Defect engineering of ZnO: Review on oxygen and zinc vacancies

Enhanced Photoelectrocatalytic Performance of ZnO Nanowires for Green Hydrogen Production and Organic Pollutant Degradation

With growing environmental concerns and the need for sustainable energy, multifunctional materials that can simultaneously address water treatment and clean energy production are in high demand. In this study, we developed a cost-effective method to synthesize zinc oxide (ZnO) nanowires via the anodic oxidation of zinc foil. By carefully controlling the anodization time, we optimized the Zn/ZnO-5 min electrode to achieve impressive dual-function performance in terms of effective photoelectrocatalysis for water splitting and waste water treatment. The electrode exhibited a high photocurrent density of 1.18 mA/cm2 at 1.23 V vs. RHE and achieved a solar-to-hydrogen conversion efficiency of 0.55%. A key factor behind this performance is the presence of surface defects, such as oxygen vacancies (OVs), which enhanced charge separation and boosted electron transport. In tests for waste water treatment, the Zn/ZnO-5 min electrode demonstrated the highly efficient degradation of methylene blue (MB) dye, with a reaction rate constant of 0.4211 min-1 when exposed to light and a 1.0 V applied voltage significantly faster than using light or voltage alone. Electrochemical analyses, including impedance spectroscopy and voltammetry, further confirmed the superior charge transfer properties of the electrode under illumination, making it an excellent candidate for both energy conversion and pollutant removal. This study highlights the potential of using simple anodic oxidation to produce scalable and efficient ZnO-based photocatalysts. The dual-function capability of this material could pave the way for large-scale applications in renewable hydrogen production and advanced waste water treatment, offering a promising solution to some of today's most pressing environmental and energy challenges.

Photothermal Laser Printing of Sub-Micrometer Crystalline ZnO Structures

During light-driven 3D additive manufacturing, an object represented in digital form is initially translated into a spatial distribution of light intensity (sequentially or in parallel), which then results in a spatial material distribution. To date, this process typically proceeds by photoexcitation of small functional molecules, leading to photochemically induced crosslinking of soft materials. Alternatively, thermal triggers can be employed, yet thermal processes are often slow and provide only low spatial localization. Nevertheless, sub-micrometer ZnO structures for functional microelectronic devices have recently been laser-printed. Herein, the photothermal laser-printing of ZnO is advanced by i) introducing single-crystalline rather than amorphous sub-micrometer ZnO shapes that crystallize in the hexagonal ZnO wurtzite structure, ii) employing dimethyl sulfoxide (DMSO) instead of water, enabling higher local process temperatures without micro-bubble formation, and iii) using substrates tailored for light absorption and heat management, resolving the challenge of light to heat conversion. Finally, the herein-demonstrated ZnO printing requires no post-processing and is a cleanroom-free technique for the fabrication of crystalline semiconductors.

Simple and low-cost colorimetric method for quantification of surface oxygen vacancy in zinc oxide

Zinc oxide (ZnO) nanoparticles with surface oxygen vacancy (OV) was found to catalyze the colorimetric reaction of 3,3',5,5'-tetramethylbenzidine (TMB)-H2O2, and the absorbance of this TMB-H2O2-ZnO system was strongly dependent the OV concentration on surface of ZnO. By taking advantage of this phenomenon, one colorimetric method was proposed for quantifying surface OV in ZnO. The surface OV amount obtained through this colorimetric method matched well with that obtained through X-ray photoelectron spectroscopy (XPS). This colorimetric method doesn't need any advanced instruments, and can be completed in any an ordinary laboratory. This colorimetric method for detecting surface OV amount was simple, rapid (about 15 min) and low-cost.

Site-Selective Nanowire Synthesis and Fabrication of Printed Memristor Arrays with Ultralow Switching Voltages on Flexible Substrate

Large area electronics (LAE) with the capability to sense and retain information are crucial for advances in applications such as wearables, digital healthcare, and robotics. The big data generated by these sensor-laden systems need to be scaled down or processed locally. In this regard, brain-inspired computing and in-memory computing have attracted considerable interest. However, suitable architectures have mainly been developed using costly and resource-intensive conventional lithography-based methods. There is a need for the development of innovative, resource-efficient fabrication routes that enable such devices and concepts. Herein, we present ZnO nanowire (NW)-based memristors on a polyimide substrate fabricated by a LAE-compatible and resource-efficient route comprising solution processing and printing technologies. High-resolution "drop-on-demand" and "direct ink write" printers are employed to deposit metallic layers (silver and gold) and a ZnO seed layer, needed for the site-selective growth of ZnO NWs via a low-cost hydrothermal method. The printed memristors show high bipolar resistance switching (ON/OFF ratio >103) between two nonvolatile states and consistent switching at ultralow voltages (all devices showed switching at amplitudes <200 mV), with the best performing device showing consistent cycled resistance switching over 4 orders of magnitude with SET and RESET voltages of about 71 and -57 mV, respectively. Thus, the presented devices offer reliable high resistance switching at the lowest reported voltage for printed memristors and prove to be competitive with many conventional nanofabrication-based devices. The presented results show the potential printed memristors technology holds for large-area, low-voltage sensing applications such as electronic skin.

Enhanced photocatalytic oxidation of gaseous acetaldehyde using Fe-grafted ZnO nanocomposites in a continuous flow reactor

The purification of indoor air is a crucial application of photocatalysis, emphasizing the urgent need for more efficient photocatalytic systems. While photocatalytic oxidation of volatile organic compounds (VOCs) has been extensively studied in the liquid phase, effective removal of VOCs in the gaseous state in indoor air remains a significant challenge. This study focuses on the continuous gas-phase oxidation of gaseous acetaldehyde using ZnO and different weight percentage of Fe-grafted ZnO catalysts under light irradiation. The surface analysis using XPS and HR-TEM confirmed the presence of Fe(III) species, and UV-Vis-DRS analysis demonstrated a shift in the absorption edge towards the visible region. Real-time gas FTIR monitoring of acetaldehyde oxidation revealed that the 0.7% Fe(III)-grafted ZnO composite catalyst achieved a higher removal efficiency (74%) compared to bare ZnO and other Fe(III)-grafted ZnO ratios. The enhanced photocatalytic efficiency of acetaldehyde by Fe(III)-grafted ZnO supports indicated direct interfacial charge transfer (IFCT) from ZnO to Fe(III) species. Additionally, the Fe(III) cluster effectively improved the separation of electrons and holes, preventing their recombination and accelerating O₂ activation to generate O₂•⁻ radicals, which lead to high photocatalytic performance. The 0.7% Fe(III)-grafted ZnO also maintained its performance over a prolonged period of 360 min, showing excellent structural stability and durability across multiple cycles. This study highlights the possible synergistic effect of the ZnO and Fe systems, offering a new perspective on the photocatalytic decomposition of gaseous acetaldehyde in indoor environments.

Enhanced Photocatalytic Performance under Ultraviolet and Visible Light Illumination of ZnO Thin Films Prepared by Modified Sol-Gel Method

Semiconductor oxides are frequently used as active photocatalysts for the degradation of organic agents in water polluted by domestic industry. In this study, sol-gel ZnO thin films with a grain size in the range of 7.5-15.7 nm were prepared by applying a novel two-step drying procedure involving hot air treatment at 90-95 °C followed by conventional furnace drying at 140 °C. For comparison, layers were made by standard furnace drying. The effect of hot air treatment on the film surface morphology, transparency, and photocatalytic behavior during the degradation of Malachite Green azo dye in water under ultraviolet or visible light illumination is explored. The films treated with hot air demonstrate significantly better photocatalytic activity under ultraviolet irradiation than the furnace-dried films, which is comparable with the activity of unmodified ZnO nanocrystal powders. The achieved percentage of degradation is 78-82% under ultraviolet illumination and 85-90% under visible light illumination. Multiple usages of the hot air-treated films (up to six photocatalytic cycles) are demonstrated, indicating improved photo-corrosion resistance. The observed high photocatalytic activity and good photo-corrosion stability are related to the hot air treatment, which causes a reduction of oxygen vacancies and other defects and the formation of interstitial oxygen and/or zinc vacancies in the films.

Efficient photocatalytic degradation of diclofenac drug using the Zn1-x-yPrxAlyO photocatalyst under UV light irradiation

Herein, we report the efficient photocatalytic degradation of the diclofenac drug using the Zn1-x-yPrxAlyO photocatalyst [x, y] = (0.00, 0.00), (0.03, 0.01), (0.03,0.03) under UV light irradiation. The analysis of the structure reveals that the Pr3+ and Al3+ cations insertion into the ZnO lattice leads to a decrease in the lattice constant (a and c), Zn-O bond length, strain lattice, and crystallite size. These alterations are linked to the high degree of atomic disorder triggered by the dopants, which produce stress and strain in the ZnO structure. The Raman measurements confirmed the structural phase and showed changes in the position and intensity of the E2High mode, associated with oxygen vibrations and material crystallinity. The presence of the dopants reduces the concentration of VZn and VO++ type defects while increasing the levels of VO, VO+, and Oi defects, as observed from the fitting of the Photoluminescence spectra. Furthermore, it was noted that de Pr3+ and Al3+ cations insertion into ZnO increases the optical band gap, which is associated with the Moss-Burstein effect. The micrograph images show that dopants transform the morphology from quasi-spherical particles to irregular cluster structures. The textural analysis indicated that an increase in the concentration of Al3+ in the ZnO lattice led to a higher surface area, likely enhancing photocatalytic activity. The sample containing 3% Pr3+ and 3% Al3+ showed the highest photocatalytic activity and degraded up to 71.42% of diclofenac. In addition, experiments with scavengers revealed that hydroxyl radicals are the main species involved in the drug's photodegradation mechanism. Finally, the Zn1-x-yPrxAlyO compound is highly recyclable and stable.

Performance Improvement and Application of Degradable Poly-l-lactide and Yttrium-Doped Zinc Oxide Hybrid Films for Energy Harvesting

Piezoelectric nanogenerators (PENGs) are booming for energy collection and wearable energy supply as one of the next generations of green energy-harvesting devices. Balancing the output, safety, degradation, and cost is the key to solving the bottleneck of PENG application. In this regard, yttrium (Y)-doped zinc oxide (ZnO) (Y-ZnO) was synthesized and embedded into polylactide (PLLA) for developing degradable piezoelectric composite films with an enhanced energy-harvesting performance. The synthesized Y-ZnO exhibits high piezoelectric properties benefiting from the stronger polarity of the Y-O bond and regulation of oxygen vacancy concentration, which improve the output performance of the composite film with Y-ZnO and PLLA (Y-Z-PLLA). The obtained open-circuit voltage (Voc), short-circuit current (Isc), and instantaneous power density of the optimized Y-Z-PLLA PENG reach 17.52 V, 2.45 μA, and 1.76 μW/cm2, respectively. The proposed PENG also shows good degradability. In addition, practical applications of the proposed PENG were demonstrated by converting biomechanical energy, such as walking, running, and jumping, into electricity.

Controlled evolution of surface microstructure and phase boundary of ZnO nanoparticles for the multiple sensitization effects on triethylamine detection

In ZnO gas sensors, donor defects (such as zinc interstitials and oxygen vacancies) are considered active sites for the chemical adsorption and ionization of oxygen on the surface of ZnO, which can significantly enhance the sensor's response. However, the influence of the surface microstructure and phase boundaries of ZnO nanoparticles on the chemical adsorption and ionization of surface oxygen has rarely been explored. In this study, we developed a mixed-phase ZnO nanoparticle gas sensor with a rich phase boundary showing 198-50 ppm improvement in response to triethylamine at 340 °C. This is attributed to the generation of defects originating from lattice mismatch at the ZnO - zincite phase boundaries, which providing more active sites for adsorption of oxygen and triethylamine molecules. This work demonstrates a feasible method of combining surface microstructure regulation with pyrolysis strategies to develop ZnO sensors with significantly enhanced gas response performance.

Photoluminescence research of the graphene quantum dots (GQD) interaction on the zinc oxide (ZnO) surface for application as H2O2 photosensor

Photoluminescence (PL) spectroscopy is one of the best methods to detect molecules due to its easiness, fast time of analysis and high sensitivity. In addition, zinc oxide (ZnO) possesses good optical properties and particularly PL emission in these materials have been exploited for their potential use as photocatalyst, light harvesting and photosensor. These PL properties enhance when graphene quantum dots (GQD) are added to ZnO. For these reasons, we investigated the PL performance of ZnO-GQD nanocomposites. In one experiment we evaluated the PL emission of solid samples ZnO and ZnO-GQD. In a second experiment, these samples were also evaluated in aqueous phase to investigate the H2O2 effect during an experiment lasting 170 minutes. Both experiments displayed six peaks and they were related to the same PL emission source. The PL emission peak around 415 nm was found to be principal source where GQD are interacting. By varying the GQD amount to low, medium, and high concentration, the effect of H2O2 acted consequently, altering the PL emission during experiment in aqueous phase. An oxygen rich environment (ORE) occurred due to H2O2 which oxides the ZnO surface. Low GQD concentration resulted affected by an ORE weakening the GQD-ZnO contact, decreasing PL emission. In high GQD concentration, H2O2 induced GQD to reach the ZnO surface, increasing the PL emission. Only medium GQD concentration prevented oxidation of ZnO and maintained the PL emission intensity constant. When H2O2 concentration increased, for the medium GQD concentration, an excess of charge by peroxides inhibited the charge transfer from GQD to ZnO. This inhibition produces a quenching of the PL emission.

Exploitation of green synthesized chromium doped zinc oxide nanorods (NRs) mediated by flower extract of Rhododendron arboreum for highly efficient photocatalytic degradation of cationic dyes Malachite green (MG) and Fuchsin basic (FB)

In this work, green method to synthesize chromium-doped zinc oxide (ZnO) nanorods (NRs) using an aqueous flower extract from Rhododendron arboretum is explored. Herein, chromium-doped ZnO NRs were prepared with different amount of chromium doping, varied as 2-10%. The green synthesized products underwent substantial analysis through X-ray diffraction (XRD), spectroscopic such as ultraviolet spectroscopy(UV-Vis) and scanning electron microscopy (SEM) methods. All samples were found to have hexagonal wurtzite ZnO, with average particle sizes of 52.41, 56.6, 54.44, 53.05, and 56.99 nm, respectively, for 2, 4, 6, 8, and 10% chromium doping in ZnO NRs. The Cr-doped ZnO NRs exhibited remarkable photocatalytic degradation activity of cationic dyes under UV-light, i.e., Malachite Green and Fuchsin Basic with degradation of 99.604 and 99.881%, respectively in 90 min. The reusability tests for these green synthesized Cr-doped ZnO NRs have also been carried out, showed 9-11 cycles with 85% of degradation efficiency. In addition, the Cr-doped ZnO NRs exhibited high selectivity for cationic dyes when experiments against mixture of dyes were performed. Photodegradation kinetics followed the pseudo-first-order model. The flower-extract-stabilized chromium-doped ZnO NRs demonstrated high photocatalytic activity toward malachite green and fuchsin basic dyes, potential material for pollution remediation.

Thin-film transistor for temporal self-adaptive reservoir computing with closed-loop architecture

Reservoir computing is a powerful neural network-based computing paradigm for spatiotemporal signal processing. Recently, physical reservoirs have been explored based on various electronic devices with outstanding efficiency. However, the inflexible temporal dynamics of these reservoirs have posed fundamental restrictions in processing spatiotemporal signals with various timescales. Here, we fabricated thin-film transistors with controllable temporal dynamics, which can be easily tuned with electrical operation signals and showed excellent cycle-to-cycle uniformity. Based on this, we constructed a temporal adaptive reservoir capable of extracting temporal information of multiple timescales, thereby achieving improved accuracy in the human-activity-recognition task. Moreover, by leveraging the former computing output to modify the hyperparameters, we constructed a closed-loop architecture that equips the reservoir computing system with temporal self-adaptability according to the current input. The adaptability is demonstrated by accurate real-time recognition of objects moving at diverse speed levels. This work provides an approach for reservoir computing systems to achieve real-time processing of spatiotemporal signals with compound temporal characteristics.

A Comprehensive Review on the Boosted Effects of Anion Vacancy in the Heterogeneous Photocatalytic Degradation, Part II: Focus on Oxygen Vacancy

Environmental problems, including the increasingly polluted water and the energy crisis, have led to a need to propose novel strategies/methodologies to contribute to sustainable progress and enhance human well-being. For these goals, heterogeneous semiconducting-based photocatalysis is introduced as a green, eco-friendly, cost-effective, and effective strategy. The introduction of anion vacancies in semiconductors has been well-known as an effective strategy for considerably enhancing the photocatalytic activity of such photocatalytic systems, giving them the advantages of promoting light harvesting, facilitating photogenerated electron-hole pair separation, optimizing the electronic structure, and enhancing the yield of reactive radicals. This Review will introduce the effects of anion vacancy-dominated photodegradation systems. Then, their mechanism will illustrate how an anion vacancy changes the photodegradation pathway to enhance the degradation efficiency toward pollutants and the overall photocatalytic performance. Specifically, the vacancy defect types and the methods of tailoring vacancies will be briefly illustrated, and this part of the Review will focus on the oxygen vacancy (OV) and its recent advances. The challenges and development issues for engineered vacancy defects in photocatalysts will also be discussed for practical applications and to provide a promising research direction. Finally, some prospects for this emerging field will be proposed and suggested. All permission numbers for adopted figures from the literature are summarized in a separate file for the Editor.

Study on the Photocatalytic Properties of Metal-Organic Framework-Derived C-, N-Co-Doped ZnO

In this study, C- and N-co-doped ZnO photocatalysts were prepared through pyrolysis using metal-organic frameworks (MOFs) as precursor materials. The crystal structure, morphology, and surface chemical composition of the samples were characterised via X-ray diffraction (XRD), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS). Their activities in photocatalytic reactions were also evaluated through photocatalytic experiments. The results show that C-, N-co-doped ZnO has a high specific surface area, which is favourable for a photocatalytic reaction. Meanwhile, C-, N-doping can effectively modulate the energy band structure of ZnO, broaden its light absorption range, and improve the separation efficiency of photogenerated electron-hole pairs. The photocatalytic experiments show that the C/N-ZnO-500 samples, which have the optimal photocatalytic performances, have improved performances of 50% and 35%, respectively, compared with those of the blank control group and the ZIF-8 samples. The preparation of ZnO materials with a morphology change and doping using metal frameworks as precursors provides a new idea for designing efficient photocatalysts.

A multiple signal amplification photoelectrochemical biosensor based on biotin-avidin system for kanamycin sensing in fish and milk via synergism of g-C3N4 and Ru@SiO2

BACKGROUND

The residues of kanamycin can accumulate in the human body for a long time and pose serious health risks, including hearing loss, kidney poisoning, and drug allergic reactions. Therefore, it is crucial to develop a rapid, highly sensitive, and low-cost method for detecting kanamycin residues in foods. However, the current methods have limitations such as low sensitivity, expensive instruments, and multiple steps, which make them impractical for use in resource-limited environments and emergencies. In this study, the creation of a multiple-signal amplification photoelectrochemical biosensor to address these aforementioned issues is discussed.

RESULTS

Herein, we proposed a multiple signal amplification photoelectrochemical (PEC) biosensor based on carboxylated g-C3N4 and avidin functionalized Ru@SiO2 for the ultrasensitive detection of kanamycin. The carboxylated g-C3N4 was a highly efficient photoactive substance for amplifying photoelectric signals and a substrate for aptamer immobilization. The DOS and PDOS of g-C3N4 were studied by simulation, and the sensing mechanism of the probe at the molecular level was revealed. Meanwhile, using Ru@SiO2 as a signal amplifying unit, through the cooperative work between Ru@SiO2 and g-C3N4, the photoelectric signal could be double amplified to produce an excellent photocurrent response. Under optimized conditions, the photocurrent response of the PEC biosensor to kanamycin was obtained at concentrations from 0.1 nM to 1000 nM with a lower detection limit of 4.1052 × 10-11 mol L-1. This protocol demonstrates high sensitivity, brilliant specific recognition ability, excellent reproducibility, and acceptable stability.

SIGNIFICANCE

The first combination of g-C3N4 and avidin-Ru@SiO2 as photocurrent materials greatly enhanced the sensitivity of the PEC biosensors. Moreover, the specificity and sensitivity of the PEC biosensor were further improved through the specific interaction between kanamycin and aptamer. The photoelectric conversion mechanism based on g-C3N4 and two pathways for enhancing the photocurrent by Ru(byp)32+ were proposed. Through simulations of the DOS and PDOS of g-C3N4, the sensing mechanism of the probe at the molecular level was revealed. Under the optimum conditions, the PEC biosensor exhibited a wide linear concentration range and a low detection limit.

Diode characteristics, piezo-photocatalytic antibiotic degradation and hydrogen production of Ce3+ doped ZnO nanostructures

Piezo-photocatalysis of ZnO nanostructures had recently well attracted due to their exceptional potential in degrading the antibiotics and scalable hydrogen production. Here, we have synthesized the Ce3+ doped ZnO nanospheres in a facile wet chemical strategy. Dopant ions induced morphological evolution and optical bandgap tuning had observed in our experiment. Optical absorbance spectrum had confirmed the bandgap shortening occurs with Ce3+ doped ZnO specimens. The bandgap gap value had reduced to 2.82 eV from 3.05eV confirming the visible light responsivity of ZnO nano specimens. Obtained Zn(1-x)CexO nanospheres were utilized to fabricate the p-Si/n- Zn(1-x)CexO heterojunction diodes as well studied the improved electrical conductivity for the Ce3+ specimen-based diodes. Besides, ideality factor and barrier height values of the heterojunction diodes ZnO/p-Si, Zn0.99Ce0.01O/p-Si, Zn0.97Ce0.03O/p-Si, and Zn0.95Ce0.05O/p-Si are 15.97 & 0.43 eV, 15.47 & 0.44 eV, 8.02 & 0.46 eV and 5.21 & 0.47 eV, respectively. Direct sunlight assisted piezo-photocatalytic tetracycline (TC) degradation efficiency of ZnO, Zn0.99Ce0.01O, Zn0.97Ce0.03O, and Zn0.95Ce0.05O nanostructures respectively are 64%, 69%, 74% and 82%. We have produced the hydrogen quantity of 1234 μ mol h-1, 1490 μ mol h-1, 1750 μ mol h-1 and 1980 μ mol h-1 with 0%, 1%, 3% and 5% Ce3+ doped ZnO specimens under the direct sunlight assisted piezo-photocatalytic H2 production from H2S splitting.

Catalytic removal of harmful volatile organic compounds by reutilizing zinc rods waste from spent batteries as a palladium catalyst support

The emission of volatile organic compounds (VOCs) has led to significant deterioration in air quality, making it imperative to ensure that these compounds are removed from emission sources before they are released into the atmosphere. In this context, the present study recycled spent primary batteries to use their zinc rods waste (ZRW) as a palladium catalyst support for the removal of harmful VOCs. To this end, palladium supported on ZRW (Pd/ZRW) catalysts were prepared and tested for the catalytic oxidation of benzene, methylbenzene and 1,2-dimethylbenzene. The physicochemical properties of the Pd/ZRW catalysts were carefully characterized by ICP-OES, BET, SEM, XRD, FE-TEM, XPS, and H2-TPR analyses. The main component of ZRW was identified as ZnO. Consistent with expectations, increases in the loading of Pd from 0.1 to 1.0 wt% in the Pd/ZRW catalysts resulted in enhanced VOCs removal efficiency. The reaction temperature required for the complete oxidation (100% removal efficiency) of methylbenzene and 1,2-dimethylbenzene on the 1.0 wt% Pd/ZRW catalyst was below 340 °C at a gas hourly space velocity of 50,000 h-1. TEM, XPS, and H2-TPR results implied that the enhancement of catalytic activity with the addition of Pd could be attributed to the readily movable surface lattice oxygen as well as the active component (Pd species). Ultimately, ZRW of spent primary batteries appear to show promise as a catalyst support for VOCs removal. This study has introduced a novel strategy for reducing air pollutants by utilizing waste, which promotes the disposal of hazardous solid waste and ensures clean air quality.

Improving photocatalytic hydrogen production by switching charge kinetics from type-I to Z-scheme via defective engineering

By providing the spatial separation of the active sites and retaining high oxidative and reducing capacity, the direct Z-scheme heterostructure is considered the most potential structure for yielding photo-electric response. However, challenges still exist in the directional transfer of charge carriers between two semiconductors in direct Z-scheme structures. In this regard, by constructing the Vzn defect and p-n junction, a direct Z-scheme ZnxCd1-xS@ZnS-NiS heterostructure was obtained for the regulated electronic structure, which ensured high-yield hydrogen properties. The Zn vacancy in the partially-coated ZnS shell led to the Vzn energy level, and the addition of NiS led to the p-n structure, which caused a drastic downshift of the band edge potentials in comparison to that of pristine CdS. This variation gave rise to a staggered band edge alignment between ZnxCd1-xS and NiS, resulting in the variation of charge transfer kinetics from type-I to direct Z-scheme. Through careful characterization, it was found that the optimal photocatalytic hydrogen precipitation activity reached 16 683.6 μmol g-1 h-1, which was 70 times that of CdS, and this improvement was considered to form a spatial barrier, providing a clear direction and path for carrier transmission.

Optimizing ZnO-Quantum Dot Interface with Thiol as Ligand Modification for High-Performance Quantum Dot Light-Emitting Diodes

As the electron transport layer in quantum dot light-emitting diodes (QLEDs), ZnO suffers from excessive electrons that lead to luminescence quenching of the quantum dots (QDs) and charge-imbalance in QLEDs. Therefore, the interplay between ZnO and QDs requires an in-depth understanding. In this study, DFT and COSMOSL simulations are employed to investigate the effect of sulfur atoms on ZnO. Based on the simulations, thiol ligands (specifically 2-hydroxy-1-ethanethiol) to modify the ZnO nanocrystals are adopted. This modification alleviates the excess electrons without causing any additional issues in the charge injection in QLEDs. This modification strategy proves to be effective in improving the performance of red-emitting QLEDs, achieving an external quantum efficiency of over 23% and a remarkably long lifetime T95 of >12 000 h at 1000 cd m-2 . Importantly, the relationship between ZnO layers with different electronic properties and their effect on the adjacent QDs through a single QD measurement is investigated. These findings show that the ZnO surface defects and electronic properties can significantly impact the device performance, highlighting the importance of optimizing the ZnO-QD interface, and showcasing a promising ligand strategy for the development of highly efficient QLEDs.

Tunable-performance all-oxide structure field-effect transistor based atomic layer deposited Hf-doped In2O3 thin films

The relocation of peripheral transistors from the front-end-of-line (FEOL) to the back-end-of-line (BEOL) in fabrication processes is of significant interest, as it allows for the introduction of novel functionality in the BEOL while providing additional die area in the FEOL. Oxide semiconductor-based transistors serve as attractive candidates for BEOL. Within these categories, In2O3 material is particularly notable; nonetheless, the excessive intrinsic carrier concentration poses a limitation on its broader applicability. Herein, the deposition of Hf-doped In2O3 (IHO) films via atomic layer deposition for the first time demonstrates an effective method for tuning the intrinsic carrier concentration, where the doping concentration plays a critical role in determine the properties of IHO films and all-oxide structure transistors with Au-free process. The all-oxide transistors with In2O3: HfO2 ratio of 10:1 exhibited optimal electrical properties, including high on-current with 249 µA, field-effect mobility of 13.4 cm2 V-1 s-1, and on/off ratio exceeding 106, and also achieved excellent stability under long time positive bias stress and negative bias stress. These findings suggest that this study not only introduces a straightforward and efficient approach to improve the properties of In2O3 material and transistors, but as well paves the way for development of all-oxide transistors and their integration into BEOL technology.

Engineering the defect distribution in ZnO nanorods through laser irradiation

In recent years, defect engineering has shown great potential to improve the properties of metal oxide nanomaterials for various applications thus received extensive investigations. While traditional techniques mostly focus on controlling the defects during the synthesis of the material, laser irradiation has emerged as a promising post-deposition technique to further modulate the properties of defects yet there is still limited information. In this article, defects such as oxygen vacancies are tailored in ZnO nanorods through nanosecond (ns) laser irradiation. The relation between laser parameters and the temperature rise in the ZnO due to laser heating was established based on the observation in the SEM and the simulation. Raman spectra indicated that the concentration of the oxygen vacancies in the ZnO is temperature-dependent and can be controlled by changing the laser fluence and exposure time. This is also supported by the absorption spectra and the photoluminescence spectra of ZnO NRs irradiated under these conditions. On the other hand, the distribution of the oxygen vacancies was studied by XPS depth profiling, and it was confirmed that the surface-to-bulk ratio of the oxygen vacancies can be modulated by varying the laser fluence and exposure time. Based on these results, four distinctive regimes containing different ratios of surface-to-bulk oxygen vacancies have been identified. Laser-processed ZnO nanorods were also used as the catalyst for the photocatalytic degradation of rhodamine B (RhB) dye to demonstrate the efficacy of this laser engineering technique.

Structural, Optical, and Electrical Properties of Hafnium-Aluminum-Zinc-Oxide Films Grown by Atomic Layer Deposition for TCO Applications

ZnO is a widely studied material that exhibits versatile doping possibilities. Most research presents singly doped ZnO, leaving the potential of codoping unexplored. Within this study, hafnium-aluminum codoped zinc oxide (HAZO) thin films were grown on a glass substrate using the atomic layer deposition technique at 200 °C. A comprehensive analysis of the surface morphology and electrical and optical properties of the samples was conducted for varying the Al/Hf doping ratio. X-ray diffraction studies showed that the obtained films are polycrystalline, exhibiting a preferential growth direction along the (1 0 0) plane without any detectable precipitates. Moreover, the electrical measurements of HAZO films revealed that they exhibit lower resistivity (∼9.5 × 10-4 Ωcm) than the commonly used aluminum zinc oxide films (AZO). This improvement can be primarily attributed to the promotion of the n-type carrier concentration to 4.45 × 1020 cm-3 while maintaining a mobility value equal to 14.7 cm2/Vs. The doping also influences the optical properties of the material by widening the band gap and changing the refractive index, as observed by spectroscopy and ellipsometry studies. These findings highlight the potential of proposed HAZO thin films for future applications in electronic devices utilizing transparent conducting oxides.

Revealing the Dependency of Dye Adsorption and Photocatalytic Activity of ZnO Nanoparticles on Their Morphology and Defect States

ZnO is an effective photocatalyst applied to the degradation of organic dyes in aqueous media. In this study, the UV-light and sunlight-driven photocatalytic activities of ZnO nanoparticles are evaluated. A handheld Lovibond photometer was purposefully calibrated in order to monitor the dye removal in outdoor conditions. The effect of ZnO defect states, i.e., the presence of zinc and oxygen defects on the photocatalytic activity was probed for two types of dyes: fuchsin and methylene blue. Three morphologies of ZnO nanoparticles were deliberately selected, i.e., spherical, facetted and a mix of spherical and facetted, ascertained via transmission electron microscopy. Aqueous and non-aqueous sol-gel routes were applied to their synthesis in order to tailor their size, morphology and defect states. Raman spectroscopy demonstrated that the spherical nanoparticles contained a high amount of oxygen vacancies and zinc interstitials. Photoluminescence spectroscopy revealed that the facetted nanoparticles harbored zinc vacancies in addition to oxygen vacancies. A mechanism for dye degradation based on the possible surface defects in facetted nanoparticles is proposed in this work. The reusability of these nanoparticles for five cycles of dye degradation was also analyzed. More specifically, facetted ZnO nanoparticles tend to exhibit higher efficiencies and reusability than spherical nanoparticles.

Synthesis of ZnO Nanoflower Arrays on a Protrusion Sapphire Substrate and Application of Al-Decorated ZnO Nanoflower Matrix in Gas Sensors

In this study, we utilized a sapphire substrate with a matrix protrusion structure as a template. We employed a ZnO gel as a precursor and deposited it onto the substrate using the spin coating method. After undergoing six cycles of deposition and baking, a ZnO seed layer with a thickness of 170 nm was formed. Subsequently, we used a hydrothermal method to grow ZnO nanorods (NRs) on the aforementioned ZnO seed layer for different durations. ZnO NRs exhibited a uniform outward growth rate in various directions, resulting in a hexagonal and floral morphology when observed from above. This morphology was particularly evident in ZnO NRs synthesized for 30 and 45 min. Due to the protrusion structure of ZnO seed layer, the resulting ZnO nanorods (NRs) displayed a floral and matrix morphology on the protrusion ZnO seed layer. To further enhance their properties, we utilized Al nanomaterial to decorate the ZnO nanoflower matrix (NFM) using a deposition method. Subsequently, we fabricated devices using both undecorated and Al-decorated ZnO NFMs and deposited an upper electrode using an interdigital mask. We then compared the gas-sensing performance of these two types of sensors towards CO and H₂ gases. The research findings indicate that sensors based on Al-decorated ZnO NFM exhibit superior gas-sensing properties compared to undecorated ZnO NFM for both CO and H₂ gases. These Al-decorated sensors demonstrate faster response times and higher response rates during the sensing processes.

Effects of Dopants and Processing Parameters on the Properties of ZnO-V2O5-Based Varistors Prepared by Powder Metallurgy: A Review

This article reviews the progress in developing ZnO-V₂O₅-based metal oxide varistors (MOVs) using powder metallurgy (PM) techniques. The aim is to create new, advanced ceramic materials for MOVs with comparable or superior functional properties to ZnO-Bi₂O₃ varistors using fewer dopants. The survey emphasizes the importance of a homogeneous microstructure and desirable varistor properties, such as high nonlinearity (α), low leakage current density (J_L), high energy absorption capability, reduced power loss, and stability for reliable MOVs. This study investigates the effect of V₂O₅ and MO additives on the microstructure, electrical and dielectric properties, and aging behavior of ZnO-based varistors. The findings show that MOVs with 0.25-2 mol.% V₂O₅ and MO additives sintered in air over 800 °C contain a primary phase of ZnO with a hexagonal wurtzite structure and several secondary phases that impact the MOV performance. The MO additives, such as Bi₂O₃, In₂O₃, Sb₂O₃, transition element oxides, and rare earth oxides, act as ZnO grain growth inhibitors and enhance the density, microstructure homogeneity, and nonlinearity. Refinement of the microstructure of MOVs and consolidation under appropriate PM conditions improve their electrical properties (J_L ≤ 0.2 mA/cm², α of 22-153) and stability. The review recommends further developing and investigating large-sized MOVs from the ZnO-V₂O₅ systems using these techniques.

Impact on the Photocatalytic Dye Degradation of Morphology and Annealing-Induced Defects in Zinc Oxide Nanostructures

In this study, three different morphologies, nanoflower (NF), nano sponge (NS), and nano urchin (NU), of zinc oxide (ZnO) nanostructures were synthesized successfully via a mild hydrothermal method. After synthesis, the samples were annealed in the atmosphere at 300, 600, and 800 °C. Although annealing provides different degradation kinetics for different morphologies, ZnO NS performed significantly better than other morphologies for all annealing temperatures we used in the study. When the photoluminescence, electron paramagnetic resonance spectroscopy, BET surface, and X-ray diffraction analysis results are examined, it is revealed that the defect structure, pore diameter, and crystallinity cumulatively affect the photocatalytic activity of ZnO nanocatalysts. As a result, to obtain high photocatalytic activity in rhodamine B (RhB) degradation, it is necessary to develop a ZnO catalyst with fewer core defects, more oxygen vacancies, near band emission, large crystallite size, and large pore diameter. The ZnO NS-800 °C nanocatalyst studied here had a 35.6 × 10^-3 min^-1 rate constant and excellent stability after a 5-cycle photocatalytic degradation of RhB.

A Heteroanionic Zinc Ion Conductor for Dendrite-Free Zn Metal Anodes

Although zinc-based batteries are promising candidates for eco-friendly and cost-effective energy storage devices, their performance is severely retarded by dendrite formation. As the simplest zinc compounds, zinc chalcogenides, and halides are individually applied as a Zn protection layer due to high zinc ion conductivity. However, the mixed-anion compounds are not studied, which constrains the Zn²⁺ diffusion in single-anion lattices to their own limits. A heteroanionic zinc ion conductor (Zn_y O_{1- x} F_x ) coating layer is designed by in situ growth method with tunable F content and thickness. Strengthened by F aliovalent doping, the Zn²⁺ conductivity is enhanced within the wurtzite motif for rapid lattice Zn migration. Zn_y O_{1- x} F_x also affords zincophilic sites for oriented superficial Zn plating to suppress dendrite growth. Therefore, Zn_y O_{1- x} F_x -coated anode exhibits a low overpotential of 20.4 mV for 1000 h cycle life at a plating capacity of 1.0 mA h cm^-2 during symmetrical cell test. The MnO₂ //Zn full battery further proves high stability of 169.7 mA h g^-1 for 1000 cycles. This work may enlighten the mixed-anion tuning for high-performance Zn-based energy storage devices.

The optimized Fenton-like activity of Fe single-atom sites by Fe atomic clusters-mediated electronic configuration modulation

The performance optimization of isolated atomically dispersed metal active sites is critical but challenging. Here, TiO2@Fe species-N-C catalysts with Fe atomic clusters (ACs) and satellite Fe-N4 active sites were fabricated to initiate peroxymonosulfate (PMS) oxidation reaction. The AC-induced charge redistribution of single atoms (SAs) was verified, thus strengthening the interaction between SAs and PMS. In detail, the incorporation of ACs optimized the HSO5- oxidation and SO5·- desorption steps, accelerating the reaction progress. As a result, the Vis/TiFeAS/PMS system rapidly eliminated 90.81% of 45 mg/L tetracycline (TC) in 10 min. The reaction process characterization suggested that PMS as an electron donor would transfer electron to Fe species in TiFeAS, generating 1O2. Subsequently, the hVB+ can induce the generation of electron-deficient Fe species, promoting the reaction circulation. This work provides a strategy to construct catalysts with multiple atom assembly-enabled composite active sites for high-efficiency PMS-based advanced oxidation processes (AOPs).

Effect of Strain Rate on Nano-Scale Mechanical Behavior of A-Plane (112¯0) ZnO Single Crystal by Nanoindentation

In this study, nanoindentation tests at three different strain rates within 100 nm indentation depth were conducted on an a-plane (112¯0) ZnO single crystal to investigate the effect of strain rate on its nano-scale mechanical behavior. The load-indentation-depth curves, pop-in events, hardness and Young's moduli of an a-plane (112¯0) ZnO single crystal at different strain rates were investigated at the nano-scale level. The results indicated that, with the indentation depth increasing, the load increased gradually at each maximum indentation depth, h_ma, during the loading process. A distinct pop-in event occurred on each loading curve except that corresponding to the h_max of 10 nm. The applied load at the same indentation depth increased with the increasing strain rate during the nanoindentation of the a-plane (112¯0) ZnO single crystal. The higher strain rate deferred the pop-in event to a higher load and deeper indentation depth, and made the pop-in extension width larger. The hardness showed reverse indentation size effect (ISE) before the pop-in, and exhibited normal ISE after the pop-in. Both the hardness and the Young's modulus of the a-plane (112¯0) ZnO single crystal increased with the increasing strain rate, exhibiting the positive strain-rate sensitivity.

Heavy Metal Removal from Aqueous Effluents by TiO2 and ZnO Nanomaterials

The presence of heavy metals in wastewater, such as Ni, Pb, Cd, V, Cr, and Cu, is a serious environmental problem. This kind of inorganic pollutant is not biodegradable for several years, and its harmful effect is cumulative. Recently, semiconductor nanomaterials based on metal oxides have gained interest due to their efficiency in the removal of heavy metals from contaminated water, by inducing photocatalytic ion reduction when they absorb light of the appropriate wavelength. The most commonly applied semiconductor oxides for these purposes are titanium oxide (TiO2), zinc oxide (ZnO), and binary nanomaterials composed of both types of oxides. The main purpose of this work is to critically analyse the existent literature concerning this topic focusing specially in the most important factors affecting the adsorption or photocatalytic capacities of this type of nanomaterials. In particular, photocatalytic activity is altered by various factors, such as proportion of polymorphs, synthesis method, surface area, concentration of defects and particle size, among others. After a survey of the actual literature, it was found that, although these metal oxides have low absorption capacity for visible light, it is possible to obtain an acceptable heavy metal reduction performance by sensitization with dyes, doping with metallic or nonmetallic atoms, introduction of defects, or the coupling of two or more semiconductors.

Photoactivated Processes on the Surface of Metal Oxides and Gas Sensitivity to Oxygen

Photoactivation by UV and visible radiation is a promising approach for the development of semiconductor gas sensors with reduced power consumption, high sensitivity, and stability. Although many hopeful results were achieved in this direction, the theoretical basis for the processes responsible for the photoactivated gas sensitivity still needs to be clarified. In this work, we investigated the mechanisms of UV-activated processes on the surface of nanocrystalline ZnO, In₂O₃, and SnO₂ by in situ mass spectrometry and compared the obtained results with the gas sensitivity to oxygen in the dark and at UV irradiation. The results revealed a correlation between the photoactivated oxygen isotopic exchange activity and UV-activated oxygen gas sensitivity of the studied metal oxides. To interpret the data obtained, a model was proposed based on the idea of the generation of additional oxygen vacancies under UV irradiation due to the interaction with photoexcited holes.

AZO Nanoparticles-Decorated CNTs for UV Light Sensing: A Structural, Chemical, and Electro-Optical Investigation

Nanocomposites formed by aluminum-doped zinc oxide nanoparticles (AZO-NP) and multiwall carbon nanotubes (CNT) are proposed here as a promising material for UV light sensing applications, with the great advantage of operating in air, at room temperature, and at low voltage. Nanocomposite layers were prepared with different AZO:CNT weight ratios by a simple methodology at room temperature. They were characterized by means of UV-Vis spectroscopy, scanning and transmission electron microscopies (SEM and TEM), and X-ray photoelectron spectroscopy (XPS). The interaction between the two nanomaterials was demonstrated by comparing the properties of the nanocomposite with the ones shown by the AZO-NPs. Dense AZO-CNT nanocomposite layers were deposited between two metal electrodes on a SiO₂/Si substrate, and the electrical properties were investigated in dark condition and under UV light irradiation. The electrical response to the UV light was a sudden current increase that reduced when the light was switched off. Several UV on/off cycles were performed, showing good repeatability and stability of the response. The mechanisms involved in the electrical response are discussed and compared to the ones previously reported for ZnO-CNT nanocomposites.

Efficient Oxygen Vacancy Defect Engineering for Enhancing Visible-Light Photocatalytic Performance over SnO2-x Ultrafine Nanocrystals

Regardless of its good electron-transfer ability and chemical stability, pure Zn₂SnO₄ (ZSO) still has intrinsic deficiencies of a narrow spectral response region, poor absorption ability, and high photo-activated carrier recombination rate. Aiming to overcome the deficiencies above-mentioned, we designed a facile hydrothermal route for etching ZSO nanoparticles in a dilute acetic acid solution, through which efficient oxygen vacancy defect engineering was accomplished and SnO_2-x nanocrystals were obtained with an ultrafine particle size. In comparison with the untreated ZSO nanoparticles, the specific surface area of SnO_2-x nanocrystals was substantially enlarged, subsequently leading to the notable augmentation of active sites for the photo-degradation reaction. Aside from the above, it is worth noting that SnO_2-x nanocrystals were endowed with a broad spectral response, enhancing light absorption capacity and the photo-activated carrier transfer rate with the aid of oxygen vacancy defect engineering. Accordingly, SnO_2-x nanocrystals exhibited significantly enhanced photoactivity toward the degradation of the organic dye rhodamine B (RhB), which could be imputed to the synergistic effect of increasing active sites, intensified visible-light harvesting, and the separation rate of the photo-activated charge carrier caused by the oxygen vacancy defect engineering. In addition, these findings will inspire us to open up a novel pathway to design and prepare oxide compound photocatalysts modified by oxygen vacancy defects in pursuing excellent visible-light photoactivity.

Visible Light-Induced Room-Temperature Formaldehyde Gas Sensor Based on Porous Three-Dimensional ZnO Nanorod Clusters with Rich Oxygen Vacancies

Oxygen vacancy (V_O) is a kind of primary point defect that extensively exists in semiconductor metal oxides (SMOs). Owing to some of its inherent qualities, an artificial manipulation of V_O content in one material has evolved into a hot research field, which is deemed to be capable of modulating band structures and surface characteristics of SMOs. Specific to the gas-sensing area, V_O engineering of sensing materials has become an effective means in enhancing sensor response and inducing light-enhanced sensing. In this work, a high-efficiency microwave hydrothermal treatment was utilized to prepare a V_O-rich ZnO sample without additional reagents. The X-ray photoelectron spectroscopy test revealed a significant increase in V_O proportion, which was from 9.21% in commercial ZnO to 36.27% in synthesized V_O-rich ZnO possessing three-dimensional and air-permeable microstructures. The subsequent UV-vis-NIR absorption and photoluminescence spectroscopy indicated an extension absorption in the visible region and band gap reduction of V_O-rich ZnO. It turned out that the V_O-rich ZnO-based sensor exhibited a considerable response of 63% toward 1 ppm HCHO at room temperature (RT, 25 °C) under visible light irradiation. Particularly, the response/recovery time was only 32/20 s for 1 ppm HCHO and further shortened to 10/5 s for 10 ppm HCHO, which was an excellent performance and comparable to most sensors working at high temperatures. The results in this work strongly suggested the availability of V_O engineering and also provided a meaningful candidate for researchers to develop high-performance RT sensors detecting volatile organic compounds.

Composition engineering of AZO films for controlled photon-electron conversion and ultrafast nonlinear optical behavior

Exploring micro-nano photonic crystals as nonlinear optical switching and optical limiting devices for Gaussian light fields with ultrashort pulse widths has attracted extensive research, mainly originating from its controllable modulation of the third/fifth-order nonlinear optical behavior and ultrafast carrier dynamics. In this work, Al-doped ZnO (AZO) films with controllable and excellent third-order nonlinear optical behavior have been uniformly deposited on quartz substrates by a single-step co-sputtering method. Al dopant-dependent ultrafast carrier dynamics and nonlinear optical properties in hexagonal ZnO films are discussed. The bonding mode of Al atoms in the ZnO lattice changed from substitutional to substitutional-decoration, which has been controllably achieved at different DC sputtering powers. The strain, crystallinity, grain size, dislocation density, and texture coefficient of the sample were quantitatively calculated by XRD and Raman spectroscopy, which confirmed that the phase parameters can be regulated by the sputtering power. In addition, Hall test and photoluminescence spectra showed the contribution of the donor level on the band structure and the electron transfer characteristics, which will provide a strategy for understanding multi-type carrier dynamics under strong light fields. The finite-difference time-domain method was used to simulate the linear optical absorption/transmittance of the sample under a plane-wave optical field, which proved that the light-matter interaction failed to be significantly suppressed by shading and scattering effects. The carrier relaxation process and nonlinear absorption/refractive effects were controllably optimized by dopant Al atoms, which were confirmed by Z-scan and transient absorption spectroscopy. Compared with pure ZnO films, the third-order nonlinear refraction and absorption coefficients of AZO-power films can reach -8.926 × 10^-15 m² W^-1 and -0.634 × 10^-7 m W^-1, respectively. AZO films with ultrafast carrier dynamics and controllable excellent third-order nonlinear optical coefficients can be used as all-optical switches and optical limiting devices, which provide a reference for advanced micro-nano optical materials.

Low recombination rates and improving charge transfer as decisive conditions for high current densities and fill factors in ZnS complex systems

The growth of ZnS photoelectrodes on ZnO particles identified as ZnO/ZnS(ZC + TAA) by the microwave-assisted hydrothermal method showed excellent photovoltaic parameters of J_SC = 1.2 mA cm^-2 and FF = 0.66, even compared to ZnS(ZC + TAA) used as a reference sample with J_SC = 0.15 mA cm^-2 and FF = 0.52. A careful analysis indicates that the better charge transfer and the higher resistance to recombination present in the ZnO/ZnS(ZC + TAA) samples were the origin of the best photovoltaic behavior. These assertions are supported by a set of samples synthesized from different precursors resulting in different crystal structures, which can be directly associated with current densities and fill factors. All aspects about synthesis and optical/electronic parameters associated with structural features will be available in this article.

Oxygen Vacancy-Dependent Chemiluminescence: A Facile Approach for Quantifying Oxygen Defects in ZnO

Defect engineering is an effective strategy to improve the catalytic activity of metal oxides, and quantitative characterization of surface defects is thus vital to the understanding and application of metal oxide catalysts. Herein, we found that ZnO nanoparticles with oxygen vacancy could trigger the luminol-H₂O₂ system to emit a strong chemiluminescence (CL), and the CL intensity was strongly dependent on the oxygen vacancy of the ZnO nanoparticles. The mechanism of this CL reaction was discussed by means of the electron-spin resonance spectrum, X-ray photoelectron spectrum (XPS), and CL spectrum. The oxygen vacancy-dependent CL was attributed to the ability of the oxygen vacancy to readily adsorb and further dissociate H₂O₂ into active ^•OH radicals. Taking advantage of this oxygen vacancy-dependent CL, we presented one method for quantifying the oxygen defects in ZnO. Compared with the current evaluation techniques (XPS and Raman spectroscopy), this CL method is rapid, low-cost, and easy to operate. This work introduces the CL technique into the field of material structure-property evaluation, and provides a new approach for exploring the defect function in ZnO defect engineering.

New insight into the regulation mechanism of visible light in naproxen degradation via activation of peroxymonosulfate by MOF derived BiFeO3

BiFeO₃ (BFO) nanocage prepared by metal-organic-framework derivatization (MOF-d) was adopted as activator to first investigate the effect mechanism of visible-light on naproxen-degradation via peroxymonosulfate (PMS) activation. MOF-d BFO expressed more excellent PMS activation ability than hydrothermal-synthetic BFO, due to highly ordered mesopores. A 3.0 times higher pseudo-first-order degradation rate constant was achieved after visible-light introduced. The quenching experiments indicated that the contribution of ROS in naproxen degradation followed the order of SO₄^•->¹O₂ ≈ •OH in MOF-d BFO/PMS/dark system, while changed into h⁺>¹O₂ > >O₂^•-≈SO₄^•-> •OH after visible-light introduced^. EPR tests first revealed that visible-light promoted ¹O₂ yield (non-radical pathway) but suppressed •OH and SO₄^•- generation (free-radical pathways). N₂-purging experiments further proved that ¹O₂ primarily originates from the reaction between h⁺ and PMS, equivalently to that between O₂ and e^--h⁺ in MOF-d BFO/PMS/vis system. Under visible-light, PMS activation via Fe (III) might be hindered by e^- filling on Fe 3d orbital and anion PMS preferred to approach h⁺ rather than e^-, resulting in the decrease of •OH and SO₄^•- yields. Moreover, PMS faces competition from adsorbed-O₂ and oxygen-vacancies for e^- capture. The degradation-pathways for naproxen in dark and under visible light were both proposed in MOF-d BFO/PMS system.

UV-Activated NO2 Gas Sensing by Nanocrystalline ZnO: Mechanistic Insights from Mass Spectrometry Investigations

In this work, the photostimulated processes of O2 and NO2 molecules with the surface of ZnO under UV radiation were studied by in situ mass spectrometry in the temperature range of 30–100 ∘C. Nanocrystalline needle-like ZnO was synthesized by decomposition of basic zinc carbonate at 300 ∘C, and the surface concentration of oxygen vacancies in it were controlled by reductive post-annealing in an inert gas at 170 ∘C. The synthesized materials were characterized by XRD, SEM, low-temperature nitrogen adsorption (BET), XPS, Raman spectroscopy, and PL spectroscopy. Irradiation of samples with UV light causes the photoabsorption of both O2 and NO2. The photoadsorption properties of ZnO are compared with its defective structure and gas-sensitive properties to NO2. A model of the sensor response of ZnO to NO2 under UV photoactivation is proposed.

Ultra-sensitive H2S sensor based on sunflower-like In-doped ZnO with enriched oxygen vacancies

In–ZnO with oxygen vacancies exhibits a higher sensing response and a shorter recovery time for H2S compared to ZnO.

Study of High-Temperature Behaviour of ZnO by Ab Initio Molecular Dynamics Simulations and X-ray Absorption Spectroscopy

Wurtzite-type zinc oxide (w-ZnO) is a widely used material with a pronounced structural anisotropy along the c axis, which affects its lattice dynamics and represents a difficulty for its accurate description using classical models of interatomic interactions. In this study, ab initio molecular dynamics (AIMD) was employed to simulate a bulk w-ZnO phase in the NpT ensemble in the high-temperature range from 300 K to 1200 K. The results of the simulations were validated by comparison with the experimental Zn K-edge extended X-ray absorption fine structure (EXAFS) spectra and known diffraction data. AIMD NpT simulations reproduced well the thermal expansion of the lattice, and the pronounced anharmonicity of Zn-O bonding was observed above 600 K. The values of mean-square relative displacements and mean-square displacements for Zn-O and Zn-Zn atom pairs were obtained as a function of interatomic distance and temperature. They were used to calculate the characteristic Einstein temperatures. The temperature dependences of the O-Zn-O and Zn-O-Zn bond angle distributions were also determined.

Progress in ZnO Nanosensors

Developing various nanosensors with superior performance for accurate and sensitive detection of some physical signals is essential for advances in electronic systems. Zinc oxide (ZnO) is a unique semiconductor material with wide bandgap (3.37 eV) and high exciton binding energy (60 meV) at room temperature. ZnO nanostructures have been investigated extensively for possible use as high-performance sensors, due to their excellent optical, piezoelectric and electrochemical properties, as well as the large surface area. In this review, we primarily introduce the morphology and major synthetic methods of ZnO nanomaterials, with a brief discussion of the advantages and weaknesses of each method. Then, we mainly focus on the recent progress in ZnO nanosensors according to the functional classification, including pressure sensor, gas sensor, photoelectric sensor, biosensor and temperature sensor. We provide a comprehensive analysis of the research status and constraints for the development of ZnO nanosensor in each category. Finally, the challenges and future research directions of nanosensors based on ZnO are prospected and summarized. It is of profound significance to research ZnO nanosensors in depth, which will promote the development of artificial intelligence, medical and health, as well as industrial, production.