Since the discovery of its photocatalytic activity under UV light, TiO 2 has been widely studied as a photocatalyst in applications such as water splitting and purification.[1] As pristine TiO 2 only absorbs UV light, much effort has been devoted to developing visible-light-active TiO 2 photocatalysts that can make use of both UV and visible radiation. Many strategies, including metal-ion [2] and nonmetal doping, [3] have been proposed to extend the absorption of TiO 2 to the visible spectrum, but, to date, new materials have typically suffered from low doping concentration and/or low stability against photocorrosion.[3d, 4] Noble-metal nanoparticles such as Au and Ag have also been used to enhance the activity of photocatalysts in visible light because of their plasmonic properties.[5] In any case, an improved absorption of photons may not necessarily guarantee significantly better photocatalytic performance because the efficiency of a photocatalyst is also determined by charge separation and transport. As most excited charges may recombine and quench before reaching the surface, small grain size and high crystallinity would be desirable for enhancing charge-separation efficiency that would result in a reduced migration distance of charges and, consequently, in a lower recombination rate.[6] Additionally, metal decoration has also been shown to enhance charge separation in TiO 2 photocatalysts by serving as an electron reservoir. [7] It is therefore expected that a composite of small doped TiO 2 nanocrystals decorated with metal nanoparticles may be a powerful photocatalyst, as all the features discussed above are combined. However, the incompatibility between the synthesis, doping, and decoration procedures means that the production of such nanocomposites has remained a great challenge.We report herein the design and synthesis, by combining simple sol-gel and calcination processes, of a highly efficient, stable, and cost-effective TiO 2 -based photocatalyst with the desired properties mentioned above. The new catalyst has a sandwich structure that comprises a SiO 2 core, a layer of gold nanoparticles (AuNPs), and a doped TiO 2 nanocrystalline shell. The sol-gel process allows for the convenient incorporation of AuNPs into the catalyst with controlled loading and location. TiO 2 is doped with both N and C using an unconventional method that involves introducing 3-aminopropyl-triethoxysilane (APTES), which originally acts as a ligand for immobilization of AuNPs on the surface of the SiO 2 support, but upon subsequent decomposition at high temperature serves as a source of both N and C for doping. Compared to traditional Au/TiO 2 composites, in which AuNPs are loosely attached to the surface of TiO 2 such that they are unstable during calcination and subsequent photocatalysis, the sandwich structures with the AuNPs embedded inside a TiO 2 matrix protects the former from moving together and coagulating.[8] The encapsulation also increases the contact area between the AuNPs and the TiO 2 matrix, and therefore allow...

Since the discovery of its photocatalytic activity under UV light, TiO 2 has been widely studied as a photocatalyst in applications such as water splitting and purification.[1] As pristine TiO 2 only absorbs UV light, much effort has been devoted to developing visible-light-active TiO 2 photocatalysts that can make use of both UV and visible radiation. Many strategies, including metal-ion [2] and nonmetal doping, [3] have been proposed to extend the absorption of TiO 2 to the visible spectrum, but, to date, new materials have typically suffered from low doping concentration and/or low stability against photocorrosion.[3d, 4] Noble-metal nanoparticles such as Au and Ag have also been used to enhance the activity of photocatalysts in visible light because of their plasmonic properties.[5] In any case, an improved absorption of photons may not necessarily guarantee significantly better photocatalytic performance because the efficiency of a photocatalyst is also determined by charge separation and transport. As most excited charges may recombine and quench before reaching the surface, small grain size and high crystallinity would be desirable for enhancing charge-separation efficiency that would result in a reduced migration distance of charges and, consequently, in a lower recombination rate.[6] Additionally, metal decoration has also been shown to enhance charge separation in TiO 2 photocatalysts by serving as an electron reservoir. [7] It is therefore expected that a composite of small doped TiO 2 nanocrystals decorated with metal nanoparticles may be a powerful photocatalyst, as all the features discussed above are combined. However, the incompatibility between the synthesis, doping, and decoration procedures means that the production of such nanocomposites has remained a great challenge.We report herein the design and synthesis, by combining simple sol-gel and calcination processes, of a highly efficient, stable, and cost-effective TiO 2 -based photocatalyst with the desired properties mentioned above. The new catalyst has a sandwich structure that comprises a SiO 2 core, a layer of gold nanoparticles (AuNPs), and a doped TiO 2 nanocrystalline shell. The sol-gel process allows for the convenient incorporation of AuNPs into the catalyst with controlled loading and location. TiO 2 is doped with both N and C using an unconventional method that involves introducing 3-aminopropyl-triethoxysilane (APTES), which originally acts as a ligand for immobilization of AuNPs on the surface of the SiO 2 support, but upon subsequent decomposition at high temperature serves as a source of both N and C for doping. Compared to traditional Au/TiO 2 composites, in which AuNPs are loosely attached to the surface of TiO 2 such that they are unstable during calcination and subsequent photocatalysis, the sandwich structures with the AuNPs embedded inside a TiO 2 matrix protects the former from moving together and coagulating.[8] The encapsulation also increases the contact area between the AuNPs and the TiO 2 matrix, and therefore allow...

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The supercapacitive behavior of the metallic cobalt recycled from Li-ion batteries has been studied in this work. The reversibility of both redox process (Co II /Co III ) and (Co III /Co IV ) in KOH 6 mol L -1 is very high and promising for capacitive applications in electrochemical devices. The specific capacitances calculated from cyclic voltammetry and electrochemical impedance spectroscopy show a good agreement, giving the value of 625 Fg -1 . The electrode morphology presents a high porosity, thus an electrical equivalent circuit composed of two parallel resistance and capacitance elements in series was proposed. The specific capacitance values calculated from charge/discharge curves at 0.23 and 2.3 mA/cm 2 are 601 and 384 Fg -1 , respectively. Thereby, it was observed that metallic cobalt recycled from ion-Li batteries is compatible with other supercapacitive materials. This shows that cobalt recycling from Li-ion batteries is economically and environmentally viable for application in supercapacitor devices.

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