Adsorption of contaminants by nanomaterials synthesized by green and conventional routes: a critical review.

Nanomaterials, due to their large surface area and selectivity, have stood out as an alternative for the adsorption of contaminants from water and effluents. Synthesized from green or traditional protocols, the main advantages and disadvantages of green nanomaterials are the elimination of the use of toxic chemicals and difficulty of reproducing the preparation of nanomaterials, respectively, while traditional nanomaterials have the main advantage of being able to prepare nanomaterials with well-defined morphological properties and the disadvantage of using potentially toxic chemicals. Thus, based on the particularities of green and conventional nanomaterials, this review aims to fill a gap in the literature on the comparison of the synthesis, morphology, and application of these nanomaterials in the adsorption of contaminants in water. Focusing on the adsorption of heavy metals, pesticides, pharmaceuticals, dyes, polyaromatic hydrocarbons, and phenol derivatives in water, for the first time, a review article explored and compared how chemical and morphological changes in nanoadsorbents synthesized by green and conventional protocols affect performance in the adsorption of contaminants in water. Despite advances in the area, there is still a lack of review articles on the topic.

Removal of propranolol by membranes fabricated with nanocellulose/proanthocyanidin/modified tannic acid: The influence of chemical and morphologic features and mechanism study.

Polymer-based membranes containing nanocellulose and natural macromolecules have potential to treat water, however few works have associated the changes in chemical and morphological membrane's features with their performance as adsorbent. Herein, a new green composite based on nanocellulose (NC) and alkylated tannic acid (ATA) and cross-linked with proanthocyanidin was produced and incorporated into polyacrylonitrile (PAN) membranes to eliminate propranolol (PRO) from water. Characterizations revealed that the increasing of NC-ATA content reduced the pore size of the membrane's upper surface and made the finger like structure of the sublayer disappear, due to the formation of hydrophilic domains of NC/ATA which speeds up the external solidification step. The presence of NC-ATA reduced the hydrophilicity, from a water contact angle of 3.65° to 16.51°, the membrane roughness, from 223.5 to 52.0 nm, and the zeta potential from -25.35 to -55.20 mV, improving its features to be a suitable adsorbent of organic molecules. The membranes proved to be excellent green adsorbent, tridimensional, and easy to remove after use, and qmax for PRO was 303 mg·g-1. The adsorption mechanism indicates that H-bonds, ion exchange, and π-π play important role in adsorption. NC-ATA@PAN kept high removal efficiencies after four cycles, evidencing the potential for water purification.

Fluoranthene adsorption by graphene oxide and magnetic chitosan composite (mCS/GO).

The oil industry faces the challenge of reducing its high polluting potential, due to the presence of aromatic pollutants, such as polycyclic aromatic hydrocarbons (PAHs). Efforts have been made to mitigate the impact of PAHs in industry through the development of detection technologies and the implementation of mitigation strategies. This study presents the adsorption of fluoranthene, through a magnetic composite of graphene oxide and chitosan as a method of remediation of produced water. The efficiency of the process was evaluated through kinetic, equilibrium, thermodynamic, and characterization analyses. The nanocomposite was able to remove 90.9% of FLT after 60 min and showed a maximum adsorption capacity of 28.22 mg/g, demonstrating that they can be implemented to remove fluoranthene. Kinetic and equilibrium experimental data showed that physisorption is the predominant adsorptive mechanism; however, the process is also influenced by chemisorption, which occurs through electrostatic interactions between the surface of the material and the adsorbate. The thermodynamic study showed that fluoranthene and graphene composite have high affinity, and that the adsorption is exothermic and spontaneous. The results presented in this paper indicate that the magnetic composite is a potential and sustainable adsorbent for fluoranthene remediation.

Comparative effect of mesoporous carbon doping on the adsorption of pharmaceutical drugs in water: Theoretical calculations and mechanism study.

In this study, mesoporous doped-carbons were synthesized from sucrose, a natural source, boric acid and cyanamide as precursors, generating B- or N-doped carbon. These materials were characterized by FTIR, XRD, TGA, Raman, SEM, TEM, BET, and XPS, confirming the preparation of a tridimensional doped porous structure. B-MPC and N-MPC showed a high surface specific area above 1000 m2/g. The effect of B and N doping on mesoporous carbon was evaluated on the adsorption of emerging pollutants from water. Diclofenac sodium and paracetamol were used in adsorption assays, reaching removal capacities of 78 and 101 mg.g-1, respectively. Kinetic and isothermal studies indicate the chemical nature of adsorption controlled by external and intraparticle diffusion and multilayer formation due to strong adsorbent/adsorbate interactions. DFT-based calculations and adsorption assays infer that the main attractive forces are hydrogen bonds and Lewis acid-base interactions.

Toxicological effects resulting from co-exposure to nanomaterials and to a ß-blocker pharmaceutical drug in the non-target macrophyte species Lemna minor.

The wide use of carbon-based materials for various purposes leads to their discharge in the aquatic systems, and simultaneous occurrence with other environmental contaminants, such as pharmaceutical drugs. This co-occurrence can adversely affect exposed aquatic organisms. Up to now, few studies have considered the simultaneous toxicity of nanomaterials, and organic contaminants, including pharmaceutical drugs, towards aquatic plants. Thus, this study aimed to assess the toxic effects of the co-exposure of propranolol (PRO), and nanomaterials based on cellulose nanocrystal, and graphene oxide in the aquatic macrophyte Lemna minor. The observed effects included reduction of growth rate in 13% in co-exposure 1 (nanomaterials + PRO 5 µg L-1), and 52-64% in co-exposure 2 (nanomaterials + PRO 51.3 mg L-1), fresh weight reduction of 94-97% in co-exposure 2 compared to control group, and increased pigment production caused by co-exposure treatments. The analysis of PCA showed that co-exposure 1 (nanomaterials + PRO 5 µg L-1) positively affected growth, and fresh weight, and co-exposure 2 positively affected pigments content. The results suggested that the presence of nanomaterials enhanced the overall toxicity of PRO, exerting deleterious effects in the freshwater plant L. minor, suggesting that this higher toxicity resulting from co-exposure was a consequence of the interaction between nanomaterials and PRO.

Hydrophobization of aerogels based on chitosan, nanocellulose and tannic acid: Improvements on the aerogel features and the adsorption of contaminants in water.

Hydrophobic chitosan aerogels are promising adsorbents for immiscible contaminants such as oils and organic solvents. However, few studies have reported the application of hydrophobic aerogels as adsorbent for organic contaminants dissolved in water. Herein, novel highly hydrophobic chitosan (CS) beads containing cellulose nanocrystals (CNC) and hydrophobized tannic acid (HTA) composite were prepared with different CS and CNC-HTA content to achieve an optimized adsorbent to remove emerging contaminants from water in batch and fixed-bed assays. The CS@CNC-HTA beads properties were assessed by FTIR, XRD, SEM, XPS, Micro-CT, WCA, and zeta potential. Supramolecular interactions and physical interlacements between CS and CNC-HTA enabled the formation of CS@CNC-HTA beads with high porosity (98.6%), great volume of open pore space (10.16 mm3) and hydrophobicity (121.8°). The 1:1 CS@CNC-HTA beads showed the best performance for removing the pharmaceutical sildenafil citrate, the basic blue 26 dye, and the surfactant cetylpyridinium chloride, reaching adsorption capacities of 86 (73%), 375 (84%), and 390 (90%) mg.g-1, respectively. The 1:1 CS@CNC-HTA beads efficiently removed sildenafil citrate, basic blue 26 and cetylpyridinium chloride in fixed-bed experiments with exhaustion times of 890, 300, and 470 min, respectively. Theoretical calculations and adsorption assays indicate that the main attractive interactions are pyridinium-π, π-π, electrostatic and hydrophobic.

Adsorption of naphthalene polycyclic aromatic hydrocarbon from wastewater by a green magnetic composite based on chitosan and graphene oxide.

A green magnetic composite mCS/GO was synthesized using water hyacinth extract, as a reducing agent, and proanthocyanidin, as a crosslinking agent, for the adsorption of naphthalene from effluents. The green composite was evaluated using different characterization techniques to determine its thermal (TG/DTG), structural (BET, XPS and FTIR), crystallographic (XRD), and textural (SEM) properties in natura and post-adsorption. The results obtained through a central composite design (CCD) experiment indicated that the initial concentration of NAP and the adsorbent dosage are significant for the adsorption capacity. The adsorption assays indicated that physisorption, through π-π and hydrophobic interactions, were the main mechanism involved in the NAP adsorption. However, the adjustment to the PSO and Freundlich models, obtained through kinetic and equilibrium studies, indicated that chemisorption also influences the adsorptive process. The thermodynamic study indicated physisorption as the mechanism responsible for the NAP adsorption. Also, the adsorbent has high affinity for the adsorbate and the process is spontaneous and endothermic. The maximum adsorption capacity (qmax) of the green mCS/GO was 334.37 mg g-1 at 20 °C. Furthermore, the green mCS/GO was effectively regenerated with methanol and reused for five consecutive cycles, the percentage of NAP recovery went from approximately 91 to 75% after the fifth cycle. The green composite was also applied in the adsorption of NAP from river water samples, aiming to evaluate the feasibility of the method in real applications. The adsorption efficiency was approximately 70%. From what we know, this it is the first time that a green adsorbent was recycled after the polycyclic aromatic hydrocarbon (PAHs) adsorption process.

Behavior of two classes of organic contaminants in the presence of graphene oxide: Ecotoxicity, physicochemical characterization and theoretical calculations.

Graphene oxide (GO) production has increased considerably and therefore its presence in the environment is inevitable. When in aquatic environment GO can interact with co-existing compounds, modifying their toxicities for several organisms. However, the toxic effects of co-exposure of GO and organic compounds are rarely reported in the literature. Herein, we studied the behavior of four organic aquatic contaminants found in surface water such as 2-phenylbenzotriazoles (non-Cl PBTA-9 and PBTA-9) and phenoxyphenyl pesticides, pyriproxyfen (PYR) and lambdacyhalothrin (LCT), in the presence of GO. GO reduced 90% and 83% of the toxicity of non-Cl PBTA-9 and PBTA for Daphnia. When PBTAs were adsorbed onto GO surface their interactions caused GO agglomeration (up to 20 mm) and consequent precipitation, making PBTAs less bioavailable. PYR and LCT's toxicities increased up to 83% for PYR and 47% for LCT in the presence of GO, because their adsorption on GO lead to the stabilization of the suspensions (up to 0.5 µm). Those particles were then easily ingested and retained in the digestive tract of the daphnids, triggering the Trojan horse effect. Based on theoretical calculations we observed that PBTA compounds are planar, electron-poorer and more reactive than the studied pesticides, suggesting a better stability of the GO/PBTA complexes. PYR and LCT are nonplanar, electron-richer and less reactive towards GO than PBTAs, forming less stable GO complexes that could facilitate the desorption of pesticides, increasing toxic effects. Our results suggest that the properties of the organic toxicants can influence the stability of graphene oxide suspensions, playing a fundamental role in the modulation of their toxicity. Further research is needed for a deep understanding of the behavior of nanomaterials in the presence of contaminants and their effect in the toxicity of aquatic organisms.

Adsorption of polycyclic aromatic hydrocarbons from wastewater using graphene-based nanomaterials synthesized by conventional chemistry and green synthesis: A critical review.

Polycyclic aromatic hydrocarbons (PAHs) are organic pollutants formed mainly by the incomplete combustion of organic matter, such as oil, gas and coal. The presence of PAHs can cause irreparable damage to the environment and living beings, which has generated a global concern with the short and long term risks that the emission of these pollutants can cause. Many technologies have been developed in the last decades aiming at the identification and treatment of these compounds, mainly, the PAHs from wastewater. This review features an overview of studies on the main methods of PAHs remediation from wastewater, highlighting the adsorption processes, through the application of different adsorbent nanomaterials, with a main focus on graphene-based nanomaterials, synthesized by conventional and green routes. Batch and fixed-bed adsorptive processes were evaluated, as well as, the mechanisms associated with such processes, based on kinetic, equilibrium and thermodynamic studies. Based on the studies analyzed in this review, green nanomaterials showed higher efficiency in removing PAHs than the conventional nanomaterials. As perspectives for future research, the use of green nanomaterials has shown to be sustainable and promising for PAHs remediation, so that further studies are needed to overcome the possible challenges and limitations of green synthesis methodologies.

Mutagenicity of a novel 2-phenylbenzotriazole (non-chlorinated 2-phenylbenzotriazole-9) in mice.

Dinitrophenylazo dyes can form 2-phenylbenzotriazoles (PBTAs) in the textile dyeing process upon the addition of chemical reducing agents. Some dinitrophenylazo dyes, as well as their respective reduced (non-chlorinated) and chlorinated PBTAs, are now found in rivers owing to wastewater from textile plants. This study aimed to investigate the genotoxicity of a new PBTA derived from C.I. Disperse Violet 93 azo dye, namely non-Cl PBTA-9. Primary DNA damage in the blood, liver, and colon cells, micronucleated cells in the bone marrow, and gene expression (NAT2, CYP1A1, TRP53, and CDKN1A) in liver cells were observed in mice, at acute oral exposure (gavage) doses of 5, 50, and 500 µg/kg body weight (b.w.). The non-chlorinated PBTA-9 caused DNA damage in the blood and liver (at 500 µg/kg b.w.) and in colon cells (at 5, 50, and 500 µg/kg), and increased the frequency of micronucleated cells in the bone marrow (at 5 and 50 µg/kg). No histological alterations or gene expression changes were observed. In conclusion, in vivo exposure to non-chlorinated PBTA-9 induced genetic damage in various rodent tissues, corroborating results previously obtained from the Ames test. Because this compound has been detected in rivers, exposure to humans and biota is a major concern.

Enhanced removal of basic dye using carbon nitride/graphene oxide nanocomposites as adsorbents: high performance, recycling, and mechanism.

The presence of dyes in wastewater streams poses a great challenge for sustainability and brings the need to develop technologies to treat effluent streams. Here, we propose a mixture of high superficial area carbon-based nanomaterial strategy to improve the removal of basic blue 26 (BB26) by blending porous carbon nitride (CN) and graphene oxide (GO). We prepared CN and GO pristine materials, as well the nanocomposites with mass/ratio 30/70, 50/50, and 70/30, and applied them into BB26 uptake. Nanocomposite 50/50 CN/GO was found to be the better adsorbent, and the optimization of the adsorption revealed a fast equilibrium time of 30 min, after sonication for 2 min, nanocomposite 50/50, and BB26 dye loading of 0.1 g/L and 100 mg/L, respectively. The pH variation had great influence on BB26 uptake, and at ultrapure water pH, the dye removal capacity by the composite reached 917.78 mg/g. At pH 2, a remarkable removal efficiency of 3510.10 mg/g was obtained, probably due to electrostatic interactions among protonated amine groups of the dye and negatively charged CN/GO nanocomposite. The results obtained were best fitted to the pseudo-second-order kinetic model and the Dubinin-Radushkevich isotherm. The adsorption process was thermodynamically spontaneous, and physisorption was the main mechanism, which is based on weak electrostatic and π-π interactions. The dye attached to the CN/GO nanocomposite could be removed by washing with ethyl alcohol, and the adsorbent was reused for five consecutive cycles with high BB26 uptake efficiency. The CN/GO nanocomposite ability to remove the BB26 dye was 21 times higher than those reported in the literature, indicating CN/GO composites as potential filtering materials to basic dyes.

New benzotriazoles generated during textile dyeing process: Synthesis, hazard, water occurrence and aquatic risk assessment.

Phenylbenzotriazoles (PBTA) can be generated unintentionally during textile dyeing factories by reduction of dinitrophenylazo dyes and their subsequent chlorination in disinfection process. Eight non-chlorinated PBTAs (non-Cl PBTA) and their related chlorinated PBTAs have been found in rivers and presented mutagenic activity. No data on their aquatic toxicity are available. In this work, two new phenylbenzotriazoles, non-Cl PBTA-9 and PBTA-9, derived from the dye C.I. Disperse Violet 93 (DV93) were synthesized and chemically/toxicologically characterized. Both compounds were more mutagenic than the parental dye in the Salmonella/microsome assay in the presence of metabolic activation (S9). Mutagenicity studies in vivo with mammals would confirm their potential hazard to humans. The two compounds were acutely toxic to Daphnia similis. We developed an analytical method to simultaneously quantify non-Cl PBTA-9, PBTA-9 and DV93 in river waters. Non-Cl PBTA-9 was found in sites under influence of textile effluents but at concentrations that do not pose risk to the aquatic life according to the P-PNEC calculated based on the acute toxicity tests. PBTA-9 was not detected in any samples analyzed. More studies on the aquatic toxicity and water occurrence of PBTAs should be conducted to verify the relevance of this class of compounds as aquatic contaminants.

Macrodiolide Formation by the Thioesterase of a Modular Polyketide Synthase.

Elaiophylin is an unusual C2-symmetric antibiotic macrodiolide produced on a bacterial modular polyketide synthase assembly line. To probe the mechanism and selectivity of diolide formation, we sought to reconstitute ring formation in vitro by using a non-natural substrate. Incubation of recombinant elaiophylin thioesterase/cyclase with a synthetic pentaketide analogue of the presumed monomeric polyketide precursor of elaiophylin, specifically its N-acetylcysteamine thioester, produced a novel 16-membered C2-symmetric macrodiolide. A linear dimeric thioester is an intermediate in ring formation, which indicates iterative use of the thioesterase active site in ligation and subsequent cyclization. Furthermore, the elaiophylin thioesterase acts on a mixture of pentaketide and tetraketide thioesters to give both the symmetric decaketide diolide and the novel asymmetric hybrid nonaketide diolide. Such thioesterases have potential as tools for the in vitro construction of novel diolides.

Iterative Mechanism of Macrodiolide Formation in the Anticancer Compound Conglobatin.

Conglobatin is an unusual C2-symmetrical macrodiolide from the bacterium Streptomyces conglobatus with promising antitumor activity. Insights into the genes and enzymes that govern both the assembly-line production of the conglobatin polyketide and its dimerization are essential to allow rational alterations to be made to the conglobatin structure. We have used a rapid, direct in vitro cloning method to obtain the entire cluster on a 41-kbp fragment, encoding a modular polyketide synthase assembly line. The cloned cluster directs conglobatin biosynthesis in a heterologous host strain. Using a model substrate to mimic the conglobatin monomer, we also show that the conglobatin cyclase/thioesterase acts iteratively, ligating two monomers head-to-tail then re-binding the dimer product and cyclizing it. Incubation of two different monomers with the cyclase produces hybrid dimers and trimers, providing the first evidence that conglobatin analogs may in future become accessible through engineering of the polyketide synthase.

Macrodiolide formation by the thioesterase of a modular polyketide synthase.

Elaiophylin is an unusual C2 -symmetric antibiotic macrodiolide produced on a bacterial modular polyketide synthase assembly line. To probe the mechanism and selectivity of diolide formation, we sought to reconstitute ring formation in vitro by using a non-natural substrate. Incubation of recombinant elaiophylin thioesterase/cyclase with a synthetic pentaketide analogue of the presumed monomeric polyketide precursor of elaiophylin, specifically its N-acetylcysteamine thioester, produced a novel 16-membered C2 -symmetric macrodiolide. A linear dimeric thioester is an intermediate in ring formation, which indicates iterative use of the thioesterase active site in ligation and subsequent cyclization. Furthermore, the elaiophylin thioesterase acts on a mixture of pentaketide and tetraketide thioesters to give both the symmetric decaketide diolide and the novel asymmetric hybrid nonaketide diolide. Such thioesterases have potential as tools for the in vitro construction of novel diolides.

Substrate-directable Heck reactions with arenediazonium salts. The regio- and stereoselective arylation of allylamine derivatives and applications in the synthesis of naftifine and abamines.

The palladium-catalyzed, substrate-directable Heck-Matsuda reaction of allylamine derivatives with arenediazonium salts is reported. The reaction proceeds under mild conditions, with excellent regio- and stereochemical control as a function of coordinating groups present in the allylamine substrate. The distance between the olefin moiety and the carbonylic system seems to play a key role regarding the regiocontrol. The method presents itself as robust, as simple to carry out, and with wide synthetic scope concerning the allylic substrates and the type of arenediazonium employed. The synthetic potential of the method is illustrated by the short total syntheses of the bioactive compounds naftifine, abamine, and abamine SG.

Palladium-catalyzed Suzuki cross-coupling of 2-haloselenophenes: synthesis of 2-arylselenophenes, 2,5-diarylselenophenes, and 2-arylselenophenyl ketones.

We present herein our results on the Suzuki coupling reaction of 2-haloselenophenes with boronic acids catalyzed by palladium salt and describe a new route established to prepare 2-arylselenophenes and 2,5-diarylselenophenes in good yields. The reaction proceeded cleanly under mild conditions and was performed with aryl boronic acids bearing electron-withdrawing, electron-donating, and neutral substituents, in the presence of Pd(OAc)2, K2CO3/H2O in DME. In addition, by this protocol unsymmetrical aryl ketones were also obtained from 2-iodoselenophene and boronic acids via a carbonylative process.