Spectral investigations to the effect of bulk and nano ZnO on peanut plant leaves

Bryophyllum pinnatum leaf extract mediated ZnO nanoparticles with prodigious potential for solar driven photocatalytic degradation of industrial contaminants

In an era of environment-friendly development plant extract-based biological techniques for synthesizing nanoparticles have gained a lot of attention over traditionally famous chemical and physical synthesis techniques. In the present study we have synthesized biogenic zinc oxide nanoparticles (BPLE-ZnO NPs) using Bryophyllum pinnatum leaf extract, compared its native properties and solar-driven photocatalytic activity with chemically prepared ZnO nanoparticles (Chem-ZnO NPs). In order to characterize and compare the Chem-ZnO and BPLE-ZnO, various techniques were used, including UV-visible spectroscopy, x-ray diffractrometry, photoluminescence spectroscopy, field emission scanning electron microscopy, electron dispersive x-ray spectroscopy, fourier transform infrared spectroscopy, and zeta potential analyzer. The results revealed the formation of hexagonal wurtzite ZnO, with no significant difference between the two methods; however, the use of Bryophyllum pinnatum leaf extract in ZnO NPs synthesis resulted in reduced size, presence of biomolecules on its surface and better monodispersity than purely chemical synthesis. Further, the BPLE-ZnO NPs showed better efficiency in the solar-driven photocatalytic degradation of methylene blue (MB) dye compared to Chem-ZnO NPs. Under solar exposure at a dose of 0.50 mg/mL BPLE-ZnO, resulted in 97.31% photodegradation with a rate constant of 0.06 min-1 of 20 mg/L MB solution within just 60 min which was 9.51% higher compared to the Chem-ZnO NPs. The BPLE-ZnO NPs were also employed to investigate their solar-driven photocatalytic performance for degrading the pharmaceutical (Metronidazole and Amoxycillin) and textile pollutants (Methyl orange dye) under sunlight. The results show that Bryophyllum pinnatum leaf extract-mediated ZnO NPs have an excellent potential in solar-based photocatalytic applications.

Evaluation of the Photocatalytic Activity of Distinctive-Shaped ZnO Nanocrystals Synthesized Using Latex of Different Plants Native to the Amazon Rainforest

ZnO nanocrystals with three different morphologies have been synthesized via a simple sol-gel-based method using Brosimum parinarioides (bitter Amapá) and Parahancornia amapa (sweet Amapá) latex as chelating agents. X-ray diffraction (XRD) and electron diffraction patterns (SAED) patterns showed the ZnO nanocrystals were a pure hexagonal wurtzite phase of ZnO. XRD-based spherical harmonics predictions and HRTEM images depicted that the nanocrystallites constitute pitanga-like (~15.8 nm), teetotum-like (~16.8 nm), and cambuci-like (~22.2 nm) shapes for the samples synthesized using bitter Amapá, sweet Amapá, and bitter/sweet Amapá chelating agent, respectively. The band gap luminescence was observed at ~2.67-2.79 eV along with several structural defect-related, blue emissions at 468-474 nm (V_O, V_Zn, Zn_i), green emissions positioned at 513.89-515.89 (h-VO+), and orange emission at 600.78 nm (VO+-VO++). The best MB dye removal efficiency (85%) was mainly ascribed to the unique shape and oxygen vacancy defects found in the teetotum-like ZnO nanocrystals. Thus, the bitter Amapá and sweet Amapá latex are effective chelating agents for synthesizing distinctive-shaped ZnO nanocrystals with highly defective and remarkable photocatalytic activity.

Visible-Light-Responsive Photocatalytic Activity Significantly Enhanced by Active [VZn+VO+] Defects in Self-Assembled ZnO Nanoparticles

Defect influences on the photoactivity of ZnO nanoparticles prepared by a powdered coconut water (ACP) assisted synthesis have been studied. The crystalline phase and morphology of ZnO nanoparticles were effectively controlled by adjusting the calcination temperature (400-700 °C). An induced transition of hybrid Zn₅(CO₃)₂(OH)₆/ZnO nanoparticles to single-phase ZnO nanoparticles was obtained at 480 °C. The morphological analysis revealed a formation of ZnO nanoparticles with semispherical (∼6.5 nm)- and rod-like (∼96 nm) shapes when the calcination temperatures were 400 and 700 °C, respectively. Photoluminescence characterizations revealed several defects types in the samples with V_Zn and V_O⁺ being in the self-assembly of semispherical- and rod-like ZnO nanoparticles. The photocatalytic activity of the ZnO nanoparticles was examined by assessing the degradation of methylene blue in an aqueous solution under low-intensity visible-light irradiation (∼3 W m^-2). The results point toward the self-assembly of semispherical- and rod-like ZnO nanoparticles that had significantly better photocatalytic activity (∼31%) in comparison to that of spherical-agglomerated- or near-spherical-like species within 120 min of irradiation. The possible photocatalytic mechanism is discussed in detail, and the morphology-driven intrinsic [V_Zn+V_O⁺] defects are proposed to be among the active sites of the ZnO nanoparticles enhancing the photocatalytic activity.

Toxicity assessment of metal oxide nano-pollutants on tomato (Solanum lycopersicon): A study on growth dynamics and plant cell death

The present study for the first time demonstrated the interactions of metal oxide (MO) nano-pollutants (CuO and Al₂O₃-NPs) with tissues and cellular DNA of tomato plants grown in soil sand: silt: clay (667:190:143) and Hoagland-hydroponic system and assessed the hazardous effects of NPs on cell physiology and biochemistry. Results of SEM equipped with EDX revealed attachment of variably shaped CuO-NPs (18 nm) and Al₂O₃-NPs (21 nm) on roots, and internalization followed by translocation in plants by ICP-MS and TEM. Significant variations in foliage surface area, chlorophyll, proteins, LPO, and antioxidant enzymes were recorded. Roots and shoots accumulated 225.8 ± 8.9 and 70.5 ± 4 μgAl g^-1 DW, whereas Cu accumulation was 341.6 ± 14.3 (roots) and 146.9 ± 8.1 μg g^-1 DW (shoots) which was significant (p ≤ 0.0005) as compared to control. The total soluble protein content in roots, shoots, and leaves collected from Al₂O₃-NPs treated plants increased by 120, 80, and 132%, respectively while in CuO-NPs treatments, the increase was 68 (roots), 36 (shoots), and 86% (leaves) over control. The level of antioxidant enzymes in plant tissues was significantly (p ≤ 0.05) higher at 2000 μg ml^-1 of MONPs over control. A dose-dependent increase in reactive oxygen species (ROS), biphasic change of lower and higher fluorescence in mitochondria due to dissipation of mitochondrial membrane potential (ΔΨm) and membrane defects using propidium iodide were observed. Comparatively, CuO-NPs induced higher toxicity than Al₂O₃-NPs. Perceptible changes in proteins (amide-I & II), cellulose, glucose, galactose and other carbohydrates were observed under FT-IR. The binding studies with TmDNA showed fluorescence quenching of EtBr-TmDNA and acridine orange-TmDNA complex only by CuO-NPs with -ΔG and +ΔH and +ΔS values. However, Al₂O₃-NPs induced lesser change in TmDNA conformation. Conclusively, the results are novel in better demonstrating the mechanistic basis of nano-phyto-toxicity and are important which could be used to develop strategies for safe disposal of Al₂O₃-NPs and CuO-NPs.