Final Report Summary - SUSNANO (Sustainable Nanocomposites for Photocatalysis)
Sustainable generation of energy is arguably the biggest challenge facing society. Investment into energy research is considerable (e.g. ~€2.5billion in EU FP7), with one key goal being the capture of solar energy. Production of electricity from sunlight (photovoltaics) is perhaps the most well-known option, but is restricted to less than 0.1% of the current market due to cost and problems with long term storage. An alternative approach, inspired by photosynthesis, is the use of sunlight to generate storable, transportable chemical fuels. These can include hydrocarbons from carbon dioxide and hydrogen from water splitting. While considerable advances have been made in artificial photosynthesis, efficient visible light catalysts are still a major challenge. Furthermore, any feasible large-scale system must be based on abundant materials and facile fabrication processes. This is emphasized in a recent White Paper prepared by the UK, US, Japanese, German and Chinese Chemical Societies. They state the need for, “new catalysts and materials from low-cost, earth-abundant elements that can be used to build affordable, sustainable solar energy transformation and storage systems”.
In our recent EU project called ‘SusNano’ we have been working towards the sustainable synthesis of nanocomposites. We initially aimed this towards the synthesis of WC/TiO2 nanocomposites but we have branched out into the more general synthesis of metal carbides for catalysis. This can be divided into three main directions, including
1. Synthesis of metal carbide nanocomposites
2. Studying the mechanisms of formation of metal carbides from biopolymers
3. Templated synthesis of graphitic carbon nitride and investigation of photocatalytic properties.
In the synthesis of metal carbide nanocomposites, we have focused on tungsten carbide and iron carbide. We discovered that the synthesis of tungsten carbide was not trivial and it took a lot of work to optimize the sol-gel synthesis to produce pure WC rather than W or other carbide phases. As part of this project, we have produced a phase diagram for the type of W-C phases produced from a range of precursors and conditions. This research is in preparation for publication. Alongside this research, we have focused on the synthesis of dispersible metal carbide nanoparticles. In the initial SusNano proposal we were keen to produce metal carbides from sol-gel precursors and decorate these with metal oxides. But having attempted some experiments and discussed with various other colleagues, we quickly discovered it would be more practical (and more generally useful) if we could produce dispersible metal carbide nanoparticles that could be combined with a second material for support/catalyst or catalyst/cocatalyst combinations. Part of the reason for this is that we were unable to avoid the production of excess carbon via sol-gel methods. We have recently demonstrated that it is possible to produce dispersible metal carbide nanoparticles using magnesium oxide as a cast to prevent sintering. This paper is in preparation.
Another challenge we were keen to address was the mechanism of formation of metal carbide nanoparticles from sol-gel precursors. Since we had discovered many challenges with sol-gel chemistry such as limited control over particle size, we were keen to understand the mechanism in order to optimize this synthesis. We used in situ synchrotron X-ray diffraction (at Diamond Light Source) to study the formation of iron carbide nanoparticles from gelatin (Chem. Mater., 2015, 27, 5094). These results produced two key observations. Firstly, the formation of Fe3C from gelatin proceeds via iron oxide, Fe3N and finally FexNyCz intermediates. Secondly, we observed a significant particle size increase in the oxide-nitride transition, 2 nm to 20 nm average diameter as estimated using the Scherrer equation. This is important as it shows the key particle growth step and we hope now to be able to minimize particle growth by controlling heating during that step. We also used small angle neutron scattering and rheology to understand why sol-gel precursors for metal carbides form foam-like structures (J. Mater. Chem. A, 2017, 5, 11644). In this study, we were able to show how metals change the structure of a biopolymer in solution, changing the viscoelastic properties. This change in the viscoelastic properties is what allows the system to stabilize bubbles as they form during drying. Understanding the formation of the foam is important as it could lead on to the production of ceramic foams generally for catalysis. Indeed, we have several projects on producing foam like structures for example for electrocatalysis.
Our final main focus during the SusNano project was the synthesis of graphitic carbon nitride. This was directed towards the photocatalysis aspect of the SusNano project. We demonstrated that biopolymers, air bubbles and MgO nanoparticles could be combined in a ‘triple templating’ approach to make porous graphitic carbon nitride. The three templates produce meso, macro and micropores respectively. The advantage of this is that it maximizes both surface area and also accessibility of the surface of this important photocatalyst. The resulting materials show promising photocatalytic activity (APL Mater., 2016, 4, 015706).
In addition to our research advances, we have also contributed to knowledge generation and dissemination by organizing and chairing a symposium (RSC postgraduate symposium on nanotechnology) and publishing two review articles (Mater. Horiz. 2016, 3, 91; J. Mater. Chem. A, 2015, 3, 14081). It should also be noted that knowledge generated in this project has led to diverse future research directions. For example, from building our expertise on biopolymer-templating of ceramics, our group received funding from DSTL (Defence Science and Technology Laboratory) to develop foam-like boron carbide for armour.
Further detail on the projects can be found in the relevant publications and also on the project website (https://schneppgroup.wordpress.com/research/susnano/)
In our recent EU project called ‘SusNano’ we have been working towards the sustainable synthesis of nanocomposites. We initially aimed this towards the synthesis of WC/TiO2 nanocomposites but we have branched out into the more general synthesis of metal carbides for catalysis. This can be divided into three main directions, including
1. Synthesis of metal carbide nanocomposites
2. Studying the mechanisms of formation of metal carbides from biopolymers
3. Templated synthesis of graphitic carbon nitride and investigation of photocatalytic properties.
In the synthesis of metal carbide nanocomposites, we have focused on tungsten carbide and iron carbide. We discovered that the synthesis of tungsten carbide was not trivial and it took a lot of work to optimize the sol-gel synthesis to produce pure WC rather than W or other carbide phases. As part of this project, we have produced a phase diagram for the type of W-C phases produced from a range of precursors and conditions. This research is in preparation for publication. Alongside this research, we have focused on the synthesis of dispersible metal carbide nanoparticles. In the initial SusNano proposal we were keen to produce metal carbides from sol-gel precursors and decorate these with metal oxides. But having attempted some experiments and discussed with various other colleagues, we quickly discovered it would be more practical (and more generally useful) if we could produce dispersible metal carbide nanoparticles that could be combined with a second material for support/catalyst or catalyst/cocatalyst combinations. Part of the reason for this is that we were unable to avoid the production of excess carbon via sol-gel methods. We have recently demonstrated that it is possible to produce dispersible metal carbide nanoparticles using magnesium oxide as a cast to prevent sintering. This paper is in preparation.
Another challenge we were keen to address was the mechanism of formation of metal carbide nanoparticles from sol-gel precursors. Since we had discovered many challenges with sol-gel chemistry such as limited control over particle size, we were keen to understand the mechanism in order to optimize this synthesis. We used in situ synchrotron X-ray diffraction (at Diamond Light Source) to study the formation of iron carbide nanoparticles from gelatin (Chem. Mater., 2015, 27, 5094). These results produced two key observations. Firstly, the formation of Fe3C from gelatin proceeds via iron oxide, Fe3N and finally FexNyCz intermediates. Secondly, we observed a significant particle size increase in the oxide-nitride transition, 2 nm to 20 nm average diameter as estimated using the Scherrer equation. This is important as it shows the key particle growth step and we hope now to be able to minimize particle growth by controlling heating during that step. We also used small angle neutron scattering and rheology to understand why sol-gel precursors for metal carbides form foam-like structures (J. Mater. Chem. A, 2017, 5, 11644). In this study, we were able to show how metals change the structure of a biopolymer in solution, changing the viscoelastic properties. This change in the viscoelastic properties is what allows the system to stabilize bubbles as they form during drying. Understanding the formation of the foam is important as it could lead on to the production of ceramic foams generally for catalysis. Indeed, we have several projects on producing foam like structures for example for electrocatalysis.
Our final main focus during the SusNano project was the synthesis of graphitic carbon nitride. This was directed towards the photocatalysis aspect of the SusNano project. We demonstrated that biopolymers, air bubbles and MgO nanoparticles could be combined in a ‘triple templating’ approach to make porous graphitic carbon nitride. The three templates produce meso, macro and micropores respectively. The advantage of this is that it maximizes both surface area and also accessibility of the surface of this important photocatalyst. The resulting materials show promising photocatalytic activity (APL Mater., 2016, 4, 015706).
In addition to our research advances, we have also contributed to knowledge generation and dissemination by organizing and chairing a symposium (RSC postgraduate symposium on nanotechnology) and publishing two review articles (Mater. Horiz. 2016, 3, 91; J. Mater. Chem. A, 2015, 3, 14081). It should also be noted that knowledge generated in this project has led to diverse future research directions. For example, from building our expertise on biopolymer-templating of ceramics, our group received funding from DSTL (Defence Science and Technology Laboratory) to develop foam-like boron carbide for armour.
Further detail on the projects can be found in the relevant publications and also on the project website (https://schneppgroup.wordpress.com/research/susnano/)