Dubinin-Radushkevich Adsorption Isotherm Research Articles

Adsorptive removal of anticarcinogen pazopanib from aqueous solutions using activated carbon: isotherm, kinetic and thermodynamic studies

Pazopanib, which is dangerous for aquatic environments due to its toxic and bioaccumulation potential, has been detected at different concentrations in oncology hospital wastewater, sewage, and surface waters. This study aimed to remove pazopanib from wastewater by activated carbon adsorption technique. The effect of the main variables such as initial concentration, pH of pazopanib solution, adsorbent dose, contact time of the phases, and temperature on the adsorption process was evaluated and the optimum adsorption conditions were determined. The experimental data were applied to Langmuir, Freundlich, Temkin, and Dubinin-Radushkevich adsorption isotherm models to describe the adsorption behavior. The experimental data were applied to pseudo-first-order, pseudo-second-order, and intra-particle diffusion kinetic models to describe the adsorption kinetics. Isotherms were established in the 20–50 °C temperature range to study the adsorption equilibrium. According to the results, the highest removal efficiency of pazopanib (95.87%) was obtained at initial concentration (100 mg L−1), adsorbent dose (0.30 g L−1), temperature (20 °C), contact time (120 min) and pH (7.0). The adsorption kinetics was well described by the pseudo-second-order kinetic model (R2 = 0.9998) and the adsorption isotherm by the Langmuir model (R2 = 0.9999). In thermodynamic studies, the negative values of standard enthalpy (ΔH°), standard free enthalpy (ΔG°), and free entropy (ΔS°) indicate that the adsorption process is spontaneous and favorable, i.e. the disorder is reduced. These results indicate that the developed adsorption process can be efficiently and spontaneously applied for the removal of pazopanib from aqueous solutions.

Adsorption studies of toxic organic pesticides from aqueous medium by sodium alginate‐cl‐poly (allyl amine‐co‐acrylic acid)/copper oxide nanocomposite hydrogel: Isotherms, kinetics, and thermodynamics

AbstractThe sodium alginate (SAG) cross‐linked poly (allyl amine‐co‐acrylic acid)/copper oxide [SAG‐cl‐poly(AAM‐co‐AA)/CuO] nanocomposite hydrogel (SNCHG) was synthesized by using a free radical initiated cross‐linked copolymerization process in‐situ. Several characterization techniques namely FTIR, PXRD, FESEM with EDAX, TGA, and BET analysis were employed to characterize the synthesized SNCHG. Water swelling properties together with swelling kinetics of SNCHG were evaluated. The highest swelling (35% after 30 minutes) was found at pH 8. The adsorption property of the developed nanocomposite hydrogel (SNCHG) was evaluated in three pesticides' solution namely chlorpyrifos (CP), phosalone (PL), and 4,4'‐ dichloro diphenyl dichloro ethane (DD) in water medium. Several factors affecting the adsorption like solution pH, time of adsorption, amount of pesticides, etc. were evaluated. The maximum adsorption were found to be 96.9% for CP at pH 7, 95.85% for PL at pH 7, and 86.72% for DD at pH 4. Pseudo‐second order kinetics and both Freundlich and Dubinin–Radushkevich adsorption isotherms were followed in all the three cases. Maximum adsorption capacity (Qm) were found to be 507.61, 158.22, and 132.97 mg g−1 for CP, PL, and DD, respectively. The adsorption process was endothermic in nature and spontaneous.Highlights A novel CuO Nps embedded sodium alginate‐based hydrogel is developed. Increment of surface area and water swelling property are illustrated. The hydrogel exhibits excellent adsorption property towards pesticides. The observed affinity of adsorption is chemisorption.

Adsorption Isotherms and Kinetics Studies on Adsorption of Malachite Green onto Activated Charcoal from Aqueous Solution

The article presents low-cost activated charcoal as an adsorbent in the adsorption process for the removal of malachite green from aqueous solution by batch process. To find the optimum condition of the process, contact time, shaking rate, concentration of malachite green, and concentration of activated charcoal were examined. The malachite green was removed up to 98.9%. The adsorption isotherms were studied to check the performance of the adsorbent. Langmuir, Freundlich, Temkin, Hill De Boer, and Dubinin-Radushkevich adsorption isotherms were studied and compared to which one was suitable in the process. The adsorption process with the activated charcoal adsorbent followed suitably with the order of the Dubinin-Radushkevich > Langmuir > Hill De Boer> Temkin > Freundlich models. According to a kinetic study, the adsorption process was second order. In thermodynamic studies, we obtained negative values of ΔG, ΔS, and ΔH. The negative ΔH and ΔS values suggest that enthalpy contributes more than entropy in producing negative ΔG values. The negative ΔG values of malachite green adsorptions indicate that is a favorable and spontaneous process. The negative value of ΔH ensures the adsorption process is characterized as chemical adsorption and exothermic. The negative ΔS value indicates that randomness decreases at the solid–solution interface during the adsorption of MG by activated charcoal. The surface morphology of the Activated charcoal ensured the adsorption process. The results indicate that the adsorption process is exothermic, spontaneous, and favorable. So, activated charcoal might be useful for removing the malachite green dye from the aqueous solution.

Highly Sensitive and Selective Detection of Dimethyl Methyl Phosphonate with Copolymer‐Based QCM Sensors

AbstractIn this work, the volatile organic compounds (VOCs) sensing properties of a quartz crystal microbalance (QCM) transducer coated with six different poly(3‐methylthiophene) (P3MT) copolymerized with polypyrrole (PPy) are investigated. The sensor preparation involves the electrochemical deposition of P3MT, PPy, and P3MT‐co‐PPy on Au‐coated QCM transducers by electrochemical deposition techniques with a three‐electrode cell. The structural properties of the copolymer films are characterized using scanning electron microscopy, and their oxidation/reduction behavior is investigated through cyclic voltammetry. The copolymer‐based QCM sensors exhibit high sensitivity and selectivity to dimethyl methyl phosphonate and benzonitrile, even at low concentrations (<1 ppm) at room temperature. Langmuir, Freundlich, Temkin, and Dubinin–Radushkevich adsorption isotherms are studied to understand the VOCs sensing mechanism machine learning classification algorithms including quadratic discriminant (QD), neural nets, K‐nearest neighbors, linear discriminant, and support vector machines are applied to classify the sensor responses for the 12 different analytes. With the help of machine learning algorithms, tested analytes are successfully classified into their groups. The highest accuracy of 97.34% is achieved using the QD method. The developed sensor, combined with machine learning algorithms, shows promising potential for accurate and reliable detection and classification of VOCs.

ADSORPTIVE REMOVAL OF HEXAVALENT CHROMIUM FROM AQUEOUS PHASE USING VEGETABLE-TANNED BUFFING DUST

Removal of hexavalent chromium from synthetic wastewater was performed by employing vegetable-tanned buffing dust, a byproduct of tanneries. Different analysis techniques such as SEM, BET, and FTIR were used to characterize the vegetable-tanned buffing dust. The experiment on adsorption was carried out in a batch manner. Investigations were conducted into the various operating parameters, such as the dose of adsorbent, contact period, and initial Cr (VI) concentration. At a dose of 1g/100 mL and a contact period of 280 minutes, the maximum adsorption capacity was noted. The Langmuir, Freundlich, Temkin, and Dubinin-Radushkevich adsorption isotherms were examined at various concentrations. With a maximum adsorption efficiency of 14.14 mg/g, the Langmuir isotherm model was found to be the most well-fitting for the current investigation. Kinetic analysis was performed for pseudo first and second order; the pseudo-second-order model demonstrated the most optimal fit with a regression coefficient (R2 ) of 0.9936.

Corrosion inhibitory studies of an eco-friendly thiourea derivative of amino acid on aluminium using 0.1M HCl solution

The inhibition efficiency and corrosion rate of aluminium were investigated at varying temperatures and immersion time using thiourea complex with an organic ligand at concentrations of 0.20, 0.40, 0.60, 0.80 and 1.00 M. The results showed that an increase in the concentration of the complex thiourea led to an increase in the inhibition efficiency, which was attributed to the availability of the proton moiety of the thiourea lost as electron in acidic media. The inhibition efficiency decreased as the immersion time increased with temperature and the largest decrease observed at 333 K due to the distortion of molecular structure of the complex thiourea at high temperatures. The corrosion rate decreased with an increase in immersion time but increased with temperature, possibly due to inhibitor molecular rearrangement. The activation energy of the suppression process of high-concentration thiourea was found to be higher than that of low-concentration, indicating that the adsorption process was triggered by physical adsorption. The formation of a thin film on the metal surface was due to the presence of complex thiourea acted as a barrier to both energy and mass transport, leading to an increase in the activation energy. The adsorption of the thiourea derivatives complex on aluminum was primarily physisorption. The Langmuir, Flory-Huggins, Tempkin, and Dubinin-Radushkevich adsorption isotherm models were investigated with Langmuir found to be the most fitted model based on high R2 values of the model.

The Cr(III) Exchange Mechanism of Macroporous Resins: The Effect of Functionality and Chemical Matrix, and the Statistical Verification of Ion Exchange Data

This study focuses on investigating and comparing the influence of the surface functional groups and chemical matrices of macroporous resin on the Cr(III) exchange mechanism. The results discussed herein indicate that sulfonic resin removed Cr(III) ions with faster kinetics than carboxylic resin. Equilibrium was established within 15 and 7 min for the carboxylic and sulfonic resins, respectively, with a 99.5% removal efficiency at 333 K. The Langmuir exchange capacity was observed to be higher for the sulfonic resin (1.5 mmol∙g−1) than the carboxylic resin (0.80 mmol∙g−1) at 333 K. The adsorption isotherms obtained for the carboxylic and sulfonic resins were H and S types, respectively, representing a higher affinity of the carboxylic resin for Cr(III) removal at a low metal ion concentration. Additionally, it was noted that the carboxylic resin preferentially co-sorbed H+ and Cr(OH)2+ ions below Cr(III) concentrations of 6–8 mmol.L−1. The H+ ions co-sorption was almost negligible, whereas the Cr(III) exchange was 87 and 34.5% for the carboxylic acid resin and sulfonic acid resins, respectively. The data of the concentration studies were evaluated using non-linear forms of Freundlich, Langmuir, and Dubinin–Radushkevich adsorption isotherm models, and the kinetic data were analyzed using pseudo-Ist- and pseudo-IIst-order kinetic models. The activation energy Ea for Amberlite IRC-50 (Na+) was greater (22.4 kJ∙mol−1) than that of Amberlyst-15 (Na+) 17 kJ∙mol−1, indicating a higher energy barrier for the ion exchange reaction on carboxylic resin. As per the findings of a statistical error analysis (RMSE and SSE) and absolute average relative distribution (AARD) statistical model, a close agreement between the experimental and theoretical values suggested that the Langmuir isotherm was well-fitted to the current adsorptive investigations. The interaction of the COO− and SO3− functional sites of the resins for the exchange of Cr(III) ions was validated through an FT-IR analysis. The macroporous resins used in the current study for Cr(III) exchange showed promising performances compared to other resins. The current investigations revealed valuable insights for choosing macroporous resins as adsorbents in water filtration systems.

Efficient removal of tetracycline, ciprofloxacin, and amoxicillin by novel magnetic chitosan/microalgae biocomposites

Two new highly-efficient and eco-friendly biosorbents comprised of magnetite, chitosan and Chlorella vulgaris (MCC) or Arthrospira platensis (MCA) were prepared in such a way to be easily separated and reused for removing different classes of antibiotics such as tetracycline (TC), ciprofloxacin (CIP) and amoxicillin (AMX) from wastewater. They were characterized using SEM, FTIR and TGA. Biosorption experiments were performed to investigate the impact of pH, biosorbent dosage, initial antibiotic concentration, contact time, and concentration of background electrolytes (NaCl, KCl and CaCl2) on adsorption. Both biocomposites showed outstanding performance in antibiotics removal. Equilibrium data were modelled using Langmuir, Freundlich, Temkin, and Dubinin-Radushkevich adsorption isotherms, among which the first one gave the best fit, with maximum TC, CIP and AMX adsorption capacities of 834.0, 394.9, and 150.8 mg/g for MCA and of 831.1, 374.2, and 140.2 mg/g for MCC, respectively. To follow the adsorption time-evolution, the pseudo-first-order, pseudo-second-order and intraparticle diffusion kinetic models were tested, the second of which proved to be the best-fitting one. Thermodynamic parameters revealed that adsorption was spontaneous and endothermic. Both biosorbents were regenerated through microwave-assisted treatment and reused repeatedly for up to four cycles, losing TC, CIP and AMX adsorption capacities at equilibrium by no >7, 4 and 9 %, respectively. This study suggests that both biocomposites may be effective and sustainable alternatives to commercial adsorbents for removing antibiotics from wastewater.

Guar Gum as an Eco-Friendly Corrosion Inhibitor for N80 Carbon Steel under Sweet Environment in Saline Solution: Electrochemical, Surface, and Spectroscopic Studies.

In this study, the corrosion inhibition performance of the natural polysaccharide guar gum (GG) for N80 carbon steel in CO2-saturated saline solution at different temperatures and immersion times was investigated by weight loss and electrochemical measurements. The results have revealed that GG showed good inhibition performance at lower and higher temperatures. The inhibition efficiency observed via weight loss measurements reached 76.16 and 63.19% with 0.4 g L-1 of GG, at 25 and 50 °C, respectively. The inhibition efficiency of GG increased as the inhibitor concentration and immersion time increased but decreased with increasing temperature. EIS measurements have shown that, even after prolonged exposure, GG was still able to protect the metal surface. Potentiodynamic measurements showed the mixed-type nature of GG inhibitive action. The Temkin and Dubinin-Radushkevich adsorption isotherm models give accurate fitting of the estimated data, and the calculated parameters indicated that the adsorption of GG occurred mainly via an electrostatic or physical adsorption process. The associated activation energy (Ea) and the heat of adsorption (Qa) supported the physical adsorption nature of GG. FTIR analysis was used to explain the adsorption interaction between the inhibitor and the N80 carbon steel surface. SEM-EDS and AFM confirmed the adsorption of GG and the formation of an adsorptive layer of GG on the metal surface.

Removal of Malachite Green Using Hydrochar from PALM Leaves

Biochar was prepared by the hydrothermal carbonization (HTC) of palm leaves, characterized, and utilized as an adsorbent for Malachite Green dye (MG). The Higher Heating Value (HHV) of biochar depends on the carbonization temperature and has a maximum value of 24.81 MJ/kg. Activation using H2O2 oxidation of HTC biochar prepared at 208 °C produced AHTC with improved capacity. The optimum pH was found to be in the range 7–8. Freundlich, Langmuir, Temkin, and Dubinin–Radushkevich adsorption isotherms were used to study MG adsorption data. The Langmuir isotherm provided the best fit for experimental data. Experiments conducted using activated biochar AHTC at 25 °C resulted in an adsorption capacity of 62.80 mg/g, far greater than what was observed for HTC biochar (45.59 mg/g). The maximum adsorption capacity was 88% when the concentration of MG solution was 66 ppm. The free energy change in adsorption DG° indicated that the adsorption process was spontaneous. Adsorption followed pseudo-second-order kinetics. Fixed-column adsorptions models, namely, Thomas, Yan et al. and Yoon–Nelson models, were investigated for AHTC. The column adsorption capacity determined by the Thomas model was 33.57 mg/g. In addition, a computational investigation has been carried out to determine the structural and electronic features, as well as the quantum chemical parameters of HTC and MG. Moreover, the interaction between the HTC and MG is investigated, which is further elaborated by performing non-covalent interaction (NCI) through the reduced density gradient (RDG) analysis. Thus, the easily prepared hydrochar from abundant waste palm leaves can be used as a high-value biocoal and efficient adsorbent of the cationic dye malachite green.

Uklanjanje metomila iz vodenih rastvora korišćenjem mikrosfera reaktiviranog aktivnog uglja

The removal of methomyl, one of the most frequent pesticides, from aqueous solutions has been studied by adsorption using the reactivated carbon microspheres separated from worn filtering protective suits. This study is significant in two aspects - the first is the in-situ adsorption of pesticides from aqueous solutions, and the second is recycling protective equipment as an effective material for water decontamination. Carbamate pesticide, methomyl is aimed to control foliage and soil-borne insect pests on various agricultural product. Also, due its toxicity, it has a great potential for usage in terroristic acts and tactical purposes during military operations. The reactivated carbon (RAC) microspheres were characterized by Scanning Electron Microscopes (SEM). The changes in relative concentration of methomyl during the adsorption onto the surface of the RAC microspheres was determinated using the UV-Visible spectrophotometer. The adsorption process is described by Langmuir, Freundlich, Temkin, and Dubinin-Radushkevich adsorption isotherm models. The adsorption kinetics follows the second-order kinetics model, and the thermodynamics study confirms that the adsorption is exothermic and spontaneous. At optimal conditions, the adsorption capacity was qe = 8.631 mol g-1 × 10-8 and the adsorption rate was k = 0.749 g mmol-1 min-1. The Langmuir, Freundlich, Temkin, and Dubinin-Radushkevich adsorption isotherm models were used to describe the adsorption process. The thermodynamic study of adsorption proves the process is spontaneous with exothermic nature.

Removal of cod from real textile wastewater using three low-cost adsorbents - its kinetic models and adsorption isotherms

ABSTRACT In this work, batch adsorption studies were carried out using three low-cost adsorbents like rice husk ash (RHA), corncob ash (CA) and sugarcane bagasse fly ash (BFA) with the aim of removing COD from textile wastewater (TWW) having an initial concentration of 1026 mg/L. Batch experiments were conducted to study the adsorption behaviour through the effect of adsorbent dosage, pH and contact time on the adsorption of COD removal. The results showed that the removal percentage of COD could be over 70–75% at the optimal adsorbent dosage of 6 g/L, at a pH of 8.0 to 8.5 and a contact time of 40 min for RHA and BFA. At the same time, less COD removal was observed while using CA as an adsorbent giving only 50–55% COD removal. The applicability of the Langmuir, Freundlich, Temkin and Dubinin–Radushkevich isotherm models for the three low-cost adsorbents adsorption data was tested. Langmuir isotherm plots indicated that the adsorption process is favourable and best fitted. In the Temkin adsorption isotherm, the values of ‘B’ (heat of adsorption) showed positive values, which indicates that the reaction with all three adsorbents was an exothermic reaction. From the results of the Dubinin–Radushkevich adsorption isotherm, the constant E (mean free energy) values lying within 8 indicated that the adsorption process is physical adsorption. Kinetics data showed that the pseudo-second-order kinetic model showed a good correlation for the adsorption than the pseudo-first-order. Therefore, RHA and BFA can be potentially used as low-cost adsorbents for treating TWW.

Effective removal of phenol from wastewater using a hybrid process of graphene oxide adsorption and UV-irradiation

The focus of this work is the removal of phenol from water by graphene oxide (GO) nanoparticles, prepared by two different methods, through a hybrid adsorption–UV-irradiation process. The GO1 and GO2 were prepared using (H2SO4 and H3PO4) and (H2SO4, H3PO4, and HNO3), respectively. The effect of different parameters namely, pH, initial phenol concentration, and temperature on the adsorption process was investigated. Fourier transform infrared spectroscopy and scanning electron microscopy were used to characterize the prepared graphene oxides (GO1 and GO2). Various adsorption isotherm models were investigated including Langmuir, Freundlich, Temkin, and Dubinin–Radushkevich adsorption isotherm models. The results showed that UV-irradiation had a positive effect on the adsorption process as the adsorption capacity increased. Additionally, maximum removal percentage was obtained at pH 2 for GO1 for both experimental sets. Similarly, GO2 without exposure to UV-irradiation showed the highest adsorption capacity at pH 2, while with the effect of UV-irradiation, the optimum pH was 6. Furthermore, increasing the initial concentration of phenol led to the increase in adsorption until it reached an equilibrium where the adsorption decreased and remained constant. Furthermore, the maximum adsorption capacity increased with the effect of UV exposure from 70.43% to 90.82% for GO1 and from 86.75% to 95.95% for GO2. Moreover, increasing the temperature caused the adsorption capacity to decrease and the thermodynamic results showed that the adsorption processes were feasible and spontaneous for GO1 (with and without UV exposure), and GO2 (only with UV exposure).

Removal of Th(IV) from aqueous solution with modified silica gel by 4-hydroxy-N ′ - ((thiophen-2-yl) methylene)benzohydrazide schiff base

ABSTRACT In this study, SiCPMS@L solid adsorbent was prepared using 4-Hydroxy-N ′- ((Thiophen-2-yl)methylene)benzohydrazide Schiff base for thorium(IV) removal from aqueous solution, and the structure of the solid adsorbent was characterized by FTIR, SEM, elemental analysis, and BET surface analysis methods. Solution pH, initial thorium concentration, contact time, adsorbent dose, and temperature parameters affecting the adsorption of Th(IV) ions with SiCPMS@L adsorbent were examined, and optimum uptake conditions were determined. The effective initial pH for adsorption was found to be 4.0. The binding sites on SiCPMS@L solid adsorbent were saturated using an initial Th(IV) concentration of 16.0 mg/L. 30 minutes was determined as the optimum contact time when the adsorption equilibrium was established. The optimum adsorbent dose for SiCPMS@L was determined as 1.0 g/L. At optimum conditions, adsorption efficiency and adsorption capacity values for SiCPMS@L adsorbent were respectively; 97.4% ± 0.1 and 15.6 ± 0.1 mg/g were obtained. The calculated thermodynamic parameters ∆S°, ∆G° and ∆H° showed that the Th(IV) sorption process is thermodynamically advantageous, spontaneous and endothermic. Langmuir, Freundlich and Dubinin-Radushkevich adsorption isotherms for removal of Th(IV) ions with SiCPMS@L solid adsorbent were investigated and found to be compatible with Langmuir isotherm.

Sustainable selenium remediation from water using aluminium–iron mixed oxide: Batch and column adsorption studies

Selenium contamination of water resources has become a potential health risk issue. The application of aluminium–iron (AlFe) mixed oxide for the rapid adsorption of both selenite (IV) and selenate (VI) ions from water was studied. The synthesized AlFe mixed oxide was characterized to understand the morphological and structural properties. Batch adsorption experiments were performed to understand the adsorption performance with variable parameters. AlFe mixed oxide was found as efficient for both selenite (IV) and selenate (VI) ion adsorption over a wide pH range up to pH < 9. Adsorption experiments revealed that the dose of 0.1 g L−1 with an initial selenium concentration of 500 μg L−1 is sufficient to meet the WHO guideline value within the first 30 min of contact time. Langmuir, Temkin and Dubinin-Radushkevich (DR) adsorption isotherm and pseudo–second order kinetics presented better fitting for selenite (IV) and selenate (VI) ions with maximum adsorption capacity for Se(VI) and Se(IV) as 33.1 mg g−1 and 6.188 mg g−1 respectively. Column adsorption and regeneration were also studied to understand the practical applicability of the adsorbent. The adsorbent was regenerated using mild alkali and can further be reused without any significant decrease in adsorption efficiency.

Efficient and selective adsorption of U(VI) by succinic acid modified iron oxide adsorbent

Abstract The iron oxide surface was modified with succinic acid moiety and the adsorbent obtained, Fe-SUC, was evaluated for the adsorption of U(VI) (Uranium (VI)) from aqueous solution. The Fe-SUC was characterized by FT-IR (Fourier Transform Infrared Spectroscopy), Raman spectroscopy, thermogravimetry, X-ray diffraction, SEM-EDX (Scanning Electron Microscope - Energy-dispersive X-ray Spectroscopy), and particle size analysis. The adsorption behavior of U(VI) on Fe-SUC was studied as a function of pH, contact time, and concentration of U(VI) in the aqueous phase. The adsorption of U(VI) increased with increase in the pH of aqueous phase, and the adsorption saturation occurred at pH = 6. The kinetic data obtained for the adsorption of U(VI) on Fe-SUC were modeled with the pseudo-first-order and pseudo-second-order rate models. Similarly, the U(VI) adsorption isotherm was fitted with Langmuir, Freundlich, Temkin, and Dubinin-Radushkevich adsorption isotherm models. The Langmuir adsorption capacity of U(VI) on Fe-SUC was about ∼176 mg g−1. The selectivity of the adsorbent toward U(VI) was evaluated in the presence of several possible interfering ions. The adsorbed U(VI) was recovered by 0.5 M sodium carbonate solution and the spent adsorbent was tested for its reusability.

Exploring the adsorption efficiency of a novel cellulosic material for removal of food dye from water

A cellulosic nanoadsorbent was developed from the fruit coat of a forest tree named, Kendu (Diospyros melanoxylon) to remove tartrazine dye, popularly known as the yellow dye, from the aqueous solution. The proximate and mineral content of the cellulosic nanoadsorbent were analyzed by AOAC methods, and it was further characterized by different analytical techniques. The X-ray diffraction studies established the cellulose I polymorph structure of the bionanomaterial. The appearance of the inherent peak of the cellulose in the fingerprint region of the Fourier Transform infrared spectroscopy (FTIR) and the absence of the lignin and hemicellulose peaks in the FTIR spectrum supported the formation of the cellulosic nanocrystal. The analysis of the morphology of the crystal through Transmission electron microscopy envisaged the spherical nature of the crystal with a particle size of around 36 nm. The optimal adsorption of the yellow dye was achieved when the pH and temperature of the solution, adsorbent dosage, initial dye concentration, and stirring speed were 6.0, 60 oC, 80 mg L−1, 10 mg L−1, and 200 rpm, respectively. The nanocrystals could remove more than 95% of the dye, whereas virgin Kendu fruit coat powder could remove around 75% of the dye. The adsorption was spontaneous and followed second-order kinetics. The adsorption data were assessed for the Langmuir, Freundlich, Tempkin, Elovich, Intraparticle diffusion, and Dubinin-Radushkevich adsorption isotherm models. The adsorption of the dye onto the nanocrystal occurred through both polar and nonpolar interactions. The overall study indicated that the Kendu fruit coat could be a cost-effective natural bioresource for the synthesis of an adsorbent that could remove the yellow food dye from the aqueous solution proficiently.

ADSORPTION OF Cd(II) IN A SEMI-CONTINUOUS PROCESS BY RESIDUAL CHARCOAL FROM THE PYROLYZED OIL PALM SHELLS

This study aims to evaluate the utilization of residual charcoal from the pyrolysis of oil palm shells as activated carbon for the adsorption of cadmium metal ions in a semi-continuous process. The charcoal was crushed with a ball mill to a size of 80-100 mesh and its activation was carried out chemically using 0.1 N NaOH. Cadmium metal ions were adsorbed in a semi-continuous operation using a cylindrical packed bed column, with variations in the inlet feed concentration, pH, column inside diameter, bed height, and flow rate. The initial concentration of cadmium before and after the adsorption was tested on an atomic absorption spectrophotometer. The adsorption isotherms were evaluated using the Langmuir, Freundlich, and Dubinin-Radushkevich adsorption isotherm models. The results showed that the best adsorption capacity was obtained at an initial concentration of 120 mg/L, pH 5, inside diameter of 26 mm, bed height of 50 cm, and flow rate of 10 ml/min. The isotherm model of cadmium metal ion adsorption followed the Langmuir isotherm with R2 = 0.99.

Investigation of dye removal ability and reusability of green and sustainable silica and carbon-silica hybrid aerogels prepared from paddy waste ash

In this study, the paddy waste ash (PA) was utilized for producing carbon-silica hybrid (PCS) and silica (PS) aerogels. X-ray fluorescence (XRF) spectrometer analysis revealed a high silica content in PA. Crystalline SiO2-cristobalite structure was observed in the X-ray diffraction (XRD) patterns of PA. As expected, the PCS and PS samples exhibited an amorphous SiO2 phase. The pore enlargement and structural improvement after aerogel synthesis were determined using a N2 adsorption-desorption analysis. The specific surface area of the PCS and PS samples were found to be 519 and 652 m2/g, respectively. From the zeta potential results, the points of zero charge (pHPZC) of the samples were found below “2” except for the PCS sample (pHPZC = 2.08). In the first stage of the Remazol Turquoise GN (RTGN) adsorption experiments, the effect of initial pH (2–8) was examined for PA, PCS, and PS sorbents. The highest dye removal value of the PCS sorbent was 61% at pH = 2, while this value was 17.9% and 21.4% for PS and PA sorbents, respectively. The removal percentage curve exhibited a similar trend to the zeta potential curve of the samples. In the experiments conducted with different amounts of sorbents, the dye removal percentage increased with increasing amounts of sorbents. The experimental results and thermodynamic calculations showed that the RTGN adsorption onto PCS was an endothermic process. Pseudo-first order, pseudo-second order and intra-particle diffusion equations were applied to determine the adsorption kinetics of RTGN onto PCS, and it was found that the experimental data was well-fitted to the pseudo-second order kinetic model. The Langmuir, Freundlich, Temkin and Dubinin-Radushkevich (D-R) adsorption isotherm models were used to define the adsorption mechanism of RTGN onto PCS. The Freundlich and Langmuir isotherm models were in agreement with our experimental data and it was concluded that RTGN adsorption on PCS surface occurred both as single layer and multi-layer, as well as took place on heterogeneous and homogeneous surfaces. Characterization analyses were conducted for the PCS sorbent after use to understand the structural changes after dye removal. The regeneration and reusability of the PCS sorbent were investigated and it was found that it preserved its initial removal ability by about 95% after four cycles. The dye removal percentage of PCS decreased by 28% after five cycles.

Enhanced adsorption removal of methyl orange from water by porous bimetallic Ni/Co MOF composite: a systematic study of adsorption kinetics

ABSTRACT Zeolitic imidazole frameworks (ZIFs) and their derivatives, being an emergent category of adsorbents, are anticipated to adsorb organic dyes from aqueous mediums. Herein, ZIF-67 and Ni-doped ZIF-67 were designated due to their high stability in aqueous mediums, porosity and straightforward synthesis. Porous Ni-doped ZIF-67 nanocomposite was produced by doping secondary metal (Ni) to ZIF-67. The fabricated Ni@ZIF-67 showed excellent adsorption efficiency to adsorb methyl orange from water. The performance of Ni-doped ZIF-67 was analysed by varying pH, contact time with adsorbent and concentration of dye. Results exposed that the Ni@ZIF-67 nanocomposite adsorbs more dye in mild acidic condition (qe = 24.24 mg. g−1 pH = 6) as compared to acidic (qe = 17.69 mg. g−1 pH = 2) and basic medium (qe = 15.74 mg. g−1 pH = 10). Langmuir, Freundlich and Dubinin-Radushkevich adsorption isotherm models were applied and results showed that Langmuir model proved to be best fitted, suggesting adsorption process as monolayer. The maximum adsorption capacity attained was 151.74 mg. g−1 with excellent recycling performance up to fifth cycle. Also with 180 min contact time, 68.5 and 82.9% of MO were adsorbed by ZIF-67 and Ni-doped ZIF-67 nanocomposite, respectively. Consequently, the as-synthesised Ni@ZIF-67 could be a prospective adsorbent material for methyl orange elimination from polluted water.