Redlich-Peterson Equations Research Articles

Optimizing oxytetracycline removal from aqueous solutions using activated carbon from barley lignocellulosic wastes with isotherms and thermodynamic studies

The excessive presence of antibiotics such as Oxytetracycline (OTC) in the wastewater has increased health problems due to their toxic impact on the aquatic ecosystem. Therefore, their removal has become an important topic. This study aims to produce high surface area-activated carbon derived from low-cost and environmentally friendly barley lignocellulosic wastes to remove OTC from aqueous solutions. The synthesized barley wastes-activated carbon (BW-AC) was characterized using Fourier-Transform Infrared spectroscopy, Thermal Gravimetric Analysis, X-ray diffraction analysis, N2 adsorption/desorption isotherms, and Scanning Electron Microscopy. A Central Composite Design under the Response Surface Methodology (CCD-RSM) was applied to optimize the operational parameters (adsorbent dosage, pH, OTC initial concentration, and contact time) affecting the adsorption capacity as the response factor. The optimum condition of OTC adsorption by BW-AC was the adsorbent dosage of 16.25 mg, pH of 8.25, initial concentration of 62.50 mg/L, and contact time of 23.46 min. An analysis of variance (ANOVA) was performed to investigate the significance of the designed quadratic model and evaluate the parameters interactions. The linear regression coefficient (R2) of 0.975 shows a good correlation between predicted and actual results. The adsorption isotherms were used to determine the contaminant distribution over the adsorbent surface, and the equilibrium data was best described by the Freundlich isotherm due to the R2 value of 0.99 compared to other isotherms and β parameter of 0.23 in Redlich-Peterson equation. Moreover, the n value of 1.25 in Freundlich equation and E value of 0.31 in Dubinin–Radushkevich equation indicates a physical nature of adsorption process. According to the equations results, the maximum adsorption capacity of BW-AC for OTC removal was 500 mg/g, based on the Langmuir isotherm equation. In addition, the thermodynamic studies indicated an endothermic process based on the 0.31 value of ΔH° and spontaneous nature due to the negative amount of ΔG° within the temperature range of 288–318 K. Consequently, the prepared BW-AC can be deemed as a highly effective adsorbent with a large surface area, resulting in significant capacity for removing OTC. This synthesized BW-AC can serve as an environmentally friendly adsorbent for affordable wastewater treatment and is poised to make valuable contributions to future research in this field.

The Redlich–Peterson isotherm for aqueous phase adsorption: Pitfalls in data analysis and interpretation

The Redlich–Peterson isotherm, a variant of the Sips isotherm, is widely used to describe the adsorption characteristics of water contaminants. Despite its popularity, this isotherm is susceptible to misuse and misinterpretation. In this article, we aim to bring to light the various deficiencies associated with the Redlich–Peterson equation, encompassing faulty mathematical formulations, unverified mechanistic interpretations, erroneous linearized versions, unnecessary parameter constraints, incorrect parameter units, inappropriate model comparisons, model misidentifications, and flawed thermodynamic calculations. These deficiencies often stem from a lack of mathematical expertise or a poor understanding of adsorption modeling, and occasionally, from egregious negligence. Our primary goal is to draw attention to these pitfalls and encourage researchers to steer clear of them. By providing guidance and shedding light on these issues, we aim to foster the judicious application of the Redlich–Peterson equation in the analysis and interpretation of adsorption equilibrium data.

Chitosan-gelatin/cetyltrimethylammonium bromide magnetic polymer composites as reusable high performance adsorbent for AR 18 removal

Magnetic chitosan (CS) cross-linked gelatin (Gel) polymer composites (MCGC) were fabricated by reacting CS with Gel in the present of carboxyl modified Fe3O4 nanoparticles and cetyltrimethylammonium bromide using glutaraldehyde as a crosslinking agent. MCGC possessed high zeta potential, abundant active functional groups including amino and hydroxyl groups and facile magnetic separation properties. The prepared MCGC exhibited excellent adsorption performance for AR 18 and the adsorption capacity reached as high as 344.63 mg/g. The adsorption kinetics was fitted well with the pseudo-second order model, while the adsorption isotherms followed the Redlich-Peterson equation best. The thermodynamic studies indicated the adsorption process was exothermic and spontaneous. The adsorption mechanism was studied including electrostatic interaction, hydrogen-bond interaction and π-π stacking between dyes and MCGC. Desorption and renewable experiments proved MCGC possessed high regeneration properties and reusability as an adsorbent.

Potential of Oil-free-Cake Dry Seed Kernels of Desert Date (Balanites aegyptiacus (L.) Delile) for simultaneous Removal of Pb (II), Cu (II) and Cd (II) ions from Battery Industry Effluent

This study was carried out to investigate the potential of oil-free-cake dry seed kernels of desert date (Balanites aegyptiacus (L.) Delile) for simultaneous removal of Pb (II), Cu (II) and Cd (II) ions from Battery Industry Effluent using standard methods in a batch sorption process.. The battery effluent was mimicked by dissolving known concentration of metal ions in distilled water. The optimum conditions for the simultaneous removal of Pb (II), Cu (II) and Cd (II) ions were: pH (6), contact time (105 min) and adsorbent dosage (6.5 g). The results obtained showed that the biosorbent was effective for the simultaneous removal of Pb (II), Cu (II) and Cd (II) ions with removal efficiencies of up to 87.7%, 78.6% and 61.6% respectively. The consistency of the model-predicted optimum conditions were confirmed by conducting experiments under those conditions. It was found that the experimental removal efficiencies under optimum conditions were very close (less than a 5% error) to the model-predicted value. The three parameter isotherm equations (Redlich-Peterson and Sips) provide better fitting than the two-parameter isotherm equations (Freundlich and Langmuir), which can be explained by the fact that these have three adjustable parameters. The best fitted was achieved with the Redlich–Peterson equation. The results of the sorption kinetic study showed that the data fitted well with the pseudo-second order model for Pb (II), Cu (II) and Cd (II) ions. In conclusion, desert date oil-free cake exhibits great potential as an efficient sorbent for removal of metal ions.

Adsorption kinetics and thermodynamics of hydroquinone with aid of diatomite-modified wood ceramics

Diatomite-modified wood ceramics (DMWCs) were successfully prepared to remove hydroquinone from wastewater. The adsorption kinetics and adsorption thermodynamics of DMWCs on hydroquinone were comprehensively studied. The results indicate that the prepared DMWCs with the porous structure are composed of quartz and crystalline graphite. When the hydroquinone dosage is 200 mg and the pH is 7, the removal rate and adsorption capacity of DMWCs reach 76.8% and 12.31 mg/g, respectively. Among the fitting parameters under different pH conditions, the correlation coefficient (R2 = 0.99) of the pseudo-second-order kinetic model is larger than the fitting results of other models, displaying a better fitting effect on the adsorption process of hydroquinone. At different temperatures, the Freundlich equation, Redlich-Peterson equation and Koble-Corrigan equation are all well fitted to the adsorption isotherm data with the correlation coefficients R2 higher than 0.93. The regeneration test shows that the elimination rate of hydroquinone remains above 73% after reuse for 11 times. This study provides a newly available adsorbent of DMWCs to remove hydroquinone from wastewater effectively.

Novel dye removing agent based on CTS-g-P(AA-co-NIPAM)/GO composite

A novel composite Chitosan graft poly (acrylic acid-co-N-isopropylacrylamide)/graphite oxide (CTS-g-P(AA-co-NIPAM/GO) is synthesized and used to remove methylene blue (MB) and fuchsin basic (FB) from aqueous solutions by adsorption. Small amount of GO brings about great improvement of the thermostability together with the adsorption amount. Adsorption capacities of MB and FB increase from 842.1 and 633.7 mg/g, respectively, to 1496.3 and 1000.8 mg/g, respectively, with 0.02 g intercalation amount of GO. The interactions between GO and main body of CTS-g-P(AA-co-NIPAM) graft copolymer are hydrogen and amide bonds, whereas that between dye molecules and CTS-g-P(AA-co-NIPAM)/GO composite is hydrogen bond as well as electrostatic interaction. Effect of various conditions on the adsorption capacities is discussed. Adsorption isotherms and thermodynamics are studied. The adsorption of both MB and FB are spontaneous and satisfy the Redlich-Peterson equation. Kinetic study shows that the adsorption of both dyes is in accordance with the Pseudo first-order kinetic model.

Simulation of surfactant adsorption at liquid-liquid interface: What we may expect from soft-core models?

The present work attempts to systematically explore the surfactant sorption at liquid-liquid interfaces with coarse-grained models targeting thermodynamic properties of reference liquid solutions. We employ dissipative particle dynamics with soft-core forcefield tested against experimental data on micellization of surfactants in water, and the previous results are reproduced in this work. We consider three different nonionic surfactants: hexaethylene glycol monododecyl ether (C12E6), 2-[4-(2,4,4-trimethylpentan-2-yl)phenoxy]ethanol) known as Triton X-100 (TX-100), and two alkyl glucoside surfactants (CnG1) with n-alkane tail fragments and a saccharide hydrophilic head at decane-water and toluene-water interfaces. For TX-100, we composed a model based on the literature forcefield and found good agreement with the experimental critical micelle concentrations (CMCs). The head-head interactions are of different origins for different surfactant groups: entropic repulsion between ethylene oxide chains of C12E6 and TX-100, and more chemically specific and complex interactions between the maltose heads of alkyl glucosides. We interpret our results with the Redlich-Peterson equation of monolayer adsorption in order to relate the adsorption to the bulk concentration of the surfactant and the interfacial tension. The densities of the adsorbed monolayer at CMC mostly agree with the experimental data, and a reasonable agreement was obtained for the interfacial tension at CMC. At the same time, we found significant discrepancies between the simulated and experimental adsorption isotherms. We explain them by the oversimplified forcefield: when the parameters are fitted to the free energies of bulk solutions, they may not correctly reproduce the interfacial free energies.

Synthesis of chitosan graft poly (acrylic acid-co-2-acrylamide-2-methylpropanesulfonic acid)/graphite oxide composite hydrogel and the study of its adsorption

Chitosan graft poly (acrylic acid-co-2-acrylamide-2-methylpropanesulfonic acid)/graphite oxide (CTS-g-P(AA-co-AMPS)/GO) composite hydrogel is synthesized and used to remove rhodamine 6G (R6G) and methyl violet (MV) from aqueous solutions by adsorption. The composite is characterized by infrared spectroscopy (IR), powder X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscope (TEM), thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC). The effect of the adsorption conditions, including the amount of graphite oxide (GO), the initial concentration of dye solutions, the adsorption time, ionic strength, and the mass of the composite, on the adsorption capacities has been studied in detail. It can be seen that small amount of GO can improve the adsorption capacities of both dyes. It is found that the adsorption capacities of R6G and MV can be increased by 57.26% and 26.39%, respectively, compared with CTS-g-P(AA-co-AMPS graft copolymer. The maximal adsorption capacity of R6G and MV is 625.3 and 326.4 mg/g, respectively. The interaction between GO and dye molecules are speculated. GO acts as crosslinking points and combine with the CTS-g-P(AA-co-AMPS) graft copolymer through hydrogen bonds and electrostatic actions. The adsorption isotherms and thermodynamics are discussed. The Gibbs free energy of R6G and MV is that △GR6GӨ = −2.478 KJ/mol and △GMVӨ = −2.577 KJ/mol and it indicates that the adsorption of R6G and MV on CTS-g-P(AA-co-AMPS)/GO is spontaneous and satisfied the Redlich-Peterson equation. Kinetic studies show that the adsorption is in accordance with the Lagergren pseudo first-order kinetic model.

The Use of High Surface Area Mesoporous-Activated Carbon from Longan Seed Biomass for Increasing Capacity and Kinetics of Methylene Blue Adsorption from Aqueous Solution.

Microporous- and mesoporous-activated carbons were produced from longan seed biomass through physical activation with CO2 under the same activation conditions of time and temperature. The specially prepared mesoporous carbon showed the maximum porous properties with the specific surface area of 1773 m2/g and mesopore volume of 0.474 cm3/g which accounts for 44.1% of the total pore volume. These activated carbons were utilized as porous adsorbents for the removal of methylene blue (MB) from an aqueous solution and their effectiveness was evaluated for both the adsorption kinetics and capacity. The adsorption kinetic data of MB were analyzed by the pseudo-first-order model, the pseudo-second-order model, and the pore-diffusion model equations. It was found that the adsorption kinetic behavior for all carbons tested was best described by the pseudo-second-order model. The effective pore diffusivity (De) derived from the pore-diffusion model had the values of 4.657 × 10−7–6.014 × 10−7 cm2/s and 4.668 × 10−7–19.920 × 10−7 cm2/s for the microporous- and mesoporous-activated carbons, respectively. Three well-known adsorption models, namely the Langmuir, Freundlich and Redlich–Peterson equations were tested with the experimental MB adsorption isotherms, and the results showed that the Redlich–Peterson model provided the overall best fitting of the isotherm data. In addition, the maximum capacity for MB adsorption of 1000 mg/g was achieved with the mesoporous carbon having the largest surface area and pore volume. The initial pH of MB solution had virtually no effect on the adsorption capacity and removal efficiency of the methylene blue dye. Increasing temperature over the range from 35 to 55 °C increased the adsorption of methylene blue, presumably caused by the increase in the diffusion rate of methylene blue to the adsorption sites that could promote the interaction frequency between the adsorbent surface and the adsorbate molecules. Overall, the high surface area mesoporous carbon was superior to the microporous carbon in view of the adsorption kinetics and capacity, when both carbons were used for the removal of MB from an aqueous solution.

Straw-Based Activated Carbon: Optimization of the Preparation Procedure and Performance of Volatile Organic Compounds Adsorption.

Straw is one of the largest agricultural biowastes and a potential alternative precursor of activated carbon. Activated carbon prepared from different types of straw have great differences in structure and adsorption performance. In order to explore the performance of different straw-based activated carbon in volatile organic compounds adsorption, five common straws were selected as potential source materials for the preparation of SAC. The straw-based activated carbons were prepared and characterized via a thermo-gravimetric analysis, scanning electron microscope and the Brunauer–Emmett–Teller method. Among the five straw-based activated carbons, millet straw-derived activated carbon exhibited superior properties in SBET, Smic and adsorption capacities of both toluene and ethyl acetate. Furthermore, the preparation process of millet straw activated carbon was optimized via response surface methodology, using carbonization temperature, carbonization time and impregnation ratio as variables and toluene adsorption capacity, ethyl acetate adsorption capacity and activated carbon yield as responses. The optimal preparation conditions include a carbonization temperature of 572 °C, carbonization time of 1.56 h and impregnation ratio (ZnCl2/PM, w/w) of 1.60, which was verified experimentally, resulting in millet straw activated carbon with a toluene adsorption capacity of 321.9 mg/g and ethyl acetate adsorption capacity of 240.4 mg/g. Meanwhile, the adsorption isothermals and regeneration performance of millet straw activated carbon prepared under the optimized conditions were evaluated. The descriptive ability of the isothermals via the Redlich–Peterson equation suggests a heterogeneous surface on millet straw activated carbon. Recyclability testing has shown that millet straw activated carbon maintained a stable adsorption capacity throughout the second to fifth cycles. The results of this work indicate that millet straw activated carbon may be a potential volatile organic compound adsorbent for industrial application.

Understanding the removal of an anionic dye in textile wastewaters by adsorption on ZnCl2 activated carbons from rice and coffee husk wastes: A combined experimental and theoretical study

Activated carbons have been prepared from rice husk (RH) and coffee husk (CH) using ZnCl2 as activating agent. These materials were characterized by thermogravimetric and elemental analysis, infrared spectroscopy (FTIR), the point of zero charge (PZC), scanning electron microscopy (SEM), and nitrogen adsorption. The removal efficiency of the obtained adsorbents was tested using indigo carmine (IC) at different pH, as a model dye, in both distilled water and textile wastewater. The results showed that the dye adsorption on the natural adsorbents and the activated carbons was favorable at acidic pH (3.0). Moreover, the best IC removal in both matrices was reached by the material prepared from CH and activated with ZnCl2 (CH-ZnCl2). This result correlated well with the higher value PZC (7.1), large specific surface area, and porosity characteristics. Additionally, the dye adsorption on the CH-ZnCl2 surface was improved using the smaller particle size and the optimal dose of adsorbent; the adsorptions obtained were much better than those of a commercial activated carbon. Furthermore, the isotherms study showed the adsorption to be monolayer type according to Langmuir and Redlich-Peterson equations. The adsorption kinetics followed a pseudo-second-order kinetic model, and intra-particle diffusion showed that IC adsorption on the surface is faster than inside CH-ZnCl2. The thermodynamic parameters suggest that the IC adsorption is a physical process, which is spontaneous and endothermic. According to density functional theory calculations and experimental FTIR analysis, oxygenated groups and aromatic rings are relevant during the IC adsorption through hydrogen bonds and π-π interactions.

Study on the Preparation and Adsorption Properties of Sodium Alginate Graft Polyacrylic Acid/Graphite Oxide Composite Hydrogel

Sodium alginate graft poly acrylic acid/graphite oxide (SA-g-PAA/GO) composite hydrogel is prepared using potassium persulfate (KPS) as an initiator and N,N '-methylenebisacrylamide (MBA) as a cross-linker by solution polymerization. The composite hydrogel has been characterized by means of infrared spectroscopy (IR), powder X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscope (TEM) and thermogravimetric analysis (TGA). Adsorption behavior of acid fuchsin (AF) and sunset yellow (SY) onto the composite hydrogel is investigated in detail. Maximal adsorption amount of AF and SY is 86.9 and 77.5 mg/g (1.484 × 10–4 and 1.713 × 10–4 mol/g), respectively, under the condition that GO is 0.02 g, initial concentration of dye solutions is 1000 mg/L, mass of SA-g-PAA/GO is 0.2 g, adsorption time is 24 h, and the temperature is 25°C. The adsorption amount AF and SY is 28.9 and 28.5% higher than that on SA-g-PAA graft copolymer which is prepared without GO. GO serves as cross-linking agent during polymerization and the interaction between GO and SA-g-PAA is intermolecular hydrogen bonds. The adsorption of AF and SY conforms to the Redlich–Peterson equation and Langmuir equation, respectively. The kinetic models of both AF and SY conform to the quasi-second-order kinetic equation.

Study of Amoxicillin Adsorption on the Silanized Multiwalled Carbon Nanotubes: Isotherms, Kinetics, and Thermodynamics Study

In this research, multiwalled carbon nanotubes (MWCNTs) were firstly oxidized with HNO3/H2SO4 mixture and then functionalized with silane groups and were used for the removal of amoxicillin (AMX) as one of the most consumed antibiotics from the solution media. In addition, NH4Cl-induced activated carbon (NAC) was also prepared as another adsorbent. Then the adsorption process was investigated by using silanized oxidized MWCNTs (S-F-MWCNTs). Physicochemical characterization of MWCNTs, F‑MWCNTs and S-F-MWCNTs was investigated by FTIR, FESEM, EDS, BET/BJH, TGA, and CA techniques. Also, NAC was characterized by FTIR technique. The effect of the operational variables such as pH, adsorbent dosage, contact time, sorbate concentration and temperature on the removal efficiency of the S‑F-MWCNTs adsorbent was studied in details by batch procedure. The results showed that maximum adsorption efficiency can be achieved under the optimized conditions of pH 7.0, adsorbate concentration = 70.0 mg/L, contact time = 45.0 min, S-F-MWCNTs adsorbent dosage = 0.020 g, and temperature = 25.0°C. Isothermic studies have showed that the Redlich–Peterson equation with a correlation coefficient of 0.995 and the lowest error rate has the highest correlation with the experimental data. The adsorption kinetics results show that AMX adsorption process was well-described by pseudo-second-order kinetic model. Thermodynamic parameters of the adsorption process were also calculated revealing that the adsorption of AMX onto S‑F‑MWCNTs and NAC is an exothermic and spontaneous process. Based on the experimental results, S‑F‑MWCNTs were regarded as an acceptable adsorbent for the removal of AMX from aqueous solutions. The AMX adsorption data under the optimum conditions via S-F-MWCNTs and NAC adsorbents revealed that the adsorption efficiency is desirable and satisfactory.

Enhanced removal of diclofenac by an organohalloysite intercalated via a novel route: Performance and mechanism

An organohalloysite was prepared using a new procedure. Halloysite (H) was pre-intercalated with dimethyl sulfoxide and then mixed with a solution of hexadecyltrimethylammonium (HDTMA) having a concentration equivalent to six times the CEC of the starting Algerian halloysite. The novel nanohybrid obtained (HH6-d) was characterized and compared with a sample intercalated from the beginning by HDTMA (HH6). Intercalation of HDTMA cations in the interlayer space was evidenced by XRD with an expansion of the basal distance from 7.6 to 26.0 Å for an intercalation rate of 75% (HH6-d) versus 42% for HH6. All materials were used to remove diclofenac (DFC). pH influence, isotherm, thermodynamic data, reusability of the best adsorbent and the mechanism of interaction have been examined. The experimental isotherms were appropriately adjusted by the Redlich-Peterson equation. The best adsorbent adsorbs 154.3 mg g−1, with an adsorption sequence as follows: HH6-d > HH6 > unmodified clay, i.e. according to the intercalated fraction, so that the HDTMA intercalating agent interacts with the diclofenac molecules. This interaction was entropically driven, endothermic and spontaneous. It would involve not only hydrophobic bond between the tail group of HDTMA represented by the hydrocarbon chain and the hydrophobic moiety of DFC represented by the aromatic groups, but also an electrostatic interaction between the negative charge of the carboxylate ion (COO−) and the positive charge of the aluminol groups coating the lumen.

CuO coated olive cake nanocomposites for rapid phenol removal and effective discoloration of high strength olive mill wastewater

The potential of solid olive wastes-based adsorbent (CuO−OC) with photocatalytic power was established for the removal of total phenolics and photocatalytic discolourization of high strength olive mill wastewater (OMW). Clear insight of the FTIR and Brunauer−Emmett−Teller analyses showed that oxygen-containing functional groups of CuO−OC likely participated in the adsorption of total phenols from the OMW via a π−π interaction, hydrogen bonding and electrostatic interaction. Also, the total pore volume of CuO−OC decreased from 0.068 to 0.052 cm3 g−1 after adsorption, which suggested that phenolics were trapped within the micro- and mesopores of CuO−OC. The adsorption kinetics revealed that ∼82.7–95% of the phenolic compounds were removed within the first 360 min which is relatively faster than adsorbents and methods reported elsewhere. The isotherm results showed that Redlich–Peterson equation fit the experimental data very well with least error (χ2 = 1.46–3.19) and high correlation coefficients (0.992–0.996), which suggested a mixture of hetero- and monolayer coverage of the phenolics on the CuO−OC surface. Results obtained herein are of practical interest and the reuse efficiency of CuO−OC remained ∼60% after 5 successive recycling.

Kinetic and static parameters of a new sorbent based on clays and ways of its determination

The paper demonstrates experimental research results obtained while studying heavy metal ions sorption ability. These ions were extracted from a multicomponent model solution. The research was conducted for a new sorption sample based on clays under static conditions and carried out in the range of low concentrations of heavy metal ions in the solution. For the development of sorption isotherms, the method of non-variant test portions and variable concentrations of heavy metal ions was used. As a result, the researchers constructed sorption isotherms for copper, zinc, manganese, iron and lead. The experimental data was approximated by the Freundlich, Langmuir, Langmuir-Freundlich, Toch and Redlich-Peterson equations. MathCAD and SciDAVis software programs were used for mathematical processing. The authors came to the conclusion that the Langmuir equation most adequately described the sorption isotherms for copper, lead and zinc, the Toch model was preferable for iron and manganese isotherms. During the experiment, sorption constants and determination coefficient were also determined for each metal.

Oil removal from produced water by agriculture waste adsorbents

In this investigation, oil was removed from PW using adsorbents prepared from agriculture waste (date pits and walnut shells) packed in filter beds. Several parameters were examined, such as (contact time, oil content, TSS, conductivity, TDS, turbidity, and pH). The study showed that both the walnut shell and date pit achieved well. Furthermore, MB adsorption on the carbonised date pits and crushed Walnut shells with different concentrations were explored. The maximum adsorption capacities of oil content for walnut shell or date bits was 87%, 80%; respectively. The oil adsorption was confirmed through three models: Freundlich, Langmuir and Redlich-Peterson models. The Redlich-Peterson equation was more applicable for Date pits and Walnut shells rather than the Freundlich or Langmuir equation. Whereas its correlation coefficients showed high R2 = 0.9998 and 0.9917; respectively. In addition, Freundlich model was more applicable for Walnut shells rather than Date pits because its R2 = 0.9507 for walnut shells.

Oil removal from produced water by agriculture waste adsorbents

In this investigation, oil was removed from PW using adsorbents prepared from agriculture waste (date pits and walnut shells) packed in filter beds. Several parameters were examined, such as (contact time, oil content, TSS, conductivity, TDS, turbidity, and pH). The study showed that both the walnut shell and date pit achieved well. Furthermore, MB adsorption on the carbonised date pits and crushed Walnut shells with different concentrations were explored. The maximum adsorption capacities of oil content for walnut shell or date bits was 87%, 80%; respectively. The oil adsorption was confirmed through three models: Freundlich, Langmuir and Redlich-Peterson models. The Redlich-Peterson equation was more applicable for Date pits and Walnut shells rather than the Freundlich or Langmuir equation. Whereas its correlation coefficients showed high R2 = 0.9998 and 0.9917; respectively. In addition, Freundlich model was more applicable for Walnut shells rather than Date pits because its R2 = 0.9507 for walnut shells.

The Effect of SBA-15 Surface Modification on the Process of 18β-Glycyrrhetinic Acid Adsorption: Modeling of Experimental Adsorption Isotherm Data.

This study aimed at the adsorption of 18β-glycyrrhetinic acid (18β-GA), a pentacyclic triterpenoid derivative of oleanane type, onto functionalized mesoporous SBA-15 silica and non-porous silica (Aerosil®) as the reference adsorbent. Although 18β-GA possesses various beneficial pharmacological properties including antitumor, anti-inflammatory, and antioxidant activity, it occurs is small amounts in plant materials. Thus, the efficient methods of this bioactive compound enrichment from vegetable raw materials are currently studied. Siliceous adsorbents were functionalized while using various alkoxysilane derivatives, such as (3-aminopropyl)trimethoxysilane (APTMS), [3-(methylamino)propyl]trimethoxysilane (MAPTMS), (N,N-dimethylaminopropyl)trimethoxysilane (DMAPTMS), and [3-(2-aminothylamino)propyl] trimethoxysilane (AEAPTMS). The effect of silica surface modification with agents differing in the structure and the order of amine groups on the adsorption capacity of the adsorbent and adsorption efficiency were thoroughly examined. The equilibrium adsorption data were analyzed while using the Langmuir, Freundlich, Redlich-Peterson, Temkin, Dubinin-Radushkevich, and Dubinin-Astakhov isotherms. Both linear regression and nonlinear fitting analysis were employed in order to find the best-fitted model. The adsorption isotherms of 18β-GA onto silicas functionalized with APTMS, MAPTMS, and AEAPTMS indicate the Langmuir-type adsorption, whereas sorbents modified with DMAPTMS show the constant distribution of the adsorbate between the adsorbent and the solution regardless of silica type. The Dubinin-Astakhov, Dubinin-Radushkevich, and Redlich-Peterson equations described the best the process of 18β-GA adsorption onto SBA-15 and Aerosil® silicas that were functionalized with APTMS, MAPTMS, and AEAPTMS, regardless of the method that was used for the estimation of isotherm parameters. Based on nonlinear fitting analysis (Dubinin-Astakhov model), it can be concluded that SBA-15 sorbent that was modified with APTMS, MAPTMS, and AEAPTMS is characterized by twice the adsorption capacity (202.8–237.3 mg/g) as compared to functionalized non-porous silica (118.2–144.2 mg/g).

Preparation of Schiff base-intercalated layered double hydroxides for selective copper(II) ion capture

This paper demonstrates a new interlayer synthesis method for producing a metal adsorbent composed of a layered double hydroxide (LDH) and a Schiff base. LDH are appropriate adsorbents for many kinds of toxic waste, especially heavy metals, in terms of preparation, handling, cost, and toxicity. Metal ions present in LDH form complexes with ligands; therefore, preparing a ligand-intercalated LDH is difficult. The specific LDH synthesized in the present study consists of magnesium, aluminum, and a Schiff base prepared in the interlayer from an aliphatic amine and salicylaldehyde. A precursor aliphatic amine-intercalated LDH was first prepared by coprecipitation and then converted into a Schiff base-intercalated LDH by reaction with salicylaldehyde in an alcoholic medium. The Schiff base-intercalated LDH obtained was characterized by X-ray diffractometry, Fourier-transform infrared spectroscopy, thermogravimetric-differential thermal analysis, elemental analysis, and scanning electron microscopy. The characterization data show that the Schiff base exists in the LDH interlayer and that the Schiff base-intercalated LDH adsorbs Cu(II) ions from an aqueous solution within 2 h under mild pH, and temperature. However, Ni(II), Zn(II), Cd(II), Pb(II), and Na(I) ions were not adsorbed by the LDH. The adsorption of Cu(II) ions onto the Schiff base-intercalated LDH conforms to the Redlich–Peterson equation, suggesting the existence of multiple kinds of Cu(II) adsorption sites in the interlayer of the Schiff base-intercalated LDH.