Carbon Dioxide Management

New family of class 1 adsorbents for DAC by loading 67 wt% branched poly(ethylenimine) (PEI) onto Mg–Al–CO3 layered double hydroxide-derived mixed metal oxides (MMOs), which exhibit unexpectedly large CO2 uptakes (2.27 mmol g−1), fast kinetics (1.1 mmol g−1 h−1), and high stability over 20 cycles at 25 °C under 0.4 mbar CO2. 

The basicity and acidity of solvent-treated layered double hydroxide (ST-LDHs) and their layered double oxides (ST-LDOs) have been fully studied using Hammett titration, in situ FTIR, CO2-TPD and NH3-TPD. Five solvents (ethanol, acetone, isopropanol, ethyl acetate and 1-hexanol) were selected to treat [Mg0.72Al0.28(OH)2](CO3)0.14 (Mg2.5Al-CO3 LDH) and compared with traditional LDH co-precipitated from water. The Brønsted basicity strength of the ST-LDHs and ST-LDOs increased but was accompanied by a decrease in basic site density. In addition, the Lewis acidity of ST-LDOs also changes significantly, with medium strength Lewis acid sites dissapearing after solvent treatment. We found that the CO2 capture capacity of solvent treated LDOs is 50% higher than that of traditional co-precipitated LDO sample. The ethanol treated LDO exhibited the highest CO2uptake of 1.01 mmol g−1. The observed CO2 capture performance of the ST-LDOs correlates linearly with the ratio of total acid sites to total basic sites.

Recent publications:

• Efficient CO2 capture from ambient air with Amine-functionalized Mg–Al mixed metal oxide nanosheets, X. Zhu, T. Ge, F. Yang, M. Lyu, C. Chen, D. O’Hare, R. Wang, J. Mater. Chem., A., (2020), 8, 16421-16428. 
• Correlations of acidity-basicity of solvent treated layered double hydroxides/oxides and their CO2 capture performance, D.W.J. Leung, C. Chen, J.-C. Buffet and D. O'Hare, Dalton Trans., (2020), 49, 9306 - 9311. 

Ultrathin (1–3 cationic-layers) (CuZn)1–xGax-CO3 layered double hydroxide (LDH) nanosheets were synthesized following the aqueous miscible organic solvent treatment (AMOST) method and applied as catalyst precursors for methanol production from CO2 hydrogenation. It is found that, upon reduction, the aqueous miscible organic solvent treated LDH (AMO-LDH) samples above a critical Ga3+ composition give consistently and significantly higher Cu surface areas and dispersions than the catalysts prepared from conventional hydroxyl-carbonate phases. Owing to the distinctive local steric and electrostatic stabilization of the ultrathin LDH structure, the newly formed active Cu(Zn) metal atoms can be stably embedded in the cationic layers, exerting an enhancement to the catalytic reaction. The best catalyst in this study displayed methanol productivity with a space-time yield of 0.6 gMeOH·gcat–1 h–1 under typical reaction conditions, which, as far as we are aware, is higher than most reported Cu-based catalysts in the literature.

CO2, a contributor to global warming, was converted into the valuable resource CH3OH by adding it to 2,2,6,6‐tetramethylpiperidine and B(C6F5)3 in toluene under H2 (1–2 atm), heating the mixture at 160 °C, and vacuum distillation. CH3OH was formed via the complex shown (C blue, N purple, O red, B orange, F green) as the sole C1 product.

Recent publications:

• CO2hydrogenation to methanol over catalysts derived from single cationic layer CuZnGa LDH precursors, M. M.-J. Li, C. Chen, T. Ayvali, H. Suo, J. Zheng, I. F. Teixera, L. Ye, H. Zou, D. O’Hare and S. C. E. Tsang, ACS Catal., (2018), 8, 4390-4401. 
• Non-metal Mediated Homogeneous Hydrogenation of CO2 to CH3OH, A.E. Ashley, A.L. Thompson and D. O’Hare, Angew Chemie Int Ed., (2009) 48, 9839 - 9843. 

The novel 14 electron species η8-Pn*TiR2 (Pn* = C8Me6; R = Me, CH2Ph) have been synthesised and spectroscopically and structurally characterised. Subsequent reaction with CO2 leads to the activation and double insertion of CO2 into both Ti–alkyl bonds to form the electronically saturated η8-Pn*Ti(κ2-O2CR)2 (R = Me, CH2Ph) complexes.

Recent publications:

• Double CO2 Activation by 14-electron η8-Permethylpentalene Titanium Dialkyl Complexes, R.T. Cooper, F.M. Chadwick, A.E. Ashley and D. O’Hare, Chemical Communications, (2015), 51, 11856 – 11859. 

Catalysis includes: alkene isomerisation, oligomerisation and polymerisation, small molecule activation for high value added chemical synthesis and heterogeneous upgrading. Details have been outlined in sections above.

We report the synthesis and characterisation of a new family of layered double hydroxides entitled Aqueous Miscible Organic Layered Double Hydroxide (AMO-LDH). AMO-LDHs have the chemical composition [Mz+ 1−xM′y+x(OH)2]a+(Xn −)a/r·bH2O·c(AMO-solvent) wherein M and M′ are metal cations, z = 1 or 2; y = 3 or 4, 0 < x < 1, b = 0–10, c = 0–10, X is an anion, r is 1–3 and a = z (1 − x) + xy  − 2. The role of the AMO-solvents such as acetone (A) or methanol (M) in the LDH synthesis is discussed. The distinguishing features between AMO, and conventional or commercial LDHs are investigated using X-ray diffraction, infrared spectroscopy, electron microscopy, thermal analysis, adsorption and powder density studies. These experiments show that AMO-LDHs are highly dispersed and exhibit significantly higher surface areas and lower powder densities than conventional or commercially available LDHs. AMO-LDHs can exhibit N2 BET surface areas in excess of 301 m2 g −1 compared to 13 m2 g −1 for the equivalent LDHs prepared by co-precipitation in water. The Zn2Al–borate LDH exhibits a pore volume of 2.15 cm3g −1 which is 2534 times higher than the equivalent conventionally prepared LDH.

Unique Technical Advance (UTA)

1. Rosette (flower-like) morphology
2. High surface density, (100-430 m2 g–1)*
3. High porosity,  (1.5-2.2 cm3 g–1) *
4. Multi-pore size range
5. Dispersible in hydrocarbon solvents
6. Generally applicable across all LDHs
7. Precursors to high surface area mixed metal oxides*
8. Particles with OAN up to 350*

Post synthesis treatment of Layered Double Hydroxides (LDHs) with aqueous immiscible solvents (AIM solvents) yields highly dispersible, high surface area materials (up to 377 m2g −1). The effect of solvent functional groups and structure, initial LDH particle morphology along with parameters such as dispersion time, and solvent recycling properties of AIM-LDHs are explored. The strength of the hydrogen bonding interactions that a given solvent can offer appears a crucial factor for the effectiveness of the treatment.

New 3D Hierarchical

Unique Technical Advance (UTA)

1. Platelet morphology

2. High Aspect ratio:  10-350

3. Generally applicable across all LDHs

4. Scaleable using non-toxic chemistry

We report the synthesis of solid catalysts based on a zirconocene supported on either silica@AMO-LDH or zeolite@AMO-LDH for the slurry phase polymerisation of ethylene. The hybrid catalysts demonstrate synergistic effects in which the polymerisation activity is up to three times higher than the zirconocene supported on analogous single phase silica or zeolite supports. We present here a simple method for the synthesis of core–shell SiO2@LDH (LDH: layered double hydroxide) particles using an in situ co-precipitation method without any pretreatment. The LDH composition, the overall particle size and morphology can be tuned giving new opportunities for the development of novel sorbents and catalyst systems.

One of the major challenges in the circular economy relating to food packaging is the elimination of metallised film which is currently the industry standard approach to achieve the necessary gas barrier performance. Here, we report the synthesis of high aspect ratio 2D non-toxic layered double hydroxide (LDH) nanosheet dispersions using a non-toxic exfoliation method in aqueous amino acid solution. High O2 and water vapour barrier coating films can be prepared using food safe liquid dispersions through a bar coating process. The oxygen transmission rate (OTR) of 12 μm PET coated film can be reduced from 133.5 cc·m−2·day−1 to below the instrument detection limit (<0.005 cc·m−2·day−1). The water vapour transmission rate (WVTR) of the PET film can be reduced from 8.99 g·m−2·day−1 to 0.04 g·m−2·day−1 after coating. Most importantly, these coated films are also transparent and mechanically robust, making them suitable for flexible food packing while also offering new recycling opportunities.

Recent publications:

• Correlations of acidity-basicity of solvent treated layered double hydroxides/oxides and their CO2 capture performance, D.W.J. Leung, C. Chen, J.-C. Buffet and D. O'Hare, Dalton Trans., (2020), 49, 9306 - 9311.
• Surface  modification of aqueous miscible organic layered double hydroxides (AMO-LDHs), C. Chen, J.-C. Buffet, D. O’Hare, Dalton Trans., (2020), 49, 8498-8503. 
• Aqueous miscible organic layered double hydroxides as catalyst precursors for biodiesel synthesis, C. Chen, Maxwell Greenwood, Jean-Charles Buffet and Dermot O’Hare, Green Chem., (2020), 22 (10), 3117-3121. DOI: 10.1039/D0GC00571A
• A facile synthesis of layered double hydroxide based core@shell hybrid materials, M. Lyu, C. Chen, J.-C. Buffet, and D. O'Hare, New J. Chem., (2020), 44, 10095-10101. DOI: 10.1039/C9NJ06341B
• Aspect Ratio Control of LDH Nanosheets and their Application for High Oxygen Barrier Coating in Flexible Food Packaging, J. Yu, J.-C. Buffet, D. O'Hare, ACS Appl. Mater. Interfaces.,  (2020), 12(9) 10973-10982.
• High gas barrier coating using non-toxic nanosheet dispersions for flwxible food packaging film. J. Yu, K. Ruengkajorn, D.-G. Crivoi, C. Chen, J.-C. Buffet and D. O’Hare, Nat. Commun., (2019), 10, 1-18.
• Bifunctional acid-base mesoporous silica@aqueous miscible organic-layered double hydroxides, H. Suo, H. Duan, C. Chen, J.-C. Buffet and D. O'Hare, RSC Adv., (2019), 9, 3749-3754. 
• Solvothermal synthesis MgAl-LDH nanosheets, K. Cermelj, K. Ruengkajorn, J.-C. Buffet, D. O’Hare, J. Energy Chem., (2019), 35, 88-94. 
• Aqueous immiscible layered double hydroxides – AIM-LDHs, K. Ruengkajorn, C. M. R. Wright, N. H. Rees, J.-C. Buffet and D. O’Hare, Mater. Chem. Front.(2018).
• Water adsorbancy of high surface area layered double hydroxides (AMO-LDHs), C. Chen, K. Ruenkajorn, J.-C. Buffet and D. O’Hare, RSC Adv.(2018), 8, 34650-34655.
• Metallocene supported core@LDH catalysts for slurry phase ethylene polymerisation, J.-C. Buffet, C. F. H. Byles, R. Felton, C. Chen and D. O’Hare, Chem. Commun., (2016), 52, 4076-4079
• Core-shell zeolite@aqueous miscible organic-layered double hydroxide, C. Chen, C. F. H. Byles, J.-C. Buffet, N. H. Rees, Y. Wu and D. O’Hare, Chem. Sci., (2016), 7, 1457-1461
• Rapid, efficient phase pure synthesis of Ca2AlNO3 layered double hydroxide, M. Yang, E. Tuckley, J.-C. Buffet, D. O'Hare, J. Mater. Chem. A, (2016), 4, 500-504
• Tuneable Ultra High Specific Surface Area Mg/Al-CO3 Layered Double Hydroxides, C. Chen, A.Wangriya, J.-C. Buffet, and D. O’Hare, Dalton Transactions, (2015), 44, 16392-16398.
• Core-Shell SiO2@LDHs with Tuneable Size, Composition and Morphology, C. Chen, R. Felton, J-C. Buffet and D. O’Hare, Chem Commun., (2015), 51, 3462 - 3465,
• Synthesis and Characterisation of Layered Double Hydroxide Dispersions in Organic Solvents, M. Yang, O. McDermott, J-C. Buffet, D. O'Hare, RSC Adv., (2014), 4 (93), 51676 – 51682
• Synthesis and Characterisation of Aqueous Miscible Organic-Layered Double Hydroxides, C. Chen, M. Yang, Q. Wang, J-C. Buffet and D. O’Hare, J. Mater Chem., A., (2014), 2 (36), 15102 – 15110