Adsorption Of Dye Molecules Research Articles

Adsorption and photocatalytic degradation of Congo red and malachite green by nanostructured Y2O3 synthesized by the coprecipitation method

Yttrium oxide is a wide bandgap semiconductor material, with a bandgap energy (Eg) between 4.86 and 5.68 eV, which may anticipate its limitations in photocatalysis. However, its ability to adsorb water and form hydroxyl radicals (•OH) suggests its possible application in the degradation of organic pollutant compounds. Therefore, Y2O3 was prepared by the coprecipitation method, with subsequent calcination at 500 °C. A unique morphology consisting of nanostructured semispheres, with sizes between 1.7 and 2.5 μm, was observed by electron microscopy. This material was used to degrade diluted aqueous solutions of Congo red (CR) and malachite green (MG). For CR, UV–vis spectra revealed a photodegradation percent of ∼24% after 60 min of exposure to UV (λ = 365 nm); meanwhile, the dissociative adsorption accounts for ∼22%, in the same period. Therefore, most of the degradation of this compound can be ascribed to this phenomenon. For MG, an average photodegradation of ∼94% was achieved in the same period, however, dissociative adsorption was estimated as ∼71%. The mechanism of degradation can be explained by the adsorption of dye molecules on Y2O3 and their degradation by reactive oxygen species (ROS). ROS are free hydroxyl radicals such as •OH and •O2− ions that have high oxidizing capacity. XPS analyses performed on samples used in dye degradation provide evidence of the role of ROS, as a significant peak increase associated with OH− groups was observed.

Adsorption of Dye Molecules and Its Potential for the Development of Photoactive Hybrid Materials Based on Layered Silicates

The present paper gives a brief account of the latest advances in understanding of the mechanism and implications of dye adsorption with a special focus on layered silicate surfaces. It has been clearly demonstrated that the controlled adsorption of novel or already well-known dyes has equally great yet unexplored potential. In principle, the well-engineered surface confinement of the molecules may lead to their aggregation, adsorption, or intercalation-induced fluorescence emission even with conventional dyes, which are not considered as luminophores in solutions or in the solid state. We envision the utilization of silicate-based heterogeneous systems to produce novel polymer blended films or structured liquids, as well as to develop a plethora of other photophysical and biomedical applications.

Amorphous tetrazine–triazine-functionalized covalent organic framework for adsorption and removal of dyes

A new amorphous tetrazine–triazine-functionalized covalent organic framework (TzTPT-COF) was developed and employed as a porous adsorbent for the static and dynamic adsorption of small dye molecules, especially methylene blue (MB).

Combining multi-scale simulations and experiments to unveil the adsorption of methylene blue in graphene tridimensional-based materials

Our work brings outstanding contributions to the theoretical–experimental understanding of the process of adsorption of dye molecules in three-dimensional graphene materials with different pore sizes and degrees of oxidation.

Correlating solvation-adsorption phenomena of some styrylpyridinium dyes on SDS modified silica surface in organic media

Sodium dodecyl sulfate modified silica (SDSMS) surface has been used to study the adsorption of some cationic styrylpyridinium dyes from organic solvent media using ultraviolet-visible (UV-Vis) spectrophotometric technique. The modifications of silica surface and subsequent modification through adsorption of dye molecules on the surface have been characterized by Fourier transform infrared (FT-IR), X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), X-ray photoelectron spectroscopy (XPS), UV-Vis spectroscopy and zeta potential measurements. Kinetics of adsorption and consequent thermodynamic parameters have been studied and discussed. The isotherm modeling, choice of solvents from sedimentation analysis, and other common adsorption related parameters such as amount of adsorbent dosage, contact time, adsorption efficiencies have been reported. The influences of solvents and the substituents present on the dye molecules, on the rate of adsorption have been discussed. A pictorial model of adsorption process has been suggested based on the experimental results.

Hexamethylenetetramine functionalized graphene oxide-alginate beads nanocomposite as efficient sorbent for dye from aqueous solution

In this study, a novel eco-friendly sorbent, hexamethylenetetramine (HMTA) functionalized calcium alginate (AG) immobilized graphene oxide (GO) composite (AG-GO-HMTA) and hexamethylenetetramine functionalized calcium alginate composite (AG-HMTA) were prepared. Adsorption factors including pH impact, contact time, initial dye concentration, dosage, selectivity and reusability on methylene blue (MB) removal from water were investigated. The prepared sorbents were characterized using structural (e.g. XRD, FT-IR, EDAX), thermal (e.g. TGA, DTG), and morphological (e.g. SEM, BET) analysis techniques. The equilibrium adsorption data was described by the Langmuir and Freundlich isotherms, and the adsorption kinetic and thermodynamic parameters were investigated. The field studies and regeneration of the beads were investigated. AG-GO HMTA displays a well-defined porous structure and this desired morphology arising from high quality dispersion of HMTA within the AG-GO matrix. The highest adsorption capacities were observed at pH ∼ 5, meanwhile the adsorption of MB dye molecules, positively charged, onto the beads became faster due to strong electrostatic interactions. When the value of dosage is 0.01 g, the equilibrium concentration (mg/g) are maximum at 103, 110, 164, 168 mg/g for AG, AG-GO, AG-HMTA and AG-GO-HMTA, respectively. The present work shows that pseudo first order could describe the MB adsorption onto AG while it couldn't describe the MB adsorption onto the functionalized sorbents due to the hybrid materials complicity.

Adsorption behavior of methylene blue on graphene and hexagonal boron nitride monolayers in aqueous solution: A first-principles treatment

Understanding the adsorption of dye molecules on nanostructured materials is important in regard to innovative potential applications, especially when the corresponding entities are combined. Here, we explore the interaction of methylene blue (MB) with graphene and hexagonal boron-nitride (h-BN) as two-dimensional nanosheets with unique electronic properties and high potential in technological applications. We study these interactions using quantum-based molecular simulations and probe these through the interaction properties and electronic structure of the adsorbed MB on the considered monolayers and especially the specific role of the surrounding environment. We discuss the importance of the findings in view of contaminant removal from wastewater and specifically sensing applications of considered monolayers. Our dispersion-corrected density functional theory (DFT) results show that MB adsorbs strongly on both the graphene and h-BN with interaction energies of −47.454 and −45.072 kcal/mol, respectively, with equilibrium distances of about 3.2 Å between the aromatic rings of adsorbate and substrates. The accuracy of the DFT calculations is validated by the coupled-cluster with single, double (triple) excitations level of theory. The charge density and atom-in-molecule theory analyses reveal the existence of non-covalent and electrostatic interactions between MB and graphene/h-BN surface. The electronic structure analysis shows that the semiconducting graphene becomes metallic after MB adsorption while the h-BN monolayer retains its semiconducting characteristic upon the adsorption. Complementary assays using DFT-based molecular dynamic simulations demonstrate the strong binding of MB to both the graphene and h-BN surfaces in the presence of water molecules as competitive entities. These findings demonstrate the potential applications of graphene and h-BN for the efficient adsorption of dye molecules and for developing promising adsorbents for wastewater treatment and functionalized sensors.

Highly Water-Stable Zn5 Cluster-Based Metal-Organic Framework for Efficient Gas Storage and Organic Dye Adsorption.

The development of multi-functional materials as physical adsorbents for gas storage and dye adsorption is of utmost importance for ecological environment management. Ionic metal-organic frameworks (MOFs) with exchangeable counterions would easily be modified to enhance their performance. Herein, we report a novel {Zn5}-based MOF (SDU-CP-2) with the dimethylamine cation [(CH3)2NH2]+ in its crystal structure, which can be readily exchanged with Li+ ions and cationic dyes. Consequently, it exhibits high CO2 and C2H2 adsorption capacities as well as charge/size-selective adsorption of dye molecules. The adsorption of SDU-CP-2 toward cationic dyes was confirmed to be efficient in terms of recyclability and ion-exchange mechanisms. The column filler experiment and high water stability decisively supported its potential application in waste water treatment.

High-Surface-Area-Activated Carbon Derived from Mango Peels and Seeds Wastes via Microwave-Induced ZnCl2 Activation for Adsorption of Methylene Blue Dye Molecules: Statistical Optimization and Mechanism.

In this study, Mango (Mangifera indica) seeds (MS) and peels (MP) seeds mixed fruit wastes were employed as a renewable precursor to synthesize high-surface-area-activated carbon (MSMPAC) by using microwave-induced ZnCl2 activation. Thus, the applicability of MSMPAC was evaluated towards the removal of cationic dye (methylene blue, MB) from an aqueous environment. The key adsorption factors, namely A: MSMPAC dose (0.02–0.1 g), B: pH (4–10), and C: time (5–15 min), were inspected using the desirability function of the Box-Behnken design (BBD). Thus, the adsorption isotherm data were found to correspond well with the Langmuir model with a maximum adsorption capacity of (232.8 mg/g). Moreover, the adsorption kinetics were consistent with both pseudo-first-order and pseudo-second-order models. The spontaneous and endothermic nature of MB adsorption on the MSMPAC surface could be inferred from the negative ∆G° values and positive value of ∆H°, respectively. Various mechanisms namely electrostatic forces, pore filling, π-π stacking, and H-bonding govern MB adsorption by the MSMPAC. This study demonstrates the utility of MS and MP as renewable precursors to produce high-surface area MSMPAC with a potential application towards the removal of cationic organic dyes such as MB.

Facet-dependent Cu2O@Zn(OH)2 composites with enhanced visible-light photocatalysis

Facet-dependent Cu2O@Zn(OH)2 composites were synthesized by wrapping morphology-controllable Cu2O crystals (cubic, cuboctahedral and octahedral) with the adsorbent Zn(OH)2 nanosheets. The cuboctahedral Cu2O@Zn(OH)2 composite exhibits the highest photocatalytic performance than cubic and octahedral ones with the degradation rate of methyl orange up to 96.6% under visible-light irradiation due to the best crystal facet-dependent photocatalytic performance of cuboctahedral Cu2O. Moreover, the presence of Zn(OH)2 nanosheets can enhance the rapid adsorption of dye molecules, and thus accelerate the photocatalytic process. The combination of Zn(OH)2 nanosheets with physical adsorption capacity and facet-dependent Cu2O crystals with catalytic performance effectively enhances the photocatalytic performance of composite catalyst.

Adsorption-Induced Fluorescence of Pseudoisocyanine Monomers in Systems with Layered Silicates

Interaction of organic dyes with layered silicates can cause various changes in dye properties, such as metachromasia (color change), fluorescence quenching, resonance energy transfer, or even fluorescence enhancement. These phenomena are caused by the molecular aggregation or adsorption of dye molecules on silicate particles. The present work studied the photophysical properties of pseudoisocyanine (PIC) in colloidal dispersions of five samples of layered silicates (smectites) at variable PIC/smectite loadings. The silicates of variable composition and layer charge included one synthetic saponite, one synthetic hectorite, two synthetic Laponites, and one montmorillonite. Chemometric analysis of the absorption spectra revealed the formation of four spectral species: monomers and three types of molecular aggregates exhibiting light absorption in both H- and J-band regions. In addition, the samples of hybrid systems with silicates of lower layer charge under the condition of the lowest PIC/silicate ratio (0.01 mmol g–1) exhibited strong fluorescence surpassing that of J-aggregates. The luminescent species achieving quantum yields of about 50% were assigned to the adsorbed PIC monomers, a phenomenon that has never been observed for this dye. Theoretical calculations found that in water solution bending of the molecule supports nonradiative deactivation of the excited state of the free molecule. Adsorption of PIC molecules on the surface of silicate particles caused the change of the dihedral angle between pyridine subunits, which hinders the nonradiative deactivation channel and favors emission. Fluorescence from adsorbed monomers exhibited a maximum at ≈535 nm, which is at significantly lower wavelengths with respect to the J-aggregates emitting at ≈570 nm and thus cannot be related to dye aggregation as supported by the fact that this phenomenon occurs only at the lowest surface concentrations of the dye.

The behavior of thiacarbocyanine dyes on the surface of few-layered hexagonal boron nitride

The adsorption and self-assembly of several thiacarbocyanine dyes on hexagonal boron nitride (hBN) was investigated by combining steady-state spectroscopy and atomic force microscopy. The adsorption isotherms indicate that at saturation the density of the cationic TDC (5,5-dichloro-3-3′-diethyl-9-ethyl-thiacarbocyanine) molecules on hBN is similar to that of TD2 (3-3′-diethyl-9-ethyl-thiacarbocyanine) molecules, while the densities of TD0 (3-3′-diethyl-thiacarbocyanine) molecules and the zwitterionic THIATS (5,5-dichloro-3-3′-disulfopropyl-9-ethyl-thiacarbocyanine) molecules are significantly higher. The intermolecular distances between neighboring adsorbed dyes, calculated from these saturation densities indicate a flat-on adsorption for TDC, TD2 and TD0 and a partial edge-on adsorption for THIATS. AFM micrographs of the adsorbed TDC, TD0 and THIATS molecules indicate that already at low dye concentrations in the solution, where only a small fraction of the hBN surface is covered, the dye molecules already form upon adsorption to hBN aggregates of at least 10 nm, separated by areas where no adsorbed dye molecules can be detected. The resolution of the micrographs was however insufficient to show details of the packing of the adsorbed molecules. For THIATS, the thickness of the adsorbed layer is compatible with an edge-on adsorption, while for TDC and TD0, the thickness of the adsorbed layer is twice the thickness expected for flat-on adsorption. The exciton interaction extracted from the steady-state spectroscopy of the adsorbed dyes is much smaller than observed for H- or J-aggregates of the same dyes in solution or adsorbed to other surfaces such as Langmuir films or silver halides. For TDC, TD2 and TD0, the values of the exciton interaction are compatible with a close packed flat-on adsorption. Hence, optimizing the interaction between the adsorbed dye and hBN rather than between the adsorbed dye molecules governs the packing of the adsorbed dye molecules. The observation of the spectral shifts attributed to the exciton interaction at low average coverage of the hBN surface indicates that the exciton interaction already occurs at low coverage of the hBN surface. This observation is in agreement with the AFM micrographs, which show clustering of the adsorbed dye molecules already at low coverages.

Adsorption of iodine and reactive dye molecules from water using chemically modified and unmodified lignocellulosic powders (Ficus Lyrata seeds)

Adsorption of iodine and reactive dye molecules from water using chemically modified and unmodified lignocellulosic powders (Ficus Lyrata seeds)

Adsorptive Analysis of Azo Dyes on Activated Carbon Prepared from Phyllanthus emblica Fruit Stone Sequentially via Hydrothermal Treatment

The present work aims to provide insight into the role of the functional group in the adsorption of azo dyes namely, ethyl orange (EO), methyl orange (MO), and metanil yellow (MY), on the activated carbon (surface area 569 m2·g−1) prepared from Phyllanthus emblica fruit stone by low-pressure hydrothermal treatment (AC-HTPEFS). More specifically, this study would facilitate a better understanding of the involvement of different amino substituents (-CH3, -C2H5, phenyl group) on the adsorption of azo dye molecules. The experimental adsorption isotherms of the azo dyes quantified with different adsorbents and temperatures (25–45 °C) were utilized to know the effect of functional groups on dye adsorption. Additionally, the equilibrium data were analyzed by applying isotherm models (Freundlich, Langmuir, and Temkin) in order to elucidate the best-fit isotherm model and adsorption capacity, with the Langmuir model fitting the isotherms best as shown by the higher correlation coefficients obtained (0.984–0.994). The Langmuir monolayer adsorption capacities of EO, MO, and MY obtained at 25 °C were found to be 0.202, 0.187, and 0.158 mmol·g−1, respectively, which was attributed to the hydrophobicity and geometry of dye molecules. Moreover, adsorption kinetics conformed well with the pseudo-second-order model. The negative ΔG°, positive ΔH,° and positive ΔS° indicated the adsorption process to be favorable, endothermic, and increased randomness at the solid–liquid interface. Our findings indicate that the porous activated carbon from hydrothermally treated Phyllanthus emblica fruit stone exhibited a promising potential for the removal of azo dyes with rapid kinetics and high adsorption capacity. The present study could thus pave a way for future utilization of activated carbons produced via hydrothermal treatment techniques for wastewater applications.

BAGS (Bio-source assisted green synthesis) strategy for preparing nanostructures; the case of MgO mesotubes for wastewater reclamation

• “BAGS (Bio-source assisted green synthesis)” is newly termed for biosynthesis of nanostructures. • Subscript to BAGS is appropriately designed for the seven kingdoms of species. • Mesotubular MgO structures are obtained through perfect mimicking of seed fibers’ structure. • High surface area of MgO mesotubes contribute to better photocatalytic removal of MB dye solution under visible radiation. The present work describes about the newly termed “Bio-source assisted green synthesis (BAGS)” strategy that has been successfully carried out for synthesizing Magnesium oxide (MgO) nanostructures by using the seed fiber templates of Calotropis gigantea . This BAGS strategy is of bio-replication mechanism that provided uniform mesotubular structures of MgO (T-MgO) without the involvement of any reducing agents. The shape effect was tested parallelly with spherical-shaped MgO nanoparticles (S-MgO) prepared through a conventional chemical co-precipitation route. Detailed structural, optical, and surface area studies were carried out for the synthesized nanostructures. Methylene blue (MB) dye degradation studies were conducted to assess the photocatalytic ability of both the T-MgO and S-MgO nanostructures under visible light radiation. T-MgO provided better degradation results because of high surface area. T-MgO and S-MgO presented 80% and 65% reduction under visible radiation, respectively. High surface area of T-MgO along with its high crystalline structure might have played a prominent role in the adsorption of dye molecules. This BAGS strategy eases the burden on environment by reducing the impact of harsh chemicals and better utilization of natural resources for effective photocatalyst development. For textile industries’ wastewater treatment plants, these recyclable T-MgO might prove them as efficient catalysts.

Synthesis and characterization of NiO/Cr2O3 nanocomposite with effective sunlight driven photocatalytic degradation of organic dyes.

In this paper, nanocomposite NiO/Cr2O3 has been synthesized by a simple chemical reduction method to study its photocatalytic activity under sunlight irradiation. Various advanced analytical techniques including powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy-dispersive spectroscopy (EDS), elemental mapping, Fourier transform infrared spectroscopy (FTIR), and UV-visible spectroscopy have been utilized to characterize the synthesized NiO/Cr2O3 nanocomposite. SEM images show the sheet-shaped morphology of NiO/Cr2O3 nanocomposite. These sheets have a rough surface with nano to micro size cracks. These cracks play important role in the enhancement of photocatalytic activity by increasing surface active sites for the adsorption of dye molecules on the surface of the photocatalyst. The organic dyes crystal violet (CV) and methylene blue (MB) have been chosen to study the photocatalytic behavior of NiO/Cr2O3 nanocomposite under sunlight irradiation. The photocatalytic efficiency of NiO/Cr2O3 nanocomposite has been obtained 88.47% and 93.63% against crystal violet and methylene blue respectively. The results of the photocatalytic kinetics exhibit that degradation rate constant value for crystal violet dye is higher as compared to methylene blue dye. Obtained kinetic results indicate that synthesized nanocomposite acts as an efficient photocatalyst for the degradation of both crystal violet dye and methylene blue dye. NiO/Cr2O3 nanocomposite also exhibited reusability and stability for photocatalytic degradation of both organic dyes. Photoelectrochemical measurements as photocurrent, electrochemical impedance spectroscopy (EIS), and Mott-Schottky plot were also performed for synthesized NiO/Cr2O3 nanocomposite. Consequently, this synthesized NiO/Cr2O3 nanocomposite can be utilized for environmental remediation of harmful dyes.

Combining pH-triggered adsorption and photocatalysis for the remediation of complex water matrices

Adsorption and photocatalysis are water remediation techniques with unique advantages and limitations that can make them complementary: while adsorption is a cheap and fast process that simply transfers the pollutant to another phase, photocatalysis is a slow and costly procedure that however can degrade recalcitrant pollutants. Here, we propose a sequential treatment based on reversible and selective adsorption, followed by heterogeneous photocatalysis. In particular, the reversible and selective adsorption of dye molecules was achieved by polyaniline (PANI)-based hybrid adsorbents. The role of the dye content, adsorbent dose, solution pH and electrolyte composition was investigated. By tuning the adsorption pH, an effective regeneration of the spent adsorbent could be achieved by the triggered release of the adsorbate in an aqueous solution and under mild conditions. Moreover, the separation of multi-dye mixtures (methyl orange and methylene blue) was proven, also in consecutive cycles. The selective recovery of one of the components could enable dye recycling. An ensuing photocatalytic step using a commercial photocatalyst could be adopted to either degrade the leftover solution or the regeneration solution. The release of a single pollutant in aqueous solvent, with controlled composition and tunable concentration, allows performing photocatalysis more efficiently. This combined approach enables a fast and effective treatment of the effluent and an easy regeneration of the spent adsorbent with ensuing treatment of the regeneration solution for a zero-waste strategy.

Rational Construction of Z‐Scheme Charge Transfer Based on 2D Graphdiyne (g‐CnH2n−2) Coupling with Amorphous Co3O4 Quantum Dots for Efficient Photocatalytic Hydrogen Generation

AbstractA novel Co3O4 quantum dots (CQDs)/2D graphdiyne (GDY) Z‐scheme heterojunction is fabricated by cross‐coupling reaction and electrostatic self‐assembly methods. GDY with the features of 2D porous structures has not only conducted the adsorption of dye molecules but also CQDs is facile to be anchored on the surface. Additionally, the construction of Z‐scheme heterojunction is conductive to conquer the shortcomings of easy agglomeration and poor dispersion for CQDs. The maximum photocatalytic hydrogen generation rate of 1500.85 µmol h−1 g−1 is gained for 30% GDY/CQDs and display an apparent quantum efficiency of 1.37% at 475 nm, which is roughly 11‐fold and 2.8‐fold higher than the pristine GDY and CQDs, respectively. The superior photocatalytic H2 production performance would be put down to the intense synergy of Z‐scheme heterostructure and the size effect of CQDs. They dramatically enhance the separation and transport of photogenerated charge carriers. Besides, the Z‐scheme charge transfer mechanism is further verified through the results of photoluminescence. This work offers new insight into the design of GDY‐based Z‐scheme heterojunction for photocatalysis.

Engineered biochar supported layered double hydroxide-cellulose nanocrystals composite-: Synthesis, characterization and azo dye removal performance

In this work, engineered biochar decorated layered double hydroxides and cellulose nanocrystals (B–CuFe–CNC) biocomposites were synthesized by the facile ultrasonicated-co-precipitation technique. The biocomposite was investigated for purification of Eriochrome Black T (EBT) dye from water. The characterization results showed that the presence of CNC in biochar-layered double hydroxides resulted in a two-dimensional rod-like structure with excellent crystallinity, improved surface functionalities, and provides an attractive platform for the enhanced adsorption of azo anionic dye molecules. The adsorption system was appropriately demonstrated by the BBD-RSM (R2 > 0.994). The biocomposite exhibited higher EBT adsorption in the acidic pH range (2–5) due to strong electrostatic and chemical interactions. The kinetic and isotherm results were well demonstrated by pseudo-second order, Freundlich, and Redlich Peterson models. The maximum adsorption capacity of biocomposite was 876.2 mg/g achieved within 45 min. The spectroscopic analyses imply that the high removal of EBT by biocomposite is mainly governed by electrostatic attraction, hydrogen bonding, and chemical/metal complexation mechanisms. The biocomposite maintained high EBT removal after six successive adsorption cycles and excellent dye adsorption in the different water matrices. The results suggest that tailoring biochar properties with layered double hydroxide and CNC is a promising way for the enhanced removal of dye contaminants from wastewater.

In-situself-polymerization of dopamine on piezo-catalysis material enhances dye degradation

Spin-coated poly (vinylidene fluoride) (PVDF) membrane and electrospun PVDF nanofibers were fabricated and surface modified with in-situ self-polymerization of dopamine or surface deposition of polydopamine. The morphology, composition and phase, hydrophilicity and dye degradation effects of these composite were quantitatively investigated. The results indicated that surface modified PVDF membrane and nanofibers exhibited excellent dye degradation capacity. Specifically, in-situ self-polymerization of dopamine could induce homogeneous distribution of polydopamine on the piezo-catalysis materials, providing favorable spatial conditions for the adsorption of dye molecules and enhancing dye degradation.