Cross-linked chitosan/sepiolite composite for the adsorption of methylene blue and reactive orange 16

A chitosan-based composite for adsorption of uranyl ions; mechanism, isothems, kinetics and thermodynamics

The present paper describes a green and cost-effective approach to investigate chitosan-sepiolite (Ch-Sep) composite as an adsorbent for removal of UO₂²⁺ ions in aqueous solution. The Ch-Sep composite was prepared as a beads using with two cross-linking agents: tripolyphosphate (TPP) and epichlorohydrin (ECH). Their adsorption properties for the removal of UO₂²⁺ ions in aqueous solution by batch experimental conditions were studied. The adsorptive removal processes of UO₂²⁺ ions from aqueous solution were evaluated by Langmuir, Freundlich and Dubinin-Radushkevich isotherm models, and was found to be perfectly fit to the Langmuir model (R² = 0.971). The maximum adsorption capacity was 0.220 mol kg^-1 at 25 °C from Langmuir isotherm model. Adsorption energy was 12.1 kJ mol^-1 indicating that the adsorption process was chemical. The adsorption kinetics followed the pseudo second order and intra particle diffusion models. The thermodynamics parameters of UO₂²⁺ ions removal from aqueous solution was confirmed spontaneous, endothermic and possible at higher temperatures behavior of adsorption process. The adsorption mechanism of UO₂²⁺ ions onto Ch-Sep composite beads was investigated by FT-IR and SEM analysis. These findings revealed the effectiveness and potential of the newly synthesized Ch-Sep composite beads for the removal of UO₂²⁺ ions.

Sustainable Removal of Contaminants by Biopolymers: A Novel Approach for Wastewater Treatment. Current State and Future Perspectives

Naturally occurring substances or polymeric biomolecules synthesized by living organisms during their entire life cycle are commonly defined as biopolymers. Different classifications of biopolymers have been proposed, focusing on their monomeric units, thus allowing them to be distinguished into three different classes with a huge diversity of secondary structures. Due to their ability to be easily manipulated and modified, their versatility, and their sustainability, biopolymers have been proposed in different fields of interest, starting from food, pharmaceutical, and biomedical industries, (i.e., as excipients, gelling agents, stabilizers, or thickeners). Furthermore, due to their sustainable and renewable features, their biodegradability, and their non-toxicity, biopolymers have also been proposed in wastewater treatment, in combination with different reinforcing materials (natural fibers, inorganic micro- or nano-sized fillers, antioxidants, and pigments) toward the development of novel composites with improved properties. On the other hand, the improper or illegal emission of untreated industrial, agricultural, and household wastewater containing a variety of organic and inorganic pollutants represents a great risk to aquatic systems, with a negative impact due to their high toxicity. Among the remediation techniques, adsorption is widely used and documented for its efficiency, intrinsic simplicity, and low cost. Biopolymers represent promising and challenging adsorbents for aquatic environments’ decontamination from organic and inorganic pollutants, allowing for protection of the environment and living organisms. This review summarizes the results obtained in recent years from the sustainable removal of contaminants by biopolymers, trying to identify open questions and future perspectives to overcome the present gaps and limitations.

Adsorption of Malachite Green Dye onto Mesoporous Natural Inorganic Clays: Their Equilibrium Isotherm and Kinetics Studies

Contamination of water with organic dyes is a major environmental concern as it causes serious life-threatening environmental problems. The present research was designed to evaluate the potential of three different natural inorganic clays (NICs) i.e., Pakistani bentonite clay (PB), bentonite purchased from Alfa Aesar (BT), and Turkish red mud (RM) for malachite green (MG) dye removal from an aqueous solution. Various analytical techniques, namely X-ray fluorescence spectrometry (XRF), X-ray diffractometry (XRD), Fourier transform infrared spectroscopy (FTIR), field emission scanning electron microscopy (FESEM), Brunauer–Emmett–Teller surface area measurement (BET), and thermogravimetric analysis (TGA), were used to investigate the physicochemical properties of the NICs samples. The effect of adsorption operational parameters such as contact time, aqueous phase pH, dye concentration, and amount of NICs on the adsorption behavior of MG onto NICs samples were investigated under the batch adsorption system. The equilibrium and kinetic inspection reflected the best description of MG adsorption behavior by the Langmuir isotherm model and pseudo-first-order kinetic model, respectively. The results indicated that the adsorption was favorable at higher pH. The maximum adsorption capacities calculated by Langmuir isotherm for PB, BT, and RM were found to be 243.90 mg/g, 188.68 mg/g, and 172.41 mg/g, respectively. It can be concluded that natural inorganic clays with a higher surface area can be used as an effective adsorbent material to remove the MG dye from an aqueous solution.

Cooperative Effects of Cellulose Nanocrystals and Sepiolite When Combined on Ionic Liquid Plasticised Chitosan Materials

Cellulose nanocrystals (CNCs) and/or sepiolite (SPT) were thermomechanically mixed with un-plasticised chitosan and chitosan/carboxymethyl cellulose (CMC) blends plasticised with 1-ethyl-3-methylimidazolium acetate ([C₂mim][OAc]). Examination of the morphology of these materials indicates that SPT aggregates were reduced when CNCs or [C₂mim][OAc] were present. Inclusion of CNCs and/or SPT had a greater effect on material properties when the matrices were un-plasticised. Addition of SPT or CNCs altered the crystalline structure of the un-plasticised chitosan matrix. Moreover, a combination of SPT and CNCs was more effective at suppressing re-crystallisation. Nonetheless, the mechanical properties and surface hydrophobicity were more related to CNC/SPT-biopolymer interactions. The un-plasticised bionanocomposites generally showed increased relaxation temperatures, enhanced tensile strength, and reduced surface wettability. For the [C₂mim][OAc] plasticised matrices, the ionic liquid (IL) dominates the interactions with the biopolymers such that the effect of the nanofillers is diminished. However, for the [C₂mim][OAc] plasticised chitosan/CMC matrix, CNCs and SPT acted synergistically suppressing re-crystallisation but resulting in increased tensile strength.

Insight into the adsorption kinetics, mechanism, and thermodynamics of methylene blue from aqueous solution onto pectin-alginate-titania composite microparticles

Abstract

In the present study, pectin-alginate-titania (PAT) composites were synthesized and the adsorptive removal behavior of methylene blue (MB) from aqueous solution, as a model of synthetic organic effluents, onto the prepared PAT composites were investigated by monitoring the effect of contact time, initial MB concentration, and temperature. The adsorption isotherm data were fitted well with the Freundlich isotherm model, suggesting the surface heterogeneity of the PAT composites and that the MB adsorption occurred on the active sites on multilayer surface of the composites. The adsorption kinetics of MB was demonstrated to be pseudo-second order, governed by two intraparticle diffusion rates, and the adsorption process was exothermic, spontaneous, and more disorder. The Langmuir isotherm model suggested that the maximum adsorption capacity of MB on the PAT composites was in the range of 435–637 mg g–1. In general, it increased with the TiO2 NPs content in the PAT composites, due most likely to the increase in surface area exposing more functional groups of the pectin and alginate to interact with the synthetic dye. The adsorptive removal of MB by the PAT composites was found to be more efficient compared with many other reported adsorbents, such as graphene oxide hybrids, pectin microspheres, magnetite-silica-pectin composites, clay-based materials, chemically treated minerals, and agricultural waste. The present study therefore demonstrated for the first time that PAT composites are not only promising to be utilized as an adsorbent in wastewater treatment, but also provide an insight into the adsorption mechanism of the synthetic dyes onto the biopolymers-titania composites.

Graphic abstract

Insight into the adsorption kinetics, mechanism, and thermodynamics of methylene blue from aqueous solution onto pectin-alginate-titania composite microparticles.

Kinetics, equilibrium and thermodynamics of dyes adsorption onto modified chitosan: a review

In view of promising sorption capacity, stability, biodegradability, cost-effectiveness, environmental friendly nature, regeneration and recycling ability, the chitosan (CS) based adsorbents are highly efficient for the sequestration of dyes. Since CS offers variable chemical structures and CS have been modified by incorporating different moieties. The CS composites with unique properties have been employed successfully for dye adsorption with reasonably high adsorption capacity versus other similar adsorbents. Modifications of CS were promising for the preparation of composites that are extensively studied for their adsorption capacities for various dyes. This review highlights the CS and its modification and their applications for the adsorption of dyes. The removal capacities of CS-based adsorbents, equilibrium modeling, kinetics studies and the thermodynamic characteristics are reported. Moreover, the FTIR, BET, SEM, TGA and XRD were employed for the characterization of CS modified adsorbents are also discussed. Results revealed that the modified CS is highly efficient and can be employed for the sequestration of dyes from effluents.

Kinetics, equilibrium and thermodynamics of dyes adsorption onto modified chitosan: a review

In view of promising sorption capacity, stability, biodegradability, cost-effectiveness, environmental friendly nature, regeneration and recycling ability, the chitosan (CS) based adsorbents are highly efficient for the sequestration of dyes. Since CS offers variable chemical structures and CS have been modified by incorporating different moieties. The CS composites with unique properties have been employed successfully for dye adsorption with reasonably high adsorption capacity versus other similar adsorbents. Modifications of CS were promising for the preparation of composites that are extensively studied for their adsorption capacities for various dyes. This review highlights the CS and its modification and their applications for the adsorption of dyes. The removal capacities of CS-based adsorbents, equilibrium modeling, kinetics studies and the thermodynamic characteristics are reported. Moreover, the FTIR, BET, SEM, TGA and XRD were employed for the characterization of CS modified adsorbents are also discussed. Results revealed that the modified CS is highly efficient and can be employed for the sequestration of dyes from effluents.

Adsorption mechanism and effectiveness of phenol and tannic acid removal by biochar produced from oil palm frond using steam pyrolysis

In order to meet the growing demand for adsorbents to treat wastewater effectively, there has been increased interest in using sustainable biomass feedstocks. In this present study, the dermal tissue of oil palm frond was pyrolyzed with superheated steam at 500 °C to produce nanoporous biochar as bioadsorbent. The effect of operating conditions was investigated to understand the adsorption mechanism and to enhance the adsorption of phenol and tannic acid. The biochar had a microporous structure with a Brunauer-Emmett-Teller surface area of 422 m²/g containing low polar groups. The adsorption capacity of 62.89 mg/g for phenol and 67.41 mg/g for tannic acid were obtained using 3 g/L biochar dosage after 8 h of treatment at solution pH of 6.5 and temperature of 45 °C. The Freundlich model had the best fit to the isotherm data of phenol (R² of 0.9863), while the Langmuir model best elucidated the isotherm data of tannic acid (R² of 0.9632). These indicated that the biochar-phenol interface was associated with a heterogeneous multilayer sorption mechanism, while the biochar-tannic acid interface had a nonspecific monolayer sorption mechanism. The residual concentration of 26.3 mg/L phenol and 23.1 mg/L tannic acid was achieved when treated from 260 mg/L three times consecutively with 1 g/L biochar dosage, compared to a reduction to 72.3 mg/L phenol and 69.9 mg/L tannic acid using 3 g/L biochar dosage in a single treatment. The biochar exhibited effective adsorption of phenol and tannic acid, making it possible to treat effluents that contain varieties of phenolic compounds.

Starch, cellulose, pectin, gum, alginate, chitin and chitosan derived (nano)materials for sustainable water treatment: A review

Natural biopolymers, polymeric organic molecules produced by living organisms and/or renewable resources, are considered greener, sustainable, and eco-friendly materials. Natural polysaccharides comprising cellulose, chitin/chitosan, starch, gum, alginate, and pectin are sustainable materials owing to their outstanding structural features, abundant availability, and nontoxicity, ease of modification, biocompatibility, and promissing potentials. Plentiful polysaccharides have been utilized for making assorted (nano)catalysts in recent years; fabrication of polysaccharides-supported metal/metal oxide (nano)materials is one of the effective strategies in nanotechnology. Water is one of the world's foremost environmental stress concerns. Nanomaterial-adorned polysaccharides-based entities have functioned as novel and more efficient (nano)catalysts or sorbents in eliminating an array of aqueous pollutants and contaminants, including ionic metals and organic/inorganic pollutants from wastewater. This review encompasses recent advancements, trends and challenges for natural biopolymers assembled from renewable resources for exploitation in the production of starch, cellulose, pectin, gum, alginate, chitin and chitosan-derived (nano)materials.

Polyvinyl Alcohol/Calcium Carbonate Nanocomposites as Efficient and Cost-Effective Cationic Dye Adsorbents

A novel polyvinyl alcohol (PVA)/calcium carbonate-based double-layer cationic dye adsorbent was developed. Polyvinyl alcohol (50 wt %) and calcium carbonate (50 wt %) were used together with borax as a cross-linking agent. The nanocomposite was prepared using only water, without the need for any toxic solvent or hazardous chemical. The final samples were obtained by the solvent casting method. The nanocomposite adsorbent was characterized using a Fourier transform infrared (FTIR) spectroscope and a scanning electron microscope (SEM). The adsorption performance on two cationic dyes, i.e., methylene blue and safranin was studied. Dye adsorption was quantified by measuring the nanocomposite swelling, contact time, and dye concentration. Pseudo first-order and pseudo second-order kinetic models as well as intraparticle diffusion model were used to model the adsorption kinetics. Moreover, the isotherm dye adsorption was investigated by Langmuir and Freundlich models. The results revealed that the developed nanocomposite has relatively high adsorption efficiency and short adsorption time and retains its performance after several successive absorption–desorption processes. The results also showed that the pseudo-second-order model best describes the adsorption kinetics, and the Freundlich isotherm model has a better compatibility with the experimental data. Finally, an adsorption mechanism was proposed for the dye removal process. The developed PVA/CaCO₃ nanocomposite can be potentially used for efficient dye removal in wastewater treatments.

Green synthesis and application of heterogeneous iron oxide based nanoparticles for dairy wastewater treatment by Photo-Fenton processes

The aim of this study is to investigate the efficiency of heterogeneous Photo-bio-Fenton-like process and adsorption process for phosphorus removal from wastewater. The results showed that both of these processes can reach 98 and 92% removal efficiencies phosphate (P) and Chemical Oxygen Demand (COD), respectively. The findings of kinetic and isotherm studies revealed that data of P removal highly correlated with the pseudo-second-order kinetic model and Langmuir isotherm. The quenching experiments determined that both hydroxyl radicals and sulfate radicals are key factors for the removal of contamination and the sulfate radicals were also the dominant radicals.

Green synthesis and application of heterogeneous iron oxide based nanoparticles for dairy wastewater treatment by Photo-Fenton processes

The aim of this study is to investigate the efficiency of heterogeneous Photo-bio-Fenton-like process and adsorption process for phosphorus removal from wastewater. The results showed that both of these processes can reach 98 and 92% removal efficiencies phosphate (P) and Chemical Oxygen Demand (COD), respectively. The findings of kinetic and isotherm studies revealed that data of P removal highly correlated with the pseudo-second-order kinetic model and Langmuir isotherm. The quenching experiments determined that both hydroxyl radicals and sulfate radicals are key factors for the removal of contamination and the sulfate radicals were also the dominant radicals.

Effective disposal of methylene blue using green immobilized silver nanoparticles on graphene oxide and reduced graphene oxide sheets through one-pot synthesis

This study reveals the feasibility of exploring highly efficient, cost-effective, and stable green adsorbents for the treatment of contaminated water. Here silver nanoparticles (AgNPs) were immobilized onto nanosheets of graphene oxide (GO) through in situ reduction process using green tea aqueous extract. GO reduction to reduced graphene oxide (rGO) and AgNPs decoration on rGO also occurred simultaneously. The impacts of the extract concentration, contact time, and temperature on the synthesis process have been investigated. The synthesized nanocomposites were examined by XRD, FTIR, Raman, SEM, TEM, and TGA. The GO nanosheets were decorated by AgNPs with a crystalline structure and an average particle size of 25 ± 3 nm. The temperature and the extract concentration were considerably affecting the type of the resulting nanocomposites. The GO/Ag nanocomposites were formed at room temperature (27 °C) using different extract concentration (2-18% (v/v)), while the rGO/Ag nanocomposite was formed only at a higher temperature (95 °C) with higher extract concentration (18%). The methylene blue (MB) dye was picked as a water pollutant to explore the adsorption ability of the nanocomposites. The adsorption behavior of the GO/Ag nanocomposites was examined under diverse factors (MB concentration, adsorbent dosage, pH, and contact time) to achieve optimization. The adsorption data concurs with Langmuir isotherm giving maximum adsorption up to 633 mg g^-1. Adsorption kinetics demonstrate good pseudo-second-order compliance. Spontaneous and endothermic nature of adsorption was affirmed via thermodynamic parameters. The nanocomposites could be utilized as eco-friendly and reliable adsorbents in wastewater treatment, as a result of their exceptional productivity and reusing potential.

Phosphoric Acid Activated Carbon from Melia azedarach Waste Sawdust for Adsorptive Removal of Reactive Orange 16: Equilibrium Modelling and Thermodynamic Analysis

Waste wood biomass as precursor for manufacturing activated carbon (AC) can provide a solution to ever increasing global water quality concerns. In our current work, Melia azedarach derived phosphoric acid-treated AC (MA-AC400) was manufactured at a laboratory scale. This novel MA-AC400 was tested for RO16 dye removal performance as a function of contact time, adsorbent dosage, pH, temperature and initial dye concentration in a batch scale arrangement. MA-AC400 was characterized via scanning electron microscopy, energy dispersive X-ray spectroscopy, Fourier transform infrared spectroscopy, dynamic light scattering (DLS) and fluorescence spectroscopy. MA-AC400 is characterized as mesoporous with BET surface area of 293.13 m² g^-1 and average pore width of 20.33 Å. pH_PZC and Boehm titration confirm the acidic surface charges with dominance of phenolic functional groups. The average DLS particle size of MA-AC400 was found in the narrow range of 0.12 to 0.30 µm and this polydispersity was confirmed with multiple excitation fluorescence wavelengths. MA-AC400 showed equilibrium adsorption efficiency of 97.8% for RO16 dye at its initial concentration of 30 mg L^-1 and adsorbent dose of 1 g L^-1. Thermodynamic study endorsed the spontaneous, favorable, irreversible and exothermic process for RO16 adsorption onto MA-AC400. Equilibrium adsorption data was better explained by Langmuir with high goodness of fit (R², 0.9964) and this fitness was endorsed with lower error functions. The kinetics data was found well fitted to pseudo-second order (PSO), and intra-particle diffusion kinetic models. Increasing diffusion constant values confirm the intraparticle diffusion at higher RO16 initial concentration and reverse was true for PSO chemisorption kinetics. MA-AC400 exhibited low desorption with studied eluents and its cost was calculated to be $8.36/kg.

Methylene Blue Adsorption onto Neem Leave/Chitosan Aggregates: Isotherm, Kinetics and Thermodynamics Studies

The work was aimed at evaluating the adsorptive properties of neem leave/chitosan aggregates for methylene blue removal. The adsorbent was screened to form coarse (CCANL, 600 µm), medium (MCANL, 300 µm) and fine (FCANL, 150 µm) neem leave/chitosan particles. The samples were characterized for pH, water binding capacity (WBC), surface chemistry by Fourier transform infrared spectroscopy, surface morphology by scanning electron microscope and textural properties by Brunauer-Emmett-Teller method. CCANL, MCANL and FCANL possessed specific surface area of 255, 258 and 242 m2/g, respectively. The effects of initial concentration, adsorbent dosage, contact time, pH and temperature were studied. CCANL, MCANL and FCANL demonstrated adsorption capacity of 102, 92.5 and 105 mg/g, respectively, in which ionic interaction and mesopore filling were the possible adsorption mechanisms. The equilibrium data were well fitted by Redlich-Peterson model, suggesting a monolayer adsorption onto a heterogeneous surface of adsorbent. The kinetics data were best described by pseudo-second-order and intraparticle diffusion models, for which the film diffusion, intraparticle diffusion and surface adsorption could co-exist as the controlling steps in adsorption. Adsorption of methylene blue onto chitosan composites was spontaneous, endothermic and demonstrated increased randomness at solid-solution interface.

Adsorption behavior of cationic and anionic dyes on magadiite-chitosan composite beads

In this paper, the composite beads were obtained by the encapsulation of a lamellar polysilicate magadiite in chitosan. The composite beads were tested as adsorbents for the removal of anionic Congo red (CR) and cationic methylene blue (MB) dyes. The obtained material was characterized by different methods such as XRD, SEM, TGA and zeta potential analysis. The adsorption mechanism of both dyes was supported by UV-vis and (FTIR) spectroscopy. The results reveal that the magadiite was immobilized in the chitosan matrix by hydrogen bond and electrostatic interactions. The influence of contact time, adsorbent dose and initial concentration of dye were investigated. The adsorption kinetics of CR onto composite beads followed the linear form of pseudo-second-order model and their equilibrium data were fitted well to the linear Langmuir model as confirmed by the calculated values of R², RMSE and SD. The adsorbed quantity registered for CR and MB dyes are 135.77 and 45.25 mg/g, respectively.

The equilibrium and fixed-bed study of malachite green adsorption on chitosan hydrogels

Chitosan hydrogel beads were prepared by a precipitation process, and were used to investigate the adsorption of malachite green (MG) oxalate under various conditions. It was found that adsorption equilibrium was most sensitive to the pH value at pH <8 while fixed bed breakthrough kinetics presented asymmetric S-shaped profiles which could not be adequately described by conventional models such as Adams-Bohart and Yoon-Nelson. The possible reasons were discussed and an improved Adams-Bohart model was proposed to better describe the changes in mass transfer mechanisms during adsorption.

Response surface methodology for optimization of methylene blue adsorption onto carboxymethyl cellulose-based hydrogel beads: adsorption kinetics, isotherm, thermodynamics and reusability studies

Environment-friendly composite hydrogel beads based on carboxymethyl cellulose (CMC), alginate (Alg) and graphene oxide (GO) were synthesized by an ionotropic gelation technique and studied as an efficient adsorbent for methylene blue (MB). The chemical structure and surface morphology of the prepared hydrogel beads were characterized by Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), thermogravimetric analysis (TGA), differential thermal analysis (DTA) and point of zero charge (pH_pzc). A hybrid response surface methodology integrated Box–Behnken design (RSM-BBD) was successfully developed to model, simulate, and optimize the biosorption process. The synergistic effects between three critical independent variables including adsorbent dose (0.3–0.7 g), pH of the MB solution (6.5–9.5) and initial MB concentration (15–45 mg L⁻¹) on the MB adsorption capacity (mg g⁻¹) and removal efficiency (%) were statistically studied and optimized. The performance of the RSM-BBD method was found to be very impressive and efficient. Results proved that the adsorption process follows a polynomial quadratic model since high regression parameters were obtained (R²-value = 99.8% and adjusted R²-value = 99.3%). Analysis of variance (ANOVA) further confirms the validity of the suggested model. The optimal conditions for 96.22 ± 2.96% MB removal were predicted to be 0.6 g of CMC-Alg/GO hydrogel beads, MB concentration of 15 mg L⁻¹ and pH of 9.5 within 120 min. The adsorption equilibrium is better described by the Freundlich isotherm, indicating that physisorption is the rate controlling mechanism. The MB adsorption process was thermodynamically spontaneous and endothermic. A reusability study revealed that the prepared adsorbent is readily reusable. The adsorbent still maintains its ability to adsorb MB for up to four cycles. Results reported in this study demonstrated that CMC-Alg/GO hydrogel beads are an effective, promising and recyclable adsorbent for the removal of MB from aqueous solutions.

Environment-friendly composite hydrogel beads based on carboxymethyl cellulose (CMC), alginate (Alg) and graphene oxide (GO) were synthesized by an ionotropic gelation technique and studied as an efficient adsorbent for methylene blue (MB).

Preparation of the Sodium Alginate-g-(Polyacrylic Acid-co-Allyltrimethylammonium Chloride) Polyampholytic Superabsorbent Polymer and Its Dye Adsorption Property

A polyampholytic superabsorbent polymer (PASAP), sodium alginate-g-(polyacrylic acid-co-allyltrimethylammonium chloride) (SA-g-(PAA-co-PTM)), was prepared by free-radical graft copolymerization and characterized. The polymer exhibited pH-dependent swelling behaviors with extremely high swelling ratios, and was saline tolerant. The dye adsorption properties of SA-g-(PAA-co-PTM) were investigated using methylene blue (MB) as a cationic dye model. It was found that its dye adsorption capacity was significantly affected by the TM content in PASAP and pH of dye solution. The dye adsorption kinetics and isotherm obey the pseudo-second-order kinetic model and the Langmuir isotherm model, respectively, and the adsorption process is chemisorption in nature. In addition, SA-g-(PAA-co-PTM) exhibited high MB adsorption capacities in a wide pH range and reusability in at least five adsorption-desorption cycles, indicating its great application potentials as the adsorbent for dye removals from effluents.

Enhanced adsorption performance of methylene blue from aqueous solutions onto modified adsorbents prepared from sewage sludge

In the present work, an attractive and creative adsorbent derived from sewage sludge was freshly fabricated via pyrolysis technology, followed by modification for improving the absorptive ability. First, the (NH₄)₂S₂O₈ modified pyrolytic sludge (MS_AP) was selected from 19 modified pyrolytic sludges for the highest removal efficiency and adsorption capacity for methylene blue (MB). Then, the adsorption performance for MB of MS_AP was compared systematically with the pristine adsorbent (MS_DW) by batch adsorption experiments. The main conclusions were that the adsorption process was better fitted with the Langmuir model, and the maximum adsorption capacity (q_max) of MS_AP was observed to be 149.05 mg g^-1. Moreover, the adsorption kinetics data showed a good fit with the pseudo second order model; when the addition of MS_AP was 1.0 g·L^-1, the rate constant was 0.05 g·mg^-1·min^-1, which was far greater than that of the other modified adsorbents.

Kinetic Study of the Bioadsorption of Methylene Blue on the Surface of the Biomass Obtained from the Algae D. antarctica

Currently, there is a great pollution of water by the dyes; due to this, several studies have been carried out to remove these compounds. However, the total elimination of these pollutants from the aquatic effluents has represented a great challenge for the scientific community, for which it is necessary to carry out investigations that allow the purification of water. In this work, we studied the bioadsorption of methylene blue on the surface of the biomass obtained from the algae D. antarctica. This material was characterized by SEM and FTIR. To the data obtained in the biosorption experiments, different models of biosorption and kinetics were applied, finding that the best fit to the obtained data is given by applying the pseudo-second-order models and the Toth model, respectively. It was also determined that the maximum adsorption capacity of MB on the surface of the biomass is 702.9 mg/g, which shows that this material has great properties as a bioadsorbent.