AN Oxford scientist who changed the world of chemistry has passed away at the age of 81.

Professor Peter Day FRS was an Oxford University lecturer, director of the Royal Institution of Great Britain and world-renowned researcher.

He born on August 20, 1938, in Wrotham in Kent and came to Wadham College, Oxford in 1957 to study chemistry as an open scholar from Maidstone Grammar School.

He described his time there as 'life changing', and went on to become a prominent member of the science community across the world.

He was an undergraduate and then a D.Phil. student in Chemistry at Wadham College and completed a D.Phil. thesis entitled Light Induced Charge Transfer in Solids under the supervision of Bob Williams in 1965.

He was a junior research fellow (1963–65) at St John’s College, and then official fellow and tutor in inorganic chemistry (1965–88) at St John’s and a university lecturer.

Prof Day defined a new field in chemistry – the chemistry of mixed valent compounds, where, contrary to what we learn at school, one chemical element in a compound has more than one charge associated with it.

This concept is now used across modern science, and underpins our understanding of how cells harvest the energy they need to live.

The idea is also crucial in the process which produced the first modern synthetic pigment, Prussian blue.

Prof Day was director of the Royal Institution of Great Britain from 1991-98 where he was the Fullerian Professor of Chemistry, and played an important role in its mission of popularising science.

This mission is encapsulated in the Christmas Lectures which the RI broadcasts annually on television.

He was director of the Institut Laue-Langevin in Grenoble in 1988 prior to this, an international centre for neutron scattering which enabled work by countless physicists, chemists and biologists.

He had a lifelong association with the Department of Chemistry at the University of Oxford, and St. John’s College.

Since 2008 he was an Emeritus Professor of Chemistry at the University College of London.

He was elected a fellow of the Royal Society 1986 and received numerous awards from learned societies around the world.

His contribution to chemistry in the UK was so profound that the Royal Society of Chemistry named a major award in the chemistry of advanced materials after him, the Peter Day award in Materials Chemistry in 2008, reflecting his championing of this discipline.

Prof Day also had a love of travel, particularly to France, good food and wine, and tending to his beautiful garden.

He passed away peacefully at his home in Marsh Baldon on May 19, following his wife Frances who died in 2018.

He is survived by his two children Alison and Christopher and five grandchildren.

His family said: "We will miss him enormously and his encyclopaedic knowledge of anything and everything, but will try and stay true to some of his last words: 'you can never know too much'.