Green synthesis of zinc oxide nanoparticles using Brassica oleracea var. botrytis leaf extract: Photocatalytic, antimicrobial and larvicidal activity

Green synthesis of nanomaterials has emerged as an ecofriendly sustainable technology for the removal of dyes in the last few decades. Especially, plant leaf extracts have been considered as inexpensive and effective materials for the synthesis of nanoparticles. In this study, zinc oxide nanoparticles (ZnO NPs) were prepared using leaves extract of Brassica oleracea var. botrytis (BO) by co-precipitation and applied for photocatalytic/antibacterial activity. The synthesized BO-ZnO NPs was characterized by different instrumental techniques. The UV-vis Spectrum of the synthesized material showed maximum absorbance at a wavelength of 311 nm, which confirmed the formation of BO-ZnO NPs. The XRD pattern of BO-ZnO NPs represents a hexagonal wurtzite structure and the average size of particles was about 52 nm. FT-IR spectrum analysis confirms the presence of hydroxyl, carbonyl, carboxylic, and phenol groups. SEM images exhibited a flower like morphology and EDX spectrum confirming the presence of the elements Zn and O. Photo-catalytic activity of BO-ZnO NPs was tested against thiazine dye (methylene blue-MB) degradation under direct sunlight irradiation. Around 80% of the MB dye got degraded at pH 8 under 75 min of sunlight irradiation. Further, the study examined that the antimicrobial and larvicidal activity of BO-ZnO NPs obtained through green synthesis. The antimicrobial study results showed that the BO-ZnO NPs formed zones against bacterial pathogens. The results showed the formation of an inhibition zone against B. subtills (16 mm), S.aureus (13 mm), K. pneumonia (13 mm), and E. coli (9 mm) respectively at a concentration of 100 μg/mL of BO-ZnO NPs. The larvicidal activity of the BO-ZnO NPs was tested against the fourth instar of Culex quinquefasciatus mosquito larvae The LC₅₀ and LC₉₀ values estimated through the larvicidal activity of BO-ZnO NPs were 76.03, 190.03 ppm respectively. Hence the above findings propose the synthesized BO-ZnO NPs by the ecofriendly method can be used for various environmental and antipathogenic applications.

Synthesis, Characterization, and Evaluation of the Remediation Activity of Cissus quadrangularis Zinc Oxide Nanoparticle-Activated Carbon Composite on Dieldrin in Aqueous Solution

In this study, zinc oxide-activated carbon nanocomposite was used as the adsorbent for the remediation of dieldrin in aqueous media. Zinc oxide nanoparticles (ZNPs) were synthesized from Cissus quadrangularis (C. quadrangularis) leaf extract, and activated carbon was derived from maize cobs. Nanocomposites were formulated by mixing the ZNPs with the activated carbon in a ratio of 1 : 50. The UV-Vis spectra showed a complete reduction of Zn2+ to Zn0 with plasmon resonance bands in the range of 361–376 nm, which is a characteristic of ZNPs. The SEM images of ZNPs showed hexagonal-shaped particles of 15–20 nm, with face-centered cubic crystals, as demonstrated by XRD analysis. FTIR results showed absorption bands in the ranges 3500–3100 cm−1 (N-H stretch), 3400–2400 cm−1 (O-H stretch), 988–830 cm−1 (C-H bend), 1612 cm−1 (C=C stretch), 400–600 cm−1 (Zn-O stretch), and 1271 cm−1 (C-O bend). Batch adsorption experiments were performed using 20 ml of dieldrin solution at varying pH values (1–14), concentrations (5–100 ppm), temperatures (293–323 K), adsorbent dosages (0.01–0.12 g), and contact times (30–180 minutes) to determine the optimum conditions. The calculated thermodynamic parameters (ΔH°, ΔS°, and ΔG°) indicated that the adsorption was spontaneous and exothermic in nature, implying decreasing randomness of dieldrin molecules at the solid-liquid interface. The isotherm and adsorption kinetics for the composite showed that the absorption process followed Langmuir isotherm and pseudo-second-order kinetics. Adsorption capacities of the nanoparticles, activated carbon, and nanocomposite at a reaction time of 120 minutes and pH of 7 were 3.72 ± 0.068 mg/g, 3.92 ± 0.061 mg/g, and 4.0 ± 0.102 mg/g, respectively, with corresponding percentage removals of 93.12 ± 0.044, 98.04 ± 0.044, and 99.76 ± 0.332. Thus, the nanocomposite exhibited a better sorbing potential for dieldrin in solution than activated carbon. This study recommends testing the remediation potential of the synthesized nanocomposite on other persistent organic pollutants.

A green synthesized recyclable ZnO/MIL-101(Fe) for Rhodamine B dye removal via adsorption and photo-degradation under UV and visible light irradiation

Metal-organic frameworks (MOFs) have recently debuted as participants and solid supports in catalysts for environmental application in water treatment. Visible light active nanocomposites; ZnO/MIL-101(Fe); were synthesized via a hydrothermal method by loading ZnO; prepared by a green method; on a porous MIL-101(Fe) to be used as a heterogeneous catalyst for Rhodamine B dye (RhB) degradation as a model pollutant. The effect of adding acetic acid during the preparation of MIL-101(Fe) was studied; [A] used for the samples prepared by acetic acid. The prepared catalysts were characterized by XPS, XRD, zeta potential, TGA, FTIR, N₂ adsorption-desorption measurements, SEM, EDX, elemental mapping, TEM, and UV-VIS diffuse reflectance spectroscopy. The loading of ZnO on MIL-101(Fe) decreased the band gap from 3.2 eV for ZnO to be 2.85 eV for ZnO/MIL-101(Fe)[A], this low band gap explaining the obtained high activity under visible light irradiation. The mechanism of the photocatalytic degradation of RhB was investigated by introducing different scavengers to compete for the possible reactive species involved in the degradation process. The trapping experiments indicated that h⁺ and ^•OH have a vital role in the RhB degradation. The reusability of MIL-101(Fe) was also investigated after three runs. Thus, the synthesized ZnO/MIL-101(Fe)[A] could be used as an alternative catalyst for the photocatalytic degradation of coloured wastewater as it can successfully degrade 97.1% of Rhodamine B (10 mg/L) with high reaction rate (k = 0.0339 min^-1) under visible light irradiation for 300 min using 0.5 g/L of the catalyst. The as-prepared ZnO/MIL-101(Fe) and ZnO/MIL-101(Fe)[A] have competitive photocatalytic dye degradation activity.

ZnO nanoparticles as photodegradation agent controlled by morphology and boron doping

ZnO nanoparticles with different morphology and doping possess different atomic planes at their interfaces. This changed their catalytic efficiency during degradation experiments with dyes, significantly dependent also on used dopant concentrations.

ZnO nanorod arrays assembled on activated carbon fibers for photocatalytic degradation: Characteristics and synergistic effects

Well-aligned ZnO nanorod arrays were assembled on activated carbon fibers by a stepwise sequence of sol-gel and hydrothermal synthesis methods. These ZnO nanorod arrays on activated carbon fibers having different characteristics such as surface area, rod concentration, aspect ratio and defect level, were applied as catalysts for the photodegradation of an aqueous methylene blue solution. They showed very promising methylene blue adsorbility in the dark (ca. 0.025-0.031 mg methylene blue m^-2 catalyst, vs. 0.072 mg methylene blue m^-2 activated carbon fibers). Significantly, the defect level of ZnO nanorod arrays has a major effect on the turnover frequency compared to other characteristics. A synergistic effect between activated carbon fibers and ZnO nanocrystals on enhancing turnover frequency was more significant for the well-assembled ZnO nanorod arrays on activated carbon fibers catalysts compared to the mechanically mixed ZnO powder with activated carbon fibers catalyst. Further, turnover frequency for the ZnO nanorod arrays on activated carbon fibers (0.00312 mol_{methylene blue} mol_ZnO^-1 h^-1) was twice higher than that for the corresponding bare ZnO nanorod arrays, and 3 times higher than that for a commercial ZnO powder. In addition, ZnO nanorod arrays on activated carbon fibers show high degradation (77.5%) and mineralization (55.0%) levels for methylene blue, and also good reusability (or stability) as demonstrated by a sequential 5-time recycle routine. These outstanding features indicate that activated carbon fibers supported ZnO nanorod arrays have significant potential to be used as catalysts for photodegradation.

Photocatalytic CO2 reduction of C/ZnO nanofibers enhanced by an Ni-NiS cocatalyst

The photocatalytic reduction of CO₂ into valuable hydrocarbon fuels via solar energy is a promising strategy for carbon utilization. In the present paper, a hierarchical Ni-NiS/C/ZnO photocatalyst was prepared via the in situ photodeposition of compact Ni-NiS nanosheets onto C/ZnO electrospun nanofibers. The existence of metallic Ni and NiS was confirmed by X-ray photoelectron spectroscopy. Photoluminescence (PL) and time-resolved PL spectra revealed that the cocatalyst Ni-NiS enhanced the charge separation efficiency of the C/ZnO nanofibers. The as-prepared Ni-NiS/C/ZnO showed enhanced CO₂ reduction activity, with CO and CH₄ production rates 10 and 15 times greater than those of pristine C/ZnO under 350 W visible light illumination. The intermediates of CH₃O^-, HCHO, and HCOO^- were detected by in situ Fourier transform infrared spectroscopy, confirming that CO₂ reduction is a complex reaction with multiple steps. The ¹³C isotopic tracer method proved that CH₄ and CO were obtained from the reduction of CO₂ rather than from other carbon species in the environment. The amorphous carbon in C/ZnO could promote optical absorption, improve conductivity and reduce the interfacial charge transport resistance. Ni-NiS improved the electron-hole-pair separation of the C/ZnO nanofibers. The observed enhancement in photocatalytic activity was largely attributed to higher light utilization and effective electron-hole separation. This work proves that Ni-NiS is a promising cocatalyst to ZnO for photocatalytic CO₂ reduction.

C, N dual-doped ZnO nanofoams: a potential antimicrobial agent, an efficient visible light photocatalyst and SXAS studies

It is crucial to develop an environmentally friendly and low-cost method to treat industrial effluent that contains soluble dyes and microbes. Most of the photocatalysts have been studied using an external light source that increases the cost of the purification process of effluent. This study focuses on developing efficient solar photocatalytic nanofoams. The controlled growth of ZnO nanofoams (CNZ nanofoams) in a simple method of thermal oxidation using a soft template is reported. Prepared nanofoams are characterized using X-ray diffraction, scanning electon microscopy and synchrotron soft X-ray absorption spectroscopy. By photocatalysis studies under direct sunlight it was found that within 120 min CNZ nanofoams degraded 99% of the dye. In addition, antimicrobial studies of multi-drug-resistant E. Fergusonii isolated from wastewater was carried out. These antimicrobial results showed a good inhibition zone, indicating that prepared nanofoams are both an effective solar photocatalyst and an antimicrobial agent.

Crystallization time in ZnO: the role of surface OH groups in its photoactivity

The crystallization time and surface modifications concerning the hydroxyl groups on the ZnO catalyst were studied and the results suggest that there is a balance between the surface groups and morphology playing a critical role in its photoactivity.

Controlled growth of ZnS/ZnO heterojunctions on porous biomass carbons via one-step carbothermal reduction enables visible-light-driven photocatalytic H2 production

Controlled growth of ZnS/ZnO heterojunctions on porous biomass carbons has been achieved via a one-step carbothermal reduction strategy.

Adsorption and visible-light photodegradation of organic dyes with TiO2/conjugated microporous polymer composites

A series of composite materials made of TiO₂ and conjugated microporous polymers (CMPs) were prepared with a hydrothermal method and used as both adsorbents and photocatalysts for the adsorption and visible-light photodegradation of organic dyes in aqueous solutions. It is found that the blending of CMPs can significantly improve both the adsorption capacity and the photocatalytic degradation activity of TiO₂ towards organic dyes.

A series of composite materials made of TiO₂ and conjugated microporous polymers (CMPs) were prepared and used as both adsorbents and photocatalysts for the adsorption and visible-light photodegradation of organic dyes in aqueous solutions.