Effect of different pyrolysis temperatures on physico-chemical characteristics and lead(ii) removal of biochar derived from chicken manure

Biochar derived from chicken manure, as an effective metal adsorbent, was prepared through a pyrolysis method at different pyrolytic temperatures (200, 400, 600, and 800 °C). The physicochemical characteristics of chicken manure biochar (CMB) and its lead (Pb²⁺) adsorption mechanisms were studied by batch adsorption experiments, DTA/TGA, XRD, SEM-EDS, FTIR and an analysis of the composition of their mineral ash. Results showed that the best-fit for the Pb²⁺ adsorption data was achieved using a Langmuir isotherm and a pseudo-second-order model. The maximum adsorption capacities of Pb²⁺ increased with increasing of pyrolytic temperatures of the CMB, being 180.21, 200.80, 239.59, and 242.57 mg g⁻¹, respectively, for CMB-200, CMB-400, CMB-600 and CMB-200. Although Pb²⁺ adsorption on CMB revealed that adsorption was controlled by multiple mechanisms, (e.g. surface complexation, ion exchange, surface precipitation, electrostatic attraction, physical adsorption, and co-precipitation), the ion exchange and surface precipitation played a dominant role in Pb²⁺ sorption. Using CMB for the removal of Pb from water is proposed as an effective, environmentally protective, novel approach.

Biochar derived from chicken manure, as an effective metal adsorbent, was prepared through a pyrolysis method at different pyrolytic temperatures (200, 400, 600, and 800 °C).     

An Amberlite IRA-400 Cl− ion-exchange resin modified with Prosopis juliflora seeds as an efficient Pb2+ adsorbent: adsorption,kinetics, thermodynamics,and computational modeling studies by density functional theory

A Prosopis juliflora-seed-modified Amberlite IRA-400 Cl⁻ ion-exchange resin (hereafter denoted as SMA resin) is used for the removal of Pb²⁺ from wastewater. SEM, EDX, FT-IR, BET, XRD, and XPS analyses were used to characterize the SMA resin. Parameters such as Pb²⁺ concentration, pH, temperature, and time are optimized. The obtained results show that the SMA resin has high efficiency for the removal of Pb²⁺ (73.45%) at a concentration of 100 mg L⁻¹ and a dosage of 0.01 g at pH 6. Thermodynamic studies indicate that the adsorption was spontaneous with negative ΔH° and ΔS° values at all temperatures; pseudo-second-order kinetics and the Langmuir adsorption isotherm provided the best fit (q_max = 106 mg g⁻¹ and R² = 0.99) from 298 to 338 K. In addition, a diffusion-controlled mechanism at 298 K was observed from intra-particle studies. A desorption and recovery process has been applied successfully to the SMA adsorbent. The obtained results showed desorption of 90.7% at pH 2.5 with 86.3% recovery over six cycles. Furthermore, the DFT results suggest that all the functional groups of the SMA resin possibly bind with Pb²⁺ and, of these, the –C O group shows the highest binding energy towards Pb²⁺. Moreover, the high-efficiency removal of Pb²⁺ from synthetic wastewater using the proposed SMA resin was demonstrated to show the real-life application potential.

We have demonstrated a high Pb²⁺ removal efficiency (73.45%) from wastewater using a Prosopis juliflora-seed-modified Amberlite IRA-400 Cl⁻ ion-exchange resin (SMA resin).     

Super rapid removal of copper,cadmium and lead ions from water by NTA-silica gel

Copper (Cu²⁺), cadmium (Cd²⁺) and lead ions (Pb²⁺) are toxic to human beings and other organisms. In this study, a silica gel material modified with nitrilotriacetic acid (NTA-silica gel) was sensibly designed and prepared via a simple amidation procedure for the removal of Cu²⁺, Cd²⁺ and Pb²⁺ from water. The NTA-silica gels showed rapid removal performances for the three metal ions (Pb²⁺ (<2 min), Cu²⁺ and Cd²⁺ (<20 min)) with relatively high adsorption capacities (63.5, 53.14 and 76.22 mg g⁻¹ for Cu²⁺, Cd²⁺ and Pb²⁺, respectively). At the same concentration of 20 mg L⁻¹, the removal efficiencies of the three metals by the adsorbent ranged from 96% to 99%. The Freundlich and Langmuir models were utilized to fit the adsorption isotherms. The adsorption kinetics for the three metal ions was pseudo-second-order kinetics. The removal performance of the NTA-silica gels increased in a wide pH range (2–9) and maintained in the presence of competitive metal ions (Na⁺, Mg²⁺, Ca²⁺ and Al³⁺) with different concentrations. In addition, the NTA-silica gels were easily regenerated (washed with 1% HNO₃) and reused for 5 cycles with high adsorption capacity. This study indicates that the NTA-silica gel is a reusable adsorbent for the rapid, convenient, and efficient removal of Cu²⁺, Cd²⁺, and Pb²⁺ from contaminated aquatic environments.

A silica gel material modified with nitrilotriacetic acid (NTA-silica gel) was sensibly designed and prepared via a simple method for the super rapid removal of Cu²⁺, Cd²⁺ and Pb²⁺ from water.     

MoS42− intercalated NiFeTi LDH as an efficient and selective adsorbent for elimination of heavy metals

The enormous increase of heavy metal pollution has led to a rise in demand for synthesizing efficient and stable adsorbents for its treatment. Therefore, we have designed a novel adsorbent by introducing (MoS₄)²⁻ moieties within the layers of NiFeTi LDH-NO₃, via an ion exchange mechanism, as a stable and efficient adsorbent to deal with the increasing water pollution due to heavy metals. Characterization techniques such as XRD, FTIR, TGA, SEM, TEM, and Raman spectroscopy were used to confirm the formation of (MoS₄)²⁻ intercalated NiFeTi LDH and structural changes after the adsorption process. The efficiency of the material was tested with six heavy metal ions, among which it was found to be effective for toxic Pb²⁺ and Ag⁺ ions. When selectivity was studied with all six of the metal ions copresent in one solution, the material showed greater selectivity for Pb²⁺ and Ag⁺ ions with the selectivity order of Ni²⁺ < Cu²⁺ < Zn²⁺ < Fe³⁺ < Pb²⁺ < Ag⁺, with great adsorption capacities of 653 mg g⁻¹ for Pb²⁺ and 856 mg g⁻¹ for Ag⁺ metal ions. Further, the kinetics adsorption study for both the metal ions had a great correlation with the pseudo-second-order model and supported the chemisorption process via the formation of M–S bonding. The adsorption process obeyed the Langmuir model. Therefore, the MoS₄-LDH material could be a promising adsorbent for the removal of heavy metals.

Elimination of the heavy metals by using the MoS₄-LDH adsorbent.     

Aqueous carbofuran removal using slow pyrolyzed sugarcane bagasse biochar: equilibrium and fixed-bed studies

Herein, biochar was produced by the slow pyrolysis of sugarcane bagasse at 500 °C in absence of oxygen. The resulting sugarcane bagasse biochar (SB500) was characterized and used for aqueous carbofuran sorptive removal. Batch carbofuran sorption studies were accomplished to ascertain the influence of solution pH, contact time, temperature (25, 35 and 45 °C) and adsorbate/adsorbent concentration. SB500 adsorbed more carbofuran at low pH values and less carbofuran at high pH values. The necessary sorption equilibrium, kinetic and thermodynamic parameters were determined. The equilibrium isotherm data were fitted to the Freundlich, Langmuir and Temkin models. The Langmuir equation best fitted the experimental sorption data. The maximum Langmuir adsorption capacity of 18.9 mg g⁻¹ was obtained at pH 6.0 and 45 °C. The enthalpy change (ΔH°), entropy change (ΔS°) and Gibbs free energy (ΔG°) were evaluated. The fixed-bed carbofuran sorption studies were carried out using the optimum parameters determined via the batch studies. The necessary fixed-bed design parameters were obtained. Carbofuran desorption and SB500 regeneration were successfully achieved. About 96% of the total carbofuran was successfully desorbed from the exhausted biochar using 20 mL ethanol in 10 mL increments. Moreover, a possible carbofuran adsorption mechanism has been proposed. A number of interactions including (1) hydrogen bonding of the protonated and neutral carbofuran to biochar, (2) carbofuran sorption onto biochar via π–π electron donor–acceptor interactions and (3) carbofuran diffusion into the biochar pores were considered to explain the sorption mechanism. The batch and fixed-bed sorption results demonstrate that the sugarcane bagasse biochar (SB500) can be effectively used for the sustainable removal and recovery of carbofuran from water.

Sugarcane bagasse biochar was prepared, characterized and used for aqueous carbofuran removal. Sorption equilibrium and dynamics studies were carried out. An adsorption capacity of 19 mg g⁻¹ was obtained at 45 °C. Carbofuran adsorption mechanism has been proposed.     

Chitin/egg shell membrane@Fe3O4 nanocomposite hydrogel for efficient removal of Pb2+ from aqueous solution

The development of adsorbents by using the byproducts or waste from large-scale industrial and agricultural production is of great significance, and is considered to be an economic and efficient strategy to remove the heavy metals from polluted water. In this work, a novel chitin/EM@Fe₃O₄ nanocomposite hydrogel was obtained from a NaOH/urea aqueous system, where the proteins of egg shell membrane and Fe₃O₄ nanoparticles were chemically bonded to chitin polymer chains with the help of epichlorohydrin. Due to the existence of a large number of –NH₂, –OH, –CONH–, –COOH and hemiacetal groups, the adsorption efficiency for Pb²⁺ into the absorbent was dramatically enhanced. The experimental results revealed that the adsorption behavior strongly depends on various factors, such as initial pH, initial Pb²⁺ concentration, incubation temperature and contact time. The kinetic experiments indicated that the adsorption process for Pb²⁺ in water solution agreed with the pseudo-second-order kinetic equation. The film diffusion or chemical reaction is the rate limiting process in the initial adsorption stage, and the adsorption of Pb²⁺ into the nanocomposite hydrogel can well fit the Langmuir isotherm. Thermodynamic analysis demonstrated that such adsorption behaviors were dominated by an endothermic (ΔH° > 0) and spontaneous (ΔG° < 0) process.

A novel kind of chitin/EM@Fe₃O₄ nanocomposite hydrogel derived from the biowastes of egg shell membrane and chitin was successfully prepared for efficient removal of Pb²⁺ from wastewater solution.     

Preparation,characterization serpentine-loaded hydroxyapatite and its simultaneous removal performance for fluoride,iron and manganese

Aiming at the problem of excessive fluorine, iron, and manganese pollution in groundwater in mining areas, a serpentine-loaded hydroxyapatite (Srp/HAP) composite adsorbent was prepared by wet chemical coprecipitation. The preparation conditions of the Srp/HAP composite adsorbent were explored, Srp/HAP was microscopically characterized, and the adsorption performance and adsorption mechanism of the Srp/HAP composite adsorbent for F⁻, Fe²⁺ and Mn²⁺ were analyzed. The results showed that the optimal preparation conditions for the composite particles were as follows: solid–liquid ratio of Srp to calcium nitrate solution 20%, aging time 20 h, calcination temperature 180 °C, and calcination time 90 min. Compact Srp/HAP composite adsorbent particles were successfully prepared, and both the lamellar crimp structure of the Srp surface and the problem of HAP surface agglomeration were resolved. After loading, the specific surface area and pore volume of the particles significantly increased, and the surface pore structure improved, which is conducive to the simultaneous adsorption and removal of fluorine, iron and manganese. The optimal reaction conditions for Srp/HAP treatment of composite water samples with F⁻, Fe²⁺ and Mn²⁺ mass concentrations of 5 mg L⁻¹, 20 mg L⁻¹ and 5 mg L⁻¹, respectively, are as follows: dosage of Srp/HAP 3 g L⁻¹, pH 7, temperature 35 °C, and reaction time 150 min. Under these conditions, the removal rates of F⁻, Fe²⁺ and Mn²⁺ were 98.6%, 99.9% and 99.8%, respectively. The quasi-second-order kinetic model and Langmuir isothermal adsorption model described the adsorption process of F⁻, Fe²⁺ and Mn²⁺ by the composite particles well. The adsorption process includes both surface physical adsorption and chemical adsorption. Chemical adsorption is mainly characterized by ion exchange and surface complexation. The Srp/HAP composite particles can be used as an excellent adsorbent for the treatment of groundwater containing fluorine, iron and manganese ions in mining areas.

A new adsorbent Srp/HAP for simultaneous removal of fluoride, iron and manganese was prepared, characterized and analyzed.     

Convenient pH-responsive removal of Acid Black 1 by green l-histidine/iron oxide magnetic nanoadsorbent from water: performance and mechanistic studies

This study was aimed at developing green histidine-modified Fe₃O₄ nanoparticles (His-MNPs) for the adsorptive removal of Acid Black 1 (AB1) from aqueous solution. The His-MNPs were characterized by atomic force microscopy, scanning electron microscopy-energy dispersive X-ray spectrometry, infra-red spectra and thermogravimetry. These MNPs were spherical (average diameter 11–28 nm) with polydispersity index of 1.40 and about 13% mass coating of histidine. To optimize AB1 adsorption on His-MNPs and understand its mechanism, the influences of different operational variables (pH, adsorbent amount, temperature, initial AB1 concentration, contact time, ionic strength, etc.) on adsorption were examined with adsorption isotherms, kinetics and thermodynamic studies. The AB1 adsorption from water was fast with equilibrium time ≤ 45 min. The adsorption equilibrium was best fitted to the Langmuir isotherm model (q_max = 166.7 mg g⁻¹ at the adsorbent dose of 0.2 g L⁻¹, temperature 30 °C and pH 4). The linearity order for other isotherms was as follows: Dubinin–Radushkevich (D–R) < Temkin < Freundlich. The kinetics of the AB1 adsorption demonstrated the best compliance with the pseudo-second-order model, predominantly controlled by film diffusion as compared to intraparticle diffusion. Thermodynamic parameters (ΔH° and ΔG°) reflected the exothermic and spontaneous adsorption process. The values of ΔG°, ΔH°, activation energy and D–R free adsorption energy were all consistent with the physisorptive removal of AB1. The spectral (electronic and IR) and pH studies further corroborated the mechanism of AB1 removal by His-MNPs. The His-MNPs showed efficient adsorption, easy regeneration and excellent reusability, assisted by their pH-responsive properties. The prepared adsorbent can provide a safe, effective and economical alternative strategy for removing azo dyes from wastewater.

Effective and eco-friendly separation of Acid Black 1 dye from water by electrostatic adsorption onto reusable Histidine-Fe₃O₄ nanoparticles, credited to their pH-responsiveness.     

Preparation of biochar by mango peel and its adsorption characteristics of Cd(ii) in solution

Biochars were prepared by pyrolyzing mango peel waste at 300, 400, 500, 600 and 700 °C. Various characterizations were carried out to explore the effect of pyrolysis temperature on the biochars. The data indicated that the physical and chemical properties of biochar such as pH, element ratio, specific surface area and functional groups changed with the increase of pyrolysis temperature. The yield and contents of hydrogen, nitrogen and oxygen decreased, while contents of the ash and carbon, pH and specific surface area of the biochars increased. In addition, the molar ratios of H/C, O/C and (O + N)/C decreased. In this study, batch adsorption experiments for Cd(ii) adsorption were performed with initial Cd(ii) concentrations of 10–300 mg L⁻¹, contact times of 0–2880 min, various pH (2–8) and biochar dose (1–20 g L⁻¹). Langmuir isotherm and pseudo-second-order kinetics models were better fits than other models, suggesting the dominant adsorption of mango peel biochars is via monolayer adsorption. Biochar derived at 500 °C was found to have the highest adsorption capacity of 13.28 mg g⁻¹ among all biochars and the adsorption efficiency was still 67.7% of the initial adsorption capacity after desorption for 4 times. Based on adsorption kinetics and isotherm analysis in combination with EDS, FTIR and XRD analysis, it was concluded that cation exchange, complexation with surface functional groups and precipitation with minerals were the dominant mechanisms responsible for Cd adsorption by mango peel biochar. The study suggested that mango peel can be recycled to biochars and can be used as a low-cost adsorbent for Cd(ii) removal from wastewater.

Biochars were prepared by pyrolyzing mango peel waste at 300, 400, 500, 600 and 700 °C.     

Novel magnetically separable anhydride-functionalized Fe3O4@SiO2@PEI-NTDA nanoparticles as effective adsorbents: synthesis,stability and recyclable adsorption performance for heavy metal ions

In this paper, a novel adsorbent, Fe₃O₄@SiO₂@PEI-NTDA, was first prepared by the immobilization of an amine and anhydride onto magnetic Fe₃O₄@SiO₂ nanoparticles with polyethylenimine (PEI) and 1,4,5,8-naphthalenetetracarboxylic-dianhydride (NTDA) for the removal of heavy metal ions from aqueous solutions. The structure of Fe₃O₄@SiO₂@PEI-NTDA was systematically investigated; the results confirmed that amine and anhydride groups were successfully covalently grafted onto the surface of Fe₃O₄@SiO₂, which showed a homogenous core–shell structure with three layers of about 300 nm diameter (Fe₃O₄ core: 200 nm, nSiO₂ layer: 20 nm, and PEI-NTDA layer: 20 nm). The adsorption performance of Fe₃O₄@SiO₂@PEI-NTDA NPs was evaluated for single Pb²⁺ and coexisting Cd²⁺, Ni²⁺, Cu²⁺, and Zn²⁺ ions in an aqueous solution in a batch system. The amine and anhydride groups may have a synergistic effect on Pb²⁺ removal through electrostatic interactions and chelation; Fe₃O₄@SiO₂@PEI-NTDA NPs exhibited preferable removal of Pb²⁺ with maximum adsorption capacity of 285.3 mg g⁻¹ for Pb²⁺ at a solution pH of 6.0, adsorbent dosage of 0.5 g L⁻¹, initial Pb²⁺ concentration of 200 mg L⁻¹ and contact time of 3 h. The adsorption mechanism conformed well to the Langmuir isotherm model, and the adsorption kinetic data were found to fit the pseudo-second order model. Fe₃O₄@SiO₂@PEI-NTDA NPs could be recovered easily from their dispersion by an external magnetic field and demonstrated good recyclability and reusability for at least 6 cycles with a high adsorption capacity above 204.5 mg g⁻¹. The magnetic adsorbents showed high stability with a weight loss below 0.65% in the acid leaching treatment by 2 M HCl solution for 144 h. This study indicates that Fe₃O₄@SiO₂@PEI-NTDA NPs are new promising adsorbents for the effective removal of Pb²⁺ in wastewater treatment.

A magnetically separable adsorbent, anhydride-functionalized Fe₃O₄@SiO₂@PEI-NTDA, was successfully constructed for removal of heavy metal ions from aqueous solution.     

Lead (Pb2+) sorptive removal using chitosan-modified biochar: batch and fixed-bed studies

Chitosan-Modified fast pyrolysis BioChar (CMBC) was used to remove Pb²⁺ from water. CMBC was made by mixing pine wood biochar with a 2% aqueous acetic acid chitosan (85% deacylated chitin) solution followed by treatment with NaOH. The characterizations of both CMBC and Non-Modified BioChar (NMBC) were done using diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), scanning electron microscopy (SEM), surface area measurements (S_BET), elemental analysis, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and ζ-potential measurements. Elemental analysis indicated that chitosan accounts for about 25% weight of the CMBC. The Langmuir maximum adsorption capacity of CMBC at pH 5 was 134 mg g⁻¹versus 48.2 mg g⁻¹ for NMBC at 318 K. CMBC column adsorption studies resulted in a capacity of 5.8 mg g⁻¹ (Pb²⁺ conc. 150 mg L⁻¹; pH 5; column dia 1.0 cm; column length 20 cm; bed height 5.0 cm; flow rate 2.5 mL min⁻¹). CMBC removed more Pb²⁺ than NMBC suggesting that modification with chitosan generates amine groups on the biochar surface which enhance Pb²⁺ adsorption. The modes of Pb²⁺ adsorption on CMBC were studied by comparing DRIFTS and X-ray photoelectron spectroscopy spectra before and after Pb²⁺ adsorption.

Batch and fixed-bed column studies for the removal of lead (Pb²⁺) from aqueous solution by chitosan-modified pinewood biochar.     

Rapid removal of Pb2+ from aqueous solution by phosphate-modified baker's yeast

Phosphate-modified baker''s yeast (PMBY) was prepared, and used as a novel bio-sorbent for the adsorption of Pb²⁺ from aqueous solution. The influencing factors, absorption isotherms, kinetics, and mechanism were investigated. The scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR) characterization and elemental analysis of PMBY showed that phosphate groups were successfully grafted onto the surface of yeast. The kinetic studies suggested that the adsorption process followed a pseudo-second-order chemisorption. The adsorption process of Pb²⁺ using PMBY was spontaneous and endothermic. Furthermore, the adsorption of Pb²⁺ on PMBY can rapidly achieve adsorption equilibrium (in just 3 min), and the maximum adsorption capacity of Pb²⁺ on PMBY was found to be 92 mg g⁻¹ at 30 °C, which was about 3 times that of the pristine baker''s yeast. The suggested mechanism for Pb²⁺ adsorption on PMBY was based upon ion-exchange, electrostatic interaction and chelation between the phosphate groups and Pb²⁺. However, compared with the pristine baker''s yeast, the higher capacity and rapid adsorption of PMBY for Pb²⁺ was mainly due to the chelation and electrostatic interactions between the phosphate groups and Pb²⁺. In addition, the regeneration experiments indicated that the PMBY was easily recovered through desorption in 0.01 M HCl, and that PMBY still exhibited 90.77% of the original adsorption capacity for Pb²⁺ after five regeneration cycles. These results showed the excellent regeneration capability of PMBY for Pb²⁺ adsorption. PMBY has shown significant potential for the removal of heavy metals from aqueous solution due to its rapid adsorption, high-capacity and facile preparation.

Phosphate-modified baker''s yeast (PMBY) was used as a novel bio-sorbent for the adsorption of Pb²⁺ from aqueous solution.     

Selective aptamer conjugation to silver-coated magnetite nanoparticles for magnetic solid-phase extraction of trace amounts of Pb2+ ions

Herein, a novel aptamer-functionalized magnetic adsorbent was developed and combined with magnetic solid-phase extraction (MSPE) for the specific enrichment of Pb²⁺ ions prior to flame atomic absorption spectrometric detection. First, silver-coated magnetite core–shell nanoparticles (Fe₃O₄@Ag MNPs) were synthesized by the chemical reduction of silver ions on the surface of magnetite nanoparticles. After that, the selective DNA aptamer against Pb²⁺ was conjugated on the surface of the synthesized nanoparticles to form aptamer-modified magnetic nanoparticles (Fe₃O₄@Ag-APT). The characterization of the prepared adsorbent was performed through SEM imaging, XRD, FT-IR, EDX, and DRS instruments. The influence of the various experimental parameters on the adsorption and desorption steps in MSPE was investigated via Taguchi experimental design to optimize different parameters. Under the optimized conditions, the Pb²⁺ calibration graph was linear in the range of 33–1000 μg L⁻¹. The relative standard deviation (RSD%) of the method for six replicates containing 100 μg L⁻¹ of Pb²⁺ ions was 0.34%. Furthermore, the limit of detection (LOD) and the limit of quantification (LOQ) were 10 μg L⁻¹ and 33.3 μg L⁻¹, respectively. Finally, the applicability of the proposed method was successfully confirmed by preconcentration and determination of trace amounts of Pb²⁺ ions in tap and seawater samples. We showed a proof of concept for Fe₃O₄@Ag-APT as an efficient bio-adsorbent, offering a promising strategy for the specific binding/removal of toxic heavy metal ions.

Herein, a novel aptamer-functionalized magnetic adsorbent was developed and combined with magnetic solid-phase extraction (MSPE) for the specific enrichment of Pb²⁺ ions prior to flame atomic absorption spectrometric detection.     

Synthesis,structural characterization and Cu(ii) adsorption behavior of manganite (γ-MnOOH) nanorods

New alternatives for the removal of transition metal ions that present an environmental risk are required. The chemical adsorption of these ions on surfaces with chemisorbent properties represents a promising area of research. In this work, manganite (γ-MnOOH) nanorods were synthesized, with a surface area of 20.22 m² g⁻¹, pore size of 32.18 nm and pore volume of 0.1627 cm³ g⁻¹. After chemical and structural characterization of the manganite sample, it was evaluated as an adsorbent of Cu(ii) from aqueous solution. The equilibrium adsorption data were well fitted by the Langmuir isotherm, and the results indicated that the maximum adsorption capacity of Cu(ii) was 11.926 mg g⁻¹. Cu(ii) ion adsorption on the manganite surface is a spontaneous and exothermic process (ΔG°< 0 and ΔH°< 0). The negative value of ΔS° suggests the stability of the adsorption process without structural change at the manganite–aqueous solution interface. A scheme for chemisorption of Cu(ii) ions on the hydroxylated surface of manganite is proposed.

Manganite (γ-MnOOH) nanorods were synthesized and Cu(ii) adsorption on their hydroxylated surface was a spontaneous process (ΔG° < 0).     

High dispersions of nano zero valent iron supported on biochar by one-step carbothermal synthesis and its application in chromate removal

A one-step carbothermal synthesis and characterization of biochar-supported nanoscale zero-valent iron (nZVI/BC) was performed for the removal of hexavalent chromium (Cr(vi)) from aqueous solution. High dispersions of nanoscale zero-valent iron supported on biochar were successfully synthesized by the pyrolysis of an iron-impregnated biomass (corn stover) as the carbon and iron source under nitrogen atmosphere. The effects of the pyrolytic temperature on the Fe mineralogies formed on the biochar are discussed. In general, the effects of the treatment time, initial solution pH, and nZVI/BC dosage on the Cr(vi) removal are presented. The results showed high crystallinity and purity, and nZVI/BC was obtained at a pyrolytic temperature of 800 °C. The batch experimental results determined that the adsorption capacity of Cr(vi) decreases with the increase in the initial pH value from 4.0 to 10.0. The Cr(vi) adsorption kinetics data effectively followed a pseudo-second-order kinetics with a calculated rate constant of 0.0.3396 g mg⁻¹ min⁻¹. The calculated thermodynamic parameters, such as ΔG°, ΔH°, and ΔS°, were evaluated, and the results indicated that the Cr(vi) reduction on nZVI/BC was a spontaneous and endothermic process. The adsorption mechanism of Cr(vi) was investigated by XRD and XPS analyses and the results demonstrated that Cr(vi) was reduced to Cr(iii) and the oxidation of nZVI occurred during the reaction process. These results prove that nZVI/BC synthesized by a one-step carbothermal method can be considered as a potential candidate for the removal of Cr(vi) from aqueous solutions.

A one-step carbothermal synthesis and characterization of biochar-supported nanoscale zero-valent iron (nZVI/BC) was performed for the removal of hexavalent chromium (Cr(vi)) from aqueous solution.     

Removal of methylene blue dye using nano zerovalent iron,nanoclay and iron impregnated nanoclay – a comparative study

There has been an increasing challenge from the emission of methylene blue (MB) dye-containing wastewater and its management methods in industry. The sorption process is one conventionally used method. In this study, nanoclay, nano zero valent iron (nZVI), and iron impregnated nanoclay were prepared and studied for the removal of MB dye in batch mode. The effects of operating parameters like pH, dye concentration, sorbent dosage, and contact time were investigated and optimized. The nZVI, nanoclay, and iron impregnated nanoclay sorbents showed zeta potentials of −32.1, −53.4, and −40.7 mV, respectively. All the nano adsorbents were crystalline. The nanoclay was characterized by an average surface area, pore volume and pore diameter of 43.49 m² g⁻¹, 0.104 cm³ g⁻¹ and 2.806 nm, respectively. nZVI showed a surface area of 47.125 m² g⁻¹, pore volume of 0.119 cm³ g⁻¹, and pore diameter of 3.291 nm. And iron impregnated nanoclay showed a surface area of 73.110 m² g⁻¹ with a pore volume of 15 cm³ g⁻¹ and a pore diameter size of 3.83 nm. A Langmuir EXT nitrogen gas adsorption isotherm (R² ∼ 0.99) was the best fit. The thermodynamics parameters, such as ΔG° (−12.64 to −0.63 kJ mol⁻¹), ΔH° (+0.1 to +62.15 kJ mol⁻¹) and ΔS° (+0.10 to +0.22 kJ mol⁻¹), confirmed that a spontaneous and endothermic adsorption process took place at a high rate of disorder. Iron impregnated nanoclay showed higher negative Gibbs free energy (−12.64 kJ mol⁻¹), higher enthalpy change (+62.5 kJ mol⁻¹) and entropy (+0.22 kJ mol⁻¹) and gave a better MB removal performance. In addition, the lower negative heat of enthalpy for all adsorptions proved the dominance of physisorption. The methylene blue adsorption isotherm on nZVI and nanoclay showed the best fit with the Freundlich isotherm model with correlation coefficients (R²) ∼0.98 and 0.99, respectively. Whereas the Langmuir adsorption isotherm was the best fit for iron impregnated nanoclay (R² ∼ 0.98). The adsorption activities of nZVI, nanoclay and iron impregnated nanoclay were fitted to a pseudo-second-order kinetic model with correlation coefficients (R²) of 0.999, 0.997 and 0.983, respectively. The optimal pH 7.0 (RE: 99.1 ± 0.73%), initial MB concentration 40 ppm (RE: 99.9 ± 0.03%), contact time 120 min (RE: 99.9 ± 0.9%), and adsorbent dose 80 (99.9 ± 0.03%) were obtained for iron impregnated nanoclay. The optimal operational parameters of nanoclay and nZVI, respectively, were pH 11.0 and 13.0, initial MB concentration 20 and 20 ppm, adsorbent dose 100 and 140 mg, and contact time 120 and 140 min. In general, iron impregnated nanoclay has shown promising cationic dye adsorbance for industrial applications; but a recyclability test is suggested before scale-up.

There has been an increasing challenge from the emission of methylene blue (MB) dye-containing wastewater and its management methods in industry.     

Facile preparation of amidoxime-functionalized Fe3O4@SiO2-g-PAMAM-AO magnetic composites for enhanced adsorption of Pb(ii) and Ni(ii) from aqueous solution

In this paper, using amidoxime as a functional monomer, different generations of polyamidoxime dendrimer magnetic microspheres (Fe₃O₄@SiO₂-g-PAMAM-AO) were fabricated to adsorb Pb²⁺ and Ni²⁺ in aqueous solution. The magnetic adsorbents were characterized by FTIR, XRD, SEM, XPS, TEM, EDS, TGA and BET. The effects of different factors (such as solution pH, adsorption time, adsorption temperature, adsorbent dosage etc.) on adsorption were evaluated. Fe₃O₄@SiO₂-g-PAMAM-AO has a maximum Pb(ii) adsorption of 157.25 mg g⁻¹ (100 mg L⁻¹) at pH 5.5. Furthermore, Fe₃O₄@SiO₂-g-PAMAM-AO showed an excellent adsorption performance for the removal of Ni(ii) with a maximum adsorption capacity of 191.78 mg g⁻¹ (100 mg L⁻¹) at pH 8.0. The sorption isotherm data fitted the Freundlich isotherm model well. Adsorption kinetics analysis showed that it was best described by the pseudo-second-order rate model. Desorption experiment results showed that the adsorbent can be reused in the adsorption–desorption cycles.

In this paper, using amidoxime as a functional monomer, different generations of polyamidoxime dendrimer magnetic microspheres (Fe₃O₄@SiO₂-g-PAMAM-AO) were fabricated to adsorb Pb²⁺ and Ni²⁺ in aqueous solution.     

Chitosan/MCM-48 nanocomposite as a potential adsorbent for removing phenol from aqueous solution

A new hybrid mesoporous nanocomposite (CMCM-48) based on chitosan and silica MCM-48 was considered as a potential adsorbent for removing phenol from aqueous solutions (toxic liquid waste) in a batch process. The new composite adsorbent was characterized by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), and nitrogen adsorption–desorption isotherms. The adsorption isotherm studies were analyzed using linear and nonlinear Langmuir, Freundlich and Dubinin–Radushkevich models for the optimum conditions when the initial phenol concentration, pH, adsorption temperature and time were 10–500 mg L⁻¹, 3–10, 25.5 °C and 300 min, respectively. It was revealed that the experimental results agree well with the Dubinin–Radushkevich model, i.e. the correlation coefficient R² was 0.983085. The adsorption kinetics was modeled with linear and nonlinear pseudo-first-order, pseudo-second-order and intra particle diffusion kinetic models. The pseudo-second-order model was the best for describing the adsorption process with a correlation coefficient R² = 0.99925. The stability of the equilibrium data was studied for a phenol sorbent with a maximum adsorption capacity of 149.25 mg g⁻¹. The results verified that the synthesized CMCM-48 was an efficient adsorbent for removing phenol from aqueous solutions.

A new hybrid mesoporous nanocomposite (CMCM-48) based on chitosan and silica MCM-48 was considered as a potential adsorbent for removing phenol from aqueous solutions (toxic liquid waste) in a batch process.     

Biosorption of anionic and cationic dyes via raw and chitosan oligosaccharide-modified Huai Flos Chrysanthemum at different temperatures

Raw Huai Flos Chrysanthemum (HFC) and modified HFC (HFC@CO) were used for the first time as a biosorbent material to remove cationic dyes Malachite green (MG) and Crystal violet (CV), and anionic dyes Sunset yellow (SY), Lemon yellow (LY), and Carmine (CM), at different temperatures (5–50 °C). The highest removal rates (R) for dye adsorption were observed at low temperature (5 °C) and room temperature (20 °C). At high (500 mg L⁻¹) dye concentration, adsorption was completed within one minute, but the time required to reach adsorption equilibrium was longer than at the low (20 mg L⁻¹) concentration. The experimental data fitted very well to the Langmuir model and the values of the maximum adsorption capacity for SY, LY, CM, CV, and MG, were 481.41, 507.23, 141.78 mg g⁻¹, 526.32, and 769.23 mg L⁻¹, respectively. The adsorption data fit well to a pseudo-second-order kinetic model.

Raw Huai Flos Chrysanthemum and modified HFC were used for the first time as a biosorbent to remove cationic dyes Malachite green and Crystal violet, and anionic dyes Sunset yellow, Lemon yellow, and Carmine, at different temperatures (5–50 °C).     

Adsorption and regeneration of leaf-based biochar for p-nitrophenol adsorption from aqueous solution

As an environmentally friendly and low-cost adsorbent, biochar has great potential in wastewater treatment. This study investigated biochar derived from Platanus orientalis L. leaves (PLB) activated by KOH in terms of its capacity and reusability to adsorb p-nitrophenol (PNP). PLB had a large specific surface area and total pore volume, and exhibits good PNP removal with a maximal adsorption capacity of 622.73 mg g⁻¹ at 298 K. Batch experiments showed that PLB had a high PNP adsorption capacity under acidic conditions. Experimental results were well described by the pseudo-second-order kinetic model and the Langmuir adsorption isotherm model. The thermodynamic study showed that PNP adsorption was a spontaneously exothermic process, and increasing temperature was not conducive to adsorption. In addition, PNP adsorption was mainly attributed to hydrophobic interaction. The regeneration experiment showed that PLB had good reusability. After the fifth regeneration, the adsorption capacity of PLB still reached 557.05 mg g⁻¹. The deactivation of oxygen-containing functional groups and pore blockage were the causes for the decrease in adsorption capacity of the recycled PLB. Moreover, the biochar showed good adsorption efficiency and reusability, thereby suggesting its potential to serve as an efficient PNP adsorbent for wastewater treatment.

As an environmentally friendly and low-cost adsorbent, biochar has great potential in wastewater treatment.