ZnO Plane Research Articles

Synthesis, characterization and estimation of performance parameters of binary ZnO–SnO2/p-Si heterojunction solar cells

The present work demonstrates the successful synthesis of binary ZnO–SnO2 nanocomposite employing a simple and efficient sol-gel method. The XRD spectra confirmed the formation of a highly crystalline domain indexed to (100) planes of ZnO and (101) and (310) planes of SnO2. The UV–vis spectroscopy analysis revealed high transmittance over 85 % and good optical absorption, a desirable aspect for efficiency enhancement of the cell by heightened photo-excited charge carrier generation through an increased number of incident photons being striking at the junction. The optical band gap was determined using the Taucs formula and found to be 3.51 eV. To probe the possible application of ZnO–SnO2 in Heterojunction Solar Cells (HJSCs), we carried out a numerical simulation for the estimation of cell parameters using MATLAB. The result revealed that the work function (WF) does not have a significant effect on short circuit current density (Jsc), whereas the open-circuit voltage (Voc), fill factor (FF) and power conversion efficiency (PCE) significantly depend on the material work function. Typically VOC increased from 0.155 V to 0.665 V, FF increased from 0.586 to 0.838 and the PCE could be enhanced from 2.55 % to 15.74 %, with an estimated WF range of 4.5 eV–4.0 eV. The effect of substrate thickness was also studied, indicating increment in parameters in the range from 25 μm to 200 μm, however, no significant effect was noticed for thickness >200 μm. The simulation provides optimization of semiconductor properties through the estimation of cell parameters such as PCE, Voc, Jsc and FF for enhanced performance.

GO/ZnO Biosensor Synthesis and Characterization for Biosensors

In this study, GO/ZnO nanoparticles were synthesized using the solvothermal method and characterized for potential biosensor applications. The synthesized nanoparticles exhibited a high degree of crystalline structural purity, as confirmed by XRD analysis. The XRD pattern revealed characteristic peaks corresponding to the crystal planes of ZnO, indicating a typical wurtzite hexagonal structure. In addition, the synthesized nanoparticles were evaluated for their physical characteristics using transmission electron microscopy. The TEM analysis showed that the ZnO nanoparticles had a narrow size distribution, with an average particle size of approximately 25.19 ± 4.1 nm. The morphology of the nanoparticles was further examined, revealing that the ZnO nanoparticles were uniformly dispersed and localized within the GO sheets. Furthermore, the exfoliation of GO into single or few-layered sheets was achieved, as evidenced by its transparency in the TEM images. These findings suggest that the solvothermal synthesis method is effective in producing highly dispersed GO/ZnO nanoparticles with a narrow size distribution. The synthesized GO/ZnO nanoparticles showed promise for biosensor applications due to their uniform shape and distribution, as well as their small size.

Coating effect of renatured triple-helix lentinan on the morphology and antimicrobial activity of ZnO synthesized by hydrothermal method.

Polysaccharides are considered to be ideal green raw materials for enhancing biocompatibility and dispersion effects of nanoparticles. In this study, we coated and dispersed ZnO nanoparticles (NPs) using the denaturation-renaturation process of a triple helix glucan lentinan (LNT), induced by changes in pH value within the reaction system. Various ZnO/LNT composites with different particle sizes and crystal morphologies were prepared and characterized. The results demonstrated that renatured LNT (r-LNT) effectively encapsulated the {101̄0} crystal planes of ZnO, preventing crystal growth during the renaturation process and resulting in smaller, uniformly dispersed nanoparticles. Among the samples, ZnO/r-LNT-2 exhibited significantly higher antimicrobial activity, and it had a certain inhibitory effect on various plant pathogens. It also displayed the highest inhibitory effect against Candida albicans, with a minimum inhibitory concentration (MIC) of up to 8 μg mL-1. Consistently, ZnO/r-LNT-2 generated the highest amount of reactive oxygen species (ROS), thus exhibiting the most effective antimicrobial activity. However, excessive introduction of the dispersant LNT may reduce these activities. This study provides a foundation for further exploring the detailed mechanism of ROS generation catalyzed by ZnO and for harnessing the full potential of this type of antimicrobial agent.

Synergistic effect of ZnO nanoparticles with Cu2+ doping on antibacterial and photocatalytic activity

The nanoparticles (NPs) of ZnO and Cu-doped ZnO samples were prepared using a chemical precipitation method specifically aimed at enhancing photocatalytic and antibacterial activity. The structural, morphological, phase constitutional, functional, elemental, and optical properties have been studied using Powder X-ray Diffraction (PXRD), Transmission Electron Microscopy (TEM), Ultra Violet diffused reflectance spectroscopy (UV-DRS), Fourier-transform infrared (FTIR) spectroscopy, and Thermogravimetric analysis (TGA). The crystallite size was calculated by using Debye Scherrer formula and the obtained average crystallite size of pure ZnO, ZnO-Cu2.5%, ZnO-Cu5%, and ZnO-Cu10% sample is 24.31 ± 0.12 nm, 25.72 ± 0.47 nm, 26.83 ± 0.39 nm, and 26.94 ± 0.29 nm, respectively. High-resolution Transmission Electron Microscope (HR-TEM) was used to calculate the d-spacing. The values of d-spacing for ZnO, ZnO-Cu2.5%, ZnO-Cu5%, and ZnO-Cu10% samples were measured as 0.248 nm, 0.266 nm, and 0.273 nm, respectively and corresponds to (101), (002) and (100) planes of ZnO, respectively which are well associated with the PXRD data (JCPDS card no. 36–1451). It was found that the doping concentration affects the crystallinity of the ZnO nanoparticles. The average grain size of ZnO, ZnO-Cu2.5%, ZnO-Cu5%, and ZnO-Cu10% is 35.75 ± 1.91 nm, 38.55 ± 2.31 nm, 45.39 ± 1.78 nm, and 50.65 ± 2.23 nm, respectively as determined from TEM images by using the ImageJ software. Further, photo-catalytic dye degradation was studied to understand the photocatalytic behavior of synthesized nanoparticles. The UV–Vis adsorption study has revealed that optimum doping of Cu is mandatory to get the highest degradation of methylene blue (MB) dye. It was observed that 5% Cu-doped ZnO NPs have the optimum photocatalytic activity. Furthermore, the antibacterial activity of various formulations on the gram-negative, facultative anaerobic, coliform bacterium Escherichia coli (E. coli) was studied to establish zone of inhibition (ZOI) values for ZnO and Cu-doped ZnO NPs. The current research indicated that 5% Cu-doped ZnO NPs have shown maximum inhibition and may be used for various antibacterial applications.

Biosynthesis of Ag/bentonite, ZnO/bentonite, and Ag/ZnO/bentonite nanocomposites by aqueous leaf extract of Hagenia abyssinica for antibacterial activities

Abstract We report the synthesis of Ag/bentonite, ZnO/bentonite and Ag/ZnO/bentonite nanocomposites (NCs) using Hagenia abyssinica plant extract and their antibacterial study. The synthesized NCs were characterized by using many advanced techniques. The X-ray diffraction and high resolution transmission electron microscopy analysis confirmed the formation of composites with different phases. The average crystallite size (D) values of pure Ag nanoparticles (NPs), ZnO NPs, and activated bentonite (Na-AB) were found to be 8.14, 18.1, and 37.6 nm, respectively. The Ag/bentonite NCs, ZnO/bentonite NCs, and Ag/ZnO/bentonite NCs exhibited the D values of 7.4, 9.4, and 9.4 nm, respectively. The Fourier transform infrared spectral analysis revealed the presence of hydroxyl, carbonyl, and other functional groups on the surface of the synthesized NCs. The transmission electron microscopic analysis revealed the formation of Ag and ZnO NPs with hexagonal, rod-shaped, and spherical structures. HRTEM also revealed the presence of (102) plane of ZnO and (220) plane of Ag in Ag/ZnO/bentonite NCs. The antibacterial activities of the composites suspension were evaluated against Escherichia coli ATCC 25922 and Staphylococcus aureus ATCC 25923 by the disc diffusion and broth dilution methods. The ternary NC and Ag/ZnO/bentonite exhibited better zone of inhibition of 14.3 ± 0.3 and 17.3 ± 0.2 mm at 10 mg·mL−1 toward E. coli and S. aureus bacterial strains. The minimum inhibitory concentration and minimum bactericidal concentration values of Ag/ZnO/bentonite NCs were found to be 156.25 and 312.5 µg·mL−1 for E. coli. The investigation results revealed that the low temperature bio-synthesized Ag/ZnO/bentonite is a promising bactericide over the binary composites.

Copper sulfide and zinc oxide hybrid nanocomposite for wastewater decontamination of pharmaceuticals and pesticides

In this work, hybrid nanocomposites of CuS QDs @ ZnO photocatalysts are fabricated through a facile microwave-assisted (MW) hydrothermal method as a green preparation process. The prepared photocatalysts (PCs) are employed under simulated sunlight (SL) for the degradation of ciprofloxacin, ceftriaxone, ibuprofen pharmaceuticals, methylene blue dye, and 2,4,5-trichlorophenoxyacetic acid (2,4-D) pesticide. The prepared photocatalysts are characterized in detail using several compositional, optical, and morphological techniques. The influence of the CuS (QDs) wt. % on morphological, structural, as well as photocatalytic degradation efficiency have been investigated. The small displacement between the (107) plane of CuS and the (102) plane of ZnO can confirmed the existence of lattice interaction, implying the formation of p-n heterojunctions. TEM and XRD results demonstrated that the CuS QDs are established and uniformly decorated on the surface of ZnO NRs, confirming the forming of an efficient CuS QDs @ ZnO heterojunction nanostructures. The CuS QDs @ ZnO hybrid nanocomposites showed enhancement in crystallinity, light absorption, surface area, separation of e–h pair and inhibition in their recombination at an interfacial heterojunction. In addition it is found that, 3 wt% CuS QDs @ ZnO has the foremost influence. The results showed improvement of photocatalytic activity of the 3% CuS QDs @ ZnO hybrid nanocomposite as compared to the bare ZnO nanorods. The impressive photocatalytic performance of CuS @ ZnO heterostructure nanorods may be attributed to efficient charge transfer. The prepared CuS QDs @ ZnO hybrid nanocomposites exhibited 100% removal for MB dye, after 45 min, and after 60 min for ibuprofen, ciprofloxacin pharmaceuticals, and 2.4.5 trichloro phenoxy acetic acid pesticide with the catalyst amount of 0.2 g/L. Although 100% removal of ceftriaxone pharmaceutical acheived after 90 min. In addition CuS QDs @ ZnO hybrid nanocomposites exhibited complete removal of COD for ibuprofen, ceftriaxone pharmaceuticals and 2.4.5 trichloro phenoxy acetic acid pesticide after 2 h with no selectivity. Briefly, 3% CuS QDs@ZnO hybrid nanocomposites can be considered as promising photoactive materials under simulated sunlight for wastewater decontamination.

Fluorometric biosensor based on boronic acid-functionalized ZnO-derived nanostructures for the detection of N-acetylneuraminic acid and its in vivo bio-imaging studies

BackgroundN-acetylneuraminic acid (Neu5Ac) is a sialic acid-based biomarker in neurological disorders like Alzheimer's disease (AD) and aging. Their abnormal concentrations in biological fluids like human serum and cerebrospinal fluid (CSF) are highly concerning. Conventional analytical methods lack time-saving, high sensitivity, and convenient labor options for their detection. In this study, a selectively recognizable fluorometric sensor was developed based on the boronic acid-functionalization of carbon-rich zinc oxide-derived nanostructures (ZnO NSs) for Neu5Ac detection. MethodsThe ZnO NSs were synthesized using the acid-alkali-assisted hydrothermal method from anionic surfactants like sodium dodecyl sulfate (SDS). These were functionalized with 3-(aminopropyl)-triethoxysilane (APTES): (APT-ZnO NSs), aspirin [acetylsalicylic acid (ASA)]: (ASA-APT-ZnO NSs), and quercetin: (Qu-ASA-APT-ZnO NSs). To enhance the detection capacity against Neu5Ac, Qu-ASA-APT-ZnO NSs were modified with 3-aminophenylboronic acid (APBA) (APBA-ZnO NSs). Their structural, functional, and optical performance were investigated using XRD and Raman, FT-IR, and UV-Vis spectroscopy. Significant findingsFlower-like ZnO NSs showed a typical ZnO plane (110) of wurtzite hexagonal crystalline phase under HRTEM analysis. The novelty of the proposed work is the development of highly sensitive and efficient APBA-ZnO NSs for Neu5Ac detection in the linear concentration range of 0 to 8 µM with a low detection limit of 0.56 µM. These results are comparable to the other reports, and their multicolor fluorescence properties in zebrafish larvae confirm them as magnificent fluorescent probes for in vivo bio-imaging studies. The practicality of the proposed APBA-ZnO NSs was explored in serum and CSF samples, which showed potential recovery percentage ranges of 97–104.66% and 96.33–105.37%, respectively. In the future, these fluorescent probes will have the appropriate scope for the in vitro and in vivo detection of diverse neurological biomarkers.

Magnetic and optical properties of ZnO/Ni/ZnO multilayer film on Si(100) and sapphire substrates

The optical absorption, band gap, and magnetic properties of ZnO/Ni(t)/ZnO multilayer film structures were investigated in various Ni layer thicknesses and substrates. We deposited 1, 4, and 5 nm of Ni film by thermal evaporation technique that sandwiched between ZnO films (~15 nm) via radio frequency magnetron sputtering method on both Si(100) and sapphire substrates. Although x-ray diffraction (XRD) analysis confirmed the (002) crystalline plane of ZnO without any Ni crystal phases on Si(100) surface, the better crystalline directions of ZnO, hexagonal wurtzite structure, was observed on the sapphire substrate. In the XRD analysis, we observed the cubic structure of NiO film formation due to thermally oxidation of Ni ions with interactions ZnO layer. Atomic force microscopy images confirmed the effect of the Ni layer on the average island size of 23.9 ± 2.9 nm and 25.6 ± 6.2 of ZnO films on 4 and 5 nm Ni films, respectively. Energy dispersive x-ray spectroscopy data confirmed that there is no other atom or impurity in the sample structure. The optical transparency of the multilayer films was reduced with increasing Ni layer thickness and maximum transparency was obtained as 97% at 800 nm of wavelength for the film with 1 nm Ni. The direct optical band gap of ZnO/Ni(t)/ZnO films was found to be 3.25, 3.20, and 3.12 eV with the contribution of 1, 4, and 5 nm Ni film in the multilayer film stack. The maximum Hc is found to be 1000 Oe for Si substrates and this value is reduced to around 400 Oe due to the crystal formation of the NiO layer for sapphire substrate samples.

High photocatalytic efficiency of α-Fe2O3 - ZnO composite using solar energy for methylene blue degradation

The present report illustrates the photocatalytic degradation of methylene blue dye under solar energy through α-Fe2O3 - ZnO composite synthesized by adopting a facile and simple chemical method. Various characterization techniques particularly X-ray diffraction (XRD), Transmission electron microscopy (TEM), and Fourier transform infrared spectroscopy (FTIR), etc., have been employed to characterize the as-synthesized composite. The XRD reveals the successful formation of the as-synthesized sample. The TEM studies illustrate the agglomeration of particles with sizes in the range of ∼10–60 nm. HRTEM micrograph indemnifies the formation of lattice fringes pertaining to inter-planner spacing∼ 0.149 nm and ∼0.138 nm corresponding to (214) reflection plane of hematite and (112) reflection plane of ZnO, respectively. The as-synthesized α-Fe2O3 – ZnO composite shows double absorption edges which correspond to the bandgap of α-Fe2O3 (2.2 eV) and ZnO (3.2 eV). Furthermore, α-Fe2O3 - ZnO composite shows a remarkable enhanced degradation capacity than bare hematite nanoparticles and zinc oxide nanoparticles, and α-Fe2O3 – ZnO (1:2) composite demonstrates the best degradation performance among all the variants. Moreover, it clearly suggests that the UV part of solar light plays a vital role in the catalytic degradation of methylene blue whereas the visible part of light remains unresponsive.

Study on the design of ZnO/PANI composites and the mechanism of enhanced humidity sensing properties

ZnO/PANI composite humidity sensor was prepared by hydrothermal method. The first principles of density functional theory study the sensing mechanism. The calculation shows that the oxygen vacancy on ZnO surface is beneficial to the adsorption of water molecules. The {0 0 0‾1} crystal plane with the largest lattice oxygen number in ZnO has a strong adsorption capacity for water molecules, which is also conducive to improving the humidity sensitivity. PANI is easy to be combined on {0 1‾1 0} plane of ZnO, and it indirectly promotes the growth of {0 0 0‾1} plane, increasing the adsorption of water molecules and the proportion of H+ and H3O+ ions. In addition, the N–H group in ZnO/PANI enhances the H+ conduction, which further improves the performance of the sensor. The results concluded that the proportion of lattice oxygen in humidity sensor is an important factor of humidity sensor sensitive detection.

Enhanced photocatalytic activity in hydro-thermally grown nano structured ZnO/SnS core–shell composites

Abstract Detoxification of water bodies from industrial pollutant dyes by semiconductor heterojunction composites briefed. Synthesis of ZnO/SnS core/shell nanocomposites by ecofriendly hydrothermal method presented. Characterization by powder X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), UV–Vis absorption spectroscopy photoluminescence (PL) etc., were presented. Abundance of orthorhombic ZnO and hexagonal SnS was confirmed by X-ray diffraction. Compression of hexagonal ZnO planes (as core nanorods) and SnS core nanoparticles infers growth of core shell structure. Average crystallite size is found to be 5.8 nm. Structure and TEM morphology correlated. XPS reveals abundance of elemental oxidation state. Photocatalytic activity was studied by using visible light irradiation. Photoluminescence for ZnO/SnS core/shell nanocomposites inferred significant emission peaks. Enhanced PCA observed against visible light. Methylene blue dye characteristic PCAby its degradation evinced. PCA is found optimal for Z-S3. Configuration of bandgap promoted growth of novel hetero junction. Physical mechanism is proposed for the enhanced photocatalytic activity as accompanied by degradation of MB dye.

An ultra-high sensitive ethanol sensor through amending surface-functionalized groups by novel acidic synthesis methods

The surface structure and functional groups of MOS materials play key roles in sensor performance. Herein, we report the first attempt to use four organic acids (citric, ellagic, oxalic, and glycolic acids), instead of a traditional alkaline environment, to synthesize ZnO sensing materials. The results demonstrate that the morphology and structure of the ZnO material cab be modified by simply varying the type of organic acid, which can straightforwardly inhibit the growth of the crystal planes through acid etching. Among those selected organic acids for the synthesis, the synthesized ZnO-based citric acid has the best gas sensitivity to ethanol, with a state-of-the-art sensing response of 121.5 (Ra/Rg) to 100 ppm ethanol at a fairly low working temperature of 180 °C. All the sensors also show good selective ethanol detection compared to other gases, including methanol, carbon monoxide, carbon dioxide, hydrogen, methane, and propane. The improved sensor sensitivity to ethanol mainly originates from the surface defects increase in the organic-acids-synthesized sensing materials, which enhances adsorption and ionization of oxygen. Molecular dynamics (MD) simulations confirmed that the ethanol gas was preferentially absorbed on almost all (002), and (100) crystal planes of ZnO, explaining the selective sensing response to ethanol gas.

Nd-doped ZnO films grown on c-cut sapphire by pulsed-electron beam deposition under oblique incidence

Nd-doped ZnO thin films were grown by pulsed-electron beam deposition (PED) on c-cut sapphire substrates under oblique angle incidence, at 10-2 mbar oxygen pressure and for a substrate temperature of 500 °C. The films were smooth, compact and constituted with columnar grains inclined at about 17°±4° from the normal to the substrate surface. From X-ray diffraction and transmission electron microscopy experiments, it was found that the wurtzite phase of Nd-doped ZnO thin films is observed with the c-axis inclined around 35° with respect to the normal axis of the substrate, with a three-fold azimuthal symmetry. Epitaxial relationships between Nd-doped ZnO films and sapphire substrate were determined from the asymmetric X-ray diffraction and are presented compared with those obtained for the films grown by non-oblique PED. The tilt of the ZnO c-axis has been explained by the epitaxy of the (2 2 9) ZnO plane on the (0 0 l) sapphire plane, such particular epitaxial growth having never been reported previously.

Ultrasensitive NO2 gas sensor based on Sb-doped SnO2 covered ZnO nano-heterojunction

Sb-doped SnO2 covered ZnO nano-heterojunction (Sb-doped SnO2/ZnO NHs) are prepared by using a microwave hydrothermal method. The effect about morphology and gas sensor performance of the SnO2/ZnO NHs with Sb-doping is studied in detail. The SEM indicated that the morphology of SnO2 changed from nanowires to nanosheets by Sb-doping and the growth direction of SnO2 was vertical to the plane of ZnO from the TEM. Compared with undoped SnO2/ZnO NHs, the gas sensor response became higher as the concentration of Sb-doping increased which shows the sensor performance can be enhanced by Sb-doped SnO2. The change of morphology by Sb-doping increased the number of surface active sites and defects. In addition, a certain concentration of O vacancy was induced by Sb-doping to provide more free electrons that can also be captured by NO2. The research may provide a reference for studying the effect of Sb-doped composite materials and gas sensor performance.

Microwave assisted facile synthesis of 3D flower-like ZnO nanostructures for enhanced photocatalytic degradation/removal of Eosin Y from water

Three-dimensional ZnO nanoflower has been synthesized via microwave irradiation technique using glycine as complexing/capping agent for the first time. TEM, SAED, XRD, FTIR, UV and PL spectra have been recorded to characterize the synthesized ZnO nanostructures. The TEM image indicates the formation of 3D flower-like ZnO nanostructures having diameter ~0.74-1.60 μm. The spacing between adjacent lattice fringes obtained from the HRTEM image is 0.145 nm which indicated the presence of (103) lattice plane of ZnO. The synthesized ZnO nanoflower show excellent luminescence properties. The photocatalytic properties of synthesized ZnO nanoflower is depicted by the degradation of Eosin Y dye under solar irradiation. It is found that 98.9% of Eosin Y dye is degraded within 50 min under solar irradiation. Henceforth, ZnO nanoflower acts as an effective photocatalyst for the degradation of Eosin Y dye.

A vertically integrated ZnO-based hydrogen sensor with hierarchical bi-layered inverse opals

Three-dimensionally ordered macro/mesoporous materials are known to possess a large accessible surface area with impressive permeability. In this work, we combine electrophoresis and electrodeposition to fabricate a hierarchical bi-layered inverse opaline film in which a ZnO sensing layer is stacked with an Au electrode for impressive H2 sensing activities. To enhance its responsiveness, both morphological and crystallographic properties of ZnO inverse opals are optimized using KCl as the porogen. The resulting ZnO inverse opals demonstrate a specific surface area that is three times larger over comparable ZnO inverse opals by the formation of nanoporous skeletons. In addition, the deposition bath was deliberately designed so the predominant crystallographic plane of ZnO is shifted from (10 1- 0) to (0001) as the latter exhibits superior activity toward reducing gases. Through X-ray photoelectron spectroscopy, we show a significant increase of chemisorbed oxygen on the (0001) plane. Consequently, our hierarchical bi-layered inverse opals reveal a 500 % improvement in the sensitivity toward 15 ppm H2 under 200 °C. In short, this is the first demonstration of a vertically-arranged inverse opaline film incorporating both metal and oxide layers to function as an integrated three-dimensional gas sensor with low detection limit.

Superficial visible-light-responsive Pt@ZnO nanorods photocatalysts for effective remediation of ciprofloxacin in water

Fabrication of mesoporous ZnO nanorods photocatalysts exploiting a facile one-pot regime of zinc methoxide and F127 triblock copolymer as a surfactant was conducted. The impact of decoration with platinum on the photocatalytic efficacy, crystallinity, morphology, and physical aspects of mesoporous Pt@ZnO nanorods accommodating various proportions of Pt was interrogated. TEM micrographs affirmed that the fabricated mesoporous ZnO nanorods displayed nanorods architecture and platinum was doped on the surface of mesoporous ZnO nanorods as dots. The measured lattice spacing of the (002) plane of ZnO was found to be about 0.270 nm, affirming the development of the ZnO lattice architecture. On the other hand, the consistent lattice spacing of the (111) plane of Pt was 0.220 nm, endorsing the progression of the metallic platinum lattice architecture. Evidently, the surface area possessed by the fabricated mesoporous ZnO nanorods was 200 m2/g; up to our knowledge, this large surface area wasn’t attained previously. Furthermore, the average pore diameter and the total pore volume possessed by the fabricated mesoporous ZnO nanorods photocatalyst were 6.90 nm and 0.140 cm3/g, respectively. Ciprofloxacin (CIP) was photocatalytically degraded adopting mesoporous ZnO nanorods photocatalyst with a performance of 10%, whereas the photocatalytic performance toward CIP destruction was enhanced up to 100% upon doping ZnO nanorods photocatalyst with 0.6 wt.% Pt. Also, doping of the mesoporous ZnO nanorods photocatalyst with 0.6 wt.% Pt enhanced the photocatalytic degradation rate by 14 times compared with that of mesoporous ZnO nanorods photocatalyst. This conclusion could be attributed to the development of a high concentration of hydroxyl radicals, the accelerated dissipation of ciprofloxacin molecules to the active centers of the developed photocatalyst in addition to the reduced light scattering owing to the large surface area and high pore volume of the photocatalyst.

Photocatalytic and Electrocatalytic Properties of NGr-ZnO Hybrid Materials.

N-doped graphene-ZnO hybrid materials with different N-doped graphene:ZnO wt% ratios (1:10; 1:20; 1:30) were prepared by a simple and inexpensive sol-gel method. The materials denoted NGr-ZnO-1 (1:10), NGr-ZnO-2 (1:20), and NGr-ZnO-3 (1:30) were investigated with advanced techniques and their morpho-structural, photocatalytic, and electrocatalytic properties were reported. Hence, pure N-doped graphene sample contains flakes with the size ranging from hundreds of nanometers to micrometers. In the case of all NGr-ZnO hybrid materials, the flakes appear heavily decorated with ZnO nanoparticles, having a cauliflower-like morphology. The X-ray powder diffraction (XRD) investigation of N-doped graphene sample revealed that it was formed by a mixture of graphene oxide, few-and multi-layer graphene. After the ZnO nanoparticles were attached to graphene, major diffraction peaks corresponding to crystalline planes of ZnO were seen. The qualitative and quantitative compositions of the samples were further evidenced by X-ray photoelectron spectroscopy (XPS). In addition, UV photoelectron spectroscopy (UPS) spectra allowed the determination of the ionization energy and valence band maxima. The energy band alignment of the hybrid materials was established by combining UV–Vis with UPS results. A high photocatalytic activity of NGr-ZnO samples against rhodamine B solution was observed. The associated reactive oxygen species (ROS) generation was monitored by electron paramagnetic resonance (EPR)-spin trapping technique. In accordance with bands alignment and identification of radical species, the photocatalytic mechanism was elucidated.

High-index crystal plane of ZnO nanopyramidal structures: Stabilization, growth, and improved photocatalytic performance

While the low-index planes of Wurtzite ZnO, such as {0001} and {101¯0} are well-understood, the high-index crystal surfaces have not yet been thoroughly researched despite possessing structural characteristics that make them suitable for many important surface chemistry processes. The high surface energy of high-index ZnO crystal surfaces makes synthesis challenging to achieve due to their instability during crystal growth. In this work, we present a combined experimental and theoretical analysis of growth and photocatalytic activity of ZnO high-index crystal facets. Density functional theory calculations are performed to determine the thermodynamic conditions necessary to stabilize the high-energy semi-polar {112¯2} facets of pyramidal ZnO nanostructures grown via chemical vapor deposition (CVD). The photocatalytic properties of as-synthesized nanopyramidal structures for water splitting applications showed a 73% improved photocatalytic performance compared to CVD-grown hexagonal ZnO nanorods with dominating low-index {101¯0} facets.

Tumoricidal and Bactericidal Properties of ZnONPs Synthesized Using Cassia auriculata Leaf Extract.

In this work, we aimed to synthesize zinc oxide nanoparticles (ZnONPs) using an aqueous extract of Cassia auriculata leaves (CAE) at room temperature without the provision of additional surfactants or capping agents. The formation of as-obtained ZnONPs was analyzed by UV–visible (ultraviolet) absorption and emission spectroscopy, X-ray photoemission spectroscopy (XPS), X-ray diffraction analysis (XRD), energy dispersive X-ray diffraction (EDX), thermogravimetric analysis/differential thermal analysis (TGA-DTA), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), and selected area electron diffraction (SAED). The XRD results reflect the wurtzite structure of as-prepared ZnONPs, which produced diffraction patterns showing hexagonal phases. The SEM images indicate that the morphology of as-prepared ZnONPs is composed of hexagonal nanostructures with an average diameter of 20 nm. The HR-TEM result shows that the inter-planar distance between two lattice fringes is 0.260 nm, which coincides with the distance between the adjacent (d-spacing) of the (002) lattice plane of ZnO. The fluorescence emission spectrum of ZnONPs dispersed in ethanol shows an emission maximum at 569 nm, revealing the semiconductor nature of ZnO. As-obtained ZnONPs enhanced the tumoricidal property of CAE in MCF-7 breast cancer cells without significant inhibition of normal human breast cells, MCF-12A. Furthermore, we have studied the antibacterial effects of ZnONPs, which showed direct cell surface contact, resulting in the disturbance of bacterial cell integrity.