Preparation of Bio-Based Aerogel and Its Adsorption Properties for Organic Dyes

Innovative biopolyelectrolytes-based technologies for wastewater treatment

Developing eco-friendly, cost-effective, and efficient methods for treating water pollutants has become paramount in recent years. Biopolyelectrolytes (BPEs), comprising natural polymers like chitosan, alginate, and cellulose, have emerged as versatile tools in this pursuit. This review offers a comprehensive exploration of the diverse roles of BPEs in combating water contamination, spanning coagulation-flocculation, adsorption, and filtration membrane techniques. With ionizable functional groups, BPEs exhibit promise in removing heavy metals, dyes, and various pollutants. Studies showcase the efficacy of chitosan, alginate, and pectin in achieving notable removal rates. BPEs efficiently adsorb heavy metal ions, dyes, and pesticides, leveraging robust adsorption capacity and exceptional mechanical properties. Furthermore, BPEs play a pivotal role in filtration membrane techniques, offering efficient separation systems with high removal rates and low energy consumption. Despite challenges related to production costs and property variability, their environmentally friendly, biodegradable, renewable, and recyclable nature positions BPEs as compelling candidates for sustainable water treatment technologies. This review delves deeper into BPEs' modification and integration with other materials; these natural polymers hold substantial promise in revolutionizing the landscape of water treatment technologies, offering eco-conscious solutions to address the pressing global issue of water pollution.

Ag Nanoparticles Deposited onto BaTiO3 Aerogel for Highly Efficient Photodegradation

Given the increasingly severe environmental problems caused by water pollution, the degradation of organic dyes can be effectively achieved through the utilization of photocatalysis. In this work, metal alkoxides and a combination of alcohol/hydrophobic solvents are employed to prepare BaTiO3 aerogels via a liquid-phase and template-free synthetic route. The preparation process of the aerogels solely entails facile agitation and supercritical drying, eliminating the need for additional heat treatment. The binary solvent of ethanol and toluene is identified as the optimal choice, resulting in a significantly enhanced surface area (up to 223 m2/g) and an abundant pore structure of BaTiO3 aerogels compared to that of the BaTiO3 nanoparticles. Thus, the removal efficiency of the BaTiO3 aerogel sample for MO is nearly twice as high as that of the BaTiO3 nanoparticles sample. Noble metal Ag nanoparticles' deposition onto the BaTiO3 aerogel surface is further achieved via the photochemical deposition method, which enhances the capture of photogenerated electrons, thereby ensuring an elevated level of photocatalytic efficiency. As a result, Ag nanoparticles deposited on BaTiO3 aerogel can degrade MO completely after 40 min of illumination, while the corresponding aerogel before modification can only remove 80% of MO after 60 min. The present work not only complements the preparatory investigation of intricate aerogels but also offers a fresh perspective for the development of diverse perovskite aerogels with broad applications.

Promising adsorbent for dye detoxification: Exploring the potential of chitosan sodium carboxymethylcellulose silk fibroin aerogel

The main goal of this study is to create a CS-CMC-SF aerogel consisting of chitosan sodium carboxymethylcellulose and silk fibroin. The aerogel is designed to remove types of dyes from water while also being environmentally friendly. This innovative adsorbent has been optimized for extracting both cationic and anionic dyes from solutions. It incorporates chitosan sodium carboxymethylcellulose and silk filament fibers to enhance its strength. Experimental data illustrates that the CS-CMC-SF aerogel possesses remarkable adsorption capabilities - 5461.77 mg/g for Congo Red (CR), 2392.83 mg/g for Malachite Green (MG), and 1262.20 mg/g for Crystal Violet (CV). A kinetic study aligns with the pseudo-second-order kinetic model suggesting predominant chemisorption phenomena occur during adsorption process. Isotherm analysis further identifies multilayered adsorption occurring on irregularly shaped surfaces of the aerogel while thermodynamic assessments validate exothermic and spontaneous characteristics inherent in its absorption mechanism. Several analytical methods such as SEM, FT-IR, XRD, and XPS were employed to examine physicochemical attributes tied to this unique material design conceptually; identifying mechanisms including pore filling, π-π interactions, ion exchange activity, electrostatic connections along with hydrogen bonding inducing overall superior performance output. Furthermore substantial soil biodegradability alongside compostable features associated with our proposed CS-CMC-SF aerogels established it's potential suitability within applications demanding sustainable options thereby validating its underlying ecological credibility.

Nanostructured Cellulose-Based Aerogels: Influence of Chemical/Mechanical Cascade Processes on Quality Index for Benchmarking Dye Pollutant Adsorbents in Wastewater Treatment

(1) Background: Nanostructured cellulose has emerged as an efficient bio-adsorbent aerogel material, offering biocompatibility and renewable sourcing advantages. This study focuses on isolating (ligno)cellulose nanofibers ((L)CNFs) from barley straw and producing aerogels to develop sustainable and highly efficient decontamination systems. (2) Methods: (Ligno)cellulose pulp has been isolated from barley straw through a pulping process, and was subsequently deconstructed into nanofibers employing various pre-treatment methods (TEMPO-mediated oxidation process or PFI beater mechanical treatment) followed by the high-pressure homogenization (HPH) process. (3) Results: The aerogels made by (L)CNFs, with a higher crystallinity degree, larger aspect ratio, lower shrinkage rate, and higher Young's modulus than cellulose aerogels, successfully adsorb and remove organic dye pollutants from wastewater. (L)CNF-based aerogels, with a quality index (determined using four characterization parameters) above 70%, exhibited outstanding contaminant removal capacity over 80%. The high specific surface area of nanocellulose isolated using the TEMPO oxidation process significantly enhanced the affinity and interactions between hydroxyl and carboxyl groups of nanofibers and cationic groups of contaminants. The efficacy in adsorbing cationic dyes in wastewater onto the aerogels was verified by the Langmuir adsorption isotherm model. (4) Conclusions: This study offers insights into designing and applying advanced (L)CNF-based aerogels as efficient wastewater decontamination and environmental remediation platforms.

Polyaniline as a Nitrogen Source and Lignosulfonate as a Sulphur Source for the Preparation of the Porous Carbon Adsorption of Dyes and Heavy Metal Ions

Using agricultural and forestry wastes as raw materials, adsorbent materials were prepared for dye adsorption in wastewater, which can minimize the environmental load and fully realize sustainability by treating waste with waste. Taking lignosulfonate as a raw material, due to its molecular structure having more reactive groups, it is easy to form composite materials via a chemical oxidation reaction with an aniline monomer. After that, using a sodium lignosulfonate/polyaniline composite as the precursor, the activated high-temperature pyrolysis process is used to prepare porous carbon materials with controllable morphology, structure, oxygen, sulfur, and nitrogen content, which opens up a new way for the preparation of functional carbon materials. When the prepared O-N-S co-doped activated carbon materials (SNC) were used as adsorbents, the adsorption study of cationic dye methylene blue was carried out, and the removal rate of SNC could reach up to 99.53% in a methylene blue solution with an initial concentration of 100 mg/L, which was much higher than that of undoped lignocellulosic carbon materials, and the kinetic model conformed to the pseudo-second-order kinetic model. The adsorption equilibrium amount of NC (lignosulfonate-free) and SNC reached 478.30 mg/g and 509.00 mg/g, respectively, at an initial concentration of 500 mg/L, which was consistent with the Langmuir adsorption isothermal model, and the adsorption of methylene blue on the surface of the carbon material was a monomolecular layer. The adsorption of methylene blue dye on the carbon-based adsorbent was confirmed to be a spontaneous and feasible adsorption process by thermodynamic parameters. Finally, the adsorption of SNC on methylene blue, rhodamine B, Congo red, and methyl orange dyes were compared, and it was found that the material adsorbed cationic dyes better. Furthermore, we also studied the adsorption of SNC on different kinds of heavy metal ions and found that its adsorption selectivity is better for Cr3+ and Pb2+ ions.

Adsorption of Safranin O Dye by Alginate/Pomegranate Peels Beads: Kinetic, Isotherm and Thermodynamic Studies

Water pollution is regarded as a dangerous problem that needs to be resolved right away. This is largely due to the positive correlation between the increase in global population and waste production, especially food waste. Hydrogel beads based on sodium alginate (Alg) and pomegranate fruit peels (PP) were developed for the adsorption of Safranin O dye (SO) in aqueous solutions. The obtained Alg-PP beads were widely characterized. The effects of the contact time (0-180 min), initial concentration (10-300 mg/L), initial pH (2-10), adsorbent dosage (1-40 g/L) and the temperature (293-333 K) were investigated through batch tests. The data proved that the adsorption kinetics of SO reached equilibrium within 30 min and up to 180 min. The dye adsorption is concentration dependent while a slight effect of pH was observed. The adsorption data of SO onto synthesized beads follow the pseudo second-order model. The experimental data fitted very well to Langmuir model with correlation factor of 0.92 which demonstrated the favourable nature of adsorption. The maximum adsorption capacity of Alg-PP could reach 30.769 mg/g at 293 K. Calculation of Gibbs free energy and enthalpy indicated that adsorption of SO onto Alg-PP is spontaneous (negative ΔG) and endothermic (ΔH = 9.30 kJ/mol). Analysis of diffusion and mass transport phenomena were presented. The removal efficiency was found to be 88% at the first cycle and decreased to 71% at the end of the seventh cycle. The reported results revealed that the Alg-PP beads could be used as a novel natural adsorbent for the removal of high concentrated solutions of Safranin O which is a cationic dye from liquid affluents and as future perspective, it can be used to remove various pollutants from wastewater.

Dual Network Hydrogel with High Mechanical Properties, Electrical Conductivity, Water Retention and Frost Resistance, Suitable for Wearable Strain Sensors

With the progress of science and technology, intelligent wearable devices have become more and more popular in our daily life. Hydrogels are widely used in flexible sensors due to their good tensile and electrical conductivity. However, traditional water-based hydrogels are limited by shortcomings of water retention and frost resistance if they are used as the application materials of flexible sensors. In this study, the composite hydrogels formed by polyacrylamide (PAM) and TEMPO-Oxidized Cellulose Nanofibers (TOCNs) are immersed in LiCl/CaCl2/GI solvent to form double network (DN) hydrogel with better mechanical properties. The method of solvent replacement give the hydrogel good water retention and frost resistance, and the weight retention rate of the hydrogel was 80.5% after 15 days. The organic hydrogels still have good electrical and mechanical properties after 10 months, and can work normally at −20 °C, and has excellent transparency. The organic hydrogel show satisfactory sensitivity to tensile deformation, which has great potential in the field of strain sensors.

Spherical Attapulgite/Silica Aerogels Fabricated via Different Drying Methods with Excellent Adsorption Performance

Dye wastewater has caused great harm to the environment, which is an urgent problem to be solved. As typical three-dimensional porous materials, aerogels have attracted great interest in dye wastewater treatment. In this work, spherical attapulgite/silica (ATP/SiO₂) gels were initially prepared by easily scalable sol-gel dripping methods and then dried to aerogels with three drying techniques, namely, supercritical CO₂ drying (SCD), freeze-drying (FD), and ambient pressure drying (APD). The effect of the drying techniques and heat-treated temperature on the physical characteristic, morphological properties, microstructure, and chemical structure of the spherical ATP/SiO₂ aerogels were investigated. The macroscopic morphology of the spherical ATP/SiO₂ aerogels was homogeneous and integrated without local cracking. The average pore diameter and specific surface area of the spherical ATP/SiO₂ aerogels prepared by the three drying techniques were in the range of 6.8-8.6 nm and 218.5-267.4 m²/g, respectively. The heat treatment temperature had a significant effect on the pore structure and the wetting properties of the aerogels. The 600 °C heat-treated aerogels were subjected to adsorption tests in methylene blue (MB) solution (60 mg/g, 100 mL), which exhibited a great adsorption capacity of 102.50 mg/g. Therefore, the resulting spherical ATP/SiO₂ aerogels possessed multipath preparation and exhibited an efficient adsorption performance, with the potential to be applied as an adsorbent for dye wastewater.

Biosorbent Based on Poly(vinyl alcohol)-Tricarboxi-Cellulose Designed to Retain Organic Dyes from Aqueous Media

Methylene Blue, a cationic dye, was retained from aqueous solutions using a novel biosorbent made of poly(vinyl alcohol) reticulated with tricarboxi-cellulose produced via TEMPO oxidation (OxC25). The study of the Methylene Blue biosorption process was performed with an emphasis on operational parameters that may have an impact on it (such as biosorbent concentration, pH of the aqueous media, and temperature). The current study focused on three areas: (i) the physic-chemical characterization of the biosorbent (scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX)); (ii) biosorption data modeling to determine the quantitative characteristic parameters employing three equilibrium isotherms (Langmuir, Freundlich, and Dubinin-Radushkevich-DR); and (iii) the study of temperature influence. The results of the study showed that the Langmuir model provided a good fit for the experimental data of biosorption, realizing a maximum capacity of 806.45 mg/g at 20 °C. The free energy of biosorption (E) evaluated by the DR equation was in the range of 6.48-10.86 KJ/mol. The values of the thermodynamic parameters indicated an endothermic process because the free Gibbs energy ranged from -9.286 KJ/mol to -2.208 KJ/mol and the enthalpy was approximately -71.686 KJ/mol. The results obtained encourage and motivate the further study of this biosorption process by focusing on its kinetic aspects, establishing the biosorption's controlled steps, identifying the mechanism responsible for the retention of textile dyes presented in moderate concentration in aqueous media, and studying the biosorption process in a dynamic regime with a view to applying it to real systems.