In this work, a chitosan-modified nanofiber membrane was fabricated and used to examine the permeation characteristics of C-phycocyanin (CPC) obtained from Spirulina platensis. The effects of NaCl concentration (0.1-1.0 M), chitosan coupling pH (6-8), chitosan coupling concentration (0.1-3.0%), algal solution pH (6-8), algal mass concentration (0.1-1.0% dw/v), and membrane flux (4.08 × 10-2-2.04 × 10-1 mL/min·cm2) on the penetration performance of the membrane for CPC were investigated. The results show that the order of binding selectivity of the membrane for these proteins is contaminating proteins (TP) > allophycocyanin (APC) > CPC. TP and APC molecules were more easily adsorbed by the chitosan-modified membrane, and the CPC molecules most easily penetrated the membrane without being adsorbed, enhancing CPC purity. The purification factor and total mass flux were 3.3 fold and 66%, respectively, in a single step.
In this work, the influence of pyrolysis temperature on the physicochemical properties of palm oil mill sludge biochar (POSB) and its adsorption properties towards cadmium (Cd) and copper (Cu) was investigated. Characterization experiments suggested that POSBs' surface functional groups play the major role in the adsorption process. POSB pyrolyzed at 400 °C showed the best characteristics for Cu and Cd removal. Adsorption study indicated that contact time and shaking speed enhances the adsorption capacity of POSB. It was affirmed that pH adjustment is not necessary for POSB to adsorb Cu and Cd. Mechanism studies fitted well with Langmuir and Pseudo-Second Order model. Thermodynamic parameters indicated that the adsorption was spontaneous, endothermic and correspond to chemical adsorption. The highest uptakes of Cu and Cd were recorded at 48.8 mg/g and 46.2 mg/g respectively. This work verifies that the temperature used for palm oil mill sludge (POS) pyrolysis and adsorption condition played the most prominent role in Cu and Cd removal from aqueous solutions.
An attempt has been made in this review to provide some insights into the possible adsorption mechanisms of hexavalent chromium onto layered double hydroxides-based adsorbents by critically examining the past and present literature. Layered double hydroxides (LDH) nanomaterials are typical dual-electronic adsorbents because they exhibit positively charged external surfaces and abundant interlayer anions. A high positive zeta potential value indicates that LDH has a high affinity to Cr(VI) anions in solution through electrostatic attraction. The host interlayer anions (i.e., Cl-, NO3-, SO42-, and CO32-) provide a high anion exchange capacity (53-520 meq/100 g) which is expected to have an excellent exchangeable capacity to Cr(VI) oxyanions in water. Regarding the adsorption-coupled reduction mechanism, when Cr(VI) anions make contact with the electron-donor groups in the LDH, they are partly reduced to Cr(III) cations. The reduced Cr(III) cations are then adsorbed by LDH via numerous interactions, such as isomorphic substitution and complexation. Nonetheless, the adsorption-coupled reduction mechanism is greatly dependent on: (1) the nature of divalent and trivalent salts utilized in LDH preparation, and the types of interlayer anions (i.e., guest intercalated organic anions), and (3) the adsorption experiment conditions. The low Brunauer-Emmett-Teller specific surface area of LDH (1.80-179 m2/g) suggests that pore filling played an insignificant role in Cr(VI) adsorption. The Langmuir maximum adsorption capacity of LDH (Qomax) toward Cr(VI) was significantly affected by the natures of used inorganic salts and synthetic methods of LDH. The Qomax values range from 16.3 mg/g to 726 mg/g. Almost all adsorption processes of Cr(VI) by LDH-based adsorbent occur spontaneously (ΔG° <0) and endothermically (ΔH° >0) and increase the randomness (ΔS° >0) in the system. Thus, LDH has much potential as a promising material that can effectively remove anion pollutants, especially Cr(VI) anions in industrial wastewater.
In this study two deep eutectic solvents (DESs) were prepared using ethylene glycol (EG) and two different ammonium-based salts. The potential of these DESs as novel agents for CNTs functionalization was examined by performing a comprehensive characterization study to identify the changes developing after the functionalization process. The impact of DESs was obvious by increasing the surface area of CNTs to reach 197.8 (m2/g), and by adding new functional groups to CNTs surface without causing any damage to the unique structure of CNTs. Moreover, CNTs functionalized with DESs were applied as new adsorbents for the removal of methyl orange (MO) from water. The adsorption conditions were optimized using RSM-CCD experimental design. The kinetics and the equilibrium adsorption data were analyzed using different kinetic and isotherm models. According to the regression results, adsorption kinetics data were well described by pseudo-second order model, whereas adsorption isotherm data were best represented by Langmuir isotherm model. The highest recorded maximum adsorption capacity (qmax) value was found to be 310.2 mg/g.
The transition from monolayer to multilayer adsorption at the air-water interface in the presence of multivalent counterions has been demonstrated for a limited range of anionic surfactants which exhibit increased tolerance to precipitation in the presence of multivalent counterions. Understanding the role of molecular structure in determining the transition to surface ordering is an important aspect of the phenomenon. The focus of the paper is on the alkyl ester sulfonate, AES, surfactants; a promising group of anionic surfactants, with the potential for improved performance and biocompatibility. Neutron reflectivity measurements were made in aqueous solution and in the presence of NaCl, CaCl2, MgCl2 and AlCl3, for a range of alkyl ester sulfonate surfactants, in which the headgroup and alkyl chain geometries were manipulated. In the regions of monolayer adsorption changing the AES headgroup and alkyl chain geometries results in an increased saturation adsorption and in a more gradual decrease in the adsorption at low concentrations, consistent with a greater adsorption efficiency. Changing the AES headgroup and alkyl chain geometries also results in changes in the transition from monolayer adsorption to more ordered surface structures with the addition of AlCl3 and mixed multivalent electrolytes. A more limited surface layering is observed for the ethyl ester sulfonate, EES, with a C14 alkyl chain. Replacing the C14 alkyl chain with a C18 isostearic chain results in only monolayer adsorption. The results demonstrate the role and importance of the surfactant molecular structure in determining the nature of the surface adsorption in the presence of different electrolytes, and in the tendency to form extended surface multilayer structures.
Preparation of selective magnetic adsorbents for dispersive micro-solid phase extraction often involves multi-step reactions which are time consuming. This study demonstrates a simplified method for the synthesis of a magnetic adsorbent, which is selective towards the adsorption of mercury(ii) ions (Hg2+). In this method, the incorporation of a metal capturing ligand (3-oxo-1,3-diphenylpropyl-2-(naphthalen-2-ylamino) ethylcarbamodithioate) and the coating of magnetic particles with silica gel was performed in a single step. This adsorbent was then used in solid-phase microextraction for the preconcentration of Hg2+ in water. In this study, a mercury analyzer was used to quantify the Hg2+. Under optimized conditions, the developed analytical method achieved a low detection limit (4.0 ng L-1), satisfactory enrichment factor (96.4) and wide linearity range (50.0-5000 ng L-1) with a good coefficient of determination (0.9985) and good repeatability (<7%). The preconcentration factor of this method was 100. This proposed method was also successfully utilized for the determination of Hg2+ in drinking water, tap water and surface water with good recovery (>91%) and high intra-day and inter-day precision.
A crosslinked chitosan-glyoxal/TiO2 nanocomposite (CCG/TNC) was synthesized by loading different ratios of TiO2 nanoparticles into polymeric matrix of crosslinked chitosan-glyoxal (CCG) to be a promising biosorbent for methyl orange (MO). Box-Behnken design (BBD) in response surface methodology (RSM) was applied to optimize various process parameters, viz., loading of TiO2 nanoparticles into CCG polymeric matrix (A: 0%-50%), adsorbent dose (B: 0.04-0.14 g/50 mL), solution pH (C: 4-10), and temperature (D: 30-50 °C). The highest MO removal efficiency of 75.9% was observed by simultaneous interactions between AB, AC, and BC. The optimum TiO2 loading, adsorbent dosage, solution pH, and temperature were (50% TiO2: 50% chitosan labeled as CCG/TNC-50), 0.09 g/50 mL, 4.0, and 40 °C. The adsorption of MO from aqueous solution by using CCG/TNC-50 in batch mode was evaluated. The kinetic results were well described by the pseudo-first order kinetic, and the equilibrium data were in agreement with Langmuir isotherm model with maximum adsorption capacity of 416.1 mg/g. The adsorption mechanism included electrostatic attractions, n-π stacking interactions, dipole-dipole hydrogen bonding interactions, and Yoshida H-bonding.
The crab carapace is a waste which cannot be decomposed. This waste was used to
remove the Reactive Orange 16 (RO16) and Basic Blue 3 (BB3) from aqueous solution
at different operational parameters such as pH, mass load, the concentrations of dye and
the temperature. The crab collected was modified to obtain quaternized crab (QC) using
(3-chloro-2-hydroxypropyl) trimethylammonium chloride solution (C6H15Cl2NO, 65% w/w
in water). The pH of the dyes solution was varied from pH 4 to 10. The highest adsorption
percentage was achieved at pH 7 for both dyes. Increasing the QC mass for the adsorption
process had granted an increase of dyes removal percentage. The highest adsorption
percentage was achieved at 91.00% for RO16 and 29.40% for BB3 dyes with 7.5 g/L QC
used. However, the adsorption capacity of QC decreased with higher QC mass because the
dye molecules occupied on the surface and prevented other molecules to diffuse into the
QC. At higher concentration beyond 20 mg/L and 10 mg/L of RO16 and BB3, respectively,
the maximum adsorption was achieved at 2.5362 mg/g and 0.6812 mg/g. The adsorption of
both dyes by QC was best fitted using Langmuir isotherm model, explaining the adsorption
mainly occurred as a single layer on the surface of QC. Comparison to the results obtained
from the kinetic models, the adsorption was
chemisorption in nature. According to the
thermodynamic studies, the adsorption of
RO16 was an exothermic, while BB3 was
an endorthermic process.
In this study, coconut leaves were used as a starting material for the production of activated carbon by thermal
carbonization using FeCl3
-activation method. The characterization of coconut leaves-FeCl3
activated carbon (FAC) were
evaluated by bulk density, ash content, moisture content, point-of-zero charge (pHpzc) analysis, iodine test, scanning
electron microscopy (SEM), Fourier transform infrared (FTIR) and elemental (CHNS-O) analysis. The effect of the adsorbent
dosage (0.02-0.25 g), initial pH (3-11), initial dye concentrations (30-350 mg/L) and contact time (1-180 min) on the
adsorption of the methylene blue (MB) at 303 K was performed via batch experiments. The Pseudo-Second Order (PSO)
describes the kinetic model well whereas the Langmuir isotherm proved that adsorption behavior at equilibrium with
maximum adsorption capacity (qmax) of 66.00 mg/g.
The functionalization of surface charges on oil palm empty fruit bunch (EFB) fibers was modified by grafted carboxylic
acid and polymer amine groups. Single and binary adsorption of Cu(II), Ni(II), Mo(VI) and As(V) were investigated
by competitiveness in the adsorbents. The mechanism of each metal ion was deliberately studied on kinetics-diffusion
(intraparticle diffusion) and isotherm adsorption models (Langmuir and Freundlich). Competitiveness of metal ions was
found in the selectivity of Cu(II) > Ni(II) and Mo(VI) > As(V) in the binary solution. The regeneration of adsorbents
was performed up to five cycles of an adsorption/desorption process and the reduction of adsorption performance was
less than 14.5%. Therefore, this promises low-cost adsorbents for metal ion uptake, showing potential for removal and
recovery in industrial wastewater treatment.
Recent advances in nanotechnology have revealed the superiority of nanocarbon species such as carbon nanotubes over other conventional materials for gas sensing applications. In this work, analytical modeling of the semiconducting zigzag carbon nanotube field-effect transistor (ZCNT-FET) based sensor for the detection of gas molecules is demonstrated. We propose new analytical models to strongly simulate and investigate the physical and electrical behavior of the ZCNT sensor in the presence of various gas molecules (CO2, H2O, and CH4). Therefore, we start with the modeling of the energy band structure by acquiring the new energy dispersion relation for the ZCNT and introducing the gas adsorption effects to the band structure model. Then, the electrical conductance of the ZCNT is modeled and formulated while the gas adsorption effect is considered in the conductance model. The band structure analysis indicates that, the semiconducting ZCNT experiences band gap variation after the adsorption of the gases. Furthermore, the bandgap variation influences the conductance of the ZCNT and the results exhibit increments of the ZCNT conductance in the presence of target gases while the minimum conductance shifted upward around the neutrality point. Besides, the I-V characteristics of the sensor are extracted from the conductance model and its variations after adsorption of different gas molecules are monitored and investigated. To verify the accuracy of the proposed models, the conductance model is compared with previous experimental and modeling data and a good consensus is observed. It can be concluded that the proposed analytical models can successfully be applied to predict sensor behavior against different gas molecules.
The optimization data presented here are part of the study planned to remove the caffeine from aqueous solution through the large surface area optimized H3PO4-activated Acacia mangium wood activated carbon (OAMW-AC). The maximum adsorption capacity of the OAMW-AC for caffeine adsorption was achieved (30.3 mg/g) through optimized independent variables such as, OAMW-AC dosage (3.0 g/L), initial caffeine concentration (100 mg/L), contact time (60 min), and solution pH (7.7). The adsorption capacity of OAMW-AC was optimized with the help of rotatable central composite design of response surface methodology. Under the stated optimized conditions for maximum adsorption capacity, the removal efficiency was calculated to be 93%. The statistical significance of the data set was tested through the analysis of variance (ANOVA) study. Data confirmed the statistical model for caffeine adsorption was significant. The regression coefficient (R2) of curve fitting through the quadratic model was found to be 0.9832, and the adjusted regression coefficient was observed to be 0.9675.
Xanthan integrated graphene oxide functionalized by titanium dioxide was successfully prepared through facile, eco-friendly and cost effective ice-templating technique. The three-dimensional (3D) graphene composite demonstrated relatively high temperature stability, chemical functionalities and porous sponge-like structure. The adsorption of lead was favored by high initial concentration and shaking speed at the operational solution pH. The process equilibrium and kinetic adhered to the Langmuir and pseudo-second-order correlations, respectively. The biomass integrated graphene composite showed maximum adsorption capacities ranging from 132.18 to 199.22 mg/g for 30-70 °C. Moreover, it was highly regenerable under mild conditions (0.1 M hydrochloric acid, 30 °C) and used repeatedly while retaining 84.78% of its initial adsorption capacity at the fifth adsorption-regeneration cycle. With comparatively high lead adsorption capacities, adequate recyclability and environmentally friendliness, the as-prepared 3D graphene composite has high application potential in heavy metal-wastewater separation for protection of the environment and human health.
Global pollution from toxic metal waste has resulted in increased research on toxic metal adsorption. A cellulose acetate-polyurethane (CA-PU) film adsorbent was successfully prepared in this research. The cellulose acetate-polyurethane film adsorbent was prepared with a polycondensation reaction between cellulose acetate and methylene diphenyl diisocyanate. The CA-PU bond formation was confirmed by functional group analysis obtained from Fourier transform infrared (FTIR) spectroscopy. The obtained film was characterized for improved tensile and thermal properties with the addition of methylene diphenyl diisocyanate (MDI). The adsorption ability of the obtained film was evaluated with laser-induced breakdown spectroscopy (LIBS). The best film adsorbent from the LIBS was selected and studied for adsorption isotherm. The FTIR analysis confirmed the formation of the CA-PU bond from the polycondensation between cellulose acetate and the methylene diphenyl diisocyanate. The result showed that the addition of methylene diphenyl diisocyanate (MDI) resulted in the urethane network's growth. The characterization result showed an improvement in the morphology, thermal stability, and tensile strength of the film. The LIBS studies showed improvement in the adsorption of Pb2+ with CA-PU compared with the neat CA. The isotherm studies revealed that Pb2+ adsorption by cellulose acetate-polyurethane film adsorbent was heterogeneously dependent on the Freundlich isotherm model (R2 = 0.97044). Overall, the polycondensation method proposed by this study enhanced the Pb2+ removal, and was comparable to those reported in previous studies.
Presence of copper within water bodies deteriorates human health and degrades natural environment. This heavy metal in water is treated using a promising biochar derived from rambutan (Nephelium lappaceum) peel through slow pyrolysis. This research compares the efficacies of artificial neural network (ANN), adaptive neuro-fuzzy inference system (ANFIS), and multiple linear regression (MLR) models and evaluates their capability in estimating the adsorption efficiency of biochar for the removal of Cu (II) ions based on 480 experimental sets obtained in a laboratory batch study. The effects of operational parameters such as contact time, operating temperature, biochar dosage, and initial Cu (II) ion concentration on removing Cu (II) ions were investigated. Eleven different training algorithms in ANN and 8 different membership functions in ANFIS were compared statistically and evaluated in terms of estimation errors, which are root mean squared error (RMSE), mean absolute error (MAE), and accuracy. The effects of number of hidden neuron in ANN model and fuzzy set combination in ANFIS were studied. In this study, ANFIS model with Gaussian membership function and fuzzy set combination of [4 5 2 3] was found to be the best method, with accuracy of 90.24% and 87.06% for training and testing dataset, respectively. Contribution of this study is that ANN, ANFIS, and MLR modeling techniques were used for the first time to study the adsorption of Cu (II) ions from aqueous solutions using rambutan peel biochar.
Currently, heavy metals and dyes are some of the most critical pollutants in the aquatic environment. So, in this paper "waste-to-resource conversion", as a new application of modified mine silicate waste to remove Pb2+ ion and methylene blue (MB) dye, adsorption properties, mechanism of action and recycling were studied. Silicate wastes are located in the alteration zone and the margin of molybdenum ore, these wastes are under the influence of hydrothermal solutions which are impregnated with iron and manganese ions. Hence, acid and base modifications have been commonly used. So, in this study, a highly porous nanostructure of modified silicate waste was used to remove MB and Pb2+ ion, in subsequent to our previous study on the application of the raw material of the same in the removal of malachite green. Acid, base, and acid/base treatments were used to activate and modify the adsorbent. Results show a significantly higher potential of modified adsorbent in the removal of MB and Pb2+ compared to the raw material. According to the isotherm and kinetic studies for MB and Pb2+ the Langmuir and Temkin and pseudo-second-order models were investigated with experimental data. Modified nanomaterial was used for several adsorption and desorption processes, without a significant decrease in the capability of the adsorbent in the removal of MB and Pb2+ pollutants. Leached iron and manganese ions (as production of modification) are deposited in the form of sludge using a simple pH adjustment and precipitation process and can be used to recover iron and manganese metals in the long run. The comparison of monolayer adsorption capacity using for Pb2+ ion and MB dye are as ((untreated SW: 29.41, 1.05); (NaOH treated: 21.74, 100); (Nitric Acid treated: 16.67, 142.86); (Citric Acid treated: 40, 125); (Nitric/Citric Acids treated: 15.63, 111.11) and (Nitric/Citric Acids/NaOH treated: 15.15, 83.33)), respectively. Higher adsorption capacity and re-generable properties of this adsorbent suggest the usage of this natural and abundant mine waste to treat wastewater containing toxic elements and dyes.
Water pollution is one of the most concerning global environmental problems in this century with the severity and complexity of the issue increases every day. One of the major contributors to water pollution is the discharge of harmful heavy metal wastes into the rivers and water bodies. Without proper treatment, the release of these harmful inorganic waste would endanger the environment by contaminating the food chains of living organisms, hence, leading to potential health risks to humans. The adsorption method has become one of the cost-effective alternative treatments to eliminate heavy metal ions. Since the type of adsorbent material is the most vital factor that determines the effectiveness of the adsorption, continuous efforts have been made in search of cheap adsorbents derived from a variety of waste materials. Fruit waste can be transformed into valuable products, such as biochar, as they are composed of many functional groups, including carboxylic groups and lignin, which is effective in metal binding. The main objective of this study was to review the potential of various types of fruit wastes as an alternative adsorbent for Pb(II) removal. Following a brief overview of the properties and effects of Pb(II), this study discussed the equilibrium isotherms and adsorption kinetic by various adsorption models. The possible adsorption mechanisms and regeneration study for Pb(II) removal were also elaborated in detail to provide a clear understanding of biochar produced using the pyrolysis technique. The future prospects of fruit waste as an adsorbent for the removal of Pb(II) was also highlighted.
Rhodamine B (RhB) is among the toxic dyes due to the carcinogenic, neurotoxic effects and ability to cause several diseases for humans. The adsorption with agricultural waste adsorbent recorded high performance for the RhB removal. The current review aimed to explore the efficiency of different adsorbents which have been used in the few last years for removing RhB dye from wastewater. The data of adsorption of RhB using agricultural wastes were collected from the Scopus database in the period between 2015 and 2021. The use of agricultural wastes and adsorbents as a replacement for the activated has received high attention among researchers. The RhB removal methods by microbial enzymes and biomass occurred between 76 and 90.1%. In comparison, the adsorption with agricultural wastes such as activated carbon white sugar reached 98% within 12 min. The adsorption process has a wide range of pH (3-10) due to the zwitterionic forms of RhB. Gmelina aborea leaf activated carbon is among the agriculture wastes absorbents that exhibited 1000 mg g-1 of the adsorption capacity. It appeared that the agricultural wastes adsorbents have a high potential for removing RhB from the wastewater.
Unique zerovalent iron (Fe0) supported on biochar nanocomposite (Fe0-BRtP) was synthesized from Nephelium lappaceum (Rambutan) fruit peel waste and were applied for the simultaneous removal of 6 selected organochlorine pesticides (OCPs) from aqueous medium. During facile synthesis of Fe0-BRtP, Rambutan peel extract was used as the green reducing mediator to reduce Fe2+ to zerovalent iron (Fe0), instead of toxic sodium borohydride which were used for chemical synthesis. For comparison, chemically synthesized Fe0-BChe nanocomposite was also prepared in this work. Characterization study confirmed the successful synthesis and dispersion of Fe0 nanoparticles on biochar surface. Batch experiments revealed that Fe0-BRtP and Fe0-BChe nanocomposites combine the advantage of adsorption and dechlorination of OCPs in aqueous medium and up to 96-99% and 83-91% removal was obtained within 120 and 150 min, respectively at initial pH 4. Nevertheless, the reactivity of Fe0-BChe nanocomposite decreased 2 folds after being aged in air for one month, whilst Fe0-BRtP almost remained the same. Adsorption isotherm of OCPs were fitted well to Langmuir isotherm and then to Freundlich isotherm. The experimental kinetic data were fitted first to pseudo-second-order adsorption kinetic model and then to pseudo-first-order reduction kinetic model. The adsorption mechanism involves π-π electron-donor-acceptor interaction and adsorption is facilitated by the hydrophobic sorption and pore filling. After being reused five times, the removal efficiency of regenerated Fe0-BChe and Fe0-BRtP was 5-13% and 89-92%, respectively. The application of this Fe0-BRtP nanocomposite could represent a green and low-cost potential material for adsorption and subsequent reduction of OCPs in aquatic system.
In this article, the nickel (Ni2+) ions removal from the wastewater is reviewed. Adsorption is widely used to remove Ni2+ ions from waters and wastewaters. The usage of biomass is becoming more common for Ni2+ ions removal, while the commercial activated carbon from different agriculture wastes is preferred as an adsorbent for Ni2+ ion removal. The present review aimed to organise the available information regarding sustainable approaches for Ni2+ ions removal from water and wastewaters. These include adsorption by nanoparticles, bacterial biomass, and activated carbon from agriculture wastes, since they are the most common used for the Ni2+ ions removal. The bacterial and agricultural waste adsorbents exhibited high efficiency with a renewable source of biomass for Ni2+ ion removal. The biosorption capacity of the Ni2+ ions by the bacterial biomass range from 5.7 to 556 mg/g, while ranging from 5.8 to 150 mg/g by the activated carbon from different organic materials. The biosorption capacity of the nanocomposite adsorbents might reach to 400 mg/g. It appeared that the elimination of nickel ions need a selective biomass adsorbent such as the tolerant bacterial cells biomass which acts as a store for Ni2+ ion accumulations as a results for the active and passive transportation of the Ni2+ ions through the bacterial cell membrane.