Fabrication of Er3+/Yb3+ Co-Doped Bi5O7I Microsphere With Upconversion Luminescence and Enhanced Photocatalytic Activity for Bisphenol A Degradation

Er-Doped BiVO4/BiFeO3 Nanocomposites Synthesized via Sonochemical Process and Their Piezo-Photocatalytic Application

In this work, Er-doped BiVO4/BiFeO3 composites are prepared using the sonochemical process with a difference of rare earth loading compositions. The crystallinity and chemical and morphological structure of as-synthesized samples were investigated via X-ray diffraction, Raman scattering, and electron microscopy, respectively. The diffuse reflectance technique was used to extract the optical property and calculate the optical band gap of the composite sample. The piezo-photocatalytic performance was evaluated according to the decomposition of a Rhodamine B organic compound. The decomposition of the organic compound was achieved under ultrasonic bath irradiation combined with light exposure. The Er-doped BiVO4/BiFeO3 composite heterojunction material exhibited significant enhancement of the piezo-photocatalytic activity under both ultrasonic and light irradiation due to the improvement in charge generation and separation. The result indicates that Er dopant strongly affects the phase transformation, change in morphology, and alternation in optical band gap of the BiVO4 matrix. The incorporation of BiFeO3 in the composite form with BiVO4 doped with 1%Er can improve the photocatalytic performance of BiVO4 via piezo-induced charge separation and charge recombination retardment.

Design and construction of a robust ternary Bi5O7I/Cd0.5Zn0.5S/CuO photocatalytic system for boosted photodegradation of antibiotics via dual-S-scheme mechanisms: Environmental factors and degradation intermediates

The detection of efficacious and environment-friendly nanomaterials with prominent photocatalytic performance is crucial for the detoxification of antibiotics in wastewater. Herein, a dual-S-scheme Bi5O7I/Cd0.5Zn0.5S/CuO semiconductor was designed and fabricated via a simple approach to degrade tetracycline (TC) and other types of antibiotics under LED illumination. However, Cd0.5Zn0.5S and CuO nanoparticles were decorated on the surface of the Bi5O7I microsphere to create a dual-S-scheme system that stimulates visible-light utilization and facilitates the dissolution of excited photo-curriers. Therefore, the Bi5O7I/Cd0.5Zn0.5S/CuO system offers strong redox ability, which reflects reinforced photocatalytic activity and robust stability. The ternary heterojunction discloses enhanced TC detoxification efficiency of 92% in 60 min with TC destruction rate constant of 0.04034 min-1, outperforming pure Bi5O7I, Cd0.5Zn0.5S, and CuO by 4.27, 3.20, and 4.80 folds, respectively. Besides, Bi5O7I/Cd0.5Zn0.5S/CuO manifests outstanding photo-activity against a series of antibiotics like norfloxacin, enrofloxacin, ciprofloxacin, and levofloxacin under the same operational conditions. The active species detection, TC destruction pathways, catalyst stability, and photoreaction mechanisms of Bi5O7I/Cd0.5Zn0.5S/CuO were accurately explained in detail. Summarily, this work introduces a new class of dual-S-scheme system with strengthened catalytic properties to effectively eliminate the antibiotics in wastewater under visible-light illumination.

Achieving improved full-spectrum responsive 0D/3D CuWO4/BiOBr:Yb3+,Er3+ photocatalyst with synergetic effects of up-conversion, photothermal effect and direct Z-scheme heterojunction

The key to obtain effective photocatalysts is to increase the efficiency of light energy conversion, and thus the design and implementation of full-spectrum photocatalysts is a potential approach to solve this problem especially by extending the absorption range to near-infrared (NIR) light. Herein, the improved full-spectrum responsive CuWO₄/BiOBr:Yb³⁺,Er³⁺ (CW/BYE) direct Z-scheme heterojunction was prepared. The CW/BYE with CW mass ratio of 5% had the best degradation performance, and the removal rate of tetracycline reached 93.9% in 60 min and 69.4% in 12 h under visible (Vis) and NIR light, respectively, which were 5.2 and 3.3 times of BYE. According to the outcome of experimental, the reasonable mechanism of improved photoactivity was put forward on the basis of (i) the up-conversion (UC) effect of Er³⁺ ion to convert NIR photon to ultraviolet or visible light, which can be used by CW and BYE, (ii) the photothermal effect of CW to absorb the NIR light, increasing the local temperature of photocatalyst particle to accelerate the photoreaction, and (iii) the formed direct Z-scheme heterojunction between BYE and CW to boost the separation of photogenerated electron-hole pairs. Additionally, the excellent photostability of the photocatalyst was verified by cycle degradation experiments. This work opens up a promising technique for designing and synthesizing full-spectrum photocatalysts by utilizing synergetic effects of UC, photothermal effect and direct Z-scheme heterojunction.

Upconversion boosting pollutants degradation efficiency in wide-spectrum responsive photocatalysts

Recently, the composite photocatalysts coupled with upconversion materials have received widespread attention due to higher utilization efficiency of solar energy in a wide-spectrum range. Novel heterojunction photocatalysts of CoWO₄@NaYF₄:Yb³⁺,Er³⁺ were designed and developed herein. The structural characterization, morphology and elemental composition analysis demonstrated that heterojunctions between CoWO₄ and NaYF₄:Yb³⁺,Er³⁺ were indeed formed in the composite photocatalysts. Moreover, CoWO₄@NaYF₄:Yb³⁺,Er³⁺ heterojunction photocatalysts exhibited higher pollutants degradation efficiency. Especially, a great enhancement of +87% on the photocatalytic activity was achieved in the heterojunction photocatalyst of 60CoWO₄-NaYF₄:Yb³⁺,Er³⁺ compared with pure CoWO₄. The dominant radicals generated from the heterojunction photocatalysts were confirmed as the photo-generated holes (h⁺) and hydroxyl radicals (⋅OH) through the radical species trapping experiments and fluorescence detection, which is fully in line with the expected band structure characteristics of CoWO₄. Eventually, an underlying mechanism was proposed that the enhanced photocatalytic activity should be attributed to the wide-spectrum responsive features of CoWO₄@NaYF₄:Yb³⁺,Er³⁺ heterojunction photocatalysts. Within the heterostructures, CoWO₄ photocatalyst can absorb both the UV-Vis light due to its narrow bandgap and the Near-Infrared energy through the upconversion NaYF₄:Yb³⁺,Er³⁺, thereby utilizing solar energy more efficiently in a wide-spectrum range for photocatalytic reactions.

Band Gap Reduction in Ferroelectric BaTiO3 Through Heterovalent Cu-Te Co-Doping for Visible-Light Photocatalysis

It is believed that ferroelectrics may serve as efficient photocatalysts as well as photovoltaic materials but for their large bandgaps which does not allow them to absorb a large part of the solar spectrum. We have explored theoretically within ab-initio density functional theory-based calculations, the efficacy of Cu and Te to co-dope BaTiO₃ in reducing its bandgap while retaining its ferroelectric properties. Examining a dopant concentration of 11%, we find an insulating ground state being realized with a band gap reduction of 0.42 eV from the value for undoped BaTiO₃ for some doping configurations. Ferroelectric distortions are found to survive even in the presence of doping suggesting possible applications in photocatalysis as well as photovoltaics.