CO2-spherical activated carbon as a new adsorbent for Methylene Blue removal: Kinetic, equilibrium and thermodynamic studies

Optimized single-bath dyeing of bio-based nylon 56/cotton blends with vat dyes: Mechanistic insights and process enhancements

Nylon 56/cotton (N/C) blended fabrics have excellent durability and can cater to various clothing needs. However, the quality and value of textile garments are significantly influenced by the dyeing process. Due to variations in the structure and characteristics of nylon 56 and cotton fibers in blended fabrics, achieving consistent coloration is challenging, resulting in noticeable color discrepancies. To tackle these issues, this study focused on dyeing nylon 56/cotton blended fabrics in a single bath using vat dyes. The three primary colors of the vat dyes were selected to be suitable for these fabrics. Subsequently, the study explored the impact of different factors on color consistency and optimized the dyeing process conditions using response surface methodology. The findings revealed that fabrics dyed using the optimized process exhibited vibrant colors, uniformity, and excellent colorfastness to soaping and rubbing, surpassing standard requirements. Furthermore, the study delved into the dyeing mechanism of nylon 56/cotton blended fabrics, analyzing the kinetic and thermodynamic properties of dye adsorption on fibers. This analysis aims to provide a theoretical foundation for developing a rational dyeing process and offer guidance for practical production.

Exploitation of expired cellulose biopolymers as hydrochars for capturing emerging contaminants from water

Expired chemicals pose a potential environmental threat to humans and living organisms. Herein, we proposed a green approach whereby expired cellulose biopolymers were converted to hydrochar adsorbents and tested for removing the emerging pharmaceutical contaminants of fluoxetine hydrochloride and methylene blue from water. A thermally stable hydrochar was produced with an average particle size of 8.1 ± 1.94 nm and a mesoporous structure that exhibited a larger surface area than the expired cellulose by 6.1 times. The hydrochar was efficient in removing the two contaminants with efficiencies that reached above 90% under almost neutral pH conditions. Adsorption exhibited fast kinetics and regeneration of the adsorbent was successful. The adsorption mechanism was hypothesized in view of the Fourier Transform Infra-Red (FTIR) spectroscopy and pH effect measurements to be mainly electrostatic. A hydrochar/magnetite nanocomposite was also synthesized, and its adsorption behavior for both contaminants was tested and it revealed an enhanced percent removal relative to the bare hydrochar by 27.2% and 13.1% for FLX and MB, respectively. This work supports the strategies for zero waste management and the circular economy.

Room temperature fabrication of cobalt mullite for the snappy adsorption of cationic and anionic dyes

Cobalt mullite adsorbent for the robust adsorption performance toward Victoria Blue (VB) and Metanil Yellow (MY) is fabricated by the sol-gel method at room temperature using dipropylamine as a structure-directing agent. The synthesized adsorbent is characterized by XRD, FT-IR, and HRTEM. From these analyses, it is found that dipropylamine binds with the alumina and cobalt oxide, which makes it into tetrahedral to octahedral form. This interaction causes the formation of cobalt mullite. It is observed that trigonal alumina and orthorhombic cobalt mullite are interlinked to form a hybrid network. The special feature of adopting this adsorbent for the adsorption of VB and MY is that it has a large amount of Brønsted acid site because of the octahedral coordination of Al and Co. The large availability of acid sites in the framework and hybridization of two different network systems favors robust adsorption. The rate of adsorption (K₂ = 0.00402 g/mg.min for VB and K₂ = 0.004 g/mg.min for MY) and adsorption capacity (Q_e = 102.041 mg/g for VB and Q_e = 19.0406 mg/g for MY) are greater for VB than MY. This may be due to the more steric factor involved in MY than VB. Thermodynamic parameter indicated that the adsorption of VB and MY is spontaneous, endothermic, and increased randomness in the adsorbent-adsorbate interface. The results from the enthalpy value (ΔH° = 65.43 kJ/mol for VB and ΔH° = 44.729 kJ/mol for MY) revealed that the chemisorption is involved in the adsorption process.

Efficient removal of dyes from aqueous solutions using short-length bimodal mesoporous carbon adsorbents

Ordered mesoporous carbons (OMCs) with controlled mesopore lengths and volumes were synthesized and investigated to remove the model dye methylene blue (MB) from aqueous solutions. The pore size, specific surface area, pore volume, and pore length of OMCs (CMK-3, sCMK-3, and sCMK-5) were analyzed and benchmarked against commercial activated carbon (AC). CMK-3 and sCMK-3 had narrow pore size distributions (PSDs) centered at ∼4.4 nm, whereas the PSD of sCMK-5 was bimodal, derived from the same pores as CMK-3 (∼4.4 nm) and the inner diameter of the carbon nanotubes (∼5.8 nm). The pore length decreased from 743 nm for CMK-3 to 173 nm for sCMK-3 and 169 nm for sCMK-5, facilitating the MB accessibility and efficient utilization of internal mesopores. The MB adsorption on the prepared adsorbents was well described by a pseudo-second-order kinetic model (R² > 0.999), and the initial adsorption rate (h) on sCMK-5 was 34.07-fold faster than that on commercial AC. The Langmuir model adequately explained the equilibrium adsorption data, and the increase in the Langmuir maximal adsorption capacity (q_m) of the OMCs was proportional to the specific surface area. The MB adsorption on sCMK-5 was endothermic and spontaneous, and proceeded primarily through physical adsorption as well as chemisorption reacting with oxygen atoms in hydroxyl groups. The prepared adsorbents were also suitable for polishing textile wastewater containing color-causing substances along with the background organic matter. These OMCs are promising for treating wastewater as efficient adsorbents for large molecular pollutants such as dyes.

Preparation of alkali lignin extracted from ligno-cellulosic populus tremula fibers: Application to copper oxide nanoparticles synthesis, characterization, and methylene blue biosorption study

The green synthesis of nanoparticles using biogenic approaches constitutes a challenge for effective applications. The massive aliphatic hydroxyl groups of lignin exhibited excellent reduction properties allowing the production of metallic nanoparticles. In this work, alkali lignin was extracted from virgin populus tremula and used for the preparation of copper oxide nanoparticles. The analysis of the prepared nanoparticles was assessed using Fourier Transform Infra-red (FT-IR), X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Energy Dispersive X-ray spectroscopy (EDX), and Transmission Electron Microscopy (TEM). FT-IR results displayed that different phytochemicals constituents of lignin extract were responsible for the production of CuO nanoparticles. XRD information demonstrated monoclinic CuO nanoparticles with a mean size of 12.4 nm. SEM images showed that some nanoparticles were quite separated from each other and some of them were agglomerated due to the oxidation of metal nanoparticles. TEM photos indicated that the overlap of the nanoparticles resulted in rectangular patterns due to the presence of lignin on the surface of CuO nanoparticles. Finally, the prepared CuO nanoparticles were applied for the removal of methylene blue from water. The results showed that the maximum adsorption capacity reached 85 mg/g at the following conditions: T = 20 °C, pH = 6, and time = 60 min.

Sweet-Potato-Vine-Based High-Performance Porous Carbon for Methylene Blue Adsorption

In this study, sweet-potato-vine-based porous carbon (SPVPC) was prepared using zinc chloride as an activating and pore-forming agent. The optimised SPVPC exhibited abundant porous structures with a high specific surface area of 1397.8 m2 g-1. Moreover, SPVPC exhibited excellent adsorption characteristics for removing methylene blue (MB) from aqueous solutions. The maximum adsorption capacity for MB reached 653.6 mg g-1, and the reusability was satisfactory. The adsorption kinetics and isotherm were in good agreement with the pseudo-second-order kinetics and Langmuir models, respectively. The adsorption mechanism was summarised as the synergistic effects of the hierarchically porous structures in SPVPC and various interactions between SPVPC and MB. Considering its low cost and excellent adsorption performance, the prepared porous carbon is a promising adsorbent candidate for dye wastewater treatment.

Rapid and efficient adsorption of methylene blue dye from aqueous solution by hierarchically porous, activated starbons®: Mechanism and porosity dependence

Hierarchically porous activated Starbons® derived from starch are found to make excellent adsorbents for methylene blue, even in the presence of other dyes and inorganic salts, highlighting their potential to be used in water purification. The optimal material (S950C90) has a methylene blue adsorption capacity (891 mg g^-1) almost nine times higher than that of unactivated S800 and four times higher than that of commercial activated carbon at 298 K. The adsorption of methylene blue onto optimal materials (S950C90 and S800K4) reaches equilibrium within 5 min. Adsorption data for all the adsorbents show a good fit to the Freundlich isotherm which allows the Gibbs free energies of adsorption to be calculated. The adsorption capacities increase as the pH of the methylene blue solution increases, allowing the dye to be desorbed by treatment with acidic ethanol and the Starbon® materials reused. Porosimetry and SEM-EDX imaging indicate that methylene blue adsorbs throughout the surface and completely fills all the micropores in the Starbon® adsorbent. The methylene blue adsorption capacities show excellent correlations with both the BET surface areas and the micropore volumes of the materials.

A review on the treatment of dyes in printing and dyeing wastewater by plant biomass carbon

Printing and dyeing wastewater (PDW) has characteristics of large amount of water, elevated content of residual dyes, poor biodegradability, high alkalinity and large change of water quality, making its treatment difficult. Development of efficient and economic PDW treatment technology has gained considerable interest in the field of environmental protection. Use of plant biomass carbon (PBC) for the adsorption of dyes is a feasible and economical technology. This review summarizes current literature discussing the preparation method and physicochemical characteristics of PBC prepared from different plant species, the effect of PBC on the removal of dyes, influencing factors affecting the removal, and relevant adsorption models. The shortcomings of current research and the direction of future research are also pointed out in the review.

Degradation of methylene blue through Fenton-like reaction catalyzed by MoS2-doped sodium alginate/Fe hydrogel

In this study, a low-cost and high-performance MoS2/sodium alginate (SA)/Fe (MSF) hydrogel catalyst was prepared. It was found that the MSF hydrogel could efficiently catalyze the degradation of methylene blue (MB) through the Fenton reaction without the addition of Fe2+. The reaction was initiated by Fe2+ which was derived from the cyclic redox reaction between MoS2 and Fe3+ and produced large quantities of ·OH to degrade the MB. The effect of MoS2 concentration, FeCl3·6H2O concentration, H2O2 dosage, solution pH, and light on the degradation was systematically studied. The MoS2 concentration of 0.5 mg/ mL, FeCl3·6H2O concentration of 0.25 g/mL, 50 μL H2O2, and the pH of 4.0 were the optimized parameters. Moreover, it was found that the MB degraded faster under the infrared radiation. The MB removal rate reached as high as 98% within 15 min in the presence of a low concentration of H2O2 and the procedure could be repeated 5 times. The MSF hydrogel provided an effective and simple strategy for the sustainable degradation of organic pollutants in wastewater.

A novel activation-hydrochar via hydrothermal carbonization and KOH activation of sewage sludge and coconut shell for biomass wastes: Preparation, characterization and adsorption properties

A two-stage method of hydrothermal carbonization and chemical activation technology was applied to prepare a novel, large surface area and rich-pore structure activation-hydrochar from sludge sewage and coconut shell due to its mild, low-cost, and well-developed merits. The pore-making mechanism of activation-hydrochar was discussed by FT-IR, XPS, SEM, TG, TG-MS, XRD, and BET characterization. These results illustrated that the first stage of hydrothermal carbonization achieved the rich-pore structure hydrochar via dehydration, decarboxylation, deamination, and rearrangement reactions. The subsequent KOH activation was conducive to the pore-forming process. Specifically, the pore structure of activation-hydrochar was ameliorated and abundant active adsorption sites were obtained by the modification. The adsorption properties of activation-hydrochar on Methylene Blue (MB) and Congo Red (CR) were systematically investigated, and the max adsorption capacities of those were obtained with 623.37 mg/g and 228.25 mg/g, respectively. The pseudo-second-order kinetics and Langmuir models were both fit to elucidate the adsorption process for both dyes. Thermodynamics revealed adsorption performance accompanied by the spontaneous and endothermic processes. In general, the research clearly indicated the synthesis route for activation-hydrochar, and its further adsorption performance, capacity, and mechanism on MB and CR. This research demonstrated that activation-hydrochar with the abundant surface area and rich-pore structure made it a candidate for the production of effective adsorption material. It is prospective to achieve the utilization of wastes and its further application in wastewater treatment.

Isolation and Characterization of Magnetic Oil Palm Empty Fruits Bunch Cellulose Nanofiber Composite as a Bio-Sorbent for Cu(II) and Cr(VI) Removal

In the present study, magnetic oil palm empty fruits bunch cellulose nanofiber (M-OPEFB-CNF) composite was isolated by sol-gel method using cellulose nanofiber (CNF) obtained from oil palm empty fruits bunch (OPEFB) and Fe₃O₄ as magnetite. Several analytical methods were utilized to characterize the mechanical, chemical, thermal, and morphological properties of the isolated CNF and M-OPEFB-CNF. Subsequently, the isolated M-OPEFB-CNF composite was utilized for the adsorption of Cr(VI) and Cu(II) from aqueous solution with varying parameters, such as pH, adsorbent doses, treatment time, and temperature. Results showed that the M-OPEFB-CNF as an effective bio-sorbent for the removal of Cu(II) and Cr(VI) from aqueous solution. The adsorption isotherm modeling revealed that the Freundlich equation better describes the adsorption of Cu(II) and Cr(VI) on M-OPEFB-CNF composite. The kinetics studies revealed the pseudo-second-order kinetics model was a better-described kinetics model for the removal of Cu(II) and Cr(VI) using M-OPEFB-CNF composite as bio-sorbent. The findings of the present study showed that the M-OPEFB-CNF composite has the potential to be utilized as a bio-sorbent for heavy metals removal.

A new biochar from cotton stalks for As (V) removal from aqueous solutions: its improvement with H3PO4 and KOH

The present study is the first attempt to evaluate the potential of acid and base activated biochar derived from cotton stalks (CSB) for the removal of As from contaminated water. The CSB was treated with 0.5 M KOH (BCSB) and H₃PO₄ (ACSB) separately to change its surface properties. The CSB, ACSB and BSCB were characterized using BET, FTIR, and SEM analysis to check the effectiveness and insight of the main mechanisms involved in the removal of As. A series of batch experiments was performed using As-contaminated synthetic water and groundwater samples. The effects of initial concentration of As, contact time, dose of the biochars, solution pH, type of the biochar and coexisting ions on the removal of As were investigated. Results revealed that BCSB efficiently removed As (90-99.5%) from contaminated water as compared with ACSB (84-98%) and CSB (81-98%) due to improved surface properties when As concentration was varied from 0.1 to 4.0 mg/L. The experimental data were best fitted with Freundlich adsorption isotherm as compared with Langmuir, Temkin and Dubinin-Radushkevich models. However, kinetic data were well explained with pseudo-second-order kinetic model rather than pseudo-first-order, intra-particle diffusion and Elovich models. The sorption energy indicated that physical adsorption was involved in the removal of As. The comparison of adsorption results with other biochars and their modified forms suggests that activation of CSB with base can be used effectively (4.48 mg/g) as a low-cost adsorbent for maximum removal of As from contaminated aqueous systems.

Kinetics and Isotherm Modeling for the Treatment of Rubber Processing Effluent Using Iron (II) Sulphate Waste as a Coagulant

There is increasing concern to determine an alternative coagulant for treating industrial effluent with minimal environmental impact and operational cost. In this study, iron (II) sulphate heptahydrate (FeSO4·7H2O) waste, an industrial byproduct from a titanium oxide processing industry, was used as a coagulant for the removal of ammonia (NH3), chemical oxygen demand (COD), biochemical oxygen demand (BOD), and suspended solid (SS) from secondary rubber processing effluent (SRPE). The highest percentage removal of BOD, COD, SS, and NH3 achieved was approximately 97%, 99%, 98%, and 95%, respectively, at pH 5.0, coagulant dose of 1 g/L, coagulation time of 60 min, sedimentation time of 60 min, and at an elevated temperature of 70 °C. The best described adsorption isotherm model was found to be the Brunauer–Emmett–Teller (BET) model, indicated that the FeSO4·7H2O adsorption took placed on the surface of iron hydroxide precipitates with multilayer formation and random distribution. The kinetics analysis showed that the adsorption mechanism was well fitted with the pseudo-second-order kinetic model. The findings of the present study show that the FeSO4·7H2O waste has the potential to be used as a coagulant for the treatment of industrial effluents, including the secondary rubber processing effluent.

A novel Fe3+-stabilized magnetic polydopamine composite for enhanced selective adsorption and separation of Methylene blue from complex wastewater

Herein, a novel Fe³⁺-stabilized magnetic polydopamine composite (Fe₃O₄/PDA-Fe³⁺) was facilely constructed, systematically characterized, and subsequently applied for the first time as a versatile adsorbent for treatment of Methylene blue (MB) in complex wastewater. Results showed that as-prepared material had prominent adsorption ability toward MB in its single dye solution over a wide pH range (3-10) with q_max value of 608.8 mg/g at 318 K. More interestingly, MB could be selectively captured by resulting adsorbent from mixed dye solutions (MB-cationic dye and MB-anionic dye) and complex aqueous solution with high ionic strength up to 0.5 mol/L NaCl. It was eventually revealed that the enhanced and selective adsorption of MB by as-resultant adsorbent was due to the synergistic effects between multiple uptake mechanisms. What's more, its adsorption efficiency toward MB in simulated wastewater still maintained higher than 80 % of its original uptake performance after several runs of adsorption-desorption. Additionally, it exhibited more superior uptake performance toward MB than commercial powder activated carbon (PAC) in column adsorption system. Thus, the outstanding sorption ability, unique capture selectivity, as well as excellent stability and recyclability for model wastewater endow it a promising candidate adsorbent for selective adsorption and separation of MB from complex wastewater.

Synthesis and characterization of hydrochar from industrial Capsicum annuum seeds and its application for the adsorptive removal of methylene blue from water

Chili seeds (CS) represent one of the most abundant residues in Mexico due to the high production and consumption. In this work, CS were used as raw material for the production of low-cost adsorbents for the removal of methylene blue from water. The adsorbents were synthesized from a hydrothermal treatment (based on a surface response experiment design) and characterized texturally by assessing changes in their properties. The mass yield (%R), carbon content (%C), and the second order adsorption rate constant (k₂) were derived in relation to a list of input variables (e.g., the reaction temperature, residence time, and water/biomass ratio). Accordingly, those output variables were affected most sensitively by temperature and/or residence time, while changes of the water/biomass ratio were insignificant. Besides, an increase in the reaction temperature favored the degradation of the lignocellulosic material with increases in the carbon fixation. The adsorption capacity of methylene blue (MB) by the hydrochars depended drastically on the oxygen/carbon ratio. As such, the maximum adsorption capacity value of 145 mg g^-1 was attained at the initial MB concentration of ~3000 μM (optimal oxygen/carbon value of 0.43). On the other hand, the maximum partition coefficient (K_D) was estimated as 2.96 μM^-1 mg g^-1 with the initial/equilibrium concentrations of 20.5/6.93 μM. The performance evaluation between different studies, when made in terms of K_D, suggests that the tested hydrochar should be one of the best adsorbents to treat methylene blue, especially at near-real environmental conditions (e.g., below micromolar levels).

Review on Activated Carbons by Chemical Activation with FeCl3

This study reviews the most relevant results on the synthesis, characterization, and applications of activated carbons obtained by novel chemical activation with FeCl3. The text includes a description of the activation mechanism, which compromises three different stages: (1) intense de-polymerization of the carbon precursor (up to 300 °C), (2) devolatilization and formation of the inner porosity (between 300 and 700 °C), and (3) dehydrogenation of the fixed carbon structure (>700 °C). Among the different synthesis conditions, the activation temperature, and, to a lesser extent, the impregnation ratio (i.e., mass ratio of FeCl3 to carbon precursor), are the most relevant parameters controlling the final properties of the resulting activated carbons. The characteristics of the carbons in terms of porosity, surface chemistry, and magnetic properties are analyzed in detail. These carbons showed a well-developed porous texture mainly in the micropore size range, an acidic surface with an abundance of oxygen surface groups, and a superparamagnetic character due to the presence of well-distributed iron species. These properties convert these carbons into promising candidates for different applications. They are widely analyzed as adsorbents in aqueous phase applications due to their porosity, surface acidity, and ease of separation. The presence of stable and well-distributed iron species on the carbons’ surface makes them promising catalysts for different applications. Finally, the presence of iron compounds has been shown to improve the graphitization degree and conductivity of the carbons; these are consequently being analyzed in energy storage applications.

Design of Crosslinked Hydrogels Comprising Poly(Vinylphosphonic Acid) and Bis[2-(Methacryloyloxy)Ethyl] Phosphate as an Efficient Adsorbent for Wastewater Dye Removal

The development of adsorbents with high adsorption capacity and fast separation is of utmost importance for the environmental management of dye-bearing wastewaters. Within this scope, crosslinked hydrogels including poly(vinylphosphonic acid) (PVPA) and bis[2-(methacryloyloxy)ethyl] phosphate (BMEP) were designed with varying mole ratios of BMEP (5-40%). The Fourier transform infrared (FT-IR) spectroscopy, thermogravimetric analysis (TGA), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and Brunauer-Emmett-Teller (BET) results revealed that the fabrication of crosslinked PVPA-BMEP hydrogels enhanced: (i) functionalities of PA groups in the structure of hydrogels, (ii) thermal stabilities up to 250 °C, and (iii) interaction between methylene blue (MB) molecules and hydrogels. The pseudo second-order kinetic model best described the experimental adsorption data. The behaviors of the isotherms were more appropriate for Langmuir than Freundlich isotherm for the experimental data. PVPA-BMEP (40%) hydrogel indicated a fast and an outstanding MB adsorption capacity of 2841 mg g-1, which has not been reported yet for polymer hydrogels, to the best of our knowledge. The thermodynamic studies concluded that MB adsorption process was spontaneous and exothermic in nature. The overall results suggest that the designed and fabricated PVPA-BMEP hydrogels have great potential for the efficient removal of coloring materials from wastewaters.

Enhanced adsorption of Cd (II) from aqueous solution by a shrimp bran modified Typha orientalis biochar

The biochar which was characterized with well-developed facial structure and O-/N-containing functional groups could effectively remove Cd (II) from water. In this paper, Typha orientalis-based biochar (BCS) with well-developed N containing functional groups was modified with shrimp bran which was rich in crude protein for the first time. There are more well-developed O-/N-containing functional groups in the structure of BCS than that of pure Typha orientalis-based biochar without any modification (BC), and this conclusion was depended on their comparisons of Brunauer-Emmett-Teller (BET), X-ray diffraction (XRD), scanning electron microscopy (SEM), elemental analysis (EA), Boehm titration, Fourier transform infrared (FTIR), and other characterization techniques. Moreover, according to the experiment, the phenomenon that the adsorption capacity of Cd(II) on these two adsorbents (BCs) decreased with the increase of solution ionic strength could be carried out. The Cd(II) adsorption studies combined with X-ray photoelectron spectroscopy (XPS) analysis revealed that the adsorption mechanism was mainly attributed to physical microporous filtration and chemical interaction between Cd(II) and the surface functional groups (surface complexation, ion exchange, and electrostatic attraction).

Activated Carbon from Yam Peels Modified with Fe3O4 for Removal of 2,4-Dichlorophenoxyacetic Acid in Aqueous Solution

The removal of organic pollutants from water sources can be enhanced using suitable adsorbents. The aim of this research was to study the adsorption capacity and potential reuse of a magnetic adsorbent prepared from agricultural wastes of yam peels (Dioscorea rotundata) for 2,4-dichlorophenoxyacetic (2,4-D) acid removal. The procedure was performed through carbonization and activation at 400 and 500 °C, respectively. Then, the as-prepared activated carbon (AC) was chemically modified using magnetite (Fe3O4) nanoparticles. The AC and magnetic activated carbon (MAC) were characterized and then used for batch adsorption and regeneration tests at different pH, initial concentrations of 2,4-D, and temperature. AC and MAC were showed to have microporous structures with surface areas of 715 and 325 m2/g, respectively. Superparamagnetic behavior was observed for MAC with a saturation magnetization of 6 emu/g. The results from the batch experiments showed higher adsorption capacity at high initial concentration of 2,4-D, low pH, and room temperature. The thermodynamic parameters indicated that the experiments proceeded as exothermic and spontaneous adsorption. Our findings also showed that MAC can be separated from the water medium through a facile magnetic procedure, and from regeneration experiments, MAC showed better results with 60% of its initial adsorption capacity after five cycles. Hence, MAC was found to be a promising alternative adsorbent of pesticides in water.

Synthesis of illite/iron nanoparticles and their application as an adsorbent of lead ions

Illite/iron nanoparticles (I-nZVI) with different iron contents were synthesized using a liquid-phase reduction method to remove Pb(II) from aqueous solution. The adsorbents were characterized by Lorentz transmission electron microscopy (L-TEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and the BET-N₂ technique. The composite adsorbents and illite removed Pb(II) from aqueous solution to explore the effect of different reaction conditions, including contact time, concentration, pH, and temperature. The results of batch experiments demonstrated that the removal efficiency mainly depends on the amount of nanoscale zerovalent iron. Under different conditions, the order of the removal efficiency was 30% I-nZVI > 20% I-nZVI > 10% I-nZVI > illite. Reactions between Fe(0) and Pb(II) took place on the surface of the absorbents, and the removal of Pb(II) was based on adsorption and reductive reactions. The adsorption of lead ions by I-nZVI and pure illite conformed to the pseudo-second-order reaction kinetic model, and intraparticle diffusion may not play a remarkable role in removing Pb(II). The adsorption of Pb(II) by 30% I-nZVI, 20% I-nZVI, 10% I-nZVI, and illite was more in line with the Langmuir adsorption model. Thermodynamic studies indicated that the Pb(II) removal process is endothermic in nature, which is in agreement with the experimental results. The high removal efficiency helps to achieve the goal of remediation.

Evaluation of activated carbon synthesized by one-stage and two-stage co-pyrolysis from sludge and coconut shell

Waste biomass and sewage sludge were used to obtain an adsorbent material with excellent performance qualities by adopting a KOH activation process via one-stage (AC_one) or two-stage (AC_two) co-pyrolysis. The main purpose of this work was to investigate the effects of both methods in terms of the physicochemical properties and adsorption capacities for methylene blue (MB). Textural analyses revealed that the surface area (S_tot= 683.82 m²/g) and total pore volume (V_tot= 0.72 cm³/g) of AC_two were more than two-fold compared with AC_one (S_tot= 285.33 m²/g; V_tot= 0.35 cm³/g). Thus, two-stage co-pyrolysis produced activated carbon with increased porosity, which was favorable for MB adsorption. Nevertheless, the intensity of the surface functional groups of AC_two was weaker than for AC_one, which could be due to the pore-forming mechanism. Two-stage co-pyrolysis increased the yield and aromaticity of activated carbon, but sufficient activation caused more functional groups to decompose. For the adsorbate MB, the maximum adsorption capacity of AC_two (602.80 mg/g) was more than five-fold greater than that of AC_one (101.88 mg/g), due to its excellent porosity properties. Furthermore, the interactions of MB molecules with activated carbon were via hydrogen bonds and electrostatic attraction. The adsorption process of MB onto activated carbon was accurately described by the pseudo-second-order kinetic model. Adsorption equilibrium evaluated Langmuir isotherms demonstrated that MB formed a monolayer by adsorption onto the activated carbon. Adsorption thermodynamics was used to investigate the influence of temperature on the adsorption process. Thermodynamic parameters indicated that MB adsorption onto activated carbon was spontaneous and endothermic. In conclusion, our results showed that two-stage co-pyrolysis improves the adsorption capabilities of activated carbon, so achieving better economic value from waste materials.

Single-step synthesis of eucalyptus sawdust magnetic activated carbon and its adsorption behavior for methylene blue

Eucalyptus wood-based magnetic activated carbon (MAC) was prepared by single-step carbonization activation magnetization with FeCl₃ and utilized for the adsorption of methylene blue (MB).