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Highlights: [•] Fractional Theoretical Capacity measure was proposed for isotherm model selection. [•] Using error analysis statistics alone may lead to wrong isotherm model selection. [•] The sorption system for all dyes was heterogeneous based on the Toth model. [•] Fractal dimension can be determined based on the theoretical sorption capacity. [•] The sorbent (GAC) surface was smooth according to the fractal dimension parameter. [Copyright &y& Elsevier]

Graphical abstract Preparation of bentonite–chitosan composite (TBCH). Highlights • Development of novel bentonite–chitosan composite adsorbent. • Application of composite adsorbent to remove humic acid from water. • Novel application of artificial neural network for RSM. • Process modelling of adsorption equilibrium and kinetics for humic acid removal. • Optimisation of process conditions for humic acid removal from water. Abstract Humic acids have a significant undesirable influence on drinking water quality. In this study, we utilized a physically and chemically treated bentonite–chitosan composite (TBCH) for the removal of humic acid from aqueous solutions. Response surface methodology (RSM) using central composite design (CCD) was used to investigate the effects of pH, adsorbent dosage, humic acid concentration and contact time on the adsorption effectiveness of humic acid by TBCH. Isotherms, kinetics and thermodynamics have been also studied. An optimum condition for humic acid uptake was achieved at pH 4, 1.4 g/L adsorbent dosage, 40 mg/L humic acid concentration, and 115 min contact time. This study showed that modified bentonite and chitosan composite (TBCH) was a promising adsorbent for the removal of humic acid from aqueous solutions due to its significant removal efficiency, natural abundance and low cost; it may be an alternative to more costly available materials. [ABSTRACT FROM AUTHOR]

Dyes or colors are one of the most important chemicals used in textile industries. It is necessary that dye-contaminated wastewater before discharging to environment treated by an appropriate and effective method. In this study, the performance of single-wall carbon nanotubes (SWCNTs) as an adsorbent for the removal of dye from aqueous solution was evaluated. The effect of operational parameters, such as contact time, solution pH, adsorbent dosage, and initial dye concentration was studied. Adsorption data were analyzed using Langmuir, Freundlich, and Temkin adsorption isotherms. The Langmuir isotherm (R² = 0.9844) was the best fitted graph for experimental data with maximum adsorption capacity (qm) of 166.667mg/g. The kinetic data were tested using pseudo-first-order, pseudo-second-order, and intraparticle diffusion models. The results of this study indicate that SWCNTs can be used as an effective adsorbent for the removal of azo dyes. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Removal of endotoxins, as a pyrogenic contaminant, from water is very important. • A novel Graphene oxide (GO)-based adsorbent decorated with dimethylamine (DMA) was synthesized. • The GO-ECH-DMA sorbents have great influence on endotoxin removal efficiency (>98%). • The endotoxin was adsorbed with a maximum Langmuir adsorption capacity of 121.47 EUmg−1. Abstract Novel graphene oxide (GO)-based adsorbent embedded with epichlorohydrin (ECH) as a coupling agent and dimethylamine (DMA) as a ligand (GO-ECH-DMA) were prepared and employed for endotoxin removal from aqueous solutions. The physicochemical properties of nanocomposite were fully characterized. The model attributed to batch adsorption process was optimized employing response surface methodology (RSM) via various parameters such as pH, GO-ECH-DMA dosage, and contact time and endotoxin concentration. The p-value with low probability (<0.00001), determination coefficient (R 2 = 0.99) and the non-significant lack of fit (p > 0.05) showed a quadratic model with a good fit with experimental terms. The synergistic effects of the linear term of contact time and GO-ECH-DMA dosage on endotoxin removal were significant. The optimum condition for endotoxin removal was obtained at pH of 5.52, GO-ECH-DMA dosage of 21 mgL−1, contact time of 56 min and endotoxin concentration of 51.3 endotoxin units per milliliter (EUmL−1). The equilibrium was the better explained by Langmuir isotherm with the maximum monolayer adsorption capacity of 121.47 EUmg-1, while the kinetics of the endotoxin adsorption process was followed by the pseudo-second-order model. The adsorbent could be recycled with NaOH. The possible mechanisms of endotoxin adsorption were proposed by hydrogen-bonding, π-π stacking, and electrostatic interaction. [ABSTRACT FROM AUTHOR]

In this work, amine riched MnFe 2 O 4 -cellulose was employed to remove toxic Cr (VI). To find out the optimum conditions R (3.3.1) software was used. The results of Cr (VI) adsorption onto three-step adsorbents were compared by interpreting kinetic and isotherm studies. The kinetic studies reveal that the adsorption of Cr (VI) onto cellulose and magnetic cellulose (MC) followed pseudo-first order model whereas the adsorption of Cr (VI) onto amine modified cellulose (AFMC) followed pseudo-second order kinetic model. From the obtained intraparticle diffusion model results it is evident that the adsorption is an external surface process. The adsorption isotherm parameters for Cr (VI) adsorption onto MC and AFMC showed that the correlation coefficient (R 2 : 0.96, 0.88) of Freundlich isotherm is more than that of Langmuir isotherm (R 2 : 0.50, 0.76); hence, it is suggested that the adsorption of Cr (VI) onto these sorbents occurs in multilayer possessing heterogeneous sorption sites whereas the adsorption onto cellulose followed Langmuir model. The maximum adsorption capacities of cellulose, MC and AFMC under optimum conditions were found to be 25, 125 and 250 mg/g, respectively; thus, it is confirmed that adsorption efficiency has been improved after modification steps. [ABSTRACT FROM AUTHOR]

Cubic zeolitic imidazolate framework-8 (ZIF-8), a new class of hybrid adsorbent, was synthesized and investigated for phosphorus (P) removal from aqueous solution. A prediction model for P adsorption was developed by performing the experiments according to central composite design. The adsorption model showed that P adsorption is associated directly with time and ZIF-8 dosage and indirectly with initial P concentration. The removal also increased with decrease in pH until reaching the critical pH of about 2.6. The efficiency of P removal under mechanically stirred increased with agitation speed from 100 to 300 rpm. In contrast to high ultrasonic frequency (130 kHz), sonication under 35 kHz provides excellent dispersive mixing and shortened the equilibrium time. Study of coexisting ions showed that P adsorption hindered considerably in the presence of carbonate. Equilibrium studies indicated that P adsorbed onto ZIF-8 in monolayer and the adsorbent has definite localized sites that are energetically identical. The maximum Langmuir sorption capacity of ZIF-8 for P was 38.22 mg/g in the present study. Analysis of experimental data also revealed that the chemosorption is the rate limiting step in P adsorption by ZIF-8. In conclusion, the present report suggest zif-8 as an efficient and fast removal sorbent for P from aqueous solutions. [ABSTRACT FROM AUTHOR]

This paper explores the possibility of employing Oxidized Multiwalled Carbon Nanotubes (MWCNT-COOH) for the removal of toxic Linear Alkyl benzene Sulfonate (LAS). LAS is among the most toxic industrial and house hold waste surfactants. This study discusses the feasibility of removing LAS from aqueous solutions using MWCNT-COOH. The effects of operational parameters such as solution pH, LAS concentration and contact time on the removal of LAS were studied. The four linear forms of Langmuir, Freundlich, Dubinin Radushkevich (D-R) and Temkin models were applied to determine the best fit of equilibrium expressions. Our results showed that the experimental adsorption isotherm complies with Freundlich model. The maximum adsorption capacity was determined to be 62.5 mg/g with an initial LAS concentration of 4 mg/L at pH 3 in 45 min. Fitting of the experimental results to kinetic models showed the relevance of the pseudo second-order (R 2 > 0.99) model for LAS. Our results confirmed that MWCNT-COOH would be promising adsorbents for LAS removal in aqueous solution. [ABSTRACT FROM AUTHOR]

Endotoxin, also called lipopolysaccharides (LPS), has strong biological effects, even at a very low concentration in humans. In this study, surface functionalization of graphene oxide (GO) with L–Arginine amino acid was successfully prepared using epichlorohydrin as a coupling agent (GO–EPI–L–Arg) for endotoxin removal from water. Characterization of Novel GO–EPI–L–Arg was confirmed by an analytical technique. The model was optimized using response surface methodology (RSM) via various input parameters. The effect of concomitant anions was also investigated to establish and simulate competitive endotoxin adsorption in real hemodialysis water supply. The pH and endotoxin concentration had an antagonistic effect on the quadratic model. The endotoxin adsorption process was better fitted by pseudo-second-order model with Q max value of 139.47 EU/mg, while the equilibrium followed the Langmuir isotherm with the maximum monolayer adsorption capacity of 154.85 EU/mg. The coefficient of determination (R 2 = 0.9761), non–significant lack of fit (p > 0.05), and p–value with low probability (<5.596 × 10–11) revealed a regression model with a good fit with input variables. The GO–EPI–L–Arg nanocomposite could be regenerated more than four times based on their adsorption-desorption cycles, with a slight loss in adsorption capacity. The results suggested that the GO–EPI–L–Arg can be applied as an effective adsorbent for endotoxin removal from water. [ABSTRACT FROM AUTHOR]