Green and feasible fabrication of loose nanofiltration membrane with high efficiency for fractionation of dye/NaCl mixture by taking advantage of membrane fouling

Loose nanofiltration membrane emerges as required recently, since it is hard for conventional nanofiltration membrane to fractionate mixture of dyes and salts in textile wastewater treatment. However, the polymeric membranes unavoidably suffer from membrane fouling, which was caused by the adsorption of organic pollutants (like dyes). Normally, the dye fouling layer will shrink membrane pore size, thus resulting in flux decline and rejection increase. It is thought that membrane fouling may be a double-edged sword and can be an advantage if properly utilized. Thereby, loose nanofiltration membranes were constructed here by a green yet effective method to fractionate dyes/salt mixture by taking advantage of membrane fouling without using poisonous ingredients. A commercially available polyacrylonitrile (PAN) ultrafiltration membrane with high permeability was chosen as the substrate, and dyes were used to contaminate PAN substrate and formed a stable barrier layer when adsorption of dyes reached dynamic equilibrium. The resultant PAN-direct red 80 (DR80) composite membranes displayed superior permeability (~128.4 L m⁻² h⁻¹) and high rejection (~99.9%) to DR80 solutions at 0.4 MPa. Moreover, PAN-DR80 membranes allowed fast fractionation of dyes/sodium chloride (NaCl) mixture, which maintained a negligible dye loss and a low NaCl rejection (~12.4%) with high flux of 113.6 L m⁻² h⁻¹ at 0.4 MPa. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47438.     

Electrospun cellulose acetate/P(DMDAAC-AM) nanofibrous membranes for dye adsorption

In recent years, organic nanofibrous membranes have received more attention because of their excellent performance in wastewater treatment. In this study, the soluble poly(dimethyldiallylammonium chloride-acrylamide) (P(DMDAAC-AM)) was first synthesized by aqueous copolymerization. Afterward, cellulose acetate (CA)/P(DMDAAC-AM) composite nanofibrous membranes were electrospun and utilized to remove acid black 172 from simulated wastewater. When the proportion of P(DMDAAC-AM) to CA was 20, 30, and 40 wt %, the equilibrium adsorption capacities were 116, 159, and 192 mg g⁻¹, respectively. The adsorption capacity of CA/P(DMDAAC-AM) composite nanofibrous membrane showed a well linear relationship with the average fiber diameter. When the average fiber diameter was 185 nm, the adsorption capacity of 231 mg g⁻¹ was achieved. The adsorption kinetics of CA/P(DMDAAC-AM) membranes with various fiber diameters was all consistent with the pseudo-second-order model. The rate-limiting step was primarily controlled by chemisorption. The adsorption isothermal data fitted well with the Langmuir isotherm model. The prepared CA/P(DMDAAC-AM) nanofibrous membrane was effective to remove the acid black 172 in the environmental interested pH range of 4.0–10.0. As an effective dye adsorbent, CA/P(DMDAAC-AM) nanofibrous membrane shows wide application prospect with its excellent adsorption performance. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48565.     

Removal of methylene blue and safranin orange pollutants from liquid effluents by soy residue

Methylene blue and safranin orange dyes, which are used in the textile and pharmaceutical industries, can severely damage the environment and human health. This study investigated the use of okara residue as an alternative biosorbent for the removal of methylene blue and safranin orange dyes. Substantial amounts of okara residue are generated daily during the processing of soy milk in the agro-industrial sector. Dye adsorption was not affected by pH. An adsorption study identified the optimal experimental conditions as: 298 K, 0.03 g of adsorbent in 30 mL of dye solution at a concentration of 50 mg L⁻¹, and a contact time of 300 min for methylene blue dye, and 298 K, 0.02 g of adsorbent in 30 mL of dye solution at a concentration of 50 mg L⁻¹, and a contact time of 200 min for safranin orange dye; the maximum adsorption capacities were 93.201 ± 0.01 and 184 592 ± 0.02 mg g⁻¹, respectively. Okara has considerable advantages over other natural materials as an alternative for the treatment of industrial effluents. Because it is easily obtained and does not require any physicochemical treatment, adsorption does not require any specific operation temperature. In addition, okara exhibited a high adsorption capacity compared to other natural materials that require chemical and physical processing for adsorbent preparation.     

Chitosan/polyaniline hybrid for the removal of cationic and anionic dyes from aqueous solutions

Nanostructured chitosan/polyaniline (CH/PANI) hybrid was synthesized via in situ polymerization of aniline in the presence of chitosan. The CH/PANI hybrid was characterized by FTIR spectroscopy, X-ray diffraction, thermogravimetric analysis, and scanning electron microscopy. The CH/PANI hybrid had a nanofibrous structure with an average diameter of 70 nm. This hybrid was employed as an ecofriendly and efficient adsorbent with high adsorption capacity for the removal of Acid Green 25 (AG) and methylene blue (MB) from aqueous solutions. AG and MB were used as anionic and cationic model dyes, respectively. The CH/PANI adsorbent showed high dependence on the pH of the medium with an excellent adsorption performance and regeneration manner. The kinetics and adsorption isotherms were studied. The CH/PANI hybrid follows the pseudo second-order adsorption kinetics and Temkin isotherm model for the adsorption of both AG and MB dyes. This assumes that the enthalpy of dyes molecules decreases with the adsorption on heterogeneous surface with various kinds of adsorption sites and as well as the ability to form multilayers of the dye. Also, intraparticle diffusion was found to play an important role in the adsorption mechanism. The maximum adsorption capacity was found to be 240.4 mg g⁻¹ of AG at pH 4 and 81.3 mg g⁻¹ of MB at pH 11. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47056.     

Fabrication of chitosan/polyvinyl alcohol/amine modified carbon nanotube composite films for rapid chromate removal

Composite adsorbent films with amine and hydroxyl functionalities were synthesized from chitosan (CS), polyvinyl alcohol (PVA), and amine-modified carbon nanotubes (a-MWCNT) by solvent casting method. Weight proportions of CS to PVA and weight percent of a-MWCNT were optimized to achieve highest chromate removal capacity. Structural characteristics of the composites were investigated using scanning electron microscopy, Fourier transform infrared spectroscopy, Raman spectroscopy, and thermal gravimetric analysis. Accordingly, incorporation of a-MWCNT to CS/PVA structure resulted in the generation of nanochannels, which enhanced adsorption capacity. Moreover, the composite comprising 0.4% wt. a-MWCNT provided over 99% of Cr (VI) removal from 50 mg L⁻¹ Cr (VI) solution within five minutes of contact time. Redlich–Peterson and Radke–Prausnitz isotherm models provided the highest conformity to adsorption data. Maximum chromate sorption capacity of CS/PVA/a-MWCNT composite film was determined as 134.2 mg g⁻¹ being 172% higher than that of CS/PVA. Regeneration was best achieved in 1.0 M NaOH and the composite was shown to retain at least 70% of its original capacity after five consecutive adsorption–desorption cycles.     

Removal of acid dyes from aqueous solutions using a new eco-friendly nanocomposite of CoFe2O4 modified with Tragacanth gum

A new composite of cobalt ferrite and Tragacanth gum (TG) was developed and applied to remove methyl orange (MO) and methyl red (MR) from wastewater samples simultaneously. The results showed that the presence of TG improved the capability of cobalt ferrite in removing the pollutants in considerably. The adsorption properties and surface morphology of the sorbent were compared with those of bare cobalt ferrite, TG, and TG grafted copolymer. The properties of the adsorbents were studied using Fourier transform infrared, scanning electron microscope, transmission electron microscope, X-ray diffraction, and vibrating sample magnetometer, and the effects of different factors such as the amount of the adsorbent, sample pH, contact time, and initial concentration were also evaluated and optimized through response surface methodology using central composite design. The optimal conditions for the adsorption of both dyes (100 mg L⁻¹ as the concentration) were pH of 4.0, adsorbent dose of 0.5 mg mL⁻¹, and contact time of 110 min. Under these conditions, the MO and MR adsorption processes were found to follow pseudo-second-order kinetic model. The equilibrium adsorption data followed the Langmuir isotherm and the highest adsorption capacity was determined to be 336 and 387 mg g⁻¹ for MO and MR, respectively. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48605.     

Synthesis of acrylamide/acrylic acid‐based aluminum flocculant for dye reduction and textile wastewater treatment

Aluminum hydroxide‐poly[acrylamide‐co‐(acrylic acid)], AHAMAA, was synthesized with a redox initiator by solution polymerization in which the effects of reactant contents were optimized. The effects of pH, temperature, and initial dye concentration on Congo red reduction were investigated. A mixture of Congo red and direct blue 71, and the composite textile dye wastewater were investigated. Adsorptions of both dyes were more effective in the nonbuffered solution than those in the buffered solution, and Congo red adsorbed more than direct blue 71 at all pHs. The adsorption of Congo red increased with increasing temperature and its initial concentration. Both dyes obeyed the Freundlich adsorption isotherm. The maximum adsorptions in 100 mg dm^?3 solution were 109 ± 0.5 mg g^?1 and 62 ± 6.6 mg g^?1 for Congo red and direct blue 71, respectively. At 150 mg dm^?3 of the mixed Congo red and direct blue 71, the adsorption was 142 ± 2 mg g^?1 by 643 ± 3 mg dm^?3 AHAMAA. The 40 mg g^?1 dyes of the textile effluent wastewater were adsorbed by 500 mg dm^?3 AHAMAA. AHAMAA could decrease turbidity of the composite wastewater containing a mixture of reactive and direct dyes from 405 to 23 NTU. POLYM. ENG. SCI., 50:1535–1546, 2010. © 2010 Society of Plastics Engineers     

Citric acid modified waste cigarette filters for adsorptive removal of methylene blue dye from aqueous solution

Waste cigarette filters (CFs) were recycled and modified with a nontoxic and low-cost citric acid (CA). The modified CFs were employed in the adsorptive removal of methylene blue (MB) dye from aqueous medium. The influence of pH, contact time, initial dye concentration, and adsorbent dose on adsorption of MB dye was evaluated. The adsorption studies were conducted by employing linear and nonlinear Langmuir and Freundlich isotherm models. The adsorption capacity of CF obtained through linear and nonlinear Langmuir model were 88.02 and 94 mg g⁻¹, which improved up to 163.93 and 168.81 mg g⁻¹, respectively, after the introduction of functional groups in CF-CA. The adsorption kinetics data were well fitted by pseudo-second order kinetics with coefficient of regression (R²) closed to unity. The removal efficiency of CF-CA was 97% at equilibrium time of 4 h. Desorption studies indicated that CF-CA could be regenerated by using HCl (0.1 M) and desorption efficiency was up to 82% upon second cycle of reusability experiment. This study proposed a green and economical use of recycled CFs in dyes wastewater treatment, simultaneously reducing the negative environmental impact due to their improper disposal.     

Poly(PEI-catechol-tetraethylenepentamine) was prepared by “one-pot method” for removing Reactive Red 195

Wastewater containing dyes is frequently discharged by industrial processes and needs separation and recycling. To solve this problem, it is important to research and develop environmentally friendly, efficient adsorbent materials for pollutant separation and recovery. In this study, a poly(PEI-catechol-tetraethylenepentamine) (PPCT) adsorbent was synthesized using a simple catecholamine reaction. This adsorbent exhibited high adsorption capacity and excellent removal efficiency for Reactive Red 195 (RR-195) in wastewater. The material was characterized using SEM, FT-IR, TGA, EA, and XPS. Its performance was optimized by varying the type of polyethyleneimine and the amount added during the preparation process. The effects of temperature, pH, contact time, and salt concentration on the adsorption were systematically investigated. Additionally, the experimental data showed consistency with both the Langmuir and pseudo-second-order kinetic models, simultaneously. The maximum adsorption capacity can reach 1754 mg g⁻¹ at 303 K, with a retention rate of 86.6% after two cycles. The removal rate exceeds 98% at a concentration of 400 mg g⁻¹ or lower. Additionally, the protonated amine group in PPCT carries a positive charge under acidic conditions, enabling selective adsorption of the anionic dye RR-195. Consequently, PPCT exhibits an excellent adsorption effect on RR-195 and holds promising applications in pollutant removal.     

Affinity microspheres and their application to lysozyme adsorption: Cibacron Blue F3GA and Cu(II) with poly(HEMA-EGDMA)

Lysozyme adsorption onto Cibacron Blue F3GA attached and Cu(II) incorporated poly(2-hydroxyethyl methacrylate–ethylene glycol dimethacrylate) [poly(HEMA-EGDMA)] microspheres was investigated. The microspheres were prepared by suspension polymerization. Various amounts of Cibacron Blue F3GA were attached covalently onto the microspheres by changing the initial concentration of dye in the reaction medium. The microspheres with a swelling ratio of 65%, and carrying different amounts of dye (between 1.4 and 22.5 µmol/g⁻¹) were used in the lysozyme adsorption studies. Lysozyme adsorption on these microspheres from aqueous solutions containing different amounts of lysozyme at different pH values was investigated in batch reactors. The lysozyme adsorption capacity of the dye–metal chelated microspheres (238.2 mg g⁻¹) was greater than that of the dye-attached microspheres (175.1 mg g⁻¹). The maximum lyzozyme adsorption capacities (q_m) and the dissociation constant (k_d) values were found to be 204.9 mg g⁻¹ and 0.0715 mg ml⁻¹ with dye-attached and 270.7 mg g⁻¹ and 0.0583 mg ml⁻¹ with dye–metal chelated microspheres, respectively. More than 90% of the adsorbed lysozyme were desorbed in 60 min in the desorption medium containing 0.5 M KSCN at pH 8.0 or 25 mM EDTA at pH 4.9. © 1999 Society of Chemical Industry     

Effects of poly (vinyl alcohol) (PVA) content on preparation of novel thiol-functionalized mesoporous PVA/SiO2 composite nanofiber membranes and their application for adsorption of heavy metal ions from aqueous solution

Thiol-functionalized mesoporous poly (vinyl alcohol)/SiO₂ composite nanofiber membranes and pure PVA nanofiber membranes were synthesized by electrospinning. The results of Fourier transform infrared (FTIR) indicated that the PVA/SiO₂ composite nanofibers were functionalized by mercapto groups via the hydrolysis polycondensation. The surface areas of the PVA/SiO₂ composite nanofiber membranes were >290 m²/g. The surface areas, pore diameters and pore volumes of PVA/SiO₂ composite nanofibers decreased as the PVA content increased. The adsorption capacities of the thiol-functionalized mesoporous PVA/SiO₂ composite nanofiber membranes were greater than the pure PVA nanofiber membranes. The largest adsorption capacity was 489.12 mg/g at 303 K. The mesoporous PVA/SiO₂ composite nanofiber membranes exhibited higher Cu²⁺ ion adsorption capacity than other reported nanofiber membranes. Furthermore, the adsorption capacity of the PVA/SiO₂ composite nanofiber membranes was maintained through six recycling processes. Consequently, these membranes can be promising materials for removing, and recovering, heavy metal ions in water.     

Preparation of graphene oxide/carboxymethyl chitosan/polyvinyl alcohol composite nanofiber membranes by electrospinning for heavy metal adsorption

In this paper, a graphene-oxide/carboxymethyl-chitosan/polyvinyl-alcohol (GO/CMC/PVA) composite nanofiber membrane was prepared by electrospinning and cross-linking with glutaraldehyde (GA) to improve the water resistance. The composite nanofiber membrane can be used in the field of heavy metal adsorption. The membrane was characterized by scanning electron microscopy, Fourier transform infrared spectroscopy, and X-ray diffraction. The effects of GO concentration, adsorption time, and initial concentration of heavy-metal ion (Ni²⁺, Cu²⁺, Ag⁺, and Pb²⁺) solution on the adsorption performance of the fiber membranes were investigated. The results showed that the addition of GO can reduce the diameter of nanofibers. GO, CMC, and PVA exhibited good compatibility, and the intermolecular hydrogen bonding improved. The addition of GO also improved the crystalline properties of the composite fiber membrane. In the optimal cross-linking condition, GA was saturated by steam cross-linking for 6 h. The introduction of GO improved the adsorption capacity of the membrane for heavy metals in water. The utmost adsorption capacities for Ni²⁺, Cu²⁺, Ag⁺, and Pb²⁺ were 262.1, 237.9, 319.3, and 413.6 mg/g when using the cross-linked composite fiber membranes, respectively. The results of adsorption kinetics and thermodynamics showed that the adsorption process accorded with the pseudo-second-order kinetic model and Langmuir–Freundlich isotherm model.     

Low-cost and biodegradable cellulose/PVP/activated carbon composite membrane for brackish water treatment

A simple fabrication of a biodegradable membrane for use in water purification systems is presented in this work. Sodium carboxymethyl cellulose and PVP are dissolved in water and crosslinked with citric acid. The presence of glycerol has given immense flexibility and mechanical strength to the membrane. The addition of activated charcoal has enhanced its purification and dye adsorption capabilities at room temperature in dark and light conditions. The polymer semiconductor composites are completely soil degradable within a week and the membrane also exhibits good electrical conductivity when compared to the membrane without charcoal. The addition of glycerol has acted as molecular spacer between polymers composite's monomer backbone that allows good electron mobility of 9.9 cm² V⁻¹ s⁻¹. The dye adsorption efficiency of the material with two commonly used toxic textile dyes is found to be 100% for methyl orange and up to 57% for Rhodamine B within 3 h. The material shows good dye adsorption efficiency under dark and light conditions with acidic, neutral, and alkaline pH. Salt rejection was also found to increase from 25.3 to 64.4% with applied voltage. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48746.     

Synthesis of citric acid modified β-cyclodextrin/activated carbon hybrid composite and their adsorption properties toward methylene blue

In this article, citric acid modified β-cyclodextrin/activated carbon hybrid (CA-β-CD/AC) composites were synthesized by crosslinking reaction, and their adsorption properties for methylene blue were studied. The scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy, and Brunauer–Emmett–Teller (BET) method were used to characterize the structure and the morphology of composite materials. It was investigated that the effect of experiment parameters on the adsorption performance including weight fraction of AC in the composite, the adsorbent dose, the initial concentration of MB, the solution pH value, contact time, and temperature. The maximum adsorption capacity calculated by the Langmuir isotherm is 862.07 mg g⁻¹. Kinetic studies show that the adsorption process follows the pseudo-first-order and pseud-second-order reaction models. Thermodynamic analysis indicated that the adsorption behavior was an exothermic reaction. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 48315.     

Bamboo charcoal modified with Cu2+ and 3-aminopropyl trimethoxy silane for the adsorption of acid fuchsin dye: Optimization by response surface methodology and the adsorption mechanism

The bamboo charcoal modified with Cu²⁺ and 3-aminopropyl trimethoxy silane (BC-Cu/Si-NH₂) was synthesized and characterized by X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, energy dispersive spectroscopy, and surface acid–base potentiometric titration. The adsorption for acid fuchsin (AF) dyes onto BC-Cu/Si-NH₂ was investigated. Moreover, response surface methodology was performed to optimize the process parameters including pH, initial dye concentration, adsorbent dosage, and temperature. The results presented that the adsorption process was mainly influenced by initial AF concentration and adsorbent dosage. Isotherm studies revealed that the adsorption data fitted well with the Sips model and Dubinin–Radushkevich (D–R) model, which indicated the monolayer, homogeneous, and physical nature of the adsorption process. The maximum adsorption capacity calculated from D–R model could approach approximately to 14.91 mg g⁻¹ at 40 °C, and the maximum adsorption capacity of Sips reached to 10.77 mg g⁻¹ at 40 °C. The kinetic experimental data matched well with Spahn and Schlunder model as well as pseudo-second-order model. In addition, intraparticle diffusion was not the only rate-controlling step of adsorption process. Thermodynamic parameters revealed the feasibility, spontaneity, and endothermic nature of adsorption. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47728.     

Assembly of gelatin biopolymer to fibrous sepiolite clay for efficient dye removal from wastewater

This work aimed to fabricate nanocomposites using low-cost and natural materials for fast and efficient dye adsorption from wastewater. To achieve this, fibrous sepiolite clay was incorporated into the gelatin (GE) biopolymer. The obtained nanocomposites were characterized by Fourier transform infrared spectroscopy and scanning electron microscope techniques. The effects of sepiolite/GE ratio, adsorbent dosage, solution pH, contact time, and initial dye concentration on the adsorption capacity of nanocomposites were well studied and optimized through batch adsorption study. Kinetics, isotherms, and thermodynamics analysis were also performed for methylene blue adsorption. The adsorption data were better fitted with the pseudo-second-order and Langmuir isotherm models. The prepared nanocomposites demonstrated a fast and efficient adsorption performance toward the MB dye with the maximum adsorption capacity as high as 684.8 mg g⁻¹ within only an equilibrium time of 30 min, which revealed their promising potential in wastewater treatment. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 48266.     

Radiation synthesis of graphene oxide/composite hydrogels and their ability for potential dye adsorption from wastewater

A high yield of graphene oxide (GO) was chemically synthesized from graphite powder utilizing adjusted Hummer's method. The contents of acidic functional groups in GO were determined using potentiometric titration. Composite hydrogels dependent on graphene oxide/poly(2-acrylamido-2-methylpropanesulfonic acid)/polyvinyl alcohol (GO/PAMPS/PVA) were synthesized utilizing a ⁶⁰Co gamma irradiation source at different doses. The synthesized graphene oxide and composite hydrogels were portrayed via X-ray diffraction, thermogravimetric analysis, and Fourier transform infrared analysis. The morphology of composite hydrogels was characterized by scanning electron microscope. The gel % and swelling % for the prepared hydrogel demonstrated that the swelling % of hydrogel increased with raising AMPS content. Whereas the increment of GO and increasing the irradiation dose lead to a reduction in the swelling %. The influences of pH, GO percentage, initial dye concentration, the adsorbent dosage, contact time, and temperature on the adsorption of basic blue 3 dye were evaluated and the adsorption capacity was 194.6 mg/g at optimum conditions; pH = 6, GO/PAMPS/PVA composite hydrogels with 5 wt% of GO, initial dye concentration = 200 mg/L, adsorbent dose = 0.1 g, solution volume = 50 mL after 360 min at room temperature (25°C). The adsorption of dye onto the GO/PAMPS/PVA composite hydrogels follows Pseudo-second-order adsorption kinetics, fits the Freundlich adsorption isotherm model.     

Preparation of poly(vinyl alcohol)/tetraethyl orthosilicate hybrid membranes modified with TMPTMS by sol-gel method for removal of lead from aqueous solutions

Poly(vinyl alcohol)/tetraethyl orthosilicate (PVA/TEOS) ion exchange hybrid membranes modified with 3-mercaptopropyltrimethoxysilane (TMPTMS) were prepared by the sol-gel method, and their applications for the removal of lead ions from aqueous solutions in a batch sorption process were studied. The functional groups of the hybrid membranes were characterized by FTIR. Batch adsorption studies such as TMPTMS content, pH, adsorbent dose, contact time, initial concentration and temperature were evaluated. The maximum adsorption capacity of lead ions was found to be 61.62mg g^?1, respectively. The kinetic data were analyzed by pseudo-first-order and pseudo-second-order kinetic models. The Freundlich and Langmuir isotherm models were applied to describe the equilibrium data. Thermodynamic parameters indicated that the lead adsorption onto the membrane is an endothermic and spontaneous process. The PVA/TEOS/TMPTMS hybrid membrane is regenerated by 0.5M HNO₃/0.1 M HCl in equal ratio solution and the adsorption capacity did not change remarkably after five sorption-desorption cycles.     

Preparation and adsorption mechanism of polyvinyl alcohol/graphene oxide-sodium alginate nanocomposite hydrogel with high Pb(II) adsorption capacity

A series of polyvinyl alcohol (PVA)/graphene oxide (GO)-sodium alginate (SA) nanocomposite hydrogel beads were prepared through in situ crosslinking for Pb²⁺ removal. It was found that PVA and SA molecules were intercalated into GO layers through hydrogen bonding interactions, leading to the destruction of orderly structure of GO, while GO uniformly distributed in PVA matrix. With increasing PVA solution concentration, the hydrogel beads became more regular, a large number of polygonal pores with thin walls and open pores formed, the average pore size decreased, and the dense network structure formed. Meanwhile, the permeability of the composite hydrogel decreased, leading to the decline of Pb²⁺ adsorption capacity of the composite hydrogel. With increasing GO content, the ballability of the hydrogel beads was weakened, the pore size increased, and relatively loose network structure formed, resulting in an increase in permeability and Pb²⁺ adsorption capacity of the hydrogel, reaching up to 279.43 mg g⁻¹. Moreover, the composite hydrogel presented relatively good reusability for Pb²⁺ removal. The adsorption mechanism was explored and showed that the adsorption system of the composite hydrogel belonged to the second-order kinetic model and fitted Langmuir adsorption isotherm model for Pb²⁺ removal, which might be mono-layer chemical adsorption. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47318.     

Adsorption of selected dyes on Ti3C2Tx MXene and Al-based metal-organic framework

MXene and metal organic framework (MOF) were used as the main adsorbents to remove synthetic dyes from model wastewater. Methylene blue (MB) and acid blue 80 (AB) were used as the model cationic and anionic synthetic dyes, respectively. To investigate the physicochemical properties of the adsorbents used, we carried out several characterizations using microscopy, powder X-ray diffraction, a porosimetry, and a zeta potential analyzer. The surface area of MXene and MOF was 9 and 630 m² g⁻¹, respectively, and their respective isoelectric points were approximately pH 3 and 9. Thus, MXene and MOF exhibited high capacity for MB (~140 mg g⁻¹) and AB (~200 mg g⁻¹) adsorption, respectively due to their electrostatic attractions when the concentrations of the adsorbents and adsorbates were 25 and 10 mg L⁻¹. Furthermore, the MOF was able to capture the MB due mainly to hydrophobic interactions. In terms of the advantages of each adsorbent according to our experimental results, MXene exhibited fast kinetics and high selectivity. Meanwhile, the MOF had a high adsorption capacity for both MB and AB. The adsorption mechanisms of both adsorbents for the removal of MB and AB were clearly explained by the results of our analyses of solution pH, ionic strength, and the presence of divalent cation, anion, or humic acids, as well as other characterizations (i.e., Fourier-transform infrared spectroscopy and X-ray photoelectron spectroscopy). According to our results, MOF and MXene can be used as economical treatments for wastewater containing organic pollutants regardless of charge (e.g., MB and AB), and positively charged one (e.g., MB), respectively.