Construction of layered embedding dual Z-Scheme Bi2O2CO3/g-C3N4/Bi2O3: Tetracycline degradation pathway, toxicity analysis and mechanism insight

Z-scheme Fe@Fe2O3/BiOBr heterojunction with efficient carrier separation for enhanced heterogeneous photo-Fenton activity of tetracycline degradation: Fe2+ regeneration, mechanism insight and toxicity evaluation

The recombination of photogenerated carrier leads to inefficient Fe2+ regeneration, which limits the extensive application of heterogeneous photo-Fenton. Here, a novel Fe@Fe2O3/BiOBr catalyst with Z-scheme heterojunction structure is designed, and the establishment of the Z-scheme heterojunction facilitates the separation and transfer of photogenerated carrier and maintains the superior redox capability of the system. As-prepared Fe@Fe2O3/BiOBr catalyst exhibits outstanding catalytic performance and stability, especially for the optimum composite FFB-3, its degradation efficiency of tetracycline (TC) achieves 98.22% and the mineralization degree reaches 59.48% within 90 min under natural pH. The preeminent catalytic efficiency benefited from the synergistic of heterogeneous photo-Fenton and Z-scheme carriers transfer mechanism, where Fe2+ regeneration was achieved by photogenerated electrons, and increased hydroxyl radicals were produced with the participation of H2O2 in-situ generated. The results of free-radical scavenging experiment and ESR illustrated that •OH, •O2-, 1O2 and h+ were active species participating in TC degradation. Furthermore, the TC degradation paths were proposed according to LC-MS, and the toxicity evaluation result showed that the toxicity of TC solutions was markedly decreased after degradation. This study provides an innovative strategy for heterogeneous photo-Fenton degradation of antibiotic contaminations by constructing Z-scheme heterojunctions.

Preparation of O-g-C3N4 nanowires/Bi2O2CO3 porous plate composite photocatalysts for the efficient degradation of tetracycline hydrochloride in wastewater

Both g-C3N4 and Bi2O2CO3 are good photocatalysts for the removal of antibiotic pollutants, but their morphological modulation and catalytic performance need to be further improved. In this study, the calcination-hydrothermal method is used to prepare a O-g-C3N4@Bi2O2CO3 (CN@BCO) composite photocatalyst from dicyandiamide and bismuth nitrate. The prepared catalyst is characterized through various methods, including X-ray diffraction (XRD) and transmission electron microscopy (TEM). Further, the effects of different parameters, such as catalyst concentration and initial pH of the reaction solution, on its photocatalytic activity are investigated. The results show that the CN@BCO sample achieves an optimal degradation rate of 98.1% for tetracycline hydrochloride (TCH) with a concentration of 20 mg/L and a removal rate of 69.4% for total organic carbon (TOC) at 40 min. The quenching experiments show that ·O2-, h+, and ·OH participate in the photocatalytic process, with ·O2- being the most dominant active species. The toxicity of the predicted TCH degradation intermediates is analyzed using Toxicity Estimation Software Tool (TEST). Overall, the CN@BCO composite exhibits excellent photocatalytic performance, making it a promising candidate for environmental purification and wastewater treatment.

Constructing 3D flower-like S-scheme N-Bi2O2CO3/g-C3N4 heterojunction with enhanced photocatalytic performance

Mineral processing wastewater contains a lot of organic matter and heavy metal ions, and poor self-degradation ability makes it a key treatment object in environmental treatment. Photocatalysis is a promising technology to efficiently mineralize refractory contaminants from wastewater. In this work, 3D flower-like S-scheme N-Bi2O2CO3/g-C3N4 heterostructures were successfully constructed by hydrothermal method with the auxiliary of ionic liquids. The photocatalytic experiments show that the catalytic activity of heterojunction photocatalysts was significantly higher than that of bare g-C3N4 and N-Bi2O2CO3 for the degradation of two pollutants. NBOC/CN-2 shows the highest photocatalytic performance, and the degradation efficiency of sodium isobutyl xanthate (SIBX) on NBOC/CN-2 is 1.85 and 3 times that of bare g-C3N4 and Bi2O2CO3, respectively. The degradation efficiency of m-Cresol on NBOC/CN-2 is 8.34 and 6.93 times that of bare g-C3N4 and N-Bi2O2CO3, respectively. This significantly enhanced photocatalytic activity is attributed to the formation of flower-like heterojunctions, which can greatly increase the specific surface area and facilitate the separation and migration of photogenerated carriers. Total organic carbon (TOC) experiment proves that the two pollutants are effectively mineralized under the action of the prepared photocatalyst. The degradation path of m-Cresol degradation products was inferred based on the ion fragments. The capture experiment and Nitro-blue tetrazolium (NBT)-•O2- measurement show that superoxide radical plays a major role in photocatalytic degradation. The outstanding stability of the prepared flower-like heterojunction samples was examined by cyclic experiments. The S-scheme charge transfer mechanism has been proposed to explain the boosted activity of the flower-like heterojunction photocatalyst. This work provides a new idea for the design of efficient and stable g-C3N4-based photocatalyst for the photocatalytic degradation of refractory wastewater.

Removal of tetracycline from wastewater using g-C3N4 based photocatalysts: A review

Tetracycline is currently one of the most consumed antibiotics for human therapy, veterinary purpose, and agricultural activities. Tetracycline worldwide consumption is expected to rise by about more than 30% by 2030. The persistence of tetracycline has necessitated implementing and adopting strategies to protect aquatic systems and the environment from noxious pollutants. Here, graphitic carbon nitride-based photocatalytic technology is considered because of higher visible light photocatalytic activity, low cost, and non-toxicity. Thus, this review highlights the recent progress in the photocatalytic degradation of tetracycline using g-C₃N₄-based photocatalysts. Additionally, properties, worldwide consumption, occurrence, and environmental impacts of tetracycline are comprehensively addressed. Studies proved the occurrence of tetracycline in all water matrices across the world with a maximum concentration of 54 μg/L. Among different g-C₃N₄-based materials, heterojunctions exhibited the maximum photocatalytic degradation of 100% with the reusability of 5 cycles. The photocatalytic membranes are found to be feasible due to easiness in recovery and better reusability. Limitations of g-C₃N₄-based wastewater treatment technology and efficient solutions are also emphasized in detail.