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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]

Abstract: The adsorptive removal of toxic para-chlorophenol using activated carbon adsorption columns is a proven effective engineering process. This paper examined the possibility to stratify an adsorbent bed into layers, in order to enhance the adsorption process performance in terms of increased column service time and adsorbent bed saturation. Four different types of fixed-bed adsorption columns are used and compared under the same operating conditions, but with the variation of column geometry and activated carbon particle size stratification. The Type 3 column – a cylindrical column with particle stratification packing, is found to be the most efficient choice, as the extent of column service time and adsorbent bed saturation are the largest. This could eventually decrease the frequency of adsorbent replacement/regeneration and hence reduce the operating cost of the fixed-bed adsorption process. The Homogeneous Surface Diffusion Model (HSDM) was applied successfully to describe the dynamic adsorption of para-chlorophenol onto Filtrasorb 400 (F400) activated carbon in different types of columns. The Redlich-Peterson isotherm model equation, an experimentally derived external mass transfer correlation and a constant surface diffusivity are used in the HSDM. The optimised surface diffusivity of para-chlorophenol is found to be 1.20E-8 cm2/s, which is in good agreement with other phenolics/F400 carbon diffusing systems in literature. [Copyright &y& Elsevier]

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: 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]

Abstract: A feasibility study has been carried out on the preliminary process design of the production of activated carbon from the bamboo scaffolding waste based on 30tonnes of bamboo waste per day throughput. A comparison of the process economics of the stand-alone bamboo carbonization plant with a plant that is integrated into another major processing facility has been studied. The preliminary process design was based on various literature sources and an economic evaluation, in which the total capital investment (TCI), the production cost, the return on investment (ROI), the cash flow and the internal rate of return (IRR) of the stand-alone plant and integrated plant were estimated. The TCI of the stand-alone plant and integrated plant are HK$ 7,430,000 and HK$ 6,430,000, respectively. Net present values of two plants at various discount factors have been determined and the IRR have been estimated as 13.0 and 20.1% for the stand-alone plant and integrated plant, respectively. Sensitivity analysis reveals that the cash flow of the project would be increased or decreased up to 40, 65 and 120% by varying production factors of cost of chemical activation agent, production capacity and selling price of activated carbon, respectively, in the extent of ±25%. [Copyright &y& Elsevier]

A review of the production of activated carbons from waste tyres is presented. The effects of various process parameters, particularly, temperature and heating rate, on the pyrolysis stage are reviewed. The influence of activating conditions, physical and chemical, nature of the activation chemicals, on the active carbon properties are discussed. Under certain process conditions several active carbons with BET surface areas over 1000 m2/g have been produced with extensive micropore volumes, over 40% of the total pore volume.A review is carried out of the reaction kinetic modeling applied to the pyrolysis of tyres and the chemical activation of tyres. The models cover one step and two step pyrolysis models, plus more recent models which are based on the actual chemical components such as natural rubber, SBR and other additives. [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]

The sorption of acid dyes from aqueous effluents onto activated carbon has been studied. The effects of initial dye concentration and activated carbon mass on the rate of Acid Blue 80 and Acid Yellow 117 removal have been investigated. Three mass transport models based on film and pore diffusion control have been applied to model the experimental concentration decay curves. The models are compared on the basis of the solid-phase loading capacity using various assumptions since the assignment of an appropriate solid-phase loading has been the subject of several papers on this topic and no comparisons have been provided on the effectiveness of each approach. The equilibrium solid-phase concentration is assumed: (i) incorporating a time-dependent solid-phase concentration Ye,t, (ii) equal to the intersection point of the equilibrium isotherm and the operating line and (iii) the point on the equilibrium isotherm where the liquid-phase concentration equals the initial concentration in the film–pore diffusion model. [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]

The widely used toxic dye malachite green (MG) poses a significant risk to human health, having a mutagenic effect. Waste date stones were used to produce microwave‐activated carbons and were applied to adsorb the highly toxic dye. The critically important task of selecting the correct design adsorption capacity for different effluent pollutant concentrations to meet effluent discharge limit standards is described and a novel design selection criteria approach is presented. [ABSTRACT FROM AUTHOR]

A low cost and high performing hybrid ceramic/carbon symmetric membrane has been fabricated and tested. The hybrid membrane was fabricated by mixing alumina powder with high surface area powdered activated carbon (PAC). The hybrid Al 2 O 3 /AC membrane has a developed complex network of micro and nano channels which enhanced the porosity of the membrane two fold compared to a pure Al 2 O 3 membrane. Furthermore, due to enhanced pore size and porosity, the hybrid membrane exhibited super-hydrophilic characteristics with the contact angle being close to zero. The increase in the membrane roughness enhanced the surface area of the membrane, which created an increase in the membrane surface area for the filtration path. The membrane exhibited a very high removal efficiency and retention (more than 99%) of oil from an oil-in-water emulsion stabilized by a surfactant. The membrane performance has been tested under harsh conditions such as a high oil concentration in a concentrated saline feed and no change in the separation efficiency or performance was observed with time. The membrane proved to be a good candidate for applications such as the treatment of oily wastewater or oil separation from seawater or from produced-water. [ABSTRACT FROM AUTHOR]

A central composite design using response surface methodology was applied for the experimental design and optimization of fluoride adsorption on an activated carbon derived from calcium chloride-modified Crocus sativus leaves (AC-CMCSL). Fluoride removal efficiency as function of independent variables, such as initial fluoride concentration, pH, adsorbent dose, and time has been investigated. The maximum percentage removal of fluoride at optimum conditions (initial fluoride concentration = 6.5 mg L−1, pH = 4.5, adsorbent dose = 15 g L−1 and time = 70 min) was 85.43%. By comparing adsorption isotherm, the Freundlich model provided the best correlation (R2 = 0.99) for the adsorption of fluoride on AC-CMCSL. The maximum adsorption capacity from the Langmuir model (qmax) was 2.01 mg g−1. The influence of the co-existing anions on fluoride adsorption was in the following order: PO43− > SO42− > Cl− > NO3−. The results of the present study showed that activated carbon derived from the leaves of calcium chloride-modified Crocus sativus has a good potential for fluoride removal from aqueous solution. [ABSTRACT FROM AUTHOR]

Altering the textural properties of activated carbons (ACs) via physicochemical techniques to increase their specific surface area and/or to manipulate their pore size is a common practice to enhance their adsorption capacity. Instead, this study proposes the utilization of the vacant sites remaining unoccupied after dye uptake saturation by removing the steric hindrance and same-charge repulsion phenomena via multilayer adsorption. Herein, it has been shown that the adsorption capacity of the fresh AC is a direct function of the dye molecular size. As the cross-sectional area of the dye molecule increases, the steric hindrance effect exerted on the neighboring adsorbed molecules increases, and the geometrical packing efficiency is constrained. Thus, ACs saturated with larger dye molecules render higher concentrations of vacant adsorption sites which can accommodate an additional layer of dye molecules on the exhausted adsorbent through interlayer attractive forces. The second layer adsorption capacity (60-200 mg·g-1) has been demonstrated to have a linear relationship with the uncovered surface area of the exhausted AC, which is, in turn, inversely proportional to the adsorbate molecular size. Unlike the second layer adsorption, the third layer adsorption is a direct function of the charge density of the second layer. [ABSTRACT FROM AUTHOR]

This paper aims at the sustainable development of activated carbons for value-added applications from the waste tyre pyrolysis product, tyre char, in order to make pyrolysis economically favorable. Two activation process parameters, activation temperature (900, 925, 950 and 975 °C) and residence time (2, 4 and 6 h) with steam as the activating agent have been investigated. The textural properties of the produced tyre char activated carbons have been characterized by nitrogen adsorption–desorption experiments at −196 °C. The activation process has resulted in the production of mesoporous activated carbons confirmed by the existence of hysteresis loops in the N 2 adsorption–desorption curves and the pore size distribution curves obtained from BJH method. The BET surface area, total pore volume and mesopore volume of the activated carbons from tyre char have been improved to 732 m 2 /g, 0.91 cm 3 /g and 0.89 cm 3 /g, respectively. It has been observed that the BET surface area, mesopore volume and total pore volume increased linearly with burnoff during activation in the range of experimental parameters studied. Thus, yield-normalized surface area, defined as the surface area of the activated carbon per gram of the precursor, has been introduced to optimize the activation conditions. Accordingly, the optimized activation conditions have been demonstrated as an activation temperature of 975 °C and an activation time of 4 h. [ABSTRACT FROM AUTHOR]

Many researches have produced porous activated carbons from various precursors for phenol removal from wastewater. A number of literature focus on the optimization of activation conditions to obtain adsorbents with higher specific surface areas as a result of the general misconception that higher surface areas result in higher adsorption capacities, disregarding the effect of the pore geometry. The aim of this study is to demonstrate the significance of micropore surface area, rather than total surface area, in the adsorption of phenol. It has been confirmed that for activated carbons with similar surface areas, the one with higher fraction of microporosity leads to higher phenol uptake. This has been attributed to the π–π London dispersion forces between the graphitic carbon basal planes and the phenol aromatic ring. Thus, it is hypothesized that hydrogen bonding does not occur between the phenol molecules and the functional groups on the carbon surface. [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]

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: 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]

Minimum total amount of microwave treated date stone carbon (S S1 + S S2) for removal of Malachite Green using Langmuir-Freundlich model for different discharge concentrations, C2. [Display omitted] • High surface area carbon from microwaved waste date stone • High adsorption capacity of 98 mg/g for Malachite Green • Optimised two-stage batch adsorber design for minimum adsorbent use Microwave and thermal treatment methods have been applied in order to produce two derived active carbons using waste date pits/stones from a date syrup processing plant. The adsorption properties of the two products have been tested for the adsorption of the toxic Malachite Green dye, which is commonly applied in the textile and plastics industry. Equilibrium isotherms were determined by experiment and evaluated using six isotherm correlations. The optimum fitting correlation for the thermally treated product was the Langmuir-Freundlich isotherm and for the microwave product was the Redlich-Peterson. The surface areas of the thermal product and the microwave product were 669.3 m2/g and 1123 m2/g respectively; and maximum malachite green adsorption capacities were 58 mg/g and 98 mg/g respectively. A two-stage batch adsorber model has been developed to optimize the two-step adsorption process to adsorb malachite green and minimize the amount of adsorbent, and therefore adsorbent cost, used for both thermal treated and microwave treated date stones. The output applications include the minimum total adsorbent for designing various percentages dye removal based on various effluent discharge concentrations and various initial dye concentrations. [ABSTRACT FROM AUTHOR]