Semiconductor-based photocatalysis is considered to be an attractive way for solving the worldwide energy shortage and environmental pollution issues. Since the pioneering work in 2009 on graphitic carbon nitride (g-C3N4) for visible-light photocatalytic water splitting, g-C3N4 -based photocatalysis has become a very hot research topic. This review summarizes the recent progress regarding the design and preparation of g-C3N4 -based photocatalysts, including the fabrication and nanostructure design of pristine g-C3N4 , bandgap engineering through atomic-level doping and molecular-level modification, and the preparation of g-C3N4 -based semiconductor composites. Also, the photo-catalytic applications of g-C3N4 -based photocatalysts in the fields of water splitting, CO2 reduction, pollutant degradation, organic syntheses, and bacterial disinfection are reviewed, with emphasis on photocatalysis promoted by carbon materials, non-noble-metal cocatalysts, and Z-scheme heterojunctions. Finally, the concluding remarks are presented and some perspectives regarding the future development of g-C3N4 -based photocatalysts are highlighted.

Polymeric Photocatalysts Based on Graphitic Carbon Nitride

The applications of copper (Cu) and Cu-based nanoparticles, which are based on the earth-abundant and inexpensive copper metal, have generated a great deal of interest in recent years, especially in the field of catalysis. The possible modification of the chemical and physical properties of these nanoparticles using different synthetic strategies and conditions and/or via postsynthetic chemical treatments has been largely responsible for the rapid growth of interest in these nanomaterials and their applications in catalysis. In addition, the design and development of novel support and/or multimetallic systems (e.g., alloys, etc.) has also made significant contributions to the field. In this comprehensive review, we report different synthetic approaches to Cu and Cu-based nanoparticles (metallic copper, copper oxides, and hybrid copper nanostructures) and copper nanoparticles immobilized into or supported on various support materials (SiO2, magnetic support materials, etc.), along with their applications i...

http://pubs.acs.org/doi/pdfplus/10.1021/acs.chemrev.5b00482

Cu and Cu-Based Nanoparticles: Synthesis and Applications in Catalysis.

Photoreduction of CO2 into sustainable and green solar fuels is generally believed to be an appealing solution to simultaneously overcome both environmental problems and energy crisis. The low selectivity of challenging multi-electron CO2 photoreduction reactions makes it one of the holy grails in heterogeneous photocatalysis. This Review highlights the important roles of cocatalysts in selective photocatalytic CO2 reduction into solar fuels using semiconductor catalysts. A special emphasis in this review is placed on the key role, design considerations and modification strategies of cocatalysts for CO2 photoreduction. Various cocatalysts, such as the biomimetic, metal-based, metal-free, and multifunctional ones, and their selectivity for CO2 photoreduction are summarized and discussed, along with the recent advances in this area. This Review provides useful information for the design of highly selective cocatalysts for photo(electro)reduction and electroreduction of CO2 and complements the existing reviews on various semiconductor photocatalysts.

Cocatalysts for Selective Photoreduction of CO2 into Solar Fuels.

BiOCl single-crystalline nanosheets with exposed {001} and {010} facets were selectively synthesized via a facile hydrothermal route. The resulting BiOCl single-crystalline nanosheets with exposed {001} facets exhibited higher activity for direct semiconductor photoexcitation pollutant degradation under UV light, but the counterpart with exposed {010} facets possessed superior activity for indirect dye photosensitization degradation under visible light.

Synthesis and Facet-Dependent Photoreactivity of BiOCl Single-Crystalline Nanosheets

Titanium dioxide (TiO2) has been the most intensively investigated binary transition metal oxide in the past four decades as indicated by Figure S1. Furthermore, the annual number of papers published on TiO2 has seen a continuous increase, particularly since the beginning of this century (Figure S2). This is understandable when one considers the wide range of applications of TiO2 from the conventional areas (i.e., pigment, cosmetic, toothpaste, and paint) to the later developed functional areas such as photoelectrochemical cell,(1-3) dye-sensitized solar cells (DSSCs),(4-11) photocatalysis,(12-24) catalysis,(25-31) photovoltaic cell,(32-34) lithium ion batteries,(35-41) sensors,(42-46) electron field emission,(47-51) microwave absorbing material, biomimetic growth, and biomedical treatments.(52-57) Nearly all these functional applications of TiO2 fall in the scope of energy, environment, and health, which are definitely the three most important and challenging themes facing the Human race that need to be addressed in this century. Besides the apparent merits including nontoxicity, elemental abundance, good chemical stability, and easy synthesis, TiO2 has attracted strong research interest worldwide due to its physicochemical properties for realizing various functions.(15, 58, 59) Especially, very encouraging progresses in photocatalysis and DSSCs with the involvement of TiO2 have greatly stimulated the rapid development of TiO2 crystals with controllable phase, size, shape, defect, and heteroatom.(58, 60-68)

Titanium dioxide crystals with tailored facets

In this study, a new series of Cu2O nanocrystals with systematic shape evolution from cubic to face-raised cubic, edge- and corner-truncated octahedral, all-corner-truncated rhombic dodecahedral, {100}-truncated rhombic dodecahedral, and rhombic dodecahedral structures have been synthesized. The average sizes for the cubes, edge- and corner-truncated octahedra, {100}-truncated rhombic dodecahedra, and rhombic dodecahedra are approximately 200, 140, 270, and 290 nm, respectively. An aqueous mixture of CuCl2, sodium dodecyl sulfate, NaOH, and NH2OH·HCl was prepared to produce these nanocrystals at room temperature. Simple adjustment of the amounts of NH2OH·HCl introduced enables this particle shape evolution. These novel particle morphologies have been carefully analyzed by transmission electron microscopy (TEM). The solution color changes quickly from blue to green, yellow, and then orange within 1 min of reaction in the formation of nanocubes, while such color change takes 10–20 min in the growth of rhomb...

Synthesis of Cu2O nanocrystals from cubic to rhombic dodecahedral structures and their comparative photocatalytic activity.

We report highly facet-dependent electrical properties of Cu2O nanocubes and octahedra and significant enhancement of gold nanocrystal cores to the electrical conductivity of Au−Cu2O core−shell octahedra. Cu2O nanocubes and octahedra and Au−Cu2O core−shell cubes and octahedra were synthesized by following our reported facile procedures at room temperature. Two oxide-free tungsten probes attached to a nanomanipulator installed inside a scanning electron microscope made contacts to a single Cu2O nanocrystal for the I−V measurements. Pristine Cu2O octahedra bounded by {111} facets are 1100 times more conductive than pristine Cu2O cubes enclosed by {100} faces, which are barely conductive. Core−shell cubes are only slightly more conductive than pristine cubes. A 10 000-fold increase in conductivity over a cube has been recorded for an octahedron. Remarkably, core−shell octahedra are far more conductive than pristine octahedra. The same facet-dependent electrical behavior can still be observed on a single nano...

Facet-Dependent and Au Nanocrystal-Enhanced Electrical and Photocatalytic Properties of Au−Cu2O Core−Shell Heterostructures

Plasmonic core–shell nanoparticles (PCSNPs) can function as nanoantennas and improve the efficiency of dye-sensitized solar cells (DSSCs). To achieve maximum enhancement, the morphology of PCSNPs needs to be optimized. Here we precisely control the morphology of Au@TiO2 PCSNPs and systematically study its influence on the plasmonic enhancement effect. The enhancement mechanism was found to vary with the thickness of the TiO2 shell. PCSNPs with a thinner shell mainly enhance the current, whereas particles with a thicker shell improve the voltage. While pronounced plasmonic enhancement was found in the near infrared regime, wavelength-independent enhancement in the visible range was observed and attributed to the plasmonic heating effect. Emission lifetime measurement confirms that N719 molecules neighboring nanoparticles with TiO2 shells exhibit a longer lifetime than those in contact with metal cores. Overall, PCSNPs with a 5 nm shell give the highest efficiency enhancement of 23%. Our work provides a new synthesis route for well-controlled Au@TiO2 core–shell nanoparticles and gains insight into the plasmonic enhancement in DSSCs.

The influence of shell thickness of Au@TiO2 core-shell nanoparticles on the plasmonic enhancement effect in dye-sensitized solar cells.

We fabricated Au–Cu2O core–shell octahedra, cuboctahedra, and nanocubes having sizes of 90–220 nm using 50 nm octahedral cores. The smaller particle sizes minimize the strong light scattering features from the Cu2O shells and enable the surface plasmon resonance (SPR) absorption band of the gold cores to be clearly identified. Beyond a lower shell thickness limit, the SPR band positions of the gold cores are independent of the shell thickness, but are strongly dependent on the exposed particle surfaces. The plasmonic band red-shifts from Au–Cu2O octahedra to cuboctahedra and nanocubes, and differs by as much as 26 nm between the octahedra and the nanocubes. The same facet-dependent optical effects were observed using larger octahedral gold cores and cubic gold cores. In contrast, simulation spectra show progressively red-shifted SPR band positions with increasing shell thickness. The Cu2O shells are also found to exhibit facet-dependent optical behavior. These nanocrystals can respond to changes in the solvent environment such as solvents with different refractive indices, indicating that the plasmonic field of the gold cores can extend beyond the particle surfaces despite the presence of thick shells. Plane-selective spectral responses to low concentrations of surfactants were also recorded.

Facet-dependent optical properties of polyhedral Au–Cu2O core–shell nanocrystals

By measuring linearly polarized photoluminescence (PL) from single, isolated gallium nitride (GaN) nanorods with the rod diameters in the subwavelength regime (30–90 nm), we present clear evidence for size dependence of polarization anisotropy. The maximum polarization ratio at room temperature (~0.9 with emission and excitation light polarized parallel to the long axis of nanorod) occurs at the rod diameter of ~40 nm. The experimental data are compared with the recent theoretical model proposed for thick semiconductor nanowires. It is concluded that the optical confinement effects in this size regime play an important role in the observed giant polarization anisotropy. Furthermore, we have performed a temperature-dependent study of polarized PL to show the importance of internal emission anisotropy at low temperatures.

/pdf/polarized-photoluminescence-from-single-gan-nanorods-effects-u7hqwjifzu.pdf

Yu-Chen Yang

Papers

Synthesis of Cu2O nanocrystals from cubic to rhombic dodecahedral structures and their comparative photocatalytic activity.

Facet-Dependent and Au Nanocrystal-Enhanced Electrical and Photocatalytic Properties of Au−Cu2O Core−Shell Heterostructures

The influence of shell thickness of Au@TiO2 core-shell nanoparticles on the plasmonic enhancement effect in dye-sensitized solar cells.

Facet-dependent optical properties of polyhedral Au–Cu2O core–shell nanocrystals

Polarized photoluminescence from single GaN nanorods: effects of optical confinement.