Adsorption Of Cr Research Articles

Chitosan-based composite featuring dual cross-linking networks for the removal of aqueous Cr(VI)

To avoid the environmental detriment caused by Cr(VI) waste, this study constructs a dual cross-linking network structure using sodium alginate (SA) and polyvinyl alcohol (PVA). Chitosan (CS) is further introduced through electrostatic attraction and hydrogen bonding and SA/PVA/CS (SPC) composite with porous structure is successfully prepared for the removal of Cr(VI) from wastewater. Batch adsorption experiments show that SPC has excellent adsorption capacity and practical usability with a broad pH applicability range. Under optimal adsorption conditions (pH = 2, t = 150 min, T = 35 °C, m/V = 2 g/L, C0 = 10 mg/L), the Cr(VI) removal rate of SPC achieves 89.2 %. Adsorption kinetics and isotherm models indicate that the adsorption process is primarily multi-layer and chemical adsorption. Additionally, FT-IR and XPS reveal that the adsorption mechanism of SPC for Cr(VI) involves a synergy of electrostatic attraction, reduction, ion exchange and complexation. Density functional theory (DFT) simulations also confirm the dominant role of CS in the Cr(VI) adsorption. In summary, SPC shows great potential for Cr(VI) wastewater treatment.

Citric acid functionalized chitosan hydrogel beads for enhanced Cr(VI) removal: Experimental assessment and COMSOL modelling of adsorption in a fixed-bed system

Chitosan hydrogel beads (CHB) and cross-linked CHB functionalized with tricarboxylic citric acid (CA-GLA-CHB) were synthesized and used for the removal of Cr(VI) from aqueous solutions in batch and dynamic adsorption systems. Applicability of COMSOL Multiphysics software as a tool for predictive modelling of column dynamics using a minimum set of experimental parameters was tested and compared with experimental results. Batch experiments demonstrated that CA-GLA-CHB showed almost 20% higher adsorption capacity and wider operational pH range compared to non-functionalized CHB. In a dynamic system, CA-GLA-CHB was used as column packing material and the column dynamics was investigated at different conditions. The breakthrough and exhaustion time of the column increased with an increase in bed height and a decrease in feed flow rate and initial Cr(VI) concentration. Computational modeling by COMSOL software with implemented Advection-Dispersion-Reaction (ADR) equation was used to simulate breakthrough curves for the applied dynamic system in order to validate the possibility of its application for process design in the scaled-up fixed-bed column systems for wastewater treatment. The simulated breakthrough curves of Cr(VI) adsorption matched well with the experimental, thus proving that COMSOL Multiphysics software can be used for scaling-up fixed-bed column systems packed with low-cost and effective CA-GLA-CHB bioadsorbent.

ZnO Impregnated Graphene Silica Composite to Enhance Cr(VI) Adsorption: Batch Studies

Abstract Hexavalent chromium [Cr(VI)] is a profoundly poisonous heavy metal due to its significant mobility across cell membranes as HCrO4 − and CrO4 2- ions. There is a limited amount of research on the effectiveness of metal oxide impregnated graphene silica composite (GSC) as adsorbents for treating [Cr(VI)]. However, the existing studies indicate that these composites are very efficient. The project involved synthesizing a new type of adsorbent by impregnating zinc oxide (ZnO) particles onto a composite material of graphene and silica. This was achieved using the co-precipitation method. The findings revealed that the highest level of Cr (VI) removal (97%) is achieved at basic, a contact period of 45 minutes. The Langmuir isotherm had the highest degree of fit, suggesting a uniform and chemical adsorption process with the highest possible adsorption capacity of 142 mg/g. The application of ZnO on GSC improves the motion of Cr(VI) in the composite, resulting in an increase in both the adsorption capacity and adsorption kinetics. The findings of this investigation show that the ZnO/GSC composite is a very effective and versatile adsorbent for treating wastewater, highlighting its new and reusable properties.

Adsorptive potential of apricot (Prunus Armeniaca) stone in the removal of Cr (VI) and Fe (II) ions from Aquatic Systems: Kinetic and isothermal investigations

Biogenic adsorbents have emerged as a promising alternative to the traditional remediation techniques of heavy-metals contaminated water treatment. Using apricot (Prunus Armeniaca) stone as a naturally derived adsorbent, the current study provides a comprehensive analysis of the kinetic and isothermal characteristics associated with Cr (VI) and Fe (II) ion adsorption. The results show that 0.5 mg of the adsorbent removed approximately 90 % of Cr (VI) and Fe (II) ions from 100 ppm solutions within 120 min at 298 K at 300 rpm stirring speed. Equilibrium was attained within 90 to 120 min, with a significant increase in the removal percentage observed in the first 30–40 min for both metals compared to the subsequent 80–90 min. The optimal pH conditions for adsorption were determined to be acidic (pH = 1.5) for Cr (VI) and neutral (pH = 7) for Fe (II). The adsorption kinetics followed a pseudo-second order model, while the isothermal equilibrium data best fit the Freundlich model over the Langmuir model. Moreover, the thermodynamic parameters, including ΔG°, ΔH°, and ΔS°, indicated that the sorption process is spontaneous, feasible, and endothermic. The response surface methodology (RSM) analysis showed a high level of accuracy in predicting the percent removal. These findings illustrate the effectiveness of apricot stone as a low-cost and environmentally conscious adsorbent, contributing to the development of sustainable water treatment technologies.

Crucial role of humic substance type in Cr(VI) reduction by humic substance-Fe(III) coprecipitates but not in adsorption

Wetlands exhibit a self-purification effect on Cr(VI) owing to the adsorption and reduction capabilities of their humic substance (HS)-Fe(III) coprecipitates. However, the similarities and differences in the adsorption and reduction of Cr(VI) by different types of HS-Fe(III) coprecipitates remains unknown. In this study, fulvic acid (FA)- and humic acid (HA)-Fe(III) coprecipitates were synthesized with initial C/Fe ratios ranging from 0.25 to 15, and a comparative analysis of their adsorption and reduction effects was conducted. The results showed that FA- and HA-Fe(III) coprecipitates exhibit similar abilities to adsorb Cr(VI) by forming inner-sphere complexes with ferrihydrite (Fh), as well as with FA/HA. The association between FA/HA and Fe(III) not only blocked certain FeOH adsorption sites, but also enhanced the electrostatic repulsion towards Cr(VI), resulting in a proportionate decrease in their adsorption ability. For reduction, inductive and intrinsic reduction were involved in both FA- and HA-Fe(III) coprecipitates. However, the synergism/antagonism differed with the inherent sites (e.g., phenolic hydroxyl, ArOH) and activated sites (e.g., alcoholic hydroxyl, AlOH). Based on the size differences between FA and HA, the AlOH contained in FA was more easily activated by Fe(III) than that in HA, owing to the shorter induction path required. Thus, consistent synergism was observed in FA-Fe(III) coprecipitates regardless of Fe(III) species. In contrast, synergism was only observed in HA-Fe(III) coprecipitates containing Fh, because the inductive ability of Fe(III) cations was too weak to activate AlOH through the longer path. Moreover, with irreversible consumption of AlOH, intrinsic reduction became the dominant pathway at concentrations >1 mM Cr(VI). The preferential elimination of ArOH subsequently led to a transition to antagonism. These outcomes deepen our scientifical understanding of the environmental effects of HS-Fe(III) coprecipitates and offer new perspectives for exploring their potential applications in the remediation of Cr-contaminated sites.

Binding mechanisms of trivalent chromium on colloidal phases from ultramafic systems: Insights from batch experiments and XAS analysis

Understanding the availability and mobility of chromium is a key factor in gaining insight into the fate of chromium and thus essential for assessing the risk of contamination and developing effective remediation strategies. In the natural environment, such as ultramafic systems, which are natural pools of chromium, chromium occurs mostly in the trivalent state (Cr(III)), which is known to have a high affinity for the solid phases such as particles and colloids. However, since Cr(VI) is more toxic, the vast majority of experimental studies focus on its reduction to Cr(III), which is often considered to form (hydr)oxide precipitates due to its poor solubility. Furthermore, while the oxidation state of Cr dictates its geochemical behavior, its interaction with particles and colloids is rarely controlled or monitored. Therefore, the interaction mechanisms between Cr(III) and particles or colloids require further attention. In this study, ten mineral phases (goethite, hematite, pyrolusite, kaolinite, montmorillonite, chlorite, serpentine, fuchsite, amphibole, and chromite) and one organic phase (humic acid), relevant to chromium bearing and carrier phases in ultramafic soils, were investigated to explore their interaction with Cr(III) species. These phases were first characterized by various techniques (including XRD, XRF, SEM, and BET). Adsorption and desorption experiments of Cr(III) on these phases were then carried out, and the distribution of Cr oxidation states in both the aqueous and solid phases was carefully monitored using UV–vis spectroscopy, geochemical speciation modeling, and Cr K-edge XAS spectroscopy. With the exception of pyrolusite, where partial oxidation of Cr(III) to Cr(VI) occurred, Cr(III) was shown to persist as a single oxidation state in all experiments. Desorption analyses showed significantly low desorbed rates, which further confirmed the prevalence of Cr(III). Experimental sorption isotherm data were interpreted using the Langmuir model and its linearized form, which provides important thermodynamic characteristics of adsorbents related to their structural and surface features. This study will provide better constraints for the understanding and prediction of Cr behavior and fate in the environment, especially in ultramafic systems.

Biodegradable taro stem cellulose aerogel: A simple approach for adsorbing microplastics and dyestuffs contaminants

Water pollution and agricultural waste are pressing global issues. Herein, a biomass aerogel derived from waste taro stem microcrystalline cellulose (TS-MCC) was fabricated, in which, the effects of cellulose amount, cross-linker content, pre-freezing protocols on the aerogel’s property were studied. The optimized TS-MCC2.0 aerogel exhibited a hierarchical porous structure with good mechanical property (65.04 kPa) and adsorption capacities, with the qm towards microplastics (Polystyrene, PS) and dye (Congo red, CR) being 418.6 mg/g and 951.51 mg/g at 298 K, respectively. Meanwhile, it exhibited good applicability under different pH (3–11) and ionic strength environments, as well as the retained notably simultaneous adsorption ability even under mixed contaminant systems. The mathematical models suggested that the adsorption of PS and CR both fitted pseudo-second-order kinetics, and the adsorption isotherms could be described by the Langmuir and Freundlich models, respectively. Hydrogen bonding, electrostatic attraction, and π–π interactions were inferred as the main adsorption mechanisms towards PS and CR according to Fourier transform infrared spectrometer and X-ray photoelectron spectroscopy analysis. Moreover, the adsorption efficiencies were 92.37 % for PS and 88.34 % for CR after 5 reuse cycles. Therefore, this study provides a green aerogel sorbent for adsorbing microplastics and dyes contaminants.

Photoresponse of Ti3C2Tx MXene promotes its adsorptive-reductive removal of Cr(VI) from water

MXenes, such as Ti3C2Tx, demonstrate tremendous potential as heavy metal adsorbents due to their abundant reaction sites, high hydrophilicity, controllable interlayer spacing, and inherent reduction ability. However, their structural dependent pollutant removal performances and the related mechanisms are far less studied. Therefore, the removing abilities of Cr(VI) from water on Ti3C2Tx MXenes with different structures (multilayer (ML-) and delaminated (DL-) Ti3C2Tx) synthesized via several etching techniques were evaluated. Focusing on the most effective ML- and DL-Ti3C2Tx obtained by acid/fluoride salt etching, the impacts of structural variations on the Cr(VI) removal performances were explored. Both ML- and DL-Ti3C2Tx demonstrate outstanding Cr(VI) adsorption and reduction capabilities, achieving equilibrium within 500 min with capacities of 92.7 and 205 mg/g, respectively. The differences in removal mechanisms stemed from the varying adsorption and reduction capacities of two MXenes. ML-Ti3C2Tx, with lower surface area and porosity, had low adsorption capacity but superior reduction ability, efficiently converting most Cr(VI) to Cr(III) (66.8%). Conversely, DL-Ti3C2Tx exhibited better removal efficiency but a lower capacity for reduction (45.7%). Notably, although the partial reduction of DL-Ti3C2Tx to TiO2 results in its limited chemical reduction capacity, Ti3C2Tx might serve as a co-catalyst for TiO2, boosting the photoresponsiveness of DL-Ti3C2Tx or TiO2 through Ti3C2Tx/TiO2 heterojunctions, thereby facilitating photocatalysis to realize the reduction of Cr(VI). Both Ti3C2Tx exhibited both excellent Cr(VI) removal capacity and detoxification capacity, demonstrating their high potential in treating heavy metal pollutants in wastewater.

Surface modified novel synthesis of Spirulina assisted mesoporous TiO2@CTAB nanocomposite employed for efficient removal of chromium (VI) in wastewater

In this study, an investigation of the adsorption efficiency of a novel Spirulina based TiO2@CTAB nanoparticle is carried out against one of the highly toxic heavy metal Cr (VI). The co-precipitation method was used to prepare the nanoparticles which were analyzed by various techniques including XRD, UV–Vis spectroscopy, Raman Spectroscopy, FT-IR, BET, FESEM with EDX, Zeta Potential, and Particle Size Analyzer. The pore diameter of the TiO2@CTAB nanocomposite was found to be 3.425 nm with a total surface area of 125.709 m2/g. The pHZPC and XPS studies were used to describe the mechanism of adsorption of Cr (VI) by TiO2@CTAB. For synthesized material, the Langmuir adsorption isotherm model exhibits improved adsorption than the Freundlich adsorption isotherm model, having a removal capacity of 127.551 mg/g. The adsorption of CR (VI) on the surface of TiO2@CTAB follows pseudo-second-order kinetics having an R2 value of 0.99983. Furthermore, the prepared mesoporous TiO2@CTAB adsorbent has high reusability without considerable degradation and may avoid the production of secondary pollutants to a large extent.

Development of two-dimensional amyloid fibril/carboxymethyl cellulose hybrid membranes for effective adsorption of hexavalent chromium

Amyloid fibrils (AFs) are protein aggregates with highly ordered fibrillar structures and can be formed via self-assembly of proteins under appropriate conditions. Owing to the unique properties of AFs, e.g., high surface-to-volume ratio and versatile functional groups, they offer abundant binding sites for the efficient adsorption of hexavalent chromium (Cr(VI)). This study was aimed at examining the performance of two-dimensional AF-based hybrid membranes for adsorbing Cr(VI). First, AF/carboxymethyl cellulose (AF/CMC) hybrid membranes were synthesized via chemical crosslinking coupled with phase inversion, followed by investigating the synthesis mechanism using Fourier transform infrared spectroscopy. Our results revealed that the surface microstructures and mechanical properties of the hybrid membranes could be affected by the AF:CMC mass ratio of the membrane. The porosity and ζ-potential of hybrid membranes were found to be dependent on both pH value and membrane composition. Analyses of the kinetics and thermodynamic behavior of Cr(VI) adsorption on the AF/CMC hybrid membranes revealed that the initial adsorption rate and maximum adsorption capacity were determined to be ∼149.20 mg g–1 h–1 and ∼311.11 mg g–1, respectively. The Cr(VI) removal percentage of hybrid membrane with high CMC content was found to remain at >75 % after five successive adsorption-desorption cycles. Finally, the mechanism and interactions involved in the adsorption of Cr(VI) on the hybrid membrane were further investigated via thermodynamic analysis and X-ray photoelectron spectroscopy. This study provides an excellent example of harnessing AF-based membranes in water remediation, highlighting the potential of AF-based hybrid materials for wastewater treatment applications.

Amine-functionalized cellulose-silica composites for the remediation of hexavalent chromium (Cr IV) in contaminated water

Adsorption method for Hexavalent chromium (Cr(VI) removal from domestic and industrial wastewater is widely desirable due to public health concern of the heavy metal. The purpose of this study was to investigate the evaluation of Cr(VI) adsorption using a novel adsorbent: amine-functionalized cellulose-silica composite derived from banana fibers. We employed the in-situ sol–gel method to create cellulose-silica silane functionalized composites, analyzing them through different characterization techniques such as Attenuated total reflectance- Fourier transform infrared spectroscopy (ATR-FTIR), X-ray Diffraction Analysis (XRD), Thermo gravimetric analysis (TGA)/differential thermogravimetric (DTG), Brunauer–Emmett–Teller (BET), Scanning Electron Microscopy (SEM), and Transmission Electron Microscopy (TEM) techniques. ATR-FTIR depicted key organic constituents in raw banana pseudo stem fibers (BF) and the formation of SiO bonds in BCSiO2 composite, and further enhanced by the grafting of N-[3-(trimethoxysilyl)propyl ethylenediamine (DAPTMS) onto the BC-SiO2 surface in BC-SiO2-DAPTMS. XRD and TGA/DTG analyses revealed changes in crystallinity and thermal stability, while BET analysis showcased altered surface area and pore characteristics in BC-SiO2-DAPTMS (2 %). SEM and TEM imaging provided visual evidence of structural modifications and improved dispersion in BC-SiO2-DAPTMS composites. The impact of composite weight, contact time, and pH on Cr(VI) removal rates was examined, revealing optimal performance at slightly acidic pH 4 value (80.7 %) and enhanced efficiency with increased contact time of 65 min (86.66 %), composite weight of 1 g (82.62 %), and initial concentration was for 0.8 mg/l (80 %). The kinetics and isotherms analyzed using pseudo second order (PSO) and pseudo first order (PFO) models, highlight the composite’s efficiency. The Freundlich model was found to better fit the adsorption isotherm data, while the PSO model described the kinetics more accurately. These insights contribute to optimizing the BC-SiO2-DAPTMS (2 %) composite for efficient Cr(VI) ion removal in water treatment applications.

A novel sequential extraction method for the measurement of Cr(VI) and Cr(III) species distribution in soil: New insights into the chromium speciation

The distribution characteristics of Cr(VI) species in contaminated soil is crucial for soil remediation; however, there is currently a lack of methods for analysing anionic Cr(VI) species in soil. This study has developed a novel sequential extraction method for speciation of Cr(VI) and Cr(III). Besides extraction experiments, simulated chromium species were prepared to verify the presence of proposed chromium species. The results show that Cr(VI) species in soil can be categorized into water-soluble Cr(VI), electrostatically adsorbed Cr(VI), Cr(VI) specifically adsorbed by minerals containing exchangeable Ca2+, Cr(VI) specifically adsorbed by hydrous metal oxides, calcium chromate Cr(VI) and stable complexed adsorption Cr(VI). These Cr(VI) species can be selectively extracted by specific solutions through ion exchange or weak acid dissolution. The most stable Cr(VI) species is Cr(VI) complexed by hydrous iron oxides through bidentate ligand binding; only by dissolution of hydrous iron oxides can this Cr(VI) species be leached. The distribution of Cr(VI) species is closely linked to particular soil compositions including exchangeable Ca2+ and hydrous iron oxides which determinate the Cr(VI) adsorption in soil. Cr(III) species comprise Fe-Cr coprecipitate hydroxides Cr(III), Fe-Mn oxide-bound Cr(III), organic matter-bound Cr(III) and residual Cr(III). Their distribution depends on the types of reductants present in the soil.

Synthesis, characterization, and application of thio-salicylaldehyde schiff base complexes for Cr (VI) adsorption

This study investigates the effectiveness of a Schiff base derived from thio-carbohydrazide and salicylaldehyde as an adsorbent for Cr(VI) removal from wastewater. The Schiff base demonstrated excellent adsorption capacity and reusability, with high removal efficiency and rapid adsorption kinetics. The results were supported by theoretical density functional theory simulations, which revealed the enhanced dynamic nature of the Schiff base system for heavy metal adsorption. These findings highlight the potential of Schiff base complexes as sustainable and efficient adsorbents for industrial wastewater treatment.

Effective removal of Cr(VI) from water by ball milling sulfur-modified micron zero-valent iron：Influencing factors and removal mechanism

To address the issues of ZVI's susceptibility to oxidation and aggregation, ball milling and Na2S·9H2O modification were employed on ZVI to enhance its efficiency in removing Cr(VI) from effluent. The characterization results expressed that S-mZVIbm had mesoporous and macroporous structures, enabling successful capture of Cr(VI). Moreover, S-mZVIbm had the highest adsorption capacity for Cr(VI) (350.04 mg/g) at pH = 2.00 and reached kinetic equilibrium within 420 min. Furthermore, the adsorption of Cr(VI) by S-mZVIbm conformed to the Avrami-fractional-order model, demonstrated that the adsorption process indicated a complex multi-adsorption process. Meanwhile, the adsorption also fit to Langmuir and Sips models, suggesting monolayer-level adsorption with heterogeneous sites located on S-mZVIbm. The S-mZVIbm could enhance Cr(VI) adsorption through various synergistic mechanisms, such as electrostatic interaction, chemical precipitation, surface complexation, and reduction. Overall, this research presented an innovative perspective for the modification of ZVI, and S-mZVIbm could be widely applied in the practical remediation of wastewater containing Cr(VI).

Fluorescent cellulose nanofibrils hydrogels for sensitive detection and efficient adsorption of Cu2+ and Cr6+

Increasing chromium and copper pollution poses a significant threat to the global environment and human health. It is crucial to detect and remove Cu (II) and Cr (VI) from water. Cellulose nanofibrils (CNF)-based hydrogels were a natural, abundant, and biocompatible material that has attracted great attention for bio adsorption applications. In this work, a new fluorescent CNF-based hydrogel (PAA-CNF-W) was prepared for the high-efficiency adsorption and sensitive detection of Cu (II) and Cr (VI). CNF was introduced as a natural backbone to construct a three-dimensional porous structure, which increased the specific surface area and provided additional active sites, exhibiting excellent adsorption properties for Cu (II) (159.24 mg/g) and Cr (VI) (173.87 mg/g). Moreover, the synthesized dansyl chloride derivatives with fluorescent properties were introduced to the hydrogel and formed chelates with the metals leading to fluorescence quenching. PAA-CNF-W hydrogels showed high sensitivity to the detection limit (LOD) of Cu (II) (28.70 mg/L) and Cr (VI) (1.45 mg/L). The kinetic study revealed that pseudo-second order kinetics was the best-fitting model. The Langmuir isotherm was the best adjustment model. The study provides a new idea for efficient detection and removal of Cu (II) and Cr (VI) from wastewater by cellulose materials.

Construction of controlled hyper-crosslinked nanofibrous tubes for Cr(VI) removal: Response surface, kinetics, and isotherm

Porous organic polymers (POPs) exhibit significant potential for adsorbing toxic metal ions in wastewater. Developing POPs with controlled morphologies is a pivotal direction in this field. This study synthesized a series of novel hyper-crosslinked nanofibrous tubes designated HCNT-Cn (n = 4, 8, 12, 16) via Friedel-Crafts alkylation and quaternization reactions. These reactions were fine-tuned through a post-synthetic strategy involving varying alkyl chain lengths. These materials were characterized using FT-IR, SEM, N₂ adsorption-desorption isotherms, among others, and they were specifically evaluated for their ability to adsorb Cr(VI). Among the variants, HCNT-C₄ exhibited the highest specific surface area (495.26 m2 g−1), superior hydrophilicity (CA = 48.7°), and optimal adsorption performance. The adsorption kinetics of HCNT-C₄ conformed to a pseudo-second-order model, while its adsorption isotherm aligned with the Langmuir model. An investigation into the impact of Cr(VI) removal was conducted using three independent variables in a Central Composite Design (CCD) response surface model, revealing that under optimal conditions, the Cr(VI) removal efficiency reached 98%. Additionally, a mechanism for Cr(VI) adsorption on HCNT-C₄ was proposed. It was also found that HCNT-C₄ could be reused up to four times, maintaining a removal efficiency of 70%. This study suggests potential applications for removing Cr(VI) from contaminated wastewater.

Synthesis and characterisation of superior AC/ZnO NPs biocomposite for hexavalent chromium Cr(VI) adsorption

This study aims to synthesize biocomposite by combining banana stem activated carbon (AC) and ZnO Nanoparticles (NPs) to evaluate their adsorption potential towards hexavalent chromium (Cr (VI)) (20 mg/L). The AC used was successfully synthesized by an impregnation method using phosphoric acid (H3PO4) for 24 h, followed by a carbonization method. ZnO NPs were synthesized using the direct precipitation method using zinc acetate dihydrate (0.2 M) and KOH (0.4 M) as precursors. The AC/ZnO NPs biocomposite was fabricated using the mechanical alloying method at a frequency of 10 Hz for 30 min. The FTIR results show that both adsorbents, namely pure AC and AC/ZnO NPs have abundant functional groups. XRD results show the adsorbent is amorphous with pure AC at 89.95% and AC/ZnO NPs biocomosite at 56.49%. SEM results showed that the morphology of AC resembled crushed bovine bone marrow, and the morphology of ZnO NPs showed a marshmallow-like shape. The UV–vis spectrometer test results show that at the absorption peak of 350 nm the Cr (VI) removal efficiency slowly decreases and disappears at a dose variation of 1.5 g pure AC, 2 g biocomposite AC/ZnO NPs, and 2 g pure AC with Cr (VI) removal efficiency of 99.61%, 99.64%, and 99.83% respectively. Finally, we can report that the high degradation ability for Cr (VI) can be related to thesharp peak of –C=O group, reduced ΔLO−TO, and smaller average crystallite size in AC/ZnO NPs biocomposite.

One-pot amination and carboxylation functionalization of lignin for efficient adsorption of Cr(VI) and Cd(II): Influence of functional groups on adsorption equilibrium and mechanism

The removal of multiple heavy metal pollutants remains a challenge. Amination and carboxylation modified lignins (NCLs) prepared by one-pot hydrothermal method were used as adsorbents for Cr(VI) and Cd(II) removal. The oxygenous groups content in adsorbents was quantitatively analyzed by Boehm titration in which NCL10 (the mass ratio of citric acid: triethylene diamine = 10) possessed a maximum carboxyl group content of 1.22 mmol/g. The Langmuir adsorption isotherm model was the most suitable, with the highest theoretical adsorption capacity of Cr(VI) and Cd(II) of 1298.6 and 103.1 mg/g, respectively. Meanwhile, FT-IR and XPS exhibited that NCL5 surface contained many functional groups beneficial to the removal of Cr(VI) and Cd(II). The contribution of carboxyl and hydroxyl groups to the removal of Cr(VI) and Cd(II) was quantitatively analyzed. After the blocking of carboxyl and hydroxyl groups, the adsorption rate of Cr(VI) and Cd(II) decreased by 26.4 %, 67.7 % and 7.2 %, 43.3 %, respectively. This study provides effective strategies to overcome the limitations of lignin adsorbents for wastewaters containing a wide range of heavy metal pollutants.

Magnetic iron-based waterworks sludge modified by chitosan and FeS for aqueous Cr(vi) adsorption and reduction.

Heavy metals have been considered an evolving environmental concern due to their harmful and long-lasting impacts. We synthesized a composite of FeS/CS@MIBWS for aqueous Cr(vi) adsorption and reduction utilizing the iron-based waterworks sludge modified by chitosan and FeS. After determining the optimal conditions for the FeS/CS@MIBWS preparation, its Cr(vi) removal capability was evaluated using material characterisation and static Cr(vi) adsorption assays. Cr(vi) elimination by the composite was a pH-dependent process, with pH 2 being the optimum in the range of 2-10. The adsorption process was befitted a pseudo-second-order model, and the equilibrium results agreed well with the Langmuir model. The thermodynamics investigation showed that Cr(vi) removal by the composite has both spontaneous and endothermic nature. Considering the ionic effects, Cl-, SO4 2- and PO4 3- decreased Cr(vi) elimination in the sequence of Cl- < SO4 2- < PO4 3-. The key mechanisms for Cr(vi) elimination were physical and chemical adsorption, chelation, and Cr(vi) reduction into Cr(iii). Furthermore, FeS/CS@MIBWS demonstrated steady reusability (removal effectiveness of 70% after 5 cycles). FeS/CS@MIBWS's rapid, high-performance, reusable, and easily separable adsorption properties make it a promising choice for heavy metal environmental cleaning.

The potential of Gd doping as a promising approach for enhancing the adsorption properties of nickel-cobalt ferrites.

The study shows that the addition of gadolinium ions has a significant impact on the structure, morphology, and adsorption properties of Ni-Co spinel ferrite that was synthesized by the sol-gel auto-combustion method. The research also indicates that the higher the Gd content, the greater the increase in the lattice parameter, which suggests that Gd3+ ions uniformly replaced the octahedral Fe3+ ions. The morphology and chemical composition of Gd-doped Ni-Co ferrites have been studied using SEM and EDS. Gd adding to the NiCoFe matrix increases the BET surface area by 50% (from 48 to 72 m2/g) and promotes the formation of mesopores with an average radius from 3.9 to 4.9nm. The pHPZC values of Gd-doped ferrites are in the range of 7.22-7.39, which means that the ferrite surface will acquire a positive charge at natural pH, so this will promote the adsorption of Congo red anionic dye through electrostatic interaction forces. Langmuir, Freundlich, and Dubinin-Radushkevich models were used to explain the mechanism of CR adsorption on the Ni0.5Co0.5GdxFe2-xO4 adsorbent surface. The ionic-covalent parameter has been estimated to describe the surface acid-base properties. Overall, this study highlights the potential of Gd3+ doping as a promising approach for enhancing the adsorption properties of nickel-cobalt ferrites.