In this study, cadmium selenide quantum dots (CdSe-QD) were synthesized and characterized. Dye removal ability of CdSe-QD with UV irradiation (UV/CdSe-QD) was investigated. The synthesized QD was characterized by X-ray diffraction, transmittance electron microscope, Fourier transformation infrared, dynamic light scattering, atomic force microscopy, UV–visible, and photoluminescence analyses. Basic Violet 16, Basic Blue 41, and Acid Blue 92 were used as model dyes. The effect of CdSe-QD dosage on dye removal in presence of UV irradiation was studied. The obtained results showed that dye removal followed by a first-order kinetic model. It has been found that CdSe-QD has dye removal ability from colored wastewater in the presence of UV irradiation.
The use of low-cost and ecofriendly adsorbents has been investigated as an ideal alternative to the current expensive methods of removing dyes from wastewater. Orange peel was collected from the fields of orange trees in the north of Iran and converted into a low-cost adsorbent. This paper deals with the removal of textile dyes from aqueous solutions by orange peel. Direct Red 23 (DR23) and Direct Red 80 (DR80) were used as model compounds. The adsorption capacity Q 0 was 10.72 and 21.05 mg/g at initial pH 2. The effects of initial dye concentration (50, 75, 100, 125 mg/l), pH, mixing rate, contact time, and quantity of orange peel have been studied at 25 °C. The Langmuir and Freundlich models were used for this study. It was found that the experimental results show that the Langmuir equation fit better than the Freundlich equation. The results indicate that acidic pH supported the adsorption of both dyes on the adsorbent. Orange peel with concentrations of 8 and 4 g/l has shown adsorption efficiencies of about 92 and 91% for DR23 and DR80, respectively. Furthermore, adsorption kinetics of both dyes was studied and the rates of sorption were found to conform to pseudo-second-order kinetics with a good correlation ( R ⩾ 0.998 ). Maximum desorption of 97.7% for DR23 and 93% for DR80 were achieved in aqueous solution at pH 2. Finally, the effect of adsorbent surface was analyzed by scanning electron microscope (SEM). SEM images showed reasonable agreement with adsorption measurements.
The application of heterogeneous photocatalysis in industrial scale has been hindered by a lack of simple mathematical models that can be easily applied to reactor design and scale-up. This work intends to use a simple mathematical model for predicting methylene blue (MB) degradation in a slurry-annular photocatalytic reactor using zinc oxide (ZnO) hybridized with reduced graphene oxide (rGO)-ZnO composite. The mathematical model presented may be used as a tool to design, scale-up, and optimize annular photocatalytic reactors for water and wastewater treatment. A mathematical model for the photocatalytic degradation of MB with rGO-ZnO under UV light irradiation was developed. This model was achieved by combination of Langmuir–Hinshelwood kinetics and Lambert–Beer law. The accuracy of developed model was checked for predicting MB degradation in other operation conditions such as different photocatalyst dosage and initial MB concentration. On the basis of these results, the accuracy of the model was tested under different experimental conditions, resulting able to be predictive in different operating conditions.
No abstract is provided for this article.
In this study, graphene oxide (GO) was synthesized via modified Hummer's method and exploited as an ideal enzyme immobilization support due to its exclusive chemical and structural features. Then, laccase from genetically modified Aspergillus was covalently immobilized onto GO (nanobiocatalyst). Enzymatic characterization of the nanobiocatalyst exhibited promising results: laccase loading of 156.5 mg g−1 and immobilization yield of 64.6% at laccase concentration of 0.9 mg/ mL. Further employment of various structural characterization techniques including Fourier Transform Infrared Spectroscopy (FTIR), X-ray Powder Diffraction (XRD), Scanning Electron Microscopy (SEM), Thermo-Gravimetric Analysis (TGA), and Transmission Electron Microscopy (TEM) comprehensively confirmed the morphological properties of the prepared nanomaterials. Furthermore, bioconversion of two anionic dyes (i.e. Direct Red 23 (DR23) and Acid Blue 92 (AB92)) using nanobiocatalyst, was investigated and optimized. Also, the average decolorization effectiveness of the nanobiocatalyst was more than 75% for both of dyes after six cycles, implies its excellent operational stability and good reusability.
The adsorption of Acid Red 14 (AR14) and Acid Blue 92 (AB92) onto the microporous and mesoporous egg shell membrane (ESM) was investigated in aqueous solution in a batch system with respect to initial dye concentration, pH, contact time, particle size and biosorbent doses at 20±1°C. The surface area, Fourier transform infrared (FTIR) and scanning electron microscopy (SEM) of ESM were obtained. The surface area of ESM was found to be 2.2098m2/g. The pseudo-first-order, pseudo-second-order kinetics and the intraparticle diffusion models were used to describe the kinetics data. The rate constants at different pH values (2–12) were evaluated. The experimental data fitted well to the pseudo-second-order kinetics model at pH values of 2–8 and pseudo-first-order kinetics model at pH values of 10 and 12 for both dyes. Equilibrium isotherms were analyzed by Langmuir, Freundlich and Redlich–Peterson adsorption models. Maximum desorption of ≥89.6% was achieved for AR14 and 82.8% for AB92 in aqueous solution at pH 12. The results indicate that ESM could be fruitfully employed as effective biomaterial for the removal of residual color from effluents.
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This paper addresses the decolorization and degradation of acid dye by a heterogeneous photocatalytic process using immobilized nano-sized TiO2 particles as the photocatalyst. Sackcloth fiber was used as a support to immobilize the nano-sized TiO2 photocatalyst. The structural properties of the immobilized photocatalyst were characterized by XRD, SEM and EDX. UV–Vis absorption spectroscopy and the measurement of the chemical oxygen demand (COD) were also used for the process performance studies. The XRD results did not show significant changes in the structure of P25 as a consequence of the immobilization procedure. The formation of titania crystallites in the sackcloth fiber was confirmed by SEM/EDX. The photocatalytic activities of TiO2-coated sackcloth fiber catalyst were evaluated using Acid Black 26 as a model organic contaminant and using UV-A radiation. Experimental results showed that after 60min, the degradation of Acid Black 26 with the immobilized TiO2 particles was higher than that with plain TiO2. Based on the COD results, after 3h, the TiO2-coated sackcloth fiber effectively decomposed all of the organic compounds present in dye solution under the studied experimental conditions. The effects of the oxidant H2O2, initial dye concentration and pH on the photocatalytic degradation were also investigated. The presence of CO3 2− as a dissolved inorganic anion had the highest inhibitory effect on the decolorization of the dye, when compared with the other anions investigated. Kinetics analysis indicates that the photocatalytic decolorization rate of Acid Black 26 can be described by a pseudo-first-order model.
Adsorption isotherms of Direct Red 80 (DR80) and Acid Blue 25 (AB25) on the egg shell membrane (ESM) were performed at 20±1°C. Physical characteristics of ESM such as surface area and presence of functional groups were verified. The Fourier transform infra-red (FTIR) spectra proved the presence of fuctional groups such as hydroxyl, amine and carbonyl groups in ESM. The surface area of ESM was found to be 2.2098m2/g. The effects of operational parameters such as initial dye concentration, pH0, contact time, particle size and ESM doses were studied. The Langmuir, Freundlich, BET, Redlich-Peterson and Temkin adsorption models were applied to describe the equilibrium isotherms. The pseudo-first-order and pseudo-second-order kinetics models were examined to evaluate the kinetics data at different pH0 values (2–12) and the rate constants were calculated. Maximum desorption of ⩾81.8% was achieved for both dyes in aqueous solution at pH0 12. Also scanning electron micrographs (SEM) of the treated and untreated adsorbent were performed. Results indicate that ESM could be employed as a natural and Eco-Friendly adsorbent material for the removal of trace organics in solutions.
