Mo-BiVO₄/Ca-BiVO₄ Homojunction Nanostructure-Based Inverse Opals for Photoelectrocatalytic Pharmaceutical Degradation under Visible Light

Homojunction engineering has emerged as a potent strategy to evade interfacial stability issues and improve the efficiency of nanostructured metal oxide photocatalysts, though rarely combined with the enhanced light capture ability of three-dimensional macroporous photonic crystal structures. Herein, the formation of nanoscale n-n+ homojunctions between different Mo- and Ca-doped BiVO4 nanocrystals in the skeleton of photonic band gap (PBG) engineered inverse opals is introduced as an advanced approach to simultaneously promote visible light harvesting, electron transport, and charge separation of BiVO4 nanomaterials for the photoelectrocatalytic degradation of pharmaceutical contaminants of emerging concern. Controlled deposition of BiVO4 inverse opal films with tailored PBGs was combined with compositional tuning by Mo- and Ca-doping for slow-photon-assisted visible-light-activated (VLA) photocatalysis. The introduction of shallow dopant states in the Mo-, Ca-doped BiVO4 nanoparticles with relatively weak structural distortions but significantly different donor concentrations resulted in a broad distribution of type-II homojunctions in the nanocrystalline inverse opal walls. Comparative photoelectrochemical evaluation showed that nanostructured homojunction Mo-BiVO4/Ca-BiVO4 photonic films largely outperformed their individual constituents in both photocurrent generation and the VLA photocatalytic degradation rate. Moreover, they exhibited markedly improved performance in the photoelectrocatalytic degradation of tetracycline and ciprofloxacin broad-spectrum antibiotics as well as salicylic acid under visible light, validating their application potential in VLA water remediation by pharmaceutical micropollutants

Epitaxial 2D SnSe₂/ 2D WSe₂ van der Waals Heterostructures

van der Waals heterostructures of 2D semiconductor materials can be used to realize a number of (opto)­electronic devices including tunneling field effect devices (TFETs). It is shown in this work that high quality SnSe₂/WSe₂ vdW heterostructure can be grown by molecular beam epitaxy on AlN(0001)/Si(111) substrates using a Bi₂Se₃ buffer layer. A valence band offset of 0.8 eV matches the energy gap of SnSe₂ in such a way that the VB edge of WSe₂ and the CB edge of SnSe₂ are lined up, making this materials combination suitable for (nearly) broken gap TFETs

Observation of Surface Dirac Cone in High-Quality Ultrathin Epitaxial Bi₂Se₃ Topological Insulator on AlN(0001) Dielectric

Bi₂Se₃ topological insulators (TIs) are grown on AlN(0001)/Si(111) substrates by molecular beam epitaxy. In a one-step growth at optimum temperature of 300 °C, Bi₂Se₃ bonds strongly with AlN without forming interfacial reaction layers. This produces high epitaxial quality Bi₂Se₃ single crystals with a perfect registry with the substrate and abrupt interfaces, allowing thickness scaling down to three quintuple layers (QL) without jeopardizing film quality. It is found by angle-resolved photoelectron spectroscopy that, remarkably, Bi₂Se₃ films maintain the 3D TI properties at very low thickness of 3QL (∼2.88 nm), exhibiting top surface gapless metallic states in the form of a Dirac cone