A novel method for removal of Cr(VI) using polypyrrole magnetic nanocomposite in the presence of unsteady magnetic fields

Insights into properties, synthesis and emerging applications of polypyrrole-based composites, and future prospective: A review

Recent advancements in polymer science and engineering underscore the importance of creating sophisticated soft materials characterized by well-defined structures and adaptable properties to meet the demands of emerging applications. The primary objective of polymeric composite technology is to enhance the functional utility of materials for high-end purposes. Both the inherent qualities of the materials and the intricacies of the synthesis process play pivotal roles in advancing their properties and expanding their potential applications. Polypyrrole (PPy)-based composites, owing to their distinctive properties, hold great appeal for a variety of applications. Despite the limitations of PPy in its pure form, these constraints can be effectively overcome through hybridization with other materials. This comprehensive review thoroughly explores the existing literature on PPy and PPy-based composites, providing in-depth insights into their synthesis, properties, and applications. Special attention is given to the advantages of intrinsically conducting polymers (ICPs) and PPy in comparison to other ICPs. The impact of doping anions, additives, and oxidants on the properties of PPy is also thoroughly examined. By delving into these aspects, this overview aims to inspire researchers to delve into the realm of PPy-based composites, encouraging them to explore new avenues for flexible technology applications.

Adsorption potential of ionic liquid-modified ZnO nanoparticles for highly efficient removal of azo dye: detailed isotherms and kinetics

In this study, bare and ionic liquid-modified ZnO nanoparticles have been fabricated using microwave irradiation method. The fabricated nanoparticles were characterized by different techniques, viz. XRD, FT-IR, FESEM, and UV-Visible spectroscopy, and were explored as adsorbent for effective sequestration of azo dye (Brilliant Blue R-250) from aqueous media. Various factors affecting the adsorption efficiency of synthesized nanoparticles (bare/ionic liquid-modified) such as concentration of dye, pH of reaction media, dose of nanoparticles, and reaction time were thoroughly investigated with varying experimental conditions; on a magnetic stirrer and in a sonicator. The results exhibited a high adsorption efficiency of ionic liquid-modified nanoparticles for removal of dye as compared to the bare one. Also, an enhanced adsorption was observed via sonication in comparison with magnetic stirring. Different isotherms such as Langmuir, Freundlich, and Tempkin were elaborated. Evaluation of adsorption kinetics showed a linear pseudo-second-order equation for adsorption process. The exothermic and spontaneous nature of adsorption was further confirmed by thermodynamic investigations. As per the results obtained, it is suggested that the fabricated ionic liquid-modified ZnO nanoparticles could successfully remediate the toxic anionic dye from aqueous media. Hence, this system can be utilized for large-scale industrial applications.

Characterization and synthesis of new adsorbents with some natural waste materials for the purification of aqueous solutions

In this study, hexavalent chromium Removal from aqueous environments was investigated by using polyaniline composites with some natural waste materials. Batch experiments were used, and some parameters such as contact time, pH and adsorption isotherms were determined for the best composite with the highest removal efficiency. Scanning Electron Microscope (SEM), Fourier Transform Infrared (FTIR) spectroscopy, and X-ray Diffraction (XRD) were used to characterize the composites. According to the results, the polyaniline/walnut shell charcoal/PEG composite outperformed other composites and showed the highest chromium removal efficiency of 79.22%. Polyaniline/walnut shell charcoal/PEG has a larger specific surface area of 9.291 (m²/gr) which leads to an increase in its removal efficiency. For this composite, the highest removal efficiency was obtained at the pH = 2 and 30 min contact time. The maximum calculated adsorption capacity was 500 mg/g.

Column study using modified banana pseudo stem as adsorbent for removal of Pb (II)

Eco-friendly adsorbents such as banana pseudo stem play a fundamental role in the removal of heavy metal elements from the wastewater. Key water resources and chemical industries have been encountering difficulties in removing heavy metal elements using existing conventional methods. The lead-removal process is currently a challenging task for environmental scientists and engineers in terms of cost, effluent disposal, and safety concerns. Hence, this work demonstrates the adsorption of Pb (II) onto modified banana pseudo stem (MBPS) powder as a potential adsorbent to treat different effluents. A characterization of modified banana pseudo-stem powder was performed using scanning electron microscopy (SEM) and Fourier-transform infrared (FTIR) spectroscopy which confirms the material. Experiments carried out using a column process for the removal of lead (II) from an aqueous solution at a fixed concentration of 50 ppm, pH 6 and contact time 120 min. The BET surface area of MBPS was found to be 7.27 m²/g. The results showed that the column studies explain better performance for the removal of Pb (II) and the maximum removal was found to be 49% at lower flow rate (5 mL/min) of fixed initial concentration of 50 ppm.

Preparation of a novel metal-free polypyrrole-red phosphorus adsorbent for efficient removal of Cr(VI) from aqueous solution

The toxicity and carcinogenicity of Cr(VI) makes it a major threat to the health of animals and people. However, how to efficiently remove Cr(VI) still faces important challenges. In this study, a new metal-free polypyrrole-red phosphorus (PPy-RP) composite is successfully synthesized by in-situ oxidation polymerization for Cr(VI) removal from wastewater. The maximum adsorption capacity (q_m) of Cr(VI) on PPy-RP-1 is 513.2 mg/g when the pH value is 2, which is far superior to RP nanosheets (207.8 mg/g) and PPy (294.9 mg/g). The improved q_m can be ascribe to the good dispersion and increased specific surface area of PPy-RP adsorbent. Encouragingly, PPy-RP adsorbent still exhibits excellent stability after 7 cycles tests without a significant decline in removal efficiency, and remain above 81.4%. Based on the fittings of adsorption isotherms and kinetics, the process conforms to the pseudo-first-order kinetic model and the single-layer adsorption of the Langmuir model with an R² value of 0.98533. The adsorption process is chemical and monolayer. The experimental result demonstrates that the PPy-RP can efficient removal Cr(VI) by electrostatic attraction and complexation reaction (formation of N-Cr(VI) bond) through the PPy on the surface. The results of this study indicate that PPy-RP is a promising adsorbent to remove the Cr(IV).

A review of novel green adsorbents as a sustainable alternative for the remediation of chromium (VI) from water environments

The presence of heavy metal, chromium (VI), in water environments leads to various diseases in humans, such as cancer, lung tumors, and allergies. This review comparatively examines the use of several adsorbents, such as biosorbents, activated carbon, nanocomposites, and polyaniline (PANI), in terms of the operational parameters (initial chromium (VI) concentration (C_o), temperature (T), pH, contact time (t), and adsorbent dosage) to achieve the Langmuir's maximum adsorption capacity (q_m) for chromium (VI) adsorption. The study finds that the use of biosorbents (fruit bio-composite, fungus, leave, and oak bark char), activated carbons (HCl-treated dry fruit waste, polyethyleneimine (PEI) and potassium hydroxide (KOH) PEI-KOH alkali-treated rice waste-derived biochar, and KOH/hydrochloric acid (HCl) acid/base-treated commercial), iron-based nanocomposites, magnetic manganese-multiwalled carbon nanotubes nanocomposites, copper-based nanocomposites, graphene oxide functionalized amino acid, and PANI functionalized transition metal are effective in achieving high Langmuir's maximum adsorption capacity (q_m) for chromium (VI) adsorption, and that operational parameters such as initial concentration, temperature, pH, contact time, and adsorbent dosage significantly affect the Langmuir's maximum adsorption capacity (q_m). Magnetic graphene oxide functionalized amino acid showed the highest experimental and pseudo-second-order kinetic model equilibrium adsorption capacities. The iron oxide functionalized calcium carbonate (IO@CaCO₃) nanocomposites showed the highest heterogeneous adsorption capacity. Additionally, Syzygium cumini bark biosorbent is highly effective in treating tannery industrial wastewater with high levels of chromium (VI).

Fabrication of N-doping activated carbons from fish waste and sawdust for Acid Yellow 36 dye removal from an aquatic environment

Acid Yellow 36 (AY36) dye is a synthetic azo dye that is excessively used in various industries, causing hazardous environmental effects. The main target of this study is the preparation of self-N-doped porous activated carbon (NDAC) and the investigation in eliminating the AY36 dye from the water solution. The NDAC was prepared by mixing fish waste (60% protein content) which was considered a self-nitrogen dopant. A combination of Fish waste, sawdust, zinc chloride and urea with a mass ratio (5:5:5:1) was submitted to hydrothermal process at 180 °C for 5 h followed by pyrolysis for 1 h under N₂ stream at 600, 700, and 800 °C. Fabricated NDAC was qualified as an adsorbent for recovering AY36 dye from water using batch trials. The fabricated NDAC samples were characterized by FTIR, TGA, DTA, BET, BJH, MP, t-plot, SEM, EDX, and XRD methods. The results showed the successful formation of NDAC with nitrogen mass percentage content (4.21, 8.13 and 9.85%). The NDAC prepared at 800 °C had the largest nitrogen content (9.85%) and was labeled as NDAC800. This later had 727.34 m²/g, 167.11 cm³/g, and 1.97 nm for specific surface area, the monolayer volume and the mean pores diameter respectively. By being the more efficient adsorbent, NDAC800 was chosen to test AY36 dye removal. Therefore, it is selected to investigate the removal of AY36 dye from aqueous solution by varying important parameters such as solution pH, initial dye concentration, adsorbent dosage and contact time. The removal of AY36 dye by NDAC800 was pH-dependent, with the optimum pH value 1.5 giving 85.86% removal efficiency and 232.56 mg/g maximum adsorption capacity (Q_m). The kinetic data exhibited the best fit model with the pseudo-second-order (PSOM), while the equilibrium data fit well with the Langmuir (LIM) and Temkin (TIM). The mechanism of AY36 dye adsorption may be ascribed to the electrostatic contact between the dye and the available charged sites on NDAC800 surface. The prepared NDAC800 may be considered as an efficient, available, and eco-friendly adsorbent for AY36 dye adsorption from simulated water.

Application of MXene-based materials in Fenton-like systems for organic wastewater treatment: A review

Recently, Fenton-like systems have been widely explored and applied for the removal of organic matter from wastewater. Two-dimensional (2D) MXene-based materials exhibit excellent adsorption and catalysis capacity for organic pollutants removal, which has been reported widely. However, there is no summary on the application of MXene-based materials in Fenton-like systems for organic matter removal. In this review, four types of MXene-based materials were introduced, including 2D MXene, MXene/Metal complex, MXene/Metal oxide complex, and MXene/3D carbon material complex. In addition, the Fenton-like system usually consists of adsorption and degradation processes. The oxidation process might contain hydrogen peroxide (H₂O₂) or persulfate (PS) oxidants. This review summarizes the performance and mechanisms of organic pollutants adsorption and oxidants activation by MXene-based materials systematically. Finally, the existing problems and future research directions of MXene-based materials are proposed in Fenton-like wastewater treatment systems.

Turning waste into valuables: In situ deposition of polypyrrole on the obsolete mask for Cr(VI) removal and desalination

The global mask consumption has been exacerbated because of the coronavirus disease 2019 (COVID-19) pandemic. Simultaneously, the traditional mask disposal methods (incineration and landfill) have caused serious environmental pollution and waste of resources. Herein, a simple and green mass-production method has been proposed to recycle carbon protective mask (CPM) into the carbon protective mask/polydopamine/polypyrrole (CPM/PDA/PPy) composite by in situ polymerization of PPy. The CPM/PDA/PPy composite was used for the removal of Cr(VI) and salt ions to produce clean water. The synergistic effect of PPy and the CPM improved the removal capability of Cr(VI). The CPM/PDA/PPy composite provided high adsorption capacity (358.68 mg g^-1) and economic value (811.42 mg $^-1). Consequently, the CPM/PDA/PPy (cathode) was combined with MnO₂ (anode) for desalination in CDI cells, demonstrated excellent desalination capacity (26.65 mg g^-1) and ultrafast salt adsorption rate (6.96 mg g^-1 min^-1), which was higher than conventional CDI cells. Our work proposes a new low-carbon strategy to recycle discarded masks and demonstrates their utilization in Cr(VI) removal and seawater desalination.

Optimization of iron-enhanced anaerobic digestion of agro-wastes for biomethane production and phosphate release

In this study, the optimization of additives (polypyrrole magnetite nanocomposites (Ppy/Fe₃O₄) and antagonists (humic acid and arsenic oxide)) for simultaneous recovery of biomethane and phosphate release from enhanced anaerobic co-digestion of okra waste and pig manure was investigated. The pre-determined dosages of additives from our previous studies were used for the batch anaerobic digestion at different ratios under mesophilic conditions based on the two level-four factors central composite design (CCD) response surface methodology (RSM). After the anaerobic digestion processes, the biomethane yields were recorded and the digestates were characterized to determine the quantity of soluble phosphates. Both the independent variables and the responses were used to model and optimize the biogas yield and phosphate release conditions. The result showed that the maximum biomethane yield and P release were respectively 502.743 mLCH4/gVS and 168.674 mg/L at the optimum conditions of Ppy/Fe₃O₄ (20.0014 mg/L), HA (5.0018 mg/L), As (1.448 mg/L) and co-digestion (25.0001%). The response models predicted biomethane yield and P release to be 528.635 mLCH4/gVS and 164.405 mg/L respectively. All the response models were highly significant with appropriate goodness of fit and had prediction differences of 4.90% and 2.597% respectively for both biomethane yield and P release. Although both the accelerants and antagonists had influences on the anaerobic digestion processes by achieving enhanced biomethane production and P release, the influence of long exposure of anaerobic digestion processes to these additives on both responses is recommended for further investigation.

Potential of magnetic quinoa biosorbent composite and HNO3 treated biosorbent for effective sequestration of chromium (VI) from contaminated water

The present study aims to prepare novel quinoa biosorbent (QB), acid activated QB (QB/Acid) and its nanocomposite with magnetic nanoparticles (QB/MNPs) for batch scale Cr removal from contaminated water. The Cr adsorption was systematically studied at different pH (2-9), adsorbent dosage (1-3 g/L), initial concentration (25-200 mg/L), contact time (180 min) and competing ions in water. Maximum Cr adsorption was observed onto QB/MNPs (57.4 mg/L), followed by QB/Acid (46.35 mg/g) and QB (39.9 mg/g). The Cr removal by QB/MNPs was higher than QB/Acid and QB. Results revealed that the highest Cr removal was obtained at optimum pH 4, 25 mg/L, and 2 g/L dosage. The FTIR spectra displayed various functional groups on adsorbents surface serving as a potential scaffold to remove Cr from contaminated water. The equilibrium and kinetic Cr adsorption data best fitted with Freundlich and pseudo-second order models, respectively (R² ≥ 0.96). The QB/MNPs showed excellent reusability in five adsorption/desorption cycles (4.7% decline) with minor leaching of Fe (below threshold level). The coexisting ions in groundwater showed an inhibitory effect on Cr sequestration (5%) from water. The comparison of Cr adsorption by QB/MNPs and QB/Acid showed better potential for Cr sequestration than various previously explored adsorbents in the literature.

Simultaneous removal of heavy metals and dye from wastewater: modelling and experimental study

In this work, heavy metals were removed simultaneously using wheat bran as an adsorbent. For batch experiments, the Box-Behnken design of response surface methodology was used and the effect of dye on metal removal was analysed. It has been observed that the presence of dye has reduced the removal of each metal in the range of 100-20% with no appreciable reduction in dye adsorption. The optimum pH, temperature, and adsorbent dose were found to be 7.59, 33.23 °C, and 2.90 g/L, respectively, for 79.70% chromium, 99.9% cadmium and 87.27% copper removal. It was found that Langmuir isotherm fits well with the experimental data (RMSE value up to 0.033). The maximum adsorption capacity obtained for copper, chromium, cadmium and dye were 2.17 mg/g, 1.76 mg/g, 1.52 mg/g and 3.215 mg/g, respectively. The continuous study was performed for parameters, i.e. bed height (0.15-0.45 m), flow rate (5-15 mL/min) and initial metal concentration (100-500 mg/L). In continuous study, dye acted as an interfering species and as a result breakthrough and exhaustion time decreased. The modelling and simulation of continuous adsorption process were performed. A dynamic mathematical model was developed for continuous fixed bed adsorption column to compare the breakthrough curve with experimental results.

Synthesis, Characterization and Dye Removal Capability of Conducting Polypyrrole/Mn0.8Zn0.2Fe2O4/Graphite Oxide Ternary Composites

Herein, ternary composites from polypyrrole (PPy), Mn0.8Zn0.2Fe2O4 (MZF), and graphite oxide (GO) were prepared to remove acid red dye (AR1) from wastewater. MZF was synthesized using spent Zn–C batteries, acid leaching, and sucrose auto-combustion processes; GO was prepared via oxidation and exfoliation of graphite. The composites were prepared by adding MZF and GO during the in-situ polymerization of pyrrole. Different PPy/MZF/GO (PMG) composites were prepared by changing the weight ratios of the PPy, MZF, and GO. We investigated the prepared composites’ structural, magnetic, and electrical/dielectric properties. We evaluated different experimental conditions’ influences on dye removal performance, such as pH, dosage, dye concentration, temperature, and contact time. XRD, FT-IR, and magnetic properties indicated that PPy completely coated the other contents. The electrical/dielectric properties improved while increasing the GO ratio. The PMG at GO content 50 wt.% (PMG50) showed the most efficient ratio for better removing AR1 from wastewater.

Adsorption of Cr6+ ion using activated Pisum sativum peels-triethylenetetramine

The adsorption of Cr6+ ions from water-soluble solution onto activated pea peels (PPs) embellished with triethylenetetramine (TETA) was studied. The synthesized activated TETA-PP biosorbent was further characterized by SEM together with EDX, FTIR and BET to determine the morphology and elementary composition, functional groups (FGs) present and the biosorbent surface area. The confiscation of Cr6+ ions to activated TETA-PP biosorbent was observed to be pH-reliant, with optimum removal noticed at pH 1.6 (99%). Cr6+ ion adsorption to activated TETA-PP biosorbent was well defined using the Langmuir (LNR) and the pseudo-second-order (PSO) models, with a determined biosorption capacity of 312.50 mg/g. Also, it was found that the activated TETA-PP biosorbent can be restored up to six regeneration cycles for the sequestration of Cr6+ ions in this study. In comparison with other biosorbents, it was found that this biosorbent was a cost-effective and resourceful agro-waste for the Cr6+ ion confiscation. The possible mechanism of Cr6+ to the biosorbent was by electrostatic attraction following the surface protonation of the activated TETA-PP biosorbent sites.

Flexible and easy-handling pristine polypyrrole membranes with bayberry-like vesicle structure for enhanced Cr(VI) removal from aqueous solution

Polypyrrole has been extensively explored for Cr(VI) removal from wastewater towing to the advantages of superior performance, low cost, facile synthesis, and high environmental stability. However, the unsatisfactory adsorption capacity and complicated process of adsorbent separation from aqueous solutions remain a huge challenge, limiting its practical application. Herein, a flexible PPy membrane with bayberry-like vesicle structures (PPy-B) was prepared via template-assisted interfacial polymerization. It was found that sodium sulfosalicylate not only improved the flexibility and strength of the PPy-B membrane for easy-handling but also participated in the polymerization of PPy as a dopant to improve the specific surface area and doping level for increasing adsorption sites. Benefiting from these, the easy-handling PPy-B membrane exhibited a high adsorption capacity (586.90-682.50 mg/g at 298-318 K), a high reusability (five adsorption-desorption cycles), and a high ultimate adsorption capacity after adsorption-desorption cycles until membrane failure (1174.86 mg/g at 298 K). The proposed mechanisms of the enhanced Cr(VI) removal involve electrostatic adsorption, reduction, and ion exchange. This flexible PPy membrane therefore shows attractive advantages in wastewater treatment.

Fabrication of a Novel (PVDF/MWCNT/Polypyrrole) Antifouling High Flux Ultrafiltration Membrane for Crude Oil Wastewater Treatment

The present work deals with the fabrication of novel poly(vinylidene fluoride) (PVDF)/Multi-wall Carbon Nanotubes (MWCNT)/Polypyrrole (PPy) ultrafiltration membrane by phase inversion technique for the removal of crude oil from refinery wastewater. In situ polymerization of pyrrole with different concentrations of MWCNT ranging from 0.025 wt.% to 0.3 wt.% in PVDF prepared solutions. Measurement of permeability, porosity, contact angle, tensile strength, zeta potential, rejection studies and morphological characterization by scanning electron microscopy (SEM) were conducted. The results showed that membrane with (0.05% MWCNT) concentration had the highest permeability flux (850 LMH/bar), about 17 folds improvement of permeability compared to pristine PVDF membrane. Moreover, membrane rejection of crude oil reached about 99.9%. The excellent performance of this nanocomposite membrane suggests that novel PVDF modification with polypyrrole had a considerable effect on permeability with high potential for use in the treatment of oily wastewater in the refinery industry.

Experimental Insights into Mesoporous Polyaniline-Based Nanocomposites for Anionic and Cationic Dye Removal

This work presents the preparation of inorganic-organic hybrid nanocomposites, namely three-dimensional polyaniline (Pani)/activated silica gel (ASG) (3D Pani@ASG), their characterization, and in removing application as a potential adsorbent for cationic brilliant green (BG), crystal violet (CV), and anionic Congo red (CR), and methyl orange (MO) dyes. Pani@ASG nanocomposites have been prepared by the in situ polymerization method and characterized using various techniques such as Fourier transform infrared (FTIR), X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM) with selected area electron diffraction, thermogravimetric analysis with derivative thermogravimetry, zeta potential analyses, and Brunauer-Emmett-Teller (BET). The scanning electron microscopy (SEM) study confirms the average particle size of the Pani@ASG nanocomposite is in the range of 5 nm. FESEM, TEM, FTIR, and XRD analysis proved the successful decoration of ASG over Pani. The BET result of Pani@ASG shows a mesoporous nature with a pore diameter of less than 3 nm and a surface area of 423.90 m² g^-1. Both SEM and TEM analyses show the proportional distribution of ASG over Pani's surface. The adsorption trend of BG and MO on the studied materials at pH 7 was found as follows: Pani@ASG > Pani > ASG. The highest sorption capacities of MO and BG on Pani@ASG were 161.29 and 136.98 mg/g (T = 298.15 K, and Pani@ASG dose: 0.04 g for MO and 0.06 g for BG), which were greater compared with bare Pani and bare ASG, respectively. The interaction mechanism behind the adsorption of BG and MO dyes onto the Pani@ASG nanocomposite includes electrostatic interaction, π-π interaction, and hydrogen bonding. The mechanistic pathway and the interactions between the targeted dyes and Pani@ASG were further studied using adsorption isotherm, adsorption kinetics, and thermodynamics.

Granulation of Nickel-Aluminum-Zirconium Complex Hydroxide Using Colloidal Silica for Adsorption of Chromium(VI) Ions from the Liquid Phase

We combined a nickel-aluminum-zirconium complex hydroxide (NAZ) with colloidal silica as a binder to prepare a granulated agent for adsorbing heavy metals from aqueous media. Three samples with different particle diameters were prepared to evaluate the effects on the properties: small (NAZ-S), medium (NAZ-M), and large (NAZ-L). We confirmed the granulation of the prepared samples at a binder content of 25%. NAZ-S had the largest specific surface area and number of hydroxyl groups, followed by NAZ-M and then NAZ-L. Regarding the adsorption capacity, NAZ-S adsorbed the most chromium(VI) ions followed by NAZ-M and then NAZ-L. The binding energy of Cr(2p) at 575-577 eV was detected after adsorption, and the effects of the temperature, contact time, and pH on the adsorption of chromium(VI) ions were evaluated. We identified the following adsorption mechanism: ion exchange with sulfate ions in the interlayer region of the NAZ samples. Finally, the chromium(VI) ions adsorbed by the NAZ samples were easily desorbed using a desorption solution. The results showed that NAZ offers great potential for the removal of chromium(VI) ions from aqueous solutions.

A Facile Review on the Sorption of Heavy Metals and Dyes Using Bionanocomposites

Presently, hazardous metal and dye removal from wastewater is one of the major areas of research focus. For the elimination of these contaminants, many approaches have been devised and applied. However, the accomplishment of various water treatment processes has largely depended on the medium utilized and the associated problem with the leaching of harmful compounds into the water process with most commercial and chemically manufactured materials for water treatment processes. Hence, this study is aimed at reviewing existing studies on the sorption of heavy metals (HMs) and dyes using bionanocomposites (BNCs). The key focus of this review is on the development of eco-friendly, effective, and appropriate nanoadsorbents that could accomplish superior and enhanced contaminant sequestration using BNCs owing to their biodegradability, biocompatible, environmentally friendly, and not posing as secondary waste to the environment. The sorption of most pollutants was observed to be pH, sorbent dosage, and initial contaminant concentration-dependent, with most contaminants’ elimination taking place in the pH range of 2-10. The sorption process of HMs and dyes to various BNCs was superlatively depicted utilizing the Langmuir (LNR) and Freundlich (FL) as well as the pseudo-second-order (PSO) models, suggestive of the sorption process of a monolayer and multilayer and the chemisorption process, the rate-limiting stage in surface sorption. The established sorption capacities for the reviewed sorption process for various contaminants ranged from 1.47 to 740.97 mg/g. Future prospective for the treatment and remediation of contaminated water using BNCs was also discussed.

Polypyrrole-based adsorbents for Cr(VI) ions remediation from aqueous solution: a review

Anthropogenic activities are principally responsible for the manifestation of toxic and carcinogenic hexavalent chromium (Cr(VI)) triggering water pollution that threatens the environment and human health. The World Health Organisation (WHO) restricts Cr(VI) ion concentration to 0.1 and 0.05 mg/L in inland surface water and drinking water, respectively. The available technologies for Cr(VI) ion removal from water were highlighted with an emphasis on the adsorption technology. Furthermore, the characteristics of several polypyrrole-based adsorbents were scrutinized including amino-containing compounds, biosorbents, graphene/graphene oxide, clay materials and many other additives with reported effective Cr(VI) ion uptake. This efficiency in Cr(VI) ions adsorption is attributed to enhanced redox properties, increased number of functional groups as well as the synergistic behaviour of the materials making up the composites. The Langmuir isotherm best described the adsorption processes with maximum adsorption capacities ranging from 3.40-961.50 mg/g. The regeneration of Cr(VI) ion-laden adsorbents was studied. Ion exchange, electrostatic attractions, complexation, chelation reactions with protonated sites and reduction were the mechanisms of adsorption. Nevertheless, there are limited details on comprehensive adsorbent regeneration studies to prolong robustness in adsorption-desorption cycles and utilization of the Cr(VI) ion-laden adsorbent in other areas of research to limit the threat of secondary pollution.

Fluoride ions sorption using functionalized magnetic metal oxides nanocomposites: a review

Fluoride is an anionic pollutant found superfluous in surface or groundwater as a result of anthropogenic actions from improper disposal of industrial effluents. In drinking water, superfluous fluoride has been revealed to trigger severe health problems in humans. Hence, developing a comprehensive wastewater decontamination process for the effective management and preservation of water contaminated with fluoride is desirable, as clean water demand is anticipated to intensify considerably over the upcoming years. In this regard, there have been increased efforts by researchers to create novel magnetic metal oxide nanocomposites which are functionalized for the remediation of wastewater owing to their biocompatibility, cost-effectiveness, relative ease to recover and reuse, non-noxiousness, and ease to separate from solutions using a magnetic field. This review makes an all-inclusive effort to assess the effects of experimental factors on the sorption of fluoride employing magnetic metal oxide nanosorbents. The removal efficiency of fluoride ions onto magnetic metal oxides nanocomposites were largely influenced by the solution pH and ions co-existing with fluoride. Overall, it was noticed from the reviewed researches that the maximum sorption capacity using various metal oxides for fluoride sorption was in the order of aluminium oxides >cerium oxides > iron oxides > magnesium oxides> titanium oxides, and most sorption of fluoride ions was inhibited by the existence of phosphate trailed by sulphate. The mechanism of fluoride sorption onto various sorbents was due to ion exchange, electrostatic attraction, and complexation mechanism.

Preparation of MES@Fe3O4@SiO2-PPy magnetic microspheres for the highly efficient removal of Cr(vi)

A novel magnetic adsorbent, PPy-modified silica-coated magnetic MES organic–inorganic composite (MFSP), with high dispersibility, abundant adsorption sites, and magnetic separation was prepared successfully for the adsorption or reduction of Cr(vi).

Enhanced adsorption performance of alginate/MXene/CoFe2O4 for antibiotic and heavy metal under rotating magnetic field

Improving the adsorption performance with simple and strong applicability has always been a research hotspot in water treatment. This study introduces sodium alginate/MXene/CoFe₂O₄ (SA/MX/CFO) as functional composite materials by sodium alginate cross-linking and as adsorbents in the removal of contaminations with an external magnetic field (MF). SA/MX/CFO beads exhibited excellent mechanical properties, with fracture stress of 1.64 MPa at 73.4%, and an elastic modulus of 2.23 MPa. The isotherm fitting chose Cu²⁺ and CIP as the model pollutants, the isotherm fitting shows that the adsorption capacity of CIP is significantly improved by 24.2%.The magnetic effect of the adsorption capacity of Cu²⁺ is not obvious, which indicated the selectivity for adsorption; however, the adsorption rates of CIP and Cu²⁺ are greatly improved by 359.76% and 371% respectively. Promoting materials transfer rate, changing of hydrogen bond, and surface functional group reactivity is the key to determine the adsorption enhancement with a rotating magnetic field (RMF). The combination of the external magnetic field and the inherent magnetic properties of the adsorbent can adjust the adsorption process and the selectivity of pollutants. It also provides an innovative and practical method for MF to remediate contaminants in the magnetically enhanced adsorption system.

Malachite Green Removal by Activated Potassium Hydroxide Clove Leaf Agrowaste Biosorbent: Characterization, Kinetic, Isotherm, and Thermodynamic Studies

Although several approaches have been explored for the removal of dyes and other toxic materials from water as well as the entire environment, notwithstanding, researchers/scientists are still pursuing novel, low-cost, and eco-friendly biosorbents for the effective removal of such contaminants. Herein, clove leaves (CL) were utilized as a biosorbent for the sequestration of malachite green (MG) from a water-soluble solution. The CL was subsequently activated using potassium hydroxide (KOH) and characterized using the FTIR and FESEM to determine the functional groups on the activated clove leaves (CL-KOH) and the morphology of the adsorbent. The adsorption of MG was observed to be relatively dependent on the dosage of sorbent utilized, initial MG concentration, and sorption process contact time. The adsorption process of MG to CL was ideally described using the Dubinin–Radushkevich and Elovich models with the determination of maximum sorption capacity of approximately 131.6 mg·g-1. Furthermore, the thermodynamic parameters calculated showed that the adsorption of MG to the adsorbent was exothermic with the process involving physical sorption as well as chemical sorption processes with negligible adsorption energy. In conclusion, the study has revealed that the CL is a cost-effective biosorbent with high adsorption efficiency for the sequestration of MG from a water-soluble solution and can be recycled for further usage.

Facile synthesis and characterization of polypyrrole - iron oxide - seaweed (PPy-Fe3O4-SW) nanocomposite and its exploration for adsorptive removal of Pb(II) from heavy metal bearing water

Lead is a widely used heavy metal which is highly toxic to kidney, nervous system and reproductive system. A special featured polypyrrole based adsorbent, with admirable salinity confrontation, environmental stability and reusability, was engaged to remove lead ions from aqueous solution. The advantages of using polypyrrole based adsorbent for heavy metal removal are: ease of synthesis, biocompatibility and high metal selectivity. In this study, polypyrrole - iron oxide - seaweed nanocomposite was proposed to remove lead ions from aqueous solution. A new method was adopted for the synthesis of polypyrrole - iron oxide - seaweed nanocomposite. The nanocomposite was prepared within a short time using ultra-assisted polymerization technique. The synthesized nanocomposite adsorbent was characterized using FTIR, SEM, TEM, EDS, XRD, XPS and zeta potential analysis. The adsorption capability of polypyrrole - iron oxide - seaweed nanocomposite towards lead was explored. The influence of pH, contact time, adsorbent dosage, metal ion concentration and recyclability were investigated. The optimum condition of these parameters was found to be: pH- 5, temperature - 40 °C, initial concentration - 100 mg/L and contact time - 20 min and the results showed that the hybrid composite adsorbed 97.25% Pb (II). Different isotherms such as Langmuir, Freundlich, Temkin and D-R models were also studied for the adsorption of Pb ions. The kinetics of the adsorption process was examined by I order, II order and intra particle diffusion kinetic models. The mechanism of lead adsorption onto the nanocomposite was also explored.

Application of magnetic fields to wastewater treatment and its mechanisms: A review

Magnetic field (MF) has been applied widely and successfully as an efficient, low-cost and easy-to-use technique to enhance wastewater treatment (WWT) performance. Although the effects of MF on WWT were revealed and summarized by some works, they are still mysterious and complex. This review summarizes the application of MF in magnetic adsorption-separation of heavy metals and dyes, treatment of domestic wastewater and photo-magnetic coupling technology. Furthermore, the mechanisms of MF-enhanced WWT are critically elaborated from the perspective of magnetic physicochemical and biological effects, such as magnetoresistance, Lorentz force, and intracellular radical pair mechanism. At last, the challenges and opportunities for MF application in WWT are discussed. For overcoming the limitations and taking advantages of MFs in WWT, fundamental research of the mechanisms of the application of MFs should be carried out in the future.

Magnesium ferrite-reinforced polypyrrole hybrids as an effective adsorbent for the removal of toxic ions from aqueous solutions: Preparation, characterization, and adsorption experiments

Contaminated waters with high contents of toxic anions are detrimental to the human health and wildlife. Thus, the quality of drinking water should be carefully monitored. Adsorption technique has been determined to be a reasonable strategy out of several methods used to remove toxic anions from water. Novel MgFe₂O₄-reinforced polypyrrole (Ppy@x%MgFe₂O₄) (x = 1%, 2%, and 5% of MgFe₂O₄) hybrids were synthesized from a pyrrole monomer and MgFe₂O₄ using a simple chemical oxidation method. The fabricated hybrids were studied for their capability to remove PO₄^3-, NO₃^-, and Cr(VI) from aqueous solutions. The results showed that PO₄^3-, NO₃^-, and Cr(VI) removal was highly pH-dependent. The adsorption isotherms of hybrids were fitted well by the Langmuir model, with the maximum adsorption efficiency of 116.90, 76.14, and 138.60 mg/g for PO₄^3-, NO₃^-, and Cr(VI), respectively. In addition, the above-mentioned toxic anions could be efficiently desorbed from spent Ppy@x%MgFe₂O₄ using a 0.1 M NaOH solution, and the hybrids exhibited good regenerability. The prepared materials are promising candidates for PO₄^3-, NO₃^-, and Cr(VI) removal and exhibit high adsorption efficiency, rapid adsorption-desorption behavior, and appropriate recovery from the aqueous medium under external magnetic field.

Effect of hexavalent chromium on the environment and removal techniques: A review

Despite the importance of chromium (Cr) in most anthropogenic activities, the subsequent environmental adulteration is now a source of major concern. Cr occurs in numerous oxidation states, with the furthermost stable and frequently occur states being Cr(0), Cr(III) and Cr(VI). Cr(0) and Cr(III) are vital trace elements while Cr(VI) is dispensable and noxious to living organisms. Predominantly in plants, Cr at low concentrations of about 0.05-1 mg/L assist to boost growth as well as increase productivity. However, accumulation of Cr could represent a potential threat to living organisms. Cr absorption, displacement and accretion depend on its speciation, which also determines its toxicity which is often diverse. Indications of its toxicity include; reduction of seed germination, retardation of growth, reduction of yield, inhibition of enzymatic activities, weakening of photosynthesis, nutrient, oxidative disparities and genetic mutation in plants as well as several injurious diseases in animals and humans. In this study, we have presented a comprehensive review as well as an informative account of the influence of Cr on the environment drawn from researches carried out over the years following an analytical approach. Uniquely, this work presents a review of the effects and remediation of Cr from soil and wastewater drawn from several evidence and meta-data-based articles and other publications. Accordingly, the write-up is intended to appeal to the consciousness of the general public that the significance of Cr notwithstanding, its environmental toxicity should not be taken for granted.

Effective immobilization of hexavalent chromium from drinking water by nano-FeOOH coating activated carbon: Adsorption and reduction

In this study, nano α-FeOOH (nFeOOH, 100-500 nm) was coated onto activated carbon (nFeOOH@AC) through a dipping means for enhanced Cr(VI) immobilization from drinking water. The nFeOOH@AC significantly improved the Cr(VI) removal from 19.9% (AC control) to 93.4%. XPS spectra and chromium speciation demonstrated that about 90% of adsorbed Cr(VI) was converted to Cr(III) by the nFeOOH@AC, accompanying with a reduction-oxidation of Fe³⁺/Fe²⁺ in the nFeOOH matrix due to electrons delivering between AC and surface-bound Cr(VI). The resultant Cr(III) subsequently reacted with Fe(III) to generate stable (Cr_χFe_1-χ)(OH)₃ precipitates, leading to a much lower Cr(III) release of 7.5% back to solution by the nFeOOH@AC as compared to the AC control of 33.8%, indicating that the nFeOOH@AC had a prospective potential for Cr(VI) immobilization and decreased Cr residue in treated drinking water. Results from column experiment also showed that the nFeOOH@AC afforded a 3.5 times higher capacity for Cr(VI) immobilization and a 3.4 times longer life-span than the pristine AC. Besides, Cr(VI) immobilization by the nFeOOH@AC was a pH-dependent process and the adsorbed Cr on the nFeOOH@AC could be readily desorbed with acetic acid. The disabled nFeOOH@AC could be refreshed by recoating nFeOOH particles with the above dipping method after stripping all the iron oxides with hydrochloric acid. This study demonstrated that nFeOOH coating is an efficient approach to enhance Cr(VI) elimination by AC during drinking water treatments.

Efficient removal of hexavalent chromium from electroplating wastewater using polypyrrole coated on cellulose sulfate fibers

In this study, cellulose sulfate was synthesized through sulfonation of cotton, and polypyrrole was coated on the surface of fibers. Then, the optimum ratio of pyrrole to cellulose sulfate was evaluated, and the physical, chemical, and morphological properties of the composite were assessed by using FESEM, EDS, FTIR, BET, and TGA analysis. Furthermore, adsorption of hexavalent chromium using the composite adsorbent was studied by the results of designed experiments with the Box-Behnken technique to assess the effect of pH, contact time, adsorbent dose and the initial concentration of hexavalent chromium and optimize the adsorption process. The removal percentage was 99.9% under the optimum conditions (adsorbent dose, 4 g L-1; initial concentration of Cr(VI), 200 mg L-1; pH value, 2; contact time, 200 min). The results of adsorption isotherms illustrated that the adsorption process followed Redlich-Peterson, Freundlich, Radke-Prausnitz, and UT models, and the calculated maximum adsorption capacity by the Langmuir model was 198 mg g-1. Based on the kinetic and thermodynamic studies, the adsorption process followed the intraparticle diffusion model and showed the endothermic and spontaneous adsorption with an increase in entropy on the adsorbent surface. The presence of copper, nickel and zinc cations had no adverse effect on the removal percentage of hexavalent chromium significantly. The adsorbent was reused successfully in four sequential treatments. Consequently, the synthesized adsorbent is efficient due to the high efficiency of hexavalent chromium removal percentage from electroplating effluent (99.87%).

Efficient Removal of Cr(VI) Ions by a Novel Magnetic 4-Vinyl Pyridine Grafted Ni3Si2O5(OH)4 Multiwalled Nanotube

The contamination of water systems by heavy metals greatly threatens human health and ecological safety. An efficient adsorbent is critical for the removal of these contaminants. In this work, magnetic Ni3Si2O5(OH)4 nanotubes (NTs) have been synthesized via in situ hydrothermal reduction and further functionalized by grafting poly(4-vinyl pyridine) (P4VP) brushes on its surface via atom transfer radical polymerization. Characterizations by Fourier transform infrared, X-ray diffraction, thermogravimetric analysis, transmission electron microscopy, and X-ray photoelectron spectroscopy proved that P4VP was successfully grafted on the surface of magnetic Ni3Si2O5(OH)4 NTs. The resultant Ni3Si2O5(OH)4-g-P4VP NTs are efficient nanosorbents for removing Cr(VI) anions from water. The Cr(VI) adsorption capacity of Ni3Si2O5(OH)4-g-P4VP NTs reaches 1.49 mmol/g at a pH of 3. The pseudo-second-order kinetic model and the Freundlich isothermal model are suitable to describe the adsorption process. The analysis using Weber-Morris and Boyd models indicates that both intraparticle diffusion and external film diffusion affect the Cr(VI) adsorption process. The adsorption enthalpy is estimated to be 18.37 kJ/mol. More than 90% of the Cr(VI) adsorption capacity of the Ni3Si2O5(OH)4-g-P4VP NTs remains after eight adsorption and desorption cycles.

Multifunctional Magnetic Oxide Nanoparticle (MNP) Core-Shell: Review of Synthesis, Structural Studies and Application for Wastewater Treatment

The demand for water is predicted to increase significantly over the coming decades; thus, there is a need to develop an inclusive wastewater decontaminator for the effective management and conservation of water. Magnetic oxide nanocomposites have great potentials as global and novel remediators for wastewater treatment, with robust environmental and economic gains. Environment-responsive nanocomposites would offer wide flexibility to harvest and utilize massive untapped natural energy sources to drive a green economy in tandem with the United Nations Sustainable Development Goals. Recent attempts to engineer smart magnetic oxide nanocomposites for wastewater treatment has been reported by several researchers. However, the magnetic properties of superparamagnetic nanocomposite materials and their adsorption properties nexus as fundamental to the design of recyclable nanomaterials are desirable for industrial application. The potentials of facile magnetic recovery, ease of functionalization, reusability, solar responsiveness, biocompatibility and ergonomic design promote the application of magnetic oxide nanocomposites in wastewater treatment. The review makes a holistic attempt to explore magnetic oxide nanocomposites for wastewater treatment; futuristic smart magnetic oxides as an elixir to global water scarcity is expounded. Desirable adsorption parameters and properties of magnetic oxides nanocomposites are explored while considering their fate in biological and environmental media.