The application of GO-Fe3O4 nanocomposite for chromium adsorption from tannery industry wastewater

Emerging trends and future outlook on chromium removal in the lab, pilot scale, and industrial wastewater system: an updated review exploring 10 years of research

Chromium (Cr) is widely recognized as a carcinogenic metal, and numerous technologies have been studied on a lab scale to manage the pollution caused by Cr contamination in wastewater. However, the removal of Cr presents several challenges and limitations in industrial wastewater management. These issues highlight the ongoing need for research to discover more efficient methods for remediating Cr from wastewater. The proposed review summarizes the current limitations, gaps, and state-of-the-art technologies on Cr removal in industrial wastewater systems over the past 10 years. It aims to lay the groundwork for future research and innovation in Cr remediation for industrial applications. The review emphasizes that conventional physicochemical techniques are often insufficient and highlights the necessity of implementing advanced integrated systems. The limitations related to industrial scaling up are also deeply investigated. Special attention is given to differentiating research conducted at laboratory, pilot, and industrial levels. The findings reveal that limited research has been conducted on an industrial scale, with most investigations focusing on treating tannery and electroplating wastewater. A few studies have also been reported on wastewater from textile, mining, steel mills, pigments, and wood processing. Despite the existence of high-performance systems demonstrated in lab-scale studies, only a handful of treatment techniques have effectively removed Cr at an industrial scale. Nevertheless, innovative breakthroughs in advanced integrated systems show promise for improved performance in the future.

The development of multifunctional biochar with NiFe2O4 for the adsorption of Cd (II) from water systems: The kinetics, thermodynamics, and regeneration

High concentrations of Cd (II) in wastewater have been reported several times which attracted top research attention to mitigate the pollution impacts of the contaminant. Therefore, this study aimed to develop a Zn-doped NiFe2O4- pinecone biochar composite (ZNiF@PB) for the adsorption of Cd (II) from wastewater. FTIR confirmed immobilization of PB on the surface of ZNiF by the presence of C = O at 1638 cm-1, COOH at 1385 cm-1, C-O at 1009 cm-1 and Fe-O at 756 cm-1. Similarly, XRD determined the crystallite structure of the adsorbents where the ZNiF crystallite size of 43 nm was obtained while the particle size of ZNiF@PB was found to be 38 nm. These XRD results agreed with those values obtained from TEM images showing ZNiF and ZNiF@PB had a spherical shape with similar particle sizes. On the other hand, the surface areas of ZNiF, PB, and ZNiF@PB were found to be 78.4 m2/g, 125 m2/g, and 104 m2/g, respectively. These high surface areas have a huge potential to enhance Cd removal. With these adsorbents, the maximum Cd (II) adsorption of 96% was recorded at the optimum experimental condition of adsorbent dosage 0.5g/50 mL, solution pH 6, initial Cd (II) concentration 100 mg/L, and contact time 120 min. Practical adsorption kinetics data were well described by the pseudo-second order model whereas the adsorption isotherm was a perfect fit to the Langmuir isothermal model implying the adsorption process to be a monolayer with mainly a chemically bonded mechanism. In conclusion, this adsorbent is efficient for the adsorption of Cd (II) from wastewater and has also a huge potential to be applied for industrial-scale water purification.

Enhanced photocatalytic and antibacterial performance of CeO2-loaded carboxymethyl chitosan nanocomposites

Carboxymethyl chitosan (CMCs) was loaded with two different concentrations of cerium dioxide (CeO2), specifically 0.3 g and 0.6 g, and compared with CMCs. XRD, FTIR and SEM analyses were used to evaluate the structural and morphological characteristics. The nanocomposites were examined for their photocatalytic degradation of Methylene Blue (MB) dye and antibacterial capabilities. Various parameters, including catalyst concentration, dye concentration, and pH levels, were assessed to determine the photocatalytic degradation efficiency of MB dye. The results demonstrated that the 0.6CeO2/CMCs nanocomposite outperformed the 0.3CeO2/CMCs and pure CMCs in terms of photocatalytic performance, achieving complete degradation of MB dye within 210 and 240 min after treatment with 0.3CeO2/CMCs and 0.6CeO2/CMCs nanocomposites. The agar well diffusion test was employed to assess the antibacterial activity of the nanocomposites against Staphylococcus aureus, Enterococcus faecalis, Escherichia coli, and Pseudomonas aeruginosa. 0.6CeO2/CMCs nanocomposite exhibited the highest antibacterial effectiveness, with zones of inhibition measuring 29 ± 0.63 mm for E. coli, 28 ± 0.18 mm for P. aeruginosa, 25.5 ± 0.25 mm for S. aureus, and 23.6 ± 0.51 mm for E. faecalis. Additionally, the durability and reusability of the nanocomposites were confirmed after undergoing 5 cycles of MB dye degradation, with only a slight decrease in efficiency. The findings of this study highlight the potential of CeO2/CMCs nanocomposites as powerful antibacterial and photocatalysts with important implications for environmental and biological applications.

Insights into the enhanced adsorption of glyphosate by dissolved organic matter in farmland Mollisol: effects and mechanisms of action

Dissolved organic matter (DOM) is easy to combine with residual pesticides and affect their morphology and environmental behavior. Given that the binding mechanism between DOM and the typical herbicide glyphosate in soil is not yet clear, this study used adsorption experiments, multispectral techniques, density functional theory, and pot experiments to reveal the interaction mechanism between DOM and glyphosate on Mollisol in farmland and their impact on the environment. The results show that the adsorption of glyphosate by Mollisol is a multilayer heterogeneous chemical adsorption process. After adding DOM, due to the early formation of DOM and glyphosate complex, the adsorption process gradually became dominated by single-layer chemical adsorption, and the adsorption capacity increased by 1.06 times. Glyphosate can quench the endogenous fluorescence of humic substances through a static quenching process dominated by hydrogen bonds and van der Waals forces, and instead enhance the fluorescence intensity of protein substances by affecting the molecular environment of protein molecules. The binding of glyphosate to protein is earlier, of which affinity stronger than that of humic acid. In this process, two main functional groups (C-O in aromatic groups and C-O in alcohols, ethers and esters) exist at the binding sites of glyphosate and DOM. Moreover, the complexation of DOM and glyphosate can effectively alleviate the negative impact of glyphosate on the soil. This study has certain theoretical guidance significance for understanding the environmental behavior of glyphosate and improving the sustainable utilization of Mollisol.

The application of Rumex Abysinicus derived activated carbon/bentonite clay/graphene oxide/iron oxide nanocomposite for removal of chromium from aqueous solution

Rapid industrialization has significantly boosted economic growth but has also introduced severe environmental challenges, particularly in water pollution. This study evaluates the effectiveness of a nanocomposite composed of Rumex Abyssinicus Activated Carbon/Acid Activated Bentonite Clay/Graphene Oxide, and Iron Oxide (RAAC/AABC/GO/Fe3O4) for chromium removal from aqueous solutions. The preparation of the nanocomposite involved precise methods, and its characterization was performed using Scanning Electron Microscopy (SEM), X-ray Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), Brunauer-Emmett-Teller (BET) surface area analysis, and the point of zero charge (pHpzc). Batch adsorption experiments were designed using Design Expert software with a central composite design under response surface methodology. The factors investigated included pH (3, 6, and 9), initial Cr (VI) concentration (40, 70, and 100 mg/L), adsorbent dose (0.5, 0.75, 1 g/200 mL), and contact time (60, 90, and 120 min). Adsorption isotherms were analyzed using nonlinearized Langmuir, Freundlich, and Temkin models, while pseudo-first-order and pseudo-second-order models were applied to adsorption kinetics. Characterization revealed a pHpzc of 8.25, a porous and heterogeneous surface (SEM), diverse functional groups (FTIR), an amorphous structure (XRD), and a significant surface area of 1201.23 m2/g (BET). The highest removal efficiency of 99.91% was achieved at pH 6, with an initial Cr (VI) concentration of 70 mg/L, a 90 min contact time, and an adsorbent dose of 1 g/200 mL. Optimization of the adsorption process identified optimal parameters as pH 5.84, initial Cr (VI) concentration of 88.94 mg/L, contact time of 60 min, and adsorbent dose of 0.52 g/200 mL. The Langmuir isotherm model, with an R2 value of 0.92836, best described the adsorption process, indicating a monolayer adsorption mechanism. The pseudo-second-order kinetics model provided the best fit with an R2 value of 0.988. Overall, the nanocomposite demonstrates significant potential as a cost-effective and environmentally friendly solution for chromium removal from wastewater.

Keratin hydrolysate as a chrome exhaust aid and keratin filler in leather processing: A cleaner technology approach for tannery solid waste management and leather manufacturing

Hair burning unhairing and dampening of tannery wastes during the hair-saving unhairing process are becoming significant problems in the tanning industry. Therefore, this research article focuses on the extraction of keratin hydrolysate (KH) and its application as a chrome exhaust aid and keratin filler in leather manufacturing process. The structure, morphology and functional groups of the extract were examined using X-Ray Diffractometer (XRD), scanning electron microscopy (SEM) and Fourier transform infrared spectrometer (FTIR), respectively. To study and contrast the degree of improvement in chromium uptake, the KH solution was applied both before tanning on the pickled pelt and after tanning during basification. The thermal stability, physical strength characteristics and organoleptic properties of the leathers obtained were characterized. Furthermore, the environmental impact of the tanning system was assessed through a comparative analysis of the spent liquors. Finally, experimental retanning process was conducted to replace the commercial protein filler (Celatan F: 50, 75, and 100 %) with KH solution, with concurrent processing of control leather using conventional chrome tanning agent at 6 % dosage of chromium. The FTIR analysis of the extract confirmed the presence of alkyl side chains of amino acids as well as carboxylic, amide, carboxyl group and aldehyde functional groups at 1400-1700 cm-1,3,303.46 cm-1,3270 cm-1 and 2752 cm-1, respectively. XRD spectrum showed two diffraction peaks at 2 theta values of 9.36° and 21.16°, respectively. Leathers with improved mechanical strength, organoleptic properties and thermal stability were obtained with 100 % substitution of Celatan F at pH 6 and 10 % chromium dosage. It was also discovered that the shrinkage temperature of the experimental leather was enhanced to more than 105 °C. Environmental impact evaluation on the spent liquor showed that the complete replacement of Celatan F with KH solution brought about a notable decrease in COD and TDS in the spent liquor. The extraction and application of tannery hair waste-based keratin hydrolysate as an efficient, environmentally friendly chrome exhaust aid and keratin filler has been attempted and established in this research article.

Adsorptive performances and valorization of green synthesized biochar-based activated carbon from banana peel and corn cob composites for the abatement of Cr(VI) from synthetic solutions: Parameters, isotherms, and remediation studies

This study intended to remove Cr(VI) from an aqueous synthetic solution employing synthesized biochar adsorbent from a blend of locally sourced banana peel, and corn cob biomass wastes. An equal ratio of the prepared powder was activated with ZnCl2 solution (1:1 wt basis) and carbonized for 2 h at 600 °C. The proximate analysis of the selected BP-CCAC@ZC3 biochar was conducted. Subsequently, its surface area, surface functions, and morphology were examined using BET analysis, FTIR, and SEM techniques, respectively. The proximate analysis of BP-CCAC@ZC3 showed a moisture content of 2.37 ± 0.80 %, an ash content of 8.07 ± 0.75 %, volatile matter of 19.38 ± 2.66 %, and fixed carbon of 70.18 %. It was found that the synthesized BP-CCAC@ZC3 had 432.149 m2/g of a specific area as per the BET surface area analysis. The highest efficiency for Cr(VI) removal was determined to be 97.92 % through adsorption batch tests using a dose of 0.4 g of BP-CCAC@ZC3, an initial Cr(VI) concentration of 20 mg/L, pH of 2, and 35 min contact time. Likewise, the adsorption process was effectively described by the Langmuir isotherm model, which had a high correlation coefficient (R 2 = 0.9977) and a maximum adsorption capacity of 19.16 mg/g, indicating a monolayer adsorption mechanism. The BP-CCAC@ZC3 biochar exhibited reusability for up to four cycles with only a slight decrease in effectiveness, highlighting its potential for sustainable wastewater treatment. Overall, using corn cob and banana peel composites to synthesize activated carbon with ZnCl2 offers a promising method for effectively removing Cr(VI) containing wastewater.

Application of Optimization Response Surface for the Adsorption of Methylene Blue Dye onto Zinc-coated Activated Carbon

The activated carbon was produced in the first phase of this investigation by chemically activating hazelnut shell waste with H3PO4. Composite materials were obtained by coating the activated carbon with zinc oxide, whose BET surface area was calculated as 1278 m2 g-1. ZnO-doped ZnO/AC composite was synthesized as an adsorbent for its possible application in the elimination of organic dyestuff MB, and its removal efficiency was investigated. Morphological properties of ZnO/AC were characterized using analytical methods such as XRD, SEM, and BET. The adsorption system and its parameters were investigated and modeled using the response surface method of batch adsorption experiments. The experimental design consisted of three levels of pH (3, 6.5, and 10), initial MB concentration (50, 100, and 150 mg L-1), dosage (0.1, 0.3, and 0.5 g 100 mL-1), and contact time (5, 50, and 95 min). The results from the RSM suggested that the MB removal efficiency was 98.7% under the optimum conditions of the experimental factors. The R2 value, which expresses the significance of the model, was determined as 99.05%. Adsorption studies showed that the equilibrium data fit well with the Langmuir isotherm model compared to Freundlich. The maximum adsorption capacity was calculated as 270.70 mg g-1.

Pinecone biochar for the Adsorption of chromium (VI) from wastewater: Kinetics, thermodynamics, and adsorbent regeneration

High concentration of chromium in aquatic environments is the trigger for researchers to remediate it from wastewater environments. However, conventional water treatment methods have not been satisfactory in removing chromium from water and wastewater over the last decade. Similarly, many adsorption studies have been focused on one aspect of the treatment, but this study dealt with all aspects of adsorption packages to come up with a concrete conclusion. Therefore, this study aimed to prepare pinecone biochar (PBC) via pyrolysis and apply it for Cr(VI) removal from wastewater. The PBC was characterized using FTIR, SEM-EDX, BET surface area, pHpzc, Raman analyses, TGA, and XRD techniques. Chromium adsorption was studied under the influence of PBC dose, solution pH, initial Cr(VI) concentration, and contact time. The characteristics of PBC are illustrated by FTIR spectroscopic functional groups, XRD non-crystallite structure, SEM rough surface morphology, and high BET surface area125 m2/g, pore volume, 0.07 cm3/g, and pore size 1.4 nm. On the other hand, the maximum Cr (VI) adsorption of 69% was found at the experimental condition of pH 2, adsorbent dosage 0.25 mg/50 mL, initial Cr concentration 100 mg/L, and contact time of 120 min. Similarly, the experimental data were well-fitted with the Langmuir adsorption isotherm at R2 0.96 and the pseudo-second-order kinetics model at R2 0.99. This implies the adsorption process is mainly attributed to monolayer orientation between the adsorbent and adsorbate. In the thermodynamics study of adsorption, ΔG was found to be negative implying the adsorption process was feasible and spontaneous whereas the positive values of ΔH and ΔS indicated the adsorption process was endothermic and increasing the degree of randomness, respectively. Finally, adsorbent regeneration and reusability were successful up to three cycles. In conclusion, biochar surface modification and reusability improvements are urgently required before being applied at the pilot scale.

Facile synthesis of magnetic intelligent sensors for the pH-sensitive controlled capture of Cr(vi)

In this work, intelligent pH-sensitive sensors (Fe3O4/RhB@PAM) for Cr(vi) detection were successfully synthesized based on polyacrylamide (PAM) and Rhodamine B (RhB) co-modified Fe3O4 nanocomposites. The characterization results indicated that the sensors had many favorable properties, including suitable size, stable crystal structure and excellent magnetic response performance (47.59 emu g-1). In addition, the fluorescence changes during the detection process indicated that Fe3O4/RhB@PAM were "ON-OFF" intelligent sensors. When the Fe3O4/RhB@PAM sensors were placed in acidic Cr(vi) solution (pH 4), PAM acted as a pH-responsive "gatekeeper" releasing RhB, and the fluorescence intensity of released RhB was weakened by the complexation of Cr(vi). Furthermore, the fluorescence changes of the magnetic sensors were remarkably specific for Cr(vi) even in the presence of other competitive cations, and the limit of detection (LOD) for Cr(vi) was lower (0.347 μM) than the value recommended by the World Health Organization (0.96 μM). All the results presented in this study showed that the Fe3O4/RhB@PAM sensors had significant potential for Cr(vi) detection in acidic environmental samples.

Biopolymer-protected graphene-Fe3O4 nanocomposite based wearable microneedle sensor: toward real-time continuous monitoring of dopamine

Neurological disorders can occur in the human body as a result of nano-level variations in the neurotransmitter levels. Patients affected by neuropsychiatric disorders, that are chronic require continuous monitoring of these neurotransmitter levels for effective disease management. The current work focus on developing a highly sensitive and personalized sensor for continuous monitoring of dopamine. Here we propose a wearable microneedle-based electrochemical sensor, to continuously monitor dopamine in interstitial fluid (ISF). A chitosan-protected hybrid nanomaterial Fe3O4-GO composite has been used as a chemical recognition element protected by Nafion antifouling coating layer. The morphological and physiochemical characterizations of the nanocomposite were carried out with XRD, XPS, FESEM, EDAX and FT-IR. The principle of the developed sensor relies on orthogonal detection of dopamine with square wave voltammetry and chronoamperometric techniques. The microneedle sensor array exhibited an attractive analytical performance toward detecting dopamine in phosphate buffer and artificial ISF. The limit of detection (LOD) of the developed sensor was observed to be low, 90 nM in square wave voltammetry and 0.6 μM in chronoamperometric analysis. The practical applicability of the microneedle sensor array has been demonstrated on a skin-mimicking phantom gel model. The microneedle sensor also exhibited good long-term storage stability, reproducibility, and sensitivity. All of these promising results suggest that the proposed microneedle sensor array could be reliable for the continuous monitoring of dopamine.

Advancing the development of nanocomposite adsorbent through zinc-doped nickel ferrite-pinecone biochar for removal of chromium (VI) from wastewater

Leather and textile industrial effluents are the main disseminating routes for chromium contamination of water bodies, causing adverse impacts on public and environmental health. The attempt to remediate chromium through conventional wastewater treatment methods is inefficient. Therefore, this study aims to synthesize zinc-doped nickel ferrite pinecone biochar (Zn-NiF@PBC) nanocomposite for the removal of chromium from wastewater systems. The Zn-NiF@PBC nanocomposite was synthesized via the co-precipitation method. The properties of zinc-doped nickel ferrite (Zn-NiF) were effectively modified by blending with biochar at 1, 5, 10, and 15 % (w/w) which was successfully embedded with Zn-Ni ferrite nanoparticles. This was characterized and confirmed by typical adsorbent properties such as a high surface area of 104 m2/g, conducive pore volume of 0.117 cm3/g and pore size of 3.41 nm (BET), interactive multi-functional groups (FTIR), surface charge determination (pHpzc,), crystalline structure (XRD) and very rough surface morphology (SEM). The maximum chromium adsorption was found to be 95 % at the specific experimental condition of pH 3, adsorbent dose 1 g/50 mL, contact time 120 min, and initial chromium concentration 100 mg/L. The adsorption experimental data was best fitted with the Langmuir isotherm at R2 0.98 indicating the adsorption process was homogeneous and monolayer whereas the kinetics adsorption was resembling the second-order kinetic at R2 0.99. Moreover, the adsorption thermodynamics was spontaneous, endothermic, and increased the change in entropy. Finally, the regeneration of Zn-NiF@PBC was found to be effective up to five 5 cycles but gradually degrading in terms of removal efficiency after 3 cycles. In general, Zn-NiF@PBC can remediate chromium from wastewater with huge potential for scale-up and extend to other pollutants clear-up.

Electro-intensified simultaneous decontamination of coexisting pollutants in wastewater

The treatment of wastewater has become increasingly challenging as a result of its growing complexity. To achieve synergistic removal of coexisting pollutants in wastewater, one promising approach involves the integration of electric fields. We conducted a comprehensive literature review to explore the potential of integrating electric fields and developing efficient electro-intensified simultaneous decontamination systems for wastewater containing coexisting pollutants. The review focused on comprehending the applications and mechanisms of these systems, with a particular emphasis on the deliberate utilization of positive and negative charges. After analyzing the advantages, disadvantages, and application efficacy of these systems, we observed electro-intensified systems exhibit flexible potential through their rational combination, allowing for an expanded range of applications in addressing simultaneous decontamination challenges. Unlike the reviews focusing on single elimination, this work aims to provide guidance in addressing the environmental problems resulting from the coexistence of hazardous contaminants.

A review of the treatment technologies for hexavalent chromium contaminated water

The toxicity of hexavalent chromium (Cr(VI)) present in the environment has exceeded the current limits or standards and thus may lead to biotic and abiotic catastrophes. Accordingly, several treatments, including chemical, biological, and physical approaches, are being used to reduce Cr(VI) waste in the surrounding environment. This study compares the Cr(VI) treatment approaches from several areas of science and their competence in Cr(VI) removal. As an effective combination of physical and chemical approaches, the coagulation-flocculation technique removes more than 98% of Cr(VI) in less than 30 min. Most membrane filtering approaches can remove up to 90% of Cr(VI). Biological approaches that involve the use of plants, fungi, and bacteria also successfully eliminate Cr(VI) but are difficult to scale up. Each of these approaches has its benefits and drawbacks, and their applicability is determined by the research aims. These approaches are also sustainable and environmentally benign, thus limiting their effects on the ecosystem.

Highly efficient Cr (VI) removal from electroplating wastewater by regenerable copper sulfides: Mechanism and magical induction effect for Cr resource recovery

The current sorbents used to remove Cr (VI) from electroplating wastewater are faced with some challenges including the difficulty in separating, regenerating, and safely disposing of adsorbed Cr species. To address these challenges, CuSx/TiO2 was developed to recover Cr (VI) from electroplating wastewater. CuSx/TiO2 had superior performance in removing Cr (VI), with the rate and capacity of approximately 9.36 mg g-1 h-1 and 68.8 mg g-1 at initial pH 4.0, respectively. Additionally, Cu2+ released from CuSx/TiO2 during Cr (VI) removal would come back to its external surface as the Cu(OH)2 precipitate at initial pH 4.0, which helped to prevent the generation of secondary pollution. The Cu(OH)2 precipitate would be decomposed into CuOx after calcination, which would then be transformed back into CuSx by re-sulfuration for regeneration. Hence, CuSx showed a magical induction effect on Cr (VI) recovery, and Cr (VI) from electroplating wastewater might be gradually enriched as Cr2O3 in the sandwich between CuSx and TiO2 through multiple regenerations and removals, which could be considered as a chromium ore resource for industrial applications when the amount of enriched Cr2O3 reached more than 30 wt%. Overall, CuSx/TiO2 showed great potential as a promising sorbent for Cr (VI) removal from electroplating wastewater.

Adsorption of chromium from electroplating wastewater using activated carbon developed from water hyacinth

Industrial wastewater polluted with high concentrations of Cr is commonly discharged into water resources without proper treatment. This gives rise to the deterioration of water quality and imposes adverse effects on public health. Therefore, this study is aimed at removing Cr from electroplating wastewater using activated carbon produced from water hyacinth under a full factorial experimental design with three factors and three levels (pH,2,5 and 8, adsorbent dose 0.5,1and1.5 in 100 mL and contact time 30, 60 and120 min). A phosphoric acid solution of 37% was used to activate the carbon, which was then subjected to thermal decomposition for 15 min at 500 °C. The activated carbon was characterized by the presence of a high surface area (203.83 m²/g) of BET, cracking of adsorbent beads of SEM morphology, amorphous nature of XRD, and many functional groups of FTIR such as hydroxyl (3283 cm^-1), alkane (2920 cm^-1), nitrile (2114 cm^-1) and aromatics (1613 cm^-1). The minimum Cr adsorption performance of 15.6% was obtained whereas maximum removal of 90.4% was recorded at the experimental condition of pH 2, adsorbent dose of 1.5 g/100 mL, and contact time of 120 min at a fixed value of initial Cr concentration of 100 mg/L. Similarly, the maximum Cr removal from real electroplating wastewater was 81.2% at this optimum point. Langmuir's model best described the experimental value at R² 0.96 which implies the adsorption is chemically bonded, homogeneous, and monolayer. Pseudo-second-order model best fits with the experimental data with R² value of 0.99. The adsorbent was regenerated for seven cycles and the removal efficiency decreased from 93.25% to 21.35%. Finally, this technology is promising to be scaled up to an industrial level.

The application of Rumex abyssinicus based activated carbon for Brilliant Blue Reactive dye adsorption from aqueous solution

The environmental pollution and human health impacts associated with the discharge of massive dye-containing effluents necessitate a search for cost-effective treatment technology. Therefore, this research work is conducted with the objective of investigating the potential of Rumex abyssinicus-derived activated carbon (RAAC) for the adsorption of Brilliant Blue Reactive (BBR) dye from aqueous solutions. Chemical activation with H₃PO₄ followed by pyrolysis was used to prepare the adsorbent. Characterization of the developed adsorbent was done using proximate analysis, pH point of zero charge (pHpzc), scanning electron microscope (SEM), Fourier transform infrared spectrometer (FTIR), Brunauer, Emmett, and Teller (BET), and X-ray diffraction (XRD). The experimental design and the effect of independent variables including pH (2, 6, and 10), initial dye concentration (50, 100, and 150 mg/L), adsorbent dosage (0.05, 0.1, and 0.15 g/100 mL), and contact time (20, 50, and 80 min) were optimized using the response surface methodology (RSM) coupled with Box Behnken design (BBD). The analysis results revealed the exitance of high specific surface area of 524 m²/g, morphological cracks, and the presence of multiple functional groups like -OH, C=C, alkene, and amorphous structure. Maximum removal efficiency of 99.98% was attained at optimum working conditions of pH 2, contact time of 50 min, dye concentration of 100 mg/L, and adsorbent dosage of 0.15 mg/100 mL, reducing the pollutant concentration from 100 to 0.02 mg/L. Evaluation of the experimental data was done using Langmuir, Freundlich, Temkin, and Sips isotherm models, in which the Langmuir model was found to be the best fit with the experimental data at R² 0.986. This shows that the adsorbent surface is homogeneous and mono-layered. Furthermore, the kinetic study confirmed that the pseudo second-order model best describes the experimental data with R² = 0.999. In general, the research work showed that the low cost, environmental friendliness and high adsorption capabilities of the activated carbon derived from Rumex abyssinicus could be taken as an effective nt for the removal of BBR dye from aqueous solutions.

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).

Adsorption of methylene blue from textile industrial wastewater using activated carbon developed from Rumex abyssinicus plant

Methylene blue (MB) is abundantly found in textile industrial effluent which can cause severe health problems for public and environmental ecology. Therefore, this study aimed to remove MB from textile wastewater using the activated carbon developed from Rumex abyssinicus. The adsorbent was activated using chemical and thermal methods, and then it was characterized by SEM, FTIR, BET, XRD, and pH zero-point charge (pHpzc). The adsorption isotherm and kinetics were also investigated. The experimental design was composed of four factors at three levels (pH (3, 6, and 9), initial MB concentration (100, 150, and 200 mg/L), adsorbent dosage (20, 40, and 60 mg/100 mL), and contact time (20, 40, and 60 min)). The adsorption interaction was evaluated using response surface methodology. The characterization of a Rumex abyssinicus activated carbon was found to have multiple functional groups (FTIR), an amorphous structure (XRD), crack with ups and down morphology (SEM), pHpzc of 5.03 and a high BET-specific surface area of 2522 m²/g. The optimization of MB dye removal was carried out using the Response Surface methodology coupled with the Box Behnken approach. The maximum removal efficiency of 99.9% was recorded at optimum conditions of pH 9, MB concentration of 100 mg/L, the adsorbent dosage of 60 mg/100 mL, and contact time of 60 min. Among the three adsorption isotherm models, the Freundlich isotherm model was the best fit with an experimental value at R² 0.99 showing the adsorption process was heterogeneous and multilayer whereas the kinetics study revealed that pseudo-second-order at R² 0.88. Finally, this adsorption process is quite promising to be used at an industrial level.

In Situ Reconstruction of Active Catalysis Sites Triggered by Chromium Immobilization for Sulfite Oxidation

Hexavalent chromium (Cr(VI)) is a highly toxic substance in wastewater, triggering grievous detriment to aquatic life and human health. Magnesium sulfite is spawned along with the desulfurization process in coal-fired power plants, which is usually disposed of as solid waste. Here, a "waste control by waste" method was proposed upon the redox of Cr(VI)-sulfite, in which highly toxic Cr(VI) is detoxicated and sequent enriched on a novel biochar-induced cobalt-based silica composite (BISC) due to the forced electron transfer from chromium to surface hydroxyl. The immobilized Cr on BISC gave rise to the reconstruction of catalytic active sites "Cr-O-Co", which further enhance its performance in sulfite oxidation by elevating O₂ adsorption. As a result, the sulfite oxidation rate increased by 10 times compared with the non-catalysis benchmark together with the maximum chromium adsorption capacity being 120.3 mg/g. Therefore, this study provides a promising strategy to simultaneously control highly toxic Cr(VI) and sulfite, achieving high-grade sulfur resource recovery for wet magnesia desulfurization.

Biosorption kinetics of cerium(III) and cobalt(II) from liquid wastes using individual bacterial species isolated from low-level liquid radioactive wastes

The existence of toxic heavy metals in the aquatic environment has emphasized a considerable exigency to develop several multifunctional biosorbents for their removal. Herein, three individual bacterial species of Cellulosimicrobium cellulans, Bacillus coagulans, and Microbacterium testaceum were successfully isolated from low-level liquid radioactive wastes. Their loading capacities towards cerium and cobalt metal ions were inclusivity inspected under variable operational parameters of pH, primary pollutant concentration, interaction time, temperature, stirring speed, and biosorbent dosage. By analyzing the influence of solution pH, concentration, temperature, biosorbent mass, and agitation speed on the biosorption kinetics, the biosorption process confirms pseudo-second-order kinetic, intraparticle diffusion, and Elovich equation. Remarkably, the isolated Microbacterium testaceum exhibited high loading capacities reaching 68.1 mg g^-1, and 49.6 mg g^-1 towards Ce(III), and Co(II) ions, respectively, at the initial concentration of 2.8 mM, pH 4.5, and 25 °C. Overall, the isolated bacterial species can potentially be offered up as a promising scavenger for Ce(III) and Co(II) from liquid waste effluents.

Synthesis of biochar-CoFe2O4 nanocomposite for adsorption of methylparaben from wastewater under full factorial experimental design

The presence of endocrine-disrupting chemicals in municipal wastewater has emerged as a threat to human health and the environment. Therefore, this study aimed to develop biochar-cobalt ferrite (BCF) nanocomposite for the removal of methylparaben from water under the full factorial experimental design of 4 factors with 3 levels (3⁴). The biochar-CoFe₂O₄ nanocomposite was developed by co-precipitation method from cobalt ferrite and biochar of Eucalyptus tree bark. Adsorbent surface morphology and functional and elemental composition were carried out by scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy, and energy-dispersive X-ray spectroscopy (EDS) techniques which showed the presence of cracks with a rough surface, reasonable surface chemical composition, and many chemical functional groups, respectively. The experimental and predicted adsorption efficiencies ranged from 25.3 to 85.6% and 21.8 to 80.3%, respectively. The maximum adsorption performance (85.6%) reduced the methylparaben concentration from 27.5 to 4.0 mg/L at the optimum condition of adsorbent dose of 55 mg/100 mL, pH 6, contact time 90 min, and the initial methylparaben concentration of 27.5 mg/L. However, the adsorbent dose was the most influential main factor whereas the least influential was the interaction between solution pH and contact time under the regression model. The model also showed that 69% methylparaben removal was described by the regression model. The experimental data best fitted with the Freundlich model indicate multilayer adsorption which is the implication of physisorption. The sorption mechanism is attributed to Vander Waals forces, H-bonding, and dipole interaction. This BCF nanocomposite adsorbent appears to be promising for the removal of methylparaben from wastewater, but a further optimization process is essential to boost the treatment performance.

Mechanism of simultaneous lead and chromium removal from contaminated wastewater by a schwertmannite-like mineral

In this study, a schwertmannite-like mineral was synthesized for the removal of lead (Pb) and chromium (Cr) from contaminated wastewater. A shaking flask test was performed (150 r/min, 1 h) with FeSO₄·7H₂O, H₂O₂, Na₂SiO₃, and CaCl₂ added for the mineral synthesis reaction. Results show that optimal performance was achieved with the addition of 1.24 g/L FeSO₄·7H₂O, 0.75 g/L H₂O₂, 1.27 g/L Na₂SiO₃, and 0.44 g/L CaCl₂ at a water temperature of 28 °C, with coexisting ion (Na⁺, K⁺, Mg²⁺) concentrations of 1.50 mmol/L and 0.50 mmol/L EDTA as a complexing agent. Under these optimal conditions, maximum Pb and Cr removal rates of 95.08% and 97.99%, respectively, were achieved within the first 1 min of the mineral synthesis reaction, with the synthesis reaction completed by 6 min. The simultaneous removal of Pb and Cr during the schwertmannite-like material synthesis process occurred via electrostatic adsorption and coprecipitation. When the concentration of the complexing agent was increased from 0.75 to 6.03 mmol/L, the Pb removal rate decreased from 71.88 to 35.45%, and the Cr removal rate decreased from 95.13 to 75.07%, showing that Pb and Cr removal exhibited significant levels of inhibition. In contrast, varying reaction temperatures induced no significant differences. The Pb and Cr dissolution rates from Pb/Cr-containing schwertmannite-like minerals were 8.18% and 2.86% after 40 days, respectively. Therefore, the risk of secondary dissolution of heavy metals is small.