Continuous flow synthesis of a highly stable, water-based metal organic frameworks (MOFs) for toxic gas capture

Alhashimi, Hashim

Continuous flow synthesis of a highly stable, water-based metal organic frameworks (MOFs) for toxic gas capture

Publication Date

July 27, 2026

Creator

Alhashimi, Hashim

University of Nottingham

Abstract

Metal-organic frameworks (MOFs) are highly porous materials composed of metal clusters or ions linked by organic ligands. This porosity makes them ideal candidates for capturing various harmful gases such CO2. Specific advantages (over conventional porous materials) include their tuneable structures and chemical functionalities, influencing their selectivity of gas adsorption. Through adjustments in their pore size, MOFs can be optimized to selectively capture targeted molecules while excluding others. However, scaling-up the synthesis of MOFs remains a major challenge for implementation in industrial application, as current synthesis methods limited by long reaction times, high costs, environmental concerns, and difficulties in maintaining consistent product quality. This thesis investigates the potential of continuous flow synthesis and performance of water-based, environmentally friendly MOFs, namely MOF-303, Mg-CUK-1 and, UiO-66(Ce), for gas capture applications, with primary focus CO2 adsorption. These materials also exhibit excellent thermal and structural stability up to 500 °C and 95% relative humidity. Using continuous flow synthesis, with simple solvents, paves the way for scale-up and minimizes energy input. For the first time, MOF-303 and DMF free UiO-66(Ce) were synthesised using hydrothermal flow synthesis at temperatures ranging from 25-250 °C with residence times of only 160-207 s, achieving average yields of 59 wt% and 79 wt%, respectively. Mg-CUK-1 was also successfully synthesised using flow synthesis at 250 °C with a residence time of 30 min. In additional, Mg-CUK-1 was synthesised using a microwave batch system in 7-25 s with an average yield of 51 wt%, representing the fastest reported procedure (to date) for Mg-CUK-1 synthesis, highlighting the potential for future microwave-assisted continuous flow synthesis. Synthesis optimisation demonstrated that molar ratios of KOH and NaOH, reaction temperature, residence time, and microwave power strongly influenced crystal morphology, structure, yield, and surface area. In general, increasing temperature reduced crystallinity and surface area, whilst shorter residence times promoted smaller, well-defined particles. However, the response to synthesis conditions was highly MOF-dependent. For Mg-CUK-1, increasing the specific energy from 1.54 to 2.79 kJ/g increased the yield from 14 wt% to 51 wt% at ultra-fast synthesis times. In contrast, increasing molar ratio of KOH from 6 to 8 equivalents reduced experimental yield from 64.8 wt% to 42.3 wt% and promoted particle agglomeration. Conversely, MOF-303 synthesised in batch showed increasing of average yield from 43 wt% to 82 wt% with an increase of molar ratio of NaOH from 1.5 to 3 equivalents with an improvement in crystallinity and more regular morphology. Under continuous-flow conditions, MOF-303 showed an average yield (59 wt%) and enhanced BET surface areas (up to 1120 m2/g) at 3 base equivalents and low preheating temperatures and moderate post heating (25:200 °C). UiO-66(Ce) was synthesised continuously only when using the H2PDC linker, due to its higher solubility in water compared to H2BDC and H2BDC-NH2. The poor solubility of H2BDC and H2BDC-NH2 resulted in low yields and poor crystallinity, with H2BDC-NH2 giving yields of only 18 wt%. In contrast, H2PDC enabled successful continuous-flow synthesis with a high yield of 79.1 wt%. However, increasing synthesis temperature from 50 to180 for the H2PDC based UiO-66 (Ce) reduced yields from 79.1wt% to 47.7 wt% and BET surface area from 836 m2/g to 674 m2/g. Optimising synthesis variables is clearly key to achieving the desired structural characteristics and adsorption performance of each MOF. All three MOFs exhibited compatible BET surface area with the reported results and maintained their CO2 adsorption capacities over 20 cycles. MOF-303 achieved a BET surface area of 1120 m2/g with a CO2 uptake of 17.6 wt% at 25 °C and 1 bar under pure CO2 (99.99 vol%). Mg-CUK-1 exhibited a BET surface area of 740 m2/g and a CO2 uptake of 10.4 wt%. UiO-66(Ce) showed BET surface areas of 836-905 m2/g with a CO2 uptake of 10.9 wt%. At industrially relevant concentrations of CO2 (15 vol% CO2 in N2), Mg-CUK-1, MOF-303, and UiO-66(Ce) achieved adsorption capacities of 2.2, 7.1, and 4.7 wt%, respectively. This work demonstrates that water-based continuous flow and microwave batch synthesis routes can produce structurally stable MOFs in relatively short reaction times while showing high CO2 adsorption uptakes. These results indicate that there are potentially environmentally friendly routes to future large-scale MOF production for all three MOFs.

Item Type

ethesis

Thesis Type

PhD

Supervisors

Lester, Edward

University of Nottingham

Tokay, Begum

University of Nottingham

Laybourn, Andrea

Leeds University

Keywords