Polypyrrole-coated cotton textile as adsorbent of methylene blue dye

Pollution caused by organic dyes is of serious environmental and health concern to the population. Dyes are widely used in textile coloring applications. In the present work, cotton textile was coated with a conducting polymer, polypyrrole (PPy), in situ during the oxidative polymerization of pyrrole. The resulting materials were utilized as easily separated and recyclable adsorbent for the removal of methylene blue (MB) as a model of cationic dyes in alkaline solutions. It showed also some affinity to remove Acid Green 25 as an anionic dye in acidic medium. The adsorption was assessed by monitoring the decrease in dye concentration by UV–Visible absorption spectroscopy. The influence of various parameters such as initial dye concentration, contact time, pH, temperature, and adsorbent dose on the adsorption process was studied. The pseudo-second-order kinetic model and Freundlich isotherm model were found to describe the adsorption process. The thermodynamic study revealed that the adsorption of MB by PPy was feasible, spontaneous, and exothermic process. Investigation of the substrate regeneration revealed that PPy deposited on cotton textile can be reused for dye adsorption several times with good efficiency and it allows for the recovery of MB for recycling purposes.     

Removal of cationic dyes: basic magenta and methylene blue from aqueous solution by adsorption on modified loofah

Modified loofah was prepared by a simple chemical graft method to improve its adsorption for cationic dyes. Experimental results showed that the maximum amounts of basic magenta and methylene blue loaded on the modified loofah were 83.5 and 85.5 mg g^?1, and that on the unmodified loofah were 22.2 and 33.7 mg g^?1, respectively. The adsorption for both dyes could reach equilibrium after 300 min. A pseudo-second-order model is suitable for describing the adsorption and desorption kinetics of both dyes on the modified sorbent. According to the intra-particle diffusion model, sorption and desorption processes for the two dyes both presented two distinct phases and were mainly controlled by intra-particle diffusion. The dye-loaded modified loofah could be regenerated by using the mixture solution of HCl and ethanol (V_HCl:V_ethanol = 3:2) as eluent. Adsorption in the binary system showed that adsorption of the dyes was depressed by the presence of the other dye, and the two dyes could be removed efficiently when the initial concentrations were lower than 5.0 × 10^?5 mol L^?1. The Langmuir competitive model was suitable to predict the sorption isotherm in the binary system.     

Application of chemometric methods in modeling of competitive multidye biosorption from ternary system

Simultaneous biosorption properties of three cationic dyes (Methylene blue, Crystal violet and Safranin) on Sargassum glaucescens were studied. In the most of previous papers in the field of dye biosorption, one dye or dyes with nearly separate spectra were used and dye concentration was determined by Beer’s law at different λ _max. Significant of this study is application of dyes with highly overlapped spectra (as many real situations) that their concentrations can be determined by chemometric methods. Plackett–Burman design was applied to identify the most significant factors, Box–Behnken design was used to determine optimal conditions, and principal component-wavelet neural network was used for the simultaneous determination of dye concentrations in ternary solutions. The optimum biosorption conditions were determined as dye concentration 10^?4 mol L^?1, biosorbent dosage 0.1 g L^?1 and biosorbent particle size 0.188 µm. At this condition, maximum biosorption capacity was 0.80 mmol g^?1. The biosorption process was slightly slower in the ternary system comparing with single system which was related to competition phenomena between dyes. It was found that the overall biosorption data were described by the pseudo-second-order kinetic model. Fourteen isotherm models were applied to experimental data, and it was concluded that Hill model had the best correlation.     

Simple Method for Determination of Lead in Hair Dyes Using Slurry Sampling Graphite Furnace Atomic Absorption Spectrometry

A fast, simple and sensitive method for determining of lead in hair dyes using graphite furnace atomic absorption spectrometry with slurry sampling was developed. Multivariate optimization was used to establish optimal analytical parameters through a fractional factorial and a central composite design. The samples were submitted for direct analysis without prior digestion and were diluted in 2.5% v/v HNO₃ and 1.5% v/v H₂O₂. Palladium (chemical modifier) and rhodium (permanent modifier) were selected from several potential modifiers. The optimal conditions were a pyrolysis time of 10 s (liquid and dust dyes) 20 s (cream dyes), a pyrolysis temperature of 789°C (liquid dyes) or 750°C (cream and dust dyes) and an atomization temperature of 1800°C for all dyes. Under optimum conditions, the calibration graph is linear in the 1.50–50.0 µg L^?1 concentration range, with a detection limit of 0.33, 0.44, and 0.39 µg L^?1 for liquid, dust, and cream hair dyes, respectively. The relative standard deviation ranged from 1.63 to 4.56%. The recovery rate ranged from 85 to 108%, and no significant differences were found between the results obtained with the proposed method and the microwave decomposition analysis method of real samples. The concentration ranges obtained for lead in the hair dyes samples were 1.00–11.3 µg L^?1 for liquid dyes, 14.0–100 µg kg^?1 for dust dyes, and 19.9–187 µg kg^?1 for cream dyes.     

Decolorization of Reactive Black 5 and Reactive Blue 4 Dyes in Microbial Fuel Cells

Microbial fuel cells (MFCs) have potential to treat industrial wastewater containing organic compounds and simultaneously generate power. Organic compounds include textile dyes with various chromophore groups, which can be decolorized reductively by microorganisms under anaerobic conditions. In the present study, we examined the decolorization of Reactive Black 5 (RB5) azo dye and Reactive Blue 4 (RBL4) anthraquinone dye under open circuit potential in MFCs with graphite plate and graphite felt electrodes and a microbial consortium originally derived from bovine rumen fluid. RB5 dye was more than 90% decolorized in 120, 165, and 225 min at 50, 100, and 200 mg L^?1 concentrations, respectively. RBL4 dye at 50 and 100 mg L^?1 took 225 and 300 min to decolorize, while 200 mg L^?1 RBL4 dye was not decolorized at all. Under closed circuit conditions, decolorization increased with decrease in external load, whereas current generation increased with external resistance. The results demonstrate that the reductive cleavage of the chromophore was more rapid with RB5 than with RBL4.     

Bio-adsorption of dyes from aqueous solution by powdered excess sludge (PES): Kinetic,isotherm, and thermodynamic study

Over 30 million tons of excess sludge is discharged from rural municipal sewage plants annually in China and it is predicted that this figure will keep increasing. However, most of the excess sludge is dumped in landfills except for minor applications. In this study, based on low-cost and recycling waste, the excess sludge was used to adsorb organic dyes from aqueous solution after being directly dewatered. The powdered excess sludge (PES) presents selective adsorption property to cationic dyes. Statics batch adsorption experiments of malachite green (MG) on PES were performed to evaluate the effects of pH, adsorbent dosage, and initial MG concentration. Results revealed that the bio-adsorption equilibrium of MG on the PES can be quickly achieved at 30 min with maximum percentage adsorption of 84% at pH 7, initial dye concentration of 20 mg L^?1, and adsorbent dosage of 1.5 g L^?1. Moreover, the adsorption kinetics follows a pseudo-second-order pathway, and the equilibrium adsorption data could be described well by the Langmuir isotherm equation. Intra-particle diffusion is not the only rate-controlling step in the entire adsorption process. The adsorption process is endothermic, spontaneous, and random. PES can be used as a low-cost adsorbent for refractory cationic organic dye in effluent.     

薄层色谱法分析酸性和阳离子染料

用相关系数法从多种展开剂中优选出酸性、阳离子染料薄层色谱分析的最佳展开剂。在相关系数最小的两种展开剂Ｖ（正丁醇）∶Ｖ（冰乙酸）∶Ｖ（水）＝２∶１∶５和Ｖ（乙酸乙酯）∶Ｖ（冰乙酸）∶Ｖ（水）＝５０∶１５∶１０中,相同颜色的毛、腈纶纤维上的酸性、阳离子染料提取液及不同厂家生产的同一种染料均得到了很好的鉴别。     

Amorphous titanium dioxide as an adsorbent for dye polluted water and its recyclability

Amorphous TiO₂, synthesized from TiCl₄ and diluted NH₃ solution, was characterized by X-ray diffraction spectrometry, UV–Vis diffused reflectance spectroscopy, Fourier-transformed infrared spectroscopy, and scanning electron microscopy. The powder exhibited high specific surface area at 508 m²/g as measured by the Brunauer-Emmett-Teller method. The pH at point of zero charge of the as-prepared amorphous TiO₂ was determined by the pH drift method to be 6.8. The product was studied for its sorption efficiency using two dyes—crystal violet (CV) and malachite green (MG). Studies on the effects of various sorption parameters (contact time, TiO₂ dosage, pH of solution, and initial concentration of dye) were carried out in order to find the optimum adsorption conditions for which the results were: contact time ~30 min, TiO₂ dosage ~0.05–0.1 g, pH 7–9, and initial concentration <1 × 10^?4 M. The adsorption data were analyzed and fitted better with the Langmuir model than the Freundlich model. The maximum adsorption capacities obtained from the Langmuir model were 0.4979 and 0.4075 mmol dye/g TiO₂ for CV and MG dye, respectively. In addition, the regeneration and the recyclability of the prepared amorphous TiO₂ were also studied. The used adsorbent should be regenerated 10–12 h before reuse in the next cycle for the best result.     

Investigation of equilibrium, kinetic, thermodynamic and mechanism of Basic Blue 16 adsorption by montmorillonitic clay

The adsorption of a cationic dye, Basic Blue 16 (BB16), by montmorillonitic clay was studied in detail. Changes in the molecular structure during adsorption were analyzed by FTIR spectroscopy. BB16 adsorption onto the clay mainly results from hydrogen bonding between OH and NH₂ groups of dye molecules and OH groups of clay and electrostatic interaction between the negatively charged clay surface and cationic dye. The montmorillonitic clay dose had an inverse effect on the adsorption performance, while the highest dye removal was 305 mg/g at pH 3.6. An increase in temperature and dye concentration positively enhanced the adsorption capacity of the montmorillonitic clay. Temperature had no effect on the adsorption at a dye concentration less than 500 mg/L, while dye adsorption was positively enhanced at elevated dye concentrations. Three-parameter equations provided higher better fitting than two-parameter equations while the Freundlich model had the highest correlation coefficient and the lowest error values with experimental data. The BB16 adsorption was well followed by pseudo-second order model and the rate of adsorption process was controlled by surface and intraparticle diffusion. Thermodynamic evaluations revealed that the adsorption process was spontaneous and endothermic, while the randomness increased during adsorption. Experimental results indicate that montmorillonitic clay from Eskisehir is a promising adsorbent for the removal of cationic dye molecules from aqueous solutions.     

Extraction of trace amounts of silver on various amino-functionalized nanoporous silicas in real samples

Aminopropyl-functionalized mesoporous silicas, NH₂-MCM-41 and NH₂-SBA-15, as absorbents were utilized for rapid extraction, preconcentration and determination of trace amounts of silver. Flow rates of sample and eluent, pH, eluent solution, type, concentration and the least amount of eluent for desorption of silver ions were optimized; moreover, break through volume and the effect of various cationic interferences on the sorption of silver were evaluated. The extraction efficiency of silver ions was greater than 95% for MCM-41-NH₂ and 85% for SBA-15-NH₂ and the limit of detection (LOD) was less than 4 ng mL^?1 for both functionalized mesoporous silicas. The preconcentration factor was greater than 210 and the relative standard deviation (RSD) was <2%. The adsorption capacity of the mesoporous silicas is higher than 143 mg g^?1 for NH₂-MCM-41 and 137 mg g^?1 for NH₂-SBA-15. Under similar experimental conditions the results for these solid phases were compared with each other. NH₂-SBA-15, in spite of larger pore size diameter and adsorption of silver ions in higher flow rates has lower recovery and a higher RSD compared to MCM-41. This method has been applied to determine silver in photographic emulsions and real samples.     

Photocatalytic degradation of triazine dyes over N-doped TiO2 in solar radiation

Photocatalytic degradation of the reactive triazine dyes Reactive Yellow 84 (RY 84), Reactive Red 120 (RR 120), and Reactive Blue 160 (RB 160) on anatase phase N-doped TiO₂ in the presence of natural sunlight has been carried out in this work. The effect of experimental parameters like initial pH and concentration of dye solution and dosage of the catalyst on photocatalytic degradation have also been investigated. Adsorption of dyes on N-doped TiO₂ was studied prior to photocatalytic studies. The studies show that the adsorption of dyes on N-doped TiO₂ was high at pH 3 and follows the Langmuir adsorption isotherm. The Langmuir monolayer adsorption capacity of dyes on N-doped TiO₂ was 39.5, 86.0, and 96.3 mg g^?1 for RY 84, RR 120, and RB 160, respectively. The photocatalytic degradation of the dyes follows pseudo first-order kinetics and the rate constant values are higher for N-doped TiO₂ when compared with that of undoped TiO₂. Moreover, the degradation of RY 84 on N-doped TiO₂ in sunlight was faster than the commercial Aeroxide^® P25. However, the P25 has shown higher photocatalytic activity for the other two dyes, RR 120 and RB 160. The COD of 50 mg l^?1 Reactive Yellow-84, RR 120 and RB 160 was reduced by 65.1, 73.1, and 69.6 %, respectively, upon irradiation of sunlight for 3 h in the presence of N-doped TiO₂. The photocatalyst shows low activity for the degradation of RY 84 dye, when its concentration was above 50 mg l^?1, due to the strong absorption of photons in the wavelength range 200–400 nm by the dye solution. LC–MS analysis shows the presence of some triazine compounds and formimidamide derivatives in the dye solutions after 3 h solar light irradiation in the presence of N-doped TiO₂.     

Water uptake and dye sorption studies of chemically crosslinked highly swollen novel ternary acrylamide‐based hydrogels including citraconic acid and sodium acrylate

Highly swollen hydrogels made by the polymerization of acrylamide (AAm) with some anionic monomers such as citraconic acid (CITA) and sodium acrylate (SA) were investigated as a function of composition to find materials with swelling and dye sorption properties. Highly swollen AAm/CITA/SA or AAm/SA/CITA hydrogels were prepared by free radical solution polymerization in aqueous solutions of AAm with CITA and SA as co‐monomers and two multifunctional crosslinkers such as ethylene glycol dimethacrylate (EGDMA) and 1,4‐butanediol dimethacrylate (BDMA). Swelling experiments were performed in water at 25°C, gravimetrically. Chemically crosslinked AAm/CITA/SA or AAm/SA/CITA hydrogels were used in experiments on sorption of water‐soluble monovalent cationic dye such as “Nil blue” (Basic Blue 12; BB 12). Equilibrium percentage swelling values of AAm/CITA/SA or AAm/SA/CITA hydrogels were calculated in the range of 1797–22,098%. Some swelling kinetic parameters were found. Diffusion behavior of water was investigated. Water diffusion into the hydrogels was found to be non‐Fickian in character. For sorption of cationic dye, BB 12 into the hydrogels was studied by batch sorption technique at 25°C. AAm/CITA/SA or AAm/SA/CITA hydrogels in the dye solutions showed coloration, whereas AAm hydrogel did not show sorption of any dye from the solution. The sorption capacity of AAm/CITA/SA or AAm/SA/CITA hydrogels was investigated. At the end of the experiments, 21.70–78.91% BB 12 adsorptions were determined. Copyright © 2007 John Wiley & Sons, Ltd.     

In Silico and in Vitro Physicochemical Screening of Rigidoporus sp. Crude Laccase-assisted Decolorization of Synthetic Dyes—Approaches for a Cost-effective Enzyme-based Remediation Methodology

The objective of this paper is to compare in silico data with wet lab physicochemical properties of crude laccase enzyme isolated from Rigidoporus sp. using wheat bran as solid substrate support towards dye decolorization. Molecular docking analysis of selected nine textile and non-textile dyes were performed using laccase from Rigidoporus lignosus as reference protein. Enzyme-based remediation methodology using crude enzyme enriched from solid state fermentation was applied to screen the effect of four influencing variables such as pH, temperature, dye concentration, and incubation time toward dye decolorization. The extracellular crude enzyme decolorized 69.8 % Acid Blue 113, 45.07 % Reactive Blue 19, 36.61 % Reactive Orange 122, 30.55 % Acid Red 88, 24.59 % Direct Blue 14, 18.48 % Reactive Black B, 16.49 % Reactive Blue RGB, and 11.66 % Acid Blue 9 at 100 mg/l dye concentration at their optimal pH at room temperature under static and dark conditions after 1 h of incubation without addition of any externally added mediators. Our wet lab studies approach, barring other factors, validate in silico for screening and ranking textile dyes based on their proximity to the T1 site. We are reporting for the first time a combinatorial approach involving in silico methods and wet lab-based crude laccase-mediated dye decolorization without any external mediators.     

Biodecolorization of Azo Dye Remazol Orange by Pseudomonas aeruginosa BCH and Toxicity (Oxidative Stress) Reduction in Allium cepa Root Cells

In this report a textile azo dye Remazol orange was degraded and detoxified by bacterium Pseudomonas aeruginosa BCH in plain distilled water. This bacterial decolorization performance was found to be pH and temperature dependent with maximum decolorization observed at pH 8 and temperature 30 °C. Bacterium tolerated higher dye concentrations up to 400 mg?l^?1. Effect of initial cell mass showed that higher cell mass concentration can accelerate decolorization process with maximum of 92 % decolorization observed at 2.5 g?l^?1 cell mass within 6.5 h. Effect of various metal ions showed Mn has inducing effect whereas Zn strongly inhibited the decolorization process at 5 mM concentration. Analysis of biodegradation products carried out with UV–vis spectroscopy, HPTLC and FTIR confirmed the decolorization and degradation of Remazol orange. Possible route for the degradation of dye was proposed based on GC-MS analysis. During toxicological scrutiny in Allium cepa root cells, induction in the activities of superoxide dismutase (SOD), guaiacol peroxidase (GPX) and inhibition of catalase (CAT) along with raised levels of lipid peroxidation and protein oxidation in dye treated samples were detected which conclusively indicated the generation of oxidative stress. Less toxic nature of the dye degraded products was observed after bacterial treatment.     

Incorporation of Triarylmethane Dyes into Sol–Gel Matrices Deposited on Textiles

The incorporation of triarylmethane dyes into sol–gel layers formed by modified silica was used for coating of textile materials. The coatings were performed with three triarylmethane dyes differ in electrical net charge and structure: The cationic dye Malachite Green, the anionic Guinea Green and the non-polar Reflex Blue 61. All coating procedures were performed using an acidic sol–gel process starting from a solution of tetraethoxysilane (TEOS) and the dye in a mixture of water and ethanol. Depositions were performed on polyester, polyamide and cotton textiles. Investigation of leaching and photobleaching fastness showed that the stability of the dyes was enhanced by incorporation into the silica layer. Sufficient leaching fastness was only achieved with the cationic dye due to direct attractive electrostatic interaction with the negatively charged silica matrix. Also the addition of a small amount of epoxysilane to the silica sols lead to an enhancement of leaching and bleaching fastness.     

Optimization of Direct Blue 71 sorption by organic rich-compost following multilevel multifactor experimental design

Removal of a troublesome textile dye, Direct Blue 71 (DB71) from water by a food waste compost was assessed in the current study. Since compost dye sorption is a multi-factor process influenced by mass, pH, concentration, temperature, contact time, and salinity, the cumulative influence of all parameters on DB71 removal was examined following an optimal multilevel multifactor experimental design. The process had to be presented using both linear and interaction terms, according to the variables analysis: Dye sorption = –0.050Mass + 0.122Conc–0.114pH + 0.132Time – 0.074Temp + 0.056Sal + 0.103Mass × Conc + 0.226 Mass × pH – 0.257Mass × Time – 0.112Mass × Temp – 0.041Mass × Sal + 0.008Conc × pH + 0.100Conc × Time + 0.089Conc × Temp + 0.167Conc × Sal – 0.245pH × Time – 0.231pH × Temp – 0.123pH × Sal + 0.358Tim × Temp + 0.355Tim × Sal – 0.045Temp × Sal (R² = 0.9241)Salinity and pH were positively correlated with concentration, and contact time with temperature and salinity, to get better dye uptake. The optimal conditions for dye removal were the following: solid:liquid ratio 1:375, pH 3.0, initial dye concentration 400 mg L^?1, contact time 240 min, salinity 0.6 M NaCl, temperature 50 °C. At the optimum combination of factors, equilibrium sorption isotherm and sorption kinetics were studied. Kinetic analysis indicated high sorption rate 4.0 mg g^?1 min^?1 while 28% of maximum capacity was reached within the first 10 min of interaction. Sorption isotherm has L2-shape which reflected surface saturation at high solute concentration with low competition with solvent molecules, with a maximum sorption capacity of 95.4 mg g^?1. In column experiments performed at bed depth 5.1–12.8 cm, flow rate 1.0–2.0 mL min^?1 and influent concentration 10–20 mg L^?1, sorption capacity was 19.6 mg g^?1, which represents 21% of the maximum capacity at equilibrium conditions. IR analysis of dye-loaded-compost confirmed the contribution of hydrophobic-hydrophobic forces in the sorption process.     

Chemical modification of a cellulose-based material to improve its adsorption capacity for anionic dyes

A cellulosic material was modified to enhance its anionic dye adsorption capacity. The chemically modified cucumber peel was characterized by FTIR, SEM, TGA, XRD, proximate and ultimate analyses, and pH_zpc measurements, and was used for the removal of toxic textile dyes. The kinetic data followed the pseudo-first-order model. The isotherm data fitted to the Langmuir model giving maximum capacities of 95.24 and 129.87 mg g^?1 for Reactive Black 5 and Direct Blue 71, respectively. Thermodynamic parameters suggest that the process is spontaneous and endothermic. The recovery of the adsorbed dyes was achieved by NH₃ and NaOH solutions.     

Development of a facile sensor for the determination of Brilliant Blue FCF in beverages

A facile method was developed for the detection of Brilliant Blue FCF (BB FCF) (E133), a synthetic soluble colorant in common beverages. The method is based on a new composite of multi-walled carbon nanotube (MWCNT)-graphite oxide (GO)-room temperature ionic liquids (MWCNT/GO-RTIL) of 1-butyl-3-methylimidazolium hexafluorophosphate with high dispersibility and strong conductivity. Differential pulse stripping voltammetry (DPSV) and the MWCNT/GO-RTIL composite-modified glassy carbon electrode (GCE) were used to determine the BB FCF in this work. Under the optimum experimental conditions, the oxidation current of BB FCF was proportional to its concentration in two linear ranges, from 6.34 μg kg^?1 to 7.93 × 10² μg kg^?1 and 7.93 × 10² μg kg^?1 to 7.93 × 10³ μg kg^?1.

The detection limit was down to 3.01 μg kg^?1 at signal-to-noise ratio of 3. Also, this method has been successfully applied in the determination of BB FCF in common beverage samples, including RIO cocktail, Bacardi Breezer and Reinnbow rum dinks. The assay results of BB FCF in drink samples obtained by the proposed method were in a good agreement with the reference values detected by high performance liquid chromatography (HPLC). The proposed method provided a useful tool for the assay of BB FCF in drink samples.     

Application of Cationic Gemini Surfactant 12-3-12 and Methylene Blue in Simple Detection of DNA and Investigation of Interaction Mechanism

The present work aims to propose a new simple assay for deoxyribonucleic acids (DNA) by applying cationic Gemini surfactant 12-3-12 and cationic dye methylene blue (MB) as resonance light scattering (RLS) probes. The formation of MB-DNA-12-3-12 complex at pH 3.99 results in enhanced RLS signals at 369 nm, which is proportional to the concentration of DNA from 0 to 0.88 mg L^?1, with determination limit of 0.014 mg L^?1. Most foreign substances do not interfere in the detection and three synthetic samples are analyzed satisfactorily. transmission electron microscopy (TEM), FTIR, and ultraviolet spectra are used to investigate the interaction mechanism.     

Structural,electrochemical, and adsorption studies of Ni and Zn benzylimidazole coordination polymers with terephthalate linkers

Two coordination polymers, [Ni(bim)₂(L1)(H₂O)₂] _n (CP-1) and [Zn(bim)(L1)(Cl)] _n (CP-2) (bim = 1-benzylimidazole, L1 = terephthalic acid), were synthesized and characterized by physicochemical and spectroscopic methods. The Ni(II) center in CP-1 is octahedral, while the Zn(II) center in CP-2 is tetrahedral. CP-1 and CP-2 were used to modify carbon paste electrodes to assess their effect on the electrochemical behavior of ferricyanide. The redox reactions of ferricyanide on both electrodes proved to be reversible and diffusion controlled, with ferricyanide diffusion coefficients for CP-1 and CP-2 of 1.88 × 10⁵ and 3.44 × 10⁵ cm² s^?1, respectively. These coordination polymers were also investigated for their adsorption behavior toward two dyes: Chicago sky blue and methylene blue. CP-1 and CP-2 both rapidly adsorbed the anionic Chicago sky blue dye by different intermolecular interactions; in contrast, the cationic methylene blue dye was adsorbed to a lesser extent. The adsorption of these CPs depends on the charge but not the size of the dye. Addition of methanolic potassium nitrate solution caused the release of the adsorbed dyes.