Hollow Au−Cu 2 O core−shell nanoparticles were synthesized by using hollow gold nanoparticles (HGNs) as the plasmon-tailorable cores to direct epitaxial growth of Cu 2 O nanoshells. The effective geometry control of hollow Au−Cu 2 O core−shell nanoparticles was achieved through adjusting the HGN core sizes, Cu 2 O shell thicknesses, and morphologies related to structure-directing agents. The morphology-dependent plasmonic band red-shifts across the visible and near-infrared spectral regions were observed from experimental extinction spectra and theoretical simulation based on the finite-difference time-domain method. Moreover, the hollow Au−Cu 2 O core−shell nanoparticles with synergistic optical properties exhibited higher photocatalytic performance in the photodegradation of methyl orange when compared to pristine Cu 2 O and solid Au−Cu 2 O core−shell nanoparticles under visible-light irradiation due to the efficient photoinduced charge separation, which could mainly be attributed to the Schottky barrier and plasmon-induced resonant energy transfer. Such optical tunability achieved through the hollow cores and structure-directed shells is of benefit to the performance optimization of metal−semiconductor nanoparticles for photonic, electronic, and photocatalytic applications.

The Cu 2 O/reduced graphene oxide (Cu 2 O/rGO) composites with effective crystallographic facet controlling of Cu 2 O crystals were fabricated through a simple one-step wet chemistry method. The crystallographic facet-dependent photocatalytic performance of Cu 2 O was confirmed, favoring the cuboctahedral Cu 2 O with f100g and f111g facets and a better photocatalytic activity when compared to cubic and octahedral ones. This was attributed to the slight difference of surface energy between f100g and f111g facets which served as a driving force to promote the separation of photogenerated electron-hole pairs. Moreover, the introduction of two-dimensional rGO sheets could accelerate the transfer of photogenerated electrons from Cu 2 O to rGO, which further promoted the separation of photogenerated electron-hole pairs and the degradation of methyl orange (MO) under visible-light irradiation. The cuboctahedral Cu 2 O/rGO composite exhibited a superb photocatalytic performance with the degradation percentage of MO about 97.6% after one periodic photocatalysis due to the synergistic effect of cuboctahedral Cu 2 O and rGO sheets, foreboding its potential application as photocatalyst.Keywords: Cu 2 O/rGO composite; crystallographic facet control; photocatalytic activity; synergistic effect.With the increasing problem of environmental pollution, particularly serious drinking water safety induced by organic contaminations has become the focus of attention. Photocatalytic degradation of organic dyes under visible-light irradiation through effective, cheap and stable catalysts is a good strategy. 1-4 Semiconductor-based nanocomposites with unique physical and chemical properties are regarded as ideal candidates and photocatalysts to solve the above problems. Among these, Cu 2 O as an intrinsic p-type semiconductor (band gap of 2.2 eV) can effectively absorb and utilize solar spectrum in the visible-light region. 5,6 Additionally, low-cost and easy-to-prepare Cu 2 O crystals with different exposed crystallographic facets show many controllable optical, electrical and catalytic properties, indicating their preponderance as photocatalysts. 7 However, many factors limit the photocatalytic efficiency of Cu 2 O crystals including the slow electron transfer, rapid electron-hole recombination, and poor photochemical stability. 2,3,7 In order to overcome these deficiencies, many attempts have been carried out to extend the wavelength range of photoresponse, increase lightharvesting and charge-separating efficiency at the material interface, and improve the photochemical stability by constructing Cu 2 O-semiconductor (Cu 2 O/TiO 2 5 and Cu 2 O/ZnO 8 ) heterojunctions, or introducing high-conductive materials (noble metal 9 and graphene 10-12 ). Until now, the research on structural, optical and photocatalytic tunability of Cu 2 Obased photocatalysts is still limited and critically important since photocatalytic activity is sensitively dependent upon synergistic properties of components in composites.In this paper, we fabricated Cu 2 O/...