Exploring the potential of nanoporous carbons Nanoporous carbons are capable of efficiently absorbing photons, which can then be converted into photochemical reactions in confined nanopore spaces. We spoke to Dr Conchi Ania about the work of the PHOROSOL project in investigating how metal-free nanoporous carbons can be modified to harvest light, which could open up wider possibilities in various fields. Since the ability
of some metallic oxides to absorb light and decompose water was first demonstrated, a lot of attention in research has been focused on modifying and tailoring the characteristics of different materials to improve their light absorption features. In particular, scientists are exploring how to achieve higher efficiencies and improve the stability of materials through tuning their composition, size, or structure. Based at the French National Centre for Scientific Research (CNRS), Dr Conchi Ania is Principal Investigator of the PHOROSOL project, an ERC-backed initiative investigating the potential use of light responsive nanoporous carbons. “We want to explore the ability of these materials to absorb light and to integrate them in various applications,” she outlines. The disruptive approach of the project is based on exploiting the potentialities of earth-abundant and metal-free carbons with well-defined nanopores for photochemical applications. “We have to address two main challenges; the first is that most of the photochemistry is based on non-porous materials, whereas we investigate the fate of the light/solid interactions upon nanoconfinement. The second is that carbon materials are strong absorbers themselves, thus it is a challenge to reach efficiencies comparable to those of common materials,” says Dr Ania. The ambition of PHOROSOL is to develop more efficient materials to boost technologies for light energy utilization, profiting from the dual nature of nanopore carbons as strong light absorbing materials with unique electronic features and nanoporosity. They are also commercially available at a relatively low cost in comparison to most competitors.
PHOROSOL project Porous carbons are some of the oldest materials known to human beings with a long history of applications going back to BC times (inks in cave paintings, Chinese ink, water purification, medicine). Their fabrication has ancient origins, and current manufacturing processes are well known and based on work carried out more than a century ago. However, these conventional methods do not allow perfect control of the pores in the full nanometric scale; this has triggered intensive research efforts, with the aim of developing new methods to obtain porous
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carbons with perfectly defined pore architectures. “Designing the perfect material for a given application is complex, as the properties must be tuned/tailored to a certain extent to fulfill the requirements of the specific application; and for this, understanding of the fundamentals of the technological process itself becomes crucial,” explains Dr Ania. Researchers are investigating novel approaches to control and tune carbon materials with ad-hoc nanopore voids (nanopores are very small in size, below 100 nanometres in length), while adjusting other properties, such as structure, chemical composition and morphology, that are essential to improving photochemical performance. An abundantly available set of materials is being considered, which includes gels and grapheneoxide frameworks.
when photochemical reactions occur in the confined space of the nanopores,” says Dr Ania. “We are not only handling these pores, we are also handling the materials. A large amount of light is absorbed directly by the matrix itself, and is not directly used in the photochemical reaction.” Another difficulty is the lack of consensus and collective understanding of how to evaluate photonic efficiencies in all type of materials. This is a central part of the project’s research agenda, along with modifying these materials and tailoring their properties. “In order to understand the interactions of light in the confined space, we have to modify the average nanopore size in these materials,” continues Dr Ania. Understanding the properties of these nanoporous carbons and how their characteristics can be modified is an important step towards the objective of
We have seen that we can tune the amount of light absorbed and the type (in terms of energy or wavelength) by modifying the composition. This is important to control the amount of energy that can be harvested and that will define the photochemical reaction where the material can be applied. It is the porosity at the nanoscale level that confers extremely interesting properties to porous carbons, as it is their photochemical activity that is being explored in this project. Such photochemical features have been reported for graphene, whereas the behaviour of nanoporous carbons (which are disordered and defective graphene layers) has not been studied. Dr Ania’s work has shown that it is possible to harvest light in these materials and to promote photoinduced reactions inside the pores. This has opened up new perspectives for the old, black nanoporous carbons (very often considered the ‘ugly duckling’ of the carbon family). Evaluating the performance of these materials using standard methods is complex. “The difficult part is determining and quantifying how light interacts in the confined space of the nanopores,” explains Dr Ania. This is mainly due to the difficulties associated with measuring the photons that have been absorbed and discriminating the fraction of light reaching the carbon surface and the pores, from that absorbed by the carbon matrix itself. “One of the big goals in the project is to understand what happens
bringing them to wider application. “In some contexts there are a few mechanisms that are well understood, but the overall picture is highly complex,” explains Dr Ania. By building a deeper understanding of the effect of pore size and chemical composition on photoactivity, researchers hope to lay the foundations for a more structured approach in future. “We hope to develop a portfolio of carbon materials with known photoactivity, defining as many physico-chemical features as possible,” says Dr Ania. While a great deal of progress has been made in this respect over the course of the project so far, there is still significant scope to further improve efficiency, which will remain an important topic in Dr Ania’s research. The composition of these materials is another major factor in terms of how effectively and efficiently the carbon nanopores absorb light. “We have seen that we can tune both the amount of light absorbed and the type (in terms of energy or wavelength) by modifying the composition,” outlines Dr Ania. This is important in terms of controlling the amount of energy that can be harvested, which will define the photochemical
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