Reactive Black 5 Concentration Research Articles

Accessible Eco-Friendly Method for Wastewater Removal of the Azo Dye Reactive Black 5 by Reusable Protonated Chitosan-Deep Eutectic Solvent Beads.

A novel approach to enhance the utilization of low-cost and sustainable chitosan for wastewater remediation is presented in this investigation. The study centers around the modification of chitosan beads using a deep eutectic solvent composed of choline chloride and urea at a molar ratio of 1:2, followed by treatment with sulfuric acid using an impregnation accessible methodology. The effectiveness of the modified chitosan beads as an adsorbent was evaluated by studying the removal of the azo dye Reactive Black 5 (RB5) from aqueous solutions. Remarkably, the modified chitosan beads demonstrated a substantial increase in adsorption efficiency, achieving excellent removal of RB5 within the concentration range of 25-250 mg/L, ultimately leading to complete elimination. Several key parameters influencing the adsorption process were investigated, including initial RB5 concentration, adsorbent dosage, contact time, temperature, and pH. Quantitative analysis revealed that the pseudo-second-order kinetic model provided the best fit for the experimental data at lower dye concentrations, while the intraparticle diffusion model showed superior performance at higher RB5 concentration ranges (150-250 mg/L). The experimental data were successfully explained by the Langmuir isotherm model, and the maximum adsorption capacities were found to be 116.78 mg/g at 298 K and 379.90 mg/g at 318 K. Desorption studies demonstrated that approximately 41.7% of the dye could be successfully desorbed in a single cycle. Moreover, the regenerated adsorbent exhibited highly efficient RB5 removal (80.0-87.6%) for at least five consecutive uses. The outstanding adsorption properties of the modified chitosan beads can be attributed to the increased porosity, surface area, and swelling behavior resulting from the acidic treatment in combination with the DES modification. These findings establish the modified chitosan beads as a stable, versatile, and reusable eco-friendly adsorbent with high potential for industrial implementation.

Removal of Reactive Black 5 by UV-C assisted peroxydisulfate process: Effect of parameters, kinetic study, and phytotoxicity assessment

ABSTRACT Photochemical removal of Reactive Black 5 (RB5) was investigated by the UV-C assisted peroxydisulfate (UV-C/PDS) process. Parameters affecting the removal of RB5 were examined. Activation of PDS by UV-C light significantly improved the removal efficiency compared to direct photolysis or PDS alone. The removal of RB5 by UV-C/PDS process fitted well with the pseudo first-order kinetic model under all tested conditions. Almost complete removal of RB5 was achieved at the end of 120 min within the pH range of 3–7, whereas 90.7 and 89.4% removal efficiency values were observed at pH = 9 and 11, respectively. An increase in PDS dosage in the range of 0.25–1 mM led to a rise in removal from 48.5 to 97.3% after 120 min, and a complete removal was observed with a dosage higher than 2 mM. Pseudo firstorder rate constant (kobs) increased linearly with PDS dosage from 0.0058 to 0.0518 min−1 in the 0.25 mM − 2.3 mM concentration range. The removal efficiency decreased with an increase in the initial concentration of RB5 from 20 to 50 mg L−1 and an exponential correlation was observed between kobs and initial concentration of RB5. Scavenging experiments conducted using t-butyl alcohol and ethyl alcohol implied that both sulphate and hydroxyl radicals were involved in the removal of RB5. Adding HCO3 − decreased the removal of RB5 within the range of 1–30 mM. The presence of CI− showed a negative impact on the removal at low concentrations (1–15 mM) and NO3 − slightly inhibited the removal of RB5. With corresponding stoichiometric PDS dosage, almost a complete mineralisation was achieved for RB5 solution and simulated dyebath effluent after 720 min of reaction time. EE/O values were determined to be 91.0, 76.8, and 41.1 kWh m−3 order−1 for UV-C/H2O2, UV-C/PMS, and UV-C/PDS processes, respectively. The phytotoxicity tests indicated that the intermediates could be more toxic than the parent compound.

Decolorization of Congo Red and Reactive Black 5 Dyes with Horseradish Peroxidase-Immobilized Cross-Linked Polymeric Microbeads

AbstractIn this study, the efficiency of poly(ethylene glycol dimethacrylate-N-methacryloyl-amido-l-tryptophan methyl ester) [PEDMT] microbeads (in the diameter range of 106–180 µm) as a support material for HRP immobilization was evaluated and the immobilized-HRP enzyme was used for decolorization of Congo Red (CR) and Reactive Black 5 (RB5) dyes. The specific surface area of the PEDMT microbeads was 1103 m2 g−1, which is very high. The PEDMT microbeads had a pore volume and pore size of 1.94 cm3 g−1 and 9.99–55.3 Å, respectively. The chemical compositions of the PEDMT and PEDMT–HRP microbead surfaces were analyzed using X-ray photoelectron spectroscopy (XPS). Immobilization yield, activity yield, and immobilization efficiency were 84.9 ± 2.1, 73.8 ± 5.9%, and 86.9 ± 6.9%, respectively. Optimum pH (6.0), temperature (45 °C and 50 °C for free and immobilized enzyme), H2O2 concentration (3% v/v) were investigated in detail. Thermal and storage stability was increased after immobilization and immobilized enzyme preserved more than 55% of its initial activity even after 10 consecutive uses. Decolorization studies were also performed by investigating the effects of pH, CR, and RB5 concentration, enzyme amount, H2O2 concentration, contact time on decolorization efficiency. The decolorization efficiency for CR and RB5 by PEDMT–HRP was 98.20% and 47.99% after 30 min at pH 6.0 and 45 °C. The immobilized-HRP retained 89% and 27% of its initial activity after three repeated cycles with CR and RB5, respectively. The PEDMT microbeads with high surface area, porosity, durability, and reusability exactly met the requirements for HRP immobilization and dye decolorization.

Removal of Reactive Black 5 from simulated textile effluents by an electrocoagulation process: optimization by response surface methodology

Abstract The textile industry creates one-fifth of the world's industrial water pollution, thus, the electrocoagulation (EC) process was proposed and investigated as an alternative eco-friendly treatment for water reuse. This study aimed to assess the removal efficiency of the Reactive Black 5 (RB5) from synthetic textile effluent by EC. Key operating parameters on EC process efficiency were optimized using response surface methodology (RSM). The main independent variables studied were the current density, EC time, concentration, and pH while the RB5 dye removal was studied as the dependent variable. The range of the studied parameters affecting the EC process ranged from 10 to 60 mA/cm2, 5 to 30 min, 4 to 10 pH and 10 to 40 ppm for current density, EC time, pH, and RB5 concentration, respectively. The optimal operating parameters turned out to be 5.5 pH, 47.5 mA/cm2, 23.75 min, 17.5 ppm, and the predicted RB5 dye removal was 96.33%. The experimental dye removal with optimum operating conditions was in good agreement with the predicted removal efficiency. Therefore, the experiment results revealed the high potential of the EC process to effectively treat textile industry effluents and the RB5 dye removal was successfully optimized using Response Surface Methodology (RSM).

Composite Activated Carbon Modified with AlCl3 for the Effective Removal of Reactive Black 5 Dye from Wastewaters

Many industries use huge amounts of synthetic dyes which may release into the wastewater in dyeing processes causing serious damage to aquatic life as they are recalcitrant, nonbiodegradable, stable to oxidizing agents, and toxic. Adsorption on activated carbon has been found to be a very efficient treatment method. In this work, a new adsorbent material composed of activated carbon and aluminum chloride (AC-Al) was prepared for the removal of a commercial anionic and anthraquinonic reactive dye, i.e., Reactive Black 5 (RB5) under various experimental conditions. Several parameters, such as the adsorbent’s dosage, initial RB5 concentration, pH, and contact time, were studied in order to determine the feasibility of AC-Al. According to the results, it was found that there was an increase in RB5 removal as the adsorbent’s dosage increased, especially, in pH 2 ± 0.1, where the removal rate increased, and reaching 100% by 1.0 g/L of AC-Al. Freundlich isotherm and pseudo-second-order kinetic models adequately fit the experimental data, indicating that favorable and heterogeneous adsorption occurred, closer to chemisorption. According to thermodynamics, it was found that the adsorption procedure was endothermic in nature (∆H0 = 62.621 kJ/mol) and spontaneous (∆G0 < 0), and according to the positive value of ∆S0 0.0293 (kJ/mol∙K), there is an increase in random interaction between solid and liquid interfaces. Finally, the AC-Al adsorbent was successfully regenerated and reused for four cycles.

Converting synthetic azo dye and real textile wastewater into clean energy by using synthesized CuO/C as photocathode in dual-photoelectrode photocatalytic fuel cell.

Cathode in photocatalytic fuel cell (PFC) plays a crucial role in degradation of organic contaminants. In this study, synthesized copper oxide (CuO) was loaded on carbon plate and used as photocathode in PFC for degradation of synthetic azo dye Reactive Black 5 (RB5) and real textile wastewater. Morphology and structural phase of the synthesized CuO were analyzed using scanning electron microscopy (SEM) and X-ray diffraction (XRD), respectively. Several operating parameters had been investigated such as light irradiation, initial dye concentration, and pH of azo dye solution within 6h of irradiation time. The lowest initial concentration of RB5 (10mg L-1) achieved 100% color removal compared to the highest initial concentration (40mg L-1) which only achieved 77.1% color removal within 6h of irradiation time. The influence of external resistance was significant in electricity generation but trivial in dye degradation efficiency. The external resistance of 6000 Ω yielded highest maximum power density, with Pmax of 0.2631μWcm-2, followed by 1000 Ω (0.2196μWcm-2) and 8000 Ω (0.1587μWcm-2), respectively. The real textile wastewater with dilution ratio (DR) 1:6 yielded the highest energy conversion efficiency, η (3.62%), followed by DR 1:4 (3.19%) and DR 1:2 (1.96%), respectively.

Synthesis of MMT−CuFe2O4 Composite as a Peroxymonosulfate Activator for the Degradation of Reactive Black 5

AbstractCopper ferrite nanoparticles loaded on montmorillonite (MMT−CuFe2O4) were prepared by co‐precipitation method and applied as catalyst for activation of peroxymonosulfate (PMS) in degradation of reactive black 5 (RB5). The maximum removal efficiency of RB5 completely depends on the operating parameters and the highest removal percentage was obtained at MMT−CuFe2O4 dosage of 250 mg/L, PMS concentration of 4 mM, initial RB5 concentration of 50 mg/L and time of 15 min. The presence of anions such as Cl−, NO3−, HCO3−, and SO42− showed a significant limitation in the degradation of RB5 in the MMT−CuFe2O4/PMS system. Trapping experiments showed that ⋅OH and SO4⋅− radicals were involved in the catalytic degradation of RB5, however ⋅OH is the major specie in the catalysis system. Consecutive cycles were considered for testing the reusability of MMT−CuFe2O4; its results showed the stability of five consecutive cycles. The toxicity test was evaluated using Daphnia magna and the results illustrated a substantial drop in the toxicity of the solution treated. The significant reduction of TOC during RB5 degradation and the production of SO42−, NH4+ and NO3− confirm the proper progress of pollutant mineralization. The high catalytic performance of the catalyst in a short time compared to other removal systems emphasizes that MMT−CuFe2O4 can be suggested as a promising catalyst for the degradation of RB5 from aqueous solutions.

Comparative Photocatalytic Activity and Total Organic Carbon Removal Efficiency of TiO2 And ZnO for Reactive Black 5 Photodegradation

AbstractThe photocatalytic performance of TiO2 and ZnO was comparatively studied for photocatalytic degradation of reactive black 5 (RB5) under artificial UVC irradiation. The effect of initial solution pH, catalyst concentration, initial RB5 concentration, purging oxygen rate, stirring rate, and process temperature on the degradation process by TiO2 and ZnO was investigated. In addition, total organic carbon (TOC) analysis has been employed for each parameter to detect the presence of organic intermediates and the photodegradation performance of catalysts simultaneously with the photocatalytic degradation process. The RB5 photodegradation was more rapid in the aqueous medium by TiO2 under UVC irradiation compared to the catalysis by ZnO. On the other hand, the slower photocatalysis by ZnO resulted in generating more organic intermediates. The structural and morphological analyses of photocatalysts TiO2 and ZnO were performed using XRD and FE‐SEM techniques. The UV‐vis spectroscopy measurements supported that the TiO2 demonstrated evidently better photocatalytic activity than ZnO for RB5 degradation.

Photocatalysis and adsorption kinetics of azo dyes by nanoparticles of nickel oxide and copper oxide and their nanocomposite in an aqueous medium.

Azo dyes are recalcitrant organic pollutants present in textile industry effluents. Conventional treatment methods to remove them come with a range of disadvantages. Nanoparticles and their nanocomposites offer more efficient, less expensive and easy to handle wastewater treatment alternative. In this study, nanoparticles of nickel oxide (NiO-NPs), copper oxide (CuO-NPs) and their nanocomposite (NiO/CuO-NC) were synthesized using co-precipitation method. The functional groups present on the surface of synthesized nanomaterials were verified using Fourier-transform infrared spectroscopy (FTIR). Surface morphology was assessed using scanning electron microscopy (SEM) whereas purity, shape and size of the crystallite were determined using X-ray diffraction (XRD) technique. The potential of these nanomaterials to degrade three dyes i.e., Reactive Red-2 (RR-2), Reactive Black-5 (RB-5) and Orange II sodium salt (OII) azo dyes, was determined in an aqueous medium under visible light (photocatalysis). The photodegradation effectiveness of all nanomaterials was evaluated under different factors like nanomaterial dose (0.02-0.1 g 10 mL-1), concentration of dyes (20-100 mg L-1), and irradiation time (60-120 min). They were also assessed for their potential to adsorb RR-2 and OII dyes. Results revealed that at optimum concentration (60 mgL-1) of RR-2, RB-5, and OII dyes, NiO-NPs degraded 90, 82 and 83%, CuO-NPs degraded 49, 34, and 44%, whereas the nanocomposite NiO/CuO-NC degraded 92, 93, and 96% of the said dyes respectively. The nanomaterials were categorized as the efficient degraders of the dyes in the order: NiO/CuO-NC > NiO-NPs > CuO-NPs. The highest degradation potential shown by the nanocomposite was attributed to its large surface area, small particles size, and quick reactions which were proved by advance analytical techniques. The equilibrium and kinetic adsorption of RR-2 and OII on NiO-NPs, CuO-NPs, and NiO/CuO-NC were well explained with Langmuir and Pseudo second order model, respectively (R2 ≥ 0.96). The maximum RR-2 adsorption (103 mg/g) was obtained with NiO/CuO-NC. It is concluded that nanocomposites are more efficient and promising for the dyes degradation from industrial wastewater as compared with dyes adsorption onto individual NPs. Thus, the nanocomposite NiO/CuO-NC can be an excellent candidate for photodegradation as well as the adsorption of the dyes in aqueous media.

Fabrication of metal-organic framework Universitetet i Oslo-66 (UiO-66) and brown-rot fungus Gloeophyllum trabeum biocomposite (UiO-66@GT) and its application for reactive black 5 decolorization

Many various industries use synthetic dyes as their raw materials. These dyes have triggered environmental problems because of the occurring effluents, and one of the environmentally safe solutions for this problem is biodegradation through microorganisms. Reactive Black 5 (RB5) dye degradation was performed by utilizing a metal-organic framework Universitetet i Oslo-66 (UiO-66) and Gloeophyllum trabeum (GT) fungus biocomposite. The UiO-66@GT composite was fabricated by inoculating the fungal culture in flasks with the PDB medium that contained UiO-66. This biocomposite was applied to decolorize and degrade RB5 dye, while pure GT culture can decolorize about 36.47% in five days. The percentage of RB5 decolorization was shown to be increased with the addition of UiO-66; the composite could decolorize RB5 up to 72.55% after five days incubation period. Moreover, the optimum conditions for the 100% targeted rate of RB5 decolorization found by the Response Surface Methodology (RSM) are: initial RB5 concentration (72.54 mg L -1 ), pH (6.53), and temperature (38.06 °C). Two novel metabolites from RB5 decolorization by the composite were detected based on LCMS-QTOF analysis and were used to propose a degradation pathway: 6-((1-amino-7,8-dihydroxy-6-sulfonaphthalen-2-yl) diazinyl) cyclohexa-2,4-dien-1-ide ( m / z = 360) and 3,4-diamino-5,6-dihydroxy-1,2,7,8-tetrahydronaphthalene-2,7-disulfonic acid ( m / z = 354).

Optimization of reactive black 5 decolorization by the newly isolated Saccharomyces cerevisiae X19G2 using response-surface methodology.

In the current investigation, the capacity of different yeast strains to decolorize reactive black 5 (RB-5) was assessed. A comparative study between the different strains demonstrated that Saccharomyces cerevisiae X19G2 exhibited the highest decolorization rate (69.20 ± 1.16%) after 48h of incubation. This strain was selected to optimize the medium components' concentrations for maximum RB-5 decolorization. Response-surface methodology (RSM) was tested for the most significant parameters (glucose, yeast extract and RB-5 dye concentrations) that were previously determined by Plackett-Burman design. A dye decolorization rate of 99.59 ± 0.24% was achieved within 48h using a maximum RB-5 concentration (0.15g/L) with glucose and yeast extract concentrations equalling to 10.5g/L and 1g/L, respectively. Experimental data results proved to fit well with the pseudo-second order kinetics model.The phytotoxicity assessment was carried out using Raphanus sativus seeds to determine the toxicity of RB-5 before and after treatment by S. cerevisiae. Results suggested that germination rate and the length of seeds radical irrigated with 0.15g/L of RB-5 decreased by 30 and 53%, compared to those irrigated with treated solution. Therefore, metabolites derived from decolorization of RB-5 by S. cerevisiae X19G2 were significantly less toxic than the original dye.

Reactive Black 5 Removal with Ozone on Lab-scale and Modeling

ABSTRACT This study investigates modeling the ozone removal of the Reactive Black 5 (RB5) dye from an aqueous solution using a combination of nonlinear regression (NLR), multiple linear regression (MLR), and Intrinsically multiple linear regression (IMLR) models. Lack of use and evaluation of the IMLR method in estimating RB5 removal by ozonation attract attention. Experimental data were used in the R Core Team software for the development of the models and estimate of RB5 removal by ozone. The effects of variables such as pH, contact time, initial dye concentration, and applied ozone dosage on RB5 removal by ozone were investigated. Maximum 92% RB5 removal rate was obtained at pH 8, 60 min contact time, 100 mg/L initial RB5 concentration, and applied ozone dosage of 66 mgO3/L. Under these conditions, the amount of specific ozone consumption was 0.678 gO3/gRB5. In order to compare the models, coefficient of determination (R2) and mean square error (MSE) were utilized as reliability and precision criteria. The best R2 and MSE values for the IMLR model were calculated as 0.8940 and 0.098, respectively. To determine the appropriate model and coefficients, analysis of variance (ANOVA), and t-test were used, respectively. Whether the model is within the confidence interval was determined by the significance value (p) and the variation was <5% for the IMLR model. As a result, it was found that the best method for modeling RB5 removal from aqueous solution by ozone was the IMLR method. Detailed explanations on results were introduced in the study.

Peroxymonosulfate enhanced photocatalytic degradation of Reactive Black 5 by ZnO-GAC: Key influencing factors, stability and response surface approach

• ZnO-GAC was used in the photocatalysis of RB5 with the presence of PMS. • Cooperative effects of UV, ZnO surf e − and GAC mediated by PMS were observed. • The mineralization and degradation pathway of RB5 were investigated. • Effect of reaction parameters was evaluated by response surface methodology. Zinc oxide supported on granular activated carbon (ZnO-GAC) was synthesized for the photocatalysis of Reactive Black 5 (RB5) with the presence of peroxymonosulfate (PMS). RB5 removal was improved with increasing temperature and dosage of PMS or catalyst, but declined with increasing pH and RB5 concentration. The reaction followed first-order kinetic model and the activation energy was determined to be 16.15 kJ mol −1 . After 60 min treatment, 43.6% of TOC was removed and further extending the reaction time to 90 min resulted in 51.9% TOC removal. The evolution profile of ammonium and nitrate ions was monitored during the treatment, and the organic degradation products of RB5 oxidation were identified by LC-MS analysis with a plausible degradation pathway being proposed. Quenching experiments indicated that electron hole (h + ) and reactive radicals (e.g. HO • /SO 4 •− ) were mainly responsible for RB5 removal in the UV/ZnO-GAC/PMS system. The catalyst reuse experiment shows that ZnO-GAC had no obvious deactivation after four cycles, which implied the reusability and stability of the prepared catalyst. Response surface methodology (RSM) with Box-Behnken design (BBD) was used to evaluate the effect of operating conditions, including PMS concentration, reaction temperature and initial pH on the removal rate of RB5. The result of adequacy check indicated the proposed RSM model was reliable and accurate to analyze the operating parameters of the UV/ZnO-GAC/PMS system.

Optimization of cotton dyeing with reactive dyestuff using multiobjective evolutionary algorithms

This work explores the optimization of the conditions for obtaining blue coloristic intensities (expressed by K/S values) in the cotton dyeing process with Reactive Black 5 (RB5), which involves two conflicting objectives: maximize the coloristic intensity and minimize the production cost. To this end, an approach that combines response surface methodology (RSM) and multiobjective evolutionary algorithms (MOEA) was developed. First, the RSM with a central composite rotatable design (RSM-CCRD) was applied for modeling the non-linear behavior of dyeing with RB5 considering the following process variables: temperature, NaCl, Na2CO3, NaOH, processing time, and RB5 concentration. The model was obtained by the least-squares method and validated through the analysis of variance (ANOVA). The determination coefficient achieved (R2 ​= ​0.945) indicates its good accuracy for making predictions. Then, we compared the results of a multiobjective genetic algorithm (MOGA) and a multiobjective particle swarm optimization (MOPSO) applied to obtain the optimized values for the process variables for obtaining maximum K/S values within predetermined ranges at the lowest production costs using the model produced by RSM-CCRD as objective function. According to the results obtained from the conducted simulations, both algorithms proved to be very useful computational tools to assist the dyeing process in the textile industry promoting economic and environmental benefits and being easy to adapt to other types of dyes or K/S ranges, although MOGA showed more consistent results.

Biotreatment of sulfonated dyestuffs with energy recovery in microbial fuel cell: Influencing parameters, kinetics, degradation pathways, mechanisms, and phytotoxicity assessment

Removal of recalcitrant sulfonated dyestuff intermediates from wastewater has been an urgent challenge for environmental technologies. In this regard, the biodegradations of monoazo Methyl Orange (MO) and diazo dyes Reactive Black 5 (RB5) towards wastewater treatment and bioelectricity generation in microbial fuel cell were investigated and compared through the studies on azo dye concentration, aeration, sampling points arrays, and electrode spacings. The degradation of diazo RB5 yielded higher chemical oxygen demand removal, decolourization efficiencies, and power generation over monoazo MO. The decolourization efficiency of RB5 (97.62%) increased with an increase of RB5 concentration (50 mg/L), suggesting that the system has the capability of removing higher RB5 concentration. However, contrary results were obtained with MO due to its toxicity. This study also demonstrated that the decolourization rate of diazo RB5 (0.1533 h−1) was ≈ 53% higher than monoazo MO (0.0727 h−1). The findings revealed that the degradation kinetic was remarkably influenced by the chemical structure of dye, where dye with more electron-withdrawing groups at para position are more susceptible to be reduced. Higher output voltage (568.59 mV) and power generation (108.87 mW/m2) were attained with RB5 due to electron donor availability and electron-shuttling characteristics of RB5 decolourized intermediates. Furthermore, detailed degradation pathways of MO and RB5 were presented based on the UV–vis and GC-MS results. The phytotoxicity assessment via Sorghum bicolor seeds had further verified the reduction in toxicity after the treatment of azo dyes.

Heterogeneous activation of peroxymonosulfate by GO-CoFe2O4 for degradation of reactive black 5 from aqueous solutions: Optimization, mechanism, degradation intermediates and toxicity

The magnetic cobalt ferrite (CoFe2O4) loaded on graphene oxide (GO) was synthesized by the co-precipitation method and used to activate peroxymonosulfate (PMS) in the degradation of the reactive black 5 (RB5). The response surface methodology (RSM) was used to optimize the laboratory parameters and the interaction between them. The maximum degradation efficiency with R2 > 99% was obtained at pH of 7, the GO-CoFe2O4 dose of 125 mg/L, the RB5 concentration of 50 mg/L, the PMS dose of 2.49 mM, and the reaction time of 3.49 min. Under optimal conditions, the degradation efficiency of the PMS/GO-CoFe2O4 process (100%) was much higher than that of GO (33%), GO-CoFe2O4 (43.12%), and PMS (14.05%) at 30 min. The RB5 degradation rate was improved with temperature, and the activation energy was calculated to be 12.47 kJ/mol. Nitrate and carbonate reduced the degradation efficiency of RB5 by reacting with the main radicals. The PMS/GO-CoFe2O4 system showed good performance for the treatment of raw water. However, it does require a longer treatment time for real wastewater. GO-CoFe2O4 showed excellent stability and reusability in five consecutive reaction cycles to remove chemical oxygen demand (COD) and total organic carbon (TOC). The proposed PMS activation mechanism based on scavenging experiments showed that SO4•- plays a dominant role in the RB5 degradation. The gas chromatography–mass spectrometry (GC–MS) analysis showed that RB5 was degraded through the pathways, including desulfonation, dechlorination, deamination, hydroxylation, dehydrogenation, and chain/ring cleavage. Toxicity tests were performed with Daphnia pulex, and the results showed that the treated effluent required more catalytic treatment and better stabilization due to the presence of cobalt ions and intermediates.

Adsorption of Reactive Black 5 Dye from Aqueous Solutions by Carbon Nanotubes and its Electrochemical Regeneration Process

: Removal of Reactive Black 5 (RB5) dye from aqueous solutions was investigated by adsorption onto Multi-walled Carbon Nanotubes (MWCNTs) and Single-walled Carbon Nanotubes (SWCNTs). A Taguchi orthogonal design including pH, initial RB5 concentration, contact time, and CNTs dose, was used in 16 experiments. The results showed that all four factors were statistically significant, and the optimum conditions for both adsorbents were as follows: pH of 3, adsorbent dose of 1000 mg/L, RB5 concentrations of 25 mg/L, and contact time of 60 min. An equilibrium study by Isotherm Fitting Tool (ISOFIT) software showed that Langmuir isotherm provided the best fit for RB5 adsorption by CNTs. The maximum predicted adsorption capacities for the dye were obtained as 231.84 and 829.20 mg/g by MWCNTs and SWCNTs, respectively. The results also indicated that the adsorption capacity of SWCNTs was about 1.21 folds higher than that of MWCNTs. Studies of electrochemical regeneration were conducted, and the results demonstrated that RB5-loaded MWCNTs and SWCNTs could be regenerated (86.5% and 77.3%, respectively) using the electrochemical process. Adsorbent regeneration was mostly due to the degradation of the dye by the attack of active species such as chlorate, H2O2, and, •OH, which were generated by the electrochemical oxidation process with Ti/RuO2-IrO2-TiO2 anodes. The results of Gas Chromatography-Mass Spectrometry (GC-MS) analysis showed that acetic acid, 3-chlorobenzenesulfonamide, and 1,2-benzenedicarboxylic acid were produced after adsorbent regeneration by the electrochemical process in the solution of regeneration. The adsorption and regeneration cycles showed that the electrochemical process with Ti/RuO2-IrO2-TiO2 and graphite is a good alternative method for the regeneration of CNTs and simultaneous degradation of the dye.

Utilisation of eco-friendly and low cost 3D graphene-based composite for treatment of aqueous Reactive Black 5 dye: Characterisation, adsorption mechanism and recyclability studies

The current research aimed to develop an eco-friendly three-dimensional (3D) graphene oxide/high molecular weight chitosan (GO/HCS) composite for the removal of Reactive Black 5 (RB5) dye. The adsorption performance of the 3D GO/HCS adsorbent was elucidated by varying the adsorbent dosage (1–50 mg), agitation speed (50–250 rpm), initial RB5 concentration (100–600 mg/L), pH (2–11), temperature (30–70 °C) and contact time (1–90 min). The equilibrium behaviour of the 3D GO/HCS adsorbent was best described by the Langmuir isotherm (SNE: 2.27 to 3.92), demonstrating a maximum adsorption capacity of 638.93 mg/g. The kinetic study showed a relatively fast RB5 dye adsorption by the as-synthesised 3D GO/HCS composite. The dye uptake by the composite was thermodynamically spontaneous (∆G: -39.15 to -17.90 kJ/mol) and endothermic (∆H: 5.60 to 31.64 kJ/mol). The adsorption mechanisms were assayed by pH test, Fourier transform infrared and X-ray photoelectron spectroscopy. The results substantiated that electrostatic attraction and π − π stacking were the prevailing uptake mechanisms. The 3D GO/HCS composite exhibited high structural stability and RB5 dye removal efficiencies within pH of 2–10. Furthermore, the exhausted 3D GO/HCS adsorbent was easily recovered from the liquid phase. The adsorbent was successfully applied in 5 cycles of adsorption-regeneration, preserving 90% of its adsorption capacity. The excellent adsorption and regeneration efficiencies inferred that the 3D GO/HCS macrostructure was highly efficient and recyclable for aqueous RB5 dye sequestration.

Green Synthesis of Kaolin-Supported Nanoscale Zero-Valent Iron Using Ruellia tuberosa Leaf Extract for Effective Decolorization of Azo Dye Reactive Black 5

Kaolin-supported nanoscale zero-valent iron (K-NZVI) was synthesized via a green synthesis method, in which leaf extract of Ruellia tuberosa was used as a reducing agent. The synthesized K-NZVI was used for decolorization of Reactive Black 5 (RB5), an azo dye widely used in textile industry. The XRD patterns of the K-NZVI particles show the characteristic peaks of Fe0, indicating that Fe0 nanoparticles (NZVI) were successfully synthesized on the kaolin surface. The SEM, TEM images and EDS elemental mapping show that the NZVI particles are well dispersed on the kaolin surface, thus, reducing the extent of NZVI aggregation. Batch experiments for decolorization of RB5 were carried out to investigate the effects of process parameters including solution pH, initial dye concentration and contact time. The results show that high decolorization efficiencies are obtained in acidic pH. Increasing initial dye concentration causes the decolorization efficiency to decrease, whereas increasing contact time results in higher efficiency. Furthermore, after five cycles of reuse of K-NZVI, the decolorization efficiency slightly decreases, indicating high reusability and stability of K-NZVI. The disappearance of the characteristic peaks of RB5 solution recorded by a UV–Vis spectrophotometer indicates cleavage of the azo bonds and, thus, the decomposition of RB5 in the solution. From a kinetic analysis performed at various RB5 concentrations, the decolorization process of RB5 by K-NZVI is well fit by the pseudo-first-order kinetic model.

LDH of NiZnFe and its composites with carbon nanotubes and data-palm biochar with efficient adsorption capacity for RB5 dye from aqueous solutions: Isotherm, kinetic, and thermodynamics studies

In the study, the layered double hydroxide (LDH) of NiZnFe and its composites with date-palm biochar (LDH-DPb) and carbon nanotubes (LDH-cnt) were synthesized for adsorbing reactive black 5 (RB5) dye from aqueous solutions. In the first 5 min, rapid adsorption was followed by a gradual increase in both dye uptake and removal efficiency of up to 60 min of starting time. In the investigated pH range (3.0–8.0), the removal efficiency linearly decreased while the sorption capacity linearly increased for all three adsorbents as their doses increased to 0.3 or 0.4 g following a decreasing trend up to 0.6 g. By increasing the initial RB5 concentration from 10 to 100 mg L−1, the removal efficiency linearly decreased. A nearly perfect fitting of the pseudo-second-order kinetic model to the adsorption data was observed; however, the Elovich kinetic model showed the heterogeneous surface of adsorbents with chemisorption. At the solid–liquid interface, from a thermodynamics point of view, we obtained the nonspontaneous nature of the adsorption of RB5 dye of the studied adsorbents with an increased disorder, which supported the endothermic nature onto the studied adsorption process. Furthermore, a nearly perfect fitting of the Langmuir model was obtained to the adsorption data, thereby suggesting the monolayer adsorption of RB5 dye onto the studied adsorbents. In the Dubinin–Radushkevich model, a good agreement of the calculated adsorption capacities to the experimental values were observed and the chemical adsorption of RB5 dye on to the studied adsorbents was proposed based on E (8 – 16 kJ mol−1).