Congo Red Molecules Research Articles

Dual-Functional Passivation Agent of Natural Dye Congo Red For Enhanced Carbon-Based Perovskite Solar Cells.

Carbon-based perovskite solar cells (C-PSCs) have acquired broad interest due to their superior stability and lower cost compared with metal-based perovskite solar cells (M-PSCs). However, the presence of perovskite defects greatly limits the power conversion efficiency (PCE) and long-term stability of C-PSCs. Herein, a natural dye Congo red molecule containing dual-functional groups of amino and sulfonic acids is first used as a surface passivation agent to treat the surface of perovskite films. High-quality perovskite films with reducing surface defect density and inhibiting nonradiative recombination are obtained. It is shown that the Congo red molecules not only effectively interact with the perovskite, enhancing the crystallization and enlarging the crystal size, but also demonstrate positive contribution for light harvesting in the visible range. The maximum PCE of 16.22% is achieved at the optimal concentration of 0.2 mg/mL Congo red, which is much higher than 13.57% for the control device. After 840 h of storage at 30-40% relative humidity at room temperature, the unencapsulated C-PSCs can still maintain a high initial performance of 87.21% compared with 43.26% for the control cells.

Computational supported experimental insights in adsorption of Congo Red using ZnO/doped ZnO in aqueous solution

The rapid growth of industrialisation has led to the discharge of harmful effluents into water bodies, severely disrupting the balance of ecosystems. The detection and removal of dyes from wastewater remains a significant challenge. In this study, we report the synthesis of zinc oxide (ZnO) and its doped derivatives through a facile chemical method, followed by comprehensive characterisation and analysis to assess their potential in various applications. The structural properties of the synthesised materials were confirmed by X-ray diffraction (XRD), which verified their crystalline nature and phase purity. Morphological analysis using field emission scanning electron microscopy (FE-SEM) coupled with energy dispersive X-ray analysis (EDAX) revealed well-defined nanostructures and uniform elemental distribution. The adsorption ability of the synthesized adsorbents was investigated through electrochemical methods, cyclic voltammetry and Tafel plots, which demonstrated enhanced conductivity and charge transfer characteristics. Additionally, theoretical studies through molecular modelling and molecular dynamic simulations were employed to elucidate the interactions between Congo red molecules and the surface of the synthesized compounds. Adsorption experiments were conducted to evaluate the efficacy of ZnO and its doped variants as adsorbents. To investigate any structural or functional changes after dye adsorption FTIR and XRD were compared, provided a deeper insight into the adsorption mechanism. This multi-faceted approach highlights the potential of ZnO-based materials for effective wastewater treatment and other environmental applications.

Rapid adsorptive removal of congo red using Cu/Fe/Al mixed metal oxides obtained from layered double hydroxide nanomaterial: Performance and optimization evaluation using BBD-RSM approach

This work utilized a one-pot synthesis method to synthesize Cu/Fe/Al mixed metal oxide (MMO) from layered double hydroxide (LDH) calcination. The adsorption potentials of Cu/Fe/Al LDH and Cu/Fe/Al MMOs were evaluated using Congo Red (CR) aqueous solution. Various advanced techniques were used to characterize the synthesized nanomaterial. XRD confirmed the successful synthesis of trimetallic carbonate intercalated LDH and MMO, while FE-SEM revealed their flaky morphology. EDX and FT-IR analyses supported the dye removal mechanism, showing that MMOs had greater adsorptive removal of CR molecules than LDH. This was primarily due to the MMOs' larger surface area and microporous structure (132 m²/g) which favoured greater adsorption. The adsorption kinetics reveal that the adsorptive removal of CR on LDH and MMOs follows a pseudo-second-order reaction. Moreover, as predicted by Freundlich the maximum adsorptive removal was obtained by LDH-derived MMO (96%) which was higher than the LDH (90%). The thermodynamics indicates that adsorption was exothermic and thus more favorable at room temperature. In addition, the Box-Behnken Design (BBD) was adopted for Response Surface Methodology (RSM) due to its simplicity in analysis and effectiveness in systematically evaluating the impact of pH, dosage of adsorbent, dye concentration, contact period, and temperature variables. The pHzpc of 7.9 indicated that lower pH enhances adsorption, and a +5.1 mV charge on the MMO surface, measured by zeta potential, supported electrostatic interaction with the anionic dye. Lastly, LDH and LDH-derived MMO were regenerated using 1 M NaOH and effectively reused for up to 5 cycles. MMOs demonstrated superior reusability compared to LDH for anionic dye removal. Thus, the synthesised Cu/Fe/Al MMO, with its large surface area, offers a superior adsorbent for removing organic pollutants.

Dual cross-linked magnetic gelatin/carboxymethyl cellulose cryogels for enhanced Congo red adsorption: Experimental studies and machine learning modelling

To achieve highly efficient and environmentally degradable adsorbents for Congo red (CR) removal, we synthesized a dual-network nanocomposite cryogel composed of gelatin/carboxymethyl cellulose, loaded with Fe3O4 nanoparticles. Gelatin and sodium carboxymethylcellulose were cross-linked using transglutaminase and calcium chloride, respectively. The cross-linking process enhanced the thermal stability of the composite cryogels. The CR adsorption process exhibited a better fit to the pseudo-second-order model and Langmuir model, with maximum adsorption capacity of 698.19 mg/g at pH of 7, temperature of 318 K, and initial CR concentration of 500 mg/L. Thermodynamic results indicated that the CR adsorption process was both spontaneous and endothermic. The performance of machine learning model showed that the Extreme Gradient Boosting model had the highest test determination coefficient (R2 = 0.9862) and the lowest root mean square error (RMSE = 10.3901 mg/g) among the 6 models. Feature importance analysis using SHapley Additive exPlanations (SHAP) revealed that the initial concentration had the greatest influence on the model’s prediction of adsorption capacity. Density functional theory calculations indicated that there were active sites on the CR molecule that can undergo electrostatic interactions with the adsorbent. Thus, the synthesized cryogels demonstrate promising potential as adsorbents for dye removal from wastewater.

Congo red stitched covalent organic framework membrane for dye separation

Covalent organic framework (COF) membranes have shown great potential in dyes’ separation. However, COFs are difficult to form large-area and highly crystalline membranes, therefore there normally exists crystal and stacking defects in COF membranes, impairing their rejection performance. Herein, we discovered the prepared COF-TATP membranes have exceptional high rejection to Congo red (CR) solution. Further study showed the presence of small proportion of CR in other dye solutions also could enhance the rejection to those dyes. 3:100 CR/Brilliant blue R250 (BB) solution could obtain 99.81% rejection to BB. Characterizations indicated CR molecules could well merged into the COF layer and strongly bonded with its N/O groups via plentiful hydrogen bonds. Inspired by the finding, we proposed a strategy of using CR to stitch the defects in COF layer. Specifically, CR was embedded into and then chemically crosslinked with COF-TATP layer by glutaraldehyde to prepare LCR-TATP-NH2CS/nylon membranes. The membranes showed obviously enhanced rejection to all dyes tested, typically BB rejection of 99.75%. It also could selectively separate BB/Methyl orange mixed solutions. This study reveals some insights into dyes’ behavior on COF membranes, and provides a simple and feasible strategy for stitching COF membranes’ defects to enhance their performance.

Dendrophthoe falcata extract mediated Fe3O4 nanoparticles: A functional agent for dye degradation and inflammation mitigation

The synthesis of metal oxide nanoparticles through green methods using plant extracts has garnered significant interest for their sustainable and multifunctional applications. In this study, the leaf extracts of Dendrophthoe falcata (D'falcata), a medicinal plant known for its rich phytochemical composition was successfully utilized as a reducing and stabilizing agent to synthesize Fe3O4 nanoparticles through a co-precipitation method. The D'falcata-mediated Fe3O4 nanoparticles were characterized using XRD, FTIR, UV–vis, SEM, EDAX, and TEM. The prepared nanoproduct was employed to decompose Congo red dye molecules through photocatalysis. XRD and FTIR analyses confirmed the cubic spinel phase of Fe3O4 nanoparticles and the Fe-O peak around 600 cm-1, while the UV–vis spectrum exhibited an absorption peak around 350 nm. Morphological studies revealed that the synthesized D'Fe3O4 nanoparticles were slightly agglomerated and ranged in size from 25 to 35 nm. The EDAX profile confirmed the presence of expected elements like Fe, O, and N in the final product. VSM studies indicated that D'Fe3O4 displayed paramagnetic behavior. Moreover, the anti-inflammatory assay demonstrated its potential for tumor therapy, with a percentage inhibition of 95 %, surpassing the standard diclofenac sodium (89 %). The smaller size of the D'falcata-mediated Fe3O4 nanoparticles also makes them a viable option for magnetic resonance imaging. Furthermore, photocatalytic studies showed the increase in dye degradation efficiency over the time. The findings from XRD, SEM, FTIR, and VSM analyses were well corroborated, highlighting the enhanced photocatalytic and anti-inflammatory activities of the synthesized D'Fe3O4 sample.

Fabrication of Bi0.90Sm0.1Fe0.97Cr0.03O3@PANI core-shell and improvement of its photocatalyst properties

Bi0.90Sm0.1Fe0.97Cr0.03O3@PANI core-shell structures were made by a two-step method, first, bismuth ferrite nanoparticles by hydrothermal method and then, aniline core-shell by co-precipitation method. The bismuth ferrite (BFO) XRD pattern showed no impurities of Sm, Cr, or their compounds in the samples, indicating that Sm+3 and Cr+3 had been replaced in the BFO structure. The XRD pattern of the Bi0.90Sm0.1Fe0.97Cr0.03O3@PANI core-shell shows all peaks of Bi0.90Sm0.1Fe0.97Cr0.03O3 composition with lower intensity, as a result, the Bi0.90Sm0.1Fe0.97Cr0.03O3 composition is phase single. This lower intensity is attributed to the presence of amorphous polyaniline in the core-shell structure. Since there is in the FT-IR spectrum of the Bi0.90Sm0.1Fe0.97Cr0.03O3@PANI core-shell, characteristic peaks of both polyaniline and bismuth ferrite simultaneously so, the FT-IR spectrum of the Bi0.90Sm0.1Fe0.97Cr0.03O3@PANI core-shell is a perovskite structure. The synthesized samples exhibit weak magnetic properties and behave as a paramagnetic material. The absorption capability of core-shell compared to core nanoparticles has increased in the visible region, and this enhancement is attributed to the influence of the presence of polyaniline. All the peaks in the UV–visible absorption spectrum characterize the nano-sized bismuth ferrite and polyaniline in the UV–visible spectrum of the core-shell. The intensity of the photoluminescence spectrum in the doped sample is significantly higher compared to the core-shell sample. This indicates a much faster recombination rate in the doped nanoparticles compared to the core-shell nanocomposite. The doping of the core with Cr and Sm elements, as well as the coating of the core with a polymeric shell, has led to an increase in the degradation rate of the red dye. We also found that shell thickness plays a vital role in dye degradation efficiency and photocatalytic performance. The Bi0.90Sm0.1Fe0.97Cr0.03O3@PANI core-shell exhibits significant photocatalytic activity under visible light. The photocatalytic studies show that the best sample is Bi0.9Sm0.1Fe0.97Cr0.03O3@PANI core-shell with aniline concentration of 0.2 mL and a pH = 2 which was able to destroy 100 % of Congo red dye molecules.

One‐pot green approach for rapid and effective anionic dye remediation: encapsulation within alginate nanocapsules

AbstractBACKGROUNDThe encapsulation technique was applied to efficiently eliminate Congo red (CR) from aqueous solutions. During the ionotropic gelation between calcium (Ca2+) ions and alginate (AL), CR was effectively entrapped within the AL nanocapsules in a one‐step process. Suitable conditions for efficient CR removal via encapsulation were revealed by the systematic optimization of parameters including pH, time and stirring speed, etc.RESULTSAccording to the experimental observations, the stirring rate and temperature were found to have an insignificant effect on the encapsulation of CR molecules. When the pH value of the medium was 3, the highest level of encapsulation efficiency was achieved in a period of 15 min. At a preliminary CR concentration of 2000 mg L−1 and pH 3, the encapsulation efficiency was calculated at ≈98.9%, with an encapsulation capacity of 2800 mg dye g−1 AL. The zeta potential values of AL and CR/AL nanocapsules were determined to be +7.05 eV and −14.9 eV, respectively, and the results showed that the particles tended to agglomerate. TEM micrographs also showed that the nanocapsules were nanosized and agglomerated. Soil and UV degradation studies showed that the dye‐entrapped nanocapsules degraded remarkably. These results highlighted the great potential of encapsulation for dye removal in economical and practical applications.CONCLUSIONEncapsulation was confirmed to be an economical and practical technique for effectively eliminating CR from aqueous solutions. Under UV light irradiation, the dye molecules entrapped within alginate nanocapsules displayed photodegradation. © 2024 Society of Chemical Industry (SCI).

A graft-modified sponge with COFs for wastewater treatment and iodine adsorption

Azo dyes, used in large quantities in drinks, have become a threat to human health. In the treatment of dyes, the method of chemical adsorption is often used due to its simple and efficient features. Covalent organic frameworks (COFs) material with the characteristics of stability and porosity has great potential for the adsorption of azo dyes. However, the application of COFs is severely limited by their poor mechanical properties and hard recovery. By the strategy of in situ growth using the original functional groups of the sponge, COFs are successfully grafted onto melamine sponges to give rise to a porous sponge@COFs material. The material can adsorb up to 621 mg g−1 of Congo red, a common azo dye. In addition, it exhibits strong adsorption of iodine solution with the saturated adsorption of 1504.76 mg g−1. More importantly, sponge@COFs can selectively adsorb azo dyes with S–O- bond. The adsorption mechanism is inferred as the connect of S–O- in the Congo red molecule with O atom of sponge@COFs. Also, the mechanism of iodine adsorption is explained to be due to the coordination of C atoms in COFs with I atom. In addition, as an adsorbent, the material is recoverable, stable and heat resistant. Relying on the stronger performance and lower cost, sponge@COFs is expected to be developed as a new adsorbent.

High capacity and selective adsorption of Congo red by cellulose-based aerogel with mesoporous structure: Adsorption properties and statistical data simulation

Large quantities of organic dyes are discharged into the environment, causing serious damage to the ecosystem. Therefore, it is urgent to develop inexpensive adsorbents to remove organic dyes. A novel cellulose-based aerogel (MPPA) with 3D porous structure was prepared by using cassava residue (cellulose) as basic construction blocks, doping ferroferric oxide (Fe3O4) for magnetic separation, and applying polyethyleneimine (PEI) as functional material for highly efficient and selective capture of Congo red (CR). MPPA exhibited porous network structure, numerous active capture sites, nontoxicity, high hydrophilicity, and excellent thermal stability. MPPA showed superior adsorption property for CR, with an equilibrium adsorption capacity of 2018.14 mg/g, and still had an adsorption property of 1189.31 mg/g after five recycling procedures. In addition, MPPA has excellent selectivity for CR in four binary dye systems. The adsorption behavior of MPPA on CR was further explored using a multilayer adsorption model, EDR-IDR hybrid model and AOAS model. Electrostatic potential and independent gradient models were used to further verify the possible interaction between MPPA and CR molecules. In conclusion, MPPA is a promising adsorbent in the field of treating anionic dyes.

Green synthesis of magnetic chitosan composite hydrogel (Fe3O4@CS photocatalyst) for the solar light driven catalytic degradation of organic contaminants

Ecofriendly magnetic chitosan composite hydrogel (Fe3O4@CS photo-catalyst) was prepared by using an aqueous extract of Boerhevia procombens leaves for the solar light mediated catalytic degradation of lethal organic Congo red dye. The prepared composite hydrogel was structurally studied using Fourier transform infrared spectroscopy (FT-IR) which reveals the formation of the Fe3O4@CS photocatalyst. The X-ray diffraction (XRD) investigation of the composite hydrogel signified high crystallinity of photocatalyst and crystallite structure of 53 nm for magnetite nanoparticles (Fe3O4 NPs). The surface investigation suggests multilayered porous photocatalyst owing to the presence of cavities offering more photoactive sites for the photodecomposition of dye molecules. The energy dispersive X-ray (EDX) scanning supports the fabrication of Fe3O4@CS photocatalyst due to the perseverance of carbon, nitrogen, oxygen, and iron. The thermogravimetric analysis (TGA) together with vibrating sample magnetometry (VSM) certifies the preparation of thermally stable and magnetic composite hydrogel. The fabricated Fe3O4@CS photocatalyst possess low bandgap energy of 2.36 eV, supporting the excellent disintegration of dye molecules in the sunlight irradiations. The photocatalyst exhibited a maximum degradation efficacy of 99.1% for Congo red dye in the solar light irradiations with refined states of 70 min radiation time, dye concentration of 20 mg/L, pH 6, and 200 mg photocatalyst amount obeying the second-order kinetic model (R2 = 0.9959). The Fe3O4@CS photocatalyst displayed a little decrease in dissociation efficiency of dye molecules after five repeated cycles owing to the coverage or rupturing of photoactive sites. Conclusively, the results support Fe3O4@ CS to be an economical and biocompatible magnetic catalyst for the catalytic decontamination of Congo red dye molecules and other organic contaminants in domestic and industrial wastewater effluents.

Green synthesis of β-cyclodextrin conjugated Fe3O4/NiO nanocomposites and its synergistic effect of adsorption and photocatalytic degradation for Congo red removal

The Fe3O4/NiO magnetic nanomaterials were prepared by microwave-assisted and hydrothermal synthesis in β-cyclodextrin (β-CD) solution, which can be employed as absorbents and photocatalysts for the degradation of Congo red (CR). The XRD, EDX and TEM characterizations were used to determine the structure, composition and morphology of the as-prepared samples. The interaction between Fe3O4/NiO nanoparticles and β-CD molecules was investigated by TGA and FT-IR spectra. The results indicate that β-CD molecules can encapsulate the as-prepared nanoparticles and control the nucleation and growth of Fe3O4/NiO nanocrystals to certain extent. The pyrolysis of β-CD molecules and calcination treatment produced porous structure that provides more adsorption sites for CR molecules. The effect of reaction factors including calcination temperature and pH values was studied to determine the optimum condition. In addition, the thermodynamic and kinetic parameters of CR absorbed on Fe3O4/NiO nanoparticles were measured to understand the adsorption mechanism. The high removal efficiency for CR in aqueous solution was achieved within 60 min of adsorption and 40 min of UV-light irradiation, which can be attributed to the synergistic effect of the adsorption–photodegradation process. The prepared Fe3O4/NiO nanocrystals exhibit high adsorption capacity, magnetic separability, good photocatalytic activity and renewability, making it a potential material for wastewater treatment.

A green cross-linking method for the preparation of renewable three-dimensional graphene sponges for efficient adsorption of Congo red dye

Graphene-based materials possess significant potential for the treatment of dye wastewater due to their exceptional adsorption properties toward stubborn pollutants. However, their utilization is hindered by high preparation costs, low yields, environmental pollution during synthesis, and challenges in regenerating the adsorbent. This study proposes a novel approach to address these limitations by developing nitrogen-doped three-dimensional (3D) polyvinyl alcohol cross-linked graphene sponges (N-PGA) using a cross-linking method with ammonium carbonate. This method offers a relatively mild and environmentally friendly approach. Ammonium carbonate serves as both a reducing and modifying agent, facilitating the formation of the intrinsic structure of N-PGA and acting as a nitrogen source. Meanwhile, polyvinyl alcohol (PVA) is utilized as the cross-linking agent. The results demonstrate that N-PGA exhibits a favorable internal 3D hierarchical porous structure and possesses robust mechanical properties. The measured specific surface area (BET) of N-PGA was as high as 406.538 m2·g–1, which was favorable for its efficient adsorption of Congo red dye molecules. At an initial concentration of 50 mg·L–1, N-PGA achieved an impressive removal rate of 89.6% and an adsorption capacity of 112 mg·g–1 for Congo red (CR) dye. Furthermore, it retained 79% of its initial adsorption capacity after 10 cycles, demonstrating excellent regeneration performance. In summary, the synthesized N-PGA displays remarkable efficacy in the adsorption of CR dye in wastewater, opening up new possibilities for utilizing 3D porous graphene nanomaterials as efficient adsorbents in wastewater treatment.

Green waste immobilized Ag/Cu feather like Bi-matrix on garment dye decomposes and their bio-efficacy

This paper describes a simple phyto-remediation of feather-like silver/copper bi-matrix (BMs) was constructed by employing pommagrant waste peel (PWP) extract as crucial role of reducing agent and chelating agents. Numerous strategies, including UV–Visible, XRD, SEM-EDX, and TEM and BET isotherm were used to analysis the optical, structural, surface area and functional properties. Ag/Cu BPNMs of TEM characterization shows feather-like architectural features with constrained size and shape. The Ag/Cu co-catalytic nanoparticles have a particle size of 34–64 nm. The photocatalytic efficiency of Ag/Cu BMs was investigated using a garment dye, Congo red (CR), at successive time intervals under halogen lamp exposure. For Ag/Cu bimetallic nanoparticles, the photocatalytic degradation rate was recorded to be 100% after 40 min which is caused by adsorption of Congo red dye molecules on Ag/Cu and their degradation by reactive oxygen species (ROS). ROS are free hydroxyl radicals such as •OH and O2• ions that have high oxidizing capacity. The developed Ag/Cu BMs shown effective bacteriostatic action against many infections.

V2O5/Cds as nanocomposite catalyst for Congo red dye photocatalytic degradation under visible light

V2O5/CdS nanocomposites were prepared using a facile method and utilized as photocatalysts for Congo red (CR) dye molecule degradation. CR is an azo-type dye, which is toxic with a complex structure. The toxicity brings harmful effects on ecotoxicological for aquatic bodies. This study investigated the feasibility of V2O5/CdS nanocomposite catalyst for CR degradation. The V2O5/CdS nanocomposite catalyst was prepared using chemical bath deposition method. The nanocomposite catalyst is evaluated based on the band gap energy using UV–Vis. The degradation of CR dyes was explored through the effect of pH, different catalyst loadings, and the effect on the initial CR dye concentration. It was found that the optimum pH for the CR degradation is pH 8, while the optimum loading and optimum initial CR dye concentration are found at 10 mg and 10 ppm, respectively.

Unleashing the dye adsorption potential of polyaminoimide homopolymer: DFT, statistical physics, site energy and pore size distribution analyses

The efficient removal of Congo Red (CR) dye from aqueous solutions is an important issue in environmental protection. This study presents the synthesis and optimization of a polyaminoimide homopolymer (PHP) adsorbent for the removal of CR dye. To optimize the synthesis of PHP, ten different compositions of maleic anhydride and ethylene diamine were tested, with PHP3 demonstrating the highest efficacy. The adsorption process was further enhanced by optimizing pH, temperature, adsorbent dose, and initial dye concentration. Isotherm and kinetic studies revealed that the Langmuir-Freundlich model and the pseudo-second-order kinetics best described the adsorption process. Moreover, PHP3 demonstrated significantly greater selectivity for CR compared to Synozol yellow, and Sulfasalazine. Advanced statistical models were used to analyze the adsorption data, and the single-layer model with single energy (M1) being the most suitable, suggesting that CR molecules were adsorbed onto PHP3 in a perpendicular position through a multimolecular process, the adsorption process is physical, endothermic, spontaneous and specific surface area of PHP3 increased from 54.31 to 115.74 m2 g−1 as temperature rose from 288 to 318 K. Site energy distribution and pore size distribution studies showed that PHP3 has a heterogeneous energy distribution on its surface, and that the adsorption of CR dye primarily takes place in the macropores of PHP3. Density Functional Theory analysis indicated that PHP3 has electron-rich amine groups that can interact with electron-deficient sulfonate groups in CR, while electron-poor amide groups in the polymer can interact with the electron-rich azo group in Congo Red. It also shows that the presence of NaF, Na2SO4, and KCl salts did not significantly affect the CR adsorption, indicating the potential affinity/selectivity of PHP3 towards CR dye. The findings suggest that PHP3 could be an effective and promising adsorbent for industrial applications in wastewater treatment.

Steric and Energetic Studies on the Synergetic Enhancement Effect of Integrated Polyaniline on the Adsorption Properties of Toxic Basic and Acidic Dyes by Polyaniline/Zeolite-A Composite.

The synergetic enhancement effect of the polyaniline (PANI) integration process on the adsorption properties of the PANI/zeolite-A composite (PANI/ZA) as an adsorbent for malachite green and Congo red synthetic dyes was evaluated based on classic equilibrium modelling in addition to the steric and energetic parameters of advanced isotherm studies. The PANI/ZA composite displays enhanced adsorption capacities for both methylene blue (270.9 mg/g) and Congo red (235.5 mg/g) as compared to ZA particles (methylene blue (179.6 mg/g) and Congo red (140.3 mg/g)). The reported enhancement was illustrated based on the steric parameters of active site density (Nm) and the number of adsorbed dyes per active site (n). The integration of PANI strongly induced the quantities of the existing active sites that have enhanced affinities towards both methylene blue (109.2 mg/g) and Congo red (92.9 mg/g) as compared to the present sites on the surface of ZA. Every site on the surface of PANI/ZA can adsorb about four methylene blue molecules and five Congo red molecules, signifying the vertical orientation of their adsorbed ions and their uptake by multi-molecular mechanisms. The energetic investigation of the methylene blue (-10.26 to -16.8 kJ/mol) and Congo red (-9.38 to -16.49 kJ/mol) adsorption reactions by PANI/ZA suggested the operation of physical mechanisms during their uptake by PANI/ZA. These mechanisms might involve van der Waals forces, dipole bonding forces, and hydrogen bonding (<30 kJ/mol). The evaluated thermodynamic functions, including enthalpy, internal energy, and entropy, validate the exothermic and spontaneous behaviours of the methylene blue and Congo red uptake processes by PANI/ZA.

Construction of a reusable Ce-Fe bimetallic oxide flocculant featuring coordinately unsaturated Fe3+ Lewis acid sites for highly efficient and selective removal of Congo Red

Numerous flocculants have been developed to target the removal of Congo Red (CR), a non-degradable and carcinogenic dye. However, challenges such as non-reusability and potential adverse effects limit their widespread application. To address this, a novel cerium oxide-iron (III) oxide (CeO2-Fe2O3, denoted as CeFe) flocculant featuring coordinatively unsaturated Fe3+ Lewis acid sites was synthesized for selective CR removal. Unlike many counterparts, CeFe maintains its efficiency over repeated uses and showcases exceptional stability. The pronounced interaction between CeO2 and Fe2O3 enhances the coordination unsaturation in CeFe, amplifying the electrophilicity of Fe3+ species and creating more Lewis acid sites. According to the results of characterizations and DFT studies, these sites effectively chelate the −NH3 and −N = N − groups on CR molecules, leading to efficient flocculation. Under optimized conditions (pH=6, initial CR concentration of 400 mg/L, and CeFe dosage of 50 mg/L), CeFe achieved a CR removal efficiency of 95.60 ± 0.90%. This research positions CeFe as a promising, reusable flocculant for efficient CR removal, suggesting a new direction in flocculant design.

Enhanced Adsorption Performance Cross-Linked Chitosan/Citrus reticulata Peel Waste Composites as Low-Cost and Green Bio-Adsorbents: Kinetic, Equilibrium Isotherm, and Thermodynamic Studies.

This study revealed the synthesis of cross-linked chitosan/Citrus reticulata peel waste (C/CRPW) composites that could be used as low-cost and green bio-adsorbents for the removal of Congo red (CR) dye from aqueous solutions. C/CRPW composites containing different amounts of Citrus reticulata peel waste (CRPW) and chitosan were prepared and cross-linked with glutaraldehyde. The composites were characterized by FESEM, EDS, FTIR, XRD, BET, and zeta potential measurements. The C/CRPW composites as a new type of bio-adsorbents displayed superior adsorption capability toward anionic CR molecules, and the adsorption capacities increased with the incorporation of CRPW. Effects of different ambient conditions, such as contact time, pH, adsorbent dosage, initial adsorbate concentration, and temperature, were fully studied. The conditions which obtained 43.57 mg/g of the highest adsorption capacity were conducted at pH 4 with an initial concentration of 100 mg/L, adsorbent dosage of 2.0 g/L, and contact time of 24 h at 328 K. The adsorption data was found to follow the pseudo-second-order kinetic model and the Freundlich isotherm model. According to the findings of this investigation, it was observed that the C/CRWP composites could be used as adsorbents due to their advantages, including the simple preparation process, being environmentally friendly, renewable, efficient, and low-cost.

Studied on highly sensitive fluorescent sensors for Fe3+, Nitrobenzene and dye adsorption properties of Ln-MOFs based on benzimidazole carboxylic acid ligand

Five new lanthanide metal-organic frameworks (Ln-MOFs) {[Ln(L)(H2O)5]·Cl}n (1–5), ([Ln=Pr(1), Nd(2), Eu(3), La(4), Ce(5)] based on benzimidazole carboxylic acid ligand [H2L = 2-(4-carboxyphenyl)-1H-benzo[d] imidazole-6-carboxylic acid]) with the same two-dimensional planar structure were synthesized by solvothermal method. Ln-MOFs 1–3 exhibited the good adsorption performance for the anionic dye Congo red (CR) and the adsorption capacities were 468, 449 and 438 mg·g−1, respectively. The adsorption kinetics indicated that the adsorption was chemical adsorption and the hydrogen bonds and π···π interactions between 1–3 hosts and CR guest molecules resulted in high adsorption capacities. Ln-MOFs 4 and 5 were developed for the exploration of fluorescence sensing performance. The results show that 4 and 5 can be used as fluorescent sensor for Fe3+ with good reusability, high sensitivity and selective detection, the detection limits were 1.1 × 10−5 and 4.3 × 10−6 M, respectively. Research shows that the quenching mechanism of Fe3+belongs to fluorescence resonance energy transfer (FRET). Meanwhile, 4 and 5 also have good detection effect on nitrobenzene (NB) and the detection limits were 1.6 × 10−6 and 2.4 × 10−7 M, respectively.