Experimental design based response surface methodology optimization of ultrasonic assisted adsorption of safaranin O by tin sulfide nanoparticle loaded on activated carbon

Application of green solvents for arsenic removal from petroleum produced water: Statistical, DFT and McCabe-Thiele determination

This work presents the novel application of green oils to extract arsenic ions from petroleum produced water via liquid-liquid extraction (LLE). In the experiment, the removal of arsenic ions from synthetic petroleum produced water is investigated, using five green oils: canola oil, corn oil, linseed oil, rice bran oil, and sunflower oil, in place of petroleum-based solvents: toluene and kerosene. Both extraction and stripping optimizations are examined. For extractants, Aliquat 336 and Cyanex 921 are implemented. The initial arsenic concentration (3.984 mg L-1) of petroleum produced water is examined. Results demonstrate that Aliquat 336 in corn oil proved to be most effective for arsenic removal. At optimal conditions via response surface methodology (RSM), the highest extraction and stripping percentages reached 99.95 % and 100.00 %, respectively. In accordance with the World Health Organization (WHO) levels of ≤0.01 mg L-1, arsenic concentration remaining in the extracted water (0.002 mg L-1), is seen to fulfill the requirement needed. The extraction and stripping kinetics are of first and second-order. Mechanisms of arsenic removal are evaluated via density functional theory (DFT). Further, selectivity, recycling of the organic phase, and the number of stages via McCabe-Thiele theory are determined under optimal conditions.

Benzopyrene elimination from the environment using graphitic carbon nitride-SnS nanocomposites

Benzopyrene (BaP) stands as a potent polycyclic aromatic hydrocarbon (PAH) molecule, boasting five fused aromatic rings, making its way into the human food chain through soil contamination. The persistent environmental presence of PAHs in soil, attributed to industrial exposure, is primarily due to their low molecular weight and hydrophobic nature. To preemptively address the entry of BaP into the food chain, the application of nanocomposites was identified as an effective remediation strategy. Post-synthesis, comprehensive characterization tests employing techniques such as UV-DRS, XRD, SEM-EDX, FTIR, and DLS unveiled the distinctive features of the g-C3N4-SnS nanocomposites. These nanocomposites exhibited spherical shapes embedded on layers of nanosheets, boasting particle diameters measuring 88.9 nm. Subsequent tests were conducted to assess the efficacy of eliminating benzopyrene from a combination of PAH molecules and g-C3N4-SnS nanocomposites. Varied parameters, including PAH concentration, adsorbent dosage, and suspension pH, were systematically explored. The optimized conditions for the efficient removal of BaP utilizing the g-C3N4-SnS nanocomposite involved 2 μg/mL of benzopyrene, 10 μg/mL of the nanocomposite, and a pH of 5, considering UV light as the irradiation source. The investigation into the mechanism governing BaP elimination closely aligned with batch adsorption results involved a thorough exploration of adsorption kinetics and isotherms. Photocatalytic degradation of benzopyrene was achieved, reaching a maximum of 86 % in 4 h and 36 % in 2 h, with g-C3N4-SnS nanocomposite acting as the catalyst. Further validation through HPLC data confirmed the successful removal of BaP from the soil matrix.

Synthesis and Characterization of High-Purity Mesoporous Alumina with Excellent Adsorption Capacity for Congo Red

We explore a more concise process for the preparation of high-purity alumina and to address the problem of some conventional micro- and nano-adsorbents having difficulty in exposing their adsorption sites to target pollutants in solution due to the heavy aggregation of the adsorbent, which confers poor adsorption properties. The methods of using gamma-phase high-purity mesoporous alumina (HPMA), with its excellent adsorption properties and high adsorption rates of Congo Red, and of using lower-cost industrial aluminum hydroxide by direct aging and ammonium salt substitution were successfully employed. The results showed that the purity of HPMA was as high as 99.9661% and the total removal rate of impurities was 98.87%, a consequence of achieving a large specific surface area of 312.43 m² g^-1, a pore volume of 0.55 cm³ g^-1, and an average pore diameter of 3.8 nm. The adsorption process was carried out at 25 °C, the concentration of Congo Red (CR) dye was fixed at 250 mg L^-1 and the amount of adsorbent used was 100 mg. The HPMA sample exhibited an extremely fast adsorption rate in the first 10 min, with adsorption amounts up to 476.34 mg g^-1 and adsorption efficiencies of 96.27%. The adsorption equilibrium was reached in about 60 min, at which time the adsorbed amount was 492.19 mg g^-1 and the dye removal rate was as high as 98.44%. One-hundred milligrams of adsorbent were weighed and dispersed in 200-mL CR solutions with mass concentrations ranging from 50-1750 mg L^-1 to study the adsorption isotherms. This revealed that the saturation adsorption capacity of the produced HPMA was 1984.64 mg g^-1. Furthermore, the process of adsorbing Congo Red in the synthesized product was consistent with a pseudo-second order model and the Langmiur model. It is expected that this method of producing HPMA will provide a productive, easy and efficient means of treating toxic dyes in industrial wastewater.

Ultrasound-enhanced remediation of toxic dyes from wastewater by activated carbon-doped magnetic nanocomposites: analysis of real wastewater samples and surfactant effect

Water pollution has become a worldwide threat as the natural water resources are shrinking day by day. Emergent actions are needed to conserve water stocks to fulfill the sustainable development goals. Herein, we have prepared activated carbon-doped magnetic nanocomposites (AC@CoFe₂O₄) with environment friendly approach and characterized for FTIR, XRD, SEM, EDS, BET surface area, and pH_zpc. AC@CoFe₂O₄ nanocomposite was applied for the decolorization of toxic food dyes (rhodamine B and tartrazine) from wastewater. Effect of ultrasonic waves, pH, contact time, surfactants, temperature, and analysis of real wastewater systems were studied. Adsorption isotherm, kinetics, and thermodynamics of the experiment were calculated for the present removal process. The effect of ultrasonication shows that the maximum removal percentage for RhB was found to be 92% and for tartrazine, it was found to be 86% at 60 min. Ultrasound-assisted adsorption and degradation revealed good results because of the formation of highly active ^·H and ^·OH radicals in the liquid through the decomposition of water molecules by the formation of hot spots under ultrasonic waves. Highest decolorization of 69% was obtained for RhB with anionic surfactant SDS and climax decolorization of tartrazine was acquired in case of CTAB as 60.5%. Analysis of real wastewater samples shows that the decolorization of RhB was found to be ~ 91% from well-water and ~ 95% removal of tartrazine was observed from submersible water on AC@CoFe₂O₄ nanocomposites. The decolorization best fitted (R² < 0.988) with Langmuir model and value of Langmuir climax decolorization efficiency (Q₀) was found to be 142.68 and 435.72 mg/g for RhB and tartrazine, respectively. Kinetic analysis revealed that adsorption follows pseudo-second-order equation. The dye-loaded AC@CoFe₂O₄ nanocomposites were recycled by 0.1 M HCl or NaOH and regenerated AC@CoFe₂O₄ nanocomposites were used up to five rounds with better adsorption efficiency.

Carboxylated cellulose nanofiber/montmorillonite nanocomposite for the removal of levofloxacin hydrochloride antibiotic from aqueous solutions

Herein, we report the facile two-step synthesis of an effective carboxylated cellulose nanofiber/montmorillonite nanocomposite (CMNFs-MMT) adsorbent for levofloxacin hydrochloride (Levo-HCl). CMNFs-MMT was characterized using scanning electron microscopy, energy dispersive X-ray spectrometry, Brunauer-Emmett-Teller measurements, X-ray photoelectron spectroscopy, X-ray diffraction, and Fourier transform infrared spectroscopy. Based on the central composite design, the effects of various factors on the removal of Levo-HCl by the CMNFs-MMT were explored, wherein the effect of pH was the most significant. To gain a clearer perspective on the adsorption process of Levo-HCl onto CMNFs-MMT, the adsorption kinetics and isotherms were also measured, revealing that the reaction is pseudo-second-order and the Sips models provide the best fit with experimental data. Comparing the adsorption in pure water with the removal in river water, the rate of river water removal (90.37%) was slightly lower than that of pure water (93.97%) when adsorption equilibrium was reached, confirming that CMNFs-MMT is not easily influenced by environmental conditions. Reusability experiments indicate that CMNFs-MMT can maintain a certain adsorption capacity for Levo-HCl after six uses. Overall, this work indicates that CMNFs-MMT is an effective adsorbent for eliminating Levo-HCl from aqueous media in future engineering applications.

Cellulose nanocrystals/graphene oxide composite for the adsorption and removal of levofloxacin hydrochloride antibiotic from aqueous solution

Residual antibiotics in water are often persistent organic pollutants. The purpose of this study was to prepare a cellulose nanocrystals/graphene oxide composite (CNCs-GO) with a three-dimensional structure for the removal of the antibiotic levofloxacin hydrochloride (Levo-HCl) in water by adsorption. The scanning electron microscope, Fourier transform infrared (FT-IR), energy-dispersive spectroscopy, X-ray photoelectron spectroscopy and other characterization methods were used to study the physical structure and chemical properties of the CNCs-GO. The three-dimensional structure of the composite material rendered a high surface area and electrostatic attraction, resulting in increased adsorption capacity of the CNCs-GO for Levo-HCl. Based on the Box-Behnken design, the effects of different factors on the removal of Levo-HCl by the CNCs-GO were explored. The composite material exhibited good antibiotic adsorption capacity, with a removal percentage exceeding 80.1% at an optimal pH of 4, the adsorbent dosage of 1.0 g l^-1, initial pollutant concentration of 10.0 mg l^-1 and contact time of 4 h. The adsorption isotherm was well fitted by the Sips model, and kinetics studies demonstrated that the adsorption process conformed to a quasi-second-order kinetics model. Consequently, the as-synthesized CNCs-GO demonstrates good potential for the effective removal of antibiotics such as levofloxacin hydrochloride from aqueous media.

One-step synthesis of Cu(II) metal-organic gel as recyclable material for rapid, efficient and size selective cationic dyes adsorption

Efficient removal of non-biodegradable and hazardous dyes from wastewater remains a hot research topic. Herein, a rationally designed a Cu(II)-based metal-organic gel (Cu-MOG) with a nanoporous 3D network structure prepared via a simple one-step mixing method was successfully employed for the removal of cationic dyes. The Cu-MOG exhibited high efficiency, with an adsorption capacity of up to 650.32 mg/g, and rapid adsorption efficiency, with the ability to adsorb 80% of Neutral Red within 1 min. The high adsorption efficiency was attributed to its large specific surface area, which enabled it to massively bind cationic dyes through electrostatic interaction, and a nanoporous structure that promoted intra-pore diffusion. Remarkably, the Cu-MOG displayed size-selective adsorption, based on adsorption studies concerning dyes of different sizes as calculated by density functional theory. Additionally, the adsorption performance of the Cu-MOG still maintained removal efficiency of 100% after three regeneration cycles. These results suggested that the Cu-MOG could be expected to be a promising and competitive candidate to conveniently process wastewater.

Modeling of azo dyes adsorption on magnetic NiFe2O4/RGO nanocomposite using response surface methodology

BACKGROUND

Azo group dyes are the largest group of synthetics dyes that widely used in industries, especially in textile industry. The presence of these organic compounds in wastewaters and their discharge into environment without efficient treatment may cause adverse effect on human, living and aquatic environment. The purpose of this study was to optimize the adsorption of azo dye of Direct Red 81 (anionic dye) and Basic Blue 41 (cationic dye) from aqueous solution onto magnetic NiFe₂O₄/RGO nanocomposite.

METHODS

In this study the response surface methodology (RSM) based on the central composite design (CCD), was used to optimization and modeling of adsorption process DR81 and BB41 dye on NiFe₂O₄/RGO. in order to investigating the effect of the operating parameters on the adsorption efficiency DR81 and BB41, four influential factors were chosen that includes of pH (3-9), contact time (5-25 min), adsorbent amount (0.02-0.05 g) and initial dye concentration (40-200 mg/L). A total of 30 experiments were performed for each dye in this study. The concentration of dye in solution was measured by spectrophotometer. The structure of synthesized adsorbent was investigated using Scanning Electron Microscope (SEM), X-ray diffraction (XRD), Fourier transform irradiation (FTIR), transmission electron microscope (TEM) and vibrating sample magnetometer (VSM).

RESULTS

Analysis of variance (ANOVA) showed that regression model for both dye adsorption with value of P value <0.001 is significant statistically. The correlation coefficient (R²) for DR81 (R² = 0.9968) and BB41 (R² = 0.9948) indicated which there is a good agreement between predicted values and the results of the experiments and the model also well predict the adsorption efficiency. Furthermore, the factors of pH, dye concentration and adsorbent dose, have the greatest effect on adsorption, respectively, while contact time have the lowest effect on adsorption of both dyes. The adsorption behavior of the DR81 and BB41 onto NiFe₂O₄/RGO was best described by the Langmuir and Freundlich isotherm, respectively. The optimum conditions for maximum removal of DR81 (96.41%) was found to be at pH 3, contact time 19.68 min, adsorbent dose 0.02 g and initial dye concentration 40 mg/L. However, the optimum conditions for maximum removal of BB41 (97.87%) was found to be at pH 9 contact time 18.16 min, adsorbent dose 0.02 g and initial dye concentration 40 mg/L.

CONCLUSION

The present study shows that magnetic NiFe₂O₄/RGO nanocomposite have much potential as a powerful adsorbent for the rapid adsorption of anionic (DR81) and cationic dyes (BB41) from aqueous solution.

Iron oxide Permeated Mesoporous rice-husk nanobiochar (IPMN) mediated removal of dissolved arsenic (As): Chemometric modelling and adsorption dynamics

Adsorption based technologies are most widely used to mitigate the global predominance of heavy-metal groundwater contaminants like Arsenic (As), owing to their high efficiency and economic operation. The current study involves the optimization of Iron oxide Permeated Mesoporous rice-husk nanobiochars (IPMN) for As removal, which were synthesized through a chemically amended pyrolytic approach. The IPMN variants were screened based on preliminary OVAT (one-variable-at-a-time) studies for As removal. Chemometric investigations employing a central composite design matrix of Response surface methodology was further used to understand the influence of the process parameters on the adsorption of As on the most efficient IPMN variant. A Multi-Layered-Perceptron based artificial neural network was further used to confirm the veracity of the experimental and predictive conditions, to derive the optimal condition for the best adsorption efficiency. In addition, the dynamics of As adsorption by the optimal IPMN variant was modelled using pseudo-first-order (Lagergren) and pseudo-second-order (Ho) rate kinetic equations followed by isotherm studies using non-linear regression of Langmuir, Freundlich and Sips adsorption isotherms. The IPMNs have an appreciably higher uptake capacity (>90%) for dissolved As, as compared to the native milled rice husk (∼20%), alongside a substantial recyclability, thereby establishing their potential as a highly efficient, economical and sustainable nanobiochar for As removal.

Adsorptive potential of Zea mays tassel activated carbon towards the removal of metformin hydrochloride from pharmaceutical effluent

In the present study, Zea mays tassel which is a zero-value agricultural waste was used to produce a low-cost activated carbon using phosphoric acid as the activating agent. The prepared Z. mays tassel activated carbon (ZMTAC) was characterized by Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD). The adsorbent was applied for adsorption of an emerging contaminant, metformin hydrochloride (MH) from pharmaceutical effluent. The effects of solution pH, contact time, adsorbent dosage, and initial MH concentration and their interactions were investigated using a response surface methodology following a central composite experimental design (CCD). The optimum experimental conditions were as follows: pH 9.5, contact time 67.50 min, dosage 0.5750 g, and MH concentration 152.50 mg/L. The isotherm data followed Langmuir isotherm model (R² = 0.979; sum of square deviation, SSD = 0.321). The saturation adsorption capacity of ZMTAC was 44.84 mg/g at 20 °C. MH adsorption process followed pseudo-second-order kinetics (higher R² and smaller SSD values). The thermodynamic properties obtained showed that the adsorption process was feasible, endothermic and spontaneous. Consequently, the study demonstrated that Z. mays tassel is a potential precursor for preparation of adsorbents for the removal of the MH from pharmaceutical effluent.

Ultrasound Assisted Adsorptive Removal of Cr, Cu, Al, Ba, Zn, Ni, Mn, Co and Ti from Seawater Using Fe2O3-SiO2-PAN Nanocomposite: Equilibrium Kinetics

This work reports the preparation and application of Fe2O3-SiO2-PAN nanocomposite for the removal of Cr3+, Cu2+, Al3+, Ba2+, Zn2+, Ni2+, Mn2+, Co2+, and Ti3+ from seawater. X-ray diffraction (XRD), scanning electron microscope/energy dispersive X-ray spectroscopy (SEM/EDS), transmission electron microscope (TEM), and Brunauer-Emmett-Teller (BET) characterized the synthesized composite. The following experimental parameters (Extraction time, adsorbent mass and pH) affecting the removal of major and trace metals were optimized using response surface methodology (RSM). The applicability of the RSM model was verified by performing the confirmation experiment using the optimal condition and the removal efficiency ranged from 90% to 97%, implying that the model was valid. The adsorption kinetic data was described by the pseudo-second order model. The applicability of the materials was tested on real seawater samples (initial concentration ranging from 0.270–203 µg L−1) and the results showed satisfactory percentage efficiency removal that range from 98% to 99.9%. The maximum adsorption capacities were found to be 4.36, 7.20, 2.23, 6.60, 5.06, 2.60, 6.79, 6.65 and 3.00 mg g−1, for Cr3+, Cu2+, Al3+, Ba2+, Zn2+, Ni2+, Mn2+, Co2+, and Ti4+, respectively.

Ultrasonic assisted synthesis of magnetic Ni-Ag bimetallic nanoparticles supported on reduced graphene oxide for sonochemical simultaneous removal of sunset yellow and tartrazine dyes by response surface optimization: Application of derivative spectrophotometry

The magnetic Ni-Ag bimetallic nanoparticles supported on reduced graphene oxide (Ni-Ag NPs/rGO) was synthesized and characterized by transmission electron microscopy (TEM), energy dispersive X-ray analysis (EDX), field emission scanning electron microscopy (FE-SEM) and vibrating sample magnetometer (VSM). Subsequently, this magnetic hybrid material as a novel adsorbent was applied for the sonochemical simultaneous removal of sunset yellow and tartrazine dyes in combination with first-order derivative spectrophotometric method to resolve the overlap between the spectra of these dyes. With magnetic properties, the adsorbent could easily be collected from aqueous solution using an external magnetic field. The parameters including initial concentration of each dye, adsorbent dosage and sonication time were studied by Box-Behnken design (BBD) and response surface methodology (RSM), while pH was studied by one-at-a-time approach. According to Box-Behnken design based on desirability function (DF), the best experimental conditions was set as initial sunset yellow concentration 10 mgL^-1, initial tartrazine concentration 8.5 mgL^-1, adsorbent dosage 0.045 g and sonication time of 15 min. The equilibrium data was fitted to different isotherm models and the results revealed the suitability of the Langmuir model. The maximum sorption capacity calculated from the Langmuir model was 28.57 and 26.31 mg g^-1 for sunset yellow and tartrazine, respectively. Kinetic data revealed that the adsorption process followed a pseudo-second-order model. The reusability of the magnetite nanoparticles revealed about 8% decrease in the removal efficiency within four consecutive runs.

Ultrasound-assisted sorption of Pb(ii) on multi-walled carbon nanotube in presence of natural organic matter: an insight into main and interaction effects using modelling approaches of RSM and BRT

In real-scale applications, where NPs are injected into the aqueous environment for remediation, they may interact with natural organic matter (NOM). This interaction can alter nanoparticles' (NPs) physicochemical properties, sorption behavior, and even ecological effects. This study aimed to investigate sorption of Pb(ii) onto multi-walled carbon nanotube (MWCNT) in presence of NOM. The predominant behavior of the process was examined comparatively using response surface methodology (RSM) and boosted regression tree (BRT)-based models. The influence of four main effective parameters, namely Pb(ii) and humic acid (HA) concentrations (mg L⁻¹), pH, and time (min) on Pb removal (%) was evaluated by contributing factor importance rankings (BRT) and analysis of variance (RSM). The applicability of the BRT and RSM models for description of the predominant behavior in the design space was checked and compared using statistics of absolute average deviation (AAD), mean absolute error (MAE), root mean square error (RMSE), and multiple correlation coefficient (R²). The results showed that although both approaches exhibited good performance, the BRT model was more precise, indicating that it could be a powerful method for the modeling of NOM-presence studies. Importance rankings of BRT displayed that the effectiveness order of the studied parameters is pH > time > Pb(ii) concentration > HA concentration. Although HA concentration showed the least effect in comparison with three other studied parameters theoretically, the experimental results revealed that Pb(ii) removal is enhanced in presence of HA (73% vs. 81.77%), which was confirmed by SEM/EDX analyses. Hence, maximum removal (R% = 81.77) was attained at an initial Pb(ii) concentration of 9.91 mg L⁻¹, HA concentration of 0.3 mg L⁻¹, pH of 4.9, and time of 55.2 min.

The proposed mechanism for effect of HA on Pb(ii) removal using MWCNTs.

Alkaline dehydration of anion-exchanged human urine: Volume reduction, nutrient recovery and process optimisation

In urine-separating sanitation systems, bacterial urease enzymes can hydrolyse urea to ammonia during the pipe transport and storage of urine. The present study investigated whether it was possible to reduce the urine volume without losing the nitrogen as ammonia. A method for stabilising the urine prior to dehydration was developed. Briefly, fresh human urine was stabilised by passage through an anion-exchanger, added to an alkaline media (wood ash or alkalised biochar), and dehydrated. Urine dehydration was investigated at three temperatures: 40, 45 and 50 °C. The influence of various factors affecting the dehydration process was modelled and the rate of urine dehydration was optimised. Results indicated that 75% (v/v) of the urine has to pass through the ion-exchanger for alkaline stabilisation of urine to occur. At all investigated temperatures, the dehydrator accomplished >90% volume reduction of ion-exchanged urine, > 70% N retention and 100% recovery of P and K. To realise high degree of nutrient valorisation, this study proposes combining source-separation of human urine with alkaline dehydration.

Removal of mercury from contaminated saline wasters using dithiocarbamate functionalized-magnetic nanocomposite

In this study, an efficient adsorbent was proposed for the removal of mercury from saline water contaminated with mercury ions. Fe₃O₄ nanoparticles were modified using tetraethylenepentamine and carbon disulfide to incorporate dithiocarbamate functional group on the surface of the adsorbent. CHNS analysis confirmed successful modification of magnetic nanoparticles. The XRD pattern of adsorbent indicated a proper match with the standard XRD pattern of cubic Fe₃O₄. The saturation magnetization of final adsorbent was 27 emu g^-1. The morphology of bare and silica-coated Fe₃O₄ and final product were investigated using FE-SEM analysis. For optimizing the adsorption process, response surface methodology was applied, which was resulted in a significant quadratic model. The effect of adsorbent dosage and initial concentration of Hg (II) was much more significant than that of pH. Different concentrations of dissolved solids up to 2000 mg L^-1 had no adverse effect on the adsorption process due to the strong interaction between dithiocarbamate functional group of adsorbent and Hg (II). The least values of RMSE (0.0950) and χ2 (0.0009) were observed for Radke-Prausnitz, Redlich-Peterson, and UT isotherms. Maximum adsorption capacities calculated using Langmuir and UT models were 109.5 and 95.07 mg g^-1, respectively. The investigation of adsorption isotherm was conducted at the pH range of 2.0-6.5. The results showed an increase in the adsorption capacity by increasing pH. Thermodynamic studies demonstrated that the nature of the adsorption process was spontaneous and endothermic. Recovery of adsorbent was successfully carried out using HCl 0.5 mol L^-1. The prepared adsorbent was successfully applied for mercury removal from a real groundwater.

Optimization of paper mill industry wastewater treatment by electrocoagulation and electro-Fenton processes using response surface methodology

This study deals with chemical oxygen demand (COD), phenol and Ca⁺² removal from paper mill industry wastewater by electrocoagulation (EC) and electro-Fenton (EF) processes. A response surface methodology (RSM) approach was employed to evaluate the effects and interactions of the process variables and to optimize the performance of both processes. Significant quadratic polynomial models were obtained (R² = 0.959, R² = 0.993 and R² = 0.969 for COD, phenol and Ca⁺² removal, respectively, for EC and R² = 0.936, R² = 0.934 and R² = 0.890 for COD, phenol and Ca⁺² removal, respectively). Numerical optimization based on desirability function was employed; in a 27.55 min trial, 34.7% of COD removal was achieved at pH 9 and current density 96 mA/cm² for EC, whereas in a 30 min trial, 74.31% of COD removal was achieved at pH 2 and current density 96 mA/cm² and H₂O₂/COD molar ratio 2.0 for EF. The operating costs were calculated to be 6.44 €/m³ for EC and 7.02 €/m³ for EF depending on energy and electrode consumption at optimum conditions. The results indicate that the RSM is suitable for the design and optimization of both of the processes. However, EF process was a more effective technology for paper mill industry wastewater treatment as compared with EC.

Improved adsorption performance of nanostructured composite by ultrasonic wave: Optimization through response surface methodology, isotherm and kinetic studies

In this work, ultrasound-assisted adsorption of an anionic dye, sunset yellow (SY) and cationic dyes, malachite green (MG), methylene blue (MB) and their ternary dye solutions onto Cu@ Mn-ZnS-NPs-AC from water aqueous was optimized by response surface methodology (RSM) using the central composite design (CCD). The adsorbent was characterized using Field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), Energy-dispersive X-ray spectroscopy (EDX) and EDX mapping images. The effects of various parameters such as pH, sonication time, adsorbent mass and initial concentrations of SY, MG and MB were examined. A total 33 experiments were conducted to establish a quadratic model. Cu@ Mn-ZnS-NPs-AC has the maximum adsorption efficiency (>99.5%) when the pH, sonication time, adsorbent mass and initial concentrations of SY, MG and MB were optimally set as 6.0, 5min, 0.02g, 9, 12 and 12mgL^-1, respectively. Sonication time has a statistically significant effect on the selected responses. Langmuir isotherm model was found to be best fitted to adsorption and adsorption capacities were 67.5mgg^-1 for SY, 74.6mgg^-1 for MG and 72.9mgg^-1 for MB. Four kinetic models (pseudo-first order, pseudo-second order, Weber-Morris intraparticle diffusion rate and Elovich) were tested to correlate the experimental data and the sorption was fitted well with the pseudo-second order kinetic model.

Removal of potentially toxic elements from aqueous solutions and industrial wastewater using activated carbon

Water contamination with potentially toxic elements (PTEs) has become one of the key issues in recent years that threatens human health and ecological systems. The present study is aimed at removing PTEs like cadmium (Cd), chromium (Cr), copper (Cu) and lead (Pb) from aqueous solutions and industrial wastewater using activated carbon (AC) as an adsorbent through different batch and column experiments. Results demonstrated that the removal of PTEs from aqueous solutions was highly pH dependent, except for Cr, and the maximum removal (>78%) was recorded at pH 6.0. However, maximum Cr removal (82.8%) was observed at pH 3.0. The adsorption reached equilibrium after 60 min with 2 g of adsorbent. Coefficient (R²) values suggested by the Langmuir isotherm model were 0.97, 0.96, 0.93 and 0.95 for Cd, Cr, Cu and Pb, respectively, indicating the fit to this model. In column experiments, the maximum removal of PTEs was observed at an adsorbent bed height of 20 cm with the optimal flow rate of 3.56 mL/min. Furthermore, PTEs removal by AC was observed in the order of Cu > Cd > Pb > Cr. Findings from this study suggest that AC could be used as a promising adsorbent for simultaneously removing several PTEs from wastewaters.

Synthesis of carbon loaded γ-Fe2O3 nanocomposite and their applicability for the selective removal of binary mixture of dyes by ultrasonic adsorption based on response surface methodology

The contemporary problems concerning water purification could be resolved by using nanosorbents. The present studies emphasis on the synthesis of γ-Fe₂O₃-activated carbon nanocomposites (γ-Fe₂O₃-NP-AC) by sol-gel method. The composition and surface morphology of them were studied by FTIR, EDS, SEM and XRD techniques. Moreover they were employed for the selective removal of binary mixture of dyes including reactive red 223 dye (RR) and Malachite Green dye (MG) by ultrasonic assisted adsorption method. Sonication is the act of applying sound energy to agitate particles in the sample. The ultrasonic frequencies (>20kHz) were used to agitate experimental solutions in current studies. The response surface methodology based on 5 factorial central composite design (CCD) was employed to investigate the optimum parameters of adsorption. The optimum operating parameters (OOP) including sonication time, solution pH, amount of adsorbent, concentration of RR and MG were estimated for the selective removal of mixture of dyes. On OOP conditions of RR, the % removal of RR and MG were observed to be 92.12% and 10.05% respectively. While at OOP of MG, the % removal of MG and RR were observed to be 85.32% and 32.13% from the mixture respectively. Moreover the mechanisms of adsorption of RR and MG on the γ-Fe₂O₃-NP-AC were also illustrated. The significance of the RR-γ-Fe₂O₃-NP-AC and MG-γ-Fe₂O₃-NP-AC adsorption models was affirmed by ANOVA test. The Pareto plots for the selective removal of the RR and MG from the binary mixture also confirm the significance of the factors. Isothermal studies were performed and RR adsorption was observed to follow Langmuir isotherm model whereas MG adsorption was observed to follow Freundlich model. Thermodynamic studies were conducted and the outcomes suggested the spontaneous nature of adsorption processes. The kinetic models were employed to study the kinetics of the process. It was observed that the system followed pseudo second order, intra-particle diffusion and Elovich models as represented by the R² values of the respective models. The comparative study from the previously studies revealed that the proposed method is amongst them is the most efficient method to eliminate RR and MG dyes from the aqueous medium. Therefore the current study will be useful in reducing the toxicity of RR and MG contaminated effluent.

Preparation, characterization, uranium (VI) biosorption models, and conditions optimization by response surface methodology (RSM) for amidoxime-functionalized marine fungus materials

Amidoxime-functionalized marine fungus Fusarium sp. #ZZF51 (ZGDA) was synthesized and studied to adsorb uranium (VI) from the aqueous solution. Different instrumental techniques such as FTIR, SEM, and TGA were employed for the characterization of the manufactured materials, and theirs ability of removal uranium (VI) was optimized using RSM. The experimental results showed the maximum adsorption capacity for the synthesized materials was 230.78 mg g−1 at the following optimization conditions: S–L ratio 150 mg L−1, pH 5.13, uranium (VI) initial concentration 40 mg L−1, and equilibrium time 122.40 min. More than 85% of the absorbed uranium (VI) could be desorbed by 0.5 or 1.0 mol L−1 HCl, and the modified mycelium could be reused at least five times. The thermodynamic experimental data of adsorption uranium (VI) could fit better with Langumir and Freundlich isotherms models, and the pseudo-second-order model was better to interpret the kinetics process. The modified fungus materials exhibited the better sorption capacity for uranium (VI) in comparison with raw biomass should be attributed to the strong chelation of amidoxime to uranium (VI) ions.

An optimized SPE-LC-MS/MS method for antibiotics residue analysis in ground, surface and treated water samples by response surface methodology- central composite design

BACKGROUND

Antibiotic residues are being constantly identified in environmental waters at low concentration. Growing concern has been expressed over the adverse environmental and human health effects even at low concentration. Hence, it is crucial to develop a multi-residues analytical method for antibiotics to generate a considerable dataset which are necessary in the assessment of aquatic toxicity of environmental waters for aquatic organisms and human health. This work aimed to develop a reliable and sensitive multi-residue method based on high performance liquid chromatography coupled with quadrupole-linear ion trap tandem mass spectrometry (HPLC-MS-MS). The method was optimized and validated for simultaneous determination of four classes of antibiotics including, β-lactam, macrolide, fluoroquinolone and nitro-imidazole in treated, ground and surface water matrices.

METHODS

In order to optimize the solid phase extraction process, main parameters influencing the extraction process including, pH, the volume of elution solvent and the amount of Na₄EDTA were evaluated. The optimization of extraction process was carried out by response surface methodology using central composite design. Analysis of variance was performed for nine target antibiotics using response surface methodology.

RESULTS

The extraction recoveries were found to be sensitive to the independent variables of pH, the volume of elution solvent and the amount of Na₄EDTA. The extraction process was pH-dependent and pH was a significant model term in the extraction process of all target antibiotics. Method validation was performed in optimum operation conditions in which the recoveries were obtained in the range of 50-117% for seven antibiotics in spiked treated and ground water samples and for six antibiotics in spiked river water samples. Method validation parameters in terms of method detection limit were obtained in the range of 1-10 ng/L in treated water, 0.8-10 ng/L in the ground water and 0.8-25 ng/L in river water, linearity varied from 0.95 to 0.99 and repeatability in term of relative standard deviation values was achieved less than 10% with the exception for metronidazole and ceftriaxone. The developed method was applied to the analysis of target antibiotics in treated, ground and surface water samples.

CONCLUSIONS

Target antibiotics were analyzed in different water matrices including treated, ground and river water. Seven out of nine antibiotics were detected in Kan River and Firozabad Ditch water samples, although none of them were detected in treated water and ground water samples.

Application of Central Composite Design in the Adsorption of Ca(II) on Metakaolin Zeolite

Metakaolin zeolite-A was synthesized from thermally activated kaolin clay and characterized by Fourier Transform Infrared Spectroscopy and X-Ray Diffraction Spectroscopy. The effects of pH (2–10), contact time (10–180 min), initial concentration (5–120 mgL−1), and dosage (0.1–2 g) and their interactions were investigated using response surface methodology following a central composite design. Optimum removal (87.70%) was obtained at pH 6, contact time 180 min, initial concentration 40.0 mgL−1, and adsorbent dosage 1.0 g by Excel Solver using the GRG solving method. The adsorption data fitted best to the Langmuir model with correlation coefficient R2=0.993 and Chi-square value χ2=4.76. The Freundlich isotherm gave a correlation coefficient R2=0.933 and χ2=37.91. The adsorption process followed the pseudo-second-order model. The calculated thermodynamic parameters showed that the adsorption process was endothermic and not thermodynamically spontaneous. The studied zeolite-A can therefore be used as a promising adsorbent for the removal of Ca(II) ions from aqueous solutions.

Synthesis of polyaniline nanoparticles and their application for the removal of Crystal Violet dye by ultrasonicated adsorption process based on Response Surface Methodology

The present study focuses the synthesis of polyaniline nanoparticles (PANP) by rapid mixing polymerization method. They were recognized by FTIR and SEM techniques. Moreover they were utilized for the removal of Crystal Violet (CV) dye by ultrasonicated adsorption process. It ensures a quick alternative method compared to other conventional processes, which led to enhancement of mass transfer by ultrasound waves. The effectiveness of the process was confirmed through the effect of certain conditions like sonication time, temperature, adsorbent dosage and CV concentrations. The validity of the process was estimated by various adsorption isotherms. Kinetics and thermodynamic studies was also conducted to authenticate the process. The optimum operating parameters (OOP) were evaluated by Response Surface Methodology (RSM) based on central composite design (CCD) for the removal of CV dye. Moreover analysis of variances (ANOVA) was employed to estimate the significance of experimental variables. The predicated removal efficiency was found to be 94.29% which prove to be effectiveness of the process.

Fabrication of Fe-doped TiO2 nanoparticles and investigation of photocatalytic decolorization of reactive red 198 under visible light irradiation

In this research, Fe-doped TiO2 nanoparticles with various Fe concentrations (0. 0.1, 1, 5 and 10wt%) were prepared by a sol-gel method. Then, nanoparticles were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), energy-dispersive X-ray analysis (EDX), BET surface area, photoluminescence (PL) spectroscopy and UV-vis diffuse reflectance spectroscopy (DRS). The photocatalytic activity of the nano-particles was evaluated through degradation of reactive red 198 (RR 198) under UV and visible light irradiations. XRD results revealed that all samples contained only anatase phase. DRS showed that the Fe doping in the titania induced a significant red shift of the absorption edge and then the band gap energy decreased from 3 to 2.1eV. Photocatalytic results indicated that TiO2 had a highest photocatalytic decolorization of the RR 198 under UV irradiation whereas photocatalytic decolorization of the RR 198 under visible irradiation increased in the presence of Fe-doped TiO2 nanoparticles. Among the samples, Fe-1wt% doped TiO2 nanoparticles showed the highest photocatalytic decolorization of RR198 under visible light irradiation.

Dispersion of hydrophobic magnetic nanoparticles using ultarsonic-assisted in combination with coacervative microextraction for the simultaneous preconcentration and determination of tricyclic antidepressant drugs in biological fluids

A two-step sample preparation technique based on dispersive micro solid-phase extraction combined with coacervative microextraction is presented for preconcentration and determination of tricyclic antidepressant drugs in biological samples. An important feature of the method is the application of hydrophobic magnetic nanoparticles, which in combination with coacervative microextraction method enables development of rapid and efficient extraction procedure in order to achievement of a high extraction efficiency. Simultaneous optimization by experimental design lead to improvement of method with low cost which supply useful information about interaction among variables. Under the optimized conditions, a linear range of 5-1000ngmL(-1) with detection limits from 0.51 to 1.4ngmL(-1) were obtained for target analytes. The method was successfully used for the determination of analytes in biological fluids (plasma and urine) with relative recoveries in the range of 89-105% (RSDs<3.5%).

Synthesis and Characterization of Reduced Graphene Oxide-Supported Nanoscale Zero-Valent Iron (nZVI/rGO) Composites Used for Pb(II) Removal

Reduced graphene oxide-supported nanoscale zero-valent iron (nZVI/rGO) composites were prepared by chemical deposition method and were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), Raman spectroscopy, N₂-sorption and X-ray photoelectron spectroscopy (XPS). Operating parameters for the removal process of Pb(II) ions, such as temperature (20–40 °C), pH (3–5), initial concentration (400–600 mg/L) and contact time (20–60 min), were optimized using a quadratic model. The coefficient of determination (R² > 0.99) obtained for the mathematical model indicates a high correlation between the experimental and predicted values. The optimal temperature, pH, initial concentration and contact time for Pb(II) ions removal in the present experiment were 21.30 °C, 5.00, 400.00 mg/L and 60.00 min, respectively. In addition, the Pb(II) removal by nZVI/rGO composites was quantitatively evaluated by using adsorption isotherms, such as Langmuir and Freundlich isotherm models, of which Langmuir isotherm gave a better correlation, and the calculated maximum adsorption capacity was 910 mg/g. The removal process of Pb(II) ions could be completed within 50 min, which was well described by the pseudo-second order kinetic model. Therefore, the nZVI/rGO composites are suitable as efficient materials for the advanced treatment of Pb(II)-containing wastewater.