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Carbon dots modified/prepared by supramolecular host molecules and their potential applications: A review. Anal Chim Acta 2022; 1232:340475. [DOI: 10.1016/j.aca.2022.340475] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2022] [Revised: 09/28/2022] [Accepted: 09/29/2022] [Indexed: 11/18/2022]
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2
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In-Depth Structural and Optical Analysis of Ce-modified ZnO Nanopowders with Enhanced Photocatalytic Activity Prepared by Microwave-Assisted Hydrothermal Method. Catalysts 2020. [DOI: 10.3390/catal10050551] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022] Open
Abstract
Pure and Ce-modified ZnO nanosheet-like polycrystalline samples were successfully synthesized by a simple and fast microwave-based process and tested as photocatalytic materials in environmental remediation processes. In an attempt to clarify the actual relationships between functionality and atomic scale structure, an in-depth characterization study of these materials using a battery of complementary techniques was performed. X-ray diffraction (XRD), field emission-scanning electron microscopy (FE-SEM), high-resolution transmission electron microscopy (HRTEM), high-angle annular dark field-scanning transmission electron microscopy (HAADF-STEM), energy-dispersive X-Ray spectroscopy-scanning transmission electron microscopy (STEM-XEDS), photoluminescence spectroscopy (PL) and UV–Visible absorption spectroscopy were used to evaluate the effect of Ce ions on the structural, morphological, optical and photocatalytic properties of the prepared ZnO nanostructures. The XRD results showed that the obtained photocatalysts were composed of hexagonal, wurtzite type crystallites in the 34–44 nm size range. The SEM and TEM showed nanosheet-shaped crystallites, a significant fraction of them in contact with bundles of randomly oriented and much smaller nanoparticles of a mixed cerium–zinc phase with a composition close to Ce0.68Zn0.32Ox. Importantly, in clear contrast to the prevailing proposals regarding this type of materials, the STEM-XEDS characterization of the photocatalyst samples revealed that Ce did not incorporate into the ZnO crystal lattice as a dopant but that a heterojunction formed between the ZnO nanosheets and the Ce–Zn mixed oxide phase nanoparticles instead. These two relevant compositional features could in fact be established thanks to the particular morphology obtained by the use of the microwave-assisted hydrothermal synthesis. The optical study revealed that in the ZnO:Ce samples optical band gap was found to decrease to 3.17 eV in the samples with the highest Ce content. It was also found that the ZnO:Ce (2 at.%) sample exhibited the highest photocatalytic activity for the degradation of methylene blue (MB), when compared to both the pure ZnO and commercial TiO2-P25 under simulated sunlight irradiation. The kinetics of MB photodegradation in the presence of the different photocatalysts could be properly described using a Langmuir–Hinshelwood (LH) model, for which the ZnO:Ce (2 at.%) sample exhibited the highest value of effective kinetic constant.
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Flow Chemistry in Contemporary Chemical Sciences: A Real Variety of Its Applications. Molecules 2020; 25:molecules25061434. [PMID: 32245225 PMCID: PMC7146634 DOI: 10.3390/molecules25061434] [Citation(s) in RCA: 33] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/17/2020] [Revised: 03/14/2020] [Accepted: 03/16/2020] [Indexed: 12/15/2022] Open
Abstract
Flow chemistry is an area of contemporary chemistry exploiting the hydrodynamic conditions of flowing liquids to provide particular environments for chemical reactions. These particular conditions of enhanced and strictly regulated transport of reagents, improved interface contacts, intensification of heat transfer, and safe operation with hazardous chemicals can be utilized in chemical synthesis, both for mechanization and automation of analytical procedures, and for the investigation of the kinetics of ultrafast reactions. Such methods are developed for more than half a century. In the field of chemical synthesis, they are used mostly in pharmaceutical chemistry for efficient syntheses of small amounts of active substances. In analytical chemistry, flow measuring systems are designed for environmental applications and industrial monitoring, as well as medical and pharmaceutical analysis, providing essential enhancement of the yield of analyses and precision of analytical determinations. The main concept of this review is to show the overlapping of development trends in the design of instrumentation and various ways of the utilization of specificity of chemical operations under flow conditions, especially for synthetic and analytical purposes, with a simultaneous presentation of the still rather limited correspondence between these two main areas of flow chemistry.
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Rehman S, Kim H, Farooq Khan M, Hur JH, Lee AD, Kim DK. Tuning of ionic mobility to improve the resistive switching behavior of Zn-doped CeO 2. Sci Rep 2019; 9:19387. [PMID: 31852939 PMCID: PMC6920484 DOI: 10.1038/s41598-019-55716-4] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/25/2019] [Accepted: 12/02/2019] [Indexed: 11/08/2022] Open
Abstract
Correlation between the resistive switching characteristics of Au/Zn-doped CeO2/Au devices and ionic mobility of CeO2 altered by the dopant concentration were explored. It was found that the ionic mobility of CeO2 has a profound effect on the operating voltages of the devices. The magnitude of operating voltage was observed to decrease when the doping concentration of Zn was increased up to 14%. After further increasing the doping level to 24%, the device hardly exhibits any resistive switching. At a low doping concentration, only isolated Vo existed in the CeO2 lattice. At an intermediate doping concentration, the association between dopant and Vo formed (Zn, Vo)× defect clusters. Low number density of these defect clusters initially favored the formation of Vo filament and led to a reduction in operating voltage. As the size and number density of (Zn, Vo)× defect clusters increased at a higher doping concentration, the ionic conductivity was limited with the trapping of isolated Vo by these defect clusters, which resulted in the diminishing of resistive switching. This research work provides a strategy for tuning the mobility of Vo to modulate resistive switching characteristics for non-volatile memory applications.
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Affiliation(s)
- Shania Rehman
- Department of Electrical Engineering, Sejong University, Seoul, 05006, Republic of Korea
| | - Honggyun Kim
- Department of Electrical Engineering, Sejong University, Seoul, 05006, Republic of Korea
| | - Muhammad Farooq Khan
- Department of Electrical Engineering, Sejong University, Seoul, 05006, Republic of Korea
| | - Ji-Hyun Hur
- Department of Electrical Engineering, Sejong University, Seoul, 05006, Republic of Korea
| | - Anthony D Lee
- Department of Mechanical Engineering Technology, Farmingdale State College, Farmingdale, New York, 11735, USA
| | - Deok-Kee Kim
- Department of Electrical Engineering, Sejong University, Seoul, 05006, Republic of Korea.
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Kellici S, Acord J, Moore KE, Power NP, Middelkoop V, Morgan DJ, Heil T, Coppo P, Baragau IA, Raston CL. Continuous hydrothermal flow synthesis of graphene quantum dots. REACT CHEM ENG 2018. [DOI: 10.1039/c8re00158h] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
A rapid, continuous hydrothermal flow synthesis route and life cycle assessment was employed for the synthesis of graphene quantum dots in the presence of calixarene.
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Affiliation(s)
- Suela Kellici
- School of Engineering
- Advanced Materials Research Centre
- London South Bank University
- London
- UK
| | - John Acord
- School of Applied Sciences
- London South Bank University
- London
- UK
| | - Katherine E. Moore
- Flinders Institute for NanoScale Science and Technology
- College of Science and Engineering
- Flinders University
- Adelaide
- Australia
| | - Nicholas P. Power
- School of Life Health & Chemical Sciences
- Open University
- Milton Keynes
- UK
| | - Vesna Middelkoop
- Flemish Institute for Technological Research – VITO
- B-2400 Mol
- Belgium
| | - David J. Morgan
- Cardiff Catalysis Institute
- School of Chemistry
- Cardiff University
- Cardiff
- UK
| | - Tobias Heil
- Department of Colloid Chemistry
- Max Planck Institute of Colloids and Interfaces
- 14424 Potsdam
- Germany
| | - Paolo Coppo
- Department of Chemistry
- University of Warwick
- Coventry
- UK
| | - Ioan-Alexandru Baragau
- School of Engineering
- Advanced Materials Research Centre
- London South Bank University
- London
- UK
| | - Colin L. Raston
- Flinders Institute for NanoScale Science and Technology
- College of Science and Engineering
- Flinders University
- Adelaide
- Australia
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Darr JA, Zhang J, Makwana NM, Weng X. Continuous Hydrothermal Synthesis of Inorganic Nanoparticles: Applications and Future Directions. Chem Rev 2017; 117:11125-11238. [PMID: 28771006 DOI: 10.1021/acs.chemrev.6b00417] [Citation(s) in RCA: 291] [Impact Index Per Article: 41.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Nanomaterials are at the leading edge of the emerging field of nanotechnology. Their unique and tunable size-dependent properties (in the range 1-100 nm) make these materials indispensable in many modern technological applications. In this Review, we summarize the state-of-art in the manufacture and applications of inorganic nanoparticles made using continuous hydrothermal flow synthesis (CHFS) processes. First, we introduce ideal requirements of any flow process for nanoceramics production, outline different approaches to CHFS, and introduce the pertinent properties of supercritical water and issues around mixing in flow, to generate nanoparticles. This Review then gives comprehensive coverage of the current application space for CHFS-made nanomaterials including optical, healthcare, electronics (including sensors, information, and communication technologies), catalysis, devices (including energy harvesting/conversion/fuels), and energy storage applications. Thereafter, topics of precursor chemistry and products, as well as materials or structures, are discussed (surface-functionalized hybrids, nanocomposites, nanograined coatings and monoliths, and metal-organic frameworks). Later, this Review focuses on some of the key apparatus innovations in the field, such as in situ flow/rapid heating systems (to investigate kinetics and mechanisms), approaches to high throughput flow syntheses (for nanomaterials discovery), as well as recent developments in scale-up of hydrothermal flow processes. Finally, this Review covers environmental considerations, future directions and capabilities, along with the conclusions and outlook.
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Affiliation(s)
- Jawwad A Darr
- Department of Chemistry, University College London, Christopher Ingold Laboratories , 20 Gordon Street, London WC1H 0AJ, United Kingdom
| | - Jingyi Zhang
- Department of Environmental & Resource Sciences, Zhejiang University , 866 Yuhangtang Road, Hangzhou, Zhejiang 310058, People's Republic of China
| | - Neel M Makwana
- Department of Chemistry, University College London, Christopher Ingold Laboratories , 20 Gordon Street, London WC1H 0AJ, United Kingdom
| | - Xiaole Weng
- Department of Environmental & Resource Sciences, Zhejiang University , 866 Yuhangtang Road, Hangzhou, Zhejiang 310058, People's Republic of China
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Kellici S, Acord J, Power NP, Morgan DJ, Coppo P, Heil T, Saha B. Rapid synthesis of graphene quantum dots using a continuous hydrothermal flow synthesis approach. RSC Adv 2017. [DOI: 10.1039/c7ra00127d] [Citation(s) in RCA: 40] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
A rapid and environmentally benign synthesis of green fluorescent graphene quantum dots (GQD) with low cytotoxicity via Continuous Hydrothermal Flow Synthesis (CHFS) aided by calix[4]arene tetrasulfonic acid (SCX4) as a particle size limiting agent.
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Affiliation(s)
- Suela Kellici
- School of Engineering
- London South Bank University
- London
- UK
| | - John Acord
- School of Applied Sciences
- London South Bank University
- London
- UK
| | - Nicholas P. Power
- School of Life Health & Chemical Sciences
- Open University
- Milton Keynes
- UK
| | - David J. Morgan
- Cardiff Catalysis Institute
- School of Chemistry
- Cardiff University
- Cardiff
- UK
| | - Paolo Coppo
- Centre for Phosphors and Display Materials
- The Wolfson Centre
- Brunel University
- Uxbridge
- UK
| | - Tobias Heil
- Nanoinvestigation Centre at Liverpool
- Liverpool University
- Liverpool
- UK
| | - Basudeb Saha
- School of Engineering
- London South Bank University
- London
- UK
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Loveridge MJ, Lain MJ, Johnson ID, Roberts A, Beattie SD, Dashwood R, Darr JA, Bhagat R. Towards High Capacity Li-ion Batteries Based on Silicon-Graphene Composite Anodes and Sub-micron V-doped LiFePO 4 Cathodes. Sci Rep 2016; 6:37787. [PMID: 27898104 PMCID: PMC5127186 DOI: 10.1038/srep37787] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/16/2016] [Accepted: 11/02/2016] [Indexed: 11/13/2022] Open
Abstract
Lithium iron phosphate, LiFePO4 (LFP) has demonstrated promising performance as a cathode material in lithium ion batteries (LIBs), by overcoming the rate performance issues from limited electronic conductivity. Nano-sized vanadium-doped LFP (V-LFP) was synthesized using a continuous hydrothermal process using supercritical water as a reagent. The atomic % of dopant determined the particle shape. 5 at. % gave mixed plate and rod-like morphology, showing optimal electrochemical performance and good rate properties vs. Li. Specific capacities of >160 mAh g−1 were achieved. In order to increase the capacity of a full cell, V-LFP was cycled against an inexpensive micron-sized metallurgical grade Si-containing anode. This electrode was capable of reversible capacities of approximately 2000 mAh g−1 for over 150 cycles vs. Li, with improved performance resulting from the incorporation of few layer graphene (FLG) to enhance conductivity, tensile behaviour and thus, the composite stability. The cathode material synthesis and electrode formulation are scalable, inexpensive and are suitable for the fabrication of larger format cells suited to grid and transport applications.
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Affiliation(s)
| | - M J Lain
- Warwick University, Coventry, CV4 7AL, UK
| | | | - A Roberts
- Warwick University, Coventry, CV4 7AL, UK
| | | | - R Dashwood
- Coventry University, Coventry, CV1 5FB, UK
| | - J A Darr
- University College, London, WC1E 6BT, UK
| | - R Bhagat
- Warwick University, Coventry, CV4 7AL, UK
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Johnson ID, Loveridge M, Bhagat R, Darr JA. Mapping Structure-Composition-Property Relationships in V- and Fe-Doped LiMnPO 4 Cathodes for Lithium-Ion Batteries. ACS COMBINATORIAL SCIENCE 2016; 18:665-672. [PMID: 27631430 DOI: 10.1021/acscombsci.6b00035] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
A series of LiMn1-x-yFexVyPO4 (LMFVP) nanomaterials have been synthesized using a pilot-scale continuous hydrothermal synthesis process (CHFS) and evaluated as high voltage cathodes in Li-ion batteries at a production rate of 0.25 kg h-1. The rapid synthesis and screening approach has allowed the specific capacity of the high Mn content olivines to be optimized, particularly at high discharge rates. Consistent and gradual changes in the structure and performance are observed across the compositional region under investigation; the doping of Fe at 20 at% (with respect to Mn) into lithium manganese phosphate, rather than V or indeed codoping of Fe and V, gives the best balance of high capacity and high rate performance.
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Affiliation(s)
- Ian D. Johnson
- Department
of Chemistry, University College London, 20 Gordon Street, London WC1H 0AJ, U.K
| | | | | | - Jawwad A. Darr
- Department
of Chemistry, University College London, 20 Gordon Street, London WC1H 0AJ, U.K
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11
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Goodall JBM, Kellici S, Illsley D, Lines R, Knowles JC, Darr JA. Optical and photocatalytic behaviours of nanoparticles in the Ti–Zn–O binary system. RSC Adv 2014. [DOI: 10.1039/c3ra48030e] [Citation(s) in RCA: 42] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
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13
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Middelkoop V, Tighe CJ, Kellici S, Gruar RI, Perkins JM, Jacques SD, Barnes P, Darr JA. Imaging the continuous hydrothermal flow synthesis of nanoparticulate CeO2 at different supercritical water temperatures using in situ angle-dispersive diffraction. J Supercrit Fluids 2014. [DOI: 10.1016/j.supflu.2013.12.022] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
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14
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Kellici S, Acord J, Ball J, Reehal HS, Morgan D, Saha B. A single rapid route for the synthesis of reduced graphene oxide with antibacterial activities. RSC Adv 2014. [DOI: 10.1039/c3ra47573e] [Citation(s) in RCA: 83] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
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15
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Tighe CJ, Cabrera RQ, Gruar RI, Darr JA. Scale Up Production of Nanoparticles: Continuous Supercritical Water Synthesis of Ce–Zn Oxides. Ind Eng Chem Res 2013. [DOI: 10.1021/ie3025642] [Citation(s) in RCA: 76] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Christopher J. Tighe
- Christopher-Ingold
Laboratories, Department of Chemistry, University College London, 20 Gordon Street, London WC1H 0AJ, United Kingdom
| | - Raul Quesada Cabrera
- Christopher-Ingold
Laboratories, Department of Chemistry, University College London, 20 Gordon Street, London WC1H 0AJ, United Kingdom
| | - Robert I. Gruar
- Christopher-Ingold
Laboratories, Department of Chemistry, University College London, 20 Gordon Street, London WC1H 0AJ, United Kingdom
| | - Jawwad A. Darr
- Christopher-Ingold
Laboratories, Department of Chemistry, University College London, 20 Gordon Street, London WC1H 0AJ, United Kingdom
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Chaudhry AA, Knowles JC, Rehman I, Darr JA. Rapid hydrothermal flow synthesis and characterisation of carbonate- and silicate-substituted calcium phosphates. J Biomater Appl 2012; 28:448-61. [PMID: 22983020 PMCID: PMC4112750 DOI: 10.1177/0885328212460289] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
A range of crystalline and nano-sized carbonate- and silicate-substituted hydroxyapatite has been successfully produced by using continuous hydrothermal flow synthesis technology. Ion-substituted calcium phosphates are better candidates for bone replacement applications (due to improved bioactivity) as compared to phase-pure hydroxyapatite. Urea was used as a carbonate source for synthesising phase pure carbonated hydroxyapatite (CO₃-HA) with ≈5 wt% substituted carbonate content (sample 7.5CO₃-HA) and it was found that a further increase in urea concentration in solution resulted in biphasic mixtures of carbonate-substituted hydroxyapatite and calcium carbonate. Transmission electron microscopy images revealed that the particle size of hydroxyapatite decreased with increasing urea concentration. Energy-dispersive X-ray spectroscopy result revealed a calcium deficient apatite with Ca:P molar ratio of 1.45 (±0.04) in sample 7.5CO₃-HA. For silicate-substituted hydroxyapatite (SiO₄-HA) silicon acetate was used as a silicate ion source. It was observed that a substitution threshold of ∼1.1 wt% exists for synthesis of SiO₄-HA in the continuous hydrothermal flow synthesis system, which could be due to the decreasing yields with progressive increase in silicon acetate concentration. All the as-precipitated powders (without any additional heat treatments) were analysed using techniques including Transmission electron microscopy, X-ray powder diffraction, Differential scanning calorimetry, Thermogravimetric analysis, Raman spectroscopy and Fourier transform infrared spectroscopy.
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Affiliation(s)
- Aqif A Chaudhry
- Clean Materials Technology Group, Department of Chemistry, University College London, Christopher Ingold Laboratories, London, UK.
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Tighe CJ, Gruar RI, Ma CY, Mahmud T, Wang XZ, Darr JA. Investigation of counter-current mixing in a continuous hydrothermal flow reactor. J Supercrit Fluids 2012. [DOI: 10.1016/j.supflu.2011.11.027] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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Kafizas A, Parkin IP. Inorganic thin-film combinatorial studies for rapidly optimising functional properties. Chem Soc Rev 2012; 41:738-81. [DOI: 10.1039/c1cs15178a] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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Warule SS, Chaudhari NS, Kale BB, Patil KR, Koinkar PM, More MA, Murakami RI. Organization of cubic CeO2 nanoparticles on the edges of self assembled tapered ZnO nanorods via a template free one-pot synthesis: significant cathodoluminescence and field emission properties. ACTA ACUST UNITED AC 2012. [DOI: 10.1039/c2jm30226h] [Citation(s) in RCA: 62] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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Chen M, Ma CY, Mahmud T, Darr JA, Wang XZ. Modelling and simulation of continuous hydrothermal flow synthesis process for nano-materials manufacture. J Supercrit Fluids 2011. [DOI: 10.1016/j.supflu.2011.07.002] [Citation(s) in RCA: 41] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/17/2022]
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21
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Weng X, Knowles JC, Abrahams I, Wu Z, Darr JA. In situ variable temperature X-ray diffraction studies on the transformations of nano-precursors to La–Ni–O phases. J SOLID STATE CHEM 2011. [DOI: 10.1016/j.jssc.2011.04.031] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
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Chaudhry AA, Yan H, Gong K, Inam F, Viola G, Reece MJ, Goodall JB, ur Rehman I, McNeil-Watson FK, Corbett JC, Knowles JC, Darr JA. High-strength nanograined and translucent hydroxyapatite monoliths via continuous hydrothermal synthesis and optimized spark plasma sintering. Acta Biomater 2011; 7:791-9. [PMID: 20883835 DOI: 10.1016/j.actbio.2010.09.029] [Citation(s) in RCA: 47] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/20/2010] [Revised: 09/08/2010] [Accepted: 09/10/2010] [Indexed: 11/25/2022]
Abstract
The synthesis of high-strength, completely dense nanograined hydroxyapatite (bioceramic) monoliths is a challenge as high temperatures or long sintering times are often required. In this study, nanorods of hydroxyapatite (HA) and calcium-deficient HA (made using a novel continuous hydrothermal flow synthesis method) were consolidated using spark plasma sintering (SPS) up to full theoretical density in ∼5 min at temperatures up to 1000°C. After significant optimization of the SPS heating and loading cycles, fully dense HA discs were obtained which were translucent, suggesting very high densities. Significantly high three-point flexural strength values for such materials (up to 158 MPa) were measured. Freeze-fracturing of disks followed by scanning electron microscopy investigation revealed selected samples possessed sub-200 nm sized grains and no visible pores, suggesting they were fully dense.
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