فصلنامه دنیای نانو
پیاپی 69 (زمستان 1401)

In recent years, food safety has become a global concern. Maintaining the safety of food products from the processing stage to the level of consumption, to prevent adverse effects on human health and the environment is one of the important challenges in the food industry. Therefore, it will always be necessary to identify, remove and control contamination from the time of harvesting the products until reaching the consumer. Metal-organic frameworks, a class of functional materials, have unique physical and chemical properties that are promising as a new technology in food safety. In this review, the new applications of MOFs and MOF-based materials in monitoring, covering preservation, hygiene, removal, purification, packaging, and authenticity guarantee labels are discussed. The purpose of this review is to learn more about MOF chemistry and applied research in the field of food safety, which potentially leads to new developments in the food industry for safety and control.

Since the toxicity of some environmental pollutants such as CO decreases during oxidation processes, high-adsorption sensors with the ability of oxidizing this gas are very effectual in detecting and removing it. Metal oxides for oxidation of CO require very high operating temperatures, which makes their use practically impossible and unsafe. According to the investigations, it is predicted that the hybrid of metal oxides and fullerene C60 will have the desired potential to catalyze the oxidation process of CO gas and thus eliminate and reduce its toxicity. Carbon based compounds, in addition to being more cost-effective than other gas oxidation catalysts, require low operating temperatures and are biocompatible. In this study, the adsorption of metal oxides Cu2O, ZnO and NiO on fullerene C60, and also CO sensing properties of these nanocomposites have been theoretically studied. All DFT calculations in this study were performed using G09 software at the B97D/6-311G(d,p) level. NBO theory to analyze charge transfers and AIM2000 software to investigate the chemical nature and strength of bonds have been used. The obtained results from the calculations show that MOx/C60 complexes and especially NiO/C60 are much stronger adsorbent for the CO than the C60 is. It is also expected that these complexes have more optical and electrical sensitivity in the selectivity of the CO gas. In addition, the results of this research show that the NiO/C60 nanocomposite has the necessary potential for the oxidation process of the CO to CO2.

Today, ZnO nanowire lasers are widely used for new applications in optical information processing and computing, and also as excitation sources in medical and biological researches. Therefore, in the paper, the ZnO laser with a lasing wavelength in the near ultraviolet region (350 to 400 nm) is investigated. ZnO nanowires with the wurtzite crystal structure are considered as the active medium of the laser, and the optical characteristics and the basis of generated radiations at the output of the laser are analyzed. Studies show that the structural defects of the active medium of a ZnO ultraviolet laser should be reduced as much as possible to achieve lasing. Also, the light-matter interactions in ZnO nanostructures are significantly stronger than in macroscopic crystals, and this optical property is influenced by the energy bandgap, size, shape, orientation, and crystallinity of the ZnO nanowire. A single ZnO nanowire can be used as a waveguide or resonator due to the difference in its refractive index with the surrounding medium, and the resonant modes depend on the dimensions of the nanowire.

The aim of this research is to fabricate a humidity sensor based on stable nanoparticles of anatase phase of titanium dioxide, for improving its characteristics such as sensitivity, response time and recovery. For this purpose, titanium dioxide nanoparticles were synthesized by hydrothermal method, then the structural characteristics of the prepared nanostructure were examined by a scanning electron microscope. The results showed that the synthetic titanium dioxide is in the form of spheres with the average dimension of 270 nm. To prepare the humidity sensor, the prepared nanoparticles were deposited on interdigitated electrode using the blade deposition method. The research’s findings indicated that the sensitivity of the prepared anatase phase sensor is 12.81 (Rair/RHumidity)/%RH in the relative humidity range of 40-98%, improved 14% compared to the previous ideal sample which was based on rutile phase and anatase. Also, the response and recovery times of this sensor were measured as 2 and 4.5 seconds, respectively, which were 14 and 7 times higher than the previous samples.

In this research, bismuth vanadate (BiVO4) nanowires were made by hydrothermal method. To study the crystal structure, morphology, optical and photocatalytic properties of the samples, the X-ray diffraction analysis (XRD), field emission scanning electron microscopy (FESEM), energy-dispersive X-ray spectroscopy (EDS), Fourier-transform infrared spectroscopy (FTIR) and ultraviolet– visible spectroscopy (UV-Vis) were used. The XRD patterns were indicated that the bismuth vanadate nanowires have a monoclinic structure. From EDS and FTIR analysis, it was found that nanowires do not contain impurities. From FESEM image, it was found that the average length and diameter of nanowires are 2.3 micrometers and 83 nanometers, respectively. The UV-Vis analysis was revealed the bismuth vanadate nanowires have an optical gap of 2.20 eV, which is in the visible light range. Investigating the photocatalytic activity of bismuth vanadate nanowires in the photodegradation of Congo red showed that bismuth vanadate nanowires are suitable choice for photocatalytic use and decomposition of organic matter with the help of sunlight.