Current Analytical Chemistry - Volume 18, Issue 3, 2022

The objective of the review paper aims to explore and provide insight into various low-cost adsorbents prepared and used in the removal of hazardous dye pollutants from the contaminated industrial effluents Background: The major untreated discharge from the textile industries constitutes a wide range of organic contaminants with the enhanced concentration of biological oxygen demand and chemical oxygen demand in the water bodies. Dyes are considered the major water contaminants and this quest the researchers to adopt various technologies to remove the hazardous dye pollutants from the aquatic environment. Dyes are the chemical compounds that tend to adhere themselves to metal or salts by covalent bond formation or complexes by mechanical retention or physical adsorption so as to impart colours to which it is being applied. Objective: The use of numerous treatment methodologies which have been applied to the degradation of dyes. The current study has been focused on the distinct low cost and cost-effective adsorbents used in the removal of various dye pollutants. Moreover, the application of nanoparticles in the removal of the hazardous dye pollutants had received great interest because of its size and high reactive nature. Methods: The treatment technologies used in the removal of dye pollutants from wastewater have been listed as adsorption, coagulation, electrocoagulation, flocculation, membrane filtration, oxidation and biological treatment. Results: The complex structure of the dyes causes a great harmful impact on the aquatic environment. Though numerous treatment technologies have been applied, adsorption has been preferred by various researchers because of its cost-effective nature. Conclusion: The various adsorbents are used in the removal of cationic, anionic and non-ionic dyes. The different types of adsorbent from agricultural waste, activated carbons, nanomaterials and biomaterials have been discussed with the advantages and limitations.

Background: Rapid industrialisation, population growth and technological race worldwide have brought adverse consequences on water resources and, as a result, affect human health. Toxic metal ions, non-biodegradable dyes, organic pollutants, pesticides, pharmaceuticals are among the chief hazardous materials released into the water bodies from various sources. These hazardous contaminants drastically affect flora and fauna globally, leading to health deterioration, thereby giving rise to new biomedical challenges. Hypothesis: Montmorillonite based nanocomposites (MMTCs) have drawn the attention of the researchers to design environmentally friendly, advanced and hygienic nanocomposites for wastewater treatment and biomedical purposes. Montmorillonite clay possesses peculiar physical and chemical properties that include enhanced surface reactivity, improved rheological performance, exorbitant miscibility in water due to which it shows highly favourable interactions with polymers, drugs, metals, mixed metals and metal oxides, leading to the fabrication of different types of advanced montmorillonite based nanocomposites that have remarkable applications. Methodology: Here, we review the structural characteristics of montmorillonite clay, advances in the synthetic techniques involved in the fabrication of montmorillonite nanocomposites, their applications in wastewater treatment and in biomedical fields. The recently developed montmorillonite nanocomposites for (1) wastewater treatment as nano-adsorbents for the elimination of toxic inorganic species such as metal ions and heterogeneous photo-catalysts for photodegradation of dyes, pesticides and pharmaceuticals (2) biomedical utilization viz drug delivery, wound amelioration, bone cement, tissue engineering, etc., are presented. Conclusion: The review exclusively focuses on recent research on montmorillonite based nanocomposites and their application in wastewater treatment and in biomedical fields.

Background: The occurrence of pharmaceuticals in surface and drinking water is ubiquitous and is a major concern of researchers. These compounds cause a destructive impact on aquatic and terrestrial life forms, and the removal of these compounds from the environment is a challenging issue. Existent conventional wastewater treatment processes are generally inefficacious because of their low degradation efficiency and inadequate techniques associated with the disposal of adsorbed pollutants during comparatively effective methods like the adsorption process. Remediation Method: Semiconductor-mediated photocatalysis is an attractive technology for the efficient removal of pharmaceutical compounds. Among various semiconductors, TiO2 and ZnObased photocatalysts gained much interest during the last years because of their efficiency in decomposing and mineralizing the lethal organic pollutants with the utilization of UV-visible light. Incessant efforts are being undertaken for tuning the physicochemical, optical, and electronic properties of these photocatalysts to strengthen their overall photocatalytic performance with good recycling efficiency. Results: This review attempts to showcase the recent progress in the rational design and fabrication of nanosized TiO2 and ZnO photocatalysts for the removal of pollutants derived from the pharmaceutical industry and hospital wastes. Conclusion: Photocatalysis involving TiO2 and ZnO provides a positive impact on pollution management and could be successfully applied to remove pharmaceuticals from wastewater streams. Structure modifications, the introduction of heteroatoms, and the integration of polymers with these nano photocatalysts offer leapfrogging opportunities for broader applications in the field of photocatalysis.

Background: Rapid escalation in textile, paper, pesticides, pharmaceuticals and several other chemical-based manufacturing industries due to amplification in human requirements have proportionately contributed to the extreme contamination of the water ecosystem, resulted from the discharge of toxic pollutants from industries. Effluents from textile industries are comprised of coloured dyes like Rhodamine B, Methyl Orange, Methylene Blue and phenolic compounds, which deserve special mention owing to their non-biodegradable, carcinogenic and severe detrimental nature. Urgent needs to ameliorate this fast declining environmental situation are of immense necessity in the current scenario. Objectives: In this regard, graphitic carbon nitride (GCN) is a distinguished material for water purification- based applications because of its exclusive characteristics, making it highly prospective for the degradation of toxic dyes from water by catalysis and adsorption techniques. GCN has been a material of conspicuous interest in recent times owing to its two-dimensional sheets like structure with favourable surface area, and cost-effective synthesis approaches along with high production yield. This article presents a detailed study of different aspects of GCN as a material of potential for water purification. Through extensive literature surveys, it has been shown that GCN is an effective material to be used in the fields of application. Several effective procedures like catalysis or adsorption for removal of dyes from water have been discussed with their basic science behind. Conclusion: This systematic effort shows that GCN can be considered to be one of the most efficient water purifiers with further advantages arising from its easy and cost-effective large scale synthesis.

Background: The world’s production of whey is estimated to be more than 200 million tons per year. Although whey is an important source of proteins with high nutritional value and biotechnological importance, it is still considered as a by-product of the dairy industry with low economic value due to low industrial exploitation. There are several challenges in the separation of whey proteins: low concentration, the complexity of the material and similar properties (pI, molecular mass) of some proteins. Methods: A narrative review of all the relevant papers on the present methodologies based on ion exchange and adsorption principles for isolation of whey proteins, known to the authors, was conducted Results: Traditional ion exchange techniques are widely used for the separation and purification of the bovine whey proteins. These methodologies, based on the anion or cation chromatographic procedures, as well as the combination of aforementioned techniques are still preferential methods for the isolation of the whey proteins on the laboratory scale. However, more recent research on ion exchange membranes for this purpose has been introduced, with promising potential to be applied on the pilot industrial scale. Newly developed methodologies based either on the ion exchange separation (for example: simulated moving bed chromatography, expanded bed adsorption, magnetic ion exchangers, etc.) or adsorption (for example: adsorption on hydroxyapatite or activated carbon, or molecular imprinting) are promising approaches for scaling up of the whey proteins’ purification processes. Conclusion: Many procedures based on ion exchange are successfully implemented for the separation and purification of whey proteins, providing protein preparations of moderate-to-high yield and satisfactory purity. However, the authors anticipate further development of adsorption-based methodologies for the separation of whey proteins by targeting the differences in proteins’ structures rather than targeting the differences in molecular masses and pI. The complex composite multilayered matrices, including also inorganic components, are promising materials for simultaneous exploiting of the differences in the masses, pI and structures of whey proteins for the separation.

Background: Cellulose is one of the most abundant, non-toxic, and renewable natural biopolymers. The presence of hydroxyl groups in cellulose leads to further modification of it. Preparation and modification of cellulose-based sorbents and their applications on water treatment gained traction in recent years Objective: A low-cost and eco-friendly biosorbent was designed and fabricated by introducing the acetate functional groups into cellulose for removing Beryllium (Be²⁺) from an aqueous solution. The sorption of Be²⁺ on acetate containing cellulose was evaluated for varying sorbent doses and initial solution pH values. Methods: The sorbent was prepared by a two-step oxidation process. In the initial step, cellulose reacted with NaIO4 and aldehyde groups were introduced to the cellulose. In the second step, newly obtained aldehyde groups were oxidized to create acetate groups Results: The kinetics of the sorption process showed that Be2+ uptake reached equilibrium in 3 minutes. The sorption isotherm was well fitted in the Langmuir model, and the maximum sorption capacity was 4.54mg/g. Moreover, the thermodynamic studies demonstrated that Be²⁺ sorption was spontaneous and exothermic. Furthermore, the prepared sorbent can be regenerated by using 0.1 M HCl or H2SO⁴ solutions. Conclusion: It is concluded that the removal of Be2+ is pH-dependent and it is favorable at high solution pH. The kinetics of the prepared sorbent were rapid and equilibrium attained in 3 minutes. The prepared sorbent can be regenerated with 0.1 M acid solution with > 99% efficiency.

Background: Rapid urbanization and industrialization have led to the depletion of water resources and the generation of an enormous amount of wastewater. One among them is the textile industry, which discharges a huge amount of dye wastewater into the aquatic environment. Methods: This study deals with adsorption of Remazol blue, Malachite green and Rhodamine B dyes into bio-char derived from Chlorella Vulgaris biomass cultivated from municipal wastewater. Column studies were performed to depict the industrial usage of bio-char for the treatment of a large quantity of wastewater. The effect of temperature, time, pH, dye concentration and adsorbent dosage on dye removal was studied in a batch process. Results: The best batch adsorption conditions are temperature (25°C), time (60min), pH (7), dye concentration (100ppm) and adsorbent dosage (1g) with ± 5% for all three dyes. Dye removal percentage of bio-char increased with increase in adsorbent dosage to 94.5%, 88.2% and 90.1% for Remazol blue, Malachite green and Rhodamine B dyes at 1g/L adsorbent dosage. Freundlich isotherm exhibited correlation coefficient (R2) values of 0.99, 0.98 and 0.99 for Remazol blue, Malachite green and Rhodamine B dyes, respectively. Kinetic studies revealed that all three dyes followed the pseudo first-order model. An increase in column bed height resulted in increased dye removal percentage since the increase in bed height resulted in an increase in bio-char quantity with more number of surface area Conclusion: From the study, it can be concluded that Bio-char was the economical and ecofriendly alternative adsorbent for the wastewater treatment process. Bio-char reusability study revealed that it could be used for 3-4 consecutive cycles.

Background: With the increasing population and decreased quality of drinking water, new materials and methods for the purification of water need to be developed. This study aims to present a solution from pollution by proposing the synthesis method of sodium lauryl sulphate (SLS)-supported thorium (IV) phosphate (ThP), its characterisation and disquisition of analytical applications by executing dual separations of calcium. Methods: SLS ThP was synthesised by the sol-gel method. The synthesised exchanger was characterised by physicochemical methods, such as powdered X-ray diffraction, scanning electron microscopy, thermo-gravimetric-differential thermal analysis, EDAX and Fourier transform-infrared study. Also, its competency towards the ion exchange processes and in analytical chemistry was verified. Results: The prominent characteristic of SLS-supported ThP was its high ion exchange capacity for sodium ions (3.10 meq/g), which is almost 2.5 times more than the exchange capacity of ThP, i.e., 1.3 meq/g. The material resulted in a fibrous sheet that is thermally and mechanically stable but poorly crystalline and shows selectivity towards Ca²⁺ and Hg²⁺ ions. Conclusion: The synthesised cation exchange material is thermally stable, showing drastically high exchange capacity and selectivity towards Hg²⁺ and Ca²⁺ metal ions, which might be because of the use of an anionic surfactant, SLS, while the synthesis of ThP plays a key role in enhancing the exchange capacity and adsorption of specific metals. Therefore, based on the results obtained, the above-said materials have applications in water purification processes and environmental pollution control where removal of Hg²⁺ and Ca²⁺ is essential.

Background: The presence of heavy metal contaminants such as chromium, lead, mercury, cadmium, arsenic, nickel, and copper has become a major issue for human health. Chromium is extremely toxic to living organisms as it acts as a carcinogen and mutagen. The high concentration of chromium may cause detrimental effects to human health in the long term. The mutagenic and carcinogenic properties, included Cr(VI) in the group “A” of human carcinogens. Cr(VI) can easily penetrate the cell wall and exert its noxious effect due to its mobility in the environment. Cr(VI) is nearly 100 times more toxic than Cr(III). Cr(VI) causes skin and stomach irritation or ulceration, damage to the liver, kidney ulceration, damage to nerve tissue, and long-term exposure above the maximum contaminated level even leads to death. Therefore, it is essential to remove chromium from wastewater prior to its final discharge into the environment. This study attempts to explore the mechanism by which chromium ions are adsorbed by these two ion exchange resins and will be extended further to investigate the uptake mechanism of other metal ions in future research. Methods: Equilibrium isotherms were obtained by reacting 20 mL of aqueous metal ion solution with different amounts of adsorbents in a shaker bath controlled at 25±0.5oC. The initial concentration of the metal ions in the aqueous solution was varied between 40-100 mg L-1. Equilibrium isotherms for the above metal ion were generated at pH 3, 4 and 5. The pH of the solution was varied between pH 3 to 5 using appropriate doses of the buffer. Preliminary runs exhibited that the adsorption equilibrium was achieved after 1–1.30 h of contact time for both the tested resins. The adsorbents used were DOWEX and AMB resins. For estimation of adsorption enthalpy, adsorption equilibrium experiments were performed at temperatures 30, 40 and 55oC. The amount of metal ion adsorbed per unit mass of the adsorbent (mg g-1) was calculated as q= VΔC/W, where ΔC is the change in solute concentration (mg L-1), V is the solution volume (L) and W is the weight of the adsorbent (g). Experiments on adsorption kinetics were performed in a stirred constant volume vessel. The liquid volume was 100 cm3 with 10g of adsorbent sample. The initial concentration of metal ion was 80 mg L-1 at 25±0.5oC. The aqueous phase concentration was examined at equal time intervals till equilibration. Results: The electrostatic interaction of Cr(VI) with the positively charged nitrogen atom of the functional groups and chelation of Cr(III) with the electron donor groups were the possible mechanistic pathways through which adsorption occurred on both the ion-exchange resins. Though electrostatic interaction was the predominant interaction in both the resins for the adsorption of anionic Cr(VI) species, but it was observed that the mechanism of Cr(VI) adsorption was not only “anionic adsorption” but also the complexation of the reduced Cr(III) with the ammonium group of the resins. Thus, “adsorption- coupled reduction” was the main mechanism for the uptake of chromium ions. Conclusion: The present work demonstrated that both resins could effectively adsorb Cr(VI) ions from an aqueous solution. More adsorption had taken place onto DOWEX compared to AMB. The adsorption characteristics of both the resins were studied under various equilibrium and thermodynamic conditions, which proposed the spontaneous nature of the process. The adsorption capacities of both resins were influenced by the pH of the medium and exhibited high adsorption performances at pH 3. The mechanism of adsorption onto the two resins studied here was anionic adsorption of Cr (VI) and chelation of Cr (III) ion. The Cr(III) ions might have formed because of the reduction of Cr(VI) by the electron donor atoms present in the resins and interacted with the adsorbent surface. FTIR spectra also supported the interaction of chromium ions with functional groups present in the resin structures. Thus chromium uptake by DOWEX and AMB resins was mainly governed by “adsorption- coupled reduction”. Desorption studies revealed that regeneration of both the ion-exchange resins is possible at basic pH and can be reused. However, the application of these two ionexchange resins using real effluent is under consideration.

Background: Removal of lead (II) ions from supply water using an inexpensive adsorbent is essential. It is recommended that low-cost adsorbents are developed to effectively remove lead (II) ions from aqueous solutions. The aim of the study was to develop and validate models for predicting the performance of carboxylated jute stick derived activated carbon (JSAC-COOH) in removing lead (II) ions from aqueous solution, which can assist the water supply authorities in supplying lead (II) free drinking water to the communities at a low-cost. Methods: Controlled laboratory experiments were conducted following the statistical “Design of Experiments” through varying the factors affecting the performance of JSAC-COOH in removing lead (II) ions. The performance of JSAC-COOH was investigated for different concentrations of lead (II) ions (range: 50 - 500 mg/L) at variable experimental conditions (temperature: 15°C and 27°C; pH: 4.0 and 7.0) and time (1, 10, 30 and 60 min). Several models (Linear and non-linear) were investigated and validated for predicting the concentrations of lead (II) ions in aqueous solution Results: The prepared JSAC-COOH had a surface area of 615.3 m2/g. In 60 min, up to 99.8% removal of lead (II) ions was achieved. Few models showed very good to excellent predictive capabilities with coefficients of determination in the range of 0.85–0.95. The model validation experiments showed the correlation coefficients in the range of 0.84 – 0.98. Conclusion: The models have the capabilities to reasonably predict the final concentrations of lead (II) ions, which can be used in controlling the effluent lead (II) ion concentrations. The proposed adsorbent is likely to be low-cost as it was developed using the commonly available agricultural by-product