Facile synthesis of ZnBi2O4-graphite composites as highly active visible-light photocatalyst for the mineralization of rhodamine B

Design of novel p-n heterojunction ZnBi2O4-ZnS photocatalysts with impressive photocatalytic and antibacterial activities under visible light

Heterojunction structures have attracted considerable attention for enhancing electron migration across interfaces. In this report, ZnBi₂O₄-ZnS(12%) heterojunction photocatalysts was found to be capable of degrading over 94% of indigo carmine in a 15 mg/L solution within 90 min of visible light irradiation at a catalytic dose of 1.0 g/L and pH 4. Furthermore, more than 82% of the total organic carbon (TOC) was removed, confirming the almost complete mineralization of the indigo carmine by ZnBi₂O₄-ZnS(12%). Moreover, the photocatalyst exhibited high stability and retained its photocatalytic activity up to the 5th cycle of operation without photocorrosion. The dramatic enhancement in the visible-light photocatalytic performance of the ZnBi₂O₄-ZnS heterojunctions over pristine ZnBi₂O₄ and ZnS was due to the formation of a superior heterojunction between the n-type semiconductor, ZnS, and the p-type semiconductor, ZnBi₂O₄. This heterojunction facilitated the separation and transfer of the photoinduced electron at the interfaces of the two semiconductors. Furthermore, the ZnBi₂O₄-ZnS(12%) exhibited an inhibition zone of 15 mm against fecal Escherichia coli (ATCC 8739), with a minimum inhibitory concentration (MIC) of 150 μg/mL. These results demonstrated that the novel ZnBi₂O₄-ZnS p-n-type heterojunction is a promising visible-light active photo-catalyst for the degradation of organic pollutants and inhibition of fecal E. coli.

Synergistic effects of the hybridization between boron-doped carbon quantum dots and n/n-type g-C3N4 homojunction for boosted visible-light photocatalytic activity

Dye wastewater has raised a prevalent environmental concern due to its ability to prevent the penetration of sunlight through water, thereby causing a disruption to the aquatic ecosystem. Carbon quantum dots (CQDs) are particularly sought after for their highly tailorable photoelectrochemical and optical properties. Simultaneously, graphitic carbon nitride (g-C₃N₄) has gained widespread attention due to its suitable band gap energy as well as excellent chemical and thermal stabilities. Herein, a novel boron-doped CQD (BCQD)-hybridized g-C₃N₄ homojunction (CN) nanocomposite was fabricated via a facile hydrothermal route. The optimal photocatalyst sample, 1-BCQD/CN (with a 1:3 mass ratio of boron to CQD) accomplished a Rhodamine B (RhB, 10 mg/L) degradation efficiency of 96.8% within 4 h under an 18 W LED light irradiation. The kinetic rate constant of 1.39 × 10^-2 min^-1 achieved by the optimum sample was found to be 3.6- and 2.8-folds higher than that of pristine CN and un-doped CQD/CN, respectively. The surface morphology, crystalline structure, chemical composition and optical properties of photocatalyst samples were characterized via TEM, FESEM-EDX, XRD, FTIR, UV-Vis DRS and FL spectrometer. Based on the scavenging tests, it was revealed that the photogenerated holes (h⁺), superoxide anions (∙O₂^-) and hydroxyl radicals (∙OH) were the primary reactive species responsible for the photodegradation process. Overall, the highly efficient 1-BCQD/CN composite with excellent photocatalytic activity could provide a cost-effective and robust means to address the increasing concerns over global environmental pollution.

Synthesis and Characterization of ZnBi2O4 Nanoparticles: Photocatalytic Performance for Antibiotic Removal under Different Light Sources

This work aims to synthesize a photocatalyst with high photocatalytic performances and explore the possibility of using it for antibiotic removal from wastewater. For that, the spinel ZnBi2O4 (ZBO) was produced with the co-precipitation method and its optical, dielectric, and electrochemical characteristics were studied. The phase has been determined and characterized by X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FT-IR). For the ZBO morphology, a Scanning Electron Microscopy (SEM) has been used. Then, the optical and dielectric properties of ZBO have been evaluated by calculating refractive index n (λ), extinction coefficient (k), dissipation factor (tan δ), relaxation time (τ), and optical conductivity (σopt) using the spectral distribution of T(λ) and R(λ). An optical gap band of 2.8 eV was determined and confirmed. The electrochemical performance of ZBO was investigated and an n-type semiconductor with a flat band potential of 0.54 V_SCE was found. The photocatalytic efficiency of ZBO was investigated in order to degrade the antibiotic Cefixime (CFX) under different light source irradiations to exploit the optical properties. A high CFX degradation of approximately 89% was obtained under solar light (98 mW cm−2) only after 30 min, while 88% of CFX degradation efficiency has been reached after 2 h under UV irradiation (20 mW cm−2); this is in line with the finding of the optical characterizations. According to the obtained data, solar light assisted nanoparticle ZBO can be used successfully in wastewater to remove pharmaceutical products.

Novel reduced graphene oxide/ZnBi2O4 hybrid photocatalyst for visible light degradation of 2,4-dichlorophenoxyacetic acid

A new highly efficient rGO/ZnBi₂O₄ hybrid catalyst has been successfully synthesized through oxidation-reduction and co-precipitation methods, followed by heating at 450 °C. The obtained rGO/ZnBi₂O₄ catalyst was characterized by X-ray diffraction (XRD), UV-vis diffuse reflectance spectroscopy (DRS), scanning electron microscopy (SEM), Fourier-transform infrared (FTIR) spectroscopy, and X-ray photoelectron spectroscopy (XPS). The catalytic activity of rGO/ZnBi₂O₄ under visible light irradiation was tested using 2,4-dichlorophenoxyacetic acid (2,4-D) in aqueous solution. The rGO/ZnBi₂O₄ hybrid catalyst containing 2% rGO (2.0rGO/ZnBi₂O₄) showed the best catalytic performance. More than 90% of 2,4-D in a 30 mg/L solution was degraded after 120 min of visible light irradiation using 2.0rGO/ZnBi₂O₄ at 1.0 g/L concentration. Moreover, the 2.0rGO/ZnBi₂O₄ catalyst showed excellent stability over four consecutive cycles, with no significant changes in the photocatalytic degradation rate. This study demonstrated that rGO/ZnBi₂O₄ may be a promising, low-cost, and green photocatalyst for environmental remediation applications.