Advances in reactive printing of MOF thin films

This thesis further develops the methodology of reactive printing towards more complex metal-organic framework (MOF) films. It also presents examples where the printed MOF films are utilised in catalysis and electrochemistry due to their specific functionalisation and chemistry. Each chapter highlights the effectiveness of reactive printing as a practical approach for developing MOF films directly applicable to various fields. The introductory chapter provides an overview of the development of films composed of microporous materials and comments on the different techniques for MOF deposition. The chapter ends by highlighting the transformative potential of reactive printing.

Chapter 3 focuses on enhancing the properties of a UiO-66-NH₂ by delivering and integrating the conductive polymer PEDOT in and around the particles via reactive printing. Setbacks in inkjet printing were overcome by moving to an extrusion-based system, which became the method of choice for the remainder of the thesis. SIMS and Raman analysis confirmed the incorporation of PEDOT, whilst PXRD and TGA-DSC were used to determine that the structure of the MOF was not damaged in the printing process. The results illustrate the successful incorporation of conductive polymers in MOF films, which in turn provides an increase in conductivity of several orders of magnitude.

Chapter 4 presents a comprehensive evaluation of the reactive extrusion printing (REP) method of HKUST-1. This chapter provides an in-depth investigation into the statistical analysis, modelling, and optimisation of the reactive printing process. Areal roughness parameters were chosen as the response values to guide the optimisation process. As a result, higher quality and more consistently reproducible films of HKUST-1 can now be obtained. Furthermore, the statistical modelling unveiled higher-order factors that had not been previously discovered.

Chapter 5 extends the reactive printing of HKUST-1 to create bimetallic composites from copper(II) and zinc(II). This was demonstrated through two approaches: doping the metal ink with zinc(II), or directly printing Zn-HKUST-1 on top of Cu-HKUST-1. The findings for the former indicate that printing only low concentrations of zinc(II) will still maintain the desired properties of pristine HKUST-1. The surface area diminished and crystal structure was not always maintained with higher amounts of zinc(II). The latter was the first attempt at reactive printing a heterogeneous film. While this was unsuccessful, the investigation sheds light on the challenges associated with reactive printing.

In Chapter 6, the focus shifts to printing with hydroxy- and nitro-functionalised surrogates of trimesic acid within the HKUST-1 structure. The hydroxy-doped HKUST-1 samples contained mesopores as indicated by gas sorption experiments. Their surface areas and structural defects moderately increased with doping and further diverged from their solvothermal counterparts. Conversely, the nitro-doped HKUST-1 composites maintained excellent chemical properties and matched their solvothermal counterparts at each level of dopant. The visual appearance and surface roughness of all the films in this chapter represented the ideal features of pristine HKUST-1 films showcased in Chapter 4.

Chapter 7 is the final results chapter and reports the first attempt at reactive printing a relatively new MOF, Cu-THQ. The ideal conditions for reactive printing Cu-THQ were established and printing was used to apply coatings onto copper foils, marking a departure from glass-based substrates in previous chapters. Cu-THQ had excellent adhesion to copper foil, and preliminary tests were conducted to prove this MOF film can facilitate the electrochemical reduction of carbon dioxide.

Chapter 8 provides concluding remarks and consolidates the findings and insights from previous chapters. It offers an overall summary of the achievements in and this and outlines potential future directions based on the trajectory of this research.