Anionic Methyl Orange Research Articles

Construction of Visible light Driven Z-Scheme 1D/1D p-CuBi2O4/n-CdWO4 Heterojunction Nanocomposite for Effective Degradation of Organic Pollutants

The effective separation and harnessing of photoinduced charge carriers in photocatalysis are significant challenges. The present study aims to overcome this obstacle by developing a Z-Scheme heterojunction between a p-type CuBi2O4 (CBO) and a n-type CdWO4 (CWO) through a straightforward heat treatment method. The powder X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) and High-resolution transmission electron microscopy (HRTEM) results revealed the successful formation of heterostructures. The photocatalytic efficiency of the materials was assessed by selecting an anionic methyl orange (MO) and cationic Rhodamine-B (Rh-B) dyes under visible light irradiation. Among all the materials, 85 wt.% CBO+ 15 wt.% CWO (CBO/CWO-15) heterostructure exhibited superior photocatalytic activity (90%) corresponding to 90 and 45 times higher than the pristine CBO and CWO, respectively. The positively charged photocatalyst surface attracts a greater number of MO dye molecules than Rh-B, thereby enhancing the degradation of MO over Rh-B. The scavenger results confirmed the involvement of hydroxy ( and superoxide () radicals in the degradation of MO. The rate constant of CBO/CWO-15 (0.01061 min-1) was 64 and 39 times higher than those of CBO (0.00016 min-1) and CWO (0.00027 min-1), respectively. The photoluminescence (PL) and electrochemical impedance spectroscopy (EIS) analyses substantiated the improved charge separation in the CBO/CWO-15 composite, establishing the Z-scheme mechanism. Cycling experiments over four cycles demonstrated consistent stability of the CBO/CWO-15 composite. The study provides an in-detail plausible mechanism of MO degradation. This type of Z-scheme composite material has potential applications in environmental remediation for the effective removal of organic pollutants and antibiotics from wastewater.

Ti3C2TX MXene/loofah-derived carbon aerogel for high-efficiency adsorption of organic pollutants in wastewater

The contamination of wastewater by organic pollutants significantly impacts human health and the environment due to their carcinogenic nature and various adverse effects. To address this issue, this study offers a high-efficiency and low-cost biomass-based carbon aerogel adsorbent, which was prepared through the hydrothermal carbonization of loofah, followed by Ti3C2TX MXene impregnation. The aerogel features a porous three-dimensional network structure and a substantial specific surface area, facilitating broad-spectrum adsorption capabilities for various dyes and drugs. The aerogel achieved impressive adsorption capacities of 175.29 and 75.73 mg/g for cationic methylene blue and Rhodamine B dyes, and 106.33 and 93.29 mg/g for anionic methyl orange and Congo red dyes, as well as 86.25 mg/g for tetracycline hydrochloride, surpassing other reported biomass-based aerogels. Furthermore, it demonstrated effective decolorization ability for wastewater containing mixed dyes. Notably, it exhibited excellent recycling and regeneration properties, maintaining a high removal rate after multiple cycles of adsorption–desorption. The adsorption process of dye/drug by the aerogel followed Langmuir’s monomolecular layer adsorption model, exhibiting spontaneous, endothermic, and disorder-increasing behavior in alignment with the pseudo-second-order kinetic model. This study presents an efficient biomass-based aerogel for the removal of organic pollutants from wastewater.

Lanthanum hydroxide@cellulose membranes with tunable pore sizes for selective removal of dyes with the same charges

Adsorptive membranes for the efficient separation of dyes with the same charges are quite desirable. Herein, a novel membrane of lanthanum hydroxide/cellulose hydrogel coated filter paper (LC) was prepared through a facile strategy of dip-coating followed by freeze-shaping. With the aid of cellulose gel, the generated La(OH)3 achieved fine dispersion. In addition, the pore size of LC membrane could be regulated by altering the cellulose concentration or the lanthanum chloride dosage, which was crucial for its water flux. In particular, the obtained membrane possessed a high water flux (128.4 L m−2 h−1) and a high dye rejection (97.2 %) for anionic Congo red (CR) only driven by the gravity, which outperformed many previously reported membranes. More intriguingly, its dye rejection for anionic methyl orange (MO) was only 0.9 %, exhibiting high selectivity for dyes with the same charges. Single-solute adsorption experiments indicated that the CR adsorption on the membrane was best fitted by the pseudo-first-order kinetic model, and it followed the Langmuir monolayer adsorption mechanism.

Mesoporous Fe3O4/SiO2/poly(2-carboxyethyl acrylate) composite polymer particles for pH-responsive loading and targeted release of bioactive molecules.

pH-responsive polymer microspheres undergoing reversible changes in their surface properties have been proved useful for drug delivery to targeted sites. This paper is aimed at preparing pH-responsive polymer-modified magnetic mesoporous SiO2 particles. First, mesoporous magnetic (Fe3O4) core-particles are prepared using a one-pot solvothermal method. Then, magnetic Fe3O4 particles are covered with a C[double bond, length as m-dash]C functional mesoporous SiO2 layer before seeded emulsion polymerization of 2-carboxyethyl acrylate (2-CEA). The composite polymer particles are named Fe3O4/SiO2/P(2-CEA). The average diameters of the Fe3O4 core and Fe3O4/SiO2/P(2-CEA) composite polymer particles are 414 and 595 nm, respectively. The mesoporous (pore diameter = 3.41 nm) structure of Fe3O4/SiO2/P(2-CEA) composite polymer particles is confirmed from Brunauer-Emmett-Teller (BET) surface analysis. The synthesized Fe3O4/SiO2/P(2-CEA) composite polymer exhibited pH-dependent changes in volume and surface charge density due to deprotonation of the carboxyl group under alkaline pH conditions. The change in the surface properties of Fe3O4/SiO2/P(2-CEA) composite polymer particles following pH change is confirmed from the pH-dependent sorption of cationic methylene blue (MB) and anionic methyl orange (MO) dye molecules. The opening of the pH-responsive P(2-CEA) gate valve at pH 10.0 allowed the release of loaded vancomycin up to 99% after 165 min and p-acetamido phenol (p-AP) up to 46% after 225 min. Comparatively, the amount of release is lower at pH 8.0 but still suitable for drug delivery applications. These results suggested that the mesoporous Fe3O4/SiO2 composite seed acted as a microcapsule, while P(2-CEA) functioned as a gate valve across the porous channel. The prepared composite polymer can therefore be useful for treating intestine/colon cancer, where the pH is comparatively alkaline.

Adsorption of Rhodamine B, methyl Orange, and phenol separately in aqueous systems by magnetic activated carbon: Optimization by central composite design

In the current study, a novel magnetic activated carbon was synthesized for efficient removal of both anionic methyl orange, cationic Rhodamine B and Phenol fromcontaminatedwater. The adsorbent was characterized by different technique. The investigation of the adsorption properties of magnetic activated carbon was studied by central composite design (CCD) coupled with response surface methodology (RSM). The optimal conditions were established as follows: dye concentration of Coat 30 mg/L, dosage at 0.8 g/L, and pH of the adsorbate solution adjusted to 4.5. The different kinetic and isotherm models were applied to fit the experimental results, and it was observed that the Pseudo-second-order kinetics and Langmuir adsorption isotherm were the best-fitted models. The maximal monolayer adsorption capacities of the adsorbent were found to be 101, 218 and 135 mg/g for phenol, methyl orange, and rhodamine B, respectively. The synthesized MAC had outstanding durability and reusability, as seen by the removal rate that persisted over 80 % following four adsorption-oxidation cycles.The advantages of facile synthesis, cost-effectiveness, non-toxicity, strong adsorption capabilities for methyl orange, Rhodamine B and Phenol, and easy separability with an external magnetic field make magnetic activated carbon novel.

Efficient adsorption of cationic and anionic dyes using hydrochar nanoparticles prepared from orange peel

Hydrochar nanoparticles biosorbent (HCNPs), derived from orange peel was prepared via an in-situ hydrothermal carbonization method. The HCNPs were tested as an effective biosorbent for removing cationic MB (methylene blue) and anionic MO (methyl orange) dyes. The prepared HCNPs was characterized using FTIR, CHN/O, SEM-EDX, UV–visible, XRD, PZC-titration, BET, and XPS. The biosorbent exhibits a good specific surface-to-volume ratio (28.23 m2/g and 0.069 cc/g, respectively) and mesopores size (2.41 nm). UV–Vis data confirm the graphitic nature of the carbon structures. XPS analysis reveals a high enrichment of multiple oxygen functionalities (including C-OH, C = O, and –COO- groups) on the surface. The optimal initial pHs are 3.0 and 5.0–8.0 for removing MO and MB, respectively. Electrostatic attraction plays a substantial role, with other hydrophobic forces in dye removal and binding. Equilibrium is attained during 60/90 min, with half-biosorption-time (tHST) for MB and MO are 4.72 and 6.71 min, respectively. The highest biosorption capacities are 203.4 mg/g for MB and 113.3 mg/g for MO, closely correlated with physiochemical characteristics. Experimental data follows Langmuir isotherm and PSO kinetic models, indicating monolayer chemisorption on a homogeneous surface. The biosorption process for both dyes is exothermic and spontaneous. HCNPs show high durability over multiple biosorption/desorption cycles using HCl and NaOH (0.1 M) for MB and MO, respectively. These findings highlight the promising potential of HCNPs as efficient biosorbents for removing both anionic and cationic dyes.

Novel amino-ethyl carboxymethyl cellulose crosslinked ampholyte hydrogel development for Methyl orange removal from waste water

In the modern era, with the rapid growth of various industries, the issues of energy crisis and environmental pollution have garnered increasing attention. One significant source of industrial pollution is printing and dyeing wastewater. This wastewater often contains dyes that have aromatic structures and azo groups, such as Methyl orange (MO), which are both toxic and difficult to degrade. If these dyes are released into the wastewater stream without any treatment, they can have adverse effects on ecological balance and human health. Therefore, it is crucial to identify suitable treatment strategies to efficiently remove dyes from wastewater systems before discharge. In this study, the Methyl orange (MO) azo dye has been removed from dyes-contaminated wastewater, for the first time, using a novel amino-ethyl carboxymethyl cellulose crosslinked ampholyte hydrogel (AECMC). Different characterization methods, including FTIR, TGA, and DSC were used to characterize the generated AECMC compounds. The water absorption and cationic exchange capacities were assessed. Factors affecting the MO anions adsorption including MO concentration, adsorption pH, temperature, time, adsorbent dose, and agitation speed have been investigated. Moreover, the kinetics of the adsorption process was assessed by the use of three models: pseudo-first-order, Pseudo-second-order, and Elovich. Moreover, the mechanism of the adsorption process was monitored using the Intraparticle diffusion and Boyd models. Additionally, the adsorption isotherm was examined using established models such as Langmuir, Freundlich, and Temkin isotherms. The thermodynamic characteristics of the MO adsorption process have been investigated at various adsorption temperatures using the Van't Hoff model. The results obtained from the study indicate that the process of MO adsorption adhered to the Pseudo-second-order kinetic model, the Langmuir isotherm model was found to be applicable, and spontaneous and exhibited an endothermic character. In conclusion, the developed novel amino-ethyl carboxymethyl cellulose crosslinked ampholyte hydrogels (AECMC) have successive in the removal of the MO anionic dye from contaminated wastewater.

Magnetic Magnetite-Graphene Oxide (Fe3O4-GO) Nanocomposites for Removal of Dyes from Aqueous Solution

AbstractMagnetic magnetite-graphene oxide (Fe3O4-GO) was synthesized using an in-situ precipitation technique and applied in the adsorption of cationic rhodamine B (RhB) and anionic methyl orange (MO) dyes from aqueous solution. The nanocomposite was characterized by different techniques including FTIR, XRD, Raman, XPS, PPMS, BET, SEM and TEM techniques. Batch adsorption studies were conducted to investigate the effect of solution pH, initial metal ion concentration, adsorbent dosage and contact time. The synthesized Fe3O4-GO exhibited characteristic magnetic properties (saturation magnetization of 34 emu/g) and it separated from aqueous solution with ease through the application of an external magnetic field. The adsorption equilibrium time on the adsorption of RhB and MO onto Fe3O4-GO showed best removal of 99.12% for RhB after 60 min, while MO was removed efficiently after 120 min with a removal efficiency of 97.60%. The adsorption of the azo dyes followed the pseudo-second-order kinetics model with high correlation coefficients (0.99995) for RhB and (0.99925) for MO. Maximum removal of the dye pollutants by occurred at pH 8 for RhB and pH 4 for MO, while the optimal adsorbent dosage was 30 mg. The results showed that adsorption equilibrium data were fitted to Langmuir isotherm model and maximum monolayer adsorption capacities for RhB and MO at 70.64 and 15.94 mgg−1, respectively. The magnetic adsorbents were reused for a maximum of 7 cycles and showed reasonable stability and reproducibility. Furthermore, the results showed that Fe3O4-GO nanocomposite can be used as an effective material in the removal of dyes from wastewater.

Removal of Anionic Methyl Orange Dye from Water by Poly[2-methyl-1H-indole] Derivatives: Investigation of Kinetics and Isotherms of Adsorption.

The adsorption properties toward methyl orange (MO) were evaluated for poly[2-methyl-1H-indole] and its derivatives. The influence of pH, ionic strength of solution, composition, and amount of sorbent on the adsorption of MO dye was investigated; the kinetics of dye adsorption was studied. The adsorption isotherms were analyzed using different models of sorption equilibrium. The presence of chemical interaction between polyindoles and dye was proved by IR and UV spectroscopy methods. The sorption of MO with polymers is realized mainly due to the formation of electrostatic interactions between the sulfogroup of the dye and the imino group of the sorbent. Microphotographs demonstrate the change in the morphology of polyindoles after adsorption, which further confirms the structural changes in the polymers. It was found that the main factors affecting the sorption capacity of the studied materials are the position and nature of substituents in the polymers and the sorption conditions. For example, polyindoles containing a methoxy group in their structure (o-OMePIn and m-OMePIn) have the best sorption activity. These polymers are effective in adsorbing dyes, which means that they can be used in wastewater treatment.

Smart pillar[5]arene-based PDMAEMA/PES beads for selective dye pollutants removal: design, synthesis, chemical-physical characterization, and adsorption kinetic studies.

This article reports on the synthesis of an innovative smart polymer, P5-QPDMAEMA, opportunely developed with the aim of combining the responsiveness of PDMAEMA polymer and the host-guest properties of covalently linked pillar[5]arenes. Thanks to a traditional Non-Induced Phase Separation (NIPS) process performed at various coagulation pH, the blending of P5-QPDMAEMA with polyethersulfone gave rise to the formation of functional beads for the removal of organic dyes in water. Adsorption tests are carried out on all the produced blend-based beads by employing two representative dyes, the cationic methylene blue (MB), and the anionic methyl orange (MO). In particular, the P5-QPDMAEMA based beads, prepared at acidic pH, featured the best MO removal rate (i. e., 91.3 % after 150 minutes starting from a 20 mg ⋅ L-1 solution) and a high selectivity towards the removal of the selected anionic dye. Based on the adsorption kinetics and isotherm calculations, the pseudo-first order and Freundlich models were shown to be the most suitable to describe the MO adsorption behavior, achieving a maximum adsorption capacity of 21.54 mg ⋅ g-1. Furthermore, zwitterionic beads are obtained by a post-functionalization of the PDMAEMA and the P5-QPDMAEMA based beads, to test their removal capability towards both anionic and cationic dyes, as shown.

Insights into simultaneous efficient removal of cationic and anionic dyes by nitrogen-rich seaweed carbon adsorbent

Textile dyes, including methylene blue (MB) and methyl orange (MO), pose a significant threat to water quality. This study delves into the competitive adsorption mechanisms pivotal for the concurrent removel of cationic MB and anionic MO dyes using nitrogen-rich seaweed-based carbon adsorbents. Synthesized through the pyrolysis and NaOH activation of Enteromorpha seaweed biomass, the preparation method is both uncomplicated and cost-effective, holding promising applications in industry. Characterization unveiled a commendable specific surface area of 911 m2/g, accompanied by abundant nitrogen- and oxygen-containing functional groups. Batch adsorption experiments showcased exceptional removal efficiencies surpassing 99.8% for both dyes. Molecular dynamics simulations offered valuable insights into the dynamic multi-stage adsorption behavior, while density functional theory calculations clarified the chemisorption-based interaction mechanism. Notably, MB displayed superior adsorption affinity compared to MO. An integrated adsorption mechanism was proposed, encompassing electrostatic attraction, migration, and enhanced chemisorptive binding of dye aggregates at active sites on the adsorbent surface. The innovative adsorption mechanism adopted by this carbon-based adsorbent prepared from nitrogen-rich seaweed can effectively remove cationic and anionic dyes, laying a solid foundation for future research on real water bodies with complex compositions.

Polypyrrole-decorated bentonite magnetic nanocomposite: A green approach for adsorption of anionic methyl orange and cationic crystal violet dyes from contaminated water

In the presented study, a novel polypyrrole-decorated bentonite magnetic nanocomposite (MBnPPy) was synthesized for efficient removal of both anionic methyl orange (MO) and cationic crystal violet (CV) dyes from contaminated water. The synthesis of this novel adsorbent involved a two-step process: the magnetization of bentonite followed by its modification through in-situ chemical polymerization. The adsorbent was characterized by SEM/EDX, TEM/SAED, BET, TGA/DTA-DTG, FTIR, VSM, and XRD studies. The investigation of the adsorption properties of MBnPPy was focused on optimizing various parameters, such as dye concentration, medium pH, dosage, contact time, and temperature. The optimal conditions were established as follows: dye concentration of Co (CV/MO) at 100 mg/L, MBnPPy dosage at 2.0 g/L, equilibrium time set at 105 min for MO and 120 min for CV, medium pH adjusted to 5.0 for MO dye and 8.0 for CV dye, and a constant temperature of 303.15 K. The different kinetic and isotherm models were applied to fit the experimental results, and it was observed that the Pseudo-2nd-order kinetics and Langmuir adsorption isotherm were the best-fitted models. The maximal monolayer adsorption capacities of the adsorbent were found to be 78.74 mg/g and 98.04 mg/g (at 303.15 K) for CV and MO, respectively. The adsorption process for both dyes was exothermic and spontaneous. Furthermore, a reasonably good regeneration ability of MBnPPy (>83.45%/82.65% for CV/MO) was noted for up to 5 adsorption-desorption cycles with little degradation. The advantages of facile synthesis, cost-effectiveness, non-toxicity, strong adsorption capabilities for both anionic and cationic dyes, and easy separability with an external magnetic field make MBnPPy novel.

Chitosan and silica nanoparticles-modified xanthan gum-derived bio-nanocomposite hydrogel film for efficient uptake of methyl orange acidic dye

In this contribution, a bio-nanocomposite hydrogel film (CS/XG.SiO2) of chitosan/silica NPs-modified xanthan gum was prepared via a facile solution casting blending approach and utilized to capture the anionic methyl orange (MO) from aqueous solution. A Taguchi standard method was used to optimize the hydrogel nanocomposite synthesis reaction conditions after comprehensive characterization using various techniques. Under various operating parameters, the hydrogel biofilm was tested for its effectiveness in adsorbing MO dye in a batch process. In agreement with Langmuir isotherm, the CS/XG.SiO2 biofilm was capable of adsorbing MO at a maximum capacity of 294 mg/g at pH 5.30, contact time 45 min, temperature 25 °C, and concentration (C0) 50 mg/L. Pseudo-second-order model and adsorption kinetics data well matched. The thermodynamic data indicate that adsorption occurred spontaneously and exothermically. The main mechanisms driving the adsorption are electrostatic interactions and hydrogen bonding between the CS/XG.SiO2 nanocomposite and the dye. Furthermore, the biofilm is regenerative, allowing for up to five reuses while maintaining a 75 % dye removal efficiency. This study highlights that the CS/XG.SiO2 hydrogel nanocomposite is an inexpensive, reusable, and eco-friendly bio-adsorbent that is capable of anionic dye adsorption.

Bio-inspired adsorption sheets from waste material for anionic methyl orange dye removal

Nano zero-valent iron (nZVI), bimetallic nano zero-valent iron-copper (Fe0–Cu), and Raw algae (sargassum dentifolium) activated carbon-supported bimetallic nano zero-valent iron-copper (AC-Fe0–Cu) are synthesized and characterized using FT-IR, XRD, and SEM. The maximum removal capacity is demonstrated by bimetallic activated carbon AC-Fe0–Cu, which is estimated at 946.5 mg/g capacity at the condition pH = 7, 30 min contact time under shaking at 120 rpm at ambient temperature, 200 ppm of M.O, and 1 g/l dose of raw algae-Fe0–Cu adsorbent. The elimination capability of the H3PO4 chemical AC-Fe0–Cu adsorbent is 991.96 mg/g under the conditions of pH = 3, 120 min contact time under shaking at 120 rpm at room temperature, 200 ppm of M.O, and 2 g/l doses of H3PO4 chemical AC-Fe0–Cu adsorbent. The Bagasse activated carbon adsorbent sheet achieves a removal capacity of 71.6 mg/g MO dye solution. Kinetic and isothermal models are used to fit the results of time and concentration experiments. The intra-particle model yields the best fit for bimetallic Fe0–Cu, AC-Fe0–Cu, H3PO4 chemical AC-Fe0–Cu and bagasse activated carbon(CH), with corrected R-Squared values of 0.9656, 0.9926, 0.964, and 0.951respectively. The isothermal results emphasize the significance of physisorption and chemisorption in concentration outcomes. Response surface methodology (RSM) and artificial neural networks (ANN) are employed to optimize the removal efficiency. RSM models the efficiency and facilitates numerical optimization, while the ANN model is optimized using the moth search algorithm (MSA) for optimal results.HighlightsThe Fe0–Cu composite, when combined with activated carbon from Bagasse Pulp (CH), exhibited the most effective decolorization effectiveness for anionic colours present in wastewater.The utilization of composites presents a promising opportunity for efficient dye removal due to its cost-effectiveness and environmentally sustainable nature. The utilization of response surface approach and artificial neural network modelling improves the efficacy of removal processes and treatment techniques.

Comparative study of cationic Nile blue and anionic methyl orange dyes adsorption in water on the (110) surface of metal chlorides by DFT and MD approaches

Computational studies using density functional theory (DFT) and molecular dynamics simulations (MD) provide a valuable way to evaluate the removal of dyes by different adsorbents. In this study, Nile blue (with a positive charge; NB+) and methyl orange (with a negative charge; MO−) were used to examine the adsorptive performance of metal chlorides MCl2 (where M = Mg, Mn, Zn or Ni) from water. The calculated gap energies of NB+ and MO− were 5.333 and 2.395 eV, respectively, suggesting that the NB+ molecule is more reactive, electrophilic and can adsorb strongly on the MCl2 surface compared to MO−. Frontier molecular orbitals, Mulliken charge and an electrostatic potential map were used to explain the redox reactive sites of the investigated molecules. In addition, possible donor–acceptor interactions of molecules were assessed by natural bond orbital analysis. The negative values of back-donation energy ΔEback-donation for both dyes reflected that back donation for both dyes was energetically favorable. Furthermore, the most stable energy configuration of NB+ and MO− adsorption on MCl2 was determined by MD simulations. These simulations showed that both dyes can be adsorbed onto the MCl2 (110) surface in a nearby horizontal position. The radial distribution function peak values for all systems occurred at distances greater than 3.5 Å, indicating that the dyes were physically adsorbed onto the MCl2 surfaces through van der Waals interactions. The negative values of adsorption energy for both studied dyes indicated spontaneity of the adsorption process. Furthermore, MD simulations revealed that the adsorption energies between NB+ and MCl2 were much higher than between MO− and MCl2.

Carbonized Leather Waste with Deposited Polypyrrole Nanotubes: Conductivity and Dye Adsorption.

This paper reports the conversion of a waste to a conducting material, exploiting the ability to adsorb pollutant organic dyes. Leather waste was carbonized at 800 °C in an inert nitrogen atmosphere. The resulting biochar was used for in-situ deposition of polypyrrole nanotubes produced by the oxidative polymerization of pyrrole in the presence of methyl orange. The composites of carbonized leather with deposited polypyrrole nanotubes of various composition were compared with similar composites based on globular polypyrrole. Their molecular structure was characterized by infrared and Raman spectra. Both conducting components formed a bicontinuous structure. The resistivity was newly determined by a four-point van der Pauw method and monitored as a function of pressure applied up to 10 MPa. The typical conductivity of composites was of the order of 0.1 to 1 S cm-1 and it was always higher for polypyrrole nanotubes than for globular polypyrrole. The method also allows for the assessment of mechanical features, such as powder fluffiness. The conductivity decreased by 1-2 orders of magnitude after treatment with ammonia but still maintained a level acceptable for applications operating under non-acidic conditions. The composites were tested for dye adsorption, specifically cationic methylene blue and anionic methyl orange, using UV-vis spectroscopy. The composites were designed for future use as functional adsorbents controlled by the electrical potential or organic electrode materials.

Adsorption of anionic methyl orange dye by polyaniline, poly(o‐methylaniline) and poly(o‐methoxyaniline)

AbstractThis study reports the effect of substituents in the ortho position of polyaniline on the adsorption capacity to remove the anionic dye methyl orange (MO) from an aqueous solution. The aim of this study is the synthesis of polyaniline (PANI) and its derivatives, poly‐o‐methylaniline (poly‐o‐toluidine, POT) and poly‐o‐methoxyaniline (poly‐o‐anisidine, POA) for the adsorption removal of MO dye. All polymers were obtained by oxidative polymerization of the corresponding monomers and characterized by scanning electron microscopy (SEM) and infrared spectroscopy (IR). The average particle size of the polymer was about 200 nm. The effect of various parameters such as pH, temperature, adsorption time and initial concentration was analyzed. It was found that the adsorption capacity for dye removal increases from 50.68 to 222.56 mg g−1 for PANI, from 16.89 to 66.57 mg g−1 for POT, and from 97.26 to 532.54 mg g−1 for POA with an increase in the initial dye concentration from 5 up to 50 mg L−1. For all polymers, the equilibrium state of MO adsorption was reached in 50 min. The results showed that MO adsorption on PANI, POT, and POA is well described by a pseudo second order kinetic model. Isothermal studies have shown that adsorption is in good agreement with the Langmuir isotherm model, as evidenced by higher values of correlation coefficients. Based on the data of thermodynamic studies, it was concluded that MO adsorption on PANI, POT, and POA is spontaneous and endothermic.

High adsorption of methyl orange by nitrogen-doped activated carbon derived from kraft lignin via self-activation

As adsorbents, nitrogen-doped activated carbons are attracting increasing interest in the field of environmental protection, pharmaceutical and food industries due to their tunable pore structures, abundant surface functional groups and variable charges. However, the main factor limiting the commercialization and mass production of the activated carbons is the cost of adsorbent preparation. A nitrogen-doped activated carbon derived from kraft lignin in black liquor was produced by self-activation via endogenous alkali, and was used as an adsorbent of anionic methyl orange for its very low cost. It was indicated that the activated carbon with a rich pore structure, having a specific surface area of 1124.78 m2 g−1 and a total pore volume of 0.60 cm3 g−1, was obtained under a mass ratio of 1:2 of organic matter in the black liquor to diethylenetriamine and an activation temperature of 850 °C. Furthermore, the adsorption capacity of the activated carbon for methyl orange in simulated wastewater was evaluated, and it exhibited excellent performance with a maximum adsorption capacity of 373.95 mg g−1 under the optimized conditions as the methyl orange solution is at an initial concentration of 175 mg L−1, pH 7.8 and an adsorbent dosage of 0.4 g L−1. Adsorption kinetics, adsorption isotherms and adsorption thermodynamics were also studied. And the adsorption process of the activated carbon was found to be in accordance with the Pseudo-second-order kinetic model and the Langmuir model. This work provides a novel strategy for producing lignin-derived activated carbon from dried black liquor by self-activation with a low cost and timesaving approach.

Selectivity of Sol-Gel and Hydrothermal TiO2 Nanoparticles towards Photocatalytic Degradation of Cationic and Anionic Dyes.

Titanium dioxide (TiO2) nanoparticles have been extensively studied for catalyzing the photo-degradation of organic pollutants, the photocatalyst being nonselective to the substrate. We, however, found that TiO2 nanoparticles prepared via the sol-gel and hydrothermal synthetic routes each possess a definite specificity to the charge of the substrate for photodegradation. The nanoparticles were characterized by SEM, FTIR, XRD, TGA, and UV-visible spectra, and the photocatalytic degradation under UV-B (285 nm) irradiation of two model compounds, anionic methyl Orange (MO) and cationic methylene blue (MB) was monitored by a UV-visible spectrophotometer. Untreated sol-gel TiO2 nanoparticles (Tsg) preferentially degraded MO over MB (90% versus 40% in two hours), while after calcination at 400 °C for two hours (Tsgc) they showed reversed specificity (50% MO versus 90% MB in one hour). The as-prepared hydrothermal TiO2 nanoparticles (Tht) behaved in the opposite sense of Tsg (41% MO versus 91% MB degraded in one and a half hours); calcination at 400 °C (Thtc) did not reverse the trend but enhanced the efficiency of degradation. The study indicates that TiO2 nanoparticles can be made to degrade a specific class of organic pollutants from an effluent facilitating the recycling of a specific class of pollutants for cost-effective effluent management.

Adsorption of anionic methyl orange dye on hybrid spherical silica in fixed-bed column

The textile sector is recognized for contributing the most dye residue, which is one of today's environmental challenges. It is a risky technique since wastewater includes toxins that can damage water sources and endanger human health and aquatic life. As a result, wastewater must be treated before disposal. There are numerous methods for removing dyes from wastewater, which categorized into chemical treatments, physical and biological procedures.. This study chose the continuous adsorption approach, which falls under the physical method since it is simple and effective. The oil-in-water emulsion was used to synthesize spherical silica (SSi) adsorbent in order to effectively remove and remediate one of the water-soluble anionic dyes, methyl orange dye (MO). The effect of influent concentration (10 to 50 ppm) and bed height (1.0 to 2.0 cm) on the continuous process was investigated. The breakthrough time exhibited an increase as the dye concentration decreased for all solutions that were examined. The removal efficiency of MO increased as the bed height increased, which can be attributed to the longer contact time between the MO dye and the adsorbent. The Thomas model exhibited a more favorable level of conformity to the data than Adams-Bohart and Yoon-Nelson. According to Thomas ' model, the maximum adsorption capacity (qo) increased as bed height decreased, and concentration increased. Moreover, Correlation values ranged from 0.882 to 0.979. Therefore, spherical silica adsorbent has the highest methyl orange dye adsorption capability at a bed height of 2.0 cm and concentration of 50 ppm.