Response surface modeling of lead (׀׀) removal by graphene oxide-Fe3O4 nanocomposite using central composite design

Removal of lead ions from aqueous solutions by modified cellulose

The new adsorbent was prepared by mixing cellulose with dicyclohexyl-18- crown-6 via microwave irradiation method and it was used to remove lead ions from aqueous solution. In contrast to the traditional way (in which grafted polymers are produced by using chemical-free radical producers), this method is rapid, reproducible, and gives a high-quality product. Different physicochemical techniques such as FTIR, SEM, and XRD and TGA were used for the characterization of the produced adsorbent. Based on the ANOVA statistical value, the adsorption of Pb2+ ion onto grafted cellulose has been found to be significant, with very low probability (p) values (<0.001). The pH and initial concentration were observed to be the most significant factors that affected the Pb2+ ion removal from the analysis of variance. Pseudo-second-order and Langmuir equations were applied to the adsorption of Pb2+ ion and under the optimized conditions, the maximum absorption capacity in modified cellulose of Pb2+ was 58.3 mg/g. Various factors which affect metal ion adsorption, including temperature, power of hydrogen, shaking time, adsorbent quantity, and metal ions concentration were studied. More importantly, the adsorbent could be reused by using 0.1 M nitric acid.

New ion-imprinted polymer for selective removal of Cu2+ ion in aqueous solution using extracted Aloe vera leaves as a monomer

The objective of this project is to create a unique type of polymer known as an ion imprinted polymer (IIP) and a non-imprinted polymer (NIP) utilizing natural waste biosorbent materials. One example of this type of waste is Aloe vera, a plant with many medicinal uses that is grown globally. Aloe vera is considered one of the most valuable medicinal plants with a wide range of applications. Extracted Aloe vera was used as functional monomers for the first time to prepare new IIPs, epichlorohydrin, and Cu²⁺ ion as the cross-linking agent and template, respectively. The NIP was also synthesized for comparison, without the use of the Cu²⁺ salt. Following polymerization, the IIP particles were cleansed of template ions through a 0.1 M EDTA leaching process, resulting in the formation of cavities within the particles, these cavities in the polymer provide selective linking zones for these specific template ions. The synthesized IIPs were characterized using the most recent identification instruments. The experimental parameters for adsorption, such as pH of a solution, contact time, initial copper concentration, adsorbent dosage, and temperature have been optimized. The most effective conditions for metal adsorption onto the ionic imprinted polymer were found to be a pH of 8.0, a temperature of 30 °C, a concentration of 0.03 g/100 mL, and a contact time of 50 min. Based on the ANOVA statistical value, the adsorption of Cu²⁺ ion on IIP is significant with very low probability (p) values (<0.001). The Langmuir isotherm model and a second-order reaction were both used in the adsorption process. According to thermodynamic characteristics, Cu²⁺ adsorption over IIPs and NIP was an endothermic, spontaneous process. Compared to NIP, the imprinted polymer exhibits a significantly better capacity and selectivity for Cu²⁺ adsorption, the maximum removal percentage of IIPs and NIP was 96.02 % and 74.3 % respectively. Moreover, the research showed that ion imprinting can be a promising technique for preparing selective adsorbents to separate and preconcentrate metal in a medium of multiple competitive metals (Co²⁺, Cd²⁺, Ni²⁺, Zn²⁺, Fe²⁺, and Pb²⁺) The most important point for this new Cu²⁺-IIPs was shown superior reusability up to 8 cycles with small decrees in uptake capability.

Highly Efficient Elimination of Pb+2 and Al+3 Metal Ions from Wastewater Using Graphene Oxide/3,5-Diaminobenzoic Acid Composites: Selective Removal of Pb2+ from Real Industrial Wastewater

In this study, graphene oxide (GO) was functionalized with 3,5-diaminobenzoic acid (DABA) by a one-step method to produce functionalized graphene oxide (FGO). FGO is a new type of absorbent crystalline substance that has a high surface area and a large porosity site as well as a large number of dentate functional groups which lead to enhanced adsorption performance for heavy metal ions. The adsorption efficiency of FGO for Pb⁺² and Al⁺³ metal ions was extra satisfactory when compared with GO due to the ease of design and the homogeneous structure of FGO. The structure of synthesized GO and FGO was confirmed by different techniques such as FTIR, XRD, TGA, BET nitrogen adsorption-desorption methods, and TEM analyses. The mass of utilized adsorbents, the pH of the medium, the concentration of ionic species in the medium, temperature, and process time were all investigated as variables in the adsorbent procedure. The experimental data recorded that the maximum adsorption efficiency of the 0.5 g/L FGO composite was 99.7 and 99.8% for Pb⁺² and Al⁺³ metal ions, respectively, while in the case of using GO, the maximum adsorption efficiency was 92.6 and 91.9% at ambient temperature in a semineutral medium at pH 6 after 4 h. The adsorption results were in good conformity with the Freundlich model and pseudo-second-order kinetics for Pb⁺² and Al⁺³ metal ions. Also, the reusability study indicates that FGO can be used repeatedly at least for five cycles with a slight significant loss in its efficiency.

A novel stochastic wastewater quality modeling based on fuzzy techniques

Measurement and prediction of wastewater quality parameters are crucial for evaluating the risk to the receiving waters. This study presents new methods for the identification of outlier data and smoothing as an effective pre-processing technique prito to modelling. This new data processing method uses a combination of the autoregressive integrated moving average (ARIMA) model and -the adaptive neuro fuzzy inference system with fuzzy C-means clustering (FCM) (ANFIS-FCM). These new pre-processing methodsare compared to previously employed non-linear approaches for modelling of wastewater influent/effluent 5-day biochemical oxygen demand (BOD₅), chemical oxygen demand (COD) and total suspended solids (TSS). Linear modelling of each parameter, 242 linear models, were investigated, and a linear model for each parameter was selected. The results of the non-linear models led to an acceptable prediction for qualitative parameters so that the high coefficient of determination (R ² ) was observed for the influent and effluent BOD and TSS, respectively. The range of the R ² for all models was recorded as 0.8-0.87 and 0.83-0.89, respectively. By a combination of the linear and non-linear mothods a hybrid model was introduced. The proposed hybrid model for the influent BOD with the highest correlation between the observed and predicted values, and limited scattering was identified as the optimal model (R² = 0.95). The use of hybrid models to predict wastewater quality parameters improved the performance and efficiency of the models. In addition, a comparison of the hybrid model with the recently developed models in the literature indicates that the developed ARIMA-ANFIS-FCM outperformed other models.

Modeling of chromium (VI) removal from aqueous solution using modified green-Graphene: RSM-CCD approach, optimization, isotherm, and kinetic studies

BACKGROUND

The aim of this study was to investigate the removal of Cr (VI) using Green-Graphene Nanosheets (GGN) synthesized from rice straw.

METHODS

Synthesis of the GGN was optimized using response surface methodology and central composite design (CCD). The effect of two independent variables including KOH-to-raw rice ash (KOH/RRA) ratio and temperature on the specific surface area of the GGN was determined. To have better removal of Cr (VI), GGN was modified using the grafting amine group method. In the Cr (VI) removal process, the effects of four independent variables including initial Cr (VI) concentration, adsorbent dosage, contact time, and initial solution pH were studied.

RESULTS

The results of this study showed that the optimum values of the KOH/RRA ratio and temperature for the preparation of GGN were 10.85 and 749.61 °C, respectively. The maximum amount of SSA obtained at optimum conditions for GGN was 551.14 ± 3.83 m 2 /g. The optimum conditions for Cr (VI) removal were 48.35 mg/L, 1.46 g/L, 44.30 min, and 6.87 for Cr (VI) concentration, adsorbent dosage, contact time, and pH, respectively. Based on variance analysis, the adsorbent dose was the most sensitive factor for Cr (VI) removal. Langmuir isotherm (R2 = 0.991) and Pseudo-second-order kinetic models (R2 = 0.999) were the best fit for the study results and the Q max was 138.89 mg/g.

CONCLUSIONS

It can be concluded that the predicted conditions from the GGN synthesis model and the optimum conditions from the Cr (VI) removal model both agreed with the experimental findings.

The fabrication of a thiol-modified chitosan magnetic graphene oxide nanocomposite and its adsorption performance towards the illegal drug clenbuterol in pork samples

A novel thiol (provided by (3-mercaptopropyl) trimethoxysilane, MPTS)-modified chitosan magnetic graphene oxide nanocomposite (Fe₃O₄@SiO₂/GO/CS/MPTS) was synthesized and characterized for the first time as an efficient magnetic sorbent for the enrichment and extraction of trace levels of clenbuterol in pork samples (muscle, fat, heart and liver). Various greatly influential parameters were optimized using a Box-Behnken design (BBD) through the response surface methodology (RSM) to obtain more satisfactory recovery. Under optimum conditions, the method detection limits (MDLs) were in the range of 0.054-0.136 ng g^-1. The recoveries of three spiked levels ranged from 84.7% to 101.1%, and the relative standard deviations (RSDs) were lower than 9.3%. The results of the adsorption experiments showed that the maximum adsorption capacity of Fe₃O₄@SiO₂/GO/CS/MPTS for clenbuterol was 214.13 mg g^-1. The adsorption process was most consistent with pseudo second-order kinetics and Langmuir adsorption isotherm, indicating a homogeneous process with a chemisorptive nature. Also, the nanocomposite exhibited high adsorption capability for clenbuterol compared with Fe₃O₄@SiO₂/GO and Fe₃O₄@SiO₂/GO/CS. In addition, regeneration of the nanocomposite was effectively achieved, and it retained about 82% of its initial capacity after four cycles. All these results indicate that the synthetic nanocomposite is a promising efficient adsorbent for the adsorption of clenbuterol with high adsorption capacity and low cost.

Phytostabilization of Polluted Military Soil Supported by Bioaugmentation with PGP-Trace Element Tolerant Bacteria Isolated from Helianthus petiolaris

Lead (Pb) and cadmium (Cd) are major environmental pollutants, and the accumulation of these elements in soils and plants is of great concern in agricultural production due to their toxic effects on crop growth. Also, these elements can enter into the food chain and severely affect human and animal health. Bioaugmentation with plant growth-promoting bacteria (PGPB) can contribute to an environmentally friendly and effective remediation approach by improving plant survival and promoting element phytostabilization or extraction under such harsh conditions. We isolated and characterised Pb and Cd-tolerant root-associated bacteria from Helianthus petiolaris growing on a Pb/Cd polluted soil in order to compose inoculants that can promote plant growth and also ameliorate the phytostabilization or phytoextraction efficiency. One hundred and five trace element-tolerant rhizospheric and endophytic bacterial strains belonging to eight different genera were isolated from the aromatic plant species Helianthus petiolaris. Most of the strains showed multiple PGP-capabilities, ability to immobilise trace elements on their cell wall, and promotion of seed germination. Bacillus paramycoides ST9, Bacillus wiedmannii ST29, Bacillus proteolyticus ST89, Brevibacterium frigoritolerans ST30, Cellulosimicrobium cellulans ST54 and Methylobacterium sp. ST85 were selected to perform bioaugmentation assays in greenhouse microcosms. After 2 months, seedlings of sunflower (H. annuus) grown on polluted soil and inoculated with B. proteolyticus ST89 produced 40% more biomass compared to the non-inoculated control plants and accumulated 20 % less Pb and 40% less Cd in the aboveground plant parts. In contrast, B. paramycoides ST9 increased the bioaccumulation factor (BAF) of Pb three times and of Cd six times without inhibiting plant growth. Our results indicate that, depending on the strain, bioaugmentation with specific beneficial bacteria can improve plant growth and either reduce trace element mobility or enhance plant trace element uptake.

Photochemical degradation of toluene in gas-phase under UV/visible light graphene oxide-TiO2 nanocomposite: influential operating factors, optimization, and modeling

The current study aimed to investigate the removal efficiency of toluene using synthesized titanium dioxide-graphene oxide composites under visible light and UV irradiation. The characterization of synthesized composites was examined by field emission scanning electron microscope equipped with energy dispersive, X-ray diffraction and fourier transforms infrared. In order to find the optimum of the main experimental parameters affecting the removal efficiency of toluene including the length of the reactor, initial concentration, and flow rates, central composite design together with response surface methodology with R software was used. The initial concentration of toluene in the inlet of the reactor as well as its concentration in the outlet was measured using gas chromatography with the flame ionization detector. Analysis of variance results for the quadratic model showed that the highly significant and simple linear regression was established as a predicting model. Multiple and adjusted R² were 0.965 and 0.974 for UV irradiation GO-TiO₂ model and 0.951 and 0.959 for visible light GO-TiO₂ model, respectively. As such, the differences less than 0.2 between multiple and adjusted R² in two models indicate that two examined models were fitted well. The highest removal efficiency of toluene using UV irradiation GO-TiO₂ and visible light GO-TiO₂ was obtained at optimum condition; length of reactor 40 cm, initial concentration of 0.1 ppm, and flow rate equal to 1 l min^-1, with 97.7 and 77.2%, respectively. The results indicated that the removal efficiency of toluene increased considerably with rising the length of the reactor, decreasing flow rates, and initial concentration.

Graphene Quantum Dots in Electrochemical Sensors/Biosensors

Background:

Graphene and its derivatives, as most promising carbonic nanomaterials have been widely used in design and making electrochemical sensors and biosensors. Graphene quantum dots are one of the members of this family which have been mostly known as fluorescent nanomaterials and found extensive applications due to their remarkable optical properties. Quantum confinement and edge effects in their structures also cause extraordinary electrochemical properties.

Objective:

Recently, graphene quantum dots besides graphene oxides and reduced graphene oxides have been applied for modification of the electrodes too and exposed notable effects in electrochemical responses. Here, we are going to consider these significant effects through reviewing some of the recent published works.

Exposure to heavy metals released to the environment through breastfeeding: A probabilistic risk estimation

Toxic heavy metals released into the environment through various anthropogenic activities, raising concerns over their potential adverse effects on human health and the environment. Biological monitoring studies are of great value in toxicological research for estimation of such health effects. The aim of this study was to evaluate the concentrations of lead (Pb), arsenic (As), and chromium (Cr) in the breast milk of urban mothers in Hamadan city, Iran and the accompanying health risk to infants. A total of 100 lactating mothers were recruited from public health care centers in Hamadan city and breast milk samples were collected at 2, 6, 8, and 12 months postpartum. Inductively coupled plasma mass spectroscopy (ICP-MS) has been used to measure target heavy metal concentrations. The median breast milk concentrations of Pb, As, and Cr were 41.90, 0.50, and 3.95 μg/L, respectively. The highest levels of Pb were observed after two months of delivery (with the mean of 96.69 μg/L and median of 45.70 μg/L). Up to 94% of the breast milk samples exceeded the WHO limit suggested for lead contamination of breast milk (<5 μg/L). The breast milk As and Cr contents were above the limit of detection (LOD) in 19% and 76% of samples, respectively. Unacceptable non-cancer health risk levels or hazard quotient (HQ) were found for Pb and As in 61% and 10% of the samples, respectively. Nevertheless, HQ from Cr was <1.0 for 100% of breastfeeding infants. Finally, our results indicated that there may be a potential risk of toxic metals, especially lead, for infants in Hamadan via the consumption of mothers' breast milk.

Hexavalent chromium removal from aqueous solution using functionalized chitosan as a novel nano-adsorbent: modeling and optimization, kinetic, isotherm, and thermodynamic studies, and toxicity testing

Hexavalent chromium is a highly toxic metal that can enter drinking water sources. Chitosan, which contains amino and hydroxyl functional groups, is considered an appropriate candidate to remove heavy metals through absorption. In this study, a novel adsorbent, magnetic nanoparticles of chitosan modified with polyhexamethylene biguanide (Ch-PHMB NPs) was synthesized and was used to successfully remove chromium from aqueous solution. Quadratic models with independent variables including pH, adsorbent dosage, time, and the initial concentration of chromium were proposed through RSM to describe the behavior of both magnetic chitosan (M-Ch) and Ch-PHMB NPs in Cr(VI) removal. Optimized models with adjusted R² values of 0.8326 and 0.74 for M-Ch and Ch-PHMB NPs were developed. Cr(VI) removal from aqueous solution by both absorbents followed pseudo-second-order kinetics. The experimental data were best fitted to the Temkin and Freundlich models for M-Ch and Ch-PHMB NPs, respectively. M-Ch and Ch-PHMB NPs can effectively remove the hexavalent chromium from aqueous solution with pH above 7. Ch-PHMB NPs have higher removal efficiency than M-Ch, removing up to 70% of Cr(VI) from aqueous solution. However, toxicity evaluation on Daphnia magna revealed that Ch-PHMB NPs was more toxic than M-Ch nanoparticles.

Synthesis and characterization of anthill-eggshell composite adsorbent for removal of hexavalent chromium from aqueous solution

In this study, adsorption behavior of anthill-eggshell composite (AEC) for the removal of hexavalent chromium (Cr⁶⁺) from aqueous solution was investigated. The raw AEC sample was thermally treated at 864 °C for 4 h and characterized using Brunauer-Emmett-Teller (BET), scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), and X-ray fluorescence (XRF) techniques. The effects of adsorption process variables including initial Cr⁶⁺ concentration, contact time, and adsorbent dosage on the Cr⁶⁺ removal efficiency were investigated using central composite design (CCD) of response surface methodology (RSM). Equilibrium adsorption isotherm and kinetic were also studied. From the analysis of variance (ANOVA), the three variables proved to be significant and the optimum conditions for Cr⁶⁺ adsorption were obtained to be 150 mg/L initial Cr⁶⁺ concentration, 45.04-min contact time, and 0.5 g adsorbent dosage, which resulted in 86.21% of Cr⁶⁺ adsorbed. Equilibrium isotherm study showed that Freundlich model fitted well to the experimental data. The pseudo-second-order kinetic model appeared to better describe the experimental data. The study showed that mixed anthill-eggshell is a promising adsorbent for removing Cr⁶⁺ from aqueous solution.

Size characterization of silver nanoparticles after separation from silver ions in environmental water using magnetic reduced graphene oxide

This study involved the synthesis of magnetic reduced graphene oxide (M-rGO) using a co-precipitation method and examined its resultant adsorption properties for mixtures containing silver ions and silver nanoparticles (AgNPs). The results indicate that M-rGO preferentially adsorbs silver ions in mixtures containing AgNPs, enabling the size characterization of smaller AgNPs (<60nm) at ultra-trace concentration levels to be more attainable. The sorbents after adsorption could be easily recovered through an external magnet. The AgNPs retained in solution were characterized using single-particle ICPMS (SP-ICPMS). The adsorption behavior of silver ions on M-rGO was well fitted with the pseudo-second-order kinetic model and the Freundlich adsorption isotherm model, with the conclusion that the adsorption of silver ions occurred primarily through the chemical bond effect and the heterogeneous surface of the sorbent. Finally, the application of M-rGO with the approach developed herein to actual environmental water samples was successful.

Selective removal of lead ions from aqueous solutions using 1,8-dihydroxyanthraquinone (DHAQ) functionalized graphene oxide; isotherm, kinetic and thermodynamic studies

The Fe₃O₄@DHAQ_GO nanocomposite can serve as an efficient adsorbent for the selective removal of lead from polluted water.

A novel technique for detoxification of phenol from wastewater: Nanoparticle Assisted Nano Filtration (NANF)

BACKGROUND

Phenol is one of the most versatile and important organic compound. It is also a growing concern as water pollutants due to its high persistence and toxicity. Removal of Phenol from wastewaters was investigated using a novel nanoparticle adsorption and nanofiltration technique named as Nanoparticle Assisted Nano Filtration (NANF).

METHODS

The nanoparticle used for NANF study were silver nanoparticles and synthesized to three distinct average particle sizes of 10 nm, 40 nm and 70 nm. The effect of nanoparticle size, their concentrations and their tri and diparticle combinations upon phenol removal were studied.

RESULTS

Total surface areas (TSA) for various particle size and concentrations have been calculated and the highest was 4710 × 10(12 )nm(2 )for 10 nm particles and 180 ppm concentration while the lowest was for 2461 × 10(11) for 70 nm and 60 ppm concentrations. Tri and diparticle studies showed more phenol removal % than that of their individual particles, particularly for using small particles on large membrane pore size and large particles at low concentrations. These results have also been confirmed with COD and toxicity removal studies.

CONCLUSIONS

The combination of nanoparticles adsorption and nanofiltration results in high phenol removal and mineralization, leading to the conclusion that NANF has very high potential for treating toxic chemical wastewaters.