Membrane Materials For Separation Research Articles

Efficient membrane separation of SO2 by choline chloride-based natural deep eutectic solvents: The role of hydrogen bonding sites

Natural deep eutectic solvents (NDESs) are recognized as promising membrane materials for sustainable SO2 separation. Evaluating their separation performances is necessary, as well as understanding of the role that each hydrogen bonding site (including anion and functional groups in NDESs) plays in SO2 separation. Herein, three choline chloride (ChCl)-based NDESs bearing different number and type of functional groups were firstly incorporated into Pebax matrix to fabricate blended membranes for removing SO2 from CO2 and N2. The Pebax/NDES membranes show SO2 permeability up to 10502 Barrer (0.20 bar and 40 °C), with excellent SO2/N2 and SO2/CO2 selectivity of 1808 and 62.5 obtained, respectively, which are enhanced by 156 %, 61.5 % and 56.1 % compared with those in neat Pebax membrane. By means of gas solubility and diffusivity measurements, quantum chemical calculations and spectral characterizations, the highly-reversible multi-site interactions between SO2 and hydrogen bonding sites in NDESs (Cl−···SO2, carbonyl O···SO2 and hydroxyl O···SO2) were revealed. Meanwhile, the strength of hydrogen bonding network inside the NDESs, which is governed by the hydrogen bonding sites, is found to significantly influence the gas diffusion. More importantly, SO2/CO2/N2 (2.5/15/82.5 mol%) mixed gas separation experiment also displays the superior separation performance and long-term stability of Pebax/NDES membrane.

Preparation and Electrochemical Performance of Alkaline Earth Metal-Doped Nd2Ce2O7 Proton Conductor Hydrogen Separation Membranes

Nd2Ce2O7 is a rare earth oxide with a fluorite structure and exhibits proton conductivity. Alkaline earth metals (Mg, Ca, Sr, Ba) doped Nd2Ce2O7 powders were synthesized using the citrate sol-gel method. The doped samples retain the fluorite structure, and enhanced oxygen vacancy concentration. Notably, Nd1.85Mg0.15Ce2O7-δ exhibited the highest oxygen vacancy concentration, reaching an electrical conductivity of 2.91×10-2 S•cm-1 in a humid atmosphere of 20%H2 and 80%N2 at 900°C. Hydrogen separation membranes were fabricated using alkaline earth metal-doped Nd2Ce2O7 as the proton-conducting phase and Pt as the electron-conducting phase. The results indicated that Pt-Nd1.85Mg0.15Ce2O7-δ had the optimal hydrogen permeation flux, reaching 8.35×10-9 mol•cm-2•s-1 at 900°C. It demonstrated short-term stability in environments containing CO2 and H2O, and an increase in temperature and hydrogen partial pressure on the feed side enhanced hydrogen permeation, highlighting its potential as a hydrogen separation membrane material.

Computational Multiscale Study of the Interaction Between the PDMS Polymer and Sunscreen-Related Pollutant Molecules

Sunscreen molecules play a critical role in protecting skin from ultraviolet radiation, yet their efficient detection and separation pose challenges in environmental and analytical contexts. In this work, we employ a multilevel modeling approach to investigate the molecular interactions between representative sunscreen molecules and the polydimethylsiloxane (PDMS) polymer, a material widely recognized for its sorbent properties. Our goal is to explore how these interactions can be fine-tuned to facilitate the effective separation of sunscreen molecules in portable membrane inlet mass spectrometry (MIMS) systems, potentially leading to the development of new membrane materials. Using a combination of advanced computational techniques—force field molecular dynamics simulations, semiempirical GFN2-xTB, and density functional theory calculations—we assess the interaction strength and noncovalent interactions of sunscreen molecules, namely oxybenzone, naphthalene, benzo[a]anthracene, avobenzone, and 1,3,5-trichlorobenzene, with PDMS. Additionally, the effect of temperature on the interaction dynamics is evaluated, with the aim of extending the sorbent capacities of PDMS beyond light polar molecules to larger, polar sunscreen compounds. This study provides critical insights into the molecular-level interactions that may guide the design of novel membrane materials for efficient molecular separation.

Preparation and properties of bio-based PA56/SiO2–NH2 composite nanofiber membranes for high efficiency oil-water separation

With the continuous development of environmental protection and resource recycling demands, the development of bio-based separation membrane materials has increasingly attracted attention. Bio-based polyamide 56 (PA56), exhibiting excellent hydrophilicity, spinnability, and mechanical properties, is expected to complement and replace traditional separation membrane materials. In this study, the electrospinning preparation and structural control of PA56 nanofiber membranes were achieved through the optimization of PA56 content and mixed solvent ratios. The study found that when the PA56 content was 16 wt% and the formic acid to acetone ratio in the mixed solvent was 8:2, the nanofiber diameter distribution was the most uniform. Building on this, amino-functionalized modified silica (SiO2–NH2) nanoparticles were introduced to prepare PA56/SiO2–NH2 composite nanofiber membranes featuring a cobweb-like nanofiber network and micro-nodule structure. The effects of the addition of SiO2–NH2 nanoparticles on the morphology, structure, and properties of the fiber membranes were studied. The results indicate that the control of the mixed solvent ratio and the addition of SiO2–NH2 nanoparticles led to the formation of a cobweb-like nanofiber network and micro-nano nodular structure on the nanofiber surface, enhancing the hydrophilicity of PA56 nanofiber membranes. The M − 3 membrane with a nanoparticle addition amount of 0.8 wt% exhibited high hydrophilicity and underwater superoleophobic properties, achieving efficient separation of stable oil-in-water emulsions with a separation efficiency of 99.8 %. This work provides a new bio-based membrane material and its preparation method for treating oily wastewater using the membrane separation method.

Mixed dimensional assembly of biodegradable and antifouling wood-based covalent organic framework composite membranes for rapid and efficient dye/salt separation

Manipulating materials of different dimensions into heterogeneous nanofiltration membranes with unique physicochemical properties and molecular sieving channels provides an effective way for accurate and fast molecular separation. Here we introduce a heterogeneous structure hybrid connection strategy to fabricate biodegradable wood-based covalent organic framework (COF) composite membranes. As a proof of concept, 3D Picea jezoensis (Siebold & Zucc.) Carrière was selected as the substrate of the membrane and in situ growth of 2D iCOF selective layers. Effective modulation of iCOF layers by 1D sulfonated polyaryletherketone (SPEEK-Na) using the “needle and thread” method. The rearrangement of the above multidimensional materials formed charge-regulated properties of laminar nano-channels and smooth hydrophilic contact area, thereby endowing specific molecular transport pathways and sieving capability for efficient dye/salt separation under ultra-low pressure of 0.5 bar. The wood-based heterostructured membranes exhibited high dye rejection (>97 %), low salt rejection (<10 %), and high permeance (172.34 L m−2 h−1 bar−1), which is superior to many reported dye/salt separation membrane materials. In addition, the system exhibited a certain degree of operational stability, good antifouling, and soil biodegradability. Overall, this work enables the design and fabrication of heterostructured separation membranes to be obtained from nature and used in nature, resulting in efficient and sustainable water purification applications.

Development of cost-effective cellulose-based bilayer hybrid composite membranes for CO2 separation in biogas purification

CO2 is the main pollutant in biogas, reducing its calorific value. Among various technological methods to eliminate carbon dioxide from biogas, membrane separation technology stands out for large-scale industrial biogas purification due to its advantages. The selection of membrane material and preparation process are key factors in membrane separation technology. In this study, a premixing process was initially used to blend different masses of packed molecular sieves TS-1 (or ZSM-5) and cellulose derivatives (ethyl cellulose, cellulose acetate) separately. These mixtures were then coated onto porous PVDF substrates using a coating process to create various bilayer hybrid composite membranes. Among these, PVDF/EC-ZSM-5 (containing 15 % ZSM-5) bilayer hybrid composite membrane is the most fitting. For CO2/CH4 gas mixtures, the gas selectivity of this membrane surpassed Robeson's 1991 standard line (the CO2 permeability was 597.48 Barrer, and the CO2/CH4 selectivity was 9.14). Overall, this composite membrane, made for the first time from PVDF, ZSM-5, and EC, is expected to be a promising CO2 selective separation membrane material for biogas purification in large-scale industrial processes due to its simple production process.

Stabilizing Bicontinuous Emulsions with Sub-Micrometer Domains Solely by Nanoparticles.

Nanoparticle-stabilized, bicontinuous interfacially jammed emulsion gels (bijels) find potential applications as battery, separation membrane, and chemical reactor materials. Decreasing the liquid domain sizes of bijels to sub-micrometer dimensions requires surfactants, complicating bijel synthesis and postprocessing into functional nanomaterials. This work introduces surfactant-free bijels with sub-micrometer domains, solely stabilized by nanoparticles. To this end, the covalent surface functionalization of silica nanoparticles is characterized by thermogravimetric analysis, mass spectrometry, Fourier-transform infrared spectroscopy, and contact angle measurements. Bijels are generated with the functionalized nanoparticles via solvent transfer induced phase separation (STrIPS), enabling the optimization of nanoparticle functionalization and surface ionization. Nanoparticles of intermediate functionalization and controlled negative surface charge stabilize bijels with sub-micrometer liquid domains. This remarkable control over bijel synthesis provides urgently needed progress to facilitate the widespread implementation of bijels as nanomaterials in research and applications.

Solvent-vapor-triggered crystallization of a ZIF-90 membrane with versatile separation properties towards light hydrocarbons

Membrane separation has been well acknowledged as a forward-looking technology for hydrocarbon separation. Zeolitic imidazole framework-90 (ZIF-90) with effective pore size of 5.0 Å is a promising membrane material for hydrocarbon separation. Owing to the enormous challenges facing the fabrication process, the research on the ZIF-90 polycrystalline membrane is fairly underexplored. Herein we report a solvent-vapor-triggered crystallization strategy for the production of ZIF-90 membranes. The resultant ZIF-90 membrane had a typical polycrystalline membrane structure where the regular ZIF-90 grains propagated inside the whole porous support. Intriguingly, the membrane displayed two obvious sharp cut-off regions falling between the C3H6/C3H8 and n-C4H10/i-C4H10 gas pairs, respectively. The ZIF-90 membrane achieved ultrafast and selective permeation of C3H6 from the C3H6/C3H8 mixture. The C3H6 flux was about 3.4 kg·m−2·h−1 which was comparable to the commercial NaA zeolite membrane for organic solvent dehydration. Further, the distinctive gas transport kinetic nature enabled the ZIF-90 membranes to exclude i-C4H10 and thus harvest unprecedented n-/i-C4H10 separation ability in high-temperature regions. As the temperature elevated from 25 to 150 °C, the n-C4H10 permeance was enhanced from 3.0 × 10−9 to 12 × 10−9 mol·m−2·s−1·Pa−1 and the n-C4H10/i-C4H10 separation factors was improved from 63 to 95, respectively. The high permeance and permselectivity at industrially relevant high temperatures and pressures make ZIF-90 membrane attractive for industrial light hydrocarbon separation.

Polymer-functionalized metal-organic framework nanosheet membranes for efficient CO2 capture

Two-dimensional metal-organic frameworks (2DMOFs) have emerged as highly appealing candidates as advanced separation membrane materials. However, constructing 2DMOF membranes with appropriate channel sizes to separate CO2 from N2 remains a great challenge. Here, we propose an in-situ crystallization approach to synthesize CO2-philic-polymer functionalized Zr-based MOF nanosheets, enabling the fabrication of efficient CO2 capture membranes. The in-situ MOF crystallization with polyethylenimine (PEI) polymers leads to a uniform distribution of amines, resulting in the formation of PEI-NUS hybrid nanosheet characterized by both high porosity and strong affinity to CO2. These nanosheets are assembled into ultrathin lamellar membranes with thicknesses ranging from 40 to 120 nm. The amines of PEI polymers significantly facilitate the CO2 transfer as reaction carriers, resulting in a substantially improved CO2/N2 separation performance with a CO2 permeance of 410 GPU and a CO2/N2 selectivity of 90, which are among the best for MOF membranes in CO2 separation. This in-situ functionalization strategy paves the way for the fabrication of ultrathin 2D membranes for various separations.

A Hydrogel-coated Wood Membrane with Intelligent Oil Pollution Detection for Emulsion Separation.

Considering the potential threats posed by oily wastewater to the ecosystem, it is urgently in demand to develop efficient, eco-friendly, and intelligent oil/water separation materials to enhance the safety of the water environment. Herein, an intelligent hydrogel-coated wood (PPT/PPy@DW) membrane with self-healing, self-cleaning, and oil pollution detection performances is fabricated for the controllable separation of oil-in-water (O/W) emulsions and water-in-oil (W/O) emulsions. The PPT/PPy@DW is prepared by loading polypyrrole (PPy) particles on the delignified wood (DW) membranes, further modifying the hydrogel layer as an oil-repellent barrier. The layered porous structure and selective wettability endow PPT/PPy@DW with great separation performance for various O/W emulsions (≥98.69% for separation efficiency and ≈1000Lm-2h-1bar-1 for permeance). Notably, the oil pollution degree of PPT/PPy@DW can be monitored in real-time based on the changed voltage generated during O/W emulsion separation, and the oil-polluted PPT/PPy@DW can be self-cleaned by soaking in water to recover its separation performance. The high affinity of PPT/PPy@DW for water makes it effective in trapping water from the mixed surfactant-stabilized W/O emulsions. The prepared eco-friendly and low-cost multifunctional hydrogel wood membrane shows promising potential in on-demand oil/water separation and provides new ideas for the functional improvement of new biomass oil/water separation membrane materials.

Process optimization and mechanism for the selective extraction of copper(ii) from polymetallic acidic solutions using a polymer inclusion membrane (PIM) with Mextral®5640H as the carrier.

This study introduces a novel approach by integrating solvent extraction and polymer inclusion membrane (PIM) separation technologies to engineer an innovative PIM membrane material for the selective separation and enrichment of strategic metals, particularly copper, from polymetallic acidic solutions. The primary objectives were to streamline the technological process, reduce production costs, and enhance separation coefficients between copper and other metals. The optimal extraction conditions were determined as a mass fraction of Mextral®5640H : PVC : NPOE = 3 : 3 : 4, extraction temperature of 35 °C, and 0.9 mol L-1 H2SO4 in the stripping solution. Under these conditions, we achieved remarkable extraction efficiencies, with copper reaching 100%, and the separation coefficients between Cu2+ and Ni2+, Co2+, and Zn2+ exceeding 106. To elucidate the substantial differences in extraction performance between Cu2+ and the other metals (Ni2+, Co2+, and Zn2+), we employed an integrative analytical approach that combines FT-IR spectroscopy, BET analysis, and theoretical calculations. All extracted complexes demonstrated molecular sizes compatible with PIMs, underscoring the critical role of stability and back-extraction performance in the selective extraction of these metal ions.

TiO2 modified basalt fiber cloth with superhydrophilicity and underwater superoleophobicity for oil-water separation

Titanium mesh, stainless steel mesh and other substrate materials for oil-water separation membranes have excellent acid and alkali resistance. However, the preparation process pollutes the environment and is costly. Therefore there is an urgent need for an economical and eco-friendly new material to replace them. Here, this research found that eco-friendly basalt fibers can replace them. In this work, superhydrophilic/underwater superoleophobic TiO2/basalt fiber cloths were prepared by solvothermal method. It has a contact angle of 0° for water in air and maximum 161° for n-hexadecane underwater. The oil-water separation efficiency was up to 99.75%, which indicated its efficient oil-water separation capability. The underwater n-hexadecane contact angle was 154° after immersing it in 6 mol of HCl and NaOH for 2 h respectively. This indicates that it has excellent acid and alkali resistance. And with titanium mesh, stainless steel mesh separation membrane acid and alkali resistance is not much different. However, the price is only one percent of titanium mesh. In addition, the softness of basalt fiber can be folded to enhance the pressure-bearing capacity. Therefore, this work provides a green, acid and alkali resistant, inexpensive new material for oil-water separation membranes, which has great potential in the field of oil-water separation.

Polynorbornenes with carbocyclic substituents: A perspective approach to highly permeable gas separation membranes

Gas transport properties of two sets of polynorbornenes bearing carbocyclic substituents of different nature (cyclohexyl, norbornyl, phenyl groups, and framed oligocyclic moieties) were systematically studied. The influence of side chain carbocyclic substituents on gas permeability and separation selectivity for CO2-containing gas pairs and gaseous hydrocarbons was evaluated. It was found that the presence of carbocyclic moieties in side chains of polynorbornenes promotes the increase in gas permeability similarly to that of SiMe3 groups, with this effect being enhanced by the increase in the number of cycles in the substituents. As a result, P(CO2) of the metathesis polymer with pentacene-based substituents is equal to 1200 Barrer. Studied polynorbornenes with carbocyclic substituents displayed promising gas separation selectivities: CO2/N2 separation selectivity up to 41 (above the 2008 upper bound in the Robeson diagram) and solubility-controlled hydrocarbon separation selectivity up to 16 for the n-butane/methane gas pair. For the polymer with pentacene-based substituents, the separation of the mixture of hydrocarbons and aging were studied. The studies revealed that the mixed gas C4/C1 separation selectivity of this polymer reaches 4, and a two-time reduction of permeability occurs in 8.5 months. Therefore, the incorporation of carbocyclic groups in the side chains of polynorbornenes can be considered as an efficient strategy for the design of polymeric gas separation membrane materials.

Effective C4 Separation by Zeolite Metal-Organic Framework Composite Membranes.

Inorganic zeolites have excellent molecular sieving properties, but they are difficult to process into macroscopic structures. In this work, we use metal-organic framework (MOF) glass as substrates to engineer the interface with inorganic zeolites, and then assemble the discrete crystalline zeolite powders into monolithic structures. The zeolites are well dispersed and stabilized within the MOF glass matrix, and the monolith has satisfactory mechanical stabilities for membrane applications. We demonstrate the effective separation performance of the membrane for 1,3-butadiene (C4H6) from other C4 hydrocarbons, which is a crucial and challenging separation in the chemical industry. The membrane achieves a high permeance of C4H6 (693.00±21.83 GPU) and a high selectivity over n-butene, n-butane, isobutene, and isobutane (9.72, 9.94, 10.31, and 11.94, respectively). This strategy opens up new possibilities for developing advanced membrane materials for difficult hydrocarbon separations.

Effective C4 Separation by Zeolite Metal–Organic Framework Composite Membranes

AbstractInorganic zeolites have excellent molecular sieving properties, but they are difficult to process into macroscopic structures. In this work, we use metal–organic framework (MOF) glass as substrates to engineer the interface with inorganic zeolites, and then assemble the discrete crystalline zeolite powders into monolithic structures. The zeolites are well dispersed and stabilized within the MOF glass matrix, and the monolith has satisfactory mechanical stabilities for membrane applications. We demonstrate the effective separation performance of the membrane for 1,3‐butadiene (C4H6) from other C4 hydrocarbons, which is a crucial and challenging separation in the chemical industry. The membrane achieves a high permeance of C4H6 (693.00±21.83 GPU) and a high selectivity over n‐butene, n‐butane, isobutene, and isobutane (9.72, 9.94, 10.31, and 11.94, respectively). This strategy opens up new possibilities for developing advanced membrane materials for difficult hydrocarbon separations.

COF-anchored design of nanoporous graphene membranes for ultrafast and selective organic separation

Nanoporous graphene has attracted extensive attention as a type of disruptive membrane materials for organic separation. However, the fabrication of an ideal graphene membrane with high permeability and selectivity remains challenging due to the inevitable non-selective defects. Here, a strategy based on synergetic effect of graphene membranes and covalent organic framework (COF) nanounits is developed. Atomically thin nanoporous graphene provides high solvent flux and stability. To prevent the leakage from inevitable non-selective pores in graphene without sacrificing flux, porous COF nanounits are directly anchored at the defective sites. The fabricated membranes exhibit record-high solvent flux of 49.81 L m−2 h−1 (1–2 orders of magnitude higher than that of state-of-the-art membranes), and relatively low reverse solute flux of 1.69 g m−2 h−1 in organic solvent forward osmosis (OSFO) process. The strategy we proposed gives dramatic impetus to the development of OSFO and other membrane separation processes.

Molecularly Mixed Composite Membranes for Gas Separation Based on Macrocycles Embedded in a Polyimide.

Polyimides are a polymer class that has been extensively investigated as a membrane material for gas separation owing to its interesting permselective properties in a wide range of operation temperatures and pressures. In order to improve their properties, the addition of different filler types is currently studied. p-tert-Butylcalix[n]arene macrocycles (PTBCs) with different cavity sizes (PTBC4, PTBC6, PTBC8) were used as fillers in a commercial thermoplastic polyimide, with a concentration in the range 1-9 wt%, to develop nanocomposite membranes for gas separation. The selected macrocycles are attractive organic compounds owing to their porous structure and affinity with organic polymers. The nanocomposite membranes were prepared in the form of films in which the polymeric matrix is a continuous phase incorporating the dispersed additives. The preparation was carried out according to a pre-mixing approach in a mutual solvent, and the solution casting was followed by a controlled solvent evaporation. The films were characterized by investigating their miscibility, morphology, thermal and spectral properties. The gas transport through these films was examined as a function of the temperature and also time. The results evidenced that the incorporation of the chosen nanoporous fillers can be exploited to enhance molecular transport, offering additional pathways and promoting rearrangements of the polymeric chains.

Enhancing contaminant rejection efficiency with ZIF-8 molecular sieving in sustainable mixed matrix membranes

Compared to pure polymer membranes and inorganic membranes, mixed matrix membranes (MMMs) loaded with metal–organic frameworks (MOFs) exhibit higher permeability and selectivity. Zeolitic imidazolate framework (ZIF) is widely regarded as the most promising candidate for separation membrane materials due to its precise molecular sieving properties. However, there is an urgent need for scalable fabrication methods to produce flexible and sustainable MOF MMMs, which is largely unmet. Here, we report a non-solvent induced phase separation-spin coating (NIPS-SC) strategy for the preparation of highly permeable MOF MMMs. A porous support layer is formed by non-solvent induced phase separation of polyvinylidene fluoride (PVDF) and polyvinylpyrrolidone (PVP). Chitosan (CS), polyvinyl alcohol (PVA), and ZIF-8 are then coated on the PVDF support layer to synthesize the symbiotic and continuous MMM membrane. The synthesized membrane shows excellent separation performance for organic dye and heavy metal ions, as well as significant stability. The water permeate flux of the membrane is 342 L m–2 h−1 bar−1. The micron-scale in the support layer facilitates rapid water permeation, while the porous ZIF-8 provides enhanced solute rejection selectivity. This strategy paves the way for the development of high-performance membranes for water purification.

Ni-doped NbC films for remarkably enhancing hydrogen permeation performance of NbC/V composite membranes

Niobium carbide (NbC) membranes have been shown to be an effective catalytic membrane for hydrogen dissociation and desorption. Here, magnetron sputtering method was applied to dope Ni in NbC films to improve the catalytic properties. It is found that the Ni doping largely affects the surface microstructure and electronic structure of the NbC films, which in turn affects the hydrogen permeation performance of the NbC/V composite membranes. By density functional theory (DFT) calculations, it is known that the doping of Ni can modulate the internal electronic structure of NbC, such as d-band center and bader charge, thus improving the catalytic properties of the NbC films. Typically, under the optimal preparation conditions, the hydrogen permeability of the Ni-doped NbC/V composite membranes was 2.59 × 10−8 mol H2 m−1 s−1 Pa−0.5，at 500 °C, which is higher than that of pure Pd under the same conditions. These findings open up a new way towards the improvement of the catalytic properties for the hydrogen separation membrane materials.

Synthesis of New Bismaleimide Homopolymer and Copolymers Derived from 4, 4ˉ-Bis[4-(N-maleimidyl) Phenyl Schiff Base] Tolidine

Polyimides are widely used in high-temperature plastics, adhesives, dielectrics, photoresists, nonlinear optical materials, separation membrane materials, and Langmuir-Blodgett (LB) films. They are commonly regarded as the most heat-resistant polymers. This work involved the synthesis of a new bismaleimide homopolymer and copolymer by performing many steps. The synthesis of compound (1) (bis [4-(amino phenyl) Schiff base] tolidine) via condensation of o-tolidine with two moles of 4-aminoacetophenone. Secondly, compound (1) was combined with maleic anhydride to form compound (2) (4, 4ˉ-bis[4-(N-maleamic acid) phenyl Schiff base] toluidine). Thirdly, a dehydration reaction was carried out affording compound (3) (4,4ˉ-bis [4-(N-maleimidyl) phenyl Schiff base] toluidine). Compound (3) represents the new vinylic monomer, which was successfully introduced in addition to homopolymerization and copolymerization with selected vinylic monomers, affording homopolymer (4) and copolymers (5, 6), respectively. The new homopolymer and copolymers showed good fusibility and solubility in many organic solvents, leading to easy processing and expected to serve a broad spectrum of applications.