was varied by either co-synthesizing or post-synthetically introducing the propylamine modification. In situ FTIR spectroscopy revealed the presence of both physisorbed and chemisorbed CO2 in the materials. We present the first direct molecular evidence for physisorption using FTIR spectroscopy in mesoporous silica sorbents modified with propylamines. Physisorption reduced the CO2-over-N2 selectivity in amine-rich sorbents. Samples with homogenous coatings showed typical CO2 adsorption trends and large quantities of IR-observable physisorbed CO2. The uptake of CO2 in mesocaged materials with heterogeneous propylamine coatings was higher at high temperatures than at low temperatures. At higher temperatures and low pressures, the post-synthetically modified materials adsorbed more CO2 than did the extracted ones, even though the surface area after modification was clearly reduced and the coverage of primary amine groups was lower. The principal mode of CO2 uptake in post-synthetically modified mesoporous silica was chemisorption. The chemisorbed moieties were present mainly as carbamate–ammonium ion pairs, resulting from the quantitative transformation of primary amine groups during CO2 adsorption as established by NIR spectroscopy. The heterogeneity in the coatings promoted the formation of these ion pairs. The average propylamine–propylamine distance must be small to allow the formation of carbamate–propylammonium ion pairs.

Keywords
carbon dioxide, propylamine, adsorption, IR, FTIR, silica, mesoporous
National Category
Materials Engineering
Research subject
Materials Science
Identifiers
urn:nbn:se:uu:diva-121987 (URN)10.1021/la1001495 (DOI)000278427600114 ()
Available from: 2010-04-06 Created: 2010-04-03 Last updated: 2017-12-12Bibliographically approved
Atluri, R., Garcia-Bennett, A. . & Sakamoto, Y. (2009). Co-Structure Directing Agent Induced Phase Transformation of Mesoporous Materials. Langmuir, 25(5), 3189-3195
Open this publication in new window or tab >>Co-Structure Directing Agent Induced Phase Transformation of Mesoporous Materials
2009 (English)In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 25, no 5, p. 3189-3195Article in journal (Refereed) Published
Abstract [en]

The synthesis of cubic Pmn mesocaged solid templated by cetyltrimethyl ammonium bromide (C16TMABr) surfactant by direct cocondensation of (3-aminopropyl)triethoxysilanes (APES) under strong alkaline conditions is reported. The novel route gives direct incorporation of amino functional groups on the porous silica wall, and the structural formation has been followed by means of in situ SAXS studies performed at a synchrotron beam line. Data shows that a molar ratio of C16TMABr/APES = 0.6 favors the formation of 3D cubic mesocaged solid with Pmn symmetry which transforms to a cylindrical mesoporous phase with p6mm symmetry at higher molar ratios. Further structural evaluation has been performed by means electron crystallography (EC). Reconstructed 3D models based on EC show the presence of spherical cages (A-cages, 45 Å) and ellipsoidal cages (B-cages, 48 × 43 Å) whereby every cage in the unit cell is connected to 14 nearest cages with a window size of 18 Å. Finally, a mechanism is proposed, denoted S+NoI, in which penetration of the neutral aminopropyl moiety within the micellar corona is responsible for the formation of the Pmn phase, accounting for the formation of the hexagonal phase at higher molar ratios and higher temperatures. In comparison to other mesocaged materials with the same symmetry this structure possesses a more open porous network which will help assess its potential in a variety of applications discussed herein.

National Category
Other Materials Engineering
Research subject
Engineering Science with specialization in Nanotechnology and Functional Materials
Identifiers
urn:nbn:se:uu:diva-99092 (URN)10.1021/la803727u (DOI)000263770800097 ()
Available from: 2009-03-06 Created: 2009-03-06 Last updated: 2017-12-13Bibliographically approved
Strømme, M., Brohede, U., Atluri, R. & Garcia Bennett, A. (2009). Mesoporous silica-based nanomaterials for drug delivery: evaluation of structural properties associated with release rate. Wiley Interdisciplinary Reviews: Nanomedicine and Nanobiotechnology, 1(1), 140-148
Open this publication in new window or tab >>Mesoporous silica-based nanomaterials for drug delivery: evaluation of structural properties associated with release rate
2009 (English)In: Wiley Interdisciplinary Reviews: Nanomedicine and Nanobiotechnology, ISSN 1939-5116, Vol. 1, no 1, p. 140-148Article in journal (Refereed) Published
Abstract [en]

We present here a study of the controlled release of amino acid-derived amphiphilic molecules from the internal pore structure of mesoporous nanoparticle drug delivery systems with different structural properties, namely cubic and hexagonal structures of various degrees of complexity. The internal pore surface of the nanomaterials presented has been functionalised with amine moieties through a one-pot method. Release profiles obtained by conductivity measurements are interpreted in terms of specific structural and textural parameters of the porous nanoparticles, such as pore geometry and connectivity. Results indicate that diffusion coefficients are lower by as much 4 orders of magnitude in two-dimensional structures in comparison to three-dimensional mesoporous solids. A fast release in turn is observed from mesocaged materials AMS-9 and AMS-8, where the presence of structural defects is thought to lead to a slightly lower diffusion coefficient in the latter. We conclude that the use of single or mixed phases of these porous systems can be utilized to provide sustained release over long time periods and expect their use in a variety of formulations.

Place, publisher, year, edition, pages
Wiley, 2009
National Category
Other Materials Engineering
Research subject
Engineering Science with specialization in Nanotechnology and Functional Materials
Identifiers
urn:nbn:se:uu:diva-86820 (URN)10.1002/wnan.13 (DOI)000276657700014 ()
Available from: 2008-12-08 Created: 2008-12-08 Last updated: 2016-11-30Bibliographically approved
Atluri, R., Garcia-Bennett, A. & Hedin, N. (2009). Nonsurfactant Supramolecular Synthesis of Ordered Mesoporous Silica. Journal of the American Chemical Society, 131(9), 3189-3191
Open this publication in new window or tab >>Nonsurfactant Supramolecular Synthesis of Ordered Mesoporous Silica
2009 (English)In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 131, no 9, p. 3189-3191Article in journal (Refereed) Published
Abstract [en]

Hoogsteen-bonded tetrads and pentamers are formed by a large variety of organic molecules through H-donor and acceptor groups capable of inducing self-organization to form columnar and hexagonal mesophases. The biological importance of such macromolecular structures is exemplified by the assembly of guanosine-rich groups of telomere units and their implication in chromosomal replication. Folic acid is composed of a pterin group, chemically and structurally similar to guanine, conjugated to an l-glutamate moiety via a p-amino benzoic acid. Our aim has been to develop a delivery vehicle for folic acid and at the same time provide a novel synthetic route for ordered mesoporous materials without the use of amphiphilic surfactants. We present a new nonsurfactant route for the synthesis of highly ordered mesoporous materials, based on the supramolecular templating of stacked arrays of the tetramer-forming pterin groups of folic acid under a variety of synthetic conditions. This method leads to hexagonally ordered mesoporous structures with gyroid, spherical, and chiral morphologies with pores on the order of 25−30 Å in diameter and surface areas above 1000 m2/g. More importantly circular dichroism studies reveal that the folate template possesses a chiral signature within the pores in the as-synthesized solid and that chirality is transferred from the folate template to the pore surface via the aminopropyl triethoxysilane costructure directing agent used in the supramolecular assembly. This novel templating approach for ordered mesoporous materials breaks the hegemony of surfactant micellar systems for the preparation of these exciting high surface area solids and opens new opportunities for structural control, design of pore geometry, and novel applications.

National Category
Engineering and Technology
Research subject
Engineering Science with specialization in Nanotechnology and Functional Materials
Identifiers
urn:nbn:se:uu:diva-99093 (URN)10.1021/ja8096477 (DOI)000264792400033 ()19220057 (PubMedID)
Available from: 2009-03-06 Created: 2009-03-06 Last updated: 2017-12-13Bibliographically approved
Strømme, M., Atluri, R., Brohede, U., Frenning, G. & Garcia-Bennett, A. E. E. (2009). Proton Absorption in As-Synthesized Mesoporous Silica Nanoparticles as a Structure-Function Relationship Probing Mechanism. Langmuir, 25(8), 4306-4310
Open this publication in new window or tab >>Proton Absorption in As-Synthesized Mesoporous Silica Nanoparticles as a Structure-Function Relationship Probing Mechanism
Show others...
2009 (English)In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 25, no 8, p. 4306-4310Article in journal (Refereed) Published
Abstract [en]

A new method to investigate the effect of pore geometry on diffusion processes in mesoporous silica nanoparticles and other types of micro- and mesoporous structures is put forward. The method is based onthe study of proton diffusion from a liquid surrounding the mesoporous particles into the particle pore system. The proton diffusion properties are assessed for a variety of as-synthesized mesoporous nano- and microparticles with two-dimensional and three-dimensional connectivity. Results show that the diffusion coefficients are higher for the proton absorption process than for the release of surfactant template molecules, and that they overall follow the same trend with the more complex three-dimensional mesocaged particles showing the highest diffusion coefficients. The pore geometry (cylindrical pores versus cage-type pores) and structure connectivity are found to play a key role for the effects observed. The results put forward in the present work should offer a valuable tool in the development of porous nanomaterials in a range of applications including the use as catalysis and separation enhancers in the petrochemical industry, as scaffolds for hydrogen storage, and as drug delivery vehicles for sustained release and gene transfection.

National Category
Engineering and Technology
Research subject
Engineering Science with specialization in Nanotechnology and Functional Materials
Identifiers
urn:nbn:se:uu:diva-100974 (URN)10.1021/la900105u (DOI)000265281700015 ()19281159 (PubMedID)
Available from: 2009-04-15 Created: 2009-04-15 Last updated: 2017-12-13Bibliographically approved
Atluri, R. & Garcia-Bennett, A. E. (2009). Structural variations in mesocaged materials with Pm3n symmetry. In: : . Paper presented at 32nd Annual Meeting British Zeolite Association. Ambleside, United Kingdom, 2009..
Open this publication in new window or tab >>Structural variations in mesocaged materials with Pm3n symmetry
2009 (English)Conference paper, Published paper (Refereed)
National Category
Other Materials Engineering
Research subject
Engineering Science with specialization in Nanotechnology and Functional Materials
Identifiers
urn:nbn:se:uu:diva-122126 (URN)
Conference
32nd Annual Meeting British Zeolite Association. Ambleside, United Kingdom, 2009.
Available from: 2010-04-06 Created: 2010-04-06 Last updated: 2016-04-14Bibliographically approved
Garcia-Bennett, A. & Atluri, R. (2008). Non-Surfactant Synthesis of Mesoporous Materials. In: : . Paper presented at Gordon Research Conference Nanoporous Materials, Waterville, Maine, United States.
Open this publication in new window or tab >>Non-Surfactant Synthesis of Mesoporous Materials
2008 (English)Conference paper, Published paper (Refereed)
National Category
Chemical Sciences Engineering and Technology
Research subject
Engineering Science with specialization in Nanotechnology and Functional Materials
Identifiers
urn:nbn:se:uu:diva-125185 (URN)
Conference
Gordon Research Conference Nanoporous Materials, Waterville, Maine, United States
Available from: 2010-05-10 Created: 2010-05-10 Last updated: 2016-04-13Bibliographically approved
Brohede, U., Atluri, R., Garcia Bennett, A. & Strömme, M. (2008). Sustained Release from Mesosporous Nanoparticles: evaluation of structural properties associated with controlled release rate. Current Drug Delivery, 5(3), 177-185
Open this publication in new window or tab >>Sustained Release from Mesosporous Nanoparticles: evaluation of structural properties associated with controlled release rate
2008 (English)In: Current Drug Delivery, ISSN 1567-2018, E-ISSN 1875-5704, Vol. 5, no 3, p. 177-185Article in journal (Refereed) Published
Abstract [en]

We present here a detailed study of the controlled release of amino acid derived amphiphilic molecules from the internal pore structure of mesoporous nanoparticle drug delivery systems with different structural properties; namely cubic and hexagonal structures of various degrees of complexity. The internal pore surface of the nanomaterials presented has been functionalised with amine moieties through a one pot method. Release profiles obtained by Alternating Ionic Current measurements are interpreted in terms of specific structural and textural parameters of the porous nanoparticles such as pore geometry and connectivity. Results indicate that diffusion coefficients are lower by as much as four orders of magnitude in 2-dimensional structures in comparison to 3-dimensional mesoporous solids. A fast release in turn is observed from mesocaged materials AMS-9 and AMS-8 where the presence of structural defects is thought to lead to a slightly lower diffusion coefficient in the latter. Amount of pore wall functionalisation and number of binding sites on the model drug are found to have little effect on the drug release rate.

National Category
Nano Technology
Research subject
Engineering Science with specialization in Nanotechnology and Functional Materials
Identifiers
urn:nbn:se:uu:diva-17498 (URN)10.2174/156720108784911686 (DOI)18673261 (PubMedID)
Available from: 2008-08-07 Created: 2008-08-07 Last updated: 2017-12-08Bibliographically approved
Atluri, R. & Garcia Bennett, A. (2007). Synthesis and Structural control of novel mesoporous material AMS-6. In: : . Paper presented at 30th Annual Meeting British Zeolite Association, York, United Kingdom.
Open this publication in new window or tab >>Synthesis and Structural control of novel mesoporous material AMS-6
2007 (English)Conference paper, Published paper (Refereed)
Abstract [en]

An in-depth study of the synthesis and growth of bicontinuous cubic mesoporous AMS-6 material in the presence of polymeric dispersant P123 is presented, resulting in controlled particle shape attainable over a small range of synthesis conditions. Unlike previous syntheses a remarkable effect on facet formation of the Iad silica particles with cubic morphologies is observed. Trapezoidal icositetrahedra, spherical and elongated morphologies have been prepared with increased faceting on addition of higher concentration of dispersant. Particles are characterised extensively by powder X-ray diffraction, transmission electron microscopy, scanning electron microscopy and nitrogen sorption isotherms. Mesoporous materials produced in this study show textural features suggesting a secondary porous network formed on the external surface of the particle and the origin of this secondary porosity is discussed. Based on the reduced dynamics generated by the presence of the P123 dispersant, we suggest possible growth models for the formation of mainly two different morphologies—the thermodynamically favoured trapezoidal icositetrahedron and elongated particles, the latter not following the expected point group symmetry, mm.

National Category
Engineering and Technology
Research subject
Engineering Science with specialization in Nanotechnology and Functional Materials
Identifiers
urn:nbn:se:uu:diva-11998 (URN)
Conference
30th Annual Meeting British Zeolite Association, York, United Kingdom
Available from: 2008-01-29 Created: 2009-02-26 Last updated: 2016-04-08Bibliographically approved
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