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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

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.

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 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.

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 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.

Crystal violet (Cry) is an essential textile dye belonging to the triphenylmethane group, that is widely used in the textile industry. It is also applied for paper printing and Gram staining. Previously, it was significant as a topical antiseptic due to its antibacterial, antifungal, and anthelmintic properties. Despite its various applications, crystal violet has been recognized as a biohazard dye due to its toxic and carcinogenic properties. It persists in the environment with long-lasting effects and has detrimental impacts. In this research, water extract from Moringa oleifera leaves is employed as environmentally friendly methods to synthesize zinc oxide nanoparticles (Mo/ZnO-NPs), and characterized by TEM, EDX, FT-IR, and Zeta potential. Mo/ZnO-NPs exhibit a Zeta potential of − 21.9 mV, and X-ray diffraction (XRD) analysis confirms their crystallographic structure. The size of the biogenic Mo/ZnO-NPs ranges from 5.52 to 41.59 nm. This study was designed to estimate and maximize the ability of Mo/ZnO-NPs to remove crystal violet using Central Composite Design (CCD), considering pH (ranging from 3 to 11), incubation time (ranging from 30 to 150), nanoparticles concentrations (ranging from 0.2 to 1.8 mg/mL), and crystal violet concentrations (ranging from 25 to 125 ppm). The maximum percentage value of removal of crystal violet by Mo/ZnO-NPs was 97.26 with optimal conditions of pH 9, incubation time 120 min, Mo/ZnO-NPs 1.4 mg/mL, and crystal violet concentration of 50 ppm. The best-predicted conditions that caused the highest removal of crystal violet (97.8%) were determined using the desirability function as pH 10, incubation time of 140 min, Mo/ZnO-NPs concentrations of 1.3 mg/mL, and a concentration of crystal violet of 80 ppm. Under these optimal conditions, the maximum experimental crystal violet removal% by Mo/ZnO-NPs was (98.7%) was verified. Mo/ZnO-NPs synthesized by Moringa oleifera  can be a promising candidate for the adsorption of crystal violet.

The presence of cationic dyes, even in a tiny amount, is harmful to aquatic life and pollutes the environment. Therefore, it is essential to remove these hazardous dyes to protect the life of marine creatures from these pollutants. In this research, crystal violet (CV) dye elimination was performed using a lignin copper ferrite (LCF) adsorbent. The adsorbent was synthesized and characterized using FTIR, Raman, SEM, EDX with mapping, and VSM, which proved the successful formation of magnetic LCF. Adsorption experiments were performed using different effective parameters. The highest adsorption potential (97%) was executed at mild operating conditions, with a 5 min contact time at room temperature and pH 8. The adsorption kinetic study utilized four kinetic models: first-order, second-order, intraparticle diffusion, and Elovich. The results revealed that the adsorption process complies with the pseudo-first-order with a maximum adsorption capacity of 34.129 mg/g, proving that the adsorption process mechanism is a physical adsorption process. Three isotherm models, Langmuir, Freundlich, and Temkin, were examined. The adsorption mechanism of CV onto LCF was also followed by the Langmuir and Freundlich models. The thermodynamic parameters were examined and revealed that the adsorption onto LCF was an exothermic process. It was proposed that the adsorption process is a spontaneous exothermic process. LCF appears to forcefully remove toxic CV dye from textile wastewater.