Optimization of Methylene Blue Dye Adsorption onto Coconut Husk Cellulose Using Response Surface Methodology: Adsorption Kinetics, Isotherms and Reusability Studies

In this study, coconut husk cellulose was employed as a cost-effective and environmentally friendly adsorbent to eliminate methylene blue (MB) dye from aqueous solutions. The successful development of response surface methodology paired with a central composite design (RSM-CCD) enabled the optimization and modelling of the adsorption process. The study investigated the individual and combined effects of three variables (pH, contact time, and initial MB dye concentration) on the adsorption of MB dye onto coconut husk cellulose. The developed RSM-CCD model exhibited a remarkable degree of precision in predicting the removal efficiency of MB dye within the specified experimental parameters. This was demonstrated by the strong regression parameters, with an R2 value of 99.79% and an adjusted R2 value of 99.6%. The study depicted that the optimal parameters for attaining a 98.8827% removal of MB dye using coconut husk cellulose were as follows: an initial MB dye concentration of 30 mg∙L−1, contact time of 120 minutes, and pH 7 at a fixed adsorbent dose of 0.5 g. The Freundlich isotherm model provided the most satisfactory description of the equilibrium adsorption isotherms, suggesting that MB dye adsorption onto coconut husk cellulose occurs on a heterogeneous surface. The experimental results demonstrated a strong agreement with the pseudo-second-order kinetics model, indicating that the number of active sites present on the cellulose adsorbent predominantly influences the adsorption process of MB dye. Additionally, the adsorbent made from coconut husk cellulose exhibited the potential to be reused, as it retained its efficiency for a maximum of three cycles of adsorption of MB dye. The results of this study show that coconut husk cellulose has the potential to be an effective and sustainable adsorbent for removing MB dye from aqueous solutions.

Adsorption of Natural Surfactant on Sandstone in Enhanced Oil Recovery: Isotherms and Kinetics Studies

In chemical enhanced oil recovery, surfactants are injected into the reservoir with the intention to lower interfacial tension (IFT) between the water and oil phases, and thereby bring about efficient displacement of oil. However, the adsorption of the surfactants to reservoir rock surfaces leads to the loss and reduction in concentration of the surfactants, which in turn reduces the overall efficiency of the oil recovery process, with attendant financial losses. In this work, the adsorption of Quillaja Saponaria (QS), a novel, natural, non-ionic surfactant, on crushed sandstone reservoir rock is investigated. X-ray diffraction (XRD) study of clean sandstone particles has been undertaken to determine the main components present in the sand particles. The conductivity method was used to measure CMC and the surfactant concentrations in aqueous solutions. Batch adsorption experiments were used to determine the amount of QS adsorbed on rock surface. Equilibrium conditions were reached after almost 5 days. From the results of the study, the Langmuir isotherm model is more suited for predicting the adsorption behaviour of QS on sandstone. The kinetic adsorption of QS obeys the pseudo-second order model. This study is particularly relevant in surfactant selection for chemical EOR processes.

High adsorption selectivity of activated carbon and carbon molecular sieve boosting CO_(2)/N_(2) and CH_(4)/N_(2) separation

Flue gas and coal bed methane are two important sources of greenhouse gases.Pressure swing adsorption process has a wide range of application in the field of gas separation,and the selection of adsorbent is crucial.In this regard,in order to assess the better adsorbent for separating CO_(2) from flue gas and CH_(4) from coal bed methane,adsorption isotherms of CO_(2),CH_(4) and N_(2) on activated carbon and carbon molecular sieve are measured at 303.15,318.15 and 333.15 K,and up to 250 kPa.The experimental data fit better with Langmuir 2 compared to Langmuir 3 and Langmuir-Freundlich models,and Clausius-Clapeyron equation was used to calculate the isosteric heat.Both the order of the adsorbed amount and the adsorption heat on the two adsorbents are CO_(2)>CH_(4)>N_(2).The adsorption kinetics are calculated by the pseudo-first kinetic model,and the order of adsorption rates on activated carbon is N_(2)-CH_(4)>CO_(2),while on carbon molecular sieve,it is CO_(2)-N_(2)>CH_(4).It is shown that relative molecular mass and adsorption heat are the primary effect on kinetics for activated carbon,while kinetic diameter is the main resistance factor for carbon molecular sieve.Moreover,the adsorption selectivity of CH_(4)/N_(2) and CO_(2)/N_(2) were estimated with the ideal adsorption solution theory,and carbon molecular sieve performed best at 318.15 K for both CO_(2) and CH_(4) separation.The study suggested that activated carbon is a better choice for separating flue gas and carbon molecular sieve can be a strong candidate for separating coal bed methane.

Thermodynamics and kinetics of adsorption for heavy metal ions from aqueous solutions onto surface amino-bacterial cellulose

Amino-bacterial cellulose（amino-BC） was prepared by chemical modification of bacterial cellulose（BC）.The adsorption characteristics and mechanism of amino-BC were studied.The results show that adsorption data can be fitted well by Langmuir equation and the pseudo-second order kinetics,indicating that the adsorption of amino-BC would obey monolayer molecule adsorption and the main action was chemisorption.Meanwhile,the adsorption process was studied by the Elovich equation and the intra-particle diffusion model,indicating that the absorption characteristics of metal ions on amino-BC is controlled by both film diffusion and particle diffusion.The increase of reaction temperature will accelerate the adsorbing rate because of endothermic reaction.

Nickel(Ⅱ) removal from water using silica-based hybrid adsorbents:Fabrication and adsorption kinetics

A series of novel silica-based hybrid adsorbents were prepared by the crosslinking reaction of N-[3- （trimethoxysilyl）propyl] ethylene diamine （TMSPEDA） with epichlorohydrin （ECH） via a sol-gel process. Fourier transform infrared （FTIR） spectra confirmed that the reaction occurred. TGA curves showed that the thermal stability of these hybrid adsorbents reached as high as 180 ℃. As a typical example, the adsorption performance of nickel（U） ions onto an adsorbent （the volume ratio of TMSPEDA and ECH was 4：1 ） was explored. It was found that the adsorption of nickel（Ⅱ） ions onto this adsorbent followed the Lagergren pseudo-second-order kinetic model. The investigation of the adsorption mechanism demonstrated that nickel（Ⅱ） adsorption was chiefly controlled by diffusion-chemisorption, suggesting that more diffusion processes were involved in the adsorption of nickel（Ⅱ） ions onto this type of adsorbents. Desorption experiment indicates that these hybrid adsorbents can be regenerated. These findings reveal that this type of silica-based hybrid adsorbent is promising in the separation and recovery of nickel（Ⅱ） ions from Ni-containing wastewater or contaminated water.

Kinetics and Mechanism of Adsorption of Phosphate on Fluorine-containing Calcium Silicate

The nanowires-reticulated calcium silicate with a specific surface area more than 100 m^2/g was prepared by a hydrothermalprocess using hydrated lime（Ca（OH）_2,HL）and silica containing soluble fluoride,which was a by-product of fluorine industry,and the soluble fluoride in raw silica was fixed as CaSiF_6 at the same time.The kinetic characteristics and mechanism of adsorbing phosphate by fluorine-containing calcium silicate were investigated in the experiments of phosphorus（P）removalfrom aqueous solution.The results show that the prepared fluorine-containing calcium silicate has excellent performance for adsorbing phosphate,the adsorption process appears to follow pseudo-second-order reaction kinetics and the process is mainly controlled by chemisorption.The product resulted from P adsorption is mainly composed of hydroxyapatite（HAP）and fluorapatite（FAP）,which are further used as adsorbents of heavy metalion Cd^（2＋） in aqueous solution and display excellent performance.

Adsorption of Methylene Blue on magnesium silicate: Kinetics, equilibria and comparison with other adsorbents

Batch adsorption from aqueous solutions in a slightly basic medium of Methylene Blue, up to 2500 mg/L, onto synthetic magnesium silicate （Florisil） of three particle size ranges （mean diameters of 112, 200 and 425 μm） was compared to the corresponding adsorption onto activated carbon and Amberlite XAD-2. The best fit of the kinetic results was achieved by a pseudo second-order equation. The equilibrium data were found to be well represented by the Langmuir isotherm equation. Amberlite XAD-2, an unspecific adsorbent capable of adsorbing exclusively through a surface effect, exhibited a poor dye uptake, confirming that the adsorption mechanism on Florisil was due to electrostatic attraction and ion exchange. Moreover, the comparison between Florisil and the other adsorbents was performed on the basis of the evaluation of the surface area and pore volume occupied by the adsorbed dye.

Adsorption Kinetics of β-Carotene and Chlorophyll onto Acid-activated Bentonite in Model Oil

The textural properties of acid-activated bentonite （AAB）, which were prepared using four different concentrations of sulfuric acid, were analyzed by adsorption-desorption isotherm of nitrogen using an automated specific surface area and porosity analyzer. The total pore volume, specific surface area and average pore diameter of these four kinds of AAB show a regular changing trend, increasing first and then decreasing, the optimum of which can be achieved at a sulfuric acid concentration of 25% （sample A25）. The kinetic analysis of the adsorption of β-carotene and chlorophyll in model oil solutions, namely, xylene and edible oil solution, has been investigated by using AAB. Experimental results indicated that the adsorption data fit the pseudo-second-order model well. The whole adsorption process of the two pigments on AAB was divided basically into two parts： the initial adsorption of pigments was rapid in the first l0 rain, followed by a slower adsorption process till equilibrium was attained at 60 rain. In addition, the amount and rate of adsorption on A25 increase synchronously with the initial pigment concentration and temperature. The results showed that the adsorption kinetics behavior of AAB with respect to the pigments is not influence by the xylene and edible oil solution.

Adsorption Kinetics of Pb^(2+) and Cu^(2+) on Variable Charge Soils and Minerals: Ⅱ. Equations for Describing Experimental Data

Different mathematical methods, including linearization, differential, integration and nonlinear least squares approximation (Newton-Marquardt method), were used to fit different kinetic equations, such as zero-order, first-order (i. e, membrane diffusion), second-order, parabolic-diffusion, Elovich, two-constant equations, to the experimental data of Pb2+ and Cu2+ adsorption on variable charge soils and kaolinite. Assuming each M2+ occupied two adsorption sites, two more equations, the so-called surface second-order equation and third-order equation were derived and compared with the above equations according to the fitting results, which showed that the second-order equation and surface second-order equation, being one equation in different expressions under some conditions, were better than the other equations in describing the Pb2+ and Cu2+ adsorption kinetics, and the latter was the best.

Relationship Between Soil Boron Adsorption Kinetics and Rape Plant Boron Response

The boron adsorption kinetic experiment in soil by means of a flow displacement technique showed that the kinetic data could be described with some mathematic equations. The average values of the correlation coefficient for zero-order, first-order, parabolic diffusion, Elovich, power function and exponential equations were 0.957, 0.982, 0.981, 0.984, 0.981 and 0.902, respectively. The correlation between adsorbed boron or its other expression form and time were the highest for first-order, parabolic diffusion, Elovich, and power function equations, the second for the zeroorder equation, and the lowest for the exponential equation. The parabolic diffusion equation fitted well the experimental results, with the least standard error among the six kinetic equations, showing that the movement of boron from soil solution to soil colloid surface may be controlled by boron diffusion speed. The boron content of rape seedling obtained from soil cultivation was correlated with the rate constants of the kinetic equations. The constants of first-order, parabolic diffusion,and exponential equations were significantly correlated with the boron content of the crop of NPK treatment at a 95% probability level, with correlation coefficients being 0.686, 0.691 and 0.641, respectively. In the case of zero-order equation, it was significant at 99% probability level (r =0.736). These results showed that the absorption kinetic constants of soil boron were closely related with the rape plant response to boron.

Adsorption Kinetics of Alkyl Polyglucoside at the Air-Solution Interface

The air-solution equilibrium tension ge and dynamic surface tension gt, of nonionic surfactant alkyl polyglucoside have been studied. ge was measured by the Wilhelmy method with Krüss K12 tensiometer. The CMC and the surface excesses Γwere determined from the surface tension vs. concentration curve. The gt decays were measured in the range 0.2～20 s using a maximum bubble pressure instrument and analyzed with the Ward and Tordai equation.

Diffusion-controlled Adsorption Kinetics at Air/Solution Surface Studied by Maximum Bubble Pressure Method

In studying the diffusion-controlled adsorption kinetics of aqueous surfactant solutions at the air/solution surface by means of the maximal bubble pressure method, Fick's diffusion equation for a sphere should be used. In this paper the equation was solved by means of Laplace transformation under different initial and boundary conditions. The dynamic surface adsorption F(t) for a surfactant solution, which was used to describe the diffusion-controlled adsorption kinetics at the solution surface, was derived. Different from the planar surface adsorption, the dynamic surface adsorption F(t) for the short time consists of two terms: one is the same as Ward-Tordai equation and the other reflects the geometric effect caused by the spherical bubble surface. This effect should not be neglected for the very small radius of the capillary. The equilibrium surface tension γeq and the dynamic surface tension γ(t) of aqueous C10E6 [CH3(CH2)9(OCH2CH2)6OH] solution at temperature 25℃ were measuredby means of Wilhelmy plate method and maximal bubble pressure method respectively. As t→ 0, the theoreticalanalysis is in good agreement with experimental results and the dependence of γ(t) on is linear.

Kinetics comparison on simultaneous and sequential competitive adsorption of heavy metals in red soils

To compare the adsorption kinetics of Cu, Zn and Cd introduced into red soils simultaneously and sequentially as well as their distribution coefficients, the ability of red soils to retain heavy metals was evaluated by performing batch experiments. The results indicate that Cu is preferentially adsorbed by red soils no matter in simultaneous or in sequential situation. The adsorption amount of Cd is the minimum in simultaneous competitive adsorption experiment. As heavy metals are added into red soils sequentially, the heavy metal adsorptions are relatively hard to reach equilibrium in 2 h. Red soils retain more Cd than Zn, which is opposite to the result in simultaneous adsorption. The addition sequences of heavy metals affect their adsorbed amounts in red soils to a certain extent. The joint distribution coefficients of metals in simultaneous adsorption are slightly higher than those in sequential adsorption.

Heterogeneity of Adsorption Sites and Adsorption Kinetics of n-Hexane on Metal–Organic Framework MIL-101(Cr)

The heterogeneity of adsorption sites and adsorption kinetics of n-hexane on a chromium terephthalate-based metal-organic framework MIL-10^1 （Cr） were studied by gravimetric method and temperature-programmed desorption （TPD） experiments. The MIL-101 crystals were synthesized by microwave irradiation method. The ad- sorption isotherms and kinetic curves of n-hexane on the MIL-101 were measured. Desorption activation energies of n-hexane from the MIL-10^1 were estimated by TPD experiments. The resulthowed that equilibrium amount ofn-hexane adsorbed on the MIL-10^1 was up to 5.62 mmol.g- 1 at 298 K and 1.6 x10^4 Pa, much higher than that of some activated carbons, zeolltes and so on. The isotherms of n-hexane on the MIL-101 could be well fitted with Langmuir-Freundlich model. TPD spectra exhibit two types of adsorption sites on the MIL-101 with desorption activation energies of 39.41 and 86.69 kJ. mol-1. It reflects the surface energy heterogeneity on the MIL-10I frameworks for n-hexane adsorption. The diffusion coefficients of n-hexane are in the range of （1.35- 2.35 ） x 10 - 1 o cm2. s - 1 with ad sorotion activation enerv of 16.33 kl. mol - 1.

Adsorption behavior of activated carbon for the elimination of zearalenone during bleaching process of corn oil

Zearalenone is a mycotoxin produced by Fusarium species.It frequently contaminates cereals used for foods or animal feeds,especially deposited in crude corn oil.Certain amounts of zearalenone can be removed during refining processes.In this study,we studied the influence of activated carbon and six industial absorbents(zeolite,diatomite,attapulgite,perlite,montmorillonite and activated clay)on the elimination of zearalenone during bleaching process of corn oil and explored the absorption mechanism of activated carbon.Results showed that activated carbon had an excellent adsorption capacity of zearalenone compared with the other six industrial adsorbents.For activated carbon,a high removal rate of zearalenone(exceeding 83%)from heavily zearalenone-polluted corn oil was achieved and the removal rate of zearalenone was kept above 60%after five regeneration cycles.The research on the adsorption mechanism of activated carbon showed that Freundlich adsorption isotherm model and pseudo-second-order kinetic model could well described the adsorption process.The thermodynamic study demonstrated that adsorption process was spontaneous and exothermic.Fourier transform infrared spectroscopy and Raman spectroscopy further revealed that activated carbon was effectively combined with zearalenone viaπ-πinteraction.Thus,activated carbon is an efficient and suitable adsorbent to control the levels of zearalenone during bleaching process of corn oil.This study not only proposed a systematic research scheme for the mechanism study of activated carbon for the elimination of zearalenone in corn oil,but also provided the scientific basis for developing effective methods to eliminate zearalenone in refined vegetable oils.

Adsorption Kinetics of Decanoyl-N-methylglucamine at the Expanding Spherical Surface

A general expression of the dynamic surface adsorption [Г（t）] on the expanding spherical surface was derived by solving the corresponding diffusion equation under different initial and boundary conditions. Different from the result of the still spherical surface, two factors （smaller than 1） appeared in the equation for the short time adsorption. Using the derived results, the adsorption kinetics of aqueous decanoyl-N-methylglucamine （Mega-10） solution was studied. In the short time region （t→0）, a good agreement of experimental results with the theory was reached and the adsorption was controlled by diffusion.

Equilibrium and kinetics of adsorption of Ca(Ⅱ) ions onto KCTS and HKCTS

The adsorption of Ca（ II ） ions from aqueous solution by ehitosan a-ketoglutaric acid （KCTS） and hydroxamated chitosan a-ketoglutaric acid （HKCTS） was studied in a batch adsorption system. The Langmuir and Freundlich adsorption models were applied to describing the equilibrium isotherms, and isotherm constants were determined. The kinetics of the adsorption with respect to the initial Ca（II） ions concentration, temperature and pH was investigated. The pseudo-first-order and second-order kinetic models were used to describe the kinetic data and the rate constants were evaluated. The results show that the experimental data fit well to the Langmuir isotherms with a high correlation coefficient （R2）. The pseudo-second-order rate expression provides the best fitting kinetic model. The pseudo second-order kinetic model is indicated with the activation energy of 26.22 kJ/mol and 6.16 kJ/mol for KCTS and HKCTS, respectively. It is suggested that the overall rate of adsorption of Ca（ II ） ions is likely to be controlled by the chemical process.

Diffusion-Controlled Adsorption Kinetics of Triton X-100 at Air/Solution Interface

In this paper, the equilibrium surface tension and the dynamic surface tension of aqueous Triton X-100 solution at temperature 25 ℃ were measured by means of Wilhelmy plate method and maximal bubble pressure method respectively. The determined critical micellar concentration（cmc） of Triton X-100 at 25 ℃ is (2.2×10-4) mol/dm3. The adsorption mechanics of Triton X-100 at air/solution was determined. For the submicellar concentrations it is diffusion-controlled. The diffusion coefficient was calculated from the experimental data in the range of short limit. In the range of long time adsorption, the subsurface concentration is fitted from the measured dynamic surface tensions.

K^+ Adsorption Kinetics of Fluvo-Aquic and Cinnamon Soil Under Different Temperature

The K+ adsorption kinetics of fluvo-aquic soil and cinnamon soil under different temperatureswere studied. The results showed: 1) The first order equations were the most suitable forfitting the adsorption under various temperature levels with constant K+ concentration indisplacing fluid. With temperature increasing, the fitness of Elovich equation increased,while those of power equation and parabolic diffusion equation decreased; 2)the apparentadsorption rate constant ka and the product of ka multiplied by the apparent equilibriumadsorption qincreased when temperature increased, while the apparent equilibrium adsorptionqreduced; 3)temperature influenced hardly the reaction order, the order of concentrationand adsorpton site were always 1 under various temperatures, if they were taken intoaccount simultaneously, the adsorption should be a two-order reaction process; 4)theGibbs free energy change △G of potassium adsorption were negative, ranged from -4444.56to -2450.63Jmol-1,and increased with temperature increasing, while enthalpy change △H,entropy change △S, apparent adsorption activation Ea, adsorption activation energy E1and desorption activation energy E2 were temperature-independent; 5)the adsorption wasspontaneous process with heat releasing and entropy dropping, fluvo-aquic soil releasedmore heat than cinnamon soil.