Carbon nanotubes/ polyacrylonitrile composite nanofiber mats for highly efficient dye adsorption

Fabrication of Porous Fibrous Membranes with Rough Surfaces via PAN-H/PVP for Cation Dye Removal and Oil/Water Emulsion Separation

The purification of organic dye pollutants and insoluble emulsified oils in wastewater has become a critical focus of environmental research. In this study, fibrous membranes were prepared through electrostatic spinning by first hydrolyzing polyacrylonitrile and then blending it with water-soluble polyvinylpyrrolidone (PVP). Subsequent hydrothermal treatment was applied to partially remove PVP from the fibers, creating rough and porous surfaces that exposed more functional carboxyl groups and increased the fibers' specific surface area. The resulting membranes exhibited superhydrophilicity (≈0°) and underwater superoleophobicity (≈157°), alongside excellent fouling resistance. The fibrous membranes, characterized by their carboxyl-rich surfaces, exhibited improved adsorption capabilities for cationic dyes, attaining capacities of 735.77 mg/g for malachite green, 429.31 mg/g for methylene blue, and 607.21 mg/g for crystal violet. The membranes achieved a remarkable separation efficiency of 99.8% for oil-in-water emulsions and maintained 98.5% efficiency after 10 cycles of separation and elution, highlighting their outstanding regeneration capability. In summary, this study demonstrates that these fibrous membranes are highly effective in removing cationic dyes and insoluble emulsified oils from wastewater. The membranes show great potential for applications in wastewater treatment, particularly for selective dye removal and oil-water separation.

Fruit peel incorporated alginate based magnetic hydrogel bio-composite beads for removal of hexavalent chromium

High adsorption capacity, reusability and sustainability are the most important features sought in the adsorbent preferences to be used in wastewater treatment. In this research work, magnetic composite beads prepared from fruit peels (nectarine and orange) and alginate (ALG) as biopolymers (NAF and OAF) were synthesized by dropping and pH-precipitation method as alternative adsorbents. By encapsulating the adsorbent using alginate and imparting magnetic properties, the separation of the adsorbent from water after the adsorption process has been simplified. Fourier transform infrared spectroscopy analysis (FTIR), scanning electron microscopy (SEM) analysis, energy-dispersive X-ray (EDX)-mapping and X-ray diffraction (XRD) analyses were performed to examine the surface chemical structure and surface morphological structure of these new synthesized biosorbents. The calculated maximum adsorption capacities were 224.3 mg/g for OAF and 256.5 mg/g for NAF at 298 K and pH =2.0. It was observed that the adsorption process for both adsorbents was endothermic and spontaneous. Moreover, the adsorptions of Cr (VI) onto both adsorbents followed the pseudo-second order model and fit the Langmuir isotherm model better. OAF and NAF were found to be reusable with stable adsorption capacity for at least five cycles. Overall, this study demonstrates the performance of OAF and NAF in the removal of Cr (VI) ions from aqueous solutions, thus highlighting the promising potential of these magnetic bio-based adsorbents for sustainable water treatment.

Microalgae derived honeycomb structured mesoporous diatom biosilica for adsorption of malachite green: Process optimization and modeling

The present study investigated the removal of malachite green dye from aquifers by means of microalgae-derived mesoporous diatom biosilica. The various process variables (dye concentration, pH, and adsorbent dose) influencing the removal of the dye were optimized and their interactive effects on the removal efficiency were explored by response surface methodology. The pH of the solution (pH = 5.26) was found to be the most dominating among other tested variables. The Langmuir isotherm (R2 = 0.995) best fitted the equilibrium adsorption data with an adsorption capacity of 40.7 mg/g at 323 K and pseudo-second-order model (R2 = 0.983) best elucidated the rate of dye removal (10.6 mg/g). The underlying mechanism of adsorption was investigated by Weber-Morris and Boyd models and results revealed that the film diffusion governed the overall adsorption process. The theoretical investigations on the dye structure using DFT-based chemical reactivity descriptors indicated that malachite green cations are electrophilic, reactive and possess the ability to accept electrons, and are strongly adsorbed on the surface of diatom biosilica. Also, the Fukui function analysis proposed the favorable adsorption sites available on the adsorbent surface.

A review on hybrid membrane-adsorption systems for intensified water and wastewater treatment: Process configurations, separation targets, and materials applied

In the era of rapid and conspicuous progress of water treatment technologies, combined adsorption and membrane filtration systems have gained great attention as a novel and efficient method for contaminant removal from aqueous phase. Further development of these techniques for water/wastewater treatment applications will be promising for the recovery of water resources as well as reducing the water tension throughout the world. This review introduces the state-of-the-art on the capabilities of the combined adsorption-membrane filtration systems for water and wastewater treatment applications. Technical information including employed materials, superiorities, operational limitations, process sustainability and upgradeing strategies for two general configurations i.e. hybrid (pre-adsorption and post-adsorption) and integrated (film adsorbents, low pressure membrane-adsorption coupling and membrane-adsorption bioreactors) systems has been surveyed and presented. Having a systematic look at the fundamentals of hybridization/integration of the two well-established and efficient separation methods as well as spotlighting the current status and prospectives of the combination strategies, this work will be valuable to all the interested researchers working on design and development of cutting-edge wastewater/water treatment techniques. This review also draws a clear roadmap for either decision making and choosing the best alternative for a specific target in water treatment or making a plan for further enhancement and scale-up of an available strategy.

Preparation of Reusable Porous Carbon Nanofibers from Oxidized Coal Liquefaction Residue for Efficient Adsorption in Water Treatment

Porous carbon nanofibers are commonly used for adsorption processes owing to their high specific surface area and rich pore structure. However, the poor mechanical properties of polyacrylonitrile (PAN)-based porous carbon nanofibers have limited their applications. Herein, we introduced solid waste-derived oxidized coal liquefaction residue (OCLR) into PAN-based nanofibers to obtain activated reinforced porous carbon nanofibers (ARCNF) with enhanced mechanical properties and regeneration for efficient adsorption of organic dyes in wastewater. This study examined the effects of contact time, concentration, temperature, pH, and salinity on the adsorption capacity. The adsorption processes of the dyes in ARCNF are appropriately described by the pseudo-second-order kinetic model. The maximum adsorption capacity for malachite green (MG) on ARCNF is 2712.84 mg g^-1 according to the fitted parameters of the Langmuir model. Adsorption thermodynamics indicated that the adsorptions of the five dyes are spontaneous and endothermic processes. In addition, ARCNF have good regenerative performance, and the adsorption capacity of MG is still higher than 76% after 5 adsorption-desorption cycles. Our prepared ARCNF can efficiently adsorb organic dyes in wastewater, reducing the pollution to the environment and providing a new idea for solid waste recycling and water treatment.

One-pot synthesis of iron oxide - Gamma irradiated chitosan modified SBA-15 mesoporous silica for effective methylene blue dye removal

The development of adsorption technology and the processing of radiation have both been influenced by chitosan adsorbent (γ-chitosan), a raw material with unique features. The goal of the current work was to improve the synthesis of Fe-SBA-15 utilizing chitosan that has undergone gamma radiation (Fe-γ-CS-SBA-15) in order to investigate the removal of methylene blue dye in a single hydrothermal procedure. High-resolution transmission electron microscopy (HRTEM), High angle annular dark field scanning transmission electron microscopy (HAADF-STEM), small- and wide-angle X-ray powder diffraction (XRD), Fourier transform-infrared spectroscopy (FT-IR) and Energydispersive X-ray spectroscopy (EDS) were used to characterize γ-CS-SBA-15 that had been exposed to Fe. By using N₂-physisorption (BET, BJH), the structure of Fe-γ-CS-SBA-15 was investigated. The study parameters also included the effect of solution pH, adsorbent dose and contact time on the methylene blue adsorption. The elimination efficiency of the methylene blue dye was compiled using a UV-VIS spectrophotometer. The results of the characterization show that the Fe-γ-CS-SBA-15 has a substantial pore volume of 504 m² g^-1 and a surface area of 0.88 cm³ g^-1. Furthermore, the maximum adsorption capacity (Q_max) of the methylene blue is 176.70 mg/g. The γ-CS can make SBA-15 operate better. It proves that the distribution of Fe and chitosan (the C and N components) in SBA-15 channels is uniform.

Electrospun Nanofiber Membrane: An Efficient and Environmentally Friendly Material for the Removal of Metals and Dyes

With the rapid development of nanotechnology, electrospun nanofiber membranes (ENM) application and preparation methods have attracted attention. With many advantages such as high specific surface area, obvious interconnected structure, and high porosity, ENM has been widely used in many fields, especially in water treatment, with more advantages. ENM solves the shortcomings of traditional means, such as low efficiency, high energy consumption, and difficulty in recycling, and it is suitable for recycling and treatment of industrial wastewater. This review begins with a description of electrospinning technology, describing the structure, preparation methods, and factors of common ENMs. At the same time, the removal of heavy metal ions and dyes by ENMs is introduced. The mechanism of ENM adsorption on heavy metal ions and dyes is chelation or electrostatic attraction, which has excellent adsorption and filtration ability for heavy metal ions and dyes, and the adsorption capacity of ENMs for heavy metal ions and dyes can be improved by increasing the metal chelation sites. Therefore, this technology and mechanism can be exploited to develop new, better, and more effective separation methods for the removal of harmful pollutants to cope with the gradually increasing water scarcity and pollution. Finally, it is hoped that this review will provide some guidance and direction for research on wastewater treatment and industrial production.

Removing methylene blue from water: A study of sorption effectiveness onto nanoparticles-doped activated carbon

In this present study, silver (Ag) and titanium dioxide (TiO₂) nanoparticles were successfully deposited on coconut shell-derived activated carbon (CSAC), to synthesize a novel nanocomposite (CSAC@AgNPs@TiO₂NPs) for the adsorption of Methylene Blue (MB) dye from aqueous solution. The fabricated CSAC@AgNPs@TiO₂NPs nanocomposite was analyzed by Scanning Electron Microscope (SEM), X-ray Diffraction (XRD), Fourier-Transform Infrared Spectroscopy (FTIR), Transmission Electron Microscope (TEM) equipped with Energy Dispersive X-ray spectroscopy (EDS) detector, X-ray Photoelectron Spectroscope (XPS), and Brunauer-Emmett-Teller (BET). The successful deposition of AgNPs and TiO₂NPs on CSAC surface was revealed by the TEM/EDX, SEM, and XPS analysis. The mesopore structure of CSAC@AgNPs@TiO₂NPs has a BET surface area of 301 m²/g. The batch adsorption studies were conducted and the influence of different parameters, i.e., adsorbent dose, adsorption time, initial dye concentration, pH and temperature were investigated. The nonlinear isotherm and kinetic modelling demonstrated that adsorption data were best fitted by Sips isotherm and pseudo-second-order models, respectively. The maximum adsorption capacity of MB onto CSAC@AgNPs@TiO₂NPs by the Sips model was 184 mg/g. Thermodynamic results revealed that the adsorption was endothermic, spontaneous and physical in nature. CSAC@AgNPs@TiO₂NPs revealed that MB absorption by CSAC@AgNPs@TiO₂NPs was spontaneous and endothermic. The uptake capacity of MB was influenced significantly by the presence of competing ions including, NO₃^-, HCO_3, Ca²⁺, and Na⁺. Repeated tests indicated that the CSAC@AgNPs@TiO₂NPs can be regenerated and reused six times before being discarded. The primary separation mechanism between MB dye and CSAC@AgNPs@TiO₂NPs was the electrostatic interaction. Thus, CSAC@AgNPs@TiO₂NPs was an outstanding material, which displayed good applicability in real water with ≥ 97% removal of MB dye.

A new type of calcium-rich biochars derived from spent mushroom substrates and their efficient adsorption properties for cationic dyes

Adsorption is commonly accepted as a most promising strategy in dye wastewater treatment, and the widespread use of adsorption emphasizes the need to explore low-cost but excellent adsorbents. Herein, a low-cost adsorbent (calcium-rich biochar) was developed, which was directly pyrolyzed from spent mushroom substate without any modification. This study evaluated the potential application of two calcium-rich biochars (GSBC and LSBC) derived from spent substrates of Ganoderma lucidum and Lentinus edodes, respectively. The effects of pyrolysis temperature on the calcium-rich biochars characteristics and their adsorption mechanism for cationic dyes (Malachite Green oxalate (MG) and Safranine T (ST)) were studied systematically. The increase in pyrolysis temperature from 350 to 750 °C led to an increase in both biochar ash, Ca content, and specific surface area, which made high-temperature biochars (GS750 and LS750) the superior adsorbents for cationic dyes. Batch adsorption results showed LS750 was more efficient to adsorb dyes than GS750 attributed to its higher Ca content and larger specific surface area. According to the Langmuir model, LS750 had high adsorption capacities of 9,388.04 and 3,871.48 mg g⁻¹ for Malachite green and ST, respectively. The adsorption mechanism of dye MG could be attributed to pore filling, hydrogen bonding, electrostatic interaction, ion exchange, and π-π stacking, while ST adsorption mainly involved pore filling, electrostatic interaction, ion exchange, and π-π stacking. Attributed to their excellent adsorption performance, cheap source, and good reusability, biochars obtained from SMSs were very promising in dyeing wastewater treatment.