Comparison of various error functions in predicting the optimum isotherm by linear and non-linear regression analysis for the sorption of basic red 9 by activated carbon

Activated Carbon for CO2 Adsorption from Avocado Seeds Activated with NaOH: The Significance of the Production Method

The rise in atmospheric greenhouse gases like CO2 is a primary driver of global warming. Human actions are the primary factor behind the surge in CO2 levels, contributing to two-thirds of the greenhouse effect over the past decade. This study focuses on the chemical activation of avocado seeds with sodium hydroxide (NaOH). The influence of various preparation methods was studied under the same parameters: carbon precursor to NaOH mass ratio, carbonization temperature, and nitrogen flow. For two samples, preliminary thermal treatment was applied (500 °C). NaOH was used in the form of a saturated solution as well as dry NaOH. The same temperature of 850 °C of carbonization combined with chemical activation was applied for all samples. The applied modifications resulted in the following textural parameters: specific surface area from 696 to 1217 m2/g, total pore volume from 0.440 to 0.761 cm3/g, micropore volume from 0.159 to 0.418 cm3/g. The textural parameters were estimated based on nitrogen sorption at -196 °C. The XRD measurements and SEM pictures were also performed. CO2 adsorption was performed at temperatures of 0, 10, 20, and 30 °C and pressure up to 1 bar. In order to calculate the CO2 selectivity over N2 nitrogen adsorption at 20 °C was investigated. The highest CO2 adsorption (4.90 mmol/g) at 1 bar and 0 °C was achieved.

Adsorption dynamics of Cd2+(aq) on microwave-synthetized pristine biochar from cocoa pod husk: Green, experimental, and DFT approaches

Biochar obtained via microwave-assisted pyrolysis (MAP) at 720 W and 15 min from cocoa pod husk (CPH) is an efficient adsorbent of Cd2+(aq). Biochar of residual biomass of CPH (BCCPH) possesses favorable physicochemical and morphological properties, featuring a modest surface area yet a suitable porous structure. Adsorption, predominantly governed by physisorption, is influenced by the oxygen-containing active sites (-COOR, -C(R)O, and -CH2OR; R = H, alkyl). CdCO3 formation occurs during adsorption. Experimental data were well-fitted into various kinetic models for a broad understanding of the sorption process. Langmuir model indicates a maximum adsorption capacity of 14.694 mg/g. The thermodynamic study confirms the spontaneous and endothermic sorption. Studies at the molecular level have revealed that the Cd2+ ion tends to bind to surface aromatic carbon atoms. This sustainable approach produces BCCPH via MAP as a solution for waste transformation into water-cleaning materials.

An Adsorption Based Downstream Processing Approach for Penicillin V from a Penicillium chrysogenum BIONCL I22 Culture Filtrate

Penicillin V (phenoxy methyl penicillin) is highly sought after among natural penicillins because of its exceptional acid stability and effectiveness against common skin and respiratory infections. Given its wide-ranging therapeutic uses, there is a need to establish a greener method for its maximum recovery to reduce the carbon footprint. Here, we have identified and validated optimized operational conditions for resin-based penicillin V recovery. It was observed that Amberlite XAD4 had the highest penicillin V hydrophobic adsorption capacity among the other screened resins. Kinetic and isothermal studies using linear and nonlinear regression analysis showed that the adsorption process well fitted with pseudo-second-order kinetics (R 2 = 0.9816) and the Freundlich adsorption isotherm model (R 2 = 0.9871). Adsorption equilibrium was attained within 4 h, while maximum adsorption was observed at 3 mg/mL penicillin V concentration. Furthermore, the optimized extraction protocol was compared with the conventional butyl acetate-based downstream processing. Under optimum conditions resin-based penicillin V recovery was 2-fold higher as compared to the solvent extraction method and the resin could be reused for over six cycles without compromising the yield. These findings signify substantial progress toward the development of an environmentally sustainable approach for penicillin V recovery and a potentially viable method for extractive fermentation.

Fabrication of date palm kernel biochar-sulfur (DPKB-S) for super adsorption of methylene blue dye from water

A novel form of biochar was created by dehydration of Date palm kernel with 85% sulfuric acid. It was examined how the newly produced biochar (DPKB-S) affected the aqueous solution's capacity to extract Methylene Blue (MB) dye. The prepared DPKB-S was categorized by BET, BJH, FT-IR, SEM, EDX, DSC, and TGA analyses. The ideal pH for the MB dye adsorption by DPKB-S is 8. With 0.75 g L-1 of DPKB-S and an initial concentration of 50 ppm MB dye, Date Palm Kernel Biochar-Sulfur (DPKB-S) had the highest removal percentage of 100%. The Langmuir and Freundlich isotherm models were used to investigate the collected data. Freundlich model is the model that best covers MB dye adsorption in DPKB-S at low concentrations (0.75-1.25 g L-1) and the Langmuir model at high concentrations (1.5-1.75 g L-1). The Langmuir model maximum adsorption capacity (Qm) of the DPKB-S was 1512.30 mg g-1. Furthermore, a variety of error function models were applied to investigate the isotherm models derived data, including Marquardt's percent standard deviation (MPSD), the sum of absolute errors (EABS), the sum of the errors squared (ERRSQ), root mean square errors (RMS), Chi-square error (X2), the average relative error (ARE), average percent errors (APE), and hybrid error function (HYBRID). Kinetic data were calculated by intraparticle diffusion (IPD), pseudo-second-order (PSO), pseudo-first-order (PFO), and film diffusion (FD) models. A PSO rate model with a strong correlation (R2 = 1.00) largely regulated the adsorption rate. The removal mechanism of MB dye by DPKB-S is based on the principle that these positively charged dyes are attracted by electrostatic attraction forces due to the growth in the number of negatively charged regions at basic pH value. According to the results, DPKB-S shows promise as an affordable and competent adsorbent for the adsorption of MB dye. It can be used frequently without experiencing a discernible decrease in adsorption efficiency.

Synthesis and characterization of cost-effective and high-efficiency biochar for the adsorption of Pb2+ from wastewater

This study aimed to investigate the adsorption mechanism of Pb2+ in wastewater using activated carbon derived from inexpensive materials, specifically avocado, bitter orange, and walnut leaves, through a single-step chemical activation process. The activated carbon was prepared using sulfuric acid as an activator, with a particle size of 1 mm. The pyrolysis reactor (slow-pyrolysis) operated at 600 °C for 90 min with a nitrogen flow rate of 5 L/min. Batch experiments were conducted under various conditions to determine the optimal dosage (1.5 g/L), equilibrium contact time (180 min), and pH (6.5). The study focused on employing cost-effective and highly efficient adsorbents, namely biochar produced from tree leaves, for the adsorption process. The results indicated that the pseudo-second-order kinetic model accurately described the adsorption process, while the Freundlich isotherm model best fit the experimental data. These findings suggest that tree leaves can serve as cost-effective and efficient adsorbents for a wide range of applications. Furthermore, multiple adsorption factors were evaluated in batch mode, including contact duration, pH, adsorbent dosage, concentration of the Pb2+ solution, and temperature. The maximum adsorption capacities for the activated carbon derived from avocado, bitter orange, and walnut leaves were found to be 60.46, 59.42, and 58.48 mg/g, respectively. Thus, this study highlights the effectiveness and economic feasibility of using pyrolysis-derived activated carbon from low-cost materials for the removal of Pb2+ from wastewater.

Competitive adsorptive removal of promazine and promethazine from wastewater using olive tree pruning biochar: operational parameters, kinetics, and equilibrium investigations

This research aims to remove two phenothiazines, promazine (PRO) and promethazine (PMT), from their individual and binary mixtures using olive tree pruning biochar (BC-OTPR). The impact of individual and combinatory effects of operational variables was evaluated for the first time using central composite design (CCD). Simultaneous removal of both drugs was maximized utilizing the composite desirability function. At low concentrations, the uptake of PRO and PMT from their individual solutions was achieved with high efficiency of 98.64%, 47.20 mg/g and 95.87%, 38.16 mg/g, respectively. No major differences in the removal capacity were observed for the binary mixtures. Characterization of BC-OTPR confirmed successful adsorption and showed that the OTPR surface was predominantly mesoporous. Equilibrium investigations revealed that the Langmuir isotherm model best describes the sorption of PRO/PMT from their individual solutions with maximum adsorption capacities of 640.7 and 346.95 mg/g, respectively. The sorption of PRO/PMT conforms to the pseudo-second-order kinetic model. Regeneration of the adsorbent surface was successfully done with desorption efficiencies of 94.06% and 98.54% for PRO and PMT, respectively, for six cycles.

A Review on the Adsorption Isotherms and Design Calculations for the Optimization of Adsorbent Mass and Contact Time

Adsorption is a widely used chemical engineering unit operation for the separation and purification of fluid streams. Typical uses of adsorption include the removal of targeted pollutants like antibiotics, dyes, heavy metals, and other small to large molecules from aqueous solutions or wastewater. To date several adsorbents that vary in terms of their physicochemical properties and costs have been tested for their efficacy to remove these pollutants from wastewater. Irrespective of the type of adsorbent, nature of the pollutant, or experimental conditions, the overall cost of adsorption depends directly on the adsorption contact time and the cost of the adsorbent materials. Thus, it is essential to minimize the amount of adsorbent and the contact time required. We carefully reviewed the attempts made by several researchers to minimize these two parameters using theoretical adsorption kinetics and isotherms. We also clearly explained the theoretical methods and the calculation procedures involved during the optimization of the adsorbent mass and the contact time. To complement the theoretical calculation procedures, we also made a detailed review on the theoretical adsorption isotherms that are commonly used to model experimental equilibrium data that can be used to optimize the adsorbent mass.

Rethinking of the intraparticle diffusion adsorption kinetics model: Interpretation, solving methods and applications

Adsorption is a widely used unit process in various fields, such as chemical, environmental and pharmaceutical, etc. The intraparticle diffusion adsorption kinetics model is one of the most widely used adsorption kinetics models. However, the application and solving method of this model have yet to be discussed. This model has two forms (q_t = kt^1/2 and q_t = kt^1/2 + constant, where q_t is the adsorption capacity at time t, k and constant are the model parameters), which have not been unified yet. Moreover, the interpretation of this kinetics model lacks a theoretical basis (if the line passes through the origin point (0, 0), the adsorption is dominated by the intraparticle diffusion; if not, it is a multiple adsorption process). In this study, we analyzed the proper equations of the intraparticle diffusion model and their applications, discussed the interpretation of the mass transfer steps revealed by this model, and provided the solving methods. The result indicated that the piecewise function q_t = k₁t^1/2 (0 ≤ t ≤ t₁); q_t - q_t = t1 = k₂(t - t₁)^1/2 (t₁ < t ≤ t₂) is the proper form of this model. The adsorbate diffusion in the pores inside the adsorbent is the mass transfer step revealed by this model. The statistical parameters should be used to evaluate the fitting results instead of judging whether the model lines pass through the origin point (0, 0). We provide the solving methods to use the Origin and Microsoft EXCEL software to solve the model. Our study established the method for application of the intraparticle diffusion model.

Hybrid Coordination Networks for Removal of Pollutants from Wastewater

The adsorption properties of two coordination polymers, resulting from the reaction of divalent metal (Ca²⁺ or Co²⁺) salts with (2-carboxyethyl)(phenyl)phosphinic acid, are presented in this paper. The structural and textural characterization before and after adsorption experiments is presented. The adsorbent materials were prepared using the hydrothermal procedure. The compound Ca[O₂P(CH₂CH₂COOH)(C₆H₅)]₂ (CaCEPPA) has a layered topology, with the phenyl groups oriented into the interlayer space and crystallizes in the monoclinic system. Compound Co₂[(O₂P(CH₂CH₂COO)(C₆H₅)(H₂O)]₂·2H₂O (CoCEPPA) has a 1D structure composed of zig-zag chains. The adsorption performances of CaCEPPA and CoCEPPA materials were tested in the removal of cadmium and lead from aqueous solutions. The optimum pH of ions adsorption was found to be five for both adsorbent materials. Pseudo-first and second-order kinetic models were used for fitting kinetic experimental data, and Langmuir and Freundlich isotherms were used for modeling the equilibrium experimental data. The pseudo-second-order kinetic model and Langmuir isotherm best described the adsorption of Cd and Pb ions onto the studied materials, judging from the results of the error function (correlation coefficient, sum of square error, chi-square test, and average relative error) analysis. The studied materials present a higher affinity for Cd ions compared with the adsorption capacity developed for the removal of Pb ions from aqueous solutions. CoCEPPA showed the highest adsorption performance in the removal process of metal ions from aqueous solutions compared with CaCEPPA (q_m = 54.9 mg Cd²⁺/g of CoCEPPA, q_m = 36.5 mg Cd²⁺/g of CaCEPPA).

Linear and Nonlinear Regression Analysis for the Adsorption of Remazol Dye by Romanian Brewery Waste By-Product, Saccharomyces cerevisiae

Earth’s water balance and economy are becoming increasingly fragile due to overpopulation, global warming, severe environmental pollution and both surface and groundwater pollution. Therefore, it is essential to find solutions to the problems of water scarcity and water pollution. In this research, an experiment was designed to optimize the technique for the adsorption of Remazol Red F3B (RR) dye by lyophilized brewery yeast waste from the fermentation process. Moreover, we proved that brewery yeast is a great adsorbent. Batch adsorption experiments were carried out for optimization of different initial parameters, such as initial dye concentration (5–1000 mg/L), amount of yeast (0.5–2.5 g), pH (3–11) and temperature (20 to 40 °C). Furthermore, the structure and elemental composition of the adsorbent were analyzed with SEM, EDS and FTIR before and after biosorption. The best fits for the mathematical isotherm models in the case of the linear form were the Langmuir I and Freundlich models (R² = 0.923 and R² = 0.921) and, for the nonlinear form, the Khan model (R² = 0.9996) was the best fit. The pseudo-second-order kinetic model showed the best fit for both linear (plotting t/q_t vs. t) and nonlinear forms, are the calculated q_e values were similar to the experimental data.

Lignocellulosic Materials Used as Biosorbents for the Capture of Nickel (II) in Aqueous Solution

Four lignocellulosic materials (walnut shell, chestnut shell, pine wood and burnt pine wood) were analyzed as biosorbents to remove nickel ions in aqueous solution. The optimal pH condition was determined. Due to this, a range of different pHs (3.0 to 7.5) was tested. The adsorption isotherms and kinetics were established. To plot Langmuir and Freundlich isotherms, batch adsorption tests were made with variable nickel concentrations (5 to 200 mg L−1). The pseudo-first order, pseudo-second order, Elovich and intraparticle diffusion models were used to describe the kinetics, batch adsorption tests were carried out with 25 mg L−1 of nickel solution and agitation time varied from 10 to 1440 min. The specific surface area of the different materials was between 3.97 and 4.85 m2g−1 with the exception for wood with 1.74 m2g−1. The pore size was 26.54 nm for wood and varied between 5.40 and 7.33 nm for the remaining materials. The diffractograms analysis showed that all the lignocellulosic materials presented some crystalline domains with the exception of burnt pine wood which was completely amorphous. The best pH was found to be around 5.0. At this pH the adsorption was higher for chestnut shells, walnut shells, burnt pine wood and wood, respectively. All samples fitted the Langmuir model well, with R2 of 0.994 to 0.998. The sorption kinetics was well described by the pseudo-second order equation with R2 between 0.996 and 1.00. No significative differences on the surface of the materials before and after adsorption could be observed by SEM. Finally, all materials tested were able to remove nickel ions in aqueous solution.

Double-side microcantilevers as a key to understand the adsorption mechanisms and kinetics of chemical warfare agents on vertically-aligned TiO2 nanotubes

Microgravimetric sensor platforms with physico- or chemo-selective interfaces offer promising sensing properties. They are widely used to detect chemical warfare agents (CWAs). However, a comprehensive insight into adsorption mechanisms and interactions between low concentrations of these adsorbates and low-mass adsorbents is still lacking. In this study, we report a complete and detailed analytical method to model the adsorption processes of low traces of vapor-phase DiMethyl MethylPhosphonate (DMMP), a conventional simulant of CWAs, on a double-side nanostructured microcantilever coated with vertically-aligned titanium dioxide nanotubes (TiO₂-NTs). We find that the geometrical configuration of NTs plays an important role in the diffusion regimes of molecules during the adsorption. This study shines light on the adsorption and kinetic mechanisms of low-traces DMMP offering opportunities to have a better insight of the adsorption of CWAs on complex nanostructures and to improve microcantilever sensors.

Green synthesis of a novel Mn-Zn ferrite/biochar composite from waste batteries and pine sawdust for Pb2+ removal

Magnetic ferrite/biochar composites are a kind of promising adsorbents due to their high adsorption efficiency and facile magnetic separation; however, their synthesis is associated with high cost and secondary environmental impacts. In this study, a novel Mn-Zn ferrite/biochar composite (MZF-BC) is synthesized via a green two-step biocheaching and hydrothermal method using waste batteries and pine sawdust. Characterization results indicate that the introduced Mn-Zn ferrite particles are successfully embedded and coated on biochar (BC), and synthesized MZF-BC₅₀ with 50% BC content exhibits best performance with a specific surface area of 138.5 m² g^-1, the saturation magnetization of 27.5 emu g^-1 and CEC value of 53.2 mmol 100 g^-1. The maximum adsorption capacity of Pb²⁺ is 99.5 mg g^-1 based on the Langmuir sorption isotherm study at 298 K, and pseudo-second-order model accurately describes the adsorption process. Regeneration test suggests that MZF-BC₅₀ can be efficiently reused for 6 cycles. In addition, it exhibits a good selective Pb²⁺ and Cd²⁺ removal performance in lead-acid battery wastewater. The results illustrate that this newly developed material has low cost and rapid remediation of Pb²⁺ as good application potential.

Mesoporous Mn-Doped Fe Nanoparticle-Modified Reduced Graphene Oxide for Ethyl Violet Elimination: Modeling and Optimization Using Artificial Intelligence

Mesoporous Mn-doped Fe nanoparticle-modified reduced graphene oxide (Mn-doped Fe/rGO) was prepared through a one-step co-precipitation method, which was then used to eliminate ethyl violet (EV) in wastewater. The prepared Mn-doped Fe/rGO was characterized by X-ray diffraction, X-ray photoelectron spectroscopy, Raman spectroscopy, high-resolution transmission electron microscopy, scanning electron microscopy, energy dispersive spectroscopy, N2-sorption, small angle X-ray diffraction and superconducting quantum interference device. The Brunauer–Emmett–Teller specific surface area of Mn-doped Fe/rGO composites was 104.088 m2/g. The EV elimination by Mn-doped Fe/rGO was modeled and optimized by artificial intelligence (AI) models (i.e., radial basis function network, random forest, artificial neural network genetic algorithm (ANN-GA) and particle swarm optimization). Among these AI models, ANN-GA is considered as the best model for predicting the removal efficiency of EV by Mn-doped Fe/rGO. The evaluation of variables shows that dosage gives the maximum importance to Mn-doped Fe/rGO removal of EV. The experimental data were fitted to kinetics and adsorption isotherm models. The results indicated that the process of EV removal by Mn-doped Fe/rGO obeyed the pseudo-second-order kinetics model and Langmuir isotherm, and the maximum adsorption capacity was 1000.00 mg/g. This study provides a possibility for synthesis of Mn-doped Fe/rGO by co-precipitation as an excellent material for EV removal from the aqueous phase.

Synthesis of novel biocomposite powder for simultaneous removal of hazardous ciprofloxacin and methylene blue: Central composite design, kinetic and isotherm studies using Brouers-Sotolongo family models

Over the past decades, extensive efforts have been made to use biomass-based-materials for wastewater-treatment. The first purpose of this study was to develop and characterize regenerated-reed/reed-charcoal (RR-ChR), an enhanced biosorbent from Tunisian-reed (Phragmites-australis). The second aim was to assess and optimize the RR-ChR use for the removal of binary ciprofloxacin antibiotic (CIP) and methylene blue dye (MB), using Central Composite Design under Response Surface methodology. The third purpose was to explain the mechanisms involved in the biosorption-process. The study revealed that the highest removal-percentages (76.66 % for the CIP and 100 % for the MB) were obtained under optimum conditions: 1.55 g/L of adsorbent, 35 mg/L of CIP, 75 mg/L of MB, a pH of 10.42 and 115.28 min contact time. It showed that the CIP biosorption mechanism was described by Brouers-Sotolongo-fractal model, with regression-coefficient (R²) of 0.9994 and a Person's Chi-square (X²) of 0.01. The Hill kinetic model better described the MB biosorption (R² = 1 and X² = 1.0E-4). The isotherm studies showed that the adsorbent surface was heterogeneous and the best nonlinear-fit was obtained with the Jovanovich (R² = 0.9711), and Brouers-Sotolongo (R² = 0.9723) models, for the CIP and MB adsorption, respectively. Finally, the RR-ChR lignocellulosic-biocomposite-powder could be adopted as efficient and cost-effective adsorbent.

Current advancement and future prospect of biosorbents for bioremediation

The increasing use of heavy metals, synthetic dyes and pesticides is a major environmental concern. Wastewaters containing heavy metals and dyes, extensively released from small and large scale industries enter excessively into food chains resulting in mutagenesis, carcinogenicity and serious health impairments in living systems. The arrays of technologies are implemented to date to remediate both inorganic and organic contaminants from wastewaters. Among which, adsorption is the most attractive method as it employs eco-friendly, sustainable and cost-effective biomaterials. Use of bioadsorbents is advantageous over the conventional adsorbents. Clay, chitin, peat, microbial biomass and agricultural wastes are commonly used bioadsorbants. These bioadsorbents are extensively used for elimination of dyes, heavy metals, adsorption of toxic industrial effluents, removal of fertilizers/pesticides, atmospheric pollutants and nuclear waste from the environment. The current review presents state of the art knowledge on various types of biosorbents, their uses, and mechanism of action. Various strategies to enhance the efficiency of bioadsorbents and physicochemical conditions to remediate dyes and heavy metals from waste streams are also incorporated in this review. Use of nano-bioadsorbents in industries to minimize the hazardous effect of solid and liquid waste has also been discussed.

Sorption of PAHs to microplastic and their bioavailability and toxicity to marine copepods under co-exposure conditions

Organic chemical pollutants associated with microplastic (MP) may represent an alternative exposure route for these chemicals to marine biota. However, the bioavailability of MP-sorbed organic pollutants under conditions where co-exposure occurs from the same compounds dissolved in the water phase has rarely been studied experimentally, especially where pollutant concentrations in the two phases are well characterized. Importantly, higher concentrations of organic pollutants on ingested MP may be less bioavailable to aquatic organisms than the same chemicals present in dissolved form in the surrounding water. In the current study, the sorption kinetics of two model polycyclic aromatic hydrocarbons (PAHs; fluoranthene and phenanthrene) to MP particles in natural seawater at 10 and 20 °C were studied and the bioavailability of MP-sorbed PAHs to marine copepods investigated. Polyethylene (PE) and polystyrene (PS) microbeads with mean diameters ranging from 10 to 200 μm were used to identify the role of MP polymer type and size on sorption mechanisms. Additionally, temperature dependence of sorption was investigated. Results indicated that adsorption dominated at lower temperatures and for smaller MP (10 μm), while absorption was the prevailing process for larger MP (100 μm). Monolayer sorption dominated at lower PAH concentrations, while multilayer sorption dominated at higher concentrations. PE particles representing ingestible (10 μm) and non-ingestible (100 μm) MP for the marine copepod species Acartia tonsa and Calanus finmarchicus were used to investigate the availability and toxicity of MP-sorbed PAHs. Studies were conducted under co-exposure conditions where the PAHs were also present in the dissolved phase (C_free), thereby representing more environmentally relevant exposure scenarios. C_free reduction through MP sorption was reflected in a corresponding reduction of lethality and bioaccumulation, with no difference observed between ingestible and non-ingestible MP. This indicates that only free dissolved PAHs are significantly bioavailable to copepods under co-exposure conditions with MP-sorbed PAHs.

Efficient removal of GenX (HFPO-DA) and other perfluorinated ether acids from drinking and recycled waters using anion exchange resins

Carcinogenic GenX chemicals, heptafluoropropylene-oxide-dimer-acid (HFPO-DA), have been recently detected in surface, ground and recycled water sources worldwide. However, GenX removals under the influence of variable characteristics of the organic and inorganic compounds present in the natural water sources, have often been overlooked in scientific literature. This is critically important given that the ionic composition and characteristics of organic matter in natural waters are spatially and seasonally variable. A strongly basic anion exchange (IX) resin was used to remove GenX and two other perfluorinated ether acids (PFEAS) from natural surface and recycled water sources. Factors influencing the uptake behavior included the PFEAS concentrations, resin dosage, and background anion characteristics. The equivalent background compound was employed to evaluate the competitive uptake between natural organic matter (NOM), inorganic ions and PFEAS in natural water matrices. Experimental data were compared with different mathematical and physical models and it was depicted that approximately 4-6% of the initial NOM competed with PFEAS for active exchange sites. Further, IX was able to achieve complete PFEAS removal (C_final<10 ng/L) with simultaneous removal of>60% NOM and >80% inorganic ions. Results of this study indicate that IX exhibits great potential for PFEAS removal from natural drinking water sources.

CuO-modified activated carbon for the improvement of toluene removal in air

We used an impregnation method to prepare CuO/AC (activated carbon) composite materials of different CuO content and characterized them via scanning electron microscope (SEM), Brunauer-Emmett-Teller (BET), and Fourier transform infrared spectroscopy (FT-IR). The effect of CuO content on toluene adsorption/desorption was evaluated. We explored the reusability of AC and AC03 (CuO modified AC with CuO loading 0.3 wt.%) adsorbents via toluene adsorption/desorption cycle testing. We used quasi-first- and quasi-second-order models, the Bangham model, and the Weber-Morris model to fit the toluene adsorption data. The introduction of CuO species evidently improved the adsorption performance of activated carbon toward toluene. The CuO content markedly affected the specific surface area, CuO dispersal, the numbers of oxygen-containing functional groups on the surface, and adsorption performance of the prepared composite adsorbents. Low CuO content was not favorable for the formation of active adsorption sites, while high content greatly reduced the specific surface area, and even covered active adsorption sites. The toluene adsorption performance varied in the order AC03 > AC02 > AC05 > AC08 > AC01 (AC03, AC02, AC05, AC08 and AC01 are CuO modifying AC with CuO loading 0.3, 0.2, 0.5 0.8 and 0.1 wt.%, respectively). The breakthrough time and toluene adsorption capacity of the AC03 composite adsorbent were 94 min and 701.8 mg/g, respectively, and the recycling efficiency was 92.8% after thermal desorption at 200°C. The adsorption process was best described by the Bangham model and adsorption could be divided into three stages.

Microcystin-LR removal by ion exchange: Investigating multicomponent interactions in natural waters

Microcystin-LR (MCLR) is the most commonly encountered toxic microcystin variant. MCLR is usually present along with common surface water constituents such as inorganic ions and natural organic matter (NOM) which compete with MCLR for active sites during ion exchange (IX) process. Consequently, development of a multicomponent competitive model is essential for practical IX applications. This is critically important given that the NOM characteristics (charge density and molecular weight distribution) and inorganic ions concentrations are spatially variable and can change seasonally. In the present study, a systematic study was carried out into the multicomponent interactions of IX resin with inorganic ions and NOM during the MCLR removal process. This involved evaluation of MCLR removal in a single component system (i.e., MCLR only), a dual component system (MCLR and one other contaminant such as NOM), and a multiple component system (MCLR with NOM and different inorganic ions present in natural waters). A comprehensive understanding of the dynamic adsorption behavior showed that the experimental data for single component systems agree well with a Freundlich isotherm. For multicomponent interactions, the Equivalent Background Concentration (EBC) model which is derived from the Ideal Adsorption Solution Theory (IAST) provided the best correlation with the experimental data in natural waters. The concentrations of competing NOM and inorganic ions estimated by the EBC model were <10% of their initial concentrations. Sulphates are the most competitive inorganic ions followed by nitrates and bicarbonates and the multicomponent interactions could be well predicted by using the IAST-EBC model. However, the EBC model failed in the presence of higher molecular weight Suwannee River Humic Acid (SRHA) molecules due to neglecting of the pore blocking phenomenon. In the presence of higher molecular weight SRHA molecules, the Redlich-Peterson Isotherm (RP) model exhibited a better performance than the Sheindorf-Rebuhn-Sheintuch (SRS) and the EBC models.

Artificial Intelligence Based Optimization for the Se(IV) Removal from Aqueous Solution by Reduced Graphene Oxide-Supported Nanoscale Zero-Valent Iron Composites

Highly promising artificial intelligence tools, including neural network (ANN), genetic algorithm (GA) and particle swarm optimization (PSO), were applied in the present study to develop an approach for the evaluation of Se(IV) removal from aqueous solutions by reduced graphene oxide-supported nanoscale zero-valent iron (nZVI/rGO) composites. Both GA and PSO were used to optimize the parameters of ANN. The effect of operational parameters (i.e., initial pH, temperature, contact time and initial Se(IV) concentration) on the removal efficiency was examined using response surface methodology (RSM), which was also utilized to obtain a dataset for the ANN training. The ANN-GA model results (with a prediction error of 2.88%) showed a better agreement with the experimental data than the ANN-PSO model results (with a prediction error of 4.63%) and the RSM model results (with a prediction error of 5.56%), thus the ANN-GA model was an ideal choice for modeling and optimizing the Se(IV) removal by the nZVI/rGO composites due to its low prediction error. The analysis of the experimental data illustrates that the removal process of Se(IV) obeyed the Langmuir isotherm and the pseudo-second-order kinetic model. Furthermore, the Se 3d and 3p peaks found in XPS spectra for the nZVI/rGO composites after removing treatment illustrates that the removal of Se(IV) was mainly through the adsorption and reduction mechanisms.

An anionic single-walled metal–organic nanotube with an armchair (3,3) topology as an extremely smart adsorbent for the effective and selective adsorption of cationic carcinogenic dyes

A novel discrete single-walled MONT with a rare armchair (3,3) CNT topology and mesoporous channels is synthesized, which exhibits exclusive and remarkable ability to adsorb cationic carcinogens BR9 and BV14.

Optimizing Low-Concentration Mercury Removal from Aqueous Solutions by Reduced Graphene Oxide-Supported Fe₃O₄ Composites with the Aid of an Artificial Neural Network and Genetic Algorithm

Reduced graphene oxide-supported Fe₃O₄ (Fe₃O₄/rGO) composites were applied in this study to remove low-concentration mercury from aqueous solutions with the aid of an artificial neural network (ANN) modeling and genetic algorithm (GA) optimization. The Fe₃O₄/rGO composites were prepared by the solvothermal method and characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), atomic force microscopy (AFM), N₂-sorption, X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR) and superconduction quantum interference device (SQUID). Response surface methodology (RSM) and ANN were employed to model the effects of different operating conditions (temperature, initial pH, initial Hg ion concentration and contact time) on the removal of the low-concentration mercury from aqueous solutions by the Fe₃O₄/rGO composites. The ANN-GA model results (with a prediction error below 5%) show better agreement with the experimental data than the RSM model results (with a prediction error below 10%). The removal process of the low-concentration mercury obeyed the Freudlich isotherm and the pseudo-second-order kinetic model. In addition, a regeneration experiment of the Fe₃O₄/rGO composites demonstrated that these composites can be reused for the removal of low-concentration mercury from aqueous solutions.

Modelling and Interpretation of Adsorption Isotherms

The need to design low-cost adsorbents for the detoxification of industrial effluents has been a growing concern for most environmental researchers. So modelling of experimental data from adsorption processes is a very important means of predicting the mechanisms of various adsorption systems. Therefore, this paper presents an overall review of the applications of adsorption isotherms, the use of linear regression analysis, nonlinear regression analysis, and error functions for optimum adsorption data analysis.

Adsorption of pharmaceuticals onto activated carbon fiber cloths - Modeling and extrapolation of adsorption isotherms at very low concentrations

Activated carbon fiber cloths (ACFC) have shown promising results when applied to water treatment, especially for removing organic micropollutants such as pharmaceutical compounds. Nevertheless, further investigations are required, especially considering trace concentrations, which are found in current water treatment. Until now, most studies have been carried out at relatively high concentrations (mg L(-1)), since the experimental and analytical methodologies are more difficult and more expensive when dealing with lower concentrations (ng L(-1)). Therefore, the objective of this study was to validate an extrapolation procedure from high to low concentrations, for four compounds (Carbamazepine, Diclofenac, Caffeine and Acetaminophen). For this purpose, the reliability of the usual adsorption isotherm models, when extrapolated from high (mg L(-1)) to low concentrations (ng L(-1)), was assessed as well as the influence of numerous error functions. Some isotherm models (Freundlich, Toth) and error functions (RSS, ARE) show weaknesses to be used as an adsorption isotherms at low concentrations. However, from these results, the pairing of the Langmuir-Freundlich isotherm model with Marquardt's percent standard of deviation was evidenced as the best combination model, enabling the extrapolation of adsorption capacities by orders of magnitude.

Simultaneous removal of binary mixture of Brilliant Green and Crystal Violet using derivative spectrophotometric determination, multivariate optimization and adsorption characterization of dyes on surfactant modified nano-γ-alumina

The present study deals with the simultaneous removal of Brilliant Green (BG) and Crystal Violet (CV) by surfactant-modified alumina. The utilization of alumina nanoparticles with an anionic surfactant (sodium dodecyl sulfate (SDS)) as a novel and efficient adsorbent is successfully carried out to remove two cationic dyes from aqueous solutions in binary batch systems. A first-order derivative spectrophotometric method is developed for the simultaneous determination of BG and CV in binary solutions. The linear concentration range and limits of detection for the simultaneous determination of BG and CV were found to be: 1-20, 1-15 mg/L, 0.3 and 0.5 mg/L, respectively. The influence of various parameters, such as contact time, initial concentration of dyes and sorbent mass on the dye adsorption is investigated. A response surface methodology achieved through performing the Box-Behnken design is utilized to optimize the removal of dyes by surfactant-modified nanoparticle alumina through a batch adsorption process. The proposed quadratic model resulting from the Box-Behnken design approach fitted very well with the experimental data. The optimal conditions for dye removal were contact time t=50 min, sorbent dose=0.036 g, CBG (Initial BG concentration)=215 mg/L and CCV (Initial CV concentration)=170 mg/L. Furthermore, FT-IR analysis, the isotherms and kinetics of adsorption were also explored.

Recent advances in the use of graphene-family nanoadsorbents for removal of toxic pollutants from wastewater

Adsorption technology is widely considered as the most promising and robust method of purifying water at low cost and with high-efficiency. Carbon-based materials have been extensively explored for adsorption applications because of their good chemical stability, structural diversity, low density, and suitability for large scale production. Graphene--a single atomic layer of graphite--is the newest member in the family of carbon allotropes and has emerged as the "celeb" material of the 21st century. Since its discovery in 2004 by Novoselov, Geim and co-workers, graphene has attracted increased attention in a wide range of applications due to its unprecedented electrical, mechanical, thermal, optical and transport properties. Graphene's infinitely high surface-to-volume ratio has resulted in a large number of investigations to study its application as a potential adsorbent for water purification. More recently, other graphene related materials such as graphene oxide, reduced graphene oxide, and few-layered graphene oxide sheets, as well as nanocomposites of graphene materials have also emerged as a promising group of adsorbent for the removal of various environmental pollutants from waste effluents. In this review article, we present a synthesis of the current knowledge available on this broad and versatile family of graphene nanomaterials for removal of dyes, potentially toxic elements, phenolic compounds and other organic chemicals from aquatic systems. The challenges involved in the development of these novel nanoadsorbents for decontamination of wastewaters have also been examined to help identify future directions for this emerging field to continue to grow.

A new approach in regression analysis for modeling adsorption isotherms

Numerous regression approaches to isotherm parameters estimation appear in the literature. The real insight into the proper modeling pattern can be achieved only by testing methods on a very big number of cases. Experimentally, it cannot be done in a reasonable time, so the Monte Carlo simulation method was applied. The objective of this paper is to introduce and compare numerical approaches that involve different levels of knowledge about the noise structure of the analytical method used for initial and equilibrium concentration determination. Six levels of homoscedastic noise and five types of heteroscedastic noise precision models were considered. Performance of the methods was statistically evaluated based on median percentage error and mean absolute relative error in parameter estimates. The present study showed a clear distinction between two cases. When equilibrium experiments are performed only once, for the homoscedastic case, the winning error function is ordinary least squares, while for the case of heteroscedastic noise the use of orthogonal distance regression or Margart's percent standard deviation is suggested. It was found that in case when experiments are repeated three times the simple method of weighted least squares performed as well as more complicated orthogonal distance regression method.

Modeling adsorption kinetics of trichloroethylene onto biochars derived from soybean stover and peanut shell wastes

Trichloroethylene (TCE) is one of the most hazardous organic pollutants in groundwater. Biochar produced from agricultural waste materials could serve as a novel carbonaceous adsorbent for removing organic contaminants from aqueous media. Biochars derived from pyrolysis of soybean stover at 300 °C and 700 °C (S-300 and S-700, respectively), and peanut shells at 300 °C and 700 °C (P-300 and P-700, respectively) were utilized as carbonaceous adsorbents to study batch aqueous TCE remediation kinetics. Different rate-based and diffusion-based kinetic models were adopted to understand the TCE adsorption mechanism on biochars. With an equilibrium time of 8-10 h, up to 69 % TCE was removed from water. Biochars produced at 700 °C were more effective than those produced at 300 °C. The P-700 and S-700 had lower molar H/C and O/C versus P-300 and S-300 resulting in high aromaticity and low polarity accompanying with high surface area and high adsorption capacity. The pseudo-second order and intraparticle diffusion models were well fitted to the kinetic data, thereby, indicating that chemisorption and pore diffusion were the dominating mechanisms of TCE adsorption onto biochars.

A promising absorbent of acrylic acid/poly(ethylene glycol) hydrogel prepared by glow-discharge electrolysis plasma

An acrylic acid/poly(ethylene glycol) (AAc/PEG) hydrogel was synthesized in aqueous solution by a simple one-step method using glow-discharge electrolysis plasma (GDEP) technique. The structure of AAc/PEG hydrogel was characterized by Fourier transform infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS). Factors influencing the adsorption of heavy-metal ions such as solution pH, contact time, initial heavy-metal ion concentration were examined systematically by batch experiments. Results showed that both chemical complexation and ion exchange played an important role for heavy-metal ion adsorption onto AAc/PEG hydrogel. The adsorption isothermals followed the Langmuir isotherm and the adsorption kinetics fitted the pseudo-second-order model at 25°C with a pH 6. In addition, AAc/PEG hydrogel can be also regenerated and re-used.

Microwave-assisted preparation and adsorption performance of activated carbon from biodiesel industry solid reside: influence of operational parameters

Preparation of activated carbon has been attempted using KOH as activating agent by microwave heating from biodiesel industry solid residue, oil palm empty fruit bunch (EFBAC). The significance of chemical impregnation ratio (IR), microwave power and activation time on the properties of activated carbon were investigated. The optimum condition has been identified at the IR of 1.0, microwave power of 600 W and activation time of 7 min. EFBAC was characterized by scanning electron microscopy, Fourier transform infrared spectroscopy and nitrogen adsorption isotherm. The surface chemistry was examined by zeta potential measurement, determination of surface acidity/basicity, while the adsorptive property was quantified using methylene blue as dye model compound. The optimum conditions resulted in activated carbon with a monolayer adsorption capacity of 395.30 mg/g and carbon yield of 73.78%, while the BET surface area and total pore volume were corresponding to 1372 m2/g and 0.76 cm3/g, respectively.

Pentachlorophenol sorption in nylon fiber and removal by immobilized Rhizopus oryzae ENHE

This study describes pentachlophenol (PCP) sorption in nylon fiber in which Rhizopus oryzae ENHE was immobilized to remove the chemical compound. The experimental sorption data were analyzed using the Langmuir, Freundlich, and Redlich-Peterson isotherm models using non-linear error functions to fit the experimental data to the three models. Results showed that the isotherm obtained from the data fitted the three models used. However, the g parameter from Redlich-Peterson model showed that the isotherm obtained approaches the Freundlich model. This support reached the sorption equilibrium concentration at 3mg PCPg(-1)nylon. To study PCP removal capability by R. oryzae ENHE and to eliminate the error caused by PCP sorbed by the nylon fiber during its quantification, nylon fiber at PCP equilibrium sorption concentration was used to immobilize R. oryzae ENHE. It was found that this fungus grew within nylon fiber cubes in presence or not of PCP, even when PCP caused growth inhibition. Maximum biomass accumulated into nylon cubes without PCP was of 32 mg biomass g(-1)nylon and into nylon cubes at PCP equilibrium concentration was of 18 mg g(-1)nylon. The results showed that R. oryzae ENHE immobilized into nylon fiber removed 88.6% and 92% of PCP in cultures with 12.5 and 25 mg PCPL(-1), as initial concentration, respectively. This is the first work to report that a zygomycete, such as R. oryzae ENHE, immobilized into nylon fiber kept its potential to remove PCP.

Removal of cobalt ions from aqueous solutions by polymer assisted ultrafiltration using experimental design approach: part 2: Optimization of hydrodynamic conditions for a crossflow ultrafiltration module with rotating part

Application of shear-enhanced crossflow ultrafiltration for separation of cobalt ions from synthetic wastewaters by prior complexation with polyethyleneimine has been investigated via experimental design approach. The hydrodynamic conditions in the module with tubular metallic membrane have been planned according to full factorial design in order to figure out the main and interaction effects of process factors upon permeate flux and cumulative flux decline. It has been noticed that the turbulent flow induced by rotation of inner cylinder in the module conducts to growth of permeate flux, normalized flux and membrane permeability as well as to decreasing of permeate flux decline. In addition, the rotation has led to self-cleaning effect as a result of the reduction of estimated polymer layer thickness on the membrane surface. The optimal hydrodynamic conditions in the module have been figured out by response surface methodology and overlap contour plot, being as follows: DeltaP=70 kPa, Q(R)=108 L/h and W=2800 rpm. In such conditions the maximal permeate flux and the minimal flux decline has been observed.