Adsorption behavior of Direct Red 12B and Rhodamine B from water onto surfactant-modified coconut coir pith

Adsorbents for water decontamination: A recycling alternative for fiber precursors and textile fiber wastes

The exponential growth in textile fiber production and commensurate release of textile waste-based effluents into the environment has significant impacts on human wellbeing and the long-term planetary health. To abate these negative impacts and promote resource circularity, efforts are being made to recycle these waste materials via conversion into adsorbents for water decontamination. This review critically examines plant- and regenerated cellulose-based fibers for removing water pollutants such as heavy metals, dyes, pharmaceutical and petrochemical wastes. The review reveals that chemical modification reactions such as grafting, sulfonation, carboxymethylation, amination, amidoximation, xanthation, carbon activation, and surface coating are normally employed, and the adsorption mechanisms often involve Van der Waals attraction, electrostatic interaction, complexation, chelation, ion exchange, and precipitation. Furthermore, the adsorption processes and thus the adsorption mechanisms are influenced by factors such as surface properties of adsorbents, pollutant characteristics including composition, porosity/pore size distribution, specific surface area, hydrophobicity/hydrophobicity, and molecular interactions. Besides, feasibility of the approaches in terms of handling and reuse, environmental fate, and economic impact was evaluated, in addition to the performances of the adsorbents, the prospects, and challenges. As current cost analysis is non-exhaustive, it is recommended that researchers focus on extensive cost analysis to fully appreciate the true cost effectiveness of employing these waste materials. In addition, more attention must be paid to potential chemical leaching, post-adsorption handling, and disposal. Based on the review, fiber precursors and textile fiber wastes are viable alternative adsorbents for sustainable water treatment and environmental management, and government entities must leverage on these locally accessible materials to promote recyclability and circularity.

Phytoremediative adsorption methodologies to decontaminate water from dyes and organic pollutants

Persistent organic pollutants and dyes cause major problems during ecofriendly wastewater treatment. To overcome this huge problem, several techniques have been considered and in practice for the safe disposal of organic pollutants in recent years; some of them are discussed and compared herein. This review focuses on new trends for wastewater treatment and compares them with certain other techniques alongside their pros and cons; adsorption is considered the safest among them. Adsorbents derived from agri-wastes have good capacity for the removal of these contaminants owing to their great sorption capacity, high reusability, easy operation, etc. Sometimes they need some modifications for the removal of dyes, which are also discussed in this review. This capacity of adsorbents to chelate dye molecules can be affected by factors, such as pH, the concentration of dyes and adsorbents, and temperature of the system. pH has direct influence on the ionization potential and charge on the outer surface of adsorbents. The findings on isotherms, kinetics, and desorption of plant waste-based biomaterials that are safe for the ecosystem and user friendly and are used for hazardous contaminant removal from water are summarized in this review. Finally, conclusions and future perspectives are presented, and some other materials, such as CNTs and MOFs, are also discussed as efficient adsorbents for eliminating dyes from wastewater. Finally, it is predicted that the adsorption of dyes is a more feasible solution for this dye pollution problem.

A comprehensive review of coconut-based porous materials for wastewater treatment and CO2 capture

For several decades, water pollution has become a major threat to aquatic and non-aquatic species, including humans. Different treatment techniques have already been proposed and implemented depending on wastewater characteristics. But many of these treatment techniques are expensive and inefficient. Adsorption-based techniques have shown impressive performances as an inexpensive treatment method previously. Coconut-based resources have been considered as adsorbents for wastewater treatment because of their abundance, low cost, and favorable surface properties. However, over the last decade, no comprehensive study has been published regarding biochar from coconut-based materials for wastewater treatment and CO2 capture. This review discusses biochar production technology for coconut-based materials, its modification and characterization, its utilization as an adsorbent for removing metals and organics from wastewater, and the associated removal mechanisms and the economic aspects of coconut-based biochar. Coconut-based materials are cheap and effective for removing various organic compounds such as pesticides, hormones, phenol, and phenolic compounds from solutions and capturing CO2 from air mainly through the pore-filling mechanism. Utilizing coconut-based biochars in a hybrid system that combines adsorption and other techniques, such as biotechnology or chemical coagulation is a promising way to increase their performance as an adsorbent in wastewater treatment.

Copolymer-MnO2 nanocomposites for the adsorptive removal of organic pollutants from water

The copolymer beads prepared by suspension polymerisation were decorated with MnO₂ nanoparticles and successfully implemented for the efficient removal of toxic organic contaminants from water. Copolymer-MnO₂ nanocomposite was further analysed using XRD, SEM and optical microscope. The SEM images showed the surface characteristics of MnO₂ nanoparticles on copolymer beads. The efficiency of the copolymer-MnO₂ nanocomposite for the removal of model pollutant methylene blue and rhodamine B is then analysed by changing the concentration of pollutant. The results obtained exhibited 18.45 mg/g for methylene blue adsorption and 3.125 mg/g for rhodamine B. The adsorption equilibrium results were fitted to Langmuir adsorption isotherm for both methylene blue and rhodamine B adsorption. The desorption studies were performed for five consecutive cycles, and material was showing good regenerating capacity towards both organic pollutants. The obtained results show that copolymer-MnO₂ nanocomposite is an efficient material for the removal of organic contaminants from wastewater.

The Use of Chitin from the Molts of Mealworm (Tenebrio molitor) for the Removal of Anionic and Cationic Dyes from Aqueous Solutions

The possibility of using chitin from the molts of an insect-ealworm (Tenebrio molitor) to remove anionic (RB5, RY84) and cationic dyes (BV10, BR46) from aqueous solutions was investigated. The scope of the research included, among others: Characteristics of chitin from mealworms (FTIR, SEM, pH_PZC), the effect of pH on sorption efficiency, sorption kinetics (pseudo-first, pseudo-second order, intramolecular diffusion models) and the determination of the maximum sorption capacity (Langmuir and Freundlich models). The sorption efficiency of anionic dyes on chitin from mealworm was the highest at pH 2-3, and for cationic dyes at pH 6. The equilibrium time of sorption of anionic dyes was 240-300 min and for cationic dyes it was 180-240 min. The experimental data on dye sorption kinetics was best described by the pseudo-second order model. The maximum sorption capacity of chitin from the mealworm for the anionic dyes RB5 and RY84 was 121.15 mg/g and 138.55 mg/g, respectively, and was higher than with some carbon-based materials (literature data). In the case of cationic dyes, the sorption capacity of the tested chitin was lower and reached 3.22 mg/g and 59.56 mg/g for BV10 and BR46, respectively.

Rational construction and understanding the effect of metal cation substitution of three novel ternary Zn-Co-Ni-LDHs from 2D to 3D and its enhanced adsorption properties for MO

The layered double hydroxides (LDHs) have attracted attention in the water treatment field. In this paper, three novel ternary Zn-Co-Ni-LDH adsorbents were prepared successfully through rational construction from 2D to 3D using triethanolamine (TEA) as an alkali source and a structural controlling reagent by hydrothermal technique. Samples were characterized by the SEM, XRD, XPS, FTIR, BET, solid-state UV/vis spectra, and TG. Three Zn-Co-Ni-LDHs exhibited higher crystallinity and surface area which were beneficial to the adsorption for methyl orange (MO). The maximum adsorption capacity of three Zn-Co-Ni-LDH adsorbents can even reach as high as 1871.65 mg·g^-1, 1799.56 mg·g^-1, and 1646.44 mg·g^-1 for MO, respectively, which surpass those of most previously reported LDH-based adsorbents. The pseudo-second-order kinetic equation fitted the kinetic data of adsorption, while the equilibrium adsorption isotherm data followed the Langmuir model. The adsorption mechanism, electrochemical, and the antibacterial properties of three Zn-Co-Ni-LDHs were also discussed. This results not only demonstrates that three Zn-Co-Ni-LDHs are practical interest as an efficient adsorbent for the removal of MO from dye waste water, but also provides a strategy for the rational design through three ternary Zn-Co-Ni-LDHs from 2D to 3D.

Elucidating the adsorption mechanism of Rhodamine B on mesoporous coconut coir-based biosorbents through a non-linear modeling and recycling approach

The search for renewable adsorbent materials has increased continuously, being the agro-wastes an interesting alternative. This work aimed to elucidate the mechanism of adsorption of Rhodamine B on crude and modified coconut fibers from aqueous systems and the feasibility of reusing the biosorbents. The chemical modification of crude coconut fiber was carried out by the organosolv process. The biosorbents were characterized by lignocellulosic composition, FTIR, TGA, WCA, SEM, nitrogen adsorption/desorption (BET-BJH), and pH of zero point of charge (pH_PZC) analyses_. The batch adsorption tests evaluated the effects of the adsorbent and adsorbate dosages, contact time, and temperature on Rhodamine B adsorption. For elucidating the adsorption mechanisms involved in the process, the non-linear forms of kinetic and isotherm models were used. The regeneration of the biosorbents was evaluated by carrying out the desorption experiments. Modified coconut fiber had an increase in the amount of α-cellulose, which influenced its structural, morphological, surface, and porous properties. The removal efficiency of Rhodamine B was about 90% for modified coconut fiber and 36% for crude coconut fiber. The dye adsorption was spontaneous and endothermic for both biosorbents, showing higher spontaneity and affinity with the adsorbate for biosorbent modified. Therefore, the coconut fiber can be considered an alternative to the traditional adsorbent materials that allows the reuse by four times without performance loss, in which its adsorptive capacity has increased through its chemical modification by a biorefinery process.

Unraveling the adsorption mechanism of methylene blue onto selective pH precipitated Kraft lignins: Kinetic, equilibrium and thermodynamic aspects

Lignin has been used on its crude or modified forms for adsorption purposes. This work evaluated the influence of selective pH precipitation of Kraft lignins (KLs) on their adsorptive performance for removing methylene blue (MB). The alkaline and acid KLs (KL A and KLB, respectively) were characterized by FTIR, ³¹P NMR, GPC and pH_PZC analyses. The effects of biosorbent and adsorbate concentrations, pH, ionic strength, contact time and temperature on the MB adsorption were evaluated. The equilibrium, kinetic and thermodynamic parameters were calculated by Langmuir and Freundlich isotherms, pseudo-first and second order and Van't Hoff and Gibbs models, respectively. KL A and KL B presented peculiar structural features, mainly hydroxyls concentration and M_w values, which have influenced on the removal efficiency of MB and the adsorptive capacities of KL A (>80 %; ≥80 mg g^-1) and KL B (>90 %; ≥20 mg g^-1), respectively. The equilibrium, kinetic and thermodynamic parameters have shown that MB adsorption presented different mechanisms for each KL, but it only has driven by chemisorption for KL B. Therefore, KL A and KL B can be considered as potential novel biosorbents obtained through a clean, fast and simple route for textile wastewater treatment.

Theoretical, Equilibrium, Kinetics and Thermodynamic Investigations of Methylene Blue Adsorption onto Lignite Coal

The interaction of methylene blue (MB) dye with natural coal (collected from coal landfills of the Kosovo Energy Corporation) in aqueous solutions was studied using adsorption, kinetics, and thermodynamic data, and Monte Carlo (MC) calculations. In a batch procedure, the effects of contact duration, initial MB concentration, pH, and solution temperature on the adsorption process were examined. The Langmuir, Freundlich, Temkin, and Dubinin–Radushkevich (D–R) isotherms were used to examine the equilibrium adsorption data. The equilibrium data fit well to the Freundlich and Langmuir adsorption isotherm models; however, the Freundlich model suited the adsorption data to a slightly better extent than the Langmuir model. The kinetics experimental data was fitted using pseudo-first-order, first-order, pseudo-second-order, second-order, Elvoich equation, and diffusion models. The pseudo-second-order rate model manifested a superlative fit to the experimental data, while the adsorption of MB onto coal is regulated by both liquid film and intraparticle diffusions at the same time. Thermodynamic parameters, such as Gibbs free energy (ΔG0), enthalpy (ΔH0), and entropy (ΔS0) were calculated. The adsorption of MB was confirmed to be spontaneous and endothermic. The theoretical results were in agreement with the experimental ones.

Trapping Rhodamine B dye using functionalized mango (Mangifera indica) pod

The use of acid-modified mango pod (AMMP) sorbent for removing Rhodamine B (Rh-B) dye from aqueous media was investigated. Raw mango pod (RMP) and AMMP sorbents were characterized using scanning electron microscopy (SEM), energy dispersive X-ray (EDX), powdered X-ray diffractogram (PXRD), Fourier transform infrared (FTIR), point of zero charge pH (pH_pzc ), and Boehm titration (BT) techniques. Batch adsorption was employed to examine the influence of operational factors. Sorption kinetic parameters were calculated using pseudo-first-order, pseudo-second-order, Elovich, and intraparticle diffusion models. The pseudo-second-order model best fitted the adsorption kinetic data most with maximum correlation coefficient (R²  > 0.99). The process of the adsorption was controlled by both boundary layer and intraparticle diffusion mechanisms. Four isotherm models (Langmuir, Freundlich, Dubinin-Radushkevich, and Temkin) were utilized to analyze the equilibrium data at various temperatures. Freundlich model gave the best fit with the maximum regression (0.99), while the Langmuir isotherm model established a maximum monolayer adsorption capacity of 500 mg g^-1 . Thermodynamic parameters studied revealed that the interaction is spontaneous and endothermic in nature. The cost analysis of the current study provides convincing proof that AMMP is efficient for removing Rh-B dye from solution by providing a saving of 225.2 USD/kg, which is eight times cheaper than commercial activated carbon. Consequently, the study revealed that AMMP is a viable, effective, and sustainable sorbent for Rhodamine B dye removal. PRACTITIONER POINTS: The powdered X-ray diffractogram (PXRD) showed the formation of new and intense peaks with the presence of highly organized crystalline structures on acid-modified mango pod (AMMP). Surface morphology of AMMP showed well-developed open surface pores required for effective adsorption of Rh B dye molecules. Economic feasibility of the present study showed that AMMP is more affordable than commercial activated carbon that costs USD 259.5/kg, thus translated to a saving cost of USD 225.2/kg and more than 7.5 times cheaper than the commercial activated carbon (CAC).

Efficient Adsorption of Anionic Dyes by Ammoniated Waste Polyacrylonitrile Fiber: Mechanism and Practicability

Adsorption is one of the commonly used methods in wastewater treatment, but it has the problem of high cost and a complicated production process. In this paper, a low-cost and efficient decolorizing adsorbent was successfully prepared based on waste polyacrylonitrile fiber (PANF). The waste PANF was ammoniated by propylene diamine derivates (PANAMF), and benzylamine (PANABMF) and quaternary ammonium ions (PANQMF) were introduced for PANAMF to regulate hydrophilicity and hydrophobicity. With acidic red 249 as the model anionic dye, influences of the adsorption center structure, the degree of modification, the concentration of acid, the dye structure, and the auxiliary agent in the solution on the dye adsorption performance were studied. Isothermal models, kinetic models, reusability, and continuous application ability of the fiber adsorbent were discussed. PANAMF, PANABMF, and PANAQF exhibit excellent adsorption performance compared to the common adsorbent. After protonation, the saturation adsorption value can reach 2051.3 mg/g for PANAMF. PANAMF also exhibited excellent reusability, and the adsorption capacity after being reused eight times still can keep 72.7% of that for the first time. The adsorption of the anionic dye for PANAMF is a chemisorption process, and the rate-determining step is changed from the diffuse step to the adsorption on the surface with the adsorption time. PANAMF can also be used in the continuous flow process, and the absorption amount is similar to that in the batch adsorption, which shows excellent commercial application potential.

Adsorptive removal of Rhodamine B dye from aqueous solution by using graphene-based nickel nanocomposite

In this work, reduced graphene oxide-nickel (RGO–Ni) nanocomposite is synthesized. X-ray diffraction (XRD), scanning electron microscopy (SEM) and SEM–EDS (Energy Dispersive X-Ray Spectroscopy) are used to study the crystalline nature, morphology and elemental composition of the RGO–Ni nanocomposite, respectively. As synthesized RGO–Ni nanocomposite is used to develop selective adsorptive removal of Rhodamine B (RhB) dye from the aqueous solution. The experiments have been performed to investigate RhB uptake via RGO–Ni nanocomposites which include, contact time (60 min), initial dye concentration (50 mg/100 ml), adsorbent dosage (0.5 mg) and pH 8 of dye solution. The equilibrium concentration is determined by using different models namely, Freundlich, Langmuir and Tempkin. Langmuir isotherm has been fitted well. Langmuir and Tempkin equations are determined to have good agreement with the correlation coefficient data. The kinetic study concluded that RhB dye adsorption follows with the pseudo-second-order kinetic model. Further, adsorption mechanism of RGO–Ni is proposed which involves three steps. The synthesized adsorbent is compared with the other adsorbents in the literature and indicates that RGO–Ni nanocomposite used in this study shown better results for a particular adsorption capacity than polymeric, natural and synthetic bioadsorbents. The regeneration and reusability experiments suggest RGO–Ni nanocomposite can be used for many numbers of times for purification/adsorption.

The use of spent coffee grounds and spent green tea leaves for the removal of cationic dyes from aqueous solutions

This study aimed to examine sorption effectiveness of cationic dyes: Basic Red 46 (BR46) and Basic Violet 10 (BV10) onto spent coffee ground (CG) and spent green tea leaves (GTL). The scope of the study included, i.a.: sorbent FTIR spectra analysis, determination of pH effect on dye sorption effectiveness, analysis of dye sorption kinetics, and determination of maximal sorption capacity of the sorbents. The effectiveness of BR46 sorption on the sorbents tested was the highest at pH 6 and that of BV10 at pH 3. Both sorbents caused changes in solution pH during the sorption process, due to the system tending to reach the pH value approximating the pH_ZPC (pH_PZC = 7.55 for CG and pH_PZC = 7.05 for GTL). The time needed to reach BR46 and BV10 sorption equilibrium onto CG and GTL ranged from 180 to 240 min. The intramolecular diffusion model demonstrated that the sorption of cationic dyes onto CG and GTL proceeded in three phases differing in the intensity and duration. The maximal sorption capacity of CG reached 179.4 mg/g for BR46 and 59.3 mg/g for BV10. The sorption capacity of GTL was lower and reached 58.0 mg/g for BR46 and 26.7 mg/g for BV10.

Coconut Shell Activated Carbon/CoFe2O4 Composite for the Removal of Rhodamine B from Aqueous Solution

Coconut shell activated carbon loaded with cobalt ferrite (CoFe2O4) composites (CAC/CoFe2O4) was synthesized via the single-step refluxing router method to manufacture adsorbents. The adsorbents were then applied to remove Rhodamine B (RhB) from aqueous environments via adsorption. The properties of coconut shell activated carbon (CAC) and CAC/CoFe2O4 were investigated through the usage of electron microscopic methods (SEM: Scanning Electron Microscopy, EDS: Energy Dispersive X-ray), powder X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR). A series of batch experiments were implemented to evaluate the influences of various experimental parameters (initial pH, RhB concentration, contact time, and dosage of CAC/CoFe2O4) on the adsorption process. It was found that CoFe2O4 was successfully attached to activated carbon particles and had the suitable adsorption capacity for RhB at a molar ratio of 1 : 2:200 corresponding to the Co : Fe:CAC order. The removal efficiency and adsorption of RhB were optimal at a pH level of 4. The maximum adsorption capacity was 94.08 mg/g at an initial concentration of 350 mg/L and adsorbent dosage of 0.05 g/25 mL. Freundlich and Langmuir's models fitted well with the results obtained from the experimental data. The pseudo-second-order model also suited the most for RhB adsorption with the most remarkable correlation coefficient (R2 = 0.934). The adsorption process was controlled by a chemisorption mechanism through electrostatic attraction, hydrogen bonding interactions, and π-π interactions.

Discarded biodiesel waste-derived lignocellulosic biomass as effective biosorbent for removal of sulfamethoxazole drug

This work aims to evaluate the removal of pharmaceutical drug using discarded biodiesel waste-derived lignocellulosic-based activated carbon biomaterial. Lignocellulosic-based activated carbon (LAC) biomaterial was prepared from Jatropha shell (biodiesel processing waste) by a zinc chloride activation method. The LAC biomaterial was characterized using various techniques including powder XRD, FT-IR, SEM-EDAX, and BET analysis. LAC biomaterial was applied to examine the adsorption of sulfamethoxazole (SMZ) drug in aqueous solution under ambient temperature. Various experimental parameters such as the effect of pH, treatment time, adsorbate concentration, and LAC dose of adsorption experiments were thoroughly examined and optimized. Under the optimal conditions, LAC biomaterial showed the maximum adsorption removal efficiency of SMZ drug. The kinetic models of Lagergren first-order, pseudo-second-order, intraparticle diffusion, and Bhangam's equation for SMZ removal onto LAC were used to recognize the probable mechanism of adsorption manner. From the experimental results, the Freundlich isotherm model (K_f = 83.56 mg g^-1 (L mg^-1)^1/n) shows similar fit than the Langmuir (Q₀ = 206.2 mg g^-1) and Dubinin-Radushkevich (Q_m = 150.69 mg g^-1) condition models of adsorption isotherms. The rate constants of adsorption were found to confirm the pseudo-first-order kinetic and Bhangam's models with a significant correlation. The separation factor (R_L) showed the favorable condition of the adsorption isotherm for the experimental system. The desorption results indicate that the ionic molecular exchange of SMZ from the hydroxyl group of LAC surface plays an important role in the recycling processes. Therefore, these results proved that the prepared low-cost LAC biomaterial could be used as an efficient adsorption material for the effective removal of pharmaceutical drugs in aqueous samples.

Synergistic modification of bentonite by acid activation and hydroxyl iron pillaring for enhanced dye adsorption capacity

Despite the fact of natural abundance, low cost and environmental friendliness, the far-from-sufficient adsorption capacity of natural bentonite (BT) has limited such a promising application to remove dye pollutants. In this paper, we proposed a facile modification strategy to enhance adsorption performance of bentonite utilizing synergistic acid activation and hydroxyl iron pillaring, by which the adsorbent (abbreviated as S-Fe-BT) exhibited the highest adsorption capacity (246.06 mg/g) and a high rapid adsorption rate for a typical organic dye, Rhodamine B (RhB). This could be ascribed to the increased interlayer spacing, the increased specific surface area, and the optimized OH/Fe ratio after the synthetic modification of the pristine BT. The adsorption behavior of RhB onto S-Fe-BT was well described by the pseudo-second-order kinetic model, indicating a chemical-adsorption-controlled process. Furthermore, its adsorption isotherm matched well with the Langmuir model due to a monolayer adsorption process. This paper opens a promising direction to remove the dye pollution using low cost bentonite adsorbents treated by such a convenient modification strategy.

Kinetics, Isotherms and Thermodynamic Modeling of Liquid Phase Adsorption of Crystal Violet Dye onto Shrimp-Waste in Its Raw, Pyrolyzed Material and Activated Charcoals

Shrimp waste and its charcoal derivatives were evaluated for the removal of crystal violet. Activation was conducted at 500 °C with phosphoric acid at the 1:2 and 1:3 ratios. Activated charcoals were more porous and had a more roughly surface containing mainly C, O, Ca N, and P. Equilibrium adsorption data were fitted using seven kinetic and six isotherms models. Activation created acidic moieties (>4700 µmol/g) and reduced the point of zero charge (<2.5). Freundlich isotherm best described the uptake of the dye onto the adsorbents suggesting a heterogeneous adsorption, whereas the Bangham and Avrami models best described the kinetics of adsorption process. An endothermic and spontaneous physisorption was responsible for the sorption phenomena in most adsorbents. The high removal of crystal violet was attributed to the high ionization capacity of the adsorbent coupled with the high external surface area (>44 m2/g). The best adsorption capacity (208 mg/g) was found for the activated and charred materials, whereas the lowest one (3.9 mg/g) was found for the pyrolyzed material. This research creates the possibility to deal with two environmental problems: (i) the reuse of shrimp waste and (ii) the removal of water pollutants such as crystal violet.

Synthesis, Characterization, and Modification of Alumina Nanoparticles for Cationic Dye Removal

In the present study, alumina nanoparticles (nano-alumina) which were successfully fabricated by solvothermal method, were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), Transmission Electron Microscopy (TEM), and Brunauer⁻Emmett⁻Teller (BET) methods. The removal of cationic dye, Rhodamine B (RhB), through adsorption method using synthesized nano-alumina with surface modification by anionic surfactant was also investigated. An anionic surfactant, sodium dodecyl sulfate (SDS) was used to modify nano-alumina surface at low pH and high ionic strength increased the removal efficiency of RhB significantly. The optimum adsorption conditions of contact time, pH, and adsorbent dosage for RhB removal using SDS modified nano-alumina (SMNA) were found to be 120 min, pH 4, and 5 mg/mL respectively. The RhB removal using SMNA reached a very high removal efficiency of 100%. After four times regeneration of adsorbent, the removal efficiency of RhB using SMNA was still higher than 86%. Adsorption isotherms of RhB onto SMNA at different salt concentrations were fitted well by a two-step model. A very high adsorption capacity of RhB onto SMNA of 165 mg/g was achieved. Adsorption mechanisms of RhB onto SMNA were discussed on the basis of the changes in surface modifications, the change in surface charges and adsorption isotherms.

Coconut endocarp and mesocarp as both biosorbents of dissolved hydrocarbons in fuel spills and as a power source when exhausted

Health and environmental problems associated with the presence of toxic aromatic compounds in water from oil spills have motivated research to develop effective and economically viable strategies to remove these pollutants. In this work, coconut shell (endocarp), coconut fiber (mesocarp) and coconut shell with fiber (endocarp and mesocarp) obtained from coconut (Cocos nucifera) waste were evaluated as biosorbents of benzene, toluene and naphthalene from water, considering the effect of the solution pH (6-9) and the presence of dissolved organic matter (DOM) in natural water (14 mg/L). In addition, the heat capacity of saturated biosorbents was determined to evaluate their potential as an alternative power source to conventional fossil fuels. Tests of N₂ physisorption, SEM, elemental and fiber analysis, ATR-FTIR and acid-based titrations were performed in order to understand the materials' characteristics, and to elucidate the biosorbents' hydrocarbon adsorption mechanism. Coconut fiber showed the highest adsorption capacities (222, 96 and 5.85 mg/g for benzene, toluene and naphthalene, respectively), which was attributed to its morphologic characteristics and to its high concentration of phenolic groups, associated with the lignin structure. The pH of the solution did not have a significant influence on the removal of the contaminants, and the presence of DOM improved the adsorption capacities of aromatic hydrocarbons. The adsorption studies showed biphasic isotherms, which highlighted the strong affinity between the molecules adsorbed on the biosorbents and the aromatic compounds remaining in the solution. Finally, combustion heat analysis of coconut waste saturated with soluble hydrocarbons showed that the heat capacity increased from 4407.79 cal/g to 5064.43 ± 11.6 cal/g, which is comparable with that of woody biomass (3400-4000 cal/g): this waste biomass with added value could be a promising biofuel.

Removal of Hexavalent Chromium by Adsorption on Microwave Assisted Activated Carbon Prepared from Stems of Leucas Aspera

This study reports adsorption of Cr(VI) ions from aqueous solution using activated carbon that was prepared from stems of Leucas aspera. Eight hundred and fifty watts power of microwave radiation, 12 min of radiation time, 60% of ZnCl2 solution and 24 h of impregnation time are the optimal parameters to prepare efficient carbon effective activated carbon. It was designated as MWLAC (Microwave assisted Zinc chloride activated Leucas aspera carbon). Various adsorption characteristics such as dose of the adsorbent, agitation time, initial Cr(VI) ion concentration, pH of the solution and temperature on adsorption were studied for removal of Cr(VI) ions from aqueous solution by batch mode. Also the equilibrium adsorption was analyzed by the Langmuir, Freundlich, Tempkin and D-R isotherm models. The order of best describing isotherms was given based on R2 value. The pseudo-second-order kinetic model best fitted with the Cr(VI) adsorption data. Thermodynamic parameters were also determined and results suggest that the adsorption process is a spontaneous, endothermic and proceeded with increased randomness.

Adsorption of Turquoise Blue Dye from Aqueous Solution using Microwave Assisted Zinc Chloride Activated Carbon Prepared from Delonix Regia Pods

Adsorption interaction of Turquoise blue dye onto microwave assisted zinc chloride activated carbon from aqueous solution was investigated. Activated carbons were prepared from pods of Delonix regia. Carbon prepared was designated as MWZAC (Microwave assisted Zinc chloride Activated Carbon). The characteristics of the MWZAC were determined by BET analysis, XRD, FTIR and pHZPC. Batch mode adsorption experiments were carried out. Influence of the parameters such as Dose of the adsorbent, agitation time, initial dye concentration, pH of the solution and temperature on adsorption were studied. Kinetics of the system was studied with linearised forms of Lagergren, Ho and Webber Morris models. Equilibrium data were fitted with Langmuir, Freundlich, Tempkin and Dubinin-Raduskevich isotherms. The order of best describing isotherms was given based on R2 value. Thermodynamic parameters such as ΔH°, ΔS° and ΔG° were determined using Vant Hoff plots. The exhausted MWZAC was regenerated by desorption processes using 0.2 M HCl, 0.2 M NaOH and distilled water.

Micelles as Soil and Water Decontamination Agents

Contaminated soil and water pose a serious threat to human health and ecosystem. For the treatment of industrial effluents or minimizing their detrimental effects, preventive and remedial approaches must be adopted prior to the occurrence of any severe environmental, health, or safety hazard. Conventional treatment methods of wastewater are insufficient, complicated, and expensive. Therefore, a method that could use environmentally friendly surfactants for the simultaneous removal of both organic and inorganic contaminants from wastewater is deemed a smart approach. Surfactants containing potential donor ligands can coordinate with metal ions, and thus such compounds can be used for the removal of toxic metals and organometallic compounds from aqueous systems. Surfactants form host-guest complexes with the hydrophobic contaminants of water and soil by a mechanism involving the encapsulation of hydrophobes into the self-assembled aggregates (micelles) of surfactants. However, because undefined amounts of surfactants may be released into the aqueous systems, attention must be paid to their own environmental risks as well. Moreover, surfactant remediation methods must be carefully analyzed in the laboratory before field implementation. The use of biosurfactants is the best choice for the removal of water toxins as such surfactants are associated with the characteristics of biodegradability, versatility, recovery, and reuse. This Review is focused on the currently employed surfactant-based soil and wastewater treatment technologies owing to their critical role in the implementation of certain solutions for controlling pollution level, which is necessary to protect human health and ensure the quality standard of the aquatic environment.

Removal of Reactive Orange 16 Dye from Aqueous Solution by Using Modified Kenaf Core Fiber

Evaluated removal of reactive orange 16 (RO16) dye from aqueous solution was studied in batch mode by using kenaf core fiber as low-cost adsorbents. In this attempt, kenaf core fiber with size 0.25–1 mm was treated by using (3-chloro-2-hydroxypropyl) trimethylammonium chloride (CHMAC) as quaternization agent. Then effective parameters include adsorbent dose, pH, and contact time and initial dye concentration on adsorption by modified kenaf core fiber was investigated. In addition, isotherms and kinetics adsorption studies were estimated for determination of the equilibrium adsorption capacity and reactions dynamics, respectively. Results showed that the best dose of MKCF was 0.1 g/100 mL, the maximum removal of RO16 was 97.25 at 30°C, pH = 6.5, and agitation speed was 150 rpm. The results also showed that the equilibrium data were represented by Freundlich isotherm with correlation coefficientsR2=0.9924, and the kinetic study followed the pseudo-second-order kinetic model with correlation coefficientsR2=0.9997forCo=100 mg/L. Furthermore, the maximum adsorption capacity was 416.86 mg/g. Adsorption through kenaf was found to be very effective for the removal of the RO16 dye.

A new absorbent by modifying walnut shell for the removal of anionic dye: kinetic and thermodynamic studies

A novel, low cost and easy regeneration biosorbent, chem-modified walnut shell (MWNS), was studied to investigate its potential for removal of an anionic dye, reactive brilliant red K-2BP. The MWNS was synthesized with epichlorohydrin and diethylenetriamine as etherifying agent and crosslinking agent, respectively, and its characteristics were performed with Fourier transform infrared spectroscopy, scanning electron microscope, electron dispersive spectroscopy and thermogravimetric analysis. The influences of pH (0.5-11) and adsorbent dosage (0.1-6g/L) on adsorption capacity of MWNS were evaluated. The maximum K-2BP adsorption capacities (Qm) calculated by best fitting model (Langmuir) were 568.18 mg/g at 313 K, which was almost 10 times than that of raw material. The adsorption kinetic was well confirmed with pseudo-second-order equation. Thermodynamic studies demonstrated adsorption process by MWNS was spontaneous and endothermic. Furthermore, the regeneration capability of MWNS implied MWNS was a cheap, excellent and promising biosorbent for K-2BP removal in azo dye wastewater treatment.