You will be shown an abstract from a biomedical research paper. Given this abstract, your task is to extract all unique entities of the following types: ["Chemical"].

Please return the output as a JSON object of the format: {"Chemical": ["Arsenic", ...]}. The keys should be entity types and values should be lists of extracted entities belonging to the corresponding type. If you cannot find entities belonging to a specific type, the value should be [].

Only output the JSON object and do not include any additional text.

Abstract:

Analysis of visible-light-active Sn(ii)-TiO2 photocatalysts. The influence of Sn(ii) species on TiO2 is investigated. The absorption spectra of these materials are red-shifted by 115 nm to the visible region of the solar spectrum compared with P25 TiO2. This prominent red-shift is attributed to the interaction of Sn(ii) 5s orbitals with the TiO2 decreasing the band gap of TiO2 by raising its valence band. The tin oxidation state and the materials electronic structure are evaluated using Mössbauer spectroscopy and valence band X-ray photoelectron spectroscopy respectively. These materials are active for sacrificial photo-generation of hydrogen in visible light.
{"Chemical": ["P25 TiO2", "TiO2", "hydrogen", "tin", "Sn(ii)"]}