Adsorption of safranine T from aqueous medium by nano mesoporous MCM-41: adsorption equilibrium, kinetics, and thermodynamics

Introduction: In industrial production, a small amount of saffron T emissions will cause increase of water color and increase of chemical oxygen consumption, so study of the decolorization of saffron T wastewater has an important practical significance. Methods: MCM (Mobil Composition of Matter)-41 molecular sieve was synthesized by hydrothermal method. Power Xray diffraction and scanning electron microscopy were used to characterize the sample. Safranine T dye was adsorbed from water by the MCM-41 prepared. Kinetics and thermodynamics of the adsorption were studied. Results: The MCM-41 sample presented spherical particles and regular. The BET (Brunner-Emmett-Teller) specific surface area of the sample determined by 77 K low temperature nitrogen adsorption-desorption isotherm was 932 m2 /g. Its average particle diameter was 110 nm. TEM (transmission electron microscopy) results showed that the sample structure presented a honeycomb pore structure and the average pore diameter was 3.0 nm. The results showed that when room temperature was 20 ± 1 ℃, adsorbate safranine T: adsorbent MCM-41 = 20 : 1，the optimum pH value of adsorption was 4.0 and contact time was 20 min, the adsorption rate reached 98.29% and the adsorption capacity was 19.66 mg/g. The entropy change and enthalpy change of the adsorption system are respectively ΔS0 = 157.5 J/(mol·K); ΔH0 = 21.544 kJ/mol. When temperature was 277.15, 293.15, 303.15 K，the free energy change was respectively △G1 0 = -22.107 kJ/mol, △G2 0 = -24.627 kJ/mol, △G3 0 = -26.202 kJ/mol. Conclusion: The adsorption of safranine T by MCM-41 belongs to a pseudo-second-order adsorption. This adsorption accords with the Freundlich equation and belongs to a heterogeneous adsorption. The adsorption is an endothermic reaction of entropy increase, being spontaneous.

Electrochemical degradation of safranine T in aqueous solution by Ti/PbO2 electrodes

The electrochemical degradation of safranine T (ST) in aqueous solution was studied. The effects of current density, initial concentration of ST, initial pH values, and Na2SO4 concentration on electrocatalytic degradation of ST in the aqueous solution by Ti/PbO2 electrode were analyzed. The experimental results showed that the electrochemical oxidization reaction of ST fitted a pseudo first order kinetics model. By using the Ti/ PbO2 electrode as the anode, 99.96% of ST can be eliminated at 120 min. It means that the electrochemical degradation of ST in aqueous solution by the Ti/PbO2 electrode was very effective. The optimal reaction conditions were as follows: current density, 40 mA cm−2; initial ST concentration, 100 mg L−1; Na2SO4 concentration, 0.20 mol L−1; initial pH, 6. It can be known from the test of UV–vis and HPLC in the reaction process that the intermediates will be generated, and the possible intermediate structure was studied by HPLC–MS test. However, with the progress of degradation reaction, the intermediates will eventually be oxidized into CO2 and H2O. Cyclic voltammetry and fluorescence experiments proved that ST was indirectly oxidized through the generation of hydroxyl radicals. Under the optimal reaction conditions, the energy required to completely remove ST was 17.92 kWh/m3.

Preparation of a Stable Nanoscale Manganese Residue-Derived FeS@Starch-Derived Carbon Composite for the Adsorption of Safranine T

To develop a novel, low-cost adsorbent with natural material and industrial waste as raw materials, nanoscale manganese residue-derived FeS@starch-derived carbon (MR–FeS@SC) composite was prepared by the carbonization of starch–manganese residue gel. Manganese residue-derived FeS (MR–FeS) and starch-derived carbon (SC) were also prepared as contrasts for comparative studies. The MR–FeS@SC nanocomposite exhibited relatively large specific surface area and micropore volume, appropriate pore size, abundant functional groups, strong interaction between the functional groups of SC and MR–FeS, and the immobilization and uniform distribution of MR–FeS nanoparticles onto SC support material, which contributed to better adsorption properties for the removal of Safranine T (ST) from the aqueous solution compared with those of MR–FeS and SC. The adsorption could be conducted at a wide range of pH and temperature to achieve a satisfy removal efficiency of ST with MR–FeS@SC nanocomposite as adsorbent. The adsorption kinetics well followed the pseudo-second-order model, and the dominant mechanism was chemisorption. The adsorption behavior was well described by the Langmuir isotherm model. Due to the strong interaction between MR–FeS nanoparticles and SC support, MR–FeS@SC nanocomposite exhibited better reusability and stability even after fifteen cycles. This study provides a facile method of preparing effective and stable adsorbents for the treatment of dye wastewater.

Adsorption Thermodynamics and Dynamics of Three Typical Dyes onto Bio-adsorbent Spent Substrate of Pleurotus eryngii

Dyeing wastewater is very hard to treat, and adsorption could be a good choice. Spent substrate of Pleurotus eryngii (SSPE) was first used to adsorb malachite green, safranine T and methylene blue from aqueous solutions, and the corresponding adsorption isotherm, thermodynamics and dynamics models were simulated. More than 93% of the dyes were removed with solutions with 100 mg/L of initial dye concentration, 1 g of SSPE and pH of 6.0 after adsorption for 4 h. Freundlich isotherm models fit better the adsorption data than Langmuir models. Adsorption of the dyes onto SSPE was a spontaneous exothermic process based on an adsorption thermodynamics model. SSPE could adsorb the dyes rapidly, and a second-order kinetics model fit better with the adsorption data than a pseudo first-order kinetics model. Accordingly, SSPE could be a good bio-adsorbent for the removal of malachite green, safranine T and methylene blue from the aqueous solution.