THE CLEAN MATERIALS TECHNOLOGY GROUP
UCL CHEMISTRY DEPARTMENT

       
Research

Below is a list of current research undertaken within the CMTG.

Click on a research topic for more information, including links to relevent publications.

Continuous Hydrothermal Flow Synthesis Technology

Nanochemistry concerns the syntheses of sub-100 nm diameter particles with different sizes, shapes, compositions, surface structures, and functionalities with applications such as components of solar cells, high efficiency fuel cell materials, active gas sensors, and fine chemical catalysts.  Nanomaterials can generally be synthesized by either topdown (e.g., communition) or bottom-up (molecules to nanoparticles) approaches. Many nanomaterials syntheses are time and energy consuming and give inconsistent results with batch to batch variations. Faster and more consistent nanomaterials synthesis and processing methods are highly desirable.

Clean Materials Technology Group at UCL is developing nanomaterials using an environmentally friendly process. The CHFS (continuous hydrothermal flow synthesis) process utilises rapidly mixes supercritical water (e.g. 450 ºC, 24 MPa) with cold aqueous solutions of metal salts. This results in a supersaturated solution from which particles rapidly crystallise and react. The mixing process by which the nanoparticles are produced is a patented confined jet mixer* which allows the reactor to produce a narrow size distribution and to allow running without blockages.  Furthermore, other chemical reagents may be added to the metal salt to control the size, shape, aspect ratio and functional properties of nanoparticles produced. Finally, products are rapidly quenched, yielding aqueous slurry at ambient conditions.

*pending

Selected Publications
1.
Cabanas, A; Darr, JA; Lester, E; Poliakoff, M. 2000. A continuous and clean one-step synthesis of nano-particulate Ce1-xZrxO2 solid solutions in near-critical water. CHEMICAL COMMUNICATIONS (11):901-902 doi: 10.1039/B001424I
2.
Boldrin, P; Hebb, AK; Chaudhry, AA; Otley, L; Thiebaut, B; Bishop, P; Darr, JA. 2007. Direct synthesis of nanosized NiCo2O4 spinel and related compounds via continuous hydrothermal synthesis methods. INDUSTRIAL & ENGINEERING CHEMISTRY RESEARCH 46 (14):4830-4838 doi: 10.1021/ie061396b
3.
Instant nano-hydroxyapatite: a continuous and rapid hydrothermal synthesis, Chaudhry AA, Haque S, Kellici S, Boldrin P, Rehman I, Fazal AK, Darr JA 2006, CHEMICAL COMMUNICATIONS  21; 2286-2288 doi: 10.1039/B518102J  
4.
Zhang, ZC; Brown, S; Goodall, JBM; Weng, XL; Thompson, K; Gong, KN; Kellici, S; Clark, RJH; Evans, JRG; Darr, JA. 2009. Direct continuous hydrothermal synthesis of high surface area nanosized titania. JOURNAL OF ALLOYS AND COMPOUNDS 476 (1-2):451-456 doi: 10.1016/j.jallcom.2008.09.036
High Throughput Nanomaterials Synthesis and Analysis

Combinatorial techniques are used where predictive theory is weak, and they allow a large number of samples to be prepared and characterized rapidly, some of the earliest efforts being made in the fields of organic chemistry, drug design, and biotechnology. The arena of combinatorial materials development is rather less developed and includes the fabrication of addressable solid state materials libraries via thin film deposition and physical masking techniques. Many have attempted to develop a fully automated combinatorial platforms which often rely on top-down approaches. Such methods usually start with metal oxide precursors, and involve metering, mixing, and firing of such mixtures possibly with a printing step. This is often followed by automated analyses of libraries using techniques such as automated powder X-ray diffraction (XRD). 

One of the limitations of starting with micron sized metal oxide powders for heterometallic solid state chemistry is that atom diffusion may be insufficient to achieve equilibrium phase composition (hence, intermittent calcining and grinding steps are often used which are difficult to automate). This limitation can often be overcome by use of a bottom-up strategy.

Our research group has developed a way to rapidly make nanoceramics manually known as high throughput continuous hydrothermal (HiTCH) flow synthesis. 

HiTCH produces many nanoceramic samples sequentially in a few hours. Despite being a manual apparatus, the HiTCH flow synthesis reactor has been used to make a 66-sample nanoparticle library (ternary phase diagram) of nanocrystalline  CexZryYzO2-δ in less than 12 h (see phase diagram on right which shows structural information and properties)  In 2009 our completed automation of the entire HiTCH flow synthesis process from individual metal salt (precursor) mixing to nanoparticle synthesis, collection and automation of cleanup and printing.  This is known as the rapid automated materials synthesis instrument (RAMSI) that is shown on top right image..

 
Selected Publications
1.
Weng, XL; Cockcroft, JK; Hyett, G; Vickers, M; Boldrin, P; Tang, CC; Thompson, SP; Parker, JE; Knowles, JC; Rehman, I; Parkin, I; Evans, JRG; Darr, JA. 2009. High-Throughput Continuous Hydrothermal Synthesis of an Entire Nanoceramic Phase Diagram. JOURNAL OF COMBINATORIAL CHEMISTRY 11 (5):829-834. doi: 10.1021/cc900041a
2.
The Rapid Automated Materials Synthesis Instrument (RAMSI): Exploring the Composition and Heat-treatment of Nano-precursors Towards Low Temperature  Red Phosphors, Lin, T; Kellici, S; Gong, K; Thompson, K; Evans, JRG; Wang, X; Darr, JA. 2010. JOURNAL OF COMBINATORIAL CHEMISTRY, 12 (3): 383–392. doi: 10.1021/cc9001108
3.
High Throughput Continuous Hydrothermal (HiTCH) Flow Synthesis of Zn-Ce Oxides; Unprecedented Solubility of Zn in the Nanoparticle Fluorite lattice.  Suela Kellici, Kenan Gong, Tian Lin, Sonal Brown, Robin J. H. Clark, Martin Vickers, Jeremy K. Cockcroft, Vesna Middelkoop, Paul Barnes, James M Perkins  Chris Tighe, and Jawwad A. Darr Royal Society Philosophical Transactions A. in press 2010 doi: 10.1098/rsta.2010.0135
4.
Wang, XZ; Perston, B; Yang, Y; Lin, T; Darr, JA. 2009. Robust QSAR model development in high-throughput catalyst discovery based on genetic parameter optimisation. CHEMICAL ENGINEERING RESEARCH & DESIGN 87 (10A):1420-1429
doi: 10.1016/j.cherd.2009.01.013
Continuous Hydrothermal Flow Synthesis Pilot Plant Scale-Up

A pilot plant CHFS reactor has been developed to investigate scale-up (200 times over current lab-scale process).  We have made on scale of 1 Kg per hour.   The plant uses our patented confined jet mixer for making nanoceramics without blocking.


*patent filed (ref GB1008721.1)

Summary
•      Customised syntheses of nanomaterials to your needs
•      Up to multi-Kg a day available (pilot plant)
•      Nanomaterials development and optimisation
•      Materials provided in an aqueous dispersed form
•      Full materials characterisation available
 
Applications
•      Photocatalysts, Dye sensitised solar cells
•      Security inks (e.g. nanomagnetics)
•      Flexible printed electronics (M, MOx)
•      Colorants and UV attenuators
•      Devices (SOFC cathode and anodes)
•      Fine chemical catalysts
•      Batteries and supercapacitors
•      Nano-additives for polymers
•      Nanoparticle therapeutics, Biolabels such as Q-dots

Selected Publications
1.
2.
3.
Photocatalysts and Water Splitting Devices

CMTG is developing water splitting devices to produce renewable hydrogen and oxygen fuels from water. We are also developing better photocatalysts for a range of solar energy and environmental applciations.

The conversion of solar to electrical energy using photovoltaic devices such as the silicon solar cell or dye-sensitised solar cells is well-established. However, electrical energy is not easily stored in large amounts and solar energy is diurnal, intermittent and least available when we most need it (i.e. at night in winter). As a consequence, there is a real need for an efficient (> 10%), inexpensive (< £5 m2) solar energy conversion device that generates a readily utilised chemical fuel , i.e. hydrogen, that can be readily transported at minimal energy cost and used when needed.

One approach is to use a photovoltaic device in conjunction with a water electrolysis cell. Such an approach has attracted considerable attention in recent years with many reports appearing on ‘hybrid photoelectrodes’ and ‘tandem’ cells. The advantage of a solar-driven, water-splitting system is that it converts the sun’s energy into a chemical form, bypassing the need to convert photovoltaic energy into chemical energy by running an electrolytic cell.

In 1977, Nozik demonstrated that a single wafer crystal of cadmium sulphide with a thin foil of Pt stuck onto one face was able to photosensitise the photoreduction of water by sulfide ions, with hydrogen evolution occurring on the Pt face of the wafer. 

Our group has been working with industrial consortia to develop more stable water splitting devices and investigate new photocatalytic nanomaterials and their coatings.  Recent work in this area has been involved in scale up of nanomaterials in order to assess the commercial potential of CHFS (see below for information regarding pilot plant scale-up).

EPSRC funding references

EP/F056168/1; "Nanocrystalline Photodiodes: Novel Devices for Water Splitting"

 

Top: PC50 ceramic wafer under 75 Xe lamp irradiation showing hydrogen gas production. (L) View directed towards back (Pt) face.  middle: sacrificial tests used to screen photoactive nanomaterials; Bottom ca. 10 nm titania particles made on the pilot plant.
Selected Publications
1.
Photocatalytic evolution of hydrogen and oxygen from ceramic wafers of commercial titanias Elouali S, Mills A,  Parkin IP, Bailey E, McMillan PF and Darr JA 2010 JOURNAL OF PHOTOCHEMISTRY & PHOTOBIOLOGY A: CHEMISTRY 216 Pages 110-114 doi: 10.1016/j.jphotochem.2010.07.033
2.
Thompson, K; Goodall, J; Kellici, S; Mattinson, JA; Egerton, TA; Rehman, I; Darr, JA. 2009. Screening tests for the evaluation of nanoparticle titania photocatalysts. JOURNAL OF CHEMICAL TECHNOLOGY AND BIOTECHNOLOGY 84 (11):1717-1725
doi: 10.1002/jctb.2237
3.
Zhang, Z; Goodall, JBM; Brown, S; Karlsson, L; Clark, RJH; Hutchison, JL; Rehman, IU; Darr, JA. 2010. Continuous hydrothermal synthesis of extensive 2D sodium titanate (Na2Ti3O7) nano-sheets. DALTON TRANSACTIONS 39 (3):711-714
doi: 10.1039/B915699B
4.
Zhang, ZC; Brown, S; Goodall, JBM; Weng, XL; Thompson, K; Gong, KN; Kellici, S; Clark, RJH; Evans, JRG; Darr, JA. 2009. Direct continuous hydrothermal synthesis of high surface area nanosized titania. JOURNAL OF ALLOYS AND COMPOUNDS 476 (1-2):451-456 doi: 10.1016/j.jallcom.2008.09.036
5.
Zhang, Z; Goodall, JBM; Morgan, DJ; Brown, S; Clark, RJH; Knowles, JC; Mordan, NJ; Evans, JRG; Carley, AF; Bowker, M; Darr, JA. 2009. Photocatalytic activities of N-doped nano-titanias and titanium nitride. JOURNAL OF THE EUROPEAN CERAMIC SOCIETY 29 (11):2343-2353 doi: 10.1016/j.jeurceramsoc.2009.02.008
Nanocatalysts and Catalyst Supports

CMTG has developed a range of catalytic nanomaterials in collaboration with industry and academia.

Catalysis is the change in rate of a chemical reaction due to the participation of a substance called a catalyst. Unlike other reagents that participate in the chemical reaction, a catalyst is not consumed by the reaction itself.

Much of our work has been in the use of nanocerias and doped analogues which are of interst as automotive and clean air catalysts. The use of nanomaterials offers high reactivity due to a large surface area to volume ratio. See ceria nanoparticles on the right.

In related research we have also developed catalysts which are inactive but show superior performance for UV protection and other applications. many of these catalytic materials can now be made on our pilot plant which can produce several Kg a day by dry mass. Nanoceramics are supplied as water based slurries which can readily be further treated before use.

   
Selected Publications
1.
Cabanas, A; Darr, JA; Lester, E; Poliakoff, M. 2000. A continuous and clean one-step synthesis of nano-particulate Ce1-xZrxO2 solid solutions in near-critical water. CHEMICAL COMMUNICATIONS (11):901-902 doi: 10.1002/chin.200035016
2.
Cabanas, A; Darr, JA; Lester, E; Poliakoff, M. 2001. Continuous hydrothermal synthesis of inorganic materials in a near-critical water flow reactor; the one-step synthesis of nano-particulate Ce1-xZrxO2 (x=0-1) solid solutions. JOURNAL OF MATERIALS CHEMISTRY 11 (2):561-568 doi: 10.1039/B008095K
3.
Weng, XL; Perston, B; Wang, XZ; Abrahams, I; Lin, T; Yang, SF; Evans, JRG; Morgan, DJ; Carley, AF; Bowker, M; Knowles, JC; Rehman, I; Darr, JA. 2009. Synthesis and characterization of doped nano-sized ceria-zirconia solid solutions. APPLIED CATALYSIS B-ENVIRONMENTAL 90 (3-4):405-415 doi: 10.1016/j.apcatb.2009.03.031
4.
Tunable and Rapid Crystalisation of Phase Pure Bi2MoO6 (koechlinite) and Bi2Mo3O12 via Continuous Hydrothermal Synthesis. 2010. Robert Gruar, Chris Tighe, James, Lee Reilly, Lee, Gopinathan Sankar and Jawwad Darr.  Solid State Sciences, Article in Press, Corrected Proof doi: 10.1016/j.solidstatesciences.2010.07.001
5.
Continuous hydrothermal syntheses of highly active composite nanocatalysts Weng XL, Zhang JY, Wu ZB, Liu Y, Wang HQ, Darr JA GREEN CHEM 13(4):850-853 2011 doi: 10.1039/C0GC00631A
The Origins of Life Project

CO2 is One of the major gases responsible for climate change would become an important feedstock for the chemical and pharmaceutical industries. Indeed, CO2 conversion is recognised as one of the major challenges in contemporary chemistry. 

The vision of this project is to employ a robust combination of state-of-the-art computation and experiment in a grand challenge project to design, synthesise, test, characterise, evaluate and produce nano-catalysts for the activation and chemical modification of CO2. The design of many of our nano-catalysts is inspired by the active sites in biological systems, which are tailored to the complex redox processes in the conversion of CO2 to biomass. 

Right: Fe-Ni sulfide cubanes that form the active sites of enzymes

Test Link

Nanobiomedical Materials

The CMTG at UCL has a strong interst in the production and use of nano-hydroxyapatite which is similar to the miner part of bone. Our group published the first ever continuous hydrothermal synthesis of this material (see ref 1 below) which showed that is could be made in seconds and without a heat treatment. This work has also given us insights into particle consolidation and doping which affects applciations of these materials.

Synthetic hydroxyapatite [HA, Ca10(PO4)6(OH)2], is a bioactive material that is chemically similar to biological apatite, the mineral component of bone. Indeed, human bone is a natural composite comprising of nano-apatite rods (<100nm) arranged in lamellae and bound to collagen.  Thus, synthetic HA is of interest as a biocompatible phase/reinforcement in biomedical composites, for filling bulk bone defects and for coatings on metal implants. HA and other calcium phosphates (CAPs) are also of interest as components in injectable bone cements; controlling particle properties (e.g. size and shape) is often used to modulate cement setting behaviour.

Hydroxyapatite powders and coatings can be synthesized using a number of methods including sol-gel processing, co-precipitation, emulsion techniques, batch hydrothermal processes, mechano-chemical methods and chemical vapour deposition.  Wet chemical syntheses require a maturation step (>18 hours), followed by a heat treatment of 650 ºC.  Failure to allow sufficient maturation gives a phase separated product, which can adversely affect biological properties in vivo.  Continuous hydrothermal flow synthesis route was pioneered by our group for the production of “instant” crystalline nano-particle hydroxyapatite. This effectively reduced the time required for maturation of the reagents from over 18 hours to less than a few seconds, and avoided the need for a further “crystallisation” heat treatment step.  Such nano-bioceramics can be sintered to extremely high densities or used as filler materials for biomimetic nanocomposites.

The top-right image is of nano-HA(450). Scale bar = 200 nm. And below it is a translucent sintered HA at full theoretical density.

Selected Publications
1.
Instant nano-hydroxyapatite: a continuous and rapid hydrothermal synthesis, Chaudhry AA, Haque S, Kellici S, Boldrin P, Rehman I, Fazal AK, Darr JA 2006, CHEMICAL COMMUNICATIONS  21; 2286-2288 doi: 10.1039/B518102J  
2.
Chaudhry, AA; Goodall, J; Vickers, M; Cockcroft, JK; Rehman, I; Knowles, JC; Darr, JA. 2008. Synthesis and characterisation of magnesium substituted calcium phosphate bioceramic nanoparticles made via continuous hydrothermal flow synthesis. JOURNAL OF MATERIALS CHEMISTRY 18 (48):5900-5908 doi: 10.1039/B807920J
3.
High-strength nanograined and translucent hydroxyapatite monoliths via continuous hydrothermal synthesis and optimized spark plasma sintering.  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 Acta Biomater 7(2):791-799 doi: 10.1016/j.actbio.2010.09.029
Materials and Nanocomposites for Solid Oxide Fuel Cell Applications

The CMTG has been developing novel materials for solid oxide fuel cells that may one day provide combined heat and power for homes and offices.

A solid oxide fuel cell (SOFC) is an electrochemical conversion device that produces electricity from oxidizing a fuel. The SOFC has a solid oxide or ceramic, electrolyte. Advantages of this class of fuel cells include high efficiency, long-term stability, fuel flexibility, low emissions, and relatively low cost.

Continuous hydrothermal flow synthesis has been used for the synthesis of anode, electrolyte and cathode materials for Solid Oxide Fuel cells.  Ion beam milling tomography on a cermet sample of 24 vol.% Ni loading (made into a disk via spark plasma sintering) suggested that the nickel nanoparticles had formed conducting 3D networks. This assessment was confirmed by electrical conductivity measurements on the Ni/10YSZ samples which showed significantly higher conductivity (∼102 S cm−1) at 24 vol.% Ni, compared to similar vol.% Ni cermets prepared using conventional methods (∼10−1 S cm−1). This fabrication technique has the potential to make nano-structured anode cermets that can be used in the active and current collecting layers of anode supported SOFCs. The significantly improved electrical conductivity at low Ni content means that the layer is likely to be more redox cycle tolerant and have better thermal expansion compatibility with the electrolyte. In the active layer, the stated advantages still hold but there is also the potential for increased TPB density due to the small feature size of the Ni phase.

Our group has also developed a new direct route for the ‘‘bottom up’’ syntheses of phases in the Lan+1NinO3n+1 series (n ¼ 1, 2, 3 and N) via single-step heat treatments of nanosized co-crystallized precursors (cathode materials for SOFC). The co-crystallized precursors were prepared using CHFS.  Overall, a significant reduction in time and number of steps for the syntheses of La3Ni2O7 and La4Ni3O10 has been achieved compared with more conventional synthesis methods, which typically require multiple homogenization and reheating steps over several days.  In more recent work which will shortly be published, this nano-precursor approach can be used to generate hundreds of new doped materials with the 4:3:10-x stiochiometry.

The image shows reconstructed tomography of a ca. 6.2×4.3×1.0 micron slice of the cermet showing, (a) the YSZ phase, (b) the Ni phase and (c) combined phases of a cermet sample nominally containing 24 vol.% Ni. image by Paul Schearing.

Selected Publications
1.

Weng, XL; Boldrin, P; Abrahams, I; Skinner, SJ; Darr, JA. 2007. Direct syntheses of mixed ion and electronic conductors La4Ni3O10 and La3Ni2O7 from nanosized coprecipitates. CHEMISTRY OF MATERIALS 19 (18):4382-4384
doi: 10.1021/cm070134c

2.
Weng, XL; Boldrin, P; Abrahams, I; Skinner, SJ; Kellici, S; Darr, JA. 2008. Direct syntheses of Lan+1NinO3n+1 phases (n = 1, 2, 3 and infinity) from nanosized co-crystallites. JOURNAL OF SOLID STATE CHEMISTRY 181 (5):1123-1132
doi: 10.1016/j.jssc.2008.02.006
3.
Highly Conductive Low Nickel Content Nano-composite Dense Cermets from Nanopowders Made via a Continuous Hydrothermal Synthesis Route. 2010.  Jawwad Darr; Xiaole Weng; Dan Brett; Vladimir Yufit; Paul Shearing; Nigel Brandon; Mike Reece; Haixue Yan, Solid State Ionics (181):827-834 doi: 10.1016/j.ssi.2010.04.014
Beamline Experiments

The CMTG has been able to investigate imaging methods and use robots to collect large numbers of X-ray powder patterns at special facilities in France (Grenoble) and UK (Diamond light Source) called synchrotrons

In collaboration with with Professor Paul Barnes group and Dr Simon Jacques, we investigated the reactions inside a special steel tube in which nanoparticles are continuously forming under very high temperaure and pressure via tomographic imaging methods. In this way we can "see" which regions of the tube they are generated in (see ref 3)

In collaboration with Jeremy Karl Cockcroft, we have also been able to use robots which can help collect X-ray data patterns of tens of samples per hour using a brand new beamline I11 for which we were amongst the first users (see ref 1,2 and all images on right).


See also the video showing the robot arm gripper loading and unloading samples on our commissioning experiments at I13 beamline
http://www.youtube.com/watch?v=V4k6z1T_wFM&feature=related

 

See webpage at diamond on the beamline

http://www.diamond.ac.uk/Home/Beamlines/I11.html

Article on first users (UCL)

http://www.diamond.ac.uk/Home/Media/LatestNews/17July2008.html

 

Selected Publications
1.
Weng, XL; Cockcroft, JK; Hyett, G; Vickers, M; Boldrin, P; Tang, CC; Thompson, SP; Parker, JE; Knowles, JC; Rehman, I; Parkin, I; Evans, JRG; Darr, JA. 2009. High-Throughput Continuous Hydrothermal Synthesis of an Entire Nanoceramic Phase Diagram. JOURNAL OF COMBINATORIAL CHEMISTRY 11 (5):829-834. doi: 10.1021/cc900041a 
2.
High-throughput powder diffraction on beamline I11 at Diamond Parker JE, Thompson SP, Cobb TM, Yuan FJ, Potter J, Lennie AR, Alexander S, Tighe CJ, Darr JA, Cockcroft JC, et al.Tang CC J APPL CRYSTALLOGR 44:102-110.
doi: 10.1107/S0021889810044948
3.
Middelkoop, V; Boldrin, P; Peel, M; Buslaps, T; Barnes, P; Darr, JA; Jacques, SDM. 2009. Imaging the inside of a Continuous Nanoceramic Synthesizer under Supercritical Water Conditions Using High-Energy Synchrotron X-Radiation CHEMISTRY OF MATERIALS 21 (12):2430-2435 doi: 10.1021/cm900118z
Processing in Supercritical CO2

The CMTG has had a longstanding interst in using clean and green solvents for industrial processes and materials manufacture. Most of our current research focusses on the use of water at very high temperature and pressure. However, carbon dioxide under milder conditions is also very much a green solvent of choice in processes from dry cleaning to making aerogels and fully carbonated cements and roofing tiles.

Carbon dioxide is essentially single phase above its critical temperature (Tc = 31.8 °C) and pressure (Pc = 73.8MPa) [20]. Under such conditions, CO2 has properties between those of a liquid and a gas. Supercritical CO2 has been used in a range of materials related applications, particularly in foaming and in emulsion templating.

Shown to the right is a SEM image and MIP data for hydrogels made via reactive emulsion templating (modal pore diameter = 43.4 lm, total pore volume =6.9 cm3 g–1, total porosity = 84%; sample 6: modal pore diameter = 44.3 lm, total pore volume = 9.3 cm3 g–1, total porosity = 90 %).

Much of our research has been involved in the use of carbon dioxide as a solvent for foaming or for impregnating poorly water soluble drugs and improving and regulating their release, or for making nanocomposites.

Selected Publications
1.
Supercritical CO2 assisted synthesis of highly selective nafion-zeolite nanocomposite membranes for direct methanol fuel cells 2007, Gribov EN, Parkhomchuk EV, Krivobokov IM, Darr JA, Okunev AG, JOURNAL OF MEMBRANE SCIENCE 1-4
doi: 10.1016/j.memsci.2007.03.020
2.
Supercritical carbon dioxide in water" emulsion-templated synthesis of porous calcium alginate hydrogels, Partap S, Rehman I, Jones JR, Darr JA 2006 ADVANCED MATERIALS  18   501.doi: 10.1002/adma.200501423  
3.
Preparation of polypropylene/sepiolite nanocomposites using supercritical CO2 assisted mixing  Ma J, Bilotti, E (Bilotti, E.)1; Peijs, T (Peijs, T.)1,2; Darr, JA 2007  EUROPEAN POLYMER JOURNAL  43   4931-4939 doi: 10.1016/j.eurpolymj.2007.09.010
4.

Synthesis and properties of polyether adducts of hexafluoropentanedionatosilver(I)  Darr JA, Poliakoff M, Blake AJ, Li WS 1998 INORGANIC CHEMISTRY  37, 5491-5496  doi: 10.1021/ic971206c

5.

Hexafluoropentanedionatosilver(I) complexes stabilised by multidentate N-donor ligands: crystal structure of a charge-separated salt species soluble in supercritical carbon dioxide, Darr JA, Poliakoff MA, Li, WS, Blake, AJ, 1997 JOURNAL OF THE CHEMICAL SOCIETY-DALTON TRANSACTIONS  Issue: 17   Pages: 2869-2874doi: 10.1039/A703668J

6.
Formation and characterization of porous indomethacin-PVP coprecipitates prepared using solvent-free supercritical fluid processing, Gong K, Viboonkiat R, Rehman IU, Buckton G, Darr JA 2006 JOURNAL OF PHARMACEUTICAL SCIENCES  94   12   2583-2590 doi: 10.1002/jps.20474
7.

Supercritical fluid assisted impregnation of indomethacin into chitosan thermosets for controlled release applications  Gong K, Darr JA, Rehman IU 2006: INTERNATIONAL JOURNAL OF PHARMACEUTICS 315  93-98 doi: 10.1016/j.ijpharm.2006.02.030 

Bioceramics and Biomedical Materials (Non-supercritical Fluids)

Biomedical ceramics is a very important area of research to our group as it concerns the replacement of bone or hard tissue that has been lost as a result of disease or accident.  A major focus for our group is about developing the manufacturing of such ceramic materials and implants at low cost in regions of the world where they are not readily aviailable.

Professor Darr worked at the IRC in Biomedical Materials from 1999-2001 at Queen Mary University of London.  After the tremendous earthquake of October 2005 in Pakistan the death toll exceeded 73 thousand, an estimated 3.5 million people were rendered homeless and another 128 thousand sustained serious causalities, including spinal injuries and limb trauma, some leading to amputations. A total of more than 740 people suffered spinal injuries while at least 700 underwent amputations. Many of these amputations were necessary to save lifes in the absence of sufficient aviabilty of high quality affordable biomedical materials such as implants and bone fillers. 

Consequently an IRC in biomedical Materials was set up in Lahore Pakistan on the campus of COMSATS Institute of Information Technology (CIIT) in October 2006 due to the vision of Dr Ihtesham Rehman (University of Sheffield) who is the co founder of our group.  Professor Darr is now a visiting role at the IRC in Pakistan and is assisting the team to develop more affordable biomedical materials. 

The team in Pakistan is also led by Dr Aqif Anwar Chaudhry who is an ex member of the group.  Current research in the UK and Pakistan has included coating methods for HA, dental composites, HA scale-up for mass production and commercial development.

Selected Publications
1.

Recent developments in processing and surface modification of hydroxyapatite
Author(s): Norton J.; Malik K. R.; Darr J. A.; et al.  Source: ADVANCES IN APPLIED CERAMICS  105   113-139
doi: 10.1179/174367606X102278

2.

Effects of incorporation of hydroxyapatite and fluoroapatite nanobioceramics into conventional glass ionomer cements (GIC)  Moshaverinia A, Ansari S,  Moshaverinia M, Roohpour N, Darr JA, Rehman I, 2008 ACTA BIOMATERIALIA  432-440
doi: 10.1016/j.actbio.2007.07.011

3.

Synthesis and characterization of grafted nanohydroxyapatites using functionalized surface agents 
Author(s): Haque, S (Haque, Saba); Rehman, I, Darr, JA (Darr, Jawwad A.) 
Source: LANGMUIR  Volume: 23   Issue: 12   Pages: 6671-6676  Published: JUN 5 2007 doi: 10.1021/la063517i