Catalytic Removal of Alizarin Red Using Chromium Manganese Oxide Nanorods: Degradation and Kinetic Studies

Streamlined synthesis of iron and cobalt loaded MCM-48: High-performance heterogeneous catalysts for selective liquid-phase oxidation of toluene to benzaldehyde

Hydrothermal synthesis of MCM-48 molecular sieves featuring the incorporation of both iron and cobalt with Si/M ratios of 20, 40 and 80 (where M represents either iron or cobalt) was performed using tetraethyl orthosilicate as the silica source and cetyltrimethylammonium bromide as a template. To gain a comprehensive understanding of the synthesized materials, these were thoroughly characterized using various techniques, including XRD, XPS, UV-Vis (DRS), FT-IR, N2 adsorption-desorption analysis, SEM with EDX, TEM, TGA and NH3-TPD analysis. XRD analysis revealed the presence of well-ordered MCM-48 structure in the metal-incorporated materials, while XPS and UV-Vis DRS confirmed the successful partial incorporation of metal ions precisely in their desired tetrahedral coordination within the framework. To assess their catalytic performance, we studied the activity and selectivity of these catalysts in liquid phase oxidation of toluene using tert-butyl hydroperoxide as the oxidant. Under optimized conditions, employing a 6% (w/w) Fe-MCM-48 (40) catalyst and maintaining a toluene to oxidant molar ratio of 1:3 at 353 K in a solvent-free environment for 8 h, the oxidation reaction resulted in the formation of benzaldehyde (88.1%) as the major product and benzyl alcohol (11.9%) as the minor product.

Mesoporous Cu-Doped Manganese Oxide Nano Straws for Photocatalytic Degradation of Hazardous Alizarin Red Dye

The present work reports the photocatalytic degradation of alizarin red (AR) using Cu-doped manganese oxide (MH16-MH20) nanomaterials as catalysts under UV light irradiation. Cu-doped manganese oxides were synthesized by a very facile hydrothermal approach and characterized by energy dispersive X-ray spectroscopy, powder X-ray diffraction, scanning electron microscopy, Brunauer-Emmett-Teller analysis, UV-vis spectroscopy, and photoluminescence techniques. The structural, morphological, and optical characterization revealed that the synthesized compounds are nanoparticles (38.20-54.10 nm), grown in high mesoporous density (constant C > 100), possessing a tetragonal phase, and exhibiting 2.98-3.02 eV band gap energies. Synthesized materials were utilized for photocatalytic AR dye degradation under UV light which was monitored by UV-visible spectroscopy and % AR degradation was calculated at various time intervals from absorption spectra. More than 60% AR degradation at various time intervals was obtained for MH16-MH20 indicating their good catalytic efficiencies for AR removal. However, MH20 was found to be the most efficient catalyst showing more than 84% degradation, hence MH20 was used to investigate the effect of various catalytic doses, AR concentrations, and pH of the medium on degradation. More than 50% AR degradation was obtained for all studied parameters with MH20 whereas the pseudo-first-order kinetic model was found to be the best-fitted kinetic model for AR degradation with k = 0.0015 and R2 = 0.99 indicating a significant correlation between experimental data.

Physical Characteristics, Blue-Green Band Emission and Photocatalytic Activity of Au-Decorated ZnO Quantum Dots-Based Thick Films Prepared Using the Doctor Blade Technique

Nanoscale ZnO is a vital semiconductor material whose versatility can be enhanced by sensitizing it with metals, especially noble metals, such as gold (Au). ZnO quantum dots were prepared via a simple co-precipitation technique using 2-methoxy ethanol as the solvent and KOH as the pH regulator for hydrolysis. The synthesized ZnO quantum dots were deposited onto glass slides using a simple doctor blade technique. Subsequently, the films were decorated with gold nanoparticles of different sizes using a drop-casting method. The resultant films were characterized via various strategies to obtain structural, optical, morphological, and particle size information. The X-ray diffraction (XRD) reveals the formation of the hexagonal crystal structure of ZnO. Upon Au nanoparticles loading, peaks due to gold are also observed. The optical properties study shows a slight change in the band gap due to Au loading. Nanoscale sizes of particles have been confirmed through electron microscope studies. P.L. studies display blue and blue-green band emissions. The significant degradation efficiency of 90.2% methylene blue (M.B.) was attained in natural pH in 120 min using pure ZnO catalyst while one drop gold-loaded catalysts, ZnO: Au 5 nm, ZnO: Au 7 nm, ZnO: Au 10 nm and ZnO: Au 15 nm, delivered M.B. degradation efficiency of 74.5% (in 245 min), 63.8% (240 min), 49.6% (240 min) and 34.0% (170 min) in natural pH, respectively. Such films can be helpful in conventional catalysis, photocatalysis, gas sensing, biosensing, and photoactive applications.

Removal of As(V) and Cr(VI) with Low-Cost Novel Virgin and Iron-Impregnated Banana Peduncle-Activated Carbons

This work reports the investigation of activated carbons from virgin banana peduncle (ZR1) and iron-impregnated banana peduncle (ZR2) as adsorbents for the removal of As(V) and Cr(VI) ions from aqueous solutions. Both adsorbents were characterized through the point of zero charge, powder X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray, Brunauer-Emmett-Teller, and Fourier transform infrared spectroscopic techniques. The effects of initial pH, contact time, temperature, and initial concentration on metal ion adsorption were investigated. Adsorbents existed as both crystalline and amorphous species having homogeneous surface cavities and surface area of 749.73 and 369.66 m²/g for ZR1 and ZR2, respectively. The maximum As(V) removal of 79.32 and 69.08% was obtained using ZR1 and ZR2, respectively, whereas the maximum Cr(VI) removal was calculated as 69.73% for ZR1 and 73.78% for ZR2. Kinetic modeling data were found to be best fitted for the pseudo-second-order reaction, and rate constants were calculated. The theoretical adsorption capacities (q _m) of ZR1 and ZR2 were calculated through Langmuir and Freundlich models. The maximum As(V) adsorption capacities calculated for ZR1 and ZR2 were 13.33 and 9.066 mg/g, respectively, whereas the maximum Cr(VI) adsorption capacity for both was 13.26 mg/g at 298-328 K. The reaction was endothermic with decreased randomness at the solid-liquid interface due to positive entropy and enthalpy values. All kinetic and thermodynamic parameters showed the feasibility of the adsorption process, and characterization after adsorption indicated ZR1 and ZR2 novel activated carbons as efficient and cheapest biosorbents for removing As(V) and Cr(VI).

Enhanced reactivity of the CuO-Fe2O3 intimate heterojunction for the oxidation of quinoline yellow dye (E104)

This research work describes the degradation of quinoline yellow (QY) in aqueous solutions by the heterogeneous Fenton and photo-Fenton processes in the presence of CuO/Fe₂O₃ photocatalyst. CuO/Fe₂O₃ derived from LDH structure was synthesized by the co-precipitation method. The physiochemical characteristics of CuO/Fe₂O₃ were described by XRD, TEM/SEM, BET surface area, and FTIR techniques. The effects of pH, H₂O₂ concentration, dye concentration, catalyst dose, reaction temperature, and reusability of catalyst on the QY decolorization efficiency were studied. The results indicated that a complete removal of QY was achieved within 150 min, when the H₂O₂ and QY concentrations were 27.6 mM and 100 mg/L, respectively. The rate constants for QY removal by the heterogeneous Fenton system were calculated, and the experimental data were found to fit the pseudo-first order model. Under optimal conditions, the rate constants were, respectively, 0.02032 and 0.01715 min^-1 for the photo-Fenton and Fenton systems; this means that the addition of light has not a noticeable effect.

Transcriptomic Analysis of Degradative Pathways for Azo Dye Acid Blue 113 in Sphingomonas melonis B-2 from the Dye Wastewater Treatment Process

Background: Acid Blue 113 (AB113) is a typical azo dye, and the resulting wastewater is toxic and difficult to remove. Methods: The experimental culture was set up for the biodegradation of the azo dye AB113, and the cell growth and dye decolorization were monitored. Transcriptome sequencing was performed in the presence and absence of AB113 treatment. The key pathways and enzymes involved in AB113 degradation were found through pathway analysis and enrichment software (GO, EggNog and KEGG). Results: S. melonis B-2 achieved more than 80% decolorization within 24 h (50 and 100 mg/L dye). There was a positive relationship between cell growth and the azo dye degradation rate. The expression level of enzymes involved in benzoate and naphthalene degradation pathways (NADH quinone oxidoreductase, N-acetyltransferase and aromatic ring-hydroxylating dioxygenase) increased significantly after the treatment of AB113. Conclusions: Benzoate and naphthalene degradation pathways were the key pathways for AB113 degradation. NADH quinone oxidoreductase, N-acetyltransferase, aromatic ring-hydroxylating dioxygenase and CYP450 were the key enzymes for AB113 degradation. This study provides evidence for the process of AB113 biodegradation at the molecular and biochemical level that will be useful in monitoring the dye wastewater treatment process at the full-scale treatment.

The mechanism of degradation of alizarin red by a white-rot fungus Trametes gibbosa

Background

Alizarin red (AR) is a typical anthraquinone dye, and the resulting wastewater is toxic and difficult to remove. A study showed that the white rot fungus Trametes gibbosa (T. gibbosa) can degrade dye wastewater by decolorization and has its own enzyme-producing traits.

Methods

In this study, transcriptome sequencing was performed after alizarin red treatment for 0, 3, 7, 10, and 14 h. The key pathways and key enzymes involved in alizarin red degradation were found to be through the analysis of KEGG and GO. The Glutathione S-transferase (GST), manganese peroxidase (MnP) and laccase activities of T. gibbosa treated with alizarin red for 0–14 h were detected. LC–MS and GC–MS analyses of alizarin red decomposition products after 7 h and 14 h were performed.

Results

The glutathione metabolic pathway ko00480, and the key enzymes GST, MnP, laccase and CYP450 were selected. Most of the genes encoding these enzymes were upregulated under alizarin red conditions. The GST activity increased 1.8 times from 117.55 U/mg prot at 0 h to 217.03 U/mg prot at 14 h. The MnP activity increased 2.9 times from 6.45 to 18.55 U/L. The laccase activity increased 3.7 times from 7.22 to 27.28 U/L. Analysis of the alizarin red decolourization rate showed that the decolourization rate at 14 h reached 20.21%. The main degradation intermediates were found to be 1,4-butene diacid, phthalic acid, 1,1-diphenylethylene, 9,10-dihydroanthracene, 1,2-naphthalene dicarboxylic acid, bisphenol, benzophenol-5,2-butene, acrylaldehyde, and 1-butylene, and the degradation process of AR was inferred. Overall, 1,4-butene diacid is the most important intermediate product produced by AR degradation.

Conclusions

The glutathione metabolic pathway was the key pathway for AR degradation. GST, MnP, laccase and CYP450 were the key enzymes for AR degradation. 1,4-butene diacid is the most important intermediate product. This study explored the process of AR biodegradation at the molecular and biochemical levels and provided a theoretical basis for its application in practical production.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12896-021-00720-8.

Catalytic Oxidation of Toluene into Benzaldehyde and Benzyl Alcohol Using Molybdenum-Incorporated Manganese Oxide Nanomaterials

Oxidation of toluene (an organic pollutant), into useful chemical products, is of great interest nowadays. However, efficient conversion of toluene under mild and sustainable conditions is a thought-provoking task. Here, we report MnMoO₄ nanomaterials (CH1-CH2), synthesized through a very facile solvothermal approach. Catalytic efficiencies of MnMoO₄ nanomaterials were evaluated by direct oxidation of toluene via C-H activation. Toluene was converted into benzaldehyde and benzyl alcohol in the presence of H₂O₂ as an oxidant at 80 °C. The reaction parameters, that is, catalyst dose, time, and toluene concentration, were varied to obtain the optimal conditions for the oxidation process. The 40.62% maximum toluene conversion rate was obtained after 18 h of oxidation activity with 0.06 g of catalyst CH1. A maximum of 78% benzaldehyde selectivity was obtained with 0.06 g of catalyst CH1 after 18 h of toluene oxidation activity. Also, 62.33% benzyl alcohol selectivity was achieved using 0.1 g of catalyst CH1 after 1 h of activity. Several catalytic cycles were run with CH1 to evaluate catalyst reusability. Potential % toluene conversion was obtained for up to six cycles and their turnover frequencies were found to be 1.94-1.01 s^-1. FTIR spectra of catalyst CH1 before and after recovery indicate no significant change. The good conversion rate of toluene and efficient selectivity toward benzaldehyde and benzyl alcohol indicates the robustness and high potential of these catalysts to oxidize toluene under a milder, greener, and hazardous chlorine-free environment.

Influence of selenium precursors on the formation of iron selenide nanostructures (FeSe2): Efficient Electro-Fenton catalysts for detoxification of harmful organic dyestuffs

In this investigation, a sequences of iron diselenide (FeSe₂) nanomaterials as the competent and highly stable catalysts for the detoxification of aqueous organic dye pollutants such as Congo red (CR) and methylene blue (MB) through Electro-Fenton (EF) process using hydrogen peroxide as an initiator have been studied. The utilized selenium precursors include selenium metal, selenious acid (H₂SeO₃) and selenium dioxide (SeO₂) which were employed for the synthesis of FeSe₂ catalysts through a wet chemical strategy. It has been observed that based on the employed precursors, different morphologies ranges of the FeSe₂ catalysts were obtained: microgranualr particles to nano-stick to nanoflakes. The crystalline nature and phase purity of the obtained FeSe₂ catalysts were determined through XRD, Raman and HR-TEM analyses which confirmed their orthorhombic ferroselite structure. Among the prepared FeSe₂ catalysts, FS-2 (using H₂SeO₃) displayed better porous properties as compared to other catalysts and achieved the highest surface area of 74.68 m²g^-1. The narrow bandgap (0.88 eV) and fast conversion of Fe²⁺/Fe³⁺ cycle of FeSe₂ led CR and MB degradation of 93.3% and 90.4%, respectively. The outcome of this study demonstrates improved catalytic properties of FeSe₂ nanostructures for the efficient detoxification of hazardous and toxic effluents.