Congo Red Adsorption Capacity Research Articles

Anionic Dye Removal by Polypyrrole-Modified Red Mud and Its Application to a Lab-Scale Column: Adsorption Performance and Phytotoxicity Assessment

In this study, polypyrrole-modified red mud (PRM) was prepared for the efficient removal of anionic dyes (methyl orange and Congo red) from aqueous solutions. The phytotoxicity (bean sprouts) of the dye solution before and after dye removal was investigated. Adsorption kinetics confirmed that the adsorption of methyl orange (MO) and Congo red (CR) on PRM was controlled by chemical reactions between the functional groups of polypyrrole and dyes. From Langmuir isotherm fitting, we found the theoretical adsorption capacities of MO and CR on PRM were 194.1 and 314.9 mg/g, respectively. The adsorption progress of MO and CR on PRM was found to be spontaneous and endothermic. The column studies demonstrated that, under dynamic flow, the PRM can efficiently remove MO and CR from aqueous solution, with adsorption capacities of 31.08 and 55.04 mg/g, respectively. In the toxicity test, the phytotoxicity of the column effluents (after dye removal) was significantly lowered compared to the initial dye influents. After the removal of MO and CR, the average root length of bean sprouts was increased from 3.30 cm to 5.18 cm and from 3.01 cm to 7.00 cm, respectively. These findings highlighted the efficient removal of dyes by PRM from aqueous solution, demonstrating the possible application of PRM for the removal of dye from dye-contaminated wastewaters.

Adsorption removal of Congo red onto L-cysteine/rGO/PANI nanocomposite: equilibrium, kinetics and thermodynamic studies

In this paper, adsorption of Congo red (CR) onto L-cysteine decorated with reduced graphene oxide/polyaniline composite at room temperature was investigated. The morphology and structure properties of as-prepared nanocomposite were verified by UV–visible spectroscopy (UV–visible), powder X-ray diffraction (XRD), Fourier transform infrared spectrophotometry (FTIR), scanning electron microscopy (SEM), and Brunauer Emmett Teller (BET) studies. Effect ofabsorbent dosage, contact time, initial dye concentration and temperature were studied and optimal conditions for the adsorption process of Congo red dye were found. The obtained results indicated that isotherms data fitted well to Langmuir model. While kinetics data fitted well to the pseudo-second-order kinetic equation and the adsorption process was generally governed via intra-particle diffusion. Thermodynamic data showed that adsorption process of CR was endothermic and spontaneous in nature. At optimal conditions, the maximum adsorption capacity of CR was calculated and found to be 56.57 mg/g, which shows that L-cysteine functionalized reduced graphene oxide/polyaniline based nanocomposite can be efficiently used for wastewater management.

Polyaniline dispersed by Kevlar fiber for uptake of organic dye

PurposeThis paper aims to focus on the preparation of Kevlar fiber (KF) and alkaline hydrolyzed KF (KF-H) to improve the dispersed condition of polyaniline (PAn), as the aggregation of PAn would lead to some adsorption sites buried. And then the materials were used to enrich anionic dye Congo red (CR) from aqueous solution.Design/methodology/approachThe materials (KF@PAn and KF-H@PAn) were designed by means of “diffusion-interfacial-polymerization” under mild condition as high affinity due to the structural properties of PAn, KF and KF-H. The dispersed degree of PAn on the surface of KF and KF-H was validated according to adsorption efficiency for CR.FindingsThe content of PAn introduced was not beyond 20 wt.%, while adsorption capacity for CR was significantly enhanced by 4–8 times (on the basis of kinetic data) according to the calculation only by the content of PAn due to KF and alkaline hydrolyzed KF exhibited almost no adsorption for CR, indicating dispersed situation of PAn coating was greatly enhanced and more active sites exposed, which was favorable for the adsorption process. Presence of NaCl would exhibit a more or less positive effect on CR uptake, suggesting the materials could be used for high salt environment.Research limitations/implicationsThe investigated means of dispersed degree of PAn on the surface of KF and KF-H are the further and future investigation.Practical implicationsThis study will provide a method to improve the dispersed situation of PAn and a theoretical support to treat anionic dyes from aqueous solution especially for salt environment.Originality/valueThe results showed that the dispersed condition of PAn on the surface of KF and KF-H was greatly improved. According to the adsorption capacities for CR, it can be concluded that part of adsorption sites were buried due to the aggregation of PAn, and introduction of KF and KF-H, buried adsorption sites decreased greatly. This study will provide a method to decrease buried adsorption sites of PAn and a contribution for their convenient application in wastewater treatment especially for high salt environment.

Preparation of Novel Magnetic Sodium Alginate-Ferric(III) Gel Beads and Their Super-Efficient Removal of Direct Dyes from Water

Novel magnetic sodium alginate-based biopolymer Fe3O4@SA-Fe was successfully prepared by the cross-linking reaction of sodium alginate (SA) and Fe(III) ions and adding magnetic ferric oxide (Fe3O4), and characterized by Scanning Electron Microscopy (SEM), Energy Dispersive Spectroscopy (EDS), UV-visible diffuse reflectance spectroscopy (UV-Vis DRS), Fourier Transform-Infrared (FTIR), X-ray Photoelectron Spectroscopy (XPS) and Vibrating Sample Magnetometer (VSM), respectively. The effects of preparation and adsorption conditions on the adsorbent were investigated by adsorbing Congo red (CR) and Direct red 23 (DR 23) dyes. The results showed that the synthesized Fe3O4@SA-Fe polymer gel beads exhibited super-high adsorption property and good stability when the mass concentrations of SA, Fe(III) ions and Fe3O4 are 16, 12.5 and 7 g/L at room temperature respectively. The adsorption rates of two dyes by Fe3O4@SA-Fe were very fast at 298 K, and the time required to reach the equilibrium was very short, which was 30 min for CR and 60 min for DR 23. Moreover, the dye removal efficiencies were over 99.4% and 95.2% in a wide pH range of 2.0 ~ 9.0 for CR and 2.0 ~ 10.0 for DR 23, respectively. The adsorption process could be accurately described by the pseudo-second-order rate model, which were mostly controlled by intra-particle diffusion. The fitting results of isothermic data by Langmuir, Freundlich and Dubinin-Radushkevich (D-R) models revealed that the equilibrium data completely obeyed the Langmuir model and the obtained maximum adsorption capacities of CR and DR 23 were 3333 and 1429 mg/g at 298 K, respectively. FTIR, UV-Vis and XPS analysis indicated that the electrostatic adsorption, hydrogen bonding and ligand exchange promoted the interaction between dye molecules and Fe3O4@SA-Fe. A green magnetic biosorbent Fe3O4@SA-Fe gel beads with simple preparation method and high-cost performance can be used for super-efficient purification of high-concentration dye effluent and quickly separated from the aqueous phase and recovered, which would have a good application prospect.

Adsorptive removal of cationic methylene blue and anionic Congo red dyes using wet-torrefied microalgal biochar: Equilibrium, kinetic and mechanism modeling.

This study aims to investigate the adsorption behavior of cationic and anionic dyes of methylene blue (MB) and Congo red (CR) onto wet-torrefied Chlorella sp. microalgal biochar respectively, as an approach to generate a waste-derived and low-cost adsorbent. The wet-torrefied microalgal biochar possessed microporous properties with pore diameter less than 2nm. The optimum adsorbent dosage of wet-torrefied microalgal biochar for MB and CR dyes removal were determined at 1g/L and 2g/L, respectively, with their natural pHs as the optimum adsorption pHs. The determined equilibrium contact times for MB and CR were 120h and 4h, respectively. Based on the equilibrium modeling, the results revealed that Langmuir isotherm showed the best model fit, based on the highest R2 coefficient, for both the adsorption processes of MB and CR using the wet-torrefied microalgal biochar, indicating that the monolayer adsorption was the dominant process. From the modeling, the maximum adsorption capacities for MB and CR were 113.00mg/g and 164.35mg/g, respectively. The kinetic modeling indicated the adsorption rate and mechanism of the dyes adsorption processes, which could be crucial for future modeling and application of wet-torrefied microalgal biochar. From the results, it suggests that the valorization of microalgae by utilizing wet-torrefied microalgal biochar as the effective adsorbent for the removal of toxic dyes with an approach of microalgal biorefinery and value-added application to the environment is feasible.

Enhancement of the Congo Red Adsorption Capacity of Biochars by Surface Modification with MgCl2 Pretreatment

Objectives : The physicochemical characteristics of Mg-biochar composites derived from kelp and pine after pretreatment with MgCl2 were analyzed, and their adsorption capacities for an anionic dye, Congo red (CR), were evaluated.Methods : After pretreating 60 g of kelp and pine sawdust in 1 L of 0.1 M MgCl2･6H2O, the raw materials were pyrolyzed at 500℃ to produce Mg-biochar composites (kelp based KB-Mg and pine based PB-Mg). The fundamental physicochemical characteristics of the Mg-biochar composites were examined, and their adsorption capacities for CR were investigated using different initial pH values, adsorption kinetic models, and adsorption isotherm models.Results and discussion : The Mg-biochar composites showed the development of uniform deposits of Mg minerals primarily as MgO crystal on the surface by the surface modification with MgCl2. When the pristine biochars were surface-modified with MgCl2, their adsorption capacities for CR were significantly increased over the entire pH range tested. The CR adsorption process by all biochars was best described with the pseudo-first order kinetics model, and the adsorption isotherm characteristics were better described with the Langmuir isotherm model for all biochars. The Langmuir maximum adsorption capacities for KB-Mg and PB-Mg were 423.0 mg/g and 394.7 mg/g, respectively. It is suggested that the main mechanism for CR adsorption on the Mg-biochars is electrostatic attraction between CR and the biochars.Conclusions : The results showed that surface modification with MgCl2 could greatly enhance the CR adsorption capacity of biochars, and the results demonstrated the great potential of KB-Mg and PB-Mg for CR removal.

Magnetic NiFe2O4/MWCNTs functionalized cellulose bioadsorbent with enhanced adsorption property and rapid separation

Magnetic NiFe2O4 nanoparticles and multi-walled carbon nanotubes functionalized cellulose composite (m-NiFe2O4/MWCNTs@cellulose) as a magnetic bioadsorbent was prepared and used for effectively removing Congo Red (CR) from aqueous solution. The chemical and physical properties of the prepared m-NiFe2O4/MWCNTs@cellulose were characterized by XRD, TGA, FT-IR, VSM, SEM and TEM. Batch experiments were carried out to investigate the adsorption capacity and mechanisms. Effects of different adsorption parameters such as initial CR concentration, adsorbent dosage and temperature were studied. Results demonstrated that m-NiFe2O4/MWCNTs@cellulose had high adsorption capacity for CR from aqueous solution. The obtained experimental data fitted well with the pseudo-second-order equation and followed the Langmuir isotherm model with a maximum adsorption capacity of 95.70 mg g−1 for CR. The m-NiFe2O4/MWCNTs@cellulose with rapid magnetic separation and high adsorption capacity can be a promising and recyclable engineering biomaterials for purification and treatment of practical wastewater.

Graphitic mesoporous carbon-silica composites from low-value sugarcane by-products for the removal of toxic dyes from wastewaters.

Highly porous carbon-silica composites (CSC) were prepared for the first time through a simple wet impregnation process and subsequent pyrolysis of low-value sugarcane by-products, namely molasses. These CSC materials demonstrate a distinct range of functionalities, which significantly differ from similar materials published in the literature. Importantly, the carbon-silica composites prepared at 800°C exhibited exceptional adsorption capacities for the azo-dye congo red (445 mg g−1), due to the graphitic carbon coating and unique functionality including C-O-C within the porous structure. Congo red adsorption capacity of the highly mesoporous graphitic carbon-silica composites significantly exceeds that of commercial activated carbon and silica, these carbon-silica composites therefore represent an effective step towards the development of porous bio-derived adsorbent for remediation of dye wastewaters. Both the porous properties (surface area and pore size distribution) and the functionality of the carbon coating were dependent on the temperature of preparation. The sustainable synthetic methods employed led to a versatile material that inherited the mesoporosity characteristics from the parent silica, demonstrating mesoporous volumes greater than 90% (as calculated from the total pore volume). Adsorption on the 800°C prepared carbon-silica composites demonstrated an excellent fit with the Langmuir isotherm and the pseudo-first-order kinetic model.

Porous carbon-based MgAlF5·1.5H2O composites derived from carbon-coated clay presenting super high adsorption capacity for Congo Red

Carbon and clay-based composites have great potential to be applied as sorbents for dye removal in wastewater treatment. Existing sorbent materials suffer from high cost and relatively low capacity. The key to solve this problem is to develop new composites as adsorbents. Here, we report a newly developed porous carbon-based MgAlF5·1.5H2O nanocomposites derived from carbon-coated palygorskite via a single-step HF etching for the first time. Structural and compositional evolution of a series of samples occured by subtly tuning of HF doses. Our results highlight the significantly enhanced adsorption capacity of Congo Red wastewater (4261.0 mg/g), which is approximately 7 and 123 times that of porous carbon (572.0 mg/g) and carbon-coated palygorskite (34.4 mg/g), respectively. The enhanced adsorption property is attributed to chemisorption mechanism between MgAlF5·1.5H2O and Congo Red via two Al atoms binding to two O atoms of the –SO3− group. The corresponding adsorption energy was calculated to be −1.01 eV. In this work, porous carbon-based MgAlF5·1.5H2O adsorbents possess the characteristics of super high adsorption capacity, low cost and no pH dependence, which meets the environmental, economical and engineering requirements for wastewater dye removal, especially, for wastewater treatment under emergency circumstances.

Comparison of Cation Anion Dye Removal Characteristics between Kelp-based Magnetic Biochar and Pine-based Magnetic Biochar

Objectives:This study investigates the adsorption capacity of magnetic biochar (KB-Fe) derived from kelp for two dyes, Congo red (CR) and crystal violet (CV), which have different charge characteristics. The adsorption capacities were compared to magnetic biochar (PB-Fe) derived from pine.Methods:Pristine biochars (KB, PB) were produced through the pyrolysis of kelp and pine sawdust at 500℃. Magnetic biochars (KB-Fe, PB-Fe) were produced by treatment of 60 g of biomass in 1 L of 0.1 M FeCl<sub>3</sub>･6H<sub>2</sub>O and pyrolysis of the raw materials at 500℃. The fundamental characteristics of the biochars were analyzed, and the adsorption capacities of the biochars for the CR and CV dyes were evaluated based on two adsorption isotherm models, two adsorption kinetics models, and adsorption characteristics based on changes to the pH between 5 and 11.Results and discussion:CR adsorption by all biochars decreased with an increase in pH. When KB and PB were surface-modified with magnetic iron oxides, their adsorption capacity for CR increased. CV adsorption by all biochars increased with pH. When KB and PB were surface-modified with magnetic iron oxides, their adsorption capacity for CV considerably decreased. According to the Langmuir isotherm model, the adsorption capacity for CR was in the order of KB-Fe, KB, PB-Fe, and PB, and the adsorption capacity for CV was in the order of KB, PB, PB-Fe, and KB-Fe. The CR adsorption was better described by the pseudo-second order kinetics model for all biochars, with the exception of KB-Fe. CV adsorption was also better described by the pseudo-second order kinetics model for all biochars, with the exception of KB.Conclusions:The results show that kelp biochar has great potential for the adsorptive removal of CR and CV compared to pine-based biochar. In addition, it was demonstrated that surface modification of kelp biochar with magnetic iron oxides can significantly improve its adsorptive capacity for anionic dyes; however, its adsorptive capacity for cationic dyes decreases.

Synthesis, crystal structure, optical and adsorption properties of BaAl2O4: Eu2+, Eu2+/ L3+ (L = Dy, Er, Sm, Gd, Nd, and Pr) phosphors

In this work, the BaAl2O4: Eu2+, Eu2+/L3+ (L= Dy, Er, Sm, Gd, Nd, and Pr) phosphors were synthesized via a facile solid-state reaction method using LiCl as a flux material at 1100 °C. The structural properties, microstructure, adsorption and photoluminescence characteristics of products were evaluated by X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), Uv–vis adsorption and photoluminescence (PL) analyses. The observation of XRD patterns showed that even 10% LiCl is not able to produce any impurity phase in BaAl2O4: Eu2+ crystal structure, although the microstructure morphology is considerably affected. The particle size of BaAl2O4: Eu2+ phosphors was about 220 nm while the use of LiCl flux resulted in a remarkable decrease of this parameter to about 120 nm. Furthermore, the PL patterns disclosed that Eu2+ ions have occupied one type of Ba2+ sites while larger quantities of lanthanides (L3+) occupied the second type of Ba2+ sites. The strongest photoluminescence emission intensity at the wavelength of 495 nm was achieved when 5 wt% LiCl was added to BaAl2O4: Eu2+. Also, the absorption analysis revealed that the addition of flux enriches the adsorption of Congo red (CR) dye on the phosphor powders. The use of 5 wt% flux material led to noticeable improvement of CR adsorption capacity from 38.53 to 48.3 mg g−1.

N-contaning UiO-67 derived multifunctional hybrid materials as highly effective adsorbents for removal of Congo red

A post-synthetic approach using nitrogen-containing substances modify UiO-67 was proposed to enhance its adsorption for Congo red (CR). The newly synthesized materials were thoroughly analyzed by SEM, TEM, EDX, XPS, XRD, FT-IR, TGA and BET techniques. Results showed that N was successfully incorporated into UiO-67 frameworks to prepare of NX-UiO-67, through coordination interaction with Zr-O clusters. Compared to parent UiO-67, the obtained NX-UiO-67 exhibited a significant increase in adsorption of CR, and the adsorption capacities for CR were in the following order: NU-UiO-67 (2360 mg g−1) > NT-UiO-67 (1986.3 mg g−1) > NA-UiO-67 (1493 mg g−1). Moreover, the pseudo-second-order kinetics and the Langmuir isothermal model exhibited a better fit to describe the adsorption behavior of CR onto the NX-UiO-67.

Solvothermal Synthesis of Humic Acid-Supported CeO₂ Nanosheets Composite as High Performance Adsorbent for Congo Red Removal.

Surface properties and structures of materials are essential for their adsorption of pollutants in water. Humic acids (HA)-supported CeO₂ nanosheet composites are synthesised by solvothermal method. The size of CeO₂ nanosheets are approximately 100-500 nm. The obtained composite exhibits superior adsorption ability for Congo Red (CR) in water, which can be attributed to its unique structure and highly dispersed CeO₂ nanosheet. The composite's adsorption behaviour of CR follows a pseudo-second-order mode and Langmuir adsorption model well, and the maximum adsorptive capacity for CR achieves 260 mg g-1. The presence of CeO₂ nanosheets enhances surface area and enriches the mesoporous structure of the composites, thereby promoting CR adsorption capacity.

NiFe-LDH nanosheet/carbon fiber nanocomposite with enhanced anionic dye adsorption performance

Excessive discharge quantity of toxic dyes has been confirmed to be detrimental to the ecological system and human health. Thus, an effective adsorbent must be developed to remove toxic dyes from wastewater. Herein, NiFe-layered double hydroxide (LDH) (NiFe-LDH) nanosheets are successfully grown on carbon fiber prepared using a facile one-pot hydrothermal route, which can integrate the advantages of carbon fiber and NiFe-LDH nanosheets. The as-prepared C/NiFe-LDH composite exhibits high specific surface area, hierarchical porous structure, and positive surface charge. These characteristics are beneficial for removing methyl orange (MO) and Congo red (CR) anionic dye. Kinetic data of MO and CR adsorbed onto as-prepared samples match well with those of pseudo-second-order model. Adsorption isotherms effectively fit Langmuir isotherm model. The Langmuir isotherm model indicates that the maximum adsorption capacities of MO and CR on the C/NiFe-LDH composite are 323.6 and 448.4 mg g−1, respectively, at 30 °C. These results are much higher than those of pure carbon fiber and NiFe-LDH. The synthesized C/NiFe-LDH is recyclable. Therefore, the C/NiFe-LDH composite can be a potential candidate for removing MO and CR in wastewater treatment given its facile synthesis method and excellent adsorption performance.

High-Strength Chitin Based Hydrogels Reinforced by Tannic Acid Functionalized Graphene for Congo Red Adsorption

In this study, a novel chitin based composite hydrogel reinforced by tannic acid modified reduced graphene oxide (TRGO) was prepared via a facile freezing–thawing approach. Epichlorohydrin (ECH) and TRGO sheets were employed as efficient crosslinkers to fabricate dually crosslinked TRGO/chitin composite hydrogels with advanced mechanical and adsorption properties. Results indicated that the TRGO reinforced chitin composites increased the mechanical property remarkably with exhibiting compression strength from 22.7 kPa for neat chitin hydrogel to 72.3 kPa for the hydrogel with loading of 7% TRGO. Multiple interactions such as hydrogen bonding between TRGO and chitin as well as the dually covalent crosslinking bonds were responsible for the extensive improvement in compression strength. Furthermore, the TRGO reinforced hydrogels exhibited an excellent adsorption capacity towards Congo red (CR). The maximum adsorption capacity of CR was 230.5 mg g−1 for chitin hydrogel with loading of 7% TRGO. The adsorption of CR was found following the Langmuir isotherm and pseudo-second-order models. Hence, the prepared TRGO/chitin hydrogels provide an easy and efficient way for the removal of CR dye from wastewater.

Removal of Congo red from aqueous solution by adsorption using gum ghatti and acrylamide graft copolymer coated with zero valent iron

Gum ghatti (Gg) and acrylamide (AAm) grafted copolymer [poly (Gg-AAm)] coated by zero valent iron (ZVI) was developed to remove toxic Congo red (CR) from waste water. Prepared composite, [poly (Gg-AAm)/ZVI] was characterized by FESEM, TEM, BET, FTIR and XRD. CR adsorption from water using [poly (Gg-AAm)/ZVI] was investigated and several parameters discussed, such as solution pH, contact time, dosage and temperature to find out removal efficiency of polymer composite. The kinetic data for the adsorption of CR followed the pseudo-second-order model and the Langmuir maximum adsorption capacity for CR at pH 7.0 were found to be 153.8, 200 and 250 mg/g at 25, 35 and 45 °C correspondingly. Desorption studies revealed that prepared composite can be used up to three cycles efficiently and thermodynamic parameters such as Gibbs free energy (ΔG0), enthalpy (ΔH0) and entropy (ΔS0) changes showed the adsorption of CR onto [poly (Gg-AAm)/ZVI] was feasible, spontaneous and endothermic.

Economical Synthesis of High Surface Area γ-Al<sub>2</sub>O<sub>3</sub> for the Adsorption of Organic Pollutant from Wastewater

A series of γ-Al₂O₃ with high surface area applied for removal of Congo red (CR) from aqueous solution was prepared from cheap inorganic aluminum precursor using simple precipitation method in presence of an inexpensive anionic surfactant (sodium dodecyl sulfate, SDS). The material characterization by several techniques revealed that SDS plays an important role on the morphology and textural properties of the resultant γ-Al₂O₃, and the largest surface area of γ-Al₂O₃ (416.65 m²/g) was obtained by varying molar ratio of SDS to aluminum precursor to be 0.375. The CR adsorption experiments identified that the adsorption isotherms on the as-synthesized γ-Al₂O₃ obey the Langmuir model. The maximum CR adsorption capacity of 831.7 mg/g was provided on the γ-Al₂O₃ having the largest surface area, verifying the importance of material surface area for achieving superior adsorption performance. The CR adsorption behaviors onto various γ-Al₂O₃ materials were analyzed using different kinetic models, and the results suggest a multistep adsorption mechanism. Besides, the equilibrium adsorption data well fitted the pseudo-second-order kinetic model, manifesting that the chemical adsorption process is the rate-limiting step. Moreover, the γ-Al₂O₃ synthesized showed good recyclability for CR removal, and thus could be a very effective and cost-saving adsorbent for the treatment of industrial wastewater containing organic pollutants.

Construction of magnetic NiO/C nanosheets derived from coordination polymers for extraordinary adsorption of dyes

Herein, a facial stratagem for the large-scale synthesis of NiO/C nanosheets used as magnetic adsorbents is proposed by using nanoscale coordination polymers (nanoCPs) as precursors. The NiO nanoparticles (NPs) scattered on the NiO/C nanosheets have an untrasmall size (~3 nm) as well as uniform dispersion, since the Ni2+ ions are preassembled into the nanoCPs precursors by coordination bonds and transformed to NiO NPs in situ under the restriction of carbon layers. Thanks to the small size and spatially uniform distribution of NiO NPs, fully exposed carbon matrix containing part of graphene structures, and the high specific surface area of the special nanosheet structure, the magnetic NiO/C nanosheets have an a great breakthrough in the adsorption performance toward Congo Red (CR) among many reported NiO-based materials. The maximum adsorption capacity for CR is up to 2000 mg/g, and the adsorption kinetics and thermodynamics are also systematically studied. Moreover, the NiO/C nanosheets can be separated from water and reused simply by an external magnetic field. The NiO/C nanosheets with low cost and extraordinary adsorption ability have great potential in water pollution treatment area.

Direct fabrication of hierarchically processed pineapple peel hydrogels for efficient Congo red adsorption

Herein, the hierarchically processed pineapple peel was achieved by water (WT-PP), alkali (AT-PP), bleaching (BT-PP) and bleaching-alkali (PPC) treatments respectively for separate or simultaneous removal of hemicellulose and lignin. These treated pineapple peel were further fabricated into hydrogels (WT-PPH, AT-PPH, BT-PPH and PPCH, respectively) by a facile dissolution-regeneration process in ionic liquid. The structure and Congo red (CR) adsorption ability of the hydrogels were investigated and compared. The adsorption process conformed better to the pseudo-second-order kinetic and Langmuir isotherm models. The maximum adsorption capacity was 114.94 mg/g for WT-PPH, 77.52 mg/g for AT-PPH, 138.89 mg/g for BT-PPH and 75.19 mg/g for PPCH, implying the separate bleaching treatment could improve the CR adsorption capacity more. Moreover, the hydrogels displayed a pH-dependent behavior and good reusability during adsorption process. Based on removal of initial components and simple preparation method, this work would be beneficial for the development of agricultural residues-based biosorbents.

Facile synthesis of a magnetic chlorapatite composite with a high efficiency and recyclable adsorption for Congo red

In this study, a composite of magnetic core and chlorapatite (Fe3O4@CLAP) is synthesized and used to remove Congo red (CR) from aqueous solution. The Fe3O4@CLAP is characterized by various analytical methods to estimate the adsorbent features. The effects of initial solution pH, adsorbent dosage, and ionic strength on the dye removal are studied to determine the optimized operating conditions. The sorption kinetics fit well with pseudo-second-order model, and the intra-particle diffusion model curve shows that three diffusion stages exist in the process. In addition, the Langmuir, Freundlich and Temkin isotherm models are used to fit the experimental data, and the fitting results show that the data are well described by Langmuir isotherm. The maximum adsorption capacity of CR is 370.4 mg g−1, which is outstanding compared with existing reports. The thermodynamic analysis reveals that the adsorption process is exothermic with a spontaneous nature. Moreover, the desorption is achieved with 0.01 M NaOH and the removal efficiency of adsorbent still remains 82.5% after 5 cycles. Therefore, Fe3O4@CLAP is a promising adsorbent with a high adsorption capacity and excellent recyclability for removing CR from aqueous solutions.