CuO-ZnO nanocomposites (NCs) were synthesized using an aqueous extract of Verbascum sinaiticum Benth. (GH) plant. X-ray diffraction (XRD), spectroscopic, and microscopic methods were used to explore the crystallinity, optical properties, morphology, and other features of the CuO-ZnO samples. Furthermore, catalytic performances were investigated for methylene blue (MB) degradation and 4-nitrophenol (4-NP) reduction. According to the results, CuO-ZnO NCs with 20 wt % CuO showed enhanced photocatalytic activity against MB dye with a 0.017 min^-1 rate constant compared to 0.0027 min^-1 for ZnO nanoparticles (NPs). Similarly, a ratio constant of 5.925 min^-1 g^-1 4-NP reductions was achieved with CuO-ZnO NCs. The results signified enhanced performance of CuO-ZnO NCs relative to ZnO NPs. The enhancement could be due to the synergy between ZnO and CuO, resulting in improved absorption of visible light and reduced electron-hole (e^-/h⁺) recombination rate. In addition, variations in the CuO content affected the performance of the CuO-ZnO NCs. Thus, the CuO-ZnO NCs prepared using V. sinaiticum Benth. extract could make the material a desirable catalyst for the elimination of organic pollutants.

Biogenic methods of synthesis of nanoparticles (NPs) using plant extracts have been given a great attention due to its nontoxicity and environmental friendliness. In this study, TiO₂ NPs were synthesized from titanium tetrabutoxide and extract of root of Kniphofia foliosa. NPs of TiO₂ were biosynthesized at different volume compositions of titanium tetrabutoxide to the plant extract with a ratio of 1 : 2, 1 : 1, and 2 : 1, respectively. These green synthesized NPs of TiO₂ were characterized by thermogravimetric analysis (TGA/DTA), X-ray diffraction (XRD), scanning electron microscope-energy dispersive X-ray spectroscopy (SEM-EDS), transmission electron microscopy (TEM), ultraviolet-visible spectroscopy (UV-Vis), and Fourier transform infrared (FTIR) spectroscopy. TGA/DTA analysis has confirmed that the synthesized NPs of TiO₂ were stable above the temperature of 500°C. The sharp and intense peaks at 2θ values of 25.3, 38.0, 47.9, 53.2, 54.8862, 62.7, 70.2, and 75.0 have confirmed formation of crystalline NPs of TiO₂ in the sample of 1 : 1 and 2 : 1 ratios, and less crystalline samples for TiO₂ NPs prepared in a 1 : 2 ratio. Comparison between FT-IR absorption bands of the plant extract and that of calcined NPs of TiO₂ confirmed the purity of synthesized nanomaterials, except unavoidable adsorption of moisture on the surface of TiO₂ NPs in an open air. The antibacterial activity of biosynthesized TiO₂ NPs and that of ethanolic root extract of Kniphofia foliosa was investigated via the disc diffusion method against human pathogen bacteria strains of Staphylococcus aureus, Escherichia coli, Klebsiella pneumonia, and Streptococcus pyogenes. Among the different ratios, TiO₂ (1 : 1) NP shows better performance towards Gram-negative bacteria due to its smaller average crystalline size and uniform morphology observed in SEM image relative to the other two ratios of TiO₂ NPs. Antibacterial activity of the ethanolic root extract of Kniphofia foliosa itself showed better performance towards Gram-negative bacteria than NPs of TiO₂ that might be due to antibacterial activity of residue of ethanol left with the plant extract.

The study was focused on the preparation and characterizations of sodium periodate-modified nanocellulose (NaIO₄-NC) prepared from Eichhornia crassipes for the removal of cationic methylene blue (MB) dye from wastewater (WW). A chemical method was used for the preparation of NaIO₄-NC. The prepared NaIO₄-NC adsorbent was characterized by using X-ray diffraction (XRD), Fourier transform infrared (FTIR), scanning electron microscope (SEM), energy-dispersive X-ray (EDX), and BrunauerEmmettTeller (BET) instruments. Next, it was tested to the adsorption of MB dye from WW using batch experiments. The adsorption process was performed using Langmuir and Freundlich isotherm models with maximum adsorption efficiency (q_max) of 90.91 mg·g⁻¹ and percent color removal of 78.1 at optimum 30 mg·L⁻¹, 60min., 1g, and 8 values of initial concentration, contact time, adsorbent dose, and solution pH, respectively. Pseudo-second-order (PSO) kinetic model was well fitted for the adsorption of MB dye through the chemisorption process. The adsorption process was spontaneous and feasible from the thermodynamic study because the Gibbs free energy value was negative. After adsorption, the decreased values for physicochemical parameters of WW were observed in addition to the color removal. From the regeneration study, it is possible to conclude that NaIO₄-NC adsorbent was recyclable and reused as MB dye adsorption for 13 successive cycles without significant efficient loss.

Nowadays, water pollution is a major concern to the globe. For this reason, various research works has been done to access pure water thereby minimizing the effect of pollutants. In this work, the cobalt doped ZnO (Co-doped ZnO) via the accumulation of cobalt ion onto Eichhornia crassipes plant tissue for different days and combined with zinc precursor was synthesized. The resulting catalyst powder samples were characterized by Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), X-Ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (FE-SEM), and Ultraviolet–vis (UV–vis) spectroscopy, and microwave plasma atomic emission spectrometer (MP-AES). The catalysts were also tested for the photocatalytic degradation of methylene blue (MB) in the presence of H₂O₂ under visible light irradiation. The best catalytic activity was gained by the 8th-days accumulation of cobalt ion onto the Eichhornia crassipes plant tissue and 99.6% of the dye was degraded within 45 min. However, 69.6, 65.7, 73.6, and 94.8% of MB dye was degraded by 1, 2, 4, and 6 days accumulations. Hence, removal of toxic heavy metal by using Eichhornia crassipes plant and recycling in the wastewater treatment gain is highly appreciated. Moreover, the Co-doped ZnO photocatalysts could enhance the photocatalytic activities due to suppressing of the electron and hole recombination and the porosity of the catalysts resulted from the Eichhornia crassipes plant after calcination.

Nanomaterial-based catalytic conversion of hazardous organic pollutants into benign substances is one of the green methods employed for wastewater treatment. This study demonstrates the fabrication of (rGO-ZnO)/CuO nanocomposites (NCs) via a microwave (MW)-assisted method for (photo)catalytic application. The crystal structure, optical, morphological, and electrochemical characteristics were examined using X-ray diffraction (XRD), spectroscopic, microscopic, and electrochemical techniques. The analysis indicated that rod-like (rGO-ZnO)/CuO NCs having a nanoscale diameter with enhanced light absorption and well-matched band positions between rGO-ZnO and CuO were formed. Furthermore, the catalytic reduction of 4-nitrophenol (4-NP) and photocatalytic degradation of methylene blue (MB) tests showed remarkable results with rate constants of 0.468 min⁻¹ for 4-NP reduction within 8 min and 0.02213 min⁻¹ for MB degradation within 105 min. Thus, the artful decoration of ZnO nanorods (NRs) with CuO into the (rGO-ZnO)/CuO NCs interface is an effective strategy for fabricating highly efficient photocatalysts.