Toxicological assessment and adsorptive removal of lead (Pb) and Congo red (CR) from water by synthesized iron oxide/activated carbon (Fe3O4/AC) nanocomposite

Dual cross-linked magnetic gelatin/carboxymethyl cellulose cryogels for enhanced Congo red adsorption: Experimental studies and machine learning modelling

To achieve highly efficient and environmentally degradable adsorbents for Congo red (CR) removal, we synthesized a dual-network nanocomposite cryogel composed of gelatin/carboxymethyl cellulose, loaded with Fe3O4 nanoparticles. Gelatin and sodium carboxymethylcellulose were cross-linked using transglutaminase and calcium chloride, respectively. The cross-linking process enhanced the thermal stability of the composite cryogels. The CR adsorption process exhibited a better fit to the pseudo-second-order model and Langmuir model, with maximum adsorption capacity of 698.19 mg/g at pH of 7, temperature of 318 K, and initial CR concentration of 500 mg/L. Thermodynamic results indicated that the CR adsorption process was both spontaneous and endothermic. The performance of machine learning model showed that the Extreme Gradient Boosting model had the highest test determination coefficient (R2 = 0.9862) and the lowest root mean square error (RMSE = 10.3901 mg/g) among the 6 models. Feature importance analysis using SHapley Additive exPlanations (SHAP) revealed that the initial concentration had the greatest influence on the model's prediction of adsorption capacity. Density functional theory calculations indicated that there were active sites on the CR molecule that can undergo electrostatic interactions with the adsorbent. Thus, the synthesized cryogels demonstrate promising potential as adsorbents for dye removal from wastewater.

Bovine bone-based activated carbon composite containing nanomagnetite as a catalyst for photo-Fenton reactions

Magnetic composites (MC) prepared from magnetite nanoparticles (MNP) and activated carbon from bovine bone (AC) in different proportions (75/25, 50/50, and 25/75) were used as catalysts in the photo-Fenton process to degrade methylene blue (MB) in aqueous solution. The materials were prepared by the citrate-nitrate sol-gel synthesis method and used as catalysts in the photo-Fenton process. The photocatalytic tests were performed in a cylindrical reactor with a 4.13-cm internal diameter and 300-mL maximum capacity, equipped with 9.9-W visible light lamps. The specific surface area of the MC increased by up to 1138.39% with the addition of AC. Morphological analysis confirmed the anchoring of MNPs on the AC surface. The band gap values of the materials ranged from 1.16 to 1.55 eV and increased proportionally with the addition of AC to the MC compositions. MC-75/25 and MC-50/50 presented predominantly superparamagnetic behavior, while for MC-25/75 superparamagnetic and superimposed paramagnetic phases were observed. All samples showed good reduction of the MB concentration, exceeding 80% after 10 cycles of use. The mineralization advanced extensively to simple organic acids, proving the non-generation of harmful by-products and the efficiency of this photocatalytic system. The use of magnetic composites favored the efficient separation of the catalyst without causing secondary pollution, in addition to increasing the stability and reusability of the catalysts.

Waste newspaper as cellulose resource of activated carbon by sodium salts for methylene blue and congo red removal

The work was aimed at evaluating the adsorptive properties of waste newspaper (WN) activated carbons chemically produced using sodium salts for methylene blue (MB) and congo red (CR) removal. The activated carbons, designated as AC1, AC2, AC3 and AC4 were prepared through impregnation with NaH2PO4, Na2CO3, NaCl and NaOH, respectively and activation at 500 °C for 1 h. The activated carbons were characterized for surface chemistry, thermal stability, specific area, morphology and composition. The AC1 with a surface area of 917 m2/g exhibits a greater MB capacity of 651 mg/g. Meanwhile, a greater CR capacity was recorded by AC2 at 299 mg/g. The pseudo-second order model fitted well with the kinetic data, while the equilibrium data could be described by Langmuir model. The thermodynamic parameters, i.e.., positive ΔH°, negative ΔG° and positive ΔS° suggest that the adsorption of dyes is endothermic, spontaneous and feasible at high solution temperature. To conclude, WN is a potential cellulose source for producing activated carbon, while NaH2PO4 activation could be employed to convert WN into activated carbon for effective dye wastewater treatment.

Methylene blue and Congo red dye elimination from synthetic wastewater using Albizia lebbeck seed pod powder: isotherm and kinetic and mechanistic studies

This research examined the effectiveness of using Albizia lebbeck seed pods (ALB) as an adsorbent to remove dye effluents and clean up wastewater. More specifically, the binding capacity of methylene blue (MB) and Congo red (CR) dyes from aqueous solution using unmodified Albizia lebbeck seed pods (UALB) and citric acid modified Albizia lebbeck seed pods (CALB) were compared. The adsorbents underwent characterization via the use of Fourier transform infrared spectroscopy and scanning electron microscopy. Several operational factors were investigated using batch tests to ascertain their effects. These parameters included pH, adsorbent dose, interaction duration, and initial dye concentration. The residual dye concentrations were determined, and the data generated were fitted to equilibrium and kinetic models. In CALB and UALB, MB adsorption ideal pH values were 10 and 12, whereas CR optimal pH values were 3 and 2. Also, MB and CR equilibrium durations were 360 and 240 min, respectively. Temkin model best described the adsorption in CALB (r 2  = 0.9916, 0.9484) whereas Freundlich worked well for UALB in MB and CR (r 2  = 0.9626, 0.9871). Kinetic modeling of the adsorption data showed that the pseudo-second-order kinetic model provided the best fit (r 2  = 0.9998, 0.9999) for CALB and (r 2  = 1, 0.9992) for UALB for both MB and CR dyes. Maximum adsorption for MB was 9.499 mg/g and for CR it was 8.628 mg/g, and the findings showed a positive linear correlation between the concentration of dye-ions and their adsorption ability. The CALB also demonstrated superior efficacy in the removal of MB (4.661 mg/g) dye relative to CR (4.113 mg/g). The results of this study demonstrate that the use of ALB, in both modified and unmodified forms, is a cost-effective and efficient approach for the removal of MB and CR from the aqueous environment.

Synthesis of magnetic MFe2O4 (M = Ni, Co, Zn, Fe) supported on porous carbons derived from Bidens pilosa weed and their adsorptive comparison of toxic dyes

Bidens pilosa is classified as an invasive plant and has become a problematic weed to many agricultural crops. This species strongly germinates, grows and reproduces and competing for nutrients with local plants. To lessen the influence of Bidens pilosa, therefore, converting this harmful species into carbon materials as adsorbents in harm-to-wealth and valorization strategies is required. Here, we synthesized a series of magnetic composites based on MFe2O4 (M = Ni, Co, Zn, Fe) supported on porous carbon (MFOAC) derived from Bidens pilosa by a facile hydrothermal method. The Bidens pilosa carbon was initially activated by condensed H3PO4 to increase the surface chemistry. We observed that porous carbon loaded NiFe2O4 (NFOAC) reached the highest surface area (795.7 m2 g-1), followed by CoFe2O4/AC (449.1 m2 g-1), Fe3O4/AC (426.1 m2 g-1), ZnFe2O4/AC (409.5 m2 g-1). Morphological results showed nanoparticles were well-dispersed on the surface of carbon. RhB, MO, and MR dyes were used as adsorbate to test the adsorption by MFOAC. Effect of time (0-360 min), concentration (5-50 mg L-1), dosage (0.05-0.2 g L-1), and pH (3-9) on dyes adsorption onto MFOAC was investigated. It was found that NFOAC obtained the highest maximum adsorption capacity against dyes, RhB (107.96 mg g-1) < MO (148.05 mg g-1) < MR (153.1 mg g-1). Several mechanisms such as H bonding, π-π stacking, cation-π interaction, and electrostatic interaction were suggested. With sufficient stability and capacity, NFOAC can be used as potential adsorbent for real water treatment systems.

Comparative analysis of the equilibrium, kinetics, and characterization of the mechanism of rapid adsorption of Congo red on nano-biosorbents based on agricultural waste in industrial effluents

This study aims to remove Congo red dye from industrial effluent using economical agriculturally-based nano-biosorbents like magnetic orange peel, peanut shells, and tea waste. The nano-biosorbents were characterized by various analytical techniques like SEM, FT-IR, BET and XRD. The highest adsorption capacity was obtained under the following ideal conditions: pH = 6 (orange peel and peanut shells), pH = 3 (tea waste), and dosages of nano-biosorbents with varying timeframes of 50 min for tea waste and peanut shells and 30 min for orange peel. The study found that tea waste had the highest removal rate of 94% due to its high porosity and responsible functional groups, followed by peanut shells at 83% and orange peel at 68%. The Langmuir isotherm model was found to be the most suitable, with R2 values of 0.99 for tea waste, 0.92 for orange peel, and 0.71 for peanut shells. On the other hand, a pseudo-second-order kinetic model was very feasible, showing an R2 value of 0.99 for tea waste, 0.98 for peanut shells and 0.97 for orange peel. The significance of the current study lies in its practical application, enabling efficient waste management and water purification, thereby preserving a clean and safe environment.

Electrochemical sensors modified with iron oxide nanoparticles/nanocomposites for voltammetric detection of Pb (II) in water: A review

Permissible limits of Pb2+ in drinking water are being reduced from 10 μgL-1 to 5 μgL-1, which calls for rapid, and highly reliable detection techniques. Electrochemical sensors have garnered attention in detection of heavy metal ions in environmental samples due to their ease of operation, low cost, and rapid detection responses. Selectivity, sensitivity and detection capabilities of these sensors, can be enhanced by modifying their working electrodes (WEs) with iron oxide nanoparticles (IONPs) and/or their composites. Therefore, this review is an in-depth analysis of the deployment of IONPs/nanocomposites in modification of electrochemical sensors for detection of Pb2+ in drinking water over the past decade. From the analyzed studies (n = 23), the optimal solution pH, deposition potential, and deposition time ranged between 3 and 5.6, -0.7 to -1.4 V vs Ag/AgCl, and 100-400 s, respectively. Majority of the studies employed square wave anodic stripping voltammetry (n = 16), in 0.1 M acetate buffer solution (n = 19) for detection of Pb2+. Limits of detection obtained (2.5 x 10-9 - 4.5 μg/L) were below the permissible levels which indicated good sensitivities of the modified electrodes. Despite the great performance of these modified electrodes, the primary source of IONPs has always been commercial iron-based salts in addition to the use of so many materials as modifying agents of these IONPs. This may limit reproducibility and sustainability of the WEs due to lengthy and costly preparation protocols. Steel and/or iron industrial wastes can be alternatively employed in generation of IONPs for modification of electrochemical sensors. Additionally, biomass-based activated carbons enriched with surface functional groups are also used in modification of bare IONPs, and subsequently bare electrodes. However, these two areas still need to be fully explored.

Review in application of blast furnace dust in wastewater treatment: material preparation, integrated process, and mechanism

Blast furnace dust (BFD) is the solid powder and particulate matter produced by dust removal process in ironmaking industry. The element composition of BFD is complex, and a direct return to sintering will lead to heavy metal enrichment and blast furnace lining corrosion. In recent years, the application of BFD in wastewater treatment has attracted widespread attention. Based on the mechanisms of action of BFD in wastewater, this paper discusses in detail the application of BFD in iron-carbon micro-electrolysis, biological enhancement, adsorption, flocculation, and Fenton/Fenton-like reactions. Iron oxides and carbon in BFD are key substances. Thus, BFD has great potential as a raw material in wastewater treatment, and the waste utilization of BFD can be realized. However, the difference in elements and composition of BFD limits its large-scale application. We can classify BFD according to different proportions of elements. In the future, it is necessary to focus on the service life of BFD in water and whether it shall bring secondary pollution to water.

Modification of cellulosic adsorbent via iron-based metal phenolic networks coating for efficient removal of chromium ion

Surface modification of durian rind cellulose (DCell) was done by utilizing the strong coordination effect of polyphenol-based metal phenolic networks (MPNs). MPNs from Fe(III)-tannic acid (FTN) and Fe(III)-gallic acid (FGN) were coated on DCell via a self-assembly reaction at pH 8, resulting in adsorbent composites of FTN@DCell and FGN@DCell for removal of Cr(VI). Batch adsorption experiments revealed that FTN coating resulted in an adsorbent composite with higher adsorption capacity than FGN coating, owing to the greater number of additional adsorption sites from phenolic hydroxyl groups of tannic acid. FTN@DCell exhibits an equilibrium adsorption capacity at 30°C of 110.9 mg/g for Cr(VI), significantly higher than FGN@DCell (73.63 mg/g); the adsorption capacity was increased at higher temperature (i.e., 155.8 and 116.8 mg/g at 50°C for FTN@DCell and FGN@DCell, respectively). Effects of pH, adsorbent dose, initial concentration, and coexisting ions on Cr(VI) removal were investigated. The kinetics fractal-based model Brouers-Sotolongo indicates the 1st and 2nd order reaction for Cr(VI) adsorption on FTN@DCell and FGN@DCell, respectively. The isotherm data can be described with a fractal-based model, which implies the heterogeneous nature of the adsorbent surface sites. The Cr(VI) adsorption via surface complexation with phenolic hydroxyl groups was confirmed by evaluating the functional groups shifting. FGN@DCell and FTN@DCell were found to have good reusability, maintaining over 50 % of their adsorption efficiency after four adsorption-desorption cycles. Environmental assessment with Arabidopsis thaliana demonstrated their potential in eliminating the Cr(VI) phytotoxic effect. Thus, this study has shown the efficient and economical conversion of durian waste into environmentally benign adsorbent for heavy metal treatment.

Sustainable remediation of toxic congo red dye pollution using bio based carbon nanocomposite: Modelling and performance evaluation

Remediation of synthetic dyes found in aqueous environment poses a serious challenge for treatment due to their resistance to chemical and biological degradation. This research study investigated the application of Chitosan-ZnO-Seaweed bio nanocomposite in the remediation of congo red. The novel bionanocomposite was characterised by FTIR, SEM, TEM, EDS and XRD studies. The FTIR spectra and SEM images indicated the adsorption of congo red onto the synthesized bionanocomposite. The batch wise experimental studies were done to explore the influence of process variables on removal of congo red from synthetic wastewater and to determine optimized conditions. Under optimized conditions of pH 3, temperature 40 °C, initial congo red concentration 50 mg/L, bionanocomposite quantity 0.03 g/L and interaction period 30 min, the bionanocomposite removed 95.64% of congo red. Thermodynamic studies were carried out and the parameters, ΔH° and ΔS° were found to be 38.386 kJ/mol and 0.1451 kJ/mol. K, respectively. The isotherm and kinetic study showed that monolayer Langmuir model was obeyed (R2 = 0.968) and the experimental value of congo red adsorption correlated well with pseudo second order model (R2 = 0.9938) respectively. The maximum adsorption capacity was found to be 303.03 mg/g. Protonated amino group of chitosan, hydroxyl group of seaweed accounts for congo red adsorption along with zinc oxide.

Process optimization of adsorptive phytoremediation of mutagenic brilliant green dye for health risk management using chemically activated Symplocos racemosa agro-waste

Textile industries use large amounts of water as well as dyes. These dyes containing water are then discharged into the water bodies causing a significant role in water pollution. Brilliant Green dye contributes to many harmful diseases related to the respiratory and gastrointestinal tract. In this study, Symplocos racemosa (SR) agro-waste was chemically treated with acid (SR-HCl) and base (SR-NaOH) and then used for removing Brilliant Green Dye (BGD) on the batch scale. They were characterized by SEM, EDX, FTIR, XRD, TGA and DSC. Optimized conditions were 30 °C temperature, pH 6, adsorbent dose of 0.10 g/25 ml dye solution, shaking speed of 100 revolutions per minute, initial dye concentration of 50 ppm and 35 min time for shaking adsorbent and dye solution. Adsorption data obtained were analyzed using isotherms. The experimental data was found to fit well with the Langmuir model and the maximum adsorption capacity (qmax) of BGD on the SR, SR-HCl, and SR-NaOH was revealed to be 62.90, 65.40, and 71 mg/g respectively. Kinetic data (pseudo-first-order and pseudo-second-order) were evaluated and adsorption tends to follow the pseudo-2nd-order, which indicated the chemisorption mechanism. The results revealed that Symplocos racemosa agro-waste can be considered as the potential biosorbent.

Synthesis and application of manganese-doped zinc oxide as a potential adsorbent for removal of Congo red dye from wastewater

Synthetic dyes are considered toxic compounds and as such are not easily removed by conventional water treatment processes. This study demonstrated the synthesis of pure and manganese- (Mn), silver- (Ag), and iron- (Fe) doped zinc oxide (ZnO) nanoparticles via the wet chemical route. In particular, it investigated the batch adsorption studies and physiochemical properties of synthesized pure and doped ZnO materials for removing toxic congo red (CR) dye. X-ray diffraction (XRD), Raman spectroscopy, and energy-dispersive X-ray spectroscopy (EDS) confirmed the synthesis of the pure and doped ZnO materials. The batch adsorption investigation revealed adsorption efficiencies of 99.4% for CR dye at an optimal dose of 0.03 g/30 ml for Mn-doped ZnO at a solution pH of 2. The adsorption capacity of each of the synthesized materials was found to be in order Mn-doped ZnO (232.5 mg/g) > Ag-doped ZnO (222.2 mg/g) > pure ZnO (212.7 mg/g) > Fe-doped ZnO (208.3 mg/g). Both pseudo-second-order kinetics model and the Langmuir isotherm model accurately explained the adsorption behaviors of CR dye. As such, Van der Waal interactions, H-bonding, and electrostatic interaction were found to be the adsorption mechanisms responsible for dye removal. In addition, the desorption-regeneration investigation indicated the successful reuse of the exhausted Mn-doped ZnO material for five cycles of CR dye adsorption with an efficiency of 83.1%. Overall, this study has demonstrated that Mn-doped ZnO could be considered a viable adsorbent for the cleanup of dye-contaminated water.

Kinetic study for removal of cationic hexamethyl pararosaniline chloride dye using phytoremediation

The present investigation provides a kinetic study for the removal of hexamethyl pararosaniline chloride, a hazardous dye, by phytoremediation using a water plant. It reveals Salvinia molesta has a phytoremediation tendency. The ability of Salvinia molesta to remove crystal violet (CV) dye is investigated with kinetic study in this research. Phytoremediation is done for different concentrations of hexamethyl pararosaniline chloride with varying pH and weight of Salvinia molesta Mitchell. About 88% of hexamethyl pararosaniline chloride has been decolourised from 50 mg L-1 solution at pH of 6 with 4 g of Salvinia molesta Mitchell. The results obtained for hexamethyl pararosaniline chloride removal at pH of 6 are studied for pseudo-first order, pseudo-second order and Elovich kinetics. The resulting curve for removal of hexamethyl pararosaniline chloride indicates that phytoremediation process follows pseudo-second order kinetics with correlation value R2 ≥ 0.985. The Salvinia molesta used at pH 6 has been reused and the decolourisation has been achieved at about 84% for 50 mg L-1 solution of CV dye. The FTIR results reveal the phytoextraction of CV in the roots by interaction of functional groups. From the experimental results, Salvinia molesta Mitchell can be used to treat textile wastewater and wet land.

Iron oxide nanoparticles/nanocomposites derived from steel and iron wastes for water treatment: A review

Iron oxide nanoparticles (IONPs) are characterized by superior magnetic properties, high surface area to volume ratio, and active surface functional groups. These properties aid in removal of pollutants from water, through adsorption and/or photocatalysis, justifying the choice of IONPs in water treatment systems. IONPs are usually developed from commercial chemicals of ferric and ferrous salts alongside other reagents, a procedure that is costly, environmentally unfriendly and limits their mass production. On the other hand, steel and iron industries produce both solid and liquid wastes which in most cases are piled, discharged into water streams or landfilled as strategies to dispose them off. Such practices are detrimental to environmental ecosystems. Given the high content of iron present in these wastes, they can be used to generate IONPs. This work reviewed published literature through selected key words on the deployment of steel and/or iron-based wastes as IONPs precursors for water treatment. The findings reveal that steel waste-derived IONPs have properties such as specific surface area, particle sizes, saturation magnetization, and surface functional groups that are comparable or sometimes better than those synthesized from commercial salts. Furthermore, the steel waste-derived IONPs have high removal efficacy for heavy metals and dyes from water with possibilities of being regenerated. The performance of steel waste-derived IONPs can be enhanced by functionalization with different reagents such as chitosan, graphene, and biomass based activated carbons. Nonetheless, there is need to explore the potential of steel waste-based IONPs in removing contaminants of emerging concern, modifying pollutant detection sensors, their techno-economic feasibility in large treatment plants, toxicity of these nanoparticles when ingested into the human body, among other areas.

Removing methylene blue from water: A study of sorption effectiveness onto nanoparticles-doped activated carbon

In this present study, silver (Ag) and titanium dioxide (TiO₂) nanoparticles were successfully deposited on coconut shell-derived activated carbon (CSAC), to synthesize a novel nanocomposite (CSAC@AgNPs@TiO₂NPs) for the adsorption of Methylene Blue (MB) dye from aqueous solution. The fabricated CSAC@AgNPs@TiO₂NPs nanocomposite was analyzed by Scanning Electron Microscope (SEM), X-ray Diffraction (XRD), Fourier-Transform Infrared Spectroscopy (FTIR), Transmission Electron Microscope (TEM) equipped with Energy Dispersive X-ray spectroscopy (EDS) detector, X-ray Photoelectron Spectroscope (XPS), and Brunauer-Emmett-Teller (BET). The successful deposition of AgNPs and TiO₂NPs on CSAC surface was revealed by the TEM/EDX, SEM, and XPS analysis. The mesopore structure of CSAC@AgNPs@TiO₂NPs has a BET surface area of 301 m²/g. The batch adsorption studies were conducted and the influence of different parameters, i.e., adsorbent dose, adsorption time, initial dye concentration, pH and temperature were investigated. The nonlinear isotherm and kinetic modelling demonstrated that adsorption data were best fitted by Sips isotherm and pseudo-second-order models, respectively. The maximum adsorption capacity of MB onto CSAC@AgNPs@TiO₂NPs by the Sips model was 184 mg/g. Thermodynamic results revealed that the adsorption was endothermic, spontaneous and physical in nature. CSAC@AgNPs@TiO₂NPs revealed that MB absorption by CSAC@AgNPs@TiO₂NPs was spontaneous and endothermic. The uptake capacity of MB was influenced significantly by the presence of competing ions including, NO₃^-, HCO_3, Ca²⁺, and Na⁺. Repeated tests indicated that the CSAC@AgNPs@TiO₂NPs can be regenerated and reused six times before being discarded. The primary separation mechanism between MB dye and CSAC@AgNPs@TiO₂NPs was the electrostatic interaction. Thus, CSAC@AgNPs@TiO₂NPs was an outstanding material, which displayed good applicability in real water with ≥ 97% removal of MB dye.

Synthesis of Green Magnetite/Carbonized Coffee Composite from Natural Pyrite for Effective Decontamination of Congo Red Dye: Steric, Synergetic, Oxidation, and Ecotoxicity Studies

Green magnetite/carbonized spent coffee (MG/CFC) composite was synthesized from natural pyrite and characterized as an adsorbent and catalyst in photo-Fenton’s oxidation system of Congo red dye (C.R). The absorption behavior was illustrated based on the steric and energetic parameters of the advanced Monolayer equilibrium model of one energetic site (R2 > 0.99). The structure exhibits 855 mg/g as effective site density which induces its C.R saturation adsorption capacity to 436.1 mg/g. The change in the number of absorbed C.R per site with temperature (n = 1.53 (293) to 0.51 (313 K)) suggests changes in the mechanism from multimolecular (up to 2 molecules per site) to multianchorage (one molecule per more than one site) processes. The energetic studies (ΔE = 6.2–8.2 kJ/mol) validate the physical uptake of C.R by MG/CFC which might be included van der Waals forces, electrostatic attractions, and hydrogen bonding. As a catalyst, MG/CFC exhibits significant activity during the photo-Fenton’s oxidation of C.R under visible light. The complete oxidation of C.R was detected after 105 min (5 mg/L), 120 min (10 mg/L), 135 min (15 mg/L), 180 min (20 mg/L), and 240 min (25 mg/L) using MG/CFC at 0.2 g/L dosage and 0.1 mL of H2O2. Increasing the dosage up to 0.5 g/L reduce the complete oxidation interval of C.R (5 mg/L) down to 30 min while the complete mineralization was detected after 120 min. The acute and chronic toxicities of the treated samples demonstrate significant safe products of no toxic effects on aquatic organisms as compared to the parent C.R solution.

A critical review on biochar-assisted free radicals mediated redox reactions influencing transformation of potentially toxic metals: Occurrence, formation, and environmental applications

Potentially toxic metals have become a viable threat to the ecosystem due to their carcinogenic nature. Biochar has gained substantial interest due to its redox-mediated processes and redox-active metals. Biochar has the capacity to directly adsorb the pollutants from contaminated environments through several mechanisms such as coprecipitation, complexation, ion exchange, and electrostatic interaction. Biochar's electron-mediating potential may be influenced by the cyclic transition of surface moieties and conjugated carbon structures. Thus, pyrolysis configuration, biomass material, retention time, oxygen flow, and heating time also affect biochar's redox properties. Generally, reactive oxygen species (ROS) exist as free radicals (FRs) in radical and non-radical forms, i.e., hydroxyl radical, superoxide, nitric oxide, hydrogen peroxide, and singlet oxygen. Heavy metals are involved in the production of FRs during redox-mediated reactions, which may contribute to ROS formation. This review aims to critically evaluate the redox-mediated characteristics of biochar produced from various biomass feedstocks under different pyrolysis conditions. In addition, we assessed the impact of biochar-assisted FRs redox-mediated processes on heavy metal immobilization and mobility. We also revealed new insights into the function of FRs in biochar and its potential uses for environment-friendly remediation and reducing the dependency on fossil-based materials, utilizing local residual biomass as a raw material in terms of sustainability.

A review on activated carbon modifications for the treatment of wastewater containing anionic dyes

Polluted water resources, particularly those polluted with industrial effluents' dyes, are carcinogenic and hence pose a severe threat to sustainable and longstanding worldwide development. Meanwhile, adsorption is a promising process for polluted/wastewater treatment. In particular, activated carbon (AC) is popular among various wastewater treatment adsorbents, especially in the organic contaminants' remediation in wastewater. Hence, the AC's synthesis from degradable and non-degradable resources, the carbon activation involved in the AC synthesis, and the AC's modification to cutting-edge and effective materials have been modern-research targets in recent years. Likewise, the main research focuses worldwide have been the salient AC characteristics, such as its surface chemistry, porosity, and enhanced surface area. Notably, various modified-AC synthesis methods have been employed to enhance the AC's potential for improved contaminants-removal. Hence, we critically analyze the different modified ACs (with enhanced (surface) functional groups and textural properties) of their capacity to remove different-natured anionic dyes in wastewater. We also discuss the corresponding AC modification techniques, the factors affecting the AC properties, and the modifying agents' influence on the AC's morphological/adsorptive properties. Finally, the AC research of future interest has been proposed by identifying the current AC research gaps, especially related to the AC's application in wastewater treatment.

Studies on the Removal of Congo Red Dye by an Adsorbent Based on Fly-Ash@Fe3O4 Mixture

The effectiveness of a Fe3O4-loaded fly ash composite for the adsorption of Congo red dye was assessed in this work. The structure and properties of the magnetic adsorbent were established by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffractometer (XRD), vibrating sample magnetometer (VSM), and dynamic light scattering (DLS). The magnetic results showed a saturation magnetization value of 6.51 emu/g and superparamagnetic behavior. The main parameters that influence the removal of Congo red dye adsorbent such as dose, initial concentration, and contact time were examined. The Freundlich adsorption isotherm and pseudo-second-order kinetic model provided the best fit for the experimental findings. The Congo red dye’s maximum adsorption capacity of 154 mg/g was reported in the concentration range of 10–100 mg/L, using the proposed magnetic adsorbent. The results of the recyclability investigation demonstrated that the circular economy idea is valid. The adsorbent that was synthesized was also further characterized by XRD and FTIR techniques after Congo red dye adsorption.