Synthesis and Characterization of rGO@ZnO Nanocomposites for Esterification of Acetic Acid

Green synthesis of ZnO-TiO2/RGO nanocomposites using Senna surattensis extract: a novel approach for enhanced anticancer efficacy and biocompatibility

The purpose of the present study is to enhance the anticancer and biocompatibility performance of TiO2 NPs, ZnO NPs, ZnO-TiO2 (NCs), and ZnO-TiO2/reduced graphene oxide (RGO) NCs against two types of human cancer (HCT116) and normal (HUVCE) cells. A novel procedure for synthesizing ZnO-TiO2/RGO NCs has been developed using Senna surattensis extract. The improved physicochemical properties of the obtained samples were investigated using different techniques such as XRD, TEM, SEM, XPS, FTIR, DLS and UV-visible spectroscopy. XRD results showed that the addition of ZnO and RGO sheets affects the crystal structure and phase of TiO2 NPs. SEM and TEM images displayed that the TiO2 NPs and ZnO NPs were small with uniform spherical morphology in the prepared ZnO-TiO2/RGO NCs. Besides, it is shown that ZnO-TiO2 NCs anchored onto the surface of RGO sheets with a particle size of 14.80 ± 0.5 nm. XPS data confirmed the surface chemical composition and oxidation states of ZnO-TiO2/RGO NCs. Functional groups of prepared NPs and NCs were determined using FTIR spectroscopy. DLS data confirmed that the addition of ZnO and RGO sheets improves the negative surface charge of the prepared pure TiO2 NPs (-22.51 mV), ZnO NPs (-18.27 mV), ZnO-TiO2 NCs (-30.20 mV), and ZnO-TiO2/RGO NCs (-33.77 mV). Optical analysis exhibited that the bandgap energies of TiO2 NPs (3.30 eV), ZnO NPs (3.33 eV), ZnO-TiO2 NCs (3.03 eV), and ZnO-TiO2/RGO NCs (2.78 eV) were further enhanced by adding ZnO NPs and RGO sheets. This indicates that the synthesized samples can be applied to cancer therapy and environmental remediation. The biological data demonstrated that the produced ZnO-TiO2/RGO NCs show a more cytotoxic effect on HCT116 cells compared to pure TiO2 NPs and ZnO-TiO2 NCs. On the other hand, these NCs displayed the lowest level of toxicity towards normal HUVCE cells. These results indicate that the ZnO-TiO2/RGO NCs have strong toxicity against HCT116 cells and are compatible with normal cells. Our results show that the plant extract enhanced the physicochemical properties of NPs and NCs compared with the traditional chemical methods for synthesis. This study could open new avenues for developing more effective and targeted cancer treatments.

Fabrication of a Fully Printed Ammonia Gas Sensor Based on ZnO/rGO Using Ultraviolet-Ozone Treatment

In this study, a room-temperature ammonia gas sensor using a ZnO and reduced graphene oxide (rGO) composite is developed. The sensor fabrication involved the innovative application of reverse offset and electrostatic spray deposition (ESD) techniques to create a ZnO/rGO sensing platform. The structural and chemical characteristics of the resulting material were comprehensively analyzed using XRD, FT-IR, FESEM, EDS, and XPS, and rGO reduction was achieved via UV-ozone treatment. Electrical properties were assessed through I-V curves, demonstrating enhanced conductivity due to UV-ozone treatment and improved charge mobility from the formation of a ZnO-rGO heterojunction. Exposure to ammonia gas resulted in increased sensor responsiveness, with longer UV-ozone treatment durations yielding superior sensitivity. Furthermore, response and recovery times were measured, with the 10 min UV-ozone-treated sensor displaying optimal responsiveness. Performance evaluation revealed linear responsiveness to ammonia concentration with a high R2 value. The sensor also exhibited exceptional selectivity for ammonia compared to acetone and CO gases, making it a promising candidate for ammonia gas detection. This study shows the outstanding performance and potential applications of the ZnO/rGO-based ammonia gas sensor, promising significant contributions to the field of gas detection.

Enhanced peroxymonosulfate activation via heteroatomic doping defects of pyridinic and pyrrolic N in 2D N‑doped carbon nanosheets for BPA degradation

Understanding the role of intrinsic defects and nonmetallic heteroatom doping defects in activating peroxymonosulfate (PMS) and subsequently degrading endocrine-disrupting compounds is crucial for designing more efficient carbon catalysts. Therefore, we synthesized N-rich carbon nanosheets (NCs) through pyrolysis of a glutamic acid and melamine mixture and utilized them to activate PMS for bisphenol A (BPA) degradation. Different weight ratios of the above mixtures were allowed for manipulating NCs' defect level and N configuration. The reaction rate constant (k) was significantly positively correlated with the pyridinic and pyrrolic N content, and negatively and weakly positively correlated with graphite N and intrinsic defects, respectively. These findings suggest pyridinic and pyrrolic N, rather than graphitic N and intrinsic defects, enhance PMS activation to generate reactive oxygen species (specifically O•-2 and 1O2) and oxidize BPA. The NC-activated PMS system with the highest N content (17.9 atom%) demonstrated a remarkably high k (0.127 min-1) using minimal concentrations of PMS (0.4 mM) and NC (0.15 g/L), highlighting the system's efficiency. Excess halide anions led to significantly increased k with only a limited formation of trichloromethane (disinfection byproducts) in presence of 100 mM Cl-. This study offers novel perspectives on identifying catalytic sites within N-doped carbonaceous materials.

Inhibition of α-glucosidase activity by curcumin loaded on ZnO@rGO nanocarrier for potential treatment of diabetes mellitus

Curcumin (Cur) is an acidic polyphenol with some effects on α-glucosidase (α-Glu), but Cur has disadvantages such as being a weak target, lacking passing the blood-brain barrier and having low bioavailability. To enhance the curative effect of Cur, the hybrid composed of ZnO nanoparticles decorated on rGO was used to load Cur (ZnO@rGO-Cur). The use of the multispectral method and enzyme inhibition kinetics analysis certify the inhibitory effect and interaction mechanism of ZnO@rGO-Cur with α-Glu. The static quenching of α-Glu with both Cur and ZnO@rGO-Cur is primarily driven by hydrogen bond and van der Waals interactions. The conformation-changing ability by binding to the neighbouring phenolic hydroxyl group of Cur increased their ability to alter the secondary structure of α-Glu, resulting in the inhibition of enzyme activity. The inhibition constant (Ki, Cur  > Kis,ZnO@rGO-Cur ) showed that the inhibition effect of ZnO@rGO-Cur on α-Glu was larger than that of Cur. The CCK-8 experiments proved that ZnO@rGO nanocomposites have good biocompatibility. These results suggest that the therapeutic potential of ZnO@rGO-Cur composite is an emerging nanocarrier platform for drug delivery systems for the potential treatment of diabetes mellitus.

Enhanced photocatalytic degradation of methylene blue dye using eco-friendly synthesized rGO@ZnO nanocomposites

Industrial chemical pollutants such as methylene blue (MB) dye are released into the water body and potentially cause harm to the human and aquatic biosphere. Therefore, this study aims to synthesize eco-friendly nanocatalysts, i.e., reduced graphene oxide (rGO), zinc oxide (ZnO), and reduced graphene oxide-zinc oxide (rGO@ZnO) nanocomposites, for efficient photocatalytic degradation of MB dye. A graphite rod was obtained from waste dry cell batteries for the electrochemical exfoliation synthesis of graphene oxide (GO) and rGO. For the eco-friendly synthesis of ZnO and rGO@ZnO nanocatalysts, Croton macrostachyus leaf extract was used as a reducing and capping agent. The synthesized nanocatalysts were characterized using a UV-Vis spectrophotometer, Fourier transform infrared spectroscopy, X-ray diffraction, and scanning electron microscopy with energy-dispersive X-ray. The eco-friendly synthesized rGO, ZnO, and rGO@ZnO nanocatalysts were applied for the photocatalytic degradation of MB dye using direct sunlight irradiation. At optimum parameters, photocatalytic degradation of MB dye efficiency reached up to 66%, 96.5%, and 99.0%, respectively. Furthermore, kinetics of the photodegradation reaction based on rGO, ZnO, and rGO@ZnO nanocatalysts follow pseudo-first-order with a rate constant of 2.16 × 10-3 min-1, 4.97 × 10-3 min-1, and 5.03 × 10-3 min-1, respectively. Lastly, this study promotes a low catalyst load (20 mg) for the efficient photodegradation of MB dye.

Zinc oxide doped on reduced graphene oxide nanosheets activated by solar radiation for degradation of organic pollutants and bacterial inactivation

Metal ion-based nanocomposite materials were recognized to exhibit a wide range of photocatalytic and biological applications. This study aims to synthesize zinc oxide doped reduced graphene oxide (ZnO/RGO) nanocomposite in sufficient quantities through the sol-gel method. The physical characters of the synthesized ZnO/RGO nanocomposite were determined by X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Scanning electron microscope (SEM), Energy-dispersive X-ray (EDS) and Transmission electron microscopy (TEM) techniques. The TEM image results revealed rod-like morphology of the ZnO/RGO nanocomposite. The X-ray photoelectron spectral data revealed the formation of ZnO nanostructures representing the banding energy gap value of 1044.6 and 1021.5 eV positions. Moreover, ZnO/RGO nanocomposites displayed excellent photocatalytic degradation with a degradation efficiency of 98.6%. This research not only demonstrates the photocatalytic efficiency of zinc oxide-doped RGO nanosheets but also illustrates the antibacterial efficacy against two different bacterial pathogens including Gram-positive E. coli and Gram-negative S. aureus. Furthermore, this research highlights an eco-friendly and inexpensive preparation of nanocomposite material for a wide range of environmental applications.