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.

STUDY ON THERMAL DECOMPOSITION KINETICS OF URUSHIOL METAL CHELATE POLYMERS

The thermal decomposition kinetics of urushiol-Cu, urushiol-Nd and urushiol-Ti chelatepolymers has been studied by non-isothermal thermogravimetry. The results suggest that thethermal decomposition kinetics of three chelate polymers are all of first order. Their averageactivation energy values of the thermal decomposition calculated by Ozawa-(I) method are 110,79, 136. 98 and 163. 64 kJ mol^(-1) respectively, which increase linearly with the metal valence of themetal chelate polymers

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.

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.

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 Pb^(2+) and Cu^(2+) on Variable Charge Soils and Minerals: Ⅲ. Adsorption Kinetics of Pb^(2+) Within 30 Minutes

The adsorption kinetics of Pb^2+ on different soils and minerals with variable charges was studied by the two ion-selective electrode technique at different pH and concentrations.The results showed that more than 95% of adsorption on all the samples occurred during the first 5 minutes.All adsorption time-dependent data could fit the surface second-order equation very well.The values of Xm were goethite>kaolinite,and latosol>red soil at the same initial reaction concentration.The values of k were kaolinite>>goethite,and latosol>red soil at the same reaction pH and initial concentration.The higher the suspension pH,the faster the adsorption occurred.The meaning of Xm got by the two ion-selective electrode technique(one kind of batch technique) was different from that by the miscible displacement technique in that the former was only the equilibrium adsorption amount at a definite concentration and pH,but the latter was almost equal to the adsorption capacity at a definite pH with much less influence of concentration.One Pb^2+ was supposed to occupy two adsorption sites as the adsorption mechanism is concerned.

Fractal-like adsorption kinetics of Pb^(2+) in rocks

The adsorption kinetics of Pb2+ in rocks has been studied using ion selective electrodes and atomic absorption spectrophotometer. The results showed that the adsorption process is a fractal-like reaction. The adsorption rate was relatively high before 30 minutes, and then dropped. The saturated adsorption capacity (a) of Pb2+ and kinetic parameters (b, α , D and k) increased with increasing initial concentrations of Pb2+. These parameters (except a) decreased while Na+ was present in the solution. Furthermore, the smaller the rocks were in grain size, the bigger these kinetic parameters would be, though the parameter a was almost constant.

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.

Ion Exchange Adsorption Kinetics of Miglitol by D001 Resins

In order to explore internal factors for adsorption kinetic effect of miglitol by D001 resin, a batch adsorption operation for miglitol kinetic adsorption at different concentrations, temperatures and vibrating rates was investigated in oscillator (SHZ-A), respectively. The different kinetic mathematical model, Webber-Morris kinetic equation, film diffusion coefficient equation and kinetic boundary model were all applied to discuss the adsorption process. The results showed that Type 1 pseudo-second order kinetic equation can be all used to describe miglitol adsorbed by D001 resin at different concentrations, temperatures and vibrating rates. Moreover, the total activation energy (Ea) can be calculated and its value is 9.7 kJ/mol, and then calculated values of the process film diffusion coefficient and pore diffusion coefficient, it may be inferred from these gotten values that the ion exchange process is all mainly controlled by film diffusion. Therefore, the results also suggest that the external adsorption factors such as solute concentration, temperature and vibrating rate for effect of mass transfer diffusion process control of miglitol onto D001 resin are relatively weak.

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.

ON THE SYNTHESES OF BENZIDINE CHELATE RESINS CONSISTING OF POLYETHER BACKBONE AND THEIR ADSORPTION PROPERTIES

Three new resins are synthesized by the reaction of polyepichlorohydrin with benzidine, O-tolidine and O-dianisidine, respecti v,ely. Their adsorption properties for Au(III), Pd(II), Pt(IV), Hg(II), Cu(II), Pb(II) and Zn(II) are investigated. The resin containing O-dianisidine group selectively sorbed Au(III) in the presence of transition metal ions. The results show that synergistic effect of anchor groups plays an important role in the adsorption of metal ions.

2-Hydroxy-1,4-napthoquinone solubilization,thermodynamics and adsorption kinetics with surfactant

2Hydroxy1,4napthoquinone(lawsone)natural redorange dye was extracted from fresh henna(Lawsonia inermis)leaves in an alkaline media.The lawsonesurfactant solubilization constants(KLS)were calculated for the first time by using cationic cetyltrimethylammonium bromide(CTAB)and anionic sodium dodecyl sulphate(SDS).The standard free energy,concentration of solubilized lawsone and number of lawsone molecules solubilized into micelles were calculated and discussed.Surface excess,minimum surface area per molecule,surface pressure,free energy(adsorption and aggregation)and equilibrium constants of different states were determined from tensiometry.Different metal ions(Ag^(+),Co^(2+),Cu^(2+),Ni^(2+),Fe^(3+),Zn^(2+)and Al^(3+)were used to determine the complex forming ability with lawsone.Out of these,Ag+ions have strong binding capacity with lawsone.The adsorption of lawsone on the surface of glass with silver ions in presence of CTAB was also observed at pH>9.0.The pseudofirst,secondorder kinetic equation,intraparticles diffusion and Elovich models were used to determine the kinetics of lawsone adsorption onto the surface of glass and a probable mechanism has been discussed.Lawsone adsorption followed secondorder kinetic equation(k_(2)=0.019 g·mg^(1)·min^(1)).

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.

LIQUID-PHASE ADSORPTION KINETICS OF ISOMALTOTRIOSE ON Ca^(2+) EXCHANGE RESIN

The adsorption of isomaltotriose from aqueous solution on Ca2+ resin was investigated. The adsorption isotherm and the rate curve were determined. The pseudo-first-order model, pseudo-second-order model and the intraparticle diffusion model were used to predict the rate constants of adsorption. The activation energy of adsorption has been also evaluated using the pseudo-second-order rate constants. The results showed that the adsorption of isomaltotriose onto Ca2+ resin is an exothermically activated process. The adsorption isotherm can be described by Langmuir equation. The pseudo-second-order model can fit well to the adsorption rate curve of isomaltotriose onto Ca2+ resin. It suggests that the adsorption of isomaltotriose onto Ca2+ resin involve chemical adsorption.

Elimination, Kinetics and Thermodynamics of Fe(II) Ions by Adsorption in Static and Dynamic Conditions on Activated Carbons in Aqueous Media

This work investigated the removal, kinetics and thermodynamics of iron(II) ions (Fe(II)) by adsorption in static and dynamic conditions in aqueous media on activated carbons (AC-i30min, AC-i1h, and AC-i24h), prepared from palm nut shells collected in the city of Franceville to Gabon, using potassium hydroxide (KOH) as the activating agent. Results on the elimination of Fe(II) in static and dynamic adsorption on prepared activated carbons (ACs) showed that the AC-i24h adsorbent has the best Fe(II) adsorption capacities at saturation (Qsat). The Qsat obtained on AC-i24h in static and dynamic conditions (17.87 and 10.38 mg/g, respectively) were higher than those of AC-i30min (13.89 and 5.54 mg/g respectively) and AC-i1h (14.92 and 8.64 mg/g respectively). Moreover, the static adsorption was more effective in the removal of Fe(II) ions in aqueous media in our experimental conditions. The percentage removal (%E) of Fe(II) obtained on prepared activated carbons in static conditions was better than those obtained in dynamic conditions, especially on AC-i24h, where the %E was 89.27% in static and 61.56% in dynamic. In kinetics, results showed that the pseudo-second-order kinetic model best described the adsorption mechanisms of Fe(II) on prepared activated carbons in static adsorption, with mainly of chemisorption on the solid surfaces. However, in dynamic conditions, the pseudo-first-order kinetic model was more suitable. In addition to the weak interactions between Fe(II) and the activated carbon surfaces, strong interactions (chemisorption) were also observed. Also, thermodynamic data obtained on AC-i24h in static adsorption indicated that the adsorption of Fe(II) was spontaneous and increased with temperature (ΔG˚ H˚ = 503.54 KJ/mol).

Biomass Carbon Improves the Adsorption Performance of Gangue-Based Ceramsites:Adsorption Kinetics and Mechanism Analysis

The large accumulation of coal gangue,a common industrial solid waste,causes severe environmental problems,and green development strategies are required to transform this waste into high-value-added products.In this study,low-cost ceramsites adsorbents were prepared from waste gangue,silt coal,and peanut shells and applied to remove the organic dye methylene blue from wastewater.We investigated the microstructure of ceramsites and the effects of the sintering atmosphere,sintering temperature,and solution pH on their adsorption performance.The ceramsites sintered at 800℃under a nitrogen atmosphere exhibited the largest three-dimensional-interconnected hierarchical porous structure among the prepared ceramsites;further,it exhibited the highest methylene blue adsorption performance,with an adsorption capacity of 0.954 mg·g^(−1),adsorption efficiency of over 95%,and adsorption equilibrium time of 1 h at a solution pH of 9.The removal efficiency remained greater than 75%after five adsorption cycles.The adsorption kinetics data were analyzed using various models,including the pseudosecond-order kinetic model and Langmuir equation,and the adsorption was attributed to electrostatic interactions between the dyes and ceramsites,n-interactions,and hydrogen bonds.The prepared coal gangue ceramsites exhibited excellent adsorption capacities,removal rates,and cyclic stabilities,demonstrating their promising application prospects for the comprehensive utilization of solid waste and for wastewater treatment.

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 of molybdenum blue with D301 ion exchange resin

The adsorption behavior of D301 for molybdenum blue was investigated.The thermodynamics parameters in adsorption process were calculated and the adsorption kinetics was studied.The experimental results show that the adsorption characteristic of D301 for molybdenum blue fits well with the Freundlich adsorption isotherm equation.In the adsorption process of D301 for molybdenum blue,both the enthalpy change ΔH and entropy change ΔS are positive,while the free energy change ΔG is negative when temperatures are in the range of 303-333 K.It is indicated that the adsorption is a spontaneous and endothermic process,and the elevated temperatures benefit to the adsorption.Kinetic studies show that the kinetic data are well described by double driving-force model,and the adsorption rate of molybdenum blue on D301 is controlled by the intraparticle diffusion during the adsorption process.The total kinetic equation is determined.