Integration of high visible-light-driven ternary dual Z-scheme AgVO3-InVO4/g-C3N4 heterojunction nanocomposite for enhanced uranium(VI) photoreduction separation

With deepening application of nuclear power technology, the problem of water ecological environment pollution caused by uranium (U(VI)) is becoming increasingly serious. Photoreduction separation of U(VI) on photocatalysts is considered as an effective strategy to solve uranium pollution. In this work, a novel ternary dual Z-scheme AgVO3-InVO4/g-C3N4 heterojunction (Z-AIGH) nanocomposite with high surface area (73.45 m2 g-1, Z-AIGH2) was designed. The batch adsorption experiment in dark environment showed that Z-AIGH2 nanocomposite had an excellent U(VI) adsorption performance. As for photocatalytic experiments, Z-AIGH2 exhibited a rapid photocatalytic response for separating U(VI) without any organic sacrifice agents. The U(VI) separation rate on Z-AIGH2 nanocomposite was over 98.7% after only 20.0 min visible light irradiation (T = 298 K, CU(Ⅵ) = 10.0 mg L-1, m/V = 0.1 g L-1 and pH = 7.0). Z-AIGH2 nanocomposite also showed good selectivity and cycle stability. The U(VI) removal rate of Z-AIGH2 nanocomposite after fifth cycles was about 96.1% (T = 298 K, CU(Ⅵ) = 10.0 mg L-1, m/V = 0.1 g L-1 and pH = 7.0). High photocatalytic activity of Z-AIGH2 for U(VI) was attributed to the construction of ternary dual Z-scheme heterojunction structure and ant nest-like hole structure. Based on above results, Z-AIGH2 nanocomposite had great potential for water environment renovation.

CdS-based artificial leaf for photocatalytic hydrogen evolution and simultaneous degradation of biological wastewater

Rational design of all-solid-state Z-scheme heterojunction with advanced structure is essential for boosting photocatalytic efficiency. Herein, we design and fabricate a novel Z-scheme photocatalyst with leaf architecture (named artificial leaf) via a simple dipping-calcination (DC) process followed by a successive ionic layer adsorption and reaction (SILAR) strategy. The prepared artificial leaf, composing of CdS, InVO₄, and BiVO₄, holds advanced leaf-like structure and Z-scheme electron transfer pathway. As a result, this novel artificial leaf exhibits outstanding capability for the harvesting of visible light and superior efficiency for the separation of photogenerated electron-hole pairs, as well as remarkably enhanced photocatalytic performance and stability for H₂ evolution (with the rate of 5033 μm g^-1∙h^-1) and pollution degradation (46% pollution can be degraded within 3 h).

Step-Scheme Heterojunction between CdS Nanowires and Facet-Selective Assembly of MnOx-BiVO4 for an Efficient Visible-Light-Driven Overall Water Splitting

The spatial separation and transport of photogenerated charge carriers is crucial in building an efficient photocatalyst for solar energy conversion into chemical energy. A step-scheme CdS/MnO_x-BiVO₄ photocatalyst was synthesized by spatial deposition of MnO_x and one-dimensional (1D) CdS nanowires on a three-dimensional (3D) decahedron BiVO₄ surface. The photocatalytic activity of CdS/MnO_x-BiVO₄ for the overall water-splitting reaction was investigated without sacrificial reagent under visible light irradiation. The synthesized photocatalysts were thoroughly analyzed using high-end characterization techniques. The 5CdS/MnO_x-BiVO₄ exhibited the highest H₂ and O₂ production rates of 1.01 and 0.51 mmol g^-1 h^-1, respectively, with an apparent quantum yield of 11.3% in the absence of any sacrificial reagent. The excellent photoactivity is due to the presence of oxygen vacancies along with effective charge separation/transfer properties and strong interaction of cocatalysts (MnO_x and Pt) with the photocatalysts (BiVO₄ and CdS) in the 5CdS/MnO_x-BiVO₄ heterojunction. The significance of the presence of MnO_x and Pt cocatalysts on the selective facets of BiVO₄ for efficient overall water splitting reaction is highlighted in this work.

Construction of a Bioinspired Hierarchical BiVO4/BiOCl Heterojunction and Its Enhanced Photocatalytic Activity for Phenol Degradation

Development of a p-n heterojunction to achieve efficient degradation of organic pollutants is a promising approach in the field of photocatalysis. Herein, BiVO₄ with bioinspired hierarchical structures was prepared with the sol-gel method and combined with BiOCl nanoplates to construct a 3D/2D configuration via an in situ deposition route. The hierarchical BiVO₄ served as an excellent substrate to achieve the uniform loading of BiOCl nanoplates. The obtained 3D/2D BiVO₄/BiOCl hybrids exhibited significantly enhanced photocatalytic efficiency for degrading phenol under visible light irradiation, with a first-order reaction rate constant that was 9.9 and 1.9 times higher than those of hierarchical BiVO₄ and the BiVO₄/BiOCl hybrids without hierarchical structures, respectively. Moreover, the hierarchical BiVO₄/BiOCl also displayed good photochemical stability for the degradation of phenol after three recycles. The p-n heterojunction and hierarchical structure worked together to form a spatial conductive network framework, which possessed improved visible light absorption, high specific surface area, as well as effective separation and transfer of photogenerated charge carriers.

MnO2 -Based Materials for Environmental Applications

Manganese dioxide (MnO₂ ) is a promising photo-thermo-electric-responsive semiconductor material for environmental applications, owing to its various favorable properties. However, the unsatisfactory environmental purification efficiency of this material has limited its further applications. Fortunately, in the last few years, significant efforts have been undertaken for improving the environmental purification efficiency of this material and understanding its underlying mechanism. Here, the aim is to summarize the recent experimental and computational research progress in the modification of MnO₂ single species by morphology control, structure construction, facet engineering, and element doping. Moreover, the design and fabrication of MnO₂ -based composites via the construction of homojunctions and MnO₂ /semiconductor/conductor binary/ternary heterojunctions is discussed. Their applications in environmental purification systems, either as an adsorbent material for removing heavy metals, dyes, and microwave (MW) pollution, or as a thermal catalyst, photocatalyst, and electrocatalyst for the degradation of pollutants (water and gas, organic and inorganic) are also highlighted. Finally, the research gaps are summarized and a perspective on the challenges and the direction of future research in nanostructured MnO₂ -based materials in the field of environmental applications is presented. Therefore, basic guidance for rational design and fabrication of high-efficiency MnO₂ -based materials for comprehensive environmental applications is provided.

Smart Assembly of Sulfide Heterojunction Photocatalysts with Well-Defined Interfaces for Direct Z-Scheme Water Splitting under Visible Light

A Z-scheme photocatalytic water-splitting system is an effective approach to integrate the advantages both hydrogen- and oxygen-evolution photocatalysts. The interfacial properties of the heterojunctions have a great influence on the efficiency through the crystal orientation and the charge kinetics. In this study, a general chemical vapor deposition process and a gentle cation-exchange method were combined to assemble Z-scheme photocatalysts between CdS and MnS. As a result of the well-defined heterojunction interfaces and distinctive structural benefits, without cocatalysts, the 1 D CdS/MnS hybrid photocatalyst exhibited a significantly increased photocatalytic H₂ evolution rate of 1595 μmol h^-1  g^-1 (apparent quantum efficiency of 22.6 % at λ=420 nm), which is over 10.5 times higher than that of CdS. Moreover, a better photocatalytic stability is demonstrated over particulate (42 h cycling measurement) and photoelectrochemical (3000 min continuous measurement) systems. Overall, this work provides a unique experimental insight into high-quality heterojunction interface design and new Z-scheme photocatalyst synthesis.