Molecular‑scale ageing of biochar in soils: evolution of functionality, performance, and implications for carbon credits

About the Project

A PhD studentship is available in the groups of Dr Valentina Erastova, School of Chemistry, co-supervised by Prof Saran Sohi, School of Geosciences, University of Edinburgh, in collaboration with Black Bull Biochar (www.blackbullbiochar.com).

Biochar is increasingly deployed as a negative-emission technology because it can stabilise carbon in soils over decadal-to-centennial timescales. However, current carbon accounting and certification frameworks often rely on bulk proxies (e.g., elemental ratios and simple lifetime assumptions) that do not capture how biochar chemistry and surface properties evolve during real soil ageing. These molecular-scale changes are also central to biochar’s value as a soil amendment, influencing nutrient retention, water holding capacity, and interactions with dissolved organics and minerals.

This interdisciplinary PhD will combine experimental characterisation (School of GeoSciences, Prof Saran Sohi) with atomistic molecular modelling and simulation (School of Chemistry, Dr Valentina Erastova) to build a mechanistic understanding of biochar ageing in soils. The project will:

1. characterise fresh and soil-aged biochars to quantify changes in bulk composition and surface functional groups;
2. develop and validate representative atomistic models of fresh and aged biochars; and
3. use molecular simulations to probe how evolving functionality controls stability and interactions with key soil components, including minerals and dissolved organic matter.

Working with Black Bull Biochar (industrial partner), the research will translate molecular insights into functionality-based indicators of durability and performance, supporting improved methodologies for high-integrity carbon removal credits and informing the rational design and certification of biochars for long-term soil use. The student will gain training across molecular simulation, environmental/soil chemistry methods, and industry-facing carbon accounting/MRV, including a placement with the partner company.

Key research questions

1. How does biochar surface chemistry (“functionality”) evolve during soil ageing at the molecular scale? (e.g., what oxygen‑containing functional groups form, how their abundance/distribution changes, and how this differs between fresh and soil‑aged biochars)
2. How does this evolving functionality control biochar durability and long‑term carbon permanence in soils? (i.e., which molecular‑scale changes increase or decrease stability over time)
3. How do ageing‑driven changes in functionality alter biochar interactions with core soil components? (especially dissolved organic matter and mineral surfaces, including how mineral association changes which functional groups are exposed/accessible)
4. How can we translate molecular‑scale descriptors into measurable, scalable indicators of “biochar quality” and durability? (linking atomistic/spectroscopic functionality to current bulk proxies and to permanence metrics relevant for certification)
5. How does functional evolution affect biochar performance as a soil amendment/fertiliser component? (impacts on nutrient interactions/retention, water affinity, and broader agronomic value as ageing progresses)

We welcome applications from motivated students with a strong degree in Chemistry, Materials Science, Chemical Engineering, Environmental/Geoscience, Physics or a related subject, who enjoy quantitative problem-solving and are interested in molecular-scale surface chemistry and sustainable technologies (biochar, soils, carbon removal). The project suits applicants who can work across disciplines and communicate well with academic and industrial partners; experience in molecular simulation, programming/data analysis (e.g. Python), or HPC is advantageous but not essential.

In the first instance, the initial application of cover letter and CV should be directed to Dr Valentina Erastova: valentina.erastova@ed.ac.uk

The position will remain open until filled. A closing date may be added at a later date.

Funding Notes

The studentship is fully funded for 42 months by the University of Edinburgh and covers tuition fees and an annual stipend at the UKRI rate, for 2025-26 this is £20,780 per annum, for a candidate satisfying EPSRC residency criteria.