Green synthesis of two-electron centre based ZnO/NiCo2S4 QDs-OVs using Punica granatum fruit peel extract for an exceptional visible light photocatalytic degradation of doxycycline and ciprofloxacin

Biosynthesis of nanomaterials using plant extract makes them attractive in the field of photocatalysis as they are environmental friendly. The current study focused on the biosynthesis of ZnO/NiCo₂S₄ QDs (NCs) using Punica granatum fruit peel extract as the reducing agent. The nanomaterials were characterized with XRD, FTIR, Raman, SEM, TEM, UV-vis DRS, BET, PL, EIS, and ESR analysis and were used for photocatalytic degradation of doxycycline (DOX) and ciprofloxacin (CIP). The bandgap of ZnO is 3.2 eV, and the decoration of NiCo₂S₄ QDs aids in narrowing the bandgap (2.8 eV), making the NCs visible light active. The fabricated NCs achieved 99 and 89% degradation of DOX and CIP respectively. The photocatalytic efficiency of ZnO/NiCo₂S₄ QDs was much higher compared to individual ZnO and NiCo₂S₄ QDs. The half-life period of DOX and CIP were evaluated to be 58 and 152 min respectively. The percentage of TOC removal in the photodegraded product of DOX and CIP was estimated to be 99 and 89% respectively, indicating the mineralization of the compounds. The enhanced photocatalytic efficiency of the NCs was attributed to the narrowed visible light active bandgap, synergistic charge transfer across the interface, and lower charge recombination. The intermediates formed during the photocatalytic degradation of DOX and CIP were analyzed using GC-MS/MS analysis, and the photodegradation pathway was elucidated. Also, the toxicity of the intermediates was computationally analyzed using ECOSAR software. The fabricated ZnO/NiCo₂S₄ QDs have excellent stability and reusability, confirmed by XRD and XPS analysis. The reusable efficiency of the NCs for the photocatalytic degradation of DOX and CIP were 98.93, and 99.4% respectively. Thus, the biologically fabricated NCs are shown to be an excellent photocatalyst and have wide applications in environmental remediation.

Direct Z-Scheme AgBr/β-MnO2 Photocatalysts for Highly Efficient Photocatalytic and Anticancer Activity

The preparation of visible light-responsive efficient photocatalysts for removing organic contaminants from water and killing cancer cells has gotten a lot of attention due to the growing global concern. In this study, we have successfully fabricated an efficient AgBr/β-MnO₂ nanocomposite via a facile deposition and precipitation method at room temperature. Techniques such as XRD, SEM-EDS, TEM, DRS, PL, EIS, ESR, and FTIR were used to determine the crystalline, structural, morphological, optical, and other properties. The SEM and TEM analyses reveal that AgBr NPs are decorated on the surface of β-MnO₂, which possesses rods with a sphere-like structure for AgBr/β-MnO₂. The EDX analysis confirms the existence of Mn, O, Ag, and Br elements in the nanocomposites without an extra peak, indicating that the synthesized samples are highly pure. The high photocatalytic performance of AgBr/β-MnO₂ could be attributed to the formation of Ag NPs and the construction of the Z-scheme heterojunction between AgBr and β-MnO₂. This may enhance fast light absorption and efficient photogenerated (e-/h+) pairs, as indicated by EIS and photoluminescence measurements, which in turn achieved high activity for the decomposition of MB (97%, in 12 min), RhB (98.9%, in 9 min), and paracetamol (80%, in 180 min), respectively. The kinetic model study proposed that the first-order model showed a better fit than the zero- and second-order for the photocatalytic decolorization of RhB dye. XRD analysis of 0.2 AgBr/β-MnO₂ before and after recycling confirms the high stability of the catalyst. HPLC results showed that no detectable by-products are produced through the decomposition of paracetamol. Interestingly, 0.2 AgBr/β-MnO₂ nanocomposites showed visible light-induced anticancer activity against A549 cancer cell lines. The mechanistic degradation pathway has been proposed using the involvement of active species like superoxide radicals (^-•O₂) and photoinduced holes (h⁺). The proposed work focuses on synthesizing effective photocatalysts in a less hazardous environment with superior biological activity.

Toxicity and removal of parabens from water: A critical review

Parabens are biocides used as preservatives in food, cosmetics and pharmaceuticals. They possess antibacterial and antifungal activity due to their ability to disrupt cell membrane and intracellular proteins, and cause changes in enzymatic activity of microbial cells. Water, one of our most valuable natural resource, has become a huge reservoir for parabens. Halogenated parabens from chlorination/ozonation of water contaminated with parabens have shown to be even more persistent in water than other types of parabens. Unfortunately, there is dearth of data on their (halogenated parabens) presence and fate in groundwater which serves as a major source of drinking water for a huge population in developing countries. An attempt to neglect the presence of parabens in water will expose man to it through ingestion of contaminated food and water. Although there are reviews on the occurrence, fate and behaviour of parabens in the environment, they largely omit toxicity and removal aspects. This review therefore, presents recent reports on the acute and chronic toxicity of parabens, their estrogenic agonistic and antagonistic activity and also their relationship with antimicrobial resistance. This article further X-rays several techniques that have been employed for the removal of parabens in water and their drawbacks including adsorption, biodegradation, membrane technology and advanced oxidation processes (AOPs). The heterogeneous photocatalytic process (one of the AOPs) appears to be more favoured for removal of parabens due to its ability to mineralize parabens in water. However, more work is needed to improve this ability of heterogeneous photocatalysts. Perspectives that will be relevant for future scientific studies and which will drive policy shift towards the presence of parabens in our drinking waters are also offered. It is hoped that this review will elicit some spontaneous actions from water professionals, scientists and policy makers alike that will provide more data, effective technologies, and adaptive policies that will address the growing threat of the presence of parabens in our environment with respect to human health.

The degradation of paraben preservatives: Recent progress and sustainable approaches toward photocatalysis

Parabens are a class of compounds primarily used as antimicrobial preservatives in pharmaceutical products, cosmetics, and foodstuff. Their widely used field leads to increasing concentrations detected in various environmental matrices like water, soil, and sludges, even detected in human tissue, blood, and milk. Treatment techniques, including chemical advanced oxidation, biological degradation, and physical adsorption processes, have been widely used to complete mineralization or to degrade parabens into less complicated byproducts. All kinds of processes were reviewed to give a completed picture of parabens removal. In light of these treatment techniques, advanced photocatalysis, which is emerging rapidly and widely as an economical, efficient, and environmentally-friendly technique, has received considerable attention. TiO₂-based and non-TiO₂-based photocatalysts play an essential role in parabens degradation. The effect of experimental parameters, such as the concentration of targeted parabens, concentration of photocatalyst, reaction time, and initial solution pH, even the presence of radical scavengers, are surveyed and compared from the literature. Some representative parabens such as methylparaben, propylparaben, and benzylparaben have been successfully studied the reaction pathways and their intermediates in their degradation process. As reported in the literature, the degradation of parabens involves the production of highly reactive species, mainly hydroxyl radicals. These reactive radicals would attack the paraben preservatives, break, and finally mineralize them into simpler inorganic and nontoxic molecules. Concluding perspectives on the challenges and opportunities for photocatalysis toward parabens remediation are also intensively highlighted.

Water hyacinth plant extract mediated green synthesis of Cr2O3/ZnO composite photocatalyst for the degradation of organic dye

The Cr2O3/ZnO composite catalysts with varying the amount of chromium precursors abbreviated as 0.02CrZn, 0.04CrZn, 0.06CrZn, 0.08CrZn, 0.1CrZn, and fixed the amount of Zn precursor (0.1 M) were prepared by using water hyacinth (Eichhornia crassipes) extract as a template/capping agent. The prepared catalysts were characterized and the catalytic performances of the catalysts were also checked for the degradation of methylene blue (MB) dye. The photocatalytic MB dye degradation by 0.08CrZn catalyst was achieved and 85% of MB dye was degraded within 90 min irradiation time. However, 0.1CrZ, 0.06CrZ, 0.04CrZ, 0.02CrZ, ZnO, and Cr2O3 catalysts degrade only 80, 74, 79, 76, 52, and 74% of MB dye, respectively. The catalytic performances indicated that the addition of optimum amount of chromium precursor in the preparation of Cr2O3/ZnO composite catalysts with the aid of Eichhornia crassipes plant extract enhances the catalytic activities. This performance enhancement could be as a result of reducing the electron/hole pair separation and the porosity resulted from the plant extract in the catalyst system.

Highly stable AgNPs prepared via a novel green approach for catalytic and photocatalytic removal of biological and non-biological pollutants

Increases in biological and non-biological pollutants pose a significant threat to environmental systems. In an effort to develop an effective means to treat such pollutants, the use of Phaseolus vulgaris (kidney beans) as reducing and capping agents is proposed for the green synthesis of highly stable silver nanoparticles (AgNPs) with a face-centered cubic (fcc) crystalline structure (size range: 10-20 nm). The potent role of the resulting AgNPs was found as triple platforms (photocatalyst, catalyst, and antimicrobial disinfectant). AgNPs were able to photocatalytically degrade approximately 97% of reactive red-141 (RR-141) dye within 150 min of exposure (quantum efficiency of 3.68 × 10^-6 molecule.photon^-1 and a removal reaction kinetic rate of 1.13 × 10^-2 mmol g^-1 h^-1). The role of specific reactive oxygen species (ROS) in the photocatalytic process and complete mineralization of dye was also explored through scavenger and chemical oxygen demand (COD) experiments, respectively. As an catalyst, AgNPs were also capable of reducing 4-nitrophenol to 4-aminophenol within 15 min. Overall, AgNPs showed excellent stability as catalyst and photocatalyst even after five test cycles. As an antimicrobial agent, the AgNPs are effective against both gram-positive (Bacillus subtilis) and -negative bacteria (Escherichia coli), with the zones of clearance as 15 and 18 mm, respectively. Thus, the results of this study validate the triple role of AgNPs derived via green synthesis as a photocatalyst, catalyst, and antimicrobial agent for effective environmental remediation.