Engineering sodium alginate-SiO2 composite beads for efficient removal of methylene blue from water

A greener one-pot synthesis of nanostructured SiO2 for the efficient emerging contaminant removal from simulated textile wastewater

Emerging contaminants are a group of chemicals that have the potential to enter the environment and cause potentially adverse effects on the ecosystems and their components. Currently, the interest in achieving the removal of emerging contaminants from water bodies and wastewater has grown considerably, which is reflected in several publications on the synthesis of nanomaterials capable of adsorbing them. Among emerging pollutants, methylene blue (MB) is a widely used model dye for the study of adsorption processes on nanomaterials. In this work, we report a facile and greener one-pot synthesis of SiO2 nanoparticles (SiO2NPs) than the classical Stöber method, involving a cheaper Si source than TEOS, only water as solvent, and shorter reaction times under neutral conditions at room temperature, i.e. a new sol-gel strategy with favorable greenness attributes. A multi-technical characterization of SiO2NPs (XRD, FTIR, UV-vis DR, TEM, SEM, EDX, Z-potential, and N2 adsorption-desorption isotherms at 77 K) confirmed the formation of spherical NPs, with amorphous and polydisperse nature, negatively charged surface, and mesoporous structure. Several batch adsorption experiments of MB were performed by varying pH, contact time, model dye concentration, and SiO2NPs dosage, and the kinetic and thermodynamic behavior of the removal reaction was elucidated. It was determined that the adsorption process followed a pseudo-second-order kinetic model and a Langmuir isotherm model. SiO2NPs showed high efficiency towards MB removal after 30 min of contact time (maximum adsorption capacity = 165.6 mg g-1) and high reusability for up to seven cycles without appreciable loss of adsorption efficiency. In addition, this work reports the first successful application of SiO2NPs as a cationic dye nanoadsorbent under simulated conditions of real textile wastewater (high pH, very high concentration of MB and dissolved salts, and high COD), proving that NPs are suitable for conditioning water resources contaminated with industrial dyes.

Preparation and characterization of zirconium-based metal-organic skeleton composite sodium alginate@SiO2 and its adsorption on methylene blue solution in water

A MOF-based dye adsorbent, sodium alginate@silica@UiO-67 (SA@SiO2@UiO-67) aerogel beads, was prepared by hydrothermal method using sodium alginate@silica (SA@SiO2) as the carrier and zirconium organic skeleton as the nanocrystals for the in-situ growth of MOF multi-sites. The properties of the composite aerogel beads were investigated using SEM, XRD, TGA, FT-IR, BET and zeta potential tests. Langmuir simulation revealed that the composite aerogel beads achieved a maximum methylene blue removal capacity of 1094.04 mg/g at room temperature (298 K). Kinetic analysis showed that methylene blue was physically adsorbed on the composite aerogel beads. The simulations of adsorption isotherms showed that the adsorption surface of the composite aerogel beads was homogeneous, and the adsorption process for MB was a monomolecular layer. Research on thermodynamics revealed that the composite aerogel beads removed MB in an exothermic and spontaneous manner. After six adsorption-desorption cycles, the removal of methylene blue by the composite aerogel beads still reached 71.64 %, and the synergistic effects of multiple mechanisms, such as hydrogen bonding, ion exchange, electrostatic interaction and diffusive mass transfer, jointly promoted the adsorption and enrichment of MB molecules on the surface of the composite aerogel.

Covalently crosslinked carboxymethyl chitosan beads containing SiO2 and ionic polymer for efficient adsorptive removal of methylene blue

The carboxymethyl chitosan (CMCS)-based porous beads are still criticized for their limited number of binding sites, which impairs their efficacy in removing aqueous pollutants. To overcome this challenge, this work introduces the production of covalently crosslinked CMCS-based beads containing SiO2 and poly(2-acrylamido-2-methylpropanesulfonic acid) (PAMPS). The porous composite beads not only possess remarkable stability under acidic conditions, but also have abundant active binding sites for adsorption. By using methylene blue (MB) as a representative pollutant, adsorption experiments have demonstrated that the presence of SiO2 and PAMPS significantly enhances the adsorption performance of the CMCS-based beads. The adsorption behavior aligns with the pseudo-second-order kinetic model and the Langmuir isotherm model, indicating the occurrence of chemical adsorption and monolayer adsorption phenomena. The optimal sample, CCMCS-SiO2@PAMPS, exhibits a maximum adsorption capacity of 606.06, 649.35, and 684.93 mg g-1 at 25, 35, and 45 °C, respectively, as calculated from the Langmuir isotherm model. The effects of pH, ionic strength, and adsorbent dosage on adsorption performance are investigated, and the porous composite beads exhibit robust reusability, maintaining their efficiency even after four adsorption-desorption cycles. The significant findings of this research confirm the superior performance of the functionalized CMCS-based beads for the effective removal of organic dyes from aqueous environments.

Assembly of Chitosan/Caragana Fibers to Construct an Underwater Superelastic 2D Layer-Supported 3D Architecture for Rapid Congo Red Removal

Developing environmentally friendly bulk materials capable of easily and thoroughly removing trace amounts of dye pollutants from water to rapidly obtain clean water has always been a goal pursued by researchers. Herein, a green material with a 3D architecture and with strong underwater rebounding and fatigue resistance ability was prepared by means of the assembly of biopolymer chitosan (CS) and natural caraganate fibers (CKFs) under freezing conditions. The CKFs can randomly and uniformly distribute in the lamellar structure formed during the freezing process of CS and CKFs, playing a role similar to that of "steel bars" in concrete, thus providing longitudinal support for the 3D-architecture material. The 2D layers formed by CS and CKFs as the main basic units can provide the material with a higher strength. The 3D-architecture material can bear the compressive force of a weight underwater for multiple cycles, meeting the requirements for water purification. The underwater compression test shows that the 3D-architecture material can quickly rebound to its original shape after removing the stress. This 3D-architecture material can be used to purify dye-containing water. When its dosage is 3 g/L, the material can remove 99.65% of the Congo Red (CR) in a 50 mg/L dye solution. The adsorption performance of the 3D architecture adsorbent for CR removal in actual water samples (i.e., tap water, seawater) is superior than that of commercial activated carbon. Due to its porous block characteristics, this material can be used for the continuous and efficient treatment of wastewater containing trace amounts of CR dye to obtain pure clean water, meaning that it has great potential for the effective purification of dye wastewater.

A critical review of sodium alginate-based composites in water treatment

The global freshwater crisis is a pressing issue, especially in areas with little rainfall and inner continental regions. The growing attention to water scarcity has induced increased interest in research on advanced water treatment technologies. As an abundant bioactive material in nature, sodium alginate (SA) has been widely used in water management due to its outstanding water absorption and holding ability, reversible swelling property, and pollutant adsorption performance. Building on this, progress made in using various modified forms of SA to access clean water is addressed in this review. Covering studies concern the adsorption and separation of pollutants in wastewater by SA-based absorbents and freshwater harvesting by SA-based collectors. This review explores SA-based composites' composition-structure-construction designs and emphasizes the impact of materials like inorganic materials, functional polymers, and porous matrices and how they can be exploited for water treatment. It also highlights the mechanisms of contaminants adsorption and freshwater desorption of SA-based composites. Finally, the shortcomings and future orientation of SA-based composites are proposed, including performance optimization, structural modification, application expansion, and mechanism in-depth investigation. This review aims to offer a theoretical basis and technical guidance for the use of natural materials to respond to the shortage of freshwater resources.

Production of activated carbon from food wastes (chicken bones and rice waste) by microwave assisted ZnCl2 activation: an optimized process for crystal violet dye removal

A major worldwide challenge that presents significant economic, environmental, and social concerns is the rising generation of food waste. The current work used chicken bones (CB) and rice (R) food waste as alternate precursors for the production of activated carbon (CBRAC) by microwave radiation-assisted ZnCl2 activation. The adsorption characteristics of CBRAC were investigated in depth by removing an organic dye (crystal violet, CV) from an aquatic environment. To establish ideal conditions from the significant adsorption factors (A: CBRAC dosage (0.02-0.12 g/100 mL); B: pH (4-10); and C: duration (30-420), a numerical desirability function of Box-Behnken design (BBD) was utilized. The highest CV decolorization by CBRAC was reported to be 90.06% when the following conditions were met: dose = 0.118 g/100 mL, pH = 9.0, and time = 408 min. Adsorption kinetics revealed that the pseudo-first order (PFO) model best matches the data, whereas the Langmuir model was characterized by equilibrium adsorption, where the adsorption capacity of CBRAC for CV dye was calculated to be 57.9 mg/g. CV adsorption is accomplished by several processes, including electrostatic forces, pore diffusion, π-π stacking, and H-bonding. This study demonstrates the use of CB and R as biomass precursors for the efficient creation of CBRAC and their use in wastewater treatment, resulting in a greener environment.