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.

Graphene wrapped Cu2O nanocubes: Non-enzymatic electrochemical sensors for the detection of glucose and hydrogen peroxide with enhanced stability

Electrocatalytic CO2 reduction to higher-value hydrocarbons beyond C1 products is desirable for applications in energy storage, transportation and the chemical industry. Cu catalysts have shown the potential to catalyse C–C coupling for C2+ products, but still suffer from low selectivity in water. Here, we use density functional theory to determine the energetics of the initial C–C coupling steps on different Cu facets in CO2 reduction, and suggest that the Cu(100) and stepped (211) facets favour C2+ product formation over Cu(111). To demonstrate this, we report the tuning of facet exposure on Cu foil through the metal ion battery cycling method. Compared with the polished Cu foil, our 100-cycled Cu nanocube catalyst with exposed (100) facets presents a sixfold improvement in C2+ to C1 product ratio, with a highest C2+ Faradaic efficiency of over 60% and H2 below 20%, and a corresponding C2+ current of more than 40 mA cm–2. Electrocatalytic reduction of CO2 to products containing multiple carbon atoms is useful for producing high-value chemicals and fuels. This work uses theory to predict the preferred copper surface for C–C coupling, and subsequent metal ion cycling to produce the desired facets results in a catalyst that is highly selective for C2+ products.

Metal ion cycling of Cu foil for selective C–C coupling in electrochemical CO2 reduction

Photocatalysis technology, using semiconductor nano-materials to decompose toxic pollutants under solar light irradiation, displays great prospects for environmental protection. This review gives an overview of the applications of BiOX (X = Cl, Br and I) photocatalysts for efficient photocatalytic degradation (PCD) removal of pollutants in water/air, such as volatile organic compounds (VOCs), organic molecule pollutants, polymer pollutants and biological substances. In addition, the hybridization, facet effects and photocatalytic mechanisms of BiOX are highlighted to offer guidelines for designing highly-active BiOX visible-light-driven (VLD) photocatalysts. Furthermore, the research trends and future prospects of BiOX photocatalysts are also briefly summarized. It may lead to feasible green and efficient photocatalytic reaction systems using BiOX as the photocatalyst.

Recent advances in BiOX (X = Cl, Br and I) photocatalysts: synthesis, modification, facet effects and mechanisms

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 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

Bimetallic icosahedral nanoframes have three-dimensional open structures, a high surface-area-to-volume ratio, and high surface site availability. Twin boundaries in these structures cause surface lattice expansion that leads to tensile strain over the nanoframes, which can improve their catalytic activity; however, robust methods for their synthesis in most metal systems are still lacking. In this work, we demonstrate a one-step synthetic strategy for the synthesis of both closed solid and hollow frame icosahedral PdRu nanoparticles (INPs) via a two-stage process of growth and dissolution. By extraction at different reaction times, INPs, concave-faceted icosahedral PdRu nanoparticles (CINPs), and icosahedral PdRu nanoframes (INFs) are obtained. High-angle annular dark-field scanning transmission electron microscopy-energy-dispersive X-ray spectroscopy and inductively coupled plasma–optical emission spectrometry analyses show that the icosahedral nanostructures are PdRu alloys with ∼5 at. % Ru relative to Pd. We also carried out the electrochemical ethanol oxidation reaction (EOR) and CO2 reduction reaction over three types of catalysts, PdRu INPs, PdRu CINPs, and PdRu INFs, as well as commercial Pd NPs, to examine their catalytic properties. PdRu INFs showed a much higher mass activity than PdRu INPs, PdRu CINPs, and Pd NPs in the EOR. PdRu INFs exhibited the highest Faradaic efficiency of CO gas (34%), which suggests that the expansive strain in the framework catalyst structure improves selectivity and activity for CO2 conversion. 

Insights into Transformation of Icosahedral PdRu Nanocrystals into Lattice-Expanded Nanoframes with Strain Enhancement in Electrochemical Redox Reactions

In this study, we observed the enhanced photocatalytic activity of a few-layer WS2/ZnO (WZ) heterostructure toward dye degradation and H2 production. The few-layer WS2 acted as a co-catalyst that separated photogenerated electron/hole pairs and provided active sites for reactions, leading to the rate of photocatalytic H2 production of WZ being 35% greater than that over the bare ZnO nanoparticles. Moreover, vortex-stirring accelerated the mass-transfer of the reactants, leading to the efficiency of dye photodegradation being 3 times higher than that obtained without high-speed stirring. We observed a similar effect for H2 production, with greater photocatalytic performance arising from the increased mass-transfer of H2 from the catalyst surface to the atmosphere.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8771954

Improved Mass-Transfer Enhances Photo-Driven Dye Degradation and H2 Evolution over a Few-Layer WS2/ZnO Heterostructure

In this study, the effect of stacking faults (SFs) on electromigration in silver nanowires (AgNWs) in particular, with respect to their effects on necking and void growth, is investigated. The galvanic replacement reaction is used to synthesize the AgNWs in bulk at low cost. By varying the concentration of silver nitrate, AgNWs are obtained with and without SFs. In situ TEM analysis provides strong evidence that the SFs can effectively suppress the migration of surface atoms. Furthermore, an investigation of the void growth process reveals that SF facets parallel to the {111} plane contribute to the anisotropic change in morphology and slow down the rate of void growth by 135 times. Thus, planar defects can be beneficial to extending the lifetimes of devices by causing intrinsic changes to the material properties.

Lian-Ming Lyu

Papers

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

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

Insights into Transformation of Icosahedral PdRu Nanocrystals into Lattice-Expanded Nanoframes with Strain Enhancement in Electrochemical Redox Reactions

Improved Mass-Transfer Enhances Photo-Driven Dye Degradation and H2 Evolution over a Few-Layer WS2/ZnO Heterostructure

In Situ/Operando Studies for Reduced Eletromigration in Ag Nanowires with Stacking Faults