Binary Dye Research Articles

Photodegradation of Binary Azo Dyes Using Core-Shell Fe<sub>3</sub>O<sub>4</sub>/SiO<sub>2</sub>/TiO<sub>2</sub> Nanospheres

Photodegradation has emerged as an environmentally friendly method of decomposing harmful dyes in wastewater. In this study, core-shell Fe3O4/SiO2/ TiO2 nanospheres with magnetic cores were obtained from synthesised magnetic Fe3O4 nanoparticles through the precipitation method, the surface of the magnetic Fe3O4 nanoparticles was coated with a silica (SiO2) layer by hydrolysis of tetramethoxysilane (TMOS) as a silica source, and finally, Fe3O4/SiO2 nanospheres were coated with titanium (TiO2) layer using tetrabutyltitanate (TBT) as a precursor through the sol-gel process. The morphology and structure of the prepared materials were characterised by X-ray diffraction (XRD) analysis, scanning electron microscopy (SEM), X-ray energy dispersive spectrometry (EDAX), Fourier transform infrared spectroscopy (FT-IR), and atomic force microscopy (AFM). The photocatalytic activities of the prepared core-shell nanospheres were studied using binary azo dyes, namely methyl orange (anionic dye, MO) and methylene blue (cationic dye, MB) in aqueous solution under UV light irradiation (365 nm), and UV-Vis spectrophotometer was utilised to monitor the amount of each dye in the mixture. It was found that 90.2% and 100% of binary MO and MB were removed for 5 h, respectively. The results revealed that the efficiency of the photocatalytic degradation of the core-shell nanospheres was not degreased after five runs that can be used as recyclable photocatalysts. The results show that the performance of the prepared core-shell nanospheres was better than that of commercial TiO2 nanoparticles. Moreover, the magnetic separation properties of the core-shell Fe3O4/SiO2/TiO2 nanospheres can enable the prepared materials to have wider application prospects.

Surface Modified Multi-walled Carbon Nanotubes: Preparation and Binary System Dye Removal

Surface modification of multiwalled carbon nanotube (CNT) using sodium dodecyl sulfate (SDS) was studied in this paper. The surface modified CNT (CNT-SDS) was used to remove dyes from single and binary systems. The surface characteristics of CNT-SDS were investigated using Fourier transforms infrared (FTIR) and scanning electron microscopy (SEM). Basic Blue 41 (BB41) and Basic Red 18 (BR18) were used as model dyes. The kinetic of dye removal from single and binary systems using CNT-SDS was studied. The kinetic of dye adsorption onto CNT-SDS followed pseudo-second order model for both systems. The Langmuir and Freundlich isotherm models were applied to experimental data of single systems and the isotherm constants were calculated. The adsorption capacities of CNT and CNT-SDS for BB41 and BR18 were 90 and 80, 185 and 135 mg/g, respectively. The results showed that the CNTSDS as an adsorbent with high dye adsorption capacity might be a suitable alternative to remove dyes from colored wastewater.

Removal of Reactive Anionic Dyes from Binary Solutions by Adsorption onto Quaternized Kenaf Core Fiber

The most challenging mission in wastewater treatment plants is the removal of anionic dyes, because they are water-soluble and produce very shining colours in the water. In this regard, kenaf core fiber (KCF) was chemically modified by the quaternized agent (3-chloro-2-hydroxypropyl)trimethylammonium chloride to increase surface area and change the surface properties in order to improve the removing reactive anionic dyes from binary aqueous solution. The influencing operating factors like dye concentration, pH, adsorbent dosage, and contact time were examined in a batch mode. The results indicate that the percentage of removal of Reactive Red-RB (RR-RB) and Reactive Black-5 (RB-5) dyes from binary solution was increased with increasing dyes concentrations and the maximum percentage of removal reached up to 98.4% and 99.9% for RR-RB and RB-5, respectively. Studies on effect of pH showed that the adsorption was not significantly influenced by pH. The equilibrium analyses explain that, in spite of the extended Langmuir model failure to describe the data in the binary system, it is better than the Jain and Snoeyink model in describing the adsorption behavior of binary dyes onto QKCF. Also, the pseudo-second-order model was better to represent the adsorption kinetics for RR-RB and RB-5 dyes on QKCF.

Random laser emission at dual wavelengths in a donor-acceptor dye mixture solution

The work was aimed to generate random laser emissions simultaneously at two wavelengths in a weakly scattering system containing mixture of binary dyes, rhodamine-B (Rh-B) and oxazine-170 (O-170) dispersed with ZnO nano-particles serving as scattering centres. Random lasing performances for individual Rh-B dye were extensively studied for varying small signal gain/scatterer density and we found lasing threshold to significantly depend upon number density of dispersed nano-particles. In spite of inefficient pumping, we demonstrated possibility of random lasing in O-170 dye solution on account of resonance energy transfer from Rh-B dye which served as donor. At optimum concentrations of fluorophores and scatterer in dye mixture solution, incoherent random lasing was effectively attained simultaneously at two wavelengths centered 90nm apart. Dual-emission intensities, lasing thresholds and rate of amplifications could be controlled and made equivalent for both donor and acceptor in dye mixture solution by appropriate choice of concentrations of dyes and scatterers.

Selective and Competitive Adsorption of Azo Dyes on the Metal–Organic Framework ZIF-67

Zeolitic imidazole frameworks (ZIFs), a new adsorbent with a high chemical and thermal stability and a high adsorption capacity, are used for adsorptive removal of azo dyes. The synthesized ZIF-67 was characterized with Fourier transform infrared spectroscopy (FTIR), thermogravimetric–differential thermal analysis (TG–DTA) and zeta potential instrument. The adsorption of some azo dyes on ZIF-67 in the single dye systems showed that the removal efficiencies are congo red > methyl orange > methyl red > methyl blue. The highest adsorption capacity of congo red and methyl orange were 3900 and 1340 mg/g, respectively. In a binary dye system the adsorption capacity of congo red decreased, while the removal efficiency of methyl orange increased in comparison with the single systems, indicating that a competitive adsorption of congo red and methyl orange over the ZIF-67 occurred. The experimental data indicate that the electrostatic attraction between ZIF-67 and congo red is the major driving force and the π–π stacking is also responsible for dye adsorption. After 5 cycles of ZIF-67 adsorption and desorption, the congo red removal efficiency maintained more than 95%.

Amine functionalized multi-walled carbon nanotubes: Single and binary systems for high capacity dye removal

The aim of this study was to develop a feasible and cost effective method to produce amine functionalized multi-walled carbon nanotubes (CNT-NH2) and investigate the ability of this CNT-NH2 material to adsorb anionic dyes in single and binary (mixture of dyes) systems. For this purpose, pristine CNTs were functionalized by primary and secondary functional groups namely (-NH2) and (-NH), respectively. Acid Blue 45 (AB45) and Acid Black 1 (AB1) were used as anionic dye models for adsorption. FTIR, SEM, BET, Raman Spectra, and Zeta potential measurements have been employed for characterizing the synthetic nanocomposite and these techniques indicated that the amino functionalized CNTs have been favorably synthesized. The effects of different operational parameters including pH, initial dye concentration, adsorbent dosage, and salt on dye removal were evaluated. The dye adsorption isotherm and kinetics were also studied. The results of this study indicated that the stronger interactions between CNT-NH2 and AB1 suggest a higher adsorption of AB45 compared to AB1 in both single and binary dye systems. Moreover, the maximum adsorption capacities of the studied functionalized nanotube in single dye solutions, for AB45 and AB1 were 714 and 666mgg−1, respectively. These capacities are exceptionally high for the removal of acid dyes. It was found that AB45 and AB1 adsorption on the CNT-NH2 followed the Langmuir isotherm model and pseudo-second order kinetics model in both single and binary systems. According to the results of this study the CNT-NH2 were an effective adsorbent to remove anionic dyes from single and binary systems.

Photocatalytic Treatment of Binary Mixture of Dyes using UV/TiO2 Process: Calibration, Modeling, Optimization and Mineralization Study

Abstract Photocatalytic treatment of a binary dye mixture (Acid Blue 113 (AB113) and Acid Red 114 (AR114)) has been done in a slurry pond reactor using TiO2 as a photocatalyst with UV light irradiation (UV-C). Two different methods, namely multivariate calibration and first order derivative spectrophotometric were used to quantify each dye separately in binary dye solutions. The behavior of the photocatalytic degradation of a binary dye mixture was predicted using an artificial neural network (ANN) model. Five process parameters (initial concentration of AB113 dye, initial concentration of AR114 dye, TiO2 dose, initial pH of the dye mixture and time were used as inputs and decolorization efficiency of AB113 and AR114 were used as output of the ANN. The parametric optimization has been done by the multi-response optimization with desirability function methodology. Optimization by Central Composite Design (CCD) effectively handles the relations among optimizing process variables and its prediction concurred well with the experimental run and artificial neural network (ANN) model. The reaction kinetic rates of decolorization of both dyes (AB113 and AR114) were found to be first order. Total organic carbon (TOC) removal and possible reaction pathway show the total mineralization of both dyes in binary dye mixture.

Removal of binary dyes mixtures with opposite and similar charges by adsorption, coagulation/flocculation and catalytic oxidation in the presence of CeO2/H2O2 Fenton-like system

In this study, the removal of binary mixtures of dyes with similar (Orange II/Acid Green 25) or opposite charges (Orange II/Malachite Green) was investigated either by simple adsorption on ceria or by the heterogeneous Fenton reaction in presence of H2O2. First, the CeO2 nanocatalyst with high specific surface area (269 m2/g) and small crystal size (5 nm) was characterized using XRD, Raman spectroscopy and N2 physisorption at 77 K. The adsorption of single dyes was studied either from thermodynamic and kinetic viewpoints. It is shown that the adsorption of dyes on ceria surface is highly pH-dependent and followed a pseudo-second order kinetic model. Adsorption isotherms fit well the Langmuir model with a complete monolayer coverage and higher affinity towards Orange II at pH 3, compared to other dyes. For the (Orange II/Acid Green 25) mixture, both the amounts of dyes adsorbed on ceria surface and discoloration rates measured from Fenton experiments were decreased by comparison with single dyes. This is due to the adsorption competition existing onto the same surface Cex+ sites and the reaction competition with hydroxyl radicals, respectively. The behavior of the (Orange II/Malachite Green) mixture is markedly different. Dyes with opposite charges undergo paired adsorption on ceria as well as homogeneous and heterogeneous coagulation/flocculation processes, but can also be removed by heterogeneous Fenton process.

Application of ZnO nanorods loaded on activated carbon for ultrasonic assisted dyes removal: Experimental design and derivative spectrophotometry method

A method based on application of ZnO nanorods loaded on activated carbon (ZnO-NRs-AC) for adsorption of Bromocresol Green (BCG) and Eosin Y (EY) accelerated by ultrasound was described. The present material was synthesized under ultrasound assisted wet-chemical method and subsequently was characterized by FE-SEM, TEM, BET and XRD analysis. The extent of contribution of conventional variables like pH (2.0–10.0), BCG concentration (4–20mgL−1), EY concentration (3–23mgL−1), adsorbent dosage (0.01–0.03g), sonication time (1–5min) and centrifuge time (2–6min) as main and interaction part were investigated by central composite design under response surface methodology. Analysis of variance (ANOVA) was adapted to experimental data and guide the best operational conditions mass by set at 6.0, 9mgL−1, 10mgL−1, 0.02g, 4 and 4min for pH, BCG concentration, EY concentration, adsorbent dosage, sonication and centrifuge time, respectively. At these specified conditions dye adsorption efficiency was higher than 99.5%. The suitability and well prediction of optimum point was tested by conducting five experiments and respective results revel that RSD% was lower than 3% and high quality of fitting was confirmed by t-test. The experimental data were best fitted in Langmuir isotherm equation and the removal followed pseudo second order kinetics. The experimentally obtained maximum adsorption capacities were estimated as 57.80 and 61.73mgg−1 of ZnO-NRs-AC for BCG and EY respectively from binary dye solutions. The mechanism of removal was explained by boundary layer diffusion via intraparticle diffusion.

Rhodamine 6G assisted adsorption of metanil yellow over succinamic acid functionalized MCM-41

The adsorption properties of succinamic acid functionalised MCM-41 (SA-MCM-41) towards dyes aqueous solution, such as rhodamine 6G (R6G), methylene blue (MB) and metanil yellow (MY), were studied. SA-MCM-41 was synthesised using a three step synthesis strategy, starting with the preparation of MCM-41 through a sol–gel methodology. Succinamic acid functionality was introduced through a ring opening reaction of succinic anhydride (SA) over the propyl amine functionality of A-MCM-41 in presence of trimethylamine. The materials at each synthesis step were characterised by X-ray diffraction, transmission electron microscopy, scanning electron microscopy, N2 adsorption–desorption isotherms, Fourier transform infrared spectroscopy, and 29Si and 13C nuclear magnetic resonance spectroscopies. SA-MCM-41 exhibited good adsorption capacity towards R6G and MB but poor adsorption for MY from the individual dye solutions. The competitive adsorption from binary and ternary dye mixtures showed that SA-MCM-41 can remove MY effectively in the presence of R6G. The adsorption behaviour of R6G and MY over SA-MCM-41 from binary and ternary mixtures highlight the possibility of multilayer adsorption. The MY removal efficiency of pristine MCM-41 from R6G-MY binary mixture was also tested.

Simultaneous photodegradation of two textile dyes using TiO2 as a catalyst

The simultaneous photocatalytic degradation of two dyes: methylene blue (MB), a cationic dye, and arylazo pyridone dye (SD), an anionic dye was investigated using sol–gel prepared TiO2 particles. The paper shows the main difference in degradation kinetics between single dye solution and binary dye solutions. The effects of competitive adsorption and the concentration of the dyes on degradation rate were analyzed. The preferential adsorption capacity of TiO2 toward MB was attributed to electrostatic interactions between the cationic dye and negatively charged TiO2 surface, while repulsion between the negatively charged surface of the catalyst and SD dye results in its lower adsorption capacity. The TiO2 surface charge and accordingly adsorption affinity of investigated dyes were found to be the main factors affecting degradation rate of the dyes. In the single dye system, the catalyst showed considerably higher degradation activity toward MB than to SD. In binary dye systems, the presence of SD did not affect the degradation of MB. On the other hand, the degradation efficiency of SD was found to be highly influenced by initial MB concentration and absorption ability of MB. In addition, higher MB concentration induces the production of a higher amount of reaction products, which also determine the SD degradation rate. Three kinetic regimes for the photodegradation of SD in binary mixtures were observed, used as a starting point to elucidate most influencing parameters for SD reaction kinetics.

Biosorption of Acid Dye in Single and Multidye Systems onto Sawdust of Locust Bean (Parkia biglobosa) Tree

Properties of raw sawdust ofParkia biglobosa, as a biosorbent for the removal of Acid Blue 161 dye in single, binary, and ternary dye systems with Rhodamine B and Methylene Blue dyes in aqueous solution, were investigated. The sawdust was characterized using Scanning Electron Microscopy, Fourier Transform Infrared spectrophotometry, X-ray diffraction, and pH point of zero charge. Batch adsorption experiments were carried out to determine the equilibrium characteristics, thermodynamics, and kinetics of the sorption processes. The data obtained were subjected to various isotherm and kinetics equations. The results showed that the adsorption processes were described by different isotherm models depending on the composition of the system; they were all spontaneous (ΔGranges from −0.72 to −5.36 kJ/mol) and endothermic (range ofΔHis 11.37–26.31 kJ/mol) and with increased randomness withΔSvalues of 55.55 and 98.78 J·mol/K for single and ternary systems, respectively. Pseudo-second-order kinetics model gave better fit for all the sorption systems studied irrespective of the differences in composition, with the initial and overall rate constants higher for the mixtures than for the single system (6.76 g·mg−1min−1). The presence of Rhodamine B and Methylene Blue had a synergetic effect on the maximum monolayer capacity of the adsorbent for Acid Blue 161 dye.

Photocatalytic degradation of binary mixture of toxic dyes by HKUST-1 MOF and HKUST-1-SBA-15 in a rotating packed bed reactor under blue LED illumination: central composite design optimization

A new composite of mesoporous materials, HKUST-1 metal organic framework and SBA-15, was synthesized and applied to the simultaneous visible-light-driven photodegradation of a binary dye mixture of safranin O and malachite green.

Mono and simultaneous removal of crystal violet and safranin dyes from aqueous solutions by HDTMA-modified Spirulina sp.

The process of mono and binary removal of crystal violet and safranin dyes by Spirulina sp. (blue-green algae) modified with cationic surfactant is evaluated. The surfactant used was hexadecyltrimethylammonium bromide (HDTMA). Spirulina sp. was cultivated in Zarrouk's medium. The adsorptive properties of the modified Spirulina sp. (HDTMA-algae) were tested as a function of pH (2–10), contact time (5–180min), temperature (25–45°C), and initial dye concentrations (25–300mg/L) and characterized with FTIR, SEM, EDX, XRD and BET analyses. The specific surface area of HDTMA-algae was 0.1990m2/g. The data were fitted to non-linear Langmuir, Freundlich, and Dubinin–Radushkevich (D–R) isotherm models and non linear pseudo-first-order and pseudo-second-order kinetic models. The adsorption was 75% and 88% at pH 2 for Crystal Violet and Safranin dye, respectively. The maximum adsorption capacities were 101.87mg/g and 54.05mg/g and the kF values were 0.96L/g and 3.56L/g for Crystal Violet and Safranin, respectively. The kinetics of Crystal Violet and Safranin dyes onto HDTMA-algae were best described by the pseudo-second-order kinetic model. The negative values of free energy and enthalpy change indicated the feasibility, spontaneity, and exothermic nature of the adsorption process. Also, binary adsorption of Crystal Violet and Safranin dyes onto HDTMA-algae from binary dye mixtures is compared.

Evaluation on the efficiency of ethylenediaminetetraacetic acid (EDTA)-modified rice husk as a low-cost sorbent for various dyes removal under continuous flow condition

The potential of ethylenediaminetetraacetic acid (EDTA)-modified rice husk (ERH) as a sorbent to remove both methylene blue (MB) and reactive orange 16 (RO 16) in single and binary dye solutions was studied. Surface characterization of natural rice husk and ERH was investigated using field emission scanning electron microscope (FESEM) and atomic force microscope (AFM). From the FESEM micrographs, due to the absence of pores and cavities, it can be concluded that ERH is a non-porous material. The adsorption behaviour of MB and RO 16 onto column packed with ERH was investigated under continuous flow mode with three different parameters: the effect of influent concentration, the effect of bed depth and the effect of flow rate. Column studies indicated that the breakthrough time is longer for MB at lower influent concentration and flow rate. Unusual breakthrough curves were obtained for RO 16 in both single and binary dye solutions with very rapid initial breakthrough. This implies that the adsorption of RO 16 is a slow process and an effective adsorption only takes place after a sufficient lapse of time. Different mathematical models were used to characterize the fixed-bed performance for the adsorption process involved, namely bed depth service time (BDST) model, Adams–Bohart model and Clark model.

Single and binary adsorption of azo and anthraquinone dyes by chitosan-based hydrogel: Selectivity factor and Box-Behnken process design

Adsorption of a binary mixture of anionic dyes onto chitosan-based hydrogel (SAH) was investigated. Erichrome black T (EBT) and reactive blue 2 (RB2) were used as a model azo and anthraquinone dyes respectively. Adsorption potential of SAH was investigated under laboratory conditions as a function of initial concentration (50–400mg/L), temperate (25–55°C) and solution pH. In a single dye system, adsorption trend follows the Langmuir and pseudo second-order kinetics models. The overall rates of EBT and RB2 were noted to be controlled by film, pore and particle diffusions throughout the adsorption period. For binary dye-system, selectivity factor (A) was introduced into the extended Langmuir model, and the equilibrium data fitted well with the modified isotherm model (R2=0.96–0.99). The values of ΔG° (−17.012 to −22.473kJ/mol) of the binary dye system are within the ranges of physisorption mechanism. Box-Behnken model was utilized to estimate the competitive effects of the variables in binary dye system, and the experimental data indicates higher affinity for EBT (520.21mg/g) compared with RB2 (407.05mg/g). The reusability of SAH has proven that the adsorbent is durable and cost-effective.

Synthesis of Silica@Ni‐Co Mixed Metal Oxide Core–Shell Nanorattles and Their Potential Use as Effective Adsorbents for Waste Water Treatment

AbstractSiO2@Ni‐Co mixed metal oxide core–shell nanorattles with different Ni2+/Co2+ molar ratios have been successfully synthesized through a facile, inexpensive self‐template route by the calcination of SiO2@Ni‐Co layered double hydroxides at 500 °C. The formation of SiO2@Ni‐Co mixed metal oxide core–shell nanorattles has been confirmed by an array of characterization techniques. Field‐emission scanning electron microscopy (FE‐SEM) analysis indicates a hierarchical flowerlike morphology for the SiO2@Ni‐Co mixed metal oxide core–shell nanorattles, and transmission electron microscopy (TEM) analysis confirms the formation of core–shell nanorattles. The diffuse reflectance spectra of the SiO2@Ni‐Co mixed metal oxide core–shell nanorattles show two band‐gap absorptions attributed to metal‐to‐ligand charge‐transfer transitions (Mn+→O2–). The SiO2@Ni‐Co mixed metal oxide core–shell nanorattles have been explored as effective adsorbents for the removal of rhodamine B, methylene blue, and their mixture from aqueous solutions. The adsorption of the single dye systems follows Langmuir and Freundlich isotherms, whereas a binary Langmuir model has been applied for the binary dye systems. The SiO2@Ni‐Co mixed metal oxide core–shell nanorattles possess higher adsorption capacity for the individual dyes than for the mixture of dyes. Kinetic studies indicate that the adsorptions of rhodamine B, methylene blue, and their mixture follow pseudo‐second‐order kinetics.

Comparison between the photocatalytic degradation of single and binary azo dyes in TiO2 suspensions under solar light irradiation

Textile industries discharge a large quantity of colored wastewater which is harmful to the ecosystem. In this study, two kinds of dyes were investigated: the mono azo Acid Orange 7 (AO7) and diazo Reactive Green 19 (RG19). The photocatalytic degradation of single (AO7, RG19) azo dye and binary (AO7 and RG19 mixture) azo dye aqueous solutions was photocatalyzed by commercial titanium dioxide (TiO2, P25) under solar light irradiation. The objectives of this study are to compare the photocatalytic degradation between single and binary azo dye aqueous solution and to study the various parameters such as the effect of different initial azo dye concentrations, different initial azo dye pH values, and compare the adsorption capacity of azo dyes with and without solar light irradiation, which influences the photocatalytic activities of single and binary azo dye aqueous solutions in a TiO2 suspension. The results showed that photocatalytic degradation of AO7 and RG19 in a single azo dye aqueous solution was faster than a binary azo dye solution under the solar light irradiation process. Chemical oxygen demand results revealed that complete mineralization could be achieved for both AO7 and RG19 azo dyes under solar light irradiation within 22 hours.

SnO2 nanoparticle-loaded activated carbon for simultaneous removal of Acid Yellow 41 and Sunset Yellow; derivative spectrophotometric, artificial neural network and optimization approach

The simultaneous adsorption of Acid Yellow 41 (AY41) and Sunset Yellow (SY) onto SnO2 nanoparticle-loaded activated carbon (SnO2–NP–AC with very high BET surface area of 1278.71m2g−1) was investigated. To overcome the severe dyes spectral overlapping, derivative spectrophotometric method and principal component analysis-artificial neural network (PCA-ANN) were successfully applied for the simultaneous determination of AY41 and SY in their binary solutions. By using central composite design (CCD) under response surface methodology, the effects of variables such as contact time, adsorbent dosage, pH, AY41 concentration and SY concentration on responses such as binary dyes removal percentages were examined. Optimal values were found to be 17.9min, 0.024g, 3.1, and 15.9mgL−1 and 18.7mgL−1, respectively. In binary solutions, the best fit to modified–extended Langmuir isotherm was obtained for the whole concentration range. In binary solutions, a synergism was observed for the AY41 and SY dyes adsorption onto SnO2–NP–AC. The adsorption rates at various times were analyzed. It indicated a pseudo-second-order kinetic model for the adsorption of both dyes.

Synergistic and competitive adsorption of cationic and anionic dyes on polymer modified yeast prepared at room temperature

Poly (allylamine) modified yeast was prepared and used as an adsorbent for removal of cationic dye (rhodamine B) and anionic dye (congo red) from aqueous solution in single and binary dye systems. XPS and zeta potential analysis showed that the polymer was modified on the sorbent surface and isoelectric point of the sorbent increased from 3.2 to 9.5 after modification. Adsorption test showed that the amine groups modified yeast had higher adsorption capacity and affinity toward congo red than rhodamine B in single and binary system, revealing the electrostatic adsorption mechanism. In the single dye system, the adsorption capacities of the modified sorbent for congo red and rhodamine B were 0.24 and 0.03 mmol/g, respectively. In the binary system, rhodamine B adsorption was promoted by the presence of congo red (synergistic effect), but congo red adsorption was not promoted by the presence of rhodamine B. Antagonistic effect was observed for congo red adsorption at comparative high concentration of rhodamine B. It was for the first time to find that the ratio of the adsorption capacities for congo red and rhodamine B on the modified yeast was proportional to the ratio of the initial concentration of the two dyes. Total adsorption capacity of the modified yeast increased linearly both with the increase of the initial concentration of the two dyes.