Graphitic Carbon Nitride/Zinc Oxide-Based Z-Scheme and S-Scheme Heterojunction Photocatalysts for the Photodegradation of Organic Pollutants

Ocimum tenuiflorum leaf-mediated graphitic carbon nitride and ZnO/GCN nanohybrid: a sustainable approach for environmental applications

Water contamination is a real concern, and safe water demand increases with the growing world population. The development of eco-friendly and cost-effective technologies that can clean water is necessary. This study investigates the bio-synthesis of pure graphitic carbon nitride nanoparticles (GCN-NPs), zinc oxide nanoparticles (ZnO-NPs), and ZnO-doped graphitic carbon nitride nanohybrids (ZnO/GCN-NHs) using Ocimum tenuiflorum (OT) leaf extract, with a focus on their potential applications in wastewater treatment, cytotoxicity assessment, and antibacterial activity. GCN synthesis using plant extract was never reported in previous studies. Under direct solar light photocatalytic performance of the synthesized NPs and NHs was tested on the degradation of methylene orange (MO) dye and compared. Among the samples, the ZnO/GCN-NHs (10 mg/100 mL) exhibits good photocatalytic activity, achieving up to 47.56% degradation in 150 min of MO dye. The cytotoxicity of the bio-synthesized NPs and NHs 50 µg/mL concentration was assessed against human dental pulp stem cells and these were found to be non-toxic, indicating their potential for biomedical applications. The antimicrobial properties were also assessed using well diffusion and disc diffusion tests against four bacterial strains, i.e., two Gram-negative (Escherichia coli and Pseudomonas aeruginosa) and two Gram-positive (Staphylococcus aureus and Streptococcus dysgalactiae). The tests demonstrate significant antibacterial activity with an excellent inhibition radius against Escherichia coli 17.5 ± 1 mm, Pseudomonas aeruginosa 15.04 ± 1 mm, Staphylococcus aureus 27.5 ± 1 mm, and Streptococcus dysgalactiae 25 ± 1 mm. The enhanced photocatalytic and antimicrobial properties of the ZnO/GCN-NHs are hypothesized to be due to the increased production of reactive oxygen species (ROS) through the combination of ZnO-NPs with biosynthesized GCN.

Graphite Phase Carbon Nitride Nanosheets-Based Fluorescent Sensors for Analysis and Detection

Fluorescent sensors reflect information such as the concentration or content of the analysis by interacting with a specific recognition group to change the signal of the fluorophore. It has attracted much attention because of its advantages of high sensitivity, fast detection speed and low cost, and it has become an effective alternative to traditional detection methods. Graphitic phase carbon nitride nanosheets (g-CNNs) are a class of carbon-based fluorescent nanomaterials derived from bulk graphite phase carbon nitride (g-C3N4), which have attracted much attention from scholars because of their advantages of low cost, simple fabrication, high quantum yield, strong stability and nontoxicity. Functional modified g-CNNs can greatly improve the photocatalytic performance. At present, although there have been some researches on fluorescent sensors based on g-CNNs. Nevertheless, there are few reviews about the g-CNNs-based fluorescent sensors. Therefore, in addition to summarizing the sensing mechanism of fluorescent sensors (such as photoinduced electron transfer, fluorescence resonance energy transfer, and intramolecular charge transfer) and the advantages and disadvantages of common signal substances, this paper focused on the application progress of g-CNNs-based fluorescent sensors in the field of analysis and detection.

Preparation and characterization of sulphur and zinc oxide Co-doped graphitic carbon nitride for photo-assisted removal of Safranin-O dye

Recently, there has been significant interest in photocatalytic reactions involving graphitic carbon nitride (g-C3N4) due to its sp2-hybridized carbon and nitrogen content and it is an ideal candidate for blending with other materials to enhance performance. Here, we have synthesized and analyzed both doped and undoped g-C3N4 nanoparticles. Specifically, we co-doped sulfur (S) into g-C3N4, integrated it with ZnO particles, and investigated the photocatalytic potential of these nanocomposites to remove Safranin-O dye. The initial step involved the preparation of pure g-C3N4 through calcination of urea. Subsequently, S-g-C3N4 was synthesized by calcining a mixture of urea and thiourea with a 3 : 1 ratio. Finally, the ZnO-S-g-C3N4 composite was synthesized using the liquid exfoliation technique, with distilled water serving as the exfoliating solvent. These samples were characterized by advanced techniques, including UV-Vis spectroscopy, Fourier-transform infrared spectroscopy (FTIR), X-ray Diffraction (XRD), energy dispersive X-ray (EDX) and scanning electron microscopy (SEM), to assess their crystallinity, morphology, optical properties, and phase purity. Subsequently, these nanocomposites were employed in catalytic and photocatalytic processes to remove the Safranin-O dye (SO). The results highlighted the formation of Z-scheme junction responsible for ZnO-S-g-C3N4's significant performance improvement. The comparison of results demonstrated that S-g-C3N4 and ZnO-S-g-C3N4 composites revealed an effective removal of Safranin-O dye in the presence of UV-light as compared to pure g-C3N4, as it was attributed to the phenomenon of improved separation of photogenerated charge carriers as a result of heterojunction formation between S-g-C3N4 and ZnO interfaces. In addition to improving photocatalytic performance, this study presents a facile route for producing ZnO-S-g-C3N4 composite with superior adsorption capabilities and selectivity.

Fabrication of carbon-based materials derived from a cobalt-based organic framework for enhancing photocatalytic degradation of dyes

The pyrolysis of metal-organic frameworks (MOFs) has emerged as a promising route to synthesize carbon/metal oxide-based materials with diverse phase compositions, morphologies, sizes and surface areas. In this paper, 1,3,5-benzoic acid (BTC) and 2,4,6-tri(4-pyridinyl)-1-pyridine (TPP) were used as ligands to prepare a novel cobalt-based MOF (Co-MOF) which was used as a precursor to obtain five carbon-based materials at different temperatures (Co-C200/400/600/800/1000). Furthermore, five dyes were used as degradation targets to investigate the photocatalytic degradation performance of the title materials under UV light irradiation. Co-C1000 exhibited the best photocatalytic degradation performance for methyl orange (MO), and the degradation rate could reach 99.21%. The enhanced photocatalytic activity was attributed to narrower band-gaps and a synergistic effect originating from the well-aligned straddling band structures between Co/CoO/Co3O4 and C, also resulting in a faster interfacial charge transfer during the photocatalytic reaction. This study will aid in the development of photocatalysts generated from carbon-based materials via the pyrolysis transformation of MOFs, therefore greatly enhancing the photocatalytic performance.