Maximum Methylene Blue Adsorption Research Articles

Polydopamine coating for enhanced electrostatic adsorption of methylene blue by multiwalled carbon nanotubes in alkaline environments

The removal of dye molecules in alkaline environments is an issue that should receive increased attention. In this study, the interaction mechanism between polydopamine-modified multiwalled carbon nanotubes (P-MWCNTs) and multiwalled carbon nanotubes (MWCNTs) with the cationic dye methylene blue (MB) in alkaline environments was explained in depth by adsorption, spectroscopy, and density functional theory (DFT). The mechanism of action and dominant forces between the adsorbent and adsorbate were analyzed graphically by introducing energy decomposition analysis (EDA) and an independent gradient model (IGM) into the DFT calculations. In addition, the force distribution was investigated through an isosurface. Moreover, batch adsorption studies were conducted to evaluate the performance of MWCNTs and P-MWCNTs for MB removal in alkaline environments. The maximum MB adsorption capacities of the MWCNTs and P-MWCNTs in solution were 113.3 mg‧g−1 and 230.4 mg‧g−1, respectively, at pH 9. The IGM and EDA showed that the better adsorption capacity of the P-MWCNTs originated from the enhancement of the electrostatic effect by the proton dissociation of polydopamine. Moreover, the adsorption of MB by MWCNTs and P-MWCNTs in alkaline environments was governed by dispersion and electrostatic effects, respectively. Through this study, it is hoped that progress will be made in the use of DFT to explore the mechanism of adsorbent-adsorbate interactions.

High-efficient removal of methylene blue by zirconium-based organic frameworks modified with 1,3,5-benzenetricarboxylic acid: Characterization, performances, and mechanisms

The vast discharge of methylene blue (MB) dye in industrial effluent, risks the ecological environment, thus making its removal unavoidable. Recently, metal organic frameworks (MOFs) due to their larger pore volume, surface area and easy synthesis have proved to be exceptionally promising materials for contaminant treatment. Based on 1,3,5-benzenetricarboxylic acid (BTC) as a modifier, a new composite material consisting of BTC and Zr-based MOF (UIO-66-BTC) was fabricated for the effective removal of MB from the effluent. Its synthesis and efficient application has been confirmed by characterization analysis. The influencing factors, adsorption isotherms, and adsorption kinetics of MB adsorption by adsorbent were studied. It was demonstrated that the removal rate of MB adsorption by UIO-66-BTC reached 98.45% and the adsorption amount reached 393.80 mg g−1 at temperature (298 K), pH 7, adsorbent dosage (0.5 g L−1), MB initial concentration (200 mg L−1), and contact time of 720 min, respectively. The maximum adsorption of MB by UIO-66-BTC was 20.827 times higher than that of UIO-66 (18.908 mg g−1). The experimental data fits with the pseudo-second-order kinetic model and Langmuir isotherm, implying that the adsorption process is a monolayer chemisorption process. The thermodynamic and regeneration experiments showed that the spontaneous process enhanced the adsorption of MB at lower temperatures and the adsorption efficiency of MB remained above 68% after five successive cycles. The mechanism of MB adsorption on adsorbents is mainly based on electrostatic interactions, pore filling, hydrogen bonding and π-π interactions. It is concluded that this new adsorbent can be effectively used to treat MB in effluents.

Construction of 3D-Printed Sodium Alginate/Chitosan/Halloysite Nanotube Composites as Adsorbents of Methylene Blue.

In this study, sodium alginate/chitosan/halloysite nanotube composites were prepared by three-dimensional printing and characterized in terms of morphology, viscosity, thermal properties, and methylene blue (MB) adsorption performance. The high specific surface area and extensively microporous structure of these composites allowed for effective MB removal from wastewater; specifically, a removal efficiency of 80% was obtained after a 60 min treatment at an adsorbent loading of 1 g L-1 and an MB concentration of 80 mg L-1, while the maximum MB adsorption capacity equaled 376.3 mg g-1. Adsorption kinetics and isotherms were well described by quasi-second-order and Langmuir models, respectively. The composites largely retained their adsorption performance after five adsorption-desorption cycles and were concluded to hold great promise for MB removal from wastewater.

Preparation of biochar adsorption material from walnut shell by supercritical CO2 pretreatment

In order to treat dyes in the wastewater of the printing industry and to reutilize walnut shell (WS) waste generate economic benefits, supercritical carbon dioxide (SC-CO2) pretreatment technology was developed to prepare porous biochar as a precursor for adsorption material. Orthogonal experiments were conducted at the temperatures of 200, 300, and 400 ℃ with durations of 20, 40, and 60 min, and a control group was set up using N2 pretreatment. Then, KOH activation was employed to prepare biochar adsorption material. The biochars were analyzed and characterized using TGA, BET, SEM, FT-IR, and XRD, and the liquid and gas phase products of the pretreatment process were analyzed semi-quantitatively and quantitatively using GC–MS and gas chromatography. Methylene blue (MB) dye was selected as an indicator to measure the adsorption capacity of biochar, and adsorption kinetics were analyzed based on the data. The results indicate that pretreatment with SC-CO2 effectively enhanced the performance and yield of the activated carbon. The highest specific surface area increased by 18%, and the maximum adsorption of MB increased by 23% compared to the N2 control group. The yield increased by 8–262% and the specific surface area increased by 50–192% compared to the direct activation of walnut shell (WS). During the pretreatment processes for the preparation of biochar adsorption material with the best specific surface area, phenol-enriched bio-oil was produced as a by-product which has economic value.Graphical

Efficient dye adsorption of mesoporous activated carbon from bamboo parenchyma cells by phosphoric acid activation.

In order to solve the environmental damage caused by the discharge of dyes as industrial wastewater, the development of efficient and sustainable adsorbents is the key, while most of the previous studies on bamboo parenchyma cells have focused on their microstructural, functional and mechanical properties, and few of the properties in adsorption have been investigated. To evaluate the role of the unique microstructure of bamboo parenchyma cells on adsorption after carbonization and activation, PC-based activated carbon (PPAC) was fabricated by the phosphoric acid activation method and tested for adsorption using methylene blue (MB). The effect of mesoporous structure on MB adsorption was investigated in detail using PPAC-30C impregnated with phosphoric acid at a concentration of 30%. The results showed that the adsorption performance was influenced by single-factor experiments (e.g., pH, activated carbon dosing). The adsorption isotherms and kinetics could conform to the Langmuir model (R2 = 0.983-0.994) and pseudo-second-order kinetic model (R2 = 0.822-0.991) respectively, and the maximum MB adsorption capacity of adsorbent was 576 mg g-1. The adsorption mechanism of MB on PPAC-30C includes physical adsorption, electrostatic attraction, hydrogen bonding, and the π-π conjugation effect, which was dominated by physical adsorption. The results of this study show that PPAC has good application prospects for cationic dye removal.

Hydrothermal synthesis of Fe3O4 nanoparticles at different pHs and its effect on discoloration of methylene blue: Evaluation of alternatives by TOPSIS method

In this study, hydrothermal synthesis was employed to produce Fe3O4 nanoparticles for the methylene blue removal from an aqueous medium. The production of magnetite nanoparticles involved the utilization of Fe2+ and Fe3+ salts, and their respective solutions were created at pH levels of 10, 11, and 12, subsequently subjected to autoclave treatment. The evaluation of pH-induced variations in nanoparticle characteristics was conducted through X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), Field emission scanning electron microscopy (FESEM), vibrating-sample magnetometer (VSM), and Dynamic light scattering (DLS) analyses. pH levels within the synthetic medium yielded diminutive Fe3O4 nanoparticles characterized by augmented saturation magnetization, heightened zeta potential, and a narrower size distribution. Following nanoparticle synthesis under varied pH conditions, their efficacy in methylene blue (MB) adsorption was investigated. Notably, nanoparticles synthesized at pH 11 demonstrated the highest adsorption capacity, registering maximum MB adsorption capacities of 188.68 mg/g, while pH 10 and 12 counterparts exhibited capacities of 169.49 mg/g and 175.44 mg/g, respectively. The adsorption processes conformed to the Langmuir–Freundlich isotherm model, with the pseudo-second-order model offering superior fitting to elucidate MB adsorption kinetics, thereby indicating the involvement of chemical adsorption mechanisms. It was discerned that MB adsorption encompassed both physical and chemical mechanisms, encompassing electrostatic attraction between the negatively charged surface of the nanoparticles and the cationic dye, as well as electron exchange interactions between MB and the functional groups present on the adsorbent surface. Thermodynamically speaking, this adsorption process exhibited an exothermic nature, with a preference for ambient temperatures. Magnetic separation post-adsorption was conveniently executed, and all nanoparticles demonstrated potential for reuse for a minimum of five cycles. Moreover, the Technique for Order of Preference by Similarity to Ideal Solution (TOPSIS) method was employed to assess and select the most favorable alternative from the available options. Based on the evaluation of 27 distinct criteria, it was determined that Fe3O4 synthesized in an environment with pH 11 emerged as the optimal choice, aligning with the initial findings from the adsorption assessments.

Chitosan-polyvinyl alcohol-diatomite hydrogel removes methylene blue from water

Dye pollution in the aquatic environment can harm ecosystems and human health. Here, we developed a new green adsorbent by applying an improved drying process. Diatomite was embedded in a network structure formed between chitosan and polyvinyl alcohol without using any crosslinking agent to prepare chitosan-polyvinyl alcohol-diatomite hydrogel beads through alkali solidification. The beads were tested for removing a cationic dye (methylene blue (MB)) from water. The structure of the adsorbent beads was analysed using scanning electron microscopy, energy-dispersive spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and Fourier-transform infrared spectroscopy. The adsorption capacity was investigated, and the results indicated excellent MB adsorption properties. The adsorbents had a rough surface and high swelling capacity of 66.9 g/g. The maximum MB adsorption capacity was 414.70 mg/g, and the adsorption followed the Freundlich isothermal and quasi-second-order kinetic models. The adsorption was an endothermic spontaneous process governed by both intra-particle and external diffusion processes. The proposed adsorption mechanisms involved hydrogen bonding and electrostatic interactions. These adsorbent beads have considerable application potentials owing to their high adsorption capacity, green composition, and non-polluting nature.

Sugarcane bagasse-derived granular activated carbon hybridized with ash in bio-based alginate/gelatin polymer matrix for methylene blue adsorption

Sugarcane bagasse (SCB) and sugarcane bagasse ash (SCB-ash) are major agricultural residues from sugar processing industries in Thailand. In this study, SCB-derived activated carbon (SCBAC) with the optimum surface area of 489 m2/g was prepared by steam activation at 900 °C for 1 h. Hybrid granular activated carbons (GACs) were successfully developed by mixing SCBAC with bio-based polymers, alginate and gelatin, at the weight ratio of 3:1 for methylene blue (MB) adsorption. SCB-ash, which was additionally mixed in the GACs, could significantly increase compressive strength of the GACs, but decrease their surface areas and MB adsorption efficiencies. An existence of gelatin up to 30 wt% in the polymer matrix of the GACs showed a slight increase in swelling degree and iodine number, but could not enhance bead strength and MB adsorption efficiency due to its relatively lower bulk density and specific surface area. Maximum MB adsorption capacities of the GACs were found at 290–403 mg/g under this study's experimental condition. MB adsorption efficiencies at above 90 % with no deformation of all of the selected SCB hybrid GACs were finally confirmed after seven consecutive adsorption-desorption cycles using a simple regeneration with ethanol.

Optimization and mechanistic approach for removal of crystal violet and methylene blue dyes via activated carbon from pyrolyzed-ZnCl2 bamboo waste

In this study, bamboo waste (BW) was subjected to pyrolysis-assisted ZnCl2 activation to produce mesoporous activated carbon (BW-AC), which was then evaluated for its ability to remove cationic dyes, specifically methylene blue (MB) and crystal violet (CV), from aqueous environments. The properties of BW-AC were characterized using various techniques, including potentiometric-based point of zero charge (pHpzc), scanning electron microscopy with energy dispersive X-rays (SEM-EDX), X-ray diffraction (XRD), gas adsorption with Brunauer–Emmett–Teller (BET) analysis, infrared (IR) spectroscopy. To optimize the adsorption characteristics (BW-AC dosage, pH, and contact time) of PBW, a Box-Behnken design (BBD) was employed. The BW-AC dose of 0.05 g, solution pH of 10, and time of 8 min are identified as optimal operational conditions for achieving maximum CV (89.8%) and MB (96.3%) adsorption according to the BBD model. The dye removal kinetics for CV and MB are described by the pseudo-second-order model. The dye adsorption isotherms revealed that adsorption of CV and MB onto BW-AC follow the Freundlich model. The maximum dye adsorption capacities (qmax ) of BW-AC for CV (530 mg/g) and MB (520 mg/g) are favorable, along with the thermodynamics of the adsorption process, which is characterized as endothermic and spontaneous. The adsorption mechanism of CV and MB dyes by BW-AC was attributed to multiple contributions: hydrogen bonding, electrostatic forces, π-π attraction, and pore filling. The findings of this study highlight the potential of BW-AC as an effective adsorbent in wastewater treatment applications, contributing to the overall goal of mitigating the environmental impact of cationic dyes and ensuring the quality of water resources.

Deep insights into kinetics, optimization and thermodynamic estimates of methylene blue adsorption from aqueous solution onto coffee husk (Coffee arabica) activated carbon

In the current study, an attempt was made to synthesize coffee husk (CH) activated carbon by chemical modification approach (sulphuric acid-activated CH (SACH) activated carbon) and was used as a valuable and economical sorbent for plausible remediation of Methylene blue (MB) dye. Batch mode trials were carried out by carefully varying the batch experimental variables: SACH activated carbon (SACH AC) dosage, pH, initial dye concentration, temperature, and contact time. The optimum equilibrium time for adsorption by SACH activated carbon was obtained as 60 min, and the maximum adsorption took place at 30 °C. Morphological and elemental composition, crystallinity behaviour, functional groups, and thermal stability were examined using SEM with EDX, XRD, FTIR, BET, TGA, and DTA and these tests showed successful production of activated carbon. The outcomes showed that chemical activation enhanced the number of pores and roughness which possibly maximized the adsorptive potential of coffee husk. The Box-Benken design (BBD) was used to optimize the MB dye adsorption studies and 99.48% MB dye removed at SACH AC dosage of 4.83 g/L at 30 °C for 60 min and pH 8.12, and the maximum adsorption was yielded for sulphuric acid-activated coffee husk carbon carbon with 88.1 mg/g maximum MB adsorption capacity. Langmuir- Freundlich model deliberately provided a better fit to the equilibrium data. The SACH AC-MB dye system kinetics showed a high goodness-of-fit with pseudo second order model, compared to other studied models. Change in Gibbs's free energy (ΔGo) of the system indicated spontaneity whereas low entropy value (ΔSo) suggested that the removal of MB dye on the SACH activated carbon was an enthalpy-driven process. The exothermic nature of the sorption cycle was affirmed by the negative enthalpy value (ΔHo). The adsorptive-desorptive studies reveal that SACH AC could be restored with the maximum adsorption efficiency being conserved after the fifth cycles. Overall, the outcomes revealed that sulphuric acid-activated coffee husk activated carbon (SACH AC) can be used as prompt alternative for low-cost sorbent for treating dye-laden synthetic wastewaters.

Simultaneous adsorption of methylene blue and amoxicillin by starch-impregnated MgAl layered double hydroxide: Parametric optimization, isothermal studies and thermo-kinetic analysis

Textile and pharmaceutical effluents contain significant amounts of dyes and antibiotics, which pose a serious threat to the ecosystem when discharged directly. Therefore, they should be treated by facile treatment techniques using low-cost materials. Layered double hydroxide (LDH) and its hybrids have emerged as robust and economic adsorbents for water treatment. Herein, magnesium/aluminum LDH and its starch-based composite were synthesized by a co-precipitation technique. The physicochemical features of the developed adsorbents were thoroughly characterized using various analytical tools. The developed materials were tested for the eradication of methylene blue (MB) and amoxicillin (AMX) in batch mode adsorption by varying operating conditions. Adsorption performance depends on the solution's pH. Under optimum adsorption conditions of pH 11, adsorbent dosage of 50 mg/L, and treatment time of 120 min, starch-impregnated MgAl-LDH exhibited maximum MB and AMX adsorption capacities of 114.94 and 48.08 mg/g, respectively. The adsorption mechanism states that hydrogen bonds and weak van der Waals forces are responsible for the removal of pollutants by the developed materials. Moreover, equilibrium and kinetic studies revealed that the removal of dye and antibiotic followed the Freundlich and Langmuir models with the pseudo-second-order reaction kinetics, respectively. The spent adsorbents were regenerated using 0.1 M HCl (for MB) and methanol (for AMX) eluent, and reusability studies ensured that the developed adsorbents retained their performance for up to four consecutive adsorption/desorption cycles. MgAl-LDH and its starch-based hybrid could thus be used to effectively remove organic contaminants from wastewater streams on a commercial scale.

Tailored mesoporous structures of lignin-derived nano-carbons for multiple applications

This work uses a one-step KOH activation for lignin precursors to produce ultra-high mesoporous activated carbons (ACs) with an unprecedented combination of the surface area of 3207 m2 g−1 and mesopore ratio of 76%. The ACs are applied for supercapacitors (SCs) and methylene blue (MB) adsorption. The capacitance of the SCs in the three-electrode system reaches 812.3 F g−1 and demonstrates a remarkable maximum MB adsorption capacity of 1250 mg g−1. By modifying the process conditions, the mesopore ratio of ACs could be controlled from 10% to 80%. Compared with one-step activation, a two-step method produced microporous carbons with a lower surface area of 1227 m2 g−1 and a high micropore ratio of 73%. The capacitance of SCs with two-step ACs reached 228.1 F g−1 and the maximum adsorption capacity of 476.19 mg g−1 for MB adsorption. The two-step method limited the surface area but had a higher oxygen surface functionality, benefiting its electrochemical performance. A techno-economic analysis reveals that the one-step KOH activation-based process develops ACs with a minimum selling price of $7648/ton. This work demonstrates tuning the processing-structure-property-performance relationship of lignin-based ACs to make an economically viable domestic carbon source.

Engineered biochar derived from lemon peel waste for highly efficient removal of organic pollutants from water

The urgent need for efficient decontamination of organic dyes from polluted waters necessitates the search for a low-cost and suitable adsorbent. The large amount of lemon peel residue in actual production can be an ideal raw material for the preparation of adsorbents. Herein, a novel magnetic nanocomposite derived from lemon (Citrus limon L.) peel residue (Fe3O4/Lp-biochar) was successfully synthesized by one-step hydrothermal method and used for the adsorptive capture of methylene blue (MB) in aqueous solution. The prepared Fe3O4/Lp-biochar are spherical with a particle size of 8.3 nm and have a saturation magnetization intensity of 52.9 emu/g and a specific surface area of 64.30 m2/g. It was found that the maximum MB adsorption capacity of 26.36 mg/g by the Fe3O4/Lp-biochar can be achieved when the amount of nanocomposite was 0.10 mg/mL, the system's pH value was 10, the reaction temperature was 25 °C, and the adsorption time was 60 min. Adsorption kinetics of MB on the Fe3O4/Lp-biochar followed the pseudo-second-order kinetic model whilst the Freundlich isotherm model could well simulate the adsorption behavior of MB on magnetic biochar. The adsorption mechanism of MB by the Fe3O4/Lp-biochar predominantly include electrostatic attraction and mesoporous interaction. Furthermore, the Fe3O4/Lp-biochar exhibited a remarkable retention of 94.7% of the initial adsorption efficiency even after the 10th cycle of repeated use. It was concluded that the lemon peel-derived magnetic biochar can be a promising alternative to conventional adsorbents for wastewater treatment.

Smart superabsorbent alginate/carboxymethyl chitosan composite hydrogel beads as efficient biosorbents for methylene blue dye removal

The presence of toxic dyes in the aqueous medium has threatened environmental safety, and thereby removing them from wastewater in an efficient way is highly desired. Herein, the efficient biosorbents were successfully fabricated via a facile physical gelation process of sodium alginate (SA) and carboxymethyl chitosan (CMCTS) in an acidic aqueous solution. The as-prepared hydrogel beads not only displayed water superabsorbent properties and pH-responsive swelling characters but also exhibited excellent methylene blue (MB) adsorption capacity removal efficiency with experimental maximum MB adsorption capacity of 2518 and 1005 mg g–1, which are comparable with most reported lignocellulosic and alginate-based hydrogels. The MB adsorption process fitted well in different kinetic and isotherm models and became more heterogeneous in concentrated MB solutions as verified by principal component analysis results. The adsorption mechanism was proposed, and the high dye absorbency was attributed to the strong electrostatic forces between adsorbents and adsorbates. Our current study provides a promising and sustainable composite hydrogels platform targeted to dye decontamination.

Valorization of food waste digestate to ash and biochar composites for high performance adsorption of methylene blue

The valorization and appropriate treatment of food waste digestate (FWD) is a critical issue for facilitating the sustainable development of anaerobic digestion and actualizing a circular economic. The FWD contains high ash contents and is conventionally considered as an inappropriate feedstock for producing high-value products such as biochar. However, this ash content may also have a chance to enhance the application performance of biochar as an adsorbent if positive synergic effect is identified. This study used industrial FWD as a widely obtainable feedstock for producing ash-biochar composites (ABCs) for methylene blue (MB) contaminated wastewater abatement. The obtained ABCs performed a maximum MB adsorption capacity of 1123.5 mg/g. Mechanism and modeling assessments demonstrated that the ash components on the surface of ABC adsorbent enhanced MB removal by providing alkaline adsorption environment and more oxygen-based n-π interaction sites. In addition, increasing pyrolysis temperature enlarged the biochar surface area and homogenously rearranged the carbon structure to strength the π-π interaction between MB and ABC adsorbent. This research suggests that FWD is principally an ideal feedstock that can be directly used for making high-performance absorbents for wastewater treatment.

Vitex doniana seed activated carbon for methylene blue adsorption: equilibrium and kinetics

This study evaluated the characteristics of zinc chloride modified vitex doniana seed activated carbon (VDZnCl2) for the removal of methylene blue. VDZnCl2 was characterized for textural properties, surface morphology and surface chemistry. Batch adsorption of methylene blue by VDZnCl2 was evaluated for the effects of concentration, contact time, adsorbent dosage, and solution pH. The surface area increased from 14 to 933 m2/g with porous texture to facilitate adsorption. The SEM micrograph showed varieties of pores with widened cavities. The FTIR spectra showed the characteristics of O–H and C=C groups commonly found in carbonaceous materials. The maximum methylene blue adsorption was recorded as 238 mg/g at concentration range of 1–800 mg/L and VDZnCl2 dosage of 50 mg. Sips isotherm fitted well with the equilibrium data, suggesting that the adsorption by VDZnCl2 was a physical process onto its heterogeneous surface, while the applicability of pseudo-first-order kinetics implies that external diffusion was the rate controlling mechanism. The performance put up by VDZnCl2 suggested that it is a potential adsorbent substitute for dye wastewater treatment.

Adsorptive performance of aminonaphthalenesulfonic acid modified magnetic-graphene oxide for methylene blue dye: Mechanism, isotherm and thermodynamic studies

In this research, a new aminonaphthalenesulfonic acid modified magnetic-graphene oxide (Fe3O4@GO@AHSA) was fabricated via in situ co-precipitation process followed by a covalent functionalization of Fe3O4@GO with aminonaphthalenesulfonic acid (AHSA) via amidation reaction. Fe3O4@GO@AHSA was featured by Zeta potential, FTIR, SEM, XRD, and TGA, then utilized in methylene blue (MB) adsorption from an aquatic media. The optimum removal efficiency of Fe3O4@GO@AHSA was assessed by batch method at different variables such as adsorbent dose (0.01–0.05 g), pH (2–8), adsorption time (1–1440 min), initial concentration of MB (25–300 mg/L), and temperature (25–45 °C). Accordingly, 0.03 g Fe3O4@GO@AHSA dose, pH: 7, contact time: 240 min at 25 °C were found to be the best optimal conditions, and a maximum experimental adsorption capacity of Fe3O4@GO@AHSA toward was 220.1 mg/g. Three nonlinear isotherm and kinetic models were utilized to assess the equilibrium experimental adsorption data. The findings show that the removal performance fits a Longmire isotherm and pseudo-second-order kinetic models. Besides, the result revealed that the maximum monolayer adsorption of MB on Fe3O4@GO@AHSA was 286.4 m/g. Based on thermodynamic results, the MB adsorption on Fe3O4@GO@AHSA nanocomposite was exothermic and a feasible process. The reusability tests displayed that the Fe3O4@GO@AHSA nanocomposite can be regenerated and reused up to the fourth cycle successfully for the uptake of MB pigment. Finally, this research indicates that the Fe3O4@GO@AHSA nanocomposite has a robust adsorption performance for MB dye from an aqueous medium.

Effect of temperature and fly ash content on the catalytically pyrolyzed rice straw biochar–fly ash composites for methylene blue adsorption

AbstractRice straw and fly ash are the wastes produced in abundance which need immediate attention for their management. In the present study, the in situ pyrolysis of rice straw in presence of fly ash was carried out and the resultant composites were studied for adsorption of methylene blue (MB). Slow pyrolysis of rice straw in presence of fly ash is evaluated using thermogravimetric analysis (TGA) and Coats–Redfern equation for pseudo‐first‐order reaction kinetics, respectively. The activation energy (Ea) for the pyrolysis of rice straw was 41.75 kJ/mol which was lowered to 37.39 kJ/mol in presence of fly ash. Biochar fly ash composites BFA41–3, BFA51–3, and BFA61–3 were prepared at three 400°C, 500°C, and 600°C pyrolysis temperature, respectively, the subscript indicating three different ratios of rice straw and fly ash (1:3, 1:1, and 3:1 w/w ratio). The composites BF4–61–3 were neutral to alkaline in pH, due to the presence of basic oxide and carbonates minerals. BFA4–61–3 was studied for batch adsorption of MB and optimized for pH, dose, and initial concentration of adsorbate. The maximum MB adsorption capacity of 25.91 mg/g was reported for the composite BFA41. MB adsorption efficiency (qe) followed the trend BFA41–3 > BFA51–3 > BFA61–3, which indicates a strong influence of biochar surface functional groups on dye adsorption, as reiterated by the multiple linear regression (MLR) analysis. Stripping of MB was achieved using methanol as a stripping agent for MB‐adsorbed BFA4–61–3 with desorption efficiency of 7% to 11% in the first cycle and 23% to 100% in the second cycle. Thus, the biochar fly ash composite with optimum ion exchangeable functional organic moieties would be suitable for dye remediation and waste generated in the process could find application in soil amelioration.

Development and characterisation of novel hybrid materials of modified ZnO-SiO2 and polyaniline for adsorption of organic dyes

ABSTRACT Polyaniline (PAni)–coated ZnO–SiO2–based hybrid material was prepared successfully with the in-situ polymerisation method and the product was subsequently analysed using XPS, XRD, TEM, UV-vis, TGA, FTIR and BET. The optical band gap calculated from the Tauc plot was found to be 2.89 eV. Moreover, this work reports an extensive study of the effect of the SiO2 on the electrochemical performance of hybrid material based on ZnO and PAni employing cyclic voltammetry. Furthermore, to evaluate the adsorption of methylene blue (MB), the parameters for the effectiveness of the adsorption process, including pH value, concentration and temperature, were investigated. The results indicated that the maximum adsorption of MB on the produced hybrid material occurred at pH 6.8 with a capacity reaching 71.2 mg.g−1. The thermodynamic studies indicate that the adsorption of MB on this adsorbent is spontaneous and endothermic in nature. Furthermore, PAni@ZnO–SiO2 is attractive for treating the effluents containing dyes due to its recyclability and high removal capacity.

A comparative study on modification of aerogel-based biosorbents from coconut fibers for treatment of dye- and oil-contaminated water

In this study, the discarded coconut fibers are treated with sodium hydroxide (NaOH) and hydrogen peroxide (H2O2) to recover the purified cellulose for further being transformed into the cellulose-based aerogels without consuming and releasing any toxic chemicals. This work also provides a comparison between two methods of synthesizing the cellulose aerogels via using physical cross-linkers polyvinyl alcohol/xanthan gum (PVA/XTG), the alkali-urea method and carbonization in terms of characteristics, dye removal, oil adsorption as well as simplicity and feasibility of the synthesis determined by the material balance of cellulose recovery and aerogel fabrication. Overall, the fabricated aerogels maintain a high porosity of 96.30–98.32%, low density of 0.034–0.063 g/cm3, and outstanding adsorption capacity for methylene blue (MB) and oil. It is worth noting that the carbon aerogels exhibit an impressive maximum MB adsorption capacity of 625 mg/g which is three times higher than that of the uncarbonized aerogels. Without modification, the carbon aerogels show the highest oil sorption capacity of 22.71 g/g among the investigated subjects. The results demonstrate that our aerogels are all promising candidates for the treatment of contaminated wastewater.