Current Analytical Chemistry - Volume 17, Issue 6, 2021

Background: The development of new emerging nanomaterials for water treatment has attracted more and more interests recently. MXenes is a generic term for a series of new twodimensional (2D) transition metal carbides and carbonitrides materials which have graphene-like structure. As a new type of 2D lamellar nanomaterial, many researches has focused on the design and synthesis of MXene-based nanomaterials owing to their large number of the inter-layer void with the two-dimensional stacking structure, large specific surface area, rich and adjustable surface functional groups, and strong hydrophilicity. On account of their unique properties, related discussion and potential of 2D MXenes nanomaterials for membrane separation and water treatment applications are provided. Objective: The goal of this paper is to review new emerging 2D MXenes nanomaterials for the fabrication of various composite membranes and related applications for water treatment. Methods: In this review, the design and synthesis of MXene-based composite membranes for water treatment was extensively discussed. Results: Membrane separation technology is an effective approach for solving the water pollution problem due to its low energy consumption, environment-friendly, and easy operation. MXene-based membranes with different molecular sieving behaviors for small organic molecules and ions and corresponding applications in water purification and desalination were discussed. Conclusion: Although composite membranes constructed by 2D MXenes nanomaterials can be prepared to achieve high water flux and satisfactory rejection, most research focused on the exploration of membrane formation with a multi-layered compound or few-layered MXenes. In the near future, the functional properties of the MXene itself should be paid more attention for the development of various novel membranes.

Background: Water contamination by noxious heavy metals due to urbanization is a global environmental problem. Heavy metal ions pollution makes the water unsuitable for drinking and is also highly toxic to human beings and eco-system. The remediation of heavy metals is therefore very crucial. Methods: Adsorbents based on biopolymer and eco-friendly polymer composites have been developed and fabricated to remediate and remove heavy metals from the ecosystem. Results: In recent years, biocomposites have been successful as cost-effective adsorbents for the remediation of various contaminants with their eco-friendly nature and sustainability. Conclusion: This review article gives an overview on the remediation of heavy metals using green biocomposites.

Background: The presence of pharmaceuticals (PACs) drugs in the environment and their detection and quantification have emerged as one of the challenging issues for the scientific community. Introduction: The gold standard, an anti-diabetic drug, Metformin has a strong potential to contaminate the aquatic bodies, being a highly polar drug. Different analytical methods based on spectroscopic evaluation or chromatographic techniques have been developed to find out the concentration of drug/ their metabolites. Methods: This review article discussed the chromatographic techniques for the analysis of Metformin (in ng/L to μg/L) in aqueous samples, pharmaceutical drugs and biological fluids such as urine and human plasma are High-Performance Liquid Chromatography (HPLC), Reverse-Phase High- Performance Liquid Chromatography (RP-HPLC), High-Performance Thin-layer Chromatography (HPTLC), Hydrophilic Interaction Liquid Chromatography HILIC-MS/MS, Liquid Chromatographic- tandem mass spectrometric (LC-MS-MS), Ultra-High Performance Liquid Chromatography (UPLC). Results: The relevance modifications of traditional HPLC methods for the separation of the mixture of drugs with a focus on the lesser time, better resolution, sensitivity, symmetry of peaks, the limit of detection and accuracy of the results have been envisaged through research findings. Hydrophilic interaction liquid chromatography (HILIC)-tandem mass spectrometry method offered the possible solution for highly polar drugs detection and quantification in effluent and surface water samples. Conclusion: HPLC based analytical techniques offer the advantages viz. less time requirement, minimum usage of organic solvents and better separation and quantification of Metformin. The futuristic research approach lies in the development of newer extraction strategies, mobile phases, and adsorbent materials for the HPLC based separations.

Background: More and more chemical substances are being released to the environment. Therefore, environmental problems caused by different pollutants have attracted long-term attention. Objective: Sample pretreatment has always been the bottleneck restricting the development of residual drug analysis, so the latest development in various pretreatment technologies and current status for different residual drugs in environmental samples are reviewed. Methods: For systematic and explicit descriptions, all of the contents were elucidated and summarized in a series of independent parts. In each part, it started from the research background or a conceptual framework and then specific examples were introduced to illustrate the theme. Finally, the important conclusions were drawn and its future was out looked after the discussion about related key problems appearing in each mentioned research. Results: The whole review was composed of four parts, and 111 papers were cited in total. Six figures were used to depict progress in potential pretreatment technologies for residual drugs in the environment, and nine tables were employed to summarize pretreatment and analysis results for various residual drugs in the environment. Conclusion: This review placed emphasis on the development of pretreatment techniques of residual drugs in a specific manner, leading to meaningful and valuable related information to some related fields and thus promoting further research and application of related methods. The deep exploration for key scientific problems is the driving force to their effective detection and strict control.

Background: Water is undoubtedly a very precious resource that helps life thrive on this planet, and its pollution is a problem, which is potent in erasing almost all forms of life on the earth. Hence, considering the magnitude of this problem, studies and experiments have been focused (from the day water pollution was recognised as an eminent issue) on monitoring and finding possible solutions for water pollution. While the latter deals with treating and purifying water using a variety of concepts, monitoring deals with the continuous assessment of water quality of a waterbody. Methodology: There are several methods for monitoring purposes, and remote sensing is a popular choice, thanks to its wide applicability and flexibility in implementation. Remote sensing deals with collecting data about a place (which is to be monitored) and sending the data to another ‘remote’ location for analysis. This article provides a description of some methods employed in recent times for remote sensing and a short section which deals with the analysis of the remotely sensed data using machine learning / deep learning models, hence making the reader aware of the concept of remote sensing and its scope for monitoring water pollution (or any form of pollution) in the future. Conclusion: The detailed comparative analysis of these methods showed that sensor-based water quality monitoring with Geographical Information System (GIS) would be more efficient for the detection of water pollutants. Further research in this field may introduce many advancements to enable efficient water pollution detection techniques.

Background: Diesel mainly consists of paraffin and thio-aromatic compounds. Sulfur present in diesel exhaust is the major challenge for oil refineries. Sulfur is an oxidizing element that discharges as acute pollutant in the environment, having adverse effects on human and animal life. Introduction: The scope of this review paper is to discuss and highlight the recent advancements in the process of desulfurization of diesel oil to explore the less energy-intensive and more economical process. Methods: Recently, different techniques are widely used for desulfurization of diesel oil to remove sulfur containing compounds from diesel. These techniques mainly involve hydrodesulfurzation, oxidative desulfurization, biodesulfurization, ionic liquid desulfurization, and adsorption desulfurization. Conclusion: Adsorptive desulfurization technique is green, less energy incentive, and more economical than hydro-desulfurization, oxidative desulfurization, ionic liquid desulfurization and bio desulfurization. Optimization of adsorptive desulfurization technique may yield up to 100% desulfurization of diesel oil.

Background: Pollution in water is of concern because of its negative influence on human health and impact on ecosystems. Three-dimensional (3D) structures in the form of inverse opals and opals-like structures were constructed on a scale of millimeters for their use in the adsorption of heavy metals adsorption on manganese oxide-covered surfaces. Objective: Manganese oxides both, as commercial powders and as synthesized coatings by the chemical bath method, have a high capacity of lead ions adsorption. The inverse opals and opals-like structures increase the contact area and regulate the flux. Methods: The chemical bath method was used to coating surfaces of inverse opals and opals-like structures. The size of structures was proposed in millimeters to guarantee an easier flow of water. Results: The manganese oxide deposits were predominantly constituted by an amorphous phase. The present crystalline forms were identified as γ − MnO2, ε − MnO2, Birnessite, and pyrolusite. The best adsorption was obtained with Mn(II, III) and Mn(II), with 91.4% and 80.6%, respectively. Conclusion: Mn(II, III) and Mn(II) had approximately three times better performance than oxides of Mn(III), Mn(IV), and chemical bath deposited MnO2 in powder form in the lead adsorption.

Background: Heavy metal toxicity has proven to be a major threat and there are several health risks associated with it. The toxic effects of these metals, even though they do not have any biological role, remain present in some or the other form harmful for the human body and its proper functioning. They sometimes act as a pseudo-element of the body while at certain times they may even interfere with metabolic processes. Sensitivity enhancement and selective pre-capillary chelation and separation method was developed for the simultaneous determination of metal ions by capillary zone electrophoresis (CZE) with UV light as a detector. Methods: This method was based on the chelation of metal ions such as nickel(II), cobalt(II), lead(II) and zinc(II) with 2.0 mM Ammonium Morpholine-4-Carbodithioate (AMC) at pH 7.2 prior to analysis in 2.0 mM of phosphate buffer. Results: Different optimal conditions such as the effect of pH, concentration of AMC, applied voltage, nature of the buffer solution and excipient ions were investigated to enhance the sensitivity of the method. Conclusion: The developed method separate nickel(II), cobalt(II), lead(II) & zinc(II) in less than 5 min with good reproducibility and recoveries ranging from 93.50 to 100.00% in agricultural materials. Furthermore, the interaction and Density Functional Theory (DFT) based studies reveal that the metal ions form relatively stable complexes with AMC and follow the experimental trend performed with CZE.

Background: Silicon Carbide (SiC) ceramics are promising engineering material due to its phenomenal properties, such as strong corrosion resistance, high-temperature hardness, wear resistance, high thermal conductivity and high stability in an aggressive environment. The key problem of SiC is low fracture toughness due to its brittle nature and to circumvent this, herein high ductile material like MWCNT was used as reinforcement by different proportions. Methods: Nanocrystalline powdered Silicon Carbide (SiC) of particle size of 40 nm and x % weight ratio of SiC (x = 95%, 90% and 85%) + y % weight ratio of multiwalled carbon nanotubes (MWCNTs) of particle size of 20 nm (y= 5%, 10% and 15%) composites were ball milled and fabricated using spark plasma sintering process with temperature rate of 100°C/min and external pressure of 50 MPa. The sintered samples were tested according to ASTM standards to verify the mechanical properties of the samples. Furthermore, lattice strain and crystalline size was determined by XRD and the crack bridging mechanism was studied by FESEM. Results: It was observed that the uniform distributions of MWCNTs were achieved through ultrasonication and ball milling processes, which play a predominant role in increasing fracture toughness. The fracture toughness of the composite improves drastically from 3.71 MPa m^1/2 (100% SiC) to 10.21 MPa m^1/2 (85% SiC-15% MWCNT). The theoretical and relative densities of the materials were gradually reduced due to the increase in MWCNTs which is due to the lower density of the reinforcement material and an increase in porosity of the samples. Conclusion: The MWCNTs act as a bridging aid in sintered samples, FESEM image signifies some pull-outs and crack branching mechanisms of MWCNTs which is the reason for an increase in the fracture toughness of SiC.

Background: Supercritical fluid chromatography (SFC) is one of the powerful analytical techniques of modern times. Recently, extensive analytical work has been reported and is in progress by utilizing the advanced features of SFC. Low solvent consumption, high sensitivity, and solvent recovery make it advantageous over the traditional liquid chromatographic techniques. It utilizes supercritical fluids having properties of both liquid and gases, making the applicability of this technique possible for a wider range of analytes. Methods: Various research reports were collected from search engines like Sciencedirect, Pubmed, Researchgate, and Google Scholar. Further, upon a thorough study of these reports, significant findings/data was collected and compiled under suitable headings. Important parameters/ conditions utilized in methodologies are depicted with the help of tables in this study. Results: It was found in various reports that SFC and its hyphenation with mass spectroscopy (MS), ultraviolet spectroscopy (UV), high-resolution mass spectrometry (HRMS), photodiode array detector (PDA), nuclear magnetic resonance (NMR), charged aerosol detector (CAD), etc., have made possible to quantify analytes even in ultra-small concentrations in complex matrices. These techniques have been successfully employed for the quantification of a wide variety of analytes with excellent accuracy, selectivity, and sensitivity. Conclusion: The present review highlights the recent applications of SFC techniques in various analytical fields, such as pesticide analysis, vitamin analysis, enantioseparation, lipid analysis, drug metabolite estimation, polycyclic aromatic hydrocarbons, and steroid analysis. Reports from 2017 to 2020 have been included in this compilation.

Background: Indole-3-acetic acid (IAA) is an important growth hormone for plants obtained by biosynthesis from tryptophan. Aim: In this paper was studied the competitive transport of two biologically active compounds, indole-3-acetic acid (IAA) and tryptophan (TRP), through a liquid membrane. Methods: The separation of the two compounds was obtained using a hybrid liquid membrane system having trioctylphosphine oxide (TOPO) as a carrier. Results: The most important operational parameters of the system, and pH influence on the efficiency of the transport process, in correlation with the speciation diagrams of the two compounds: TRP and IAA, were studied. The evaluation of the transport process was performed by calculating the composition of the phases at the end of the transport process and the organic substrate flow at the membranes exit. Conclusion: Due to the transport efficiency of over 90% in the case of IAA and the high selectivity at the transport between IAA and TRP, the procedure can be applied for the preparation of a sample containing these analytes.