Removal of emerging contaminants from the environment by adsorption

Recent applications of carbonaceous nanosorbents for the analysis of mycotoxins in food by liquid chromatography: a short review

Carbonaceous nanomaterials (multi-walled carbon nanotubes (MWCNTs), graphene, and graphene oxide (GO)) have attracted attention over the last decade as adsorbents suitable for the analysis of organic and inorganic pollutants. In the present paper we review methods of mycotoxin analysis that involve sample extraction with carbonaceous nanosorbents, reported from 2011 onwards. Recent studies have highlighted the advantages of magnetically modified MWCNTs and GO in mycotoxin analysis, which may enable sample isolation through magnetic separation, reduce the interaction of nanoparticles, and enhance the recovery of analytes. The papers covered in this review point to promising applications of functionalised carbonaceous nanosorbents in mycotoxin analysis. While GO based sorbents can be effective for the adsorption of relatively polar aflatoxins, MWCNTs with high specific surface area and reduced agglomeration achieved through modification with silica and magnetic particles are preferred for the extraction of less polar mycotoxins.

Kinetic, equilibrium, and thermodynamic studies on the adsorption of ciprofloxacin by activated carbon produced from Jerivá (Syagrus romanzoffiana)

High specific surface area activated carbon prepared from endocarp of Jerivá (Syagrus romanzoffiana) (ACJ) was used for ciprofloxacin (CIP) antibiotic removal from aqueous effluents. The activated carbon (AC) was characterized via scanning electron microscope, Fourier transform infrared spectroscopy, N₂ adsorption/desorption, and pH value at the zero-charge point. Avrami kinetic model was the one that best fit the experimental results in comparison to the pseudo-first-order and pseudo-second-order kinetic models. The equilibrium data obeyed the Liu isotherm equation, showing a maximum adsorption capacity of 335.8 mg g^-1 at 40 °C. The calculated thermodynamic parameters indicate that the adsorption of CIP was spontaneous and endothermic at all studied temperatures. Also, the free enthalpy changes (∆H° = 3.34 kJ mol^-1) suggested physical adsorption between CIP and ACJ. Simulated effluents were utilized to check the potential of the ACJ for wastewater purification. The highly efficient features enable the activated carbon prepared from endocarp of Jerivá, an attractive carbon adsorbent, to remove ciprofloxacin from wastewaters.

Preparation of Magnetic Fe₃O₄/MIL-88A Nanocomposite and Its Adsorption Properties for Bromophenol Blue Dye in Aqueous Solution

Metal-organic frameworks (MOFs) are considered as good materials for the adsorption of many environmental pollutants. In this study, magnetic Fe₃O₄/MIL-88A composite was prepared by modification of MIL-88A with magnetic nanoparticles using the coprecipitation method. The structures and magnetic property of magnetic Fe₃O₄/MIL-88A composite were characterized and the adsorption behavior and mechanism for Bromophenol Blue (BPB) were evaluated. The results showed that magnetic Fe₃O₄/MIL-88A composite maintained a hexagonal rod-like structure and has good magnetic responsibility for magnetic separation (the maximum saturation magnetization was 49.8 emu/g). Moreover, the maximum adsorption amount of Fe₃O₄/MIL-88A composite for BPB was 167.2 mg/g and could maintain 94% of the initial adsorption amount after five cycles. The pseudo-second order kinetics and Langmuir isotherm models mostly fitted to the adsorption for BPB suggesting that chemisorption is the rate-limiting step for this monomolecular-layer adsorption. The adsorption capacity for another eight dyes (Bromocresol Green, Brilliant Green, Brilliant Crocein, Amaranth, Fuchsin Basic, Safranine T, Malachite Green and Methyl Red) were also conducted and the magnetic Fe₃O₄/MIL-88A composite showed good adsorption for dyes with sulfonyl groups. In conclusion, magnetic Fe₃O₄/MIL-88A composite could be a promising adsorbent and shows great potential for the removal of anionic dyes containing sulfonyl groups.

Pharmaceuticals and pesticides in secondary effluent wastewater: Identification and enhanced removal by acid-activated ferrate(VI)

The emergence of resistance to antibacterial drugs and pesticides in water is unprecedented. This may have adverse consequences to human health and ecological systems. This paper first sought the identification of a wide range of pharmaceuticals and pesticides in two secondary effluent wastewaters (SEW) of different quality characteristics, followed by their removal by ferrate(VI) (Fe(VI), FeO₄^2-). Screening for 22 pharmaceuticals and 32 pesticides, revealed that 11 pharmaceuticals and 3 pesticides in SEW of plant A, and 14 pharmaceuticals and 5 pesticides in SEW of plant B were present at concentrations higher than the liquid chromatography mass spectrometry method quantitation limit. The concentrations of pharmaceuticals and pesticides ranged from 0.15 ng/L-413.03 ng/L. Investigation of the removal of these pharmaceuticals and pesticides by Fe(VI) showed that some had recalcitrant activity towards their oxidation. Acid-activated Fe(VI) resulted in enhanced oxidation (12.6%-56.2% degradation efficiency) of 6 and 7 pharmaceuticals in SEW of plant A and plant B, respectively, at a shorter time than Fe(VI) without activation (i.e. 3-5 min versus 15-30 min). The degradation of 1 and 3 pesticides in SEW of plant A and plant B respectively, has also been enhanced by activating Fe(VI) (13.8%-86.2% degradation efficiency). Results on testing of organic matter characterization of treated SEW with and without acid-activated Fe(VI) treatment are also presented. Acid-activated Fe(VI) treatment has potential in enhancing the removal of micropollutants in real wastewater.

Physicochemical Properties of Activated Carbon: Their Effect on the Adsorption of Pharmaceutical Compounds and Adsorbate–Adsorbent Interactions

The adsorption of salicylic acid, acetaminophen, and methylparaben (pharmaceutical products derived from phenol) on carbons activated with different surface chemistries was carried out. We evaluated the effect of the physicochemical properties of the adsorbent and adsorbates on the adsorption capacity. A study of the adsorbate–adsorbent interactions via immersion calorimetry in the analytes solutions at different concentrations was included, in addition to the equilibrium data analysis. The results show that the pharmaceutical compounds (2.28–0.71 mmol g−1) have lower adsorption capacities in the activated carbon with the highest content of oxygenated groups (acids), while the activated carbons with amphoteric characteristics increase the capacities of adsorption (2.60–1.38 mmol g−1). This behavior may be associated with the increased affinity between the adsorbent and solvent due to the presence of polar groups, which was corroborated by the high immersion enthalpy value in water (ΔHimmH2O = −66.6 J g−1). The equilibrium data, adjusted to the Freundlich adsorption model, indicated that the heterogeneous adsorption processes involve immersion enthalpy values between −9.42 and −24.3 J g−1.

Facile synthesis of Fe3O4@MOF-100(Fe) magnetic microspheres for the adsorption of diclofenac sodium in aqueous solution

In this research, the adsorptive removal of diclofenac sodium, one of the representative pharmaceuticals and personal care products, from aqueous solution using Fe₃O₄@MOF-100(Fe) magnetic microspheres was studied for the first time. The Fe₃O₄@MOF-100(Fe) microspheres exhibit strong magnetism and stability, which were observed as a core-shell structure. The maximum adsorption capacity of Fe₃O₄@MOF-100(Fe) for diclofenac sodium can reach 377.36 mg L^-1, which was higher than most of the adsorbents reported. The adsorption kinetics follows the pseudo-second-order kinetic equation. And the adsorption equilibrium of DCF can be described with Langmuir isotherm. In the cycle experiment, Fe₃O₄@MOF-100(Fe) material performed high adsorption efficiency for low-concentration diclofenac sodium solution, and the removal rate can still reach 80% after 5 cycles of adsorption without desorption. The mechanisms including electrostatic interaction, H-bond interaction, and π-π interaction that coexisted in the adsorption processes would be of benefit to enhance the adsorption capacity. The Fe₃O₄@MOF-100(Fe) magnetic microspheres offer exciting opportunities for further application.

Mesoporous activated carbon from starch for superior rapid pesticides removal

Pesticides contamination of water has caused considerable concern due to the potential hazard to human health. For the first time, mesoporous activated carbon from starch (ACS) was applied to remove pesticides from water. ACS could remove 11 pesticides rapidly (shake five times). The adsorption rates of ACS (>80%) for the 11 pesticides were higher than those of other adsorbents, including commercial activated carbon (AC), graphitised carbon black (GCB), C18, and primary secondary amine adsorbent (PSA). The mechanisms of the adsorption process for pyraclostrobin were also investigated. The pseudo-second-order model could better describe the adsorption for pyraclostrobin (R² = 0.99950). Langmuir model gave the best fit for the isotherm data (R² = 0.99899). Our findings demonstrate that oxygen-containing functional groups, N atom and π-bonding network of benzene promoted the adsorption. The adsorption efficiency of the ACS for 11 pesticides was still over 80% after five cycles.

Polyaniline-derived porous carbons: Remarkable adsorbent for removal of various hazardous organics from both aqueous and non-aqueous media

Polyaniline (pANI) was pyrolyzed under a nitrogen atmosphere to get porous pANI-derived carbons (PDCs). To increase the porosity of the carbons further, the PDCs were activated at 600-800 °C in the presence of KOH. The obtained PDCs were firstly applied in liquid-phase adsorptions in order to remove hazardous organics from both water and fuel effectively via adsorption. PDC-700, activated at 700 °C, showed record high adsorption capacities from water for the removal of hazardous organics such as diethyl phthalate and Janus Green B, as representative organics for industrial chemicals (endocrine disturbing agent) and organic dyes, respectively. Moreover, PDC-700 had record high adsorption capacity for the removal of 4,6-dimethyldibenzothiophene from a model fuel. The plausible mechanisms were also suggested to explain the remarkable adsorptions both from water and fuel. The adsorbents could be regenerated in a facile way and reused in adsorption up to several cycles. Therefore, the PDCs could be suggested as a new class of adsorbents for the purification of both water contaminated with organics and fuel having a high concentration of thiophenics.

Effect of magnetic ion exchange (MIEX®) on removal of emerging organic contaminants

In this study, the removal of nine emerging organic contaminants was investigated by using anion exchange resins. The selected compounds were carbamazepine, atrazine, simazine, estrone, bisphenol A, methylparaben, ethylparaben, propylparaben and butylparaben. Two different magnetic anionic exchanger resins were tested: MIEX^® DOC and MIEX^® GOLD. The optimal resin dose (40 mL/L) and contact time (20 min) had been previously determined. Once these optimum parameters were set, the effect of the initial concentration of contaminants on the removal efficiency of the contaminants by the resins was studied. The study was carried out using mono and multicomponent systems, with distilled water and natural waters, to which contaminants had been previously added, in order to evaluate the competitive and matrix effects. Results showed that the average removal percentages obtained with the MIEX^® DOC resin were: 51%, 61%, 68% and 80% for methyl-, ethyl-, propyl-, and butylparaben, respectively. For bisphenol A the result was similar, i.e., 66%, whereas for the rest of the compounds studied, removal efficiencies lower than 15% were obtained. The MIEX^® GOLD resin achieved lower elimination rates than the MIEX^® DOC resin in all cases.

Adsorption mechanism of emerging and conventional phenolic compounds on graphene oxide nanoflakes in water

Emerging contaminants (ECs) such as bisphenol A (BPA), 4-nonylphenol (4-NP) and tetrabromobisphenol A (TBBPA) have gained immense attention worldwide due to their potential threat to humans and environment. Graphene oxide (GO) nanomaterial is considered as an important sorbent due to its exceptional range of environmental application owing to its unique properties. GO was also considered as one of ECs because of its potential hazard. The adsorption of organic contaminants such as phenolic ECs on GO affects the stability of GO nanoflakes in water and the fate of organic contaminants, which would cause further environmental risk. Therefore, the adsorption behaviors of emerging and common phenolic compounds (PCs) including phenol, 4-chlorophenol, 2,4-dichlorophenol, 2,4,6-trichlorophenol, 4-NP, BPA and TBBPA on GO nanoflakes and their stability in water were studied. The adsorption equilibrium for all the compounds was reached <10h and was fitted with Langmuir and Freundlich isotherms. In addition to hydrophobic effect, adsorption mechanisms included π-π bonding and hydrogen bonding interactions between the adsorbate and GO, especially the electrostatic interactions were observed. Phenol has the highest adsorption affinity due to the formation of hydrogen bond. GO has a good stability in water even after the adsorption of PCs in the presence of a common electrolyte, which could affect its transport with organic contaminants in the environment. These better understandings illustrate the mechanism of emerging and common PC interaction with GO nanoflakes and facilitate the prediction of the contaminant fate in the aquatic environment.

Adsorption Separation of Analgesic Pharmaceuticals from Ultrapure and Waste Water: Batch Studies Using a Polymeric Resin and an Activated Carbon

The performance of a polymeric resin (Sepabeads SP207, from Resindion, Binasco, Italy) was compared with that of an activated carbon (GPP20, from Chemviron Carbon, Feluy, Belgium) in the adsorption of acetaminophen and ibuprofen from either ultrapure or waste water. Kinetic and equilibrium adsorption experiments were carried out under batch operation conditions, and fittings of the obtained results to different models were determined. The kinetic experimental results fitted the pseudo-first and -second order equations, and the corresponding kinetic rates evidenced that the pharmaceuticals adsorption was faster onto GPP20 than onto Sepabeads SP207, but was mostly unaffected by the aqueous matrix. The equilibrium results fitted the Langmuir-Freundlich isotherm model. The corresponding maximum adsorption capacity (Qm, mg-1) was larger onto GPP20 (202 mg g-1 ≤ Qm ≤ 273 mg g-1) than onto the polymeric resin (7 mg g-1 ≤ Qm ≤ 18 mg g-1). With respect to the parameter KLF (mg g-1 (mg L-1)-1/n), which points to the adsorbent-adsorbate affinity, greater values were determined for the pharmaceuticals adsorption onto GPP20 than onto Sepabeads SP207. For both adsorbents and pharmaceuticals, neither Qm or KLF were affected by the aqueous matrix.

Equilibrium and kinetic studies of the adsorption of antibiotics from aqueous solutions onto powdered zeolites

The performances of two FAU-type zeolites with different SiO₂/Al₂O₃ ratios were evaluated for the removal of antibiotics of three different classes, namely azithromycin, ofloxacin, and sulfamethoxazole, from aqueous solutions. Commercial zeolites were used, without any previous treatment. Use of a small adsorbent dosage resulted in fast antibiotic adsorption that followed pseudo-second order kinetics. The removals of azithromycin and sulfamethoxazole were highly pH-dependent, with low removal percentages observed under acid (pH 2.5-4.5) and basic (pH 8.5-10.5) conditions, respectively. The Freundlich isotherm model provided the best fits to the adsorption data. The adsorption mechanisms appeared to involve both electrostatic and H-bonding interactions. Using an antibiotics mixture, percentage removals of azithromycin and ofloxacin onto the zeolites of up to 79% were obtained. Both materials presented good adsorption (>50%) of azithromycin and ofloxacin from a real sample of effluent wastewater. The results showed that zeolites with FAU structure can be used as effective adsorbents for the removal of antibiotics with different physicochemical properties, including molecules with large volumes, such as azithromycin.

Development of CO2 activated biochar from solid wastes of a beer industry and its application for methylene blue adsorption

An alternative activated biochar was developed from barley malt bagasse (BMB) through pyrolysis followed by CO₂ activation. The materials BMB, biochar and activated biochar (CO₂-biochar) were characterized and tested as adsorbents for the removal of methylene blue (MB) from aqueous solutions. Adsorption kinetics, equilibrium and thermodynamics were studied. It was found that BMB and biochar presented surface area values lower than 1 m² g^-1, while CO₂-biochar was a typical mesoporous material with surface area around 80 m² g^-1. As consequence, the adsorption potential for methylene blue was in the following order CO₂-biochar ≫ biochar > BMB. Adsorption kinetics of MB on CO₂-biochar followed the pseudo-second order model. Langmuir presented the best fit with the equilibrium adsorption isotherms. The maximum adsorption capacity was 161 mg g^-1. MB adsorption on CO₂-biochar was spontaneous, favorable and exothermic. Pyrolysis followed by CO₂ activation was a suitable route to produce an alternative mesoporous adsorbent from barley malt bagasse.

Conversion of Eragrostis plana Nees leaves to activated carbon by microwave-assisted pyrolysis for the removal of organic emerging contaminants from aqueous solutions

Eragrostis plana Nees leaves, abundant lignocellulosic biomass, was used as carbon source for preparation of activated carbon, by using microwave-assisted pyrolysis and chemical activation. The novel activated carbon (MWEPN) was characterised by FTIR, CHN elemental analysis, Boehm's titration method, TGA, SEM, N₂ adsorption/desorption curves and pH of the point of zero charge (pH_pzc). Afterwards, the adsorbent was successfully employed for adsorption of the two emerging contaminants (caffeine and 2-nitrophenol). The results indicated that MWEPN had a predominantly mesoporous structure with a high surface area of 1250 m² g^-1. FTIR analysis indicated the presence of carbonyl, hydroxyl and carboxylic groups on the surface of MWEPN. The Boehm analysis showed the existence of the high amount of acid moieties on the surface of activated carbon. Adsorption kinetic indicated that the system followed the Avrami fractional order at the optimal pH of 7. The equilibrium time was attained at 30 min. The Liu isotherm model better described the isothermal data. Based on the Liu isotherm, the maximum sorption capacities (Q_max) of caffeine and 2-nitrophenol adsorbed onto activated carbon at 25 °C were 235.5 and 255.8 mg g^-1, respectively.

Removal of Patent Blue (V) Dye Using Indian Bael Shell Biochar: Characterization, Application and Kinetic Studies

The prospective utilization of bael shell (Aegle marmelos) as an agro-waste for the production of biochar was investigated along with its characterization and application for the abatement of hazardous aqueous Patent Blue (PB) dye solution. The sorptive removal of PB on bael shell biochar (BSB) was investigated under the following operational conditions: (pH, 2.7–10.4; biochar dosage, 2–12 g/L; and contact time, 0–60 min). The removal efficiency of PB by BSB in a batch adsorption experiment was 74% (pH 2.7 and 30 ± 5 °C). In addition, a clear relationship between the adsorption and pH of the solution was noticed and the proposed material recorded a maximum sorption capacity of 3.7 mg/g at a pH of 2.7. The adsorption of PB onto BSB was best explained by the pseudo-second order kinetic model (R2 = 0.972), thereby asserting the predominant role of chemisorption. The active role of multiple surface-active functionalities present on BSB during PB sorption was elucidated with the help of Freundlich isotherm (R2 = 0.968). Further, an adsorption mechanism was proposed by utilizing Fourier transform infrared spectroscopy (FTIR).

Removal of priority and emerging pollutants from aqueous media by adsorption onto synthetic organo-funtionalized high-charge swelling micas

In this work, the removal of different types of emerging pollutants (four perfluoroalkyl compounds, two preservatives, three surfactants and nine pharmaceutical compounds) from aqueous solution by adsorption onto two novel synthetic clays, a high-charge swelling mica (Na-Mica-4) and an organo-functionalized mica (C₁₈-Mica-4), was evaluated. Na-Mica-4 and C₁₈-Mica- 4 were prepared and characterized by X-Ray diffraction, Zeta potential, specific surface area, thermogravimetric analysis and transmission electron microscopy, before and after adsorption experiments. The influence of the aqueous sample pH, salt addition and extraction time in the removal were evaluated. The results showed the high adsorption affinity of C₁₈-Mica-4 for most of the emerging pollutants analysed after a removal time of 24 h (14 out of 18 pollutants were effectively removed [70-100%]). A high correlation was observed between the log K_ow of the selected emerging pollutants and the adsorption onto C₁₈-Mica-4. The results also indicate that adsorption occurs in the interlayer space. While the removal rates with Na-Mica-4 were in the range 8-97% after seven days, some of the compounds, perfluorobutanoic acid and most of pharmaceutically active compounds, were not adsorbed onto the high-charge mica. C₁₈-Mica- 4 was effectively used for the removal of contaminants from four types of water samples.