Highly selective removal of cationic dyes from water by acid-base regulated anionic functionalized polyacrylonitrile fiber: Fast adsorption, low detection limit, reusability

Rapid, Massive, and Green Synthesis of Polyoxometalate-Based Metal-Organic Frameworks to Fabricate POMOF/PAN Nanofiber Membranes for Selective Filtration of Cationic Dyes

Developing high-efficiency membrane materials for the rapid removal of organic dyes is crucial but remains a challenge. Polyoxometalates (POMs) clusters with anionic structures are promising candidates for the removal of cationic dyes via electrostatic interactions. However, their shortcomings, such as their solubility and inability to be mass-produced, hinder their application in water pollution treatment. Here, we propose a simple and green strategy utilizing the room temperature stirring method to mass produce nanoscale polyoxometalate-based metal-organic frameworks (POMOFs) with porous rhomboid-shaped dodecahedral and hexagonal prism structures. The products were labeled as POMOF1 (POMOF-PW12) and POMOF2 (POMOF-PMo12). Subsequently, a series of x wt% POMOF1/PAN (x = 0, 3, 5, and 10) nanofiber membranes (NFMs) were prepared using electrospinning technology, where polyacrylonitrile (PAN) acts as a "glue" molecule facilitating the bonding of POMOF1 nanoparticles. The as-prepared samples were comprehensively characterized and exhibited obvious water stability, as well as rapid selective adsorption filtration performance towards cationic dyes. The 5 wt% POMOF1/PAN NFM possessed the highest removal efficiency of 96.7% for RhB, 95.8% for MB, and 86.4% for CV dyes, which realized the selective separation over 95% of positively charged dyes from the mixed solution. The adsorption mechanism was explained using FT-IR, SEM, Zeta potential, and adsorption kinetics model, which proved that separation was determined via electrostatic interaction, hydrogen bonding, and π-π interactions. Moreover, the POMOF1/PAN membrane presented an outstanding recoverable and stable removal rate after four cycles. This study provides a new direction for the systematic design and manufacture of membrane separation materials with outstanding properties for contaminant removal.

Nitrogen Removal from Landfill Leachate Using Biochar Derived from Wheat Straw

Landfill leachate (LLCH) disposal poses challenges due to high pollutant concentrations. This study investigates the use of biochar (BC) derived from wheat straw for nitrogen content reduction. Laboratory experiments evaluated BC's adsorption capacity (qm) for nitrogen removal from ammonium chloride solution (NH4Cl) and LLCH, along with testing isotherm models. The results demonstrated that BC was more efficient (95.08%) than commercial activated carbon AC (93.11%), the blank, in adsorbing nitrogen from NH4Cl. This superior performance of BC may be attributed to its higher carbon content (57.74%) observed through elemental analysis. Lower results for BC/LLCH may be due to LLCH's complex chemical matrix. The Langmuir isotherm model best described BC/NH4Cl adsorption (qm = 0.5738 mg/g). The AC/NH4Cl data also fitted into the Langmuir (R2 ˃ 0.9) with a qm of 0.9469 mg/g, and 26.667 mg/g (R2 ˂ 0.9) was obtained for BC/LLCH; the BC/LLCH also gave higher qm (R2 ˃ 0.9) using the Jovanovich model (which also follows Langmuir's assumptions). The mean energy of the adsorption values estimated for the AC/NH4Cl, BC/NH4Cl, and BC/LLCH processes were 353.55, 353.55, and 223.61 kJ/mol, respectively, suggesting that they are all chemisorption processes and ion exchange influenced their adsorption processes. The Freundlich constant (1/n) value suggests average adsorption for BC/LLCH. The BC/LLCH data followed the Harkins-Jura model (R2: 0.9992), suggesting multilayered adsorption (or mesopore filling). In conclusion, biochar derived from wheat straw shows promising potential for landfill leachate remediation, offering efficient nitrogen removal capabilities and demonstrating compatibility with various adsorption models. This research also lays the groundwork for further exploration of other biochar-based materials in addressing environmental challenges associated with landfill leachate contamination.

Selective Adsorption of Methyl Orange and Methylene Blue by Porous Carbon Material Prepared From Potassium Citrate

As the discharge amount of dye wastewater increases with the development of the textile printing and dyeing industries, the treatment of the dyes in the wastewater becomes more complex. The adsorption method is a commonly used method for treating dye wastewater. The adsorbent is the key factor affecting the adsorption performance. To develop a high-performance adsorbent, a porous carbon material prepared from potassium citrate by the calcination method was applied in the adsorption of dye-containing water in this study. The morphology and pore structure of the porous carbon materials were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), and N2 adsorption/desorption isotherm. The porous carbon material with a specific surface area of 1436 m2 g-1, PC-900, was used as an adsorbent for the adsorption of methyl orange (MO) and methylene blue (MB). The results showed that the maximum adsorption capacity of PC-900 for MO and MB reached 927 and 1853.6 mg g-1, respectively. Studies on adsorption kinetics and adsorption isotherms showed that the pseudo-second-order kinetic model and the Langmuir isotherm model were more appropriate to describe the adsorption process of MO and MB by PC-900. In addition, the results of the mixed adsorption experiment of MO and MB dyes showed that PC-900 had selective adsorption for MB.

A Review on Polyacrylonitrile as an Effective and Economic Constituent of Adsorbents for Wastewater Treatment

Water gets polluted due to the dumping of untreated industrial waste into bodies of water, particularly those containing heavy metals and dyes. Industrial water contains both inorganic and organic wastes. Numerous adsorbents that are inexpensive and easily available can be used to address the issue of water deterioration. This review report is focused on polyacrylonitrile as an efficient constituent of adsorbents to extract toxic ions and dyes. It discusses the various formulations of polyacrylonitrile, such as ion exchange resins, chelating resins, fibers, membranes, and hydrogels, synthesized through different polymerization methods, such as suspension polymerization, electrospinning, grafting, redox, and emulsion polymerization. Moreover, regeneration of adsorbent and heavy metal ions makes the adsorption process more cost-effective and efficient. The literature reporting successful regeneration of the adsorbent is included. The factors affecting the performance and outcomes of the adsorption process are also discussed.

Synthesis, characterization and application of high adsorption performance of novel 1,4-polyketone

This study aims to develop an alternating polyketone containing cationic groups in one and four alternating positions for increased functionality. A novel polyarylidene ketone was synthesized using simple condensation polymerization of terephthaldehyde and 2,5-hexane dione (PAK) The physicochemical properties of the resulting polymer were evaluated using Fourier-transform infrared spectroscopy, thermogravimetric analysis, X-ray diffraction, UV-Visible absorbance, fluorescence, and SEM investigations. The findings show that the polymer is amorphous, has good thermal stability, and emits red light. It can also be used as a dye adsorbent in aqueous solutions, with high selectivity for the cationic dye methylene blue (MB). The adsorbent efficiency of PAK was measured as a function of pH, dosage, and initial dye concentration; the greatest dye removal of 96 % was obtained at pH 10, 50 mg dosage, and initial dye concentration of 20 ppm. Kinetics and isotherms were studied, showing that the pseudo-second-order model described kinetic data better than Freundlich and Langmuir and revealed a satisfactory chemisorption process. This study suggests that PAK can purify MB dyeing wastewater, remove Zn²⁺, Cu²⁺, Ni²⁺, Co²⁺, Cd²⁺, Fe³⁺ metal ions well, and is selective for Fe³⁺ and Cu²⁺; ion adsorption is chelating-based.

Removal of Ionic Dyes by Nanofiber Membrane Functionalized with Chitosan and Egg White Proteins: Membrane Preparation and Adsorption Efficiency

Electrospun polyacrylonitrile (PAN) nanofiber membrane was functionalized with chitosan and proteins for use in the treatment of dye-containing wastewater. The PAN nanofiber membrane was subjected to alkaline hydrolysis, before being grafted with chitosan and subsequently the proteins from chicken egg white. The resultant nanofiber membrane (P-COOH-CS-CEW) was comprehensively characterized using thermogravimetric analysis, Fourier-transform infrared spectroscopy, and scanning electron microscopy. The efficiency of P-COOH-CS-CEW in removing cationic dye toluidine blue O (TBO) and anionic dye acid orange 7 (AO7) in aqueous solution was evaluated. Based on the performance of model fitting, Langmuir and pseudo-second-order kinetic model could be used to describe the performance of P-COOH-CS-CEW in the removal of TBO (pH 10) and AO7 (pH 2) from the dye solutions. The adsorbed TBO and AO7 dyes can be completely desorbed by an elution solution made of 50% (v/v) ethanol and 1 M sodium chloride. After five consecutive adsorption-desorption cycles, the efficiency of dye removal by P-COOH-CS-CEW was maintained above 97%.

Investigation of magnetic silica nanocomposite immobilized Pseudomonas fluorescens as a biosorbent for the effective sequestration of Rhodamine B from aqueous systems

In the current research work, a novel eco-friendly Fe₃O₄@SiO₂ nanocomposite immobilized with Pseudomonas fluorescens biomass in calcium alginate beads (MSAB) was used as biosorbent for the elimination of hazardous Rhodamine B dye from aqueous system. The FTIR, XRD and SEM results showed that the MSAB possessed excellent surface properties for the effective sequestration of Rhodamine B. The batch adsorption results concluded that the adsorption of Rhodamine B using MSAB is highly influenced by the parameters such as pH, adsorbent dosage, initial dye concentration and contact time. The equilibrium and kinetics data get best fitted in the Freundlich isotherm and Pseudo first order kinetics for the studied adsorption system. The Langmuir monolayer adsorption capacity was found to be 229.6 mg/g. The thermodynamic studies showed that the adsorption was spontaneous, feasible and exothermic in nature. The adsorption mechanisms are understood using the Intraparticle diffusion and Boyd model. Thus, this Magnetic silica alginate beads (MSAB) containing dead biomass of Pseudomonas fluorescens is considered to be an ideal biosorbent which can be used as an effective tool in treating the industrial dye wastewater treatment.

Modification of bio-hydroxyapatite generated from waste poultry bone with MgO for purifying methyl violet-laden liquids

In the present work, biological hydroxyapatite (Bio-HAp) was generated from waste poultry bone and modified with magnesium oxide (MgO) nanoparticles (Bio-HAp/MgO) and used in the adsorption process of methyl violet (MV). The Bio-HAp and Bio-HAp/MgO mesoporous composites were characterized using physicochemical techniques. Bio-HAp and Bio-HAp/MgO composites had crystalline and mesoporous structures. The specific surface area of Bio-HAp/MgO mesoporous composites (14.7 m²/g) was higher and lower than that of Bio-HAp (4.6 m²/g) and MgO (154.9 m²/g), respectively. The effect of pH (2-10), temperature (25-45 °C), contact time (10-50 min), initial MV concentration (5-25 mg/L), and Bio-HAp/MgO quantity (0.5-2.5 g/L) on the adsorption efficiency was optimized through response surface methodology-central composite design (RSM-CCD). Among four isotherm models, the Freundlich isotherm (R² > 0.98) was better matched with the equilibrium data. Based on the isotherm parameters (E, n, and R_L), the MV adsorption process using Bio-HAp particles and Bio-HAp/MgO mesoporous composites is physical and desirable. The pseudo-second-order (R² > 0.97) was more potent than the other models for modeling kinetic data. According to the thermodynamic investigation, the MV adsorption was an exothermic and spontaneous process. The mesoporous composite had good reusability to remove MV dye from liquid media up to 5 steps. Bio-HAp particles and Bio-HAp/MgO mesoporous composites were tested for treatment, which significantly reduced the dye content of the real sample.

Cetyl trimethyl ammonium bromide modified magnetic biochar from pine nut shells for efficient removal of acid chrome blue K

Biochar was prepared by rapid pyrolysis using pine nut shell as raw materials. Then cetyl trimethyl ammonium bromide modified magnetic biochar material (CTAB-MC) was obtained after modifying biochar by FeCl₃ and cetyl trimethyl ammonium bromide. The CTAB-MC was characterized by SEM, FTIR, XRD and Magnetic analyses. Adsorptive property of the CTAB-MC for acid chrome blue K (AK) was studied. It was found that adsorption capacity was affected by solution pH, temperature, adsorption time, initial concentration and ionic strength. The CTAB-MC showed higher adsorption ability toward acid chrome blue K, which was up to 40% higher than that of MC. The experimental results showed that adsorption data of AK on the CTAB-MC well conformed to the Langmuir isotherm adsorption model and the pseudo-second order kinetic model. The CTAB-MC can be recycled three times. This work reveals that CTAB-MC is a promising adsorbent with broad application prospects.

Synergistic Adsorption for Parabens by an Amphiphilic Functionalized Polypropylene Fiber with Tunable Surface Microenvironment

A series of novel amphiphilic functionalized fibers with polarity tunable surface microenvironment were constructed by introducing hydrophilic polyamines and hydrophobic linear alkyl chain groups, aiming to selectively remove parabens from water. In addition, Fourier-transform infrared spectroscopy, X-ray powder diffraction, scanning electron microscopy, etc. were employed to determine the successful preparation of amphiphilic functionalized fibers. The adsorption experimental data indicated that the amphiphilic fibers showed excellent selectivity for parabens. In the amphiphilic fibers, hydrogen bonding and hydrophobic interaction existing in one molecular unit can effectively act together to enhance the interaction between substrate and fibers. Kinetic studies illustrated that the adsorption process was a physical adsorption with chemical characteristics. The overall initial adsorption rate together with the stepwise adsorption rate was quantified, and it is inferred that the hydrophobic interaction plays a leading role in the first step of the adsorption process. Moreover, the Freundlich model well described the sorption process with a maximum adsorption of 138.4 mg/g. What's more, the fiber still keeps excellent adsorption capacity (>90%) even after 10 adsorption/desorption cycles, which certifies it is an excellent adsorbent and can be utilized to remove paraben in practice.