Insight into the adsorption kinetics, mechanism, and thermodynamics of methylene blue from aqueous solution onto pectin-alginate-titania composite microparticles

Polysaccharide Composite Alginate-Pectin Hydrogels as a Basis for Developing Wound Healing Materials

This article presents materials that highlight the bioengineering potential of polymeric systems of natural origin based on biodegradable polysaccharides, with applications in creating modern products for localized wound healing. Exploring the unique biological and physicochemical properties of polysaccharides offers a promising avenue for the atraumatic, controlled restoration of damaged tissues in extensive wounds. The study focused on alginate, pectin, and a hydrogel composed of their mixture in a 1:1 ratio. Atomic force microscopy data revealed that the two-component gel exhibits greater cohesion and is characterized by the presence of filament-like elements. The dynamic light scattering method indicated that this structural change results in a reduction in the damping of acoustic modes in the gel mixture compared to the component gels. Raman spectroscopy research on these gels revealed the emergence of new bonds between the components' molecules, contributing to the observed effects. The biocompatibility of the gels was evaluated using dental pulp stem cells, demonstrating that all the gels exhibit biocompatibility.

Arsenic pollution remediation mechanism and preliminary application of arsenic-oxidizing bacteria isolated from industrial wastewater

Microbial remediation is vital for improving heavy metal-polluted water. In this work, two bacterial strains, K1 (Acinetobacter gandensis) and K7 (Delftiatsuruhatensis), with high tolerance to and strong oxidation of arsenite [As(III)], were screened from industrial wastewater samples. These strains tolerated 6800 mg/L As(III) in a solid medium and 3000 mg/L (K1) and 2000 mg/L (K7) As(III) in a liquid medium; arsenic (As) pollution was repaired through oxidation and adsorption. The As(III) oxidation rates of K1 and K7 were the highest at 24 h (85.00 ± 0.86%) and 12 h (92.40 ± 0.78%), respectively, and the maximum gene expression levels of As oxidase in these strains were observed at 24 and 12 h. The As(III) adsorption efficiencies of K1 and K7 were 30.70 ± 0.93% and 43.40 ± 1.10% at 24 h, respectively. The strains exchanged and formed a complex with As(III) through the -OH, -CH3, and C]O groups, amide bonds, and carboxyl groups on the cell surfaces. When the two strains were co-immobilized with Chlorella, the adsorption efficiency of As(III) improved (76.46 ± 0.96%) within 180 min, thereby exhibiting good adsorption and removal effects of other heavy metals and pollutants. These results outlined an efficient and environmentally friendly method for the cleaner production of industrial wastewater.

A review on remediation of dye adulterated system by ecologically innocuous "biopolymers/natural gums-based composites"

The mitigation of wastewater exploiting biopolymers/natural gums-based composites is an appealing research theme in today's scenario. The following review presents a comprehensive description of the polysaccharides derived from biopolymers (chitosan, collagen, cellulose, starch, pectin, lignin, and alginate) and natural gums (guar, gellan, carrageenan, karaya, moringa oliefera, tragacanth, and xanthan gum). These biopolymers/natural gums-based composites depicted excellent surface functionality, non-toxicity, economic and environmental viability, which corroborated them as potential candidates in the decontamination process. The presence of -OH, -COOH, and -NH functional groups in their backbone rendered them tailorable for modification/functionalization, and anchor an array of pollutants via electrostatic interaction, hydrogen bonding, and Van der Waals forces. Further, due to these functional moieties, these bio-based composites revealed an excellent adsorption capacity than conventional adsorbents. This review provides an overview of the classification of biopolymers/natural gums based on their origin, different ways of their modification, and the remediation of dye-contaminated aqueous environments employing diverse bio-based adsorbents. The isotherm, kinetic modelling along with thermodynamics of the adsorption process is discussed. Additionally, the reusable efficacy of these bio-adsorbents is reviewed.

Aquatic Bacteria Rheinheimera tangshanensis New Ability for Mercury Pollution Removal

To explore the strong tolerance of bacteria to Hg pollution, aquatic Rheinheimera tangshanensis (RTS-4) was separated from industrial sewage, with a maximum Hg(II) tolerant concentration of 120 mg/L and a maximum Hg(II) removal rate of 86.72 ± 2.11%, in 48 h under optimum culture conditions. The Hg(II) bioremediation mechanisms of RTS-4 bacteria are as follows: (1) the reduction of Hg(II) through Hg reductase encoded by the mer operon; (2) the adsorption of Hg(II) through the production of extracellular polymeric substances (EPSs); and (3) the adsorption of Hg(II) using dead bacterial biomass (DBB). At low concentrations [Hg(II) ≤ 10 mg/L], RTS-4 bacteria employed Hg(II) reduction and DBB adsorption to remove Hg(II), and the removal percentages were 54.57 ± 0.36% and 45.43 ± 0.19% of the total removal efficiency, respectively. At moderate concentrations [10 mg/L < Hg(II) ≤ 50 mg/L], all three mechanisms listed above coexisted, with the percentages being 0.26 ± 0.01%, 81.70 ± 2.31%, and 18.04 ± 0.62% of the total removal rate, respectively. At high concentrations [Hg(II) > 50 mg/L], the bacteria primary employed EPS and DBB adsorption to remove Hg(II), where the percentages were 19.09 ± 0.04% and 80.91 ± 2.41% of the total removal rate, respectively. When all three mechanisms coexisted, the reduction of Hg(II) occurred within 8 h, the adsorption of Hg(II) by EPSs and DBB occurred within 8-20 h and after 20 h, respectively. This study provides an efficient and unused bacterium for the biological treatment of Hg pollution.

Dynamics of Diffusion- and Immobilization-Limited Photocatalytic Degradation of Dyes by Metal Oxide Nanoparticles in Binary or Ternary Solutions

Photocatalytic degradation employing metal oxides, such as TiO2 nanoparticles, as catalysts is an important technique for the removal of synthetic dyes from wastewater under light irradiation. The basic principles of photocatalysis of dyes, the effects of the intrinsic photoactivity of a catalyst, and the conventional non-fundamental factors are well established. Recently reported photocatalysis studies of dyes in single, binary, and ternary solute solutions opened up a new perspective on competitive photocatalytic degradation of the dyes. There has not been a review on the photocatalytic behavior of binary or ternary solutions of dyes. In this regard, this current review article summarizes the photocatalytic behavior of methylene, rhodamine B, and methyl orange in their binary or ternary solutions. This brief overview introduces the importance of the dynamics of immobilization and reactivity of the dyes, the vital roles of molecular conformation and functional groups on their diffusion onto the catalyst surface, and photocatalytic degradation, and provides an understanding of the simultaneous photocatalytic processes of multiple dyes in aqueous systems.

Dynamics and thermodynamics for competitive adsorptive removal of methylene blue and rhodamine B from binary aqueous solution onto durian rind

Concurrent adsorptive removal of methylene blue (MB) and rhodamine B (RhB) onto durian rind (DR) agricultural waste, from an aqueous binary solution as a model of wastewater containing multiple synthetic dyes, was investigated. The concurrent adsorption of the dyes followed pseudo-second-order kinetics. The adsorption isotherm was well simulated by the Langmuir model, implying a monolayer adsorption to the surface with a homogeneous binding energy. The adsorption process was governed by external mass transfer through two-step intraparticle diffusion of the dyes onto the adsorbent surface. The adsorption efficiency of MB (96.4%) is much higher than that of RhB (56.3%). This is attributed to the higher rate constant for the adsorption of MB (0.348 g mg^-1 min^-1) as compared to that of RhB (0.151 g mg^-1 min^-1). The adsorption behavior suggested that the two cationic dyes in the binary solution diffused and adsorbed independently and randomly onto the DR surface. The adsorption capacity of MB and RhB in the binary solution (47.4 mg g^-1 and 32.9 mg g^-1, respectively) is lower than those of their single solute solutions (93.3 mg g^-1 and 62.8 mg g^-1, respectively), suggesting a competitive effect in their concurrent adsorption. This was confirmed based on the adsorption characteristics of the binary solution with different molar ratios. The competitive effect was attributed to either non-interactive or repulsive electrostatic interactions between the positively charged dyes in the binary system. The domination of MB is attributed to its smaller molecular size, higher planarity, and faster adsorption kinetics compared with RhB.

Adsorption Behavior and Dynamic Interactions of Anionic Acid Blue 25 on Agricultural Waste

In this study, adsorption characteristics of a negatively charged dye, Acid Blue 25 (AB25), on pomelo pith (PP) was studied by varying the adsorption parameters, with the aim of evaluating the adsorption mechanism and establishing the role of hydrogen bonding interactions of AB25 on agricultural wastes. The kinetics, intraparticle diffusion, mechanism, and thermodynamics of the AB25 adsorption were systematically evaluated and analyzed by pseudo-first-order and pseudo-second-order kinetic models, the Weber–Morris intraparticle and Boyd mass transfer models, the Langmuir, Freundlich, Dubinin–Radushkevich, and Temkin isotherm models, and the Van’t Hoff equation. It was found that AB25 adsorption followed pseudo-second-order kinetics, governed by a two-step pore-volume intraparticle diffusion of external mass transfer of AB25 onto the PP surface. The adsorption process occurred spontaneously. The adsorption mechanism could be explained by the Langmuir isotherm model, and the maximum adsorption capacity was estimated to be 26.9 mg g−1, which is comparable to many reported adsorbents derived from agricultural wastes. Changes in the vibrational spectra of the adsorbent before and after dye adsorption suggested that AB25 molecules are bound to the PP surface via electrostatic and hydrogen bonding interactions. The results demonstrated that the use of pomelo pith, similar to other agricultural wastes, would provide a basis to design a simple energy-saving, sustainable, and cost-effective approach to remove negatively charged synthetic dyes from wastewater.

Pectin Microspheres: Synthesis Methods, Properties, and Their Multidisciplinary Applications

There is great contemporary interest in using cleaner technologies through green chemistry and utilizing biopolymers as raw material. Pectin is found on plant cell walls, and it is commonly extracted from fruit shells, mostly apples or citrus fruits. Pectin has applications in many areas of commercial relevance; for this reason, it is possible to find available information about novel methods to transform pectin and pursuing enhanced features, with the structuring of biopolymer microspheres being highly cited to enhance its activity. The structuring of polymers is a technique that has been growing in recent decades, due to its potential for diverse applications in various fields of science and technology. Several techniques are used for the synthesis of microspheres, such as ionotropic gelation, extrusion, aerosol drying, or emulsions, with the latter being the most commonly used method based on its reproducibility and simplicity. The most cited applications are in drug delivery, especially for the treatment of colon diseases and digestive-tract-related issues. In the industrial field, it is used for protecting encapsulated compounds; moreover, the environmental applications mainly include the bioremediation of toxic substances. However, there are still many possibilities for expanding the use of this biopolymer in the environmental field.

Structural analysis and dye removal behavior of amorphous titania embedded poly(vinyl butyral) hybrid fiber

This study reports on the efficient methylene blue (MB) dye removal properties of a polyvinyl butyral (PVB)-amorphous titania (amTiO₂) hybrid fiber (PVB-amTiO₂F) made by air-gap spinning in acetone solvent. The successful fabrication of PVB-amTiO₂F was confirmed by employing Fourier transform infrared, scanning electron microscopy, X-ray photoelectron spectroscopy, thermogravimetric analysis, and energy dispersive X-ray measurement. Batch experiments were used to examine the cationic MB dye adsorption performance in the dark. The observed data showed that the developed PVB-amTiO₂F exhibited moderate adsorption efficiency (68-70%) which is comparable to other amorphous titania-rich adsorbents. The adsorption kinetics was well fitted with a pseudo-second-order model, suggesting that adsorption is mainly led by chemisorption. In addition, the MB degradation properties under visible light were also studied afterwards. A possible adsorption mechanism is discussed. Moreover, the as-fabricated fiber exhibited average to good reusability after 6 cycles. Only cationic MB dye solution was able to demonstrate such properties.

Synergistic effect in concurrent removal of toxic methylene blue and acid red-1 dyes from aqueous solution by durian rind: kinetics, isotherm, thermodynamics, and mechanism

In the present study, a synergistic effect between cationic methylene blue (MB) and anionic acid red 1 (AR1) on their concurrent adsorptive removal from aqueous binary solution onto durian rind (DR) was systematically investigated in batch mode across different parameters. The concurrent adsorption was pseudo-second-order kinetics and followed the Langmuir isotherm model, similar to their respective single component. The kinetics and intraparticle diffusion analyses demonstrated that the adsorption rate of MB was a 15-fold faster than AR1, and mass transports were governed by a combination of intraparticle and film diffusion. The synergistic effect was evidenced by an enhanced adsorption efficiency of AR1 from 27 to 42%, while that of MB was almost unchanged (97-98%). By changing the molar ratios of MB and AR1, it was found that the maximum adsorption capacity of MB and AR1 was 249 and 200 mg g^-1, respectively, in the binary system higher compared with those in their respective single system (108 and 16 mg g^-1). Overall data indicated that the synergistic effect was due to electrostatic interactions between cationic and anionic synthetic dyes, supported by negatively charged DR surface, leading to the formation of their stacking layers on the adsorbent surface. Novelty statement: A synergistic effect in concurrent adsorptive removal of synthetic dyes from multicomponent wastewater remains a critical research challenge. We believed that electrostatic interaction between ionic dyes could be explored to enhance their removal efficiency. This report is the first time that such a synergistic effect between cationic methylene blue (MB) and anionic acid red 1 (AR1) on their concurrent adsorption from aqueous binary system is systematically investigated. The kinetics, isotherm, thermodynamics, and mechanism of the concurrent adsorption of MB and AR1 attributed to the synergistic effect are elucidated in detail.