Dye Reduction Research Articles

Optimizing catalytic performance: Reduction of organic dyes using synthesized Fe3O4@AC magnetic nano-catalyst

This article presents a sustainable method for the catalytic reduction of both simple and binary dye systems using magnetic activated carbon (Fe3O4@AC) synthesized from almond shells, an agricultural waste biomass. The reduction of methylene blue (MB) and Congo red (CR) was investigated in the presence of NaBH4, and a series of physical-chemical experiments were conducted to elucidate the mechanism of dye conversion and its performance. The results confirmed the successful synthesis of Fe3O4 nanoparticles on the activated carbon surface. The calculated rate constants in a simple system were 0.34 min⁻1 for MB and 0.25 min⁻1 for CR, in the binary system, the Fe3O4@AC catalyst demonstrated enhanced selectivity for the cationic MB dye, attributable to the robust, attractive surface charge. The study aimed to enhance catalytic performance by employing optimization curves generated from a three-level Box-Behnken Design (BBD) simulation. Experimental results indicated that the optimal catalyst dose, dye concentration, and reaction duration were 4–7 mg, 80–120 mg/L, and 5–20 min, respectively. Response surface methodology (RSM) was developed by processing the findings from 17 replicated experiments using a two-quadratic polynomial model, establishing a functional link between the experimental parameters and MB conversion. Optimal conditions for MB conversion were determined to be 7 mg of catalyst, 80 mg/L of MB concentration, and a reaction time of 12.5 minutes, resulting in an estimated conversion rate of 99.99 %. This prediction was validated by experimental findings, with regression analysis confirming a high correlation (R2 > 0.99) between the predicted and observed values. Additionally, the Fe3O4@AC catalyst demonstrated good recyclability and stable performance over three consecutive cycles, maintaining high conversion efficiency without loss of performance. These findings demonstrate that Fe3O4@AC is a viable approach for the rapid and efficient remediation of dyes in water.

Dicarboxylate cellulose nanofibrils-supported silver nanoparticles as a novel, green, efficient and recyclable catalyst for 4-nitrophenol and dyes reduction

This study reports dicarboxylate cellulose nanofibrils (DCNF) as a novel reducing and supporting agent for producing silver nanoparticles (AgNPs) with high efficiency (63.82 % reduction) and loading (6.88 %) using UV light. Unlike previous research, AgNPs formation with DCNF doesn't involve cellulose oxidation. Instead, it appears to involve a loss of carboxyl groups from DCNF. In comparative studies, pristine CNF (PCNF) and TEMPO-oxidized CNF (TOCNF) were also examined for AgNPs production. The resulting AgNPs from DCNF exhibited a significantly smaller average size (3.9 ± 0.7 nm) compared to those from PCNF (26.9 ± 10.9 nm) and TOCNF (13.5 ± 4.5 nm). Catalytic activity evaluation by the 4-nitrophenol (4-NP) reduction reaction revealed a high rate constant of 8.47× 10−3 s−1 by AgNPs/DCNF, which surpassed AgNPs/TOCNF (1.79 × 10−3 s−1) and AgNPs/PCNF (0.63 × 10−3 s−1) by 4.7 and 13.4 times, respectively. Besides 4-NP, AgNPs/DCNF aerogels were also applied for methyl orange and Rhodamine B dyes reduction. The aerogels showed excellent reusability, maintaining over 95 % conversion even after five cycles and also effective in treating real samples and mixed dye solutions. This study opens the door for future research exploring DCNF as a support material for various metal, metal oxide, and carbon nanoparticles.

Physiological and biomolecular interventions in the bio-decolorization of Methylene blue dye by Salvinia molesta D. Mitch

Methylene blue, a cationic dye as a pollutant is discharged from industrial effluent into aquatic bodies. The dye is biomagnified through the food chain and is detrimental to the sustainability of aquatic flora. Despite of number of physico-chemical techniques of dye removal, the use of aquatic flora for bio-adsorption is encouraged. Thus, we used Salvinia molesta D. Mitch in bio-reduction of methylene blue on concentrations of 0, 10, 20, and 30 mg L−1 through 5 days with biosorption kinetics. The dye removal was concentration-dependent, maximized at 2 days with 30 mg L−1 which altered the relative growth rate (44%) of plants. Biosorption recorded 71% capacity at optimum pH (8.0), 24 h reducing major bond energies of amide, hydroxyl groups, etc. Bioaccumulation of dye changed potassium content (446%) under maximum dye concentration modifying tissues for dye sequestration. Reactive oxygen species were altered on dye reduction by oxidase (33%) with redox homeostasis by enzymes. Plants altered the metabolism with over accumulation of polyamines (51%), abscisic acids (448%), and phosphoenolpyruvate carboxylase (83%) on dye reduction. Thus, this study is rationalized with a sustainable approach where aquatic ecosystems can be decontaminated from dye toxicity with the exercise of bioresources like Salvinia molesta D. Mitch as herein.

The Antarctic Yeast Sporobolomyces roseus AL103 as a Promising Source of Health-Promoting Biologically Active Compounds

Antarctic yeasts represent a poorly explored source of novel bioactive compounds with antineoplastic activity and a favorable toxicological profile. The present paper presents the newest data on the antiproliferative and antimicrobial potential of extracts obtained from the psychrophilic strain AL103 of the species Sporobolomyces roseus. The capacity of AL103 to grow under different cultivation conditions, including in a bioreactor system with optimal biomass quantities of approximately 6.0 g/L, was demonstrated. A comparative examination of the metabolic profiles (GC-MS-based) of yeast extracts revealed a wide variety of synthesized molecules responsible for the different levels of antineoplastic activity depending on the tissue origin of the malignant cell lines. Concentration response curves were generated by the MTT dye reduction test. The respective IC50 values were extrapolated and found between 35.3 and 163 µg/mL. The antibacterial potential of both extracts was evaluated with the broth microdilution test against four referent pathogenic bacterial strains. The estimated minimal inhibitory concentrations revealed a moderate antibacterial activity. According to the GC-MS results, both extracts are rich in long-chain fatty acids which are known for their antibacterial properties. In conclusion, the Antarctic strain AL103 possesses promising potential for further pharmacological investigations aiming to elucidate its application as a health-promoting food additive or/and as a source of biologically active compounds.

From plant to nanomaterial: Green extraction of nanomucilage from Cordia dichotoma fruit and its multi-faceted biological and photocatalytic attributes

This study aimed to evaluate the extraction efficiency of mucilage from Cordia dichotoma fruits using various aqueous extraction methods, including microwave-assisted water extraction (MWE), hot-water extraction (HWE), and cold-water extraction (CWE). Different analytical techniques were employed to characterize the Cordia dichotoma mucilage (CDM). Additionally, the functional properties, anti-microbial, anti-inflammatory, and dye reduction potential of CDM were assessed. The results indicated a significantly (p < 0.05) higher yield of CDM (13.44 ± 0.94 %) using MWE compared to HWE (12.08 ± 0.82 %) and CWE (7.59 ± 0.73 %). The optimal extraction condition was utilized for the spray-drying process, yielding a spray-dried mucilage powder (SDMP) with a yield of 9.52 ± 1.27 %. The presence of galactose and arabinose as major sugar and functional groups such as OH, COOH, CH, and NH from proteins, uronic acids, and sugars were identified. CDM predominantly comprises galactose and arabinose as major sugars. CDM particles exhibited an irregular morphology and demonstrated thermal stability, with maximum weight loss occurring between 221.83 and 478.66 °C. The particle size of CDM was 681.16 ± 2.18 nm with a zeta potential of −21.46 ± 1.72 mV. Rheological analysis revealed that CDM exhibits shear-thinning behavior. Furthermore, CDM displayed inherent biological activities, including antimicrobial and anti-inflammatory properties. The dye reduction potential of CDM was evidenced by an 88.67 % degradation of indigo carmine dye. In summary, this study provides insights into the cost-effective extraction methods for CDM and its potential utilization as an eco-friendly material for dye reduction.

Effect of surface charge on laser-produced silver nanoparticles for dye reduction and surface-enhanced Raman spectroscopy

Silver nanoparticles (Ag NPs) are widely used in biological, chemical, and physical fields due to their distinct properties. However, the effect of surfactants with different polarities on the catalytic and surface-enhanced Raman spectroscopy (SERS) performance of Ag NPs has not been thoroughly studied. Here, we tailor the surface charge of laser-synthesized Ag NP without changing their morphology and investigate their catalytic and SERS capabilities. The surfactant-free silver nanoparticles (NPBare), synthesized via pulsed laser ablation in liquid (PLAL), are subsequently coated with ionic surfactants sodium dodecyl sulfate (NPSDS) and cetyltrimethylammonium bromide (NPCTAB). The synthesis and morphology of Ag NPs are confirmed using UV-Vis absorption spectroscopy and scanning electron microscopy. The surface charge of fabricated NPs is determined using zeta potential (ZP) measurements. The ZP values of NPBare, NPSDS, and NPCTAB are determined to be -17 mV, 28.7 mV, and 5.58 mV, respectively. The catalytic activity of bare and coated Ag NPs was tested against the cationic and anionic dyes, Methylene blue (MB) and Methyl orange (MO) respectively. The reduction rate of both dyes was highest when using NPBare. However, in the case of coated nanoparticles, the rate of MB and MO reduction depends on the difference between the ZP of the dye and nanoparticles: the rate of reduction increases with the difference between the zeta potentials of the dye and coated nanoparticles increases. The SERS capability of bare and coated NPs was evaluated for anionic (MO) and cationic (MB, Rhodamine B, and Crystal Violet) dyes. The SERS intensity of dyes strongly enhanced with the increase in ZP difference between the dye molecules and NPs. Surface charge modified NPs shown excellent SERS sensitivity with detection limit up to nanomolar for dye molecules as well as the homogeneity of NPs demonstrated in Raman mapping results with relative standard deviation of 17%. The results suggest that the electrostatic interaction between the nanoparticles and dye molecules plays a dominant role in SERS enhancement. These findings highlight the significance of surface charge in improving the catalytic and sensing properties of noble metal nanoparticles.

Construction of Ba-doped Ag3PO4/SnO2 type-II nanocomposites as a promising photocatalyst for boosting photocatalytic degradation of BY28 dye and redox conversion of Cr(VI)/Cr(III)

In the present study, Ba-doped Ag3PO4/SnO2 type-II heterojunction nanocomposites were fabricated and systemically investigated for the degradation of basic yellow 28 (BY28) dye and Cr(VI) reduction in the photocatalytic process under visible-light irradiation. XRD, XPS, FESEM, DRS, and PL analyses were performed to determine the characterization of synthesized photocatalysts. The optimal 1.5 wt% Ba-doped Ag3PO4/SnO2 nanocomposite exhibited an efficient photocatalytic activity with rate constant of 0.0491 min−1 for BY28 degradation and 0.0261 min−1 for Cr(VI) reduction, which is 13.3 and 7.5 times higher than that of the SnO2 nanorods. Such enhanced performance can arise from the one-dimensional structure, extended light absorption toward the visible region, formation of the type II heterojunction, the new defect-related energy states, and efficient charge separation. Furthermore, the photostability of the photocatalysts was studied and a plausible photocatalytic mechanism was proposed.

Therapeutic Applications of Azo Dye Reduction: Insights From Methyl Orange Degradation for Biomedical Innovations.

This paper emphasizes the possible application of methyl orange reduction as a therapeutic technique, highlighting the potential of azo dye reduction in biomedical fields. The generally used azo dyes are toxic and carcinogenic; hence, they implicitly threaten the environment and health. The degradation of methyl orange, a famous example of azo dyes, is used to describe the degradation process for other azo dyes. This work discusses the ability of different methyl orange degradation methods, focusing on biocatalysts and nanomaterials, among the methods that identified enzymatic degradation with azoreductase enzymes as the method that quickly breaks down azo dyes under mild conditions as the most appropriate method, as well as its specificity as environmentally friendly. Moreover, metal nanoparticles such as silver and gold impellers increase the reducing efficiency because they offer a pivotal surface for the reduction reactions that undergo electron transfer. The complete breakdown of methyl orange is essential in biomedical usage. The strategies for treating azo dye reduction can be extended to next-generation drug delivery systems (DDS), biosensors, and therapeutic agents. Organisms involved in degradation can be functionalized to selectively degrade specific cells or tissues, thus presenting a new targeted therapy. Knowledge of degradation pathways and non-toxic products is essential in creating programs that build better and more efficient therapeutic agents. This work endeavors to illustrate the development of enzymatic and nanomaterials-based approaches to achieve sustainable azo dye decolorisation to open the gateway to developing other biomedical applications that tend to promote environmental and health-friendly solutions.

FeCo Alloy Nanoparticles Supported on N-doped Mesoporous Carbon Spheres for Hydrogen Evolution and Reduction of Organic Dyes

FeCo Alloy Nanoparticles Supported on N-doped Mesoporous Carbon Spheres for Hydrogen Evolution and Reduction of Organic Dyes

Antibiofilm activity of truncated Staphylococcus aureus phenol soluble modulin α2 (SaΔ1Δ2PSMα2) against Candida auris in vitro and in an animal model of catheter-associated infection

Candida auris has emerged as a major multidrug-resistant nosocomial pathogen. The organism exhibits a persistent colonising phenotype, and causes recalcitrant infections often strongly linked to biofilm formation. Alternate strategies are urgently needed to combat this yeast and its biofilm-associated phenotype. This work aimed to evaluate the efficacy of select staphylococcal phenol soluble modulins (PSMs), namely, a truncated version of Staphylococcus aureus PSMα2 shortened by two amino acids at the N-terminal (SaΔ1Δ2PSMα2) and Staphylococcus epidermidis PSMδ against C. auris in vitro and in vivo. The antifungal and antibiofilm activity was tested by broth microdilution and XTT dye reduction assay. Combination effect with antifungal drugs was determined by fractional inhibitory concentration test. The efficacy of combination therapy using SaΔ1Δ2PSMα2 with amphotericin B or caspofungin was evaluated in murine model of C. auris catheter-associated infection. Based on antifungal activity, antibiofilm activity and cytotoxicity data, SaΔ1Δ2PSMα2 exhibited promising activity against C. auris biofilms. Nearly 50 % inhibition in biofilm formation was noted with 0.5–2 μM of the peptide against multiple clinical and C. auris colonizing isolates. It was synergistic with amphotericin B (ΣFIC = 0.281) and caspofungin (ΣFIC = 0.047) in vitro, and improved the activity of voriconazole in voriconazole-resistant C. auris. Combination therapy using amphotericin B or caspofungin (1 μg/ml) with SaΔ1Δ2PSMα2 resulted in 99.5 % reduction in C. auris biofilm in murine model, even when the peptide was used at a concentration that was neither fungicidal nor antibiofilm (0.125 μM; ≈0.26 μg/ml). The study provides insight into the potential utility of SaΔ1Δ2PSMα2-antifungal drug combination against C. auris biofilm-associated infections.

Magnetic Silver Nanoparticles Stabilized by Superhydrophilic Polymer Brushes with Exceptional Kinetics and Catalysis.

Stimuli-responsive catalysts with exceptional kinetics and complete recoverability for efficient recyclability are essential in, for example, converting pollutants and hazardous organic compounds into less harmful chemicals. Here, we used a novel approach to stabilize silver nanoparticles (NPs) through magneto/hydro-responsive anionic polymer brushes that consist of poly (acrylic acid) (PAA) moieties at the amine functional groups of chitosan. Two types of responsive catalyst systems with variable silver loading (wt.%) of high and low (PAAgCHI/Fe3O4/Ag (H, L)) were prepared. The catalytic activity was evaluated by monitoring the reduction of organic dye compounds, 4-nitrophenol and methyl orange in the presence of NaBH4. The high dispersity and hydrophilic nature of the catalyst provided exceptional kinetics for dye reduction that surpassed previously reported nanocatalysts for organic dye reduction. Dynamic light scattering (DLS) measurements were carried out to study the colloidal stability of the nanocatalysts. The hybrid materials not only showed enhanced colloidal stability due to electrostatic repulsion among adjacent polymer brushes but also offered more rapid kinetics when compared with as-prepared Ag nanoparticles (AgNPs), which results from super-hydrophilicity and easy accumulation/diffusion of dye species within polymer brushes. Such remarkable kinetics, biodegradability, biocompatibility, low cost and facile magnetic recoverability of the Ag nanocatalysts reported here contribute to their ranking among the top catalyst systems reported in the literature. It was observed that the apparent catalytic rate constant for the reduction of methyl orange dye was enhanced, PAAgCHI/Fe3O4/Ag (H) ca. 35-fold and PAAgCHI/Fe3O4/Ag (L) ca. 23-fold, when compared against the as prepared AgNPs. Finally, the regeneration and recyclability of the nanocatalyst systems were studied over 15 consecutive cycles. It was demonstrated that the nanomaterials display excellent recyclability without a notable loss in catalytic activity.

Effect of sintering temperature on magnetic, catalytic and photocatalytic properties of Cu-Co-Mn ferrite catalyst

Wastewater pollution is a pressing environmental issue, necessitating effective remediation strategies to mitigate its impact. This study investigates the use of an efficient catalyst for degrading nitrophenols by converting them into useful aromatic amines, which are crucial building blocks for many pharma industries, and photodegradation of various dyes in their unitary solution as well as in mixture. The Cu-Co-Mn ferrite was synthesized using the sol-gel process and sintered at different temperatures. Structural analysis using XRD and Rietveld refinement revealed a crystal structure corresponding to the Fd3‾m space group having high purity in all the samples. Additionally, the impact of sintering temperature on the magnetic features of the phases were also studied and the findings suggest that all the phases exhibit ferromagnetic behaviour, which means they can be easily separated from reaction mixtures using an external magnetic field. It was also found that higher sintering temperatures lead to a rise in saturation magnetization and magnetic moment with decrease in coercivity (Hc). Further, it was observed that Curie temperature (Tc) increases with increase in sintering temperature with the exception of CFM400. The catalytic performance of all the catalysts, including CFM400, CFM500, CFM600, CFM800, and CFM1000, was evaluated and the results indicate that CFM400 exhibits the highest catalytic activity for nitrophenols reduction and photodegradation of dyes, which could be accredited to its larger BET surface area and lower PL intensity. Overall, the structural and magnetic features of the catalyst’s sheds light on the underlying mechanisms governing their catalytic activity. These insights offer valuable guidance in the designing and development of effective catalysts for sustainable wastewater treatment practices, emphasizing the importance of considering both structural and magnetic features in catalyst design.

Green NiO nanoparticle-integrated PVA-alginate hydrogel: potent nanocatalyst for efficient reduction of anthropogenic water pollutants.

Hydrogel nanocatalyst composed of nickel oxide (NiO) nanoparticles embedded in PVA-alginate hydrogels were potentially explored toward the reduction of anthropogenic water pollutants. The NiO nanoparticleswas accomplished via green method using waste pineapple peel extract. The formation of the nanoparticles was affirmed from different analytical techniques such as UV-Vis, FTIR, XRD, TGA, FESEM, and EDS. Spherical NiO nanoparticles were obtained having an average size of 11.5nm. The nano NiO were then integrated into PVA-alginate hydrogel matrix forming a nanocomposite hydrogel (PVALg@ NiO). The integration of nano NiO rendered an improved thermal stability to the parent hydrogel. The PVALg@ NiO hydrogel was utilized as a catalyst in the reduction of 4-nitrophenol (4-NP), potassium hexacyanoferrate (III), rhodamine B (RhB), methyl orange (MO), and malachite green (MG) in the presence of a reducing agent, i.e., NaBH4. Under optimized conditions, the reduction reactions were completed by 4.0min and 3.0min for 4-NP and potassium hexacyanoferrate (III), respectively, and the rate constant was estimated to be 1.14min-1 and 2.15min-1. The rate of reduction was found to be faster for the dyes and the respective rate constants were be 0.17s-1 for RhB, MG and 0.05s-1 for MO. The PVALg@ NiO hydrogel nanocatalyst demonstrated a recyclability of four runs without any perceptible diminution in its catalytic mettle. The efficacy of the PVALg@ NiO hydrogel nanocatalyst was further examined for the reduction of dyes in real water samples collected from different sources and the results affirm its high catalytic potential. Thus, this study paves the path for the development of a sustainable hydrogel nanocatalyst for reduction of hazardous pollutants in wastewater treatment.

A highly efficient and stable PtNi bimetallic nanoparticles modified on Mo2C decorated N-doped carbon flowers catalysts for the remediation of environmental pollutants

The unregulated discharge of nitroaromatics (NAs) and organic dye contaminants into aquatic ecosystems is a growing global concern, highlighting the urgent need for the development of effective wastewater treatment technology. In this study, we prepared Mo2C decorated on N- doped carbon flowers supported with PtNi bimetallic (PtxNiy@Mo2C/NCF) nanoparticles using the self-polymerization of dopamine and followed by the chemical reduction methods. These catalysts, with varying Pt:Ni ratios, were designed for the highly efficient catalytic reduction of NAs and rhodamine b (RhB) under the mild reaction conditions. The HR-TEM images confirmed the formation of spherical PtNi bimetallic NPs with an average diameter of 1.68 ± 0.6 nm. The prepared PtxNiy@Mo2C/NCF catalysts exhibited significantly higher catalytic efficiency for 4-nitrophenol (4-NP) reduction compared to their respective monometallic counterparts using NaBH4. Particularly, the Pt0.75Ni0.25@Mo2C/NCF catalyst showed superior catalytic activity with the apparent rate constant (kapp: 0.6703 min−1) and TOF (17.0 × 10−7 mol mg−1 min−1) and high recyclability over eight consecutive recycles. Furthermore, the Pt0.75Ni0.25@Mo2C/NCF catalyst also exhibited high catalytic activity for other NAs and RhB dye reduction with excellent yields. This enhanced catalytic activity of Pt0.75Ni0.25@Mo2C/NCF catalyst could be ascribed to the synergistic effect of the bimetallic systems, leading to more efficient reactions. Additional experiments were conducted on a fixed bed reactor to demonstrate that the Pt0.75Ni0.25@Mo2C/NCF catalyst effectively reduce both 4-NP and RhB dye over 15 successive runs. This work may pave the way for using PtxNiy@Mo2C/NCF catalysts in various wastewater treatment applications.

Cu@Zn@800 bimetallic-based carbon nanomaterials for dark-catalyzed degradation and 4-NP-catalyzed reduction of azo dyes

Metal-organic frameworks (MOFs) were adaptable templates that might be used to create multifunctional materials containing carbon nanostructures. In this work, we had prepared a novel Cu-MOF using fumaric acid (H2FA) and N,N′-bis(pyridin-3-yl)isophthalamide (3-bpia) as the mixed ligands. Then, the Cu-MOF was served as a template to derive bimetallic-based carbon nanomaterials by introducing a second metal through doped ZnO by both re-calcined and directly calcined methods (Cu@Zn@800) and single-metal-based carbon nanomaterials (Cu@800). Cu@Zn@800 was able to catalyze the degradation of azo dyes at a rate higher than 99.40 % because of its capacity to create h+ and ·OH active substances and the uniformity of its metal active sites. Additionally, Cu@Zn@800 might use NaBH4 to decrease 4-NP in 30 s with the rate of decline was over 100 %. Cu@Zn@800 was a special and efficient dual-functional material that might be used in a variety of ways to remove contaminants from water.

Synthesis and characterization of a bimetal nickel manganese oxysulfide (NiMnOS) catalyst for the reduction of methylene blue dye

Noble metal-free nickel manganese oxysulfide (NiMnOS) catalysts were successfully prepared via a facile and eco-friendly approach at a low synthesis temperature of 90 °C in a water bath. The catalysts were synthesized by varying Ni: Mn molar ratios such as 25:75, 50:50, 75:25 and abbreviated as NiMnOS-25, NiMnOS-50, and NiMnOS-75, respectively. The bare NiOS and MnOS were also prepared for comparison purposes. The characterizations of the prepared samples were conducted with different techniques, and the catalytic activity was investigated through the reduction of methylene blue (MB) dye in the presence of NaBH4 in an aqueous solution. Among the prepared catalysts, NiMnOS-25 exhibited excellent performance and reduced 98.46% of MB within 5 min. However, NiOS, NiMnOS-50, NiMnOS-75, and MnOS were reduced 9.6%, 98.41%, 97.04%, and 6.40% of MB dye, respectively, within 7 min. The catalytic reduction activity could be mainly attributed to the synergistic effects of the metals (Ni and Mn), more exposed active sites. Therefore, the bimetal NiMnOS catalyst could be a promising candidate for the reduction of organic dyes in wastewater treatment technologies.

Croton macrostachyus leaf-mediated biosynthesis of copper oxide nanoparticles for enhanced catalytic reduction of organic dyes

Introduction. Owing to the increasing use of organic dyes, the biosynthesis of metal oxide nanocatalysts is urgently needed as an economical and environmentally friendly solution to reduce their waste release. Method. In this study, we synthesized copper oxide nanoparticles (CuO NPs) by the sol–gel method using Croton macrostachyus leaf extracts as capping and reducing agents. The biosynthesized CuO catalysts were characterized using x-ray diffraction analysis (XRD), thermogravimetric differential thermal analysis (TGA-DTA), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and Fourier transform infrared spectroscopy (FTIR). Result. The result showed that the synthesized CuO NPs had a crystallite size of about 9 nm and had good crystalline texture. Furthermore, the catalyst showed the best catalytic reduction performance in 1 min for methylene blue (MB) and 3 min for methyl orange (MO). Furthermore, the CuO catalyst synthesized using Croton macrostachyus leaf extract resulted in apparent rate constant (Kapp) values for MB and MO of 0.06793 s−1 and 0.01877 s−1, respectively. Discussion. The recyclability of the CuO catalyst was investigated, and it was shown that the catalysts are suitable for reuse in dye reduction. Therefore, the catalytic activity of this study suggests that the CuO nanocatalysts prepared in this work are a potential candidate for controlling organic pollutants or trace amounts of naturally occurring active organic chemicals in all environmental dye wastes.

The enhancement effect of n-Fe3O4 on methyl orange reduction by nitrogen-fixing bacteria consortium

Although the anaerobic reduction of azo dyes is ecofriendly, high ammonia consumption remains a significant challenge. This work enriched a mixed nitrogen-fixing bacteria consortium (NFBC) using n-Fe3O4 to promote the anaerobic reduction of methyl orange (MO) without exogenous nitrogen. The enriched NFBC was dominated by Klebsiella (80.77 %) and Clostridium (17.16 %), and achieved a 92.7 % reduction of MO with an initial concentration of 25 mg·L−1. Compared with the control, the consortium increased the reduction efficiency of MO, cytochrome c content, and electron transport system (ETS) activity by 11.86 %, 89.86 %, and 58.49 %, respectively. When using 2.5 g·L−1 n-Fe3O4, the extracellular polymeric substances (EPS) of NFBC were present in a concentration of 85.35 mg·g−1. The specific reduction rates of MO by NFBC were 2.26 and 3.30 times faster than those of Fe(II) and Fe(III), respectively, while the enrichment factor of the ribosome pathway in NFBC exceeded 0.75. Transcriptome, carbon consumption, and EPS analyses suggested that n-Fe3O4 stimulated carbon metabolism and secreted protein synthesized by the mixed culture. The latter occurred due to the increased activity of consortium and the content of redox substances. These findings demonstrate that n-Fe3O4 promoted the efficiency of mixed nitrogen-fixing bacteria for removing azo dyes from wastewater. This innovative approach highlights the potential of integrating nanomaterials with biological systems to effectively address complex pollution challenges.

New insights into the mechanism of azo dye biodegradation by Lactococcus lactis

Azo dye reduction by syntrophic microbial communities is still unclear, with conflicting observations reported in the literature. In this study, the biodegradation mechanism of a model azo dye by Lactococcus lactis strain LLSP-01 isolated from an acidogenic reactor system was investigated. Proteomics and RT-PCR analysis results showed that LLSP-01 azoreductase (AzoL) was not expressed by the isolate during exposure to Direct Black 22. In contrast, the mechanism appears to involve biosorption by glycoconjugates, particularly exopolysaccharides (EPS) and rhamnolipids, as proteins from the LPS O-antigen metabolism were statistically higher expressed in cells challenged with the target compound. Based on the proteomic observations, it is hypothesized that Direct Black 22 is adsorbed into the biofilm matrix and indirectly reduced by an SDR family oxidoreductase, in a mechanism mediated by riboflavin carriers. Induction of a ring-cleaving dioxygenase in the presence of azo dye indicates further degradation of the resulting aromatic amines. The collected results show that azo dye reduction by L. lactis is mediated by enzymes with broad range specificity, and not the typical azoreductases. This information can assist in the design of new strategies for the bioremediation of textile azo dyes.

Microwave-assisted one-pot synthesis of carbon dots from biomass: Fe(III) ion sensing and in-situ methylene blue reduction catalytic activity

In this study, zero-dimensional fluorescent carbon dots were synthesized from affordable organic bio-precursors derived from chayote seeds using a one-pot microwave-assisted carbonization process. These biomass-derived carbon dots display excellent fluorescence properties, with an average size of approximately 3.3 nm and a fluorescence quantum yield about 9.56 %. The fluorescence emission spectra were recorded at different excitation peaks, with the highest intensity emission peak observed at 387 nm with an excitation wavelength of 320 nm. These carbon dots effectively detect Fe3+ ions, with a detection limit of 4.5 µmol. Carbon dots show strong catalytic reduction activity against a reduction of Methylene Blue dye, achieving an 81 % reduction in a short period. These biomass-derived carbon dots presents sustainable and promising option for applications in metal sensing and catalytic degradation.