Boyd Plot Research Articles

Evaluation of the sorption/desorption processes of pesticides in biodegradable mulch films used in agriculture

Microplastics from mulch films can be a source of chemical contamination to agricultural soils. In this context, biodegradable films have been widely positioned as a greener choice. However, their sorption/desorption capabilities, in contrast to the conventional plastic types remain understudied. It is for this reason that objective evaluation of their interactions with residual agricultural contaminants becomes important. Our findings reveal that polyethylene (PE) mulch films retained lower amounts of pesticide residues and demonstrated a higher desorption/release [median desorption = 71.86 μg/L or about 50%], while polybutylene adipate terephthalate (PBAT) mulch films retained higher amounts of pesticide residues onto their surface and demonstrated a much lower desorption [median desorption = 24.27 μg/L or about 17%] after a spraying event. A higher ambient temperature had no significant effect on final desorption amounts in both PE [median = 65.27 μg/L at 20 °C and 74.23 μg/L at 40 °C] and PBAT [median = 24.26 μg/L at 20 °C and 24.78 μg/L at 40 °C] mulch films. However, it did favour a faster desorption pace in PE films. Desorption in PBAT and PE plastic types was correlated with the log Kow value [Spearman's correlation: 0.857 and 0.837 respectively, p < 0.05]. However, only a moderate correlation with pKa was observed in PBAT [Spearman's correlation: 0.478, p < 0.05], while none for PE plastic type. Sorption of pesticides onto biodegradable PBAT microplastics were best explained by Elovich [R2: 0.937–0.959] and pseudo-second order kinetics [R2: 0.942–0.987], suggesting the presence of chemisorption. Furthermore, Weber Morris plots suggested the presence of a multi-step process and Boyd plots indicated that film diffusion or chemical bond formation was the rate-limiting step governing this phenomenon.

Extraction Kinetics of Rare Earth Elements from Ion-Adsorbed Underclays

Citric acid has been identified as an environmentally sustainable organic acid capable of leaching up to ~30% of easily accessible REEs from underclay material. An analysis of the leaching profiles was performed to discern the reaction rates, extraction efficiencies, and potential leaching mechanisms of REEs and cations of interest from ion-adsorbed underclays. The initial leaching stage follows a slow intraparticle diffusion mechanism followed by a second stage controlled by a mixed diffusion regime. The leaching profiles of Ca and P were similar to those of REEs, suggesting that REEs are most likely derived from mineral surfaces such as hydroxyapatite or crandallite rather than predominately from underclays. Fitting to a modified diffusion control model found diffusion-controlled leaching to be the primary mechanism whereas non-diffusive mechanisms made up about 22% of the extracted REEs. Gangue cations associated with underclays had less non-diffusive leaching than REE species, indicating that their leaching kinetics may be dominated by diffusion from within the material or potentially from product layer formation. Fitting to Boyd plots further indicated that REEs were leached following intraparticle diffusion control. These results have important implications for the development of more efficient and sustainable methods for extracting REEs or critical minerals from alternative feedstocks.

Evaluation of synergistic adsorption approach for terbinafine removal by cotton shell powder immobilized zerovalent copper: Adsorption kinetics and DFT simulation

Cotton shell powder (CS), nano zerovalent copper (nZVC) and cotton shell powder immobilized zerovalent copper (ZVC@CS) were evaluated for their adsorption efficiencies towards terbinafine hydrochloride (TBH), an antifungal drug. The nZVC and ZVC@CS synthesized via one pot redox precipitation method were characterized by FTIR, XRD, BET, FESEM and TGA analysis. The TGA and AAS analysis confirmed the loading of nearly 10% of nZVC on cotton shell powder in ZVC@CS. The effect of operational parameters (pH, adsorbent dose, initial drug concentration, time, etc.) determining the extent of terbinafine hydrochloride adsorption on ZVC@CS were investigated to ascertain the optimal experimental conditions to achieve maximum adsorption efficiencies. To investigate the adsorption behavior of TBH on ZVC@CS, the experimental data were fitted for five different adsorption models viz. Langmuir, Freundlich, Temkin, Redlich-Peterson and Hill isotherms. The TBH adsorption data was best fit with Hill isotherm model indicating cooperative sorption of TBH molecules on ZVC@CS surface. Among the five kinetic equations namely the pseudo-first-order (PFO), the pseudo-second-order (PSO), Elovich model, the intraparticle diffusion model, and Boyd kinetic model used to estimate the adsorption mechanism, the PFO kinetic model give best fit with a good correlation for the physisorption of TBH on ZVC@CS composite. The mechanism of the adsorption process was observed to be complex, consisting of both surface adsorption and pore diffusion. However, the Boyd plot confirms external mass transport as the rate limiting step for the adsorption of TBH on ZVC@CS. The synergistic adsorption of TBH on ZVC@CS was hypothesized, and the idea was supported by structure optimization results from DFT studies. The ZVC@CS exhibits equilibrium TBH adsorption efficiency (qmax) of 285.3 mg.g−1, significantly higher than adsorbents used in literature for the TBH removal.It is suggested that ZVC@CS may serve as sustainable adsorbents for the removal of cationic contaminants from acidic medium.

Alteration of Tecoma chip wood waste into microwave-irradiated activated carbon for amoxicillin removal: Optimization and batch studies

Amoxicillin (AMOX) in wastewater can promote antibiotic resistance in bacteria and affecting aquatic ecosystems, due to inadequate removal by conventional wastewater treatment plants. This study aimed to (i) optimizing Tecoma chip wood based activated carbon (TCAC) to adsorb amoxicillin (AMOX) using response surface methodology (RSM) and (ii) evaluating AMOX adsorption through batch and continuous modes. The RSM revealed the optimum conditions to be 657 W, 20 min and 0.99 g/g for radiation power, radiation time and impregnation ratio (IR), respectively. These optimum conditions resulted in AMOX removal efficiency of 88.07 mg/g and 27.68 % of TCAC’s yield. The BET surface area and total pore volume of TCAC were 924.85 m2/g and 0.3485 cm3/g respectively. The surface of TCAC was occupied with several functional groups namely primary amine, hydroxy, alkyl carbonate and terminal alkyne. These functional groups enhanced the adsorption process by forming hydrogen bond with AMOX molecules. The isotherm study revealed that AMOX-TCAC adsorption system obeyed the Langmuir model and the maximum monolayer adsorption capacity, Qm is 357.14 mg/g. Pseudo-second order (PSO) model fitted the best for the adsorption of AMOX by TCAC in the kinetic studies. Boyd plot divulged that the rate limiting step in the adsorption process was the film diffusion. Thermodynamic study confirmed the adsorption process to be endothermic, spontaneous and controlled by physisorption. In bed column studies, the percentage removal of adsorbates was found to increase when the adsorbates flowrate decreased, adsorbates initial concentration decreased, and bed height increased. For the breakthrough curve model, the adsorption is best fitted to Yoon Nelson model. TCAC demonstrated its efficacy in the removal of AMOX, proving successful in both batch mode and continuous mode operations. These findings suggest the potential for scaling up TCAC production for industrial purposes, indicating its suitability for larger-scale applications.

Removal of Bisphenol S from Aqueous Solution using Activated Carbon Derived from Rambutan Peel via Microwave Irradiation Technique

Bisphenol S (BPS) was introduced to replace Bisphenol A (BPA) in plastic production. Unfortunately, recent studies have shown that BPS is toxic. This study explores the conversion of rambutan peel into rambutan peel-based activated carbon (RPAC) via the economic route of single-stage microwave irradiation technique at radiation power and radiation time of 440 W and 6 min, respectively, under CO2 gasification. The resulted RPAC posed BET surface area of 402.68 m2/g, mesopores surface area of 332.98 m2/g, total pore volume of 0.23 cm3/g, and average pore diameter of 2.26 nm, which lies in the mesopores region. The surface of RPAC was filled with various functional groups such as methylene, aliphatic fluoro, phenol, nitro, and alkyl compounds. Adsorption of BPS onto RPAC achieved equilibrium faster at lower BPS initial concentration as compared to the higher ones. Isotherm study found that the Langmuir model suits this adsorption process the best with a maximum monolayer adsorption capacity of 27.89 mg/g whereas the kinetic study showed that pseudo-second order (PSO) represented the kinetic data the best. Intraparticle diffusion plots suggested that the adsorption process consisted of three regions and each region was controlled by a different type of diffusion mechanism. Boyd plot confirmed that film diffusion was responsible for the slowest step in the adsorption process whilst thermodynamic parameters disclosed that adsorption of BPS onto RPAC was spontaneous, exothermic, governed by physisorption, and the randomness of the adsorption process was found to reduce at the solid-liquid interface.

Removal of Methyl Orange Using Hybrid Spherical Silica Adsorbents

This study investigated the potential of adsorption behaviour of methyl orange onto hybrid spherical silica adsorbent. Removal of dye has been a problem worldwide and the study of removing dye through adsorption method is quite limited. This study aims to synthesize and characterize spherical silica (SSi) adsorbent and evaluate its adsorption capacity of it. The spherical silica adsorbent (SSi) was prepared using oil-in-water (o/w) emulsion polymerization modification where Tetraethyl Orthosilicate (TEOS) acts as the silica precursor. The physicochemical properties of SiNs were characterized using Fourier transform infrared (FTIR), field emission scanning (FESEM), nitrogen adsorption/desorption analysis (NAD), and transmission electron microscopy (TEM). The batch adsorption study for the methyl orange removal parameters such as pH (2-10 ) and agitation time (0-180 minutes). The experimental adsorption data were further evaluated using several adsorption kinetic models, namely pseudo-first-order, pseudo-second-order and Elovich kinetic models. The diffusion kinetics model includes the Weber-Morris plot, Fick’s Law equation and Boyd plot. The result shows that the spherical silica (SSi) adsorbent at pH 2 has the highest adsorption capacity amongst another adsorbent towards methyl orange which is 45.05 mg/g. Furthermore, the equilibrium time for methyl orange adsorption onto SSi was 120 min. The data fitted into a pseudo-second-order kinetic model indicating chemical adsorption, limited by film diffusion.

Rapid Removal of Toxic Remazol Brilliant Blue-R Dye from Aqueous Solutions Using Juglans nigra Shell Biomass Activated Carbon as Potential Adsorbent: Optimization, Isotherm, Kinetic, and Thermodynamic Investigation.

Recently, the treatment of effluent by agricultural waste biomass has significantly attracted wide interest among researchers due to its availability, efficacy, and low cost. The removal of toxic Remazol Brilliant Blue-R (RBBR) from aqueous solutions using HNO3-treated Juglans nigra (walnut) shell biomass carbon as an adsorbent has been examined under various experimental conditions, such as initial pH, adsorbate concentration, adsorbent dosage, particle size, agitation speed, and type of electrolyte. The experiments are designed to achieve the maximum dye removal efficiency using the response surface methodology (RSM). The optimum pH, adsorbent dosage, and particle size were found to be 1.5, 7 g L−1, and 64 μm, respectively for maximum decolorization efficiency (98.24%). The prepared adsorbent was characterized by particle size, Brunauer–Emmett–Teller (BET) surface area, pore volume, zero-point charge (pHzpc), Fourier transform infrared spectroscopy (FT-IR), field emission scanning electron microscopy/energy dispersive X-ray spectroscopy (FE-SEM/EDX), X-ray diffraction (XRD), and thermogravimetric analysis (TGA). Based on fitting the experimental data with various models, the isotherm and kinetic mechanism are found to be more appropriate with Langmuir isotherm and pseudo-second-order kinetics. The adsorption mechanism can be described by the intra-particle diffusion model, Bangham, and Boyd plots. The overall rate of adsorption is controlled by the external film diffusion of dye molecules. The maximum monolayer adsorption capacity, (qmax) 54.38 mg g−1 for RBBR dye, was obtained at a temperature of 301 K. From a thermodynamic standpoint, the process is endothermic, spontaneous, and the chemisorption process is favored at high temperatures. Desorption studies were conducted with various desorbing reagents in various runs and the maximum desorption efficiency (61.78% in the third run) was obtained using the solvent methanol. Reusability studies demonstrated that the prepared adsorbent was effective for up to three runs of operation. The investigation outcomes concluded that walnut shell biomass activated carbon (WSBAC) is a cost-effective, eco-friendly, and bio-sustainable material that can be used for synthetic dye decolorization in aqueous media.

Conversion of teak wood waste into microwave-irradiated activated carbon for cationic methylene blue dye removal: Optimization and batch studies

The objective of this study is to find optimum preparation conditions in converting teak wood waste into activated carbon (TWAC) and to evaluate its performance in adsorbing cationic dye of methylene blue (MB). TWAC was produced via physiochemical activation (potassium hydroxide, KOH chemical treatment, and carbon dioxide, CO 2 gasification) and heated through microwave irradiation technique. With the aid of response surface methodology (RSM), optimized TWAC was successfully synthesized at radiation power, radiation time, and impregnation ratio (IR) of 366 W, 5.30 min, and 1.15 g/g, respectively. These preparation conditions produced TWAC with MB adsorption uptakes of 66.69 mg/g and a yield of 38.23%. Characteristics of TWAC in terms of BET surface area, mesopores surface area, total pore volume, and average pore diameter were determined to be 1345.25 m 2 /g, 878.63 m 2 /g, 0.6140 cm 3 /g, and 2.85 nm, respectively. Isotherm studies divulged that the MB-TWAC adsorption system followed the Langmuir model with a maximum monolayer adsorption capacity of 567.52 mg/g. In terms of kinetic studies, this adsorption system fit pseudo-second order model the best whereas Boyd plot confirmed that the adsorption process was controlled by the film diffusion mechanism. Thermodynamic parameters of enthalpy change, ΔH°, entropy change, ΔS°, Gibbs free energy, ΔG° and Arrhenius activation energy, E a were calculated to be −4.06 kJ/mol, 0.06 kJ/mol.K, –22.69 kJ/mol and 16.03 kJ/mol, respectively. The activation and microwave heating methods employed succeeded to produce TWAC with excellent adsorption performance in removing MB dye. TWAC was also successfully regenerated for 5 cycles via microwave heating technique.

Synthesis of novel reduced graphene oxide decorated β-cyclodextrin epichlorohydrin composite and its application for Cr(VI) removal: Batch and fixed-bed studies

• The novel RGO-βCD-ECH composite was synthesized as a new adsorbent by wet chemical method. • The Cr(VI) adsorption was pH-dependent, equilibrium time was 75 min and the optimum temperature is 30 °C. • The data were fitted by Langmuir Isotherm and maximum capacity was 1321.01 mg/g. • The rate of adsorption was in good agreement with the pseudo-second-order kinetic model. • From FBAC study it was confirmed that at low flow rate and at higher bed height the performance was maximum. A novel ternary composite was synthesized comprising reduced graphene oxide (RGO), beta-cyclodextrin (βCD), and epichlorohydrin (RGO-βCD-ECH). The electrical and structural properties of the composite were analyzed by using Zeta potential, RAMAN, XRD, FTIR, BET, and SEM. It was encouraging to find out that the composite shows exceptional adsorption performance for Cr(VI) removal from water both in batch as well as Fixed bed adsorption column (FBAC) study. The optimized adsorption parameters were: adsorbent dosage 0.2 g/L, initial Cr(VI) concentration 300 mg/L, contact time 75 min, temperature 30 °C, and solution pH 1.0. Among the isotherm models, the Langmuir model proved to be a better fit, and maximum capacity ( q m ) can reach up to 1321.01 mg/g, whereas kinetic data follows the pseudo-second-order kinetic model. From the Boyd plot, it was confirmed that the rate-limiting step was controlled by intra-particle diffusion. The thermodynamic analysis confirmed that the adsorption process was an endothermic, entropy-driven, and spontaneous process. From the FBAC study, it was observed that with an increase in bed height, the parameters like bed capacity ( q bed ), breakthrough time ( t b ), and exhaustion time ( t e ) of the composite increase, and as the Cr(VI) flow rate increases the value decreases. To fit experimental data of the FBAC study, Thomas, Yoon-Nelson, and BDST model was used. Besides, it can easily and efficiently regenerate with a small effect on removal percentage. In binary solution, the results showed that coexisting ions like S O 4 2 - , N O 3 - , C l - , C u 2 + , C o 2 + , and, N i 2 + had no such substantial effect on Cr(VI) adsorption. These characteristics implied the applicability of these novel composites in the application of Cr(VI) contaminated groundwater or industrial wastewater in both batch and continuous mode.

Detoxification of toxic cations Pb(II) and Cd(II) from liquid phase by employing Pennisetum glaucum biowaste: a kinetic investigation

Biosorption potential of Pennisetum glaucum has elaborated by investigating its kinetic behavior in nonlinear fashion. RMSE values supported the pseudo second order (PSO) and elovich model, but correlation coefficient (R 2) values supported the PSO only. Study of intra-particle diffusion model (IPDM) and Boyd plots revealed the multi-linear diffusion pattern of the studied metal ions toward biosorbent. Initially, IPDM was found to be the rate-determining step, however boundary layer diffusion was found to be the slowest step later on. There was no correlation between calculated and experimental values of intercept, calculated by applying mass transfer model. Conclusive findings of Boyd plot supported the governing of biosorption process by film diffusion. Novelty Statement In this work, biosorption potential of Pennisetum glaucum has been investigating in terms of kinetic studies in nonlinear fashion. Biosorbent is obtained from indigenous sources and its processing is easy, which in turns leads to its cost-effectiveness for better removal of toxic materials from waste water streams. All related theoretical investigations were summarized for showing biosorption efficiency of this novel material.

Adsorption of toxic Congo red dye from aqueous solution using untreated coffee husks: kinetics, equilibrium, thermodynamics and desorption study

ABSTRACT In this study, the potential of using dried coffee husk adsorbent is systematically evaluated by conducting batch studies involving various process parameters, such as initial pH, dye concentration, adsorbent dosage, particle size, electrolytes, and temperature for the removal of Congo red (CR) dye from aqueous solutions. The prepared adsorbent was characterised with Attenuated Total Reflection, Field Emission Scanning Electron Microscopy/Energy Dispersive X-ray Spectroscopy, thermogravimetric, particle size, zero-point charge, Brunauer–Emmett–Teller surface area, and pore volume analysis. The maximum adsorption efficiency is obtained at an initial pH, 6, dye concentration, 50 mg L−1, adsorbent dosage, 10.5 g L−1, and adsorbent particle size, 89 µm. The kinetic rate constants and isotherm parameters were determined using various kinetic and isotherm models, respectively. The pseudo-second-order kinetic model gave a good fit to the experimental data at various dye concentrations. The adsorption mechanisms were described by intra-particle diffusion and Boyd plots. The overall rate of adsorption is controlled by external film diffusion of dye molecules. The experimental equilibrium data fit the Langmuir isotherm model with a maximum monolayer adsorption capacity (qmax) of 38.65 mg g−1 at 303 K. Thermodynamic studies were performed to evaluate the change in Gibbs free energy (ΔG), change in enthalpy (ΔH), and change in entropy (ΔS) of the adsorption process. Based on the thermodynamic analysis, the adsorption was found to be endothermic in nature, and the process was chemisorption, spontaneous and favoured at high temperatures. Desorption studies were conducted with various desorbing reagents in various runs and the maximum desorption efficiency (60.36% in third run) was determined using the solvent methanol. Reusability studies demonstrated that the prepared adsorbent was effective up to three runs of operation. These results show that waste coffee husks are cost-effective, eco-friendly bio-sustainable materials, and can be used for the removal of colour from synthetic dye wastewater.

Diffusion analysis and modeling of kinetic behavior for treatment of brine water using electrodialysis process

In this study, the removal of monovalent and divalent cations, Na+, K+, Mg2+, and Ca2+, in a diluted solution from Chott-El Jerid Lake, Tunisia, was investigated with the electrodialysis technique. The process was tested using two cation-exchange membranes: sulfonated polyether sulfone cross-linked with 10% hexamethylenediamine (HEXCl) and sulfonated polyether sulfone grafted with octylamine (S-PESOS). The commercially available membrane Nafion® was used for comparison. The results showed that Nafion® and S-PESOS membranes had similar removal behaviors, and the investigated cations were ranked in the following descending order in terms of their demineralization rates: Na+ > Ca2+ > Mg2+ > K+. Divalent cations were more effectively removed by HEXCl than by monovalent cations. The plots based on the Weber–Morris model showed a strong linearity. This reveals that intra-particle diffusion was not the removal rate-determining step, and the removal process was controlled by two or more concurrent mechanisms. The Boyd plots did not pass through their origin, and the sole controlling step was determined by film-diffusion resistance, especially after a long period of electrodialysis. Additionally, a semi-empirical model was established to simulate the temporal variation of the treatment process, and the physical significance and values of model parameters were compared for the three membranes. The findings of this study indicate that HEXCl and S-PESOS membranes can be efficiently utilized for water softening, especially when effluents are highly loaded with calcium and magnesium ions.

Scavenging malachite green dye from aqueous solution using durian peel based activated carbon

Physiochemical activation consists of heat treatment coupling with CO2 gasification and KOH chemical treatment were applied in preparing durian peel based activated carbon (DPAC) to remove basic dye, malachite green (MG) from aqueous solution. Several parameters namely, effect of initial MG concentration as well as contact time, solution temperature and initial solution pH were carried out in this study. Characterization study revealed that DPAC pose high BET surface area which is 886.31 m2/g and its surface was found to be mesoporous in nature with heterogeneous type of pore structures. Eight isotherms and four kinetic models were utilized and it was revealed that the adsorpttion system followed Freundlich isotherm and pseudo-first order (PFO) kinetic model. Mechanism study using intraparticle diffusion and Boyd plot confirmed that adsorption of MG onto DPAC was controlled by the film-diffusion mechanism. Thermodynamic study indicated that the adsorption system was exothermic, spontaneous, feasible and governed by physical-type of adsorption.

High effective removal of diazinon from aqueous solutions using the magnetic tragacanth-montmorillonite nanocomposite: isotherm, kinetic, and mechanism study.

Health and environmental impact of pesticide contamination of groundwater has been reported repeatedly in many studies. The removal of diazinon from agricultural wastewater is still of great interest due to using widely in many developing countries. In the presented study, the magnetic tragacanth-montmorillonite nanocomposite was utilized as an adsorbent to remove diazinon from an aqueous solution. The adsorbent properties were characterized using FE-SEM, EDX, FTIR, XRD, BET, and VSM techniques. The influence of adsorbent dosage, pH, contact time, and initial concentration of diazinon was studied in a batch system. Different adsorption kinetics and isotherm models were used to describe the kinetic and equilibrium data. The results indicated that the adsorption kinetic was fitted better with a Elovich kinetic model, and the adsorption isotherm was well described by the Langmuir-Freundlich model, and the maximum adsorption capacity was 416mgg-1. According to Weber and Morris's model and Boyd plot, the results demonstrated that the adsorption kinetic was controlled simultaneously by film diffusion and intraparticle diffusion. Besides, a thermodynamic study showed that the removal of diazinon is an endothermic process. Considering the results, magnetic tragacanth-montmorillonite nanoadsorbent has a high capability to remove diazinon from aqueous solution.

Facile green synthesis of ZnO-CdWO4 nanoparticles and their potential as adsorbents to remove organic dye.

In this work, ZnO-CdWO4 nanoparticles have been synthesized by the ecofriendly green method with lemon leaf extract to favorably anchor functional groups on their surface. The prepared ZnO-CdWO4 nanoparticles are used as adsorbent to treat Congo red (CR) dye after characterization through FT-IR, UV-Vis, TEM, SEM-EDX, and HRTEM techniques. The equilibrium partition coefficient and adsorption capacity values for CR by ZnO-CdWO4 are estimated as 21.4mgg-1μM-1 and 5mgg-1, respectively (at an initial dye concentration of 10mgL-1). The adsorption process is found as exothermic and spontaneous, as determined by the ΔG°, ΔS°, and ΔH° values. The Boyd plot has been used as a confirmatory tool to fit the adsorption kinetics data along with intraparticle diffusion and pseudo-second-order models. Based on this research, ZnO-CdWO4 nanoparticles are validated as an effective adsorbent for CR dye in aqueous solutions.

Improved arsenite adsorption using iron-impregnated marble dust with surface functionalized by quaternary ammonium ions

The present study investigates the application of marble dust impregnated with iron and functionalized with quaternary ammonium ions [using ammonium persulphate (APS)] as a novel adsorbent for the removal of arsenite ions from wastewater. The optimal modification parameters were found to be 0.1 M FeCl3, 0.125% NaOH (w/v) and 0.0125 M of APS at a temperature of 80 °C. The maximum uptake capacity of As(III) ions was found to be 50 mg/g with 3.5 g/L of adsorbent for 90 min at pH = 7.0. Maximum negative ∆G° value (− 7.7 kJ/mol) was obtained at 298 K, indicating that low temperature favoured adsorption. Freundlich and Temkin isotherm models gave the best correlation coefficient (R2 > 0.95). The kinetic data were suitably described by pseudo-second-order kinetics. Film diffusion was inferred to be the rate-controlling mechanism based on Boyd plots. The synthesized adsorbent can be regenerated by flushing with an alkaline solution.

The role of kaolin and kaolin/ZnO nanoadsorbents in adsorption studies for tannery wastewater treatment

In the present study, comparative studies of kaolin and kaolin/ZnO nanocomposites for the adsorption of Cr(VI), Fe(III), COD, BOD, and chloride from tannery wastewater were investigated. ZnO nanoparticles and kaolin/ZnO nanocomposites were prepared by sol–gel followed by wet-impregnation methods. The prepared adsorbents were characterized using different analytical tools such as X-ray diffraction, Fourier transforms infrared, high-resolution transmission electron microscopy, energy dispersive spectroscopy, selective area electron diffraction and Brunauer Emmett–Teller (BET) and X-ray Photoelectron Spectroscopy (XPS). The HRSEM/EDS/XPS analysis confirmed successful immobilization of clay structural network on the lattice layers of zincite hexagonal structure of ZnO nanoparticles. BET measurement showed an increase in the surface area of kaolin/ZnO nanocomposites (31.8 m2/g) when compared to kaolin (17 m2/g). Batch adsorption studies were carried out by varying the parameters such as contact time, adsorbent dosage and temperature. The maximum removal of Cr(VI) (100%), Fe(III) (98%), COD (95%), BOD (94%) and Chloride (78%) was obtained at 15 min by kaolin/ZnO composites. While 78% Cr(VI), 91% Fe(III), 91% COD, 89% BOD and 73% Chloride were removed by kaolin under the same conditions. The kaolin/ZnO nanocomposites exhibited better adsorption performance than kaolin due to higher surface area of the former than the latter. It was found that the Jovanovic isotherm model fitted the adsorption experimental data most with the highest correlation (R2 > 0.99) for both nanoadsorbents and indicate the occurrence of adsorption on monolayer and heterogeneous surfaces. The mechanism for the adsorption of metal ions in tannery wastewater onto the nano-adsorbents was examined using Weber Morris intra-particle diffusion model and Boyd plot which showed that the adsorption process was both intra-particle and film diffusion controlled. The thermodynamic parameters such as enthalpy change showed that that adsorption of metal ions and other parameters was feasible, spontaneous and endothermic. The ZnO/clay nanocomposites exhibited excellent recyclable and re-useable properties even after six repeated applications and can, therefore, be applied in wastewater treatment for removal of heavy metals and other physicochemical parameters.

Modeling of adsorption flux in nickel-contaminated synthetic simulated wastewater in the batch reactor

In the present investigation, physico-chemical characterization of composite material revealed the presence of fluffy surface structure with crystalline look and negatively charged surface functional groups. The study of adsorption flux by using dimensionless numbers φ (2.62), Nk (62.68) and λ (1.17 × 10−5) proved that adsorption of nickel ions on the surface of composite material was mostly film diffusion-limited with maximum surface area coverage coupled with weakened surface tension. The results of intraparticle diffusivity and Boyd plot model showed that at the onset of process, film diffusion was the primary mechanism involved and at the later stage intraparticle diffusion played a critical role as rate governing step. The values of film (0.65 × 10−8 cm2 sec−1) and pore diffusivity (1.8 × 10−12 cm2 sec−1) coefficients showed that the adsorption process is dependent upon two different types of diffusion namely film and pore diffusion. Overall, transport and reshuffling mechanism had no substantial role in adsorption dynamics of nickel ions on the surface of composite material. Sorption isotherm and kinetics modeling showed higher values of regression coefficients for Langmuir isotherm (R2 = 0.99) and pseudo-second-order kinetic model (R2 = 0.99) compared to other models. This showed that sorption of nickel followed monolayer coverage with chemisorption at optimized process parameters like pH 6, biosorbent dose 0.1 g/L, temperature 50 °C, agitation rate180 rpm, adsorbate concentration100 mg/L and contact time 60 minutes. The positive value of enthalpy of adsorption (ΔH = + 10.41 kJ/mole) and entropy (ΔS = +58.19 J/mol K) showed that binding of nickel ions on the surface of the composite material was endothermic with improved randomness at solid-liquid interface. The negative value of (ΔG = −6.4 to -8.67 kJ/mol) showed spontaneous nature of nickel adsorption on composite material in the liquid phase.

Removal of chlorhexidine gluconate in presence of a cationic surfactant using acid functionalized activated carbon: Validation of multicomponent models

Abstract Commercial antiseptic solutions containing a mixture of antibacterial agents such as, chlorhexidine gluconate, in presence of a cationic surfactant like cetrimide, are commonly used as floor, toilet and kitchen cleaning agents. Although a specific composition may be beneficial for disinfecting human beings, these are toxic to aquatic organisms, the plant biota and useful microorganisms present in soil and in municipal sewer pipes. In this study, functional modification of granular activated carbon (GAC) is carried out with hydrochloric and hydrofluoric acids in order to enhance the adsorption capacity of GAC for simultaneous removal of both chlorhexidine gluconate and cetrimide. Hydrofluoric acid functionalized activated carbon shows highest removal of both cetrimide and chlorhexidine gluconate (maximum adsorption capacitypure component chlorhexidine gluconate =349.0 g/g; maximum adsorption capacitypure component cetrimide =23.0 g/g). Average removal of cetrimide by GAC, FAC-HCl and FAC-HF are 36.64 %, 47.09 % and 75.74 % respectively. Surface charge of modified activated carbons is significantly altered as compared to unmodified GAC which provided an enhanced net available driving potential for the positive cetrimonium ions to reach the surface much faster as compared to the bulky chlorhexidine gluconate molecules. Cetrimide then undergoes pure physical adsorption through pore diffusion. However, chlorhexidine gluconate forms surface complexes with the functional groups as confirmed by the relative quantities of oxygenated surface functional groups and Fourier Transform Infrared (FT-IR) analysis. Intraparticle diffusion and Boyd plots show that film diffusion and not intraparticle diffusion is the rate controlling step.

Design of a new low cost natural phosphate doped by nickel oxide nanoparticles for capacitive adsorption of reactive red 141 azo dye

Nickel oxide doped natural phosphate (NP/NiO) nanoparticles were thermally synthesized for effective adsorption of Reactive Red 141 (RR141) as toxic dye model, characterization methods such as X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy combined with energy dispersive X-ray analysis(SEM-EDAX)and have been employed to identify the adsorbent. Surface area and pore size volume were determined by the Brunauer, Emmett and Teller (BET) method. Environmental factors such as pH, time of contact, initial RR141 concentration, the dose of adsorbent and solution temperature have been all put to the test to evaluate optimum adsorption activity. Thermal processing NP/NiO at 1% NiO doping percentage was effectual for exhibiting best adsorption behavior at an annealing temperature of 600 °C. Furthermore, batch experiments revealed significant adsorption activity reaching 96%. The maximal adsorption capacity was found to be 38.91 mg of RR 141 per 0.1 g of the adsorbent in only 40min of contact, at an initial colorant concentration of 20 mg L−1, pH 6 at ambient temperature and a volume of 100 ml. Langmuir isotherm model was more adequate to describe the adsorption process than the Freundlich model. The rate mechanism of the adsorption process was determined from the intraparticle diffusion model, Boyd plot revealed that the adsorption of the dye on the NP/NiO was mainly governed by film diffusion. Moreover, the dye adsorption was spontaneous and exothermic. The mechanism of adsorption may involve chemical adsorption through hydrogen bonding mechanism and electrostatic interactions between the dye molecules and the adsorbent. Thermal regeneration was feasible only for three cycles, the adsorbent also showed great potential for real textile wastewater treatment.