Zinc oxide nanostructures enhanced photoluminescence by carbon-black nanoparticles in Moiré heterostructures

ZnO/carbon-black heterostructures were synthesized using a sol-gel method and crystallized by annealing at 500 °C under 2 × 10^-2 Torr for 10 min. The crystal structures and binding vibration modes were determined by XRD, HRTEM, and Raman spectrometry. Their surface morphologies were observed by FESEM. The Moiré pattern that is observed in the HRTEM images confirms that the carbon-black nanoparticles were covered by the ZnO crystals. Measurements of optical absorptance revealed that the optical band gap of the ZnO/carbon-black heterostructures increased from 2.33 to 2.98 eV as the carbon-black nanoparticle content increases from 0 to 8.33 × 10^-3 mol owing to the Burstein-Moss effect. The photoluminescence intensities at the near-band edge and of the violet, and blue light were increased by factors about 68.3, 62.8, and 56.8, respectively, when the carbon-black contents is of the 2.03 × 10^-3 mol. This work reveals that the proper carbon-black nanoparticle content involved increases the PL intensities of the ZnO crystals in the short wavelength regime, supporting their potential application in the light-emitting devices.

Recent progresses on ion beam irradiation induced structure and performance modulation of two-dimensional materials

Two-dimensional (2D) materials are receiving significant attention for both fundamental research and industrial applications due to their unparalleled properties and wide application potential. In this case, the controllable modulation of their structures and properties is essential for the realization and further expansion of their applications. Accordingly, ion beam irradiation techniques, with large scope to adjust parameters, high manufacturing resolution, and a series of advanced equipment being developed, have been demonstrated to have obvious advantages in manipulating the structure and performance of 2D materials. In recent years, many research efforts have been devoted to uncovering the underlying mechanism and control rules regarding ion irradiation induced phenomena in 2D materials, aiming at fulfilling their application potential as soon as possible. Herein, we review the research progress in the interaction between energetic ions and 2D materials based on the energy transfer model, type of ion source, structural modulation, performance modification of 2D materials, and then their application status, aiming to provide useful information for researchers in this field and stimulating more research advances.

Evaluation of N doped rGO-ZnO-CoPc(COOH)8 nanocomposite in cyanide degradation and its bactericidal activities

In the present study, an attempt has been made to design a solar light driven N-rGO-ZnO- CoPc(COOH)₈ nanocomposite for the degradation of cyanide. The morphological and structural characterization of the synthesized nanocomposite was performed by XRD, FT-IR, XPS, UV-vis DRS, FESEM, TEM, EDS, PL spectra and BET surface area. The results revealed that almost 91% degradation and 86% toxicity removal occurred at 25 mgL^-1 of initial cyanide concentration by the N-rGO-ZnO-CoPc(COOH)₈ nanocomposite under illumination of solar light within 120 min. Analysis of free radicals reveals that the generation of OH^. radicals was the predominant species in the photocatalytic degradation process. The cyanide degradation follows pseudo-first order kinetics. The estimated apparent rate constant (K_app) of the above nanocomposite was 3 times higher than that of the ZnO photocatalyst alone together with a very good recycle activities. This might be due to the application of metallpthalocyanine photosensitizer CoPc(COOH)₈ which enhances the rate of visible light absorption efficiency and activates the higher band gap ZnO photocatalyst under visible light. In addition, the presence of residual oxygen in N-rGO also promotes nucleation and anchor sites for interfacial contact between ZnO and N-rGO for effective charge transfer. Further, the N-rGO-ZnO-CoPc(COOH)₈ photocatalytic system showed significant antibacterial activities against mixed culture systems. Therefore, the N-rGO-ZnO-CoPc(COOH)₈ nanocomposite may be an alternative solar light driven photocatalyst system for the removal of cyanide from the wastewater along with its strong disinfectant activities.

Signature of strong localization and crossover conduction processes in doped ZnO thin films: synergetic effect of doping fraction and dense electronic excitations

Ga_xZn_1-xO thin films with varying Ga fraction within the solubility limit were irradiated with high-energy heavy ions to induce electronic excitations. The films show good transmittance in the visible region and a reduction of about 20% in transmittance was observed for irradiated films at higher ion fluences. The Urbach energy was estimated and showed an augmenting response upon increase in doping fraction and ion irradiation, this divulges an enhancement of localized states in the bandgap or disorder in the films. The evolution of such localized states plays a vital role in charge transport and thus the temperature dependent electrical conductivity of irradiated thin films was studied to elucidate the dominant conduction mechanisms. The detailed analysis unfolds that in the high-temperature regime (180 K <T< 300 K), the charge conduction was dominated by thermally activated band conduction followed by the nearest neighbor hopping (NNH) mechanism. Whereas in the lower temperature regime (25 K <T< 170 K), the conduction mechanism was governed by Mott-VRH (variable range hopping) followed by Efros-Shklovskii (ES)-VRH. A sudden and steep rise in resistivity below 30 K was observed for GZO films with higher doping fraction at higher ion fluence and proclaims the presence of strong localization of carriers.

Synthesis, characterization and bioactivity of thio-acetamide modified ZnO nanoparticles embedded in zinc acetate matrix

ZnO nanoparticles embedded in zinc acetate matrix were synthesized by chemical route. The effect of thio-acetamide concentration during its synthesis was probed by structural, morphological, optical and bioactivity studies. XRD characterization indicated the formation of dominant phase of zinc acetate along with the low intensity peak of wurtzite ZnO. Morphological transition from bulky-like feature to flower-like feature via flake-like feature, is evidenced with increasing thio-acetamide molar concentrations. The optical band gap of samples decreased from ∼3.29 to 3.24 eV whereas the emitted color shifted from near green to blue region with increasing of molar concentration of thio-acetamide from 0 to 30% in the sample. The nanoparticles exhibited antimicrobial activity against seven (7) common human pathogenic bacteria including drug resistant varieties K. pneumonaie and S. aureus. The nanoparticles formed pores in the biological model membranes made from egg-phosphatidyl choline. Our study reveals that the thio-acetamide modified ZnO nanoparticles embedded in zinc acetate matrix could be used as potential drug lead to fight drug resistance against K. pneumoniae and S. aureus.

Defect-mediated photoluminescence enhancement in ZnO/ITO via MeV Cu++ ion irradiation

Zinc oxide (ZnO) nanowires play a pivotal role in the nanoworld due to their broad range of characteristics and applications. In this work, structural and optical properties of ZnO nanowires grown on indium doped tin oxide (ITO) coated glass have been modified by copper (Cu⁺⁺) ions irradiation at constant energy of 0.7 MeV. The X-ray diffraction (XRD), photoluminescence (PL), and field emission scanning electron microscope (FESEM) are used to examine changes in the nanowires. XRD results show that the crystallite size first decreases and then increases with high ion dose while peaks' intensity decreases continuously with increasing the dose. The absence of (102) plane after irradiation depicts the defects formation. FESEM clearly shows the damage that occurred in the density of nanowires and also depicts the reduced charging effect with increasing dose. The PL spectra indicate the strong near-band edge peak and green luminescence enhancement has been recorded due to low dose ion irradiation.

The effect of crystallinity on the surface modification and optical properties of ZnO thin films

We have studied the effects of crystallinity on the emergence of porous morphology and strong green emission in ZnO thin films after H₂ annealing treatment. The unique multiple-stacked porous structure is observed after performing H₂ annealing treatment on the film with low crystallinity. However, the annealed high-crystallinity film exhibits surface morphology with a shallow porous structure, as revealed by SEM images. To study the effects of these unique porous structures on the optical properties, photoluminescence (PL) spectroscopy, Raman spectroscopy, spectroscopic ellipsometry, and X-ray photoelectron spectroscopy (XPS) are conducted. The multiple-stacked porous structure produces strong green emission as compared to the shallow porous structure centered at 2.5 eV, as detected by PL. Here, the green emission originates from the electronic transition related to the oxygen vacancy (V_O). XPS spectra show that the high density of V_O located on the multiple-stacked porous surface is much higher as compared to that for the shallow porous structure due to a high surface-to-volume ratio. The results show that the multiple-stacked porous structure has the potential to enhance the functionality of ZnO for applications in light-emitting.

Perspectives on plasma-assisted synthesis of N-doped nanoparticles as nanopesticides for pest control in crops

Green plasma-based technology production of N-doped NPs for a new agri-tech revolution in pest control.