Nanoporous Filters Research Articles

Selective Labeling of Small Microplastics with SERS-Tags Based on Gold Nanostars: Method Optimization Using Polystyrene Beads and Application in Environmental Samples.

Microplastics pollution is being unanimously recognized as a global concern in all environments. Routine analysis protocols foresee that samples, which are supposed to contain up to hundreds of microplastics, are eventually collected on nanoporous filters and inspected by microspectroscopy techniques like micro-FTIR or micro-Raman. All particles, whether made of plastic or not, must be inspected one by one to detect and count microplastics. This makes it extremely time-consuming, especially when Raman is adopted, and indeed mandatory for the small microplastic fraction. Inspired by the principles of cell labeling, the present study represents the first report in which gold nanostars (AuNS) are functionalized to act as SERS-tags and used to selectively couple to microplastics. The intrinsic bright signals provided by the SERS-tags are used to run a quick scan over a wide filter area with roughly 2 orders of magnitude shorter analysis time in respect of state of the art in micro- and nanoplastics detection by μ-Raman. The applicability of the present protocol has been validated at the proof-of-concept level on both fabricated and real offshore marine samples. It is indeed worth mentioning that a SERS-based approach is herein successfully applied on filters and protocols routinely adopted in environmental microplastics monitoring, paving the way for future implementations and applications.

3D Printed and Electrospun, Transparent, Hierarchical Polylactic Acid Mask Nanoporous Filter.

Face masks are becoming one of the most useful personal protective equipment with the outbreak of the coronavirus (CoV) pandemic. The entire world is experiencing shortage of disposable masks and melt-blown non-woven fabrics, which is the raw material of the mask filter. Recyclability of the discarded mask is also becoming a big challenge for the environment. Here, we introduce a facile method based on electrospinning and three-dimensional printing to make changeable and biodegradable mask filters. We printed polylactic acid (PLA) polymer struts on a PLA nanofiber web to fabricate a nanoporous filter with a hierarchical structure and transparent look. The transparent look overcomes the threatening appearance of the masks that can be a feasible way of reducing the social trauma caused by the current CoV disease-19 pandemic. In this study, we investigated the effects of nozzle temperature on the optical, mechanical, and morphological and filtration properties of the nanoporous filter.

A Nanostructured Protein Filtration Device for Possible Use in the Treatment of Alzheimer's Disease-Concept and Feasibility after In Vivo Tests.

Alzheimer's disease (AD), along with other neurodegenerative disorders, remains a challenge for clinicians, mainly because of the incomplete knowledge surrounding its etiology and inefficient therapeutic options. Considering the central role of amyloid beta (Aβ) in the onset and evolution of AD, Aβ-targeted therapies are among the most promising research directions. In the context of decreased Aβ elimination from the central nervous system in the AD patient, the authors propose a novel therapeutic approach based on the "Cerebrospinal Fluid Sink Therapeutic Strategy" presented in previous works. This article aims to demonstrate the laborious process of the development and testing of an effective nanoporous ceramic filter, which is the main component of an experimental device capable of filtrating Aβ from the cerebrospinal fluid in an AD mouse model. First, the authors present the main steps needed to create a functional filtrating nanoporous ceramic filter, which represents the central part of the experimental filtration device. This process included synthesis, functionalization, and quality control of the functionalization, which were performed via various spectroscopy methods and thermal analysis, selectivity measurements, and a biocompatibility assessment. Subsequently, the prototype was implanted in APP/PS1 mice for four weeks, then removed, and the nanoporous ceramic filter was tested for its filtration capacity and potential structural damages. In applying the multi-step protocol, the authors developed a functional Aβ-selective filtration nanoporous ceramic filter that was used within the prototype. All animal models survived the implantation procedure and had no significant adverse effects during the 4-week trial period. Post-treatment analysis of the nanoporous ceramic filter showed significant protein loading, but no complete clogging of the pores. We demonstrated that a nanoporous ceramic filter-based system that filtrates Aβ from the cerebrospinal fluid is a feasible and safe treatment modality in the AD mouse model. The presented prototype has a functional lifespan of around four weeks, highlighting the need to develop advanced nanoporous ceramic filters with anti-biofouling properties to ensure the long-term action of this therapy.

Nanoporous membrane filter cascade for size‐selective analysis of nano‐ and microplastic particles

AbstractAnalytical routes for sampling and analysis of microplastic particles in the range of several 10 µm to 1000 µm are well established in environmental research. However, the current scientific efforts are targeting human health impact with an enhanced focus on nanoparticle analysis in drinking water, the food chain, and its disposition in the human body. A major challenge lies in the availability of cascade filter setups spanning several orders of magnitude down to 10 nm dimensions in a single filtration workflow allowing fast and reliable routines for size‐selective nano‐ and microplastic (NMP) particle analysis. In this work, we present a novel cascade filter system containing filters made of microporous Si (pore size >10 µm) and nanoporous Al2O3 (pore size 100 nm), thus realizing the corresponding NMP size selectivity. Inorganic filter materials are chosen due to their beneficial properties as substrates for NMP particle analysis, which are nonpolymer materials with high planarity for micro‐spectroscopy investigations. In our first experiments, we demonstrate the successful NMP size separation on Si and Al2O3 filter substrates. For this purpose, we implement a well‐defined NMP test material composed of a mixture of polyethylene terephthalate microplastic reference material and monodisperse nanoscale polystyrene particles. The NMP test material is applied in a laboratory filtration workflow for samples in liquid solution. Both filter stages are subsequently investigated with optical microscopy, electron microscopy (scanning electron microscopy), Raman spectroscopy, and scanning force microscopy (atomic force microscopy) to demonstrate their applicability as combined NMP particle analytic substrates. Here, we characterize the fundamental NMP properties such as particle shape, size, and spectroscopic fingerprints—optical and chemical—both qualitatively and quantitatively. Finally, requirements and limitations for a standardized NMP filtration and analytic workflow will be discussed.

Real-Time On-Site Multielement Analysis of Environmental Waters with a Portable X-ray Fluorescence (pXRF) System

Strict regulations are in place to control the effluents of mining sites and other industries. Heavy metal contamination of aquatic systems caused by leakages is difficult to mitigate as it takes time to detect and localize the leak. Dynamic sampling would drastically reduce the time to locate leakages and allow faster actions to reduce the impact on the environment. The present study introduces a novel portable multielement water analysis system to simultaneously measure Mn, Ni, Cu, Zn, Pb, and U in water samples from natural sources within 15 min from the sampling. The metals are preconcentrated from a 10 mL water sample into a nanoporous filter based on bisphosphonate-modified thermally carbonized porous silicon. The metals can be conveniently analyzed from the filter with a portable XRF analyzer in field conditions. The system was empirically calibrated for a lake water matrix with neutral pH and low alkaline metal concentration. A strong correlation between the XRF intensities and the ICP-MS results was obtained in a concentration range from 50 to 10 000 μg/L. With a DPO-2000C XRF analyzer, the detection limits were 103, 86, 92, 35, 44, and 43 μg/L for Mn, Ni, Cu, Zn, Pb, and U, respectively. The corresponding values with X-MET8000 Expert Geo were 137, 46, 62, 38, 29, and 54. The system was successfully validated with simulated multielement lake water samples and piloted in field conditions. The system provides an efficient way to monitor metals in environmental waters in cases where quick on-site results are needed.

Fabrication of SiNx Nanopore Filters Using Combined Process of Nanoimprint and Dual‐Side Aligned Photolithography for Purified Cs3MnBr5 Green Phosphors (Adv. Mater. Technol. 7/2022)

Nanoporous Filters The frontispiece presented by Young Rag Do and co-workers (article number 2101519) shows filtration images of reactant ionic solutions with 2D SiNx nanofilters, used to synthesize Cs3MnBr5 phosphors via eco-friendly water-based evaporative crystallization process. Numerous nanofilters have been successfully fabricated with a dual-sided alignment process between nanoimprinting-patterned front side and photolithographically-patterned back side. Unnecessary residual nano-particles were removed by 50 nm-nanohole arrayed SiNx nanofilter to improve PLQY of purified Cs3MnBr5 phosphor by 2.3 times.

Multiscale Analysis of the Performance of Micro/nano Porous Filtration Membranes with Double Concentric Cylindrical Pores: Part I-Analysis Development

In nanoporous filtration membranes, when the radius of the filtration pore is so big that the flow of the adsorbed layer on the pore wall is comparable with the flow of the continuum fluid in the central region of the pore, the multiscale analysis is required for estimating the performance of the membranes. The present paper presents such a multiscale analysis for the performance of nanoporous filtration membranes with double concentric cylindrical pores. The dimensionless flow resistance of the membrane was calculated for a weak fluid-pore wall interaction for varying operational parameter values. It was found that there is the optimum ratio of the radius of the filtration pore to the radius of the other bigger pore for the highest flux of the membrane.

Solar water purification with photocatalytic nanocomposite filter based on TiO2 nanowires and carbon nanotubes

Water contamination due to environmental conditions and poor waste management in certain areas of the world represents a serious problem in accessing clean and safe drinking water. This problem is especially critical in electricity-poor regions, where advanced water purification methods are absent. Here, we demonstrate that titanium dioxide nanowires (TiO2NWs)-based photocatalytic filters assisted only with sunlight can efficiently decontaminate water. Moreover, interweaving TiO2NWs with carbon nanotubes (CNTs) leads to the formation of a TiO2NWs/CNTs composite material and offers an additional water decontamination channel, that is of pasteurization with the visible part of the solar emission spectrum. Our results demonstrate that this nanoporous filter can successfully intercept various types of microbial pathogens, including bacteria and large viruses. In addition, photo-catalytically generated reactive oxygen species (ROS) on the surface of the TiO2NWs/CNTs-based filter material under exposure to sunlight contribute to an efficient removal of a broad range of organic compounds and infective microbes. A pilot study also yielded encouraging results in reducing traces of drugs and pesticides in drinking water.

Oxide/ZIF-8 Hybrid Nanofiber Yarns: Heightened Surface Activity for Exceptional Chemiresistive Sensing.

Though highly promising as powerful gas sensors, oxide semiconductor chemiresistors have low surface reactivity, which limits their selectivity, sensitivity, and reaction kinetics, particularly at room temperature (RT) operation. It is proposed that a hybrid design involving the nanostructuring of oxides and passivation with selective gas filtration layers can potentially overcome the issues with surface activity. Herein, unique bi-stacked heterogeneous layers are introduced; that is, nanostructured oxides covered by conformal nanoporous gas filters, on ultrahigh-density nanofiber (NF) yarns via sputter deposition with indium tin oxide (ITO) and subsequent self-assembly of zeolitic imidazolate framework (ZIF-8) nanocrystals. The NF yarn composed of ZIF-8-coated ITO films can offer heightened surface activity at RT because of high porosity, large surface area, and effective screening of interfering gases. As a case study, the hybrid sensor demonstrated remarkable sensing performances characterized by high NO selectivity, fast response/recovery kinetics (>60-fold improvement), and large responses (12.8-fold improvement @ 1ppm) in comparison with pristine yarn@ITO, especially under highly humid conditions. Molecular modeling reveals an increased penetration ratio of NO over O2 to the ITO surface, indicating that NO oxidation is reliably prevented and that the secondary adsorption sites provided by the ZIF-8 facilitate the adsorption/desorption of NO, both to and from ITO.

Fabrication of SiNx Nanopore Filters Using Combined Process of Nanoimprint and Dual‐Side Aligned Photolithography for Purified Cs3MnBr5 Green Phosphors

AbstractA combined process of nanoimprint lithography and dual‐side aligned photolithography to address misalignment of subsequent layers for the fabrication of SiNx nanoporous membrane filters (SiNx nanofilter) is suggested. Here, in one process, 21 SiNx nanofilter chips are fabricated on a 6 inch Si wafer by aligning nanopore area of nanofilter and template area of nanofilter chip. An SiNx nanofilter chip‐integrated fluidic device is used to test the purification ability of the nanofilter in terms of its pore size and surface hydrophobicity or hydrophilicity. This is the first attempt at separating unnecessary chemical residues from a mixed reactant solution by nanoscale purification process using the tremendous number of nanoholes in the nanofilter. After purification by the nanofilter, high efficiency and narrow‐band Cs3MnBr5 phosphor is synthesized by evaporative crystallization. Here, the photoluminescent quantum yield (PLQY) of the purified Cs3MnBr5 phosphor is monitored to evaluate the purification ability of the SiNx nanofilter. The highest PLQY (53%) of Cs3MnBr5 green phosphors is obtained by purification of reactant solution using nanofilter with 50 nm nanopore diameter and hydrophilic surface. This combined process proves its potential for scalable manufacturing of complex designed SiNx nanofilter chips for chemical species sieving and other applications.

High-performance intellectual information technologies for the study of filtration systems in different-sized nanoporous particles media

In the paper, the technologies for the high-performance intellectual nanoporous filtration systems based on the mathematical model of the two-level transport «filtration-consolidation» in the system of nanopores in two intraparticle spaces, which includes two subspaces of different-sized nanoporous particles are developed.

Bioconjugation of Bacteriophage Pf1 and Extension to Pf1-Based Bionanomaterials

Background: Filamentous bacteriophages such as M13 are an important class of macromolecular assembly, rich in chemical moieties that can be used to impart modifiable positions at the nanoscale. Objective: To explore the structurally more complex Pf1 bacteriophage with respect to a diverse set of bioconjugation reactions and to prepare novel fluorescently-labelled Pf1-based composite biomembranes for future applications in areas such as nanoporous filtration biofilms and photoconducting nanocomposite materials. Methods: Pf1 was characterized with respect to amine (N-terminal, Gly1 and Lys20), carboxylate (aspartate, glutamate), and aromatic (tyrosine) modification and its extension to the creation of functional biomaterials. Modification with an amine reactive fluorophore was carried out with Pf1. Results: The reaction profiles between M13 and Pf1 differ, with M13 capable of modification at two primary amines on its major coat protein, while Pf1 is capable of a single reaction per coat protein. Subsequent to the production of dye-functionalized Pf1, a biocomposite of wild type and functionalized Pf1 could be fabricated into a bulk material by glutaraldehyde (amine-reactive) crosslinking. These biomaterials were characterized by scanning electron and confocal microscopy, showing a distribution of patches of functionalized Pf1 within the main Pf1 construct. Conclusion: The current study provides a framework for future fabrication of advanced bionanomaterials based on the Pf1 bacteriophage.

Study of functionality of polymer films by dense electron beams

Methodology of using megavolt electrons for investigation of the functionality of thin polymer films of polycyanurates (PCN) is described. The relevance of research is determined by the prospects of using films as a functional basis for improvement of track-etched technologies of nanoporous nuclear filters, where ionizing radiation is used in most of technological stages of their production. Functionality control is the main criterion for the qualification of films on the suitability for production of nuclear filters on their base. Development of megavolt electrons radiation methods is promising for monitoring the functionality of filters. Radiation technologies are universal and able to provide maximum information content on investigations of the characteristics of materials to qualify them for suitability of practical use. To control the functionality of the films, the methodology for research and testing of thin polymer films using powerful electron beams of 1-2 MeV has been developed. The features of these methods and the results of their application at the control of functionality and for the qualification of the films based on crosslinked polycyanurates, synthesized by in situ polycyclotrimerization of dicyanate ester of bisphenol E in the presence of dimethylphthalate (DMPh) of the composition PCN/DMPh=70/30 wt.%, on the suitability for production of nanoporous track membranes are discussed. Key words: electron beams, nuclear membranes, thermostable polycyanurates, radiation stability, functional testing.

Free Standing Porous Graphene and Reduced Graphene Papers Manufactured from Sedimentation of Arc Discharge of Graphite Rods

Free Standing Porous Graphene and Reduced Graphene Papers manufactured from Sedimentation of Arc Discharge of Graphite Rods. At SignEcoTech, novel and newer nano-carbons such as hard carbons, homogenized graphene, low defect highly crystalline graphene’s, and wrinkled graphene [1-14]. Here, Graphene Oxide papers have been synthesized previously by flow-directed assembly, where the pressure of air within the assembly supports graphene oxide sheets in their nano-crystalline colloidal solution being filtered on nano-porous filter paper. However in this research, we haven’t used any filter paper, or directed flow assembly, but sedimentation of the colloidal solution in ethyl alcohol in a dish. Then, the wrinkled the hierarchical GO sheets fall under gravity by sedimentation. Wrinkling in GO was enhanced by low defects, multi-layer clusters, and variegated + edge interaction amongst graphene clusters, as such the sedimented graphene papers were porous, intertwined and free standing. The composition of GO was confirmed by XPS, while the low defect level clearly marked by higher planar order and low ID/IG band. The wrinkled, multilayer clusters and carbonic surface properties of the graphene oxide sheets enhanced fast sedimentation, evaporation of the alcohol and formation of porous GO structure. The porous reduced\\GO morphology is captured by optical microscope. Keywords: Wrinkled GO Papers, Reduced Graphene, Arc Discharge, Modified Hummers Method

Recent Patents on Nanoporous Filtration Membranes with Complex Pores

Background:: The challenges to nanoporous filtration membranes are small fluxes and low membrane mechanical strengths. Objective:: To introduce newly invented nanoporous filtration membranes with complex pores, improved fluxes and mechanical strengths as registered in patents. Methods:: The analytical results are presented for the addressed membranes. Results:: The geometrical parameter values of the addressed membranes can be optimized for the highest fluxes. Conclusion:: The overall performances of nanoporous filtration membranes with complex cylindrical or/and conical pores can be significantly better than that of the conventional nanoporous filtration membranes with single cylindrical or conical pores.

Nanoporous high-temperature filters based on Ti–Al ceramic SHS materials

The research is devoted to the development of scientific bases for creating a technology for manufacturing heat-resistant membranes based on a highly porous ceramic material with nanoscale pores (nanoporous), which allows increasing the efficiency of high-temperature purification of liquids from submicron dispersed contaminants by tangential filtration. Membranes based on a mixture of Ti and Al powders (40% by 60% mass ratio) were synthesized in one stage using the SHS method in the thermal explosion mode and used as filter elements in the ultrafiltration unit. Using X-ray and SEM methods, it was found that the synthesized material consists of the main phases TiAl3 and Al2O3. Analysis of the microstructure showed that the resulting ceramic material has a multilevel highly developed web-like nanostructure that forms an open porosity of the membrane, providing the possibility of ultrafiltration.

Natural Nanoporous Filter Material as a New High-Efficiency Natural Adsorbent to Remove Textile Dyes

The objective of this paper is to perform the innovation design of removing most textile dyes that are harmful to the environment and might induce cancer. However, many methodologies had been developed for various chemical and physical processes to remove different dyes, such as ozone oxidation, electrochemical methods, chemical coagulation, hypochlorite oxidation, and adsorption to remove dyes from wastewater. A novel nanoporous filter methodology and mathematic simulations for adsorption were established as an effective medium for removing dyes from wastewater which was compared to other expensive treatments. The different concentrations of the dye liquid are used as a tester, and the different concentrations of nanoporous adsorbent were added in a uniform distribution and were tested with different time courses and under different temperatures. The final readings were measured by a spectrophotometer and fit into a mathematic model. The result indicates that this nanoporous and natural adsorbents are very good at cleaning the dyes in this system. The fit-in mathematic models could be applied in these tests which can be used in the industrial conditions for a low cost without secondary dye pollutions.

Realization of high-quality optical nanoporous gradient-index filters by optimal combination of anodization conditions.

High-quality nanoporous anodic alumina gradient-index filters (NAA-GIFs) are realized by sinusoidal pulse anodisation (SPA) of aluminum. A three-level factorial design of experiments is used to determine the effect of three critical anodization parameters -electrolyte temperature, concentration of the electrolyte and anodization time- on the quality of light control in these photonic crystal (PC) structures. Quantitative analysis of the effect of these anodization parameters on the quality of the characteristic photonic stopband (PSB) of NAA-GIFs reveals that all three anodization parameters and their respective combinations have statistically significant effects. However, anodization time is found to have the highest impact on the quality of light control in NAA-GIFs, followed by the electrolyte concentration and its temperature. Our findings demonstrate that NAA-GIFs fabricated under optimal conditions achieve an outstanding quality factor of ∼86 (i.e.∼18% superior to that of other NAA-based PCs reported in the literature). This study provides new insight into optimal anodization conditions to fabricate high-quality NAA-based PC structures, opening new exciting opportunities to integrate these nanoporous PCs as platform materials for light-based technologies requiring a precise control over photons such as ultra-sensitive optical sensors and biosensors, photocatalysts for green energy generation and environmental remediation, optical encoding and lasing.

Constructing geometrically-ordered alumina nanoporous filters and alumina nanowire arrays by using ultrahigh voltage two step anodization

Abstract A simple ultrahigh voltage two-step anodization was developed to fabricate nanopore and nanowire arrays which can be utilized in various applications like water purification filter technology. Investigation of the electrolyte concentration effect on controlling the morphology and geometry of the alumina nanopore and nanowire (ANW) arrays has been done. The anodization was carried out in H2C2O4/H3PO4 mixture at about 0 °C to reach the best ordered nanopores array. In hard anodization step, the current density showed a peak shape profile so that its maximum was directly depended on the H3PO4 concentration. The SEM images of the arrays were studied by image histogram and fast Fourier transform (FFT). The model curves demonstrated direct dependency of the nanopores ordering on electrolyte concentration. The most ordered array was achieved by utilizing 0.3 M H2C2O4 and 0.35 M H3PO4. The SEM images showed that the pores became wider by etching the nanopores in an acidic solution. In addition, fast fabrication of nanowire arrays was achieved by managing the anodization process at 30 °C in a short time. The ANWs were obtained from nanopores etching through the anodization, without an extra etching step requirement. The studies on SEM images demonstrated succeeding high ordered ANWs bundle.

Wood‐Derived Nanofibrillated Cellulose Hydrogel Filters for Fast and Efficient Separation of Nanoparticles

AbstractFast water permeable filters with an efficient rejection ratio are desirable for nanoparticle separation and water/air purification. Ultrathin nanoporous filters are effective because of their features, including narrow and tunable pore size distributions capable of handling a high solvent flux. However, it remains challenging to develop antifouling filters that maintain a stable flux with high rejection efficiency over long‐term filtration of nanoparticle solutions. Here, a facile and low‐cost approach is reported to fabricate biocompatible hydrogel filters with interconnected nanofiber network structures through the use of high aspect ratio, wood‐derived nanofibrillated cellulose (NFC). The super‐hydrophilia and high porosity of these materials endow the NFC hydrogel filters (NFC‐HFs) with high solvent permeance. Nanofibrous networks and interconnected nanoporous structures of NFC‐HFs promote efficient rejection and precise size‐selective separation of nanoparticles. Specifically, small and irregular nanopores of NFC‐HFs fail to match the size of relatively large nanoparticles, which ensures a relatively stable flux of the NFC‐HFs over the whole filtration process, even under continuous filtration of highly concentrated nanoparticle solutions.