Methyl Orange Aqueous Solution Research Articles

Preparation of anion‐uptake powder compact containing layered double oxide and metakaolinite

AbstractA powder compact with anion‐uptake ability was prepared prior to the proceeding of the solid‐state reaction involving layered double hydroxide (LDH) and kaolinite during calcination. LDH features anion‐exchangeable capability, and kaolinite is used as a raw potty material because of the sintering property. In the present study, the solid‐state reaction of LDH with kaolinite did not proceed at 750°C, resulting in the formation of a mixture of layered double oxide (LDO) and metakaolinite. Unlike LDO, which typically undergoes anion‐uptake accompanied by LDH reconstruction, metakaolinite does not revert to kaolinite without the use of hydrothermal conditions. In addition, the powder compact composed of LDO crumbled, whereas the one containing a mixture of LDO and metakaolinite remained intact. When the powder compact of LDO and metakaolinite mixture was immersed in a methyl orange (MO) aqueous solution, an LDH–MO intercalation compound was generated within the compact. By contrast, no such compound was generated when LDO powder was immersed in an MO aqueous solution. These results indicated that the successful preparation of a powder compact with distinct anion‐uptake ability was different from powder, owing to that the solid‐state reaction of LDO with metakaolinite did not proceed at 750°C.

Evaluation of the Adsorptive Performance of Rambutan-shaped γ-Al2O3 Micro-nanostructure against Wastewater Containing the Azo Dye: Methyl Orange

Aim: The aim of this study is to explore and evaluate the possibility of rambutan-shaped micro-nanostructured γ-Al2O3 material’s usage as an adsorbent in industrial wastewater processing. Background: Every year, more than 7 million tons of dyestuff-containing wastewater are produced in the industry. Although there are many adsorbents like fly ash and clays, the shortages limit their actual applications. It is still necessary to find a new cheaper adsorbent. Objective: The paper aimed to investigate the adsorption capacity and decolorization ability of rambutan- shaped γ-Al2O3 material synthesized via a composite soft template method. Methods: The rambutan-shaped γ-Al2O3 material was prepared and characterized via XRD, TEM, FE-SEM, and FT-IR (See our group’s published article in “Ming Shen*, et al., Acta Phys.-Chim. Sin. 2013, 29 (10), 2286-2294”). The methyl orange aqueous solution was selected as the model of industrial wastewater. The methyl orange solution (15.0 mg·L-1) with different pH (2~9) was exposed to a series of amounts of γ-Al2O3 powder ranging from 10.0 to 70.0 mg. Different concentrations of methyl orange solution, ranging from 5.0 to 200.0 mg·L-1 were also tested with the same amount of γ-Al2O3 powder (50.0 mg). The adsorption-calcination cycle analysis was performed with methyl orange solution (50.0 mg·L-1) and 500.0 mg of γ-Al2O3 powder at pH=3. Results: The γ-Al2O3 material exhibits excellent adsorption capacity (114.10 mg·g-1) towards acidic methyl orange aqueous solution. At the same time, the decolorization rate of the γ-Al2O3 material reaches about 88%. This material still keeps a 50% decolorization rate after 6 repeats of the adsorption- calcination cycle. Moreover, the excellent self-sedimentation ability of this material also provides an easy separation for future industrial applications. Conclusion: The γ-Al2O3 material with rambutan-like micro-nanostructure presents excellent adsorption capacity/decolorization ability and self-sedimentation ability. It can be used as a new type of adsorbent for wastewater processing. The rambutan-shaped micro-nanostructure plays an important role in maintaining the adsorption ability of the γ-Al2O3 material.

High-entropy selenide catalyst for degradation of organic pollutants

In this study, pollution from sewage was addressed using a novel high-entropy material to decompose organic pollutants containing azo groups. Se_(AlCrCuFeNi) (Se_HEC) nanomaterials were employed as an active catalyst to restore organic pollution in aqueous solutions by using the electro-Fenton technique. The efficacy of Se_HEC catalysts in degrading pollutants during the electro-Fenton reaction and the potential of functionalized high-entropy materials to decompose pollutants were investigated. The Se_HEC material was synthesized through rapid calcination followed by selenization. This Se_HEC cathode demonstrated a remarkable removal efficiency of 98% for methyl orange in aqueous solutions and high stability in an acidic environment with a pH of 3. Additionally, the effects of various parameters, such as applied current and pH, were assessed. The results revealed that an increase in the current led to a higher reaction rate for the entire process, with the optimal conditions occurring at pH 3. The potential methyl orange degradation pathway was elucidated through a reactive oxygen species (ROS) test conducted during the electro-Fenton process.

Magnetic chitosan-functionalized waste carton biochar composites for efficient adsorption of anionic and cationic dyes

In this study, BC-CoFe2O4-CS magnetic composite was successfully prepared from waste cardboard and investigated as an efficient adsorbent for the removal of amaranth and methyl orange in aqueous solution. First, the fibers obtained from the cardboard waste were carbonized by a hydrothermal process to produce biochar. Subsequently, the final magnetic composites were synthesized by in situ growth and Schiff base crosslinking reactions. The composites were characterized by zeta potential, Brunauer–Emmett–Teller measurements, Fourier transform Infrared spectroscopy, Scanning electron microscopy, Energy dispersive spectrometer,X-ray Diffraction, Thermogravimetry analysis and Vibrating sample magnetometer. The effects of adsorbent dosage and initial solution pH on dye removal efficiency were studied. The results showed that the maximum adsorption capacity of amaranth could reach 500.6 mg·g−1 at pH = 2, the adsorbent dosage of 0.5 mg·ml−1, and methyl orange could reach 644.0 mg·g−1 at pH = 4, the adsorbent dosage of 0.5 mg·ml−1. The adsorption process followed the pseudo-second order kinetic models and Langmuir isotherm. BC-CoFe2O4-CS was easily separated from the aqueous solution due to the loading of CoFe2O4 magnetic nanoparticles. Besides, the BC-CoFe2O4-CS could be further used after the adsorption experiments with or without desorption and still showed good adsorption performance in the actual water samples. Therefore, it is expected that the composite material prepared from waste cartons can be used for the treatment of dye-containing wastewater due to its low cost, high efficiency, and simple application.

Chemical waste treatment based on hydrogen energy (II): Aqueous methyl orange solution under the oxyhydrogen flame

The oxyhydrogen flame (OHF) can generate temperatures as high as 2800 K and a jet flow of highly reactive free radicals including H, OH, HO2 and O. Therefore, it could serve as an effective means for treating various chemical wastes, particularly organic wastes. Building upon our previous research on metal chlorides, we present here a study on the degradation mechanism of aqueous methyl orange (MO) solution under OHF. Although the decolorization of MO solution is rapid, complete degradation is a slow and intricate process. Initially, MO solution undergoes decolorization by breaking the azo bond followed by oxidation processes that convert aminobenzene compounds to benzoquinone and break down the benzene ring until ultimately being fully converted into CO2 and H2O.

A bifunctional imidazolium-based porous organic polymer for efficient detection of Cr2O72− and adsorptive separation of Cr2O72− and MO in water

The presence of heavy metal ions and organic dyes in aqueous solutions has a significant impact on the ecological environment and human health. Herein, a novel bifunctional imidazolium-based porous organic polymer (IMSPF-Br-C=C) was prepared successfully via quaternization reaction of spirobifluorene and 1,4-dibromo-2-butene. The synthesized material was characterized by scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS), Fourier transform infra-red spectra (FTIR), Thermogravimetric analysis (TGA), X-ray diffraction (XRD), N2 adsorption-desorption analysis and solid-state 13C CP/MAS NMR spectroscopy, confirming its structure and stability. Owing to the conjugated structure of spirobifluorene, IMSPF-Br-C=C showed excellent recognition performance for dichromate anion (Cr2O72−) with the limit of detection (LOD) of 1.58 μmol/L. In addition, IMSPF-Br-C=C with the abundant imidazolium cations showed the outstanding adsorption performance in the removal of Cr2O72− and methyl orange (MO). Removal efficiencies and adsorption capacities of IMSPF-Br-C=C were 98.3 % and 99.4 %, 452.8 and 1304.2 mg/g in 6 min, respectively. The results show that the electrostatic interactions and π-π stacking play crucial roles in the fluorescence detection of Cr2O72− and adsorptive separation of Cr2O72− and MO. Furthermore, physico-chemical techniques, density functional theory (DFT) calculation and frontier molecular orbital theory (FMO) were used to explain action mechanism. This work provides a cost-effective IMSPF-Br-C=C as a bifunctional platform for sensing Cr2O72− and adsorptive separation of Cr2O72− and MO in aqueous solution.

Characterization of an Iron-Copper Bimetallic Metal-Organic Framework for Adsorption of Methyl Orange in Aqueous Solution.

Iron-based organic frame material MIL-53 (Fe) was synthesized by the hydrothermal method with Cu2+ incorporated to obtain bimetallic composite MIL-53 (Fe, Cu). The structure and morphology of the material were characterized by SEM, XRD, BET, FTIR, XPS, and zeta potential. The adsorption performance of MIL-53 (Fe, Cu) on methyl orange was tested under a variety of conditions, including the effects of pH and material dosage, by the static adsorption test. The results show that under the condition of pH = 7, a temperature of 30°C, and an adsorbent dosage of 20 mg, the removal rate of MIL-53 (Fe, Cu) for methyl orange can reach more than 96% within 4 h, and the maximum adsorption capacity after fitting by the thermodynamic model can reach 294.43 mg/g, showing the excellent adsorption performance of MIL-53 (Fe, Cu) on methyl orange. In addition, by exploring the adsorption mechanism of MIL-53 (Fe, Cu) on methyl orange, it is found that the adsorption of MIL-53 (Fe, Cu) on methyl orange depends on chemical adsorption, as evidenced by combining Fe3+ and Cu2+ in the material with methyl orange molecules to form complexes to achieve adsorption. While the specific surface area of the material had no obvious effect on adsorption, the effects of pH, temperature, and concentration were explored. At a pH of 6.5, greater adsorption occurred at higher temperatures, as determined by thermodynamic model fitting, as well as with higher initial methyl orange molecule concentration.

Removal of Methyl Orange in Aqueous Solutions Using Hydrochloric Acid-Modified Kaolinite Supported Nanosized Zero-Valent Iron

Removal of Methyl Orange in Aqueous Solutions Using Hydrochloric Acid-Modified Kaolinite Supported Nanosized Zero-Valent Iron

Synthesis, Crystal Structure, and Photocatalytic Properties of Two Isoreticular Ce(IV)-MOFs with an Infinite Rod-Shaped Inorganic Building Unit.

The use of the V-shaped linker molecules 4,4'-oxydibenzoic acid (H2ODB) and 4,4'-carbonyldibenzoic acid (H2CDB) led to the discovery of two isoreticular Ce(IV)-based metal-organic frameworks (MOFs) of composition [CeO(H2O)(L)], L = ODB2-, CDB2-, denoted CAU-58 (CAU = Christian-Albrechts-University). The recently developed Ce-MOF synthesis approach in acetonitrile as the solvent proved effective in accessing Ce(IV)-MOF structures with infinite rod-shaped inorganic building units (IBUs) and circumventing the formation of the predominantly observed hexanuclear [Ce6O8] cluster. For the structure determination of the isoreticular MOFs, three-dimensional electron diffraction (3D ED) and powder X-ray diffraction (PXRD) data were used in combination with density functional theory (DFT) calculations. [CeO(H2O)(CDB)] shows reversible H2O adsorption by stirring in water and thermal treatment at 190 °C, which leads to a unit cell volume change of 11%. The MOFs feature high thermal stabilities (T > 290 °C), which exceed those of most Ce(IV)-MOFs and can be attributed to the infinite rod-shaped IBU. Surface and bulk oxidation states of the cerium ions were analyzed via X-ray photoelectron spectroscopy (XPS) and X-ray absorption near-edge spectroscopy (XANES). While Ce(III) ions are observed by the highly surface-sensitive XPS method, the bulk material contains predominantly Ce(IV) ions according to XANES. Application of the MOFs as catalysts for the catalytic degradation of methyl orange in aqueous solutions was also studied. While degradation activity for both MOFs was observed, only CAU-58-ODB revealed enhanced photocatalytic activity under ultraviolet (UV) light. The photocatalytic mechanism likely involves a ligand-to-metal charge transfer (LMCT) from the linkers to the Ce(IV) centers. Analyses by XANES and inductively coupled plasma-optical emission spectroscopy (ICP-OES) demonstrate that leaching of Cerium ions as well as partial reduction of Ce(IV) to Ce(III) takes place during catalysis. At the same time, PXRD data confirm the structural stability of the remaining MOF catalysts.

Adsorption of methyl orange dye by SiO2 mesoporous nanoparticles: adsorption kinetics and eco-toxicity assessment in Zea mays sprout and Artemia salina.

Herein, we prepared the silica nanoparticles (SiO2 NPs) by a modified Stober's method for methyl orange (MO) removal. The SiO2 NPs were found to be spherical with a zeta size of 152.5 d. nm, a PDI of 0.377, and a zeta potential of -5.59 mV. The effect of different parameters (initial dye concentration, reaction time, temperature, and pH) on the adsorption of MO by SiO2 NPs was determined. The adsorption pattern of SiO2 NPs was highly fitted with the Langmuir, Freundlich, Redlich-Peteroen, and Temkin isotherm models. The highest adsorption rate was recorded at 69.40 mg/g of SiO2 NPs. Furthermore, the toxic effect of before and after removal of MO in aqueoussolution was tested in terms of phytotoxicity and acute toxicity. The SiO2 NPs treated MO dye solution were not exhibited significant toxicity to corn seeds and Artemia salina. These results indicated that SiO2 NPs can be used for the adsorption of MO.

Synthesis of TiO<sub>2</sub>/Gd<sub>2</sub>O<sub>3</sub> and TiO<sub>2</sub>/Gd<sub>2</sub>O<sub>3</sub>/Ag Nanomaterials. Application in Photocatalytic Degradation Reactions

A technique for the template synthesis of nanocrystalline titanium(IV) oxide and its modification with nanoparticles of gadolinium(III) oxide and silver has been developed. The composition and structure of the obtained materials were characterized by X-ray phase analysis and IR spectroscopy. The specific surface area and pore size distribution were determined. The photocatalytic properties of the synthesized TiO2/Gd2O3 and TiO2/Gd2O3/Ag nanomaterials were evaluated in the reaction of degradation of aqueous solutions of methyl orange upon irradiation with UV light. It was found that the introduction of gadolinium (III) oxide increases the photocatalytic activity, and the introduction of silver particles makes the photocatalyst sensitive to light with a shorter wavelength.

Defective multi-element hydroxides nanosheets for rapid removal of anionic organic dyes from water and oxygen evolution reaction

Water pollution by dyes is one of the biggest environmental problems. Adsorption technology has been widely used in wastewater treatment. In this work, high-entropy concept is used to design surface defective hydroxides realizing the rapid removal of dyes from water. Multi-element hydroxides (MEHs) containing three (CoMnNi, MEH-Ternary), four (CoMnNiZn, MEH-Quaternary), and five (CoMnNiZnFe, MEH-Quinary) metal elements are successfully synthesized through a polyol process. These as-synthesized MEHs are composed of nanosheets with a brucite-like structure. Along with the increase in compositional complexity (i.e., configurational entropy), the thickness of the nanosheets in these MEHs decreases, while the degree of surface defects increase. These surface defects are probably the active sites for anionic dyes adsorption, suggesting rapid adsorption kinetics with shortened diffusion path length. For MEH-Quinary in 0.2 mM Congo red (CR) and MEH-Ternary in 0.4 mM methyl orange (MO) aqueous solutions, respectively, high removal efficiency > 99.0% is achieved in the first 30 s. Their pseudo-second-order rate constants are two orders of magnitude higher than that of activated carbon and hydrotalcite. MEH-Quinary has maximum CR and MO adsorption quantity of 546.4 and 404.9 mg g-1, respectively, by Langmuir model. The MEH-Quinary is also a potential electrocatalyst for oxygen evolution reaction.

Degradation of Methyl Orange in Aqueous Solution via Magnetic TiO2/Fe3O4 Conjugated with Persulfate

Degradation of Methyl Orange in Aqueous Solution via Magnetic TiO2/Fe3O4 Conjugated with Persulfate

Preparation of metal organic framework materials with defects via a mixed-metallic centers strategy for enhanced removal of organic dye

Metal organic framework (MOF) materials display intriguing potential in wastewater treatment applications. In this study, a series of mixed MOF materials with several defects were designed and prepared via a strategy of mixed-metallic centers and the reaction process was lasted for only several hours at room temperature with water as environmental-friendly reaction medium. The MOF materials were characterized by Brunauer-Emmett-Teller (BET), Thermogravimetric analysis (TGA), Fourier transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD), and were employed to enrich organic dyes from aqueous solution with methyl orange (MO) and methylene blue (MB) as model molecules. Several factors influencing adsorption efficiency such as contact time, initial concentration, pH of dye solution and ionic strength were systematically explored. Due to the difference of structure and charge of MO and MB, the adsorption behaviors of the materials for both model dyes were obviously different from each other. The results showed that the adsorption process could be better described by pseudo-second-order kinetics and Freundlich isotherm model. The adsorption capacity of mixed MOF material with the ratio of Co2+ and Ni2+ of 1:1 for MO was 380.91 mg/g, much higher than those of MOF materials with single metallic center (255.15 mg/g of the material with Co2+ and 176.65 mg/g of the material with Ni2+), indicating the advantages of the preparation strategy and defects of the mixed MOF material produced in the preparation process in the adsorption field. However, the adsorption capacities of the prepared MOF materials for MB were close to each other. Furthermore, it would be possible to achieve a highly selective adsorption of MO from the mixed aqueous solution of MO and MB through choosing the appropriate NaCl concentration. This study can provide a method of increasing the diversity and functionality of the MOF materials.

Green Synthesis of NiO-SnO2 Nanocomposite and Effect of Calcination Temperature on Its Physicochemical Properties: Impact on the Photocatalytic Degradation of Methyl Orange

Background: Nickel stannate nanocomposites could be useful for removing organic and toxic water pollutants, such as methyl orange (MO). Aim: The synthesis of a nickel oxide-tin oxide nanocomposite (NiO-SnO2 NC) via a facile and economically viable approach using a leaf extract from Ficus elastica for the photocatalytic degradation of MO. Methods: The phase composition, crystallinity, and purity were examined by X-ray diffraction (XRD). The particles' morphology was studied using scanning electron microscopy (SEM). The elemental analysis and colored mapping were carried out via energy dispersive X-ray (EDX). The functional groups were identified by Fourier transform infrared spectroscopy (FTIR). UV-visible diffuse reflectance spectroscopy (UV-vis DRS) was used to study the optical properties such as the absorption edges and energy band gap, an important feature of semiconductors to determine photocatalytic applications. The photocatalytic activity of the NiO-SnO2 NC was evaluated by monitoring the degradation of MO in aqueous solution under irradiation with full light spectrum. The effects of calcination temperature, pH, initial MO concentration, and catalyst dose were all assessed to understand and optimize the physicochemical and photocatalytic properties of NiO-SnO2 NC. Results: NiO-SnO2 NC was successfully synthesized via a biological route using F. elastica leaf extract. XRD showed rhombohedral NiO and tetragonal SnO2 nanostructures and the amorphous nature of NiO-SnO2 NC. Its degree of crystallinity, crystallite size, and stability increased with increased calcination temperature. SEM depicted significant morphological changes with elevating calcination temperatures, which are attributed to the phase conversion from amorphous to crystalline. The elemental analysis and colored mapping show the formation of highly pure NiO-SnO2 NC. FTIR revealed a decrease in OH, and the ratio of oxygen vacancies at the surface of the NC can be explained by a loss of its hydrophilicity at increased temperatures. All the NC samples displayed significant absorption in the visible region, and a blue shift is seen and the energy band gap decreases when increasing the calcination temperatures due to the dehydration and formation of compacted large particles. NiO-SnO2 NC degrades MO, and the photocatalytic performance decreased with increasing calcination temperature due to an increase in the crystallite size of the NC. The optimal conditions for the efficient NC-mediated photocatalysis of MO are 100 °C, 20 mg catalyst, 50 ppm MO, and pH 6. Conclusions: The auspicious performance of the NiO-SnO2 NCs may open a new avenue for the development of semiconducting p-n heterojunction catalysts as promising structures for removing undesirable organic pollutants from the environment.

In situ synthesis and immobilization of CuO nanoparticles in alginate-poly(amido amine) nanogels for photocatalytic applications

Herein, we report a feasible approach for preparation of crosslinked alginate (Alg) and poly(amido amine) (PAMAM) nanogels (Alg-PAMAM NGs), using a water-in-oil-in-water (w/o/w) double emulsion route, via strong electrostatic interactions between anionic groups coming from alginate and previously incorporated Cu2+ ions. CuO nanoparticles (NPs) with average diameter about 65 nm were in situ obtained into Alg/PAMAM nanogels by treatment of embedded Cu2+ ions in NGs with NaBH4 at 25 °C under air atmosphere. The prepared Alg-PAMAM and Alg-PAMAM-CuO NGs were characterized using FT-IR and UV–visible spectroscopy, as well as scanning transmission electron microscopy (STEM). The presence of PAMAM dendrimers helped both to obtain structurally compact nanogels and an adequate stabilization of CuO NPs. Finally, the photocatalytic performance of the Alg-PAMAM-CuO NGs was tested via the decomposition of methyl orange in aqueous solution, under visible light irradiation.

Structure and optical, magnetic and photocatalytic properties of Cr3+ substituted zinc nano-ferrites

In this paper, the Cr3+ substituted zinc ferrite (ZnCrxFe2-xO4 with x = 0, 0.15 and 0.25) nanoparticles with single cubic spinel structure (Fd-3 m space group) were prepared by chemical co-precipitation method, and their structure and optical, magnetic and photocatalytic performaces were investigated. With Cr added, the lattice parameter and average grain size of the ferrites remarkably changed. High-quality nanostructured ferrite with an average particle size of 22–31 nm are revealed by TEM and SEM. The vibrational stretching modes of tetrahedral and octahedral sites were confirmed by FTIR. The optical studies proved a gradual decrease in the optical band gap which indicated the emergence of sub-band-gap energy levels by the chromium content. The magnetic properties were investigated through magnetization technique. The saturation magnetization measured from M-H hysteresis plot show decreasing trend with increase in Cr3+ content. The photocatalytic degradation of aqueous solution of Methyl Orange (MO) in the presence of prepared nano-ferrite under visible-light irradiation has been studied and discussed. The photodegradation efficiency of MO over ZnCrxFe2-xO4 photocatalysts is enhanced; (69%, 74% and 82% with increasing Cr3+content, respectively) compared with its modest value 12% without addition.

Investigation of Interaction Mechanisms of High Energy Electrons and Gamma Quantum with Aqueous Solution of Methyl Orange Dye

The level of development of modern nuclear technologies forms a request for the development of new branches of science. At the same time, chemical dosimetry methods are also being improved [1, 2]. The essence of such methods consists in the quantitative determination of the radiation-chemical damages to the molecules of a substance when it is exposed to ionizing radiation [3, 4]. Liquid and solid solutions of organic dyes have intense bands optical absorption and fluorescence in the visible region of the spectrum, which makes it possible to use them in dosimetry systems [5, 6]. The use of organic dyes makes it possible to determine the absorbed dose in the range from 10-6 to 104 M Rad [7, 8]. In this work, we studied the processes of interaction of gamma-ray and high-energy electron fluxes with an aqueous solution of the organic dye methyl orange (C14H14N3О3SNa) [9, 10]. The calculations and experiment were carried out on a resonant electron accelerator with energies up to 30 MeV. The electron beam energy was 15 MeV. A tungsten converter was used to generate gamma quanta. The thickness of the converter varied from 0 to 6 mm. We have developed a computer program in C++ to simulate the irradiation process. This program uses the Geant4 class library based on the Monte Carlo method and runs in multi-threaded mode. For calculations, the model “PhysicsList emstandard_opt3” was chosen as the most suitable one. The value of radiation damage per one incident electron and produced gamma-quantum is determined in the work. The simulation results are compared with experimental data. Based on the results obtained, conclusions were drawn about the main mechanisms leading to the decomposition of organic dye molecules, and methods for optimizing the experiment for further research were proposed.

Activation of sulfite by metal-organic framework-derived cobalt nanoparticles for organic pollutants removal

Sulfite (SO32−) activation is one of the most potential sulfate-radical-based advanced oxidation processes, and the catalysts with high efficiency and low-cost are greatly desired. In this study, the cobalt nanoparticles embedded in nitrogen-doped graphite layers (Co@NC), were used to activate SO32− for removal of Methyl Orange in aqueous solution. The Co@NC catalysts were synthesized via pyrolysis of Co2+-based metal-organic framework (Co-MOF), where CoO was firstly formed at 400℃ and then partially reduced to Co nanoparticles embedded in carbon layers at 800℃. The Co@NC catalysts were more active than other cobalt-based catalysts such as Co2+, Co3O4 and CoFe2O4, due to the synergistic effect of metallic Co and CoxOy. A series of chain reaction between Co species and dissolved oxygen was established, with the production and transformation of SO3•−, SO52−, and subsequent active radicals SO4•− and HO•. In addition, HCO3− was found to play a key role in the reaction by complexing with Co species on the surface of the catalysts. The results provide a new promising strategy by using the Co@NC catalyst for SO32− oxidation to promote organic pollutants degradation.

Fast and effective catalytic degradation of an organic dye by eco-friendly capped ZnS and Mn-doped ZnS nanocrystals.

Undoped and manganese doped ZnS nanocrystals encapsulated with thioglycolic acid(ZnS-TGA) were synthesized and characterized with different techniques, and finally tested in the photodegradation of a methyl orange in aqueous solution under UV and sunlight irradiations. FTIR and X-ray diffraction results confirmed the functionalization of these nanocrystal surface by thioglycolic acid and the formation of crystalline structures of ZnS and Mn-doped ZnS with cubic and hexagonal phases. Calculated average size of ZnS nanocrystals was in the range of 2-3nm. It was observed a blue shift of the absorbance threshold and the estimated bandgap energies were higher than that of Bulk ZnS thus confirming the quantum confinement effect of charge carriers. Photoluminescence spectra of ZnS nanocrystals exhibited emission in the range of 410-490nm and the appearance of an additional emission band around 580nm (2.13eV) connected to the 4T1 → 6A1 transition of the Mn2+ions. Photodegradation of methylene orange with undoped and Mn-doped ZnS-TGA nanocrystals was investigated. Dye adsorption prior to photocatalysis using nanocrystals was studied via kinetic and equilibrium experiments. The maximum dye adsorption capacity on doped ZnS-TGA was ~ 26.98mg/g. The adsorption kinetic was found to follow the pseudo-second-order kinetic model. A statistical physics model was used to analyze the equilibrium data where the calculated adsorption energy was 17-18kJ/mol. It was concluded that the dye adsorption was associated to the hydrogen interaction where the removal process was feasible and multi-molecular at 25°C. The photocatalytic activity of undoped ZnS nanoparticles under UV irradiation showed better efficiency than doped nanocrystals thus indicating that manganese doping generated a dropping of the photocatalytic degradation of the dye. Dye degradation efficiency of 81.37% using ZnS-TGA nanocrystals was achieved after 6min, which indicated that ZnMnS-TGA nanocrystals may be considered an alternative low cost and environmental friendly material for facing water pollution caused by organic compounds via photodegradation processes.