Removal of heavy metal ions (Pb2+, Cu2+, Cr3+, and Cd2+) from multimetal simulated wastewater using 3-aminopropyl triethoxysilane grafted agar porous cryogel

In this study, we have developed agar, a seaweed derived polysaccharide based green adsorbent for the removal of heavy metal ions (Pb2+, Cu2+, Cr3+ and Cd2+) from multimetal solution. Porous cryogels of agar grafted with 3-aminopropyl triethoxysilane (APTES) were prepared by freeze-drying. The adsorption capacity and selectivity of the optimized APTES-agar cryogel for heavy metal ions (Cu2+, Cr3+, Pb2+, Cd2+) were investigated in multimetal solutions. >95 % of all the cationic metal ions were removed from 400 mg/L multimetal metal solutions having equal concentrations of each metal at pH 5.5. The experimental adsorption capacities of Cr3+, Cu2+, Pb2+, and, Cd2+ were changed from 39.14, 39.0, 39.20, 37.93 mg/g, to 52.58, 52.70, 45.53, 31.10 mg/g, respectively, for the 400 mg/L and 800 mg/L multimetal solutions suggesting competitive adsorption of the metal ions for active sites. The competitive adsorption studies showed that Cd ions had lower affinity than other metal ions for active sites on APTES grafted agar surface, and adsorption followed in the order of Cu2+ ≈ Cr3+ > Pb2+ > Cd2+. The developed seaweed-derived agar-based porous adsorbent exhibits promise in the removal of several heavy metal ions from wastewater, and this approach would increase the use of natural polysaccharides that are sustainable.

Agarose Cryogels Loaded with Polydopamine Microspheres for Sustainable Wound Care with Enhanced Hemostatic and Antioxidant Properties

Excessive bleeding presents a grave risk to life, especially in scenarios involving deep wounds such as those inflicted by gunshots and accidental stabs. Despite advancements in wound care management, existing commercial hemostatic agents have limitations, necessitating the development of enhanced solutions. In this study, we developed cryogels using agarose and polydopamine microspheres as a hemostatic dressing to effectively manage profuse bleeding. The resulting cryogels demonstrated impressive attributes, such as high absorption capacity (>4000%), shape recovery ability, antioxidant properties, and excellent biocompatibility in mammalian cell lines. Particularly noteworthy was the rapid blood clotting observed in vitro, with the agarose/PDA cryogels achieving complete clotting within just 90 s. Subsequent validation in the rat trauma model further underscored their hemostatic efficacy, with clotting times of 40 and 53 s recorded in tail amputation and liver puncture models, respectively. The porous structure and hydrophilicity of the cryogels facilitated superior blood absorption and retention, while the amine groups of polydopamine played a pivotal role in enhancing blood clotting activity. This study represents a significant step forward in utilizing agarose/polydopamine cryogels as advanced materials for hemostatic wound dressings, promising an impactful contribution to wound therapy.

Preparation and assessment of agar/TEMPO-oxidized bacterial cellulose cryogels for hemostatic applications

In this work, we have demonstrated agar and oxidized bacterial cellulose cryogels as a potential hemostatic dressing material. TEMPO-oxidized bacterial cellulose (OBC) was incorporated into the agar matrix, improving its mechanical and hemostatic properties. The oxidation of bacterial cellulose (BC) was evidenced by chemical characterization studies, confirming the presence of carboxyl groups. The in vitro blood clotting test conducted on agar/OBC composite cryogels demonstrated complete blood clotting within 90 seconds, indicating their excellent hemostatic efficacy. The cryogels exhibited superabsorbent properties with a swelling degree of 4200%, enabling them to absorb large amounts of blood. Moreover, the compressive strength of the composite cryogels was appreciably improved compared to pure agar, resulting in a more stable physical structure. The platelet adhesion test proved the significant ability of the composite cryogels to adhere to and aggregate platelets. Hemocompatibility and cytocompatibility tests have verified the safety of these cryogels for hemostatic applications. Finally, the material exhibited remarkable in vivo hemostatic performance, achieving clotting times of 64 seconds and 35 seconds when tested in the rat tail amputation model and the liver puncture model, respectively. The experiment results were compared with those of commercial hemostat, Axiostat, and Surgispon, affirming the potential of agar/OBC composite cryogel as a hemostatic dressing material.

Fruit waste-derived cellulose-polyaniline composite for adsorption-coupled reduction of chromium oxyanions

Hexavalent chromium oxyanions, known as potentially toxic micropollutants, exist in the effluents and discharges of metallurgical, electroplating, refractory, chemical, and tanning industries. The exposure of chromium-contaminated water causes severe health hazards. The present work outlines a facile approach to grow polyaniline (PANI) on fruit-waste-derived cellulose (CEL) via oxidative polymerization of aniline; followed by chemical processing with NH4OH to obtain CEL-PANI-EB composites for adsorptive separation-coupled reduction of highly toxic hexavalent chromium oxyanions. The spectroscopic analyses of the CEL-PANI-EB composite before and after adsorption of Cr(VI) oxyanions revealed hydrogen bonding, electrostatic, and complexation as major interactive pathways. The adsorbed hexavalent chromium oxyanions are reduced into Cr(III) species by oxidation of PANI-based benzenoid amine into quinoid imine in the CEL-PANI-EB composite. The adsorption of Cr(VI) oxyanions by the CEL-PANI-EB composite showed negligible effects of other anionic co-pollutants, like NO3- and SO42-. The CEL-PANI-EB composite adsorbed Cr(VI) oxyanions with a removal capacity of 469 mg g-1, based on the Langmuir adsorption isotherm model. The hydroxyl functionalities in cellulose and amine/imine functionalities in PANI facilitate the electrostatic attraction between the CEL-PANI-EB and Cr(VI) oxyanions in an acidic environment beside the hydrogen linkages. The adsorbed Cr(VI) oxyanions are reduced to Cr(III)-based species by the benzenoid amines of PANI, as revealed from the XPS analyses. The CEL-PANI-EB composite showed excellent recyclability and maintained 83.4% adsorption efficiency after seven runs of chromium adsorption-desorption. The current findings reveal the potential of CEL-PANI-EB composites for the adsorptive removal of Cr(VI) oxyanions and their conversion into a lesser toxic form, making them promising materials for wastewater treatment applications.

Fabrication of Pea pods biochar-NH2 (PBN) for the adsorption of toxic Cr6+ ion from aqueous solution

Chromium (Cr) ion is regarded as a particularly hazardous contaminant due to its high toxicity and potential carcinogens. The Cr6+ ions were removed in the current work using a new fabricated low-cost adsorbent called Pea pods biochar-NH2 (PBN). PBN was characterized using BET, BJH, SEM, FTIR, TGA, DSC, XRD, XPS and EDX. The surface area and the pore size of PBN were decreased due to the amination process on the pea pods’ biochar-H2O2 (PBO). Optimized condition of different parameters of Cr6+ ions adsorption by PBN was observed at the pH 1.5, contact time (180 min), starting concentration (100 mg/L), and 0.1 g of PBN. The maximal adsorption capacity (Qm) of PBN is 384.62 mg/g. Different error models were used to test the isotherm models’ results. The mechanism of the adsorption was proposed based on the XPS analysis. The adsorption process had an R2 value of 0.999 as the best fit with the Freundlich isotherm (FIM) and pseudo-second-order kinetic (PSOM) models. These obtained data explored that the generated PBN can be a novel, cost-effective material for the adsorption of Cr6+ ions from an aqueous solution.

The effect of inorganic salt on the morphology and nucleation of polyaniline nanofibers synthesized via self-assembly

Polyaniline (PANI), due to the various and controllable shapes, the environmental stability, the excellent physical and chemical property, has gained significant attention. PANI with abundant morphologies were successfully prepared through adjusting and controlling the state of the initial micelle-like in the micelle-like system composed by aniline and organic acids with relatively weak intermolecular interaction. Although the influence of the inorganic salts on their morphology, including the surface and the diameter, was investigated, the influence of salt on the nucleation of PANI was still unclear. Therefore, PANI nanofibers were fabricated through the addition of inorganic salt such as NaCl, MgSO₄ and AlCl₃ into the micelle-like composed of aniline and D-camphor-10-sulfonic acid. The influence of types and concentration of inorganic salts, doped acids and temperature on PANI was studied by Transmission Electron Microscope (TEM), UV-vis and Fourier Transform Infrared Spectroscopy (FTIR) spectroscopy. In addition, in situ UV-vis and ¹H Nuclear Magnetic Resonance technology (NMR) were applied to observe the process of aniline polymerization, and it was indicated the polymerization rate of aniline changed after the addition of inorganic salt NaCl into the initial solution.

Development of a PANI/Fe(NO3)2 nanomaterial for reactive orange 16 (RO16) dye removal

Polyaniline-iron(II) nitrate was prepared by the polymerization of aniline hydrochloride with Fe(NO₃)₂. The as-prepared materials were characterized for surface area and pore volume and were used to remove the reactive orange 16 (RO16) dye from an aqueous solution. Batch studies were conducted as a function of pH (2-12), adsorbent amount (10-100 mg), initial RO16 concentration (100-300 mg L^-1), contact time (10-240 min), and temperature (303-323 K). RO16 was removed at high speed, and equilibrium was achieved in 80 min. Langmuir (six linear forms, i.e., L-I-VI) and other isotherm models were explored for their applicability. With the maximum adsorption capacity of 508.7267 mg g^-1 and a pH of 4 at 313 K, the adsorption isotherm could be adequately characterised using the Langmuir (L-V) model. The kinetics of the adsorption process were investigated by fitting experimental data to pseudo-second order (PSO) (type-I-VI) and other kinetic models, with the findings indicating that the adsorption closely matched the PSO-I model. For isotherm models, twelve linear error functions were investigated. The absorption process was spontaneous, endothermic, and feasible according to the thermodynamics study (ΔG° = -8.8888 kJ mol^-1, ΔH° = 3.1940 kJ mol^-1, and ΔS° = 39.8749 J mol^-1 K^-1). The phototoxicity studies revealed that the untreated dye was highly toxic compared to the treated dye. It was also shown that the material could be recycled substantially, with an RO16 value of 82.8%. The findings also indicated that the PANI/Fe(NO₃)₂ material was sufficient for RO16 dye adsorption in both model and real water samples.