Activation of H2O2 by Amberlyst-15 resin supported with copper(II)-complexes towards oxidation of crystal violet

Selective removal of ammonia from wastewater using Cu(II)-loaded Amberlite IR-120 resin and its catalytic application for removal of dyes

Cationic ligand exchange is one of the most predominant mechanisms for the removal of ammonia from wastewater through complex formation. The complexation technique occurs between the metal ions loaded on the surface of Amberlite IR-120 and ammonia which is present in the medium. Cu(II)-loaded Amberlite IR-120 (R-Cu2+) was prepared and described using FT-IR, TGA, SEM, and EDX techniques. The prepared R-Cu2+ was applied for the elimination of ammonia from an aqueous solution. Different cations such as Co2+ and Ni2+ were loaded onto Amberlite IR-120 to study the impact of counter cation on the removal efficiency of ammonia. The ammonia removal percentage followed the order; R-Cu2+  > R-Ni2+  > R-Co2+. The effects of contact time, pH, initial concentration, temperature, and coexisting ions on the removal of ammonia from wastewater by R-Cu2+ were investigated. The equilibrium adsorbed amount of ammonia was found to be 200 mg/g at pH = 8.6 and 303 K within 60 min using 0.1 g R-Cu2+ and an initial concentration of ammonia of 1060 mg/L. The removal of ammonia using R-Cu2+ obeyed the non-linear plot of both Freundlich and Langmuir isotherms. According to the thermodynamic parameters, the adsorption of ammonia onto R-Cu2+ was an endothermic and spontaneous process. The time-adsorption data followed the pseudo-second-order and intraparticle diffusion models. Moreover, the resulting product (R-Cu(II)-amine composite) from the adsorption process exhibited high catalytic activity and could be low-cost material for the elimination of dyes such as aniline blue (AB), methyl green (MG), and methyl violet 2B (MV2B) from wastewater.

Activated Carbon/ZnFe2O4 Nanocomposite Adsorbent for Efficient Removal of Crystal Violet Cationic Dye from Aqueous Solutions

The aim of this study was to investigate the potential advantage of ZnFe₂O₄-incorporated activated carbon (ZFAC), fabricated via a simple wet homogenization, on the removal of cationic dye crystal violet (CV) from its aqueous solutions. The as-prepared ZFAC nanocomposite was characterized using Fourier transform infrared (FTIR), X-ray diffraction (XRD), nitrogen adsorption, scanning electron microscope (SEM), thermogravimetric analysis (TGA), and ultraviolet-visible (UV-Vis). Batch adsorption operating conditions such as the pH (3-11), CV concentration (25-200 ppm), ZFAC dose (10-50 mg), temperature (23-45 °C), and contact time were evaluated. The results indicate pH-dependent uptake (optimum at pH 7.2) increased with temperature and CV concentration increase and decreased as adsorbent dose increased. Modeling of experimental data revealed better fit to the Langmuir than Freundlich and Temkin isotherms, with maximum monolayer capacities (Q_m) of 208.29, 234.03, and 246.19 mg/g at 23, 35, and 45 °C, respectively. Kinetic studies suggest pseudo-second order; however, the intra-particle diffusion model indicates a rate-limiting step controlled by film diffusion mechanism. Based on the thermodynamic parameters, the sorption is spontaneous (-ΔG°), endothermic (+ΔH°), and random process (+ΔS°), and their values support the physical adsorption mechanism. In addition to the ease of preparation, the results confirm the potential of ZFAC as a purifier for dye removal from polluted water.

Amberlyst-15 supported zirconium sulfonate as an efficient catalyst for Meerwein-Ponndorf-Verley reductions

The Meerwein-Ponndorf-Verley (MPV) reaction is an important chemoselective route for carbonyl group hydrogenation, and thus designing new and effective catalysts for this transformation remains important and challenging. In this work, a new sulfonate coordinated Zr(IV) catalyst was prepared by the coordination of Zr(IV) onto the sulfonate groups of Amberlyst-15, which can effectively catalyze the MPV reaction and quantitatively convert carbonyl compounds to the corresponding alcohols with high reactivity and stability. Detailed mechanistic investigations reveal that the catalytic performance of Zr-AIER can be attributed to the synergetic effect between Zr⁴⁺ and the sulfonate group, and the porous structure with high surface area.

Adsorptive Performance of Polypyrrole-Based KOH-Activated Carbon for the Cationic Dye Crystal Violet: Kinetic and Equilibrium Studies

The aim of this work was to investigate the adsorptive performance of the polypyrrole-based KOH-activated carbon (PACK) in the removal of the basic dye crystal violet (CV) using a batch adsorption system. The equilibrium data, obtained at different initial CV concentrations ( $C_0=50–500\text{mg}/\text{L}$ ) and temperatures (25–45°C), were interpreted using the Langmuir, Freundlich, Temkin, and Dubinin-Radushkevich isotherms, with the Langmuir model providing a better fit ( $R^2\ge 0.9997$ ) and a maximum adsorption capacity of 497.51 mg/g at 45°C. Under the examined conditions, the values of the thermodynamic parameters free energy, enthalpy, and entropy indicate a spontaneous, endothermic, and physisorption adsorption process. The kinetic data of the adsorption process were very well described by a pseudo-second-order model ( $R^2\ge 0.9996$ ). However, surface diffusion seems to be the main rate-controlling step. Thus, we concluded that PACK shows commercial potential for the removal of cationic dyes such as CV from industrial effluent.

Heterogeneous PVC cation-exchange membrane synthesis by electrospinning for reverse electrodialysis

Blue energy (or salinity gradient energy) is a renewable, carbon-neutral, and continuous electrical energy source that can be obtained via the reverse electrodialysis (RED) technique. The viability of this technology strictly depends on the performance and cost of the ion-exchange membranes (IEMs) that compose the RED units; designing the optimal membrane represents a critical challenge due to the complex relation between the performance, properties, and structure of the membrane. In this work, we present our findings on an electrospun cation-exchange membrane based on polyvinyl chloride (PVC), a strongly acidic cation exchange resin, with sodium dodecyl sulfate (SDS) as an additive. We contrast it with a similar membrane produced with the more conventional casting solution technique. The electrospinning technique provides thinner and more homogeneous membranes than those synthesized via casting. The membranes were characterized using morphological, spectroscopic, and analytical methods. Scanning electron microscopy images depicted an intertwined nanofiber mesh within the membrane. We also synthesized the same electrospun cation exchange membrane without SDS; this membrane presented 63% less swelling, and a significant increase in the fixed charge density (CDfix) (119.6 meq/g) when compared to its casting solution counterpart (34 meq/g). This suggests an enhanced permselectivity, and thus better performance for blue energy generation in RED units.

Custom-Made Ion Exchange Membranes at Laboratory Scale for Reverse Electrodialysis

Salinity gradient power is a renewable, non-intermittent, and neutral carbon energy source. Reverse electrodialysis is one of the most efficient and mature techniques that can harvest this energy from natural estuaries produced by the mixture of seawater and river water. For this, the development of cheap and suitable ion-exchange membranes is crucial for a harvest profitability energy from salinity gradients. In this work, both anion-exchange membrane and cation-exchange membrane based on poly(epichlorohydrin) and polyvinyl chloride, respectively, were synthesized at a laboratory scale (255 c m 2) by way of a solvent evaporation technique. Anion-exchange membrane was surface modified with poly(ethylenimine) and glutaraldehyde, while cellulose acetate was used for the cation exchange membrane structural modification. Modified cation-exchange membrane showed an increase in surface hydrophilicity, ion transportation and permselectivity. Structural modification on the cation-exchange membrane was evidenced by scanning electron microscopy. For the modified anion exchange membrane, a decrease in swelling degree and an increase in both the ion exchange capacity and the fixed charge density suggests an improved performance over the unmodified membrane. Finally, the results obtained in both modified membranes suggest that an enhanced performance in blue energy generation can be expected from these membranes using the reverse electrodialysis technique.

In situ synthesis and immobilization of a Cu(ii)–pyridyl complex on silica microspheres as a novel Fenton-like catalyst for RhB degradation at near-neutral pH

A Cu(ii)–pyridyl complex was in situ synthesized and immobilized onto silica microspheres as a highly effective Fenton-like catalyst at near-neutral pH.

Application of montmorillonite-Cu(II)ethylenediamine catalyst for the decolorization of Chromotrope 2R with H₂O₂ in aqueous solution

The kinetics of decolorization of Chromotrope 2R (C2R) was studied spectrophotometrically using the montmorilloniteK10-Cu(II)ethylenediamine composite (MMTK10-Cu(en)2) as catalyst and H2O2 as oxidant in aqueous solution. The catalyst was prepared and characterized by SEM, FTIR, XRD and TGA techniques. The dependence of reaction rate on H2O2 concentration was examined under UV irradiation in the presence and absence of the catalyst, and in the presence of the catalyst without the UV irradiation. In all these reaction systems, the rate increased up to a maximum value and then decreased. The rate increased with increasing the concentration of the dye reaching a maximum. Also, the rate of decolorization reaction showed a significant increase with increasing the amount of the catalyst and temperature. The addition of NaCl to the reaction medium has accelerated the rate effectively. A similar catalyst, MMTKSF-Cu(en)2, has also been employed and was found to be less efficient compared with MMTK10-Cu(en)2.

Removal of crystal violet from water by magnetically modified activated carbon and nanomagnetic iron oxide

Magnetically modified activated carbon, which synthesized by nanomagnetic iron oxide, was used for fast and effective removal of Crystal Violet from aqueous solutions. The scanning electron microscopy (SEM) images of nano-adsorbent showed that the average sizes of adsorbent are less than 100 nm. The various parameters, affecting on adsorption process, were examined including pH and temperature of dye solution, dose of adsorbent, and contact time. Then, thermodynamic parameters of sorption were calculated. Langmuir and Freundlich isotherms were used to fit the resulting data. Adsorption kinetics was consistent with a pseudo second order equation. Thermodynamic parameters of adsorption, ∆H(0), and ∆S(0) were calculated. Also, for further investigations, nano magnetic iron oxides was synthesized and used as adsorbent. Sorption capacities were depending on the temperature varied from 44.7 to 67.1 mg/g and from 12.7 to 16.5 mg/g for magnetically modified activated carbon and nanomagnetic iron oxide, respectively.

Heterogeneous Photocatalytic Discoloration/Degradation of Rhodamine B with H2O2 and Spinel Copper Ferrite Magnetic Nanoparticles

The discoloration/degradation of the artificial dye Rhodamine B (RhB) was investigated using advanced oxidation technologies. Aqueous solutions of RhB containing spinel copper ferrites (CuFe2O4) as a heterogeneous catalyst were exposed to UV irradiation/hydrogen peroxide. Under these experimental conditions the discoloration/degradation of RhB is strongly promoted by copper ferrites, reaching 95 % discoloration of the dye in 10 min and 97 % degradation in 200 min. The influence of the catalyst amount, H2O2 concentration, light source, and UV light intensity were studied. Optimum concentrations of H2O2 and catalyst dosage were found for the RhB degradation reaction. The catalyst had high magnetic sensitivity under an external magnetic field, which allowed its magnetic separation from water avoiding secondary pollution processes, and its recycling. A markedly synergetic effect of spinel copper ferrite and UV light irradiation was observed for the RhB discoloration/degradation with H2O2 as a green oxidant.

Kinetics and mechanism of the heterogeneous catalyzed oxidative decolorization of Acid-Blue 92 using bimetallic metal-organic frameworks

The kinetics study of the oxidative decolorization of Acid-Blue 92 has been investigated by hydrogen peroxide catalyzed with bimetallic metal-organic frameworks. The used metal-organic frameworks (MOF) are [Ph3SnCu(CN)2·L] where L=pyrazine (pyz) 1, methylpyrazine (mepyz) 2, 4,4'-bipyridine (bpy) 3, trans-1,2-bis(4-pyridyl)ethene (tbpe) 4 or 1,2-bis(4-pyridyl)ethane (bpe) 5. The reaction was followed by conventional UV-Vis spectrophotometer at λmax=571 nm. The reaction exhibited first-order kinetics with respect to [dye] and [H2O2]. The reactivity of the catalysts depends on the type of the medium and thereafter decreases in strong alkaline media. Addition of NaCl enhances the reaction rate. Also, the irradiation of the reaction with UV-light enhanced the rate of AB-92 mineralization by about 86.9%. The reaction was entropy-controlled as confirmed by the isokinetic relationship. A reaction mechanism was proposed with the formation of free radicals as an oxidant.

Effects of sonochemical parameters and inorganic ions during the sonochemical degradation of crystal violet in water

This work deals with the ultrasonic degradation (800 kHz) of crystal violet (CV) under different experimental conditions. The effects of saturating gas (argon, carbon dioxide and air), CV concentration (2.45-1225 μmol L(-1)), pH (3-9) and power (20-80 W) were evaluated. The best performances were obtained at 80 W with argon as a saturating gas. The pH had no significant effect. The influence of several water matrices containing anions (chloride, sulphate and bicarbonate) and cations (Fe(2+)) on the sonolytic degradation of CV was also investigated. Significant differences were not observed with the presence of chloride and sulphate. However, at relatively low pollutant concentration (2.45 μmol L(-1)) bicarbonate showed a particular effect: a high bicarbonate concentration (350 mmol L(-1)) produced a detrimental effect, while a low bicarbonate concentration (3 mmol L(-1)) increased the efficiency of the process. The presence of Fe(2+) (1 mmol L(-1)) also increased the CV (49 μmol L(-1)) degradation by 32% after 180 min. Analyses of intermediates by GC-MS led to the identification of several sonochemical by-products: N,N-dimethylaminobenzene, 4-(N,N-dimethylamino)-4'-(N',N'-dimethylamino)benzophenone, and N,N,N',N'-tetramethyl-4,4'-diaminodiphenylmethane. The presence of these aromatic structures showed that the main ultrasonic CV degradation pathway is linked to the reaction with *OH radicals. At the end of the treatment, these early products were converted into biodegradable organic by-products which could be easily treated in a subsequent biological treatment.

Sorption of SPADNS azo dye on polystyrene anion exchangers: equilibrium and kinetic studies

The sorption of SPANDS from aqueous solution onto the macroporous polystyrene anion exchangers of weakly basic Amberlyst A-21 and strongly basic Amberlyst A-29 in a batch method was studied. The effect of initial dye concentration and phase contact time was considered to evaluate the sorption capacity of anion exchangers. Equilibrium data were attempted by various adsorption isotherms including the Langmuir, Freundlich and Dubinin-Radushkevich (D-R) models. A comparison of kinetic models applied to the adsorption rate constants and equilibrium sorption capacities was made for the Lagergren first-order, pseudo second-order and Morris-Weber intraparticle diffusion kinetic models. The results showed that the adsorption isotherm is in the good agreement with the Langmuir equation and that the adsorption kinetics of SPADNS on both anion exchangers can be best described by the pseudo second-order model.

Development of a new approach for microbial decontamination of water using modified Fenton's reaction

Microbial decontamination of water was carried out using a novel radical generating system consisting of ion exchange resin, copper and hydrogen peroxide. The system was successful in reducing the microbial load in water by more than 99% in 15 min and is effective against all the microorganisms tested. The method was also successful in decontaminating the flood water obtained from Industrial Canal and 17th Street Canal in New Orleans. Decontamination is due to the formation of hydroxyl radicals, formed during the decomposition of hydrogen peroxide by the metal-polymer complex.

Removal kinetics and mechanism for crystal violet uptake by surfactant-modified alumina

Sodium dodecyl sulfate (SDS), an anionic surfactant (AS) was used for the surface modification of neutral alumina. Micelle-like structures are formed on the surface of alumina, which was used for the removal of crystal violet (CV), a well-known cationic dye from aquatic environment. This process is called adsolubilization. The surfactant-modified alumina (SMA) was found to be very efficient showing >99% CV removal from a 200 ppm CV bearing solution with only 6 g/L of adsorbent dose. The kinetic studies showed that 60 minutes' shaking time was sufficient to achieve the equilibrium. The reaction kinetics data were analysed using four reaction kinetic models, viz., first-order reaction model, pseudo-first-order reaction model, second-order reaction model and pseudo-second-order reaction model, and it was found that the removal of CV followed the pseudo-second order reaction model. It was found that neither film diffusion nor pore diffusion was rate limiting for this process. Isotherm studies showed that Langmuir isotherm fitted more accurately compared to Freundlich isotherm. To test whether the removal of CV was possible from real water using SMA, the experiments were conducted using CV spiked distilled water and synthetic wastewater. It was interesting to note that the removal efficiency was better for wastewater as compared to that of distilled water.

Dechlorination and destruction of 2,4,6-trichlorophenol and pentachlorophenol using hydrogen peroxide as the oxidant catalyzed by molybdate ions under basic condition

The dechlorination and destruction of 2,4,6-trichlorophenol (TCP) and pentachlorophenol (PCP) under basic condition using hydrogen peroxide as the oxidant catalyzed by molybdate ions have been studied. Under ambient conditions of temperature and pressure, more than 95% of millimolar solutions of TCP and PCP can be converted to CO2 and CO, chlorinated and nonchlorinated carboxylic acid in 40 min. Up to 2.4 chloride ions per TCP and 3.5 chloride ions per PCP were released. TOC measurements indicated that 18% and 11% of the carbon was mineralized for TCP and PCP respectively after an hour of reaction. The results of ESR measurements suggested that the reaction possibly proceeded via the pathway with singlet oxygen.

Kinetics and Mechanisms of the Non-Catalyzed and Manganese(II) Catalyzed Oxidation of Neutral Red with Potassium Periodate in Aqueous Solution

A detailed kinetic and spectrophotometric investigation has been made for the oxidation of neutral red, a cationic phenazine dye, using potassium periodate in aqueous media. The rate of the oxidation reaction attained a first order dependence on the dye and the oxidant only at lower concentrations of the latter. The rate of reaction increases with increasing pH of the medium due to the deprotonation of the substrate nitrogen atoms. Moreover, the rate of reaction decreases with increasing ionic strength of the medium, suggesting an interaction between two singly oppositely charged ions in the activated complex. However, addition of trace amounts of manganese(II) ions sharply increases the oxidation rate. Mechanisms are proposed for both the non-catalyzed and manganese(II) catalyzed reactions which are in agreement with the experimental data.