Magnetic arginine-functionalized polypyrrole with improved and selective chromium(VI) ions removal from water

Sulfhydryl-Functionalized Amino Group Polymer Microcomposites toward Efficient Adsorption of Aqueous Cr(VI), As(III), Cd(II), and Pb(II)

The development of efficient adsorbents for heavy metal pollution, especially five toxic heavy metals, has attracted great research interest. Polymer-based adsorbents have aroused research value for their abundant functional groups and high porosity to the ability to capture metal ions. We designed a sulfhydryl-functionalized polymer microcomposite to take up Cr(VI), As(III), Cd(II), and Pb(II). The adsorption capacity achieved was 64.2 mg g-1 for Cr(VI), 44.9 mg g-1 for As(III), 35.5 mg g-1 for Cd(II), and 18.2 mg g-1 for Pb(II). Langmuir and Sips isotherm model is dominant for As(III), Cd(II), and Pb(II) adsorption. Pseudo-second-order kinetic models can better describe the adsorption behavior of Cr(VI), implying that chemisorption is accompanied by Cr(VI) adsorption. Cr(VI) simultaneous reduction to Cr(III) through the benzenoid amine oxidate pathway was the dominant mechanism, precipitation for Cd(II) adsorption was convinced, and chelation between As(III)/Pb(II) and─SH group and complexation between Pb(II) and C═O or benzene hydroxyl were a plausible mechanism for As(III) and Pb(II) adsorption.

Efficient, fast, simple, and eco-friendly methods for separation of toxic chromium(VI) ions based on ion exchangers and polymer materials impregnated with Cyphos IL 101, Cyphos IL 104, or D2EHPA

In this study, we present the results of the first comparison of the elimination of toxic Cr(VI) ions, which are hazardous contamination of the environment, from aqueous solutions using ion exchangers (IEs) and polymer materials (PMs) impregnated with D2EHPA or ionic liquids (Cyphos IL 101 and Cyphos IL 104). Sorption of Cr(VI) ions and desorption from the formulated sorption materials were carried out. In comparison, classical solvent extraction was accomplished. Fourier transform infrared-attenuated total reflectance spectroscopy (FTIR-ATR), scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS), and atomic force microscopy (AFM) have been used for characterization of the structure of developed IEs and PMs. The highest efficiency of adsorption of Cr(VI) ions was obtained using PMs with ionic liquids (>82%). Desorption from these materials were also very efficient (>75%). On the contrary, the application of IEs allowed for obtaining the best results of both, sorption and desorption processes when using D2EHPA (75% and 72%, respectively). The application of PMs and IEs is part of the green chemistry, and the conducted elimination of chromium(VI) ions using developed materials allows for the conclusion that they can potentially be used on a larger scale, e.g., for the treatment of industrial wastewater rich in Cr(VI) ions.

PANI/MCM-41 adsorption for removal of Cr(VI) ions and its application in enhancing electrokinetic remediation of Cr(VI)-contaminated soil

In this study, a polyaniline/mesoporous silica (PANI/MCM-41) composite material that can be used as a filler for permeable reactive barrier (PRB) was prepared by in situ polymerization. Firstly, the adsorption capacity of PANI/MCM-41 on Cr (VI) in solution was investigated. The results show that the prepared PANI/MCM-41 exhibits a significant Cr (VI) adsorption capacity (~ 340 mg/g), and the adsorption process is more accurately described by the Langmuir isotherm and pseudo-second-order kinetic model. The thermodynamic functions evidenced that the Cr(VI) adsorption was an endothermic spontaneous process. In addition, adsorption-desorption cycle experiments proved the excellent reusability of the material. Subsequently, the material was utilized as a filler in the PRB for the remediation of Cr(VI)-contaminated soil using electrokinetic-permeable reactive barrier (EK-PRB) technology. The results show that compared with traditional electrokinetic remediation, the use of PANI/MCM-41 as an active filler can enlarge the current during remediation and enhance the conductivity of soil, which increases the removal rates of total Cr and Cr(VI) in soil (17.4% and 10.2%).

Magnetic Polypyrrole-Gelatin-Barium Ferrite Cryogel as an Adsorbent for Chromium (VI) Removal

Polypyrrole-gelatin aerogels, containing magnetic barium ferrite (BaFe) particles, (PPy-G-BaFe) were synthesized by oxidative cryopolymerization and used as adsorbents for the removal of Cr(VI) from aqueous media. The removal was performed at pH 4, which was shown to be the optimal value, due to HCrO4- being the dominant species in these conditions and its more favorable adsorption and reduction compared to CrO42-, present at pH > 4. It was found that the presence of magnetic BaFe particles had no effect on the adsorption performance of PPy aerogels in terms of capacity and kinetics, which was attributed to its relatively low content in the composite. After the adsorption, the presence of chromium in the composites was confirmed by EDX and its electrostatic interaction with the adsorbent was pointed at by vibrational spectroscopy, corresponding to the accepted adsorption mechanism. The adsorption kinetics followed the pseudo-second-order model pointing at chemisorption being the rate-limiting step. The adsorption isotherm data was best fitting with the Temkin model. The maximum adsorption capacity, calculated using the Langmuir model, was 255.8 mg g-1 (the maximum experimental value was 161.6 mg g-1). Additionally, the possibility of Cr(VI) adsorption in the presence of Cl-, Br-, NO3- and SO42- as interfering ions was shown.

Coal Fly Ash Decorated with Graphene and Polyaniline Nanocomposites for Effective Adsorption of Hexavalent Chromium and Its Reuse for Photocatalysis

Coal fly ash was functionalized and modified with graphene oxide and polyaniline (CFA/GO/PANI nanocomposite) through hydrothermal synthesis, which was used for remediation of hexavalent chromium (Cr(VI)) ions. Batch adsorption experiments were carried out to investigate the effects of adsorbent dosage, pH, and contact time on the removal of Cr(VI). The ideal pH for this work was 2, and it was used for all other studies. The Cr(VI)-loaded spent adsorbent CFA/GO/PANI + Cr(VI) was reused as a photocatalyst for the degradation of bisphenol A (BPA). The CFA/GO/PANI nanocomposite removed Cr(VI) ions rapidly. The adsorption process was best described by pseudo-second-order kinetics and the Freundlich isotherm model. The CFA/GO/PANI nanocomposite demonstrated a high adsorption capacity of 124.72 mg/g for Cr(VI) removal. In addition, the Cr(VI)-loaded spent adsorbent played a significant role in the photocatalytic degradation of BPA with 86% degradation. The reuse of the Cr(VI)-loaded spent adsorbent as a photocatalyst presents a new solution for the reduction of secondary waste from the adsorption process.

A controllably fabricated polypyrrole nanorods network by doping a tetra-β-carboxylate cobalt phthalocyanine tetrasodium salt for enhanced ammonia sensing at room temperature

The morphology adjustment and functional doping optimization of polypyrrole (PPy) are of great significance in improving its gas sensing performance. Here, the PPy-0.5TcCoPc nanorods with a uniform dispersed 3-D network were prepared using one-step in situ polymerization using the electrostatic interaction between dopant counterion substituents in tetra-β-carboxylate cobalt phthalocyanine tetrasodium salt (TcCoPcTs) with larger space structure and pyrrole (Py) molecules, in which TcCoPcTs is not only used as a dopant molecule crosslinking PPy chains to obtain a 3-D network, thus improving the conductivity, but also as a sensor accelerator to improve the gas-sensing performance. The resulting PPy-TcCoPc hybrid exhibits superior NH3-sensing properties than PPy and tetra-β-carboxylate cobalt phthalocyanine (TcCoPc) under the same test conditions, especially the PPy-0.5TcCoPc sensor shows ultrafast response/recovery time to 50 ppm NH3 (8.1 s/370.8 s), low detection limit of 8.1 ppb and excellent gas selectivity at room temperature (20 °C). Besides, the PPy-0.5TcCoPc sensor also maintains superior response (49.3% to 50 ppm NH3), humidity resistance and conspicuous stability over 45 days. The excellent NH3-sensing performance of the PPy-0.5TcCoPc hybrid arises from the excellent gas selectivity of TcCoPc, the remarkable response mechanism between PPy and NH3, the high electrical conductivity, abundant active sites and good electron transport ability of the unique 3-D network with large specific surface area. The morphology regulation and functional doping optimization strategy of TcCoPcTs doped PPy broaden the research direction of ideal gas sensor materials.

Recent developments of polysaccharide based superabsorbent nanocomposite for organic dye contamination removal from wastewater - A review

One of the main problems with water pollution is dye contamination of rivers, industrial effluents, and water sources. It has endangered the world's sources of drinking water. Several remediation strategies have been carefully developed and tested to minimize this ominous picture. Due to their appealing practical and financial benefits, adsorption methods in particular are often listed as one of the most popular solutions to remediate dye-contaminated water. Biopolymer-based hydrogel nanocomposites are a cutting-edge class of materials with a wide range of applications that are effective in removing organic dyes from the environment. Since the incorporation of various materials into hydrogel matrices generated composite materials with distinct characteristics, these unique materials were often alluded to as ideal adsorbents. The fundamental emphasis of the conceptual and critical review of the literature in this research is the significant potential of hydrogel nanocomposites (HNCs) to remediate dye-contaminated water (especially for articles from the previous five years). The review also provides knowledge for the development of biopolymer-based HNCs, prospects, and opportunities for future research. It is also focused on optimum conditions for dye adsorption processes along with their adsorption kinetics and isotherm models. In summary, the information gained in this review research may contribute to a strengthened scientific rationale for the practical and efficient application of these novel adsorbent materials.

Kinetic and Isothermal Investigations on the Use of Low Cost Coconut Fiber-Polyaniline Composites for the Removal of Chromium from Wastewater

Pollution due to various heavy metals is increasing at an alarming rate. Removal of hexavalent chromium from the environment is a significant and challenging issue due to its toxic effects on the ecosystem. Development of a low-cost adsorbent with better adsorption efficiency is presently required. In this study, waste coconut fibers (CF) were used to prepare its composite with polyaniline (PANI) via in-situ oxidation. The obtained composites with varying loading of PANI (15, 25, 50, and 75% w/w) were characterized by FE-SEM, TGA, and FTIR spectroscopy. The prepared composites were evaluated for their adsorption performance for removal of Cr(VI). It was concluded that the composite with 50% w/w polyaniline loading on coconut fiber exhibited a maximum adsorption efficiency of 93.11% in 30 min. The effect of pH, dosage, and concentration of the aqueous solution of chromium on the Cr(VI) adsorption efficiency of the composite was also studied. From the optimization studies it was observed that the absorbents exhibited the best adsorption response for Cr(VI) removal with 0.25 mg/mL adsorbent at pH 4, in 30 min. The effect of pH, dosage, and concentration of the aqueous solution of chromium on the Cr(VI) adsorption efficiency of the composite was also studied. This study highlights the application of low-cost adsorbent as a potential candidate for the removal of hexavalent chromium. A detailed study on the adsorption kinetics and isothermal analysis was conducted for the removal of Cr(VI) from aqueous solution using coconut fiber-polyaniline composite. From the kinetic investigation, the adsorption was found to follow the pseudo second order model. The data obtained were best fitted to the Elovich model confirming the chemisorption of the Cr(VI) on coconut polymer composites. The analysis of the isothermal models indicated monolayer adsorption based on the Langmuir adsorption model.

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.

Adsorption and reduction from modified polypyrrole enhance electrokinetic remediation of hexavalent chromium-contaminated soil

Toxic metal pollutant Cr(VI) in the environment will pose a severe threat to animal and human health. In this work, Fe₃O₄@PPy, Arg@PPy, and Arg/Fe₃O₄@PPy were prepared to enhance adsorption of Cr(VI) by doping Fe₃O₄ nanoparticles and amino radicals into the original PPy structure. Their characteristics were investigated by FTIR, SEM, EDS, BET analysis, and batch adsorption experiments. And they were used as permeable reaction barriers (PRB) to combine with electrokinetic remediation (EKR) to remediate Cr-contaminated soil. Adsorption experiment results showed that the maximum adsorption capacities of PPy, Fe₃O₄@PPy, Arg@PPy, and Arg/Fe₃O₄@PPy for Cr(VI) were 60.43 mg/g, 67.12 mg/g, 159.86 mg/g, and 141.50 mg/g, respectively. They all followed the kinetic pseudo-second-order model and the Langmuir isothermal model with a monolayer adsorption behavior. In the EKR/PRB system, the presence of Fe₃O₄@PPy, Arg@PPy, and Arg/Fe₃O₄@PPy obtained the higher Cr(VI) removal efficiency near the anode than that of the PPy, increasing by 74.60%, 26.04%, and 68.64%, respectively. A strong electrostatic attraction between anion contaminants and protonated modified PPy and a reduction from Cr(VI) to Cr(III) appeared in the EKR remediation process under acid conditions. This study opened up a prospect for applying modified PPy composites to treat toxic metal-contaminated soil.

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.

Efficient detoxification of Cr(VI)-containing effluents by sequential adsorption and reduction using a novel cysteine-doped PANi@faujasite composite: Experimental study supported by advanced statistical physics prediction

Nowadays, the global spreading of hazardous heavy metals becomes a top-priority environmental challenge, owing to its serious detrimental health outcomes. Herein, a novel cysteine-doped polyaniline@faujasite hybrid composite (Cys-PANi@FAU-50) was synthesized via a facile in-situ polymerization route for the effective detoxification of Cr(VI)-bearing wastewaters. The Cys-PANi@FAU-50 composite displayed an open mesoporous structure richly decorated with nitrogen/oxygen-containing functional groups, which consequently boosted the diffusion, adsorption and reduction of Cr(VI) oxyanions. The Cr(VI) adsorption behavior was satisfactorily tailored via pseudo-second-order law and Langmuir model with a maximum uptake capacity of 384.6 mg/g. Based on the advanced statistical physics theory, the monolayer model with two distinct receptor sites provided a reliable microscopic and macroscopic prediction of the Cr(VI) adsorption process. Stereographically, the Cr(VI) ions were adsorbed through horizontal multi-anchorage and vertical multi-molecular mechanisms on the amine and hydroxyl groups of Cys-PANi@FAU-50, respectively. The thermodynamic functions evidenced that the Cr(VI) adsorption was an endothermic spontaneous process. XPS analysis proved that Cr(VI) ions were electrostatically adsorbed, and subsequently reduced to Cr(III), which were in turn immobilized by chelation with imine/sulfonate groups and electrostatic interactions with carboxylate groups. The Cys-PANi@FAU-50 featured an effortless regenerability and good reusability. Overall, the Cys-PANi@FAU-50 composite owns outstanding potentiality for detoxifying Cr(VI)-laden effluents.

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).

Conductive Polymers and Their Nanocomposites as Adsorbents in Environmental Applications

Proper treatment and disposal of industrial pollutants of all kinds are a global issue that presents significant techno-economical challenges. The presence of pollutants such as heavy metal ions (HMIs) and organic dyes (ODs) in wastewater is considered a significant problem owing to their carcinogenic and toxic nature. Additionally, industrial gaseous pollutants (GPs) are considered to be harmful to human health and may cause various environmental issues such as global warming, acid rain, smog and air pollution, etc. Conductive polymer-based nanomaterials have gained significant interest in recent years, compared with ceramics and metal-based nanomaterials. The objective of this review is to provide detailed insights into different conductive polymers (CPs) and their nanocomposites that are used as adsorbents for environmental remediation applications. The dominant types of CPs that are being used as adsorbent materials include polyaniline (PANI), polypyrrole (Ppy), and polythiophene (PTh). The various adsorption mechanisms proposed for the removal of ODs, HMIs, and other GPs by the different CPs are presented, together with their maximum adsorption capacities, experimental conditions, adsorption, and kinetic models reported.

In Situ Stabilisation of Silver Nanoparticles at Chitosan-Functionalised Graphene Oxide for Reduction of 2,4-Dinitrophenol in Water

This investigation reports the in situ growth of silver nanoparticles onto covalently bonded graphene oxide-chitosan, which serve as supported nanocatalysts for the NaBH4 reduction of 2,4-dinitrophenol in aqueous systems. Fumaryl chloride reacted with chitosan in an acidic environment to yield a tailored polymeric material. The latter was, in turn, treated with the pre-synthesised graphene oxide sheets under acidic conditions to generate the GO-functionalised membrane (GO-FL-CS). The adsorption of Ag+ from aqueous media by GO-FL-CS yielded a set of membranes that were decorated with silver nanoparticles (Ag NPs@GO-FL-CS) without any reducing agent. Various analytical tools were used to characterise these composites, including Fourier transform infrared spectroscopy, Brunauer-Emmett-Teller surface area analysis, X-ray diffraction, scanning electron microscopy/energy-dispersive X-ray analysis, inductively coupled plasma-mass spectrometry, and transmission electron microscopy. The silver-loaded materials were further used for the remediation of 2,4-dinitrophenol from aqueous solutions under batch operation. The BET analysis revealed that the functionalisation of GO with chitosan and Ag NPs (average size 20-60 nm) resulted in a three-fold increased surface area. The optimised catalyst (Ag mass loading 16.95%) displayed remarkable activity with an apparent pseudo-first-order rate constant of 13.5 × 10-3 min-1. The cyclic voltammetry experiment was conducted to determine the nitro-conversion pathway. The reusability/stability test showed no significant reduction efficiency of this metal-laden composite over six cycles. Findings from the study revealed that Ag NPs@GO-FL-CS could be employed as a low-cost and recyclable catalyst to convert toxic nitroaromatics in wastewater.

Bi-layered hollow amphoteric composites: Rational construction and ultra-efficient sorption performance for anionic Cr(VI) and cationic Cu(II) ions

Here, we have developed a novel bilayer hollow amphiphilic biosorbent (BHAB-3) with large adsorption capacity, rapid adsorption kinetics, and cost-effective for the removal of Cr(VI) and Cu(II) from aqueous solutions. The synthesis was based on the clever use of freeze-drying to fix the structure, secondary modification of the carboxymethyl cellulose microspheres with polyethyleneimine and cross-linking by glutaraldehyde. The consequences of pH, initial concentration, contact time and temperature on adsorption were investigated. The Langmuir model fits showed that the maximum adsorption capacities of the two target heavy metal ions reached 835.91 and 294.79 mg/g, respectively. Moreover, BHAB-3 was characterized by SEM, FT-IR, TGA, and XPS synergistically, showing that it exhibits a strong complexation ability for Cu(II) and a strong electrostatic effect for Cr(VI). Adsorption and desorption experiments showed only a slight decrease in the adsorption capacity of the BHAB-3 for Cr(VI) and Cu(II) ions after 5 and 26 cycles, respectively. Given the excellent properties of this adsorbent, it is a promising candidate for heavy metal ion removal.

Synthesis of Polymer-Based Magnetic Nanocomposite for Multi-Pollutants Removal from Water

A magnetic polymer-based nanocomposite was fabricated by the modification of an Fe3O4/SiO2 magnetic composite with polypyrrole (PPy) via co-precipitation polymerization to form PPy/Fe3O4/SiO2 for the removal of Congo red dye (CR) and hexavalent chromium Cr(VI) ions from water. The nanocomposite was characterized using various techniques including X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscope (SEM), vibration sample magnetometer, and thermogravimetric analysis (TGA). The results confirm the successful fabrication of the nanocomposite in the size of nanometers. The effect of different conditions such as the contact time, adsorbent dosage, solution pH, and initial concentration on the adsorption process was investigated. The adsorption isotherm suggested monolayer adsorption of both contaminants over the PPy/Fe3O4/SiO2 nanocomposite following a Langmuir isotherm, with maximum adsorption of 361 and 298 mg.g-1 for CR dye and Cr(VI), respectively. Furthermore, the effect of water type on the adsorption process was examined, indicating the applicability of the PPy/Fe3O4/SiO2 nanocomposite for real sample treatment. Interestingly, the reusability of the nanocomposite for the removal of the studied contaminants was investigated with good results even after six successive cycles. All results make this nanocomposite a promising material for water treatment.

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.

Palladium nanoparticles dispersed on functionalized macadamia nutshell biomass for formic acid-mediated removal of chromium(VI) from aqueous solution

Driven by the need for sustainably sourced catalysts and the use of reaction systems that generate environmentally benign by-products, the present study aimed to deposit stable, dispersed palladium (Pd) nanoparticles on the modified surfaces of granular macadamia nutshell (MNS) biomass for catalytic reduction of hexavalent chromium (Cr(VI)) to trivalent chromium (Cr(III)). Through wet impregnation with Pd(II) ions and subsequent hydrazine-mediated reduction to Pd(0), Pd nanoparticles were embedded in a scaffold of polyethyleneimine grafted on bleached MNS previously coated with a chemically bound layer of polyglycidyl methacrylate. Imagery from scanning electron microscopy showed the formation of different layers of the polymeric coating and dispersed palladium resulting from surface modification and palladium nanoparticle synthesis, respectively. X-ray diffraction analysis confirmed the formation of Pd on the modified MNS surface and suggested an estimated crystallite size of 5.0 nm. The supported nanoparticles exhibited catalytic activity in formic acid-mediated Cr(VI) reduction and showed promising stability with consecutive reuse. These findings set the stage for advanced studies into performance optimization.

Facile synthesis and characterization of a novel 1,2,4,5-benzene tetracarboxylic acid doped polyaniline@zinc phosphate nanocomposite for highly efficient removal of hazardous hexavalent chromium ions from water

The present study describes the preparation of a novel 1,2,4,5-benzene tetracarboxylic acid doped polyaniline@zinc phosphate (BTCA-PANI@ZnP) nanocomposite via a facile two-step procedure. Thereafter, the as-prepared composite material adsorption characteristics for Cr(VI) ions removal were evaluated under batch adsorption. Kinetic approach studies for Cr(VI) removal, clearly demonstrated that the results of the adsorption process followed the pseudo second order and Langmuir models. The thermodynamic study indicated a spontaneous and endothermic process. Furthermore, higher monolayer adsorption was determined to be 933.88 mg g^-1. In addition, the capability study regarding Cr(VI) ions adsorption over BTCA-PANI@ZnP nanocomposite clearly revealed that our method is suitable for large scale application. X-ray photoelectron spectroscopy (XPS) analysis confirmed Cr(VI) adsorption on the BTCA-PANI@ZnP surface, followed by its subsequent reduction to Cr(III). Thus, the occurrence of external mass transfer, electrostatic attraction and reduction phenomenon were considered as main mechanistic pathways of Cr(VI) ions removal. The superior adsorption performance of the material, the multi-dimensional characteristics of the surface and the involvement of multiple removal mechanisms clearly demonstrated the potential applicability of the BTCA-PANI@ZnP material as an effective alternative for the removal of Cr(VI) ions from wastewater.

An Enhanced Reduction-Adsorption Strategy for Cr(VI): Fabrication and Application of L-Cysteine-doped Carbon@Polypyrrole with a Core/Shell Composite Structure

Reclamation and recycling of heavy metal ions can offer environmental protection and sustainable development. Here, we report the preparation of L-cysteine (L-cys)-doped glucose carbon sphere (GCS)@polypyrrole (PPy) composites (GCS@PPy/L-cys). The adsorption performance and mechanism of GCS@PPy/L-cys toward Cr(VI) from water were investigated in detail. The chromate enrichment on GCS@PPy is significantly facilitated by doping with L-cys, which prevents the oxidative collapse of the structure. This approach leads to many reduction-adsorption sites that reduce the highly hazardous Cr(VI) into less toxic Cr(III). More significantly, the composite can be reused to fabricate supercapacitors that avoid secondary pollution. This strategy offers high-efficiency treatment and sustainable utilization of hypervalent metals in water.

Multi-objective optimization of permeable reactive barrier design for Cr(VI) removal from groundwater

The present study aims to develop a practical approach for the optimal permeable reactive barrier (PRB) design towards Cr(VI) removal from groundwater. Batch and column experiments were performed to investigate the characteristics of the four proposed reactive materials; nanoscale zero-valent iron (Fe⁰), bimetallic nanoscale zero-valent iron (Fe⁰/Cu), activated carbon (AC) and sand/zeolite mixture (S/Z). Kinetic analysis and dynamic modeling of the experimental data were implemented to determine the controlling conditions of the reactive performance of the PRB's materials. The sensitivity index of the design parameters was examined as an indicator of their effect on the reactive responses. Moreover, the Response Surface Methodology (RSM) was considered for optimizing the design variables of the PRB based on the practical factorial analysis. Results revealed that Fe⁰ and Fe⁰/Cu showed high performance in Cr(VI) removal, with a slight superiority to Fe⁰, with final removal efficiency values of 89.7 and 84.1%, respectively. Kinetic analysis depicted that pseudo second order was the best fitting model for Cr(VI) removal in the four materials' cases. ANOVA statistical analysis revealed that quadratic polynomial model was the best model, corresponding to the highest correlation efficiency and adequate precision, to describe the relationships in the four PRB's cases between the selected dependent variables; resident time (t_R), reactive material mass per sectional area of contaminant plume (M/A) and reactive material cost (Cost_PRB) towards the independent parameters; barrier thickness (b) and permeability (K_r). Additionally, sensitivity analysis has been conducted which depicted the high sensitivity, in the four PRB's cases, of average pore water velocity within the barrier (v_r) v_r and K_r with the highest and the second-highest sensitivity index (SI) values towards t_R, respectively. The RSM-optimization revealed that Fe⁰ is the most feasible reactive material, comparing to the other considered materials, with respect to the optimal conditions regarding the long residency (t_R = 22 days) and low cost (b = 0.521 m), with around 95.2% desirability of its optimal solution. Overall, the current study represents a significant contribution and a vital step towards an accurate PRB's design based on previously determined optimal conditions.

Efficient removal of Cr(VI) from water by the uniform fiber ball loaded with polypyrrole: Static adsorption, dynamic adsorption and mechanism studies

A novel adsorbent, the uniform fiber ball (UFB) loaded with polypyrrole (UFB-PPy), was synthesized for Cr(VI) removal from water in this paper. The structure of the UFB and UFB-PPy were characterized by SEM, EDS, FT-IR, BET, XPS and TG. The adsorption properties of UFB-PPy towards Cr(VI) were investigated by the effects of temperature, initial concentration of Cr(VI), interfering ions and contact time in batch experiments, the isothermal models (Langmuir, Freundlich and Temkin) and the kinetic models (Pseudo first-order kinetic, Pseudo second-order kinetic and Intra-particle diffusion models) were used to describe the adsorption behavior. The effects of the initial concentration and flow rate of the Cr(VI) solution in the column experiments were also studied, and the dynamic models (Yoon-Nelson, Adams-Bohart and Wolborska model) were applied to predict the adsorption performance. The Cr(VI) removal mechanism of UFB-PPy was revealed by studying the effect of pH on adsorption, testing of Cl^-, and analyzing the XPS. The results showed that UFB-PPy exhibited excellent adsorption properties for Cr(VI) both in batch and column adsorption. The possible adsorption mechanism involved electrostatic attraction, ion exchange and reduction. Conveniently, the chromium resources can be recovered with the form of high-purity Cr₂O₃ by simple calcination of Cr(VI)-captured UFB-PPy (UFB-PPy-Cr).

Effective Adsorption of Hexavalent Chromium and Divalent Nickel Ions from Water through Polyaniline, Iron Oxide, and Their Composites

Water pollution caused by industrial wastes containing heavy metals and dyes is a major environmental problem. This study reports on the synthesis, characterization, and utilizations of Polyaniline (PANI) and its composites with Fe3O4 for the removal of hexavalent chromium Cr(VI) and divalent nickel Ni(II) ions from water. The adsorption data were fitted in Freudlich, Langmuir, Tempkin, Dubbanin–Ruddishkawich (D–R), and Elovich adsorption isotherms. The Freundlich isotherm fits more closely to the adsorption data with R2 values of 0.9472, 0.9890, and 0.9684 for adsorption of Cr(VI) on Fe3O4, PANI, and PANI/Fe3O4 composites, respectively, while for adsorption of Ni(II) these values were 0.9366, 0.9232, and 0.9307 respectively. The effects of solution pH, initial concentration, contact time, ionic strength, and adsorbent dosage on adsorption behavior were investigated. The adsorption ability of composites was compared with pristine PANI and Fe3O4 particles. Activation energy and other thermodynamic properties such as changes in enthalpy, entropy, and Gibbs free energy indicated spontaneous and exothermic adsorption.

A structurally aligned nickel oxide encapsulated polypyrrole nanocomposite for hydrogen peroxide sensing

Chemically responsive and structurally aligned nickel oxide encapsulated polypyrrole nano-composite has been prepared for H₂O₂ sensing in liquid and vapor phase.

Enhanced adsorption-coupled reduction of hexavalent chromium by 2D poly(m-phenylenediamine)-functionalized reduction graphene oxide

To improve the mass transfer efficiency of poly(m-phenylenediamine) for the effective removal of hexavalent chromium (Cr (VI)) from aqueous solution, a facile and one-step method to prepare two-dimensional poly(m-phenylenediamine) functionalized reduction graphene oxide (rGO-PmPD) by dilution polymerization is developed. The structure and morphology of rGO-PmPD as well as rGO and PmPD were characterized by scanning electron microscope (SEM), transmission electron microscope (TEM), Brunauer-Emmett-Teller (BET), Fourier-transformed infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), Raman, and X-ray diffraction (XRD). The preparation mechanism, adsorption performance, and mechanism of rGO-PmPD were then investigated in detail. The obtained rGO-PmPD exhibited thin 2D nanosheet morphology with much improved specific surface area and pore volume (18 and 25 times higher than that of PmPD, respectively). The Cr (VI) adsorption of rGO-PmPD was fitted well with the pseudo-second-order kinetic model and Langmuir isotherm model, and the maximum adsorption capacity of rGO-PmPD reached 588.26 mg g^-1, higher than that of PmPD (400 mg g^-1) and rGO (156.25 mg g^-1). Moreover, the regeneration efficiency of the rGO-PmPD nanosheet is also promising that the adsorption performance after five times of adsorption-desorption cycles still maintains more than 530 mg g^-1. The removal mechanism involved reduction coupled with adsorption and electrostatic interaction between rGO-PmPD and Cr (VI), and ~ 65% of Cr (VI) removal was attributed to reduction and ~ 35% was ascribed to adsorption and electrostatic interaction. This study thus provides a simple and effective route to achieve high accessible surface area of adsorbent materials with enhanced mass transfer efficiency and thereafter improved adsorption performance.

Recent advances in hexavalent chromium removal from aqueous solutions by adsorptive methods

Chromium exists mainly in two forms in environmental matrices, namely, the hexavalent (Cr(vi)) and trivalent (Cr(iii)) chromium. While Cr(iii) is a micronutrient, Cr(vi) is a known carcinogen, and that warrants removal from environmental samples. Amongst the removal techniques reported in the literature, adsorption methods are viewed as superior to other methods because they use less chemicals; consequently, they are less toxic and easy to handle. Mitigation of chromium using adsorption methods has been achieved by exploiting the physical, chemical, and biological properties of Cr(vi) due to its dissolution tendencies in aqueous solutions. Many adsorbents, including synthetic polymers, activated carbons, biomass, graphene oxide, and nanoparticles as well as bioremediation, have been successfully applied in Cr(vi) remediation. Initially, adsorbents were used singly in their natural form, but recent literature shows that more composite materials are generated and applied. This review focused on the recent advances, insights, and project future directions for these adsorbents as well as compare and contrast the performances achieved by the mentioned adsorbents and their variants.