Silver-loaded nitrogen-doped yolk-shell mesoporous TiO2 hollow microspheres (Ag-N-TiO2-YSM) were prepared by employing acetic acid as the hollowing controller and triethanolamine as the N source for the first time. Ag nanoparticles (NPs) were uniformly deposited by a simple in situ photo-reduction method, which can prevent the aggregation of Ag NPs. The efficiency of the as-prepared samples was investigated by monitoring the degradation of rhodamine B and ciprofloxacin under visible light irradiation. The experimental results indicate that N-doped yolk-shell mesoporous TiO2 hollow microspheres show higher photocatalytic activity than P25 TiO2 under visible light irradiation because of N doping and the unique yolk-shell structure. In addition, Ag-N-TiO2-YSM shows enhanced activity compared with N-TiO2-YSM due to the SPR absorption of silver NPs and the fast generation, separation and transportation of the photogenerated carriers. Moreover, the Ag contents can affect the photocatalytic activity of the Ag-N-TiO2-YSM composite. A suitable amount of Ag deposition gives the highest photocatalytic activity. A higher loading does not improve the photocatalytic activity of N-TiO2-YSM further. The active species generated in the photocatalytic system were also investigated. Based on our experimental results, a possible photocatalytic mechanism was proposed. The strategy presented here gives a promising route towards the development of delicate metal@hollow semiconductor composites for many applications in photocatalysis.

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Sponge-based materials have recently gained much attention in the field of oil/water separation due to their easy fabrication, recyclability, environmental friendliness, and low cost. Commercial sponges such as melamine sponge, polyurethane sponge, graphene-based sponge, and cellulose sponge have large surface area and high absorption capability, but they are hydrophilic/oleophilic (absorb both oil and water) in nature, which makes them not applicable in oil/water separation. To make them applicable in oil/water separation, the sponges have been modified with low surface energy materials and nano/micro hierarchical roughness, hence changing their wettability to superhydrophobicity/superoleophilicity (absorb oil and repel water). These materials include organosilicons, carbon-based materials, oxides, and metal−organic frameworks (MOFs) among others. We summarized the modifying materials for the fabrication of superhydrophobic/superoleophilic sponges used in oil/water separation even under harsh conditions such as pH-universal, high temperature, and so on. Furthermore, ideas for future application of the coating sponge materials in the field are discussed.

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