Removal of triphenylmethane dyes by bacterial consortium

Comparative study on efficiency of surface enhanced coal fly ash and raw coal fly ash for the removal of hazardous dyes in wastewater: optimization through response surface methodology

Crystal violet (CV) dye, because of its non-biodegradability and harmful effects, poses a significant challenge for wastewater treatment. This study addresses the efficiency of easily accessible coal fly ash (CFA)-based adsorbents such as raw coal fly ash (RCFA) and surface enhanced coal fly ash (SECFA), in removing CV dye from waste effluents. Various analytical techniques such as FTIR, XRD, SEM, TEM, BET, zeta sizer and zeta potential were employed for the characterization of the adsorbents and dye-loaded samples. BET revealed that RCFA possesses a surface area of 19.370 m2 g-1 and SECFA of 27.391 m2 g-1, exhibiting pore volumes of 0.1365 cm3 g-1 and 0.1919 cm3 g-1 respectively. Zeta-sizer and potential analysis showed the static charges of RCFA as -27.3 mV and SECFA as -28.2 mV, with average particle sizes of 346.6 and 315.3 nm, respectively. Langmuir and Freundlich adsorption isotherms were also employed for adsorption studies. Employing central composite design (CCD) of response surface methodology (RSM), the maximum CV removal was 81.52% for RCFA and 97.52% for SECFA, providing one minute contact time, 0.0125 g adsorbent dose and 10 ppm dye concentration. From the thermodynamic studies, all the negative values of ΔG° showed that all the adsorption processes of both adsorbents were spontaneous in nature.

Design of a Novel Delivery Efficiency Feedback System for Biphasic Dissolving Microarray Patches Based on Poly(Lactic Acid) and Moisture-Indicating Silica

Dissolving microarray patches (DMAPs) represent an innovative approach to minimally invasive transdermal drug delivery, demonstrating efficacy in delivering both small and large therapeutic molecules. However, concerns raised in end-user surveys have hindered their commercialization efforts. One prevalent issue highlighted in these surveys is the lack of clear indicators for successful patch insertion and removal time. To address this challenge, a color-change-based feedback system is devised, which confirms the insertion and dissolution of DMAPs, aiming to mitigate the aforementioned problems. The approach combines hydrophilic needles containing model drugs (fluorescein sodium and fluorescein isothiocyanate (FITC)-dextran) with a hydrophobic poly(lactic acid) baseplate infused with moisture-sensitive silica gel particles. The successful insertion and subsequent complete dissolution of the needle shaft are indicated by the progressive color change of crystal violet encapsulated in the silica. Notably, distinct color alterations on the baseplate, observed 30 min and 1 h after insertion for FITC-dextran and fluorescein sodium DMAPs respectively, signal the full dissolution of the needles, confirming the complete cargo delivery and enabling timely patch removal. This innovative feedback system offers a practical solution for addressing end-user concerns and may significantly contribute to the successful commercialization of DMAPs by providing a visualized drug delivery method.

Kinetics of dye decolorization using heterogeneous catalytic system with immobilized Achromobacter xylosoxidans DDB6

Textile effluents containing toxic dyes must be treated effectively before discharge to prevent adverse environmental impacts. Traditional physical and chemical treatment methods are costly and generate secondary pollutants. In contrast, biological treatment is a more suitable, clean, versatile, eco-friendly, and cost-effective technique for treating textile effluent. It is well established that indigenous microbial populations present in effluents can effectively degrade toxic dyes. In this regard, Achromobacter xylosoxidans DDB6 was isolated from the effluent sample to decolorize crystal violet (CV), Coomassie brilliant blue (CBB), and alizarin red (AR) by 67.20%, 28.58%, and 20.41%, respectively. The growth parameters of A. xylosoxidans DDB6 in media supplemented with 100 ppm of various dyes were determined using the modified Gompertz growth model. The immobilized cells in calcium alginate beads showed apparent decolorization rate constant of 0.27, 0.18, and 0.13 h-1 for CV, CBB, and AR, respectively. The immobilized cells in a packed bed reactor with an optimum flow rate of 0.5 mL/min were used to treat 100 ppm of CV with a percentage decolorization of 79.47% after three cycles. Based on the findings, A. xylosoxidans DDB6 could be effectively used for decolorization of various dyes.

Removal of doxorubicin hydrochloride and crystal violet from aqueous solutions using spray-dried niobium oxide coated with chitosan-activated carbon: Experimental and DFT calculations

Spray-dried niobium oxide coated with chitosan-activated carbon (NIC) was synthesized and used to remove doxorubicin hydrochloride and crystal violet from aqueous solutions under different parameters such as solution pH (2, 4, 6, and 8), contact time (1 to 9 h), initial concentration (20 to 200 mg L-1), and competing ions (0.1 M of CaCl2 and NaCl). The addition of 5 % chitosan-activated carbon to the matrix of niobium oxide slightly increased the specific surface area from 26 to 30 m2 g-1, with the introduction of a carboxylic functional group. This led to an increase in the amount of adsorbed doxorubicin hydrochloride (DOH) from 30 to 44 mg g-1 and that of crystal violet (CV) from 15 to 32 mg g-1 from the initial respective 100 mg L-1 at pH 8. The data from the concentration study fitted into Liu isotherm having adsorption capacity of 128 and 57 mg g-1 for DOH and CV respectively, while pseudo first and second order are more suitable for adsorption kinetics. The additional functional groups on the IR spectrum of NIC after the adsorption of DOH and CV confirmed the interaction between NIC and the adsorbates' molecules. The mechanism of adsorption was supported by DFT calculations.

Decolorization of various dyes by microorganisms and green-synthesized nanoparticles: current and future perspective

Various types of colored pigments have been recovered naturally from biological sources including shells, flowers, insects, and so on in the past. At present, such natural colored substances (dyes) are replaced by manmade dyes. On the other hand, due to their continuous usage in various purpose, these artificial dyes or colored substances persist in the environmental surroundings. For example, industrial wastewater contains diverse pollutant substances including dyes. Several of these (artificial dyes) were found to be toxic to living organisms. In recent times, microbial-based removal of dye(s) has gained more attention. These methods were relatively inexpensive for eliminating such contaminants in the environmental system. Hence, various researchers were isolated microbes from environmental samples having the capability of decolorizing synthetic dyes from industrial wastewater. Furthermore, the microorganisms which are genetically engineered found higher degradative/decolorize capacity to target compounds in the natural environs. Very few reviews are available on specific dye treatment either by chemical treatments or by bacteria and/or fungal treatments. Here, we have enlightened literature reports on the removal of different dyes in microbes like bacteria (including anaerobic and aerobic), fungi, GEM, and microbial enzymes and also green-synthesized nanoparticles. This up-to-date literature survey will help environmental managements to co-up such contaminates in nature and will help in the decolorization of dyes.

Simultaneous conversion of chromium and malachite green coexists in halophilic bacterium Halomonas xianhensis SUR308 isolated from a solar saltern

Many industries are known to use heavy metals like chromium (Cr) to fix dyes in the fabrication processes and malachite green (MG) as colorant. Alkalinity, elevated temperature, or salinity of the industrial effluents makes conventional physicochemical removal of MG and hexavalent chromium [Cr(VI)] more difficult to apply and demands to perceive potential cost-effective and environment-friendly treatment methods to eliminate or convert them into less toxic compounds. Here, we report simultaneous removal and bioconversion of MG and Cr(VI) by a halophilic biofilm-forming bacterium Halomonas xianhensis SUR308. It can efficiently produce exopolysaccharides as extracellular polymeric substances (EPS) and form biofilm under oxygen limiting condition. The reduction of hexavalent chromium [Cr(VI)] to trivalent chromium [Cr(III)] is about 100%, and 95% after 84 h of growth in shaken and stagnant culture, respectively. The strain completely decolorizes MG after 48 h of growth in shaken culture. Furthermore, we found that strain SUR308 can efficiently detoxify chromium by reduction and degrades MG via producing various intermediate products simultaneously. Most interestingly, such conversions can also take place in alkaline environment and in environment where substantial amount of salt is present. These unique features of strain SUR308 make it suitable for the simultaneous remediation of toxic heavy metals and hazardous dye even from the environment having higher pH and salinity. The detail molecular mechanism of the bioconversion with its application in open environment would be the future research focus for bioprospecting strain SUR308.

Adsorption of Safranin O Dye by Alginate/Pomegranate Peels Beads: Kinetic, Isotherm and Thermodynamic Studies

Water pollution is regarded as a dangerous problem that needs to be resolved right away. This is largely due to the positive correlation between the increase in global population and waste production, especially food waste. Hydrogel beads based on sodium alginate (Alg) and pomegranate fruit peels (PP) were developed for the adsorption of Safranin O dye (SO) in aqueous solutions. The obtained Alg-PP beads were widely characterized. The effects of the contact time (0-180 min), initial concentration (10-300 mg/L), initial pH (2-10), adsorbent dosage (1-40 g/L) and the temperature (293-333 K) were investigated through batch tests. The data proved that the adsorption kinetics of SO reached equilibrium within 30 min and up to 180 min. The dye adsorption is concentration dependent while a slight effect of pH was observed. The adsorption data of SO onto synthesized beads follow the pseudo second-order model. The experimental data fitted very well to Langmuir model with correlation factor of 0.92 which demonstrated the favourable nature of adsorption. The maximum adsorption capacity of Alg-PP could reach 30.769 mg/g at 293 K. Calculation of Gibbs free energy and enthalpy indicated that adsorption of SO onto Alg-PP is spontaneous (negative ΔG) and endothermic (ΔH = 9.30 kJ/mol). Analysis of diffusion and mass transport phenomena were presented. The removal efficiency was found to be 88% at the first cycle and decreased to 71% at the end of the seventh cycle. The reported results revealed that the Alg-PP beads could be used as a novel natural adsorbent for the removal of high concentrated solutions of Safranin O which is a cationic dye from liquid affluents and as future perspective, it can be used to remove various pollutants from wastewater.

Multifunctional 3D magnetic carbon aerogel for adsorption separation and highly sensitive SERS detection of malachite green

This work presents a novel strategy for the synthesis of a recyclable aerogel and its multifunctional application as effective adsorption material for organic pollutants and as a high-quality SERS substrate for on-site detection measurement. Silver nanoparticles (Ag NPs) were uniformly dispersed and adsorbed on the surface of an Fe3C-loaded carbon aerogel, resulting in the formation of a three-dimensional Ag-Fe3C-MCA (magnetic carbon aerogel) composite. The substrate preparation led to Ag-Fe3C-MCA with a mesoporous structure for high adsorption capacity, together with magnetic properties for easy separation capability. The Ag-Fe3C-MCA composite demonstrated an efficient removal ability for malachite green (MG), with an adsorption capacity of 296.7 mg g-1. Moreover, Ag-Fe3C-MCA composite provided ultrasensitive surface-enhanced Raman scattering detection for MG molecules, obtaining a limit of detection (LOD) of 3 × 10-10 M. Aquaculture water samples with spiked MG concentrations were used to simulate practical scenarios. The Ag-Fe3C-MCA presented has a significant potential for the removal of hazardous residues in wastewater, together with an efficient and sensitive method of quantification, all on the same substrate.

Efficient malachite green biodegradation by Pseudomonas plecoglossicide MG2: process optimization, application in bioreactors, and degradation pathway

Microbial degradation of synthetic dyes is considered a promising green dye detoxification, cost-effective and eco-friendly approach. A detailed study on the decolorization and degradation of malachite green dye (MG) using a newly isolated Pseudomonas plecoglossicide MG2 was carried out. Optimization of MG biodegradation by the tested organism was investigated by using a UV-Vis spectrophotometer and the resultant degraded products were analyzed by liquid chromatography-mass spectrometry and FTIR. Also, the cytotoxicity of MG degraded products was studied on a human normal retina cell line. The optimum conditions for the significant maximum decolorization of MG dye (90-93%) by the tested organism were pH 6-7, inoculum size 4-6%, and incubation temperature 30-35 °C, under static and aerobic conditions. The performance of Pseudomonas plecoglossicide MG2 grown culture in the bioreactors using simulated wastewater was assessed. MG degradation (99% at 100 and 150 mg MG/l at an optimal pH) and COD removal (95.95%) by using Pseudomonas plecoglossicide MG2 culture were the best in the tested culture bioreactor in comparison with that in activated sludge or tested culture-activated sludge bioreactors.The FTIR spectrum of the biodegraded MG displayed significant spectral changes, especially in the fingerprint region 1500-500 as well as disappearance of some peaks and appearance of new peaks. Twelve degradation intermediates were identified by LC-MS. They were desmalachite green, didesmalachite green, tetradesmalachite green, 4-(diphenylmethyl)aniline, malachite green carbinol, bis[4-(dimethylamino)phenyl]methanone, [4-(dimethylamino)phenyl][4-(methyl-amino)phenyl]methanone, bis[4-(methylamino)phenyl]methanone, (4-amino- phenyl)[4-(methylamino)phenyl]methanone, bis(4-amino phenyl)methanone, (4-amino phenyl)methanone, and 4-(dimathylamino)benzaldehyde. According to LC-MS and FTIR data, two pathways for MG degradation by using Pseudomonas plecoglossicide MG2 were proposed. MG showed cytotoxicity to human normal retina cell line with LC50 of 28.9 µg/ml and LC90 at 79.7 µg/ml. On the other hand, MG bio-degraded products showed no toxicity to the tested cell line. Finally, this study proved that Pseudomonas plecoglossicide MG2 could be used as an efficient, renewable, eco-friendly, sustainable and cost-effective biotechnology tool for the treatment of dye wastewater effluent.

Hydrothermal synthesis of a photocatalyst based on Byrsonima crassifolia and TiO2 for degradation of crystal violet by UV and visible radiation

This work presents a one-step synthesis methodology for preparing a hydrochar (HC) doped with TiO2 (HC-TiO2) for its application on the degradation of crystal violet (CV) using UV and visible radiation. Byrsonima crassifolia stones were used as precursors along with TiO2 particles. The HC-TiO2 sample was synthesized at 210 °C for 9 h using autogenous pressure. The photocatalyst was characterized to evaluate the TiO2 dispersion, specific surface area, graphitization degree, and band-gap value. Finally, the degradation of CV was investigated by varying the operating conditions of the system, the reuse of the catalyst, and the degradation mechanism. The physicochemical characterization of the HC-TiO2 composite showed good dispersion of TiO2 in the carbonaceous particle. The presence of TiO2 on the hydrochar surface yields a bandgap value of 1.17 eV, enhancing photocatalyst activation with visible radiation. The degradation results evidenced a synergistic effect with both types of radiation due to the hybridized π electrons in the sp2-hybridized structures in the HC surface. The degradation percentages were on average 20% higher using UV radiation than visible radiation under the following conditions: [CV] = 20 mg/L, 1 g/L of photocatalyst load, and pH = 7.0. The reusability experiments demonstrated the feasibility of reusing the HC-TiO2 material up to 5 times with a similar photodegradation percentage. Finally, the results indicated that the HC-TiO2 composite could be considered an efficient material for the photocatalytic treatment of water contaminated with CV.

Dye degradation by early colonizing marine bacteria from the Arabian Sea, India

Malachite green dye belongs to the triphenylmethane group and is a common environmental pollutant that threatens non-target organisms. We report the potential of the early colonizing marine bacterium Pseudomonas sp. ESPS40 isolated from the Arabian Sea, India, to decolorize malachite green (MG). The bacterium ESPS40 exhibited a higher ability for MG degradation (86-88%) at varying NaCl concentrations (1-3%). The highest MG degradation (~ 88%) was observed at 1% NaCl. The bacterial strain ESPS40 showed degradation up to 800 mg L^-1 MG. Further, enzyme activities such as tyrosinase (63.48-526.52 U L^-1) and laccase (3.62-28.20 U L^-1) were also analyzed with varying concentrations (100 mg L^-1-1000 mg L^-1) of MG during the degradation process. The dye degradation was confirmed by Fourier transform infrared spectroscopy (FTIR) and high-performance liquid chromatography (HPLC). The outcome of the present study demonstrated Pseudomonas sp. ESPS40 as a potential strain for the efficient degradation of MG at higher concentrations. Thus, Pseudomonas sp. ESPS40 can be utilized as a potential candidate for the biodegradation of MG in wastewater treatment.

Sphagnum perichaetiale Hampe biomass as a novel, green, and low-cost biosorbent in the adsorption of toxic crystal violet dye

In this study, the Sphagnum perichaetiale Hampe biomass was collected, characterized, and used as a biosorbent in the removal of crystal violet from water. The chemical and morphological results suggest that even after minimal experimental procedures, the biomass presented interesting properties regarding the adsorption of contaminants. Results of adsorption showed that the pH was not a relevant parameter and the best adsorbent dosage was 0.26 g L^-1. The kinetic results presented an initial fast step and the equilibrium was reached after 180 min. For the equilibrium data, the best adjustment occurred for the Sips model, reaching a maximum adsorption capacity of 271.05 mg g^-1 and the removal percentage obtained in the maximum adsorbent dosage was 97.11%. The thermodynamic studies indicated a reversible process and that the mass-transfer phenomena is governed by the physisorption mechanism. In addition to its great performance as a biosorbent, Sphagnum perichaetiale biomass also presents economic and sustainable benefits, as its production does not require costs with reagents or energy, usually used in chemical and physical activation. The reversible process indicated that the biosorbent could be reused, decreasing the costs related to the treatment of the effluents. Thus, Sphagnum perichaetiale biomass can be considered an efficient low-cost and eco-friendly biosorbent.

Origanum vulgare manganese ferrite nanocomposite: An advanced multifunctional hybrid material for dye remediation

The purpose of the study was to fabricate sustainable and cost-effective material for the thorough cleansing of polluted water. In this context, an economical, phytogenic and multifunctional Origanum vulgare plant-based nanocomposite material, MnFe₂O₄/OV, was prepared via one-pot synthetic technique. The synthesized nanocomposite with a band gap of 2.02 eV behaved as an efficient nano-photocatalyst for the degradation of both cationic (crystal violet) and anionic (congo red) dyes under direct sunlight irradiation. The material also inhibited the growth of E. coli and S. aureus bacteria and simultaneously adsorbed both cationic and anionic dyes from water through adsorption. A variety of techniques have been used to characterize the nanocomposite, including X-ray powder diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX) and transmission electron microscopy (TEM). Additionally, the kinetics of photodegradation of the aforementioned organic dyes has also been investigated. The MnFe₂O₄/OV exhibited excellent photocatalytic performance, leading to 43% and 72% degradation within 3 h at rate constants of 2.0 × 10^-3 min^-1 and 6.0 × 10^-3 min^-1 for crystal violet and congo red, respectively. The crystal violet and congo red were used to testify to the composite's potential for adsorption under the influence of several process variables, including initial solution pH, contact time, temperature, initial dye concentration, and amount of MnFe₂O₄/OV. The Langmuir maximum adsorption capacity Q_max as in the range 14.06-14.59 mgg^-1 for crystal violet and 34.45-23.93 mgg^-1 for congo red at pH 7 within 90 min contact time in the temperature range of 30-50 °C. The phenomenon of adsorption was found feasible and endothermic at all the investigated temperatures. Also, E. coli and S. Aureus bacteria have shown growth suppression activity when exposed to MnFe₂O₄/OV.As a result, the synthesized nanocomposite, MnFe₂O₄/OV, proved to be an antimicrobial, multifunctional novel nanocomposite, which is in high demand, and could serve as an affordable, and sustainable material for comprehensive water filtration.

Liquid-liquid phase reaction between crystal violet and sodium hydroxide: kinetic study and precipitate analysis

To investigate reaction order and kinetic parameters of the reaction between crystal violet (CV) and sodium hydroxide (NaOH), various concentrations of the reactants were applied. The present work also verifies the unknown solid product produced under highly concentrated conditions. The reaction orders of CV and NaOH were determined to be 1 and 1.08 by pseudo rate method, respectively, with a rate constant, k, of 0.054 [(M^-1.08) s^-1]. In addition to pseudo rate method, the half-life approach was used to calculate the overall reaction order to verify the accuracy of pseudo rate method. The overall reaction order was determined to be 1.9 by the half-life method. The overall reaction order based on the two methods studied was approximately 2. The precipitate formation was observed when high concentrations of CV (0.01-0.1 M) and NaOH (1.0 M) were applied. Fourier transform infrared (FTIR) spectroscopy was used to compare the spectra of the precipitate generated and a commercial solvent violet 9 (SV9). Based on the FTIR spectra, it was confirmed that the molecular structure of the precipitate matched that of solvent violet 9.

Fabrication of glutathione functionalized self-assembled magnetite nanochains for effective removal of crystal violet and phenol red dye from aqueous matrix

A novel fabrication of magnetite (Fe₃O₄) nanochains, surface functionalized with glutathione (GSH), has been attempted through a basic wet reduction method, coalesced with oxidative etching for the removal of crystal violet (CV) and phenol red (PR) from an aqueous solution. The structural and functional characterizations of GSH@Fe₃O₄ MNPs were performed using SEM-EDX, DLS, XRD, and FTIR. The nanochain-structured adsorbent was found to have an average size of 24 ± 1.29 nm and a zeta potential value of - 6.44 mV. The batch experiments showed that GSH@Fe₃O₄ MNPs have a brilliant removal efficiency of 97% and 79% for CV and PR dyes, respectively, within a period of 60 min. The influence of different operational parameters like adsorbent dosage, pH, temperature, reaction time, and initial dye concentration on the removal behaviour of the adsorbent was studied in detail. The adsorbate-adsorbent reaction was tested over isotherm models, and the reaction fitted well for Langmuir isotherm with an excellent q_max value of 1619.5 mg/g and 1316.16 mg/g for CV and PR dye, respectively. The experimental results were also validated using different reaction kinetics, and it was found that the pseudo-first-order model fits well for PR dye adsorption (R² = 0.91), while adsorption of CV dye was in best agreement with the pseudo-second-order kinetic model (R² = 0.98). Thermodynamic studies revealed that the adsorption reaction was spontaneous and endothermic in nature. Furthermore, GSH@Fe₃O₄ MNPs can be reused effectively up to 5 cycles of dye removal. Major mechanisms involved in the adsorption reaction were expected to be electrostatic attraction, hydrogen bonding, and π-interactions. The efficiency of GSH@Fe₃O₄ MNPs in real water samples suggested that it has a high potential for dye removal from complex aqueous systems and could be used as an effective alternative for remediation of dyes contaminated water.

Activated Carbon/ZnFe2O4 Nanocomposite Adsorbent for Efficient Removal of Crystal Violet Cationic Dye from Aqueous Solutions

The aim of this study was to investigate the potential advantage of ZnFe₂O₄-incorporated activated carbon (ZFAC), fabricated via a simple wet homogenization, on the removal of cationic dye crystal violet (CV) from its aqueous solutions. The as-prepared ZFAC nanocomposite was characterized using Fourier transform infrared (FTIR), X-ray diffraction (XRD), nitrogen adsorption, scanning electron microscope (SEM), thermogravimetric analysis (TGA), and ultraviolet-visible (UV-Vis). Batch adsorption operating conditions such as the pH (3-11), CV concentration (25-200 ppm), ZFAC dose (10-50 mg), temperature (23-45 °C), and contact time were evaluated. The results indicate pH-dependent uptake (optimum at pH 7.2) increased with temperature and CV concentration increase and decreased as adsorbent dose increased. Modeling of experimental data revealed better fit to the Langmuir than Freundlich and Temkin isotherms, with maximum monolayer capacities (Q_m) of 208.29, 234.03, and 246.19 mg/g at 23, 35, and 45 °C, respectively. Kinetic studies suggest pseudo-second order; however, the intra-particle diffusion model indicates a rate-limiting step controlled by film diffusion mechanism. Based on the thermodynamic parameters, the sorption is spontaneous (-ΔG°), endothermic (+ΔH°), and random process (+ΔS°), and their values support the physical adsorption mechanism. In addition to the ease of preparation, the results confirm the potential of ZFAC as a purifier for dye removal from polluted water.

Quick and hassle-free smartphone's RGB-based color to photocatalytic degradation rate assessment of malachite green dye in water by fluorescent Zr-N-S co-doped carbon dots

Sunlight active blue emissive zirconium, nitrogen, and sulfur co-doped carbon dots (Zr-N-S-CDs) have been synthesized by microwave-induced pyrolysis for achieving efficient photocatalytic degradation of pollutant malachite green dye (MG) in water. Surface morphology studies using high-resolution transmission electron microscopy confirmed the formation of spherical-shaped CDs with an absorbance peak at 350 nm and emission peak at 437 nm in UV-vis and fluorescence spectroscopy, respectively. Surface functional groups, elemental composition, and metal/non-metal co-doping were confirmed by Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. To understand the photocatalytic performance of Zr-N-S-CDs, various parameters, such as the source of energy, concentration of dye, catalyst dosage, and change in pH, were investigated. MG dye (20 ppm) at a pH 7 with 0.5 mg/mL of Zr-N-S-CDs could be photodegraded efficiently in 90 min under sunlight (99%) compared to dark and artificial light conditions. Moreover, real-time analysis of degradation rate could be conveniently calculated by integrating the colorimetric responses of MG dye with RGB values obtained by the "Color Picker" app of a smartphone. The degradation rate obtained using a smartphone (97.89%) was found to be in agreement with the UV-vis spectroscopy (99%), thus, providing a new, handy, and instrument-free route for speedy and quantitative estimation of the degradation of hazardous MG dye by Zr-N-S-CDs.

Use of bacterial isolates in the treatment of textile dye wastewater: A review

The textile industry uses large amounts of dyes like reactive, azo, anthraquinone, and triphenylmethane to colour textiles. Dyes that are not used up during the colouration process usually end up in water bodies as waste leading to the pollution of the water bodies. This makes the industry to be one of the major contributors to water pollution in the world. Bacterial agents isolated from various sources like dye contaminated soil and textile wastewater have shown to have the ability to effectively decolourise and degrade these dye pollutants leading to improved water quality. This review discusses bacterial isolates that have been used successfully to degrade and decolourise textile dyes, their mode of dye removal as well as the factors that affect their dye degradation ability. It further looks at the latest wastewater treatment technologies that incorporate bacterial microorganisms to treat dye wastewater.

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Bacterial isolates offer environmentally friendly solution to dye degradation.

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Pure and mixed bacterial cultures can remove textile dyes in optimised conditions.

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Dyes are removed through biosorption or biodegradation mechanisms.

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Latest technologies provide more effective dye removal options.

Indigenous Bacillus paramycoides spp. and Alcaligenes faecalis: sustainable solution for bioremediation of hospital wastewater

Farmers near towns and cities are using a wide range of highly polluted wastewaters for crop irrigation in Pakistan due to severe freshwater shortage. The present study aimed to promote indigenous bacterial strains isolated from domestic, hospital, textile, pharmaceutical and mixed wastewaters to remove contaminants and colour and render these wastewaters safer for irrigation. Thirty seven bacterial strains were isolated from five wastewater samples collected from different sites in Lahore, Pakistan. Under optimal growth conditions, three isolates (D6, D7 and P1) showed >93% decolourisation potential in the treatment of hospital wastewater. 16S rDNA sequencing identified two of these isolates (D6 and D7) as showing 100% and 99.86% homology to Bacillus paramycoides spp. - novel strains from B. cereus group. Isolate P1 showed 97.47% homology to Alcaligenes faecalis. GCMS analysis of the untreated hospital wastewater revealed the presence of pharmaceutic pollutants, i.e. Phenol (876 µg/L), Salicylic acid (48 µg/L), Caffeine (7 µg/L), Naproxen (23 µg/L), Octadecene (185 µg/L) and Diazepam (14 µg/L). The analysis of treated hospital wastewaters showed percentage degradation of pharmaceutic pollutants (100%-43%) and significant reduction in the BOD₅ (91%-68%), COD (89%-52%) and heavy metals concentrations. These strains therefore can represent a low-cost and low-tech alternative to bioremediate complex matrices of hospital wastewater prior to crop irrigation to support the achievement of clean re-usable water in developing countries like Pakistan.

Application of random forest for modeling batch and continuous fixed-bed removal of crystal violet from aqueous solutions using Gypsophila aretioides stem-based biosorbent

In this work, the Gypsophila aretioides (GYP-A) stem is used as a biosorbent to remove crystal violet (CV) by the static and dynamic systems from aqueous solutions; the biosorbent is interesting in green chemistry and, on the other hand, cheaper than activated carbon and does not have the limitation of industrialization. The effects of different operating parameters such as pH(3-9), biosorbent dosage(0.4-1.8 mg/L), and initial concentration of CV(100-250 mg/L) and time for the batch method and the bed height, inlet CV concentration(75-250 mg/L), and flow rate(3-8) on the breakthrough curves for the continuous method is investigated. The result of CV adsorption onto GYP-A using the batch method indicates that the model fits Freundlich > Temkin > Langmuir > R-D, and R² equal 0.9953, 0.9847, 0.9161, 0.7909 were obtained for isotherm model, respectively. A pseudo-second-order model (R² = 0.9995-0.9997) is recommended to describe the adsorption kinetics. The Thomas and Yoon-Nelson models were analyzed to study the adsorption kinetics. The random forest model shows an excellent ability to predict the parameters involved in the CV adsorption process with appropriate accuracy and useable for large data, robust against noise; it can be very effective in selecting important variables.

Adsorption of cationic dyes onto carrageenan and itaconic acid-based superabsorbent hydrogel: Synthesis, characterization and isotherm analysis

Polysaccharide-based hydrogels offer a great overlook for environmental applications and help in the elimination of various noxious pollutants from the water system. Novel carrageenan and itaconic acid-based superadsorbent hydrogel having appreciable swelling properties and adsorption capacity towards Methylene blue (MB), Crystal violet (CV), and Methyl Red (MR) was synthesized by suspension polymerization technique. The swelling study showed the dependency upon the temperature in which the swelling rate increased with increasing temperature with a maximum swelling rate of 417% at 318 K. For ascertaining the maximum adsorption capacity, various influential parameters such as contact time, adsorbent dose, dye concentration, and temperature were systematically studied. Maximum adsorption capacity as calculated from the Langmuir isotherm was 2439.02, 1111.11, and 666.68 mg/g for MB, CV, and MR, respectively. Thermodynamic studies revealed the spontaneous nature of the undertaken dye adsorption experiment. Overall, the present study reveals that the synthesized superadsorbent hydrogel can be used as an efficient adsorbent for the removal of dyes from an aqueous solution.

Amyloid Fibril Templated MOF Aerogels for Water Purification

Design and fabrication of versatile adsorbents for universal water purification following green chemistry principles remain challenging. Here, it is shown that amyloid fibrils from protein waste can be used as a functional scaffold for metal organic framework (MOF) biomimetic mineralization. The resulting amyloid fibrils/ZIF-8 hybrid aerogels can effectively remove nine different heavy metal ions from water due to their hierarchical porous structure. Importantly, amyloid fibrils/ZIF-8 hybrid aerogels can efficiently remove Hg²⁺ and Pb²⁺ from water over five consecutive adsorption-regeneration cycles. Furthermore, a dual removal pathway of adsorption and catalytic degradation is observed in the synthetic dyes, indicating that the aerogel preserves its porous nature and maintains the integrity of versatile functional ligands within ZIF-8. Finally, it is shown that these hybrid aerogels can also perform successfully in oil-water separation. Considering the facile synthesis procedure, high removal efficiency, affordable cost, and regeneration possibilities, the amyloid fibrils/ZIF-8 hybrid aerogel stands as an ideal candidate for addressing open challenges in wastewater treatment and water purification.

Statistical modeling of methylene blue degradation by yeast-bacteria consortium; optimization via agro-industrial waste, immobilization and application in real effluents

The progress in industrialization everyday life has led to the continuous entry of several anthropogenic compounds, including dyes, into surrounding ecosystem causing arduous concerns for human health and biosphere. Therefore, microbial degradation of dyes is considered an eco-efficient and cost-competitive alternative to physicochemical approaches. These degradative biosystems mainly depend on the utilization of nutritive co-substrates such as yeast extract peptone in conjunction with glucose. Herein, a synergestic interaction between strains of mixed-culture consortium consisting of Rhodotorula sp., Raoultella planticola; and Staphylococcus xylosus was recruited in methylene blue (MB) degradation using agro-industrial waste as an economic and nutritive co-substrate. Via statistical means such as Plackett-Burman design and central composite design, the impact of significant nutritional parameters on MB degradation was screened and optimized. Predictive modeling denoted that complete degradation of MB was achieved within 72 h at MB (200 mg/L), NaNO3 (0.525 gm/L), molasses (385 μL/L), pH (7.5) and inoculum size (18%). Assessment of degradative enzymes revealed that intracellular NADH-reductase and DCIP-reductase were key enzymes controlling degradation process by 104.52 ± 1.75 and 274.04 ± 3.37 IU/min/mg protein after 72 h of incubation. In addition, azoreductase, tyrosinase, laccase, nitrate reductase, MnP and LiP also contributed significantly to MB degradation process. Physicochemical monitoring analysis, namely UV-Visible spectrophotometry and FTIR of MB before treatment and degradation byproducts indicated deterioration of azo bond and demethylation. Moreover, the non-toxic nature of degradation byproducts was confirmed by phytotoxicity and cytotoxicity assays. Chlorella vulgaris retained its photosynthetic capability (˃ 85%) as estimated from Chlorophyll-a/b contents compared to ˃ 30% of MB-solution. However, the viability of Wi-38 and Vero cells was estimated to be 90.67% and 99.67%, respectively, upon exposure to MB-metabolites. Furthermore, an eminent employment of consortium either freely-suspended or immobilized in plain distilled water and optimized slurry in a bioaugmentation process was implemented to treat MB in artificially-contaminated municipal wastewater and industrial effluent. The results showed a corporative interaction between the consortium examined and co-existing microbiota; reflecting its compatibility and adaptability with different microbial niches in different effluents with various physicochemical contents.

Adsorption Behavior of Crystal Violet and Congo Red Dyes on Heat-Treated Brazilian Palygorskite: Kinetic, Isothermal and Thermodynamic Studies

The effect of heat treatment on the adsorptive capacity of a Brazilian palygorskite to remove the dyes crystal violet (CV) and congo red (CR) was investigated. The natural palygorskite was calcined at different temperatures (300, 500 and 700 °C) for 4 h. Changes in the palygorskite structure were evaluated using X-ray diffraction, X-ray fluorescence, thermogravimetric and differential thermal analysis, N₂ adsorption/desorption and Fourier transform infrared spectroscopy. The adsorption efficiency of CV and CR was investigated through the effect of initial concentration, contact time, temperature, pH and dosage of adsorbent. The calcination increased the adsorption capacity of palygorskite, and the greatest adsorption capacity of CV and CR dyes occurred in the sample calcined at 700 °C (Pal-700T). The natural and calcined samples at 300 and 500 °C followed the Freundlich isothermal model, while the Pal-700T followed the Langmuir isothermal model. Adsorption kinetics results were well described by the Elovich model. Pal-700T showed better adsorption performance at basic pH, with removal greater than 98%, for both dyes. Pal-700T proved to be a great candidate for removing cationic and anionic dyes present in water.

Polyaniline Supported Ag-Doped ZnO Nanocomposite: Synthesis, Characterization, and Kinetics Study for Photocatalytic Degradation of Malachite Green

Ag-ZnO/PANI nanocomposite was prepared via the sol-gel technique following in situ oxidative polymerization of polyaniline (PANI). XRD, UV-Vis, and FT-IR spectroscopy were employed to study the crystal size, bandgap energy, and bond structure of as-synthesized nanocomposites. The mean crystallite size of the nanocomposite determined from XRD was 35.68 nm. Photocatalytic degradation of malachite green (MG) dye using as-synthesized photocatalysts was studied under visible light irradiation. The highest degradation efficiency was recorded for Ag-ZnO/PANI nanocomposites (98.58%) than Ag-ZnO nanoparticles (88.23%) in 120 min. The kinetics of photocatalytic degradation of MG follows pseudo-first-order reaction with rate order of 1.16 10−2 min−1. Moreover, the photocatalytic activity of Ag-ZnO/PANI nanocomposites was evaluated and compared with Ce-Cd oxide, electrospun P(3HB)-TiO2, and with other catalysts in the literature. The optimal conditions for photocatalytic degradation are as follows: the concentration of malachite green (0.2 g/l), pH (8), and the concentration of catalyst load (0.2 g/l) under visible light with an irradiation time of 120 min.

Adsorption Behavior of Acid-Treated Brazilian Palygorskite for Cationic and Anionic Dyes Removal from the Water

The effect of acid treatment on the adsorptive capacity of a Brazilian palygorskite to remove the crystal violet (CV) and congo red (CR) dyes was investigated. The raw palygorskite was acid-treated by different HCl solutions (2, 4, and 6 mol/L). The modifications on the palygorskite structure were investigated using X-ray diffraction, X-ray fluorescence, Fourier-transform infrared spectroscopy, N2 adsorption/desorption, and thermogravimetric and differential thermal analysis. The efficiency of CV and CR adsorption was investigated, and the effect of the initial concentration, contact time, pH, and adsorbent amount was analyzed. The results revealed that CV adsorption in the acid-treated palygorskite was higher than that of the raw material. A Langmuir isotherm model was observed for the adsorption behavior of CV, while a Freundlich isotherm model was verified for the CR adsorption. A pseudo-second-order model was observed for the adsorption kinetics of both dyes. The higher CV adsorption capacity was observed at basic pH, higher than 97%, and the higher CR removal was observed at acidic pH, higher than 50%. The adsorption parameters of enthalpy (ΔH), entropy (ΔS), and Gibbs energy (ΔG) were evaluated. The adsorption process of the CV and CR dyes on the raw and acid-treated Brazilian palygorskite was predominantly endothermic and occurred spontaneously. The studied raw palygorskite has a mild-adsorption capacity to remove anionic dyes, while acid-treated samples effectively remove cationic dyes.

Adsorption of Malachite Green and Alizarin Red S Dyes Using Fe-BTC Metal Organic Framework as Adsorbent

Synthetic organic dyes are widely used in various industrial sectors but are also among the most harmful water pollutants. In the last decade, significant efforts have been made to develop improved materials for the removal of dyes from water, in particular, on nanostructured adsorbent materials. Metal organic frameworks (MOFs) are an attractive class of hybrid nanostructured materials with an extremely wide range of applications including adsorption. In the present work, an iron-based Fe-BTC MOF, prepared according to a rapid, aqueous-based procedure, was used as an adsorbent for the removal of alizarin red S (ARS) and malachite green (MG) dyes from water. The synthesized material was characterized in detail, while the adsorption of the dyes was monitored by UV-Vis spectroscopy. An optimal adsorption pH of 4, likely due to the establishment of favorable interactions between dyes and Fe-BTC, was found. At this pH and at a temperature of 298 K, adsorption equilibrium was reached in less than 30 min following a pseudo-second order kinetics, with k″ of 4.29 × 10⁻³ and 3.98 × 10⁻² g∙mg⁻¹ min⁻¹ for ARS and MG, respectively. The adsorption isotherm followed the Langmuir model with maximal adsorption capacities of 80 mg∙g⁻¹ (ARS) and 177 mg∙g⁻¹ (MG), and K_L of 9.30·10³ L∙mg⁻¹ (ARS) and 51.56·10³ L∙mg⁻¹ (MG).

Novel cobalt-carbon@silica adsorbent

Recently, carbon nanostructures are of high importance due to their unique characteristics and interesting applications. Pyrolysis of anthracene with cobalt complex Co(2,2'-bipy)Cl2 (1), where (2,2'-bipy) is 2,2'-bipyridine, in the absence and presence of silica gave in high yield cobalt-carbon nanocomposite CoCNC (2) and CoCNC@SiO2 (3) at 600 °C and 850 °C, respectively. They were characterized using SEM, TEM, PXRD, Raman and XPS. (3) and (2) contain core-shell cobalt(0)/cobalt oxide-graphite with or without silica support. PXRD indicates that (2) contains crystalline hexagonal α-Co and cubic β-Co phases while (3) contains only cubic β-Co phase and silica. The structure of (2) is 3D hierarchical carbon architecture wrapping spherical and elliptical cobalt nanoparticles. (3) consists of graphitized structures around cobalt nanoparticles embedded in the silica matrix. XPS reveals that the nanocomposites contain oxygen functional groups that enhance uptake of cationic dyes. CoCNC@SiO2 (3) has higher capacity and thus is better adsorbent of Basic Violet 3 than CoCNC (2). The Langmuir adsorption capacity of (3) is 19.4 mg g-1 while column capacity is 12.55 mg g-1 at 25 °C. Freundlich isotherm and pseudo-second-order kinetic models fit well the adsorption data. Thermodynamics indicate that adsorption(3) is exothermic. Column regeneration was tested for three cycles and Yan et al. was found the best kinetic model.

Decoding social behaviors in a glycerol dependent bacterial consortium during Reactive Blue 28 degradation

Biodegradation of reactive azo dyes has been an arduous problem for decades. Several efficient biosystems have been proposed for dye degradation, but most of them are dependent on the availability of costly co-substrates such as peptone, yeast extract, and/or glucose. The present study describes the azo dye degradation by a bacterial consortium using glycerol as a sole co-substrate. The consortium was developed from a mixed bacterial culture obtained upon enrichment of soil sediment for Reactive Blue 28 (RB28) decolorization in the presence of glycerol (0.1%; v/v). The consortium with three bacterial species, i.e., Stenotrophomonas acidaminiphila APG1, Cellulomonas sp. APG4, and Pseudomonas stutzeri APG2, designated as "SCP," decolorized 92% of 100 ppm dye in 96 h. The intricacies of the interactions existing within the members of the consortium were resolved by a simple and unique analysis called "BSocial." Among all the members, Cellulomonas sp. APG4 exerted a net-positive impact for decolorization (%) on the consortium. The net fitness of the community increased when all the three species were present, and thus, all of them were selected for further analysis. Moreover, APG4 seemed to be central in the reductive decolorization as it possessed the highest reductase activity. The dye degradation by the consortium was demonstrated by UV-Visible spectroscopy, HPTLC, and FTIR spectroscopy of control and decolorized cell-free supernatant. The LC-ESI-MS analysis of metabolites extracted from decolorized cell-free medium led to the identification of degradation products, thus leading us to propose the plausible pathway for degradation of RB28 by bacterial consortium.

Cobalt-carbon/silica nanocomposites prepared by pyrolysis of a cobalt 2,2'-bipyridine terephthalate complex for remediation of cationic dyes

Recently, carbon nanostructures have attracted interest because of their unique properties and interesting applications. Here, CoC@SiO₂-850 (3) and CoC@SiO₂-600 (4) cobalt–carbon/silica nanocomposites were prepared by solid-state pyrolysis of anthracene with Co(tph)(2,2′-bipy)·4H₂O (1) complex in the presence of silica at 850 and 600 °C, respectively, where 2,2′-bipy is 2,2′-bipyridine and tph is the terephthalate dianion. Moreover, Co(μ-tph)(2,2′-bipy) (2) was isolated and its X-ray structure indicated that cobalt(ii) has a distorted trigonal prismatic coordination geometry. 2 is a metal–organic framework consisting of one-dimensional zigzag chains within a porous grid network. 3 and 4 consist of cobalt(0)/cobalt oxide nanoparticles with a graphitic shell and carbon nanotubes embedded in the silica matrix. They were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), powder X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET), Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS). XPS revealed that the nanocomposites are functionalized with oxygen-containing groups, such as carboxylic acid groups. In addition, the presence of metallic cobalt nanoparticles embedded in graphitized carbon was verified by XRD and TEM. The efficiency of 3 for adsorption of crystal violet (CV) dye was investigated by batch and column experiments. At 25 °C, the Langmuir adsorption capacity of 3 for CV was 214.2 mg g⁻¹ and the fixed-bed column capacity was 36.3 mg g⁻¹. The adsorption data were well fitted by the Freundlich isotherm and pseudo-second-order kinetic model. The adsorption process was spontaneous and endothermic.

A cobalt–carbon@silica nanocomposite was synthesized from a cobalt 2,2′-bipyridine terephthalate complex and its adsorption behavior towards crystal violet dye was tested using batch and column techniques.

Microbial degradation, spectral analysis and toxicological assessment of malachite green by Streptomyces chrestomyceticus S20

Malachite green (MG), a triphenylmethane dye is extensively used for coloring silk, aquaculture and textile industries, it has also has been reported toxic to life forms. This study aimed to investigate the biodegradation potential of MG by actinobacteria. The potent actinobacterial strain S20 used in this study was isolated from forest soil (Sabarimala, Kerala, India) and identified as Streptomyces chrestomyceticus based on phenotype and molecular features. Strain S20 degraded MG up to 59.65 ± 0.68% was studied in MSM medium and MG (300 mg l^-1) and degradation was increased (90-99%) by additions of 1% glucose and yeast extract into the medium at pH 7. The treated metabolites from MG by S20 characterized by FT-IR and GC-MS. The results showed MG has been degraded into nontoxic compounds evaluated by (1) phytotoxic assay on Vigna radiata, (2) microbial toxicity on Staphylococcus aureus, Bacillus subtilis, Micrococcus luteus, Streptococcus sp. and Escherichia coli, (3) cytotoxicity assay in a human cell line (MCF 7). The toxicity studies demonstrated that the byproducts from MG degradation by S. chrestomyceticus S20 were no toxic to plants and microbes and less toxic to human cells as compared to the parent MG. Perhaps this is the first work reported on biodegradation of MG by S. chrestomyceticus which could be a potential candidate for the removal of MG from various environments.

Antimicrobial photodynamic therapy on Staphylococcus aureus and Escherichia coli using malachite green encapsulated mesoporous silica nanoparticles: an in vitro study

BACKGROUND

Rise in the number of healthcare associated or hospital acquired infections is a major problem affecting the global healthcare sector. We evaluated superior antibacterial and antibiofilm photodynamic therapy (aPDT) using malachite green encapsulated mesoporous silica nanoparticles (MG-MSN) against Staphylococcus aureus and Escherichia coli, which are known to be major causative agents of nosocomial infections.

METHODS

Malachite green (MG) was encapsulated on mesoporous silica nanoparticles (MSN). Fourier-transform infrared spectroscopy, Transmission electron microscopy, and spectroscopic analysis were performed to characterize the MG-MSN. The antimicrobial efficacies of MSN, MG, and MG-MSN were investigated and the results were recorded.

RESULTS

MG-MSN was effective against both the tested bacteria. S. aureus was more phototoxic to MG-MSN compared to E. coli. The antibiofilm efficacy of MG-MSN on E. coli and S. aureus was also studied. Biofilm inhibition was 65.68 ± 2.62% in E. coli and 79.66 ± 3.82% in S. aureus. Cell viability assay, exopolysaccharides quantification, and confocal laser scanning microscopy studies also revealed the enhanced antibiofilm activity of MG-MSN when used as a potential photosensitizer for aPDT. This study can be extended to eradicate these strains from localized superficial infections and medical appliances, preventing nosocomial infections.

Microwave-accelerated sorption of cationic dyes onto green marine algal biomass

Monolithic algal green powder (MAGP) was fabricated based on the marine green macroalga Enteromorpha flexuosa. It was scrutinized by using scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX), Fourier transform infrared (FT-IR), point of zero charge (PH_PZC), and Brunauer-Emmett-Teller (BET) surface area. The ability of Enteromorpha flexuosa to capture both crystal violet (CV) and methylene blue (MB) from aqueous solutions was evaluated. The influence of variable conditional parameters on CV dye and MB dye batch sorption was investigated. Results showed that percentage removal of 90.3% and 93.4% were obtained under optimum conditions of variables for CV and MB, respectively. Effect of microwave radiation on dye sorption was also appraised. Processing the sorption under microwave irradiation (microwave-enforced sorption, MES) increases mass transfer and a contact time as low as 1 min is sufficient under optimized conditions (exposure time and power) reaching the equilibrium. The reusability of MAGP sorbent was achieved for four cycles of sorption/desorption by using 0.5 M HCl. The ability of MAGP for cationic dyes removal from spiked tap water and petrochemical plant discharge wastewater samples was successfully registered. Ultimately, the displayed data showed a superior and excellent ability of algal powder to be exploited as a green, harmless, and effective sorbent for cationic dye removal.

Malachite green-conjugated multi-walled carbon nanotubes potentiate antimicrobial photodynamic inactivation of planktonic cells and biofilms of Pseudomonas aeruginosa and Staphylococcus aureus

Purpose: Infections associated with medical devices that are caused by biofilms remain a considerable challenge for health care systems owing to their multidrug resistance patterns. Biofilms of Pseudomonas aeruginosa and Staphylococcus aureus can result in life-threatening situations which are tough to eliminate by traditional methods. Antimicrobial photodynamic inactivation (aPDT) constitutes an alternative method of killing deadly pathogens and their biofilms using reactive oxygen species (ROS). This study investigated the efficacy of enhanced in vitro aPDT of P. aeruginosa and S. aureus using malachite green conjugated to carboxyl-functionalized multi-walled carbon nanotubes (MGCNT). Both the planktonic cells and biofilms of test bacteria were demonstrated to be susceptible to the MGCNT conjugate. These MGCNT conjugates may thus be employed as a facile strategy for designing antibacterial and anti-biofilm coatings to prevent the infections associated with medical devices. Methods: Conjugation of the cationic dye malachite green to carbon nanotube was studied by UV-visible spectroscopy, high-resolution transmission electron microscopy, and Fourier transform infrared spectrometry. P. aeruginosa and S. aureus photodestruction were studied using MGCNT conjugate irradiated for 3 mins with a red laser of wavelength 660 nm and radiant exposure of 58.49 J cm^-2. Results: Upon MGCNT treatment, S. aureus and P. aeruginosa were reduced by 5.16 and 5.55 log₁₀ , respectively. Compared to free dye, treatment with MGCNT afforded improved phototoxicity against test bacteria, concomitant with greater ROS production. The results revealed improved biofilm inhibition, exopolysaccharide inhibition, and reduced cell viability in test bacteria treated with MGCNT conjugate. P. aeruginosa and S. aureus biofilms were considerably reduced to 60.20±2.48% and 67.59±3.53%, respectively. Enhanced relative MGCNT phototoxicity in test bacteria was confirmed using confocal laser scanning microscopy. Conclusion: The findings indicated that MGCNT conjugate could be useful to eliminate the biofilms formed on medical devices by S. aureus and P. aeruginosa.

Xerogel activated diatoms as an effective hybrid adsorbent for the efficient removal of malachite green

The surface of a naturally available diatom was modified using a xerogel for the enhanced removal of malachite green from aqueous media.

Facile synthesis, growth process, characterisation of a nanourchin-structured α-MnO2 and their application on ultrasonic-assisted adsorptive removal of cationic dyes: A half-life and half-capacity concentration approach

Textile dyes pose a serious threat in terms of water pollution due to its complex aromatic structures and poor degradability. In order to reduce the toxic effects of Crystal Violet (CV) and Methylene Blue (MB), an ultrasonic-assisted dye adsorption using urchin like α-MnO₂ nanostructures was studied. The adsorbent was synthesised by hydrothermal method at low-temperature. The crystallinity and morphology were determined to investigate the growth mechanism of α-MnO₂ nanourchins which consists of two main stages. The initial stage includes the formation of α-MnO₂ microspheres followed by the epitaxial growth of nanoneedles on to the surface of them. The α-MnO₂ was characterised by BET, XRD, FT-IR, XPS, SEM, TEM and TGA. At 5.6, the point of zero charge of α-MnO₂ nanostructures was determined. The total pore volume and average pore radius were confirmed to be 4.751 × 10^-2 cc/g and 10.99 Å respectively from the BET analysis. Batch adsorption experiments were performed to investigate the effect of pH, adsorbent dosage, sonication time, initial dye concentration, temperature, ultrasonic frequency and power. The adsorption mechanism was studied using several isotherm and kinetic models. The adsorption data of CV and MB at equilibrium was observed to adopt the Langmuir isotherm model and pseudo-second order kinetic model. The maximum adsorption capacities for CV and MB were found to be 5882.3 and 5000 mg/g respectively. The thermodynamic study predicted that the process was exothermic for CV and endothermic for MB. The effects of competitive ions, ionic strength and humic acid on the uptake of both the dyes were also investigated. And finally, the reusability of recovered α-MnO₂ after dye adsorption was studied up to five cycles for its potential industrial applications.

Amino-modified molecular sieves for adsorptive removal of H2S from natural gas

Amine-modified MCM-41 adsorbents (APTMS/MCM-41, PEI/MCM-41 and AAPTS/MCM-41) were prepared and characterized by XRD, N2 adsorption-desorption, FT-IR, TEM, SEM and TG-DTA. The performance of each adsorbent in a fixed adsorption bed for H2S removal was measured using a mixture of oxygen, nitrogen and hydrogen sulfide gases. It was found that the specific surface area decreased and the topography changed significantly after the use of each modified adsorbent. Nevertheless, all amine-modified MCM-41 adsorbents retained mesoporous silica of MCM-41. The H2S removal rate and saturated H2S capacity of APTMS/MCM-41 improved from 32.3% to 54.2% and 119.5 to 134.4 mg g-1, respectively, compared with that of MCM-41, and it showed the best performance among all adsorbents. APTMS/MCM-41, PEI/MCM-41 and AAPTS/MCM-41 were regenerated by maintaining at 423, 523 and 373 K in nitrogen for 3 h, respectively, and thus possessed high regenerability.

Graphene oxide-dye nanocomposites: effect of molecular structure on the quality of laser-induced graphene

The nanocomposite coatings made using graphene oxide (GO) and six different organic dyes were used to produce the laser-induced graphene (LIG) coatings by means of near infrared picosecond laser irradiation. The coatings were investigated by means of contact angle measurement with three liquids (1-bromonaphtalene, glycerol and water), Raman spectroscopy, scanning electron microscopy, Fourier transform infrared (FTIR) spectroscopy and thermogravimetric analysis. It was found that the more hydrophilic is the precursor surface the more hydrophobic LIG surface is produced after the laser treatment. Contact angle values obtained on LIG produced from pure GO reached 143°. FTIR spectra have shown that the interaction between GO and dye molecules is realized through the nitrogen atoms. Raman spectra have shown that the best quality LIG coating is obtained using a GO-neutral red nanocomposite precursor. A correlation among contact angle, Raman spectra and topological indices of dye molecules was found, and will serve for the further investigation of the mechanism of LIG production and development of low-defect coatings.