Continuous Hydrothermal Flow Synthesis of S-Functionalised Carbon Quantum Dots for Enhanced Oil Recovery

I. Baragau, Z. Lu, N. P Power, D. J Morgan, J. Bowen, P. Diaz, S. Kellici (2021), Chemical Engineering Journal, 405, pp 126631

Currently, there is a paucity in the exploration and application of carbon-based nanomaterials for enhanced oil recovery. Carbon quantum dots (CQDs), 0D materials consisting of a graphitic core covered by an amorphous carbon framework, were produced from glucose and p-sulfonic acid calix[4]arene (SCX4) via Continuous Hydrothermal Flow Synthesis (CHFS), an environmentally benign synthetic approach. The S-functionalised carbon quantum dots (S-CQDs) demonstrated excellent colloidal stability in aqueous and brine solutions, low retention on sand surface, and impressive enhanced oil recovery (EOR) of 17% at very low concentrations of 0.01 wt%. 

Chemical Functionalisation of 2D Materials by Batch and Continuous Hydrothermal Flow Synthesis

U. Alli,  S. J. Hettiarachchi, and S. Kellici (2020),  Chemistry–A European Journal 26(29), pp 6447-6460. (Invited article)

In this Minireview, we present batch and continuous hydrothermal flow synthesis of a selection of 2D derivatives (graphene, MXene and molybdenum disulfide), their chemical functionalisation as an advantageous approach in exploring properties of these materials as well as the benefits and challenges of employing these processes, and an outlook for further research.

Vortex Fluidic Mediated Synthesis of TiO2 Nanoparticle/MXene Composites

A. H. Mohammed Al-Antaki, T. MD Alharbi, S. Kellici, N. P Power, W. D Lawrance, C. L Raston (2020), ChemNanoMat, 6(4), pp 657-662.

Oxidation of MXene in a vortex fluidic device (VFD) operating under continuous flow results in exfoliation and fragmentation into nanoparticles of surface oxidised 2D material with further oxidation of the nanoparticles into anatase (TiO2). These MXene and anatase nanoparticles co‐assemble into stable micron sized spheres which are topologically smooth, decorating the surface of exfoliated MXene.

Continuous flow vortex fluidic-mediated exfoliation and fragmentation of two-dimensional MXene

A. H. Mohammed Al-Antaki, T. MD Alharbi, S. Kellici, N. P Power, W. D Lawrance, C. L Raston (2020), Royal Society Open Science, 7(5), pp 192255.

MXene is exfoliated in a vortex fluidic device (VFD), as a thin film microfluidic platform, under continuous flow conditions, down to ca 3 nm thin multi-layered two-dimensional (2D) material, as determined using AFM. The optimized process, under an inert atmosphere of nitrogen to avoid oxidation of the material, was established by systematically exploring the operating parameters of the VFD, along with the concentration of the dispersed starting material and the choice of solvent.

Continuous Hydrothermal Flow Synthesis of Blue-Luminescent, Excitation-Independent Nitrogen-Doped Carbon Quantum Dots as Nanosensors

Next Frontiers in Cleaner Synthesis: 3D Printed Graphene-Supported CeZrLa Mixed-Oxide Nanocatalyst for CO2 Utilisation and Direct Propylene Carbonate Production

V. Middelkoop, T. Slater, M. Florea, F. Neațu, S. Danaci, V. Onyenkeadi, K. Boonen, B. Saha, I. A Baragau, S. Kellici (2019), Journal of Cleaner Production, 214, pp.606-614.
For the first time, directly printed graphene-based 3D structured nanocatalysts have been developed combining the exceptional properties of graphene and active CeZrLa mixed-oxide nanoparticles. It constitutes a significant advance on previous attempts at 3D printing graphene inks in that it does not merely explore the printability itself, but enhances the efficiency of industrially relevant reactions, such as CO2 utilisation for direct propylene carbonate (PC) production in the absence of organic solvents

Continuous Hydrothermal Flow Synthesis of Graphene Quantum Dots

S. Kellici, J. Acord, K. Moore, N . P. Power, V. Middelkoop, D. J. Morgan, T. Heil, P. Coppo, I. Baragau, C. L. Raston, (2018), Reaction Chemistry and  Engineering, pp. 949-958.
Green fluorescent graphene quantum dots (GQD) have been synthesized via hydrothermal fragmentation using a continuous hydrothermal flow synthesis (CHFS) process as a single, rapid and environmentally benign method. This is in the presence of p-phosphonic acid calix[4]arene which enhances the optical properties of the graphene quantum dots through surface functionalization, with photoluminescence quantum yields of up to 4.5%. Potential environmental impact of a lab-scale supercritical CHFS process compared with that of conventional batch processing of GQDs has been assessed using the method of the International Reference Life Cycle Data System (ILCD).

Greener Synthesis of Dimethyl Carbonate using a Novel Tin-Zirconia/Graphene Nanocomposite Catalyst

R. Saada, O. AboElazayem, S. Kellici, S, T. Heil, D. Morgan, D, G. I. Lampronti, B Saha (2018), Applied Catalysis B: Environmental 168-69, pp. 353-362.

A green, rapid and continuous hydrothermal flow synthesis (CHFS) route has been employed to synthesise highly efficient and active novel heterogeneous catalysts. Tin doped zirconia (Zr–Sn–O) and tin doped zirconia/graphene nanocomposite (Zr–Sn/GO) have been assessed as suitable heterogeneous catalysts for the synthesis of dimethyl carbonate (DMC). 

Selective Calixarene Directed Synthesis of MXene Plates, Crumpled Sheets, Spheres and Scrolls

A. Vaughn, J. Ball, T. Heil, D. Morgan, G. Lampronti, G. Maršalkaitė, C. L Raston, N. P. Power, S. Kellici (2017), Chemistry  European Journal, 23, (34), 8128–8133.

MXenes are a rapidly emerging new class of laminar materials with unique properties. However, access to other morphologies of MXenes has not yet been fully realised. To this end we have developed the synthesis of MXenes (Ti2C) as plates, crumpled sheets, spheres and scrolls, which involves selective intercalation of p-phosphonic calix[n]arenes, with control in morphology arising from the choice of the size of the macrocycle, n = 4, 5, 6 or 8. This opens up wider avenues of discovery/design for new morphologies from the wider family of MXenes beyond Ti2C, along with opportunities to exploit any new physico-chemical properties proffered.

Graphic design: Mr. Rodrigo Fernando Pedro Carvalho

Rapid Synthesis of Graphene Quantum Dots Using a Continuous Hydrothermal Flow Synthesis Approach

S. Kellici, J. Acord, N. Power, D. J. Morgan, P. Coppo, T. Heil, B. Saha (2017),  RSC Advances, 7, 14716-14720.

A rapid, continuous, environmentally benign and innovative approach is employed for the synthesis of green fluorescent graphene quantum dots (GQD) with low cytotoxicity by utilising a Continuous Hydrothermal Flow Synthesis (CHFS) process as an efficient cutting tool in combination with calix[4]arene tetrasulfonic acid (SCX4) as an effective particle size limiting agent.

Calixarene Assisted Rapid Synthesis of Silver-Graphene Nanocomposites with Enhanced Antibacterial Activity

S. Kellici, J. Acord, A. Vaughn, N. Power, D. Morgan, T. Heil, S. Facq, G. Lampronti (2016),  ACS Applied Materials & Interfaces, 8(29), pp. 19038–19046.

Demonstrated herein is a single rapid approach employed for synthesis of Ag-graphene nanocomposites, with excellent antibacterial properties and low cytotoxicity, by utilizing a Continuous Hydrothermal Flow Synthesis (CHFS) process in combination with p-hexasulfonic acid calix[6]arene (SCX6) as an effective particle stabilizer. The nanocomposites showed high activity against E. coli (Gram-negative) and S. aureus (Gram-positive) bacteria, and in selected cases outperformed antibiotics. This rapid, single step synthetic approach not only provides a facile means of enabling and controlling graphene reduction, but also offers an optimal route for homogeneously producing and depositing highly crystalline Ag nanostructures into reduced graphene oxide substrate.

Greener Synthesis of Dimethyl Carbonate Using a Novel Ceria–Zirconia Oxide/Graphene Nanocomposite Catalyst

R. Saada,  S. Kellici,  T. Heil,  D. Morgan, B. Saha (2015) Applied Catalysis B: Environmental, Volumes 168–169, 2015, 353–362.

A green, rapid and continuous hydrothermal flow synthesis (CHFS) route has been used to produce highly stable and active novel ceria–zirconia oxide/graphene nanocomposite catalyst [Ce–Zr oxide/graphene, where nominal atomic ratio of Ce:Zr (1:1)]. The catalyst has been investigated for the direct synthesis of dimethyl carbonate (DMC) from methanol (MeOH) and carbon dioxide (CO2). The ceria–zirconia oxide (Ce–Zr oxide)/graphene nanocomposite catalyst showed highest MeOH conversion of 58% at a DMC yield of 33%. Catalyst reusability studies have been conducted at optimum reaction condition and it has been found that this catalyst could be reused several times without losing its catalytic activity. These experimental findings indicated that novel ceria–zirconia oxide/graphene nanocomposite has a huge potential as a heterogeneous catalyst for the synthesis of DMC. 

Greener Synthesis of Propylene Carbonate Using Graphene-Inorganic Nanocomposite Catalysts

I. Adeleye, S. Kellici, T. Heil, D. Morgan, M. Vickers, B. Saha (2015), Catalysis Today, 256 (2), 347-357.


Continuous hydrothermal flow synthesis (CHFS) has been employed as rapid and cleaner route for the synthesis of a novel, highly efficient graphene-inorganic heterogeneous catalyst, denoted as Ce–La–Zr–GO nanocomposite. The catalyst was used for the direct synthesis of propylene carbonate (PC) from the cycloaddition of carbon dioxide (CO2) and propylene oxide (PO) in the absence of any organic solvents. 

Imaging the Continuous Hydrothermal Flow Synthesis of Nanoparticulate CeO₂ at Different Supercritical Water Temperatures Using In Situ Angle-Dispersive Diffraction

V. Middelkoop, C. Tighe, S. Kellici, R. Gruar, J. M. Perkins, D.M. Jacques, J. A. Darr (2014), Journal of Supercritical Fluids, 87, 118-128.


Editor’s-in-chief feature article

In situ high-energy synchrotron X-ray diffraction, a non-destructive synchrotron-based technique was employed to probe inside the steel tubing of a continuous hydrothermal flow synthesis (CHFS) mixer to spatially map, for the first time, the superheated water crystallisation of nanocrystalline ceria (CeO2) at three different (superheated-water) temperatures representing three unique chemical environments within the reactor. Rapid hydrothermal co-precipitation at the three selected temperatures led to similarly sized ceria nanoparticles ranging from 3-7 nm. X-ray tomographic imaging study amounted to a formidable technical and engineering challenge, nevertheless one that has been met; this represents a significant achievement in imaging science, given the dynamic nature and hostile environment of a working CHFS reactor.

A Single Rapid Route for the Synthesis of Reduced Graphene Oxide with Antibacterial Activities

S. Kellici, J. Acord, J. Ball, H. Reehal, D. Morgan, B. Saha (2014), RSC Advances, 2014, 4, 14858-14861.

An innovative approach is employed for synthesising reduced graphene oxide with antibacterial properties via utilisation of continuous supercritical water (in alkaline medium) which enabled reduction of graphene oxide in a single rapid route and thus eliminating hazardous conventional chemicals.

Green Process Engineering as the Key to Future Processes

D. Patel, S. Kellici, B. Saha (2014) Processes, 2(1), 311-322.

Growing concern for the environment, increasing stringent standards for the release of chemicals into the environment and economic competiveness have led to more environmentally friendly approaches that have resulted in greater pollution prevention via waste reduction and efficiency maximisation. Green process engineering (GPE) is an important tool that could make significant contributions in the drive toward making hazardous and wasteful processes more sustainable for the benefit of the economy, environment and society. This article highlights the guidelines that could be used by scientists and engineers for designing new materials, products, processes and systems. Few examples of current and future applications of GPE, particularly in the areas of biofuels, supercritical fluids, multi-functional reactors and catalytic processes, have been presented. 

Optical and Photocatalytic Behaviours of Nanoparticles in the Ti–Zn–O Binary System

J. Goodall, S. Kellici. D. Illsey, R. Lines, J. Knowles, J. A. Darr (2014) RSC Advances, 4, 31799 - 31809.

Continuous hydrothermal flow synthesis (CHFS) has been used as a rapid and clean, synthetic method to produce a range of crystalline nanoparticles in the Ti–Zn–O binary system. Because of the interest for these materials in UVA and UVB attenuating materials, the UV-Vis profiles of the nanocomposites and solid solutions were studied. Photocatalytic activity of the samples towards the decolourisation of methylene blue dye was also assessed.

Some Novel Aspects of Green Process Engineering

D. Patel, S. Kellici, B. Saha (2013) Chimica Oggi - Chemistry Today, 31, 3, 57-62. 

Green process engineering (GPE) is an approach to make a hazardous and wasteful process more sustainable. The implementation of a wide range of innovative and effective green process technologies over the years has led to more environmentally friendly approaches that have resulted in greater pollution prevention via waste reduction and ef ciency maximisation. This paper highlights some novel applications of green process engineering, particularly in the areas of supercritical carbon dioxide and catalytic processes, including the guidelines utilised in designing a green process, following twelve principles of green engineering. 

High-Throughput Continuous Hydrothermal Flow Synthesis of Zn–Ce oxides: Unprecedented Solubility of Zn in the Nanoparticle Fluorite Lattice

S. Kellici, K. Gong, T. Lin, S. Brown, R. J. H. Clark, M. Vickers, J. K. Cockcroft, V. Middelkoop, P. Barnes, J. M. Perkin,C. J. Tighe, J. A. Darr (2010) Phil. Trans. R. Soc. A,  368, 4331-4349. 

High-throughput continuous hydrothermal flow synthesis has been used as a rapid and efficient synthetic route to produce a range of crystalline nanopowders in the Ce–Zn oxide binary system. High-resolution powder X-ray diffraction data were obtained for both as-prepared and heat-treated (850°C for 10 h in air) samples using the new robotic beamline I11, located at Diamond Light Source. The influence of the sample composition on the crystal structure and on the optical and physical properties was studied. High-resolution transmission electron microscopy images revealed that the phase-pure nano-CeO2 (x=0) consisted of ca 3.7 nm well-defined nanoparticles. The nanomaterials produced herein generally had high surface areas and possessed combinations of particle properties (e.g. bandgap, crystallinity, size, etc.) that were unobtainable or difficult to achieve by other more conventional synthetic methods.

Rapid Automated Materials Synthesis Instrument: Exploring the Composition and Heat-Treatment of Nanoprecursors Toward Low Temperature Red Phosphors

T. Lin. S. Kellici, K. Gong, K. Thompson. Evans, X. Wang, J. A. Darr (2010), Journal of Combinatorial Chemistry, 12(3),  383-392. 

We report on the commissioning experimental run of the rapid automated materials synthesis instrument (RAMSI), a combinatorial robot designed to manufacture, clean, and print libraries of nanocrystal precursor solid compositions. 

Rapid Automated Materials Synthesis Instrument (RAMSI): A High Throughput Combinatorial Robot for Nanoceramics Discovery

T. Lin. S. Kellici, K. Gong, K. Thompson. Evans, X. Wang, J. A. Darr (2010), Advances in Science and Technology, 62, 215-220. 

A high throughput combinatorial robot RAMSI (Rapid Automated Materials Synthesis Instrument) has been developed for nanoceramics synthesis. It can rapidly produce nanoparticle libraries that can be used for new materials discovery. The RAMSI robot has 3 motor-driven axes moving in X-Y-Z space and linking the synthesis, cleanup and printing sections. A High Throughput Continuous Hydrothermal (HiTCH) flow synthesis reactor is contained within RAMSI, and reaches significant production capability of 48 tubes of 50mL samples in 8 hours. Supported by the high throughput hardware design, the control system adopts parallel operations and multi-task assignments. Key strategies include intelligent supernatant detection, dot printing protocols and robot arm route schedule etc. The commissioning of RAMSI showed its high efficiency by producing samples of yttrium hydroxide doped with europium. In a 6-hour experiment, 8 unique 100mL samples were synthesized then cleaned and printed into 96 dots (100 minutes only for synthesis time). The ceramic dots were heat-treated at different temperatures up to 1200°C and affixed into a well-plate library. The brightest phosphors could be readily identified by illumination under UV light.

Screening Tests for the Evaluation of Nanoparticle Titania Photocatalysts

K. Thompson, J. Goodall, S. Kellici, J. A. Mattinson, T. A. Egerton, I. Rehman, J. A. Darr (2009) Journal of Chemical Technology and Biotechnology, 84 (11), 1717-1725.

Nano-sized titanium dioxide has potential as a photocatalyst, and doped variants may have different photocatalytic properties. Nano-titanias with a wide range of dopants and compositions can be prepared using continuous hydrothermal flow synthesis (CHFS), but when many samples are made, a large-scale screening test is required to investigate their properties. A range of doped nano-titanias were prepared using a CHFS route, and investigated as powders using a range of photocatalytic test methods. These tests included decolourization of methylene blue (in the presence of oxygen), partial oxidation of a simple alcohol (propan-2-ol) and the degradation of aqueous solutions of dichloroacetic acid. The practicality of the tests for large-scale screening was considered, and the test results were cross-correlated to see if any of them gave similar ranking for activity of the photocatalysts.

Direct Continuous Hydrothermal Synthesis of High Surface Area Nanosized Titania

Z. Zhang, S. Brown, J. B.M. Goodall, X. Weng, K. ThompsonK. GongS. Kellici, R. J.H. Clark,  J. R.G. EvansJ A. Darr (2009), Journal of Alloys and Compounds, 476 (1-2), 451–456.

Nanosized titania powder of high surface area was prepared using a continuous hydrothermal flow synthesis (CHFS) reactor which uses superheated water at 400 °C and 24.1 MPa as a crystallizing medium. Nano-TiO2 was heat-treated in air over a range of temperatures. It was found that the onset of the anatase–rutile transition of heat-treated nano-TiO2 in air occurred at 500 °C and reached 100% rutile at 900 °C. The Raman band (Eg) of anatase softens as the particle size increases with heat-treatment temperature (up to 600 °C).  The effects of nano-titania anatase-rutile phase composition, crystallinity, and crystallite size on the catalytic activity were investigated.

Titanium Dioxide and Composite Metal/Metal Oxide Titania Thin Films on Glass: A Comparative Study of Photocatalytic Activity

A. Kafizas, S. Kellici, J. A. Darr, I. P. Parkin (2009) J. Photochem. Photobio. A: Chem. 204 (2-3), 183-190.

Titania and composite (Ag, Au, W) titania coatings were prepared on glass microscope slides via a sol–gel dip-coating method. The resulting coatings were characterised by X-ray diffraction, Raman, scanning electron microscopy (SEM), wavelength dispersive X-ray (WDX), Brunauer–Emmett–Teller (BET) surface area analysis, atomic force microscopy (AFM) and UV–visible absorption techniques. Photocatalytic activity of the coatings was determined by photomineralisation of stearic acid under 254, 365 nm and white light sources monitored by FT-IR spectroscopy. Water contact angle measurements were made before and after irradiation with monochromatic 254 or 365 nm light; all films demonstrated photo-assisted super hydrophilicity (PSH). A Ag:Au titania composite coating was found to be the most significant photoactive film. The Ag:Au TiO2 coating showed potential as a useful coating for hard self-cleaning surfaces due to its robustness, stability to cleaning and reuse and its photoactive response to indoor lighting conditions.

Direct Syntheses of La–Ni–O Phases from Nanosized Co-Crystallites

X. Weng, P. Boldrin, I. Abrahams, S. Skinner, S.Kellici,  J.A. Darr, (2008) Journal of Solid State Chemistry, 181 (5), 1123-1132.

A new direct route for the “bottom up” syntheses of phases in the Lan+1NinO3n+1 series (n=1, 2, 3 and ∞) has been achieved via single-step heat treatments of nanosized co-crystallized precursors. The co-crystallized precursors were prepared using a continuous hydrothermal flow synthesis system that uses a superheated water flow at ca. 400 °C and 24.1 MPa to produce nanoparticulate slurries. Overall, a significant reduction in time and number of steps for the syntheses of La3Ni2O7 and La4Ni3O10 was achieved compared with more conventional synthesis methods, which typically require multiple homogenization and reheating steps over several days.

Controlled Growth of Titania Nanospheres in Supercritical Carbon Dioxide Using a Novel Surfactant Stabilised Precursor

S. Kellici, I. Rehman, J. A. Darr (2006), Journal of  Material Chemistry, 16, 159-161. 

Titania nanospheres have been synthesised via the controlled hydrolysis of a mixture of novel precursor [Ti(OPri)3(Krytox)]n and titanium (IV) isopropoxide, [Ti(OPri)4], in supercritical carbon dioxide (sc-CO2). The use of sc-CO2 in the reaction, eliminates the need for organic solvents, optimises manufacturing efficiency and produces materials with tailored properties; additionally the use of the functionalised precursor [Ti(OPri)3(Krytox)]n, during co-hydrolysis with [Ti(OPri)4], gave a significantly narrower particle size distribution for the products than when the functionalised compound was not present.

Instant Nano-Hydroxyapatite: A Continuous and Rapid Hydrothermal Synthesis

 A. A. Chaudhry,  S. Haque,  S. Kellici, P. Boldrin,  I. Rehman,  F.  A.Khalid, J.A. Darr (2006) Chemical Communications,  21, 2286-2288


Nano-particle hydroxyapatite (HA) rods, were rapidly synthesised using a three pump continuous hydrothermal process (using a water feed at up to 400 °C and at 24 MPa): the product was obtained as a highly crystalline and phase pure material, without the need for an ageing step or subsequent heat treatment.


Synthesis of Titania Nanoparticles from Supercritical Carbon Dioxide Mixtures

S.Kellici, I. Rehman, J.A. Darr (2005) IEE Proceedings of Nanobiotechnology, 152, 109-115.

Surfactant-coated amorphous titania nanospheres have been synthesised using templating 'water-in-supercritical carbon dioxide' emulsion droplets; the process represents a clean and controlled method for the manufacture of high-purity nanoparticles.

Participation in Book Chapters

  1. “Green and continuous hydrothermal synthesis of nanophosphors for biomedical applications”, Gruar, R.; Kellici, S.; Tighe, C.; Darr. J.A.; Nanotechnology 2011: Advanced Materials, CNTs, Particles, Films and Composites, Volume 1, 2011, CRC Press Inc, ISBN-10: 1439871426

  2. “Design and Engineering of Microreactor and Smart-Scaled Flow Processes”, MDPI AG Basel, Switzerland ISBN-10: 1439871426


Miscellaneous Publications

  1. “In the Ink”, EPRSC Newsline, 2004, 29, 3.

  2. “Development of clean materials technology”, Kellici, S.; Darr, J. A.; Epichem Group Newsletter, First Quarter 2005.

  3. “LSBU academic awarded first prize at ChemEngDayUK 2014” – LSBU website, 22 April 2014

  4. Characterization and sintering behaviour of nanosized alumina obtained through Sol-Gel”, Rasul, S.; Khan, A.A.; Darr. J.A; Kellici. S.; Proc. 9th Int. Symp. Adv. Mat. (ISAM2005), 2005, Islamabad, Pakistan, 466

  5. “Nanograined, hard copper films from water-in-CO2 emulsion electrodeposition”, Soman, Y.S; Kuzmenko, T., Hebb, A..; Kellici, S.; Darr, J.A.; Indian Surf. Finishing, 2006, 3, 215.

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