Indigo Research Articles

Effective removal of different dyes using run-of-mine and processed coal samples

Coal, traditionally utilised solely for combustion, is now being investigated for its potential as an adsorbent in purifying drinking water by eliminating hazardous metal ions. Limited research exists regarding its effectiveness in reducing organic dye levels. Presented here are the outcomes of an extensive investigation into various carbon samples' efficacy as adsorbents for wastewater color removal. Samples of coal sourced from Western Coalfield Limited (WCL) were meticulously processed and characterized, encompassing run-of-mine coal and acid-leached coal. A comprehensive array of techniques, including scanning electron microscopy (SEM) coupled with energy dispersive X-ray spectroscopy (EDX), powder X-ray diffraction (PXRD), Fourier transform infrared spectroscopy (FTIR), and Raman spectroscopy, was employed for coal characterization. Proximate analysis and gross calorific value (GCV) were employed to assess coal's physical attributes. The adsorption behavior of methylene blue (MB) and crystal violet (CV) on coal was scrutinized, varying factors such as contact time, pH, initial MB and CV concentrations, and adsorbent doses. Optimal adsorption parameters for MB were determined as pH 2, initial concentration of 1 ppm, 0.2 g adsorbent dose, and 60 min contact time. For CV, optimal conditions were pH 8, initial concentration of 6 ppm, 0.4 g adsorbent dose, and 45 min contact time. MB adsorption kinetics favored the pseudo-second-order reaction model, with Freundlich isotherms providing a better fit than Langmuir isotherms. Conversely, CV adsorption kinetics favored the pseudo-second-order reaction model, with Langmuir isotherms exhibiting a superior fit compared to Freundlich isotherms.

High removal of methylene blue and methyl violet dyes from aqueous solutions using efficient biomaterial byproduct

Dyes are among the toxic contaminants that significantly impact water ecosystems. A biomaterial prepared from Zizyphus Spina-Christi seed (ZSCS) to remove methylene blue (MB) and methyl violet (MV) from an aqueous solution was investigated. Several techniques have been used, including FTIR, SEM, EDX, XPS, and TGA, to characterize the physical and chemical properties of ZSCS. The effect of various parameters such as pH, adsorbent dosage, contact time, temperature, and initial dye concentration on the adsorption process were studied. The ZSCS adsorbent showed efficient MB and MV dye adsorption with Langmuir adsorption capacity of 666.66 and 476.19 mg/g, respectively, at experimental condition [(pH = 6; time = 30 min; T = 45 °C, dye concentration: 500 mg/L, and adsorbent dose = 0.6 g/L for MB and 1 g/L for MV dye)]. Kinetic and isotherm models were applied to fit the experimental outcomes. The result showed that ZSCS showed an ultrafast absorption process with a high removal efficiency of MB and MV within 5 min indicating its effective adsorption properties. The Langmuir isotherm model was the most suitable model for describing the adsorption of MB and MV dyes on ZSCS. The pseudo-second-order model kinetic fits better to MB and MV adsorption onto ZSCS than other models, suggesting that the adsorption mechanism followed chemisorption. Our results could offer an efficient cost-effective approach for dye removal from wastewater.

Copper supported Dowex50WX8 resin utilized for the elimination of ammonia and its sustainable application for the degradation of dyes in wastewater

To obtain high efficient elimination of ammonia (NH4+) from wastewater, Cu(II), Ni(II), and Co(II)) were loaded on Dowex-50WX8 resin (D-H) and studied their removal efficiency towards NH4+ from aqueous solutions. The adsorption capacity of Cu(II)-loaded on D-H (D-Cu2+) towards NH4+ (qe = 95.58 mg/g) was the highest one compared with that of D-Ni2+ (qe = 57.29 mg/g) and D-Co2+ (qe = 43.43 mg/g). Detailed studies focused on the removal of NH4+ utilizing D-Cu2+ were accomplished under various experimental conditions. The pseudo-second-order kinetic model fitted well the adsorption data of NH4+ on D-Cu2+. The non-linear Langmuir model was the best model for the adsorption process, producing a maximum equilibrium adsorption capacity (qmax = 280.9 mg/g) at pH = 8.4, and 303 K in less than 20 min. The adsorption of NH4+ onto D-Cu2+ was an exothermic and spontaneous process. In a sustainable step, the resulting D-Cu(II)-ammine composite from the NH4+ adsorption process displayed excellent catalytic activity for the degradation of aniline blue (AB) and methyl violet 2B (MV 2B) dyes utilizing H2O2 as an eco-friendly oxidant.

Development of banana pseudo stem cellulose fiber based magnetic nanocomposite as an adsorbent for dye removal

A hybrid hydrogel nanocomposite derived from cellulose fiber extracted from Banana Pseudo Stem (BPS) was developed as an adsorbent material for wastewater treatment. The hydrogel was developed by graft copolymerization of N-hydroxyethylacrylamide on Cellulose Fiber (BPSCF-g-PHEAAm) with potassium peroxodisulphate (KPS) as an initiator and N, N′-methylene bisacrylamide (MBA) as a crosslinker using microwave irradiation. Magnetic nanoparticles generated by an in-situ method were incorporated into the network structure. Fourier Transform Infrared Spectroscopy (FTIR), Powder X-ray Diffraction (XRD), Thermogravimetric analysis (TGA), Vibrating Sample Magnetometer (VSM), Brunauer-Emmett-Teller analysis (BET), Field Emission Scanning Electron Microscopy (FESEM), and Energy Dispersive Spectrometer (EDS) were employed. The adsorption capacities of hydrogel and its nanocomposite were evaluated using Methylene Blue (MB) and Crystal Violet (CV) as model dyes. The parent gel exhibited the maximum absorption capacity of 235, and 219 mg g−1 towards MB and CV respectively which was enhanced to 320 and 303 mg g−1 for the nanocomposite. Adsorption data were best fitted with the pseudo-second-order kinetic model and the Freundlich isotherm model. Negative ΔG° and positive ΔH° indicated spontaneous and endothermic adsorption. Desorption was effective to an extent of 99 % in the HCl medium suggesting high reusability potential of the developed adsorbent material.

Shape-Specific Gold Nanoparticles for Multiplex Biosensing Applications.

The biosensing field faces a significant challenge in efficiently detecting multiple analytes in a single diagnostic sample in order to compete with other established multiplex molecular diagnostic technologies such as PCR and ELISA. In response, we have developed a colorimetric nanobiosensor based on multiple morphological forms of functionalized gold nanoparticles (AuNPs) for the simultaneous detection of the influenza virus and SARS-CoV-2 virus. Gold nanospheres (GNSp) were modified with oligonucleotides specific for the influenza A virus, while gold nanoshells (GNSh) were modified with oligonucleotides specific for the SARS-CoV-2 virus. In the presence of their respective targets, AuNPs remain stable due to DNA-DNA interactions; conversely, in the absence of targets, AuNPs aggregate. Consequently, the hybrid system exhibits an indigo color with the SARS-CoV-2 target, a blue color with the Influenza A target, and a purple color with both targets, visible to the naked eye. Analytical sensitivity was 100 nM, and no cross-reactivity was observed with potentially confounding pathogens. This approach holds great promise for the simultaneous identification of multiple pathogens in a rapid manner without the need for equipment or trained personnel.

Highly Porous Multiwalled Carbon Nanotube-Foam Composite for Batch Adsorption Performances of Dyes.

Treatment of dye pollutants prior to their release into the environment remains a formidable challenge, persisting as a longstanding issue. This study focuses on the development of a multiwalled carbon nanotube-foam (MWCNT-foam) composite through low-temperature chemical fusion (LTFC), resulting in a composite with a remarkably high accessible surface area (>475 m2 g-1). The MWCNT-foam composite exhibits a three-dimensional porous structure and demonstrates a notable affinity for organic dye adsorption. The efficacy of this composite was evaluated against various cationic dyes such as Methylene blue (MB) and Crystal Violet (CV) as well as anionic dyes such as Congo red (CR) and Eriochrome black T (EB), and the composite showed removal rates exceeding 99%. Furthermore, the study delved into the impact of the initial dye concentration, adsorbent dosage, kinetics, and other factors on the performance of the MWCNT-foam composite. The adsorption process achieved equilibrium in 10 min and strongly correlated with the pseudo-second-order kinetic model and Langmuir isotherm. The maximum adsorption capacity of MWCNT-foam for MB, CV, CR, and EB was found to be 168.63, 147.49, 99.50, and 93.11 mg g-1, respectively. In order to showcase the potential of this material for continuous adsorption, a specialized cartridge was designed and employed to treat dye solutions, demonstrating the feasibility of continuous mode adsorption.

Enhanced removal of hazardous organic contaminants with advanced visible light-active F-doped TiO2/rGO/PVDF photocatalytic membranes

Polyvinylidene fluoride (PVDF) membranes and composite variants with x% FGT/PVDF photocatalytic membranes were prepared at different concentrations (x = 1 %, 5 %, and 10 %) using the phase inversion technique. The synthesized photocatalysts and the membrane materials were thoroughly characterized using different analytical methods. The focus was on determining the photocatalytic efficiency of these materials in degrading two important harmful dyes, namely methylene blue (MB) and crystal violet (CV), under visible light irradiation. High degradation percentages of MB (96 %) and CV (92 %) at 90 minutes were observed with 5 % F-TiO2/rGO (named as 5 %FGT). Similarly, the 5 % F-TiO2/rGO/PVDF (5 %FGT/PVDF) photocatalytic membranes showed 98 % and 93 % degradation of MB and CV, respectively. Kinetic studies revealed that the photocatalytic degradation reaction followed a pseudo-first-order mechanism. The total organic carbon (TOC) analysis of the treated MB and CV dyes showed a degradation of 78 % and 71 %, respectively. Recycling of the most active 5 % FGT/PVDF composite membrane exhibited very high stability of 800 min. The composite material utilizes the photocatalytic properties of TiO2 and the stimulating transport properties of rGO. Additionally, fluorine doping enhances charge carrier separation, tunes the bandgap for visible light response, and increases surface activity, thereby improving the overall degradation of organic pollutants. These properties make the composite material promising for various applications in environmental remediation and wastewater treatment.

Adsorptive removal of cationic dyes from wastewater using a novel sodium alginate-based iron oxide nanocomposite hydrogel: DFT and advanced statistical physics modelling

A novel Sodium alginate-based hydrogel reinforced with varying Fe2O3 nanoparticles loading (NCH) was synthesized to remove cationic dyes methylene blue (MB) and crystal violet (CV). The NCH, with 5 % Fe2O3 loading, demonstrated optimal removal efficiency for both dyes. Detailed spectroscopic, microscopic, and spectrometric characterization techniques verified the nanocomposite structure and dye adsorption. Batch experiments revealed that at pH: 9, with a 20 mg 100 mL−1 adsorbent dose and times of 60 min for MB and 40 min for CV, with an initial concentration of 500 mg L−1, maximum adsorption capacities were achieved. MB and CV adsorption onto NCH showed distinct mechanisms: MB via physical interaction, CV via both physical and chemical interactions, including electrostatic forces and hydrogen bonding. Despite differences, the Langmuir-Freundlich model best fit the equilibrium isotherms, suggesting monolayer adsorption dominated, even with heterogeneous surface sites on NCH. A dual-site M2 statistical physics model revealed that MB and CV adsorption occurred via a multi-molecular vertical configuration on the binding sites, with heterogeneous adsorption sites contributing to dye uptake. Density functional theory demonstrated higher adsorption affinity for MB over CV, primarily due to hydrogen bonding and electrostatic interactions. NCH exhibited 80 % dye removal efficiency after five cycles, highlighting its potential for industrial effluent treatment.

A green solution for eliminating methylene blue and crystal violet dyes using eco-friendly zinc oxide nanoparticles synthesized from Dracaena trifasciata

Modern technological development has unavoidably resulted in more pollution, especially in aquatic environments. While extensively utilized in various industries, cationic dyes pose a significant threat to both the environment and human health, ranking among the most hazardous pollutants. When exposed to these dyes, one may experience skin irritation and allergic dermatitis because they are frequently mutagenic, toxic, carcinogenic, and resistant to biodegradation. The continued release of these dyes into the environment exacerbates human health and ecosystem concerns. This work investigates the possibility of eco-friendly zinc oxide nanoparticles, which are produced by the co-precipitation method from leaf extracts of the Dracaena trifasciata plant, also referred to as snake plant, for the elimination of the cationic dyes methylene blue and crystal violet. This work presents a novel approach for synthesizing eco-friendly zinc oxide nanoparticles using leaf extract from Dracaena trifasciata. To examine the eco-friendly zinc oxide nanoparticles, characterization studies were carried out using various instrumental methods. The best conditions for removing methylene blue and crystal violet were found through batch adsorption investigations, which produced removal percentages of 86 % and 88 %, respectively, under specific conditions. The eco-friendly zinc oxide nanoparticles achieved maximum adsorption capacity and effective removal of methylene blue and crystal violet dyes under the following conditions: a pH value of 10, nanoparticle concentration of 0.06 g, reaction time of 50 min, dye concentration of 50 mg/L, and reaction temperature of 40 °C. Isotherm investigations demonstrated that the adsorption of methylene blue dye by eco-friendly zinc oxide nanoparticles followed the Temkin isotherm model, whereas the adsorption of crystal violet dye followed the Freundlich isotherm model. The kinetic parameters describing the adsorption of methylene blue and crystal violet dye onto eco-friendly zinc oxide nanoparticles were identified as pseudo-first-order and Elovich models, respectively. Following the above-mentioned studies, eco-friendly zinc oxide nanoparticles were subjected to additional characterization in order to assess their potential for wastewater treatment.

Mechanistic insights into the reaction pathway for efficient cationic dye photocatalytic degradation and the importance of the enhanced charge isolation over dual Z-scheme CeO2/BiOCl/Ag2WO4 photocatalyst

Fabricating a multi-component heterojunction system with enhanced charge isolation efficacy remains challenging. A photoactive CeO2/BiOCl/Ag2WO4 heterojunction was successfully constructed using a co-precipitation technique to degrade crystal violet and methylene blue dyes. It was found through a combination of characterization and experiments that the dual Z-scheme system not only augmented the charge isolation and migration efficiency but also maintained superior redox ability with extended visible light absorption capacity. In the CeO2/BiOCl/Ag2WO4 system, 97 % of methylene blue and 98 % of crystal violet were degraded in 75 min using 50 mg/L of ternary photocatalyst. The rate of reaction of CeO2/BiOCl/Ag2WO4 for methylene blue (0.0445 min−1) and crystal violet (0.05053 min−1) exhibited a multi-fold increase in comparison to the bare photocatalysts. The electron spin resonance (ESR) analysis has remarkably identified hydroxyl and superoxide radicals (•OH, •O2−) as the primary reactive species in the photodegradation process. Liquid chromatography-mass spectrometry analysis was utilized to obtain potential degradation pathways for methylene blue and crystal violet, respectively. The dual charge transferal mechanism by the ternary photocatalyst resulted in a significant increase in photocatalytic activity. It provided new perspectives on the principles guiding the rational development of a multicomponent system for environmental remediation.

Surface Modification of a Zeolite Microfiltration Membrane: Characterization and Application to the Treatment of Colored and oily Wastewaters

Membrane-based technologies used for water treatment can be an excellent alternative to handle wastewater including both conventional and emerging pollutants as they can provide technological (e.g., high quality of treated water) and economic (e.g., small footprint and low unit cost of production) advantages over other water treatment processes. Recently, low cost ceramic membranes fabricated from natural resources like kaolinitic clay, bentonite clay, phosphate are increasingly used owing to their low-cost starting materials, low sintering temperature and their excellent additional properties. Moreover, the modification of the surface by grafting process provides membranes appropriate for low UF process (dp < 10 nm) and suitable for micropollutants removal at relatively high permeate flux value which can be maintained during filtration due to antifouling characteristics of the UF active layer. In this work, the surface of microfiltration membranes made from natural zeolite was chemically modified by grafting with 1 H, 1 H, 2 H, 2 H-perfluorodecyltriethoxysilane molecule named PFAS. Various characterization methods and techniques, including scanning electron microscopy (SEM), mercury porosimetry, FTIR, TGA, and contact angle, were used to check the properties of the membranes surface before and after grafting. The grafted membranes pore size and porosity were reduced, as proved by SEM images. The determination of the water permeability shows a reduction from 1218 L.h−1.m−2.bar −1 to 204 L.h−1.m−2.bar −1 which confirm the surface densification. The application of the grafted membrane to the treatment of Indigo Blue (IB) colored solution and oily wastewater was investigated to evaluate the performances of this membrane in terms of permeate flux and pollutants retention. The filtration results revealed a good retention of color and oil, exceeding 95% for both parameters. Therefore, it is interesting to recommend this new low-cost membrane for the treatment of industrial wastewater containing recalcitrant pollutants such as color. The study of the effect of the treated colored solution on plant growth, shows that the presence of some residual nutrients required for crops growth, might make the IB treated water beneficial for irrigation purposes.

Physiological Maturity and Harvesting Date on Seed Yield and Quality of Indigo (Indigofera suffruticosa Mill.)

Background: Indigo is used to dye many fabrics, which also needs a lot of indigo plants enough to dye the fabric. Indigo seeds were used for propagation, but the seed of indigo is not simultaneous. The physiological maturity and optimum harvesting date affected the yield and quality of indigo seeds. This research aims to study the physiological maturity and harvesting date of indigo on seed yield and quality. Methods: Indigo plants were grown in the dry season. The experiment was a randomized complete block design (RCBD) with 4 replications, consisting of 4 harvesting dates; 140, 150, 160 and 170 days after planting (DAP). Result: The results showed that the first indigo flower was at 51 DAP and matured to pods at 59 DAP. It takes 113 DAP for the indigo color to change from green to brown. The appearance of the pods changed from green to yellowish green, brown and black, respectively. As the indigo pods became 50% brown, they started harvesting. The weights of a dry pod, a fresh pod and a seed were different. When harvesting at 140 DAP, the fresh pod weight had the maximum of 82.60 g/plant and dropped as the indigo harvesting date grew (P less than 0.01). The dry pod weight was the lowest, at 27.58 g/plant (P less than 0.05). The seed weight per plant for harvesting at 170 DAP was 25.57 g. The harvesting date, however, did not differ statistically. The highest percentage of germination and vigor were from the indigo seeds, which were harvested at 140 DAP, 31.94% and 38.81%, respectively (P less than 0.01). Therefore, the optimum harvesting date at 140 DAP is the physiological maturity stage and harvesting of the pods when they turn brown for the highest seed quality.

Effect of KOH- and NaOH-modified fly ash on the adsorption of methylene blue and crystal violet dyes: a Box-Behnken design study

ABSTRACT Coal Fly Ash (FA) and modified fly ash (mFA), treated with either KOH or NaOH, were used to remove methylene blue (MB) and crystal violet (CV) dyes from aqueous solution. Several techniques, including Thermogravimetric analysis, X-Ray diffraction analysis, Fourier-transform infrared spectroscopy, Brunauer-Emmett-Teller, and Scanning Electron Microscopy, were used to characterise both FA and mFA. To optimise the adsorption process, the Response Surface Methodology (RSM) with the Box – Behnken design (BBD) was applied. Key parameters such as solution pH (4–10), initial dye concentration (200–300 mg/L), contact time (15–180 minutes), and temperature (30–50°C) were varied to assess their impact on adsorption efficiency. The adsorption followed the Langmuir model and pseudo-second-order (PSO) kinetic model. The adsorption capacity of mFA for MB dye was 49.5 mg/g at 50°C, while for CV dye, it was 495.5 mg/g at the same temperature. The adsorption mechanism involved electrostatic attraction, n-π interaction, Yoshida hydrogen bonding, and hydrogen bonding. These results highlight the effectiveness of mFA as a high-capacity adsorbent for treating MB and CV dyes in water solutions.

Acid Mine Drainage Precipitates from Mining Effluents as Adsorbents of Organic Pollutants for Water Treatment.

Acid mine drainage (AMD) is one of the main environmental problems associated with mining activity, whether the mine is operational or abandoned. In this work, several precipitates from this mine drainage generated by the oxidation of sulfide minerals, when exposed to weathering, were used as adsorbents. Such AMD precipitates from abandoned Portuguese mines (AGO, AGO-1, CF, and V9) were compared with two raw materials from Morocco (ClayMA and pyrophyllite) in terms of their efficiency in wastewater treatment. Different analytical techniques, such as XRD diffraction (XRD), Fourier Transform Infrared spectroscopy (FTIR), N2 adsorption isotherms, and Scanning Electron Microscopy (SEM) with Energy Dispersive X-ray (EDX) were used to characterize these natural materials. The adsorption properties were studied by optimizing different experimental factors, such as type of adsorbent, adsorbent mass, and dye concentration by the Box-Behnken Design model, using methylene blue (MB) and crystal violet (CV) compounds as organic pollutants. The obtained kinetic data were examined using the pseudo-first and pseudo-second order equations, and the equilibrium adsorption data were studied using the Freundlich and Langmuir models. The adsorption behavior of the different adsorbents was perfectly fitted by the pseudo-second order kinetic model and the Langmuir isotherm. The most efficient adsorbent for both dyes was AGO-1 due to the presence of the cellulose molecules, with qm equal to 40.5 and 16.0 mg/g for CV and MB, respectively. This study confirms the possibility of employing AMD precipitates to adsorb organic pollutants in water, providing valuable information for developing future affordable solutions to reduce the wastes associated with mining activity.

Design and evaluation of a polyaniline-Azadirachta indica composite for efficient dye removal: Insights from experimental and theoretical simulations

In this study, a novel composite of polyaniline and Azadirachta indica sawdust (PAIS) was synthesized to explore its potential in the adsorptive removal of methylene blue (MB) and crystal violet (CV) dyes from aqueous solution. PAIS was characterized using various instrumental techniques, including FTIR, SEM/EDXS, XRD, TEM/SAED, BET, and TGA-DTG/DTA analyses. Batch adsorption tests revealed that pH, medium temperature, initial adsorbate concentration, adsorbent dose, and contact duration significantly influence adsorption efficiency. Adsorption equilibrium was reached at 30 min for MB and 90 min for CV in an acidic medium (up to pH 7), with minimal changes observed beyond these times. The Langmuir isotherm provided the best validation, with a maximum monolayer adsorption capacity of 454.54 mg/g for MB and 370.37 mg/g for CV, showcasing superior performance compared to most reported materials. The adsorption process adhered to a pseudo-second-order approach for both dyes, with a high coefficient of determination value. The adsorption of MB and CV by this innovative adsorbent was spontaneous, endothermic, and accompanied by entropy enhancement. The adsorbent loaded with dyes was subjected to different desorbing agents (HCl, NaOH, NaCl, CH3COOH, and H2O), and HCl was the most effective. Computational studies using Density Functional Theory supported the experimental results, confirming the higher efficiency of PAIS for MB removal over CV. It is submitted that PAIS uniquely exhibits highly adaptable, recyclable, and potent low-cost adsorbent properties for eliminating both dyes from aqueous systems, representing a significant advancement in the field of dye removal.

Harnessing synergy: Polydopamine-hBN integration in electrospun nanofibers for Co (II) ion, methylene blue and crystal violet dyes adsorption

In today's world, major pollutants, such as cationic dyes and heavy metals, pose a serious threat to human health and the environment. In this study, a novel adsorbent was created through the electrospinning of polyvinyl alcohol/polyacrylic acid (PVA/PAA), incorporated with hexagonal boron nitride (hBN) coated with polydopamine (PDA). The integration of hBN and PDA substantially enhanced the adsorption capacity of the PVA/PAA fibers, making them highly effective in adsorbing cationic dyes such as methylene blue and crystal violet, as well as cobalt (II) ions, from contaminated water. The adsorbents were assessed to understand how their adsorption behavior varies with pH, as well as to examine their adsorption kinetics and isotherms. The results indicate that the PVA/PAA-hBN@PDA adsorbent has maximum adsorption capacities of 1029.57 mg/g, 793.65 mg/g, and 62.46 mg/g for methylene blue, crystal violet, and cobalt (II) ions, respectively. This underscores the superior performance of the PVA/PAA-hBN@PDA adsorbent when compared to both the PVA/PAA and PVA/PAA-hBN adsorbents. The adsorption kinetics adhered to a pseudo-second-order model, indicating chemisorption, whereas the Langmuir model implied a monolayer adsorption. Overall, the findings of this study highlight the efficacy of harnessing the synergistic capabilities of hBN and PDA within the PVA/PAA-hBN@PDA adsorbents, providing an efficient and eco-friendly approach to removing cationic dyes and heavy metals from contaminated water, and thereby contributing to a cleaner and safer environment for all.

Mo-doped Co LDHs as Raman enhanced substrate for detection of roxarsine

BackgroundRoxarsone (ROX) is widely used as a feed additive, which is indigestible after ingestion by poultry, and most of it can only be excreted into the natural environment and degraded into highly toxic and carcinogenic inorganic arsenic compounds, which pose a hazard to the ecosystem and human health. However, for roxarsone, traditional detection methods require complex and time-consuming procedures, so it is urgent to find a new fast detection method for detection of ROX. ResultsIn this work, we developed a novel Raman enhancement material and utilized the Surface-enhanced Raman scattering (SERS) technique to achieve rapid and sensitive detection of roxarsone. Specifically, Mo-doped cobalt layered double hydroxides (Co-LDHs) semiconductor material (abbreviated as CMM-100) was prepared by a simple method of using ion-assisted MOF etching. Under laser excitation at a wavelength of 532 nm, the CMM-100 showed excellent SERS property to various organic dye molecules such as methylene blue (MB), Toluidine Blue(TB), and Crystal Violet (CV). Especially, an enhancement factor (EF) of 1.4 × 106 was achieved for MB. Compared with the traditional method, this work utilized the fast and non-destructive SERS technology, which achieved a rapid detection of ROX. The detection limit was as low as 9.73 × 10−10 M, and the detection range was from 10−9 M to 10−3 M. SignificanceIn this work, SERS technology was adopted for the rapid and sensitive detection of ROX. This study provides a Raman-enhanced substrate named CMMs for detection of food additives, pesticides, biomolecules, etc., which also broadens the application areas of SERS materials.

Efficiently removing four cationic dyes from aqueous solution by magnetite@polypyrrole@2-acrylamido-2-methyl-1-propanesulfonic acid microspheres

Water pollution caused by various cationic dyes is becoming more and more serious. A combination of magnetic materials, conductive polymers, and some strong adsorption groups is expected to solve this challenge. Herein, magnetite (Fe3O4)@polypyrrole@2-acrylamido-2-methyl-1-propanesulfonic acid (Fe3O4@PPy@AMPS) is fabricated as adsorbent for removing methylene blue (MB), rhodamine B (RhB), malachite green (MG), and crystalline violet (CV) from aqueous solution. The investigation of the factors including adsorbent type, adsorbent concentration, time, and temperature demonstrates that Fe3O4@PPy@AMPS has superior properties to adsorb the four cationic dyes. The maximum adsorption capacity of these dyes is separately 183.486, 215.054, 144.718 and 194.175 mg/g. Notably, although it goes through five cycles, the composite maintains a remarkable dye removal efficiency exceeding 95 %. Kinetic analysis reveals that the adsorption process conforms more closely to the pseudo-second-order kinetic model. The adsorption isotherm conforms to the Langmuir model, signifying monolayer adsorption of the dyes. Thermodynamic parameters also indicate that the adsorption process is endothermic and spontaneous. Furthermore, density functional theory (DFT) simulations affirm the molecular interactions between Fe3O4@PPy@AMPS and four dyes, elucidating the adsorption mechanism. The high efficiency and recyclable nature of the Fe3O4@PPy@AMPS composite underscores its significance in addressing dye wastewater pollution remediation.

From indigo to isoindigo: Rationalizing the high efficiency of photoprotective molecular mechanisms

Indigo (IND) and its natural derivatives, including Tyrian purple and indirubin (INR), are examples of molecules with a history of millions of years. They also illustrate molecular evolution and longevity, linked to their extraordinary molecular stability associated with excited state decay mechanisms. In the excited state, these molecules efficiently undergo a radiationless deactivation process resulting in negligible fluorescence and triplet state formation (less than 0.1 % of the quantum loss in indigo for both processes). Here, we demonstrate that in isoindigo (ISO) this process is even more efficient than in IND, resulting in nearly 100 % of the excited state deactivation. In IND, the molecular mechanism behind this decay process involves intramolecular proton transfer (ESPT). In the case of INR, ESPT efficiently competes with the formation of a conformational species –the syn-rotamer– for deactivation to the ground state. With ISO, the ESPT process is absent. Instead, the deactivation mechanism involves a rotation of a few degrees around the central C–C bond, aRotational Isomerization (RI). This rotation leads to a sloped conical intersection (CI), making the radiationless deactivation process more efficient than the ESPT found with IND.

A visual ratio PVA/curcumin/indigo nanofibre membrane based on natural pigments for detecting mutton freshness

SummaryIn the storage process, meat is susceptible to external factors that produce corruption and deterioration, affecting consumers' health. Therefore, preparing an indicator membrane that can detect freshness in real time, non‐destructively, and visually is significant. Herein, an indicator membrane was prepared by electrostatic spinning technology using polyvinyl alcohol (PVA) as the substrate and curcumin (CUR) and indigo (IND) as the mixed indicator for freshness detection. When curcumin and indigo were mixed at 3:1 (w/w), CUR was transformed from ketone type to enol type with the gradual increase of pH, and IND underwent electron leaps, which resulted in green, brown, and reddish‐brown colour changes in the solution, and the colour development effect was effectively improved. The characterisation results showed that the average fibre diameter of the PVA/0.8 indicator membrane was 252 nm, the hybrid indicator was successfully loaded in the nanofibres, and the water contact angle was 103.6°, which was hydrophobic. In addition, the indicator membrane was sensitive to trimethylamine (limit of detection 17.38 ppm) and triethylamine (limit of detection 27.77 ppm) but insensitive to saline, ethanol, ethyl acetate, and other contaminants with detection specificity. Finally, the colour of the indicating membrane changes from green to brown during the storage of mutton in the mutton was rotten, indicating that the naked eye can judge the freshness of the mutton. Therefore, the PVA/CUR/IND indicator membrane has excellent potential for application in real‐time and non‐destructive detection of mutton freshness.