Black carbon traces of human activities in stalagmites from Turkey

Speleothems are recognized as sensitive recorders of climatic fluctuations in the past and provide precisely dated and highly resolved environmental records. However, their potential as an archaeological archive is not fully acknowledged yet. Here we present several stalagmites containing soot and charcoal layers from various caves in Turkey and provide evidence that these black carbon layers are directly related to human activity. The archaeological artefacts found in Tabak and Kocain caves in SW Turkey support the linkage between soot and charcoal layers existence and human activity in the caves. For this study, we focus on stalagmites from Tabak and Kocain cave. To explore the age and nature of the soot and charcoal layers within stalagmites Ta-9, Ta-10 and Ko-1, Uranium series dating, scanning electron microscope (SEM) and thin section analyses were performed. The episodic soot and charcoal deposition in stalagmites Ta-9 and Ta-10 occurred between 7424 +/- 225 yr BP and 6670 +/- 218 yr BP while the soot and charcoal layers in stalagmite Ko-1 formed between 2830 +/- 189 yr BP and 470 +/- 56 yr BP. In combination with the archaeological inventory in Tabak Cave, the soot and charcoal layers within stalagmites Ta-9 and Ta-10 show that the cave was used repeatedly as a burial site during Chalcolithic period. In Kocain Cave was also used repeatedly between the Iron Age and Medieval Period, most likely for ritual activities and for providing animals with water from a small spring in the entrance to the cave. The soot and charcoal layers within stalagmites from Turkey prove that speleothems are also important as archaeological archives

Building an iron chromophore incorporating prussian blue analogue for photoelectrochemical water oxidation

The replacement of traditional ruthenium-based photosensitizers with low-cost and abundant iron analogs is a key step for the advancement of scalable and sustainable dye-sensitized water splitting cells. In this proof-of-concept study, a pyridinium ligand coordinated pentacyanoferrate(II) chromophore is used to construct a cyanide-based CoFe extended bulk framework, in which the iron photosensitizer units are connected to cobalt water oxidation catalytic sites through cyanide linkers. The iron-sensitized photoanode exhibits exceptional stability for at least 5 h at pH 7 and features its photosensitizing ability with an incident photon-to-current conversion capacity up to 500 nm with nanosecond scale excited state lifetime. Ultrafast transient absorption and computational studies reveal that iron and cobalt sites mutually support each other for charge separation via short bridging cyanide groups and for injection to the semiconductor in our proof-of-concept photoelectrochemical device. The reorganization of the excited states due to the mixing of electronic states of metal-based orbitals subsequently tailor the electron transfer cascade during the photoelectrochemical process. This breakthrough in chromophore-catalyst assemblies will spark interest in dye-sensitization with robust bulk systems for photoconversion applications

Building an iron chromophore incorporating prussian blue analogue for photoelectrochemical water oxidation

Invited for the cover of this issue is the Ferdi Karadas and Ekmel Ozbay groups at Bilkent University and co-workers. The image presents an utopic city in Iron Age, which is powered by an iron photosensitizer that bridges semiconductor buildings (TiO2 nanowires) and the catalyst (cobalt site). Read the full text of the article at 10.1002/chem.202100654