“…Nevertheless, critical problems are still unresolved, such as the instability of the metal-doped titania, relatively low absorption coefficiency of the nonmetal-doped titania in the visible light region, toxicity and self-photodegradation of the organic sensitiser [3,15]. Thus, exploring the high efficiency photocatalysts with narrow band gap which function in the visible light region has attracted a remarkable attention [16,17].…”