Synthesis, characterization, and photocatalytic activities of green sol-gel ZnO nanoparticles using Abelmoschus esculentus and Salvia officinalis: A comparative study versus co-precipitation-synthesized nanoparticles

Background

The development of green chemistry methods involving plant-based nanoparticle synthesis presents an affordable and eco-friendly approach for wastewater treatment and color removal. This study aimed to synthesize ZnO nanoparticles using the sol-gel method with Salvia officinalis and Abelmoschus esculentus plants, examining their photocatalytic efficiency for organic dye removal.

Methods

To compare the properties of ZnO nanoparticles, another type of ZnO-NPs was synthesized using the co-precipitation method. The characterization of synthesized nanoparticles was performed using thermogravimetric analysis (TGA-DTG), X-ray diffraction (XRD), Dynamic Light Scattering (DLS), Zeta potential (ZP), field emission scanning electron microscopy (FE-SEM), Energy Dispersive X-ray (EDX), Fourier transform infrared spectroscopy (FTIR), and UV-Vis spectrophotometry.

Results

Based on XRD results, the average crystalline size of nanoparticles was calculated using the Debye-Scherer equation for synthesized nanoparticles using the S. officinalis at 22.99 nm and for the A. esculentus at 29.79 nm, and for the co-precipitation method at 18.83 nm. The FE-SEM images showed spherical ZnO nanoparticles. Photocatalytic properties of ZnO-NPs were investigated for remove of methylene blue organic dye in the presence of UV light. The pH 10 was identified as the best pH, which had the highest percentage of color degradation. All three types of nanoparticles were tested by up to 360 min to optimize the dyeing time. For A. esculentus, the highest percentage of color removal occurred in the first 90 min (41.0 %), for S. officinalis nanoparticles between 75 and 90 min (86.9 %), and for chemically synthesized nanoparticles between 30 and 45 min (100 %).

Conclusions

In conclusion, the best MB dye degradation capacity belonged to co-precipitation ZnO nanoparticles followed by S. officinalis and A. esculentus nanoparticles.

Zn(II) porphyrin-encapsulated MIL-101 for photodynamic therapy of breast cancer cells

The photodynamic treatment is a non-aggressive and clinically accepted procedure for removing selected cancer cells with the activation of a photosensitizer agent at a specific light. In this study, the zinc porphyrin (Zn[TPP]) was prepared and encapsulated into the MIL-101 (Zn[TPP]@MIL-101). It was used in photodynamic therapy (PDT) against MCF-7 breast cancer cells under a red light-emitting diode. The structure, morphology, surface area, and compositional changes were investigated using conventional characterization methods including FTIR, FESEM, EDX, and BET analyses. The MTT assay was performed under light and dark conditions to explore the ability of Zn[TPP]@MIL-101 in PDT. The results have demonstrated the IC50 of 14.3 and 81.6 mg/mL for light and dark groups, respectively. As the IC50 revealed, the Zn[TPP]@MIL-101 could efficiently eradicate cancer cells using PDT.

Fabrication of Graphene-Based TiO2@CeO2 and CeO2@TiO2 Core-Shell Heterostructures for Enhanced Photocatalytic Activity and Cytotoxicity

Development of light-harvesting properties and inhibition of photogenerated charge carrier recombination are of paramount significance in the photocatalytic process. In the present work, we described the synthesis of core-shell heterostructures, which are composed of titanium oxide (TiO₂) and cerium oxide (CeO₂) deposited on a reduced graphene oxide (rGO) surface as a conductive substrate. Following the synthesis of ternary rGO-CeO₂@TiO₂ and rGO-TiO₂@CeO₂ nanostructures, their photocatalytic activity was investigated toward the degradation of rhodamine B dye as an organic pollutant under UV light irradiation. The obtained structures were characterized with high-resolution transmission electron microscopy, field-emission scanning electron microscopy, energy-dispersive X-ray spectroscopy, Fourier transform infrared spectroscopy, X-ray diffraction, Brunauer-Emmett-Teller, X-ray photoelectron spectroscopy surface analysis, and UV-Vis spectroscopy. Various parameters including pH, catalyst dosage, temperature, and contact time were studied for photocatalysis optimization. Heterostructures showed considerable advantages because of their high surface area and superior photocatalytic performance. In contrast, rGO-CeO₂@TiO₂ showed the highest photocatalytic activity, which is attributed to the more effective electron-hole separation and quick suppression of charge recombination at core-shell phases. A biological assay of the prepared heterostructure was performed to determine the cytotoxicity against breast cancer cells (MCF-7) and demonstrated a very low survival rate at 7.65% of cells at the 17.5 mg mL^-1 concentration of applied photocatalyst.

Adsorption and photocatalytic properties of porphyrin loaded MIL-101 (Cr) in methylene blue degradation

In this study for the very first time, zinc tetraphenylporphyrin (ZnTPP) was loaded into MIL-101 (Zn[TPP]@MIL-101) to perform an adsorptive and photocatalytic dye removal. The physicochemical attributes of the catalyst were thoroughly determined by the usage of XRD, FTIR, FESEM, BET, UV-vis, and inductively coupled plasma (ICP). The obtained XRD pattern exhibited the phase purity of MIL-101 and its structural stability. The solid-phase diameter of the catalyst was observed to be ~ 270.76 ± 119.95 nm, while its gas adsorption data was indicative of a decrease in the specific surface area after the loading of ZnTPP. The ICP analysis displayed the amount of encapsulated Zn[TPP] (~ 17%) in MIL-101. The UV-vis confirmed the presence of Zn[TPP] in MIL-101 with the lack of any interferences or overlaps with the λ_max of methylene blue (MB) with the support. The dye removal of MB was investigated under dark conditions (adsorption) and UV light (photodegradation). The observed adsorption under dark conditions using Zn[TPP]@MIL-101 (99.27% yield) demonstrated a superior dye removal in comparison to the cases of photodegradation of MB by MIL-101 and Zn[TPP]@MIL-101 or adsorption by MIL-101. In conformity to the gathered results, [ZnTPP] was able to increase the adsorption capacity at pH = 7 at room temperature.

Tragacanth-mediate synthesis of NiO nanosheets for cytotoxicity and photocatalytic degradation of organic dyes

In this study, NiO nanosheets have been manufactured using a co-precipitation approach that involved the usage of nickel nitrate (Ni (NO₃)₂.6H₂O) as the raw material and tragacanth in the role of a stabilizing agent. NiO nanosheets have been fabricated through the reduction of nickel nitrate solution that had been obtained by the application of aqueous extract of tragacanth, which is capable of functioning as a reducing and stabilizing agent. In the following, the physical and chemical properties of tragacanth-stabilized NiO nanosheets have been identified via FESEM, EDS, XRD, UV-Vis, and FT-IR techniques. According to the XRD pattern, these particular nanosheets have contained a cubic structure and group space Fm3m, along with the average size of about 18 to 43 nm that had been in agreement with the FESEM measurements. In addition, we have evaluated the photocatalytic activity of tragacanth-stabilized NiO nanosheets on the degradations of methylene blue (MB) and methyl orange (MO) dyes. The performed photocatalytic assessment has displayed that the nanosheets can degrade 82% of MO within 210 min and 60% of MB in 300 min. The cytotoxicity of tragacanth-stabilized NiO nanosheets on human Glioblastoma cancer (U87MG) cell lines has been investigated via the MTT assay, while it has been detected in the obtained results that the inhibitory concentration (IC₅₀) had been 125 µg/mL.