Activated carbon blended with grape stalks powder: Properties modification and its application in a dye adsorption

In this study, activated carbon was blended with grape stalks powder to adsorb methylene blue (MB) dye with various concentrations from a wastewater. For this purpose, five independent variables involving pH (2–13), contact time (5–270 min), grape stalks powder dosage (0.1–10 g/l), methylene blue initial concentration (20–300 mg/l), and activated carbon dosage (0.1–10 g/l) for methylene blue adsorption were studied. The Central Composite Design (CCD) under Response Surface Methodology (RSM) was applied to estimate the independent variables effects on the methylene blue adsorption. The pseudo- first order, pseudo-second order, Elovich and intraparticle diffusion models were employed to study the adsorption kinetics and isotherm. The Langmuir, Freundlich, Temkin and Dubinin-Radushkevich isotherm models were applied to investigate the adsorption isotherm. It was concluded that the intraparticle diffusion isotherm and pseudo-second order kinetic models could show the best results. Furthermore, some data such as physical adsorption (by analyzing FTR and applying some standard equations) and mean free energy (E) were discovered in this research. Finally, activated carbon blended with grape stalks powder as an effective bio-adsorbent for the methylene blue reduction from a wastewater was introduced.     

TiO2/柚子皮生物质活性炭复合材料的制备和吸附光降解性研究

本文以自制柚子皮生物质活性炭为原料,采用凝胶-溶胶法合成TiO2/柚子皮生物质活性炭复合材料(TiO2/BAC)。对复合材料进行SEM、FTIR、XRD等表征,并研究该复合材料对中性红、亚甲基蓝染料及甲醛的吸附降解性能。结果表明,在复合材料中柚子皮生物质活性炭的添加量为7 g、预吸附时间为2 h时,对染料具有最佳的吸附降解效果,复合材料在循环使用5次后对染料的吸附降解率仍达到了80 %以上。当活性炭的添加量为6 g、复合材料的添加量为2 g时,复合材料对甲醛的吸附降解达到最大,可达61%。表明该复合材料对中性红、亚甲基蓝染料及甲醛具有良好的吸附降解效果,有望用于废水染料的去除和家居甲醛净化。     

Activated carbon prepared by physical activation of olive stones for the removal of NO2 at ambient temperature

Activated carbon was prepared from olive stones by physical activation using water vapor at 750 °C. Textural, morphology and surface chemistry characterizations were achieved (nitrogen adsorption, SEM, FTIR and TPD–MS). NO₂ adsorption was performed for different inlet gas compositions and temperatures. NO₂ may adsorb directly on the oxygenated surface groups, and can also be reduced to NO. Therefore, a second NO₂ molecule adsorbs on the oxygen left on the carbon surface. TPD performed after NO₂ adsorption showed the presence of various surface groups. The adsorption capacity was about 131 mg/g, which is higher than with several activated carbon prepared from classical lignocellulosic biomass. NO₂ reduction into NO decreased with increasing the inlet oxygen concentration. In contrast, a slight decrease in the NO₂ adsorption capacity was observed with increasing temperature. It seems that the activated carbons prepared from olive stones by steam activation could be used as efficient adsorbents for NO₂ removal.     

Immobilization of cellulose extracted from Robinia Pseudoacacia seed fibers onto chitosan: Chemical characterization and study of methylene blue removal

The design of economical adsorbents to remove pollutants from contaminated water is attracting more attention. In this study, cellulose was successfully extracted from Robinia Pseudoacacia seed fibers and immobilized onto chitosan beads. The prepared spherical beads were then used for the biosorption of methylene blue dye from aqueous media. Samples were investigated using several analytical methods, namely FT-IR, XRD, EDX, SEM, and TGA analyses. The adsorption experiments showed that combining cellulose with chitosan improved the removal of methylene blue. The maximum uptake amount of methylene blue using cellulose–chitosan composite beads was 55 mg/g. However, it was about 35 mg/g at 20 °C for chitosan beads. The kinetic data complied strongly with the pseudo-second order equation, suggesting that the biosorption phenomenon has predominantly a chemical nature. Overall, the current study has shown a promising technique to design new adsorbents from abundant natural polymers for eliminating cationic dyes from water.     

Fe3O4-CuO-activated carbon composite as an efficient adsorbent for bromophenol blue dye removal from aqueous solutions

Dye wastewater from industries is posing tremendous health hazards. The lethal dyes can be eliminated using nanomaterials and scientific approach like adsorption which is facile, cheap, safe as well as ecofriendly. Fe₃O₄-CuO-AC composite was prepared by a hydrothermal method and used for the removal of dyes in wastewater. The composite material was characterized by various techniques such as XRD, SEM, EDS, TEM and FT-IR. The Fe₃O₄-CuO-AC composite was used to treat five types of dyes in water. Fe₃O₄-CuO-AC composite showed the highest adsorption capability for bromophenol blue (BPB) dye. The effects of initial concentration, pH, the amount of adsorbent and temperature were also studied. The optimum conditions were found to be 20 ppm dye concentration, pH 9, an adsorbent dose of 0.06 gL^─1 at 65 °C. A removal efficiency of 97% was obtained for BPB dye during 120 min of adsorption. Kinetic studies indicated that a pseudo-second order is the most suitable model for the adsorption process. The Fe₃O₄-CuO-AC composite showed better adsorption capacity as compare to Fe₃O₄-AC except for the Methyl green dye. The maximum adsorption capacity was found to be 88.60 mg/g for BPB. Additionally, the thermodynamic parameters (ΔS°, ΔH° and ΔG°) showed that the process was spontaneous and exothermic. All the above results revealed that the Fe₃O₄-CuO-AC compositecan be an effective adsorbent for removing dyes from wastewater.     

Synthesis of NiO coated chitosan-cenosphere buoyant composite for enhanced adsorptive removal of methylene blue

The objective of the present study is to utilize fly ash cenosphere to remove methylene blue (MB) from the water streams. Nickel oxide is a typical semiconductor used as proficient adsorbent material for degradation of dye with environment friendly applications due to its excellent chemical stability and high catalytic activity. The chitosan cenosphere buoyant composite coated with NiO was synthesized with hydrothermal grafting reaction using silane coupling agent and epichlorohydrin as a cross-linking reagent. The batch adsorption experiments were carried out with a cationic dye, methylene blue as a representative organic pollutant to investigate the adsorptive capabilities of the composite as adsorbent. The influence of pH (2-12), initial concentration of dye (50–200 mg/L), temperature (37–47 °C) and contact time (0–24 h) were taken as parameters in the study. On the relative elimination of MB, the effect of time and temperature were investigated. The adsorption kinetics for MB was correlated and found to observe the pseudo-second order kinetic model, whereas the equilibrium adsorption isotherm follows the Langmuir model (R² > 0.99). The results indicate that the floating fly ash cenosphere coated with NiO proved to be more responsive for enhanced degradation of methylene blue.     

Preparation and characterization of nanocomposite,silica aerogel,activated carbon and its adsorption properties for Cd (II) ions from aqueous solution

A novel composite adsorbent, silica aerogel activated carbon was synthesized by sol-gel process at ambient pressure drying method. The composite was characterized by Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), differential scanning calorimetry (DSC) and Nitrogen adsorption/desorption isotherms (BET).In the present study, the mentioned adsorbent was used moderately for the removal of cadmium ions from aqueous solutions and was compared with two other adsorbents of cadmium, activated carbon and silica aerogel. The experiments of Cd adsorption by adsorbents were performed at different initial ion concentrations, pH of the solution, adsorption temperature, adsorbent dosage and contact time. Moreover, the optimum pH for the adsorption was found to be 6.0 with the corresponding adsorbent dosage level of 0.1 g at 60 °C temperature. Subsequently, the equilibrium was achieved for Cd with 120 min of contact time.Consequently, the results show that using this composite adsorbent could remove more than 60% of Cd under optimum experimental conditions. Langmuir and Freundlich isotherm model was applied to analyze the data, in which the adsorption equilibrium data were correlated well with the Freundlich isotherm model and the equilibrium adsorption capacity (q_e) was found to be 0.384 mg/g in the 3 mg/L solution of cadmium.     

Nanostructured spinel-type M(M = Mg,Co, Zn)Cr2O4 oxides: novel adsorbents for aqueous Congo red removal

Nanostructured spinel-type M(M = Mg, Co, Zn)Cr₂O₄ oxides with novel adsorbents for aqueous Congo red removal were synthesized by a polyacrylamide gel method and studied for their phase structure, microstructure, adsorption performance, and multiferroic behavior. The phase structure and purity analysis revealed that the nanostructured spinel-type M(M = Mg, Co, Zn)Cr₂O₄ oxides presented a spinel-type cubic structure, and the formation of a secondary phase such as Cr₂O₃, MgO, ZnO, or Co₃O₄ was not observed. The microstructure characterization confirmed that the spinel-type MCr₂O₄ oxides grew from fine spherical particles to large rhomboid particles. Adsorption experiments of spinel-type MCr₂O₄ oxides for adsorption of Congo red dye were fitted well with the pseudo-second-order kinetics. The adsorption capacity of the ZnCr₂O₄ oxide (44.038 mg/g, pH 7, temperature 28 °C, initial dye concentration 30 mg/L) was found to be higher than that of MgCr₂O₄ oxide (43.592 mg/g, pH 7, temperature 28 °C) and CoCr₂O₄ oxide (28.718 mg/g, pH 7, temperature 28 °C). The effects of initial adsorbent concentration, initial dye concentration, pH, and temperature between the ZnCr₂O₄ oxide and Congo red dye at which optimal removal occurs, were performed. The thermodynamic studies confirmed that a high temperature favors the adsorption of Congo red dye onto ZnCr₂O₄ oxide studied. The nanostructured spinel-type M(M = Mg, Co, Zn)Cr₂O₄ oxides that exhibited high adsorption performance for adsorption of Congo red dye can be ascribed to the synergistic effect of electrostatic interaction, pore filling, and ion exchange. The present work suggested that the nanostructured spinel-type M(M = Mg, Co, Zn)Cr₂O₄ oxides have excellent adsorption performance and multiferroic behavior, which shows potential applications for removal of the Congo red dye from wastewater, magnetic memory recording media, magnetic sensor, energy collection and conversion device, and read/write memory.     

Conversion of teak wood waste into microwave-irradiated activated carbon for cationic methylene blue dye removal: Optimization and batch studies

The objective of this study is to find optimum preparation conditions in converting teak wood waste into activated carbon (TWAC) and to evaluate its performance in adsorbing cationic dye of methylene blue (MB). TWAC was produced via physiochemical activation (potassium hydroxide, KOH chemical treatment, and carbon dioxide, CO₂ gasification) and heated through microwave irradiation technique. With the aid of response surface methodology (RSM), optimized TWAC was successfully synthesized at radiation power, radiation time, and impregnation ratio (IR) of 366 W, 5.30 min, and 1.15 g/g, respectively. These preparation conditions produced TWAC with MB adsorption uptakes of 66.69 mg/g and a yield of 38.23%. Characteristics of TWAC in terms of BET surface area, mesopores surface area, total pore volume, and average pore diameter were determined to be 1345.25 m²/g, 878.63 m²/g, 0.6140 cm³/g, and 2.85 nm, respectively. Isotherm studies divulged that the MB-TWAC adsorption system followed the Langmuir model with a maximum monolayer adsorption capacity of 567.52 mg/g. In terms of kinetic studies, this adsorption system fit pseudo-second order model the best whereas Boyd plot confirmed that the adsorption process was controlled by the film diffusion mechanism. Thermodynamic parameters of enthalpy change, ΔH°, entropy change, ΔS°, Gibbs free energy, ΔG° and Arrhenius activation energy, E_a were calculated to be ?4.06 kJ/mol, 0.06 kJ/mol.K, –22.69 kJ/mol and 16.03 kJ/mol, respectively. The activation and microwave heating methods employed succeeded to produce TWAC with excellent adsorption performance in removing MB dye. TWAC was also successfully regenerated for 5 cycles via microwave heating technique.     

Production of activated carbon from sludge of food processing industry under controlled pyrolysis and its application for methylene blue removal

The present work aims to conduct a process optimization for the production of activated carbon from sludge of food processing industry. The significant feature of this sludge based activated carbon that makes it unique and economic is that it can be produced from waste material. The carbonaceous nature of this sludge does not allow its direct disposal to land because of excess organic and nutrient load contents, however, can be converted to a value added product. This process not only eliminates the need for further treatment of sludge but also reduce the cost of its handling, land filling, and transportation as well as the utilization in the same industry in the purification system.In the present work, activated carbon produced from pyrolysis of sludge was chemically activated by various activating agents. Optimization of impregnation ratio, impregnation time, activation temperature, and activation time was studied. The product was characterized through its iodine value and yield percentage. It was observed that the product had maximum iodine value of 624 mg g⁻¹ with ZnCl₂ as an activating agent. The FT-IR analysis depicts the presence of a variety of functional groups attached on the surface of activated carbon which are used in the interaction with the adsorbate during the process of adsorption. The XRD analysis reveals that the produced activated carbon has low content of inorganic constituents compared with the precursor. The product formed was applied for methylene blue adsorption. The adsorption equilibrium of methylene blue dye was examined at room temperature. Adsorption isotherm was drawn by applying Langmuir and Freundlich models fitting the data indict, with an adsorption capacity of 23.6 mg g⁻¹ and 14.2 mg g⁻¹, respectively. The data show that methylene blue adsorption is best suited to Langmuir equation.     

Optimization and mass transfer simulation of remazol brilliant blue R dye adsorption onto meranti wood based activated carbon

Remazol brilliant blue R dye (RBBR) brings toxicity to living organisms once it enters the environment. This study utilized response surface methodology (RSM) and Polymath software for optimization and mass transfer simulation purposes, respectively. RSM revealed that the optimum preparation conditions of meranti wood-based activated carbon (MWAC) were 441 W, 5.76 min, and 1.35 g/g for radiation power, radiation time, and KOH:char impregnation ratio (IR), respectively, which translated into 86.39 mg/g of RBBR uptakes and 31.94 % of MWAC’s yield. The simulation study predicted the mass transfer rate, r_m to be 112.20 to 1007.50 s^?1 and the adsorption rate, k₁ to be 3.96 to 4.34 h^?1. The developed model predicted the adsorption surface area, a_m to be 790.04 m²/g and this value is highly accurate as compared to the actual mesopores surface area of 825.58 m²/g. Mechanism analysis divulged that the interaction that occurred between RBBR molecules and MWAC’s surface were hydrogen bond (methylene and alkyne), dipole–dipole force (alkyl carbonate, terminal alkyne, and methoxy), and ion–dipole force (primary amine). The isotherm and kinetic studies found that the adsorption data obeyed the Freundlich model and pseudo-first-order (PFO) model the best, respectively. The Langmuir maximum adsorption capacity, Q_m was computed to be 327.33 mg/g. Thermodynamic parameters were calculated to be ?4.06 kJ mol^?1, 0.06 kJ mol^?1 K^?1, –22.69 kJ mol^?1, and 16.03 kJ mol^?1 for ΔH°, ΔS°, ΔG°, and E_a, respectively, which signified the adsorption process studied was exothermic, spontaneous and governed by physisorption.     

Construction of physically crosslinked cellulose nanofibrils/alkali lignin/montmorillonoite/polyvinyl alcohol network hydrogel and its application in methylene blue removal

Herein, cellulose nanofibrils (CNF), alkali lignin (AL), and montmorillonite (MMT) were used to produce reinforced polyvinyl alcohol (PVA) hydrogels. The effects of MMT and AL contents on the rheological properties of reinforced hydrogel were studied. Compared with PVA/CNF hydrogel, the storage modulus of 40 wt% MMT-reinforced PVA hydrogel was increased by 41.4%. The rheological properties of MMT-enhanced PVA hydrogel could be adjusted by the variation of MMT loading. Also, as the PVA matrix had a synergistic effect with the embedded MMT and AL, the composite hydrogel demonstrated high efficiency in the removal of methylene blue dye (MB) from wastewater. Adsorption tests conducted at various time intervals (60–360 min) show that the hydrogels containing same content of MMT had higher removal efficiency. The MB adsorption of PVA/2CNF-0Li-40MMT was over 98.0%, whereas its adsorption equilibrium time and maximum adsorption capacity (q_m) were 360 min and 67.2 mg/g, respectively. However, an extremely high content of MMT reduced the MB adsorption rate.

Graphic abstract

     

Localized hydrogels based on cellulose nanofibers and wood pulp for rapid removal of methylene blue

Access to clean water has become increasingly difficult, motivating the need for materials that can efficiently remove pollutants. Hydrogels have been explored for remediation, but they often require long times to reach high levels of adsorption. To overcome this limitation, we developed a rapid, locally formed hydrogel that adsorbs dye during gelation. These hydrogels are derived from cellulose—a renewable, nontoxic, and biodegradable resource. More specifically, we found that sulfated cellulose nanofibers or sulfated wood pulps, when mixed with a water-soluble, cationic cellulose derivative, efficiently remove methylene blue (a cationic dye) within seconds. The maximum adsorption capacity was found to be 340 ± 40 mg methylene blue/g cellulose. As such, these localized hydrogels (and structural analogues) may be useful for remediating other pollutants.     

Porous SiOC composites fabricated from preceramic polymers and wood powders for efficient dye adsorption and removal

Porous SiOC composites for efficient treatment of dye wastewater were prepared using polysiloxane preceramic polymer mixed with wood biomass by pyrolysis under Ar atmosphere. The influences of the pyrolysis temperature on the microstructure, pore feature and adsorption behavior were investigated. The composites contain the α-quartz, cristobalite, nanosized β-SiC and free carbon embedded in a SiOC matrix. The composite obtained at 1300 °C presents a high specific surface area up to 463 m²/g. The adsorption capacity is enhanced by increasing pyrolysis temperature. The adsorption for the removal of methylene blue on the composites follows the pseudo second-order kinetics, and the adsorption data can be described by the Langmuir and Freundlich adsorption isotherms very well. The composite at 1300 °C displays a maximum adsorption capacity up to 173.5 mg/g caused by the enhancement of specific surface area and the existence of sp² carbons, resulting in many favorable adsorption sites and strong electrostatic attraction.     

Insight the mechanism of MgAl/layered double hydroxide supported on rubber seed shell biochar for Remazol Brilliant Violet 5R removal

The ever-increasing concentration of Remazol Brilliant Violet 5R discharged mainly from textile industry had cause serious environmental issues towards human and the surrounding ecosystem. Therefore, solving the issue related to dye contamination is seriously important. In this research study, MgAl/layered double hydroxide supported on rubber seed shell biochar (RSSB) had been prepared for Remazol Brilliant Violet 5R (RBV5R) dye adsorption. BET surface area and pore volume of RSSB were found to be 132.40 m²/g and 0.0732 cm³/g, respectively with presence of LDH metals on the RSSB surfaces. The batch adsorption studies showed that RBV5R uptake capacity was significantly enhanced (125.88 mg/g) compared to pristine RSSB (58.69 mg/g) at initial RBV5R concentration, contact time, adsorption temperature and pH of 300 mg/l, 1440 min, 60 °C and pH 2, respectively. The equilibrium and kinetic adsorption data were best fitted into the Freundlich and pseudo-first order model, respectively. The thermodynamic study confirmed the RBV5R adsorption was endothermic in nature and governed by physisorption process. All these findings signified that the MgAl/LDH-RSSB is a promising adsorbent for treating wastewater containing RBV5R dye.     

Removal of methylene blue by two zeolites prepared from naturally occurring Egyptian kaolin as cost effective technique

The optimum condition as well as adsorption behavior of two zeolite types prepared from Egyptian kaolin (namely, zeolite A and zeolite X) with methylene blue (MB) are demonstrated in this study. This will be a step to remove such dyes from textile as well as dying industries.MB removal was investigated using synthetic solutions at initial concentrations 15 mg/L of MB at constant temperature and pH (25 ± 0.1 °C and 7.5 ± 0.2) respectively. The removal efficiency was determined at different contact times and different zeolite doses.The optimum contact times for the removal of MB were 60 min and 75 min for zeolite X and zeolite A, respectively. 0.6 g was the optimum dose for removal of MB with both zeolite types.The batch method has been employed, using MB concentration in solution ranging from 2 to 25 mg/L. The percentage removal and distribution coefficients (K_d) were determined for the adsorption system as a function of sorbate concentration. The isothermal models investigated in this study show that adsorption ratios of MB on both zeolites match to Langmuir and Freundlich equation adding to that every equation constant has been calculated. According to the equilibrium studies, adsorption of zeolite X in higher concentrations is much better than that of zeolite A. Dublin–Kaganer–Radushkevich (DKR) shows physisorption endothermic adsorption process for both zeolites and also linear correlation of Redlich–Peterson and Tekman isothermal models were proved.These results show that zeolites prepared from naturally abundant Egyptian kaolin hold great potential to remove dying materials such as MB from wastewater. This will encourage using such low cost technique in removal of dyes from industrial wastewater.     

Adsorption of cationic methylene blue dye using microwave-assisted activated carbon derived from acacia wood: Optimization and batch studies

This study assesses the performance of optimized acacia wood-based activated carbon (AWAC) as an adsorbent for methylene blue (MB) dye removal in aqueous solution. AWAC was prepared via a physicochemical activation process that consists of potassium hydroxide (KOH) treatment, followed by carbon dioxide (CO₂) gasification under microwave heating. By using response surface methodology (RSM), the optimum preparation conditions of radiation power, radiation time, and KOH-impregnation ratio (IR) were determined to be 360 W, 4.50 min, and 0.90 g/g respectively, which resulted in 81.20 mg/g of MB dye removal and 27.96% of AWAC’s yield. Radiation power and IR had a major effect on MB dye removal while radiation power and radiation time caused the greatest impact on AWAC’s yield. BET surface area, mesopore surface area, and pore volume of optimized AWAC were found to be 1045.56 m²/g, 689.77 m²/g, and 0.54 cm³/g, respectively. Adsorption of MB onto AWAC followed Langmuir and pseudo-second order for isotherm and kinetic studies respectively, with a Langmuir monolayer adsorption capacity of 338.29 mg/g. Mechanism studies revealed that the adsorption process was controlled by film diffusion mechanism and indicated to be thermodynamically exothermic in nature.     

Highly Efficient Methylene Blue Dye Removal by Nickel Molybdate Nanosorbent

Removing methylene blue (MB) dye from aqueous solutions was examined by the use of nickel molybdate (α-NiMoO₄) as an adsorbent produced by an uncomplicated, rapid, and cost-effective method. Different results were produced by varying different parameters such as the pH, the adsorbent dose, the temperature, the contact time, and the initial dye concentration. Adsorbent dose and pH had a major removal effect on MB. Interestingly, a lower amount of adsorbent dose caused greater MB removal. The amount of removal gained was efficient and reached a 99% level with an initial methylene blue solution concentration of ≤160 ppm at pH 11. The kinetic studies indicated that the pseudo-second-order kinetic model relates very well with that of the obtained experimental results. The thermodynamic studies showed that removing the MB dye was favorable, spontaneous, and endothermic. Impressively, the highest quantity of removal amount of MB dye was 16,863 mg/g, as shown by the Langmuir model. The thermal regeneration tests revealed that the efficiency of removing MB (11,608 mg/g) was retained following three continuous rounds of recycled adsorbents. Adsorption of MB onto α-NiMoO₄ nanoparticles and its regeneration were confirmed by Fourier transform infrared spectroscopy (FTIR) analysis and scanning electron microscopy (SEM) analysis. The results indicated that α-NiMoO₄ nanosorbent is an outstanding and strong candidate that can be used for removing the maximum capacity of MB dye in wastewater.     

Scalable sulfonate-coated cotton fibers as facile recyclable adsorbents for the highly efficient removal of cationic dyes

Adsorbents that exhibit a high adsorption capacity and facile recyclability are considered promising materials for dye wastewater remediation. In this work, a novel sulfonate-decorated cotton fiber was fabricated as a recyclable adsorbent for the highly efficient removal of cationic dyes. Herein, poly(sodium p-styrene sulfonate-co–N-methylol acrylamide) (P(SSNa-co-NMAM)) with SSNa units as adsorption sites and NMAM units as thermal-crosslinking points was synthesized for the modification of cotton fibers. As expected, the as-obtained P(SSNa-co-NMAM)-coated cotton fibers (PCFs) presented outstanding adsorption capacities toward cationic dyes, even in the simulated effluents. The processes of cationic dye absorbing onto the PCFs were well fitted by the Langmuir isotherm model and pseudo-second-order kinetics. The thermodynamic study revealed that the adsorption reaction of the cationic dyes onto PCF was spontaneous, and the efficiency of adsorption was more desirable at higher temperatures. The maximum adsorption capacities of PCF toward methylene blue (MEB), rhodamine B (RhB), and malachite green (MG) were 3976.10, 2879.80, and 3071.55 mg/g, respectively. The dye removal mechanism was ascribed predominantly to electrostatic interactions. Moreover, the adsorption capacity of the PCFs toward cationic dyes was slightly influenced by the pH of the solutions because of the sulfonate moieties, which exhibit stability under acidic and alkaline conditions. Furthermore, the recyclability and reusability of the as-prepared PCFs were satisfactory and good mechanical properties and thermal stability were observed compared to those of pristine cotton fibers. Given the aforementioned results, the as-obtained PCFs are highly promising as ideal adsorbents for the remediation of dye-contaminated wastewater.

Graphical abstract

     

Removal, preconcentration and determination of Mo(VI) from water and wastewater samples using maghemite nanoparticles

Removal and recovery of Mo(VI) from aqueous solutions were investigated using maghemite (γ-Fe₂O₃) nanoparticles. Combination of nanoparticle adsorption and magnetic separation was used to the removal and recovery of Mo(VI) from water and wastewater solutions. The nanoscale maghemite with mean diameter of 50 nm was synthesized by reduction coprecipitation method followed by aeration oxidation. Various factors influencing the adsorption of Mo(VI), e.g. pH, temperature, initial concentration, and coexisting common ions were studied. Adsorption reached equilibrium within <10 min and was independent of initial concentration of Mo(VI). Studies were performed at different pH values to find out the pH at which maximum adsorption occurred. The maximum adsorption occurred at pHs between 4.0 and 6.0. The Langmuir adsorption capacity (q_max) was found to be 33.4 mg Mo(VI)/g of the adsorbent. The results showed that nanoparticle (γ-Fe₂O₃) is suitable for the removal of Mo(VI), as molybdate, from water and wastewater samples. The adsorbed Mo(VI) was then desorbed and determined spectrophotometrically using bromopyrogallol red as a complexation reagent. This allows the determination of Mo(VI) in the range 1.0–86.0 ng mL⁻¹.