Adsorbent For Removal Of Tetracycline Research Articles

Evaluation and optimization of six adsorbents for removal of tetracycline from swine wastewater: Experiments and response surface analysis

The removal of tetracycline antibiotics using adsorbents is becoming an environmentally friendly and cost-effective method. This study systematically analyzed the stability, structure, morphology, and chemical properties of various adsorbents. Batch adsorption experiments (pH, time, temperature, tetracycline concentration, and adsorbent dosage) were conducted to compare the adsorption capacity of the six adsorbents (biochar, activated carbon, montmorillonite, zeolite, chitosan, and polymerized aluminum chloride) for tetracycline removal. The results indicated that montmorillonite had the highest adsorption efficiency, followed by biochar, with chitosan showing the lowest efficiency. At an adsorbent dose of 25 g/L and an initial tetracycline concentration of 120 mg/L, the removal rates of tetracycline by montmorillonite, biochar, and chitosan were 97.6%, 69.3%, and 12.2%, respectively. Furthermore, the removal rate of tetracycline by biochar, following the response surface methodology optimal mode, increased by 5.5%. The Elovich model was better suited to explain the adsorption process of tetracycline compared to the conventional pseudo-first kinetic model and second-order kinetic model. The isothermal adsorption model suggested that both chemisorption and physisorption occurred in all removal processes, in which chemisorption dominated. Tetracycline was efficiently adsorbed through the combined effects of pore filling, electrostatic attraction, π-π interactions, and complexation reactions of surface functional groups. Additionally, montmorillonite demonstrated superior performance as an adsorbent for tetracycline removal from swine wastewater compared to the other adsorbents studied.

Iron terephthalate metal-organic framework (MOF‑235) modified with zinc as an efficient adsorbent for removal of tetracycline from aqueous solution

The study focused on synthesizing and modifying the MOF235-Zn composite to enhance its catalytic properties for removing tetracycline from water systems. Incorporating zinc into the MOF235 structure significantly improved its efficiency in tetracycline removal. Characterization methods such as SEM, mapping, EDS, and FTIR confirmed the successful synthesis and modification of the MOF235-Zn composite. The addition of zinc reduced the time needed for tetracycline removal and minimized the required amount of MOF235-Zn, even at room temperature. The study also investigated the impact of operational parameters on tetracycline adsorption and identified optimal conditions for tetracycline removal. Overall, the findings highlight the potential of the MOF235-Zn composite to effectively remove tetracycline, particularly under optimized operational conditions.

Chitin/calcite composite extracted from shell waste as a low-cost adsorbent for removal of tetracycline and ciprofloxacin: Effects and mechanisms

Recently, water contamination caused by the misuse of antibiotics has become a growing concern. In this study, an economical chitin/calcite composite (CCA) was extracted from crab shell waste, and the effects and mechanisms of its removal of ciprofloxacin (CIP) and tetracycline (TC) from aqueous solution were investigated. The functional groups of chitin and the metal phase of calcite gave CCA the ability to remove antibiotics. Experiments on kinetics, isothermal adsorption, thermodynamics, co-removal, and reusability were conducted to systematically explore the adsorption performances of CCA toward antibiotics. The pseudo-second-order (FSO) and Langmuir models suited the data obtained from experiments best and displayed a good fit for the chemisorption and a certain homogeneity of adsorption sites. At 25 °C, the maximum adsorption capacities (Qmax) toward CIP and TC were 228.86 and 150.76 mg g−1, respectively. The adsorption mechanisms of CCA with TC and CIP are pH dependent since pH can affect the surface charge of CCA and the form in which CIP and TC are existing. The X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FTIR) demonstrated that the keto-O and carboxyl groups of CIP and the carbonyl, hydroxyl, and amido groups of TC could be responsible for the binding with the calcite and the functional groups of chitin through surface complexation, cation bridge and hydrogen bonding.

Synthesis and characterization of new composite from modified silica-coated MnFe2O4 nanoparticles for removal of tetracycline from aqueous solution.

In this study, a new composite from silica coated MnFe2O4 nanoparticles, diethylenetriamine, 3-chloropropyl trimethoxysilane and Mg-Al Layered Double Hydroxide (Mg-Al LDH/DETA/CPTMS/SCNPs) composite was synthesized. The Mg-Al LDH/DETA/CPTMS/SCNPs composite was examined by Fourier transform infrared spectrometer (FT-IR), Scanning Electron Microscopy (SEM), Energy Dispersive X-ray (EDS), X-ray diffraction (XRD), Thermogravimetric Analysis (TGA) and Vibrating Sample Magnetometry (VSM). The synthesized composite exhibited magnetic property with a saturation magnetization of 0.40 emu g-1. The Mg-Al LDH/DETA/CPTMS/SCNPs composite was utilized as a successful adsorbent for removal of tetracycline from aqueous solutions. The effect of various operation factors such as initial drug concentration, adsorbent dosage, pH and contact time were investigated. The optimized variable conditions such as adsorbent dose of 60 mg L-1, drug concentration of 100 mg L-1, pH = 7 and contact time 30 min were obtained. For describing the adsorption isotherms, the Langmuir, Freundlich and Temkin adsorption models were utilized. The results indicated that the adsorption isotherm is in good agreement with Langmuir model. According to the Langmuir analysis, the maximum adsorption capacity (qm) of the Mg-Al LDH/DETA/CPTMS/SCNPs composite for tetracycline was obtained to be 40.16 mg g-1. The kinetic studies revealed that the adsorption in all cases to be a pseudo second-order process. The negative value of ΔG° and the positive value of ΔH° showed the adsorption process to be spontaneous and endothermic.

Room-temperature synthesis of bimetallic ZnCu-MOF-74 as an adsorbent for tetracycline removal from an aqueous solution.

The novel bimetallic MOF, ZnCu-MOF-74, has been evaluated for the remediation of tetracycline-contaminated water. ZnCu-MOF-74 was obtained at room temperature, avoiding high pressure and temperature. ZnCu-MOF-74 exhibited chemical stability in the 4-8 pH range. The adsorption result analysis was described using the Elovich kinetic model and the Langmuir adsorption isotherm, suggesting a physicochemical process. The maximum adsorption capacity was estimated at 775.66 mg g-1. The pH of the solution and the presence of ions such as NO3-, SO42-, Na+, Mg2+, Cl-, and Ca2+ had no influence on the removal of tetracycline. In addition, π-interactions and metal complexation were proposed as possible adsorption mechanisms through FT-IR and XPS. ZnCu-MOF-74 showed outstanding cyclability performance, preserving its adsorption capacity after 4 adsorption-desorption cycles, besides exhibiting chemical stability, proving the benefits of applying ZnCu-MOF-74 in the water treatment process.

Adsorption modeling of tetracycline removal by multi-walled carbon nanotube functionalized with aspartic acid and poly-pyrrole using Bayesian optimized artificial neural network

BackgroundThe high use of tetracycline (TC) for the prevention and treatment of diseases has led to the formation of unknown compounds and various metabolized products of TC in aquatic environments. It seems that compounds containing carbon nanotubes have a good performance as an adsorbent for TC removal. MethodsMulti-Walled Carbon Nanotubes doped with aspartic acid (Asp) and polypyrrole (PPy) were synthesized to adsorb TC. The adsorbent morphology and its corresponding physicochemical properties were characterized by FTIR, XRD, FESEM, EDS and BET analysis. The adsorption capacity was investigated as a function of adsorbent dosage, pH, temperature, contact time, and initial concentration. Significant findingsThe maximum adsorption capacity was 34.50 mg/g, for an adsorbent dosage of 0.005 g, pH = 5, contact time of 60 min, and the temperature of 25℃. Reusability studies demonstrate that the removal efficiency of adsorbent after seven cycles has been more than 70%. Also, An Artificial Neural Network was developed to predict the adsorption capacity of the adsorbent. ANN performance was enhanced using Bayesian Optimization as the hyperparameter tuning scheme and 11 hyperparameters of the network as the decision variables. The improved ANN performance demonstrated a remarkable ability to model the adsorption process of TC (RMSE=0.33 and R2=0.9996).

Novel ZIF-67-derived Co@CNTs nanocomposites as effective adsorbents for removal of tetracycline and sulfadiazine antibiotics

Tetracycline (TCC) and sulfadiazine (SDZ) are two of the most consumed antibiotics for human therapies and bacterial infection treatments in aquafarming fields, but their accumulative residues can result in negative effects on water and aquatic microorganisms. Removal techniques are therefore required to purify water before use. Herein, we concentrate on adsorptive removal of TCC and SDZ using cobalt@carbon nanotubes (Co@CNTs) derived from Co-ZIF-67. The presence of CNTs on the edge of nanocomposites was observed. Taguchi orthogonal array was designed with four variables including initial concentration (5–20 mg L−1), dosage (0.05–0.2 g L−1), time (60–240 min), and pH (2–10). Concentration and pH were found to be main contributors to adsorption of tetracycline and sulfadiazine, respectively. The optimum condition was found at concentration 5 mg L−1, dosage 0.2 g L−1, contact time 240 min, and pH 7 for both TCC and SDZ removals. Confirmation tests showed that Co@CNTs-700 removed 99.6% of TCC and 97.3% of SDZ with small errors (3–5.5%). Moreover, the kinetic and isotherm were studied, which kinetic and isotherm data were best fitted with pseudo second-order model and Langmuir. Maximum adsorption capacity values for TCC and SDZ were determined at 118.4–174.1 mg g−1 for 180 min. We also proposed the main role of interactions such as hydrogen bonding, π–π stacking, and electrostatic attraction in the adsorption of antibiotics. With high adsorption performance, Co@CNTs-700 is expected to remove antibiotics efficiently from wastewater.

Adsorptive removal of tetracycline and methylene blue from aqueous solution with a water resistance copper-based metal–organic framework

Copper-1,3,5-benzenetricarboxylic acid (Cu–BTC) is a research hotspot for metal–organic frameworks (MOFs) because of its remarkable intrinsic structural features.

Adsorptive removal of tetracycline from aqueous solutions using magnetic Fe2O3 / activated carbon prepared from Cynometra ramiflora fruit waste

Herein, the sustainable fabrication of magnetic iron oxide nanoadsorbent prepared with activated carbon of inedible Cynometra ramiflora fruit has been investigated. Activated carbon was obtained from phosphoric acid-treated C. ramiflora fruit, which was then utilized for the synthesis of magnetic nanocomposite (CRAC@Fe2O3). The formed nanocomposite was a porous irregular dense matrix of amorphous evenly sized spherical nanoparticles, as visualized by FESEM, and also contained carbon, oxygen, iron, and phosphorous in its elemental composition. FT-IR spectrum depicted characteristic bands attributing to Fe–O, C–OH, C–N, CC, and –OH bonds. VSM and XRD results proved that CRAC@Fe2O3 was superparamagnetic with a moderate degree of crystallinity and high saturation magnetization value (1.66 emu/g). Superior surface area, pore size, and pore volume of 766.75 m2/g, 2.11 nm, and 0.4050 cm3/g respectively were measured on BET analysis of CRAC@Fe2O3 nanocomposite, indicating their suitability for use as an adsorbent. On application of this nanocomposite for adsorption of tetracycline, maximum removal of 95.78% of 50 ppm TC at pH 4, CRAC@Fe2O3 0.4 g/L in 240 min. The adsorption of TC by CRAC@Fe2O3 was confirmed as monolayer sorption by ionic interaction (R2 = 0.9999) as it followed pseudo-second-order kinetics and Langmuir isotherm (R2 = 0.9801). CRAC@Fe2O3 showed a maximum adsorption capacity of 312.5 mg/g towards TC antibiotics indicating its potential for the treatment of antibiotic-contaminated samples. Since negative ΔGo and positive ΔHo and ΔSo values were obtained at all tested temperatures during the thermodynamic studies, the adsorption was confirmed to be endothermic, spontaneous, and feasible with an enhanced degree of randomness.

Insights into high-efficient removal of tetracycline by a codoped mesoporous carbon adsorbent

Adsorbents with simple preparation and high surface area have become increasingly prevalent for the removal of organic contaminants. Herein, a carbon nanoplate codoped by Co and N elements with abundant ordered mesoporous (Co/N-MCs) was applied as an adsorbent for tetracycline removal. Taking integrated advantages of ordered mesopores on carbon-based structures and N-doping inducing the strengthened π–π dispersion and generation of pyridinic N, as well as cobaltic nanoparticles embedded in carbon nanoplates, the Co/N-MCs was tailored for high efficiently absorbing tetracycline via π-π interaction, Lewis acid-base interaction, metal complexation and electrostatic attraction. The Co/N-MCs had the advantages of high surface area, porous structure, plenty adsorption sites, and easy separation. As such, the as-prepared Co/N-MCs adsorbents significantly enhanced tetracycline removal performance with a maximum adsorption capacity of 344.83 mg·g −1 at pH 6 and good reusability, which was finally applied to removal tetracycline from tap water sample. Furthermore, the adsorption process towards tetracycline hydrochloride could be well attributed to the pseudo-second-order kinetic and Langmuir isotherm models. Compared with traditional carbon-based adsorbents, it owns a simpler synthesis method and a higher adsorption capacity, as well as it is a promising candidate for water purification.

Co-doped Fe-MIL-100 as an adsorbent for tetracycline removal from aqueous solution.

In the study, Fe-MIL-100 was modified by adding Co2+ in the synthesis process; Co/Fe-MIL-100 was successfully synthesized and used to adsorb tetracycline. The addition of Co2+ increased the thermal stability of Fe-MIL-100 without changing the crystal structure. It was found that Co/Fe-MIL-100 exhibited satisfactory performance in tetracycline removal, the tetracycline removal efficiency reached almost 100% in the initial concentration range of 10-40mg/L, and it still reached 82.38% under the condition of 60mg/L tetracycline. Besides, the factors of tetracycline concentration, pH and inorganic anion on removal efficiency were explored. The coexistence of inorganic anion decreased the adsorption capacity of tetracycline due to the competitive adsorption. CO32- had a more obvious inhibition effect on the adsorption efficiency of tetracycline than Cl-. The fitting correlation coefficient of Langmuir model was higher and the kinetics better fitted by pseudo-second-order, respectively. As a result of its high removal efficiency and excellent recycling performance, it has great potential in application fields such as removing tetracycline from wastewater.

Vinasse-based biochar magnetic composites: adsorptive removal of tetracycline in aqueous solutions.

Highly efficient and cost-effective adsorbents for antibiotic removal are the key to mitigate pollution by industrial wastewaters. Pyrolyzing low-cost winemaking waste into biochar is a promising means for waste biomass utilization. This study assembled vinasse-derived biochar with manganese ferrite into vinasse-manganese ferrite biochar-magnetic composites (V-MFB-MCs) through simultaneous pyrolysis of waste biomass and metal (Mn and Fe) hydroxide precipitates. Batch experiments were conducted to evaluate the kinetics and isotherms of tetracycline (TC) adsorption as well as the influence of pH value, humic acid, and ionic strength. Morphological characterization showed that crystalline MnFe2O4 nanoparticles were impregnated within the framework of fabricated V-MFB-MCs. Superior TC adsorption capacity and fast pseudo-second-order kinetics could be achieved by the V-MFB-MCs-800 at pH 3.0. The TC adsorption onto V-MFB-MCs-800 was highly pH-dependent and controlled by the positive influence of ionic strength and humic acid. V-MFB-MCs-800 showed excellent adsorption performance in different natural water. Multiple interaction mechanisms including pore filling effect, π-π stacking interaction, and hydrogen bonding contribute to TC removal by V-MFB-MCs-800, which can be an innovative biowaste-derived material for industrial wastewater treatment.

Adsorptive removal of tetracycline and ciprofloxacin drugs from water by using a magnetic rod-like hydroxyapatite and MIL-101(Fe) metal-organic framework nanocomposite.

A novel porous nanocomposite composed of hydroxyapatite nanorods (HAP), a MIL-101(Fe) metal-organic framework, and Fe3O4 nanoparticles was successfully fabricated in this work. The magnetic HAP/MIL-101(Fe)/Fe3O4 ternary nanocomposite was identified by various techniques, namely FT-IR spectroscopy, XRD, Raman spectroscopy, SEM, EDX, TEM, BET specific surface area, zeta potential, and VSM measurements. Tetracycline (TC) and ciprofloxacin (CIP) aqueous solutions were used to evaluate the adsorption performance of the resulting HAP/MIL-101(Fe)/Fe3O4 composite. The adsorption rate and capacity of HAP/MIL-101(Fe)/Fe3O4 were increased as compared with HAP, MIL-101(Fe), and HAP/MIL-101(Fe) samples due to the increased attraction. The influence of initial drug concentration, adsorbent dosage, temperature, and pH on the adsorption process was investigated. The results showed that the removal efficiencies of HAP/MIL-101(Fe)/Fe3O4 for TC and CIP were 95% and 93%, under the determined optimum conditions: pH of 7, drug concentration of 50 mg L-1, adsorbent dosage of 30 mg, and temperature of 25 °C. The maximum adsorption capacities of HAP/MIL-101(Fe)/Fe3O4 for TC and CIP were 120.48 mg g-1 and 112.35 mg g-1, respectively. Reusability of the prepared nanocomposite was easily achieved up to three times without significant change in its structure. As a result, the synthesized magnetic nanocomposite can be reused as a suitable absorbent for TC and CIP removal from aqueous solutions.

Adsorptive removal of tetracycline from aqueous solution by surfactant-modified zeolite: equilibrium, kinetics and thermodynamics

Adsorptive removal of tetracycline from aqueous solution by surfactant-modified zeolite: equilibrium, kinetics and thermodynamics

Nanocomposites of zirconia@activated carbon derived from a hazelnut shell for the adsorption of tetracyclines from water

A nanocomposite of activated carbon derived from hazelnut shell functionalized with zirconia nanoparticles (ZrO2@AC) was prepared via a pyrolysis method and was used for the adsorptive removal of tetracycline, chlortetracycline and oxytetracycline.

Optimization of tetracycline adsorption onto zeolitic–imidazolate framework-based carbon using response surface methodology

This study investigated the fabrication of zeolitic–imidazolate framework (ZIF-8) and ZIF-8-derived porous carbon and their application in the adsorptive removal of tetracycline from water. The materials were analysed by X-ray photoelectron spectroscopy, scanning electron microphotography, and the measurement of pH point of zero charge. The results indicated the presence of N-doped carbon network and functional groups on ZIF-8-derived porous carbon. Response surface methodology was used for statistical analysis. The effect of operating parameters involving tetracycline concentration (25–100 mg/L), dose (0.05–0.75 g/L), and pH (4–10) were conducted. The results indicated that the quadratic regression models were statistically significant and the parameters of tetracycline concentration and adsorbent dose profoundly affected the adsorption capacity. The optimum conditions for adsorption of tetracycline were suggested and verified. The highest tetracycline actual adsorption capacity obtained by ZIF-8 and ZIF-8-derived porous carbon were 171.3, and 339.06 mg/g, respectively. The study proposed the participation of hydrogen bonding and π–π interactions as main mechanism. With the high suitability, the response surface methodology can be an efficient optimization tool.

Adsorptive removal of tetracycline and lincomycin from contaminated water using magnetized activated carbon

The release of antibiotics such as tetracycline (TC) and lincomycin (LM) used in livestock production into the environment and the development of antimicrobial resistance represents a great concern. To utilize the adsorption process for the removal of antibiotics and to facilitate separation of spent adsorbent from the treated water, a magnetized activated carbon (MAC) was developed using ultrasonic-assisted co-precipitation of iron oxide nanoparticles (γ-Fe2O3). The superparamagnetic properties of the adsorbent allowed a separation efficiency of 95 ± 3% from water, while magnetization changed the physiochemical properties of activated carbon including BET surface area, pore volume and PZC. The developed adsorbent was used for adsorption of TC from water at various concentrations and temperatures, and for simultaneous adsorption of TC and LM. The adsorption capacities of MAC toward TC either as an individual or in the presence of LM in water were slightly lower than that of AC, and the adsorption process had an endothermic nature. The adsorption capacities of MAC for TC was lower when LM was present in adsorption media (0.4 < qMixture,TC/qSingle,TC < 1.0), and vice versa. This indicates the competitive nature of TC and LM adsorption. The obtained data were fitted non-isothermally into different adsorption models (single and binary solute) and the associated coefficients were determined. Redlich–Peterson isotherm predicted the TC adsorption data in the range of 5–35 °C with accuracy and estimated the enthalpy change of adsorption as 54.3 kJ mol−1. Also, extended Langmuir model provided the most accurate prediction of the binary adsorption system.

Simultaneous carbonization, activation, and magnetization for producing tea waste biochar and its application in tetracycline removal from the aquatic environment

Facile modification of biochar to greatly improve its properties and then promoting its potential application is still a challenge. In this study, magnetic porous tea waste biochar (MKHBC) was produced first by hydrothermal pretreatment, impregnation with FeCl3·6H2O and KHCO3, and then pyrolysis at 700 °C to realize simultaneous carbonization, activation, and magnetization. Pristine biochar (HBC) was also prepared as a control. Biochars were characterized by SEM, TEM, XRD, Raman, BET, FTIR, XPS, and elemental analysis. The results showed that MKHBC had a surface area of 1035.11 m2g−1, a total pore volume of 0.583 cm3g−1, and a micropore volume of 0.344 cm3g−1. More mesoporous structure was present in MKHBC. γ-Fe2O3 and Fe0, which determined the magnetic property of MKHBC, were observed in it. The saturated magnetization of MKHBC was 7.28 emug−1, suggesting that rapid separation of adsorbent can be achieved by an external magnet. Carbon-, nitrogen-, and oxygen-containing groups in biochar significantly changed after modification. Langmuir isotherm and Elovich kinetic model fitted well with the adsorption process of tetracycline (TC) on biochar. The maximum adsorption capacity of TC on MKHBC reached 236.93 mgg−1, which was 14-fold than that of HBC (16.71 mgg−1). MKHBC could effectively remove TC in a wide pH range and in the presence of co-existing ions. The dominant mechanisms of TC removal on MKHBC were pore filling and π-π interaction, followed by surface complexation, and H bonding. Therefore, MKHBC has the potential to act as an adsorbent for TC removal from the aquatic environment.

Tetracycline removal from aqueous solution using zirconium-based metal-organic frameworks (Zr-MOFs) with different pore size and topology: Adsorption isotherm, kinetic and mechanism studies

The adsorptive removal of tetracycline (TC) was studied with three types of zirconium-based metal–organic frameworks (Zr-MOFs), UiO-66, NU-1000 and MOF-525. The adsorption kinetics best fitted with the pseudo-second-order kinetic model and the adsorption equilibrium was rapidly reached within 40 min on UiO-66 and NU-1000, and 120 min on MOF-525. The adsorption isotherms best fitted with Sips model, and the maximum Sips adsorption capacities of TC on UiO-66, NU-1000 and MOF-525 were 145 mg·g−1, 356 mg·g−1 and 807 mg·g−1 respectively, which were much higher than common adsorbents. The X-ray photoelectron spectra measurements and the influence of pH suggested that the π-π interaction played a crucial role during the adsorption. Pore characteristics and topology of MOFs showed great effect on adsorption performance. The cages whose size match well with TC helped MOF-525 to get highest adsorption amount per surface area among MOFs we studied. The proper topology of NU-1000 contributed to its high adsorption rate. River water was also used to confirm the excellent adsorptive performance of these three Zr-MOFs in practical application. These results might aid us to comprehend the adsorption of TC on Zr-MOFs and expand the application of Zr-MOFs in water treatment for removal of emerging contaminants.

Adsorptive removal of tetracycline and amoxicillin from aqueous solution by leached carbon black waste and chitosan-carbon composite beads

Carbon black waste as waste by-product of oil refineries, exhibits improved specific surface area and is rich in surface functional groups after leaching. In this work, both powdered leached carbon black waste (LCBW) and LCBW-chitosan composite beads prepared via instantaneous gelation method were utilized as adsorbent to study their adsorption capabilities and behaviors for removal of tetracycline (TC) and amoxicillin (Amox) in distilled and tap water. The characterization showed that LCBW is high in specific surface area (~375 m2/g) and contains carboxyl (‒COOH) and hydroxyl (‒OH) groups which are essential to the adsorption. Under the experimental conditions, adsorption capacities ranging from 12 to 205 mg/g were obtained. It was observed that the adsorption performance of powdered LCBW was enhanced by the cations presented in the tap water while the effect was insignificant to LCBW-chitosan beads. The kinetics studies showed that the adsorption of the studied antibiotics on powdered LCBW and composite beads fitted well with pseudo 1st-order and pseudo 2nd-order model, respectively. The fitting of intraparticle diffusion model showed that the adsorption process was not governed solely by intraparticle diffusion. LCBW-chitosan beads was used to investigate the continuous adsorption of TC in a fixed bed column and the experimental data was fitted to Adams-Bohart model and Thomas model.