Synthesis and adsorption behavior of hydroxypropyl-β-cyclodextrin-polyurethane magnetic nanoconjugates for crystal and methyl violet dyes removal from aqueous solutions

Poly(acrylic acid-co-2-acrylamido-2-methyl-1-propanesulfonic acid)-grafted chitosan hydrogels for effective adsorption and photocatalytic degradation of dyes

As a result of the growth of industrialization and urbanization, the water ecosystem is contaminated by various pollutants, including heavy metal ions and dyes. The use of low-cost and environmentally friendly dye adsorbents has been investigated. A hydrogel was fabricated via graft polymerization of acrylic acid (AA) and 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS) onto chitosan. The hydrogel was used as a dye adsorbent and support for a zinc oxide (ZnO) powder photocatalyst. The adsorption capacity of the bare hydrogel was greater towards cationic dyes than anionic dyes. Grafting P(AA-co-AMPS) exhibited a 23-time increase in adsorption capacity towards crystal violet (CV) compared to pristine chitosan. The effect of the AA-AMPS molar ratio on CV adsorption was studied. A hydrogel with an AA-AMPS ratio of 10 : 1 had the highest adsorption capacity towards CV in water, removing 91% of the dye in 12 h. The maximum adsorption capacity was 2023 mg g-1. The adsorption kinetics and isotherm were described by the pseudo-second-order model and the Langmuir model, respectively. ZnO particles were in situ synthesized within the 10 : 1 hydrogel to facilitate the recovery of the photocatalyst. The ZnO hydrogel composite could remove 95% and 92% of CV from solutions on the 1st and 2nd cycle, respectively. In addition, the hydrogel composite containing only 8.7 wt% of ZnO particles effectively degraded adsorbed CV under sunlight and could be reused without requiring a chemical regeneration or photocatalyst recovery procedure. This hydrogel composite is an effective dual-functional material for the adsorption and photodegradation of dye pollutants in wastewater.

Removal of crystal violet from water by poly acrylonitrile-co-sodium methallyl sulfonate (AN69) and poly acrylic acid (PAA) synthetic membranes

The current investigation is focused on the removal of crystal violet (CV) from water by adsorption process (bach method). To achieve this purpose, specific membranes were prepared from poly acrylonitrile-co-sodium methallyl sulfonate (AN69) and poly acrylic acid (PAA) blends. The adsorption of CV onto AN69/PAA membranes was studied under various conditions: membrane composition, pH, contact time, initial concentration and temperature. To understand the effect of membrane morphology on adsorption process, scanning electronic microscopy (SEM) was employed to determine the features of section and membrane’s surface. From isotherm results, it was found that: the maximum adsorption capacity Q m was 1250 mg g−1, the Langmuir separation factor R L was lying between 0.33 and 0.76, the Freundlich intensity was higher than Unit (n = 1.25) and the adsorption process follows preferentially the Langmuir model (correlation constant R 2 = 0.99). The mechanism of adsorption is perfectly fitted by pseudo second order. The obtained results tend to confirm that the removal of dye molecules is due to the establishment of strong electrostatic interactions between cationic dye molecules and anionic membrane groups. The high adsorption capacity (1250 mg g−1) for the small dye molecules may open wide opportunities to apply these membranes in the removal of various hazardous pollutants commonly present in water.

Recent advances in the polyurethane-based adsorbents for the decontamination of hazardous wastewater pollutants

The pollution of aquatic systems with noxious organic and inorganic contaminants is a challenging problem faced by most countries. Water bodies are contaminated with diverse inorganic and organic pollutants originating from various diffuse and point sources, including industrial sectors, agricultural practices, and domestic wastes. Such hazardous water pollutants tend to accumulate in the environmental media including living organisms, thereby posing significant environmental health risks. Therefore, the remediation of wastewater pollutants is a priority. Adsorption is considered as the most efficient technique for the removal of pollutants in aqueous systems, and the deployment of suitable adsorbents plays a vital role for the sustainable application of the technique. The present review gives an overview of polyurethane foam (PUF) as an adsorbent, the synthesis approaches of polyurethane, and characterization aspects. Further emphasis is on the preparation of the various forms of polyurethane adsorbents, and their potential application in the removal of various challenging water pollutants. The removal mechanisms, including adsorption kinetics, isotherms, thermodynamics, and electrostatic and hydrophobic interactions between polyurethane adsorbents and pollutants are discussed. In addition, regeneration, recycling and disposal of spent polyurethane adsorbents are reported. Finally, key knowledge gaps on synthesis, characterization, industrial applications, life cycle analysis, and potential health risks of polyurethane adsorbents are discussed.

Hydroxypropyl-β-cyclodextrin-polyurethane/graphene oxide magnetic nanoconjugates as effective adsorbent for chromium and lead ions

In this work, hydroxypropyl-β-cyclodextrin-polyurethane magnetic nanoconjugates/reduced graphene oxide (HPMNPU/GO) supramolecules were prepared. The adsorbent was characterized using FTIR and SEM. The adsorbent was evaluated for its efficiency to remove Cr⁶⁺ and Pb²⁺ from aqueous solutions through batch adsorption studies following a Definitive Screening Design (DSD). Effects of solution pH, contact time, adsorbent dosage, initial metal concentration, ionic strength, GO/NC ratio and temperature on Cr ⁶⁺ and Pb ²⁺ adsorption were investigated. Optimization of the adsorption process was done using a desirability function of the Design Expert V11 software. A good agreement between experimental and predicted data proved the efficiency of this model for prediction of real optimum point. The batch experiments implied that the pseudo-second-order model (lowest sum of square error (SSE) values and correlation coefficients (R²) > 0.999) was better to describe the adsorption kinetics of Cr⁶⁺ and Pb²⁺ onto the HPMNPU/GO.

Preparation and characterization of a novel Fe3O4-graphene-biochar composite for crystal violet adsorption

A novel Fe₃O₄-graphene-biochar composite (GBC-Fe₃O₄) was prepared to enhance the adsorption capacity and recollection efficiency of graphene-biochar composites (GBCs). The adsorption characteristics were tested to remove crystal violet (CV), which is a refractory compound in industrial wastewater. Structural and morphological analysis exhibited that a larger surface area, greater thermal stability, and more functional groups were present after Fe₃O₄ nanoparticles coated the GBC surface. This improved the CV adsorption versus uncoated GBC. The introduction of G and Fe₃O₄ nanoparticles collectively reduced the zeta potentials of GBC-Fe₃O₄ to -38.1 ± 1.1 mV versus -24.3 ± 2.2 mV for GBC and -20.7 ± 1.2 mV for BC. The maximum Q_max values were obtained 436.68 mg/g at 40 °C. Fourier transform infrared analysis suggested that the interactions of functional groups, such as aromatic C = C and C = O, -OH, C-C, and π-π played an important role in CV adsorption. The thermodynamic analysis of Langmuir and Freundlich isotherms indicated that the adsorption improved as a spontaneous endothermic process. The saturation magnetization of GBC-Fe₃O₄ reached 61.48 emu/g, allowing efficient recollection of the material with a magnet. The CV adsorbability of the re-collected GBC-Fe₃O₄ was 157.31 mg/g, which was slightly lower than freshly prepared GBC-Fe₃O₄ (199 mg/g). These findings demonstrated that GBC-Fe₃O₄ was an efficient and reusable multifunctional biochar.