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Considering the risk associated with exposure to benzene and toluene in water resources, researchers have been motivated to conduct studies to remove them from aqueous solutions. Thus, by performing the present study, the potential of Fe3O4/zeolite imidazolate framework nanoparticles (Fe3O4@ZIF-8) was evaluated for the adsorption of benzene and toluene. Accordingly, the solution pH, Fe3O4@ZIF-8 dosage, mixing time, concentration of benzene and toluene, and temperature, were the parameters considered for conducting the batch experiments, for which their effect on adsorption efficiency was evaluated. Our conducted experiments introduced the neutral pH as the best pH range to obtain the maximum removal. Fitting the adsorption data into the various models revealed the aptness of the Langmuir isotherm equation in describing experimental information and highest adsorption capacity; for benzene it was 129.4, 134.2, 137.3, and 148.2 mg g−1, but for toluene it was 118.4, 125.2, 129.6, and 133.1 mg g−1, for temperature 20, 30, 40, and 50 °C, respectively. Using obtained optimal conditions, the adsorption efficiencies of benzene and toluene were obtained to be 98.4% and 93.1%, respectively. Kinetic studies showed acceptable coefficients for PSO kinetics and confirmed its suitability. Also, the recyclability results showed that for six consecutive periods of the adsorption-desorption process, the percentage of removal decreased by only 6% for benzene and toluene. Moreover, calculating thermodynamic parameter changes for benzene and toluene removal confirmed the favorability and spontaneity of the studied process and its endothermic nature. Considering the above findings, Fe3O4@ZIF-8 was found to be an operative adsorbent for removing pollutants. [ABSTRACT FROM AUTHOR]

MXene as two dimensional (2-D) Titanium (III) Carbide (II) (Ti 3 C 2 T x ) nanosheets was synthesized and processed by etching bulk MAX phase Titanium (III) Aluminium Carbide (II) (Ti 3 AlC 2 ) powders in HF solution. This material demonstrated an extraordinary efficiency for the removal of barium from synthetic produced/co-produced water. The synthesized nanosheet was characterized using field emission scanning electron microscopy (FE-SEM), the Brunauer, Emmett and Teller (BET) nitrogen surface area adsorption, X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), particle size analysis and zeta potential. The effect of adsorption parameters such as adsorbent dosage, contact time, and initial barium concentration were investigated and the optimum parameters for maximum removal of barium have been investigated. The experimental adsorption equilibrium data were correlated by the Langmuir and Freundlich isotherms, while the sorption energy was calculated using Dubinin-Radushkevich (D-R) model. The kinetic data were analyzed using two kinetic models. Optimization of process variables including shaking speed, contact time, pH, and amount of MXene has been performed to determine the maximum adsorption capacity of barium from water. MXene has a combination of unique properties such as a large number of available active sites, hydrophilic surface, highly negative surface charge, chemical stability, reasonable surface area, and the possibility of cations intercalating through its layers. MXene showed a large sorption capacity, fast kinetics, enormous trace barium removal, and reversible adsorption properties which offer an efficient removal performance of barium with a capacity of 9.3 mg/g and removal efficiency reaching up to 100% under optimized conditions. [ABSTRACT FROM AUTHOR]

Oil removal from water is a highly important area due to the large production rate of emulsified oil in water, which is considered one of the major pollutants, having a negative effect on human health, environment and wildlife. In this study, we have reported the application of high quality carbon nanotube bundles produced by an injected vertical chemical vapor deposition (IV-CVD) reactor for oil removal. High quality, bundles, super hydrophobic, and high aspect ratio carbon nanotubes were produced. The average diameters of the produced CNTs ranged from 20 to 50 nm while their lengths ranged from 300 to 500 μm. Two types of CNTs namely, P-CNTs and C-CNTs, (Produced CNTs from the IV-CVD reactor and commercial CNTs) were used for oil removal from water. For the first time, thermogravimetric analysis (TGA) was conducted to measure maximum oil uptake using CNT and it was found that P-CNT can take oil up to 17 times their weight. The effect of adsorbent dosage, contact time, and agitation speed were examined on the oil spill clean-up efficiency using batch sorption experiments. Higher efficiency with almost 97% removal was achieved using P-CNTs compared to 87% removal using C-CNTs. [ABSTRACT FROM AUTHOR]

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]

Abstract: The rates of adsorption of cadmium, copper and zinc ions onto bone char have been studied in three single component systems using an agitated batch adsorber. The effects of initial metal ion solution concentration and bone char mass have been studied. The capacities of the three metals on bone char are 0.477, 0.709 and 0.505 mmolg−1 for cadmium, copper and zinc respectively which are much higher than most other adsorbents reported in the literature for these three metals. In order to model the experimental concentration decay curves, a film-surface diffusion equation proposed by Crank (1979) has been solved. The model results correlate the experimental better than a previously applied film-pore diffusion model. However, the results indicate that the surface diffusion coefficient was a variable function of initial metal ion concentration. The surface diffusivities vary from 3.00×10−9 to 8.80×10−9 cm2 s−1, 2.11×10−9 cm2 s−1 to 5.4×10−9 cm2 s−1 and 3.10×10−9 to 8.49×10−9 cm2 s−1 for cadmium, copper and zinc respectively, for metal ion solution concentrations of 2.10–5.40 mmoldm−3. [Copyright &y& Elsevier]

Abstract: The sorption of cadmium, copper and zinc from aqueous solutions onto bone char has been studied in both single and binary multi-component systems. Equilibrium experimental studies have been performed to determine the sorption capacity of bone char for each metal ion. The isotherm results have been analysed using single and multi-component equilibrium models. The rate of sorption of the metal ions onto bone char has been studied using an agitated batch adsorber. The concentration versus time decay curves have been measured and a number of mass transfer models have been developed and tested based on diffusion controlled sorption. The results of the equilibrium and rate studies are presented and discussed in the paper. The possible mechanisms of metal sorption are also discussed. Finally a series of fixed bed column studies have been performed and analysed using a diffusion mass transport model. The experimental results show a displacement effect for the binary metal ion breakthrough curves. [Copyright &y& Elsevier]

• Literature review of phosphate removal by modified and unmodified biochars. • Desorption studies and direct use of phosphate laden biochars were considered. • Adsorption mechanism, effect of coexisting ions and thermodynamics were outlined. • Modified biochars demonstrated significant enhancement in phosphate sorption capacity. • Research challenges of phosphate removal by biochars have been identified. In the last decade, biochar (BC) has attracted significant attention for the removal of pollutants from aqueous solutions. Biochar exhibits many distinctive characteristics that make it an attractive adsorbent due to its availability, low manufacturing cost and compelling surface properties. This review presents a comprehensive summary of BC's application in phosphate remediation. Adsorption isotherm, kinetics, experimental conditions and the effect of different adsorption parameters on phosphate removal are outlined. The adsorption mechanisms, effect of coexisting ions, desorption studies and reuse of exhausted BCs are also considered. The results demonstrate that unmodified BCs possess low phosphate sorption capacity with the exception of BCs with high minerals content. As such, engineered BCs by decoration with different elements have been shown to alter the surface characteristics of the adsorbents such as surface charge, surface area, pore diameter, pore volume and the surface functional groups. Therefore, the phosphate sorption capacity of modified BCs has been significantly improved compared to unmodified adsorbents. Magnesium, aluminum, calcium and lanthanum were of significant interests for BC decoration due to their high affinity toward phosphate ions. Iron has been also widely used in BC composites for increasing the adsorption capacity of phosphate, in addition to providing an opportunity for magnetic recovery of the adsorbent. Based on this review, future research for BC applications in terms of phosphate removal is also discussed. [ABSTRACT FROM AUTHOR]

The presence of traces of heavy metals in wastewater causes adverse health effects on humans and the ecosystem. Adsorption is a low cost and eco-friendly method for the removal of low concentrations of heavy metals from wastewater streams. Over the past several years, graphene-based materials have been researched as exceptional adsorbents. In this review, the applications of graphene oxide (GO), reduce graphene oxide (rGO), and graphene-based nanocomposites (GNCs) for the removal of various metals are analyzed. Firstly, the common synthesis routes for GO, rGO, and GNCs are discussed. Secondly, the available literature on the adsorption of heavy metals including arsenic, lead, cadmium, nickel, mercury, chromium and copper using graphene-based materials are reviewed and analyzed. The adsorption isotherms, kinetics, capacity, and removal efficiency for each metal on different graphene materials, as well as the effects of the synthesis method and the adsorption process conditions on the recyclability of the graphene materials, are discussed. Finally, future perspectives and trends in the field are also highlighted. [ABSTRACT FROM AUTHOR]

This study deals with removing crude oil droplets from colloidal oil in water emulsions. The target was the development of efficient adsorbents for the tertiary treatment of industrial-produced water (PW). The novel adsorbent was designed from recycled low-density polyethylene (LDPE) powder grafted by the cationic polymer. The cationic polymer was synthesized directly on the LDPE surface by plasma-induced radical polymerization. A positively charged adsorbent was chosen due to the negative character of oily droplets to enhance separation efficiency in treating oil-water emulsions. The separation was performed in both batch and filtration modes. Absorption/adsorption uptake capacities showed a sigmoidal S-shape that was analyzed using the Sips model and compared with the newly developed empirical model. Both models showed a remarkable coincidence in the description of experimental data. The separation efficiency of the novel adsorbent was also tested in a filtration mode mimicking a commonly used deep-bed filtration technology. The comparison of the separation efficiency for various sorbents indicated a supreme performance of novel adsorbent. This study demonstrates the potential of a relatively cheap, prepared commodity-based adsorbent for the purification of emulsified oily polluted water in both batch and filtration configurations. This study also contributes to the recycling of polyethylene waste because LDPE attracts meager interest in recycled LLDPE due to many obstacles to reusing LDPE waste for its reprocessing as packaging materials. [ABSTRACT FROM AUTHOR]

Ongoing global population boom has led to the rise in waste and related research on increasing its economic value. In such an attempt, this study aims to activate gas-to-liquids (GTL) derived biosolids (BS) and cardboard (CB) and mixed samples (50:50) using potassium carbonate to produce three activated carbons (ACs): KBS, KCB and KM respectively. The characterization of the samples revealed surface areas of 156, 515, and 527 m2/g for KBS, KCB, and KM, respectively based on Brunauer–Emmett–Teller (BET) analysis, with increased porosity and metal content after activation evident from the Scanning Electron Microscopy-Energy Dispersive Spectroscopy (SEM-EDS) results, as well as the presence of magnetite in the KBS and KM samples apparent from the X-ray powder diffraction (XRD) results. Additionally, Fourier Transform Infrared Spectroscopy (FTIR) results indicate increased C–O–C stretches and O–H bonds after activation of the samples. The ACs were used for methylene blue (MB) removal process which is a rapid for all three samples, reaching equilibrium after 9 h, and optimal at neutral pH and maximum at the highest temperature, 40 °C. The MB adsorption capacity was highest for KM (191.07 mg/g), followed by the KCB and KBS samples. Isotherm modelling of the samples showed best fits for KBS, KCB and KM as Langmuir-Freundlich (LF), Langmuir and Toth models respectively. On the contrary, kinetic modelling using contact time study data for all samples exhibited best fits by the Diffusion-chemisorption (DC) model. Finally, the thermodynamic calculations of the mixed sample disclosed the adsorption process to be exothermic and spontaneous, with potential mechanisms being electrostatic attraction, ion exchange, π-π interactions, and hydrogen bonding. Multiple cycles of KM regeneration was also achieved with good adsorption capacities. Future work will explore other activation methods and examine the magnetic properties of KBS and KM for real water treatment. [Display omitted] • Biosolids, cardboard, and mixed (50:50) samples were activated by potassium carbonate. • Single-stage activated mixed samples (KM) revealed the best surface area of 527 m2/g. • KM showed maximum methylene blue adsorption from water (qe = 191.07 mg/g). • Studies were done on isotherm and kinetic modelling in addition to thermodynamics. • A mechanism was proposed based on the samples' characterization and other results. [ABSTRACT FROM AUTHOR]

With rapidly growing industrial development worldwide, the need for a new class of nanoparticles and techniques for treating wastewater remains a major concern to protect the environment. Layered double hydroxides and particularly LDH-containing hybrids are emerging as potential nano-sized adsorbents for water treatment. Recent studies have demonstrated LDH-containing hybrids as promising multifunctional materials for potential utilization in various applications such as, photo-catalysis, energy storage, nanocomposites and water purification. This article reviews the recent applications of LDH-containing hybrids as adsorbents for water remediation. The maximum adsorption capacities of various toxic heavy metals and dyes on different LDH hybrids were reported as 483 mg/g for Pb 2 + , 95 mg/g for Cd 2 + , 181 mg/g for Cu 2 + , 649 mg/g for Cr 6 + , 180 mg/g As 5 + , 813 mg/g for Hg 2 + , 450 for Ag + , 277 mg/g for U 6 + , 1062 mg/g for methyl orange, 185 mg/g for methylene blue, and 1250 mg/g for Congo red, which is comparatively higher than other commercial adsorbents. This review discusses the adsorption performance of manifold LDH-containing hybrids for treating various pollutants such as heavy metals and dyes. The mechanisms of interaction of LDH-containing hybrids with pollutants and the influence of key adsorption parameters such as pH, contact time, adsorbent dose and temperature have been comprehensively discussed. Moreover, the regeneration potential and reuse of spent LDH-containing hybrids and its toxicity effects have also been reviewed. [ABSTRACT FROM AUTHOR]

Oil contaminated water is one of the challenges in water resources management. It is crucial to remove the oil droplets from water in order to meet the discharge regulations set by the environmental authorities. Carbon nanotubes (CNTs) have generated a lot of attention as a new type of adsorbent due to their exceptionally high adsorption capacity for oil–water separation. The high hydrophobicity of CNTs makes them good candidates to enhance the de-oiling process from wastewater. In this study, we have reported the synthesis and evaluation of novel iron-oxide/CNTs nanocomposites for oil–water separation. The CNTs were doped with different loadings of iron oxide nanoparticles using a wet impregnation technique. The synthesized nanocomposite nanomaterials were characterized using field emission scanning electron microscopy (FE-SEM), high resolution transmission electron microscopy (TEM), Brunauer, Emmett and Teller (BET) technique, X-ray diffraction (XRD), and thermogravimetric analysis (TGA). The effect of adsorption parameters, including, adsorbent dosage, contact time, and agitation speed on the oil removal efficiency were optimized using batch experiments. The sorption capacities of doped CNTs were found to be greater than 7 g/g for gasoline oil. The doped CNTs reached maximum sorption capacity after only 15 min providing one of the fastest minimum contact times reported of all oil sorbent materials. The loading of Fe 2 O 3 nanoparticles on the negative surface of CNT decreases the negative sign and magnitude of the zeta potential by overcoming the repulsive effects of the electrical double layers to allow the finely sized oil droplets to form larger droplets through coalescence. Therefore increasing percentage of the Fe 2 O 3 on the surface of CNT increased the removal of the emulsified oil from the water. [ABSTRACT FROM AUTHOR]

The study provides a review of various applications of biomass-derived biochars, waste-derived biochars, and modified biochars as adsorbent materials for removing dyestuff from process effluents. Processing significant amounts of dye effluent discharges into receiving waters can supply major benefits to countries which are affected by the water crisis and anticipated future stress in many areas in the world. When compared to most conventional adsorbents, biochars can provide an economically attractive solution. In comparison to many other textile effluent treatment processes, adsorption technology provides an economic, easily managed, and highly effective treatment option. Several tabulated data values are provided that summarize the main characteristics of various biochar adsorbents according to their ability to remove dyestuffs from wastewaters. [ABSTRACT FROM AUTHOR]

In this study, graphene oxide (GO) was synthesized using Hummers method. The synthesized GO was characterized using field-emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), Fourier transformed infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), and Brunauer–Emmett–Teller (BET) nitrogen adsorption. The analyses confirmed the presence of oxygen functional groups (C=O and C-O-C) on the GO surface. These oxygen functional groups act as active sites in the adsorption Sr (II). The BET analysis revealed the surface area of GO of 232 m2/g with a pore volume of 0.40 cm3/g. The synthesized GO was used as an adsorbent for removing Sr (II) from aqueous solutions. The adsorption equilibrium and kinetic results were consistent with the Langmuir isotherm model and the pseudo-second-order kinetic model. A maximum strontium adsorption capacity of 131.4 mg/g was achieved. The results show that the GO has an excellent adsorption capability for removing Sr (II) from aqueous solutions and potential use in wastewater treatment applications. [ABSTRACT FROM AUTHOR]

Abstract: The adsorption of two acid dyes Acid Black 1 (AB1) and Acid Blue 113 (AB113) onto mesoporous granular pine-cone derived activated carbon and the adsorption of three acid dyes Acid Black 80 (AB80), Acid Red 114 (AR114) and Acid Yellow 117 (AY117) onto microporous Granular Activated Carbon (GAC) type F400, from aqueous solution, has been studied in a batch system. Seven two-parameter isotherm models – Langmuir, Freundlich, Dubinin–Radushkevich, Temkin, Halsey, Jovanovic and Harkins–Jura – were used to correlate the experimental data. Adsorption isotherm modeling shows that the interaction of dye with activated carbon surface is by localized monolayer adsorption. In order to determine the best fit isotherm for each system, nine error analysis methods, namely, chi-square (χ 2), log-likelihood (G 2), residual root mean square error (RMSE), sum of the squares of the errors (ERRSQ), composite functional error (HYBRD), derivative of Marquardt''s percent standard deviation (MPSD), average relative error (ARE), sum of absolute error (EABS) and average percentage error (APE) were used to evaluate the data. In order to facilitate decision making for the best fit data set, a procedure of normalizing and combining the error results was adopted producing a “sum of the normalized errors” for each parameter set from which the “lowest normalized error set” is selected. [Copyright &y& Elsevier]

Abstract: A number of chars from waste tyre rubber were prepared by carbonisation at 673–1173K. The effects of holding time, heating rate and particle size on the textural characteristics and elemental composition of the resultant chars were investigated. It was demonstrated that temperatures over 773K did not have a significant improvement on the total surface area but resulted in lower char yields following increased aromatisation. Modelling of dye adsorption isotherms showed that the Redlich–Peterson expression yields the best-fit between experimental and predicted data. Furthermore, for a larger sized dye like Acid Yellow 117 (MW=848g/mol), the amount adsorbed by the tyre char is not directly proportional to the total surface area when compared with a commercial carbon, revealing that factors other than total surface area are involved in the adsorption potential of the tyre chars. [Copyright &y& Elsevier]

Abstract: The adsorption of a large reactive dye, Reactive Black 5, onto four adsorbents has been studied. A commercial active carbon, F400, was selected as a standard and two active carbons prepared from bamboo, a biomaterial. The two bamboo derived carbons, BACX2 and BACX6 had high specific surface areas, namely, 2123 and 1400m2/g, respectively. A fourth widely used adsorbent, bone char, was also tested. The adsorption capacities for F400, bone char, BACX2 and BACX6 were 198, 160, 286 and 473mg/g, respectively. A series of batch kinetics were carried out to investigate the rate and possible mechanism of Reactive Black 5 adsorption. Two pseudo-kinetic models and one intraparticle diffusion model were tested. The experimental concentration versus time decay curves were best explained by the intraparticle diffusion model. [Copyright &y& Elsevier]

The adsorption of three acid dyes onto activated carbon has been studied. Three single, three binary and one ternary systems have been investigated and both equilibrium and kinetic studies have been determined. The equilibrium capacities based on the Langmuir analysis are 0.253, 0.125 and 0.219 mmol g-1 carbon for Acid Blue 80, Acid Red 114 and Acid Yellow 117, respectively. The batch adsorber rate data for the seven systems have been analysed based on an intraparticle diffusion rate parameter derived from the plots of dye adsorbed versus the square root of time. The data indicate the adsorption mechanism is predominantly intraparticle diffusion. The multicomponent system rate parameters have been correlated with the single component rate parameters by the use of the Langmuir equilibrium parameters. [Copyright &y& Elsevier]

In the last decades, phosphate is considered the main cause of eutrophication and has received substantial attention from the scientific community. Phosphate is a major pollutant that deteriorates water quality, which has been increasing in water resources, primarily due to the increasing global population and corresponding activities. Adsorption technology is amongst the different technologies used to decrease the phosphate levels in water, and has been found to be highly effective even at low phosphate concentrations. Carbonaceous materials and their composites have been widely used for phosphate removal due to their exceptional surface properties and high phosphate sorption capacity. Considering the importance of the topic, this study reviews the reported literature in the field of adsorptive removal of phosphate over various carbon-based adsorbents such as activated carbon, charcoal, graphene, graphene oxide, graphite and carbon nanotubes. Moreover, insights into the adsorption behaviour, experimental parameters, mechanisms, thermodynamics, effect of coexisting ions and the possible desorption processes of phosphate onto modified and unmodified carbonaceous adsorbents are also considered. Finally, research challenges and gaps have been highlighted. [Display omitted] • Review of the literature of phosphate adsorptive removal by carbon based materials. • Adsorption mechanisms, thermodynamics and desorption studies were considered. • Metals impregnation has significantly increases the phosphate sorption capacity. • Knowledge gaps of phosphate removal by carbonaceous adsorbents were outlined. [ABSTRACT FROM AUTHOR]

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]

In the present study, hydroxyiron-modified montmorillonite (HyFe-MMT) nanoclay was prepared using a simple wet chemical synthesis method. Arsenite (As (III)) removal using raw montmorillonite and HyFe-MMT was compared and evaluated by adsorption experiments conducted under various conditions (adsorbent dosage, iron loading, contact time, pH, and initial As (III) concentration). The nanoclays were characterized using X-ray diffraction (XRD), X-ray fluorescence (XRF), Fourier transform infrared spectrometry (FTIR), BET surface area analysis, thermogravimetric analysis, scanning electron (SEM) microscopy, and transmission electron microscopy (TEM). Fast adsorption kinetics were observed in which more than 55% of As (III) was removed using HyFe-MMT within the first 30 s of the adsorption process. The kinetics were most accurately modeled using the pseudo-second-order equation (R 2  = 1). Optimum As (III) adsorption was obtained between a pH of 6 to 7. The Freundlich model properly described the adsorption process (R 2  > 0.99). It was determined that the adsorption capacity of raw MMT was increased to more than five times after iron modification. The HyFe-MMT adsorbent presented could be used for arsenic contaminated groundwater, drinking water, or wastewater. [ABSTRACT FROM AUTHOR]

Palm kernel shell (PKS) was physically activated by carbon dioxide at 900 °C for 1.5 h and tested for its ability to remove Atenolol (ATE), Acebutolol (ACE) and Carbamazepine (CBM), which are pharmaceutically active compounds (PhACs). Rapid adsorption of PhACs took place in the first 90 min and reached equilibrium after 4 h. The kinetic data were best fitted by the Ritchie-second-order model and confirmed by the diffusion-chemisorption model implying a predominantly chemisorption mechanism. The isotherm adsorption studies showed that the maximum adsorption capacities of ATE, ACE and CBM were 0.69, 0.67 and 0.72 mmol/g respectively. The best fit isotherm was the Sips equation. [ABSTRACT FROM AUTHOR]

Amino functional poly propyleneimine (PPI, G5) dendrimer linked silica (PPI/SiO 2 ) was synthesized with a divergent procedure. PPI/SiO 2 nanohybrid was analyzed by XRD, FTIR, TGA, BET, Zeta potential, TEM and SEM. The above analysis was applied to determine good grafting between PPI and SiO 2 . The adsorption performance of the PPI/SiO 2 nanohybrid for the uptake of Pb 2 + , Ni 2 + , Cu 2 + , and Co 2 + metal ions was monitored under the efficacy of nanohybrid dosage, metal ion concentration, contact time, solution pH, and regeneration. The outputs of the investigation showed high removal efficiency and great desorption performance. The isotherms, kinetics and thermodynamics of Pb 2 + , Ni 2 + , Cu 2 + , and Co 2 + metal ions uptake by the PPI/SiO 2 were evaluated. The results revealed that the highest adsorption capacity of Pb 2 + , Ni 2 + , Cu 2 + , and Co 2 + onto PPI/SiO 2 was 700, 800, 900 and 1000 mg/g at 298 K pursuant to an analysis using the Langmuir model that was coordinated very good to the sorption data. The outputs of the kinetic investigations' demonstrated that the adsorption procedure fitted the pseudo second-order equation. The monitored thermodynamic parameters of ΔS, ΔH and ΔG indicated that the uptake of Pb 2 + , Ni 2 + , Cu 2 + , and Co 2 + metal ions by PPI/SiO 2 was spontaneous and endothermic. This research illustrated that PPI/SiO 2 could be successfully applied as a high performance adsorbent for heavy metal ions removal from aqueous solutions. [ABSTRACT FROM AUTHOR]

The aim of this study was to investigate the applicability of the adsorption process for the removal of organophosphorus pesticide malathion 57% from water by using multi-walled carbon nanotubes (MWCNTs). The impact of various experimental conditions such as pH, quantity of adsorbent, concentration of pesticides, contact time and temperature was studied and optimized for the maximum removal of malathion. Unlike conventional optimization, a limited number of experiments (26 steps) were performed in a cost-effective manner for different independent variables such as MWCNTs concentration (0.1–0.5 g/L), the malathion (57%) concentration (6 mg/L and 10 mg/L), contact time (2–30 min) and pH (neutral range). Based on the experimental data obtained in a lab-scale batch study, a three-factor response surface modeling (RSM) approach was implemented in order to optimize the conditions for maximum removal of malathion, and compare experimental results with standardized malathion samples. The optimized conditions to achieve the maximum removal of malathion (100%) were determined to be a malathion concentration of 6 mg/L, an initial MWCNTs concentration of 0.5 g/L, and a contact time of 30 min. Findings of this study clearly indicated that 100% of the malathion could be cost-effectively removed by MWCNTs in conditions predicted by the proposed optimization methodology. [ABSTRACT FROM AUTHOR]

The water cleaning applications of carbon nanotubes (CNT) have generated much research interest since their initial discovery. However, in the early stages of research, the efficiency of CNTs for the removal of heavy metal ions has been severely limited because of the intense agglomeration of CNTs and their deficiency of functional groups. In this research, a new method has been discovered for the preparation of dendrimer functionalized CNTs and a PAMAM/CNT nanocomposite was prepared. FTIR, SEM, TEM, Raman spectroscopy, zeta potential measurements, and dispersion observing methods have been employed for characterizing the synthetic nanocomposite and these techniques indicated that the dendrimer functionalized CNTs have been favorably synthesized. In addition, the uniquely high adsorption capacities properties of PAMAM/CNT nanocomposite for Ni 2 + , Zn 2 + , As 3 + , Co 2 + were examined. The effects of several parameters including initial metal ion concentration, temperature, solution pH, the nanocomposite dosage and contact time were studied. The experimental data were analyzed using equilibrium isotherm relationships (Langmuir, Temkin and Freundlich) and the uniquely high adsorption capacities and rates were studied using (pseudo-first order, intraparticle diffusion and pseudo second-order) adsorption kinetics models. The results indicated that the maximum adsorption occurred at pH = 8. With increasing nanocomposite dosage and increasing contact time, there was increased adsorption capacity. Analysis of the adsorption process demonstrated that the Langmuir isotherm and pseudo-second order kinetics are the most appropriate models for heavy metal ions adsorption onto PAMAM/CNT nanocomposite. [ABSTRACT FROM AUTHOR]

In the present study, defluoridation study of liquid phase with the help of multi-walled carbon nanotubes (MWCNTs) and single-walled carbon nanotubes (SWCNTs) were well investigated and elucidated. The impact of different experimental conditions such as solution pH, initial fluoride concentration, adsorbent dose, and contact time was well studied and optimized for the maximum fluoride removal from water. The experimental data were fitted by the Freundlich, Langmuir and Dubinin–Radushkevich (D–R) isotherm models and the related equilibrium constants were calculated. The results of the isotherm studies showed that fluoride removal by both adsorbents followed the Freundlich isotherm model. Kinetic studies were conducted and the results demonstrated that the experimental data were fitted well with the pseudo-second order kinetic model. Furthermore, two multiple regression-based equations were also derived to model the removal of fluoride from aqueous solutions by the carbon nanotubes. This study demonstrated that the polynomial equations satisfactorily described the behavior of the present defluoridation process for both MWCNTs ( R 2 = 0.913) and SWCNTs ( R 2 = 0.941). [ABSTRACT FROM AUTHOR]

Due to serious public health threats resulting from mercury pollution and its rapid distribution in our food chain through the contamination of water bodies, stringent regulations have been enacted on mercury-laden wastewater discharge. Activated carbons have been widely used in the removal of mercuric ions from aqueous effluents. The surface and textural characteristics of activated carbons are the two decisive factors in their efficiency in mercury removal from wastewater. Herein, the structural properties and binding affinity of mercuric ions from effluents have been presented. Also, specific attention has been directed to the effect of sulfur-containing functional moieties on enhancing the mercury adsorption. It has been demonstrated that surface area, pore size, pore size distribution and surface functional groups should collectively be taken into consideration in designing the optimal mercury removal process. Moreover, the mercury adsorption mechanism has been addressed using equilibrium adsorption isotherm, thermodynamic and kinetic studies. Further recommendations have been proposed with the aim of increasing the mercury removal efficiency using carbon activation processes with lower energy input, while achieving similar or even higher efficiencies. [ABSTRACT FROM AUTHOR]

Sludge, a byproduct produced from numerous industrial activities, has been recognized as an ecological burden for the society. However, viewing the sludge, as a carbon-rich material, has stimulated new gateways for the production of porous activated carbons for water treatment applications. Herein, various textural properties of the sludge-based activated carbons have been compiled and critically reviewed with the focus on surface area, pore size and pore size distribution for both physically and chemically activated carbons. It has been found that chemical activation using various activating agents yields more superior adsorbents with high specific surface areas than physical activation methods. Moreover, the potential of sludge-derived activated carbons for the sequestration of metals and dyes from aqueous media has been discussed. Furthermore, the adsorption mechanism in several adsorbent–adsorbate systems and the effect of various parameters on the adsorption behavior of different dyes and metals on sludge-based activated carbons have been reviewed. It has been shown that the pollutant uptake capacities of the adsorbents derived from sewage sludge are not only governed by the textural properties of the adsorbents, but also by their surface properties, such as the functional groups and the surface charge and thus it is proposed that both of these crucial factors be considered concurrently. [ABSTRACT FROM AUTHOR]

Highlights: [•] An initial short arsenate adsorption followed by desorption at low pH was observed. [•] A novel pseudo-first order reversible model to describe the process was developed. [•] Effect of pH on the equilibrium and kinetic studies on adsorption was examined. [•] The speciation of arsenate and protonation of chitosan at various pH were studied. [•] Both interactive effects revealed the adsorption/desorption mechanism. [Copyright &y& Elsevier]

Abstract: Printed circuit boards (PCBs) constitute one of the major sources of toxicity in landfill areas throughout the world. Hence, PCB recycling and separation of its metallic and nonmetallic components has been considered a major ecological breakthrough. Many studies focus on the metallic fraction of the PCBs due to its economic benefits whereas the nonmetallic powder (NMP) has been left isolated. In this work, the feasibility of using NMP as an adsorbent to remove charged toxic heavy metal ions have been studied and its efficiency has been compared with two widely-used commercial adsorbents. The results indicated that the virgin NMP material has no adsorption capacity, while the application of an activation stage to modify the NMP process has a significant effect on its porosity and thus adsorption capacity. The Cu and Pb removal capacity of the activated sample (A-NMP) at a pH level of 4 was 3mmol and 3.4mmol per gram of the adsorbent, respectively, which was considerably higher than the commercial ones. [Copyright &y& Elsevier]

Abstract: It is well-known that chitosan consists of amino groups for the chelation of metal ions while NH2-MCM-41 has excellent adsorption selectivities for metals. This work compares both adsorption capacities and selectivities of chitosan and NH2-MCM-41. It has been found that chitosan has adsorption capacities of 1.76mmol/g, 1.03mmol/g and 1.30mmol/g for Cu2+, Ni2+ and Zn2+ respectively whereas NH2-MCM-41 has adsorption capacity of 1.52mmol/g, 0.8mmol/g and 0.83mmol/g for Cu2+, Ni2+ and Zn2+. The higher adsorption capacity in chitosan is attributed to its higher loading of amine groups. The single component adsorption isotherms were well-fitted using Freundlich model. The binary adsorptions of Cu2+–Zn2+ and Ni2+–Zn2+ systems showed similar adsorption selectivities for both adsorbents. However, chitosan has no preferential adsorption for Ni2+–Zn2+ system while NH2-MCM-41 has a good selectivity towards Zn2+. It is believed that the difference can be attributed to the heterogeneous surface of chitosan due to its organic nature. The multi-component adsorptions were best described by a multicomponent extended Freundlich model. Despite the surface functional group, this work indicates the importance of the adsorbent support on selective adsorption. [Copyright &y& Elsevier]

Abstract: In this work, the recovery of base oils from waste lubricants was investigated using a novel combination of solvent extraction and adsorption on solids. The performance of six extracting solvents (n-hexane, 1-butanol, petroleum ether, 1-hexanol, carbon tetra chloride, and acetone) was evaluated experimentally. Solvent to oil ratios from 1:1 to 4:1 were also examined. This research has studied the effect of the use of KOH to enhance flocculation. The results show that 1-butanol achieved the best performance with the maximum percent sludge removal, followed by n-hexane, petroleum ether, 1-hexanol, carbon tetrachloride, and acetone. The percentage of oil sludge was found to increase with the increase of solvent to oil ratio until it reached the maximum at the ratio of 3:1. The application of an adsorption process using different adsorbent materials was investigated. Adsorbent materials such as almond shell, walnut shell, eggshell, and acid activated clay which were prepared locally were used. It was found that the acid activated clay was able to give the best conditions for treating the waste oil followed by the almond shell powder. The results from the test showed that, viscosity increased from 38.3cst for used lube oil to 85cst for acid/clay treatment and the flash point increase from 178°C to 238°C, while the density decreased from 912 to 896kg/m3, the pour point from −6 to −13.2°C and colour from 0.53 to 0.12. Other results from the different tests showed varying degrees of improvement with the best results obtained using the acid/clay treatment. [Copyright &y& Elsevier]

Abstract: Novel Fe loaded activated carbons have been prepared from sugar beet pulp (BP) agricultural residues by direct steam activation followed by iron impregnation with or without previous oxidation. The corresponding activated carbons were: BP–H2O, BP–H2O–Fe, BP–H2O–H2O2–Fe and BP–H2O–MnO2–Fe. The textural characterization of these tailored activated carbons was based on nitrogen adsorption/desorption isotherms leading to BET surface area values between 741 and 821m2/g and total porous volumes between 0.58 and 0.79cm3/g. Elemental analysis and ash content showed that carbon content reached 78% for BP–H2O with 13.6% of ash and decreased to 50% in iron-based materials. BP–H2O and BP–H2O–Fe revealed a basic nature with pHPZC values of 9.8 and 9 respectively while BP–H2O–H2O2–Fe and BP–H2O–MnO2–Fe had acid pHPZC (5.1 and 3.6). Their surface chemistry has been investigated by XPS analysis and by the quantification of the surface chemical moieties based on Boehm’s approach. A clear relationship was found between the surface iron content and the strong acidic groups. Arsenic (As(V)) adsorption isotherms were performed and Langmuir, Freundlich, Redlich–Peterson models were used to describe the experimental data by non-linear regression. It was found that Redlich–Peterson isotherm provided the best fit and the Langmuir adsorption capacities confirmed that the iron-based activated carbons were highly attractive for As(V) removal with capacities up to 17mgg−1. Finally, it has been shown that the surface iron content determined by XPS analysis is very well correlated with Langmuir qm values (r 2 =0.982) and with the strong acidic moieties deduced from the Boehm’s method. [Copyright &y& Elsevier]

Abstract: A series of activated carbons were prepared from bamboo by chemical activation with HCl, HNO3 and H2SO4. Unlike phosphoric acid, these three acids are not commonly used as an activating agent for lignocellulosic materials. The effect of operating variables such as activation temperature, impregnation ratio (the mass ratio between bamboo/acid) and holding time were investigated. The resultant carbons were evaluated for the yield, surface area, pore size distribution, pH, elemental composition and ash. At an impregnation ratio (the mass ratio between bamboo/acid) of 1, activated carbon with BET surface area and micropore volume as high as 553m2/g and 0.239cc/g was obtained at 1173K using H2SO4 as an activating agent. Lower impregnation ratio and shorter holding time were favourable to the yield and surface area while increasing impregnation ratio enhanced mesoporosity of the carbons. This can be attributed to the transformation of micro- to mesopores in the presence of higher ‘basic’ element contents such as nitrogen and sulphur. [ABSTRACT FROM AUTHOR]

Abstract: Two types of activated carbons from tyre char (with or without sulphuric acid treatment) were produced via carbon dioxide activation with BET surface areas in the range 59–1118m2/g. Other characterisation tests include micropore and mesopore surface areas and volumes, pH, and elemental compositions, particularly heteroatoms such as nitrogen and sulphur. They were correlated to the adsorption capacity which were in the range of 0.45–0.71mmol/g (untreated) and 0.62–0.84mmol/g (acid-treated) for Acid Blue 25. In the case of larger-sized molecules like Acid Yellow 117, capacities were in the range of 0.23–0.42mmol/g (untreated) and 0.29–0.40mmol/g (acid-treated). Some tyre carbons exhibit a more superior performance than a microporous, commercial activated carbon (Calgon® F400). By modelling the dye adsorption equilibrium data, the Redlich–Peterson isotherm is adopted as it has the lowest SSE. Based on the surface coverage analysis, a novel molecular orientation modelling of adsorbed dyes has been proposed and correlated with surface area and surface charge. For the acid dyes used in this study, molecules were likely to be adsorbed by the mesopore areas. [Copyright &y& Elsevier]

Abstract: Experiments have been carried out to prepare char from waste bamboo scaffolding for wastewater treatment. Carbonisation parameters such as temperature, holding time, heating rate and particle size were investigated. When the material was heated to 1173K for 2h, surface area and total pore volume (V total) were 327m2/g and 0.185cm3/g, respectively. Particle size and heating rate appear less influential to the yield and textural characteristics of the resultant chars. Bamboo char obtained in this study did not show very high adsorption capacities for two acid dyes (Acid Blue 25 and Acid Yellow 117) but exhibited significant uptake of Methylene Blue. The equilibrium data were modelled by three different isotherms, namely, Langmuir, Freundlich and Redlich–Peterson model. Comparing the predicted data using optimised parameters from each model based on the SSE error function, the Redlich–Peterson isotherm appears the ‘best’ model to correlate experimental data. [Copyright &y& Elsevier]

Abstract: The disposal of waste tyre represents a serious concern in environmental management. Owing to the high carbon content of waste tyre rubber, it is feasible to convert waste tyres to a value-added product, i.e. activated carbon, for environmental applications. This study focuses on the effect of different activation conditions (e.g. temperature, holding time and acid treatment) on the porosity of activated carbons produced from tyre rubber. Experimental studies showed that nitric acid treatment to tyre chars is able to remove certain mineral contents such as Ca, K and Na, which affect the reactivity of gas–solid reactions in the subsequent physical activation process (CO2 as activating agent). Those acid-treated carbons developed high surface areas (over 1000m2/g) that were comparable to commercial products. They also posses high mesopore volume up to 0.855cc/g which has been shown favourable to the adsorption of larger-sized dye molecules. The Redlich–Peterson equilibrium isotherm model yielded the best-fit to experimental data for all three dyes using the non-linear error functions. [Copyright &y& Elsevier]

Abstract: Selective gold adsorption was investigated for the NH2-MCM-41 and SH-MCM-41 adsorbents prepared by grafting aminopropyl and thiolpropyl groups on the surface of the MCM-41 mesoporous silica. The single component adsorption of gold, copper and nickel from salt solutions, and the binary adsorption studies of Au3+/Cu2+ and Au3+/Ni2+ solutions were carried out for the two adsorbents. Gold adsorption from simulated gold mining solution and gold electroplating wastewater were also reported. The NH2-MCM-41 and SH-MCM-41 displayed strong affinity for gold in the solution and both exhibited 100% selectivity for the gold in the binary Au3+/Cu2+ and Au3+/Ni2+ solutions. The NH2-MCM-41 is more suitable for the gold mining solution, while SH-MCM-41 is efficient for gold adsorption from the electroplating waste containing high amount of organics. The gold was recovered as high purity salt solution by elution with mineral acid for NH2-MCM-41 and thiolsulfate for SH-MCM-41. The regenerated adsorbent remained selective to gold and exhibited the same adsorption capacity as the fresh adsorbent. Also, the regenerated adsorbent performed well even after several reuses. [Copyright &y& Elsevier]

The ability of bone char to adsorb three metal ions, namely, copper(II), zinc(II) and cadmium(II) ions from wastewater has been studied. Three single-component equilibrium systems and three binary equilibrium systems have been measured experimentally. The three single-component equilibrium data were analyzed using the Langmuir and the Sips equilibrium isotherm equations. The Sips isotherm gave a better fit of the experimental data than the Langmuir isotherm based on the sum of squares errors (SSE) analysis. The Cu–Zn, Cu–Cd and Cd–Zn binary equilibrium experimental data were examined by incorporating the Langmuir and the Sips isotherm equations into the ideal adsorbed solution theory (IAST). The solution methods and the predicted results for the three binary systems at different metal ion compositions have been evaluated. In addition, the application of the IAST to the model prediction for the fixed bed system is presented. [Copyright &y& Elsevier]