Construction of direct all-solid-state Z-scheme p-n copper indium disulfide/tungsten oxide heterojunction photocatalysts: Function of interfacial electric field

Oxygen Vacancy-Mediated CuWO4/CuBi2O4 Samples with Efficient Charge Transfer for Enhanced Catalytic Activity toward Photodegradation of Pharmacologically Active Compounds

Photocatalytic degradation is a promising method for controlling the increasing contamination of the water environment due to pharmacologically active compounds (PHACs). Herein, oxygen vacancy (OV)-modulated Z-scheme CuWO4/CuBi2O4 hybrid systems were fabricated via thermal treatment by loading of CuWO4 nanoparticles with OVs on CuBi2O4 surfaces. The synthesized CuWO4/CuBi2O4 hybrid samples exhibited an enhanced photodegradation ability to remove PHACs under visible-light irradiation. More importantly, an optimized sample (10 wt % CuWO4/CuBi2O4) exhibited superior catalytic activity and excellent recycling stability for PHAC photodegradation. In addition, possible degradation paths for PHAC removal over the CuWO4/CuBi2O4 hybrid systems were proposed. The enhanced photocatalytic performance could be attributed to the efficient separation and transfer of photoformed charge pairs via the Z-scheme mechanism. This Z-scheme mechanism was systematically analyzed using trapping experiments of active species, ultraviolet photoelectron spectroscopy, electron spin resonance, and the photodepositions of noble metals. The findings of this study can pave the way for developing highly efficient Z-scheme photocatalytic systems for PHAC photodegradation.

Recent Advances in Semiconductor Heterojunctions and Z-Schemes for Photocatalytic Hydrogen Generation

The formation of semiconductor heterojunctions and Z-schemes is still a very prominent and efficient strategy of materials chemists to extend the absorption range of semiconductor combinations. Moreover, the spatial separation of photoexcited charge carriers and thereby the reduction of their recombination ultimately lead to increased photocatalytic activities. The present article reviews recent trends in semiconductor heterojunctions and Z-schemes with a focus on hydrogen generation and water splitting, exhibiting specific needs for charge carrier separation. We also included recent material trends, i.e. 2D/2D combinations, direct Z-schemes, MOFs and COFs, and combinations with upconversion materials.

Interfacial Bi-S bonds modulate band alignment for efficient solar water oxidation

Introducing suitable interfacial chemical bonds into heterojunctions can increase the charge carrier density, propel the charge separation, and facilitate interfacial charge extraction in photoanodes for photoelectrochemical (PEC) water oxidation. However, tuning chemical bonds at heterojunction interfaces and elucidating their influences on band alignment and the associated evolution of PEC performance remain elusive. Herein, Bi-S bonds were introduced into the interface of a CdIn₂S₄ (CIS)/Bi₂WO₆ (BWO) heterojunction. In situ irradiated X-ray photoelectron spectroscopy and electron spin resonance signals confirm that the Bi-S bond transforms the band alignment from type II to the direct Z-scheme, significantly enhancing the carrier separation efficiency. Theoretical calculations show that the Bi-S bond not only acts as an atomic-level charge transfer channel, but also changes the migration pathway and distance within the heterojunction. As a result, the optimized CIS/BWO photoanode exhibits a relatively high PEC performance of 4.25 mA cm^-2 at 1.23 V vs. RHE (V_RHE) and a low onset potential of 0.30 V_RHE. This work presents a new avenue to construct comprehensively improved photoanodes by tuning the interfacial structures at the atomic level.

The pivotal role of defects in fabrication of polymeric carbon nitride homojunctions with enhanced photocatalytic hydrogen evolution

Fabrication of homojunctions is a cost-effective efficient way to enhance the photocatalytic performance of polymeric carbon nitride (CN), but the generation of defects upon synthesizing CN homojunctions and their roles in the homojunction fabrication were hardly reported. Herein, nitrogen-deficient CN homojunctions were simply synthesized by calcining dicyandiamide-loaded CN (prepared from urea and denoted as UCN) with dicyandiamide polymerizing into CN (denoted as DCN) and simultaneous formation of nitrogen vacancies in the surface of UCN. Fabrication of the nitrogen-deficient UCN (dUCN)/DCN homojunction depends on the nitrogen vacancy content in dUCN which can tune the energy band structure of dUCN from not matching to matching with that of DCN. The dUCN/DCN homojunction exhibits extended optical absorption and remarkably enhanced charge separation and photocatalytic H₂ evolution, compared with UCN and DCN. This work illustrates the pivotal role of defects in fabricating CN homojunctions and supplies a new facile way to synthesize nitrogen-deficient CN.

NIR-Driven Intracellular Photocatalytic O2 Evolution on Z-Scheme Ni3S2/Cu1.8S@HA for Hypoxic Tumor Therapy

Hypoxia in a tumor microenvironment (TME) has inhibited the photodynamic therapy (PDT) efficacy. Here, Ni₃S₂/Cu_1.8S nanoheterostructures were synthesized as a new photosensitizer, which also realizes the intracellular photocatalytic O₂ evolution to relieve hypoxia in TME and enhance PDT as well. With the narrow band gap (below 1.5 eV), the near infrared (NIR) (808 nm) can stimulate their separation of the electron-hole. The novel Z-scheme nanoheterostructures, testified by experimental data and density functional theory (DFT) calculation, possess a higher redox ability, endowing the photoexited holes with sufficient potential to oxide H₂O into O₂, directly. Meanwhile, the photostimulated electrons can capture the dissolved O₂ to form a toxic reactive oxygen species (ROS). Moreover, Ni₃S₂/Cu_1.8S nanocomposites also possess the catalase-/peroxidase-like activity to convert the endogenous H₂O₂ into ·OH and O₂, which not only cause chemodynamic therapy (CDT) but also alleviate hypoxia to assist the PDT as well. In addition, owing to the narrow band gap, they possess a high NIR harvest and great photothermal conversion efficiency (49.5%). It is noted that the nanocomposites also exhibit novel biodegradation and can be metabolized and eliminated via feces and urine within 2 weeks. The present single electrons in Ni/Cu ions induce the magnetic resonance imaging (MRI) ability for Ni₃S₂/Cu_1.8S. To make sure that the cancer cells were specifically targeted, hyaluronic acid (HA) was grafted outside and Ni₃S₂/Cu_1.8S@HA integrated photodynamic therapy (PDT), chemodynamic therapy (CDT), and photothermal therapy (PTT) to exhibit the great anticancer efficiency for hypoxic tumor elimination.

BiOI Particles Confined into Metal-Organic Framework NU-1000 for Valid Photocatalytic Hydrogen Evolution under Visible-Light Irradiation

Herein, a surface site engineering strategy is used to construct a porous Z-scheme heterojunction photocatalyst for photocatalytic hydrogen evolution (PHE) by integration of BiOI in a mesoporous Zr-based metal-organic framework (MOF) NU-1000. Three high-quality and highly dispersed BiOI@NU-1000 heterojunction materials are synthesized, and a set of methods is used to characterize these materials, indicating that the BiOI@NU-1000 heterojunction can retain high porosity and crystallinity of the parent NU-1000. Furthermore, the built-in electric field of the BiOI@NU-1000 composite can effectively tune the band gap, promote the separation of photoinduced charge carriers, improve photocurrent intensity, and reduce photoelectric impedance. Under visible-light irradiation, BiOI@NU-1000-2 showed the best photocatalytic performance in the field of MOF-based photocatalysts for PHE, with a hydrogen production rate of up to 610 μmol h^-1 g^-1. This study will open up opportunities for the construction of Z-scheme photocatalysts based on the highly porous MOF materials to inspire the development of innovative photocatalysts.

Facile synthesis of the Z-scheme graphite-like carbon nitride/silver/silver phosphate nanocomposite for photocatalytic oxidative removal of nitric oxides under visible light

In this study, a novel ternary Z-scheme Graphite-like Carbon Nitride (g-C₃N₄)/Silver (Ag)/Silver Phosphate (Ag₃PO₄) photocatalyst was designed and prepared using a two-step method (sodium chloride (NaCl) template-assisted strategy plus selective deposition). Its photocatalysts performance against removing 400 ppm of Nitric Oxides (NOx) was then investigated. We found 50 wt% g-C₃N₄/Ag/Ag₃PO₄(AP-CN 2:1) catalyst removes up to 74% of NO in 90 min under the illumination of visible light (>420 nm), which is respectively 3.5 and 1.8 times higher than using g-C₃N₄ or Ag₃PO₄, alone. This improved performance was attributed to the formation of Z-scheme g-C₃N₄/Ag/Ag₃PO₄ heterojunction, driven by the built-in electric field across the g-C₃N₄/Ag/Ag₃PO₄ interface. These separated the electron-hole but enhanced the original strong oxidation and reduction performance of related components. The superior performance is also attributed to the improved surface area, enhanced hydrophilicity (H₂O₂) and better visible-light-harvesting capability of the composite compound. More importantly, the AP-CN 2:1 sample maintained a NO removal rate of more than 73% even after four rounds of recycling. The photocatalytic oxidation removal mechanism was evaluated using the radical-capture experiments, electron spin resonance (ESR) and ion-exchange high-performance liquid chromatography (HPLC) analysis. The findings of this work offer a simple but effective design of a highly reactive and practical ternary Z-scheme heterojunction photocatalysts for the removal of toxic NO.

TiO2 as an interfacial-charge-transfer-bridge to construct eosin Y-mediated direct Z-scheme electron transfer over a Co9S8 quantum dot/TiO2 photocatalyst

A novel eosin Y-mediated Z-scheme Co₉S₈ QDs/TiO₂ photocatalytic system was constructed and a high AQE of 37.4% is obtained at 470 nm for 20%Co₉S₈/TiO₂ heterojunction.