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:

Photocatalytic properties of graphdiyne and graphene modified TiO₂: from theory to experiment. The chemical structure and electronic properties of two-dimensional (2D) carbon-supported TiO₂, TiO₂-graphdiyne, and TiO₂-graphene composites have been studied by first-principles density functional theory. Calculation results show that TiO₂(001)-graphdiyne composites possess superior charge separation and oxidation properties, having the longest lifetimes of photoexcited carriers among all of the 2D composites containing TiO₂ of different facets. Our experimental results further proved that TiO₂(001)-graphdiyne composites could be a promising photocatalyst. For photocatalytic degradation of methylene blue, the rate constant of the TiO₂(001)-graphdiyne composite is 1.63 ± 0.15 times that of the pure TiO₂(001) and 1.27 ± 0.12 times that of the TiO₂(001)-graphene composite.
{"Chemical": ["methylene blue", "TiO\u2082", "carbon", "TiO\u2082-graphene", "TiO\u2082-graphdiyne", "graphene", "graphdiyne"]}