Micro and Nanosystems - Volume 15, Issue 1, 2023

Hollow nanomaterials, which emerged from nanotechnology, earned a lot of interest due to their unique morphology and extensive surface area. This technology has been widely utilized in water treatment branches such as photocatalysis, membrane technology, and the sorption process. There are several types of hollow nanomaterials, all of which have the potential to treat contaminated water, including pollutants, namely heavy metals and organic compounds. Here, we provide a review of the benefits and downsides of hollow nanomaterials advancement as well as new progress in those fields. The challenges of using hollow nanomaterials, as well as their prospects, are also discussed.

Nanomaterials are defined as materials with at least one dimension in the range of 1 to 100 nanometers and offer new exceptional properties for membrane development. These include nanosized adsorbents, nanomembranes, nanocomposites, photocatalysts, nanotubes, nanoclays, etc. Nanomaterials have remarkable capabilities for preventing the worldwide water crisis through their outstanding performance in membrane development technology. Nanomaterial-based membranes comprising nanoparticles, nanofibers, and 2D layered materials have superior permeability characteristics and antifouling, antibacterial, and photodegradation properties. These extraordinary properties make the membranes highly efficient and selective for water purification. This review article summarizes recently developed nanomaterial-based membranes and their applications for the water treatment process. The focus is on the nanomaterial-based membrane structure design. The variety in constituent structure and alterations provide nanomaterial-based membranes, which are expected to be perfect separation membranes in the future.

Background: The present study aims to explore the feasibility of using flocculation combined with filtration for microalgae harvesting, i.e., Chlorella vulgaris. This is important because microalgae have small sizes and its broth is stable, which makes it difficult to be harvested. The aforementioned facts cause the harvesting cost to be relatively high and become the bottleneck of microalgae processes. Objective: The objective of this research is to find the relation between microalgae concentration, chitosan dosing as a flocculant, and its filterability on membranes. Methods: Research was performed by first cultivating the microalgae in a lab-scale photobioreactor, followed by jar test, flocculation, and filtration experiment. Jar test flocculation was performed using chitosan and microalgae with different concentrations, by simply mixing it in a 100 mL bottle and analyzing the results with UV Vis Spectroscopy. Filtration experiments were performed using lab-made polyvinylidene fluoride membrane, in a 100 mL dead-end filtration cell and in a 5 L tank for submerged filtration. During both filtration tests, filtration flux and fouling were monitored and compared. Results: Results showed that the chitosan concentration needed as a flocculant depends on the microalgae biomass concentration. For the filterability tests, the results proved that flocculation with chitosan enhanced the filterability of the microalgae broth both in dead-end and submerged filtration mode. For the used biomass concentration of around 400 mg/L, the filterability test showed an optimum concentration of chitosan at 7.5 to 10 mg/L, which resulted in a higher filtration flux and lower irreversible fouling in the dead-end filtration and a higher critical flux in the submerged filtration setup. Conclusion: This increased filterability allowed higher fluxes to be operated, thus resulting in a more efficient harvesting process.

Background: Membrane technology demonstrates a sustainable methodology for water reclamation from oily wastewater but is prone to fouling during longer filtration runs. In this study, fouling- resistant polyvinylidene fluoride (PVDF) mixed matrix membranes (MMMs) containing nanoclays, such as halloysite (HT) and montmorillonite (MMT), were fabricated for the effective treatment of oily wastewater. Methods: The phase inversion technique was followed for the fabrication of HT-PVDF and MMTPVDF MMMs. Physiochemical characterization and filtration experiments were studied to evaluate the influence of nanoclays on PVDF membrane performance. Results: Fourier transform infrared spectroscopy (FTIR) and morphology analyses indicated that both nanoclays were layered and structured with abundant hydrophilic functional groups. The dispersions of HT and MMT were confirmed by surface morphology and topography analysis of PVDF MMMs. The hydrophilicity property was improved in HT-PVDF and MMT-PVDF MMMs, which was evident in the contact angle analysis. Among the membranes, MMT-PVDF MMMs held a higher water permeability of 2.59 x10^-8 m/s.kPa. For oil-water filtration, HT-PVDF and MMT-PVDF MMMs displayed higher normalized flux with a maximum rejection of more than 95%. Conclusion: Overall, MMT would be a cost-effective nanofiller for developing antifouling PVDF MMMs against oil-water filtration.

Oral vaccines have been proposed as a potential vaccine against a variety of infections, particularly invading pathogens throughout the GIT. Oral vaccinations targeting the large intestine could be a viable alternative to intracorneal immunizations, which have been shown to be effective against rectogenital infections but are impractical during mass vaccination. Furthermore, the oral route allows the development of humoral and cellular immune responses in both systemic and mucosal locations, resulting in a larger and longer-lasting protective effect. Oral administration, on the other hand, is difficult, needing formulations to overcome the harsh GI efficiency and reduce tolerance induction to obtain adequate protection. This review article highlights the mode of action of oral vaccines, the list of licensed oral vaccine, type of vaccines, and the physiological and immunological barriers to the oral transport of peptides and proteins.

Background: The Si- and GaAs-based devices are not suitable for very high-speed and high-power applications. Therefore, GaN-based devices have emerged as a potential contender. Further improvement in the device characteristics using appropriate mole fractions of Al and InN in the barrier layer of AlInN has become inevitable. Objective: To design AlInN/GaN HEMT and present its salient features. Methods: The design method for the proposed AlInN/GaN HEMT includes a selection of materials, optimization of mole fraction in AlInN barrier layer, optimization of gate oxide thickness, optimization of device dimensions, and doping concentration. The fabrication steps necessary for the AlInN/GaN HEMT are also explained in the paper. Analysis of the structure has been carried out using the Silvaco TCAD tool. Results: All the obtained results have revealed that the proposed device can operate up to the cut-off frequency of 102 GHz and a maximum oscillation frequency of 230 GHz, which are suitable for radiofrequency applications. The minimum noise figure and maximum transducer power gain (~18 dB) achieved by the proposed device is quite acceptable. Conclusion: The use of the AlN spacer layer has improved the AlInN film quality and mitigates strain at the heterointerface. Moreover, it reduces the Coulomb attraction between ions in the supply layer and electrons in the channel layer thereby improving carrier mobility. Usage of a SiO2 layer between the gate and AlInN barrier layer has decreased the gate leakage current. This has reduced the subthreshold slope and increased ON/OFF current ratio (~10¹⁰). The proposed Si3N4 passivated HEMT offers a breakdown voltage of ~1395 V.

Background: Tin monoxide (SnO) attracts considerable interest for p-channel Cylindrical Thin Film Transistors (CTFTs) applications due to their merits, including low hole effective mass, Sn s and O p orbital hybridization at the valance band maxima, and ambipolar nature, among other p-type oxide semiconductors. Objective: This article analyses the influence of channel radius and the impact of dielectric materials on the performance of SnO-based CTFT devices through 3D numerical simulations. Methods: The radius of the active layer in the CTFT was varied in the range from 10 nm to 30 nm, and it has been observed that an increase in channel radius reduces the switching behavior of the devices. Results: The 10 nm thick CTFT exhibited superior results with a lower threshold voltage of 1.5 V and higher field-effect mobility of 13.12 cm²/V-s over other simulated CTFTs. Conclusion: The obtained mobility values are superior to the existing planar TFTs reports. To improve the device performance further, the CTFTs with various dielectric materials have been simulated and optimized with high field-effect mobility and low sub-threshold swing values.