Conducting macroporous polyaniline/poly(vinyl alcohol) aerogels for the removal of chromium(VI) from aqueous media

Transparent and Flexible Hierarchical Porous Structure of Polyvinyl Alcohol Aerogel: A Microstructure Study

Aerogels have gained increasing attention due to their unique properties since their introduction in 1932. Silica aerogel, one of the earliest and most advanced types, is known for its high transparency and excellent thermal insulation. However, its internal pearl-like structure makes it extremely brittle, which limits its practical applications. To address this, through multiple refinements in formulation and production techniques, we developed a novel Polyvinyl Alcohol (PVA) aerogel using an innovative one-step standing method. This method significantly reduces the gelling time compared to the freeze-thaw method and eliminates the need for refrigeration, making it a more environmentally friendly and sustainable process. The resulting one-step standing PVA aerogel features a hierarchical porous structure, remarkable transparency, improved strength, and enhanced thermal insulation. Mechanical tests demonstrated that the PVA aerogel produced by the one-step standing method exhibited a significantly higher Young's modulus of 4.2596 MPa, surpassing that of silica, copper nanowire (Cu NM), and graphene aerogels. Additional tests, including transmittance and thermal analysis, further confirmed that the one-step standing PVA aerogel excels in both transparency and thermal insulation. This combination of improved mechanical performance and light transmission opens novel potential applications, such as drug delivery systems, where the aerogel's pore structure can store drugs while maintaining strength and transparency.

Novel pyridine isonicotinoyl hydrazone derivative: synthesis, complexation and investigation for decontamination of DR-81 from wastewater

Herein, novel aroylhydrazone (E/Z)-N'-((3-methylpyridin-2-yl)methylene)isonicotinohydrazide ligand (MPIH) 3 and its Zn(ii)-MPIH complex 4 were synthesized and investigated to adsorb direct red 81 dye (DR-81) from aqueous media. MPIH was synthesized by the condensation reaction of isonicotinohydrazide with 3-methylpicolinaldehyde 2, then performed in a basic medium with zinc chloride to form Zn(ii)-MPIH complex. The synthesized MPIH ligand 3 and Zn(ii)-MPIH complex 4 were further characterized via proton nuclear magnetic resonance (1H NMR), 13C nuclear magnetic resonance, Fourier transform infrared spectroscopy (FT-IR), UV-visible, mass spectra analysis (EI MS), and elemental analysis. The synthesized MPIH ligand 3 and Zn(ii)-MPIH complex 4 were evaluated for their ability to decontaminate DR-81 from wastewater. The performance of MPIH ligand 3 to adsorb DR-81 from wastewater was lower than Zn(ii)-MPIH complex 4 over contact times of 180 minutes. The optimal dosage of the Zn(ii)-MPIH complex 4 was determined to be 1.0 g L-1 at pH 7, achieving 88.3% adsorption of 10 ppm DR-81 within 45 minutes. Thermodynamic analysis showed that the decontamination process was spontaneous and exothermic when using the fabricated Zn(ii)-MPIH complex 4. The kinetic parameters aligned well with the pseudo-second-order kinetics model, and the adsorption process was accurately described by the Freundlich isotherm. The adsorption data confirmed that the Zn(ii)-MPIH complex 4 is an effective adsorbent for DR-81 in aqueous solutions, demonstrating high stability, the ability to be recycled for up to seven cycles, and ease of regeneration.

"Green" electrostatic droplet-assisted forming cellulose microspheres with excellent structural controllability and stability for efficient Cr(VI) removal

This study presents a novel and environmentally friendly method for producing cellulose microspheres (CM) with controllable morphology and size using electrostatic droplets. The traditional droplet method for CM production requires complex equipment and harmful reagents. In contrast, the proposed method offers a simple electrostatic droplet approach to fabricate CM10 at 10 kV, which exhibited a smaller volume, linear microscopic morphology, and a larger specific surface area, with a 36.60 % improvement compared to CM0 (prepared at 0 kV). CM10 also demonstrated excellent underwater structural stability, recovering in just 0.5 s, and exhibited the highest adsorption capacity for Cr(VI) at 190.16 mg/g, a 72.15 % improvement over CM0. This enhanced adsorption capacity can be attributed to the unique structure of CM10 and the introduction of more amino groups. Moreover, CM10 displayed good cyclic adsorption capacity and high dynamic adsorption efficiency, making it highly suitable for practical applications. CM10 exhibited remarkable adsorption capacity, stability, and practical value in treating Cr(VI) wastewater. This work proposes a simple and eco-friendly method for producing CM with excellent structural controllability and stability, providing an effective route for wastewater treatment.

Microbial bio-film calcite mediated removal of heavy metals from industrial wastewater of Kasur, Pakistan

Heavy metals in the industrial wastewater are an area of great concern as act as source of bioaccumulation in edible plants and posing a major health risk to humans like cancers. This study was planned by exploiting the bio-film producing microbes that have the potential to remediate heavy metals by calcite mediated removal from industrial wastewater. Samples (n = 10) from a marble factory wastewater were collected. Samples were serially diluted and were spread on nutrient agar media supplemented with 2% urea and 0.28 g calcium chloride. All the isolates were observed for colony morphology, gram staining, and spore staining, for biochemical profile and for their efficacy in producing calcium carbonate crystals. All isolates showed cell densities at varying metal (chromium) concentrations ranging from 100 to 500 µg/mL. Determination of biofilm formation is performed by recording Optical density (OD = 600 nm). Normalized biofilm (570/600 nm) was formed. Different concentrations of chromium were used to measure their reduction ability and also by using tannery water. In tannery wastewater, significant reduction was recorded (p = 0.05) by AS4 bacterial isolate as compared to rest of the isolates and treatments. It showed remarkable chromium VI reduction ability.

Polypyrrole- and Polyaniline-Coated Cotton Fabrics as Efficient Adsorbents for the Pharmaceutical Water Contaminants Diclofenac and Salicylic Acid

The emerging pharmaceutical contaminants diclofenac (DCF) and salicylic acid (SA) pose potential hazards to humans and living organisms due to their persistence in water environments. In this work, the conductive polymers polypyrrole (PPY) and polyaniline (PANI) were successfully coated on cotton fabrics, as confirmed by FTIR and SEM measurements. The coated fabrics efficiently removed DCF at pH 5.3 and SA at pH 4, with removal efficiencies that exceeded 90% and 70%, respectively. Adsorption was rapid for most of the tested contaminant-fabric systems and reached equilibrium within 20-30 min. The best adsorption performance for both contaminants was shown on the PPY-coated fabrics, which yielded adsorption capacities of about 65 and 21 mg/g for DCF and SA, respectively. This could be explained by molecular modeling simulations, which mostly estimated higher total cohesive energy densities for adsorption on the PPY-coated fabrics than on the PANI-coated ones. The adsorption mechanism involved both coulombic electrostatic attractions and non-coulombic van der Waals and π-π stacking. The fabrics could be reused for three adsorption-desorption cycles. Immobilization of the conductive polymers on cotton fabrics provides a facile method for their handling and collection during adsorption and regeneration cycles while maintaining their multi-functionality in adsorbing different contaminants.

Polypyrrole Aerogels: Efficient Adsorbents of Cr(VI) Ions from Aqueous Solutions

Three-dimensional and porous polypyrrole (PPy) aerogels were prepared using a facile two-step procedure in which cryogels were synthesized via the cryopolymerization of pyrrole with iron (III) chloride in the presence of supporting water-soluble polymers (poly(N-vinylpyrrolidone), poly(vinyl alcohol), gelatin, methylcellulose or hydroxypropylcellulose), followed by freeze-drying to obtain aerogels. The choice of supporting polymers was found to affect the morphology, porosity, electrical conductivity, and mechanical properties of PPy aerogels. PPy aerogels were successfully used as adsorbents to remove toxic Cr(VI) ions from aqueous solutions.

Enhanced adsorptive removal of hexavalent chromium in aqueous media using chitosan-modified biochar: Synthesis, sorption mechanism, and reusability

Hexavalent chromium (Cr(VI)) is deemed a priority contaminant owing to its carcinogenicity, teratogenicity, and mutagenicity towards flora and fauna. A novel Chitosan-modified Mimosa pigra biochar (CMPBC) was fabricated and efficiency of Cr(VI) oxyanion removal in aqueous systems was compared with the pristine biochar. The gross composition of pyrolyzed biomass was determined through the proximate analysis. The instrumental characterization of X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared spectroscopy (FT-IR) confirmed the amino modification of MPBC when treated with chitosan. Characteristic features of the Cr(VI) sorptive process by CMPBC and MPBC were examined by performing batch sorption studies. Experimental data suggested that sorption is heavily dependent on pH, with the highest adsorption capacity (14.4 ± 0.9 mg g^-1) occurring at pH 3. It was further noted that the removal efficiency of CMPBC (92%) was considerably greater than that of MPBC (75%) when the biochar dose and initial concentration of Cr(VI) are 1 g L^-1 and 5 mg L^-1 respectively. The kinetic data were best interpreted by the power function model (R² = 0.97) suggesting a homogenous chemisorption process. The isotherm data of removal of Cr(VI) by CMPBC was inferred well by Redlich Peterson and Temkin isotherms. Results of sorption-desorption regeneration cycles indicated that the Cr(VI) uptake by CMPBC is not fully reversible. The electrostatic attractions between cationic surface functionalities and Cr(VI) oxyanions, partial reductive transformation of Cr(VI) species to Cr(III), as well as complexation of Cr(III) onto CMPBC were the possible mechanisms of mitigation of Cr(VI) by CMPBC. The results and outcomes of this research suggest the possibility of utilizing the chitosan-modified Mimosa pigra biochar as an easily available, environmentally sustainable, and inexpensive sorbent to decontaminate Cr(VI) pollution from aqueous media.

Novel aspartic-based bio-MOF adsorbent for effective anionic dye decontamination from polluted water

In this study, a cost-effective powdered Zn l-aspartic acid bio-metal organic framework (Zn l-Asp bio-MOF) was reported as an efficient adsorbent for Direct Red 81 (DR-81) as an anionic organic dye. The prepared bio-MOF was characterized using Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), field emission transmission electron microscopy (FETEM), surface area analysis (BET), and thermal gravimetrical analysis (TGA). The resulting bio-MOF has a large surface area (180.43 m2 g-1) and large mesopore volume (0.144 cm3 g-1), as well as good chemical inertness and mechanical stability. The optimum dosage from the Zn l-Asp bio-MOF was 1.0 g L-1 at pH = 7 for 95.3% adsorption of 10 ppm DR-81 after 45 min. Thermodynamic analysis results demonstrated that the decontamination processes were done with spontaneous, thermodynamically, and exothermic nature onto the fabricated bio-MOF. Kinetic parameters were well-fitted with pseudo-second-order kinetics, and the adsorption process was described by the Freundlich isotherm. The adsorption data proved that Zn l-Asp bio-MOF is an effective adsorbent for DR-81 from aqueous solutions with high stability and recycling ability for eight cycles, as well as the easy regeneration of the sorbent.

Efficient detoxification of Cr(VI)-containing effluents by sequential adsorption and reduction using a novel cysteine-doped PANi@faujasite composite: Experimental study supported by advanced statistical physics prediction

Nowadays, the global spreading of hazardous heavy metals becomes a top-priority environmental challenge, owing to its serious detrimental health outcomes. Herein, a novel cysteine-doped polyaniline@faujasite hybrid composite (Cys-PANi@FAU-50) was synthesized via a facile in-situ polymerization route for the effective detoxification of Cr(VI)-bearing wastewaters. The Cys-PANi@FAU-50 composite displayed an open mesoporous structure richly decorated with nitrogen/oxygen-containing functional groups, which consequently boosted the diffusion, adsorption and reduction of Cr(VI) oxyanions. The Cr(VI) adsorption behavior was satisfactorily tailored via pseudo-second-order law and Langmuir model with a maximum uptake capacity of 384.6 mg/g. Based on the advanced statistical physics theory, the monolayer model with two distinct receptor sites provided a reliable microscopic and macroscopic prediction of the Cr(VI) adsorption process. Stereographically, the Cr(VI) ions were adsorbed through horizontal multi-anchorage and vertical multi-molecular mechanisms on the amine and hydroxyl groups of Cys-PANi@FAU-50, respectively. The thermodynamic functions evidenced that the Cr(VI) adsorption was an endothermic spontaneous process. XPS analysis proved that Cr(VI) ions were electrostatically adsorbed, and subsequently reduced to Cr(III), which were in turn immobilized by chelation with imine/sulfonate groups and electrostatic interactions with carboxylate groups. The Cys-PANi@FAU-50 featured an effortless regenerability and good reusability. Overall, the Cys-PANi@FAU-50 composite owns outstanding potentiality for detoxifying Cr(VI)-laden effluents.