Synthesis of citric acid functionalized magnetic graphene oxide coated corn straw for methylene blue adsorption

In-situ synthesis of ZIF-8 on magnetic pineapple leaf biochar as an efficient and reusable adsorbent for methylene blue removal from wastewater

The presence of organic dyes in aquatic systems poses a significant threat to ecosystems and human well-being. Due to recycling challenges, traditional commercial activated carbon is not cost-effective. To address this, an imidazolate acid zeolite framework-8 (ZIF-8)-modified magnetic adsorbent (ZMPLB-800) was synthesized through the in-situ formation of ZIF-8 and subsequent carbonization at 800 °C, using magnetic pineapple leaf biochar (MPLB) as a carrier. The porous structure of ZMPLB-800 facilitates the rapid passage of dye molecules, enhancing adsorption performance. ZMPLB-800 exhibited remarkable adsorption capacity for methylene blue (MB) across a pH range of 3-13, with a maximum adsorption capacity of 455.98 mg g-1. Adsorption kinetics and thermodynamics followed the pseudo-second-order kinetic model and Langmuir isotherm model. Mechanisms of MB adsorption included pore filling, hydrogen bonding, electrostatic interactions, π-π interactions, and complexation through surface functional groups. Additionally, ZMPLB-800 demonstrated excellent regeneration performance, recording a removal efficiency exceeding 87% even after five adsorption/desorption cycles. This study provides a novel strategy for treating dye wastewater with MOF composites, laying the foundation for waste biomass utilization.

Decoration of polylactic acid on graphene oxide for efficient adsorption of methylene blue and tetracycline

Decorating nanomaterials on graphene oxide (GO) can enhance its adsorption capacity and removal efficiency of water pollutants. In this study, for the first time, nano-sized polylactic acid (PLA) has been successfully decorated on the surface of GO through a facile synthesis approach. The adsorptive efficiency of GO-PLA for removing methylene blue (MB) and tetracycline (TC) from an aqueous solution was examined. The characterization confirmed the successful decoration of PLA on GO nanosheets with the nano size of PLA. It was hypothesized that the PLA was decorated on the surface of GO through covalent bonding between oxygen-containing functional groups and lactide molecules. The optimum adsorption parameters determined were at the adsorbent dose of 0.5 g L^-1, pH 4, contact time of 120 min, and temperature of 318 K. The pseudo-second-order kinetic model described the contaminants' adsorption behaviour, and the intraparticle diffusion model revealed that both surface adsorption and intraparticle diffusion controlled the adsorption process. Langmuir isotherm model best described the adsorption behaviour of the pollutants on GO-PLA and demonstrated the maximum monolayer uptake capacities of MB (332.5 mg g^-1) and TC (223.7 mg g^-1). The adsorption results indicated that the uptake capacities of GO-PLA in comparison to GO have increased by approximately 70% and 110% for MB and TC, respectively. These observations reflect the remarkable role of nano-sized PLA that enhanced the adsorption capacity due to its additional functional group and larger surface area.

Effective decontamination of methylene blue from aqueous solutions using novel nano-magnetic biochar from green pea peels

The conversion of agricultural waste into high-value carbon products has been an attractive area in waste management strategy. This study highlighted the synthesis and effectiveness of green pea peels (GPP), green pea biochar (GPBC), and nano-ferromagnetic green pea biochar (NFGPBC) by the ferrous/ferric co-precipitation synthesis method for eliminating cationic dyes molecules from solutions. The morphological, physicochemical, and structural properties of GPP, GPBC, and NFGPBC were approved by Scanning Electron Microscopy (SEM), Transmission Emission Microscopy (TEM), Energy Dispersive X-ray (EDX), Bruneau Emmett Teller (BET), Fourier Transform Infrared spectroscopy (FTIR), and X-ray Diffraction (XRD) techniques. Vibrating Sample Magnetometry (VSM) analysis confirmed the NFGPBC magnetization performance. The capacity of each adsorbent for methylene blue removal was evaluated at various parameters of material dosage (50-250 mg/150 mL), pH (2-12), initial concentration (50-250 mg/L), contact time (0-90 min) and temperature (20-60 °C). The three developed adsorbent materials GPP, GPBC, and NFGPBC, possessed reasonable BET surface areas of 0.6836, 372.54, and 147.88 m2g-1, and the corresponding monolayer adsorption capacities of 163.93, 217.40, and 175.44 mg/g, respectively. The superior performances of GPBC and NFGPBC were due to their increased surface area compared with the parent green pea peels (GPP). The results from adsorption kinetics studies of all prepared materials were pseudo-second-order and Elovich kinetics models. The thermodynamic parameters exhibited MB sorption's favorability, spontaneity, and endothermic nature. The NFGPBC material experienced Vander Waal forces, electrostatic interaction, hydrogen bonding, and hydrophobic interactions as predominant modes of the solid-liquid interaction. The regeneration, recycling, and reusability of the synthesized GPP, GPBC, and NFGPBC performed at five adsorption cycles revealed that NFGPBC demonstrated excellent cyclical performances attaining a minimum 8.9% loss in capacity due to paramagnetic properties. Thus, NFGPBC is a green, efficient, and eco-friendly material recommended for large-scale production and application in wastewater.

Removal of Methylene Blue Dye from Aqueous Solutions by Pullulan Polysaccharide/Polyacrylamide/Activated Carbon Complex Hydrogel Adsorption

In this study, composite hydrogels were prepared using a simple synthetic technique to adsorb methylene blue (MB) from water. The hydrogel comprised potassium persulfate (KPS) as the initiator, N,N'-methylene bisacrylamide as the crosslinking agent, and sodium hydroxide (NaOH) as the activator. It was employed to adsorb MB at different concentrations from water. The morphology and properties of PUL/PAM/GO composites were characterized through thermogravimetric analysis, Fourier transform infrared spectroscopy, and scanning electron microscopy. Moreover, the adsorption properties, adsorption isotherms, adsorption kinetics, adsorption thermodynamics, and swelling properties of the hydrogel for MB were investigated. The optimal ratio of PUL to AC was obtained as 6:1 by fixing the amount of PUL and loading AC of different masses. The maximum adsorption capacity was obtained as 591.4 mg/g. It also exhibited certain mechanical strength. The adsorption of MB conforms to pseudo-first-order kinetics and Langmuir isotherms. In this study, an environment-friendly, cheap, simple, and efficient way was presented for the composite hydrogel in the direction of water treatment.

Elemental mercury (Hg0) removal from coal syngas using magnetic tea-biochar: Experimental and theoretical insights

Mercury is ranked 3^rd as a global pollutant because of its long persistence in the environment. Approximately 65% of its anthropogenic emission (Hg⁰) to the atmosphere is from coal-thermal power plants. Thus, the Hg⁰ emission control from coal-thermal power plants is inevitable. Therefore, multiple sorbent materials were synthesized using a one-step pyrolysis method to capture the Hg⁰ from simulated coal syngas. Results showed, the Hg⁰ removal performance of the sorbents increased by the citric acid/ultrasonic application. T5CUF_0.3 demonstrated the highest Hg⁰ capturing performance with an adsorption capacity of 106.81 µg/g within 60 min at 200 °C under complex simulated syngas mixture (20% CO, 20% H₂, 10 ppmV HCl, 6% H₂O, and 400 ppmV H₂S). The Hg⁰ removal mechanism was proposed, revealing that the chemisorption governs the Hg⁰ removal process. Besides, the active Hg⁰ removal performance is attributed to the high dispersion of valence Fe₃O₄ and lattice oxygen (α) contents over the T5CUF_0.3 surface. In addition, the temperature programmed desorption (TPD) and XPS analysis confirmed that H₂S/HCl gases generate active sites over the sorbent surface, facilitating high Hg⁰ adsorption from syngas. This work represented a facile and practical pathway for utilizing cheap and eco-friendly tea waste to control the Hg⁰ emission.

Recent Developments in the Application of Bio-Waste-Derived Adsorbents for the Removal of Methylene Blue from Wastewater: A Review

Over the last few years, various industries have released wastewater containing high concentrations of dyes straight into the ecological system, which has become a major environmental problem (i.e., soil, groundwater, surface water pollution, etc.). The rapid growth of textile industries has created an alarming situation in which further deterioration to the environment has been caused due to substances being left in treated wastewater, including dyes. The application of activated carbon has recently been demonstrated to be a highly efficient technology in terms of removing methylene blue (MB) from wastewater. Agricultural waste, as well as animal-based and wood products, are excellent sources of bio-waste for MB remediation since they are extremely efficient, have high sorption capacities, and are renewable sources. Despite the fact that commercial activated carbon is a favored adsorbent for dye elimination, its extensive application is restricted because of its comparatively high cost, which has prompted researchers to investigate alternative sources of adsorbents that are non-conventional and more economical. The goal of this review article was to critically evaluate the accessible information on the characteristics of bio-waste-derived adsorbents for MB's removal, as well as related parameters influencing the performance of this process. The review also highlighted the processing methods developed in previous studies. Regeneration processes, economic challenges, and the valorization of post-sorption materials were also discussed. This review is beneficial in terms of understanding recent advances in the status of biowaste-derived adsorbents, highlighting the accelerating need for the development of low-cost adsorbents and functioning as a precursor for large-scale system optimization.

Development of quaternized polyethylenimine-cellulose fibers for fast recovery of Au(CN)2- in alkaline wastewater: Kinetics, isotherm, and thermodynamic study

The purpose of this study was to fabricate quaternized polyethylenimine-cellulose fibers (QPCFs) for the fast recovery of Au(I) from alkaline e-waste leachate. QPCFs were prepared by quaternizing PEI-modified cellulose fibers using a (3-chloro-2-hydroxypropyl)trimethylammonium chloride solution. The maximum Au(I) adsorption capacity of QPCFs was estimated to be 109.87 ± 3.67 mg/g at pH 9.5 using the Langmuir model. The values of k₁ and k₂ calculated by the pseudo-first and pseudo-second-order models were 1.79 ± 0.15 min^-1 and 0.045 ± 0.003 g/mg min, respectively. Adsorption equilibrium was reached within 5 min. Thermodynamic studies revealed that the Au(I) adsorption process by the QPCFs was spontaneous (ΔG° < 0) and exothermic (ΔH° < 0). The characterization and adsorption mechanism of QPCFs were investigated by Fourier transform infrared spectroscopy, X-ray diffraction, and X-ray photoelectron spectrometry. Quaternary amine sites were well developed in the QPCFs. Oxidation or reduction of adsorbed Au(I) was not observed. When QPCFs were applied to the solution obtained by bioleaching of e-waste, the recovery efficiencies of Au and Cu were 61.7 ± 3.1% and 11.1 ± 2.9%, respectively, indicating that QPCFs have Au selectivity. Therefore, QPCFs are suitable for actual wastewater applications because of their high adsorption performance and fast adsorption rate.

Bifunctional two-dimensional copper-aluminum modified filter paper composite for efficient tetracycline removal: Synergy of adsorption and reusability by degradation

Herein, bifunctional two-dimensional copper-aluminum modified filter paper composite (2D-Cu/Al-C) was successfully prepared by simple calcination and showed ultrahigh adsorption performance and degradation potential. The adsorption removal of TC on 2D-Cu/Al-C all exceeded 92.2% under solution conditions of 10-200 mg/L TC, 100 mg/L 2D-Cu/Al-C, pH 8 and 298 K. The pseudo-second-order kinetic and Langmuir models better fitted the kinetic and isotherm data via spontaneous and exothermic process, and the maximum capacity of the 2D-Cu/Al-C was 2391.78 mg/g. Additionally, 2D-Cu/Al-C showed desired specific adsorption for TC (TC: 98.7%, norfloxacin: 5.8%, sulfamethoxazole: 2.1%, and ciprofloxacin: 1.8%) and it could effectively adsorbed TC even in the binary system (various coexisting ions or natural organic matter). After TC adsorbed on adsorbent was mineralized into CO₂ and H₂O by adding peroxydisulfate to generate high electrode potential radical in another limited systems, the 2D-Cu/Al-C still had ∼89.12% on TC removal (initial concentration of 50 mg/L) after five experimental cycles. Zeta potential, FT-IR and XPS results indicated that the multi-adsorption mechanism, including electrostatic interactions, complexation, and H-bonds, played a vital role in the fast and efficient adsorption process. Thus, the way of combining adsorption and regeneration via degradation are green, non-polluting strategy which are expected to be applied for water purification in future environmental remediation.

Experimental Study of the Adsorption of Nitrogen and Phosphorus by Natural Clay Minerals

Nitrogen and phosphorus are commonly recognized as causing eutrophication in aquatic systems, and their transport in subsurface environments has also aroused great public attention. This research presented four natural clay minerals (NCMs) evaluated for their effectiveness of NH4+ and PO43- adsorption from wastewater. All the NCMs were fully characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), BET analysis, and adsorption kinetics and isotherms to better understand the adsorption mechanism-property relationship. The results show that the adsorption efficiency of the four NCMs for phosphate was better than that for ammonia nitrogen. The removal rate of phosphate was higher than 65%, generally in the range of 80%-90%, while the removal rate of ammonia nitrogen was less than 50%. The adsorption kinetic behavior followed the pseudo-second-order kinetic model. The ammonia nitrogen adsorption isotherm was in good agreement with the Freundlich isotherm equilibrium model, and the phosphate adsorption isotherm matched the Langmuir model. Among all the NCMs studied, bentonite (7.13 mg/g) and kaolinite (5.37 mg/g) showed higher adsorption capacities for ammonia nitrogen, while zeolite (0.21 mg/g) and attapulgite (0.17 mg/g) showed higher adsorption capacities for phosphate. This study provides crucial baseline knowledge for the adsorption of nitrogen and phosphate by different kinds of NCMs.

Charge-driven interaction for adsorptive removal of organic dyes using ionic liquid-modified graphene oxide

A facile approach is presented to synthesize the ionic liquid-grafted graphene oxide (GO-ImOH) for fast and efficient adsorptive removal of cationic dyes. A coupling reaction between the hydroxyl terminal of imidazolium ionic liquid and the carboxylic group of GO, yielded the GO-ImOH hybrid material. The higher surface negative charge (-32 mV) and excellent dispersibility make the GO-ImOH an efficient adsorbent for cationic dyes. The GO-ImOH showed excellent removal efficiency for methylene blue (cationic dye), whereas it could adsorb only 22% methyl orange (anionic dye). The GO-ImOH displayed significantly higher adsorptive removal capacity for cationic dye compared to that of GO adsorbent. The chemical and structural features of GO-ImOH and spectroscopic analyses (FTIR and Raman) of pristine and recovered GO-ImOH adsorbent suggested multiple adsorptive interaction pathways (electrostatic, π-cation, π-π interactions, and hydrogen linkages) between the GO-ImOH adsorbent and the dye molecules. The work paves a new direction for the development of ionic liquids-modified 2D nanomaterials for efficient and fast adsorptive removal of organic pollutants, where the adsorptive sites on the surface of 2D nanomaterials can be tuned by selecting the desired functionalities from a diversified library of cations and anions of ionic liquids.

Effective multi-functional biosorbent derived from corn stalk pith for dyes and oils removal

In this study, malic acid-modified corn stalk pith (MA-CSP) was prepared as an environmentally friendly multi-functional bio-sorbent for adsorbing of dyes and oils. The sorption capacity of the MA-CSP for single and binary dyes is 328.46 mg/g - 566.27 mg/g. In addition, the MA-CSP also had good sorption for lubricating oil, soybean oil, diesel oil, and isopropyl alcohol, which were 37.2 g/g, 44.1 g/g, 33.8 g/g, and 29.3 g/g, respectively. Physical and statistical models were used to analyze the adsorption behavior of methylene blue (MB) and crystal violet (CV). And its sorption behavior for dyes was also affected by the co-existing salts in water. The sorption mechanism of the dye was mainly electrostatic attraction and hydrogen bonding action. The sorption of oil was primarily via the role of van der Waals force and hydrophobic interaction. The MA-CSP, as an eco-friendly, economical and efficient multi-functional sorbent, holds promise for effective dyes and oil removal from contaminated water, and its application in other fields is also highly anticipated.

A hydrophobic bio-adsorbent synthesized by nanoparticle-modified graphene oxide coated corn straw pith for dye adsorption and photocatalytic degradation

A novel bio-adsorbent was prepared from corn straw pith (CSP), graphene oxide (GO) and TiO₂ through one-step synthesis for adsorption and photocatalytic reduction of dyes. CSP and GO acted as stent and coat, respectively. TiO₂ nanoparticles attached on the surface of the adsorbent played a role in the degradation of dyes and endowed the adsorbent with hydrophobicity. When the loading of GO and TiO₂ were 5 and 20 wt.% respectively, the adsorbent had quite an ideal structure and satisfactory removal efficiency. There were an electrostatic attraction, hydrophobic and π-π interactions in the process of adsorption. The pseudo-second-order and the Langmuir model described the adsorption behaviour well. The dyes loaded on the adsorbent could be degraded by irradiation with ultraviolet light (UV). After five cycles, the removal efficiency of malachite green, methylene blue and rhodamine b by CSP-5GO-20TiO₂ decreased by 3.77%, 23.89% and 32.01%, respectively. Therefore, the bio-adsorbent has the advantages of economy, environmental protection, and the concept of sustainable development.

State of the art: synthesis and characterization of functionalized graphene nanomaterials

Nanomaterials play nowadays a preponderant role in the field of materials science due to the wide range of applications and synergy with other fields of knowledge. Recently, carbonaceous nanomaterials, most notably bi-dimensional graphene (2D graphene), have been highlighted by their application in several areas: electronics, chemistry, medicine, energy and the environment. The search for new materials has led many researchers to develop new routes of synthesis and the expansion of the current means of production, by the anchoring of other nanomaterials on graphene surface, or by modifications of its hexagon sp2 structure, through the doping of heteroatoms. By adding functional groups to the graphene surface, it is possible to increase its affinity with other materials, such as polymers, magnetic nanoparticles and clays, leading to the formation of new nanocomposites. Several covalent and non-covalent functionalization processes, their advantages and disadvantages with respect to their interactions with other chemical species, are discussed in this review. The characterization of these materials is a sensitive topic, since the insertion of functional groups over the graphene basal plane causes changes in its morphology and the so-called chemistry of surface. In this sense, beyond the classical techniques, such as x-ray Diffraction (XRD), Infrared Spectroscopy (FTIR), Raman Spectroscopy and Transmission Electron Microscopy (TEM), modern characterization techniques of graphene-based nanomaterials are discussed, focusing on those more indicated according to the proposed modifications. A significant attention was driven to environmental applications of functionalized graphenes, specifically in the removal of pollutants from wastewaters.

Eco-friendly synthesis of self-regenerative low-cost biosorbent by the incorporation of CuO: a photocatalyst sensitive to visible light irradiation for azo dye removal

Acid pretreated biomass Lemna minor (BM-H3PO4) was used as support for CuO nanoparticles loading, to investigate the dye biosorption capacity and the photocatalytic performance under artificial visible light. The surface morphology, crystal structure, elemental composition, and the bandgap of modified biomass have been determined using FE-SEM, XRD, EDX, XPS, FTIR, and UV-DR analysis. The results showed that NH2 and P-O functional groups of (BM-H3PO4) can attract the copper ions (Cu2+), which can facilitate the loading of CuO nanoparticles hence, smaller nanoparticles with an average diameter of 21 nm was obtained. It was also found that when the CuO was incorporated in BM-H3PO4 in a proper mass ratio of 0.4, the biosorption efficiency was enhanced to 3 times compared with BM-H3PO4 and reached a maximum of 91%, at a dye concentration of 20 mg/L, solution pH equal to 5, and an ambient temperature of 25 °C. Furthermore, CuO-modified BM-H3PO4 exhibits a better photocatalytic activity than pure CuO in the presence of H2O2 and visible light irradiation, where the dye was completely removed and mineralized after 240 min, evidenced by COD measurement. The photocatalytic regeneration also shows that the biosorption efficiency was maintained at 91% over 3 cycles, indicating the significant self-regenerative capacity of the biosorbent.

Green synthesis of magnetic 3D bio-adsorbent by corn straw core and chitosan for methylene blue removal

In this work, a novel bio-adsorbent with a unique structure was prepared through one-step crosslinking in the emulsion using corn straw core (CSC), CoFe₂O₄ and chitosan (CS) as raw materials for adsorption of methylene blue (MB). The preparation method of the adsorbent was simple and environmentally friendly. In the adsorbent, the agricultural waste of CSC acted as scaffold and was wrapped with CS. CoFe₂O₄ was embedded in CS, giving magnetic property to the adsorbent, which was beneficial to the separation process. XRD, FTIR, SEM and TEM were utilized to characterize the adsorbent and the factors affecting adsorption removal efficiency were explored. The pseudo-second-order model and the Langmuir model described the adsorption behaviour well. The equilibrium adsorption capacity was 122 mg g^-1 for MB at 298 K. The thermodynamic studies suggested that the adsorption was a spontaneous, exothermic and randomness decrease process. MB loaded on the adsorbent could be desorbed by immersing in dilute acid solution, indicating that this kind of biomass adsorbent can be widely used in the field of adsorption.

Valorization of agro-industry residues in the building and environmental sector: A review

Environmental pollution has become a relevant issue as the population rises and resources decrease. Reuse and recycling still have the greatest potential as they turn the waste into a new resource, representing the 'closed-loop' step of a circular economy (CE). Looking for new applications for agro-industry waste represents both an environmental issue, as its incorrect disposal is a cause of pollution, and a chance to exploit zero-cost natural wastes. The present review, with around 200 articles examined, focuses on possible reuses of these residues in (a) building construction, as additives to produce thermal and acoustic insulation panels, and (b) in water treatments, exploited for removal of pollutants. The selected materials (coconut, coffee, corn, cotton and rice) have industry production wastes with suitable applications in both sectors and huge worldwide availability; their reuse may thus represent a new resource, with an impact based on the production rate and the possible replacement of current inorganic materials. Along with possible implementation of the selected materials in the building industry and environmental engineering, a brief description of the production and supply chain are provided.

One step forward: How can functionalization enhance the adsorptive properties of graphene towards metallic ions and dyes?

Functionalized graphene and its derivatives have been subject of many recent studies investigating their use as scavenger of various industrial pollutants. Adsorption is a feasible treatment, which can employ a wide variety of materials as adsorbents. Additionally, graphene has been distinguished for its remarkable properties, such as mechanical resistance, flexibility and electric conductivity. A relevant aspect of functionalized graphene is related to its selectivity, resulting in increased removal rates of specific pollutants. Hence, the functionalization process of graphene nanosheets is the cutting edge of the materials and environmental sciences, promoting the development of innovative and highly capable sorbents. The purpose of this review is to assemble the available information about functionalized graphene nanomaterials used for the removal of water pollutants and to explore its wide potential. In addition, various optimal experimental conditions (solution pH, equilibrium time, adsorbent dosage) are discussed. In each topic, aspects of environmental protection of adsorption process were evaluated, as well as the most recent works, available from high impact journals in the field, have been explored. Additionally, the employment of natural compounds to functionalize, reduce and support graphene, was evaluated as green alternatives to chemicals.

Wheat Straws and Corn Straws as Adsorbents for the Removal of Cr(VI) and Cr(III) from Aqueous Solution: Kinetics, Isotherm, and Mechanism

In this paper, the adsorption properties of wheat straw (WS) and corn straw (CS) for Cr(VI) and Cr(III) in solution were studied. The effects of adsorption time, pH of the solution, temperature, and initial concentration of metal ions on adsorption capacity were investigated. The adsorption mechanism was discussed. The results showed that the adsorption isotherms of WS and CS for Cr(VI) and Cr(III) satisfied the Langmuir equation. By fitting the Langmuir equation, the saturated adsorption capacity of WS for Cr(VI) and Cr(III) can reach 125.6 and 68.9 mg g^-1, and that of CS for Cr(VI) and Cr(III) can reach 87.4 and 62.3 mg g^-1 , respectively. The adsorption kinetics conformed to the pseudo-second-order kinetic equation. The effect of temperature on the adsorption capacity was not significant. Physical diffusion and chemical adsorption coexist in the process of adsorption of metal ions by straws, and chemical adsorption is dominant, and the effect of physical diffusion on the chemical adsorption rate can be neglected. It can be seen from the experimental results that the treatment of chromium-containing wastewater by using cheap and easily available wheat straw and corn straw had a remarkable effect. The adsorbed straw could be completely desorbed and had excellent recyclability, indicating that the straws are ideal adsorbents.

Synthesis and cationic dye biosorption properties of a novel low-cost adsorbent: coconut waste modified with acrylic and polyacrylic acids

Coconut waste (CW), a novel, low cost adsorbent, has been utilized for the removal of methylene blue (MB) dye from an aqueous solution. CW was chemically modified with acrylic (AcA) and polyacrylic acids (PAcA) using different modification methods, such as esterification with AcA, chemically grafting of PAcA, and plasma-enhanced chemical vapor deposition (PECVD) coating with PAcA. CW-based adsorbents were used in the experiments to study MB adsorption probability, and their activities were compared. The adsorption behavior of MB onto the adsorbents was investigated with respect to parameters such as sorbent dosage (0.5-4 g/L), pH (2-10), initial dye concentration (50-250 mg/L), and temperature (22-65 °C). The time taken of AcA modified CW (CW-AcA), PAcA-grafted CW (CW-PAcA_grafted), and PAcA-coated CW (CW-PAcA_coated) for the removal of 94.6%, 97.7%, and 91.0% of MB from 50 mg/L of dye solution is 180 min. Characterization of CW-based adsorbents was achieved using SEM, XRD, BET, XPS, and FT-IR analysis. The adsorption fitted the Langmuir model, and the adsorption kinetics were consistent with a pseudosecond-order kinetics model. The results obtained from the maximum adsorption capacity (q_max) for AcA-, PAcA_coated-, and PAcA_grafted-CWs were 138.88, 136.98, and 98.03 mg/g at adsorbent dose of 0.1 g/50 mL for initial dye concentration of 200 mg/L, 22 ± 1 °C, and pH 10:10:8.

Adsorption of Dye by Waste Black Tea Powder: Parameters, Kinetic, Equilibrium, and Thermodynamic Studies

Waste black tea powder was used as a potential adsorbent to remove methylene blue (MB) from aqueous solution. Several operating factors in adsorption of MB onto waste black tea powder were investigated, including contact time, initial MB concentration, solution pH, adsorption temperature, and dosage of waste black tea powder. Experimental results revealed that the adsorption efficiency increased with contact time and solution pH values and decreased with initial MB concentration and adsorption temperature. The equilibrium time was estimated to be around 60 min. The maximum adsorption capacity and the highest adsorption efficiency were 302.63 mg·g−1 and 100%, respectively. In kinetic study, pseudo-first-order and pseudo-second-order kinetic models, intraparticle diffusion model, and Boyd and Elovich models were employed to analyze the adsorption behavior and the adsorption mechanism. It was found that the pseudo-second-order kinetic model was suitable to describe the adsorption process, and the calculated equilibrium adsorption capacity was well close to the experimental data for different initial MB concentrations. The internal diffusion was not the only rate-controlling step, and the existence of boundary effect was observed in this study. From isotherm analysis, the equilibrium data were well represented by the Langmuir model, rather than Freundlich, Dubinin–Redushckevich, or Temkin models. The nonlinear fitting for various isotherm models implied that the adsorption behavior between MB and waste black tea powder was complication. Thermodynamic parameters including changes in Gibb’s free energy, enthalpy, and entropy suggested that adsorption of MB onto waste black tea powder was a spontaneous and exothermic process. The multiple regeneration/adsorption experiments indicated that the used black tea powder efficiently remained more than 75% after five cycles using NaOH as a regenerative reagent and thus be used for many times. Therefore, as a low-cost and easily available material, waste black tea powder could be applied in wastewater treatment.

A novel Fe3O4/graphene oxide/citrus peel-derived bio-char based nanocomposite with enhanced adsorption affinity and sensitivity of ciprofloxacin and sparfloxacin

To create more active adsorption sites on biochar, the Fe₃O₄/GO/citrus peel-derived magnetic bio-nanocomposite (mGOCP) with hierarchically porous architectures was synthesized by a facile one-pot hydrothermal approach for efficient removal of fluoroquinolone antibiotics ciprofloxacin (CIP) and sparfloxacin (SPA). The characterization analysis of bio-nanocomposites showed that the incorporation of GO could ensure relatively higher surface area (1556 cm² g^-1), more abundant pore structure, and higher thermal stability within mGOCP bio-nanocomposites than Fe₃O₄/citrus peel-derived magnetic bio-nanocomposites (mCP). And the mGOCP-1% attained outstanding adsorption capacity for CIP (283.44 mg g^-1) and SPA (502.37 mg g^-1), respectively. The primary adsorption mechanisms for CIP and SPA included π-π electron donor-acceptor interaction, H-bonding, hydrophobic interaction and electrostatic interaction. Overall, the surface morphology and structural composition of biochars could be regulated with GO to facilitate the adsorption capacity. Moreover, the developed mGOCP could be extended as a potential adsorbent for removal of other emerging organic pollutants in water.

Compressive Alginate Sponge Derived from Seaweed Biomass Resources for Methylene Blue Removal from Wastewater

Low cost fabrication of water treatment polymer materials directly from biomass resources is urgently needed in recent days. Herein, a compressive alginate sponge (AS) is prepared from seaweed biomass resources through a green two-step lyophilization method. This material is much different from conventional oven-, air-, vacuum-dried alginate-based adsorbents, which show limitations of shrinkage, rigidness, tight nonporous structure and restricted ions diffusion, hindering its practical applications, and was used to efficiently remove methylene blue (MB), a main colorful contaminant in dye manufacturing, from wastewater. The batch adsorption studies are carried out to determine the impact of pH, contact time and concentration of dye on the adsorption process. The maximum adsorption capacity can be obtained at 1279 mg g-1, and the shape-moldable AS can be facilely utilized as a fixed-bed absorption column, providing an efficient approach for continuous removal of MB within a short time. It is also important that such a compressive AS can be regenerated by a simple squeezing method while retaining about 70% capacity for more than ten cycles, which is convenient to be reused in practical water treatment. Compressive AS demonstrates its merits of high capability, large efficiency and easy to recycle as well as low cost resources, indicating widespread potentials for application in dye contaminant control regarding environmental protection.

Partly reduced graphene oxide aerogels induced by proanthocyanidins for efficient dye removal

In this study, a novel surface modified and partly reduced graphene oxide (PRGO) induced by mild oligomeric proanthocyanidins (OPC) was prepared for efficient dye removal. The in situ partial reduction, modification and assembly of GO sheets into OPC-PRGO aerogels were readily realized by a hydrothermal process. Systemically characterizations were performed to confirm the partial reduction and modification of GO by OPC. The OPC-PRGO aerogels exhibited a honeycomb-like structure rather than a snowflake-like structure of GO aerogel. Due to its unique structure, the OPC-PRGO aerogels exhibited an excellent adsorption property towards organic dyes, such as methylene blue (MB), neutral red (NR), amino black (AB) and Congo red (CR). The removal efficiencies of OPC-PRGO towards MB, NR, AB and CR were observed to be 97.5, 94.5, 87.2 and 88.2%, respectively. This study opens a new insight for understanding and preparing partly reduced GO instead of completely reduced GO for hydrophilic polymer/graphene composites.

Development of α- and γ-Fe2O3 decorated graphene oxides for glyphosate removal from water

In this study, the proposed adsorbent composed of graphene oxide (GO) functionalized by magnetic nanoparticles of iron oxide (α-γ-Fe2O3) was obtained by a simple ultrasonication process. This new material was used for the removal of glyphosate in water. The nanoparticulated iron oxide used was synthesized by means of a modified sol-gel method, which does not use organic solvents. The adsorbent material (GO-α-γ-Fe2O3) obtained was characterized by magnetic measurements, and it can be proved that it has superparamagnetic properties, allowing fast and efficient magnetic separation. The equilibrium time for the adsorption of glyphosate when using GO-α-γ-Fe2O3 was 2 hours and the maximum removal was 92% at 15°C, with a maximum adsorption capacity of 46.8 mg g-1. Langmuir model and pseudo-second-order kinetic model correlated satisfactorily to the experimental data. The thermodynamic parameters showed that the adsorption of glyphosate on GO-α-γ-Fe2O3 was spontaneous, exothermic and thermodynamically favorable at temperature of 15-45°C. Thus the adsorbent material GO-α-γ-Fe2O3 proposed in this study is considered a good candidate to be used in the removal of glyphosate from aqueous solutions, presenting high adsorption capacity, low cost and magnetic properties that facilitate the separation of the adsorbent material.

Advances in the applications of graphene adsorbents: from water treatment to soil remediation

Graphene, a novel carbon allotrope, is single-layered graphite with honeycomb lattice. Its unique structure endows graphene many outstanding physical/chemical properties and a large surface area, which are beneficial to its applications in many areas. The potential applications of graphene in pollution remediation are adsorption, membrane separation, catalysis, environmental analysis, and so on. The adsorption efficiency of graphene adsorbents largely depends on its surface area, porous structure, oxygen-containing groups and other functional groups, adsorption conditions, and also the properties of adsorbates. With appropriate modifications, graphene materials are mostly efficient adsorbents for organic pollutants (e.g. dyes, pesticides, and oils) and inorganic pollutants (e.g. metal ions, nonmetal ions, and gas). Since our first report of graphene adsorbents in 2010, plenty of studies have been dedicated to developing various graphene adsorbents and to evaluating their performance in treating contaminated water. Recently, there is a growing trend in graphene adsorbents that could be applied in soil remediation, where the situation is much more complicated than in aqueous systems. Herein, we review the design of graphene adsorbents for water treatment and analyze their potential in soil remediation. Several suggestions to accelerate the research on graphene-based soil remediation technology are proposed.

Landfill leachate treatment by sorption in magnetic particles: preliminary study

Leachates are still an open issue in environmental protection. Many of the applied methods for their treatment present low efficiency and thus need to be used collectively. In practice reverse osmosis is mostly used, as it is the most effective option, regardless of its cost. Magnetic methods to treat effluents have been used for water and wastewater treatment by the use of magnetic particles together with magnetic separation for the removal of contaminants. However, large-scale applications are few or even non-existent when we deal with complex contaminated media such as landfill leachates, for which not even research studies at laboratorial scale with real samples have been done yet. In this work, we apply for the first time magnetic sorption for the treatment of leachates, and close the full cycle by studying the regeneration and re-use of the magnetic particles; we also study the influence of the concentration of magnetic particles, the use of several pre-treatment methodologies and the type of particle used in the process, in real landfill samples from the waste treatment plant of Salamanca (Spain), for the removal of COD, NO₃^-, NO₂^-, NH₄⁺, Total-N, PO₄^3-, SO₄^2- and Cl^-. Regeneration of the magnetic particles after being used in the sorption stage is also studied, as well as their efficiency regarding their re-use. It is also determined the optimum number of batches for complete desorption and for regeneration of the particles, the effect of successive regeneration and re-use cycles, the use of two different regeneration methods, the efficiency of the desorption, the effect of the quantity of solvent and the influence of the time of sorption. Due to its innovative character and the complexity of the media, this work represents a first preliminary approach and, although some promising results have been obtained, further studies are required to completely understand and evaluate the proposed treatment process.

Agricultural waste/graphene oxide 3D bio-adsorbent for highly efficient removal of methylene blue from water pollution

The objective of this study was to synthesize a novel, efficient and economical bio-adsorbent with three dimensions (3D) structure using a direct assembly method for removal of methylene blue (MB) from aqueous solution. The raw materials were corn straw core (CSC) and graphene oxide (GO). The variables that affected adsorption capacity were tested. GO loading could facilitate the removal rate. When 5wt% GO was added (CSC-5GO), the removal rate was increased by 21.62% compared to pure CSC (64.58%). Furthermore, the adsorption by CSC-5GO fitted pseudo-second-order kinetic model (R²>0.998) and Temkin model (R²>0.955). The maximum adsorption capacity was 414.03mgg^-1 for MB at pH=12, 298K and MB concentration of 1000mgL^-1. The adsorption thermodynamic test results suggested that the adsorption was a spontaneous, exothermic and randomness decrease process. Furthermore, after five cycles of adsorption-desorption test, the adsorbent removal rate was >90%, which implied that CSC-5GO had an excellent reproducibility.

A novel biosorbent prepared by immobilized Bacillus licheniformis for lead removal from wastewater

Magnetic polyving akohol (PVA) immobilized the endogenous bacterium Bacillus licheniformis with sodium alginate to get a novel biosorbent. The optimum preparation and adsorption conditions were studied. The optimal preparation conditions was the fraction of magnetic PVA was 9%, the fraction of sodium alginate was 0.8%, the fraction of microbial suspensions was 5% and the crosslinking time was 20 h. The best adsorption conditions were listed as follows: pH was 6, the biosorbent dosage was 0.7 g L^-1, the initial concentration of lead ions was 200 mg L^-1 and the optimal adsorption time was 12 h. The results of SEM and FTIR spectroscopy analysis displayed this novel biosorbents had good structure and the functional groups on the surface was abundant. The VSM analysis confirmed the novel biosorbents had good magnetic magnetization and were easily separated from aqueous medium. Under the optimum conditions, the removal rate of lead ions from waste water could reach 98%, the calculated maximum adsorption capacity could be up to 113.84 mg g^-1. The whole adsorption process was well fit by the pseudo-second order kinetic and it was also a Langmuir monolayer adsorption. The desorption experiments showed the biosorbent had good re-usability.

Development of an auto-phase separable and reusable graphene oxide-potato starch based cross-linked bio-composite adsorbent for removal of methylene blue dye

In this work, we report the development of a cross-linked bio-composite consisting of graphene oxide, potato starch, cross-linker glutaraldehyde and its application to adsorption of the industrial dye, methylene blue, from aqueous solution. The inexpensiveness, non-hazardous nature and easy bio-degradability are the major reasons for the selection of starch material as one of the components of the bio-composite. The bio-composite has been characterized by FTIR, SEM, XRD, particle size and zeta potential analysis. The FTIR analysis reveals the nature of the binding sites and surface morphology of the bio-composite can be understood through SEM. The auto-phase separability of the adsorbent i.e., the precipitation of the adsorbent without any mechanical means is another factor which makes this particular material very attractive as an adsorbent. Parameters like adsorbent dosage, pH, temperature, rotation speed and salt concentration have been varied to find out the suitable dye adsorption conditions. Furthermore, the time dependence of adsorption process has been analyzed using pseudo-first and pseudo-second order kinetics. The adsorption isotherms have been constructed to suggest convincing mechanistic pathway for this adsorption process. Finally, desorption studies have been successfully performed in 3 cycles, establishing the reusability of the material, which should allow the adsorbent to be economically promising for practical application in wastewater treatment.

Magnetically Modified Agricultural and Food Waste: Preparation and Application

The annual food and agricultural waste production reaches enormous numbers. Therefore, an increasing need to valorize produced wastes arises. Waste materials originating from the food and agricultural industry can be considered as functional materials with interesting properties and broad application potential. Moreover, using an appropriate magnetic modification, smart materials exhibiting a rapid response to an external magnetic field can be obtained. Such materials can be easily and selectively separated from desired environments. Magnetically responsive waste derivatives of biological origins have already been prepared and used as efficient biosorbents for the isolation and removal of both biologically active compounds and organic and inorganic pollutants and radionuclides, as biocompatible carriers for the immobilization of diverse types of (bio)molecules, cells, nano- and microparticles, or (bio)catalysts. Potential bactericidal, algicidal, or anti-biofilm properties of magnetic waste composites have also been tested. Furthermore, low cost and availability of waste biomaterials in larger amounts predetermine their utilization in large-scale processes.