Metal oxide semiconductors hold great promise for applications in energy conversion and storage, environmental remediation, optoelectronics, memory, light emission and other areas, but critical factors such as the high rate of charge-carrier recombination and limited light absorption have restricted more practical and viable applications. The remarkable ability of plasmonic noble metals to concentrate and scatter visible light has found a versatile potential in harvesting and converting solar energy. Plasmonic nanostructures of noble metals in combination with semiconductors offer a promising future for the next generation of energy needs. The overlap of the spectral range of the incident photon with absorbance wavelength of the semiconductor and the surface plasmon bands of the plasmonic metal provides a useful tool to predict the enhancement in optical and electrical properties of hybrid semiconductor-noble metal nanostructures. Here we make an attempt to comprehensively review the role of plasmonic noble metals in the enhanced functions for photocatalytic activity, photoenergy conversion in DSSCs, enhanced light emission and photochromatism. We mainly focus on the improvement of performance in TiO2 or ZnO in combination with noble metals on representative photophysical applications. The mechanism behind their interaction with light is discussed in detail in each section.

This work is focused on the development of a surface plasmon-induced visible light active photocatalyst system composed of silica–titania core–shell (SiO2@TiO2) nanostructures decorated with Au nanoparticles (Au NPs). The influence of size and distribution of Au NPs on photocatalysis, its fabrication methods, and exploration of the mechanism of visible light activity were investigated. A favorable architecture of SiO2 beads with a thin layer of TiO2 was decorated with Au NP arrays having different size and areal density. Surface modification of SiO2@TiO2 leads to a viable and homogeneous loading of Au NPs on the surface of TiO2, which renders visible light-induced photocatalytic activity on the whole TiO2 surface. An optimized system employing Au NP arrays with 15 nm size and 700/μm2 density showed best catalytic efficiency due to a synergistic effect of the firm contact between Au NPs and TiO2 and efficiently coupled SPR excitation. A brief mechanism relating the electron transfer from surface-plasmon-stimulated Au NPs to the conduction band of TiO2 is proposed.

We report an efficient and environmentally benign biomimetic mineralization of TiO(2) at the graphitic carbon surface, which successfully created an ideal TiO(2)/carbon hybrid structure without any harsh surface treatment or interfacial adhesive layer. The N-doped sites at carbon nanotubes (CNTs) successfully nucleated the high-yield biomimetic deposition of a uniformly thick TiO(2) nanoshell in neutral pH aqueous media at ambient pressure and temperature and generated N-doped CNT (NCNT)/TiO(2) core/shell nanowires. Unlike previously known organic biomineralization templates, such as proteins or peptides, the electroconductive and high-temperature-stable NCNT backbone enabled high-temperature thermal treatment and corresponding crystal structure transformation of TiO(2) nanoshells into the anatase or rutile phase for optimized material properties. The direct contact of the NCNT surface and TiO(2) nanoshell without any adhesive interlayer introduced a new carbon energy level in the TiO(2) band gap and thereby effectively lowered the band gap energy. Consequently, the created core/shell nanowires showed a greatly enhanced visible light photocatalysis. Other interesting synergistic properties such as stimuli-responsive wettabilites were also demonstrated.

In this contribution we have developed TiO inverse opal based photoelectrodes for photoelectrochemical (PEC) water splitting devices, in which Au nanoparticles (NPs) and reduced graphene oxide (rGO) have been strategically incorporated (TiO@rGO@Au). The periodic hybrid nanostructure showed a photocurrent density of 1.29 mA cm at 1.23 V vs RHE, uncovering a 2-fold enhancement compared to a pristine TiO reference. The Au NPs were confirmed to extensively broaden the absorption spectrum of TiO into the visible range and to reduce the onset potential of these photoelectrodes. Most importantly, TiO@rGO@Au hybrid exhibited a 14-fold enhanced PEC efficiency under visible light and a 2.5-fold enrichment in the applied bias photon-to-current efficiency at much lower bias potential compared with pristine TiO. Incident photon-to-electron conversion efficiency measurements highlighted a synergetic effect between Au plasmon sensitization and rGO-mediated facile charge separation/transportation, which is believed to significantly enhance the PEC activity of these nanostructures under simulated and visible light irradiation. Under the selected operating conditions the incorporation of Au NPs and rGO into TiO resulted in a remarkable boost in the H evolution rate (17.8 μmol/cm) compared to a pristine TiO photoelectrode reference (7.6 μmol/cm). In line with these results and by showing excellent stability as a photoelectrode, these materials are herin underlined to be of promising interest in the PEC water splitting reaction.

We developed plasmonic dye-sensitized solar cells (DSSCs) with tailor-designed Au-TiO₂ nanostructures integrated into the photoanode. Mutually antagonistic Au-TiO₂ core-shell structures supported on SiO₂ spheres (SiO₂@TiO₂@AuNP and SiO₂@AuNP@TiO₂) were prepared and incorporated as additives into the photoanodes of the DSSCs. The DSSCs employing the nanocrystalline-TiO₂ (nc-TiO₂)/SiO₂@TiO₂@AuNP and nc-TiO₂/SiO₂@AuNP@TiO2₂ as photoanodes showed remarkably enhanced power conversion efficiencies up to about 14% and 10%, respectively, with respect to a reference cell containing an nc-TiO₂/SiO₂@TiO₂ photoanode. This can be mainly attributed to the enhanced dye absorption by the intensified near-field effect of AuNPs and plasmon-enhanced photocurrent generation.