ABSTRACTTwo-dimensional membranes are considered as the most energy-efficient alternatives to various traditional separation processes. To date, atomically thin hexagonal boron nitride, covalent organic frameworks, graphene, graphene oxide, transition metal carbides and nitrides, layered double hydroxide, transition metal dichalcogenides (TMDCs), and metal-organic frameworks have been extensively investigated for high-performance lamellar membranes, which is due to their tunable physicochemical properties, single-layered structure, and in-plane pore structure. This comprehensive review summarizes the different fabrication methods of TMDC-based membranes and introduces the recent modification strategies to improve their microstructural properties. TMDCs-based membranes for wastewater treatment, desalination, proton exchange, gas separation, and energy devices are extensively discussed. Finally, we highlight the current engineering hurdles and suggest research directions for improving the separation efficiency, stability, and permeability of these membranes.

ABSTRACTMembrane technology has evolved to be one of the main filtration processes in various water/wastewater treatment applications. The success of the treatment process lies on the improved properties of membranes, notably water permeation, solute rejection, and antifouling capabilities. Over the past decade, hyperbranched macromolecules that comprise star polymers and dendrimers have gained increasing attention in membrane research as synthesis materials and modifying agents. These macromolecules which are composed of branched structure, high-density terminal functional groups, and large intramolecular free volume could offer an opportunity to design a new generation membrane with desirable characteristics. This review looks into the recent advances in the polymeric membrane synthesis and its modification using branched macromolecules. Highlights are given to the factors contributing to the changes in membrane properties (structural, morphological, and chemical functional groups) and performance after branched macromolecules are used as main membrane forming material or modifying agent. The review also discusses outlook and future works that can be further explored on utilizing branched macromolecules in membrane application. Challenges in promoting and commercializing branched macromolecules-based membranes are also discussed. This review can serve as a valuable reference for further development of membranes with improved performance and functionalities for water treatment application.

ABSTRACTGas adsorption is widely used in air pollution control, with mainly activated carbon and zeolites used as adsorbents. Although physical and chemisorption can be used, most air pollution applications involve physical adsorption, now also increasingly investigated for CO2 abatement from combustion gas. Empirical adsorption treatments have been presented since many decades, but solely rely on the comparison of adsorbate feed and exhaust concentrations of the adsorption bed. In-situ measurements, to study the absorbate/adsorbent interactions in real time, are compared in the present review when performed by a three-dimensional (3D) Positron Emission Tomography of an adsorbing 11CO2 radioactive tracer on activated carbon versus a zeolite adsorbent. The overall results are validated by conventional exit gas analysis. Results are defining both the time-dependent adsorption parameters, such as the progressing adsorption front and Mass Transfer Zone along the adsorbent bed length, and enable to assess previous semi-empirical adsorption correlations toward their optimum validity in predicting adsorption isotherms, kinetics and mechanisms.

ABSTRACTWorldwide thin layer chromatography (TLC) is still in very much use in various different application fields (e.g. natural products chemistry, monitoring the organic/enantioselective synthesis, and routine analysis in analytical laboratories). Herein is presented an account of the efficient resolution/enantioseparation of racemic and non-racemic mixtures of several different types of active pharmaceutical ingredients, and biologically important compounds by TLC using a direct approach along with quantitative determination and isolation of native forms via non-covalent diastereomer formation. Different approaches and mechanisms of direct enantioseparation using different chiral reagents are discussed. It provides a route for a wide range of chiral stationary phases (CSPs) which can be in-home thought out, produced, assessed, and customized. The achievements and new challenges in the field are presented. Besides, it presents a very useful coverage for the non-specialists to the subject who want to understand where this study fits into the existing literature in this general area.

ABSTRACTHaloacetic acids (HAAs) are a class of disinfection by-products (DBPs), widely occurring in drinking water, wastewater and swimming pool water with concentrations at sub-μg/L to mid-μg/L levels. HAAs arose public attention due to their cytotoxicity, genotoxicity and carcinogenicity. Monitoring HAA concentration levels in aqueous environments is required. This review presents an overview of all techniques or methods for sample pretreatment, analysis and removal of HAAs in aqueous environments since 2000. For the pretreatment methods, the commonly used methods are compared and discussed in terms of advantages and drawbacks. Microextraction techniques are preferred as they are efficient, rapid and environment-friendly. Emerging pretreatment methods, such as techniques based on novel materials or liquids, have also been introduced. For the analytical methods, LC and GC coupled with various detectors are frequently used allowing detection at the required low μg/L levels in aquatic environments. The advances in mass spectrometers (MS) and a comparison between their pros and cons are summarized herein. Recent high resolution MS gave give mass accuracy of 0.0001 Da with a resolving power up to 140,000 full width at half maximum height improving feature identifications in nontargeted analyses. For HAA removal methods, advanced oxidation techniques, adsorption and biodegradation were updated, improved and upscaled. Combining two or more removal techniques, the efficiency can reach 99%. Lastly, this review points out critical gaps and proposes future trends.

ABSTRACTIncreasing applications of precious metals (PMs: Au, Ag and platinum group metals) and the growing demand is a matter of great concern for supply security. The hydrometallurgical route through chloride-based leaching has been considered as the most promising method to recover almost all the metals. However, separation of metal-chloro complexes formed during the leaching is difficult to achieve because of similar properties of these complexes. Among the methods developed to extract and separate the metal-chloro complexes, ionic liquid (IL)-based solvent extraction has been recognized as one of the most promising approaches. The ionic liquids possess unique characteristics of ‘greener,’ ‘designer’ and ‘highly effective’ solvents. This paper reviews extraction and separation of PM-chloro complexes by ionic liquids. Mechanisms and IL role in the process, along with merits and drawbacks of IL-assisted solvent extraction are discussed comprehensively. Effects of operational conditions, stripping, and regeneration of the loaded ILs and possible use of ionic liquids in other separation methods are also presented. A flow-sheet for separation of PM-chloro complexes has been developed as a part of basic process approach using ionic liquids. In addition, future directions for the development and application of IL-assisted solvent extraction in separation of precious metals are provided.

ABSTRACTIn groundwater, excess fluoride concentration (>1.5 mg/L) is a primary concern for various countries. Nanoadsorbents have been proven to possess higher adsorption capacity than conventional adsorbents. This review aims to provide insights into recent advancements in the adsorption of fluoride using various nanoadsorbents. Nanoparticles have very high specific surface area but are usually found unsuitable for real field applications as they tend to agglomerate. They are also difficult to recover after use and pose a significant threat to the environment through leaching. These limitations have given rise to the trend of the development of nanocomposites for defluoridation. Nanocomposites often involve a polymeric matrix that serves as a medium for their homogenous dispersion. This reduces agglomeration and leaching into the surroundings without altering the original activities of the nanoadsorbent. This review classifies the fluoride nanoadsorbents into three categories: bare nanoparticles, nanocomposites with nanoparticles inside the porous matrix, and nanocomposites with nanoparticles coated with or anchored on the matrix surface. Critical analyses of the importance and shortcomings of these classes have been presented. In general, bare nanocomposites show the best fluoride adsorption performance compared to other classes of nanoadsorbents.

ABSTRACTEstimation of antibiotic residues in environmental matrices; veterinary products; food and biological samples has become very important in order to protect the human health and limit the spread of antimicrobial resistance. To achieve this, sensitive and efficient sample preparation procedures for the extraction of antibiotics from complex matrices are essential. Reproducible and effective sample preparation processes together with sensitive analytical techniques directly impact the final accuracy of the data and further interpretation. Exhaustive solvent-based extraction techniques such as liquid–liquid extraction have several limitations and suffer from a negative impact on environment. Past two decades have witnessed paradigm shift from solvent based to sorbent-based techniques in the extraction of contaminants. Innovative non-exhaustive techniques such as solid-phase microextraction and magnetic solid-phase extraction using advanced (nano)materials (e.g. molecularly imprinted polymer) have brought radical changes to the way traditional sample extraction was carried out. As the advanced techniques are specific to a target antibiotic or to its class, design consideration for the in-house synthesis of novel (nano)materials and optimization of the extraction technique is a crucial step in the quantification of antibiotic contaminants. The aim of this review is to assess the critical design parameters to be considered to synthesize novel sorbent materials for the extraction of antibiotics and to improve their extraction techniques.

ABSTRACTArsenic pollution in water sources has been a recurring issue for the nations where groundwater is the sole source of survival. While conventional pressure-driven membrane is the epitome of a water treatment solution, it is not without limitations for arsenic removal. Thus, adsorptive membranes are studied since they combine positive features of adsorption and ultrafiltration technology that makes them able to remove arsenic effectively while offering promising flux. While there are studies reporting on the roles of adsorptive membranes for arsenic removal, there is much to discover on the performance of different adsorptive membranes in terms of adsorption capacity, regeneration potential, and stability. In this review, we survey the characteristics of a wide range of nanoadsorbents focussing on the membrane properties for arsenic removal as well as regeneration process of adsorptive membrane using different solutions. The key challenges faced during membrane fabrication and operation are also highlighted providing a better insight toward development of more robust adsorptive membranes. It is hoped that through this review, researchers will be inspired to develop more functional adsorptive membranes with not only outstanding performance but also stable performance for arsenic removal.

ABSTRACTMatrix solid phase dispersion (MSPD) is a rapid and flexible sample pretreatment method that accomplishes sample disruption, extraction, filtering and purification in one step and is especially suitable for solid, semisolid and viscous samples. More than 30 years have elapsed since it was first proposed, and there are many published reviews. However, there is no review on the use of MSPD to extract active compounds from natural products. In this review, the latest developments from 2015–2021 in MSPD microextraction techniques, including sorbents, elution solvents and assisted MSPD extraction, along with their applications in natural products, are systematically discussed and classified according to the structure of the active constituents, which mainly refer to phenolic acids, flavonoids, alkaloids, anthraquinones and terpenes.

ABSTRACTDesalination is considered one of the strongest alternatives to face global water scarcity. Since conventional reverse osmosis is an energy-intensive process, Aquaporin biomimetic membranes (ABM) emerge as an effective alternative to increase productivity and reduce energy consumption. Despite the highly theoretical water permeability and selectivity of aquaporins (Aqps), in practice, ABM did not achieve the expected performance. This review is focused on each step of the ABM fabrication process in order to find critical points where efforts should be made for future studies. Fabrication procedures include Aqp production, reconstitution into vesicles, immobilization in porous substrates and filtration performance. The principal identified challenge is the need for implementing monitoring and optimization techniques. Also, new strategies for protein production, stabilization, reconstitution, and support affinity could offer significant breakthroughs for developing ABMs as a viable emerging technology.

ABSTRACTSurface ion-imprinting technology (SIIT) is a novel and effective alternative to conventional methods of preparing ion-imprinted polymers. SIIT involves the coating of support materials with a polymeric layer that selectively binds with imprinted metal ions, particularly heavy metal ions. Given its specificity, predictability, and stability, SIIT has been quickly adopted in ion detection, separation, enrichment, and sensing. Here, building on the latest advances in this emerging new technology, we carried out a systematic review to summarize the 1) principles and basic components of surface ion-imprinted polymers (SIIPs); 2) preparations, properties, advantages, and disadvantages of three types of SIIP supporting materials, including inorganic (minerals, carbonaceous materials, metal oxides), organic, and composite (organic/organic, organic/inorganic, inorganic/inorganic) supports; 3) current applications of SIIT, and 4) future challenges and opportunities related to SIIT. Finally, perspectives and future research are discussed to address the pressing need for the development of SIIT for heavy metal ion treatment.

ABSTRACTSilicon carbide (SiC) nanomaterials are being used in a large range of fields because of their excellent mechanical strength, high thermal resistance and conductivity, high chemical stability and being semiconductors. In the present review, we evaluate SiC nanomaterials as membranes and adsorbents to separate different species. In addition, applications of SiC nanomaterials as membranes or in a membrane structure are described. In this regard, experimental studies which used porous SiC in membrane structure confirmed that SiC can enhance the performance of any membrane because of its large surface area, anti-fouling nature, high porosity, and high-water permeability. Next, molecular dynamics simulation studies examined the ability of SiC nanosheets and SiCNTs in water desalination, gas and dissolved molecule separations. Ultimately, based on the reviewed articles and their findings, areas requiring further attention by researchers are proposed.

ABSTRACTFluoride and arsenic are hazardous inorganic contaminants due to associated health risks and relatively higher levels of occurrence in groundwater. Metal-organic frameworks, (MOFs) with their high surface area, versatile building blocks and numerous active sites, are a novel approach to fluoride and arsenic uptake. This review presents the different types of MOFs for fluoride and arsenic removal along with a study of dynamic breakthrough times and cost analysis. MOF performances are based on a variety of synthesis methods, notable among which solvothermal one is more described. However, all research works concluded that MOFs have poor yield compared to conventional adsorbents. But, their high adsorption capacity, tailored chemical structure and ionic uptake of fluoride and arsenic make them a more favorable option than many other adsorbents. The cost of different MOFs usually varies between 0.1 and 5 US$/g depending on the synthesis routes.

ABSTRACTThe extensive use of lithium-ion batteries (LIBs) has generated a huge amount of their wastes. As waste, LIBs can be used as a source for valuable metals such as lithium, cobalt, manganese, and nickel. Like the ores of these metals, their values are recognized as raw material. This can ultimately help bring down the cost of LIB production while reducing their harmful environmental impacts. As a result, recycling has become a major opportunity for industrialists and a challenge to environmentalists all across the globe. Researchers have explored various methods to recover cobalt and lithium precious metals from worn out batteries. This review provides an overview of the recent technological solutions on the recovery from waste LIBs using organic acids-based hydrometallurgical processes concerning chemical reactions, structures, and leaching efficiency with different organic acids. Subsequently, the advantages of organic acids over inorganic acid have also been discussed with an emphasis on possible complex formations during the recovery process. At last, the potent role of process variables: reductant concentration, reaction time, temperature, solid:liquid ratio, and concentration of complexing agent during the Co and Li leaching has been discussed along with prospects in this research area.

ABSTRACTThe choice of an appropriate method for rare earth element (REE) preconcentration from industrial by-products is a very difficult task. Most of the REE separation reviews focus on liquid extraction methods, whereas sorption processes are usually mentioned in connection with chromatographic individual REE separation. Limited information is currently available on ion exchange methods for REE preconcentration. The REE sorption methods are gradually acquiring great practical significance due to depleting REE sources. The present review deals with the history, recent studies and commercial applications of REE sorption from various complex industrial by-products such as products of apatite treatment, phosphogypsum and uranium ores. It covers an extensive study on the recent research related to use of polymeric ion-exchange sorption materials for REE preconcentration and recovery from various industrial wastes.

ABSTRACTSince past decades, membrane science and technology have received great attention in academia and practice because of their potential for industrial applications. A diverse range of industrial applications has been benefited from this technology thanks to the advances in membrane science. Membranes are of paramount importance in chemical technology and play a key role in a broad range of applications.Membranes incorporating nanosize pores or channels have a tremendous contribution to membrane science discipline, particularly in gas separation technologies. Performing pore-level modeling with the help of computer simulation opens a route to membrane characterization in high accuracy and less observational. By utilizing molecular dynamics simulations, one can provide a fundamental understanding of the static and dynamic features of membranes at a molecular scale. In this work, we have reviewed the recent advances in nanofluidics for gas separation applications, with a major focus on the theoretical literature discussing the gas molecular transport mechanisms through the carbon-based nanopores. Describing the nanofluidics systems, solid-state nanopores, fabrication of nanofluidic devices, pore generation on graphene nanosheets, and pore-level flow modeling, this article expects to provide a platform for understanding the permeation and separation of gases across a variety of nanopores and attracting more attention of audiences from industry and academia.

ABSTRACTPropane (C3H8) and propylene (C3H6) are important energy resources and raw materials for industrial chemistry. Today, propylene/propane separations are carried out by expensive distillation operations which are energy intensive. Therefore, there is a great interest in the development of new separation technologies like membrane modules. In this work, we collected and analyzed the data from neat polymers and mixed matrix membranes (MMM) for propylene/propane separations. Polymeric membranes are easily processed, but one important problem is plasticization since both propylene and propane are condensable gases resulting in a loss of selectivity. To improve the properties of polymer membranes, MMM were developed based on an inorganic filler and a polymer matrix to get improved performances with a synergistic effect. However, these performances strongly depend on the filler type and content, as well as their compatibility. In this review, the separation performances of neat polymers and MMM flat membranes and hollow fibers are reported. A comparison of the single gas and mixed gas permeation is presented where both permeability and selectivity are lost due to plasticization and the competitive sorption between gas molecules. Based on the results available, it can be concluded that more development can lead to improved performances for industrial-scale applications in the petroleum industries. Also, an upper bound for C3H6/C3H8 separation is proposed using neat polymers.

ABSTRACTThis review article provides an overview of supercritical fluid chromatography (SFC) techniques for the separation of amino acids and peptides and modifications of mobile phases in SFC for the separation of highly polar and hydrophilic compounds. Furthermore, it covers SFC applications for the chiral and achiral separations of amino acids and peptides. In this review, detailed explanations of possible and already performed achiral and chiral separations by individual amino acids and peptides are presented. Different stationary phases, separation conditions such as backpressure and temperature, and compositions of the mobile phase with possible additives for each amino acid and peptide are summarized.

ABSTRACTCoffee is recognized worldwide as a top beverage owing to its several associated health benefits mediated by a complex mixture of unique bioactive substances. Chlorogenic acids are the key components of the phenolic fraction in green coffee seeds, accounting for up to 14% of the dry matter. The manufacturing of decaffeinated coffee demands efficient caffeine extraction from seeds and spent without solvent history effect for safety considerations. This has prompted researchers to investigate eco-friendly and cost-effective extraction technologies. Current extraction processes are not environmentally sustainable and have harmful consequences on humans. To date, developing a single standard method for effective extraction of certain complex compounds from coffee seeds remained a challenging procedure. The current review aims to give updated technical information regarding coffee plant green extraction methods, their advantages and disadvantages, and factors affecting efficacies for the recovery of bioactive compounds in coffee seeds and coffee spent. A comparative review of the uses of innovative green extraction techniques for coffee bioactive substances is introduced to present alternatives to conventional extraction methods. The most interesting finding was that the maximum total extractions of catechin (50.6 g/100 g) and caffeine (46.2 g/100 g) were achieved with enzymes in pressurized liquid extraction (PLE), and PLE-assisted with enzymes exhibited an enhancement in total phenolics and overall antioxidant compared to 50% hydro-ethanolic solutions. In addition, it has been claimed that the ultrasonic extraction can cut extraction time by 37% and temperature by 13%. These green extraction techniques represent favorable approaches to the exploitation of coffee chemicals as bioactives to explore their wide-reaching applications at an industrial level and for their valorization.