Modification Of ZnO Research Articles

Role of Sulfur in Enhancing UV‐Light Absorption and Photoelectrochemical Performance of ZnO/N,S‐doped CQDs Nanocomposite

AbstractThe modification of ZnO, such as transforming it from 1‐D to 3‐D nanostructures or compositing it with carbon‐based materials, has been extensively explored to enhance light energy harvesting and reduce electron‐hole recombination‐key limitations of ZnO. Herein, the effect of different composite materials, specifically nitrogen‐doped carbon quantum dots (N‐CQDs) and nitrogen, sulfur‐doped carbon quantum dots (N,S‐CQDs), on ZnO's morphology and photocurrent response was studied. Various morphologies were synthesized on conductive glass substrate using a one‐pot hydrothermal method, including flower‐like structure for ZnO/N‐CQDs (∼d = 0.9 µm) and multilayered microspheres for ZnO/N,S‐CQDs (∼d = 1.1 µm). The inclusion of sulfur atoms in the composite resulted in a reduced bandgap value from 3.22 to 3.11 eV, along with enhanced light absorption efficiency and improved separation of photogenerated electron‐hole pairs. Furthermore, the crystallinity of ZnO/N,S‐CQDs was significantly enhanced compared to ZnO without sulfur doping. These improvements were reflected in the photoelectrochemical (PEC) measurements, where ZnO/N,S‐CQDs showed a current density of 21.8 µA/cm2 at 0.5 V (vs. Ag/AgCl), which is 5.5 times higher than that of ZnO/N‐CQDs (4.0 µA/cm2). These findings demonstrate that sulfur doping improves photocatalytic efficiency, making 3D ZnO/N,S‐CQDs a promising candidate for various UV‐driven PEC applications.

Significantly energy‐efficient ethanol sensor based on bougainvillea‐like Au/ZnO hierarchical nanostructured materials

AbstractThe energy consumption of MOS (metal oxide semiconductor) sensors has always been a challenge in improving their performance. In this study, bougainvillea‐like Au/ZnO nanostructures were successfully synthesized using the hydrothermal method and the sol fixation technique. The composition, crystallinity, crystal structure, and morphology of the materials were characterized using X‐ray diffraction, energy‐dispersive spectroscopy, and field emission scanning electron microscopy. The experimental results confirm the successful synthesis of a substantial quantity of bougainvillea‐like Au/ZnO nanostructures through nanoparticle self‐assembly. The sensitive performance of the bougainvillea‐like Au/ZnO sensor was evaluated using a CGS‐8 intelligent gas‐sensitive analysis system. Results demonstrate that modification of ZnO with Au in a bougainvillea‐like nanostructure significantly enhances sensitivity to ethanol vapor compared to those of unmodified material sensors. Specifically, the optimal work temperature was greatly reduced by 64%, whereas the sensitivity increased approximately 12 times and the response time decreased nearly 5 times. The significantly enhanced ethanol sensitivity can be attributed to the precious metal modification and unique three‐dimensional morphology. It provides the necessary experimental exploration for reducing energy consumption and improving the performance of MOS gas sensors.

Efficient window layer modification enabling the remarkable FF and efficiency improvement of kesterite solar cell

As the core structure of kesterite thin-film solar cell (TFSC), the nature of N-type functional layer and its interface is a key issue impacting device performance, typically its influence on carrier recombination and electron charge transportation. Here, a modified window layer to tailor N-type bulk and its interface properties for efficiency carrier collection and device performance is incorporated by co-sputtering ZnO and SiO2. Research has found that the modified window layer not only has an excellent wide optical spectrum with high transmittance, enabling additional photon harvesting and short-wave absorption, but also modulates the energy band position for better band alignment to facilitate charge transportation, ensuring higher conductivity. Simultaneously, the significantly reduced carrier recombination and increased uniformity of the device further accelerate charge efficient collection and enhance filling factor (FF). Consequently, the modified window layer of kesterite TFSC enables a remarkable efficiency improvement from 8.4% to 12.0% with a boosted FF from 61% to 73%. These novel results provide the inherent physical origin for improving the photovoltaic performance of kesterite TFSC by appropriate modification of ZnO:SiO2 window layer and open up an effective and feasible strategy, which can also be applied to other optoelectronic devices.

Highly sensitive and selective NO2 detection using face-centered cubic Zn2SnO4 nanostructures

This study reports the synthesis and modification of hexagonal ZnO to face-centered cubic (Fcc) Zn2SnO4 via a single hydrothermal method. We systematically investigated the synthesized materials' structural, morphological, surface area, and sensing properties. X-ray diffraction (XRD) analysis confirmed the Fcc structure of the Sn-modified ZnO samples. X-ray photoelectron spectroscopy (XPS) was employed to elucidate the influence of Sn modified on defect levels in these chemical sensors. Remarkably, Zn2SnO4 exhibited outstanding NO2 sensing properties, including high response, selectivity, and recovery characteristics. The sensor demonstrated a rapid response time of less than 18s and an optimal operating temperature of 260 °C. Furthermore, the cubic face-centered Zn2SnO4 displayed a wide detection range of 1–100 ppm for NO2. The synergistic effects of chemical sensitization and catalytic activity are responsible for the enhanced sensing mechanism in Zn2SnO4.

Wireless Gas Sensor Based on the Mesoporous ZnO-SnO2 Heterostructure Enables Ultrasensitive and Rapid Detection of 3-Methylbutyraldehyde.

Achieving ultrasensitive and rapid detection of 3-methylbutyraldehyde is crucial for monitoring chemical intermediate leakage in pharmaceutical and chemical industries as well as diagnosing ventilator-associated pneumonia by monitoring exhaled gas. However, developing a sensitive and rapid method for detecting 3-methylbutyraldehyde poses challenges. Herein, a wireless chemiresistive gas sensor based on a mesoporous ZnO-SnO2 heterostructure is fabricated to enable the ultrasensitive and rapid detection of 3-methylbutyraldehyde for the first time. The mesoporous ZnO-SnO2 heterostructure exhibits a uniform spherical shape (∼79 nm in diameter), a high specific surface area (54.8 m2 g-1), a small crystal size (∼4 nm), and a large pore size (6.7 nm). The gas sensor demonstrates high response (18.98@20 ppm), short response/recovery times (13/13 s), and a low detection limit (0.48 ppm) toward 3-methylbutyraldehyde. Furthermore, a real-time monitoring system is developed utilizing microelectromechanical systems gas sensors. The modification of amorphous ZnO on the mesoporous SnO2 pore wall can effectively increase the chemisorbed oxygen content and the thickness of the electron depletion layer at the gas-solid interface, which facilitates the interface redox reaction and enhances the sensing performance. This work presents an initial example of semiconductor metal oxide gas sensors for efficient detection of 3-methylbutyraldehyde that holds great potential for ensuring safety during chemical production and disease diagnosis.

Regeneration of copper catalysts mediated by molybdenum-based oxides

Cu catalysts, known for their unparalleled catalytic capabilities due to their unique electronic structure, have faced inherent challenges in maintaining long-term effectiveness under harsh hydrogenation conditions. Here, we demonstrate a molybdenum-mediated redispersion behavior of Cu under high-temperature oxidation conditions. The oxidized Cu nanoparticles with rich metal-support interfaces tend to dissolve into the MoO3 support upon heating to 600 °C, which facilitates the subsequent regeneration in a reducing atmosphere. A similar redispersion phenomenon is observed for Cu nanoparticles supported on ZnO-modified MoO3. The modification of ZnO significantly improves the performance of the Cu catalyst for CO2 hydrogenation to methanol, with the high activity being well maintained after four repeated oxidation-reduction cycles. In situ spectroscopic and theoretical analyses suggest that the interaction involved in the formation of the copper molybdate-like compound is the driving force for the redispersion of Cu. This method is applicable to various Mo-based oxide supports, offering a practical strategy for the regeneration of sintered Cu particles in hydrogenation applications.

An Efficient and Stable Inverted Structure Organic Solar Cell Using ZnO Modified by 2D ZrSe2 as a Composite Electron Transport Layer

AbstractAs an electron transport layer (ETL) widely used in organic solar cells (OSCs), ZnO has problems with energy level mismatch with the active layer and excessive defects on the ZnO surface, which can reduce the efficiency of OSCs. Here, ZnO/ZrSe2 composite is fabricated by modifying ZnO with 2D ZrSe2. The XPS and first‐principles calculation (FPC) show that ZnO obtains electrons from ZrSe2 and forms interfacial dipoles toward the active layer, which decreases the work function of ZnO, thus reducing the interface barrier and favoring the collection of electrons in OSCs. At the same time, after ZrSe2 modification, the oxygen vacancy density on the ZnO surface decreases, thus improving the conductivity of ZnO. More importantly, the femtosecond transient absorption (Fs‐TA) shows that ZrSe2 selectively traps holes from the active layer, which prevents the holes from entering the ZnO, thereby reducing the probability of electron recombination. Finally, ZnO/ZrSe2 composite is used as a novel ETL in OSCs with PBDB‐T: ITIC, PM6:Y6 and PM6: L8‐BO as active layers, and obtaining 12.09%, 16.34%, and 18.24% efficiency, respectively. This study provides a method for the interface modification of ZnO, and further investigates the role of 2D nanosheets in the interface modification.

Synthesis, characterizations, and photocatalytic activity of ZnO/NiBi2O4

ZnO/NiBi2O4 was successfully synthesized using patikan kebo leaf extract (PKLE) in a two-phase system. The band gap value of ZnO/NiBi2O4 was 2.72 eV, which is actively in the visible region. The photocatalytic activity of ZnO/NiBi2O4 showed better degradation of malachite green than that of ZnO and NiBi2O4. The degradation efficiency over ZnO/NiBi2O4, NiBi2O4, and ZnO were 92.30 %, 77.33 %, and 55.99 %, respectively, under visible light for 120 min. The reaction rate constant using ZnO/NiBi2O4 was greater than that of ZnO and NiBi2O4, suggesting that the modification of ZnO with NiBi2O4 increased the photodegradation activity by hindering the photorecombination of electron-holes in ZnO. Notably, O2∙–, ∙OH, and h+ are identified as crucial species that play a vital role in the degradation process confirmed by reactive oxygen species (ROS) analysis. This work studied potential ZnO/NiBi2O4 materials for photocatalytic dye degradation applications.

Green-Synthesized Sm3+-Doped ZnO Nanoparticles for Multifunctional Applications

The present study focuses on the green-mediated synthesis of pristine and Sm3+-doped ZnO nanoparticles using Syzygium cumini fruit extract. The prepared material was characterized by various characterization techniques. Photocatalytic degradation of a fast orange red (FOR) dye under UV light resulted in 88% degradation, with a minimal decrease (87.90%) observed even after five successive runs, indicating the stability and effectiveness of the catalyst. The enhancement in degradation efficiency is attributed to the incorporation of Sm3+ ions into the ZnO lattice. Utilizing the optimized Sm3+ (5 mol%)-doped ZnO nanoparticles, cyclic voltammetry (CV) and electrochemical impedance spectra (EIS) were performed on the prepared electrode, demonstrating the excellent CV properties; this enhancement is attributed to the modification of ZnO’s redox chemistry and the alteration of charge transfer kinetics at the electrode-electrolyte interface due to the addition of Sm3+ into the ZnO structure. The antibacterial activity was performed against two pathogenic strains, i.e., Escherichia coli and Streptococcus aureus. The obtained results suggest that the prepared material holds great promise for catalytic, energy storage, antibacterial, and other multifunctional applications.

Nano-Confined Effect and Heterojunction Promoted Exciton Separation for Light-Boosted Osmotic Energy Conversion.

The osmotic energy conversion properties of biomimetic light-stimulated nanochannels have aroused great interest. However, the power output performance is limited by the low light-induced current and energy conversion efficiency. Here, nanochannel arrays with simultaneous modification of ZnO and di-tetrabutylammonium cis-bis(isothiocyanato)bis(2,20-bipyridyl-4,40-dicarboxylato) ruthenium (II) (N719) onto anodic aluminum oxide (AAO) to combine the nano-confined effect and heterojunction is designed, which demonstrate rectified ion transport behavior due to the asymmetric composition, structure and charge. High cation selectivity and ion flux contribute to the high power density of ≈7.33Wm-2 by mixing artificial seawater and river water. Under light irradiation, heterojunction promoted the production and separation of exciton, enhanced cation selectivity, and improved the utilization efficiency of osmotic energy, providing a remarkable power density of ≈18.49Wm-2 with an increase of 252% and total energy conversion efficiency of 30.43%. The work opens new insights into the biomimetic nanochannels for high-performance energy conversion.

Modification of ZnO gas-diffusion-electrodes for enhanced electrochemical CO2 reduction: optimization of operational conditions and mechanism investigation

Amino-functionalized ZnO exhibits enhanced CO2 adsorption capacity and selectivity for electrochemical conversion of CO2 to CO.

Enhancement in CO Selectivity by Modification of ZnO with CuxO for Electrochemical Reduction of CO2

Enhancement in CO Selectivity by Modification of ZnO with Cu_<i>x</i>O for Electrochemical Reduction of CO₂

Effect of oxygen vacancy modification of ZnO on photocatalytic degradation of methyl orange: A kinetic study

This study investigated a novel kinetic model of the adsorption and photocatalytic degradation of methyl orange, an anionic dye, using a commercial ZnO and reduced commercial ZnO photocatalysts. The results were compared and discussed with our previous study on methylene blue, a cationic dye, providing new insights into the interaction of the catalyst with molecules with different charges. The kinetic model was applied to describe adsorption in the dark, followed by photocatalytic degradation under simulated sunlight. In addition, the predicted pKa values of methyl orange were estimated using the kinetic model, which were found to be 4.40 and 9.34. The effect of ZnO oxygen vacancies (created through hydrogen reduction at 500 °C) on the adsorption and photocatalytic degradation of methyl orange was investigated. The existence and effects of oxygen vacancies on ZnO were analyzed using TPR, PL, XPS, XRD, FE-SEM, EDS, BET, Tauc plot, Mott-Schottky, and cyclic Voltammetry. The appearance of oxygen vacancies was clearly observed by the characterization results, while the morphology of the nanoparticles was found to be unchanged. Additionally, the band gap of ZnO was decreased from 3.22 to 3.07 eV, and the maximum valence band of the catalyst was increased from 2.43 to 2.67 eV due to the reduction pretreatment. The findings suggest that the photocatalytic degradation rate of the reduced ZnO substantially increased. However, the adsorption removal of the anionic dye declined, which could be attributed to the more negative zeta potential of ZnO after hydrogen reduction. Finally, the quantum yield of photocatalytic process was calculated and compared with the results of methylene blue.

Adsorption properties of CuO/ZnO modified HfSe2 monolayer upon SF6 decomposition gases (H2S, SO2, SOF2 and SO2F2)

In this paper, the adsorption properties of CuO-HfSe2 and ZnO-HfSe2 substrates towards SF6 decomposition gas (H2S, SO2, SOF2 and SO2F2) were analyzed based on the first-principle calculations. The optimal position of the two metal oxides doping on HfSe2 was calculated, and the binding energies of –2.530 eV and –1.906 eV ensure the stability of CuO-HfSe2 and ZnO-HfSe2 during adsorption process. The results show that, the modification of CuO and ZnO changes the band structure of the HfSe2 monolayer, and the CuO and ZnO molecules are charged with –0.0339 e and –0.0368 e, showing the potential of adsorbed gas. Compared to the pristine HfSe2 monolayer, the adsorption distances of CuO-HfSe2 and ZnO-HfSe2 to the four gases decrease from about 3.5 Å to about 2 Å, and the adsorption energies increase from about –0.35 eV to more than –2.1 eV and more than –1.1 eV, respectively. Moreover, charge deformation density, density of states, partial density of states and molecular orbital theory were explored to clarify the interaction between the gas molecules and the substrates. The results show that, CuO-HfSe2 shows better adsorption performance than ZnO-HfSe2 for H2S, SO2, SOF2 and SO2F2. For CuO-HfSe2 system, the adsorption capacity for the four gases is ranked as: H2S > SO2 > SOF2 > SO2F2; and the sort is: SO2 > SOF2 > H2S > SO2F2 for ZnO-HfSe2 system. After gas adsorption, the conductivity of the system changes to different degrees, through which the adsorption of the gas can be detected. All adsorption systems have a long recovery time, and the methods of increasing the temperature or UV irradiation are needed to excite the gas desorption process. This study provides new sensing materials for H2S, SO2, SOF2 and SO2F2.

Surface Modification of ZnO with Sn(IV)-Porphyrin for Enhanced Visible Light Photocatalytic Degradation of Amaranth Dye.

Two hybrid composite photocatalysts, denoted as SnP/AA@ZnO and SnP@ZnO, were fabricated by a reaction of trans-dihydroxo[5,10,15,20-tetrakis(4-pyridyl)porphyrinato]tin(IV) (SnP) and ZnO with and without pretreatment of adipic acid (AA), respectively. In SnP@ZnO, SnP and ZnO are likely held together by a coordinative interaction between the pyridyl N atoms of SnP and the Zn atoms on the surface of ZnO. In the case of SnP/AA@ZnO, the SnP centers were robustly coupled with ZnO nanoparticles through the AA anchors. SnP/AA@ZnO exhibited largely enhanced photocatalytic activities for the degradation of anionic amaranth (AM) dye under a visible light irradiation, compared to SnP, ZnO, and SnP@ZnO. The degradation efficiency of AM by SnP/AA@ZnO was 95% within 60 min at a rate constant of 0.048 min-1. The remarkable photocatalytic oxidation performance of SnP/AA@ZnO was mainly attributed to the synergistic effect between SnP and ZnO. This study is valuable for the development of highly effective composite photocatalytic systems in advanced oxidation processes and is of importance for the treatment of wastewater containing dyes.

Enhancement of photocatalytic activity of ZnO by ZnMoO4 compositing under visible light via hydrothermal green synthesis

ZnO has excellent photocatalytic activity under UV light, but its photocatalytic activity under visible light is relatively low due to its wide band gap. Modification of ZnO to a composite with ZnMoO4, which has a band gap energy of 2.61 eV, triggers heterojunction photocatalytic reactions under visible light. Here in this research, ZnO-ZnMoO4 nanocomposites have been successfully synthesized using the green synthesis hydrothermal method with Mentha x piperita leaf extract containing alkaloids as a source of weak bases and other secondary metabolites as capping agents. The development of green synthesis methods in this study aims to reduce the use of hazardous and toxic materials. The synthesized photocatalysts have been fully characterized and evidence of increased photocatalytic activity of ZnO/ZnMoO4 composites is based on the degradation of Rhodamine B (RhB) dye in visible light. The results showed that the degradation of RhB by ZnO/ZnMoO4 nanocomposites could reach 83.7%, and this was better than using ZnO which only reached 13.9%.

Enhancement in CO Selectivity by Modification of ZnO with CuxO for Electrochemical Reduction of CO2

The electrochemical reduction reaction of carbon dioxide (CO2RR) has garnered significant attention due to its potential for the formation of carbon monoxide, which has industrial relevance. Herein, an oxide‐derived Cu–Zn electrocatalyst with an optimized Cu x O layer that shows high selectivity toward CO with a faradic efficiency of 75% at a low overpotential (−0.8 V vs reversible hydrogen electrode) is reported. Various structural characterizations and activity tests are conducted to understand the origin of this improvement depending on the Cu x O amount. Electrochemical surface area and electrochemical impedance spectroscopy measurements suggest that the addition of Cu x O increases double‐layer capacitance and decreases charge transfer resistance. Scanning electron microscopy images indicate that the electrodes undergo a severe reconstruction process, which is further confirmed by X‐ray diffraction that shows the formation of CuZn4 alloy during the reduction reaction. Furthermore, X‐ray photoelectron spectroscopy depth profile analysis shows that after CO2RR at −0.8 V, the Cu/Zn ratio is higher than that after −1.2 V, which suggests that applied potential plays a significant role in the reconstruction process and hence the difference in selectivity. The presence of copper in the surface layer has a significant impact on the improvement of selectivity toward CO.

Thin-Film Nanocrystalline Zinc Oxide Photoanode Modified with CdO in Photoelectrocatalytic Degradation of Alcohols

Thin-film nanocrystalline zinc oxide electrodes were fabricated by electrochemical deposition of ZnO on FTO-coated glass slides. ZnO electrodes were promoted by CdO coating on top of ZnO in amounts corresponding to 0.8, 0.1, and 0.05 C cm−2 in electric units. Modification of ZnO by a small amount of CdO, corresponding to 0.05 C cm−2, shifts the photoactivity of the composite photoanode into the visible part of the solar spectrum. It is shown that the ZnO/(0.05C)CdO/FTO electrode demonstrates high efficiency in photoelectrochemical degradation of methanol, ethylene glycol, and glycerol when irradiated by a simulated sunlight. According to intensity-modulated photocurrent spectroscopy (IMPS), the effect is due to suppression of the electron–hole pairs recombination and increase in the rate of photo-induced charge transfer. Therefore, thin-film photoanodes based on zinc oxide modified by CdO can be used for photoelectrochemical degradation of byproducts of biofuel production glycerol, and of other alcohols.

ZnO-decorated green-synthesized multi-doped carbon dots from Chlorella pyrenoidosa for sustainable photocatalytic carbamazepine degradation.

The promising green synthesis of carbon dots (CDs) from microalga Chlorella pyrenoidosa was achieved using simple hydrothermal and microwave-assisted methods. Doping of nanomaterials by nonmetals (N, S, and P) was confirmed by X-ray photoelectron spectroscopy (XPS), while the existence of metals in the CDs was confirmed by inductively coupled plasma optical emission spectroscopy (ICP-OES) and transmission electron microscopy (TEM), and Mg, Ca, K, and Na were found as the dominant doped metals. The novel nanomaterials with excellent photoluminescence (PL) properties were used for the modification of ZnO obtained by a simple hydrothermal process. In this regard, a series of ZnO decorated with multi-doped carbon dots (xCDs) was prepared and their photocatalytic properties were evaluated. The ZnO-xCD photocatalysts were characterized by various advanced techniques including X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), XPS, Brunauer-Emmett-Teller (BET), PL, ultraviolet-visible (UV-vis) spectroscopy and electrochemical impedance spectroscopy (EIS) analysis. The photocatalytic behaviour of the obtained materials was investigated in the degradation of carbamazepine (CBZ). The influence of the synthesis method of xCDs and their content on the activity of the photocatalyst was examined. The photocatalyst ZnO modified with 3% xCDs obtained by the microwave-assisted method revealed the highest effectiveness for CBZ degradation and allowed for a first-order degradation rate of 2.85 times in comparison with non-modified ZnO. The improvement of the photocatalytic process was achieved by support with peroxymonosulphate resulting in up to 3.18 times a first order kinetic rate constant compared with that of simple photocatalysis in the presence of ZnO-xCDs. Taken together, our synthesized multi-doped CDs and their nanohybrids with ZnO, can be considered as promising candidates for photocatalytic applications.

MoS2-coupled coniferous ZnO for photocatalytic degradation of dyes

BackgroundThe modification of ZnO through structural engineering and coupling with different 2D materials as a photocatalyst has received considerable attention. Few studies have reported the coupling of 2D material, MoS2, with ZnO for photocatalysis. However, no study has been conducted on MoS2-coupled coniferous T-shaped ZnO and its photocatalytic performance to the best of our knowledge. MethodsIn this study, the flame transport synthesis technique was employed for the preparation of coniferous T-shaped ZnO (T-ZnO). The as-prepared coniferous-like T-ZnO was coupled with MoS2 by hydrothermal treatment at 200 °C for 18 h and used for the photocatalytic dye removal. Significant findingsAfter coupling with MoS2, T-ZnO and spherical O-shape (O-ZnO) exhibited improved photocatalytic activities for the removal of dyes (methyl blue (MB) and rhodamine B (RhB)). Thanks to the heterojunction formation between MoS2 and ZnO, the electron transfer could be facilitated, evidenced by the small Tafel slope with a value of approximately 95.6 mv dec‒1. Moreover, the MoS2@T-ZnO sample could be recycled for photocatalytic MB removal at least 5 times. Our results suggested that the coupling of MoS2 over structural-engineered ZnO could be an alternative approach to further improving the photocatalytic activity of ZnO.