Optimum Adsorption Conditions Research Articles

Optimization of Adsorption Conditions Using Response Surface Methodology for Tetracycline Removal by MnFe2O4/Multi-Wall Carbon Nanotubes

In this study, the optimal conditions and effects of external factors on tetracycline adsorption by magnetic multi-walled carbon nanotubes (MMWCNTs) were established by a response surface methodology for the first time. Batch adsorption experiments showed that increasing the dosage and contact time effectively promoted the adsorption of tetracycline and maximum removal of 97.93–99.13% was achieved at pH 3–7. The pseudo-second-order model and Fourier-transform infrared spectroscopy spectra indicated that the mechanism of adsorption may be π–π electron interaction and cation–π electron bonding. Design Expert was utilized to develop a response surface methodology for the analysis and optimization of tetracycline adsorption by magnetic multi-walled carbon nanotubes. The Box–Behnken design (BBD) results showed that the optimization exhibited high significance and reliability. The main effect plots and Pareto chart indicated that pH exerted a significant individual effect on the regulation of adsorption, while 3D response surface plots and interaction effect plots exhibited a significant antagonistic interaction between pH and contact time. A maximum tetracycline removal of 99.16% was achieved under the optimal conditions of 12 mg adsorbent dosage at pH 5.43, with an adsorption time of 120 min. Mathematical and experimental results confirmed the accuracy of the established optimal conditions.

Preparation of novel Zn–Al layered double hydroxide composite as adsorbent for removal of organophosphorus insecticides from water

In this work, a new and efficient composite LDH with high adsorption power using layered double hydroxide (LDH), 2,4-toluene diisocyanate (TDI), and tris (hydroxymethyl) aminomethane (THAM) was designed and prepared, which was used as an adsorbent to adsorb diazinon from contaminated water. The chemical composition and morphology of the adsorbent were evaluated using Fourier transform infrared (FTIR), X-ray diffraction (XRD), thermal gravimetric analysis (TGA), Energy dispersive X-ray (EDX) and Field emission scanning electron microscopy (FESEM) techniques. Also, the optimal conditions for adsorption of diazinon from water were determined by LDH@TDI@THAM composite. Various parameters like the effect of adsorbent dosage, pH, concentration and contact time of diazinon were studied to determine the optimal adsorption conditions. Then, different isotherm models and kinetic adsorption were used to describe the equilibrium data and kinetic. Also, the maximum adsorption capacity is obtained when the pH of the solution is 7. The maximum adsorption capacity for LDH@TDI@THAM composite was 1000 mg/g at 65 °C and the negative values of ΔG indicate that the adsorption process is spontaneous. After that, studying the reusability of LDH@TDI@THAM composite showed that the removal of diazinon by LDH@TDI@THAM was possible for up to four periods without a significant decrease in performance.

Ultra-efficient removal of methylene blue, oxytetracycline, and lead(II) by activated carbon derived from black cumin (Nigella sativa) processing solid waste

Accumulating dyes, drugs, and heavy metals in water creates a lasting environmental problem that affects living things in different ecosystems. Their removal is imperative for environmental necessity in a habitable world. Adsorption with carbonaceous materials produced especially for the evaluation of agricultural wastes is a low-cost and effective removal technique. This study is related to the investigation of the adsorbing performance of a new activated carbon (BAC) synthesized from black cumin (Nigella sativa) processing solid waste (BW) under optimal conditions determined by single-step carbonization/activation with potassium carbonate to remove methylene blue, oxytetracycline, and lead (II) in an aqueous medium. Their optimum adsorption conditions were decided based on the maximum effects of important operational parameters. Experimental kinetic and isotherm findings for each adsorption system were modeled by evaluating widely used kinetic and isotherm equations. The maximum adsorption capacity of BAC was determined as 752 mg/g for methylene blue, 911 for oxytetracycline, and 556 mg/g for lead (II) from the Langmuir isotherm model. The thermodynamic parameters determined showed that the adsorption processes were self-occurring and also endothermic for methylene blue and oxytetracycline and exothermic for lead(II). In addition, BAC showed stability and recyclability in adsorption-desorption cycles for the pollutants studied. These findings suggest that BAC can be used as an ultra-efficient adsorbent for larger-scale wastewater treatment.

Ce(III) and La(III) ions adsorption using Amberlite XAD-7 resin impregnated with DEHPA extractant: response surface methodology, isotherm and kinetic study

In this paper, the removal efficiency of Cerium (Ce(ΙΙΙ)) and lanthanum (La(ΙΙΙ)) ions from aqueous solution using Amberlite XAD-7 resin impregnated with DEHPA(XAD7-DEHPA) was studied in the batch system. The adsorbent ( XAD7–DEHPA) was characterized by SEM–EDX, FTIR and BET analysis Techniques. The response surface methodology based on the central composite design was applied to model and optimize the removal process and evaluate operating parameters like adsorbent dose (0.05–0.065), initial pH (2–6) and temperature (15–55). Variance analysis showed that the adsorbent dose, pH and temperature were the most effective parameters in the adsorption of Ce(ΙIΙ)and La(IΙI) respectively. The results showed that the optimum adsorption condition was achieved at pH = 6, the optimum amount of absorbent and the equilibrium time equal to 0.6 gr and 180 min, respectively. According to the results, the adsorption percentage of Ce(ΙIΙ) and La(ΙΙΙ) ions onto the aforementioned resin were 99.99% and 78.76% respectively. Langmuir, Freundlich, Temkin and sips isotherm models were applied to describe the equilibrium data. From the results, Langmuir isotherm (R2 (Ce) = 0.999, R2 (La) = 0.998) was found to better correlate the experimental rate data. The maximum adsorption capacity of the adsorbent ( XAD7–DEHPA) for both Ce(IΙI) and La(III) was found to be 8.28 and 5.52 mg g−1 respectively. The kinetic data were fitted to pseudo-first-order, pseudo-second-order and Intra particle diffusion models. Based on the results, the pseudo-first-order model and Intra particle diffusion model described the experimental data as well. In general, the results showed that ( XAD7–DEHPA) resin is an effective adsorbent for the removal of Ce(IΙI) and La(III) ions from aqueous solutions due to its high ability to selectively remove these metals as well as its reusability.

Pretreatment of Used Cooking Oil Using Avocado Seed Adsorbent for Biodiesel Production Preparation

Used cooking oil (UCO) can be used as raw material for biodiesel production, but its free fatty acid (FFA) content is still quite high, so it is necessary to do pretreatment in the form of an adsorption process to reduce FFA levels. This study aims to determine the optimum conditions for the adsorption process and determine FFA levels of UCO before and after pretreatment. The adsorbent used is avocado seed activated charcoal, because it has a surface area of 19.62 m2/g. The larger the surface area of the adsorbent material, the greater the adsorption capacity of the adsorbent. Optimization of the UCO adsorption process includes variations in adsorbent mass (6, 8, 10 g), adsorbent particle size (60, 100, 140 mesh), contact time (2, 6, 10 hours), and temperature (60, 80, 100oC). The results showed that the optimum conditions for adsorption of UCO were obtained at mass (10 g), particle size (100 mesh), contact time (6 h), and temperature (80oC). This condition can reduce the FFA content of UCO by 71.64% (w/w), from 5.29% (w/w) to 1.50% (w/w). The FFA content of UCO [1.50% (w/w)] produced after pretreatment was qualified as a raw material for the preparation of biodiesel production through the transesterification stage.

Optimization of adsorption performance of cerium-loaded intercalated bentonite by CCD-RSM and GA-BPNN and its application in simultaneous removal of phosphorus and ammonia nitrogen

Excessive phosphorus (P) and ammonia nitrogen (NH3–N) in water bodies can lead to eutrophication of the aquatic environment. Therefore, it is important to develop a technology that can efficiently remove P and NH3–N from water. Here, the adsorption performance of cerium-loaded intercalated bentonite (Ce-bentonite) was optimized based on single-factor experiments using central composite design-response surface methodology (CCD-RSM) and genetic algorithm-back propagation neural network (GA-BPNN) models. Based on the determination coefficient (R2), mean absolute error (MAE), mean square error (MSE), mean absolute percentage error (MAPE), and root mean square error (RMSE), the GA-BPNN model was found to be more accurate in predicting adsorption conditions than the CCD-RSM model. The validation results showed that the removal efficiency of P and NH3–N by Ce-bentonite under optimal adsorption conditions (adsorbent dosage = 1.0 g, adsorption time = 60 min, pH = 8, initial concentration = 30 mg/L) reached 95.70% and 65.93%. Furthermore, based on the application of these optimal conditions in simultaneous removal of P and NH3–N by Ce-bentonite, pseudo-second order and Freundlich models were able to better analyze adsorption kinetics and isotherms. It is concluded that the optimization of experimental conditions by GA-BPNN has some guidance and provides a new approach to explore adsorption performance after optimizing the conditions.

Novel cetyltrimethylammonium bromide modified mixed adsorbent for efficient treatment of dyeing and printing wastewater

The treatment of dyeing and printing wastewater is a formidable challenge due to its high chemical oxygen demand (COD) and chromaticity, which pose severe threats to both the environment and human health. In this study, a composite modified adsorption material was prepared based on the applicability and feasibility in practical engineering applications. A novel mixed modified adsorbent was developed by incorporating activated carbon and activated clay as the foundation materials, followed by the addition of cetyltrimethylammonium bromide (CTAB) for modification. The performance of the composite adsorbent was evaluated via adsorption experiments of bromophenol blue (BPB) solution and dyeing and printing wastewater. The results demonstrated that the mixed modified adsorbent achieved a remarkable removal rate of 99% for BPB and 99.3% for chromaticity, under the optimal adsorption conditions. Furthermore, the regeneration performance of the mixed modified adsorbent was found to be exceptional. The adsorption process of BPB by the composite adsorbent was governed by the quasi-second-order kinetic model and Freundlich isotherm model, as evidenced by adsorption kinetics and isotherm analyses. The straightforward preparation method, coupled with the superior adsorption performance, underlines the promising potential of the proposed composite adsorbent for practical applications.

Ultra-effective modified clinoptilolite adsorbent for selective thorium removal from radioactive residue

This study investigated the efficacy of using phosphate-modified zeolite (PZ) as an adsorbent for removing thorium from aqueous solutions. The effects of various factors such as contact time, adsorbent mass, initial thorium concentration, and pH value of the solution on the removal efficiency were analyzed using the batch technique to obtain optimum adsorption condition. The results revealed that the optimal conditions for thorium adsorption were a contact time of 24 h, 0.03 g of PZ adsorbent, pH 3, and a temperature of 25 °C. Isotherm and kinetics parameters of the thorium adsorption on PZ were also determined, with equilibrium studies showing that the experimental data followed the Langmuir isotherm model. The maximum adsorption capacity (Qo) for thorium was found to be 17.3 mg/g with the Langmuir isotherm coefficient of 0.09 L/mg. Using phosphate anions to modify natural zeolite increased its adsorption capacity. Furthermore, adsorption kinetics studies demonstrated that the adsorption of thorium onto PZ adsorbent fitted well with the pseudo-second-order model. The applicability of the PZ adsorbent in removing thorium from real radioactive waste was also investigated, and nearly complete thorium removal was achieved (> 99%) from the leached solution obtained from cracking and leaching processes of rare earth industrial residue under optimized conditions. This study elucidates the potential of PZ adsorbent for efficient removal of thorium from rare earth residue via adsorption, leading to a reduction in waste volume for ultimate disposition.

Preparation and Adsorption Properties of Lignin/Cellulose Hydrogel.

With the development of global industry, industrial wastewater pollution has caused serious environmental problems, and the demand for green and sustainable adsorbents is increasingly strong in the society. In this article, lignin/cellulose hydrogel materials were prepared using sodium lignosulfonate and cellulose as raw materials and 0.1% acetic acid solution as a solvent. The results showed that the optimal adsorption conditions for Congo red were as follows: an adsorption time of 4 h, a pH value of 6, and an adsorption temperature of 45 °C. The adsorption process was in line with the Langmuir isothermal model and a quasi-second-order kinetic model, which belonged to single molecular layer adsorption, and the maximum adsorption capacity was 294.0 mg/g. The optimal adsorption conditions for Malachite green were as follows: an adsorption time of 4 h, a pH value of 4, and an adsorption temperature of 60 °C. The adsorption process was consistent with the Freundlich isothermal model and a pseudo-second-order kinetic model, which belonged to the chemisorption-dominated multimolecular layer adsorption with the maximum adsorption capacity of 129.8 mg/g.

The feasibility study of CAU-1 as an adsorbent for Cu, Zn, Pb, As, Fe and endocrine disrupting chemical bisphenol-A (BPA)

This work discusses the feasibility of CAU-1 as an adsorbent for both heavy metals and bisphenol A (BPA). CAU-1 was synthesised solvothermally at 120 °C for 8 h. Batch adsorption study was done to investigate the feasibility of CAU-1 as the adsorbent. The CAU-1 weight was constant throughout the study, 0.01 g. CAU-1 was characterised using zeta potential analysis, SEM, FTIR, TGA, and XRD. CAU-1 was only able to remove BPA and not able to adsorb heavy metals due to the repulsion forces between CAU-1 and the heavy metals. Thus, BPA was used as adsorbate for CAU-1 adsorption study. The optimum conditions for BPA adsorption on CAU-1 were at pH 7 and 3 h contact time. The adsorption capacity increased infinitely with increasing concentration of the BPA. The maximum equilibrium adsorption capacity (qe) of CAU-1 for BPA was 310.1 mg/g at 25 °C, and the adsorption followed the pseudo-second-order kinetic model. The thermodynamic studies indicate that the adsorption reaction is a spontaneous and endothermic process, a favourable reaction.

Smart guanyl thiosemicarbazide functionalized dialdehyde cellulose for removal of heavy metal ions from aquatic solutions: adsorption characteristics and mechanism study

In recent years, facing the problem of improving environmental quality, cellulose and cellulose-based (nano) composites have received great attention as adsorbents. In this work, we report the modification and functionalization of cellulose by nitrogen- and sulfur-containing moieties through a three-steps process; native cellulose is first oxidized by potassium periodate (KIO4) to form dialdehyde cellulose (DAC), which then condenses with aminoguanidine and react with phenyl isothiocyanate to form 4-phenyl guanyl thiosemicarbazide dialdehyde cellulose (DAC@GuTSC). The prepared DAC@GuTSC is characterized by a number of techniques, including Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), elemental analysis (EA), Brunauer–Emmett–Teller (BET) and thermogravimetric analysis (TGA). The prepared DAC@GuTSC adsorbent was used to remove Cu2+ Hg2+ and Pb2+ from aqueous solution and environmental water samples. The influence of various factors on the adsorption efficiency including pH, initial metal concentration, contact time, adsorbent dosage, temperature, and ions interfering with adsorption was investigated. Under optimal adsorption conditions, the adsorption capacity of Cu2+, Hg2+ and Pb2+ was 50, 94 and 55 mg g−1, respectively. The adsorption process is well described by the Langmuir model, and it was found to follow the pseudo-second-order kinetics model. The spontaneous and endothermic adsorption of Cu2+, Hg2+ and Pb2+ was confirmed by the calculated thermodynamic functions. The prepared DAC@GuTSC composite has been successfully applied to remove Cu2+, Hg2+ and Pb2+ from real water samples with recovery greater than 90% and relative standard deviation (RSD) less than 3%. The reasonable Cu2+, Hg2+ and Pb2+adsorption mechanism on the prepared DAC@GuTSC composite has been elucidated.

Synthesis of Amino-Engineered Graphene Oxidize Nanocomposite (GO/SBA-15) for Potential Copper Ions and Dye Removal from Aqueous Solution

Air, water, and soil pollution are worldwide problems. Of these, heavy metals and organic dyes are the main targets for removal. Graphene oxide (GO), especially functionalized GO, has shown great application potential for the removal of contaminants from wastewater. This study used Santa Barbara Amorphous-15 (SBA-15) with amino acid to functionalize GO, not only to increase the adsorption sites, but also chelate with heavy metals to improve the adsorption efficiency. The optimal experimental conditions for Cu2+ adsorption were obtained by response surface methodology (RSM): pH=5.8, C0=38.38 mg/L, M=0.56 g/L, and T=35.68°C. The optimum experimental conditions for MB adsorption were pH=10.24, C0=82.70 mg/L, M=0.33 g/L, and T=35.27°C, and absorption rates all above 70%. Also, the adsorption mechanism, desorption, and reusability of the complexes are reviewed. Finally, the application potential of GO/SBA-15 as an adsorbent in the field of industrial wastewater treatment is summarized and its prospects are discussed.

Application of modified cellulose for Pb2+ and Cu2+ removal from aqueous solutions: Kinetic and isotherms studies

In this work, acrylamide grafted Kolanut Pod Husk cellulose adsorbents were successfully prepared via chemical modification of Kola nut pod husk cellulose with acrylamide and N, N’- methylenebisacrylamide. The modified adsorbents were successfully applied for the adsorptive removal of Pb2+ and Cu2+ ions from aqueous solutions at different parameters, such as pH of the solution, adsorbent dosage, contact time, and initial metal ion concentrations were optimized. Qualitative analysis of the modified adsorbents was performed by Fourier Transformed Infra-Red Spectroscopy and Scanning Electron Microscopy. Characterization analyses portrayed the surface of adsorbents as being short elongated shaped with dispersed pores and composed of hydroxyl and carbonyl groups as the main binding sites. The optimum conditions for adsorption of Pb2+ and Cu2+ were found to be: pH; 5, adsorbent dosage; 3.5 and 4 g L-1 , concentration; 60 mg L-1 and contact time; 160 min. Adsorption data were fully fitted with the Freundlich, Langmuir isotherm model, and a pseudo-second order, Elovich kinetic model. The adsorption of metal ion was heterogenous in nature with qmax of 55.14 mg g-1 and 62.09 mg g-1 for Pb2+, 54.82 mg g-1 , and 60.43 mg gfor Cu2+ respectively. These results showed that the modified adsorbents were able to efficiently remove Pb2+ and Cu2+ from aqueous solutions.

Adsorption properties of cellulose/guar gum/biochar composite hydrogel for Cu2+, Co2+ and methylene blue

Herein, Typha angustifolia was used as a charcoal source and chemically modified with a strong oxidizing agent, potassium permanganate (KMnO4), to obtain modified Typha angustifolia (MTC). Then, the green, stable and efficient CMC/GG/MTC composite hydrogel was successfully prepared by compounding MTC with carboxymethyl cellulose (CMC) and guar gum (GG) by free radical polymerization. Various variables that influence adsorption performance were explored, and optimal adsorption conditions were determined. The maximum adsorption capacity calculated from the Langmuir isotherm model was 805.45, 772.52, and 598.28 mg g−1 for Cu2+, Co2+, and methylene blue (MB), respectively. The XPS results revealed that the main mechanism of removing pollutants by adsorbent is surface complexation and electrostatic attraction. After five adsorption-desorption cycles, the CMC/GG/MTC adsorbent still exhibited good adsorption and regeneration capacity. This study provides a low-cost, effective and simple method for preparation of hydrogels from modified biochar, which has excellent application potential in the removal of heavy metal ions and organic cationic dye contaminants from wastewater.

A Green Approach of Utilising Banana Peel (Musa paradisiaca) as Adsorbent Precursor for an Anionic Dye Removal: Kinetic, Isotherm and Thermodynamics Analysis

Methods for removing pollutants include membrane isolation, ion exchange, precipitation, transformation, and biosorption. Adsorption is a cost-effective method of treating industrial wastewater and a common commercial method for concentrating valuable molecules or eliminating contaminants. Banana peel is one of the largest underutilized agricultural wastes in Malaysia. A novel method of using a low-cost biosorbent made from banana peel and Evans blue (EB) dye as a target is the target of this study. The optimal conditions for EB dye adsorption occurred at a dye concentration of 200 mg/L, adsorbent dosages between 10 and 20 g/L, temperature of 25 °C, incubation time of 180 min, and agitation speeds of 100 rpm. Statistical discriminatory analysis showed that the pseudo-second-order kinetic model and the Redlich–Petersen isotherm model were the best models. The maximum adsorption capacity based on Langmuir’s isotherm prediction was 58.51 mg g−1. A non–linear regression of the thermodynamic van’t Hoff plot based on a dimensionless equilibrium constant resulted in negative values for Gibb’s free energy and enthalpy, indicating that the adsorption process is spontaneous and exothermic.

Modeling, optimization and efficient use of MMT K10 nanoclay for Pb (II) removal using RSM, ANN and GA

Regarding the long-term toxic effects of Pb (II) ions on human health and its bioaccumulation property, taking measures for its reduction in the environment is necessary. The MMT-K10 (montmorillonite-k10) nanoclay was characterized by XRD, XRF, BET, FESEM, and FTIR. The effects of pH, initial concentrations, reaction time, and adsorbent dosage were studied. The experimental design study was carried out with RSM-BBD method. Results prediction and optimization were investigated with RSM and artificial neural network (ANN)-genetic algorithm (GA) respectively. The RSM results showed that the experimental data followed the quadratic model with the highest regression coefficient value (R2 = 0.9903) and insignificant lack of fit (0.2426) showing the validity of the Quadratic model. The optimal adsorption conditions were obtained at pH 5.44, adsorbent = 0.98 g/l, concentration of Pb (II) ions = 25 mg/L, and reaction time = 68 min. Similar optimization results were observed by RSM and artificial neural network-genetic algorithm methods. The experimental data revealed that the process followed the Langmuir isotherm and the maximum adsorption capacity was 40.86 mg/g. Besides, the kinetic data indicated that the results fitted with the pseudo-second-order model. Hence, the MMT-K10 nanoclay can be a suitable adsorbent due to having a natural source, simple and inexpensive preparation, and high adsorption capacity.

Adsorption of Phosphate by Synthesized Silver/Calcium Oxide-Activated Carbon Nanocomposite

Developing adsorbents with appreciable morphology will create new approaches for better phosphate adsorption performance. This study aims to investigate the design of an adsorbent by impregnating silver nanoparticles (AgNPs) onto calcium oxide-activated carbon (CaO-AC). The Ag/CaO-AC nanocomposite was used as an adsorbent to remove phosphate. Batch adsorption studies were performed to evaluate the effects of adsorbent dose, initial phosphate concentration, contact time, and pH on removing phosphate from an aqueous solution. The optimized conditions were applied to a real wastewater sample. The optimum condition for phosphate adsorption on Ag/CaO-AC nanocomposite was at an adsorbent dose of 0.02 g, an initial phosphate concentration of 40 mg∙L<sup>-1</sup>, an equilibrium contact time of 45 minutes, and pH 7. Pseudo-second-order proved to be more accurate in representing the data of phosphate adsorption onto Ag/CaO-AC nanocomposite. The adsorption isotherm fitted well on the Langmuir model with a maximum adsorption capacity of 77.4 mg∙g<sup>-1</sup>. From the kinetics and isotherm studies, chemisorption was the primary adsorption mechanism through ion exchange and ligand exchange mechanisms. The results of this study show that Ag/CaO-AC nanocomposite is a promising adsorbent for removing phosphate from wastewater.

Removal of ammonia nitrogen from wastewater using activated carbon prepared from waste tyres

Abstract In this work, the removal of ammonia nitrogen (NH4-N) on activated carbon prepared from waste tyres was conducted in batch studies as a function of adsorbent dosage, pH, temperature, contact time and initial concentration. The pore structure of activated carbon was characterized by N2 adsorption. The optimal conditions for the efficient adsorption of ammonia nitrogen onto waste tyre-activated carbon were found to be an adsorbent dosage of 0.4 g/L, pH 9.0, temperature of 20 °C, contact time of 90 min and initial ammonium nitrogen concentration of 50 mg/L. The kinetics studies showed that the pseudo-second-order model offered the best connection of the adsorption data. The Langmuir model was found to provide the best fit for the experimental data. The thermodynamic results showed that the adsorption of ammonia onto waste tyre-activated carbon was exothermic, random and spontaneous in nature.

Removal of Colour and COD from vegetable tannery wastewater onto bone char– Effect of process parameters, adsorption mechanism, kinetics and equilibrium modelling

ABSTRACT In this study, bone char derived from head bones of cattle was used as an adsorbent in the removal of Chemical Oxygen Demand (COD) and colour from vegetable tannery wastewater. The char was characterized by proximate analysis, pHpzc, FTIR, BET surface area analysis and SEM-EDX spectroscopy. The effects of operational parameters (pH, contact time, adsorbent mass and temperature), the kinetics and isotherms of the adsorption process were investigated. Optimal conditions for maximum adsorption of COD (77.4%) and colour (98.01%) occurred at pH 2 after 60-minute contact time with 50 g of adsorbent at 25°C. The adsorption kinetics were analyzed using Elovich and the pseudo-first and – second-order models. The pseudo-second order model gave the best fit for the kinetic data. Application of the intra-particle diffusion and Boyd models to the kinetic data revealed that COD and colour adsorption onto the bone char were predominantly controlled by film diffusion. The Langmuir, Freundlich, Temkin and Redlich-Peterson isotherm models were applied. The Freundlich model best described the adsorption of COD and colour. The maximum monolayer adsorption capacities for COD and colour were 559.61 mg/g and 2011.76 Pt-Co/g, respectively. These results indicate that bone char can be an effective low-cost adsorbent in wastewater treatment.

Adsorption kinetics of Cd(II) from aqueous solutions onto live vs. dead biosorbents of Sphingomonas sp. GX_15

In this study, the adsorption capacity and removal efficiency of Cd(II) via the live and dead biosorbents of Sphingomonas sp. GX_15 were studied using a batch experiment. The adsorption characterization was investigated using scanning electron microscopy (SEM) and Fourier transform infrared (FT-IR) analysis. The optimal adsorption conditions were determined to be pH of 6.0, contact time of 60 min and dosage of 1.0 g/L. The highest removal efficiency and maximum biosorption capacity of the live and dead biomasses were 78.35% and 90.99%, and 28.33 mg/g and 26.60 mg/g, respectively. R2 values (0.9582 vs. 0.8468 and 0.9784 vs. 0.9831) implied that the data obtained from the dead pellets were better fitted to the Langmuir isotherm model while the Freundlich isotherm model was better fitted for the live pellets. The parameters of KL (0.0875 vs. 0.0646), RL (0.0541 vs. 0.0719) and n (3.8640 vs. 2.7218) in the two isotherm models showed that the adsorption process of dead cells demonstrated a higher affinity and was easier and stronger than that of the live cells. The pseudo-second-order kinetic model was a better fit for depicting the adsorption process, meaning that the rate-limiting step might be chemisorption. The rate parameter of k2 (0.0465 vs. 0.0294) showed that the adsorption was faster for the dead biosorbent. The positive parameters of ΔH° and ΔS° indicated that the adsorption process was endothermic and was increasing in the randomness degree. SEM analysis revealed that the cell surface changed from invaginated to plump, confirming the metals adsorbed into the cell wall. Additionally, the FT-IR spectra study demonstrated that the O–H, N–H, C–H, C = O, C–N, COO-, and –SO3 groups were involved in Cd(II) binding. In sum, we strongly suggest that the dead cells of Sphingomonas sp. GX_15 can act as alternative novel biosorbents for Cd-contaminated soil or water.