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.
Quesada-Cabrera, Raul; Weng, Xiaole; Hyet, Geoff; Clark, Robin J.H.; Wang, Xue Z..; Darr, Jawwad A., 2013, High-Throughput Continuous Hydrothermal Synthesis of Nanomaterials (Part II): Unveiling the As-Prepared CexZryYzO2-delta Phase Diagram, ACS COMBINATORIAL SCIENCE 15(9), 458-463 doi: 10.1021/co3001346
2.
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
3.
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
4.
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
5.
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)

Confined Jet Mixer
•      Products rapidly carried away
•      Heat carried away by reagents
•      Constructed from off-the-shelf part
•      316 stainless steel
•      Can readily replace parts

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.
Tighe, Christopher J.; Cabrera, Raul Quesada; Gruar, Robert I.; Darr, Jawwad A., 2013. Scale Up Production of Nanoparticles: Continuous Supercritical Water Synthesis of Ce-Zn Oxides, INDUSTRIAL & ENGINEERING CHEMISTRY RESEARCH  52(16), 5522-5528 doi: 10.1021/ie3025642
2.

Gruar, Robert I.; Tighe, Christopher J.; Darr, Jawwad A., 2013. Scaling-up a Confined Jet Reactor for the Continuous Hydrothermal Manufacture of Nanomaterials, INDUSTRIAL & ENGINEERING CHEMISTRY RESEARCH  52(15) 5270-5281
doi: 10.1021/ie302567d

3.
Tighe, Christopher J.; Gruar, Robert I.; Ma, Cai Y.; Mahmud, Tariq; Wang, Xue Z.; Darr, Jawwad A., 2012. Investigation of counter-current mixing in a continuous hydrothermal flow reactor, JOURNAL OF SUPERCRITICAL FLUIDS 62 165-172
doi:10.1016/j.supflu.2011.11.027
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.
A simple and low-cost method for the preparation of self-supported TiO2-WO3 ceramic heterojunction wafers, Makwana, Neel M.; Quesada-Cabrera, Raul; Parkin, Ivan P.; McMillan, Paul F.; Mills, Andrew; Darr, Jawwad A.,  JOURNAL OF MATERIALS CHEMISTRY A 2014, 2(41), 17602-17608doi: 10.1039/C4TA03257H
2.
Single-step synthesis of doped TiO2 stratified thin-films by atmospheric-pressure chemical vapour deposition, Sotelo-Vazquez, Carlos; Quesada-Cabrera, Raul; Darr, Jawwad A.; Parkin, Ivan P., JOURNAL OF MATERIALS CHEMISTRY A  2014, 2(19),  7082-7087 doi: 10.1039/C4TA00935E
3.
Critical influence of surface nitrogen species on the activity of N-doped TiO2 thin-films during photodegradation of stearic acid under UV light irradiation, Quesada-Cabrera, Raul; Sotelo-Vazquez, Carlos; Darr, Jawwad A.; Parkin, Ivan P., APPLIED CATALYSIS B-ENVIRONMENTAL  2014, 160, 582-588 doi: 10.1016/j.apcatb.2014.06.010
4.
Atmospheric pressure chemical vapour deposition of boron doped titanium dioxide for photocatalytic water reduction and oxidation, Carmichael, Penelope; Hazafy, David; Bhachu, Davinder S.; Mills, Andrew; Darr, Jawwad A.; Parkin, Ivan P.,  PHYSICAL CHEMISTRY CHEMICAL PHYSICS 2013, 15(39), 16788-16794 doi: 10.1039/C3CP52665H
5.
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
6.
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
7.
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
8.
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
9.
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
CO2 Reduction Catalysts

Bio-inspired nanocatalysts: From proof of concept to 'real' catalysis [CO2 reduction]. 
EPSRC grant ref.: EP/K035355/1

There is overwhelming concern that the natural equilibrium of the greenhouse effect is being perturbed by the increasing concentration of CO2 and other greenhouse gases in the atmosphere. Anthropogenic activities such as the combustion of fossil fuels and worldwide industrialisation have led to a rapid rise of CO2 build up in the atmosphere. This has meant that the amount of CO2 released into the atmosphere has increased from levels of 280 ppm (by volume) in the year 1000 to 401 ppm in the year 2014. Utilizing carbon dioxide and converting it into more useful products such as formic acid, methanol, syn gas, CO, hydrocarbons, etc. is an attractive proposition. There are a number of challenges in this area as CO2 is a thermodynamically stable molecule; and its conversion to various products is often viewed unfavourably due to high-energy consumption.

The vision of this project is to employ expertise from multi-disciplinary academics in areas of computational and experimental chemistry for design, synthesis and characterisation of nano-catalysts for CO2 activation and conversion. This is combined with expertise from chemical engineering on device development to test and evaluate the products from CO2 conversion. The nano-catalysts are synthesised using Continuous Hydrothermal Flow Synthesis (CHFS)

The nano-catalysts are inspired from a number of essential proteins that contain reactive sites, which reduce the CO2 molecule into useful chemicals. The active sites are (Fe, Ni)S cubane clusters, which are similar to sulfide minerals, such as the iron sulfide greigite. Iron sulfides have been associated as catalysts for key biochemical processes where redox processes involving CO2 at the surface of iron sulfide solids have been implicated in iron sulfur world theories of the origins and development of life. Other catalysts such as copper and its oxides are of interest as well, due to their excellent activity towards CO2.


Modelled surfaces of mackinawite, greigite and violarite

Test Link

New Transparent Conducting Oxides

Transparent Conducting Oxide (TCO) Nanoparticles and Thin Films

EPSRC grant ref.: EP/L017709/1: Sustainable Manufacturing of Transparent Conducting Oxide (TCO) Inks and Thin Films (£2.3M)

TCO materials, which exhibit the uncommon combination of high transparency (>80% in the visible region) and low resistivity (10-4 Ω cm), are of sizable interest due to their application in modern technologies such as flat panel displays, smart windows, solar cells and light emitting diodes (LEDs). The use of highly crystalline TCO nanomaterials has the potential to broaden the application of TCOs to heat-sensitive and flexible substrates through low sintering temperatures and compatibility with deposition methods such as inkjet printing.

Nanoparticle synthesis is largely dominated by batch processes, often involving the use of environmentally harmful organic solvents, limiting the production of materials on an industrially relevant scale. Our CHFS process allows for the production of high-performing TCO materials, such as indium tin oxide (ITO), in a continuous process utilising only water as a solvent. In-process surface functionalisation also presents the ability to produce highly dispersible materials suitable for formulation into inks.


TEM images of indium tin oxide (ITO) synthesised by CHFS

Our research focusses on several vital aspects in the development of industrially-relevant TCO nanomaterials, namely sustainability and the discovery of novel materials.

(1) More Sustainable TCOs: ITO remains the industry standard TCO material. However, the scarcity of indium and expense of tin requires the synthesis of alternative, earth-abundant materials offering comparable performance. We focus on the CHFS of alternative systems such as doped-TiO2 and doped-ZnO with a view to the production of materials to replace ITO.

(2) TCO Materials Discovery: Given the encroaching scarcity of the materials currently ubiquitous in TCO manufacture, there is an ever increasing need to find sustainable alternatives. With several potential candidates already prevalent in literature, this strand of our research is based on identifying new materials for use as TCOs using Density Functional Theory (DFT) then to synthesise them using the CHFS and test them both optically and electronically to gauge their suitability.

(3) Novel manufacturing routes: the team will explore a range of novel manufacturing routes, from inkjet to sputtering to aerosol assisted deposition methods for the development of new TCOs.
Nanostructured Lithium Ion Batteries

Latest news
The UCL team working on batteries has recently secured grants in energy storage related areas, including being part of the £2.3M ELEVATE, ELEctrochemical Vehicle Advanced Technology (EPSRC grant ref.: EP/M009394/1: PI = Prof R. Thring of Loughborough University and a large team of academic and others including High Value Manufacturing (HVM) Catapult, Intelligent Energy Ltd, Jaguar Land Rover, Johnson Matthey, National Physical Laboratory and Yuasa Battery UK Ltd.).  More information to follow.
link http://gow.epsrc.ac.uk/NGBOViewGrant.aspx?GrantRef=EP/M009394/1

Introduction
Our group has been developing such materials and relevant facilities for testing since 2011 (in collaboration with Dan Brett and Paul Shearing in Chemical Engineering, UCL in the Electrochemical Innovation Laboratory).  We have also undertaken a number of industry collaborations to assess our materials and processes. Researchers in CMTG have successfully also scaled up a number of key anode and cathode nanomaterials recently at UCL.

There is significant interest in increasing the energy and power densities of rechargeable batteries, as they are currently much lower than those of petroleum fuel. Hence the driving range of electric vehicles is much lower than that of a conventional petrol-driven vehicle, and this has limited their widespread adoption.

This group focuses on the continuous hydrothermal flow synthesis (CHFS) of anode and cathode materials for lithium-ion batteries, particularly those with high energy and/or power densities. The aim is to improve on the performance of these materials by utilising dopants and nanosizing them.  To date, we have focussed on making more cyclable and low cost anodes based on TM oxides such as Fe, Ti and V, as well as anodes based on lithium iron phosphates (LFP) and their derivatives. Dopants such as Sn and V have also been investigated (work submitted for publication January 2015)


Carbon-coated nano-LFP (left) and high rate performance in blue and red plots for the same material versus some of the best performing in the literature.  This early work showed that the materials retained high capacity at high C-rates, i.e. >10C.


The facilities at UCL for small scale battery manufacture and testing.  These have now been extended by our collaborators for grid scale energy storage research.

The ELEVATE Project

The ELEVATE project will deliver a technology innovation chain that adopts a material-to-system approach. We will identify, optimise and scale-up new materials into devices, develop novel diagnostic techniques in the lab and for on-board monitoring and control, and validate the technologies in a hybrid vehicle.The objectives will be met by five interconnected work packages (WPs): Hierarchical Structured Electrodes (WP1) will combine the nano-micro scale structuring of lithium ion battery (LIB) materials with meso-scale electrode structuring to create novel hierarchical structured electrodes. The target will be to produce a range of new high power and high energy density combinations, achieved through a rational design approach based on arrangements of porosities and materials. Critical to this work will be close interaction with WP2 where meso-structure will be characterized by X-ray tomography. These 3D data will show to what extent manufacturing designs are realized (WP3), help to rationalize electrochemical performance, and guide subsequent iterations of design-make-test in a way not previously possible. Diagnostics and Correlative Metrology (WP2) will develop new methods of analysis to provide an unparalleled level of information about the internal working of batteries, fuel cells and supercapacitors and provide a mechanism for improving device design and materials formulation through a tightly integrated programme with WP1 on materials and WP3 on devices. System Level Integration and Evaluation (WP3), sits in a central position between materials and analysis in WP1 and 2 and grid and vehicle interfacing in WP4 and 5. This WP will integrate new materials into functioning devices and develop understanding of their performance and degradation characteristics. To examine on-board performance, real-time, system-level diagnostics and prognostics (to include, system models, state estimators and data management) will be developed to ensure safety, enable fault detection and extend system life.  In WP4, Optimised Design of High-Rate Grid Interface, the interface of vehicle with the grid will be considered, with a particular focus on high-rate charging of electric vehicles (EV), whilst also minimising the grid impact of such high power chargers. This is envisaged via use of local off-vehicle energy storage at the charging station, to permit rapid recharge of EVs to the new high capacity on-vehicle energy stores (e.g. from WP1). This WP will study the optimal off-vehicle energy storage technology (e.g. supercapacitors, batteries, flow cells), characterise and diagnose the energy store performance at high rates and perform laboratory scale testing of a rapid charger.  Finally, in WP5, In-Vehicle Aspects, Validation Platform and Impact, the newly-evolved electrochemical energy storage packages developed in earlier WPs will be validated in a hybrid vehicle. The data generated and derived equivalent circuits will be fed back into the design and innovation cycle, leading to better materials and devices. Findings will be delivered to project partners, and ultimately back to UK industry.  The cross-disciplinary nature of the work and collaborative approach is ingrained in the work-plan, where, as well as having individual responsibility for a specific aspect of the work, each partner will contribute to at least two work-packages.

Sustainable Oxidation Catalysts for Production of Solar Hydrogen

[EPSRC grant reference EP/M008754/1]: Sustainable Oxidation Catalysts for the Production of Solar Hydrogen and Chlorine from Brine

Current research focuses on the production of sustainable oxidation catalysts for the production of hydrogen (H2) from water and salt water. The materials are envisaged to be applied to solar driven devices and to conventional electrolysers used in industry. Sustainable, robust and inexpensive oxidation catalyst nanoparticles will be produced.

The proposed novel oxidation catalysts developed in the project will utilise inexpensive, abundant nanomaterials (such as oxides of Mn, Ni or Co), although, in some cases, these will be doped with well-dispersed, much more active, but less abundant ones, such as RuO2. These nanomaterials will also be coated onto high surface area conducting carbons, which will allow them to be partly supported and active.
A novel, combinatorial approach, using a new type of High-throughput Continuous Hydrothermal (HiTCH) flow synthesis reactor, will be developed to produce a wide range of oxidation catalysts. Novel, colour-based rapid screening methods will be used to provide initial assessments of their activities and a wide range of techniques will be used to assess their physical properties.

The best of the catalysts generated will be optimised in terms of performance as electrocatalysts and subjected to more detailed electro-kinetic and structural studies (e.g. XANES and XAFS) and subsequent mechanistic and structural modelling. This work will help toidentify key structural features associated with the most active of the electrocatalysts tested, and inform on the best routes to be taken in the subsequent synthesis of related materials as oxidation catalysts of possible greater potential. Finally, the best of all the electrocatalysts tested will be used to create simple, exemplar, scalable working wireless photodiode solar energy conversion devices, which utilise inexpensive, efficient, triple-junction Si photovoltaic cells as the light-absorbing unit, for the photocleavage of water or brine.

Our group's previous publications on related solar-driven chemistry and heterojunction devices are available here.
Nanoparticle Adjuvant for Healthcare
This is a project led by UCL School of Pharmacy (USP) group of Dr Gareth Williams and is focussed on the discovery of nanoparticulate adjuvants for use in humans.  Any materials synthesised in CMTG are tested in USP in vitro to deduce their adjuvanticity.

Aluminium oxyhydroxide is an adjuvant of interest because “alum”-based compounds have been added safely to vaccine formulations since 1926. Adjuvants improve the efficacy of the vaccine in terms of eliciting a stronger immune response in the recipient for protective immunity against the injected pathogen.

Therefore, we are currently synthesising crystalline aluminium oxyhydroxide (AlOOH) in flow reactors to gain better control of size and shape. Future work includes increasing the temperature of the reactions to improve the crystallinity of the AlOOH.
Industrial Nanoparticles

Work in this team focuses the development of nanomaterials for industrial applications.  We work closely with our technology transfer colleagues in UCL Business, particularly Marcus Manning. This development involves the particle size control of nanoparticles through reactor design, surface functionalisation, and doping.  

Areas of interest include:

  • Titianium dioxide for solar cells
  • Cobalt oxide for Fischer-Tropsch catalysis and carbon nanotube growth
  • Zinc oxide for UV protection applications
  • Biomaterials for medical applications
  • Cerium oxide based materials for novel oxygen separation membranes (in collaboration with Brandon Group at Imperial College)
  • Metal oxides for abrasion resistance coatings
  • Ceramic inks

A number of publications have been generated or are in press.

Selected Publications
1.
Li, Xuemin; Qiu, Yin; Wang, Shasha; Lu, Shan; Gruar Robert I.; Zhang, Xuehua; Darr, Jawwad A.  2013. Electrophoretically deposited TiO2 compact layers using aqueous suspension for dye-sensitized solar cells, PHYSICAL CHEMISTRY CHEMICAL PHYSICS  15(35), 14729-14735. doi: 10.1039/C3CP51705E
2.
Ruiz-Trejo, Enrique; Boldrin, Paul; Lubin, Alexandra; Tariq, Farid; Fearn, Sarah; Chater, Richard; Cook, Stuart N.; Atkinson, Alan; Gruar, Robert I.; Tighe, Christopher J.; Darr, Jawwad; Brandon, Nigel P. 2014. Novel Composite Cermet for Low-Metal-Content Oxygen Separation Membranes, CHEMISTRY OF MATERIALS 26(13), 3887-3895. doi: 10.1021/cm501490n
3.
Goodall, Josephine B. M.; Kellici, Suela; Illsley, Derek; Lines, Robert; Knowles, Jonathan C.; Darr, Jawwad A. 2014. Optical and photocatalytic behaviours of nanoparticles in the Ti-Zn-O binary system, RSC ADVANCES  4(60), 31799-31809.
doi: 10.1039/C3RA48030E
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.
Chaudhry AA, Haque S, Kellici S, Boldrin P, Rehman I, Fazal AK, Darr JA. 2006. Instant nano-hydroxyapatite: a continuous and rapid hydrothermal synthesis. 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.
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. 2011. High-strength nanograined and translucent hydroxyapatite monoliths via continuous hydrothermal synthesis and optimized spark plasma sintering. Acta Biomater 7(2):791-799 doi: 10.1016/j.actbio.2010.09.029
4.
Chaudhry, Aqif A.; Knowles, Jonathan C.; Rehman, Ihtesham; Darr, Jawwad A. 2013. Rapid hydrothermal flow synthesis and characterisation of carbonate- and silicate-substituted calcium phosphates, JOURNAL OF BIOMATERIALS APPLICATIONS  28(3), 448-461 doi: 10.1177/0885328212460289
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.
Middelkoop, Vesna; Tighe, Christopher J.; Kellici, Suela; Gruar, Robert I.; Perkins, James M.; Jacques, Simon D.M.; Barnes, Paul; Darr, Jawwad A., 2014, Imaging the continuous hydrothermal flow synthesis of nanoparticulate CeO2 at different supercritical water temperatures using in situ angle-dispersive diffraction, JOURNAL OF SUPERCRITICAL FLUIDS 87, 118-128
doi: 10.1016/j.supflu.2013.12.022
2.
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 
3.
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
4.
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