Visible-Light Degradation of Organic Dye Based on a Heterostructure Photocatalyst

Enhanced photocatalytic degradation of levofloxacin over heterostructured C3N4/Nb2O5 system under visible light

The growing usage of antibiotics and their subsequent release in water bodies have become a serious environmental concern. In this study, heterostructured photocatalysts C3N4/Nb2O5 have been synthesized using a simple hydrothermal method and applied to facilitate the degradation of the widely used antibiotic levofloxacin. The structural, morphological, and optical properties of the photocatalysts were characterized using XRD, SEM, TEM, UV-Vis and PL to establish the structure-property relationship. The type-II heterojunctions C3N4/Nb2O5 show remarkable activity under visible light irradiation, where Nb2O5 facilitates preferential adsorption of levofloxacin at the catalyst surface while C3N4 extends visible light absorption. This synergy resulted in superior catalytic performance (91%) in the optimized system, exceeding that of individual materials (Nb2O5 30% and C3N4 56%). The effect of catalyst dosage, pH, oxygen and point of zero is also investigated. The process is mainly photo-driven, and the trapping experiments reveal superoxide radicals as key species responsible for the degradation. Additionally, the adsorption behaviour, reformation of the degraded pollutant and reusability factors are evaluated to assess the practical feasibility of the photocatalytic system.

Key Role of Corncob Based-Hydrochar (HC) in the Enhancement of Visible Light Photocatalytic Degradation of 2,4-Dichlorophenoxyacetic Acid Using a Derivative of ZnBi-Layered Double Hydroxides

A superior heterojunction of HC-ZnBi-LDO was synthesized in two steps, namely hydrothermal carbonization, followed by co-precipitation. The 2% HC-ZnBi-LDO heterojunction photocatalysts could degrade over 90.8% of 30 mg/L 2,4-dichlorophenoxyacetic acid (2,4-D) using 1.0 g/L of the catalyst after 135 min of visible light exposure at pH 4. The activity of 2% HC-ZnO-LDO was remarkably stable. Approximately 86.4-90.8% of 30 mg/L 2,4-D was degraded, and more than 79-86.4% of TOC was mineralized by 2% HC-ZnBi-LDO at pH 4 after 135 min of visible light exposure during four consecutive cycles. The rapid separation and migration of charge carriers at the interfaces between HC and ZnBi-LDO were achieved within 2% HC-ZnBi-LDO. Moreover, the electron acceptor characteristic of HC in 2% HC-ZnBi-LDO caused the recombination of charge carriers to decrease significantly, thus generating more reactive radicals, such as hydroxyl radicals (OH^●) and superoxide radicals (O₂^●-). These results demonstrate that the novel 2% HC-ZnBi-LDO is a superior photocatalyst for the remediation of hazardous organic pollutants.

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.