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Dye-based industries, particularly small and medium scale, discharge their effluents into waterways without treatment due to cost considerations. We investigated the use of biochars produced from the woody tree Gliricidia sepium at 300 °C (GBC300) and 500 °C (GBC500) in the laboratory and at 700 °C from a dendro bioenergy industry (GBC700), to evaluate their potential for sorption of crystal violet (CV) dye. Experiments were conducted to assess the effect of pH reaction time and CV loading on the adsorption process. The equilibrium adsorption capacity was higher with GBC700 (7.9 mg g−1) than GBC500 (4.9 mg g−1) and GBC300 (4.4 mg g−1), at pH 8. The CV sorption process was dependent on the pH, surface area and pore volume of biochar (GBC). Both Freundlich and Hill isotherm models fitted best to the equilibrium isotherm data suggesting cooperative interactions via physisorption and chemisorption mechanisms for CV sorption. The highest Hill sorption capacity of 125.5 mg g−1 was given by GBC700 at pH 8. Kinetic data followed the pseudo-second-order model, suggesting that the sorption process is more inclined toward the chemisorption mechanism. Pore diffusion, π–π electron donor–acceptor interaction and H-bonding were postulated to be involved in physisorption, whereas electrostatic interactions of protonated amine group of CV and negatively charged GBC surface led to a chemisorption type of adsorption. Overall, GBC produced as a by-product of the dendro industry could be a promising remedy for CV removal from an aqueous environment.

To effectively remove Diazinon (DZ), Amoxicillin (AMX), and Crystal Violet (CV) from aquatic environments, a novel granular activated carbon (GAC) modified with Polyethylene glycol 600 (PEG) was created and manufactured. The chemical properties were investigated using a variety of characteristic analyses, including FT-IR, XRD, FESEM, and N 2 adsorption/desorption. The effectiveness of GAC-PEG’s adsorption for the removal of DZ, AMX, and CV was assessed under a variety of conditions, including a pH of 4–9 for the solution, 0.003–0.05 g doses of adsorbent, 50–400 ppm starting concentration, and a reaction time of 5–25 min. For DZ, AMX, and CV adsorption, the maximum adsorption capacity (Q max ) was 1163.933, 1163.100, and 1150.300 mg g- 1 , respectively. The Langmuir isotherm described all of the data from these adsorption experiments, and the pseudo-second-order well explains all-adsorption kinetics. Most contacts between molecules, electrostatic interactions, π–π interactions, hydrogen bonding, and entrapment in the modified CAG network were used to carry out the DZ, AMX, and CV adsorption on the GAC-PEG. The retrievability of the prepared adsorbent was successfully investigated in studies up to two cycles without loss of adsorption efficiency, and it was shown that it can be efficiently separated.

Araucaria angustifolia bark (AA-bark), a waste generated in wood processing, was evaluated as a potential adsorbent to remove Gentian Violet (GV) dye from aqueous solutions. The AA-bark presented an amorphous structure with irregular surface and was composed mainly of lignin and holocellulose. These characteristics indicated that the adsorbent contains available sites to accommodate the dye molecules. The GV adsorption on AA-bark was favored at pH 8.0 with adsorbent dosage of 0.80 g L−1. Pseudo-nth order model was adequate to represent the adsorption kinetics of GV on AA-bark. A fast adsorption rate was verified, with the equilibrium being attained within 30 min. Equilibrium data were well represented by the Langmuir model. The maximum adsorption capacity was 305.3 mg g−1. Adsorption was spontaneous, favorable and endothermic. AA-bark was able to treat a simulated dye house effluent, reaching color removal values of 80%. An excellent performance was found in fixed bed experiments, where the length of the mass transfer zone was only 5.38 cm and the breakthrough time was 138.5 h. AA-bark can be regenerated two times using HNO3 0.5 mol L−1. AA-bark can be used as a low-cost material to treat colored effluents in batch and fixed bed adsorption systems.

Growing concerns about pollution caused by industrial and agricultural wastes have increased interest in converting waste materials into useful products. Bacterial nanocellulose has garnered global interest due to its environmentally friendly production, excellent mechanical properties, and biocompatibility, making it a promising material for various industries. This study explores the production of bacterial nanocellulose (BNC) by Bacillus strains utilizing fruit waste as a sustainable carbon source. Six potential BNC-producing Bacillus strains were isolated and identified. Among them, Bacillus haynesii showing the highest BNC productivity. A Box-Behnken experimental design was employed to optimize cost-effective technique for BNC production. Key factors like temperature, date waste extract percentage, and initial pH level influencing bacterial cellulose production by  Bacillus haynesii  were optimized. The highest BNC productivity with a value of 2.6 g/L was obtained under optimized conditions of 29 °C, 15% date waste extract, and pH 6. The glass transition temperature of the bacterial nanocellulose ranged from 21.51 to 42.06 °C, with a low negative charge for colloidal stability. Moreover, crystal violet elimination experiments revealed efficient dye removal (84.7%) with adsorbent concentrations of 2 mg/L and a contact time of 60 min. This study concluded that the Bacillus haynesii 9.1AP strain is a promising candidate for sustainable BNC production. To the best of our knowledge, this study represents the initial documentation of Bacillus haynesii’s capability for BNC production, highlighting its potential in environmental and industrial applications, particularly in dye adsorption.

The current study explores the effectiveness of coconut husk for crystal violet dye sequestration employing a batch experimental setup. Characterization of adsorbent was carried out via FTIR, and SEM techniques and results confirmed the involvement of OMe, COC and hydroxyl functional groups in dye uptake, and the rough, porous nature of adsorbent and after adsorption dye molecules colonized these holes resulting in dye exclusion. Effects of various adsorption parameters such as pH, adsorbent dose, contact time, initial dye concentration, and temperature of solution were studied. Crystal violet adsorption on coconut husk was highly pH-dependent, with maximum removal occurring at basic pH. Maximum removal of dye, i.e., 81%, takes place at optimized conditions. Kinetic data was analyzed by pseudo-first, pseudo-second order and an intra-particle diffusion model. Results showed that the pseudo-second order kinetic model best described adsorption of crystal violet onto coconut husk. Langmuir, Freundlich, and D-R adsorption isotherms were also used to test their appropriateness to experimental data and the Freundlich isotherm fits best to data. Thermodynamic parameters showed that the current process was spontaneous, endothermic in nature with continuous decrease in entropy. Established practice is 79% applicable to tap water and in acidic medium nearly 80% of adsorbent was recovered, confirming the effectiveness and appropriateness of coconut husk for crystal violet dye exclusion from wastewater.

Staphylococcus aureus ( S. Aureus ) is a common food-borne pathogenic microorganism. Biofilm formation remains the major obstruction for bacterial elimination. The study aims at providing a basis for determining S. aureus biofilm formation. 257 clinical samples of S. aureus isolates were identified by routine analysis and multiplex PCR detection and found to contain 227 MRSA, 16 MSSA, 11 MRCNS, and 3 MSCNS strains. Two assays for quantification of S. aureus biofilm formation, the crystal violet (CV) assay and the XTT (tetrazolium salt reduction) assay, were optimized, evaluated, and further compared. In CV assay, most isolates formed weak biofilm 74.3 %), while the rest formed moderate biofilm (23.3 %) or strong biofilm (2.3 %). However, most isolates in XTT assay showed weak metabolic activity (77.0 %), while the rest showed moderate metabolic activity (17.9 %) or high metabolic activity (5.1 %). In this study, we found a distinct strain-to-strain dissimilarity in terms of both biomass formation and metabolic activity, and it was concluded from this study that two assays were mutual complementation rather than being comparison.

The potential of Pterocladia capillacea , a marine red seaweed, as a sustainable and eco-friendly adsorbent was investigated for the removal of toxic hexavalent chromium Cr(VI) (or Cr 6+ ) and crystal violet dye (CVD) from contaminated water. Characterization of P. capillacea using Fourier-Transform Infrared (FTIR), Scanning Electron Microscopy (SEM), and Brunauer-Emmett-Teller (BET) analysis revealed a porous structure with a high specific surface area (87.17 m²/g) and a negative surface charge (-29.5 mV), ideal for adsorbent applications. Adsorption studies were conducted to assess the impact of operational parameters, such as pH, adsorbent dose, initial pollutant concentration, and temperature. Optimal removal was achieved at pH 1.0 for Cr 6+ and CVD. Increasing the adsorbent dose led to higher Cr 6+ adsorption, achieving near-complete removal with 0.4 g. An optimal dose of 0.8 g was selected for subsequent experiments. Cr 6+ Cr 6+ removal was faster during the initial adsorption stage (within 30–60 min), followed by a slower rate due to saturation and reduced pore diffusion. Adsorption was more effective at lower temperatures and followed pseudo-second-order kinetics, suggesting chemisorption as the dominant mechanism. Six isotherm models were used to describe equilibrium adsorption, with the Freundlich model providing the best fit for both Cr 6+ and CVD, indicating multilayer adsorption and heterogeneous surface interactions. P. capillacea showed potential for Cr 6+ removal in seawater and real wastewater, although efficiency was reduced due to complex matrix effects. Reusability studies indicated a decline in efficiency over multiple cycles; however, Cr 6+ uptake remained above 89.2% for CVD. Similar reusability was observed, with an initial removal efficiency of 87.29% for CFD. Although removal efficiency decreased in subsequent cycles, the material remained effective for repeated CVD adsorption. The study demonstrates the potential of P. capillacea as a readily available, cost-effective, and sustainable material for the bioremediation of Cr 6+ and synthetic dyes from water, contributing to the development of environmentally friendly water treatment technologies.

In this research, activated carbon was obtained from rubber fruit shells (ACRPs). The obtained activated carbon (ACRPs) was modified by magnetite particle coating and silanization with triethoxyiphenylsilane (TEPS) to produce a new magnetic adsorbent (ACRPs-MS). The affinity of as-prepared adsorbent (ACRPs-MS) toward methylene blue (MB) and crystal violet (CV) dyes was tested in mono-component and bi-component solutions. Structural characterization proves the success of the magnetite coating process and the silanization of ACRPs. In the infrared (IR) spectroscopy spectrum of ACRPs-MS, Si–O-Fe and Si–O-Si bonds were identified, which indicated the presence of magnetite and silane. This is also supported by the elemental composition contained in the energy-dispersive X-ray (EDX) diffractogram. In addition, the presence of the porous structure of the surface of the material and the increase in the specific surface area increase the accessibility of contaminants such as MB and CV dyes to be adsorbed to the ACRPs-MS adsorption site effectively. The experimental results showed that the adsorption of mono-component MB and CV dyes by ACRPs-MS was optimum at pH 8 and an interaction time of 60 min. The adsorption kinetics of mono-component MB and CV dyes by ACRPs-MS tended to follow pseudo-second-order kinetics (PSO) models with PSO rate constant ( k 2 ) values of 0.198 and 0.993 g mg −1  min −1 , respectively. The adsorption of MB and CV dyes by ACRPs-MS in a bi-component mixture tends to follow the Langmuir isotherm model with adsorption capacity ( q m ) values of 85.060 and 90.504 mg g −1 , respectively. Analysis of adsorption data on the bi-component mixture between MB and CV by ACRPs-MS with the Langmuir isotherm equation for a binary mixture resulted in q m of 22.645 × 10 –3  mmol equiv g −1 . ACRPs-MS material can be used repeatedly five times with adsorption ability > 80%. Desorption of MB and CV dyes was carried out using 0.05 M HCl solution. ACRPs-MS material was able to adsorb MB and CV dyes with a large adsorption capacity and could be used in repeated adsorption. Thus, it can be stated that ACRPs-MS can be used as an effective adsorbent for MB and CV dyes, either singly or in a bi-component mixture. Graphical Abstract

A simple procedure to develop antibacterial surfaces using thiol-capped gold nanoparticles (AuNPs) is shown, which effectively kill bacteria under dark and light conditions. The effect of AuNP size and concentration on photo-activated antibacterial surfaces is reported and we show significant size effects, as well as bactericidal activity with crystal violet (CV) coated polyurethane. These materials have been proven to be powerful antibacterial surfaces against both Gram-positive and Gram-negative bacteria. AuNPs of 2, 3 or 5 nm diameter were swell-encapsulated into PU before a coating of CV was applied (known as PU-AuNPs-CV). The antibacterial activity of PU-AuNPs-CV samples was tested against Staphylococcus aureus and Escherichia coli as representative Gram-positive and Gram-negative bacteria under dark and light conditions. All light conditions in this study simulated a typical white-light hospital environment. This work demonstrates that the antibacterial activity of PU-AuNPs-CV samples and the synergistic enhancement of photoactivity of triarylmethane type dyes is highly dependent on nanoparticle size and concentration. The most powerful PU-AuNPs-CV antibacterial surfaces were achieved using 1.0 mg mL −1 swell encapsulation concentrations of 2 nm AuNPs. After two hours, Gram-positive and Gram-negative bacteria were reduced to below the detection limit (>4 log) under dark and light conditions.

Precise quantification of biofilm is critical as the formation and persistence of biofilm have significant implications in the environmental, therapeutic and industrial contexts. The microtiter plate assay using crystal violet with 33% glacial acetic acid or 94–100% ethanol as the resolubilising agent is widely used for the categorisation of biofilms into weak, moderate and strong categories. But, the use of varying wavelengths for the measurement of biofilm resulted in discrepancies in categorisation across the studies due to the difference in the extinction coefficient of CV. This study emphasises the importance of measuring the biofilm at the absorbance maximum (λ max ) of resolubilized CV, identified as 585 nm for 33% acetic acid and 580 nm for 94–100% ethanol. To address the challenge of harmonizing the results across studies, a method was developed to adjust the biofilm categorisation threshold based on the extinction coefficient ratios of CV at different wavelengths enabling consistent classification regardless of the wavelength used. Validation with E. coli and S. aureus demonstrated that the adjusted thresholds produced results similar to that obtained with the λ max . This standardised approach not only enables the researchers to obtain accurate and consistent results in the future studies, but also facilitates the comparison of previously published data on biofilm research, which is essential for the exploration of newer therapeutic strategies against biofilm related infections.