Adsorption of naphthalene and its derivatives on magnetic graphene composites and the mechanism investigation

Polycyclic aromatic hydrocarbons in water environments: Impact, legislation, depollution processes and challenges, and magnetic iron oxide/graphene-based nanocomposites as promising adsorbent solutions

Environmental pollution is a big challenge of today's world, as population continues to grow, and industrialisation and urbanisation increase. Out of the different micropollutants in the atmosphere and aquatic environments, polycyclic aromatic hydrocarbons are of particular importance because they have known severe associated health risks to human life and they have high stability, leading to their persistence in the environment. They are generally present in the environment in low concentrations, but, even at these levels, they pose threats. This review thus focuses on this family of pollutants, on their occurrence and consequences, as well as the current methodologies employed to remove them from water environments and the challenges that remain. This work then focuses on the potential of magnetic iron oxide/graphene nanocomposites for the adsorption of PAHs, extensively discussing past and undergoing works, as well as the interactions between these adsorbents and PAHs.

Inbuilt self-cascade catalysis of the bimetal-confined structural nanozyme CoNi@CNTs-N/GO for increased bienzymatic activity and H2O2-free smartphone-based visual assay of total antioxidant capacity in foods

The level of total antioxidant capacity (TAC) reflects the overall ability of food to resist oxidative damage, maintain quality and nutritional stability. In this work, we pioneered a CoNi alloy-confined N-doped carbon nanozyme (CoNi@CNT-N/GO) with a self-cascade catalysis. Compared to other nanozymes, the synergistic effect of OXD and POD realized self-sustained generation of H2O2, eliminating the need of exogenous addition, and further decomposition of H2O2 into ·OH and oxidizes colorless 3,3',5,5'- tetramethylbenzidine (TMB) to blue oxTMB as an efficient catalyst. The integration of multiple components and the built-in unique mechanism enhance bienzymatic activity. A "Thing Identify" APP was utilized to construct a smartphone-based visualization platform, demonstrating satisfactory linearity (0.01-1.2 mM) and low detection limit (3.3 μM) in TAC detection of real-world foods. This platform yielded data comparable to those from commercially colorimetric kits. Overall, it proposes a novel idea for engineering multi-functional and non-additional H2O2 nanozymes in on-site food-quality monitoring.

Great truths are always simple: A millimeter-sized macroscopic lanthanum-calcium dual crosslinked carboxymethyl chitosan aerogel bead as a promising adsorbent for scavenging oxytetracycline from wastewater

Given their increasing environmental and health harms, it is crucial to develop green and sustainable techniques for scavenging antibiotics represented by oxytetracycline (OTC) from wastewater. In the present work, a structurally simple lanthanum-calcium dual crosslinked carboxymethyl chitosan (CMCS-La3+-Ca2+) aerogel was innovatively synthesized for adsorptive removal of OTC. It was found that CMCS and La3+ sites collaboratively participated in OTC elimination, and OTC removal peaked over the wide pH range of 4-7. The process of OTC sorption was better described by the pseudo-second-order kinetic model and Redlich-Peterson model, and the saturated uptake amount toward OTC was up to 580.91 mg/g at 303 K, which was comparable to the bulk of previous records. The as-fabricated composite also exerted exceptional capture capacity toward OTC in consecutive adsorption-desorption runs and high-salinity wastewater. Amazingly, its packed column continuously ran for over 60 h with a dynamic uptake amount of 215.21 mg/g until the adsorption was saturated, illustrating its great potential in scale-up applications. Mechanism studies demonstrated that multifarious spatially-isolated reactive sites of CMCS-La3+-Ca2+ cooperatively involved in OTC capture via multi-mechanisms, such as n-π EDA interaction, H-bonding, La3+-complexation, and cation-π bonding. All the above superiorities endow it as a promising adsorbent for OTC-containing wastewater decontamination.

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 (q_max) 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.

The interaction mechanisms of co-existing polybrominated diphenyl ethers and engineered nanoparticles in environmental waters: A critical review

This review focuses on the occurrence and interactions of engineered nanoparticles (ENPs) and brominated flame retardants (BFRs) such as polybrominated diphenyl ethers (PBDEs) in water systems and the generation of highly complex compounds in the environment. The release of ENPs and BFRs (e.g. PBDEs) to aquatic environments during their usage and disposal are summarised together with their key interaction mechanisms. The major interaction mechanisms including electrostatic, van der Waals, hydrophobic, molecular bridging and steric, hydrogen and π-bonding, cation bridging and ligand exchange were identified. The presence of ENPs could influence the fate and behaviour of PBDEs through the interactions as well as induced reactions under certain conditions which increases the formation of complex compounds. The interaction leads to alteration of behaviour for PBDEs and their toxic effects to ecological receptors. The intermingled compound (ENPs-BFRs) would show different behaviour from the parental ENPs or BFRs, which are currently lack of investigation. This review provided insights on the interactions of ENPs and BFRs in artificial, environmental water systems and wastewater treatment plants (WWTPs), which are important for a comprehensive risk assessment.

[Adsorption characteristics of six bisphenol compounds on magnetic three-dimensional nitrogen-doped carbon nanomaterials and their use in effervescent reaction-assisted dispersive microextraction]

Herein, we successfully prepared magnetic Co/Ni-based N-doped 3D carbon nanotubes and graphene nanocomposites (CoNi@NGC) using a simple high-temperature calcination method. The CoNi@NGC nanocomposites were used as adsorbents to study their adsorption performances and underlying kinetic mechanisms for six types of bisphenol compounds (BPs) in water. They were also used as extractants, and acid-base effervescent tablets were used to enhance extractant dispersion with the aid of vigorous CO₂ bubbling. Thus, a novel pretreatment method was developed, denoted effervescent reaction-assisted dispersive solid-phase microextraction (ER-DSM), which was combined with high performance liquid chromatography-fluorescence detection (HPLC-FLD) to rapidly quantify trace-level BPs in several drinks. The morphology and structure of the CoNi@NGC adsorbent were characterized in detail using scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FT-IR), N₂ adsorption and desorption (BET-BJH), X-ray photoelectron spectroscopy (XPS), and vibrating sample magnetometry (VSM). The CoNi@NGC nanocomposites were successfully doped with N and exhibited large specific surface areas (109.42 m²/g), abundant pores, and strong magnetic properties (17.98 emu/g).Key parameters were rigorously optimized to maximize the adsorption performance of CoNi@NGC, including adsorbent dosage, solution pH, temperature, and time. Under the constant conditions of pH=7, 5 mg of CoNi@NGC, initial BP concentrations of 5 mg/L, and 5 min of shaking at 298 K, the adsorption percentages of bisphenol M (BPM) and bisphenol A (BPA) reached respective maxima of 99.01% and 98.21%. Remarkably, those of bisphenol Z (BPZ), BPA, and BPM reached almost 100% after 90 min. The adsorption between the BPs and CoNi@NGC was mainly governed by hydrogen bonds, electrostatic interactions, and π-π conjugation. The entire adsorption process was consistent with Freundlich adsorption and a quasi-second-order kinetic equation, representing spontaneous adsorption. Via integration with HPLC-FLD, ER-DSM was used to rapidly extract and analyze trace-level BPs in six types of boxed drinks. Critical factors were optimized individually, including the type of eluent and elution time and volume, which influenced the enrichment effect. Under the optimized extraction conditions (pH=7, 5 mg CoNi@NGC, elution with 2 mL acetone for 6 min), the limits of detection and quantification of the novel extraction method were 0.06-0.20 and 0.20-0.66 μg/L, respectively. The intra- and inter-day precisions spanned the ranges 1.44%-4.76% and 1.69%-5.36%, respectively, and the recoveries in the actual samples were in the range 82.4%-103.7%. Moreover, the respective residual levels of BPA and BPB in peach juice samples were 2.09 and 1.37 μg/L. Regeneration studies revealed that the CoNi@NGC adsorbent could be reused at least five times, which significantly reduced the cost of evaluation. In summary, compared to other methods, this method displays the advantages of a high sensitivity, rapid extraction, and environmental friendliness, thereby exhibiting considerable potential for use in conventional monitoring of trace-level BPs in food matrices.

A Theoretical Study of the Interactions between Persistent Organic Pollutants and Graphene Oxide

Persistent organic pollutants (POPs) have adverse effects on the human health and ecosystem functioning. Graphene oxide (GO) has been developed to remove trace levels of POPs from wastewater samples. However, many questions involved in these processes are still unresolved (e.g., the role of π-π interaction, the effect of GO on the degradation of POPs, and so on). Revealing the microscopic interactions between GO and POPs is of benefit to resolve these questions. In the present study, a quantum chemical calculation was used to calculate the molecular doping and adsorption energy between eight representative POPs and GO. The influences of GO on the thermodynamic parameters, such as the Gibbs free energy and the highest occupied molecular orbital (HOMO)-lowest unoccupied molecular orbital (LUMO) gap, were also reported. We found the molecular doping is dependent on the species of POPs. The adsorption energy of the majority of POPs on GO is between 7 and 8 kJ/mol. Consequently, the GO may make degradation of POPs in wastewater more productive and lead to a change of kinetics of the degradation of POPs.

Synthesis and Characterization of New Catalysts Grains Based on Iron(Oxy)Hydroxides supported on Zirconium for the Degradation of 4-Nitrophenol in Aqueous Solution

This study reports the preparation of catalyst grains based on oxyhydroxides of iron and zirconium via the coprecipitation method and their application in the degradation of 4-nitrophenol. The morphology, microstructure, and surface composition of these catalysts were characterized by scanning electron microscopy, X-ray diffraction, nitrogen physisorption, and Fourier transform infrared spectroscopy. The catalytic activity of the grains was assessed in the degradation of 4-nitrophenol in a heterogeneous system at different operating conditions. Degradation rates up to 93% were obtained after 4 h of contact time where the catalytic activity of tested materials was higher at pH 7 than in acidic and basic conditions. Amorphous iron hydroxide with a ratio of 75% Zr+25%Fe showed the best catalytic properties. These novel materials are an interesting alternative for facing the water pollution caused by organic compounds.

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.

Sorption of benzo[a]pyrene by Chernozem and carbonaceous sorbents: comparison of kinetics and interaction mechanisms

Benzo[a]pyrene (BaP) is a polycyclic aromatic hydrocarbon, highly persistent and toxic and a widespread environmental pollutant. Although various technologies have been developed to remove BaP from the environment, its sorption through solid matrixes has received increasing attention due to cost-effectiveness. The present research compares the adsorption capacity of Haplic Chernozem, granular activated carbon and biochar in relation to BaP from water solution. Laboratory experiments with different initial BaP concentrations in the liquid phase and different ratios of the solid and liquid phases show that Freundlich model describes well the adsorption isotherms of BaP by the soil and both sorbents. Moreover, the BaP isotherm sorption by the Haplic Chernozem is better illustrated by the Freundlich model than the Langmuir equation. The results reveal that the sorption capacity of the carbonaceous adsorbents at a ratio 1:20 (solid to liquid phases) is orders of magnitude higher (13 368 ng mL^-1 of activated carbon and 3 578 ng mL^-1 of biochar) compared to the soil (57.8 ng mL^-1). At the ratio of 0.5:20, the adsorption capacity of the carbonaceous sorbents was 17-45 times higher than that of the soil. This is due to the higher pore volume and specific surface area of the carbonaceous sorbents than soil particles, assessed through scanning electron microscopy. The sorption kinetic of BaP by Chernozem was compared with the adsorption kinetics by the carbonaceous sorbents. Results indicate that the adsorption dynamic involves two steps. The first one is associated with a fast BaP adsorption on the large available surface and inside macro- and meso-pores of the sorbent particles of the granular activated carbon and biochar. Then, the adsorption is followed by a slower process of BaP penetration into the microporous space and/or redistribution into a hydrophobic fraction. The effectiveness of the sorption process depends on both the sorbent properties and the solvent competition. Overall, the granular activated carbon and biochar are highly effective adsorbents for BaP, whereas the Haplic Chernozem has a rather limited capacity to remove BaP from contaminated solutions.

Graphene and carbon nanotubes interfaced electrochemical nanobiosensors for the detection of SARS-CoV-2 (COVID-19) and other respiratory viral infections: A review

Recent COVID-19 pandemic has claimed millions of lives due to lack of a rapid diagnostic tool. Global scientific community is now making joint efforts on developing rapid and accurate diagnostic tools for early detection of viral infections to preventing future outbreaks. Conventional diagnostic methods for virus detection are expensive and time consuming. There is an immediate requirement for a sensitive, reliable, rapid and easy-to-use Point-of-Care (PoC) diagnostic technology. Electrochemical biosensors have the potential to fulfill these requirements, but they are less sensitive for sensing viruses/viral infections. However, sensitivity and performance of these electrochemical platforms can be improved by integrating carbon nanostructure, such as graphene and carbon nanotubes (CNTs). These nanostructures offer excellent electrical property, biocompatibility, chemical stability, mechanical strength and, large surface area that are most desired in developing PoC diagnostic tools for detecting viral infections with speed, sensitivity, and cost-effectiveness. This review summarizes recent advancements made toward integrating graphene/CNTs nanostructures and their surface modifications useful for developing new generation of electrochemical nanobiosensors for detecting viral infections. The review also provides prospects and considerations for extending the graphene/CNTs based electrochemical transducers into portable and wearable PoC tools that can be useful in preventing future outbreaks and pandemics.

Advances in water treatment technologies for removal of polycyclic aromatic hydrocarbons: Existing concepts, emerging trends, and future prospects

In the last two decades, environmental experts have focused on the development of several biological, chemical, physical, and thermal methods/technologies for remediation of PAH-polluted water. Some of the findings have been applied to field-scale treatment, while others have remained as prototypes and semi-pilot studies. Existing treatment options include extraction, chemical oxidation, bioremediation, photocatalytic degradation, and adsorption (employing adsorbents such as biomass derivatives, geosorbents, zeolites, mesoporous silica, polymers, nanocomposites, and graphene-based materials). Electrokinetic remediation, advanced phytoremediation, green nanoremediation, enhanced remediation using biocatalysts, and integrated approaches are still at the developmental stage and hold great potential. Water is an essential component of the ecosystem and highly susceptible to PAH contamination due to crude oil exploration and spillage, and improper municipal and industrial waste management, yet comprehensive reviews on PAH remediation are only available for contaminated soils, despite the several treatment methods developed for the remediation of PAH-polluted water. This review seeks to provide a comprehensive overview of existing and emerging methods/technologies, in order to bridge information gaps toward ensuring a green and sustainable remedial approach for PAH-contaminated aqueous systems. PRACTITIONER POINTS: Comprehensive review of existing and emerging technologies for remediation of PAH-polluted water. Factors influencing efficiency of various methods, challenges and merits were discussed. Green nano-adsorbents, nano-oxidants and bio/phytoremediation are desirous for ecofriendly and economical PAH remediation. Adoption of an integrated approach for the efficient and sustainable remediation of PAH-contaminated water is recommended.

Magnetite doped metal–organic framework nanocomposites: an efficient adsorbent for removal of bisphenol-A pollutant

The removal of bisphenol-A (BPA) from the aqueous environment is a vital issue for public health due to its toxic effect.

An Overview and Evaluation of Highly Porous Adsorbent Materials for Polycyclic Aromatic Hydrocarbons and Phenols Removal from Wastewater

Polycyclic aromatic hydrocarbons (PAHs) and phenolic compounds had been widely recognized as priority organic pollutants in wastewater with toxic effects on both plants and animals. Thus, the remediation of these pollutants has been an active area of research in the field of environmental science and engineering. This review highlighted the advantage of adsorption technology in the removal of PAHs and phenols in wastewater. The literature presented on the applications of various porous carbon materials such as biochar, activated carbon (AC), carbon nanotubes (CNTs), and graphene as potential adsorbents for these pollutants has been critically reviewed and analyzed. Under similar conditions, the use of porous polymers such as Chitosan and molecularly imprinted polymers (MIPs) have been well presented. The high adsorption capacities of advanced porous materials such as mesoporous silica and metal-organic frameworks have been considered and evaluated. The preference of these materials, higher adsorption efficiencies, mechanism of adsorptions, and possible challenges have been discussed. Recommendations have been proposed for commercialization, pilot, and industrial-scale applications of the studied adsorbents towards persistent organic pollutants (POPs) removal from wastewater.

Nanomaterials with Tailored Magnetic Properties as Adsorbents of Organic Pollutants from Wastewaters

Water quality has become one of the most critical issue of concern worldwide. The main challenge of the scientific community is to develop innovative and sustainable water treatment technologies with high efficiencies and low production costs. In recent years, the use of nanomaterials with magnetic properties used as adsorbents in the water decontamination process has received considerable attention since they can be easily separated and reused. This review focuses on the state-of-art of magnetic core–shell nanoparticles and nanocomposites developed for the adsorption of organic pollutants from water. Special attention is paid to magnetic nanoadsorbents based on silica, clay composites, carbonaceous materials, polymers and wastes. Furthermore, we compare different synthesis approaches and adsorption performance of every nanomaterials. The data gathered in this review will provide information for the further development of new efficient water treatment technologies.

Embryotoxicity assessment and efficient removal of naphthalene from water by irradiated graphene aerogels

Naphthalene has remained a challenge how to eradicate it from the water because of its carcinogenic risk to humans. In the present study, naphthalene prominently increased the rates of embryonic mortality and malformation, and decreased the hatchability of zebrafish which have a high developmental similarity to humans. Moreover, multiple-organ toxicity were notably found in naphthalene-treated zebrafish. Here, irradiated graphene aerogel (IGA) was successfully prepared from high-energy electron beam to generate more wrinkles, folds, defects and a strong absorption capability for naphthalene, compared with the non-irradiated graphene aerogel. IGA was outstandingly found to remove naphthalene from the embryo culture medium, and subsequently inhibit the embryotoxicity and maintain tissue integrity by restoring cardiac function, attenuating apoptosis signals, recovering eye morphology and structure, reducing expression of heat shock protein 70 in the tissues and promoting behavioral capacity. Meanwhile, no obvious negative impact of IGA was found in the developing zebrafish from embryo to larvae. Consequently, reduction in the toxicity of naphthalene during zebrafish embryogenesis was mediated by IGA as an advanced strategy.

Key factors affecting graphene oxide transport in saturated porous media

This study focuses on the transport in porous media of graphene oxide nanoparticles (GONP) under conditions similar to those applied in the generation of in-situ reactive zones for groundwater remediation (i.e. GO concentration of few tens of mg/l, stable suspension in alkaline solution). The experimental tests evaluated the influence on GO transport of three key factors, namely particle size (300-1200 nm), concentration (10-50 mg/L), and sand size (coarse to fine). Three sources of GONP were considered (two commercial and one synthesized in the laboratory). Particles were stably dispersed in water at pH 8.5 and showed a good mobility in the porous medium under all experimental conditions: after injection of 5 pore volumes and flushing, the highest recovery was around 90%, the lowest around 30% (only for largest particles in fine sand). The particle size was by far the most impacting parameter, with increasing mobility with decreasing size, even if sand size and particle concentration were also relevant. The source of GONP showed a minor impact on the mobility. The transport test data were successfully modeled using the advection-dispersion-deposition equations typically applied for spherical colloids. Experimental and modeling results suggested that GONP, under the explored conditions, are retained due to both blocking and straining, the latter being relevant only for large particles and/or fine sand. The findings of this study play a key role in the development of an in-situ groundwater remediation technology based on the injection of GONP for contaminant degradation or sorption. Despite their peculiar shape, GONP behavior in porous media is comparable with spherical colloids, which have been more studied by far. In particular, the possibility of modeling GONP transport using existing models ensures that they can be applied also for the design of field-scale injections of GONP, similarly to other particles already used in nanoremediation.

Reduced graphene oxide contains a minimum of six oxygen atoms for higher dipolar strength: A DFT study

The present work focused on the reduced graphene oxide contains a minimum of six oxygen atoms for the higher dipolar strength. The ionization potential and electron affinity decreased only for the six oxygen atoms based graphene. The six oxygen atoms based graphene have the highest dipole moment. The reduced graphene has 0.25 eV bandgap, which is very suitable for electron transfer. The six oxygen atoms based graphene leads to the least gauge including atomic orbital (GIAO) rotational tensor; however, it has the highest isotropic polarizability difference, diamagnetic susceptibility tensor difference, paramagnetic susceptibility tensor difference, and total susceptibility. The C-C bond length has increased only for the six oxygen atoms based graphene.

Reduced graphene oxide-wrapped silver nanoparticles for applications in ultrasensitive colorimetric detection of Cr(vi) ions and the carbaryl pesticide

The Ag@rGO nanohybrid can be used as a colorimetric sensing platform for ultrasensitive detection of Cr(vi) ions and the carbaryl pesticide.

Applications of Graphene and Its Derivatives in Chemical Analysis

In this review, the applications of graphene and its derivatives in the chemical analysis have been described. The properties of graphene materials which are essential for their use in chemical and biochemical analysis are characterized. The materials are used in sensors and biosensors, in electrochemistry, in chromatography and in the sample preparation techniques. Chemical and electrochemical sensors containing graphene materials are useful devices for detecting some chemical and biochemical compounds. Chromatographic columns for HPLC with graphene containing stationary phases may be used for separation of polar and nonpolar components of some specific mixtures. Graphene materials could be successfully employed during sample preparation for analysis with SPE, magnetic SPE, and SPME techniques. HighlightsThe review of the applications of graphene (G) and its derivatives, graphene oxide (GO) and reduced graphene oxide (rGO), in chemical and biochemical analysis is proposed.The electron donor-acceptor and proton donor-acceptor interactions for the graphene based materials - analytes systems and their impact on the analysis results are discussed, particularly:    i) in electrochemistry,ii) in chromatography,iii) in modern sample preparation techniquesiv) in sensors of different types.The essence of the thermal stability and the nomenclature of the graphene based materials in their different applications in chemical systems of different classes was discussed (and suggested).The benefits of using SPME fibers with immobilized graphene materials have been presented in detail.

Optimization of the sorption of selected polycyclic aromatic hydrocarbons by regenerable graphene wool

A novel graphene wool (GW) material was used as adsorbent for the removal of phenanthrene (PHEN) and pyrene (PYR) from aqueous solution. Adsorption kinetics, adsorption isotherms, thermodynamics of adsorption and effect of pH, ionic strength, and temperature on the adsorption of PHEN and PYR onto GW were comprehensively investigated. Isothermal and kinetic experimental data were fitted to Langmuir, Freundlich, Temkin, Sips and Dubinin-Radushkevich models, as well as pseudo-first-order and pseudo-second-order kinetic models. The adsorption kinetic data best fit the pseudo-second-order kinetic model for PHEN and PYR sorption with R² value >0.999, whilst the Sips model best fit isotherm data. Kinetic data revealed that 24 hr of contact between adsorbent and polycyclic aromatic hydrocarbons (PAHs) was sufficient for maximum adsorption, where the Langmuir maximum adsorption capacity of GW for PHEN and PYR was 5 and 20 mg g^-1 and the optimum removal efficiency was 99.9% and 99.1%, respectively. Thermodynamic experiments revealed that adsorption processes were endothermic and spontaneous. Desorption experiments indicated that irreversible sorption occurred with a hysteresis index greater that zero for both PAHs. The high adsorption capacity and potential reusability of GW makes it a very attractive material for removal of hydrophobic organic micro-pollutants from water.

Graphene based adsorbents for remediation of noxious pollutants from wastewater

The contamination of water resources with noxious pollutants is a serious issue. Many aquatic systems are contaminated with different toxic inorganic and organic species; coming to wastewater from various anthropogenic sources such as industries, agriculture, mining, and domestic households. Keeping in view of this, wastewater treatment appears to the main environmental challenge. Adsorption is one of the most efficient techniques for removing all most all types of pollutants i.e. inorganics and organics. Nowadays, graphene and its composite materials are gaining importance as nano adsorbents. Graphene; a two-dimensional nanomaterial having single-atom graphite layer; has attracted a great interest in many application areas (including wastewater treatment) due to its unique physico-chemical properties. The present paper is focused on the remediation of noxious wastes from wastewater using graphene based materials as adsorbents, and it contains all the details on materials - i.e., from their synthesis to application in the field of wastewater treatment (removal of hazardous contaminants of different chemical nature - heavy and rare-earth metal ions, and organic compounds - from wastewater effluents. The efficiency of the adsorption and desorption of these substances is considered. Certainly, this article will be useful for nano environmentalist to design future experiments for water treatment.

Removal of 2,4-D, glyphosate, trifluralin, and butachlor herbicides from water by polysulfone membranes mixed by graphene oxide/TiO2 nanocomposite: study of filtration and batch adsorption

PURPOSE

Degradation or decomposition of the chemical herbicides by natural reagents after using can lead to produce various types of harmful intermediates. Ultrafiltration by the mixed matrix membranes blended with the graphene oxide/TiO₂ can remove the residual herbicides from aqueous solution.

METHODS

Graphene oxide/TiO₂x% (x = 10, 30, 50%) was prepared by solvothermal method and blended by polysulfone to prepare GO/TiO₂/PSf membranes for dynamic rejection of aqueous solutions of glyphosate, 2,4-D, butachlor, and trifluralin in a dead-end flow system. The blended membranes were also applied for the adsorption of herbicides in batch experiments.

RESULTS

Addition of GO/TiO₂ nanocomposite increased water flux from 7.3 for pure membrane to 211-326 kg/m² h for mixed matrix samples in order to increase of the membrane porosity and surface hydrophilicity. The herbicides rejections were found in the range of 50-70% related to GO/TiO₂ content. It was found that the membrane blended with 0.5 wt.% of GO/TiO₂(10%) demonstrated the most efficiency.

CONCLUSIONS

Details of dynamic filtration showed that the blended membrane acted based on the size exclusion mechanism. Adsorption experiments indicated that the strong attractions between H-bond donor sites of the herbicide and GO/TiO₂ nanoparticles in membranes played a key role in the increase of adsorption of herbicides on the membrane.

A review on the interactions between engineered nanoparticles with extracellular and intracellular polymeric substances from wastewater treatment aggregates

Engineered nanoparticles (ENPs) will inevitably enter wastewater treatment plants (WWTPs) due to their widespread application; thus, it is necessary to study the migration and transformation of nanoparticles in sewage treatment systems. Extracellular polymeric substances (EPSs) such as polysaccharides, proteins, nucleic acids, humic acids and other polymers are polymers released by microorganisms under certain conditions. Intracellular polymeric substances (IPSs) are microbial substances contained in the body with compositions similar to those of extracellular polymers. In this review, we summarize the characteristics of EPSs and IPSs from sewage-collecting microbial aggregates containing pure bacteria, activated sludge, granular sludge and biofilms. We also further investigate the dissolution, adsorption, aggregation, deposition, oxidation and other chemical transformation processes of nanoparticles, such as metals, metal oxides, and nonmetallic oxides. In particular, the review deeply analyzes the migration and transformation mechanisms of nanoparticles in EPS and IPS matrices, including physical, chemical, biological interactions mechanisms. Moreover, various factors, such as ionic strength, ionic valence, pH, light, oxidation-reduction potential and dissolved oxygen, influencing the interaction mechanisms are discussed. In recent years, studies on the interactions between EPSs/IPSs and nanoparticles have gradually increased, but the mechanisms of these interactions are seldom explored. Therefore, developing a systematic understanding of the migration and transformation mechanisms of ENPs is significant.

Constructing a Z-scheme Heterojunction of Egg-Like Core@shell CdS@TiO₂ Photocatalyst via a Facile Reflux Method for Enhanced Photocatalytic Performance

A well designed and accurate method of control of different shell thickness and electronic transmission in a Z-scheme core@shell system is conducive to obtaining an optimum photocatalytic performance. Herein, the Z-scheme heterojunction of egg-like core@shell CdS@TiO₂photocatalysts with controlled shell thickness (13 nm, 15 nm, 17 nm, 22 nm) were synthesized by a facile reflux method, and the CdS@TiO₂ structure was proved by a series of characterizations. The photodegradation ratio on methylene blue and tetracycline hydrochloride over the 0.10CdS@TiO₂ composites with TiO₂ shell thickness of 17 nm reached 90% in 250 min and 91% in 5 min, respectively, which was almost 9.8 times and 2.6 times than that of TiO₂ and CdS on rhodamine B respectively under visible light. Besides, the higher total organic carbon removal ratio indicated that most of the pollutants were degraded to CO₂ and H₂O. The Z-scheme electronic transfer pathway was studied through radical species trapping experiments and electron spin resonance spectroscopy. Moreover, the relationship between shell thickness and photocatalytic activity demonstrated that different shell thickness affects the separation of the electron and holes, and therefore affected the photocatalytic performance. In addition, the effects of pollutants concentration, pH, and inorganic anions on photocatalytic performance were also investigated. This work can provide a novel idea for a well designed Z-scheme heterojunction of core@shell photocatalysts, and the study of photocatalytic performance under different factors has guiding significance for the treatment of actual wastewater.

Tailored Design of Differently Modified Mesoporous Materials To Deeply Understand the Adsorption Mechanism for Polycyclic Aromatic Hydrocarbons

A series of SBA-15 with different modifications have been successfully prepared and applied as adsorbents to remove polycyclic aromatic hydrocarbons (PAHs) from aqueous solutions. The morphology and structural properties of the chemically modified materials are all similar to those of pure SBA-15, and thus the difference of PAHs adsorption capacity can be directly attributed to the different functional groups, which is favorable to deeply explore the adsorption mechanism. Adsorption kinetics and isotherm experiments for naphthalene (Nap), anthracene (Ant), and pyrene (Pyr) were carried out, and the results reveal that the adsorption processes follow a pseudo-second-order rate equation and the equilibrium can be achieved within 120 min for Nap and Ant, whereas only 90 min for Pyr, indicating that the more hydrophobic molecules, the easier and faster adsorption can be obtained. All of the adsorption isotherms fit well with the Freundlich model, suggesting the unevenly distributed active sites on adsorbents. The phenyl-functionalized materials possess the highest adsorption capacity, implying that the π-π interaction is the most primary interaction and plays the predominant role in the studied PAHs adsorption, superior to the acidic and hydrophobic interaction. Our research sheds light on the design and synthesis of advanced and highly efficient adsorbents to remove PAHs from aqueous solutions.

Removal of emerging contaminants from the environment by adsorption

Emerging contaminants (EC's) are pollutants of growing concern. They are mainly organic compounds such as: pesticides, pharmaceuticals and personal care products, hormones, plasticizers, food additives, wood preservatives, laundry detergents, surfactants, disinfectants, flame retardants, and other organic compounds that were found recently in natural wastewater stream generated by human and industrial activities. A majority of ECs does not have standard regulations and could lead to lethal effects on human and aquatic life even at small concentrations. The conventional primary and secondary water treatment plants do not remove or degrade these toxic pollutants efficiently and hence need cost effective tertiary treatment method. Adsorption is a promising method worldwide for EC removal since it is low initial cost for implementation, highly-efficient and has simple operating design. Research has shown that the application of different adsorbents such as, activated carbons(ACs), modified biochars (BCs), nanoadsorbents (carbon nanotubes and graphene), composite adsorbents, and other are being used for EC's removal from water and wastewater. The current review intends to investigate adsorption process as an efficient method for the treatment of ECs. The mechanism of adsorption has also been discussed.

Preparation of a novel polyacrylic acid and chitosan interpenetrating network hydrogel for removal of U(vi) from aqueous solutions

A clean and simple method has been developed for preparation of interpenetrating polymer networks using polyacrylic acid (PAA) and chitosan (CS) for extraction of uranium from polluted water. The peak of Fourier transform infrared spectroscopy (FTIR) occurred at 928 cm-1 indicating combination of uranium and PAA/CS. The energy dispersive X-ray (EDX) and the scanning electron microscope (SEM) studies illustrated the formation of a crosslinking structure and excellent binding ability of uranium on PAA/CS. The maximum adsorption capacity was 289.6 mg g-1 calculated using the equation of the Langmuir model. The adsorption capacity reached a plateau at pH 4 and the sorption process fits the pseudo-second-order model well. The PAA/CS composite has stability of reuse, with the adsorbent capacity decreasing slowly with increasing usage frequency. The experimental results confirm that the PAA/CS hydrogel could be a novel alternative for highly efficient removal of uranium from wastewater.

Coconut endocarp and mesocarp as both biosorbents of dissolved hydrocarbons in fuel spills and as a power source when exhausted

Health and environmental problems associated with the presence of toxic aromatic compounds in water from oil spills have motivated research to develop effective and economically viable strategies to remove these pollutants. In this work, coconut shell (endocarp), coconut fiber (mesocarp) and coconut shell with fiber (endocarp and mesocarp) obtained from coconut (Cocos nucifera) waste were evaluated as biosorbents of benzene, toluene and naphthalene from water, considering the effect of the solution pH (6-9) and the presence of dissolved organic matter (DOM) in natural water (14 mg/L). In addition, the heat capacity of saturated biosorbents was determined to evaluate their potential as an alternative power source to conventional fossil fuels. Tests of N₂ physisorption, SEM, elemental and fiber analysis, ATR-FTIR and acid-based titrations were performed in order to understand the materials' characteristics, and to elucidate the biosorbents' hydrocarbon adsorption mechanism. Coconut fiber showed the highest adsorption capacities (222, 96 and 5.85 mg/g for benzene, toluene and naphthalene, respectively), which was attributed to its morphologic characteristics and to its high concentration of phenolic groups, associated with the lignin structure. The pH of the solution did not have a significant influence on the removal of the contaminants, and the presence of DOM improved the adsorption capacities of aromatic hydrocarbons. The adsorption studies showed biphasic isotherms, which highlighted the strong affinity between the molecules adsorbed on the biosorbents and the aromatic compounds remaining in the solution. Finally, combustion heat analysis of coconut waste saturated with soluble hydrocarbons showed that the heat capacity increased from 4407.79 cal/g to 5064.43 ± 11.6 cal/g, which is comparable with that of woody biomass (3400-4000 cal/g): this waste biomass with added value could be a promising biofuel.

Relationship of cellulose and lignin contents in biomass to the structure and RB-19 adsorption behavior of activated carbon

Activated carbon microspheres prepared from biomass resources serve as green, highly efficient, and reusable adsorbents for reactive blue 19.

Adsorption of organic contaminants by graphene nanosheets: A review

Graphene nanosheets (GNS) such as graphenes and graphene oxides (GOs) have been widely investigated as next-generation adsorbents in both water and wastewater treatment processes due to their unique physicochemical properties and their affinity towards different classes of organic contaminants (OCs). In the last five years, more than 40 articles investigating adsorption of different classes of OCs by graphene and GO were published in peer-reviewed journals. Adsorption mechanisms were controlled by molecular properties of OCs (e.g., aromatic vs aliphatic, molecular size and hydrophobicity), characteristics of adsorbents (e.g., surface area, pore size distribution, and surface functional groups), and background solution properties (e.g., pH, ionic strength, surfactants, NOM, and temperature). This literature survey includes: (i) a summary of adsorption of OCs by GNS, (ii) a comprehensive discussion of the mechanisms and factors controlling the adsorption of OCs by GNS and a comparison of their adsorption behaviors with those of CNT. This literature survey also identifies future research needs and challenges on the adsorption of OCs by GNS.

Linear solvation energy relationship to predict the adsorption of aromatic contaminants on graphene oxide

In this study, adsorption capability of aromatic contaminants on graphene oxide (GO) was predicted using linear solvation energy relationship (LSER) model for the first time. Adsorption data of 44 aromatic compounds collected from literature and our experimental results were used to establish LSER models with multiple linear regression. High value of R² (0.919), strong robustness (Q_Loo² = 0.862), and desirable predictability (Q_ext² = 0.834) demonstrated the model worked well for predicting the adsorption of small aromatic contaminants (descriptor V＜3.099) on GO. The adsorption process was governed by the ability of cavity formation and dispersion forces captured by vV and hydrogen-bond interactions captured by bB. Effect of equilibrium concentrations and properties of GO on the model were explored; and the results indicated that upon an increase of equilibrium concentration, the values of regression coefficients (a, b, v, e, and s) changed at different levels. The oxygen content normalization of logK_0.001 decreased the value of b dramatically; however, no obvious changes of the model deduced by the surface area normalization of logK_0.001 were witnessed. Overall, our study showed that LSER model provided a potential approach for exploring the adsorption of organic compounds on GO.

A Valuable Biochar from Poplar Catkins with High Adsorption Capacity for Both Organic Pollutants and Inorganic Heavy Metal Ions

In this paper, biochar derived from poplar catkins was used as an economical and renewable adsorbent for adsorption organic and inorganic pollutants such as, dyes, organic compounds, and heavy metal ions from wastewater. Mesoporous activated carbonized poplar catkins (ACPCs) were produced from char as a by-product by carbonized poplar catkins (CPCs). With their high surface area, ACPCs exhibited the maximum adsorption capacities of 71.85 and 110.17 mg/g for the removal of inorganic U(VI) and Co(II). Compared other biochars adsorbents, ACPCs can also adsorb organic pollutants with the maximum adsorption capacities of 534, 154, 350, 148 and 384 mg/g for methylene blue (MB), methyl orange (MO), Congo red (CR), chloramphenicol (CAP) and naphthalene. The adsorption of organic pollutants was fitted with pseudo-first order, pseudo-second order, and intra-particle diffusion kinetic models figure out the kinetic parameters and adsorption mechanisms. Langmuir adsorption isotherm was found to be suitable for Co(II) and U(VI) adsorption and thermodynamic studies indicated adsorption processes to be endothermic and spontaneous. The adsorption process includes both outer-sphere surface complexes and hydrogen-bonding interactions. The results showed that biochar derived from poplar catkins was a potential material to remove pollutants in wastewater.