Crystalline ZnO Research Articles

Starch-Assisted Eco-Friendly Synthesis of ZnO Nanoparticles: Enhanced Photocatalytic, Supercapacitive, and UV-Driven Antioxidant Properties with Low Cytotoxic Effects.

This study presents an efficient and environmentally sustainable synthesis of ZnO nanoparticles using a starch-mediated sol-gel approach. This method yields crystalline mesoporous ZnO NPs with a hexagonal wurtzite structure. The synthesized nanoparticles demonstrated remarkable multifunctionality across three critical applications. In photocatalysis, the ZnO NPs exhibited exceptional efficiency, achieving complete degradation of methylene blue within 15 min at pH 11, significantly surpassing the performance of commercial ZnO. Under neutral pH conditions, the nanoparticles effectively degraded various organic dyes, including methylene blue, rhodamine B, and methyl orange, following pseudo-first-order kinetics. The methylene blue degradation process was aligned with the Langmuir-Hinshelwood model, emphasizing their advanced catalytic properties. For supercapacitor applications, the ZnO NPs attained a high specific capacitance of 550 F/g at 1 A/g, underscoring their potential as energy storage solutions. Additionally, the nanoparticles demonstrated strong UV-induced antiradical activity, with an EC50 of 32.2 μg/mL in DPPH assays. Notably, the cytotoxicity evaluation revealed an LC50 of 1648 μg/mL, indicating excellent biocompatibility. This study highlights a sustainable approach for the synthesis of multifunctional ZnO NPs that offers effective solutions for environmental remediation, energy storage, and biomedical applications.

Synthesis and application of aluminum substituted ZnO nanowires on carbon fibers photocatalyst for the removal of methylene blue dye from aquatic mediums

In this research, pristine and aluminum substituted ZnO nanowires grown on carbon fibers synthesised by hydrothermal method. The effect of Al concentration on morphology, structure, optical properties and photocatalytic activity on methylene blue was investigated. The aluminum concentration values of 0.5 %, 1 %, 5 % and 10 % of Zn(NO3)2·6 H2O concentration were tested. Resulting structures were characterized by scanning electron microscopy, X-ray Diffraction, diffuse reflectance spectroscopy and UV-Vis diffuse reflectance spectroscopy. XRD results indicates that pristine and aluminum substituted ZnO nanowires has hexagonal zincite crystal structure. The changes of crystal size, crystal parameters, strain and stress with aluminum substitution were investigated. Increasing concentration of aluminum reduced the crystallinity of ZnO. A dramatic change was seen in crystallite size from 40.78 nm to 22.73 nm. Distortion is seen on crystal structure of substituted ZnO causing stress due to different ionic radii between Zn2+ and substituent ions. Tensile stress of 1.38 Pa is calculated for aluminum substituted ZnO nanowires. Smaller ionic radii of aluminum causes positive tensile stress. Optical band gap of structures was analysed. Al substitution reduces the band gap of ZnO NWs/CFs. DRS results shows that Al incorporation led to a 0.05 eV decrease in the bandgap of ZnO NWs/CFs structure. Photocatalytic activity of pristine and aluminum substituted ZnO nanowires on carbon fibers structures were tested on degradation of methylene blue (MB). Al substitution enhances the photocatalytic activity of ZnO nanowires coated on carbon fibers. 1 % Al substituted ZnO NWs on CFs demonstrated highest degradation efficiency with 0.9879 h−1 kinetic rate.

Femtosecond-laser-induced suprawavelength two-dimensional ZnO microstructures for multi-wavelength photodetector devices.

Herein, we report on two-dimensional (2D) suprawavelength crystalline ZnO microstructures induced by a single ultraviolet (UV) femtosecond laser beam (400 nm, 35 fs, 666 Hz) with significant absorption enhancement. The achieved absorption values of 90-99% and 75-80% in the UV and visible spectral regions, respectively, were approximately 1.16 and 12 times higher than those of the blank ZnO crystal. Furthermore, large-area 2D ZnO microstructures were fabricated to be used as photodetectors (PDs). The experimental results demonstrated that, compared with the blank ZnO, these 2D ZnO microstructures effectively enhanced the PD performance by nearly four times at 375 nm. More importantly, the ZnO microstructure exhibited great response value, ∼7.12 A/W at 532 nm as well as acceptable response at 660 and 808 nm, whereas the blank ZnO crystal showed almost no response. Raman analyses demonstrated that no change occurred after the femtosecond laser induced the microstructure on ZnO. Thus, the enhancement in photoelectric performance can be attributed to the strong absorption of the ZnO microstructure.

Synthesis of zinc oxide semiconductor nanoparticles using natural extract: a systematic evaluation of cationic dye photodegradation influenced by extract concentration, catalyst dose, and pH.

This work obtained zinc oxide nanoparticles (ZnO NPs) using organic components extracted from Waltheria americana at different concentrations. ZnO materials were subsequently applied in the photodegradation of two cationic dyes, Rhodamine B (RB) and methylene blue (MB), at different doses of catalyst and pH. The crystallinity and hexagonal Wurtzite structure of ZnO were established through XRD analysis. The Zn-O bond in the ZnO NPs was confirmed in the FTIR, with the characteristic signals observed in the fingerprint region at ~ 400cm-1. SEM and TEM revealed the formation of quasi-spherical particles with an average size ranging from 2 to 12nm, depending on extract concentrations during synthesis. UV-Vis studies indicated the optical bandgap of ZnO, with values below 3eV, also dependent on extract concentration. PL analysis revealed the recombination of free excitons and defects in ZnO. Photocatalytic studies of ZnO materials demonstrated excellent degradation efficiency of RB and MB dyes, which was influenced by the extract concentration of NPs, while the degradation of MB was enhanced with a 1:1 dye-to-catalyst ratio under acidic conditions. In contrast, due to RB more complex structure, an increased ratio of 1:1 to 1:3 and acidic pH conditions improved its degradation. Green-synthesized ZnO NPs using photocatalysis techniques exhibit significant potential as eco-friendly alternatives for removing contaminants from water.

Enhanced optoelectronic characteristics of La-doped ZnO and its compatibility with Cs-doped MAPbI3 perovskite absorber material

Abstract The present study investigates the structural, electrical and optical characteristics of pristine and lanthanum (La)-doped zinc oxide electron transport layers (ETLs) fabricated by the sol gel method and their compatibility with Cs0.10MA0.90Pb(I0.9Br0.10)3 absorber layer for perovskite solar cells. All the ETLs were deposited under same deposition conditions, with the only difference in La percentage in the precursor solutions, ranging from 0 to 6%. X-ray diffraction (XRD) analysis demonstrated the presence of crystalline ZnO thin films and the absence of any impurity phases after La-doping. The calculated crystallite size, determined using Scherrer’s equation, increased from 11.13 to 21.76 nm after the introduction of dopant. The doping with 4% La led to the decrease in the optical bandgap from 3.32 eV of pristine ZnO to 3.23 eV. SEM analysis revealed better morphology of perovskite/4% La:ZnO specimen, which facilitated the absorbance and reduced the charge carrier recombination. It also exhibited superior resilience towards moisture and humidity which will eventually contribute to the development of more stable and efficient planar perovskite solar cells (PCSs).

Enhancing low-temperature sensor applications: Synergistic effects of Ni doping and SnO2 interlayer on spin-coated ZnO thin films on glass substrate

This study investigates the effects of Nickel doping and a SnO2 interlayer on the structural, morphological, optical, and electrical properties of ZnO thin films. Undoped and Ni-doped ZnO films were fabricated on glass substrates, with and without an SnO2 interlayer, using the sol-gel spin coating method. The samples—denoted as ZG (undoped ZnO), NZG (Ni-doped ZnO), ZSG (undoped ZnO with SnO2 interlayer), and NZSG (Ni-doped ZnO with SnO2 interlayer)—underwent comprehensive characterization via XRD, AFM, PL, UV–Vis spectroscopy, Hall effect measurements, Hot probe, and Two-point method. XRD analysis confirmed successful Ni incorporation and enhanced ZnO crystallinity, particularly in the presence of the SnO2 interlayer. AFM analysis revealed improved grain distribution and size due to the synergistic effects of Ni doping and the SnO2 interlayer. UV–Vis results indicated significant impacts on transparency and the Urbach energy, with Ni doping alone broadening the bandgap. PL measurements showed that the synergistic effects quenched UV luminescence associated with the glass substrate, enhancing visible luminescence. Chromaticity analysis suggested that ZSG and NZSG samples are suitable for warm blue region applications. Electrical measurements revealed n-type conductivity across all films except NZG, with Ni doping increasing resistivity. Additionally, the ZSG (PTC) sensor exhibited a slightly higher sensitivity (0.3852 Ω/°C) compared to the NZSG sensor (0.3782 Ω/°C), with a similar trend observed in NTC sensors. These findings suggest that Ni-doped ZnO films with SnO2 interlayers could potentially serve as thermistors and RTDs, offering promising applications in temperature sensing and optoelectronics.

Development of a new carbon xerogel/ZnO/BaSnO3 photocatalyst for solar and visible light photodegradation of salicylic acid

A novel carbon xerogel/ZnO/BaSnO3 photocatalyst was developed, characterized, and evaluated for the photodegradation of salicylic acid (SA) under solar and visible radiation. The development of the proposed photocatalyst involved the investigation of multiple synthesis parameters, aiming to optimize the photocatalytic activity of the ternary system. The best photocatalytic efficiency was obtained at 5 % w/w BaSnO3, 0.375 g of added tannin, and calcination temperature of 600 °C, yielding the 0.375CX/ZnO/BaSnO3 5 % 600 °C photocatalyst. After thorough characterization, it was concluded that the ternary materials are composed of a mixture of crystalline ZnO and BaSnO3 structures and carbon xerogel (CX). Additionally, the ternary materials displayed significant capacity to absorb visible radiation, mostly due to CX addition. Morphology-wise, the 0.375CX/ZnO/BaSnO3 5 % 600 °C was composed of nodular and polyhedral nanometric particles, displaying higher surface area when compared to materials without CX. Through chronoamperometry and electrochemical impedance spectroscopy, it was determined that the optimized ternary material achieved the highest photocurrent generation and lowest charge transfer resistance among the materials evaluated, indicating a superior photocatalytic activity. Photocatalytic tests demonstrated the superiority of the ternary system in the degradation of SA under solar and visible light irradiation, achieving 93 % and 52.3 % degradation after 5 h, respectively. The superior mineralization of SA (72.2 %) achieved by the optimized ternary material under solar radiation further demonstrated its increased efficacy. The suppression methodology allowed for the identification of the hydroxyl radical as the major active species in the SA degradation. A Z-type heterojunction was proposed for the ternary system, based on the staggered band alignment between ZnO and BaSnO3 and the role of CX as a solid-state mediator, possibly leading to effective charge separation and enhanced redox activity. Phytotoxicity tests showed favorable Lactuca sativa growth in SA solutions treated with 0.375CX/ZnO/BaSnO3 5 % 600 °C (especially under solar radiation), indicating reduced toxicity.

Effect of Calcination Temperature on the Surface of Prepared ZnO Nanocatalysts

ZnO nanoparticles (NPs) having nsemiconducting properties are important nanocatalysts for many surface reactions. Because of their extensive use as heterogeneous nanocatalyst for energy production and environmental cleaning, it is essential to understand their surface properties to design better chemical and photochemical nanocatalysts. Here, we used the sol-gel method to develop numerous ZnO NPs at various calcination temperatures (300 - 800 oC) and analyzed by different surface characterization techniques such as FTIR, SEM, XRD and UV-visible absorption spectroscopy. To investigate the catalytic activity a series of photooxidation studies on Remazol Red RR (RRR) were carried out at different conditions. From the surface characteristic analysis, it is found that the crystalline ZnO NPs are formed at above 400 oC temperature. The highest photocatalytic efficiency is found at 500 oC which might be related to the lowest particle size (35.4 ± 5.2 nm) and surface heterogeneity. The experimental results suggest that temperature-controlled growth rate and intra/inter-particle heterogeneity of ZnO nanoparticles have a great impact on the surface properties and photocatalytic activity. In addition to surface area, surface defects and crystal deformation may have a considerable impact on the photocatalytic activity by ZnO NPs. Finally, this study will help to understand what type of surface properties need to optimize to design industrial suit ZnO nanocatalysts. Journal of Engineering Science 15(1), 2024, 75-81

Green synthesis of ZnO nanoparticles and biological applications as broad-spectrum bactericidal, antibiofilm effects and biocompatibility studies on Zebrafish embryo

This work generated zinc oxide nanoparticles (ZnO NPs) using Ocimum tenuiflorum in an inexpensive and environmentally friendly manner. The generated ZnO NPs were analysed using Ultra visible spectroscopy (UV–Vis), Fourier transformed infrared spectroscopy (FTIR), Scanning electron microscopy-Energy X-ray diffraction spectroscopy (SEM-EDX), Transmission electron microscopy (TEM), and X-ray diffraction (XRD). Bio-synthesized ZnO NPs showed UV–Visible absorbance maxima at 290 nm, indicating bio reduction and stability. The DRS spectra revealed a straight band gap value of 3.24 eV. Alcohols, alkanes, phenols, and amines in FTIR may contain reduced and capped zinc ions. Crystalline ZnO nanoparticles were verified by XRD. Biosynthesized ZnO NPs were exhibited in spherical and 5–35.49 nm in size by FESEM and TEM. EDX confirmed NPs zinc elemental signatures. Antibacterial properties showed that ZnO NPs effectively inhibited gram (+ve) and gram (−ve) pathogens, including E. coli (20.0 ± 0.8 mm), E. faecalis (20.0 ± 0.5 mm), S. aureus (18.01 ± 1.2 mm), and S. mutans (17.5 ± 1.0 mm). This study shows that biosynthesized ZnO NPs inhibit biofilm growth by 0.198–1.431 O.D values (Optical density). Antibiofilm inhibition was concentration-dependent. Nanoparticles proved effective against E. coli, S. mutans, S. aureus, and E. faecalis with MICs of 15 and 25 µg/mL. Time-dependent death kinetic studies indicated that 8–12 h ZnO NPs killed all bacteria. Also, ZnO NPs had low harmful effects on zebrafish eggs at doses upto 1 mg/mL. In summary, the production of green ZnO NPs offers a sustainable and biocompatible approach that is well-suited for various biological applications.

High-efficient separation of photoinduced charge carriers in CoFe2O4-ZnO magnetic heterostructures mediated by oxygen vacancies

In this work, magnetic heterostructures were obtained by the in-situ growth of various ZnO amounts on the preformed CoFe2O4 nanoparticles. The X-ray diffraction characterization shows the presence of both ZnO and CoFe2O4 crystalline phases, and the crystallite size is about 13–14 nm for both components. X-Ray Photoelectron Spectroscopy (XPS) analysis revealed a CoFe2O4 inversion degree of 0.7. The composite samples demonstrated an extended absorption edge into the visible range. The sample’s magnetic properties were investigated by vibrating-sample magnetometer (VSM) and correlated with Electron Paramagnetic Resonance (EPR) results. The magnetic behavior was attributed to the combination of CoFe2O4 and ferromagnetic ZnO. The emergence of a ferromagnetic phase within ZnO was elucidated to originate from charge/spin transfer of spin-up polarized states from the CoFe2O4 Fermi level into empty oxygen vacancies of ZnO. High efficiency in Rhodamine B (RhB) degradation under visible light was observed in the prepared composite materials, particularly with an optimal CoFe2O4-ZnO ratio of 1:5, achieving an 81 % degradation rate within 6 h. The proposed photodegradation mechanism, based on various spectroscopic and magnetic investigations, highlights the role of spin transfer and oxygen vacancies in facilitating reactive oxygen species (ROS) generation for pollutant degradation.

Enhancement of photodetector performance of aluminum-doped zinc oxide thin films fabricated via SILAR method: Structural, optical, and electrical analysis

This study presents a comprehensive analysis of the structural, optical, electrical, and photosensing characteristics of aluminum-doped zinc oxide (Al:ZnO) thin films, fabricated via successive ionic layer adsorption and reaction (SILAR) techniques. The Raman and X-ray diffraction (XRD) analyses validated the hexagonal wurtzite structure and revealed that Al doping enhances crystallinity and crystal growth of ZnO. The average crystallite size increased from 21.6 nm in undoped sample to 23.8 nm in 5.0 wt% Al-doped sample, while strain effects decreased from 4.67 × 10-3 to 4.36 × 10-3. Scanning electron microscopy (SEM) images revealed improved film morphology and more defined geometries with increased Al doping, while energy-dispersive X-ray analysis (EDAX) confirmed successful Al integration into the ZnO lattice. Optical analyses indicate a narrowing of the ZnO bandgap to 2.81 eV in 5.0 wt% Al:ZnO from 3.02 eV in the undoped variant, while photoluminescence (PL) peak positions remains unchanged. Time-resolved fluorescence (TRF) indicated a reduction in electron lifetime with higher Al doping. Furthermore, Hall effect assessments reveal a decrease in carrier mobility and electrical resistivity, alongside a rise in carrier concentration with higher Al content. The photodetection efficacy was substantially improved with Al doping, particularly at 2.5 wt% Al, achieving a responsivity of 42.5 × 10-2 A/W, external quantum efficiency of 99.3 %, and detectivity of 1.8 × 1011 Jones. These findings exhibit that Al-doping substantially enhances the photodetection properties of ZnO thin films.

The Development and Atomic Structure of Zinc Oxide Crystals Grown within Polymers from Vapor Phase Precursors.

Sequential infiltration synthesis (SIS), also known as vapor phase infiltration (VPI), is a quickly expanding technique that allows growth of inorganic materials within polymers from vapor phase precursors. With an increasing materials library, which encompasses numerous organometallic precursors and polymer chemistries, and an expanding application space, the importance of understanding the mechanisms that govern SIS growth is ever increasing. In this work, we studied the growth of polycrystalline ZnO clusters and particles in three representative polymers: poly(methyl methacrylate), SU-8, and polymethacrolein using vapor phase diethyl zinc and water. Utilizing two atomic resolution methods, high-resolution scanning transmission electron microscopy and synchrotron X-ray absorption spectroscopy, we probed the evolution of ZnO nanocrystals size and crystallinity level inside the polymers with advancing cycles─from early nucleation and growth after a single cycle, through the formation of nanometric particles within the films, and to the coalescence of the particles upon polymer removal and thermal treatment. Through in situ Fourier transform infrared spectroscopy and microgravimetry, we highlight the important role of water molecules throughout the process and the polymers' hygroscopic level that leads to the observed differences in growth patterns between the polymers, in terms of particle size, dispersity, and the evolution of crystalline order. These insights expand our understanding of crystalline materials growth within polymers and enable rational design of hybrid materials and polymer-templated inorganic nanostructures.

Ultra-selective hydrogen sensors based on CuO - ZnO hetero-structures grown by surface conversion

Synergistic effects of mixed oxides have the potential to improve sensing performances of environmental, domestic and industrial monitoring devices. However, mixed oxides often come in the form of separate particles and are thus addressed separately by the environment, instead of capitalizing on the interface between the metal oxides. This paper describes a new core@shell gas sensing material of tetrapodal zinc oxide with a surface coating of crystalline copper oxide(t-ZnO@CuO). The special surface conversion strategy yields a unique, self-assembled and pinhole-free coating of CuO nanoplatelets. The morphologies, structural, chemical and gas sensing properties of the heterostructure were investigated. To evaluate the sensing properties of the heterostructure, t-ZnO@CuO was fabricated as nanosensors, consisting of one core-shell rod of CuO-coated crystalline ZnO. The single core@shell rod showed high selectivity towards hydrogen already at comparatively low operation temperatures of 150 °C. Computational calculations based on the density functional theory (DFT) have been carried out to understand the interaction of the H2 gas molecule with the surface of the CuO nanostructures. The surface conversion was done wet chemically and is a novel method for generating heterostructures that can be potentially transferred to heterojunctions with unique properties for chemosensors.

Biogenic ZnO/MgO nanocomposite synthesized from Ficus hispida and investigation of its biological properties

Biogenic ZnO/MgO nanocomposite was synthesized using Ficus hispida bark extract. Diffraction patterns showed highly crystalline ZnO and MgO formation with hexagonal and cubic crystal structures. Zn-O, Zn-OH, and Mg-O vibrations authenticate the material formation with elongated rods as well as flakes-like morphologies. Optimal biocompatibility was observed from MCF-7 cell line and zebrafish model. ZnO/MgO nanocomposite showed effective anti-bactericidal activity against gram negative Klebsiella pneumonia, Escherichia coli and gram positive Staphlococcus aureus, Streptococcus mutans. There are no significant reports in ZnO/MgO with the reduction of Ficus hispida and similar materials are being used as dental cement and for other applications. Hence, this biogenic ZnO/MgO nanocomposite can be a preferable material for biomedical applications.

Shelf-life enhancement of Gerbera jamesonii flowers by the green synthesised ZnO nanoflowers

ABSTRACT This study has been aimed to synthesise the self-assembled, flower-shaped zinc oxide nanoparticles (ZnO NFs) by using a green synthesis method using the aqueous extract from the peels of Citrus reticulata. Both HR-TEM and Fe-SEM analyses have confirmed the flower-like morphology for the synthesised nanoparticles. The observed zeta potential value of −48.0 mV further indicated its highly stable structure. The X-ray diffractogram of the ZnO NFs showed the characteristic diffraction peaks for the crystalline ZnO without any impurity peak, indicating the complete reduction into nanoparticles and thereby, the formation of pure crystalline ZnO NFs. The antibacterial activity of ZnO NFs was then studied using the standard well diffusion method and demonstrated significant bactericidal effects against Staphylococcus aureus and Escherichia coli, with a minimum inhibitory concentration (MIC) of 0.048 mg mL−1. Additionally, the ZnO NFs were evaluated for their potential to enhance the shelf life of Gerbera jamesonii flowers when treated with different concentrations in a chitosan-based solution. The ZnO NFs supplemented solution here was found to preserve the freshness of the cut flowers for up to 9.3 ± 0.3 days compared to the 3-day shelf life of the control group. These findings suggest ZnO NFs to have significant antibacterial properties and can effectively extend the shelf life of cut flowers.

Sputter deposition of ZnO–AlN pseudo-binary amorphous alloys with tunable band gaps in the deep ultraviolet region

ZnO–AlN pseudo-binary amorphous alloys (a-ZAON hereinafter) with tunable band gaps in the deep ultraviolet (DUV) region have been synthesized using magnetron sputtering. The miscibility gap between ZnO and AlN has been overcome using room-temperature sputtering deposition, leveraging the rapid quenching abilities of sputtered particles to fabricate metastable but single-phase alloys. X-ray diffraction patterns and optical transmittance spectra revealed that the synthesized films with chemical composition ratios of [Zn]/([Zn] + [Al]) = 0.24–0.79 likely manifested as single-phase of a-ZAON films. Despite their amorphous structures, these films presented direct band gaps of 3.4–5.8 eV and thus high optical absorption coefficients (105 cm−1). Notably, the observed values adhered to Vegard’s law for crystalline ZnO–AlN systems, implying that the a-ZAON films were solid solution alloys with atomic-level mixing. Furthermore, atomic force microscopy analyses revealed smooth film surfaces with root-mean-square roughness of 0.8–0.9 nm. Overall, the wide-ranging band gap tunability, high absorption coefficients, amorphous structures, surface smoothness, and low synthesis temperatures of a-ZAON films position them as promising materials for use in DUV optoelectronic devices and power devices fabricated using large-scale glass and flexible substrates.

Morphological, structural and electronic properties of zinc oxide nano structures deposited on ZnO substrate layer – A theoretical perspective

The work investigates the deposition of zinc and oxygen atoms on a Zinc terminated ZnO substrate, maintaining their stoichiometric ratio (O:Zn) at 0.8, under varying incident energies (0.5 eV and 5 eV) and temperatures (300 K and 700 K) using the ReaxFF potential in Molecular Dynamics (MD) simulation. The study explores the impact of deposition conditions on growth mechanisms, film morphology, and structural parameters such as Radial Distribution Function (RDF) and Coordination Number (CN). RDF analysis highlights disordered atomic arrangements and diverse bonding configurations within the film, with CN showing deviations from perfect crystalline ZnO, indicating non-uniform, non-crystalline, and nano behaviour. Post-heating the films to temperatures approaching the ZnO melting point results in enhanced crystallinity, as evidenced by distinct, dominant, and multiple RDF peaks. Density Functional Theory (DFT) approach of the deposited structures elucidates the formation of ZnO nanoclusters-(ZnO)3 and (ZnO)4 and investigates their electronic structure properties. DFT analysis of the post-heated films reveals the formation of ZnO monomers (ZnO), indicating an approaching crystalline behaviour, yet the films exhibit non-epitaxial and non-uniform characteristics. DFT calculations were instrumental in validating the observed structural behaviours in the deposited films. The study underscores the significance of stoichiometric ratio in film deposition and demonstrates the temperature-dependent evolution of structural properties towards crystallinity, shedding light on the intricate dynamics of ZnO film growth offering tailored control over film properties for enhanced performance in practical applications such as optoelectronics and gas sensing.

FORMATION MECHANISM AND SYNTHESIS OF HIGHLY CRYSTALLINE POROUS ZnO SUPERSPHERES VIA SOL-GEL PROCESS: EVOLUTION FROM INTACT HOLLOW STRUCTURES TO POLLEN-LIKE MORPHOLOGIES

The synthesis of hollow and porous (HP) ZnO superspheres with intact hollow structures is crucial for various applications, yet it poses significant challenges. This article explores the fundamental aspects of preparing highly crystalline HP ZnO superspheres via a sol-gel process, elucidating the synthetic strategy, formation mechanism, and subsequent utilization for generating pollen-like ZnO superstructures. Under solvothermal conditions at 200°C, employing zinc acetate (0.065 M) in diethylene glycol with varying molar ratios of H2O/Zn, a range of ZnO particles and superspheres were synthesized. Within a molar ratio range of 2 - 4, initial nanoparticles self-assembled into solid and porous (SP) superspheres, evolving dominantly towards or along the c-axis, resulting in HP superspheres with intact hollow structures. Conversely, molar ratios of 6 - 20 yielded only separate nanocrystals instead of superspheres. The critical role of the H2O/Zn molar ratio in forming HP superstructures with intact hollows was highlighted, controlling Ostwald ripening and outward diffusion rates, with a molar ratio of 2 identified as a prerequisite for intact HP superspheres. The resultant intact HP superspheres exhibited intense and sharp band gap emission at 389 nm, indicating potential for optoelectronic applications. Furthermore, the study introduces pollen-like ZnO colloids derived from these intact HP ZnO superspheres, offering stable dispersion. Crystal growth predominantly occurred along the outward-oriented c-axis. The intact HP ZnO superspheres serve as a promising template system for biomimetic pollen-like ZnO superstructures.

Crafting defective ZnO nanoparticles: A green synthesis for enhanced photocatalytic degradation of organic pollutants

Surface defect engineering is a promising strategy for enhancing the number of surface-active sites to facilitate efficient redox reactions that occur on the surface of a photocatalyst. A green approach was employed to prepare urea- and choline-chloride-based deep eutectic solvent (DES) for the synthesis of ZnO/Zn(OH)2 supported by a DES complex (Zn precursor). Surface defects on ZnO nanoparticles (NPs) were tailored by decomposing the Zn precursor in air. In addition, calcination improved the crystallinity and surface-active sites of the defective ZnO by creating surface oxygen vacancies (Vo). The appearance of an Electron paramagnetic resonance peak at a g value of 1.96 confirms the formation of single-charged Vo defects on the surface of ZnO. The photocatalyst prepared at a reaction bath temperature of 75 °C (Vo-ZnO-75) showed the highest photocatalytic activity. The observed green emission in the photoluminescence spectrum and X-ray photoelectron spectroscopy analysis suggests the formation of defects on the ZnO surface. Consequently, Vo-ZnO-75 enhanced surface donor density (14.4×1020 cm−3) and lower charge transfer resistance (88.89 × 103 Ω). The optimized photocatalyst of Vo-ZnO-75 has 94% removal efficiency for rhodamine B degradation within 60 min. This study sheds new light on the development of an efficient and eco-friendly approach for preparing defective ZnO NPs for photocatalytic applications.

Effect of acidic and basic leachants on the synthesis of ZnO nanoparticles from Egyptian zinc ore, their optical/surface characteristics and photocatalytic performance

It is of pivotal significance to optimize the parameters affecting the extraction of metals from natural ores to convert them to value-added products. Owing to their semiconducting nature, most metal oxides, including ZnO, have various electronic, optical, and photocatalytic applications. Hence, we are investigating the leaching of Zn from Smithsonite (an Egyptian ore) using acidic/basic leaching agents (leachants). The leached salts were employed in a co-precipitation method followed by calcination to obtain crystalline ZnO nanoparticles. Both photocatalytic performance of the ZnO nanoparticles obtained from acid leaching and basic leaching were investigated toward the photodegradation of Rhodamine B dye. The ZnO(A) prepared using the acid leaching route has achieved about 5.6-fold enhancement in the dye photodegradation% and 5.3-fold enhancement in the observed rate constant compared to ZnO(B) prepared from basic leaching. Finally, the superior photocatalytic activity of the ZnO(A) is attributed to the smaller particle size, larger surface area, and existence of some defects that enhanced the photocatalytic performance.